DESIGNING & MANUFACTURING OF SPLIT CAVITY TWO PLATE INJECTION MOULD FOR GAS CAP

SYNOPSIS

Any product to be manufactured invariably requires tools, tool design and development and planning. Tool is an aid for mass production it should be accurate & economical for achieving good quality products at lesser cost.

The economy & life of moulds entirely rests on the designer & his role is very important.  This project work incorporates the details of designing process planning & manufacturing Injection mould for GAS CAP

This project incorporates the literal survey of plastic material properties plastic moulding, steel is used in mould making functional aspects of component & various aspects such as feed system ejection of the comp.  Parting surface, cooling of mould various consideration, where done prior to actual design of mould.

The process planning for manufacture & electrode planning of cavities required for mould & assembling tryout & trouble shooting.

1. INTRODUCTION TO PLASTICS

            The class of materials known as polymers is characterized by a structure made up of molecular chains with a large aspect ratio, that is, they are very long relative to their transverse dimensions, corrosive resistance, good electrical and thermal insulation properties, low co-efficient of friction and so on. Natural polymers such as shellac horn, bitumen, lacquer gutta percha etc. are available for many centuries and have provided much of the basic knowledge of mould making.

          When considering the evolution of plastics, it is apparent that they have had on unfortunate history as substitute materials. Special new materials could be fabricated with sufficiently consistent properties to facilitate the manufacture of products with relatively intricate geometries and a unique combinations of properties coupled with ease of fabrication has revolutionized the modern industry. To the enlightened designer, plastics are a major complement to the range of more traditional materials.

          The plastic industry is composed of three divisions:        

1.     The manufacture of plastic resins, synthesizing polymeric materials from chemical compounds.

2.     The manufacture of compound plastic mixtures known as moulding compounds.

3.     The process, which produces plastic articles by moulding and fabricating methods.

The primary function of the plastics resin producer is to make available various types and grades of polymeric substances which the plastic compound can formulate with other ingredients into powders, pellets, flakes, granules, liquid resins or solutions for processing by moulder in to the finished plastics products.

There are many ways of transforming plastic materials into finished plastic articles. The basic principle consists of partially melting the plastic mass by the application of heat and compression. By this process the plastics softened and formed into desired shapes by using of rolls, dies, moulds etc. with the aid of pressure.

The intent of using the plastic material as useful articles usable in different areas like is intended.

Finally, the shaped hot plastic is solidified through further polymerization in curing stage. Solidification of plastic in case of thermo set materials is by applying pressure at curing stage and by chilling in the case of thermoplastic materials.

          Plastics may be classified in various ways depending upon their basic raw materials, their distinctive properties and their applications.

  However the two important divisions namely:

THERMO-PLASTICS

            In thermoplastic material the individual molecules are often described as being chain like but not actually bonded together. When they are heated the intermolecular forces are weakened so that it becomes soft and flexible and after cooling they will solidify again. They are obtained from the substituted derivatives of ethylene polystyrene, acetyl, nylons, vinyl’s acrylics and fluorocarbons. Generally they are processed by injection or blow moulding.

THERMOSET-PLASTICS

          They are formed by chemical reactions in which first long chain line molecules form further a close network structure is formed usually under the application of heat and pressure.

            Since molecules are cross linked by covalent bonds, they are characterically quite rigid. So if once it is heated then it cannot be reheated. They are generally processed by compression or transfer moulding. However some properties can be achieved by reinforcement of chemicals or additives.

E.g.: Formaldehydes, Epoxies, Glyptal, Formica etc.

2. MOULDS AND INJECTION MOULDING MACHINE

MOULDING

Moulding of plastic material comprises of forming an article to the desired shape by the application of heat and pressure in a hollow form or cavity.

The following major methods of transforming plastic materials into finished form are as follows.

THERMOSET PLASTIC MOULDING METHODS

·     Compression Moulding

·     Transfer Moulding

·     Injection Moulding.

THERMO PLASTIC MOULDING METHODS

·     Injection moulding

·     Blow moulding

·     Extrusion moulding

·     Roto moulding

·     Thermo forming

·     Calendaring

INJECTION MOULDING

It is one of the most widely used method for processing plastics (usually thermoplastic). In this phenomenon the raw material is plasticised outside the mould in a separate cylinder where it is heated. The plasticised material is then injected into the cavity and is allowed to cool by means of cooling water or oil circulating in the mould. After the material is cooled and solidified the mould is opened and component is ejected.

ADVANTAGES OF INJECTION MOULDING.

1.     Parts can be produced at high rate even with high volume of moulding.

2.     Different colours with matt finish can be obtained.

3.     Scrap is minimized as runners, gates and sprues are reground.

4.     Close tolerances can be achieved even for small parts.

5.     Moulding with reinforcement and inserts (metallic and non metallic) can be moulded with ease.

6.     Thermo set elastomers can also be processed in this moulds occasionally.

DISADVANTAGES

1.     Comparatively costly process.

2.     Skilled workers are necessary for manufacturing and operating these moulds.

3.     Assembly is not easy as there are more number of mating parts.

FOUR CAVITY- INJECTION MOULD

Component is having offset feeding system so the mould can be constructed Four cavity center feeding feeding directly from the sprue runner & gate. There is a edge gate provided at the side core  itself.

The basic mould(two plate mould) consists of two parts namely a fixed half and moving half. When these two halves are opened moulding can be extracted such as assembly is sometime reffered as single day light mould. When mould is opened here is only one space or as it is normally termed as daylight.

This type of mould consists of two main units namely.

1)    Fixed Half.

2)    Moving Half.

INJECTION MOULDING MACHINES

Injection moulding machine essentially consists of the units namely

Ø     The mould-clamping unit.

Ø     The injection unit.

Ø     Controlling unit.

Types of injection moulding machines

Mainly there are three types of machines.

1)    Hand injection-moulding machine.

2)    Piston type injection-moulding machine.

3)    Reciprocating screw type injection moulding machine.

HAND INJECTION MOULDING MACHINE

The hand injection moulding machines, which are available in ranges of capacities upto 2 ounce (28.4 grams). They are generally being used without thermo regulators.  The temperature controls provided along with the machine under the category thermostat, which are only indirect controls.

PISTON TYPE INJECTION MOULDING MACHINE

In this type of machines a cold piston moves inside a hot cylinder, which contains plastic materials. In order to facilitate dispersion of heat and get a homogeneous melt the cylinder is provided with a torpedo.  Actually when the piston moves forward the molten material diverges at one end of the torpedo.  Before getting shot through the nozzle.

 

THE PRINCIPAL VARIABLES THAT MUST BE CONTROLLED ARE

1.     The amount of plastic material introduced into the cylinder.

2.     The pressure applied to the piston.

3.     Piston speed.

4.     Temperature of the heating cylinder (nozzle temperature may also be controlled)

5.     Temperature of the mould.

6.     Piston forward time.

7.     Mould closing time.

8.     Mould clamping force.

9.     Mould opening time.

SCREW TYPE INJECTION MOULDING MACHINE

The screw type injection-moulding machine consists of a screw rod rotating In a hot barrel capable of elevating continuous melt of plastic.  By operating screw intermittently, one can get an intermittent flow of plastic through the nozzle. Because of the shearing action and material flowing in different patterns there is a homogeneous in the melt.

In screw type machine the mechanical energy from the screw is converted into heat, which is distributed uniformly throughout plastic as the screw rotates and mixes it.  Heating time and thermal degradation is reduced, and mixing of pigment in the plastic is more homogeneous.

INFLUENCE OF MATERIAL PROPERTIES ON THE MOULDING

As the plastic cools in the mould, it contracts, so the moulding smaller than the mould in which it was formed.  When the mould is being designed from a dimensioned drawing of the part, a shrinkage allowance must be added to the dimensions of the mould.

Shrinkage allowances are obtained from the plastics resin producer, usually given as a range of shrinkage values, the exact value depending on the shape of the moulding conditions.

3. COMPONENT ANALYSIS

The successful design of a component and the relevant tool to produce such component largely depends on how one analysis it. That is both on technical and commercial aspects. A brief analysis of the component

“GAS CAP is given below.

          This depends upon:

1)                Material Selection.

2)                Critical dimensions of component.

3)                Function or purpose for which the component is used.

4)                Advantages of the component.

5)                Properties.

 

COMPONENT DETAILS

 Name                  :-  GAS CAP]

 Customer              : -PRIME TECHONOLGIES.

 Material               : - NYLON 66

Shrinkage              : - 0.6%

Melting temp         : - 260˚ – 290 ˚C

FUNCTIONAL ASPECTS OF THE COMPONENT:

The Gas cap is a auto mobile product mainly used in   two wheelers. Using as a regulator in the fule tank of two wheelers mainly for the Baja pulsar, discover bikes. The gas cap product uses in a fuel system both vacuum and pressure to insure that as few gasoline vapors reach the air as possible. The gas cap regulates this balance. The cap has relief and pressure valves that regulate the pressure in

SHRINKAGE

             As the hot plastic material cools in the mould, it contracts towards the centre and will stick to core because of the shrinkage factor.

