Innovative tool geometries, materials, ease machining challenges
by Tim Wilson
One bright spot in the current manufacturing climate is aerospace. The big players are seeing order backlogs, with the industry being transformed by newer designs and materials that can ensure lighter, stronger aircraft.
“We see the use of aluminum shrinking, and a greater reliance on composites to lighten up aircraft,” says Jason Wells, product manager at SGS Tools.
Randy McEachern, product and application specialist, holemaking, for Sandvik Coromant Canada, Mississauga, ON, concurs and adds that with the increasing use of composites comes machining challenges.
“Its natural abrasiveness makes it hard to machine from a tool life viewpoint and has led to the use of PCD tooling for wear resistance.”
The industry is focused on controlling costs and upping production rates, with an added emphasis on surface finish and precise tolerances–areas where composites can provide unique challenges.
“SGS is focused on composites,” says Wells. “We have three tools designed for composites in aerospace now, and launched four more at IMTS in September.”
The new SGS tools include a coarse cut CCR, a compressions router, a slow helix end mill, and an eight facet double angle drill.
Composites: a unique challenge
Composites are made from a recipe. Resins provide the shape, and fibres the strength. Because they are man-made they can vary greatly. At times there are multiple layers that sandwich in diverse materials.
“The term ‘composite’ refers to carbon fiber in its different forms, such as uni-directional, multi-directional, weave, glass and metallic stacked, for example, but does not refer to materials such as Honeycomb and Kevlar,” says Sandvik Coromant’s Randy McEachern.
“Metal is easier – it’s lighter and simpler to repair,” says Bob Patterson, president and owner of Patterson AeroSales in Brampton, ON. “Composites are levels of magnitude of more work.”
Nonetheless, major aircraft such as the Boeing 787 Dreamliner have embraced composites, and smaller manufacturers such as Diamond Aircraft in London, ON, are also going with composite construction.
In part, it’s because of composites’ high weight/strength ratio, says McEachern, and the ability to mould rather than form or machine that make these materials “ideal for aircraft surfaces.”
“Our aircraft are factory built and FAA or Transport Canada certified,” says Cathy Wood, who is in charge of sales and marketing at Diamond. “Some of our aircraft use traditional Lycoming and Continental Engines, but the Austro Engine is our proprietary jet fuel piston engine.”
For competitive purposes, manufacturers like Diamond like to keep information regarding materials and processes close to their chests, hoping for an edge on the unique challenges presented by composites. This was proven to Darryl Murphy, owner of Murphy Aircraft Manufacturing on Chilliwack, BC, when he had a peek inside a major composite aircraft parts plant in Manitoba.
“We had on hair nets and white booties, and when I walked out I saw a bunch of parts and asked, ‘what’s wrong with them?’” says Murphy. “Turns out they were rejects. This was in an impressive facility that was highly controlled for temperature, humidity, and cleanliness.”
Consequently, such material requirements can provide a barrier to entry for smaller job shops. However, with the success of composites and the need to systematize processes there is more shared knowledge throughout the industry.
“There are manufacturing processes that are effective when dealing with current composites,” says Phil Kurtz, president of Wetmore Cutting Tools in Chino, CA, which specializes in aircraft extension drills.
For example, delamination of composites can be a problem when drilling. But one accepted approach is to enter the workpiece in stages, which then allows for more pressure control. This approach gradually brings the hole to size, minimizing delamination and fiber breakout. It can still be tricky, particularly when composites are sandwiched between metallic materials, because edge contact has to be maintained through the entire depth of cut for good finishes.
Aluminum, though much easier to deal with that composites, presents its own challenges. Much of this has to do with the fact that a lot of aircraft manufacturing is labour intensive. Murphy Aircraft, which works with Patterson AeroSales to manufacture and sell aircraft kits, uses a laser cutter for aluminum parts. It also has a CNC punch press and a large rubber forming press.
For its part, Wetmore has an aircraft extension drill with clearance for the fastener to get into tight spots. There is no flute, and no coolant. It is not difficult work, but still requires know-how.
“These parts cost thousands of dollars – if you ruin a hole engineering might not sign off on the part,” says Kurtz.
Despite the popularity of composites and aluminum, titanium is, if anything, becoming more common. “Our aerospace customers have anticipated that the use of titanium in the frame structure of aircraft would increase significantly over time,” says Thomas Long, global engineering manager, indexable milling, at Kennametal.
Long says when it comes to dollar per metal removal rates, customers want to see strong efficiency improvements with titanium, which is one reason why Kennametal has focused on how to deliver the coolant.
“It is essential to remove the heat through efficient coolant management,” says Long. “This is why we bring the coolant through the insert to connect with the chip-tool interface. It removes heat more efficiently.” SMT
Tim Wilson is a contributing editor based in Peterborough, ON. [email protected]