Injection molding design

11 Tips for Designing for Injection Molding

11 Tips for Designing for Injection Molding

If you’re looking to get into injection molding, there are two things you need to know. First, it can be a great way to create your own product, but it does take some design skills that aren’t common among non-engineers. Second, there are plenty of resources out there to help you learn about designing for injection molding, so it doesn’t have to be difficult! With that in mind, here are five tips for designing for injection molding.

1. Understand the Manufacturing Process

Injection molding parts

Your design needs to be manufacturable, or you’ll end up paying someone else to fix it. Know exactly how your item will be manufactured and make sure your design meets all of their criteria before getting started. Having a strong understanding of your manufacturing process is critical to designing a functional product. If you aren’t familiar with injection molding, you can learn more about it by contacting an injection molding supplier near you.

2. Work with Materials That are Appropriate

When it comes to injection molding, there are two main types of plastic that are used: thermoplastics and thermosets. Thermoplastics can be remelted and reused repeatedly, but thermosets—once cured—cannot be softened again (but can be machined like metal). There is an increased amount of time required to machine a part from a thermoset compared to thermoplastic; therefore, it’s recommended that you design with that in mind. If you’re designing a plastic part for manufacturing via injection molding, here are some materials you might want to consider: PET resin (like Eastman TritanTM), nylon, or ABS resin (like Eastman ABSTM).

3. Keep Parts as Simple as Possible

black injection molding parts

When designing a part to be injection molded, it’s important to keep in mind that you’re working with a machine. A CNC machine will have its own rules and limitations, which means your part needs to fit within them. Whenever possible, try to design a single-cavity part or an assembly that can be made from two or more parts; otherwise, you may end up doing some rework on your mold.

4. Avoid Sharp Corners and Oversized Holes

The sharp corners of your part will act as stress risers, creating a weak point in your plastic part that is susceptible to cracking. Oversized holes and irregularly shaped features are difficult to remove from injection molds; they may not be removable at all. Both of these characteristics can cause major headaches with your supplier, increasing design changes and manufacturing costs.

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5. Think About Finishing Touches

Too often, people worry about their initial design and then don’t spend enough time thinking about how that item will be finished. They decide on a color or material but don’t think through how to apply it. For injection molding, finishing touches like paint or powder coating is extremely important because it can change an item’s appearance, add durability, and increase its value (and therefore your profits). Before you finalize your design, think about what kind of finishing touches are best suited to achieving your goals.

6. Material Choice

The key to choosing a material is knowing exactly what your product will be used for and how it will be used. Different plastics have different characteristics, some of which are perfect for certain uses. So, if you’re designing a cheap water bottle that will live most of its life in a grocery bag or backpack then ABS plastic is a great choice because it’s durable and won’t crack easily—but it does tend to feel less premium in terms of visual appeal. For something like an iPhone case or fashion accessory, where you want something that looks more high-end, take a look at high-impact polystyrene (HIPS) or PETG because they give off a more refined feel.


plastic that solidifies at a certain temperature and stays solid. The amount of time it takes to reach its solid state is called setting time or gel time, which is usually between 30 minutes and 6 hours. Plastics used in injection molding have a relatively long set time because they need to be completely cooled before they are removed from their molds. If they cool too quickly, you could end up with small cracks on your product. Therefore, thermoplastics with short set times (less than 10 minutes) aren’t ideal for injection molding.

8. hermoplastics

These plastic materials are characterized by their ease of molding. They can be molded at temperatures as low as 150 degrees F, or plastic pellets can be molded at 300 degrees F. Most resins do not require waxes to flow properly in injection molds, although some have additives that help them flow easier in injection molds. These plastics include: Polypropylene (PP), Acrylonitrile Butadiene Styrene (ABS), High Density Polyethylene (HDPE), Polystyrene (PS) and Thermoplastic Elastomers. Because of their versatility and ease of manufacturing, they are generally considered less expensive than thermosets when mass-produced.

9. Amorphous

A solid-state polymer is typically amorphous, which means it lacks a crystalline structure. If you have an amorphous material, it’s probably best to design a custom tool as other processing options may not work well with your material. Specifically, stereolithography (SLA) processes are not compatible with amorphous materials. What are some other things to consider when designing for injection molding? Keep reading!

10. Semi-Crystalline

Properties of amorphous materials fall between those of crystalline and polycrystalline materials. Amorphous materials can be processed in injection molding, including blow molding or casting. Blow molded amorphous materials are known as parisons, preforms, or semi-finished products. The demold time is fast enough that these components can immediately go into a subsequent process such as thermoforming, compression molding, extrusion or roto-molding. Polycarbonate and acrylic are examples of semi-crystalline thermoplastics that exhibit high strength and good abrasion resistance with short demold times suitable for injection molding.

11. Selecting A Parting Line

A parting line is a unique characteristic of injection molded parts. In general, there are two different types of parting lines – horizontal and vertical. Depending on your application, either one can be used; but each presents a different set of challenges to engineers. Horizontal parting lines are easy to design and produce, but they often require overmolding or additional material to create an enclosure. Vertical parting lines are harder to design and produce, but they leave space available inside your enclosure without any extra materials. Talk with your injection molding supplier before designing a part with a parting line so that you know how much room you’ll have once it’s been molded. You may want to factor those considerations into your design right from the start! And don’t forget about the draft!

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The world's best injection molding manufacturer:

  • Protolabs 

    Protobals was founded in 1999 by Larry Lukis, with headquarters and manufacturing facilities in Maple Plains, Minnesota, specializing in the rapid manufacture of custom injection molded parts.

  • Xometry

    Xometry was founded in 2013 by Altschuler and Laurence Zuriff. It is based in Derwood, Maryland.

  • Aria (China plastic injection molding manufacturer)

    Aria was founded in 2010 by Lance Lin and is headquartered in Dong Guan, China. 

    It is an online manufacturing platform offering a range of manufacturing services, including injection molding, Mold Making, sheet metal, CNC machining services.

  • 3DHubs (Buyout by Protolabs)

    3DHubs was founded by Bram de Zwart and Brian Garret in 2013 and is headquartered in Amsterdam, The Netherlands. Protolabs acquired it in January 2021. And renamed Hubs.