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Chip formation is part of the process of cutting materials by mechanical means, using tools such as
three chip types
are the original characterisation, by Dr. Norman Franz. The type of chip that forms depends on many factors, of both tool and material. In general, main factors are the angle formed by the edge faces of the tool and also the angle at which this is presented to the surface. Sharpness of the cutting tool does not usually define the ''type'' of chip, but rather the ''quality'' of the chip, and the clear distinctions between types. A blunt tool produces a degenerate chip that is large, torn and varies from one means of formation to another, often leaving behind a poor quality surface where this means changes.
Type I chips form when a material splits ''ahead'' of the cutting edge, owing to some upwards wedge action of the tool exceeding the ''tensile'' strength of the material, perpendicular to the surface. They are thus particularly important in fibrous materials, such as wood, where individual fibres are strong but they may be levered apart relatively easily. Type I chips generally form in cutting by tools with shallow cutting angles.
Type I chips may form long, continuous
Type II chips form when a shearing force is produced by the wedge of the tool angle. The material fails along a short angled plane, from the apex of the tool edge, diagonally upwards and forwards to the surface. The material deforms along this line, forming an upward curling chip. These chips generally form from intermediate cutting angles.
Type II chips may form in ductile materials, such as metals.
Type II chips may also form long, continuous
Type III chips form a compression failure of the material, ahead of a relatively obtuse cutting angle, approaching 90°. In some weak or non-ductile materials this may form an acceptable chip, usually as a fine dust, but often it gives rise instead to a random "snowplough" effect where the waste material is bunched up ahead of the tool but not cleared decisively away as a well-formed chip.
This type of chip is formed by routers. It is also formed by woodworking scrapers, although when properly sharpened and used, these form such a thin Type III chip that it instead appears as a well-formed Type II chip. Their waste chip is thin enough that the compression failure volume is small enough to act as for the well-defined shear plane of the Type II.
saw
A saw is a tool consisting of a tough blade, Wire saw, wire, or Chainsaw, chain with a hard toothed edge used to cut through material. Various terms are used to describe toothed and abrasive saws.
Saws began as serrated materials, and when man ...
s, lathe
A lathe () is a machine tool that rotates a workpiece about an axis of rotation to perform various operations such as cutting, sanding, knurling, drilling, deformation, facing, threading and turning, with tools that are applied to the w ...
s and milling
Milling may refer to:
* Milling (minting), forming narrow ridges around the edge of a coin
* Milling (grinding), breaking solid materials into smaller pieces by grinding, crushing, or cutting in a mill
* Milling (machining), a process of using ro ...
cutters.
The formal study of chip formation was encouraged around World War II
World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...
and shortly afterwards, with increases in the use of faster and more powerful cutting machines, particularly for metal cutting with the new high speed steel
High-speed steel (HSS or HS) is a subset of tool steels, commonly used as cutting tool material.
Compared to high-carbon steel tools, high-speed steels can withstand higher temperatures without losing their temper (hardness), allowing use of f ...
cutters. Pioneering work in this field was carried out by Kivima (1952) and Franz (1958).
Chip formation is usually described according to a three-way model developed by Franz. This model is best known within the field of machine tool design, although it is also used when an application area, such as woodworking
Woodworking is the skill of making items from wood, and includes cabinetry, furniture making, wood carving, joinery, carpentry, and woodturning.
History
Along with stone, clay and animal parts, wood was one of the first materials worked b ...
, requires a vocabulary to describe chip formation in more detail than is usually attempted.
Chip classification
The firsthree chip types
are the original characterisation, by Dr. Norman Franz. The type of chip that forms depends on many factors, of both tool and material. In general, main factors are the angle formed by the edge faces of the tool and also the angle at which this is presented to the surface. Sharpness of the cutting tool does not usually define the ''type'' of chip, but rather the ''quality'' of the chip, and the clear distinctions between types. A blunt tool produces a degenerate chip that is large, torn and varies from one means of formation to another, often leaving behind a poor quality surface where this means changes.
Type I chip
Type I chips form when a material splits ''ahead'' of the cutting edge, owing to some upwards wedge action of the tool exceeding the ''tensile'' strength of the material, perpendicular to the surface. They are thus particularly important in fibrous materials, such as wood, where individual fibres are strong but they may be levered apart relatively easily. Type I chips generally form in cutting by tools with shallow cutting angles.
Type I chips may form long, continuous swarf
Swarf, also known as chips or by other process-specific names (such as turnings, filings, or shavings), are pieces of metal, wood, or plastic that are the debris or waste resulting from machining, woodworking, or similar subtractive (material-r ...
, limited in size only by the length of cut.
This is the idealised chip formation for wood shaving
A hand plane is a tool for shaping wood using muscle power to force the cutting blade over the wood surface. Some rotary power planers are motorized power tools used for the same types of larger tasks, but are unsuitable for fine-scale planing, ...
s, particularly those produced by a well-tuned plane with a finely adjusted mouth.
Type II chip
Type II chips form when a shearing force is produced by the wedge of the tool angle. The material fails along a short angled plane, from the apex of the tool edge, diagonally upwards and forwards to the surface. The material deforms along this line, forming an upward curling chip. These chips generally form from intermediate cutting angles.
Type II chips may form in ductile materials, such as metals.
Type II chips may also form long, continuous swarf
Swarf, also known as chips or by other process-specific names (such as turnings, filings, or shavings), are pieces of metal, wood, or plastic that are the debris or waste resulting from machining, woodworking, or similar subtractive (material-r ...
.
Type III chip
Type III chips form a compression failure of the material, ahead of a relatively obtuse cutting angle, approaching 90°. In some weak or non-ductile materials this may form an acceptable chip, usually as a fine dust, but often it gives rise instead to a random "snowplough" effect where the waste material is bunched up ahead of the tool but not cleared decisively away as a well-formed chip.
This type of chip is formed by routers. It is also formed by woodworking scrapers, although when properly sharpened and used, these form such a thin Type III chip that it instead appears as a well-formed Type II chip. Their waste chip is thin enough that the compression failure volume is small enough to act as for the well-defined shear plane of the Type II.
Type 0 chip
This type was characterised later, by William McKenzie (1960).References
{{Woodworking Cutting tools Cutting processes Woodworking Metalworking