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.
