Milling - Definition, Meaning and different types

What is Milling? Technology quickly explained

Milling ist a manufacturing process in which material is removed in form of chips with the aid of a milling cutter. Unlike other manufacturing processes, milling can only be performed by a machine. CNC milling means that the axes are additionally controlled by a computer. But what do you have to consider when milling? We explain the various milling processes and technical terms and tell you what you need to pay attention to when milling.


MillingMilling

No milling without end mill

The end mill is the tool that is used to remove material. It is therefore of central importance. End mills are available in a wide variety of forms and can possess different cutting edges. They are selected depending on the respective material and application. While a single-flute end mill is the perfect choice when working with plastic, a V-Groove or engraving bit should be used for engraving jobs. On Router Bit Wood we have compiled all information on tools for wood milling. For all other end mills, please see our general overview.

Different Milling Processes

There are many different ways of milling a workpiece. The machining process differs in the design of the milling tool, the surface to be produced and the feed motion. According to DIN 8589, the individual milling processes are divided into face milling, circular milling, helical milling, hobbing, profile milling and form milling.

Face milling

Face milling

Face milling is used to produce flat surfaces. Perfect for this job are face milling cutters with indexable knives in the milling head. The feed motion is straight.

In short:

  • For producing flat surfaces
  • Straight feed motion
Circular milling

Circular milling

Circular milling serves to create circular cylindrical surfaces. It is used to produce inside and outside contours, such as pins and holes. The feed motion is circular.

In short:

  • For producing circular cylindrical surfaces
  • Circular feed motion
Helical milling

Helical milling

Helical milling is a manufacturing process used to produce helical surfaces, such as threads, spindles or cylindrical screws. The feed motion is helical.

In short:

  • For producing helical surfaces
  • Helical feed motion
Hobbing

Hobbing

Hobbing serves to create gear teeth, such as gear wheels. For this purpose, a hob is hobbed against the workpiece in a simultaneous feed and hobbing motion.

In short:

  • For producing gear teeth
  • Simultaneous feed and hobbing motion
Profile milling

Profile milling

In profile milling, the contour of the profile cutter is transferred to the workpiece, for example in slot milling. Straight, circular and other feed motions are possible.

In short:

  • For producing profiles
  • Straight, circular and other feed motions
Form milling

Form milling

Form milling is used to create workpieces with arbitrary planar or spatial surfaces. In this way, any three-dimensional shapes can be created.

In short:

  • For producing three-dimensional shapes

Climb milling vs. conventional milling

When it comes to milling, a basic distinction is made between two cutting directions, climb milling and conventional milling. Which direction is best suited for milling a CNC project depends on the CNC machine used and the material to be machined.


Climb milling

Climb milling

If the cutting edge of an end mill is to the right of the cutter's center, seen in milling direction, it is called climb milling. It is the most frequently used cutting direction. Climb milling is especially suited for machining harder materials and for CNC machines with backlash-free ball bearing guides.

*Figure shows view from above of the vertically positioned end mill

Conventional milling

Conventional milling

If the cutting edge of an end mill is to the left of the cutter's center, seen in milling direction, it is called conventional milling. It is especially suited for machining softer materials, such as foam, as well as with CNC machines with backlash in the threaded lead screws and without ball bearing guides.

*Figure shows view from above of the vertically positioned end mill

Which materials can be milled?

There are almost no limits to creativity when it comes to milling. From silver jewelry to wooden toys to shadowboards, a milling machine can be used to produce many different DIY projects from a wide variety of materials. Depending on the material and the project, the respective parameters have to be adjusted individually. With the free STEPCRAFT cutting data calculator from the App Store and Playstore, this can be done very quickly. Simply select the material, the cutter and the machine and the app calculates the appropriate cutting data for you.

Wood

Wood

  • Softwood
  • Hard wood
  • MDF
  • Multiplex
  • etc.
Non-ferrous metal

Non-ferrous metal

  • Aluminum
  • Brass
  • Silver
  • Gold
  • etc.
Plastic

Plastic

  • Acrylic
  • Plexiglas®
  • Foam
  • POM
  • etc.
Carbon

... and more

  • Carbon
  • Composites

Milling parameter and formulas

In order to achieve optimal milling results, the correct milling parameters are crucial. Thus, it is important to set the appropriate values for the cutting speed, the speed rate, the cutting depth and the feed rate. This not only produces smooth cuts and a clean surface, it also increases the tool life. The following parameters are important for calculating the values:

n = Speed rate in revolutions per minute (rpm)

vc= Cutting speed (m/min)

d = Tool diameter in millimeters (mm)

z = Number of teeth

ƒz = Tooth feed (mm/tooth)

vƒ = Feed rate (mm/min)


Cutting speed

Cutting speed

Cutting speed is the speed at which a cutting edge removes material. The cutting speed depends on the speed rate and the diameter of the end mill and is usually given in meters per minute.

vc = π * d * n * 1 m/1000 mm

Speed rate

Speed rate

The term speed rate describes the number of revolutions that an end mill makes within one minute. The speed rate depends on the cutting speed and the diameter of the respective end mill.

n = vc/ (d * π)

Cutting depth

Cutting depth

Cutting depth or immersion depth describes the depth at which the tool plunges into the workpiece. The value determines how much material is removed in one pass. The optimum cutting depth depends on the respective workpiece material and the milling cutter used.

Feed rate

Feed rate

The feed rate is the speed at which the milling cutter is moved through the material in feed direction. The lower the feed rate, the finer the surface, but also the longer the machining time. With milling, the feed rate depends on the speed rate and the number of teeth.

vƒ = n * ƒz * z

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