Basic Machining Operations and Cutting
Technology
Basic Machining Operations
China CNC machining Machine tools have evolved from the early foot-powered lathes of the
Egyptians and John Wilkinson's boring mill. They are designed to provide rigid
support for both the workpiece and the cutting tool and can precisely control
their relative positions and the velocity of the tool with respect to the
workpiece. Basically, in metal cutting, a sharpened wedge-shaped tool removes a
rather narrow strip of metal from the surface of a ductile workpiece in the
form of a severely deformed chip. The chip is a waste product that is
considerably shorter than the workpiece from which it came but with a
corresponding increase in thickness of the uncut chip. The geometrical shape of
workpiece depends on the shape of the tool and its path during the machining
operation.
Most machining operations produce parts of differing geometry. If a
rough cylindrical workpiece revolves about a central axis and the tool
penetrates beneath its surface and travels parallel to the center of rotation, China CNC machining a surface of revolution is produced, and the operation is called turning. If a
hollow tube is machined on the inside in a similar manner, the operation is
called boring. Producing an external conical surface uniformly varying diameter
is called taper turning, if the tool point travels in a path of varying radius,
a contoured surface like that of a bowling pin can be produced; or, if the
piece is short enough and the support is sufficiently rigid, a contoured surface
could be produced by feeding a shaped tool normal to the axis of rotation.
Short tapered or cylindrical surfaces could also be contour formed.
Flat or plane
surfaces are frequently required. They can be generated by radial turning or
facing, in which the tool point moves normal to the axis of rotation. In other
cases, it is more convenient to hold the workpiece steady and reciprocate the
tool across it in a series of straight-line cuts with a crosswise feed
increment before each cutting stroke. This operation is called planning and is
carried out on a shaper. For larger pieces it is easier to keep the tool
stationary and draw the workpiece under it as in planning. The tool is fed at
each reciprocation. Contoured surfaces can be produced by using shaped
tools.
Multiple-edged tools can also be used.
Drilling uses a twin-edged fluted tool for holes with depths up to 5 to 10
times the drill diameter. Whether the
drill turns or the workpiece rotates, relative motion between the
cutting edge and the workpiece is the important factor. In milling operations a
rotary cutter with a number of cutting edges engages the workpiece. Which moves
slowly with respect to the cutter. Plane or contoured surfaces may be produced,
depending on the geometry of the cutter and the type of feed. Horizontal or
vertical axes of rotation may be used, and the feed of the workpiece may be in
any of the three coordinate directions.
Basic Machine Tools
Machine tools are used to produce a part of a specified geometrical shape
and precise I size by removing metal from a ductile material in the form of
chips. The latter are a waste product and vary from long continuous ribbons of
a ductile material such as steel, which are undesirable from a disposal point
of view, to easily handled well-broken chips resulting from cast iron. Machine
tools perform five basic metal-removal processes: I turning, planning,
drilling, milling, and grinding. All other metal-removal processes are
modifications of these five basic processes. For example, boring is internal
turning; reaming, tapping, and counter boring modify drilled holes and are
related to drilling; bobbing and gear cutting are fundamentally milling
operations; hack sawing and broaching are a form of planning and honing;
lapping, super finishing. Polishing and buffing are variants of grinding or
abrasive removal operations. Therefore, there are only four types of basic
machine tools, which use cutting tools of specific controllable geometry: 1.
lathes, 2. planers, 3. drilling machines, and 4. milling machines. The grinding
process forms chips, but the geometry of the abrasive grain is
uncontrollable.
The amount and rate of
material removed by the various machining processes may be I large, as in heavy
turning operations, or extremely small, China CNC machining as in lapping or super finishing
operations where only the high spots of a surface are removed. A machine tool performs three major
functions: 1. it rigidly supports the workpiece or its holder and the cutting
tool; 2. it provides relative motion between the workpiece and the cutting
tool; 3. it provides a range of feeds and speeds usually ranging from 4 to 32
choices in each case.
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