How It’s Made: Transforming Polyurethane Foam Into Production Tooling

The process of creating the tool needed to produce parts is a critical portion of the manufacturing process. It is critical enough where the quality of the finished part is dependent on choosing the right tool design.

When conditions dictate the need for soft tooling, polyurethane foam (also known as high-density urethane or HDU) is commonly used because of the low cost of materials and short lead times. In addition to affordability and availability, LAST-A-FOAM^® tooling boards in particular, are exceptionally machinable and dimensionally stable which makes it easy to create intricate designs. It can be easily bonded to allow users to create monolithic tools and molds for large-scale projects, while the high Tg and low CTE makes it suitable for use in vacuum-forming applications where other urethane products may deform. Other applications include layup molds, short production runs, prototyping, and high-temperature curing prepregs. In this article, we’ll talk about the step-by-step process of converting LAST-A-FOAM^® tooling boards into a production-ready tool.

Tool Design

The first step is to design the tool that will produce the part or another tool. Designing a tool is dependent on several factors. Common questions to answer include:

Under what conditions will the tool be used?
What are its performance criteria, such dimensional stability, etc?
What are the curing conditions and how many cure cycles must be performed?
What is the desired surface finish?
What are the dimensions of the finished part?
What are the tolerances of the design?
How many parts will be produced from the tool?

Tool Fabrication Example Using PU Foam to Create a Carbon Prepreg Fiber Tool

In this example, we created a large tool using the LAST-A-FOAM^® FR-4700 high-temperature tooling foam board. The summarized steps are as follows:

Bonding

Alternating layers of FR-4700 boards and a high temperature ambient-cure epoxy adhesive are stacked together to form a bonded block of foam. The bonded blocks are vacuum bagged to ensure thin bond lines, then it is cured, and prepared for machining.

2. Machining

A rough cut of the tool is made using CNC machines and large routers, leaving 1 to 3 mm of material for finishing. Filling, sanding, and sealing follows to clean up the foam.

3. Prepreg Lay-up

The surface area is prepared with 3 to 4 mils of release film (such as Airtech Tooltec^® fiberglass-reinforced PTFE tape). Then several sheets or plies of prepreg (such as Hexcel HexTool^® M61) are applied on top. Once the pregpreg is debulked and the desired thickness is achieved, additional layers of perforated release film and breather cloth are laid on the tool and vacuum bagged to the metal working plate.

4. Curing

A modified autoclave cool down cycle is used to ensure there is no cracking or deformation of the foam.

5. Finishing

After post-cure and demolding, the tool goes through final machining and polishing. Then the structural support is attached and the surface is sealed.

Fig. 1: Bonding, Prepreg and Layup Illustration

Quality Assurance

At General Plastics, every tool goes through a First Article Inspection (FAI) to confirm the mold is correct and accurately manufactures the designed part. The finished products are thoroughly examined to make sure they meet all of the required design requirements.

Our superior quality LAST-A-FOAM^® tooling boards fulfill your tooling and mold applications. With a wide-range of high density foam formulations to satisfy every application requirement, we can supply you with the specified tooling foam material, create prototypes and CNC-machine molds to your design specifications.

To find out more about General Plastics’ LAST-A-FOAM^® polyurethane foam tooling boards and our in-house CNC machining services, contact us today.