Tooling for manufacturing composite parts is unique in many ways. And because producing precision tools capable of withstanding repeated curing cycles is so challenging, a lot of companies are forced to continually make their own tools to keep up with manufacturing demands. The industry needs a solution, and it could be found in polyurethane foam.
To understand the issue at hand, it is important to first understand what tooling is in the composite setting. Tooling in a tool and die shop refers to the lathes, drill presses, etc. that transform cast parts into machined parts with incredibly tight tolerances. In composites manufacturing and fabricating, tools are essentially molds.
A fabrication shop may use a precision tool to facilitate a manual layup of prepreg materials that will eventually become a door panel, for example. Upon completion of the layup, the tool and its multiple layers are heat cured in an autoclave to create one solid piece from a combination of carbon fiber fabric and resin.
The challenge in composite tooling is create tools from materials that can stand up to repeated cure cycles without compromising precision. Finished parts still have to meet tolerances or they are no good to customers, explains Utah-based Rock West Composites, a company that provides prototyping services along with composite materials like carbon fiber tubing and fiberglass sheets.
Hard vs. Soft Tooling
Most composite tooling relies on hard substances, like metals for instance. These hard tools are more than capable of withstanding the punishment of evacuation and heat curing. Yet the intrinsic limits of hard materials do not allow for some of the more unique shapes and configurations composite designs call for. Thus, fabricators have to turn to soft tools for more complex layups.
Soft tools have their own limits, though. At the top of the list is the difficulty of keeping to tight tolerances in the midst of high heat curing. And of course, many small tools cannot endure more than a couple of cycles. Soft tools are a good option for small-run projects, prototypes, and jobs that require a quick turnaround. They do not tend to be the best choice for every day, long-term use in a high output setting.
The Promise of Polyurethane
Toolmakers have been working with polyurethane foam as a material for soft tools for some time now. But standard polyurethane has the same limitations as other soft tools. Now however, a small handful of companies are developing more advanced polyurethane foam products capable of overcoming many of the challenges of soft tooling.
One particular polyurethane product cited by an AZO Materials article published earlier in 2018 could be the soft tooling answer fabricators have been looking for. Known generically as high-density urethane, it is a very good product for master models and composite tooling utilizing both low temperature curing and high-temperature autoclaves.
A big advantage of this product is that it cuts down on the time and effort needed to create a new tool. Thanks to the physical properties of polyurethane, a tool can be cut out of a block of high density urethane using the same kinds of tools you might find in a tool and die shop. The result is a precision tool with tight tolerances that can be fabricated in a virtually endless number of shapes and sizes.
Polyurethane foam is not the right soft tool choice for every application. But it is gaining traction among toolmakers who need other options. It is an excellent choice for short run projects, prototypes, and jobs that require quick turnaround or complex designs.