The
necessity for design changes
Historically, machine tool
designs have been kept as simple as possible consistent with the specification
they offered. The high-quality of parts manufactured was traditionally the
responsibility of the skilled machine tool operator. The demand for machine
tools design for continuous operation has increased which makes the skilled
operator no longer has to control the functions of the machine via hand
controls. It is now possible to combine functions into a single machine tool
that previously only existed on separated machines.
All machine tools are designed to
fulfill three prime objectives
- To achieve and maintain accuracy.
- To achieve and maintain repeat ability.
- To achieve and maintain reliability.
CNC machine tools enjoy
considerable additions and improvements in some main design areas:
- Structural details
- Mechanical details
- Control system facilities
Structural details - CNC Machining
Structural errors are largely
concerned with structural design and configuration. Structural configuration
refers to the external physical shape of the design and the relative positons
of associated elements. A horizontal machining centre, for example has a
different configuration to that of a vertical machining centre. Structural
design concerns the physical construction of the structure. Traditional machine
tool beds, for example, are almost exclusively made from cast iron. Because is
relatively easy to produce complex shapes.
Mechanical details - CNC Machining
Transmission of motive power in
driving spindle and worktable elements are the chief sources of mechanical
inaccuracy. From the motor, transmission will pass through a number of stages.
- Gear box/Belt drive stage
- Motion transmission stage
- Slide way stage
Control system facilities - CNC Machining
One of the first features
apparent on most CNC machine tools is that there no longer any handwheels to be
seen. All controls have been totally transferred to the computerised control
system. The facilities offered by the control unit may be considered under
three broad headings.
- Status Indicators
- Manual/Semi-Manual Controls
- Programming Controls
