Machining centres
A further development in the automation of machine
tools is the "machining centre," usually a
vertical milling machine fitted with automatic
tool-changing facilities and capable of several axes of
control. The tools, of which there can be more than 100,
are generally housed in a rotary magazine and may be
changed by commands from the machine tool program. Thus,
different faces of a workpiece can be machined by a
combination of operations without moving it to another
machine tool. Machining centres are particularly
suitable for the batch production of large and complex
components requiring a high degree of accuracy.
Computer-aided design and computer-aided
manufacturing (CAD/CAM)
The technology of CNC machine tools has been enhanced
by parallel advances in CAD/CAM. In the first NC
systems, CAD and CAM were regarded as separate
functions. Gradually they have come to be treated as an
integrated operation, with manufacturing processes being
considered at the product design stage.
CAD enables designers to use computers to analyze and
manipulate design data. Using a graphics workstation or computer
terminal to display three-dimensional figures, the
designer can examine a proposed design from different
angles, in various cross sections, and in many sizes.
Details of the completed design are transferred to a
second terminal on which a set of engineering drawings
can be produced. All aspects of the design are closely
scrutinized at this stage, and, after final changes are
made, the finished, fully dimensioned design is drawn on
a specialized computer printer called a plotter.
CAD/CAM systems also allow design data to be stored
in numerical (digitized) form, from which
machine-control tapes and disks may be prepared
directly. The CAD and CAM systems may then be linked by computer-assisted
part programming. With this technique a CAD system can
produce a geometrical profile of a required component
as, for example, a series of connected points. The
position of each point, and the ways in which it can be
reached by movements of the tool, is fed to the computer.
After calculating the necessary tool movements, the computer
develops a complete machining program for the part to be
manufactured on the CNC machine.
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