CNC Milling

Concepts of Milling

Precision Milling is the machining process of using rotary cutters to remove swarfs and stock material from a workpiece advancing (or feeding) in a direction at an angle with the axis of the tool.

Precision Milling is a cutting process that uses a milling cutter to remove material from the surface of a workpiece. The milling cutter is a rotary cutting tool, often with multiple cutting points. As opposed to drilling and other simple machining processes, where the tool is advanced along its rotation axis, the cutter in Milling is usually moved perpendicular to its axis so that cutting occurs on the circumference of the cutter. As the milling cutter enters the workpiece, the cutting edges (flutes or teeth) of the tool repeatedly cut into and exit from the material, shaving off chips (swarf) from the workpiece with each pass.

The milling process removes material by performing many separate, small cuts. This is accomplished by using a cutter with many teeth, spinning the cutter at high speed. A sufficient stock material is useful for finishing parts to precise sizes and shapes and flat surface,and to maintain the tolerances specified and the surface roughness parameters.

• Milling Cutter
  • End mills are those tools which have cutting teeth at one end, as well as on the sides. The words end mill are generally used to refer to flat bottomed cutters.
  • Roughing end mills quickly remove large amounts of material. This kind of end mill utilizes a wavy tooth form cut on the periphery. These wavy teeth form many successive cutting edges producing many small chips, resulting in a relatively rough surface finish. During cutting, multiple teeth are in contact with the workpiece reducing chatter and vibration. Rapid stock removal with heavy milling cuts is sometimes called hogging. Roughing end mills are also sometimes known as ripping cutters.
• Roughing end mills quickly remove large amounts of material. This kind of end mill utilizes a wavy tooth form cut on the periphery. These wavy teeth form many successive cutting edges producing many small chips, resulting in a relatively rough surface finish.
• Ball nose cutters are similar to slot drills, but the end of the cutters are hemispherical. They are used to add a radius between perpendicular faces to reduce stress concentrations.
• Special Milling cutters come in several shapes and many sizes: cylindrical cutters, eyptical cutters and drills to performe milling operations.

Precision Milling Types

Precision Milling types are:

• Shoulder face milling
• Face milling
• Profile Miling
• Slot milling
• Holes and cavities

Shoulder Milling

Shoulder Milling generates two faces simultaneously, which requires peripheral milling in combination with face milling. Achieving a true, ninety degree shoulder, is one of the most important requirements. Shoulder milling can be performed by traditional square shoulder cutters, and also by using end milling cutters, long edge cutters and side and face milling cutters. Due to these numerous options, it is essential to consider the operational requirements carefully to make an optimal choice.

Face Milling

Face Milling is the most common milling operation and can be performed using a wide range of different tools. Cutters with a 45º entering angle are most frequently used, but round insert cutters, square shoulder cutters and side and face mills are also used for certain conditions.

Profile Milling

Profile Milling covers Multi-axis Milling of convex and concave shapes in two and three dimensions.

The larger the component and the more complicated the configuration to machine, the more important the process planning becomes.

The machining process should be divided into at least three operation types:

• Roughing/semi-roughing
• Semi-finishing
• Finishing.

Super-finishing, often performed using high-speed machining techniques, is sometimes required. Milling of remaining stock, so called rest milling, is included in semi-finishing and finishing operations.

For best accuracy and productivity it is recommended to perform roughing and finishing in separate machines, and to use dedicated cutting tools for each operation.

The finishing operation should be carried out in a 4/5-axis machine tool with advanced software and programming techniques. This can considerably reduce, or even completely eliminate, time consuming manual completion work. The final result will be a product with better geometrical accuracy and a higher surface structure quality.

Side and face milling cutters

Side and face milling cutters can handle long, deep, open slots in a more efficient manner, and provide the best stability and productivity for this type of milling. They can also be built into a “gang” to machine more than one surface in the same plane at the same time.

End Milling

End milling is selected for shorter, shallower slots, especially closed grooves and pockets, and for milling key-ways.
End mills are the only tools that can mill closed slots that are:

• Straight, curved or angled
• Wider than tool diameter, designated pockets.

Heavier slotting operations are often performed using long edge milling cutters.

Milling machining can be done with a wide range of Milling cutters on Machine Tools known as Milling Machines and Boring-and Milling machines.

Milling machines evolved into Machining Centers,  4- or more axis Milling Machines.