• Posted in: Blog
  • By ProMed Staff

Plastic injection molding is an effective and popular method of producing large quantities of identical components with high precision. This process entails melting thermoplastic flakes or pellets before injecting them into a mold. After the mixture cools or hardens, ejector pins push the finished part out.

Injection-molded parts can have intricate structures, and making design changes after manufacturing the product is difficult. As such, it is critical to carefully craft and lay out the plastic component to reduce the likelihood of tool issues, achieve the desired results, and save injection molding costs.

Here are ten design tips for plastic injection molding:

1. Choose the Most Appropriate Surface Finish for the Design

Making the right decision regarding the surface finish is vital to ensure a proper molding design. Aside from its aesthetic value, it improves grip, increases paint adhesion, and allows gases to escape the mold during the process. However, the surface finish you select is related to the molding type required based on production volume and the material type from which you will make it. For instance, steels are more durable and have more surface finish options than aluminum ones. You can also polish them for a smoother finish.

2. Uniformly Design the Parts

Any thickness limitations or changes in the components can disrupt the injection molding flow, potentially leading to other negative consequences. Therefore, keeping the thickness constant between 2 mm. and 3 mm. is recommended because layer thicknesses less than 1 mm. or greater than 4 mm. might lead to manufacturing issues.

3. Add Drafting to the Parts

Adding a draft angle allows the parts to be ejected from the injection mold. The angles should be at least 1° on an untextured surface and 3° on a textured one to properly let the components loose without prying. For applications that require a tight mating area, position the zero-draft area as close to the mating portion as possible rather than a complete surface.

4. Add a Radius Wherever Possible

Sharp corners on any injection molded part are challenging to form because they trap air. The most secure solution to this problem is to design them out. A radius also extends to a draft angle, aiding in smooth transitions and ensuring you can remove the part from the mold.

5. Always Design Resin Flow From Thick to Thin Sections

Thicker sections are needed for structure and strength. Because molten resin loses pressure and temperature as it continues to flow through the mold, it must first cover the thicker sections before moving on to the thinner areas.

6. Determine Which Molding Defects Are Acceptable

Injection molding defects are to be expected during the process. For example, sinks caused by bosses designed into the backside may occur on thicker sections, whereas adding structure to the part by strengthening the ribs may increase the possibility of visual defects. While advanced molding conditions can reduce some of these defects, they cannot eliminate them. As a workaround, determine which defects are acceptable and which are not, and then design around them.

7. Reduce Strengthening Rib Sizes As Much As Possible

Rib strengthening plays an essential role, but having too large of a feature can cause complications. Therefore, each rib must meet three primary design criteria: base thickness, rib height, and overall thickness.

First, the rib base must be structured at 60% or less of the wall thickness to reduce a sink mark on the surface. Second, the rib height should be as low as possible (at least less than three times the part thickness) to avoid getting stuck in the mold. Lastly, the overall thickness should be less than the rib base, which is connected to the designed draft angle.

8. Avoid Tooling Undercuts

An undercut in an injection molding tool occurs when the device’s opening and closing prevent the formation of a feature. A lifter and slide are recommended to form the component rather than complicated shapes. Therefore, it is best to maintain simplicity because they can create complex structures while still allowing the part to be removed.

9. Design for Manufacturing and Error Proofing

Most injection molded products are intended to be part of more extensive manufacturing. Use coordinates or datums when designing to ensure that each one is assembled the same way every time. Moreover, remember that huge businesses require manufacturing-ready designs, and minimizing error potential should be a part of every configuration.

10. Use Rapid Prototyping To Immediately Detect Problems

Rapid prototyping can help improve your design, manufacturing, and secondary processes. It can also detect early design flaws in a model that you might overlook. You can choose one from many rapid prototyping options, including metal 3D printing, digital light processing, CNC machining, binder jetting, rapid injection molding, and laminated object manufacturing.

ProMed for Your Injection Molding Needs

ProMed uses cutting-edge technology, relies on a highly experienced technical team, and uses a creative system to give our customers dependable, high-quality, and cost-effective service options for their production needs! We also specialize in small, finely crafted silicone and plastic components that can be implanted for short or long periods, with or without drug-releasing agents.

Contact us today to learn more about ProMed’s molding solutions and services! You can also request a quote now.