|
|
MDS Project Case Studies
(Highlights from twenty-five years of success!)
Case Study 4: Plastic Part Tolerance Study
An MDS customer was in the process of constructing a new plastic injection mold
to increase its manufacturing capacity. This mold would be used to make two
components of a Class III device. During the course of the development of the
two components, the original mold had been revised many times and the parts drawings
were out of date. During the construction of the new mold, the original material
became unavailable. The new mold was being constructed by a different molding vendor
who had never produced these parts.
Updated drawings needed to be created that were based on actual released parts that
were produced by the previous vendor. Tolerances needed to be added to the revised drawings.
The toolmaker had made rapid progress on construction of the new mold and needed the
revised drawings within one calendar week in order not to significantly delay the tool
construction. Unfortunately, four days of that week were customer company holidays.
MDS's customer requested that MDS initiate the tolerance study and do a red line of the
part drawing that indicated the proper tolerance for each dimension while all personnel
were on holiday. On their last workday, the customer's laboratory supplied MDS key
dimension measurements that were taken from actual released old parts.
MDS took the laboratory data, conducted statistical analysis of the data, and calculated
probability curves for each measurement. Interference fits were then determined. The
plastic manufacturer data was obtained for the specific resin and reviewed for lot
reproducibility. The design of the mold and mold flow were analyzed. A tolerance was
then set for each dimension. Critical dimensions were identified. A set of the part
drawings was red lined per ANSI standards. The red lined drawing set was supplied to
the customer on the customer's first day back at work.
The customer updated its print and the mold was completed on schedule. The mold
produced functional parts within specification on its initial production run.
|
|
