Soft vs. Hard Tooling for Injection Molding

There are two broad categories of injection molding tools: soft tooling and hard tooling. Selecting the appropriate material depends on a variety of factors, such as budget limitations, volume requirements, and material selection. Soft tooling is used for prototyping or small production runs while hard tooling is used for high-volume production.

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What is Soft Tooling?

Soft tooling is most commonly used to produce low volumes of rubber moldings and urethane castings. Production runs using soft tooling typically produce less than 100 parts. Soft tooling molds are usually made with silicone, carbon fiber, or fiberglass, and each mold cavity is good for about 25&#;50 shots.

Soft tooling is the preferred injection molding process for some industrial applications. Some of the use cases for soft molding include:

• Prototyping to prove a design concept. Soft tooling is a fast and easy way to model a design concept for visualization, demonstrations, functionality testing, and approvals.

• Making test units for quick evaluation by customers. The quick turnaround time for soft tooling injection molding makes it ideal for generating small batches of prototypes used for market testing.

• Custom and small-volume orders. Soft tooling makes the most sense for very low-volume injection molding projects ranging from single prototypes to a few hundred pieces.

Some of the advantages of soft tooling injection molding include:

• Cost-effectiveness

• Short lead times and fast order turnarounds

• A variety of material options

• When using a 3D-printed master pattern, minute details and complex geometries are quicker to implement into soft tooling vs. hard tooling

What is Hard Tooling?

When the production volume is in the thousands or millions of parts, hard tooling is the preferred method. Hard tooling molds are made of sturdier materials such as aluminum, nickel, and steel alloys. Though they take longer to make and are more expensive than molds for soft tooling, hard tooling molds last for a long time.

Hard tooling is expensive to fabricate, so the molds must be crafted with care to avoid costly errors. The fabrication of hard tooling molds is often outsourced to a third party since they require specialized precision machining and finishing capabilities.

The major advantages of hard tooling include:

• The harder molds facilitate high-volume production into the millions.

• Parts with simple designs may be used right off of the production line.

• A single hard tooling mold can have multiple cavities, allowing several of the same part to be created simultaneously.

• Hard tooling molds can withstand higher temperatures than molds for soft tooling, so they are suitable for materials that soft tooling cannot handle.

Soft Tooling vs. Hard Tooling

To summarize, here are the main takeaways when comparing soft tooling and hard tooling:

• Soft tooling is appropriate for making prototypes or for fabricating a small number of parts, typically less than 100. Hard tooling is suitable for manufacturing a large number of parts, typically in the thousands or even millions.

• While metals are used for making hard tooling molds, soft tooling molds are typically made with softer materials like silicone or composites like fiberglass and carbon fiber.

• Soft tooling molds can be made quickly and cheaply but they wear out rapidly. However, since they are cheap, multiple soft tooling molds can be made at a lower cost than a single hard tooling mold. Hard tooling molds take longer to make and are significantly more expensive, but they last for a long time and offset their own cost over large production runs.

3ERP is an ISO :-certified company that provides high-quality rapid prototyping and injection molding services. Our turnaround time for prototyping is sometimes as little as a few hours, which gives our customers plenty of time to evaluate designs, demo an engineering idea to upper management, or get customer approvals. We also offer a variety of value-added services, such as CNC machining, pressure die casting, and 3D printing.

For more information about our injection molding capabilities, please contact us or request a quote.

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the interrelationship of tooling complexity and tight tolerances

Tooling design, materials, and cavitation all impact tolerance. In general, the more simple the process, the more likely it is to achieve and maintain tight tolerances.

Conversely, complex parts can put tight tolerances at risk since there are more variables to consider, such as the number of cavities in the mold or the need to precisely heat or cool the tools. For example, if tooling is not designed for consistent cooling, shrink rates will vary and tight tolerances will be harder to achieve. Mold cooling and part cooling are also critical for determining surface finish.

Logically, it follows that sophisticated injection-molded components require sophisticated tooling. Added features such as undercuts and threads are common. In the case of complex geometries, injection molding tooling could require the addition of rotating mechanical racks/gears, rotational hydraulic motors, hydraulic cylinders, floating plates, or multi-form slides.

sensors, benchmarking, and process repeatability

Directly correlated to scientific molding is the use of strategically placed transducers in multi-cavity and hot manifold tools to monitor and control the process in real time. Sensors can also be placed on the surface of the tool as a cooling lines or unit failure back-up. Upper and lower limits can be set on these sensors to monitor the cooling rate and the cavity pressure profile.

Establishing a production-capable process with in-tool sensors is also important for benchmarking. Having verified data to reference when making tooling material, process, or molding machine changes is essential for accurate monitoring, documentation, set-up, and future production repeatability.

tooling materials selection

A critical but sometimes overlooked injection molding tooling design consideration is proper tooling materials selection. The choice impacts several aspects of tool longevity:

• The proper steel grade and hardness properly balances wear and toughness, so tooling components that run together don&#;t wear out prematurely.

• Steel hardness can also introduce steel brittleness. Harder steel is not a good choice for tooling components subject to side-loading or impact, because if it flexes it will crack.

• Harder steel is required for molding glass-filled material, which can prematurely wear down tooling, including runner systems and gates.

ENGINEERING CONSIDERATIONS

Details matter in plastic injection tooling. Engineers play pivotal roles in ensuring an optimized production process, reduced costs, and unparalleled product quality.

Among chief responsibilities for tooling engineers is:

• Placement of waterlines to maximize cooling and minimize warping.

• Calculation of gate/runner sizing specifications for proper filling and minimal cycle times.

• Determination of the best shut-off methods for tooling durability over the life of the program.

Likewise, design engineers are accountable for several key tooling decisions. Principle among them is determining gate types and locations in order to:

• Achieve optimum flow, fill pressure, cooling time, and dimensions/tolerance.

• Assure proper part performance.

• Prevent part defects and flawed aesthetics (e.g., flow marks, shrinkage, warping).

Part art and part science, plastic injection tooling is all done to guide customers toward an optimized production process, reduced costs, and unparalleled product quality. Learn more about the process of scientifically qualifying a tool by downloading our infographic.

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