Page 658 - 04. Subyek Engineering Materials - Manufacturing, Engineering and Technology SI 6th Edition - Serope Kalpakjian, Stephen Schmid (2009)

Section 23.3 Lathes and Lathe Operat|ons 6

volume of the chips can be in the range of 600 to 12,000 cm3 depending on chip
type. Likewise, the milling of 15 cm3 of steel produces 450 to 750 cm3 of chips, and
cast iron produces 105 to 225 cm3 of chips.
Also called chip management, the operation involves collecting chips from
their source in the machine tool in an efficient manner and removing them from the
work area. Long and stringy chips are more difficult to collect than short chips,
which are produced by using tools with chipbreaker features (see Figs. 21.7 and
22.2). Thus, the type of chip produced is an integral aspect of the chip-collecting
system.
Chips can be collected by any of the following methods:

° Allowing gravity to drop them onto a steel conveyor belt.
° Dragging the chips from a settling tank.
° Using augers with feed screws (similar to those in meat grinders).
° Using magnetic conveyors (for ferrous chips).
° Employing vacuum methods of chip removal.

Modern machine tools are designed with automated chip-handling features.
Note that there may be a considerable amount of cutting fluid mixed with and
adhering to the chips produced; hence, proper filtration or draining is important.
The cutting fluid and sludge can be separated using chip wringers (centrifuges).
Chip-processing systems usually require considerable floor space and can cost from
$60,000 for small shops to over $1 million for large plants.
The collected chips may be recycled if it is economical to do so. Prior to their
removal from a manufacturing plant, the large volume of chips can be reduced to as
little as one-fifth of the loose Volume by compaction (crushing) into briquettes or by
shredding. Dry chips are more valuable for recycling because of reduced environ-
mental contamination. The method chosen for chip disposal depends on economics,
as well as on compliance with local, state, and federal regulations. The trend is to
recycle all chips, the used cutting fluids, and the sludge.

23.3.8 Cutting Screw Threads
Screw threads are extremely common features. A screw thread may be defined as a
ridge of uniform cross section that follows a helical or spiral path on the outside or
inside of a cylindrical (straight thread) or tapered surface (tapered thread). Machine
screws, bolts, and nuts have straight threads, as do threaded rods for applications
such as the lead screw in lathes and various machinery components (Fig. 23.2).
Threads may be right handed or left handed. Tapered threads commonly are used
for water or gas pipes and plumbing supplies, which require a watertight or airtight
connection.
Threads traditionally have been machined, but they are increasingly being
formed by thread rolling (described in Section 13.5). Rolled threads now constitute
the largest quantity of external threaded parts produced. It also may be possible to
cast threaded parts, but there are limitations to dimensional accuracy, surface finish,
and minimum dimensions. Production rates are not as high as those obtained in
other processes.
Threads can be machined externally or internally with a cutting tool by a
process called thread cutting or threading. Internal threads also can be produced with
a special threaded tool, called a tap, and the process is called tapping (Section 23.7).
External threads also may be cut with a die or by milling. Although the process adds
considerably to the cost, threads subsequently may be ground for high dimensional
accuracy and surface finish for applications such as screw drives in machines.