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liliconcom

DOE setupHi there!
I have a four step process whose process robustness I'm evaluating and I was hoping to do this with a DOE. Here's the basic process:

Input stream--->Step A--->output/input-->Step B-->output/input-->
Step C-->output/input-->Step D--> product!

Step B has three factors affecting the product purity and yield of its in-process output while steps C and D each have four factors affecting the product purity and yield of their in-process output. What I want to do now is correlate changes of these factors to the PRODUCT purity and yield. It seems to me that a fractional factorial DOE is the way to go. What are your thoughts? Also, is there a mechanism that could allow me to correlate analytical data from output/input of one step with the analytical data from the product? We have a debate going with some of our group arguing that the tolerance intervals of a given step output can serve as a predictor of the product quality. I argue that the remaining process steps aren't accounted for in those tolerance intervals and thus limit their ability to predict the final product quality. Your thoughts?