Thus, while designing a mould the shrinkage allowance must be added to core and cavity. Different materials will have different shrinkage and they are supplied by the material manufacturers.

            For the given material average shrinkage is 0.6%.

CRITICAL DIMENSIONS

a)    Square 94.20 ± 0.1mm

b) Square 92.60 ±0.1mm

c) Pitch 52.00, width 2.00 & height 29.00 ± 0.1mm

d) Angle 45’0 of the side pocket. 

e) All ribs thickness ±0.05mm

4. DESIGN ANALYSIS

The product design drawing is the basis for constructing mould. Designing requires a lot of planning and visualization of what can be accomplished by the resources at hand in a given time. A design with proper implementation and good workmanship can produce accurate parts.

This design is to construct a strong and a big tool of 496 x 496 mm size and a shut height of approximate 398mm.

The following chart and designs gives us clear idea of designing and construction of the mould.

          The important factors to be considered while designing the injection mould are.

1)                Number of cavities.

2)                Parting line.

3)                Feed system.

4)                Effective cooling of mould.

5)                Ejection.

NUMBER OF CAVITIES

          The designed mould is a single cavity two-plate injection mould, which is offset gated from the centre of the component.

          The decision concerning the number of cavities depends upon.

1)                Rate of production required.

2)                Quantity of production.

3)                Shot capacity of injection moulding machine.

4)                Bulk of component.

5)                Mould cost.

           As the number of cavities increases the locking pressure also increases. For this mould the locking pressure is Kg/Sq. inch. The component has thin ribs and hinge with different wall thickness. The component is with intricate profiles.

PARTING SURFACE

The surface of line at which the two halves of the mould i.e. core and cavity mate and form a seal, which prevents the plastic material from escaping. There are different surfaces like flat, irregular, angled, stepped profiled etc.

This tool has a profile surface it is noted here that in cross section, the moulding form is constant with some profiles curves. Component has straight parting surface.

FEED SYSTEM

The flow way, which connects the nozzle of the injection, moulding machine to the cavity is referred as feed system. Normally feed system comprises of sprue, runner system and method of gating.

SPRUE

It is connecting member between the machine nozzle and runner system. This is designed in such a way that is should minimize the pressure drop and delivers material to the extreme end position. Normally the sprue chosen has a taper of 3-5º, which facilitates for easy removal.

RUNNER SYSTEM

The runner is a channel machined into the mould plate to connect the sprue with the gate. The criterion of efficient runner design is that the runner should provide a maximum area for flow of material without heat and pressure loss. The walls should be smooth enough to prevent flow of material.

When deciding the size of runner the factors to be considered are wall thickness of component, distance of impression from sprue, runner cooling considerations and plastic material used.while designing the runner system following should be considered.1)shpe

While designing the runner system following should be considered.

1.     Shape or cross-section of runner.

2.     Size of runner.

RUNNER LAY OUT

The runner layout should be balanced that is the distance traveled by elasticized material from the sprue to each of the impression should be same.

DIFFERENT SHAPES OF RUNNERS ARE

1.     Rectangular.

2.     Round.

3.     Half round.

4.     Hexagonal.

5.     Trapezoidal

6.     Modified trapezoidal.

For two-plate moulds, usually  modified trapezoidal type of runner is always specified. The runner channel is machined into ejection half from which it is pulled as the mould opens. It gives large area and reduces the area of contact i.e., loss of superheat is reduced. The end gate should be provided on single side such that the pressure should be balanced. If injection force is unbalanced, will tend to open the mould on one side.

METHOD OF GATING

The gate is a channel or orifice connecting the runner with the impression. It has small cross sectional area, when compared with rest of the feed system. This is because.

1)    The gate freezes soon after the impression is filled.

2)    It allows for simple de-gating and this can be automatic in some moulds. 

3)    A small witness mark is left after de-gating.

4)    Better filling is achieved.

There is no definite or theoretical size for ideal gate. It is chosen in practice for a particular component is normally with the experience. It is generally 1/3 of the runner. In case of moulding with wall sectors between 0.75 to 4mm

.

The different types of gates are used for different components as mentioned.

1)    Sprue gate.                             

2)    Rectangular or end gate.         

3)    Pinpoint gate.

4)    Spoke or spiral gate.

5)    Dia-form or disk gate.

6)    Tab gate.

7)    Ring gate.

8)    Fan gate.

9)    Submarine or submerged gate.

10)   Film gate.

11)   Direct inject gate.

12)   Overlap gate.

13)   Pin-hook gate.

Since this is single-cavity mould sprue gate can be given.

RECTANGLURE EDGE GATE

This is the general-purpose gate. The rectangular channel machined on mould plate to connect the runner to the impression. The typical gate sige is is6%to 75%of the part thicken(0.4toi6.4mm thick)and1.6and12.7mm wide. The gate land should be no more than  .0mm in length , width 0.5mm being optimum.

Advantages

·        The cross-sectional form is simple and easy to machine .

·        Close accuracy in gate dimensions can be achieved.

·        The gate dimensions can be easily and quickly modified.

DIS ADVANTAGE

·        One dis advantage is that after de-gating a small witness

Marks remains on the visible surface of the mould.

 COOLING

The designer must calculate the heat transfer from molten plastic to the mould, which determines the cooling method that brings about its rapid solidification for ejecting the product from the core.

Cooling is provided in the mould to maintain a uniform mould temperature to heat the mould to the working temperature before start of production. The rate of cooling affects the quality of the component and number of shots.

Cooling system should be divided into several separate cooling circuits as much possible. This ensures the better control on temperature of individual spots easily.

Cooling is achieved by circulating water or oil through holes or channels (flow ways) within the mould. The complete system of flow way is termed as circuit.

Different types of cooling methods are:

1)                ‘U’ Circuit.

2)                Rectangular circuit.

3)                ‘Z’ Circuit.

4)                Angle hole method.

5)                Annular method.

6)                Baffle cooling.

7)                Helical channels.

8)                Bubbler cooling.

The cooling system in this mould is rectangular circuit. The side cores have a rectangular cooling system in which dia 6 holes are done to a depth of 30mm. The brass inserts are fitted on other ends. core insert having baffle cooling hole depth of 165mm , baffle are made of flat strips of brass or stainless ,aluminum varying the thickness from 1mm to3mm.function of baffle is to splitting drilled channels in to two semi circular channels. Providing rubber ‘O’ rings, bottom side of the core inserts, prevents the leakage. The liquid cooling medium enters the bottom plate and is made to direct in the core insert and again joins at the other end of the insert and flows out through the channel in the bottom plate. The side core is similarly provided with rectangular circuits around the moulding area.

COOLING CONSIDERATIONS:

1.     If the wall thickness varies, cooling should be divided into zones.

2.     Active area of cooling may be equal to area of component.

3.     The cooling should ensure rapid and uniform cooling of the                moulding.

4.     The temperature difference between inlet and outlet water is tobe 3 to5º degree.

5.     The quantity of coolant through each system shall be between 3 to 5 liters/minute.

EJECTION

          Ejection is part of the mould cycle. When the component cures it contracts or shrinks towards the core depending upon the material being processed, it needs a positive ejection to remove it from the mould. There are different techniques to choose depending upon the shape of moulding as in the chart.

          In this tool we have selected only one technique for positive ejection.

1) SLEEVE EJECTION

          With this method the moulding is ejected by means of a hallow ejector pin termed as sleeve. It is used in one of three circumstances. For the ejection of certain types of circular moulding.  

·        For the ejection of circular bosses on a moulding of any shape.

·        To provide positive ejection around a local core pin forming a round hole in moulding. The sleeve, which is sliding fit in the core insert. Sleeve fitted at its rear end to the ejector assembly. When the ejector assembly is actuated the sleeve is removed relative to the core and the moulding is ejected. The ejection force is applied to a relatively large surface area. this design is restricted to circular types.    

5. RAW MATERIAL SELECTION

          The selection of raw material plays a vital role in the manufacturing of the mould, which has a direct impact on the life of a mould. Different applications require specific characteristics for the material to be used. To select the material that provides the most economical overall performance and imparts necessary quality required is very important. The selection of material for a particular application is governed by the working condition to which it will be subjected. The raw material for tool can be chosen from the following-steel, cast steel, aluminum and copper.

Generally mould makers use the following 4 kinds of steel with different composition.

1)          Low carbon steel (<0.2% carbon)

2)          Medium carbon steel (0.2 to 0.6% carbon)

3)          High carbon steel (0.7 to 1.3% carbon)

4)          Alloy steel

The raw materials used in this mould are mainly tool steels. The raw materials distinguished by their special physical and mechanical properties influenced by the addition by alloying elements like Nickel, Vanadium, Chromium, Molybdenum silicate etc.

EFFECTS OF ALLOYING ELEMENTS ON STEEL

CARBON:  This is very much essential for heat treatment. The carbon content of die steel generally does not exceed 0.3 to 0.35%.

