During the early summer 2010, I had an extended speak with Dale Hill, applications engineer at Greenleaf Corp., the cutting tool manufacturer in Saegertown, Pennsylvania.
Greenleaf design engineers say they combined a very high shear cutting geometry rich in edge strength at the point of cut to generate the Excelerator ballnose milling inserts.
During the early summer 2010, I had an extensive chat with Dale Hill, applications engineer at Greenleaf Corp., the cutting tool manufacturer in Saegertown, Pennsylvania. Greenleaf carries a tightly focused yet innovative product line but doesn’t do a lot of splashy promotions to draw in attention beyond its target markets. I was thinking about the company’s new collection of carbide end mills because the product descriptions hinted at some revealing insights into 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 regarding the insert geometry preventing excess “tool pressure” also got my attention.
The discussion with Mr. Hill turned out to be enlightening. What is important he clarified was the relationship 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. Here is my comprehension of the key concepts. In summary, the way an insert generates a chip determines the way the heat generated during metal cutting behaves. Ideally, the cutting action of an insert can provide enough heat to market efficient plasticizing in the workpiece material. Plasticizing signifies that the material becomes soft enough to become displaced within the form of a chip.
However, exactly the same cutting action must allow many of the heat being absorbed from the chip and carried outside the workpiece before affecting the properties of the workpiece material. “For the Excelerator, we came up with an insert geometry that can cause a chip by using a cross section that is certainly thicker toward the OD in the carbide corner radius end mill and thinner toward the centre of the tip,” Mr. Hill told me. This, he says, signifies that the thicker section of the chip carries off proportionately more heat compared to the thinner part. This effect is desirable for the reason that relative cutting speed is less at the center of the tip. Extra heat put aside through the thinner chip when this occurs assists with plasticizing the information to compensate for lower cutting speed. Meanwhile, the thicker part of the chip prevents excessive and potentially damaging heat build-up that may occur at the outer area of the really advanced. “The chip acts such as a variable heat sink, carrying off the heat that you don’t need it and leaving it that you do,” Mr. Hill explained.
The real key, he explained, is always to balance this just right so that the optimum conditions are created evenly across the entire cutting edge. One result would be that the tool pressure (an item 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, although the cutting forces are the same at any point.
“We experimented with cutter geometry until we had derived the actual profile we necessary for this to happen. Then we could program our high-performance, five-axis tool grinders to generate this geometry inside 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 over the entire leading edge, which extends the life span of your insert by reducing the chance that concentrated wear at some point will result in fracture or any other failure.
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 3 to 4 times greater than speeds for coated carbide. Therefore, ceramic cutting tools have the possibility to get very much more productive than carbide. However, many tapperedend do not possess machine tools with sufficient spindle speeds and axis travel rates to aid those cutting speeds. And if they did, they might also have to use shrink- or press-fit tool holders and properly balance the cutter assemblies.
That is why, Greenleaf is seeing its greatest inroads using the tapered end mill within the carbide version, Mr. Hill said. Applications in mild steel, for example, typically notice a 20-percent increase in metal removal rates and lower insert costs while using carbide inserts, he says. Applications in cobalt-based alloys also benefit. Harder steels and nickel-based alloys will even see significant improvement with all the carbide end mills, but these applications are candidates for ceramic inserts that permit higher cutting parameters on suitable machines. Titanium, however, needs to be milled with carbide simply because this workpiece material is very 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 manufactured from heat-treated alloy steel and can be found in standard and extended lengths. Diameters vary from 3/8 to 1. inch.