Creating a Cost-Effective Part & Mold Design for Injection Molding

custom plastic injection mold designs

Having a good part design and injection mold design is critical to producing high-quality, high-precision, and repeatable injection molded parts. The plastic part design features along with the mold defines the final part’s tolerances, surface finish, and overall quality. They play an essential role in molding cycle times, production throughput, and the cost of the final product. 

A poor part or mold design can result in product inefficiencies, quality control issues, and wasted money. To create a cost-effective part and injection mold design, follow these five steps.

1. Follow Important Part Design Rules When Possible

When creating your plastic part design, remember that following a few basic design rules can save a lot of production costs and possibly thousands of dollars in mold build costs. With plastic injection molding, production cycle times are measured in seconds. The faster the production cycle time, the lower your part costs will be. In addition, optimizing features like draft angles and rounded vs sharp corner features can lower mold costs significantly. Here are a few part design topics to review before sending your part design out for production and tooling quotes:

  • Maintaining a consistent wall thickness throughout the part design will help prevent warpage and distortions to the part as it cools
  • Using nominal wall thicknesses that make sense for the proper function of the part can help minimize cycle times and save on plastic costs
  • Applying the proper tooling draft angles to part surfaces and parting line shut-offs will avoid mold wear and potential future part quality concerns
  • Avoiding sharp corners on part features that can become rounded, and sometimes rounding part features that are designed sharp will significantly reduce mold costs

Consulting with MSI Mold for advanced target cost planning will create realistic budgeting for mold and part pricing.

2. Select the Right Plastic Materials

Next, you’ll want to ensure you’re choosing the right plastic materials for your part design. Selecting injection molding materials comes down to understanding how each plastic resin performs. 

Choosing the proper target plastic material for the part is absolutely essential for the part to function properly and ensure costs are targeted properly.

For example, polypropylene is a low-cost plastic with good fatigue and chemical resistance, while Acrylonitrile butadiene styrene (ABS) can provide a nice surface finish, and has good impact resistance and toughness. Additionally, polycarbonate resins produce very tough, transparent, and durable parts with excellent optical qualities and weatherability. 

Ultimately, you must understand a plastic resin’s molding characteristics and mechanical properties in terms of its tensile strength, operating temperature range, rigidity, toughness, and weatherability. All these properties must be considered during plastic part and mold design, as these properties essentially determine the final part’s fit, form, function, and final cost.

Lastly, plastic injection molding companies that do custom injection molding already have a wide library of plastic materials that they keep in-stock inventory. After you decide on the proper family of plastic material for your product, discuss which specific grades your injection molding supplier already purchases. By allowing them to use a stock grade of plastic you will save on costs. 

3. Only Design for Secondary Processes If Necessary

Plastic part designers should always strive for the most robust functional design. For appearance parts it’s common to design text, images, or other features into plastic parts. However, adding secondary processes like painting, labeling, assembly, and inserts drive up the per-unit cost of your plastic parts a lot. The setup and run times for these secondary processes can also quickly add up.

This doesn’t mean you can’t mold complex parts with unique features to stand apart from the crowd. However, it’s often best to consult with your target injection molding supplier on these different processes for your design. This may help save a lot of time upfront with your plastic part and mold design, and you’ll reduce your costs overall by minimizing the number of additional processes.

4. Production Quantities and Mold Design for Injection Molding

In plastic injection molding, the higher your production quantities, the lower your overall run costs are. For example, if you will require 10,000 parts per year It’s best to order and take delivery of all 10,000 units at one time as opposed to splitting them up. Molding as many parts as possible in a single high-volume production run will reduce your setup costs and allow your injection molding supplier to purchase raw materials in larger quantities at a lower price than small lot purchases.

Single-cavity molds are excellent for low quantity production plastic parts. However, dual-cavity or multiple-cavity molds allow your manufacturer to produce higher quantities of plastic parts in a single production run. Using multiple mold cavities means that every cycle of the injection molding machine will produce a multiple of parts that matches the number of mold cavities. Keep in mind that there is an inverse relationship between your mold costs and your production part costs. Please reference the graphic below:

Plastic Injection Mold Cost Relationship to Mold Cavities
Plastic Part Cost Relationship to Mold Cavities

5. Work With a USA Injection Molding Company

Lastly, consulting with an experienced injection molding company in the USA can help you reduce design costs and improve final product quality. Your chosen partner should have the requisite skill set, experience, and capabilities to help you during your R&D and design phase. A high-quality plastic injection molding company will also be with you every step of the way, from evaluating your part design, helping you with plastic material selection, and providing advanced target cost planning for your production runs.

When selecting a plastic molding company, do your research. Look at their online reviews and referrals, ask them to show you similar projects they’ve completed, and be sure you understand their current capabilities and how they can support your project.

Other Cost and Quality Factors in Injection Molding 

In addition to the injection molded part design, there are a few additional costs associated with injection molding that buyers should be aware of. 

  • Plastic Molding Equipment Costs: a plastic injection molding company invests hundreds of thousands of dollars into machinery and equipment for producing custom molded parts. There is a wide range of equipment quality and capabilities across thousands of suppliers. As discussed above, the quality of your production parts depends on a lot of factors. The quality of your supplier’s machinery is one of the least investigated by buyers of injection molded parts. As a rule, low-quality companies have old slow machinery which lacks precision in production, and high-quality suppliers have modern, fast and clean manufacturing equipment. Modern equipment costs a lot more, but choosing an injection molding supplier with modern machinery can prevent a lot of quality or reliability issues with your orders.
  • Mold & CNC Machinery Costs: The more complex your injection molded part’s design, the higher your mold costs. Keep in mind that there’s a cost for designing the mold, manufacturing, and machining the mold. And like the costs mentioned above for the plastic molding machinery, the CNC machinery that is used to manufacture the molds also costs hundreds of thousands of dollars. High-quality injection mold makers use high-speed machining centers that can machine customer molds with very close tolerances and provide mirror-like surface finishes when needed.
  • Plastic Material Costs: Different injection molding materials have a very wide range of prices. The primary function of your product and the physical environment it will need to perform within will define the type of resin to use. When you are ready to find an injection molding supplier make sure you clearly outline these items to ensure the proper plastic material is targeted for production.
  • Labor Costs: The more processing steps that your part’s design will require, the higher the labor costs will be to produce your product. Again, if you’ve opted for additional processing after molding, ensure you discuss these extra steps with your plastic injection molding supplier. They will help you understand the cost associated with those processes and to save on costs many buyers choose to perform the post-molding operations on their own.

Ask About your Plastic Part Design and Production with MSI Mold

MSI Mold is a full-service, U.S.A. plastic injection molding company. We’re also proud to be a lean manufacturing facility. As a customer-centered manufacturer, we take a no-hoopla approach to our process. From plastic material selection to in-house mold design & builds to plastic injection molding and assembly, our only goal is to help you get exactly what you need during every stage of your injection molding needs. If you have general questions about plastic parts or injection mold design or want to learn more about our capabilities, fill out our online form today to request a free consultation.