Prototyping is a familiar part of the product development process for manufacturing industries such as automotive, aerospace, wind energy, and marine. It is frequently utilized for product demonstrations, R&D testing, and regulatory certifications.
Program managers and design engineers have the challenge of keeping turnaround times fast and costs low throughout the prototyping phase, whilst still creating accurate models.
When choosing the best tooling technique these objectives are paramount, whether you’re creating one-off components, prototype parts, or composite layup tools. The tooling material must not only meet the budget and scheduling requirements of the project, but also adhere to the specifications of the application (e.g., Coefficient of thermal expansion (CTE), density, and strength).
This article will discuss soft versus hard tooling choices for custom builds and rapid prototyping, plus ideal applications and real-world case studies using soft tooling which push the boundaries of dimensional and temperature stability.
Tooling Options for Prototyping and Custom Builds
To maintain a fast and economical prototyping process, people often turn to clays, wood structures, plasters, composites, and sometimes cheaper fiberglass materials for their tooling requirements.
Yet, these materials often cannot withstand the curing process, complexity, dimensional accuracy, and other specifications. In these instances, the natural inclination may be to switch directly to hard tooling options such as aluminum, ceramics, steel, and Invar steel alloy.
Though these hard tooling materials are great for applications with extremely tight tolerances or long-term production runs, their lengthier lead times and higher costs are not as conducive for low-volume applications or quick prototyping.
The tooling option you choose affects the project budget, time-to-market, and product quality – so which method is best for your application?
Which Method is Best for Your Application?
What some engineers may not have considered before is employing high-performance polyurethane foam tooling for their proofs-of-concept, one-off builds, and demo models. Foam does not have cure inhibition issues, does not generate off-gassing, and is available in a wide variety of high temperature and high density formulations (as discussed later in the article).
Soft tooling actually exhibits many characteristics that benefit the objectives of rapid prototyping directly, such as:
- Time Savings: Polyurethane foam tooling is known for having quicker processing times in comparison to metal tooling, this is because harder materials naturally take more time to machine. Even composite tools need a three-step process which involves creating the plug, making the tool on top of it, and then supporting the tool with an egg crate structure for intensive autoclave curing cycles. Foam tooling can be done in one step via machining and consequently, from possessing the block of material to having a prototype in hand, saves around two-thirds of the time.
- Dimensional Accuracy: Polyurethane foam is machined easily into complex shapes with a smooth surface finish as it is a softer material. Last-minute modifications can be easily made by simply filling voids with common industrial-grade fillers, bonding additional foam pieces with an adhesive, or carving off any excess which is not the case with metallic tooling. To constantly enhance tolerances, General Plastics has developed high-performance foam with a low coefficient of thermal expansion (CTE) similar to that of aluminum.
- Cost Savings: On a per pound basis, soft tooling has a much better price point in comparison to hard tooling options like Invar and aluminum. For example, one client was comparing the costs to create their tool using aluminum versus polyurethane foam, and the foam tool came to around 20% of the cost of the aluminum tool. This cost analysis included the price of the raw material, machining (setup and run time), design time for the model, programming, and shipping.
- Weight and Handling: You may not consider the weight and size of the tool required to create a very large prototype or component when designing it. Maneuvering and working with an extremely heavy tooling material can slow down the overall build time significantly. Compared to other materials, polyurethane foam has the advantage of being lighter. Low CTE, high-temperature tooling foam at 48 lbs/ft3 is around 10% of the weight of Invar, and less than 30% of the weight of aluminum. The foams are available in a wide variety of strengths and densities, and can be prepared in almost any size you need.
- Low Volume: Typically, custom builds and prototypes do not need a big amount of units, so there is no need to spend extra money on tooling that will last for thousands of production cycles. Soft tooling is perfect for low-volume applications which do not need to be kept in storage for years.
Ideal Applications and Real-World Examples Utilizing Soft Tooling
Soft tooling is ideal for short production runs and is typically employed for custom projects, making prototypes, demo units, and composite tool master plugs and molds given the features of polyurethane foam outlined earlier in this article.
For large-sized tools where utilizing metal material, processing, and shipping is cost prohibitive, soft tooling is also the preferred alternative. Lastly, for projects where tight turnaround times are necessary, foam tooling can shorten your R&D cycles significantly and get your product to market quicker.
A motorcycle manufacturer may need to make very specialized fairings for a custom chopper for example. There is no reason to create a heavy-duty tool that will last forever given that these are one-off components.
