Cutting Speeds and Feeds of Milling cutters

Cutting Speeds and Feeds of Milling cutters
Points : Cutting Speeds and Feeds of Milling cutters, Cutting Speed of a Milling Cutter, Revolution Per Minute (Speed), Cutting Speed Selection Milling machine operates and numerical control programmers must know how to calculate correct milling cutter rpm and feed rates. The cutter rpm rates varies according to the diameter of the cutter, the kind of tool material the cutter is made of, and cutting speed for the kind of material to be cut. The feed rate varies according to the type of cutter, the size of the cutter teeth, the rigidity of the machine and work setup, and whether a rough or finish cut is to be made. The time required to complete a milling operation and the quality’ of the finish of the machined surface is almost completely governed by the Cutting Speed and Feed of the cutter. Cutting Speed of a Milling Cutter The cutting speed of a milling cutter refers to the distance, measured in feet or meters a point (tooth of a cutter) on the circumference of the cutter moves in one minute. Cutting speed is expressed in terms of Feet per Minute or Meter Per-Minute and is directly dependent on the Revolution Per-Minute (RPM) of the cutter. If the cutting speed is too high during milling, the cutter becomes overheated and dulls rapidly. If the cutting speed is too low, the production rate is low and inefficient. Revolution Per Minute (Speed) RPM refers to the number of revolution of the milling cutter during on minute. To cut at a given cutting speed, a small milling cutter must rotate at a higher rpm than a larger cutter. For example to cut at 15.24 mpm (50 fpm), a 25.4mm (1 in.) diameter cutter must rotate at 191 rpm, while a 76.2 mm (3 in.) diameter cutter must rotate at only 64 rpm. Therefore to prevent cutter damage, the milling machine operator must know to calculate or select the correct rpm for a cutter of any size to run at any cutting speed. Cutting Speed Selection There is no exact cutting speed for milling any single type of material. It is common practice to start an average cutting speed which is then increased or decreased according to the results produced. One of the most important factors determining cutting speeds is the machinability of the metal. Machinability refers to the ease with which the metal may be machined.
The following Factors effect cutting speeds (and also feeds) selected for milling operations:
1. The hardness of the material being cut.
2 The depth of the cut.
3. The material from which the cutter is made.
4. The shape, size, and construction of the job being machined.
5. Rigidity and condition of the machine and cutter.
6. The power available, machine and its drive.
7. The quality of the finish specified.
8. The amount of feed.
9. The nature of operation.
10. The use of coolant, the type of coolant, and its efficiency.