MOULD MANUFACTURING AND TERMINOLOGY

 

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

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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.