MANGANESE: Addition of more than 0.5% of manganese increases hardens ability and strength of steel. It is an excellent deoxidize. It increases the cooling rate.

SILICON: The increase in silicon content will raise the critical temperature, increases susceptibility to de-carbonization and graphitization and when combined with other an alloy promotes resistance to high temperature oxidation. Gives strength and toughness to steel.          

NICKEL: Nickel permits lowering of carbon content to achieve a given strength level thereby increasing toughness and fatigue resistance.

CHROMIUM: It improves hardness, wear resistance, toughness, corrosion resistance and it helps in retaining high surface finish. It varies from 0.25% to 14% depending upon the properties required.

MOLYBDENUM: It restores hardness at elevated temperatures. It improves hardness; polish ability, toughness and mach inability. It eliminates temp brittleness in steels. It acts as a grain growth inhibitor when steel is heated to high temperatures. Molybdenum also intensifies the effects of other alloys.

TUNGSTEN: Increases hardness, strength and toughness up to 1.5% tungsten in steel increases wear resistance. Retains hardness unto 600ºC to 650ºC.

VANADIUM:       It is quite expensive, where as it increases the strength, hardness and impact resistance. It inhibits the grain growth during heating, permitting high temperature. The percentage of vanadium in steel varies from 0.15-2%.

      There are different types of mould materials like Hot die steel, Cold work die steel, Cast steels, Aluminum, Copper etc.

In this mould the different materials used are

1)      Mild Steel.

2)      Case hardened steel.

3)      Oil hardened non shrinkable steel

4)      Hot die steel.

1) MILD STEEL:

                                    Trade name          : MS (Mild Steel)

                             Is Codification      : St-42

                             Tensile Strength    : 42kgs/mm²

                             Carbon                 : 0.25%

                             Silicon                  : 0.65%

                             Phosphorus           : 0.05%

    This has high toughness and shock resistive property so it is used in plates, locating ring, male hose ends etc. this material withstands the clamping force, injection and ejection pressure and economical.

2) CASE HARDENING STEEL

                                    Trade name          : En 35

                             Is Codification      : 17Mn1 Cr95

                             Tensile strength     : 65kgs/ mm²

                             Carbon                 : 0.17%

                             Manganese           : 1.0%

                             Chromium            : 0.95%

         This type of steel is used to manufacture the parts, which should have a very hard surface to resist wear along with a tough interior, to resist the impact the occurs during operation. Used for a guide pillar and guide bushes etc.

3) OIL HARDENED NON SHRINKABLE STEEL

                                    Trade name          : OHNS

                             Is Codification      : T110 W2 CR1

                             Tensile strength     : 62kgs/mm²         

                             Carbon                 : 1.1%

                             Manganese           : 2% 

                             Chromium            : 1%

        This is a cold working tool steel whose important properties are good mach inability, high wear resistant and temperature resistant properties combined with remarkable toughness. This is used for Sprue bush, ejector pins, locking wedges, rest pins etc.

4)1.2767

                                    Trade name           : 1.2767Equievalent to OHNS

                             Is Codification      : T55 Ni2 Cr65 Mo30

                             Tensile strength     :       

                             Carbon                 : 1.1%

                             Manganese           : 2% 

                             Chromium            : 1% 

        Sub Core and Sub Cavity inserts are manufactured from this material. They should be hardened and have good properties like wear resistance, tough, should obtain high finish, and should restore hardness at elevated temperature.

5)1.2083

                                    Trade name           : 1.2083= stavax supreme

                             Is Codification      : T55 Ni2 Cr65 Mo30

                             Tensile strength     :       

                             Carbon                 : 0.24%

                             Manganese           : 0.5%        

                             Chromium            : 13.3%      

                             Nickel                             : 1.40%

                             Molybdenum         :  0.35%

                             Vanadium             : 0.35%

                             Silicon                  : 0.3%

       

        Core and Cavity inserts are manufactured from this material. They should be hardened and have good properties like wear resistance, tough, should obtain excellent polishibility, and should restore hardness at elevated temperature.

ORVAR SUPREME

ORVAR SUPREME is chromium-molybdenum-vanadium-alloyed steel which is characterized by:

v    High level of resistance to thermal shock and thermal fatigue

v    Good high-temperature strength.

v    Excellent toughness and ductility in all directions

v    Good machinability and polish ability

v    Excellent through-hardening properties

v    Good dimensional stability during hardening.

 

IMPROVED TOOLING PERFORMANCE

The name "SUPREME" implies that by special processing techniques and close control, the steel attains high purity and a very fine structure. Further, ORVAR SUPREME shows significant improvements in isotropic properties compared to conventionally produced AISI H 13 grades.

          These improved isotropic properties are particularly valuable for tooling subjected to high mechanical and thermal fatigue stresses, e.g. die casting dies, forging tools and extrusion tooling. In practical terms, tools may be used at somewhat higher working hardness (+1 to 2 HRC) without loss of toughness. Since increased hardness slows down the formation of heat checking cracks, improved tool performance can be expected.

ORVAR SUPREME meets the North American Die Casting Association (NADCA) #207-97 for premium high quality H-13 die steel.

6. MOULD MANUFACTURING AND TERMINOLOGY

          Injection mould is an assembly of parts containing within it an impression into which the plastic material is injected and cooled. It is the impression, which gives the moulding it’s required from. The impression may be defined as the part of the imparts shape with accurate dimensions to the moulding

.

Two important parts from the impression.

1)    The cavity, which is the female portion, it gives the moulding its external form.

2)    The core, which is the male portion of the mould, forms the internal shape of the moulding.

1. TOP PLATE

As the name it suggests. This is the top most part of tool. This is made up of C-45 material and it butts on the fixed platen of the moulding machine. It may either be a separate plate on to which the cavity plate is clamped. It holds locating ring, sprue bush and cavity plate through main guide bushes and also holds and supports the cavity insert.

2. BOTTOM PLATE

It is the bottom most plate of the mould and it is also made up of C-45 material. It literally holds the whole of the bottom unit by screws passing through spacers and core back plate engaging with the main guide pillars, which in turn hold the core plate by collars. This is fixed to moving platen of the machine and it has a hole of dia 35 at the center, which allows for ejector rod to actuate the ejector assembly.

3. CORE AND CAVITY PLATE

The most important parts in the mould where core and cavity inserts are accomplished either by integer or bolster method. The core and cavity plates help to incorporate cooling media into the mould.

·       INTEGER METHOD

The core and cavities can be machined from steel parts, which become parts of the structural build up of the mould. It is termed as an integer cavity plate. This is preferred for single impression mould, because of strength and low cost. In this tool the handle portion gives us an idea of integer method.

                                                                                                            

·       BOLSTER METHOD

Where the core and cavity can be machined from small blocks of steel termed as inserts subsequently bolstered.

Since this component is very large, complicated and not easy to manufacture by integer method, some inserts are subsequently bolstered. This reduces cost and machining difficulties.

4) CORE AND CAVITY

These are the most important parts from which the mouldings are manufactured. The material for core and cavity is 1.2083. This highly wear resistant steel, which is heat-treated to 48-52 HRC, is machined accurately to fulfill the component requirement. The intricate profile may need some special machining process. The core and cavity will have H7/H6 fit in their respective plates. High surface finish will result in a good surface finished component.

5) EJECTOR PLATE ASSEMBLY

The ejector plate assembly consists of ejector plate and ejector back plate. They are made of C-45 material. The ejector plate houses the ejector pins and push back pins and the ejector back retains them in the ejector plate.

6) SPACERS

As the name itself suggests these are means to create a space in which the ejector assembly can operate. It also supports the core  plate. They are made up of C-45 material.

7) GUIDE PILLARS AND BUSHS

The accurate mould assembly needs the perfect alignment between a top half and bottom half any time and every time, while closing and disclosing. The main guide pillars and bushes provide this to the assembly with a suitable hardness and ground to match the requirement with H7/g6 fit between them. They have k6 fit in the plate in which they are fitted. They are made of 17Mn1 Cr95 material.

8) EJECTOR GUIDE PILLARS AND BUSH

These guide pillars and bushes provide uninterrupted free movement of the ejector plate and back plate ensuring smooth ejection of the component and these mainly avoids undue strain on the ejector pins. They are made of 17Mn1Cr95 material.

9) PUSH BACK PINS

These pins are fitted closely to the four corners of the ejector assembly. Since they protrude more than the ejector pins, they take care of positioning the ejector assembly on the rest pins. Push back pins are accurately guided in the core plate with H7/g6 fit. They are made of T110 W2 Cr1 material.

10) EJECTOR PINS

They are very important with respect to ejection of the component. They are fitted in ejector plate. They are made up of T110 W2 Cr1 material.

11) REGISTER OR LOCATING RING

The front face of the top plate is fitted with the locating ring. The main function of this is to align mould in correct position with the nozzle of injection moulding machine. This ensures the small aperture of the nozzle is in direct alignment of sprue bush hole. This is made up of st-42 material.

