Building an injection tool is a complex undertaking. Every mold is custom machined in terms of core placement, cavities, cooling lines and ejectors. Knowing the variables that influence injection tool costs enable you to manage the cost of your tool, thereby making the most efficient use of your project budget.
Tool Material
Aluminum and steel are the most standard mold materials. Generally speaking, both are readily available. Aluminum, which has better thermal heat transfer, is typically used for shorter production runs because it lacks the resiliency and durability of hardened tool steel.
Tool steel is the gold standard for injection molds because of its resiliency and suitability for a broad range of different materials. Tool steel is typically used when building high-volume, tight-tolerance molds. Although it’s more expensive, steel lasts longer than aluminum and therefore can produce more parts over its lifetime.
Various steels are available for making an injection tool, and the specific type required for your project depends on the type of material being molded. For example, some high-temperature thermoplastics may require steel with higher hardness.
Steel provides long-term value, as it is able to withstand the pressures of a long production run while still meeting tight tolerances. In fact, some of the stainless-steel molds used by our customers have been in production for decades.
Number of Cavities
Building an injection mold is a manufacturing process itself. An injection mold with fewer cavities requires less tooling work and less time to build, making it less costly. Having said that, it’s important to consider potential advantages of building a family mold with multiple cavities for different parts. Family molds may produce inferior parts and tend to have more downtime due to maintenance issues, but in some situations that risk may be tolerable.
The number of tool cavities also influences production costs. More cavities mean longer press time, and longer press time increases costs. This underscores the importance of understanding the tradeoffs between a single part mold and a family mold before finalizing your tool’s design.
The Mold Base
A mold base is essentially the cabinet which holds all mold components together. Mold bases come in standard sizes. The cost of mold base is determined by the size of the mold itself and the type of steel used.
Keep in mind that your mold base may require additional machining by your toolmaker to meet specific requirements of your project.
Tool Complexity
Just as the number of cavities plays a role in determining cost, so does part complexity.
Complex parts require complex molds. And complex molds require more tooling than a simple mold, which makes them more expensive. For example, machining a mold for a complex part might require secondary EDM procedures for undercut features. This additional production time by the toolmaker increases the cost of making your mold.
Part complexity involves the surface finish, the number of undercuts, and tolerance requirements. As you would expect, parts with tight tolerances require additional steps in the tool-making process. With that said, our customers tell us the value gained from tight tolerances is worth the incremental cost.
Sampling Your Parts
Avoiding unnecessary engineering changes during the tool-making process saves everyone time and money. We think it makes sense to select a mold builder with on-site sampling presses that can simulate your production environment. Sampling your parts is vital in assessing multiple parameters such as tolerance, temperature, flow rate, resin, etc.
Remember, time is money. On-site sampling eliminates time spent shipping the injection tool between the mold builder and injection molder.
In Summary
The largest upfront cost of a project is often the injection tool itself. That’s why it’s smart to consider the various factors that influence the cost of building a mold. Optimal material choice, smart design and selecting a toolmaker capable of achieving tight tolerances will ensure the highest quality parts.