Question 14: Is there any point in controlling the process when the machine capability is too low?
Machine capability is a measure of how well the machine succeeds in producing within tolerance limits. A common reaction when machine capability is inadequate is to refrain from using SPC to control the process. It is not considered worth the trouble, as the machine performs so poorly anyway.
However, the process result is always best, even with low performance, if SPC is applied; in many cases it can be enough to get better results in the next stage, e.g. a grinding machine or an assembly line.
Thus even at low machine capability, SPC has a significant effect on the reject rate and customer-perceived quality.
One might even go so far as to say that a poorly performing machine is in greater need of proper control than one that performs better.
Another advantage of using SPC with low-capability machines is that any action taken to improve performance shows up immediately on the control graphs; you get an early readout on whether the action has had the desired effect.