Tài liệu Cutting Tools P7 doc

Both the shaper and the planer usually cut only in one direction, so that the return stroke is lost time.. Work which, due to size or shape, can-not be held in the vise, is clamped direc

Cutting Tool

Applications

Jr CMfgE

7.1 Introduction Both the shaper and the planer are single point tools and cut only in straight lines They both make the same types of cuts

The shaper handles relatively small work The planer handles work weighing up to several tons The cutting stroke of the shaper is made by moving the tool bit attached to the ram The cutting stroke of the planer is achieved by moving the work past a station-ary tool bit

The types of cuts which can be made with either machine are shown in Figure 7.1 Both the shaper and

the planer usually cut only in one direction,

so that the return stroke is lost time

However, the return stroke is made at up

to twice the speed of the cutting stroke

7.2 The Shaper The shaper is a rela-tively simple machine It is used fairly often in the toolroom or for machining one or two pieces for proto-type work Tooling

is simple, and shapers do not always require opera-tor attention while cutting The horizon-tal shaper is the most common type, and its principal components are shown in Figure 7.2, and described as follows:

Chapter 7 Shaping

& Planing

Metal Removal

Cutting-Tool Materials

Metal Removal Methods

Machinability of Metals

Single Point Machining

Turning Tools and Operations

Turning Methods and Machines

Grooving and Threading

Shaping and Planing

Hole Making Processes

Drills and Drilling Operations

Drilling Methods and Machines

Boring Operations and Machines

Reaming and Tapping

Multi Point Machining

Milling Cutters and Operations

Milling Methods and Machines

Broaches and Broaching

Saws and Sawing

Abrasive Processes

Grinding Wheels and Operations

Grinding Methods and Machines

Lapping and Honing

George Schneider, Jr CMfgE

Professor Emeritus

Engineering Technology

Lawrence Technological University

Former Chairman

Detroit Chapter ONE

Society of Manufacturing Engineers

Former President

International Excutive Board

Society of Carbide & Tool Engineers

Lawrence Tech Univ.: http://www.ltu.edu

Prentice Hall: http://www.prenhall.com

FIGURE 7.1: Typical cuts made by both shapers and planers.

Chap 7: Shaping & Planing

Ram: The ram slides back and forth

in dovetail or square ways to transmit

power to the cutter The starting point

and the length of the stroke can be

adjusted

Toolhead: The toolhead is fastened

to the ram on a circular plate so that it

can be rotated for making angular cuts

The toolhead can also be moved up or

down by its hand crank for precise

depth adjustments

Attached to the toolhead is the

tool-holding section This has a tool post

very similar to that used on the engine

lathe The block holding the tool post

can be rotated a few degrees so that the

cutter may be properly positioned in the

cut

Clapper Box: The clapper box is

needed because the cutter drags over the

work on the return stroke The clapper

box is hinged so that the cutting tool

will not dig in Often this clapper box is

automatically raised by mechanical, air,

or hydraulic action

Table: The table is moved left and

right, usually by hand, to position the

work under the cutter when setting up

Then, either by hand or more often

automatically, the table is moved

side-ways to feed the work under the cutter

at the end or beginning of each stroke

Saddle: The saddle moves up and

down (Y axis), usually manually, to set

the rough position of the depth of cut

Final depth can be set by the hand crank

on the tool head

Column: The column supports the

ram and the rails for the saddle The mechanism for moving the ram and table is housed inside the column

Toolholders: Toolholders are the same as the ones used on an engine lathe, though often larger in size The cutter is sharpened with rake and clear-ance angles similar to lathe tools, though the angles are smaller because the work surface is usually flat These cutters are fastened into the toolholder, just as in the lathe, but in a vertical plane

Work Holding: Work holding is

fre-quently done in a vise The vise is spe-cially designed for use in shapers and has long ways which allow the jaws to open up to 14 inches or more, therefore quite large work pieces can be held

The vise may also have a swivel base so that cuts may be made at an angle

Work which, due to size or shape, can-not be held in the vise, is clamped directly to the shaper table in much the same way as parts are secured on milling machine tables

Shaper Size: The size of a shaper is

the maximum length of stroke which it can take Horizontal shapers are most often made with strokes from 16 to 24

inches long, though some smaller and larger sizes are available These shapers use from 2 to 5 HP motors to drive the head and the automatic feed

Shaper Width: The maximum width

which can be cut depends on the avail-able movement of the tavail-able Most shapers have a width capacity equal to

or greater than the length of the stroke The maximum vertical height available

is about 12 to 15 inches

7.2.1 Drive Mechanisms Shapers are available with either mechanical or hydraulic drive mecha-nisms Figures 7.3a and 7.3b show dia-grams of both shaper drive mechanisms Mechanical Drive

