Upslope and downslope describe segments of the weld cycle where the weld current is either gradually increasing or decreasing. In upslope the weld current gradually increases from a low level to some higher current value. It might be to allow all components to warm up and reform, come together into full contact, before the full current is applied, to reduce expulsion. Downslope is the opposite. It is a gradual decrease from full welding current. This might be to prevent quenching of steel or other heat sensitive material.
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What is Upslope in Resistance Welding?
What is Downslope in Resistance Welding?
Reference: RWMA - Resistance Welding Manual 4th Edition