In single point cutting of
metals
A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typical ...
, a built up edge (BUE) is an accumulation of material against the rake face, that seizes to the tool tip, separating it from the chip.
[The Open University (UK), 2001. T881 Manufacture Materials Design: Block 2: Cutting, page 14. Milton Keynes: The Open University.]
Formation
Because
shear
Shear may refer to:
Textile production
*Animal shearing, the collection of wool from various species
**Sheep shearing
*The removal of nap during wool cloth production
Science and technology Engineering
*Shear strength (soil), the shear strength ...
is strongest at the initial contact surface with the cutting tool, the first layer of metal impacting and seizing on it work-hardens more than the rest of the volume of metal. As a consequence of this
work hardening
In materials science, work hardening, also known as strain hardening, is the strengthening of a metal or polymer by plastic deformation. Work hardening may be desirable, undesirable, or inconsequential, depending on the context.
This strengt ...
, this first layer of
metal
A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...
is stronger than the adjacent metal moving away from the workpiece. Effectively, said first layer becomes part of the tool. The process repeats itself and, after some time, a built up edge (which could be several hundred
micrometres
The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Unit ...
thick) forms.
The conditions necessary for a noticeable edge to build up are that:
* the cutting speed is low.
[The Open University (UK), 2001. T881 Manufacture Materials Design: Block 2: Cutting, page 14 and 15. Milton Keynes: The Open University.] This is because at high cutting speeds the metal moving away from the workpiece becomes hot enough to
recover before seizing onto the tool, preventing the formation of a BUE.
[The Open University (UK), 2001. T881 Manufacture Materials Design: Block 2: Cutting, page 15. Milton Keynes: The Open University.]
* the metal being cut is one that work-hardens and is reluctant to recover.
A BUE will not form with pure metals since they do not work-harden much. Conversely,
alloy
An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductilit ...
s, such as
steel, do work-harden and recover less so they are prone to forming a BUE.
Effects on the cutting process
The built up edge effectively changes tool geometry and rake steepness. It also reduces the contact area between the chip and the cutting tool,
leading to:
* A reduction in the power demand of the cutting operation.
* Slight increase in tool life, since the cutting is partly being done by the built up edge rather than the tool itself.
However, the formation of BUEs have negative effects on the quality of the workpiece,
specifically:
* Excessive work hardening at the surface of the workpiece.
* Poor
surface finish, since bits of the BUE eventually break off and stick to the workpiece. These bits tend to be problematic since, due to the work-hardening they underwent, they are very
hard
Hard may refer to:
* Hardness, resistance of physical materials to deformation or fracture
* Hard water, water with high mineral content
Arts and entertainment
* ''Hard'' (TV series), a French TV series
* Hard (band), a Hungarian hard rock supe ...
and so become
abrasive
An abrasive is a material, often a mineral, that is used to shape or finish a workpiece through rubbing which leads to part of the workpiece being worn away by friction. While finishing a material often means polishing it to gain a smooth, reflec ...
.
* A reduction in the dimensional control of the process, due to the dynamically changing geometry of the cutting tool.
See also
*
Metalworking
Metalworking is the process of shaping and reshaping metals to create useful objects, parts, assemblies, and large scale structures. As a term it covers a wide and diverse range of processes, skills, and tools for producing objects on every scal ...
*
Machinability Machinability is the ease with which a metal can be cut (machined) permitting the removal of the material with a satisfactory finish at low cost.Degarmo, p. 542. Materials with good machinability (free machining materials) require little power to c ...
References
{{DEFAULTSORT:Built Up Edge
Metalworking terminology