Proper Tooling Design Matters

Early in my composites career, I owned a small shop focused exclusively on manufacturing whitewater racing kayaks and canoes, which was really just an excuse to support my own personal racing habit and postpone adulthood. However, it paid some bills and taught me many valuable lessons about vacuum bagging, resin/fiber ratios, delamination, infusion and the importance of good tooling design. A poorly designed tool transfers a cost and quality burden into every part associated, even if intended for single usage. For example, according to legend, at the 1971 World Whitewater Canoe & Kayak Championships, the Polish team had designed a new type of C-2 (2-man decked canoe) called a Hartung. The night before the race, two Austrians swam across the river under the cover of darkness and “borrowed” two Hartung C-2s from the Poles’ camp. They took them to an abandoned shack and proceeded to fabricate a hull mold from one and a deck mold from the other. The borrowed boats were returned before dawn without the Poles knowing. A few days later, the Austrians took their new pirated Hartung out for a spin and pronounced it a terrible performer, but assumed they just needed time to get used to the radical new design. They then traveled to a race in England where the telltale design caught the Polish team’s attention so they all gathered around for a look. After a few moments, they erupted in laughter. When the uproar had subsided, one of them explained, “You’ve got the hull on backwards!” In their midnight switch, the Austrians had failed to mark their molds and had been paddling the boat backwards. Tooling design matters! Tooling falls into a few broad categories – traditional lay-up molds, trim/mill fixtures, bonding/assembly fixtures and facility or “work cell” integration fixtures that interface with robotics and automation. Every composites shop manager should ask a few standard questions: • What cycle times do I need to achieve with my tooling to hit my production targets? • What tolerances do I require of my tooling to ensure accurate and worry-free assembly? • How can I incorporate safety and ease-of-use features into my tooling, such as rotating molds, pneumatic clamping, suspended walkways and automatic lifting? • How can my tooling assist in reducing touch labor? At my company, Janicki Industries, those questions and other key factors are part of our holistic approach to tooling design. The following list, though not exhaustive, includes typical issues that we take into consideration. This tooling design approach can be used to fabricate everything from shower stalls to wind blades and aerospace parts. Usage Temperature of Lay-up Tooling This drives potential coefficient thermal expansion (CTE) mismatches between tool coatings, resin matrix, fiber reinforcement and substructure. Even relatively small differences of 1 – 2 inch/inch/°F over a large tool can cause significant stress resulting in warpage or cracking. A good rule of thumb is to match the CTE of your part materials with the CTE of your tooling for any application above 180 F. Surface Profile Tolerance Composite tooling can either be cast or machined. Metal tooling is almost always machined. Due to factors such as expansion, exothermic, shrinkage and a phenomena known as spring-in, cast tooling will not reflect your actual design, with typical variances ranging from +/-.060 inches to +/-.125 inches. A common practice at Janicki is to perform computer-aided design (CAD) compensation of surfaces to mitigate these effects. However, machined tooling consistently achieves surface profile tolerances within +/-.010 inches. Machining also allows for very fine surface features to be included in the tool surface that would be difficult to cast, such as scribes or ply steps. Tooling Cycle Time In a higher volume or higher temperature environment, tooling often needs to be cycled quickly and frequently benefits from incorporating heating and/or cooling into the design. A good example is automotive high-pressure resin transfer molding (HP-RTM), which commonly features heated steel tooling in a dedicated press. Another example is wind blade tooling, which is too large to easily move to an oven, so air, electrical or water heating systems are integrated into the composite face sheet. Optimizing tool cycle time also can pay benefits by requiring less total tool count, which reduces facility needs and valuable floor space. Getting Materials into the Tool Tooling bushings (TBs) that allow laser trackers to “clock-in” allow for surface profile verification, ply projection and automated tape laying/automated tape placement indexing and are frequently required by aerospace customers. Marine and wind customers benefit from surface scribes to assist with both edge of laminate (EOL) and edge of part (EOP). Vacuum and/or resin feed ports also can be integrated, thus eliminating potential vacuum bag failures and reducing labor. Large tools require careful consideration when applying materials. Marine molds are commonly put on pivoting spindles. Another approach is illustrated with a NASA pressure bulkhead tool Janicki fabricated with a suspended walkway that rotates 360 degrees. The bulkhead part was fabricated from out-of-autoclave prepreg that could not be walked on prior to cure or critical air pathways would have prematurely collapsed. Tooling Life Expectations A critical issue in tooling design is balancing cost, quality and schedule within the expectations of tooling life. One needs a completely different approach for a single usage 350 F tool than for fabricating 200 parts at 350 F. I frequently see prototype tooling being stretched beyond its design life, which sometimes results in catastrophic failure! Other factors that drive lay-up tool design are the release systems utilized by customers as well as indoor or outdoor storage. I have seen military tools stored in the desert that are sand etched and boat molds that are stored outside in Maine at -20 F. We recently shipped a tool to South Africa that sat on the deck of a transatlantic voyage. The steel substructure was not adequately painted and became badly corroded. Tooling Cost The phrase “there is a right tool for every job” certainly applies, and at Janicki we are stubbornly material agnostic with solutions ranging from $100 to more than $3,000 per square foot. Lower cost solutions exist across all markets, with performance and quality reductions. Ancillary assembly tooling design is often overlooked, but can play a key role in such activities as trimming part edges, drilling accurate holes and cutting hatches. These do not need to be overengineered or expensive and often can be fabricated from fiberglass, steel or aluminum. Vacuum clamping of parts is effective, cheap and easy to incorporate. Spend some time studying your tooling design needs upfront, and hopefully you will avoid putting parts together backwards!