resistance mash welding for joining of copper conductors2

sulficker@outlook.com

1

RESISTANCE MASH WELDING FOR JOINING OF COPPER CONDUCTORS

FOR ELECTRIC MOTORS

sulficker@outlook.com

2

CONTENT

1.Introduction2.Objective3.Experimental plan4.Experimental approach5.Evaluation of welded joints6.Process analysis7.Results8.Conclusion

sulficker@outlook.com

3

1.INTRODUCTION

Vehicle electrification requires efficient motors with increased power and minimized losses.

While there are other forms of losses in the motor , minimizing resistive losses is crucial to boosting motor efficiency.

Bar wound stators have best packing density and has maximum conductive metal area.

sulficker@outlook.com

4

Cont..

Individual pieces of rectangular solid piece copper are bent into hairpin shape and joined together to create required electrical circuit.

Joining of copper can be complicated by the material’s very high thermal conductivity.

sulficker@outlook.com

5

2.OBJECTIVE

To identify and develop copper joining process to achieve high quality copper to copper joints with a minimum of time, energy, and applied force.

To assess the influence of variations in wire to wire alignment on weld strength

sulficker@outlook.com

6

3. EXPERIMENTAL PLAN

Resistance Mash Welding (RMW) joints are made using a conventional spot welding machine with a fast follow up head.

C101 copper wires with rectangular cross section 3.44mm x 3.66 mm were used.

A pneumatic spot welding machine was used.

sulficker@outlook.com

7Cont..

Two styles of electrodes were used:1. A 16mm diameter flat faced electrode.2. A non-standard chisel faced electrode.

The electrode were produced from RWMA Class 20 AL-60 material with good anti-sticking and electrical conductivity properties.

A fast-follow-up head was used in the machine to maintain force on the wires due to rapid softening and collapse of the wires during welding.

sulficker@outlook.com

8

4.EXPERIMENTAL APPROACH

Iterative tests were performed to obtain the optimum process parameters and system design.

Variables manipulated: Weld and forge forces Timing between weld and forge initiation Weld current and time Pre-welding parameters Anneal(pulse welding) parameters Cool times Placement of wires relative to the chisel tip location

sulficker@outlook.com

9Cont..

For parallel wire joints: Variations in wire overlap Angular alignment Weld end position with respect to electrode face

position were studied.

For cross wire joints variation was studied at three percentages of full wire extension.

sulficker@outlook.com

105.EVALUATION OF WELDED JOINTS

A weld schedule that achieved High average peak strengths A relatively small minimum to maximum range Final wire thickness greater than 2mmwas considered acceptable.

sulficker@outlook.com

11

6. PROCESS ANALYSIS

In RMW a multistep process was developed using control of applied force and current to manage the temperature and deformation of wires during the joining process.

sulficker@outlook.com

12Cont..Resistance heating in a spot welder occurs when

current flows through the spot welding gun into the base metal, across the faying interface, into the second piece of base metal and back to ground through remainder of gun structure.

The low weld force levels increased the heat generation at the faying surface without collapsing the joint.

After heating the weld zone to forging temperature, forge force applied provided the deformation needed to strain the heated metal and produce a forge bond.

sulficker@outlook.com

13

7.RESULTS

Cross-wire weld Flat faced electrodes were used.

Achieved tensile strength values between 1.44 and 1.60 KN.

sulficker@outlook.com

14Cont..

sulficker@outlook.com

15Cont..Parallel-wire weld

Using the same parameters tensile strength was between 540 and 800N

Using the special trapezoidal designed tip the weld tensile strengths were between 780N and 1.15KN

sulficker@outlook.com

16Cont..The strongest joints were generally

produced by the standard condition(Just under 1200N).

sulficker@outlook.com

17Cont..The average weld thickness was about

2.5mm.The average joint width for the standard

condition was about 7mm.The wire extension of the final weld joint

with the standard condition of about 3.5mm

sulficker@outlook.com

18Cont..For parallel-wire geometry, a critical value

of 2.5mm final joint thickness was observed to produce optimum weld tensile strength.

sulficker@outlook.com

19

8.CONCLUSION

For the parallel wire geometry, joints with acceptable strength can be produced by the following : The standard condition i.e., properly aligned ±10% width lateral misalignment Short extension -15% angular misalignments

sulficker@outlook.com

20Cont..The cross-wire joint geometries appeared to

provide sufficient process capability, providing no insulation was entrapped in the weld joint.

In a properly controlled process, means of producing overheating of the weld joint can be avoided.

Smooth fast-follow-up and weld force head motions were required to prevent collapse of the wires during welding.

sulficker@outlook.com

21

THANK YOU !