Box Dimensions

What is a "box dimension"?
The box dimension is used to define a dimension that does not need SPC charting nor a GRR and is measured for (plastic injection) mold start-up only.
It is a dimension that is indicated on a drawing that is not a QA dimension for which conformance during production needs to be demonstrated.

Regarding the utility of a box dimension.  A box dimension may be indicated for use to perform a dimensional check at mold qualification only under very specific circumstances.  The following questions are a useful guide to determining if treatment as a box dimension is appropriate:

  • Is the dimension expected to not vary at all during on-going production?
  • Is the dimension extremely difficult to access for measurement during on-going production?
  • In the case that the dimension is extremely difficult to measure, can it be adequately measured indirectly?

Does a box dimension require SPC charting? It may, depending on the application.

Does a box dimension require a GR&R study?  Measurement capability should be acceptable regardless of the classification as a box dimension, either for a one-time validation study, or as a quality checkpoint for on-going production measurement.