Section 13. qxd

High-pressure refrigerated coolant systems
are very effective in remov-
ing heat at high rates, particularly in computer-controlled machine tools.
The fluid is directed generally at the relief angle of the cutting tools and
at pressures as high as 5,000 lb/in
2
(35,000 kPa). Continuous filtering
of the fluid is essential to eliminate any damage to workpiece surfaces
due to the impact of any contaminants that may be present in the coolant
system. More recent methods of application include delivering the coolant
to the cutting zone through the tool and the machine spindle.
For economic as well as environmental reasons, an important trend is
near-dry
and 
dry machining.
In near-dry machining, the cutting fluid typ-
ically consists of a fine mist of air containing a very small amount of
cutting fluid (including vegetable oil) and is delivered through the
machine spindle. Dry machining is carried out without any fluids but
using appropriate cutting tools and processing parameters. Unlike other
methods, however, dry machining cannot flush away the chips being
produced; an effective means to do so is to use pressurized air.
MACHINE TOOLS
The general types of 
machine tools
are lathes; turret lathes; screw, boring,
drilling, reaming, threading, milling, and gear-cutting machines; planers
and shapers; broaching, cutting-off, grinding, and polishing machines.
Each of these is subdivided into many types and sizes. General items
common to all machine tools are discussed first, and individual machin-
ing processes and equipment are treated later in this section.
Automation
is the application of special equipment to control and per-
form manufacturing processes with little or no manual effort. It is
applied to the manufacturing of all types of goods and processes, from
the raw material to the finished product. Automation involves many
activities, such as handling, processing, assembly, inspecting, and pack-
aging. Its primary objective is to lower manufacturing cost through con-
trolled production and quality, lower labor cost, reduced damage to
work by handling, higher degree of safety for personnel, and economy
of floor space. Automation may be partial, such as gaging in cylindrical
grinding, or it may be total.
The conditions which play a role in decisions concerning automation
are rising production costs, high percentage of rejects, lagging output,
scarcity of skilled labor, hazardous working conditions, and work
requiring repetitive operation. Factors which must be carefully studied
before deciding on automation are high initial cost of equipment, main-
tenance problems, and type of product. (See also Sec. 16.)
Mass production with modern machine tools has been achieved
through the development of self-contained