ULTRASONIC METAL WELDING

CONTENTS

n INTRODUCTION

n HISTORY

n COMPONENTS

n PRINCIPLE OF OPERATIONS

n ADVANTAGES

n DISADVANTAGES

n APPLICATIONS

n CONCLUSION

n REFERENCES

 

 

INTRODUCTION

     The process of ultrasonic metal welding uses high-frequency vibrations. Ultrasonic metal welding works by placing the parts to be welded on the anvil.

     Next, force is applied to the parts. Then the upper part is vibrated back and forth with the ultrasonic horn.

     This causes the parts to rub together. The ultrasonic energy disperses oxide film layers (cleaning the surface) and results in the mixing of nietal atoms, without melting the metals. The activated metal atoms join each other, causing a true metallurgical bond.

     Ultrasonic metal welding is sometimes called “cold welding” because it works without melting the metals. It cleans and welds at temperatures lower than the melting point of the metals. It most commonly joins nonferrous metals, but can also be used with others, such as when welding aluminum to ceramics.

HISTORY

   In 1960 Sonobond Ultrasonics, originally known as Aeroprojects, Incorporated, developed the first metal ultrasonic welding machine to be awarded a United States Patent

COMPONENTS

All ultrasonic welding systems are composed of the same basic elements:

 

n  A press to put the 2 parts to be assembled under pressure

n  A nest or anvil where the parts are placed and allowing the high frequency vibration to be directed to the interfaces

n  An ultrasonic stack composed of a converter or piezoelectric transducer, an optional booster and a sonotrode (US: Horn). All three elements of the stack are specifically tuned to resonate at the same exact ultrasonic frequency (Typically 20, 30, 35 or 40 kHz)

nConverter: Converts the electrical signal into a mechanical vibration

nBooster: Modifies the amplitude of the vibration. It is also used in standard systems to clamp the stack in the press.

nSonotrode: Applies the mechanical vibration to the parts to be welded.

PRINCIPLE OF OPERATION

n Step 1 - Parts in fixture

    The two thermoplastic parts to be assembled fixture are placed together, one on top of the other, in a supportive nest called a fixture.

 

n Step 2 - Horn contact

    A titanium or aluminum component called a horn is brought into contact with the upper plastic part.

 

n Step 3 - Pressure applied

     A controlled pressure is applied to the parts, ppIied clamping them together against the fixture.

 

n Step 4 - Weld time

     The horn is vibrated vertically 20,000 (20 time kHz) or 40,000 (40 kHz) times per second, at distances measured in thousandths of an inch (microns), for a predetermined amount of time called weld time. Through careful part design, this vibratory mechanical energy is directed to limited points of contact between the two parts.

     The mechanical vibrations are transmitted through the thermoplastic materials to the joint interface to create frictional heat. When the temperature at the joint interface reaches the melting point, plastic melts and flows, and the vibration is stopped. This allows the melted plastic to begin cooling.

 

n Step 5 - Hold time

     The clamping force is maintained for a time predetermined amount of time to allow the parts to fuse as the melted plastic cools and solidifies. This is known as hold time. (Note: Improved joint strength and hermeticity may be achieved by applying a higher force during the hold time. This is accomplished using dual pressure.)

 

n Step 6 - Horn retracts

     Horn Once the melted plastic has solidified, the retract clamping force is removed and the horn is retracted. The two plastic parts are now joined as if molded together and are removed from the fixture as one part.

ADVANTAGES

n  Excellent weld quality and a tight seal can be obtained

n  Minimal electrical and thermal contact resistances in the seams

n  Electronic monitoring of the weld parameters with interface to central computer for data storage and for statistical evaluations (SPC)

n  Very short welding times (fractions of a second)

n  No filler metal necessary

n  Clean and safe process (no sparks, flames and smoke formation) therefore environmentally friendly very low energy consumption

n  Can be easily automated and intagrated in production lines optimum cost I benefit ratio

DISADVANTAGES

n Pose the risk of some hazards

n High heat levels and voltages

n This equipment should always be operated using the safety guidelines

n Operators must never place hands or arms near the welding tip

n Routine maintenance

APPLICATIONS

     The fields of application are extremely varied and range from solar technology via the electrical and automotive industry to pharmaceuticals, packaging. Listed below are examples of a few applications from the various fields of application:

 

CONCLUSION

            Ultrasonic welding are extensive and are found in many industries including electrical and computer, automotive and aerospace, medical, and packaging. Whether two items can be ultrasonically welded is determined by their thickness. If they are too thick this process will not join them.

 

            This is the main obstacle in the welding of metals. However, wires, microcircuit connections, sheet metal, foils, ribbons and meshes are often joined using ultrasonic welding. Ultrasonic welding is a very popular technique for bonding thermoplastics. It is fast and easily automated with weld times often below one second and there is no ventilation system required to remove heat or exhaust. This type of welding is often used to build assemblies that are too small, too complex, or too delicate for more common welding techniques

REFERENCES

n www.answers.com

n www.googlesearch.com

n www.ultrasonicppt.com