12) SPRUE BUSH

Below locating ring a sprue bush is provided made of T110 W2 Cr1 and is held with a collar. It is hardened to 52-54 HRC because the elasticized material during moulding will transfer to impression through a tapered hole in this bush. The material in the tapered passage is termed as sprue and the bush as sprue bush.

13) RUNNER AND GATE SYSTEM

The plastic zed material flows through a runner and a small opening termed as gate to a deserved opening or impression. The runner and gates acts as a pathway for the material to reach the impression.

14) SUPPORT PILLAR

The support rods acts as additional supporting property for the core back plate and as especially provided in the middle regions and also at places where the spacers do not acts as a support. It prevents the plate from bucking due to the locking and injection pressure.

15) FEET BUTTONS

These buttons are press fitted into the bottom plate on which the ejector back plate rests. This design will help the effective seating area and leaves the space in between the plates which also helps for the removal of foreign materials filling in between bottom plate and ejector plate assembly.

7. PROCESS PLANNING

Process planning is defined as a systematic procedure of developing and determining an economical method or series of methods by which a product can be successfully manufactured in a given time.

Tooling is a part of production engineering so process planning plays an important role in selecting proper equipment and tooling. This also specifies that application and operation in such a manner that the end product will meet all the requirements stipulated in the specification. At the same time the process will be performed as minimum cost and maximum profitability.

REQUIREMENTS IN PROCESS PLANNING

The following principle data and information are required to plan a manufacturing process.

1.     A brief description of the job to be manufactured which clearly and comprehensively defines its service function.

2.     Specification and standard that stipulate the service function.

3.     Working drawings of the job with complete specification.

4.     Data on the quantity of the parts to be manufactured in a period.

5.     Total quantity of space parts required for unit.

6.     Equipment, capacity of tools and data of all other equipments necessary including manpower.

7.     Date of starting and date of delivery.

              Above all these requirements it is important to have a good knowledge of machining sequences and their capabilities.

             The process planning followed in tool making may be summarized as follows:

First a good design is prepared and passed on to planning and toolmaker. Then the manufacturing of parts, which are to hardened, are given more priority and they are sent to heat treatment. In the due time the other parts such as bolster plate are finished. At the same time it is important to design and manufacture the electrode if they are any. After heat treatment the process of EDM starts along with bench work. Finally the parts will be ready for assembly.

PROCESS PLAN SHEET

Process plan sheet is a detail record where all information’s relating to different operations to manufacture is listed in a tabular form known as analysis sheet. The character of a process sheet will depend mainly on the scale of production of the degree of importance of the product being manufactured.

PLANNING OF OPERATION SEQUENCE

The following points should be considered while planning the sequence of operations.

a)           List of available machines.

b)           Accuracy and surface finish required.

c)            Convenience in operating the machine tool.

d)           Capacity of the machine tool.

e)             Performance of operation is economical or not.

CHECK LIST FOR MOULD PIECE PART

a)                Is the piece part drawing approved?

b)                Whether all the notes pertaining to job are clear?

c)                 Is the type of plastic material indicated?

d)                Is the function, location and use of piece part understood?

e)                 Can any changes be recommended to make a simplest of better pieces?

f)                  Are the numbers of cavities correct?

g)                Can these tolerances be maintained?

h)                Are the dimensions given including or excluding shrinkage?

i)                  What shrinkage factor should be used?

j)                  Has the parting line be approved?

k)                 Is the runner location correct?

l)                  Is the gate location correct?

m)              Will the piece hang on the injection side?

n)                Is the ejection mechanism sufficient?

o)                  Has the polish be specified?

MOULD

A)   The mould parting line chosen is most efficient for operation and construction is of mould?

B)   Is the capacity of adequate strength to resist internal cavity pressure?

C)  Have the materials for core and cavity and other parts been specified?

D)  Whether ‘O’ rings, springs etc. are provided wherever necessary?

E)   Has the mould been properly marked for identification?

F)   Are the dimensions on the prints are the same as the dimensions on the mould?

MACHINE

A)   Is the weight of the sum of moulding, runners, sprue is within the shot capacity of press?

B)   Is the clamping pressure of the machine sufficient for projected area of the moulding and runners?

C)  Will the mould pass between the machine tie bars?

D)  Do the clamping arrangements for the mould suit the platen boltholes?

E)   Is the length of work of mould and shoot weight within the capacity of the machine?

CONSTRUCTION

A)          Is the mould free from horizontal flash?

B)          Does the ejection assembly provide sufficient support to prevent distortion under cavity pressure?

C)         Can all the parts be dismantled and separated in the event of break down or modification?

D)         Are all necessary parts hardened?

E)          Is the ejection stroke sufficient to clear the moulding?

F)          Have sufficient ejectors been provided to prevent distortion cranking or sticking of the mouldings?

G)         Is the ejection assembly suitable for particular machine ejector systems?

H)         Have adequate cooling system been provided?

I)             Is the cooling too close or too distant from mould surface?

J)            Is the cooling too close or too distant from mould surface?

K)         Are the runners of sufficient size used?

L)          Has the sufficient opening provided between the halves to allow the extraction of mouldings?

M)        Do the spherical nose radius and cylindrical nozzle meet with the spherical seating on the sprue bush?

N)         Have mould lifting bolts holes been provided?

MANUFACTURING PROCESS

Manufacturing is a process of making the raw material into a finished product according to the planned drawing.

Manufacturing process is classified in two groups.

a)           Conventional manufacturing process.

b)           Non-conventional manufacturing process.

Manufacturing of injection mould mainly consists of:

1)           Mould box manufacturing.

2)           Manufacturing of core and cavity.

MANUFACTURING OF MOULD BASE

A mould base is an assembly of top plate, bottom plate, pillars and bushes; cavity plate, core plate, core back plate, ejector plate and ejector back plate.

TOP PLATE

Item No                          : -01

Material                         :-C-45

Raw material size1                   :-470X260X40

Finished size                   :- 460X250X35

Milled keeping 0.5mm excess for grinding with right angle to each of the surfaces. Thickness should be ground for proper seating of plate on which top surface butts on fixed platen of machine and the bottom side with cavity plate. A bore diameter of 50mm+0.1mm is done in the top surface for seating of locating ring. Three M5 screw holes are done to clamp the locating ring and the same setting a hole of dia. 25 for depth of 12mm is done for seating of sprue bush. A bore of dia36 H7 X 4 holes are done for seating of pillars and anchor pieces. M12X4 relieved holes are done for the screws to clamp the cavity plate to the top plate, which are transferred from cavity plate to the top plate. M8relived holes are done for screws to clamp the wedges.   The sides of the plate are chamfered with 5 X 45º to avoid the physical injuries.

BOTTOM PLATE

Item No                   :- 02

Material                  :- C-45

Raw material           :- 470X260X40             

Finished size           :- 460X25X35

The material is first milled right angle to each of the surfaces with 0.5mm grinding allowance. Thickness is ground because, the bottom surface will be clamped to machine platen and top is fixed to spacers. A hole of dia 40 is drilled to accommodate the ejector rod from the machine. Four relief holes for M16 screws are done so that it should hold pillars and core plate with spacer and core back.Dia M8reliufe hole for holding the core holder plate. The side’s plate is chamfered with 5 x 45º to avoid physical injuries.

GUIDE PILLAR

Item No.                  :-04  

Raw material size    :-Ø40X160 

Finished size           :- Ø36X155

        Material                 :- 17Mn1 Cr95

HRC                       :-CHDN52-55 HRC

It is a cylindrical part, which give alignment to the top half and bottom half of the tool with a sliding fit in the guide bush. Turning is done between centers keeping 0.5mm grinding allowance. After heat treatment it is inspected and ground on a cylindrical grinding machine to the finished size. Among four guide pillars three pillars are grinded to 36H7/g6 fit with the guide bush and have a dia36H7/k6 fit in the cavity plate. And one pillar is grinded to achieve 35H7/g6fit with guide bush for fool proofing. An entry lead of 10 degree is provided for easy entry and radius of R3 is done to provide an entry into guide bushes.

GUIDE BUSH

Item No.                  :- 05

Raw material size    :- Ø50X 140        

Finished size           :- Ø42X60

Material                  : -17Mn1 Cr95.   

  HRC                     :-CHDN 52-55 HRC

It is a cylindrical part, which give alignment to the top half and bottom half of the tool with a sliding fit in the guide pillar. Turning is done keeping 0.5mm grinding allowance. After heat treatment it is inspected and ground on a cylindrical grinding machine to the finished size. 36H7/g6 fit with three guide pillar and 35H7/g6  fit with one pillar and has a dia42H7/k6 fit in the liners

CORE HOUSEING

Item No.                  :-  03

Raw material size    :- 430X210X

Finished size           :- 420X210X36

Material                  :- C-45   

HRC                       :-  20-25 HRC

A milling operation of all the sides is performed with 0.5mm grinding allowance.DIA45H7X4 holes done in cnc milling for to house the sleeve bush to slide the sleeve.dia12H7relife hole for return pin. And M6X8 taping hole for clamping the wear plate.M10X4taping hole and Dia8H7X4 NOS dowel done for housing liners..M6X8mm relieve hole is done from bottom side for ball catch. Four holes of M16 are done for holding core plate with bottom plate...   All the edges are chamfered to be safe against the cuts.

