During the early summer 2010, I needed an extensive talk with Dale Hill, applications engineer at Greenleaf Corp., the cutting tool manufacturer in Saegertown, Pennsylvania.
Greenleaf design engineers say they combined a higher shear cutting geometry with higher edge strength at the aim of cut to create the Excelerator ballnose milling inserts.
During early summer 2010, I had a long talk 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 lots of splashy promotions to attract attention beyond its target markets. I had been enthusiastic about the company’s new collection of carbide end mills for the reason that product descriptions hinted at some revealing insights in to the nature of insert cutting action. The fact that the fishing line includes both ceramic (WG-600 grade) and carbide (G-925 grade) inserts for a 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. What is important he clarified was the relationship between chip thinning, cutting speed as well as heat transfer. This relationship forms the theoretical grounds for the potency of the Excelerator end mills, he says. Here is my comprehension of the true secret concepts. In a nutshell, just how an insert generates a chip determines the way the heat generated during metal cutting behaves. Ideally, the cutting action of your insert will create enough heat to promote efficient plasticizing of the workpiece material. Plasticizing signifies that the material becomes soft enough to be displaced from the shape of a chip.
However, the identical cutting action must allow a lot of the heat being absorbed through the chip and carried away from the workpiece before affecting the properties of the workpiece material. “For the Excelerator, we created an insert geometry that creates a chip with a cross section which is thicker toward the OD of your rough end mill and thinner toward the middle of the tip,” Mr. Hill explained to me. This, he says, signifies that the thicker part of the chip carries off proportionately more heat than the thinner part. This effect is desirable because the relative cutting speed is less at the center of the tip. Extra heat put aside through the thinner chip at that time assists with plasticizing the content to make up for lower cutting speed. Meanwhile, the thicker section of the chip prevents excessive and potentially damaging heat build-up that might occur with the outer area of the really advanced. “The chip acts like a variable heat sink, carrying from the heat that you don’t want it and leaving it where you do,” Mr. Hill explained.
The important thing, he said, is always to balance this perfect so the optimum conditions are created evenly over the entire leading edge. One result is that the tool pressure (a product of cutting speed and chip load) is evenly distributed. To put it differently, the chip is thinner where the speed is slower and thicker in which the speed is higher, nevertheless the cutting forces are similar at any point.
“We experimented with cutter geometry until we had derived the exact profile we needed for this to occur. We could program our high-performance, five-axis tool grinders to make this geometry within the inserts,” Mr. Hill said. This geometry incorporates a complex flank clearance and rake angle combination that varies appropriately from periphery to center. Even tool pressure contributes to even tool wear across the entire really advanced, which extends the lifespan in the insert by reduction of the likelihood that concentrated wear at some time can cause fracture or other failure.
Precisely what does this indicate for ceramic vs. carbide applications? Mr. Hill answered by pointing out that cutting speeds (sfpm) for today’s ceramic insert materials are usually three or four times higher than speeds for coated carbide. Therefore, ceramic cutting tools have the potential being much more productive than carbide. However, many tapperedend do not have machine tools with sufficient spindle speeds and axis travel rates to assist those cutting speeds. And in case they did, they could also need to use shrink- or press-fit tool holders and effectively balance the cutter assemblies.
For that reason, Greenleaf is seeing its greatest inroads using the tapered end mill within the carbide version, Mr. Hill said. Applications in mild steel, for instance, typically see a 20-percent boost in metal removal rates and minimize insert costs while using carbide inserts, he says. Applications in cobalt-based alloys also benefit. Harder steels and nickel-based alloys will likely see significant improvement using the carbide end mills, nevertheless these applications are candidates for ceramic inserts that permit higher cutting parameters on suitable machines. Titanium, however, needs to be milled with carbide because this workpiece material is extremely vunerable to thermal damage and cannot tolerate the heat generated with the speeds and feeds essential for milling with ceramic inserts.
The cutter bodies for that ballnose inserts are produced from heat-treated alloy steel and are available in standard and extended lengths. Diameters cover anything from 3/8 to 1. inch.