Hole making made good

Through its partnership with Novator, Sandvik Coromant's Sheffield-based facility for R&D on composite machining is researching the manufacturing benefits of orbital drilling.   The R&D centre in Sheffield, UK is the main facility of Sandvik Coromant for research and development on composite machining, with onsite facilities for prototyping, testing and measurement. The increasing use of advanced composite materials in combination with metallic stacks in aircraft manufacturing presents particular challenges to carry out accurate and cost-effective hole making operations. As an alternative to using a whole range of drilling tools, the hole making process can be modified by using a single milling cutter in an operation that is known as orbital drilling or orbital machining. In this operation the cutter moves in an eccentric motion around the hole centre while it rotates around its own axis and is fed through the workpiece. The orbital drilling process is particularly attractive in cases where: complex stacks of materials are being drilled but disassembly for cleaning or deburring is too time consumable or not possible; tolerances are extremely tight for all materials in a stack, especially on surface roughness; extraction of chips must be carefully managed to avoid disassembly. To develop specific tooling solutions for hole making, Sandvik Coromant is working closely with orbital drilling manufacturer Novator, one of the world leaders in portable orbital drilling solutions for the aerospace industry. The R&D centre in Sheffield is looking forward to the delivery of new PM80 machines from Novator. The new machines will give the centre the possibility to test new orbital cutting tools, ensuring a close replication of the customer application. Both cutters with exchangeable head and solid carbide cutters can be tested. The PM80 also offers the possibility to drill thicker stacks than was possible with the PM60 machine that it replaces. The Sheffield centre has close links with its sister department in Rovereto, Italy. There they do research and development of solid carbide end mills, which is of course useful to orbital drilling. The facility is based only a few hundred meters from the world leading Advanced Manufacturing Research Centre (AMRC) at the University of Sheffield, and enjoys a close relationship with their engineers, in particular the composites machining group. Lately the centre has been performing some research on tools and the application to minimise the size of the endcap and to reduce the burr height in metallic stack drilling. An endcap is a chip that looks like a washer and is detached from the material while cutting through a CRFP/metallic stack material. The endcap must not be too big/thick since it is important that it is small enough to be removed by the airflow system. End users and material suppliers are becoming increasingly interested in the temperatures that are generated in the machining process. While for most CFRP materials, conventional machining when tools and conditions are well selected is not a problem. But for lower temperature materials, or those where there are some other thermal sensitivity aspects, orbital drilling presents a good option, with measured temperatures generally being significantly lower than for conventional drilling. One study showed that temperatures remained below 90°C. The extensive knowledge and expertise of Sandvik Coromant in coating and substrate optimisation makes sure that they provide not only the right geometry for the application, but the best tool material too. As carbide and PCD is offered, a lot of effort is focused around improving diamond coated tooling solutions to extend tool life in the carbide cutters. www.sandvik.coromant.com