All cutting tools eventually wear out. Although modern engineering, materials, and methods have all helped to extend useful life, cutting tools should not be abused, and operators should be aware of these common causes of tool failure. Here are the most frequent causes of premature end mills failure, along with suggestions on how to recognize and correct problems that undermine productivity.
1. Excessive Heat: Heat build up is a major cause of cutting tool edge failure and shortened tool life.
2. Abrasion: is the wearing away of the cutting tool.
3. Chipping/ crumbling of cutting edges: When cutting forces put a greater load on the cutting edges than the tool material can withstand, small fractures in the end mill can result in portions of the cutting edge chipping away.
4.Clogging: The material of some work-piece produces longer, stringy, compressible chips.
5. Built-up Edges:Particles of the workpiece material may cold weld, gall, or otherwise adhere to faces of teeth adjacent to the cutting edges.
6. Hardening of the workpiece: (strain hardening, cold working, or glazing) cutting edges compress or deform the workpiece surface. Changing the material structure of the work-piece- increasing its hardness. Many high alloyed carbon tool steels, high strength superalloys and all austenitic stainless steel are susceptible.
7. Cratering: In the area of high heat & abrasion- the chips can erode a barrow hollow or groove into the tooth face. Once it starts it gets progressively worse until the tool fails.
1. Excessive Heat- Heat can never be completely eliminated, but it can be minimized. Always use the correct, properly sharpened tool for the specific cutting operation. Operate at the speed and feed recommended for the work-piece material. And always use the correct coolant. 2. Abrasion: Since heat and abrasion are interrelated problems, the suggestions for minimizing heat also apply to abrasion. 3. Chipping: Should be avoided or corrected by addressing the following: a. excessive feed per tooth fpt) b. Poor cutter design c. End mill brittleness caused by improper heat treating d. Chattering due to a loose fixture, workpiece, and/or machine e. Inefficient washout that permits chips to be caught between cutting edges of the tool and work-piece surfaces f. Build-up of edge break-away.
4. Clogging: minimized by reducing the depth or width of the cut when machining materials that tend to clog. Or by reducing the feed per tooth (FTP), or by using tools with fewer teeth that provide space for the chips. Flushing the area with a coolant under pressure will lubricate the tooth face and help to remove chips.
5. Built-up Edges:this can be helped by reducing the feed and/or the depth of cut. The most effective solution is usually pressurized application of a good cutting fluid that lubricates the face where the build-up can form.
6. Hardening of the workpiece: extremely important to use sharp cutting tools at generous feeds to minimize friction. Proper speeds and climb cutting with a generous application of cutting oil is highly recommended. If surface is already glazed try roughing up the surface; it makes it easier for the end mill to bite into the material. 7. Cratering: This can be minimized by applying a coolant that provides either a high pressure fluid film or a chemical oxide film on the tool. The film prevents metal to metal contact. Or apply a tool surface treatment that imparts a high abrasion-resistant, superficial hardness to the faces of the teeth and resists erosion.