Mould Design

No composite part can be produced without a mould. A composite material is made of two com- ponents: the matrix and the reinforcement. On this case, the composite material used is carbon fibre pre-impregnated fabrics so, the matrix is an epoxy resin solution and the reinforcements are carbon fibre filaments, woven in case of the plain weave fabric or unidirectional in case of the HM fibre. In any case, pre-impregnated fibres need to be laid down on a mould and later cured until the epoxy matrix turns from liquid to solid and the part is ready.

Designing a good mould is as important as designing the part itself and various considerations need to be taken into account when designing the part to guarantee the best possible result. Although fairly flexible, composite parts manufacturing has its limits and the designer can end up with a part impossible to produce if these limitations are not taken into account. A good mould will not only provide the best final part but also must help the laminator do its job properly by making the laminating process as easy as it can be. Good access to tighter areas of the part to guarantee that the laminator’s hands fit and good margins after the trimline to ensure the part fits perfectly after trimming and also to provide mould support to attach curing consumables provide simple solutions that improve the quality of the lamination process and of course, of the final part. Since every moulded part needs to be de-moulded, considering draft angles and leverage zones to open closed moulds makes the de-moulding process easier and directly, preventing the part from being damaged during the process.

Since the wing has three composite components, one mould per component is needed and as such, three moulds need to be designed.

5.2.1 Top Skin Mould

The top skin mould is the most complex of the three moulds designed. Since the wing needs to be easily adapted to both the ADESS-03 LMP3 and the Pininfarina H2 Speed 2018, the mould needs to reflect this ability. A solution to this problem was to use add-ons that go on the mould as seen in Figure 5.3.

According to whether a wing for the ADESS-03 LMP3 or the Pininfarina H2 Speed 2018 is being manufactured, these add-ons just need to be swapped to manufacture one top skin or the other. For the ADESS-03 wing, two add-ons are used to create the two cavities for both pillar supports. If the top skin is intended for the H2 Speed though, one add-on is used on the middle to create the single cavity for the single pillar support of the H2 Speed wing.

To attach the add-ons securely in place, the bottom of the add-ons is both drilled and tapped. The mould main body also needs to be perforated to allow screws to pass so they can attach to the bottom of the add-ons as illustrated in Figure 5.4. The holes on the main body of the mould are blind so not to difficult the passage of the screws and they are countersunk, as can be seen in Figure 5.4, so the head of the screws is aligned with the bottom surface of the mould. This way it is possible to easily work with the mould on the top of a table without the mould moving around too much.

In order to create the bonding area on the top skin, another part needs to be added to the mould

Figure 5.3: Top skin mould with add-ons for the ADESS-03 top skin manufacture.

Figure 5.4: Add-ons attachment to the main body of the mould.

assembly. This new part is once again attached to the main body of the mould using screws and can be made from a simple plate of the same material used on the rest of the mould. See in Figure 5.5 the exploded view of the top skin mould with all the five separate components that make up the whole top skin mould assembly.

Before the mould is finished, a trim line must be added. Either by scratching the surface of the mould with the appropriate tool or by using an adhesive film to limit the contour of the final part, the trim line is essential for the final finish of the component. While laminating, prepreg fabrics are tacky to the touch due to the resin in them. They must be kept inside a freezer while they are stored to prevent the resin from completely curing and so rendering the fabrics useless. While laminating at ambient temperature, the fabrics will continuously get tackier as the resin on them starts to heat up and loosen from the carbon filaments.

After laminating and when on the oven, the fabrics will heat up and the resin will became liquid before curing. Since the trimline is an engraving or an embossing on the mould surface, this line will appear on the final part as a slender groove on its surface. After de-moulding, the trimmer equipped with an appropriate cutting tool will remove the excess material from the carbon part cutting the part by the trimline engraved on its surface. Perfect trimlines ensure the best fitting of the final part.

Figure 5.5: Top skin mould with add-ons and bonding area plate removed.

In Figure 5.6 the final Top Skin Mould can be seen with the respective trimline in pink.

Figure 5.6: Top Skin mould completely assembled to begin the manufacture of the component. Notice the trim line in pink.

5.2.2 Lower Skin Mould

The Lower Skin mould follows the same principles as the Top Skin mould with the exception of the add-ons to produce the cavities. For the wings for the ADESS-03 and the Pininfarina H2 Speed, all the components are the same except for the top skin so, the mould used to produce the lower skin for the ADESS-03 wing is the same mould used to produce the lower skin used on the H2 Speed wing. What keeps this mould from being just a single part is the plate needed to, once again, create the bonding area on the leading edge of the wing. A duplicate of the plate used on the top skin mould can be used for the lower skin mould. In Figure 5.7 is shown the Lower Skin Mould with the respective trimline in pink.

Figure 5.7: Lower Skin mould with trim line in pink.

5.2.3 Rib Mould

Finally, despite looking like the most complex part of the three, the rib mould is actually the easiest of the three to design since there are no special precautions to take while manufacturing the part. Despite being easier to design, this mould is probably the most expensive one due to the complexity of the final part. Regarding design constraints, all the limitations regarding the wing adaptation from the ADESS-03 LMP3 to the Pininfarina H2 Speed 2018 were accounted for during the design phase of the rib to ensure a simpler overall process. As with the lower skin, the rib used on both wings is the same so the same mould can be used for both wings. Shown in Figure 5.8 is the rib mould with the respective trimline in pink.