Nine factors that impact the cost of your plastic injection mold

Recognizing the key cost drivers in mold manufacturing

A well-designed and well-constructed mold is one of the most important factors in producing consistent and quality injection molded plastic (IM plastic) parts. Your tooling cost, what you spend to produce your plastic injection mold, is also likely the biggest cost driver for your project.  So, how do you create a mold that can properly support your plastic part’s intended use and production volume but doesn’t also price you out of the market? Knowing the factors that affect mold cost upfront will ensure your project is set up for success. 

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Plastic injection mold design

As with most manufacturing projects, design is a critical driver of your production costs. This applies not only to the design of your part but also to the plastic injection mold itself. Of course, some complexity may be required to achieve the desired part; however, having a critical eye to avoid unnecessary complexity is a sure way to avoid unnecessary costs. 

Part complexity. A more complex part requires a more complex mold, which takes longer to produce and requires additional and/or more precise machining. Design decisions related to your injection molded plastic part—the finish, for example—will affect how your mold is produced. A very smooth part will likely require a harder and more costly metal for your mold. Some specialty finishes may not be machinable, creating the need for costly hand-finishing. The need for close tolerances and the presence of design features such as holes, threading, and undercuts (which make it difficult to eject your part from the mold) are additional factors that add complexity to your part and will increase your tooling cost. 

Mold complexity. Complexities related to the plastic injection mold itself, especially the size and number of cavities, can make it more difficult and costly to produce. The more cavities, the more machining will be needed to form the mold. The addition of lifters and sliders to accommodate undercuts or complex features will also add to your mold’s complexity and cost. What’s more, increasing the number of cavities increases the chance for inconsistencies in quality and finish of your final parts. This article from the Mold Making Technology Magazine provides some ideas on how to avoid filling imbalances and temperature variations within a multi-cavity mold.

Size of the part. A larger part requires a larger mold, which in turn requires a larger mold base. This requires more materials, more machining, more time, and—you guessed it—more money. Gas assist can help prevent short-shot and give the right plastic pressure to ribs, bosses, and gussets. Additionally, the larger the part, the fewer pieces can be produced with each mold. This increases the number of production cycles to make the same number of units.

As an aside, larger injection molded plastic parts are also more susceptible to quality variations and should be tested thoroughly prior to moving into full production. 

injection molded plastic parts

Production needs

While plastic injection molding is most well-known for high-volume production, it can support many different output levels and circumstances. Your project’s specific production needs can greatly affect your tooling costs and should be considered thoroughly and early on in the process.  

Mold material and lifespan. The type of metal that is appropriate for your mold will vary based on your anticipated production volume and how long you plan to use the mold. As an example, the longevity and strength requirements for your plastic injection mold will vary greatly if you’re producing a one-time batch of 5,000 pieces vs. ongoing production in the millions of units. The resin you select for your part can also affect your mold material choice: a more abrasive resin may degrade softer metals, necessitating a mold made from abrasion-resistant steel.  

The Plastics Industry Association (formerly known as the Society of Plastics Industry, or SPI) has issued standards to help manufacturers determine what type of mold material is appropriate for various uses. 

There are five standard classes, from 101 to 105, which take into account varying measures of hardness, different construction approaches, the type of material typically processed, and the number of cycles expected. Differences due to design requirements and mold circumstances may impact the estimated cycle times.  

Volume and speed considerations. Especially in high-volume applications, the ability to turn out a high number of parts per cycle is paramount. While maximizing the efficiency of your mold will save money in production costs in the long-run, we’ve already established that a mold with multiple cavities costs more to construct and runs a higher risk of quality issues. To avoid potentially costly issues down the road, it’s critical to weigh any efficiency gains against increased tooling costs and testing requirements. 

Choosing a mold manufacturing partner 

As it relates to selecting who will construct your mold, there are several factors to keep in mind to ensure you’re working with someone who can get it right the first time.  

Experience. It likely won’t surprise you that experience can be a key cost driver in producing your plastic injection mold. An experienced toolmaker understands what’s important in terms of cost and quality, is familiar with the materials and machinery that will be used, has the know-how to avoid common mistakes, and can generally save you time and money during tooling. A partner who has worked on similar projects may even be able to minimize customization to your mold by finding a similar design in their catalog of past work. 

Technology. Not all manufacturers are created equally when it comes to technology. Working with a partner that employs Computer-Aided Design (CAD) and Computer-Aided Engineering (CAE)—or, even better, one that has integrated CAD and CAE systems—allows you to really test your mold design before even starting fabrication. This enables you to identify and correct potential issues ahead of time, avoiding costly corrections once your mold has already been produced. 

Equipment. Based on the specifications identified for your mold, you’ll need to ensure your chosen tool shop has the right type of equipment to support your needs. In a best-case scenario, your manufacturer will have the needed tooling equipment in-house, simplifying the process and saving time and money transporting your mold to the factory prior to first article creation (and, hopefully, not back to the tool shop thereafter). According to Plastics News, as of 2020 only about 5-10% of processors had the capability to build their own molds, so working with someone who knows the market and various vendors’ capabilities can help you find the right manufacturer for the job. 

Location, location, location. It’s not just true for real estate—location can also impact your tooling cost. At Nelson Miller Group, we have a 46,000-square-foot injection molding facility located in New Jersey, as well as relationships with several providers internationally, allowing us to advise you regarding the most ideal location to produce your mold and manufacture your plastic parts—not only from a cost perspective, but to ensure your finished product meets or exceeds quality expectations. 

cups showing range of color pellets for injection molding plastic
injection molding machine

NMG’s injection molding experience makes mold creation a breeze.

With so many factors to keep in mind, working with a reliable and experienced team will create a smoother project and lower your tooling costs. NMG can help you ask the right questions, scope your project thoroughly from the start, and produce the most cost-effective mold for your project. Once tooling is successfully complete and the output has been thoroughly tested, you can enjoy the low-cost production that has made injection molding such a universally popular production method. 

Want to learn more? Find additional information about our injection molded plastics capabilities, certifications, and equipment on our website. 

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About NMG 

NMG has more than 85 years of experience partnering with organizations to bring their industrial, IoT, lighting, medical, telecommunications, consumer, and aerospace products to life. We solve your most complex challenges in engineering design, manufacturing, and supply chain management.  

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