CAVITY PLATE

Item No.                            : -   02        

Raw material size              : - 415X215X35mm                

Finished size                     : - 410 X210X30mm

Material                            : - C-45   

HRC                                 : - 20-25 HRC

A milling operation of all the sides is performed with 0.5mm grinding allowance. Eight small profile pockets of size5.08H7 X11.88H7X 30 is done in wire cut machine, for inserting  the    cavity pin. Dia15H7X4Holes alose done in wire cut machine for  inserting The cavity insert. two slots sige of 240x25x30 machining in  cnc machine for inserting the wedges block. Four holes of dia 35k6 with dia42x6 machining for aligning piller.M14 taping hole for clamping the top plate.dia12H7 with collar dia 20x7are drilled at an angle of 22degree for cam pin. at a centre of the plate dia 16H7hole done for spruebush.         

EJECTOR PLATE

Item No.                 :-   08          

Material                 :-    C-45 

        Raw material size   :-   415X128X22           

        Finished size           :-  410X122X20

        HRC                        :-  20-25 HRC

The size is maintained in milling machine with grinding allowance of 0.5mm. After that grinding is done. six M8 holes are drilled and tapped to fix the plate to the ejector back plate. Drilling and boring holes for guiding ejector guide bush of dia26H7.  Four relief holes of dia12H7 with counter bore of dia20 are done for return pins. A boring is done for the sleeve bush the bore size is dia 35H7x4holes. A chamfering of 5 x 45º is done to avoid injuries.

EJECTOR BACK PLATE

Item No.                   :-   09        

Material                  :-   C-45 

Raw material size   :-   450X335X26  

Finished size          :-   446X330X26

        HRC                       :-  20-25 HRC

The sizes are maintained in milling. The purpose using this plate is to retain the ejector pins. Two holes of dia26H7 is drilled and reamed to fit the ejector bush along with counter bore of dia 34 for depth of 5mm. The relieved holes for M8 screws and counter bores are also done. It is chamfered to 5x 45º to avoid cuts and injuries.

SPACERS

Item No.                  :-   07         

Raw material size   :-   450X130X60

Finished size           :-  446X126X56

Material                  :-  C-45   

        HRC                        :   20-25 HRC

They are machined to size and ground. The four relief holes are done for M16 screws holes for clamping purpose. Grinded to the finished size. All the sharp edge are chamfered to avoid injury.

MANUFACTURE OF CYLINDRICAL PARTS

All cylindrical parts are pre machined on lathe keeping 0.5mm allowance for grinding. But locating ring is completely finished in lathe only. The other parts are sprue are sprue bush, return pins, guide pillar aligning bushes, rest pins, feet buttons, etc.

All the above which are made up of OHNS (T110 W2 Cr1) material are heat treated and then ground to required dimensions.

HINTS FOR PURCHASING RAW MATERIAL & STANDARD ITEMS

RAW MATERIAL

1       A careful study of current market status should be made before buying anything

2       Make a complete list of different materials required.

3       While purchasing do not overlook the raw material size to the finishing size.

STANDARD ITEMS

While purchasing STD items like ejector pins, screws etc buy some extra numbers for easy replacement in case of damages. Inspections should be done whether they are in given tolerances. Keep them in a clean place by applying a thin film of oil.

CORE AND CAVITY INSERTS

After heat treatment they are inspected for required hardness. The hardness may vary between 46-48HRC

.

MAIN CORE INSERT

Item No.                         :- 25

Material                         :-H13(OS)  

Raw material size            :- dia35X215mm

Finished size                   :- dia31X208

HRC                               :- 46-48HRC

Quantity                         :- 4NO

CORE forms internal profile of the component, at first it is pre machined on lathe machine and keep allowance 0.5 for harnding. At center of the core insert M5taping for clamping the core sub inset, in back side dirll8x170mmdrilling for baffle cooling hole they are sent for heat treatment. After coming from heat treatment all the dimension are maintained with reference to tooling hole. And first sent for cylindrical grinding to mateine exact sige .finally profile sparking for core sub insert are finished on EDM  using electrode roughing and finishing living spark gap. Totally two electrode are sparked. After completing all machining core is Inspected as per drawing. 

MAIN CAVITY INSERT

Item No.                                   :- 26

Material                          :-H13(os)   

Raw material size            :- dia 32x55

Finished size                   :- dia30x50

HRC                               :-  46 - 48 HRC   

Quantity                         :- 4NO

          The insert has an H7/k6 fit with the cavity plate. This cavity insert forms the outside profile of the component. First it is pre machining on lathe machined ground living0.5mm for cylindrical grinding .in center1.5mm drill for wire entry hole, and it sent for  heat treatment. After coming from heat treatment first send for wire cut for wire cutting the hole size of 3k6for inserting the cavity sub insert. And sparking the collar dia 6x3mm depth. All machining process are completed the cavity inserts are sent to the inspectioning the cavity as per drawing.

SUB CORE INSERTS

Item No.                :- 27

Material               :-OHNS)

Raw material size:- Ø8x30mm

Finished size       :- Ø6.38x25.5mm    

Hardness            :- 50-52HRC

Quantity             :- 4NO

The material used is OHNS.

         This is pre machined on turning with 0.5mm grinding allowance on all dimensions. In back side M5 taping for clamping in the main core insert .And It  sent to heat treatment. After coming from heat treatment dimensions of the sub core insert maintained by cylindrical grinding.

.

SUB CAVITY INSERTS

 Item No.                 :-   30

Material                            :-H-13(OS)

Raw material size    :-  Dia8X60mm

Finished size           :- Dia6X 55.8mm

HRC                       :-45-485HRC

Quantity                 :-   4NOS

          This is pre machined on turning with 0.5mm grinding allowance on all dimensions. Then sent to heat treatment. After coming from heat treatment dimension3K6X55.8mm are maintained as per size. dia1.36and 0.5radius is matiane in profile grinding machine. . All machining process are completed the cavity inserts are sent to the inspectioning the cavity as per drawing..

SUB CAVITY INSERTS

Item No.               : 31

Material              :- H-13(OS)

Finished size       :-  68X11.88X5.08mm     

HRC                   :-  50-52HRC

Quantity              :- 8NOS                                     

     The material used is H-13(OS)

This insert is directly blanked out from wire cut .In first setting the fitting size68X11.88X5.08h6 mm was done and in second setting radius profile was done. This insert H7g6 fit in cavity plate.

MANUFACTURING OF SLIDERS

Item No.                :-  36

Material               :-          HDS

Raw material size :-   312X72X65mm

Finished size         :- 308X70X60mm            

Hardness             :- 50-52HR

Quantity             :-2NOS

Slider is used for side profiling with cam pin actuaction.The material used is HDS. This is pre machined on milling with 0.5mm grinding allowance on all dimensions. After grinding slider was moved to rough profiling on Cnc milling. After cnc job was moved to milling for angular drilling at an angle of 20 degree and angular milling by tilting spindle to an angle of 22 degree. After that Rectangular circuit cooling hole done as per drawing.M5X4Taping is done for clamping the wear palate. Then slider was sent to heat treatment. After treatment slider was ground and all the dimension are maintained as per drawing and angular grinding was also done ,and then job was moved to finish cnc, and then to EDM  for profile sparking in four position in one slider using electrode of roughing and finishing achieve  projection profile. .After completing all machining slider is inspected as per drawing.

ELECTRODES

The flat insert pressed inside the core insert provides a square opening inside the component. It matches with with the depth of the component resulting in the square profile inside the component. It is first milled and then ground to the required size.

MANUFACTURING OF ELECTRODES

This is a most precision work and it plays an important role in tool manufacturing. Actual planning depends upon splitting of the profiles. Material and manufacturing of electrode depends upon.

1)               Complexity of the profile to be produced.

2)               Depth of sparking.

3)               Finish needed.

4)               Machining process involved.

Mainly graphite and copper are used. Copper should be used for thin and deeper sparking. Since there are thin ribs of 1.01 and 2mm graphite cannot be used. So copper is must preferred. They are machined in CNC and wire cut machines. The spark gap being 0.2 mm/side for roughing and 0.1mm/side for finishing. The round and rectangular electrodes are machined in lathe and milling respectively. The handle parts in the cavity insert are sparked with graphite electrode made in CNC.

The electrodes for runners, gates etc are sparked with graphite electrode.

The electrodes are given 0.15 drafts while machining. Inspite of this, an added advantage is that the taper formed by this while sparking, since it helps in easy release of component from core and cavity during ejection.

