How to Get Your Plastic Part Design Made Properly – as Told by an Injection Molder

Here are tips from molder CY Plastics on how to best leverage the skills and expertise of your molding partner to produce a well-engineered and manufacturable plastic component.

January 14, 2016

4 Min Read
How to Get Your Plastic Part Design Made Properly – as Told by an Injection Molder

When you need a plastic component engineered for your new product, it’s a great idea to take your concept to an experienced injection molding company. Using a design for manufacturing (DFM) strategy, engineers can help incorporate features into the part to make it more economical and reliably manufacturable. This will optimize part performance, meet your cost targets, and in many cases avoid changes or delays later on.

Creating a 3D CAD model of your part concept is a good starting point for the process. When laying out the preliminary part design, you can make changes as needed along the way. An injection molding specialist will use the CAD model for part weight calculations and to determine what size and style of mold would best fit the part’s requirements, with consideration for the materials chosen.

An injection molding press at CY Plastics.
(Source: CY Plastics)

By this point there will be enough information to calculate a budgetary mold cost and molded piece price. The 3D CAD design also can be used to create a 3D-printed proof-of-concept part for presentations and, sometimes, functional testing.

The engineering team at the molding specialist will continue the DFM strategy by reviewing options which will determine the next steps to produce a mold while meeting your specifications and cost targets. It is best to bring the entire product assembly design into the discussion, as this gives opportunities to solve problems while keeping the design intent with clear expectations.

Not all part concepts are good candidates for molding –- at first. For example, long and thin part features may be difficult to fill properly in the mold and also create issues when ejecting the part from the mold. It may be challenging to hold tolerances on multiple areas of a complex part, as shrinkage is not always linear during the cooling phase of the molding cycle. Experienced molding team members will identify potential problem areas and explore ways to adjust the part design.

Key personnel from the engineering, quality, manufacturing, and assembly departments will consider the material resin used to produce the part and its ability to meet the part’s intended function, drawing their experience with working on previous similar parts. It is especially important to review your design and material with process technicians, who have years of experience working with a wide variety of resins. The team will also rely on a network of resin suppliers for technical support and material selection.


Part aesthetics are important. Factors include color compatibility to the resin, the locations of parting lines (seams), and whether knit lines are acceptable and how they can minimized. Secondary operations, such as ultrasonic welding, assembly, painting, hot stamping, and pad printing, should be discussed. Having these secondary operations performed in the same facility where the parts are molded will save time and money, with the added value of the molder managing the supply chain.

Once you have settled on the final design and specifications, material, aesthetics, and other requirements, the injection molding specialist can finalize the price and lead time for the creation of the mold and production parts.

Working through this process, you will gain another valuable piece of information: how easy the molder is to work with. A supplier’s ability to understand your needs, provide guidance, and give realistic feedback will be as important as price and lead time in your project’s success.

John Cavagnaro is engineering manager at CY Plastics. He has more than 15 years of experience in mold making, engineering, and engineering management in the tooling and plastics industry, at companies including Syntec Optics and Mikron Plastics Technology.

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