Injection Mold Tooling

Injection molding is a process in which molten plastic resin is injected into an injection mold under high pressure and allowed to cool and solidify, becoming a high-precision finished part that is then ejected from the mold. The process is repeated until the desired number of parts has been made (some molds are multi-cavity and can run multiple parts at the same time). Injection molding is a well-established, cost-effective process for manufacturing both short and high-volume runs of complex plastic parts.

Part 1: What is injection mold tooling?

Many people refer to the injection mold itself as tooling; both are acceptable terms for the mold. More broadly, tooling also includes other mold components such as jigs, gauges, and fixtures. Inside the mold are other components that are critical to the injection molding process, such as bushings, ejectors, pins, slides, lifters, guides, and other positioning devices.

All of these tooling components have key roles to play in the injection molding process and can be customized to the details of the project, depending on the quality and complexity of the part and budget cost. Although high-quality injection molding tooling is expensive, it can produce millions of parts, each one with the same quality and precision.

Aluminum and steel are most common materials for making injection molding tooling. Because of its toughness and heat resistance, steel tooling is preferred for high-volume production. Steel tooling will not oxidize and usually provides an excellent finish.

Aluminum mold tooling, because it is softer and less resistant to abrasion, typically turns out between 20,000 and100,000 parts (low-volume production). Unlike steel, aluminum mold tooling is not compatible with electrical discharge machining (EDM) and therefore is produced using conventional methods like CNC machining, which is a more expensive process.

Aluminum mold tooling wears out quickly and must be replaced often. Yet, because it is less expensive than steel, and does not take nearly as much time to make compared to steel, aluminum mold tooling can be the ideal choice for limited, small-volume runs.

Part 2: The essential components of injection molding tooling.

Essential parts of injection mold tooling are:

  • Injection mold—the injection mold has two halves—the cavity half and the core half. The cavity half is typically attached to the side of the molding machine and the core half opens and closes against the cavity half. The core half opens when it is time to remove the part from the mold.
  • Molding press—this machine injects the molten plastic into the mold and controls the temperature and pressure during the process. Delivery equipment helps to dry the plastic resin pellet and deliver it into the molding press.
  • Cooling lines—these channels help control the cooling process for the plastic part
  • Ejector system—pins on the core half of the tool are activated to help release the finished part once it has solidified
  • Runner—the runner is the flow path the plastic resin will follow when it is injected into the mold.
  • Side actions—these moving pieces within the cavity allow for undercuts in the part

Injection mold tooling can be soft or hard.

Hard tooling is typically required for high-volume production. Because it is made from tough, long-lasting metals, such as steel or nickel alloys, hard tooling can withstand multiple production cycles—allowing manufacturers to produce high volumes of durable, high-precision parts at lower cost. Key considerations are:

  • Tool life can be last over several million shots  
  • Molds can have multiple cavities, which increases production efficiency
  • Hard tooling is more temperature-resistant than soft tooling molds
  • Compared to soft tooling, it takes longer to create hard molds because of the hardening process

Soft tooling does not need to be as durable as hard tooling and is typically preferred for prototyping or small production runs. The material selected depends on several factors, including budget and volume requirements. Soft tooling is effective for quickly producing low volumes of parts—up to about 100,000 shots—before needing to be replaced. Other considerations are:

  • Lead time is much shorter for soft tooling compared to hard tooling
  • More material options are available, giving manufacturers another way to control costs without impacting performance
  • Soft tooling is often used to create complex mold patterns that would be too time-consuming or expensive to make with hard tooling
  • Faster for prototyping, thanks to its quick turnaround time

In summary, soft tooling is usually the best option for speed and affordability when prototyping or making short-volume runs. Although soft tooling molds do not last as long as hard tooling, their lower price compared to the higher cost of hard tooling makes them highly cost-competitive. Hard tooling, even though it is more expensive, is the better choice for high-volume runs and, because it is so durable and has a long lifespan, ultimately reduces cost per part.

Part 3: Injection molding tool design considerations.

Molds are designed around customer requirements, which include annual production volumes, part finish, critical dimensions, and other features. The mold design process is usually a collaborative effort between the SPG and client engineering teams. Usually the first step in determining tool design and selecting materials for the mold is deciding what are the critical features/qualities that must be included in the design, such as:

  • Mechanical and chemical properties of the resin being injected
  • Special tooling that may be required, such as slides and threading
  • Component size, thickness, complexity, and tolerances
  • Cooling for gates and vents
  • Injection pressure required to fill the cavity
  • Prototype needs
  • Production volume requirements
  • Budget expectations

Flow studies are effective for optimizing the design of the mold, especially for determining ideal locations for gates, parting lines, and ejection locations. A variety of sophisticated prototype tools are available for troubleshooting the tooling design to create the best-possible injection molding solution for the project, maximizing quality while streamlining production and reducing costs.

Part 4: Injection molding tooling cost factors.

The final injection molding tooling solution is customized to meet the client’s project requirements, performance criteria, and budget.

Every mold is different and costs can vary depending on part complexity, required characteristics, and volume demands.

The majority of the cost for plastic injection molding is machining the injection mold. Factors that impact this cost are the size and complexity of the mold, followed by number of mechanical actions within the mold and the number of injection cavities.

Of course, material costs are also a factor, with plastic resins ranging from about $3 per pound to $20 per pound. Price varies according to the chemical or mechanical properties required, such as heat, impact, and UV resistance, as well as gloss and other surface qualities.

When determining an acceptable cost for the injection molding project, the cost of the mold must be weighed against the number of parts being produced, high volume versus low volume, and the number of runs expected. For example, high-volume runs will reduce the final per-piece cost of each part as the total injection mold cost can be spread out over hundreds or thousands of parts and multiple cycles.

Injection molding is a well-established, cost-effective way to manufacture both short runs and higher volumes of complex plastic parts. SPG’s expert injection molders collaborate with client engineers to customize the injection molding process and make critical design and molding decisions based on how the part functions, volume expectations, and longevity and toughness. Cost, too, is always a consideration. If costs are too high, there are ways to control or reduce costs without impacting performance—for example, trying different materials and additives, eliminating or re-designing non-essential features, or using other methods such as overmolding to create more options regarding aesthetics, touch, and finish.

Frequently Asked Questions

In our tool room, our teams of technical experts collaborate to find engineered tooling solutions for SPG clients. This includes disassembling, inspecting, repairing, and releasing the tools to production or the process validation team to ensure project success.

Yes, injection molding tooling can be customized to individual projects, providing high-precision parts with sub-micron tolerances. SPG engineers and designers work in close collaboration with the customer engineering teams to determine the most cost-effective, customized injection molding process that meets or exceeds all project requirements.

Injection molding is an incredibly reliable and repeatable process that can make millions of high-resolution parts with the right tooling, allowing us to manufacture to client specifications and deliver products on time. We also repair and maintain customer-owed molds, ensuring uninterrupted production by using preventative maintenance schedules.

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