1. A spot welder, comprising: at least two electrodes having tips engageable with a stack-up of material; a power supply for energizing said electrodes to spot weld said stack-up when said electrodes are engaged with said stack-up; a current sensor coupled to said power supply and generating a first signal representative of current supplied to said electrodes; a voltage sensor coupled to said power supply and generating a second signal representative of voltage across said electrodes and said stack-up; a neural network for processing, in real time, data representative of said first and second signals for a weld in progress according to a learning rule determined by data from previous welds, said neural network generating a predicted time of optimal weld strength for said weld in progress; and, a controller responsive to said neural network for terminating said weld in progress responsive to said predicted optimal time.