Report: Sandvik Coromant composites machining course

Sandvik Coromant, working with subsidiary Precorp, offered a three-day training course in April on the latest technologies for machining and drilling of composite materials.

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Composites are like snowflakes; no two are alike

—Kim Nixon, MARCS group manager, Precorp (Spanish Fork, Utah, USA)

Cutting tool specialists Sandvik Coromant (Sandviken, Sweden) drew about 50 machinists from airframe and other composite manufacturing facilities for its seminar on machining composite materials April 22-24 at its two-year old Productivity Center in Cypress, Calif., USA. Under the overall direction of Sandvik composite specialist Linn Win, speakers explained to the attendees why composite construction varies according to the applied loads, and demonstrated how to machine the materials without doing damage to the fibers or the laminate.

The seminar stressed the many variables in carbon composite parts that affect cutting tool decisions, notably: resin type, resin-rich or resin-starved laminate, type of fiber and type of material—such as multi-directional or plain weave.

Sandvik engineers and manufactures standard and custom tools for manual and CNC machining of composite materials, including tooling for milling, drilling countersinking and reaming. Presentations and demonstrations covered cutting through stacks of carbon composite and titanium; carbon/aluminum; and carbon/carbon—with hand tools as well as with CNC machines.

Sandvik’s wholly-owned affiliate Precorp Inc. MARCS Group (Manufacturing Applications Research and Customer Service) presented its Aerospace Cutting Tool Guide for selecting the correct tool for the job. Precorp makes a full line of custom polycrystaline diamond (PCD) and carbide tools designed specifically for drilling, reaming and countersinking advanced composite materials (but cutting metals with improper settings and techniques may damage or destroy PCD cutters). “It’s important to select the correct tool,” stressed Cody Cluff, MARCS engineer for Precorp, who noted that about 35 percent of the machining market is manual.

Sandvik and Precorp stressed that they will provide engineering solutions for challenging tooling and machining situations. They suggest companies contact their local representative first; then come to Sandvik engineers if solutions prove elusive. Sandvik also maintains a blog for composite cutting questions and information: see compositemachining.org.

A major issue in either manual or CNC drilling is evacuating metallic chips when machining metal materials stacked with carbon composites, as the chips can damage the laminate. Attendees therefore expressed considerable interest in the micro-peck technique when drilling composite/metal stacks. This is the principle of applying periodic low-frequency axial motions—vibrating gently back and forth—in conjunction with constant spindle feed during drilling operations. When properly applied, this motion reduces the size of the chips and thereby reduces composite erosion that may be caused when drilling through composite/metal stacks.

Machining of honeycomb cores is a new product area for Sandvik and a training course is planned for July 8-10 in Cypress, limited to 25. Win pointed out that honeycomb core materials are typically seven times more rigid than solid sheet and stiffen the part with minimal weight increase. Improper machining methods or use of the wrong tool can compress cells on the bottom of the core, and excessive heat can also compromise core quality. “Machining core is not like machining composites,” Win stresses. Sandvik provides best practice guidance and Precorp recommends its 85 drill for carbon/honeycomb core sandwich structures.

Sandvik Coromant is represented in more than 130 countries with some 8,000 employees worldwide. Sandvik’s 17,051-ft2/1,584m2 Productivity Center—one of three in the United States—is located in an industrial park on a quiet tree-lined street. Its “Solutions” room provides a near clean-room environment for training and R&D, with two glass-enclosed cells for work with hand tools, and a variety of six CNC machines with programmable selection and automated delivery of the desired tool. The HAAS VF-3 CNC machine has been retrofitted for continuous removal of composite dust during machining.  A “tool bin” is also automated; the desired tool is selected from programmable list, and the tray containing that tool is automatically conveyed from the storage area into the bin.