                        MACHINES USED IN TOOLING

                        CONVENTIONAL MACHINES

1)      LATHE

It is a machine tool where the excess material is removed in a round piece by a single point tool when the job is revolving around its own axis. It is a most versatile machine. All cylindrical parts are pre tooled in this machine. First facing is done and then center drilling and counter sinking at the each end of the stock is done to turn the job between centers. For guide bushes, it needs to be bored inside, so jobs are held in the check, the material removing is very fast. Due to its wide usage it is known as 'Mother of machines'

2)       MILLING

Milling is a process of removing excess material by feeding a work piece against a rotating multipoint cutter. It is widely used machine tool both for Tool Room and production work. In this machine we can perform 64 operations like slotting indexing, ball milling, helical milling, etc.

3)      DRILLING

This machine produces holes or enlarging holes in a work piece by forcing a rotating tool called drill. All holes, pinholes are done in this machine.

4)      GRINDING MACHINE

It is a machine tool in which less amount of material is removed to impart highly accurate with good surface finished jobs. Here an abrasive wheel is used for the removal of excess stock kept while pre tooling. There are different types of grinding machines like surface grinding, cylindrical grinding machines. For flat surfaces surface grinding is used and for round jobs cylindrical grinding machines are used. All cylindrical and flat jobs are ground after heat treatment to the required size and shape.

2)      NON-CONVENTIONAL OR SPECIAL PURPOSE         MACHINES

1)      CNC MILLING:

It is the most advanced milling machine. Here the parameter and co-ordinates are strictly controlled by computer system to achieve good accuracy and finish. Any  kind of intricate profiles can be done.

Since the machine cost is more and the cost of manufacturing is also the same parts that is produced are accurate with respective to pitches, profile and contours etc.

2)      EDM AND EDNC MACHINES:

Electro discharge machining and Electro discharge numerical Control Machining is a process of metal removing by means of electric discharge between a shaped electrode and electrode conductive work piece (core and cavity in this tool) in the presence of a dielectric fluid. In simple words an electric arc is used to erode. The work-piece, which takes a shape opposite to that of the electrode.

The gap between electrode and job is raised until dielectric barrier is ruptured, which usually occurs at a distance of 0.03mm or less at about 70V. Technically, the dielectric is ionized to form a column or path between the work piece and tool so that a surge of current takes place as spark is produced. Thus a minute part of work is vaporized and tiny particles are cooled into spheres and are swept away by the machining gap through the flushing of dielectric fluid.

Utility of EDM process

1)    Completely finishing the profiles before heat treatment could have resulted in distortion during the heat treatment process.

2)    Moreover, surface finish obtained by this process is very good, as there is no cutting force acting on the work, by this, error due to elastic deformation is eliminated.

3)    Accuracy of the profile up to 0.02mm can be achieved.

4)    Except polishing, no other finishing operation is required.

3)      WIRE EDM

As the name indicates a wire of less than 0.2mm diameter brass coated is used to cut the material. The process is employed where high accuracy is required to produce through slots, holes and intricate profiles. NC program for the required profile is fed into the control of the machine and according to this program the worktable moves against the wire to cut the profile.

8. HEAT TREATMENT

In order to produce an efficient tool it is necessary not only to select the correct steel but also subject it to a proper and careful heat treatment. Any solid metal normally has a definite infrastructure at a certain energy state. But the chemical as well as physical change will occur by the application of heat. Therefore heat treatment may be defined as the process of heating and cooling of metals or alloys in the solid state to induce desired properties. Some requirements are listed below:

1)           To improve mach inability.

2)           To change or reefing grain size.

3)           To improve magnetic and electrical properties.

4)           To increase resistance to wear, heat and corrosion.

5)           To produce a hard surface on ductile interior.

The steps for hardening are:

1)           Stress relieving.

2)           Preheating for hardening.

3)           Heating to hardening temperature and soaking.

4)           Quenching.

5)           Tempering.

6)           Inspection and testing.

1)    STRESS RELIEVING

The parts are loaded in a metal box which has hydro carbons like charcoal, cast iron chips etc. which prevent decarborization. Then it is heated steadily from room temperature to 650° C in a muffle furnace. It is soaked for 12 hrs and then furnace is cooled at rate of 50° C/hr. This operation eliminates machining stresses, which may result in cracking during hardening. If heavy machining is to be performed stress relieving is recommended intermittently.

2)    PRE-HEATING FOR HARDENING:

It is very important in hardening operation. Parts are heated to 300-500°C and soaked. Then it is transferred to neutral salt bath. Preheating relieves thermal stress induced for having exposed suddenly to hardening temperature.

3)    HEATING TO HARDENING TEMPERATURE AND SOAKING

After pre heating, tool parts are transferred into salt bath, which is maintained at a temperature of 820-850°C. Depending upon the mass of the tool parts, each part is soaked. Soaking is essential in order to ensure solid solution state in the tool throughout the phase.

4)    QUENCHING

It refers to rapid cooling of material from austenising temperature to room temperature by choosing appropriate cooling media. The usual quenching media for hot die steel is air. Air quenching provides a cooling rate of about 65°C/Sec at the surface. It is the most suitable for quantity tool steels. Still air is normally recommended for better results

5)    TEMPERING

The parts should be tempered immediately after quenching (within half an hour). Parts are tempered as per the ensure toughness. Tempering is done in a tempering bath maintained at a temperature of about 150-250°C. After soaking for one and half hours they are allowed cool in air with a little loss in brittleness. After tempering the brittleness of steel reduces with some decrease in hardness, but the toughness and impact strength of steel increases and also the internal stresses due to quenching are relieved in tempering.

HEAT TREATMENT PROCESS FOR CASE HARDENING STEEL

Case hardened steels cannot be hardened directly as other steels because of less percentage of carbon transformation of pearlite and ferrite to austenite and marten site is very less. So before hardening a process called carbonizing is done.

CARBURISING

It is defined as the method of heat treatment by which carbon content at the surface of ferrous material in increased. To increase the carbon content at the surface of steel following factors to be considered.

1)                Ferrite phase of iron.

2)                Austenite phase of iron.

Depending upon the procedure of carburising and state of medium used, they are classified as:

1)                     Pack carburising.

2)                     Gas carburising.

3)                     Liquid carburising.

Here the parts to be carburised are placed in containers containing carbonaceous material like charcoal etc. the container is heated to a temperature of about 850°C-925°C. At this temperature diffusion takes place and carbon is absorbed. After soaking time the container is allowed to cool by this the carbon percentage will be increased.

HEAT TREATMENT PROCESS FOR OIL HARDENING NON SHRINKAGE STEELS (OHNS)

HARDENING

Since this material contains 1.1% of carbon it can be hardened without any pre-operations like carbourising etc. Here the material is heated to about 850°C, the part is then soaked which helps for structural changes. To retain the martensitic structure quenching in oil suddenly cools the material. The hardness range obtained is about 56-64HRC. The martensite structure will be hard and brittle.

ANNEALING:

The steel is annealed for following purposes:

1)           To make steel soft i.e., to reduce hardness and increase mach inability.

2)           To relieve internal stresses.

3)           To obtain microstructure.

4)           To improve magnetic and electric property.

The steel is heated uniformly to the austenite phase and then cooled slowly in the furnace where the cooling rate is 50°C/hr and therefore results in the formation of coarse peralite, which is soft.

The annealing temperature for hypo eutectoid is HCT+50°C and for the hypereutectoid steel is LCT+50°C. Because steel when heated above the critical range consists entirely of austenite, transforms into peralite with the free constituents of cementite, which is hard. The presence of cemetite makes the steel hard.

At the temperature LCT+50° C, the formation of austenite will still be in progress and after cooling results in the formation of lesser amount of cementite. Therefore steel becomes much softer.

TEMPERING

The material is heated to a temperature of about 150°C -300°C. The tempering time depends on the temperature. There the temperature is inverse of the time, but tempering time depends on the size of the material to be tempered. The hardness is reduced by 3-6 HRC.

After tempering time, material is brought to room temperature by air quenching.

HEAT TREATMENT PROCESS FOR ORVAR SUPREME

This is most important because of its application for core and cavity. Here the material is heated to a temperature range of 980°C to 1040°C. Soaking time is allowed till the required structural changes are done. After soaking the parts are cooled in furnace up to 600°C. That is below critical temperature point. Then it is air quenched to obtain 46-48HRC hardness.

TEMPERING.

The material is heated to about 550°C -590°C. Tempering time depends upon the size of the material. Then it is allowed to cool in open air. The hardness may be reduced by 3-6 HRC and eliminating the internal stresses developed during hardening induces toughnes.

MAR TEMPERING.

After hardening surface becomes hard and brittle. The center of the piece transfers and expands often cracking the surface of martensite. This happens due to rapid quenching so they are called as quench cracks. This process produces fully martensitic structure with least internal residual stresses distortion and quenches cracks. When the steel reaches the austenitic range is followed by lead alloy bath maintained with same temperature at both core and the surface about 180°C 300°C but not long enough to bainite formation.

MULTI TEMPERING.

Also multi tempering at temperature 500°C-650°C should always be employed to ensure the total transformation of austenite to martensite. This has proved advantageous for large or sharp cornered tools.

STABILIZING.

