Sometimes, the forecast demand from customer is so huge. It requires many production lines to cover the required amount. In order to prevent the production variation from different manufacturing equipment including Injection Molding Machine (IMM) and molds…etc. Apart from picking IMM with similar performance (evaluated and categorized by the activity discussed in D-10), we could also mass produce the enough qty. of molds with same design.

If the mass-produced molds could fulfill following request, these molds could be considered as equivalent. Manufacturing department could have more flexibility in mass production schedule arrangement.

A. Mold manufacturing
Following items are suggested to be remain consistent to ensure the equivalency between mass produced molds.

• Part and mold design
• Mold fabrication
  It includes Mold maker, fabrication equipment, standard part suppliers…etc.
• Molding process
  These molds shall be capable to run on same specification molding equipment.

Molds produced according to principles mentioned above could ensure they are looks same. To see if they could produce same part, we can check following items during trial shot.

B. Mold performance
It could be decided through checking part quality including perspective of appearance and dimension:

• Appearance
  There shall be no issue(for more information please refer to B-6) on every part produced by new molds, but sometimes some issues are not avoidable (such as welding line due to part design, parting line/ejector mark due to mold design…etc.).
  The appearance of part produced by the first mass produced mold shall be approved. Since if there is any appearance issue, it happens on the parts produced by all same molds/process.

• Dimension
  A complete dimension in drawing includes the mean value and (upper/lower) tolerance. The measurement result from the part includes within/without specification, statistic calculation…etc. is the performance of the dimension.
  In general, part dimension measurement results shall be as concentrate and close to mean value as possible, this could maximize the Cpk value.
  Between mass produced molds, if the part (produced by the first mold) dimension measurement results have acceptable Cpk but the data dots are close to upper tolerance, the part (produced by other mass produced molds) dimension measurement result shall have the same behavior, and vice versa. The same behavior also called as equivalence.
  Equivalence is based on an Equivalence Acceptance Criterion (EAC). Generally, EAC is set as 20% of Upper Specification Limit (USL) minus 20 % of Lower Specification Limit (LSL) which is 20% (USL-LSL). Within this tolerance, the performance of molds could be claimed as equivalence.

From my previous experience.
Practically, by performing the trial shot with same parameter and mold combination as below:

• Mold A fixed side with Mold B moving side or
• Mold B fixed side with Mold A moving side

If the dimension measurement results could meet statistic calculation acceptance criteria, these molds could be considered as equivalent.