Figure 11-5.--Direct numerical control.
design a part. The computer is used to place the design
elements (lines, curves, circles, and so on) and
machine has a slant bed. The slant bed allows the chips
dimensions on the computer display screen.
to fall into the chip pan, rather than on tools or bedways.
Despite this odd appearance, the slant bed CNC lathe
The machinist defines the geometry of the part to
functions just like a conventional lathe.
the computer using one or more input devices. These
devices may be the keyboard, a mouse, a digitizer, or a
As with CNC milling machines, you must have the
pen light. When the design has been edited and proofed,
controller manual for your machine's controller to
the computer can be instructed to analyze the geometry
program it and operate the machine.
of the part and calculate the tool paths that will be
required to machine the part. Each tool path is translated
into a detailed sequence of machine axes movement
commands that will enable a CNC machine tool to
There are many different tool-holding devices used
produce the part. No engineering drawing is required.
for CNC machines. They can be as simple as a quick-
change tool post or as complicated as an automatic tool
The computer-generated instructions can be stored
change system, but they all serve the same purpose. The
in a central computer for direct transfer to a CNC
tool-holding devices for each shop will vary since each
machine tool for parts manufacture as shown in
machine comes with different tooling and because shop
personnel will purchase the tooling they prefer.
(DNC). The data also can be stored on disk for future
Cutting tools are available in three basic material
types: high-speed steel, tungsten carbide, and ceramic.
The system that makes all this possible is computer-
Since we covered cutting tools in chapter 5, we will only
aided design/computer-aided manufacturing (CAD/
briefly discuss them now. High-speed steel is generally
CAM). There are several CAD/CAM software
used on aluminum and other nonferrous alloys, while
programs. They are constantly being upgraded and
tungsten carbide is used on high-silicon aluminums,
made more user friendly.
steels, stainless steels, and exotic metals. Ceramic
To state it simply, CAD is used to draw the part and
inserts are used on hard steels and exotic metals.
to define the tool path. CAM is used to convert the tool
Inserted carbide tooling is becoming the preferred
path into codes that the computer on the machine can
tooling for many CNC applications.
NUMERICAL CONTROL SYSTEMS
A CNC machine consists of two major components:
the machine tool and the controller, which is an onboard
Computer technology has reached the stage where
computer. These components may or may not be