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.