A vertical mill is designed to provide highly accurate cutting of both simple and complex shapes. As opposed to a horizontal mill, the cutting head on a vertical mill moves up and down while the table moves on the horizontal axis. This design allows for the high degree of accuracy in vertical milling, and it also permits highly stable bed arrangements.
One of the factors that enables accurate milling is the cutter speed. Mismatching the speed of the cutter to the speed of the material feed can reduce accuracy, and it can also be damaging to the cutter.
Chip Cutting and Removal
As a milling machine makes a cut, the milling head removes tiny slices of material from the main block in order to form the finished piece. This action of cutting by removing chips has a lot to do with determining the proper speed of the cutting head and the feed.
Every cutting surface, or flute, on a cutting head removes a single chip every time it contacts the surface of the material. The removed chips, sometimes called āswarf,ā need to be pushed away from the main block of material so cutting can proceed. Cutters with smaller flutes set more closely together can often move faster because each flute removes a smaller chip. But there needs to be enough space between the flutes for the swarf to be carried out of the way, or cutting speed and accuracy could be reduced.
Different Types of Cutters
Another factor in determining the proper speeds of cutter and feed is the type of cutter being used. The type of cutter influences how quickly material can be removed from the piece being milled, as well as how much friction the tool will naturally create through contact with the material. End mill cutters may experience more friction than slot cutters, for example.
The type of material a cutter is made out of also influences the appropriate cutter speed. Steel cutters made with cobalt can run more quickly than plain steel cutters. Cemented carbide cutters can run even more quickly. The hardness of the cutter increases speed, although cutters made from harder materials are more expensive.
Types of Cuts
The cuts being made also have a big influence on the proper speeds for the cutter and feed. A deeper cut may create more contact between the cutter and material, causing increased friction. Shallow cuts may cause less friction and therefore be faster. Cuts on an angle are more difficult than cuts on perpendicular planes, so these types of cuts generally need to be produced more slowly. Simple shapes and straight lines may be faster to cut than complex shapes with many intricate direction changes.
There are many factors involved in setting the right cutter speed and feed speed for a vertical CNC mill. Learning how to balance all of these factors correctly increases milling accuracy, lengthens the life of a cutting head and reduces strain on the vertical mill itself.