We haven't been using CPH (chips per hour) as an index of our production capability, but it seems more and more attractive as a basis by which we can compare the capability of different plants producing different products. Are there any other advantages to using CPH?
BTW, correct if I'm wrong, but I'm calculating CPH as the total number of components on board divided by the cycle time of my bottle neck process.
FInd your botle-neck process (use a stop watch). You assume it is a P&P machine...(it could also be print or glue etc.)
Your only concern is that bottle neck process and how many parts / hour that process can deliver. That is your gating factor. I hear this all the time...my chip shooter does 40K per hour...but your IC machine is limping along at 3K perhour causing all buffers to fillup with built boards until eventually your chip shooter stops. As far as I'm concerned you are only as effective as your slowest process...3K per hour! Then then counter arguement is...but my PPH is accumulative with all machines per hour (in a line)...or 43K per hour. Wrong! That chip shooter is not running for the full hour as the buffers fill up and eventually stop production.
I only focus on the line bottleneck. Maximize my efficiency and process around that bottleneck. Then move on to the next bottleneck. Simplify.
I would be more interested in comparing pure yields, scrap factors and rework costs between plants. PPH is useless if you placed the wrong parts!