Milling - Principles

In principle, milling is a mechanical manufacturing process involving cutting (material removal), with the coordinated rotational movement of a multi-edged tool (cutting movement) and the rectilinear feed of a workpiece (feed movement). Today, however, there is also a movement of the tool relative to the workpiece, which can take place in virtually any direction. The milling tool, the cutter, has several cutting edges, each of which removes a certain amount of metal in the form of chips. The advantages of milling are high yield, good surface finish and high precision, as well as great flexibility in generating different shapes. Milling is most often used to produce flat surfaces, shoulders and grooves, but its effectiveness in contouring is growing with the use of CNC (Computerized Numerical Control) techniques.

Milling is becoming an increasingly universal machining method, with an ever wider range of machines, control systems and cutting tools. Machining centers, for example, make extensive use of milling, and therefore require a wide variety of tools. Milling is therefore carried out on different types of machine, ranging from conventional milling machines, whose design dates back to the beginning of the century, to sophisticated multi-axis CNC machines.

As we shall see, milling not only enables a wide variety of operations to be carried out, but also involves many different types of machine, tools and workpieces. It is largely influenced by the condition of the equipment used and of the part being machined, and requires the operator to have a thorough knowledge of the various existing limitations.

The choice of milling operation and tool is made on the basis of the part drawing and production requirements. Conventional methods must always be called into question, given the new perspectives opened up by milling developments over the years.

The type of machining involved must therefore be studied in order to determine how best to carry it out, thus saving time and improving the quality of the result. It is also important to consider whether a single or multiple operation is required.

Once it has been decided that a part is to be machined by milling, the next step is to select the appropriate machine: horizontal, vertical, universal, gantry, CNC or machining center - in other words, the best solution for the operation in question. Once a good match has been found between the machining parameters and the capabilities of the chosen machine, various factors need to be determined, such as stability, precision and the desired surface finish. Instability is the main threat in metal-cutting machining, not only in terms of the quality of the results obtained, but also in terms of tool life and performance,...