APPENDIX G: DEFINING THE OPTIMUM PROCESS
HF25D LINEAR DC RESISTANCE WELDING CONTROL
990-333
G-7
The figure on the right
shows a typical welding
sequence where the force is
applied to the parts; a
squeeze time is then
initiated which allows the
force to stabilize before the
current is fired. Squeeze
time also allows time for
the contact resistances to
reduce as the materials start
to come into closer contact at their interface. A hold time is the initiated after current flows to allow
the parts to cool under pressure before the electrodes are retracted from the parts. Hold time is
important as weld strength develops in this period of time. This basic form of weld profile is
sufficient for the majority of small part resistance welding applications.
Power supply technology selection is based on both the requirements of the application and process. In
general, closed loop power supply technologies are the best choice for their consistent, controlled output
and fast response to changes in resistance during the weld (for further details comparison see Unitek
Equipment "slide rule").
Approach to Weld Development
The first stage in developing a quality welding process is to fix as many of the variables as possible in
the welding equipment set up. The welding variables can be grouped in the following categories:
•
Material variables
−
Base material
−
Plating
−
Size
−
Shape
•
Weld head & mechanical variables
−
Force, squeeze, hold
−
Actuation method
−
Electrode material and shape
•
Power supply variables
−
Energy
−
Time (squeeze, weld, hold)
•
Process variables
−
Tooling, level of automation
−
Repetition rate
−
Part positioning
−
Maintenance, electrode cleaning
•
Quality requirements
−
Pull strength
−
Visual criteria
−
Test method, other weld joint requirements
Squeeze
Heat
Hold
Welding Force
Trigger Force
Current
Summary of Contents for HF25A
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