Information Technology Reference
In-Depth Information
3.3 Cutting conditions
Properly selection of cutting tools and cutting conditions such as cutting speed, feed, and
depth of cut is of great importance in the success of any machining operation. When SPM is
in use, due to the stability requirements of the production process in order to produce high
quantities of the product, appropriate cutting tools and cutting conditions should be
employed. As frequent tool changes influence the productivity of the machine tool, it is
suggested to employ long lasting hard material cutting tools made from tungsten carbides
and ceramics for high production rates. These tool materials provide longer tool lives and
higher production rates. Other important considerations in the selection of cutting tools are
the shape and geometry of the tool. Cutting tools are generally divided into standard and
special groups. By use of specially designed cutting tools sometimes it is possible to
combine different machining operations in a single operation.
3.4 Setup and clamping
Machining jigs and fixtures are frequently used to increase the speed and quality of
production and to reduce production times and required skill level of machinists.
Uniformity of production due to use of jigs and fixtures has an important effect on
production quality. Accordingly, properly design and application of jigs and fixtures is very
important in SPM utilization. Fixtures used in SPMs are complex as normally a number of
machining operations are performed in a single part setup. Fixtures should be designed
such that (a) there is adequate tool access to the workpiece in all work stations; (b) the part is
easily, quickly, and accurately positioned inside the fixture, and removed from it, and (c) the
fixture is rigid enough to withstand large cutting forces applied by multiple cutting tools
working on the part simultaneously. In locating the part in the fixture, the most difficult and
accurate operation should be considered first in order to achieve the best result. Because
there are different machining operations, locating surfaces need to be machined accurately
before the workpiece is placed in the fixture. Appropriate measures should be taken for free
flow of coolant and chip removal from the fixture.
3.5 Machining and sliding units
As described in the previous sections, machining and sliding units are the most important
components of SPMs that make the cutting tool capable of rotational and linear motions
necessary for cutting. Consequently, the selection of machining units, sliding units and
accessories should be accomplished such that following three conditions are met.
1.
Previously determined cutting tools are capable of performing all rotational and linear
motions necessary for performing corresponding machining operations.
2.
Proper cutting conditions such as spindle speed, feed, and depth of cut are provided.
3.
Required machining power is provided.
In is important to note that selection of machining and sliding units should always be
accomplished after selection of cutting tools and cutting conditions. This is due to the fact
that cutting tools' geometry and cutting conditions dictate required powers, velocities, and
motions of machining and sliding units.
