Constant chip load machining

Most people’s eyes glaze over at the mere mention of radial chip thinning (RCT), but it is important. Essentially, when machining at step-overs of 50 percent or less, everything most of us over 30 have been taught about CNC machining parameters goes out the window.

Decreasing the step-over can be effective because it:

• reduces stresses on the tool, the part and the machine;
• allows up to the entire flute length of an endmill to be used for full depth cutting;
• requires cutting at a higher metal-removal rate to effectively evacuate chips and, therefore, heat; and
• substantially reduces tool wear and associated costs as a result.

To use RCT effectively, all you need is a good machine, good CAM software, appropriate carbide cutting tools and a basic knowledge of the appropriate settings for a given machine, workpiece material and cutting tool combination. You can vary the feeds, speeds and tool engagement as much as you want, as long as you keep the toolmakers’ recommended chip load constant. The benefits of constant chip load machining are far greater than the sum of the individual cost benefits.

High-speed machining using Mastercam’s Dynamic Motion Technology is shown here in combination with the advanced tabs fixturing for fast transitions between top and bottom side machining. This allowed Five Axis Industries to improve in its metal-removal rates by up to 70 percent. Image courtesy CNC Software.

Five Axis Industries, Seattle, is a job shop that specializes in complex, multiple-axis machining of titanium, Inconel and the hardest grades of stainless steel. The company started as a hobby shop for the owner to produce advanced propellers for his race boat, but soon racing-boat enthusiasts throughout the world were buying them. The expertise gained in adapting 5-axis machining to making propellers led to additional opportunities for making geometrically complex parts for aerospace and other industries.

In 2013, the company retained Jason Koger as a programming consultant. His mission was to use his extensive experience with Mastercam CAM software from CNC Software Inc., Tolland, Conn., to devise efficient machining strategies that would reduce costs and enhance competitiveness.

An early project he worked on was a difficult part that was consuming 8 hours of machining time and leaving a trail of broken cutters in its wake. Koger was familiar with Mastercam’s Dynamic Motion technology, a version of constant chip load machining, and he applied it to the job.

“The goal was to make these parts as fast as possible without breaking a cutter,” said Erik Ellstrom, president. “The machine cycle was reduced to a little over 3 hours and there were no broken cutters.”

Today, Five Axis Industries applies this roughing strategy at every possible opportunity.