Foam tooling is good for not only making prototypes but also production-ready parts that are employed in the final build in low-volume use instances. Custom builds can benefit from polyurethane foam for prototyping because they do not require high durability that will last for decades.
Custom builds, would benefit from polyurethane foam for prototyping since they do not need high durability that will last for decades.
In another example, an aerospace manufacturer approached General Plastics about rapid prototyping for composite products employed in aircraft interiors. The manufacturer was looking at new techniques for making mold tools for the prototypes, their specifications included:
- Maximum pressure of 87 psi (600 kPa)
- Temperatures of 266 °F (130 °C)
- Maximum of 12 pulls per tool
After discussing the application with the client, a recommendation on the most appropriate foam for the project was quickly provided, technical documentation with more details, a sample sheet of material to experiment with, and an estimated cost. For rapid prototyping applications such as this where speed is of the essence, soft tooling has the unique ability to meet engineering challenges at a low budget.
Pushing the Boundaries of Tooling Technology
One of the key concerns for design engineers when exploring tooling methods and CTE is the temperature rating. If the product material or prototype hits high temperatures during the curing cycle then it would be eliminated from consideration automatically.
General Plastics is constantly working on the next generation in polyurethane foam technology, and the recently released LAST-A-FOAM® FR-4800 tooling board has been formulated to withstand higher processing temperatures, with peak temperatures of up to 480 °F (249 °C) and continuous use temperatures of up to 400 °F (204 °C).
The lower CTE of the FR-4800 allows its users to reliably produce high-accuracy products, unlike other plastics on the market. This means the FR-4800 is a great alternative to aluminum tooling with only a third of the density at 48 pounds per cubic foot. The increased thermal conductivity of FR-4800 also means it does not twist, warp, or change shape during the course of thermal cycling, avoiding thermal shock and out-of-tolerance parts.
Figure 1. CTE comparison for various tooling materials.
Our goal with LAST-A-FOAM® FR-4800 was to create a predictable and reliable tooling board that can serve applications where dimensional stability does not dramatically impact autoclave cycle times.
Mitchell Johnson Ph.D., CEO/President, General Plastics
With lower CTE and higher temperature ratings, this new tooling board paves the way for new automotive and aerospace applications, like roof covers and components, dashboards, composite framing, and seats, to name a few. Its smooth, hard finish is also waterproof and does not require the use of a sealant compound, making it perfect for industrial and marine use.
Other popular LAST-A-FOAM® products used for prototyping and custom builds include the LAST-A-FOAM® FR-4500, FR-3700, and FR-4700. Each of these tooling boards have different properties – such as density, dimensional accuracy, temperature ratings, and impact and fire resistance – which can be matched to best fit the specifications of your project.
For example, Applied Aerospace Structures Corp. (AASC) is a defense subcontractor that was tasked with fabricating composite aerodynamic coverings (also called aeroshells) for containing large projectile missiles. AASC had previously created prototypes using advanced composites to test the aerodynamics of the aeroshell but now they wanted to acquire a more budget-friendly alternative.
The new prototyping material had to meet the following requirements:
- Fast tool turnaround to meet crucial testing dates
- Ability to accommodate low-temperature curing process
- Cost-effective solution for one-time use
- In-house machinability for rapid prototyping
General Plastics assisted AASC in selecting the LAST-A-FOAM® FR-7100 series foam board at a 30 pound density which was utilized to make a 10-foot by 4-foot mold tool for curing graphite laminates. The material was chosen for its dimensional stability, low cost, and ability to be easily modified for a range of applications.
Furthermore, AASC received the foam and machined it into a finished prototype tool within four weeks of issuing the purchase order (in contrast to the 12-16 weeks required for a similar metal tool). By choosing polyurethane foam, AASC significantly reduced 75% of its prototyping time and costs.
Because of the significant budget and time savings, AASC chose the FR-7130 rigid polyurethane foam for rapid prototyping of large missile coverings capable of traveling at Mach 2 speeds.
Make Your Next Prototype a Success
Soft tooling could be the right option for low-volume applications like rapid prototyping, custom components, and composite layup tools. Polyurethane foam gives a high-performance yet economical choice for generating limited runs of a part to test functionality, demonstrate features, or be employed in final production.
General Plastics has engineered an extensive offering of rigid and flexible polyurethane foam solutions to meet your specifications, with over 75 years of experience working with manufacturers on complex, cutting-edge projects.
This information has been sourced, reviewed and adapted from materials provided by General Plastics.
For more information on this source, please visit General Plastics.