Milling Processes

Question 1

Define the milling process

Answer 1

Milling is performed with a rotating, single or multi-edged cutting tool which performs programmed feed movements against a workpiece in almost any directions.

Milling is most applied to generate flat faces, but there are increasing demands to produce other forms including complex 3D surfaces.

Question 2

Define Climb Milling

Answer 2

Each tooth engages the material at a definite point, and the width of the cut starts at the maximum and decreases to zero.

The chips are disposed behind the cutter, leading to easier swarf removal.

The tooth does not rub on the material, and so tool life may be longer. However, climb milling can apply larger loads to the machine, and so is not recommended for older milling machines or machines which are not in good condition. This type of milling is used predominantly on mills with a backlash eliminator

Question 3

Define Conventional Milling

Answer 3

The chip thickness starts at zero thickness and increases up to the maximum.

The cut is so light at the beginning that the tool does not cut, but slides across the surface of the material until sufficient pressure is built up and the tooth suddenly bites and begins to cut.

This deforms the material work hardening it and dulling the tool. The sliding and biting behavior leave a poor finish on the material.

Question 4

Define the following equation components and identify the units they are measured in. 
Surface cutting speed: 
Spindle speed:
Feed per tooth:
Feed rate:
The depth of Cut:

Answer 4

Surface cutting speed:
This is the speed at which each tooth cuts through the material as the tool rotates. This is measured in metres per minute, m/min.

Typical values for cutting speed are:
10 m/min to 60 m/min for some steels
100 m/min and 600 m/min for aluminum.

Spindle speed:
This is the rotational speed of the tool, and is measured in revolutions per minute (RPM).

Typical values are from hundreds of RPM, up to tens of thousands of RPM.

Feed per tooth:
This is the distance the material is fed into the cutter as each tooth rotates. This value is the size of the deepest cut the tooth will make.

Feed rate:
This is the speed at which the material is fed into the cutter. Typical values are from 20 mm/min to 10,000 mm/min.

The depth of Cut:
This is how deep the tool is under the surface of the material being cut.

This will be the height of the chip produced. Typically, the depth of cut will be less than or equal to the diameter of the cutting tool.

Question 5

Explain how to calculate Surface cutting speed.

Answer 5

Multiply:
PI x Tool Diamater x Spindle speed = (mm/min)
PI x Tool Diamater x Spindle speed / 1000 = (m/min)

Question 6

Explain how to calculate the Cutting feed rate.

Answer 6

Multiply:
The number of cutting edges x Feed rate per cuttign edge x Spindle speed

= Feedrate (mm/min)

Question 7

Explain the material removal rate, the units it uses and how it is calculated.

Answer 7

Definition: The volume of material removed per minute.
Multiply:
Feed rate x Depth of Cut x Width of Cut = (mm^3/min)

Question 8

Explain how to calculate the Material unit power factor and the units it uses.

Answer 8

Definition: The unit power factor is the amount fo power to machine 1 mm^3 of material per second.
Multiply:

Unit Power factor x Material Removal rate = (N-M/min)
Unit Power factors x Material Removal rate / 60 = (Watts)