Page 657 - Manufacturing Engineering and Technology - Kalpakjian, Serope : Schmid, Steven R.

8 Chapter 23 Machining Processes: Turning and Hole Making

TABLE 23.9
General Troubleshooting Guide for Turning Operations
Problem Probable causes
Tool breakage Tool material lacks toughness, improper tool angles, machine
tool lacks stiffness, worn bearings and machine components,
machining parameters too high
Excessive tool wear Machining parameters too high, improper tool material, ineffec-
tive cutting fluid, improper tool angles
Rough surface finish Built-up edge on tool; feed too high; tool too sharp, chipped, or
worn; vibration and chatter
Dimensional variability Lack of stiffness of machine tool and work-holding devices,
excessive temperature rise, tool wear
Tool chatter Lack of stiffness of machine tool and work-holding devices,
excessive tool overhang, machining parameters not set properly

3. Sharp corners, tapers, steps, and major dimensional variations in the part
should be avoided.
4. Blanks to be machined should be as close to final dimensions as possible (such
as by near-net-shape forming) so as to reduce production cycle time.
5. Parts should be designed so that cutting tools can travel across the workpiece
without obstruction.
6. Design features should be such that commercially available standard cutting
tools, inserts, and toolholders can be used.
7. Workpiece materials should be selected for their machinability (Section 2l.7)
as much as possible.

Guidelines for Turning Operations. A general guide to the probable causes of
problems in turning operations is given in Table 23.9. Recall that Chapters 21 and
22 described the factors influencing the parameters listed.
In addition to the various recommendations concerning tools and process pa-
rameters described thus far, an important factor is the presence of vibration and
chatter (Section 25.4). Vibration during cutting can cause poor surface finish, poor
dimensional accuracy, excessive tool wear, and premature tool failure. The follow-
ing list outlines some generally accepted guidelines for turning operations (because
of the complexity of the problem, however, some of the guidelines have to be imple-
mented on a trial-and-error basis):
I. Minimize tool overhang.
2. Support the workpiece rigidly.
3. Use machine tools with high stiffness and high damping capacity.
4. When tools begin to vibrate and chatter, modify one or more ofthe process pa-
rameters, such as tool geometry, cutting speed, feed rate, depth of cut, and use
of cutting fluid. (See also adaptive control, Section 37.4.)

23.3.1 Chip Collection Systems
The chips produced during machining must be collected and disposed of properly.
The volume of chips produced can be very high, particularly in ultra-high-speed
machining and high-removal-rate machining operations. For example, in a drilling
operation on steel during which only 15 cm3 of metal is removed, the loose bulk