Page 47 - MetalForming-Apr-2018-issue

Welding Well
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Fig. 3—This standard press-type spot welder features a low-inertia ram equipped with a spring for fast follow-up. The ram's cover has been removed to show the spring.
A properly sized press-type resist- ance-welding machine (not a rocker arm), with a rigid frame and a low- inertia ram with fast follow-up, will deliver the best results in applications involving high weld force, high weld current and a short weld time (Fig. 2). This welding schedule creates intense heat at the projections and allows the welding/forging process to take place rapidly—before the projections col- lapse and blow out.
In other words, success usually results from setting the machine to weld “hot and fast.” And, whether con- nected to a pneumatic or servo-actu- ated ram, the importance of using high weld force and a fast follow-up device, such as a spring built into the ram (Fig. 3), cannot be over-emphasized.
With proper weld-lobe parameters established, start a production run with settings that fall at the center of a graph that documents optimum settings proven through careful testing. Given this, the machine should produce con- sistently successful results throughout the shift, and if variables begin to drift, some margin is available before the welds fail. However, to avoid shipping a batch of parts that might be rejected,
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MetalForming/April 2018 45