Generally these steels tend to retain sustained amount of austenite in the hardened state. This is due to high quality content and is apparent by the low martensite formation temperature, generally below zero sub zero treatment in refrigerator at –75°C or in liquid nitrogen at -196°C is recommended.

CASE HARDENING

After hardening only core remains soft that is, only core will be in cementite (soft) structure and the surface will have marten site (hard) structure. Thus the items will have soft core and hard surface. The parts will be tough hard and wear resistant.

TYPES OF CASE HARDENING:

Nitriding.

Cyaniding.

Carburising.

NITRIDING: -

This is a process of case hardening resulting from the presence of iron nitrites and alloy nitrites within the steel. Special steels containing small amount of aluminum and chromium, molybdenum are used for nitriding.

Here the steel is heated in a closed furnace containing ammonia gas, which partially dissociates at the surface of the hard steel, forming N2 and H2. The N2 diffuses into the surface forming nitrites, which are hard and wear resistant. Quenching is not necessary is an added advantages.

This is a costly process and time consuming. But the nitrated surfaces are very hard (62-67HRC), very good wear resistant, high fatigure strength improved corrosion resistance.

2)      CYANIDING

It is also called as liquid carbonitriding. It is a process by which the carbon and nitrogen content at the surface of steel is increased.

Commonly used cyanide bath consist of sodium chloride, sodium cyanide and sodium carbonate. These Na2Co3 and Nacl are used to provide fluidity and to control the melting point of bath (540 to 620°C).

Here cyanide decomposes in the presence of O2 and at the surface of the bath to produce Sodium Cyanide, which in turn decomposes to form nitrogen and carbon as per the reactions shown below.

2NaCN + O2 ----------  2NaCNO

4NaCNO + 2N ---------  Na2Co3 + 2NaCN

2Co------------ Co2 +C

2NaCN + 2CO2---------- 2NaCNO + O2

Both are operated in the range of 760- 870°C with an immersion time of 30 to 100 minutes and temperature varies directly to the case hardness. Here the case depth varies from 0.025 to 0.25 depending upon temperature and time of immersion. It is used to produce file hard, wear resistant surface of the steel. It is less costly then liquid carburising but the ingredients are highly poisonous. So care should be taken while handling.

Carburising is explained in heat treatment process of case hardening steel.

9. POLISHING

Polishing is the important phase of mould construction because the  final finish given to the moulding determines the finished obtained on the piece part of the casting.

ADVANTAGES OF POLISHING

1)      Easier ejection of the component .

2)      Reduce risk of corrosion

3)      Reduce risk of fracture and cracking of component during ejection.

4)      Imparts high surface finish to the moulding.

5)      Easy flow of plasticised material in the cavity.

  Surface smoothness that can be achieved depends on some factors such as:

1)    Polishing technique.

2)    Tool steel grade.

3)    Heat treatment

      

First the rough machining marks are removed using oilstone or emery cloth, the part is then polished with rough emery paper. Then going from coarse grit to intermediate and then to fine grit results in good polishing. Mirror finish is obtained by finest grade of emery paper or diamond paste.

10. INSPECTION

Inspection gives the measurement of the quality of the product or its utility in terms of the prescribed standards .in tool making the quality of each part of tool is reflected on the quality of the component .the quality must be specified in terms of strength, surface texture and dimensional accuracy.

  Inspection of the core & cavity should be thoroughly done after the final machining because any slight dimensional variations will affect the accuracy of the product.

OBJECTIVES OF THE INSPECTION:

1)    Inspection traces defects in raw materials and flows in process.

2)    It reduces further work on semi finished items thereby avoiding further wastage of time & recovery.

3)    It improves the quality of the product.

TYPES OF INSPECTION:

1)FLOOR INSPECTION :

Inspection taking place in the shop floor while the work is under progress on the machines .

2) CENTRALIZED INSPECTION:

          This kind of inspection is carried in a separate room where high accuracy measuring and comparing devices are available all the items are brought here only for inspection .the above two types are incorporated for this tool

Normally in inspection we used measuring instruments like:

1)    Vernier

2)    Micrometer

3)    Bore dial gauge

4)    Dials

5)    Trimos

6)    Profile projector

11. ASSEMBLY

Assembly is a highly skilled operation in which each parts manufactured is fitted into their respective places considering the function.

Each part should be checked for fit or mating relation such as core and cavities, guide bush and pillars etc .

FIXED HALF ASSEMBLY

              After completing all machining operation inspect main cavity and sub cavity insert thoroughly as per drawing .And then check for the assembly designs and part list. Guide pillars (item no10) are fitted in the respective holes with collar system, & Rest pins (item no20) are placed inside the cavity plate (item no04). And then suit the sub cavity insert in main insert than check for fixed half, fit the Cam pin in cavity plate and now suit main cavity insert in cavity plate. fit the wedges in cavity plate and clamp with M8screw on six side .now clamp cavity plate to top plate with M12 screws on four the side,  And Next sprue bush (item no21) is fitted in the front and movement is restricted with the locating ring on the top which in turn is fixed on top plate (item no 18) with the help of M20mm screws.  These are all care should be taken during the assembling of fixed half.           

MOVABLE HALF ASSEMBLY

Before assembling core side inspect main core ,sub insert, slider, slider insert and guide rail and all spotting area. And than main core insert(item no25)are placed inside the core holder plate housing (item no03)and another core sub insert clamped in the core insert.

          After suiting core now suit the guide rail ,since there are two slider two guiderail  are used so two guide rail one on each side is screw to core plate with M10x60mm  and8mm dowel  it. And fit the Ball catchers from back side of core plate in calculated position.              

 

Inserting  return pins and sleeve in respective hole maintain H7g6 fit ejector assembly is completed; the return pin heads are matched with ejector plate surface, the ejector pillars and bushes are fitted, then back plate is fitted to the ejector plate with help of M8X30mm screws. The pillars are oiled and the movement of ejector assembly is checked. The core half is inverted and spacer on the core plate and bottom plate is spaced on the spacers. Then both of them clamped together with M12 screws, And core holder is clamped with bottom plate with screw of M8. The leveled feet buttons are screw to ejector back plate to resist back pressure. After assembly of both halves the mould was closed for blue matchi

12. BLUE MATCHING & WEDGE MATCHING OF CORE & CAVITY

Blue matching was the final stage of assembly work. It is the process in which both the core and cavity parting surface are matched exactly to avoid plastic flow during moulding (flash free). In this process a thin film of blue was applied on any one side, either core or cavity parting lines. The tool was closed; a slight force was applied and was opened. The high spots where blue is picked up was removed either by diamond file, oilstone or by pneumatic grinders, if it was irregular parting line; otherwise the parting line levels were surface ground. This process is done till blue matches on both halves evenly.

            Wedge matching is a process in which wedges are ground and matched to the side cores ensuring efficient locking of side cores with the matching face and at the same time correct matching at the parting surface.

            The core and the cavity halves are assembled. The ball catch was fixed in the wear plates and guide rails by screws in order to position the sides’ cores. Finally side cores are were assembled.

               

Blue is applied on the parting surfaces. The two halves are then closed. There will be some gap between the parting surfaces, as there will be some stock on the angled surface of wedges for wedge matching. Depending upon the gap between both halves, which is checked using feelers gauge or lead the stock material, is ground so as to achieve the matching of the core and cavity.

The method of calculating the gap between the two halves is as follows;

      

         Calculation is done for the amount of material to be removed in wedge using formula

                                     A=SIN XB

      Where,                   A=material to be removed,

                                       =Wedge angle,

                                    B=gap between parting surfaces.

13. TRY OUT

After final assembly, the mould is taken for try out before loading in the injection machine, some important things to be checked.

MOULD MANUFACTURING CHECK LIST:

Are all parts secured properly & tightly?

Is the cavity polished in the direction of the ejection?

Is any negative taper in the inserts?

Is the ejection system are actuation proper?

Is the die set actuation proper?

Is the locating ring suit the machine hole?

Is the cooling circuit proper with any leakage?

Is the tie bar tightened properly?

Are the proper lifting holes are provided?

When the tool is subjected to the actual working conditions, the performance is noted and if there are any defects they will be reworked if necessary.

TOOL CLAMPING:

There are two methods of securing the tool to the press platens namely direct bolting & clipping .the first system employs bolts which pass through holes into the back plate and threaded holes is pulled by the bolt and later engaged a conveniently positioned hole in the platens, with one end on the packing and other on the tool back plate.

ESTIMATING CYCLE:

For estimating cycle the important point to be necessary are: -

MOULD

Mould opening -300mm

Ejector stroke -45mm

Shot weight –

PRESSURE

Clamping pressur -150Ton

Injection pressur -108Bar

Holding pressur -38Bar

Ejector pressur -30Bar

Back pressur -5Bar

SPEED

Injection speed -60rpm

Screw speed -20rpm

TIME

Dosing time -2.79Sec

Injection time -0.49Sec

Holding time -5.0Sec

Cooling time -40Sec

Mould opening time  -4.05Sec

Mould closing time -3.07Sec

Cycle time -78Sec

TEMPERATURE

Nozzle temp -295Deg.c

Feed temp -60Deg.c

SCREW TYPE INJECTION MOULDING MACHINE:

This type of the machine consists of the screw, rotating in the hot barrel capable of delivering continuos melt of the plastic material through the nozzle can be had because of the shearing action and the material flowing in different patterns there is homogeits in the melt.

