During early summer 2010, I needed 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 very high shear cutting geometry rich in edge strength at the aim of cut to generate the Excelerator ballnose milling inserts.
During early summer 2010, I had an extensive speak 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 plenty of splashy promotions to bring in attention beyond its target markets. I used to be considering the company’s new line of Custom Carbide End Mills because the product descriptions hinted at some revealing insights into the nature of insert cutting action. The truth 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 proved to be enlightening. The most important thing he clarified was the connection between chip thinning, cutting speed and also heat transfer. This relationship forms the theoretical grounds for the effectiveness of the Excelerator end mills, he says. The following is my understanding of the important thing concepts. In summary, the way an insert results in a chip determines the way the heat generated during metal cutting behaves. Ideally, the cutting action of an insert will create enough heat to enhance efficient plasticizing from the workpiece material. Plasticizing means that the fabric becomes soft enough to become displaced from the model of a chip.
However, a similar cutting action must allow the majority of the heat to be absorbed by the chip and carried from the workpiece before affecting the properties from the workpiece material. “For the Excelerator, we came up with an insert geometry that creates a chip by using a cross section which is thicker toward the OD from the carbide corner radius end mill and thinner toward the middle of the tip,” Mr. Hill informed me. This, he says, means that the thicker portion of the chip carries off proportionately more heat compared to thinner part. This effect is desirable because the relative cutting speed is less at the middle of the tip. Extra heat left behind by the thinner chip at that time assists with plasticizing the fabric to compensate for lower cutting speed. Meanwhile, the thicker section of the chip prevents excessive and potentially damaging heat build-up which may occur at the outer portion of the innovative. “The chip acts like a variable heat sink, carrying away from the heat that you don’t want it and leaving it the place you do,” Mr. Hill explained.
The important thing, he stated, is to balance this just right in order that the optimum conditions are produced evenly over the entire really advanced. One result is the tool pressure (a product or service of cutting speed and chip load) is evenly distributed. Put simply, the chip is thinner in which the speed is slower and thicker the location where the speed is higher, however the cutting forces are exactly the same at any point.
“We experimented with cutter geometry until we had derived the precise profile we essential for this to occur. We could program our high-performance, five-axis tool grinders to make 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 results in even tool wear across the entire really advanced, which extends the life of the insert by reducing the likelihood that concentrated wear at one point may cause fracture or another failure.
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 typically three or four times greater than speeds for coated carbide. Therefore, ceramic cutting tools have the possibility to get that 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. And if they did, they might must also use shrink- or press-fit tool holders and properly balance the cutter assemblies.
For this reason, 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 visit a 20-percent surge 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, but these applications are candidates for ceramic inserts that permit much higher 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 from the speeds and feeds required for milling with ceramic inserts.
The cutter bodies to the 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.