During the early summer 2010, I had an extended talk to Dale Hill, applications engineer at Greenleaf Corp., the cutting tool manufacturer in Saegertown, Pennsylvania.
Greenleaf design engineers say they combined a high shear cutting geometry with high edge strength at the purpose of cut to produce the Excelerator ballnose milling inserts.
During early summer 2010, I needed an extended chat with Dale Hill, applications engineer at Greenleaf Corp., the cutting tool manufacturer in Saegertown, Pennsylvania. Greenleaf has a tightly focused yet innovative product line but doesn’t do a lot of splashy promotions to get attention beyond its target markets. I had been considering the company’s new collection of Custom Carbide End Mills for the reason that product descriptions hinted at some revealing insights into the nature of insert cutting action. The reality that the line includes both ceramic (WG-600 grade) and carbide (G-925 grade) inserts for the similar cutter bodies intrigued me. Statements about the insert geometry preventing excess “tool pressure” also got my attention.
The discussion with Mr. Hill became enlightening. It is important he clarified was the connection between chip thinning, cutting speed and also heat transfer. This relationship forms the theoretical grounds for the potency of the Excelerator end mills, he says. This is my comprehension of the key concepts. The bottom line is, just how an insert produces a chip determines the way the heat generated during metal cutting behaves. Ideally, the cutting action of an insert can provide enough heat to enhance efficient plasticizing of the workpiece material. Plasticizing signifies that the content becomes soft enough to be displaced within the form of a chip.
However, the identical cutting action must allow most of the heat to be absorbed through the chip and carried away from the workpiece before affecting the properties in the workpiece material. “For the Excelerator, we created an insert geometry that produces a chip using a cross section that is certainly thicker toward the OD of your carbide ball end mill and thinner toward the center of the tip,” Mr. Hill explained. This, he says, implies that the thicker part of the chip carries off proportionately more heat compared to the thinner part. This effect is desirable because the relative cutting speed is lower at the core of the tip. Extra heat put aside through the thinner chip at that time assists with plasticizing the information to compensate for lower cutting speed. Meanwhile, the thicker section of the chip prevents excessive and potentially damaging heat build up which may occur in the outer portion of the really advanced. “The chip acts like a variable heat sink, carrying away from the heat the place you don’t want it and leaving it that you do,” Mr. Hill explained.
The important thing, he was quoted saying, is to balance this perfect in order that the optimum conditions are set up evenly over the entire really advanced. One result would be that the tool pressure (a product of cutting speed and chip load) is evenly distributed. To put it differently, the chip is thinner the location where the speed is slower and thicker in which the speed is higher, but the cutting forces are similar at any point.
“We experimented with cutter geometry until we had derived the specific profile we required for this to happen. Then we could program our high-performance, five-axis tool grinders to produce this geometry in the inserts,” Mr. Hill said. This geometry comes with a complex flank clearance and rake angle combination that varies appropriately from periphery to center. Even tool pressure contributes to even tool wear throughout the entire leading edge, which extends the lifespan from the insert by reducing the chance that concentrated wear at some time may cause fracture or another failure.
What does this imply for ceramic vs. carbide applications? Mr. Hill answered by pointing out that cutting speeds (sfpm) for today’s ceramic insert materials are usually 3 or 4 times greater than speeds for coated carbide. Therefore, ceramic cutting tools have the potential to become so much more productive than carbide. However, many tapperedend do not have machine tools with sufficient spindle speeds and axis travel rates to support those cutting speeds. Of course, if they did, they might also have to use shrink- or press-fit tool holders and effectively balance the cutter assemblies.
For this reason, Greenleaf is seeing its greatest inroads with the micro diameter end mill from the carbide version, Mr. Hill said. Applications in mild steel, for instance, typically view a 20-percent surge in metal removal rates and lower insert costs utilizing the carbide inserts, he says. Applications in cobalt-based alloys also benefit. Harder steels and nickel-based alloys may also see significant improvement with all the carbide end mills, but these applications are candidates for ceramic inserts that permit greater cutting parameters on suitable machines. Titanium, however, must be milled with carbide because this workpiece material is very prone to thermal damage and cannot tolerate the high temperature generated through the speeds and feeds necessary for milling with ceramic inserts.
The cutter bodies for your ballnose inserts are manufactured from heat-treated alloy steel and can be purchased in standard and extended lengths. Diameters vary from 3/8 to 1. inch.