East West Manufacturing Blog

DFM Rules of Thumb for Accurate Plastic Injected Parts

Written by Patty Rasmussen | December 05, 2017

Accuracy demands attention and making accurate parts, consistently, requires close attention to design for manufacturablility (DFM). The goal of the DFM process is to reduce manufacturing costs without reducing performance, and that means every detail of your product or part is on the table. Yes, we harp a lot on DFM, but it’s a critical part of the manufacturing process. We engage in DFM well before tools are cut or samples are produced. It's no wonder 80 percent of product development cost is invested in the design stage. It’s that important.


There are five key factors examined during the DFM process:

1 | Design

Your design itself must follow good manufacturing principles to achieve the form, fit or function of the product or part. 

2 | Process

The manufacturing process will be reviewed to ensure it’s appropriate for that type of design. REMEMBER: The more complex the process the more variables for error. All processes have limitations and capabilities. Only include those operations that are essential to the function of the design.

3 | Material selection

The material chosen will be determined by the performance criteria of the part. For example, does it need to be hard or soft? Does it need to conduct electricity or be waterproof? The right material will allow your product to achieve the aesthetic and functional performance you’re looking for. 

4 | Environmental considerations

Every component in the part or product must be able to withstand the environmental conditions it will be subjected to.
The product needs to be able to perform under every possible condition whether extreme heat or cold; power surges; extreme moisture or dry condition; pressure.

>>>> Click here to learn more about How to Design Electronics for Harsh Conditions <<<<

5 | Compliance + Testing

Products must comply with standards related to safety or quality requirements.
Your product might need third-party quality testing. Make sure the contract manufacturer doing your product’s DFM has ISO-certified testing facilities. It’s helpful if they can also provide UL, ETL and other third-party testing on site.

When designing plastic injection molded parts or products, keep these DFM rules of thumb in mind:

  • Try to minimize the number of parts in your product. It’s a quick and easy way to lower the cost since you’ll lower the amount of material necessary to make the product. It also lowers the amount of engineering, production, labor — even shipping costs.
  • Customizing is expensive and time consuming. Look to use standardized parts wherever possible. Not only can you save time and money, but standardized parts are tried and true. No wondering whether it will meet the quality metrics.
  • Can you use non-customized modules/modular assembles in your product? Doing so will allow you to make changes to the product without losing functionality.
  • Where possible, design your product to join without using screws, fasteners or adhesives. Can the parts interlock or clip together? If you have to use fasteners remember to keep the size, number and variation to a minimum; use standard fasteners wherever possible design your product to join efficiently using interlocking pieces or clips. The goal is to design the part so that a minimum of manual interaction is required during production and assembly.
  • Choose function over flashy. For example, what’s an acceptable surface finish? You’ll save money if you go with a less polished finish, as long as it doesn’t compromise functionality.

If you're going to invest your hard-earned capital to develop a product, make sure made affordably and consistently to your quality standards. The way to ensure that's the case is to take the time to execute the best DFM possible.