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Reducing mold qualification time

Lead-time reduction remains a critical factor in the development of new injection molded products. While there are many areas that can be addressed to reduce the time it takes to validate the mold and parts, the time from initial mold sampling until the parts are production-approved is one of the biggest windows of opportunity for improvement. Based on experience, about one-third of the total amount of time used for designing, building and qualifying a new injection mold is consumed in the qualification/validation cycle.

John Linder

June 10, 2013

3 Min Read
Reducing mold qualification time

Lead-time reduction remains a critical factor in the development of new injection molded products. While there are many areas that can be addressed to reduce the time it takes to validate the mold and parts, the time from initial mold sampling until the parts are production-approved is one of the biggest windows of opportunity for improvement. Based on experience, about one-third of the total amount of time used for designing, building and qualifying a new injection mold is consumed in the qualification/validation cycle. That means that a mold with an eight-week lead time to produce might take another four to five weeks to get ready for production. Most suppliers don’t allow for enough time for mold qualification and process validation, and the team becomes frustrated by the delays.

Normally a new mold is sampled the first time and parts are inspected and compared to the product drawing. This may be accompanied by a capability study examining the critical part features to ensure the potential does not exist to produce a part outside of the print tolerance zone. Once this process is competed, a “punch list” is created outlining all the out-of-spec dimensions that require steel adjustments in order to mold a good part. The next steps of adjusting the mold, re-sampling and inspecting, can take weeks to complete and in some cases will need to be done a second time.

What may well lie at the root of this issue is a poorly engineered mold design. A large number of molds are built each year that have had no or minimal computer simulation analysis performed prior to beginning the mold design phase. Those who run an analysis at the beginning of the process many times stop short of using all the available data.

With today’s latest mold simulation software it is possible to develop a solid part model that includes windage which can produce (mold) a part that very closely mirrors the design intent – a 3D part model. Developing such a part model without the help of the mold simulation software would be very time consuming and difficult to produce accurately.

By taking the part model that is developed as part of a shrinkage and warpage simulation it is possible to reverse that model which then provides the new moldable part model with windage. When this newly created part model is analyzed and the resulting shrinkage/warpage is compared to the original design intent part model it will in many cases very accurately reflect the product master.

Everyone seems to want an iron-clad guarantee that this process works. Mold simulations are only as good as the material data base and knowledge of the actual molding parameters and machine limitations. An accurate shrinkage/warpage can produce a very accurate baseline which will allow the user to design, manufacture and develop an injection mold that produces a part much closer to the product specification without excessive steel modifications. It is possible to qualify a new mold without the need for any steel changes. This can eliminate weeks of delays and reduce cost and frustration for everyone involved in the supply chain.

John Linder is a partner in Inject Engineering LLC, a Rockford, IL-based mold engineering company that uses scientific principles and software to design molds for optimum molding processing and part quality. John can be contacted at 815-997-4545 or by e-mail at [email protected].

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