Injection Mold Tooling

The injection mold itself is often referred to as tooling; both are acceptable terms for the mold. More broadly, tooling also includes other mold components such as jigs, gauges, and fixtures. Components inside of the mold include slides, guides, lifters, pins, bushings, ejectors, and alignment 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.

Steel and aluminum are the most common metals used to make injection molding tooling. Because of its toughness and heat resistance, steel tooling is preferred for full-scale, high-volume production. Steel tooling is also easier to maintain, will not oxidize, and usually provides an excellent finish.

Aluminum mold tooling, because it is softer and less resistant to abrasion, typically make 20,000-100,000 parts. Unlike steel, aluminum mold tooling is not compatible with electrical discharge machining and must be made with conventional methods like CNC machining, adding cost. 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.

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 of the plastic part
• Ejector system—pins on the core half of the tool help release the finished part after molding is complete
• 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 mainly used for high-volume production. It is made from durable and long-lasting metals, such as steel or nickel alloys, that can be used for multiple production cycles, allowing manufacturers to quickly produce high volumes of parts. This tooling type is ideal for making durable high-precision parts. 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 is typically used for prototyping or small production runs. The material selected depends on several factors, including budget and volume requirements. Soft tooling permits manufacturers to quickly produce relatively low volumes of parts—about 100,000 shots—before the mold needs 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, flexibility, and affordability, as well as prototyping and making short-volume runs. Although soft tooling molds wear out rapidly, their low price means multiple soft tooling molds can be made at a lower cost than a single hard tooling mold. Hard tooling, even though it is more expensive, is the better choice for high-volume runs and, because it is so durable, has a long lifespan, which ultimately reduces cost per part.

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
• Any special tooling required, such as threading, slides, and lifters
• 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

Engineers can use flow analyses to optimize the mold, especially finding the best locations for parting lines, gates, and ejection locations. Prototype tools created through 3D printing, machining, or other methods are used by molders to troubleshoot the tooling design to create the best-possible injection molding solution for the project, maximizing quality while streamlining production and reducing costs.

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.

Most 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. Standard resins range in price from $2 to $20 per pound. For special highly engineered resins the cost per pound could exceed $3k per pound. Some of the plastic characteristics that can impact cost include impact resistance, gloss, heat resistance, UV resistance, and food-grade.

Finally, it is important to weigh the cost of the mold against the number of parts being produced. Higher production numbers will lower the final per-piece cost of each part as the total injection mold cost can be spread out over hundreds or thousands of parts. While the up-front cost for injection molding can be significant, it is still the fastest, most economical way to produce large quantities of plastic parts.