In 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 high shear cutting geometry with good edge strength at the aim of cut to generate the Excelerator ballnose milling inserts.
During the early summer 2010, I needed a lengthy talk with Dale Hill, applications engineer at Greenleaf Corp., the cutting tool manufacturer in Saegertown, Pennsylvania. Greenleaf includes a tightly focused yet innovative product line but doesn’t do a great deal of splashy promotions to draw in 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 the nature of insert cutting action. The point that the 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. The most important thing he clarified was the relationship between chip thinning, cutting speed and heat transfer. This relationship forms the theoretical grounds for the potency of the Excelerator end mills, he says. Is my comprehension of the real key concepts. The bottom line is, how an insert results in a chip determines the way the heat generated during metal cutting behaves. Ideally, the cutting action of your insert can create enough heat to promote efficient plasticizing from the workpiece material. Plasticizing implies that the fabric becomes soft enough being displaced within the model of a chip.
However, exactly the same cutting action must allow the majority of the heat to become absorbed by the chip and carried away from the workpiece before affecting the properties from the workpiece material. “For the Excelerator, we created an insert geometry that can cause a chip by using a cross section that is thicker toward the OD of the carbide ball end mill and thinner toward the centre of the tip,” Mr. Hill informed me. This, he says, implies that the thicker portion of the chip carries off proportionately more heat in comparison to the thinner part. This effect is desirable because the relative cutting speed is lower at the middle of the tip. Extra heat put aside with the thinner chip when this occurs assists with plasticizing the content to compensate for lower cutting speed. Meanwhile, the thicker portion of the chip prevents excessive and potentially damaging heat increase that could occur with the outer area of the innovative. “The chip acts such as a variable heat sink, carrying off the heat the place you don’t want it and leaving it in which you do,” Mr. Hill explained.
The key, he explained, is usually to balance this just right so that the optimum conditions are created evenly across the entire cutting edge. One result is the fact that tool pressure (a product or service of cutting speed and chip load) is evenly distributed. To put it differently, the chip is thinner in which the speed is slower and thicker the location where the speed is higher, but the cutting forces are identical at any time.
“We experimented with cutter geometry until we had derived the exact profile we required for this to occur. Then we could program our high-performance, five-axis tool grinders to create this geometry within the inserts,” Mr. Hill said. This geometry includes a complex flank clearance and rake angle combination that varies appropriately from periphery to center. Even tool pressure results in even tool wear across the entire leading edge, which extends the lifestyle from the insert by reduction of the chance that concentrated wear at some point can cause fracture or other failure.
Precisely what does this suggest 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 more than speeds for coated carbide. Therefore, ceramic cutting tools have the possibility to become 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 if they did, they could 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 together with the aluminum end mill inside the carbide version, Mr. Hill said. Applications in mild steel, for example, typically notice a 20-percent increase in metal removal rates and reduce insert costs while using carbide inserts, he says. Applications in cobalt-based alloys also benefit. Harder steels and nickel-based alloys will also see significant improvement using the carbide end mills, however, these applications are candidates for ceramic inserts that permit greater cutting parameters on suitable machines. Titanium, however, needs to be milled with carbide since this workpiece material is highly prone to thermal damage and cannot tolerate the temperature generated through 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 purchased in standard and extended lengths. Diameters range from 3/8 to 1. inch.