The Cutting Edge of Productivity

One market sector where U.S. manufacturing must stay ahead of foreign competition is in the value curve for demanding cutting applications of exotic materials. The next generation of high performance solid carbide end mills addresses the major challenges facing manufacturers in this market by enabling the production of high quality exotic alloys for a fraction of the cost of conventionally produced parts.

To lower your costs and raise your productivity, the design of the next end mill you purchase should focus attention on advanced geometries, polished flutes and application-specific coatings that eliminate chatter on corners, increase feeds/speeds that are too slow, improve chip and heat removal to enhance surface finish, and improve tool balance and stiffness for higher quality cuts.

For example, chatter is a major productivity waster when machining advanced materials. It occurs when milling corners, particularly with non-ferrous material such as aluminum. The stress of chatter is hard on the spindle bearings and can ultimately reduce machine life. Normally the machinist will lower the feed rate to minimize chatter, especially in the corners when the diameter of the end mill meets the corner. The paradox here, of course, is that while slowing down the machine improves cut quality, the overall operation becomes less productive.

End mills can address this issue by using a changing helix with flute angles that progressively increase up the flute to break up the harmonics and run smoother at greater speeds and feeds (see Figure 1). A changing helix can run 50 to 200 percent faster speeds, depending on the application.

Another problem faced in many aluminum applications is the inability to run end mills at high speeds and feeds. When milling a thin aluminum pocket, the machinist must decrease his rpm due to the increase in chip load to avoid packing and re-cutting. This again slows down the cycle time and reduces productivity. This problem is further complicated when milling other exotic alloys (especially titanium) at high velocity, because significant heat is generated that shortens tool life.

A 20 percent increase in speeds and feeds can dramatically reduce the cost per part. The secret here is better utilization of available machine time. Even if the cost of the end mill is greater, the end mill cost represents only 3 percent of the total manufacturing cost of a part. So if a machinist can drastically reduce cycle time, the cost per part will be lower and lead to significant savings for the company.

Comparison tests prove that a 5-fluted tool will achieve 30 to 50 percent higher feed and speed rates than a conventional 4-flute tool (see Worksheet Summary).

When selecting tools for non-ferrous applications, particularly in tough materials such as titanium, consider a variable helix with offset flutes that enable the machinist to run smoother at elevated speeds and feeds with reduced vibration (see Figure 2). A variable helix can slot, plunge and finish with the same tool.

End mills with a gash rollout enable better chip flow, avoiding chip "packing" and re-cutting when running at high speeds (see Figure 3A). On ferrous applications where heat is generated, having the right TiALN coating will also help maintain the cutting edge. Where traditional TiALN coatings have 40 percent aluminum content, new TiALN coatings have a 60 percent aluminum content that withstands higher temperatures (up to 1600 deg F) at greater speeds.

Another issue, especially in aluminum, is achieving a finer surface finish in a single pass. Aluminum applications typically require a fine axial and radial finish. The machinist must typically do a secondary benching operation to achieve the desired finish. This relates to the problem in some applications of optimizing cuts less than one inch by trading off the low cost of indexables versus the need to make perhaps three passes to achieve the desired depth of cut and finish. Adding the mechanical variables associated with indexables can be less efficient than a solid tool.

To overcome this, wiper flats and cylindrical margins on the OD provide a superior finish without having to do these secondary hand operations (see Figure 4). A wiper can achieve a 16 RMS radial finish in a single pass. A solid carbide tool can outperform an indexable tool under one inch by a wide margin and the benefit can far outweigh the additional purchase price of a high performance tool.

The other partner in performance that ties the spindle to the tool is the toolholding device. Using a wrong end mill holder can negate the expensive investments made in your tool and machine.

Staying on the cutting edge of productivity – staying profitable – can be achieved by using the next generation of high performance solid carbide end mills. Before you run your next job, be sure to revisit your end mill design. The advanced geometries, polished flutes and application-specific coatings of these new tools enable high speeds and feeds with minimal chatter, longer tool life, single-pass fine surface finishes while dramatically improving productivity.

John Edinburg is a product manager for Toolmex Corporation, 1075 Worcester Road, Natick, MA 01760, 508-653-9987,
john.edinburg@toolmex.com,
www.toolmex.com.