CNC machining | Unisign Machine Tools

CNC machining
What methods are there?

What is CNC machining?
In short: shaping a metal product by cutting away material in a controlled manner. There are various techniques for this cutting, such as milling, boring, reaming and tapping. In this article we explain each machining technique. We also describe the different tools that you can use and indicate for each tool what requirements it places on a CNC machine. Or in other words, the pros and cons of using it.

Milling

Milling is a machining operation in which you remove material from the product with a rotating tool, the cutter. This way you can mill a slot, profile or corner or mill a product nice and flat/smooth.

Milling a slot

Do you want to mill a slot? Then you can choose from several tools. The choice is determined by a number of factors: such as the depth and width and whether it is an open or closed slot. We compare two tools: the disc mill and end mill.

Disc mill

Suitable for open slots.
Suitable for deep and narrow slots.
Poor chip removal – the chip chambers fill up.
High torque and low speed.
High power and high stability.
Low costs – the inserts have multiple usable cutting edges.
The teeth must remain in contact with the material to limit unwanted vibrations.

End mill

Suitable for open and closed slots.
Unsuitable for deep and narrow slots. Only suitable for shallow slots due to limited tool length.
Good chip removal.
Low torque and high speed.
Low power.
Stability – sensitive to high forces and vibration at large tool lengths.
High costs – entire tool replacement due to complete wear and tear.
When resharpening tools, the diameter becomes smaller.

Profile milling

Profile milling is used to create complex 3D shapes in workpieces. Or to achieve smooth surface finishes of these complex shapes. Profile milling is highly suitable for making parts such as moulds.

Suitable for complex shapes.
Suitable for light machining.
Suitable for long-term operations – it does require high machine dynamics.
Good chip removal.
Low torque and high speed.
Low power.
Low stability is required.
Low costs. The inserts have multiple usable cutting edges.
Maintaining a constant material contact and chip thickness. This results in little changes in workload.

Face milling (45°)

Face milling is used when a large amount of material should be removed simultaneously over a flat surface and the productivity of the machine should be increased. For this purpose, face milling cutters are generally used with an entering angle of 45° in order to reduce the required machine power.

Suitable for making surfaces smooth and even.
Good chip removal.
High torque and low speed.
Average power.
Good stability.
High productivity due to the chip thinning effect.
Low costs. The inserts have 4 usable cutting edges.
Cutting edges must remain in contact with the material to limit unwanted vibrations.
Balanced cutting forces due to axial stiffness of the machine. This reduces radial forces on the tool.
Reduces vibrations with long overhangs and weak configurations.

Shoulder milling (90°)

You use a corner mill to machine corners and low edges (often together with the surface). Are there high edges? Then you use a shoulder cutter. This has multiple layers of inserts.

Suitable for working on corners and low edges. Use a shoulder milling cutter for high edges.
Good chip removal.
High torque and low speed.
Average power.
Poor stability and low productivity.
High cost. Relatively high tool costs. The inserts have only 2 usable cutting edges.
Teeth must remain in contact with the material to limit unwanted vibrations.
Reduce the cutting speed at higher cutting depths to prevent unwanted vibrations.
Low axial force on the workpiece: therefore suitable for thin-walled products.
High radial forces on the workpiece.
Provides a relatively large depth of cut in relation to the insert size.

High feed milling (10°)

High feed milling is machining with a cutter with a small depth of cut and a high feed rate. This machining method maximizes material removal speed and productivity. The technique requires not only a robust and stable tool but also a correct selection of cutting parameters. This is essential to ensure efficient material removal. Naturally, the surface finish and tool life are preserved.

Suitable for quickly removing material.
Good chip removal.
Low torque and high speed.
Low power.
High stability. Requires a stiff and stable machine to absorb higher cutting forces.
High productivity with small depth of cut.
Low costs. The inserts have 4 usable cutting edges.
Cutting forces are absorbed axially in the spindle direction and stabilize the spindle.
Often requires high spindle speeds to handle high feeds and maintain productivity.
The machine must support high feed rates for efficient material removal.

Reaming or boring

Reaming and boring are machining techniques in which existing holes and bores are finished in terms of their dimensions, position and accuracy.

Reaming

Reaming is used to refine the dimensions of a hole. You do this after a hole has already been made. It ensures accurate sizing and a better finish. Reamers have cutting edges in specific locations. They use this to machine the hole and achieve the desired dimensions. However, reaming does not allow you to adjust the position of the hole because the reamer follows the hole already made.

Suitable for enlarging existing holes or reworking. Especially with serial production.
Poor chip removal.
High torque and high power required at low speed.
Low speed and high power.
Good stability.
High productivity.
High costs because the entire tool must be replaced.
Reamer has a fixed diameter and is not adjustable.
Stable because many cutting edges are engaged.
Hole gets smooth surface.

Boring

It is common practice to bore a hole when the diameter, roundness, position or finish of the hole are important. You will be boring existing holes to enlarge them, improve the shape, adjust the position or correct the roundness and straightness.

Suitable for enlarging existing holes or reworking. Especially for single pieces.
Good chip removal.
Low torque and high speed.
Low power.
Good stability.
Low productivity.
High costs due to high wear associated with single cutting edge.
Diameter is adjustable.
Is sensitive to inaccuracies.
Hole gets smooth surface.

Threading

To make screw thread, you can choose from three techniques.

Rolling tap

With a rolling tap you use a rolling process. You get a smooth thread without burrs or chips. This keeps the threaded hole free of chips. The material is pushed away instead of chipped. You use a rolling tap when higher quality and accuracy of the screw thread is required. The result is a stronger thread with better fit and finish.
If you use a roller tap in thin-walled material, this can result in deformation of the workpiece. The material that is pushed away can cause a dent on the outside of the workpiece.

Suitable for making smooth threads without burrs/chips.
Good chip removal.
High torque and high speed.
High power and good stability.
High productivity.
High cost. The entire tool must be replaced.
Longer life span / tool life.
Stronger thread.
Flanks get a better surface quality.
Deeper tapping of blind holes possible.

Cutting tap

A cutting tap uses cutting edges to cut the thread. The tap cuts away the material to create the thread. The disadvantage of this is that the chips that are released contaminate the threaded hole. You use a cutting tap for applications where the quality of the screw thread is less important.

Suitable for making screw threads where quality is less important.
Poor chip removal; chips contaminate the threaded hole.
Low torque.
Low rotational speed and therefore lower speed.
High power and good stability.
Low productivity.
High cost. The entire tool must be replaced.

Thread milling

With this method you create threads via a milling operation. You need a CNC machine that can make a spiral movement. The tool rotates and follows a circular path while simultaneously moving in the axial direction.

Suitable for making screw threads. Only with a CNC machine that can make a spiral movement.
Good chip removal due to short chips.
Low torque and high speed.
Low power and low stability.
Low productivity. It is a slow and therefore less economical processing strategy.
Low costs. The inserts are replaceable.
No tap outlet, so blind holes can be tapped all the way to the bottom.
Poorer surface quality and less precise threading.

This article provides insight into the various machining methods, their applications and considerations when selecting the most suitable method and tool. We also looked at the requirements that the tools place on a CNC machine.

CNC machining What methods are there?