MOULDING PARAMETERS:

Mould height          :346mm

Mould size              :396X296X346mm

Shot capacity of PP:3.48 ounces

Plasticizing capacity of LDPE:15.29kg/hour

Shot weight             :75 gms approx.

TRY OUT

Tool is loaded onto the injection moulding machine all necessary parameters are set in the machine the material is poured into screw cylinder through the hopper the mould is pre heated to the temperature of 120-125deg for 3hrs before injecting the material the tool is closed & the material is injected through the machine nozzle after noting the cycle time the component is ejected out in first some shots the component was not filled properly since there are some in profiles so effective heating and increased injection pressure gives us the fully filled component.

After taking care of all the defects in first try out our second try out was successful.

CYCLE TIME

          This is the tool time taken for the  complete cycle for the production of the one component .it consists of the following stages

1)    Closing of the mould: The releasing agent is sprayed on the core and cavity  before closing .the clamping force of 250 tonnes is applied to close the mould on the projected area. Clamping force is also referred to as the locking force. After the mould is closed cam pin are actuated which enable the side core to  but the core inserts.

2)    Injection: The injection ram comes forward along with the hot plasticise material and then injected under pressure by screw which acts like a plunger the hot material is injected through the nozzle into the closed mould cavity via sprue bush runners & gates. The plunger provides necessary pressure to inject the plasticised material.

3)    Cooling: The cold water or oil is circulated through the cooling channels to cool the core and cavity and maintain mould working temperature .After injection the mould is held under pressure until the mould piece is cured.

4)    Opening of the mould: First the nozzle is retracted back  and  then the clamping force is released and the mould is opened.

5)    Ejection: As the mould open’s further at first slider are moved back and locked by ball catch, the fixed stopper provided in the machine actuates the ejector system of the mould components are ejected.

14. TROUBLE SHOOTING

               By inspecting the component after the corrections to be made.

 

TOOL COST & ESTIMATION

The process of compiling a statement of the quantities of material required, the amount of time involved in production and the procedures to be followed in putting an order through is called estimation.

Advantages of estimation: -

It helps in determining the expenses incurred in connection with the production.

The department efficiency is determined.

The actual cost is early compared with the estimation cost.

It helps in taking decision whether to make or buy, economically.

COSTING:

          The techniques and process of ascertaining cost is known as costing. Costing enables the business not only to find out various jobs or processes have coasted it indicates where losses & wastage’s are occurring before the work is finished so that the immediate action will be taken if possible to avoid such losses are wastage.

ELEMENT OF COSTING

          The main elements of cost, which make up the total cost of any job, are given under the following-

 Material:

a) Direct material

b) Indirect material

Labour:

a)direct labour

b)indirect labour

Expenses:

a) Direct expenses

b) Indirect expenses

CLASSIFICATION OF THE COSTING:

1) Direct material

2) Direct labour

3)Direct expenses

4) Overhead expenses

a) Factory:

1) Departmental

2) General

3) Services

b) Administration

c) Selling & distribution

The tool can be understood from the table -

Since estimation of labor cost maching cost & raw material cost is a laborious process and calculation, only conclusion part of the calculation is shown

Inspection-Rs 350/hr

Bench work-Rs 80/hr

Machining /Hr=cost of the machine/life span

They are as follows:

MATERIAL COST:

Material                                    round                                flat

OHNS                                     Rs 60/kg                                   Rs 80/kg

HDS                                        Rs210/kg                                  Rs250/kg

Case hardened                        Rs45/kg          

Copper                                    Rs200/kg

1.2767                                    Rs.320/kg

MACHINING COST:

The machining cost depends upon totally upon the life span &cost of the machine ,that is

Turning-Rs 40/hr

Milling –Rs 70/hr with DRO – Rs 120

Shaping-Rs 30/hr

Drilling-Rs 20/hr

Grinding-Rs75/hr

Jig boring-Rs 350/hr

Jig grinding-Rs 350/hr

Non-coventional machines charges

CNC milling-Rs 800/hr

EDM-Rs 120/hr

EDNC -Rs 450/hr

WEDM-Rs 350/hr

DIRECT MATRIAL COST

S.N DESCRIPTION RM QTY               SIZE  wgh rate amoun L W H DIA kg R.S 01 TOP PLATE C-45 01 430 255 35 30.16 65 1960.71 02 CAVITY PLATEE C-45 01 430 205 35 24.45 65 1576.25 03 CORE PLATE C-45 01 430 205 40 31.09 65 1801.43 04 SPACER C-45 02 430 40 115 27.71 65 2021.12 05 EJECTOR PLATE C-45 01 430 127 25 10.73 65 697.51 06 EJ BACK PLATE C-45 01 430 127 25 10.73 65 697.51 07 BOTTOM PLATE C-45 01 430 255 35 30.16 65 1960.71 08 LOCKETING RING C-45 01 18 105 1.22 65 79.59 09 GUIDE PILLER OHNS 04 165 45 8..25 85 700.94 10  GUIDE BUSH OHNS 04 55 45 2.75 85 233.65 11 TAPER CAM PIN OHNS 04 135 20 1..33 85 113.28 12 PUSH BACK  PIN EN-31 04 200 20 1..97 85 167.83 13 REST BUTTON EN-31 04 20 25 1.54 65 100.26 14 SPRUE BUSH OHNS 01 85 35 0.64 85 54.61 15 EJ GUIDE PILLER OHNS 04 115 35 3.48 85 295.53 16 EJ GUIDE BUSH OHNS 04 60 35 1.81 85 154.19 17 SLIDER 1 HDS 01 315 75 65 12.07 580 7000.61 18 SLIDER 2 HDS 01 315 75 65 12.07 580 7000.61 19 WEAR PLATE OHNS 02 150 165 10 3.89 85 330.71 20 LINERS OHNS 02 210 65 65 13.95 85 1185.54 21 WEDGE 1 OHNS 01 240 42 72 5.66 85 481 22 WEDGE 2 0HNS 01 240 42 72 5.66 85 481 23 CAVITY SUB INSERT1 OHNS 04 20 51 5.4 85 459 24 CAVITY SUB INSERRT 2 OHNS 04 56 6 1.6 85 136 25 CORE SUB INSERT OHNS 04 25 7 1.64 85 139.4 26 SLEEVE OHNS 04 139 44 28.6 85 2431 27 SLEEVE BUSH OHNS 04 36 55 11.2 85 952
	TOTAL	29968.39

PART  :-- Cost of STD Items  :- 1400/-
SR.NO.	ITEM DESCRIPTION	QTY	RATE	TOTAL COST
1	RETURN PIN	04	100	400
2	O RING	12	10	100
3	NIPPEL	06	100	600
4	GURB SCREW	6	10	60
3	BALL CATCH	4	60	240
			TOTAL	1400

PART:-- Cost of Labour  :-83731/-
SR.NO.	DESCRIPTION	Hrs	Rs./Hour	Total
1	Millling	40	115	4600
2	Surface Grinding	30	70	2100
3	CNC Milling	75	600	45000
4	Sparking (EDM)	100	115	14375
5	Bench Work	128	45	5760
		Sq. mm	Rs/sq mm
6	WIRE CUT(SQ/MM)	39584	0.25	9896
			Total	83731/-

PRIME COST

DIRECT MATRIAL COST			29,968,39/-
DIRECT LABORE COST			83,731,00/-
COST OF STD ITMES			1400/-
ELECTRODE COST			4,250,97
HEAT TREMENT CHARGE			2000/-
		TOTAL	1,19,950.36

DESIGN COST             = 15% OF Prime Cost

                                       = Rs.17,992

OVERHEAD COST      = 20%Of Prime cost

                                      =23,990

          SAFETY             =10%Prime cost

                                      =11,995

15. CONCLUSION

            This project report on “Two Cavity Injection Mould” gives the general  idea of tool making by explaining the various aspects, from designing process to tryout.

 

Going through all stage of manufacturing and desiging of injection mould for “HOUSING 96” practically and theoretically I gained  experience to very good extent.The machining knowledge and designing of tool imparted to us during the processing of our tool thus I am easily conclude that I reached stage that I can handle the designing and manufacturing of tool independently making it in the economical way.

As a whole this project has helped in improving my overall skills as a toolmaker and aiso helped me in presenting my views, regarding  this trade and project, so I conclude by thanking all to those who helped me for project  success.

BIBLIOGRAPHY

Reference Books

ü     Injection MouldDesign

                                              ……R.g.w.pye

ü     Plastic Tooling

                                           ……..William.p

ü     Hand Book on Plastic

                                                      …..CIPET

ü     Plastic Technology

                                          …….William.j

ü     Theory of moulds

                                                ……Nagesh