Abstract:
Resistance welding is used very extensively in industry for a wide range of applications.
Knowledge and measurement of the dynamic characteristics of resistance welding equipment
is important in the design of the equipment and in optimization of welding procedures using
finite element software. This is especially true for projection welding where accurate
measurements of effective lumped mass and damping of the welding head as well as its
maximal acceleration and velocity are required for accurate modelling.
This thesis describes a new concept where a mechanical model of the welding head is used
together with the imposition of a mechanical load step function with simultaneous
measurement of resulting head motion to calculate effective lumped mass and damping factor.
Two test systems were devised to implement the step function. In the “free fracture test”, a
metal or ceramic bar is loaded to its breaking point and resulting welding head velocity is
measured. This data allows accurate calculation of machine parameters. The second test uses
the explosion of a small metallic element to impose a step function, when the welding current
causes the metallic element to explode. The final version of this test “the exploding button
test” uses a small cylindrical element fabricated from welding filler wire, with the advantage
that both button geometry and material can be controlled. The exploding button test has
proved to be very effective, can easily be used for in-situ measurements and avoids the
vibrations associated with the free fracture test. These test were applied to evaluate a range of
resistance welding machines.
Finally, an innovative projection geometry was developed to significantly increase projection
weld quality and this design has now been used extensively in industry.
The techniques developed in this thesis have been shown to be practical and effective and
have enabled much better understanding of machine kinematics. The measurements provide
essential data for modelling of projection welding and in guiding the development of
resistance welding machines and procedures.