Machine manufacturers and operators have decades' worth of experience managing the chips that are produced in the process of cutting metal. That is not the case with the waste produced in the machining of composite parts, which presents a number of challenges that will only grow as airframers turn to a greater percentage of composites in their aircraft.
"Composite materials do not lend themselves well to net-shape manufacturing," said Randal Von Moll, Manager of Aerospace Product Development at MAG Cincinnati. "They need lots more drilling and trimming operations to get to the net shape of the part."
Machines designed to work composite parts exhibit two characteristics: they are typically lighter-duty machines because they do not have to exert the machine forces necessary to work metal; and because these lighter-duty machines do not have the structural rigidity of machines built for metal work, they must maintain the accuracy of the part features over large areas of a composite panel, for example.
The major difference between machining composites and machining metal, though, is in the type of waste produced and how it is transferred away from the machine. Each of the two major cutting techniques—dry or wet with a water-based synthetic coolant—generates different wastes with unique challenges for the machine operator.
"Waste from dry machining is more akin to a dust, so you’ve got dust-collection issues," said Von Moll. "Composite dust also contains carbon, which is electrically conductive so heat is a big problem and tool life is terrible. If you were cutting metal, you would just need more coolant, but some resins in composites can’t be violated with a lubricant so you have to go dry.
"On the wet side, that dust turns to mud. Anywhere it settles turns into a mud slide, and if you don’t take care of it, it turns to concrete and has to be chipped away. Both the dust and the mud can be very abrasive and can contaminate parts on the machine."
The desire to control waste has helped lead to the development of horizontal machines vs. vertical machines.
"Ten years ago, it was common for factories to be filled with vertical machines that were operated by teams of people, and which had ergonomic and health and safety issues," said Von Moll. "Horizontal machines offer excellent containment of chips and coolant. It seems simple, but the industry is slow to change."
MAG Cincinnati recently introduced its first horizontal profiler. The HyperMach H4000 is a five-axis machine in which the cutting operation is totally enclosed with chip fall-through to a high-volume conveyor, which prevents chip recutting (which reduces tool life) and precludes the need for a blow-off attendant.
Horizontal machines are not the solution for all metal-cutting jobs, though. Because they operate with square pallets, they are less suitable for long pieces.
"With a horizontal machine, you can’t just take a vertical machine and put it on its side," said Cliff Harden, Sales Manager, Mazak Corp., who has serviced the company’s Boeing account since the 1980s. "The pallets on horizontals start at 16 inches square and go up to 40 inches. Once you get to an 8-foot-long part, you’re going to need a giant horizontal machine. Vertical machines have tables that are fashioned in rectangles, and the rectangle can just get longer and longer as needed."