1. Technical Field
This application relates to tools, such as end mills, for the milling of materials. This application further relates to at least one possible embodiment that provides improved torsional and bending rigidity of a tool's body in an end mill, thereby to extend tool life while making possible machining at increased metal removal rates, and better surface quality, while minimizing vibration.
2. Background Information
End mills are widely used in milling operations due to their versatile range of application and due to the moderate first cost of the tool. End mills are often of cylindrical shape, and are generally available up to about 80 mm diameter. Many end mills have flat ends; however other shapes such as conical and rounded ends are also used. An end mill typically has 2 to 10 teeth, depending on diameter, size and whether configured for rough cutting or finishing. The teeth are usually spiral shaped, but can be straight and parallel to the longitudinal axis. Common materials used in the construction of end mills are high speed steel, solid carbide, cermets or ceramic, or combinations thereof.
In the following text the words “end mill” refer to a cutter made of steel, or of solid carbide, or of hard ceramic materials or combinations thereof, whether the cutter is plated with a hard coating or not.
Torsional and bending rigidity are highly desirable properties in an end mill, particularly for roughing, finishing and super finishing.
During rough machining much material is removed, and the removal of chips from the cutting area requires adequate space between cutting teeth. Such space can only be provided when the number of teeth is low, typically 2-4 teeth depending on cutter diameter, and the core diameter of the tool is small, although still large enough to prevent tool breakage. The smaller core diameter may lead to minor loss of accuracy due to tool bending under pressure, but this is of little concern for roughing operations.
In choosing an appropriate core diameter, there is always a need to balance the requirements of chip clearance and coolant access on the one hand, which call for a small core diameter, and on the other hand the demand for tool rigidity and break resistance which require a large core diameter.
High torsional and bending stiffness of an end mill is an advantage also in finishing and super finishing operations as a better surface finish is obtained.
During rough machining, the milling cutter is subjected to high torsion and bending as the machine tool drives the end mill shank while the teeth of the cutter in contact with the work piece encounter high resistance. An end mill with inadequate torsional and bending stiffness will vibrate angularly with high amplitude and not achieve high metal removal rates. Attempts to make deep cuts at high feed rates are liable to result in poor accuracy and surface quality, noise, and early breakage of the cutter.
Some examples of end mills are seen in U.S. Pat. Nos. 4,812,087; 5,188,487; 5,971,671; 6,231,275 B1 and the documents cited as references therein. Further examples of end mills according to the prior art are shown in FIGS. 1-4 in the present application.