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11 Tips to Keep Your Molding Project from Failing

Source: MDDI

Lindsay Mann, Mandy Beaumont, and Lynzie Nebel

Selecting a manufacturer to build your tool, validate the molding process, and be your partner through full-scale production is an important decision for the success of your program.  An experienced molding house will have a proven, standardized process and will work with your team throughout the process to ensure your expectations and requirements are met.

One thing is for certain: Projects never go as planned. But there are some things your team should know and be prepared for to help a project run more smoothly and minimize the risk of problems and failure. The majority of botched molding projects are caused by miscommunication up front. From part design to process validation, here are 11 tips to know to keep your molding project from failing.


While realizing less than a 20% IV loss can be difficult, MTD developed a bioresorbable fastener with an IV loss of less than 4%. Shown on the left is MTD's version; at right is a competitor's attempt.

Image courtesy of MTD MICRO MOLDING

Understand the Plan
If you are unsure why you are doing a step in the development process, ask. Your molder should have the tools and knowledge to explain the process thoroughly. As Albert Einstein said, “If you cannot explain something simply, you do not understand it well enough.”

Know What Your Part Requires
Be prepared to evaluate other options for materials based on the mechanical properties you require for your component. Know what you need from your part performance, and let your molder guide you on material selection. There might be a less expensive material option that meets your part’s needs. Also, consider incorporating a range of material lots into your validation plan to account for any lot variation.

Avoid Overly Restrictive Designs
A well-designed mold is the product of a comprehensive understanding of injection molding, the tooling required to enable it, and a part design marrying the two. Obey the proper rules and guidelines of part design, including avoiding varying wall sizes, optimizing gate locations, and ensuring proper cooling. Sometimes the challenge of an unorthodox design opens new opportunities.

Run a Moldflow simulation
A simulation can help you identify critical mold design elements, such as gate location(s), how large of a press may be needed, and how the part will warp. Doing this proactively can save you molding and tooling costs down the line. It may even prevent you from having to rebuild a mold later on. With existing molds, the majority of problems can prevented if proper upfront engineering is applied. When used correctly, Moldflow will almost always save time and money in the long run.

Build in Dimensional Flexibility
If your part design is frozen prior to validation completion, it can make the road to production more difficult to navigate. It’s important to know what aspects of the part are the most critical and, just as important, the least critical. Divulge this information early and collaborate with your molder to understand dimensional and tolerance feasibility. If you are prepared to be flexible on certain aspects of your drawing, entertain that route before changing steel or measurement systems, especially if that aspect is deemed a nonissue because the parts are acceptable and functioning properly.

Flash Happens
In your mold design review, your molder should identify potential flash areas. Unfortunately, “no-flash” tolerances are a myth. Suppliers can highlight areas that could be prone to flashing and help you create realistic tolerances for flash that will not jeopardize your part’s designed function.

Part Drawings Drive Cost
Be aware of your drawing and how it can drive the cost of your validation. Ways to control or minimize your project cost include reducing the number of total drawing dimensions, reducing the total number of critical dimensions, and considering less expensive material options. Focus on what is critical to function and make sure your print reflects that.

Use Your Drawing as a Blueprint
Discuss what is important to your part’s function in the mold design review with your supplier. Leave no stone unturned. Your part drawing is the main point of communication between you and your supplier. Ensure any critical requirements, dimensional and visual, are clearly specified. Inspectors use your drawing as a blueprint for success. A shift inspector rejects parts based on drawing requirements; if there is no drawing criteria specified for flash, for example, then it cannot be documented as a violation to the drawing, thus resulting in passing parts.

Share Your Functional Test Requirement
Ensure functional testing requirements are part of your specification. Know what you need and quantify or let your supplier help you quantify it with controlled experiments. A good test is one that closely mimics the actual application.

Insert Molding is Only as Strong as Your Weakest Insert
Make sure the insert supplier validates its process. Defects in inserts may result in increased molding costs due to high fall out and probable 100% inspection requirement.

Keep It Under One Roof
Usually the smallest component in a medical device is the most critical. When your product carries a lengthy list of requirements and specifications, the job at hand becomes easier to manage if you can keep the major manufacturing operations under one roof. Having tooling, prototyping, and inclusive manufacturing done in the same facility produces your device with better quality and greater efficiency.

Lindsay Mann is director of marketing at MTD Micro Molding. Reach her at This email address is being protected from spambots. You need JavaScript enabled to view it..

Mandy Beaumont handles marketing and corporate communications at Beaumont Technologies. Reach her at This email address is being protected from spambots. You need JavaScript enabled to view it..

Lynzie Nebel is a project engineer at MTD Micro Molding.

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