Nine factors that impact the cost of your plastic injection mold

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.