The less expensive shaper, the one most often purchased, uses a mechanical drive This drive uses a crank mecha-nism (Fig 7.3a) The bull gear is driven

by a pinion which is connected to the motor shaft through a gear box with four, eight or more speeds available The RPM of the bull gear becomes the strokes per minute (sometimes abbrevi-ated SPM) of the shaper

Cutting Speed: The cutting speed of

the tool across the work will vary during the stroke as shown by the velocity dia-gram in Figure 7.3a The maximum is

at the center of the stroke However, if the cutting speed chosen is somewhat

on the slow side, the average speed may

be used, and computations are greatly simplified

Although the ratio varies some-what,several shapers have a linkage using 220 degrees of the cycle for the cutting stroke and 140 degrees for the return stroke This is close to a 3:2 ratio

In setting up a mechanically operated shaper, the length of cut (in inches) is known, and the cutting speed (in feet per minute) is selected according to the kind of metal being cut It is then nec-essary to compute the strokes per minute since that is how the shaper speed is controlled Such calculations are beyond the scope of this text The stroke per minute available on a shaper will vary according to the size of the shaper The larger shapers will have lower speeds A 16 inch shaper may have speeds of 27 to 150 strokes per minute, while a 24 inch shaper will have

10 to 90 strokes per minute speeds available

FIGURE 7.2: The horizontal shaper is the most common type; its princpal components

are shown here (Courtesy: Cincinnati Machine)

Cutting Feed: Feed per stroke on a

shaper is comparable to the feed per

revolution on a lathe Coarse feeds for

roughing range up to 0.100 inch per

stroke (sometimes abbreviated as IPS),

and finish cuts from 0.005 to 0.015 inch

per stroke Finish would also depend on

the nose radius of the cutting tool

Hydraulic Drive

The hydraulic shaper (Fig 7.3b) has the

same major parts as the mechanical one,

however, the ram is driven by a

hydraulic cylinder as shown in the

sim-plified sketch These shapers use 5 to

10 HP motors

Cutting Speed and Feed: The

cut-ting speed of the hydraulic shaper is

infinitely variable by means of

hydraulic controls, as is the cross feed The reverse stroke is made faster than the power stroke because of the smaller area in the return side of the cylinder, if a con-stant volume pump is used

Another method is to have the rate of fluid flow increased to speed up the return stroke

Speed and feed on a hydraulic shaper are often controlled by simple dials

Speed is read directly in feet per minute and feed is read directly in decimal inches

The cutting speed remains nearly constant through the full stroke

7.2.2 Vertical Shapers The vertical shaper, sometimes called a slotter, has a verti-cal ram, with table and saddle similar

to the horizontal shaper If a rotary table is mounted on the regular table, a number of slots can

be made at quite accurately spaced intervals This machine can work either outside or inside a part, pro-vided that the inte-rior opening is

larg-er than the tool head A schematic illustration

of a vertical shaper is shown in Figure 7.4

7.3 The Planer

A planer makes the same types

of cuts as a shaper However,

it is a production-type machine for certain types of work It can machine any flat or angu-lar surface, including grooves and slots, in medium and large sized workpieces (see Fig

7.1) Typical work would be machine beds and columns, marine diesel engine blocks, and bending plates for sheet metal work These parts are usually large iron castings or

steel weldments and may weigh a few hundred pounds or several tons The most frequently used type of planer is the double-housing planer, shown in Figure 7.5, with the following components:

Frame: The frame is basically two

heavy columns fastened together at the top with a large bracing section and fas-tened at the bottom to the machine bed This creates a very strong, rigid struc-ture which will handle heavy loads without deflection

Crossrail: The crossrail is also a heavy box, or similar construction It slides up and down on V- or flat ways, controlled by hand or by

power-operat-ed screws These crossrails are so heavy that they are counterweighted,

Ram connection

Max forward position Rocker arm Bull gear sliding block Adjusting screw Crank pin Pivot bearing (a)

Max rear

position

Bevel gears

(stroke

adjustment)

Bull gear

Cut

Stroke length

Velocity diagram

Cutting stroke

Return stroke

1.0

Velocity diagram

Forward cutting speed

Return

stroke

(faster)

Shaper ram

Cutting stroke

4-way valve

Pump Tank Motor

Base

Ram with annular adjustment

Drive gear box

Longitudinal feed

Tool holder Rotating table Table rotation

Transverse feed

FIGURE 7.3: Shapers are available with either (a)

mechanical drive mechanisms or (b) hydraulic drive

mechanisms.

FIGURE 7.4: Schematic illustration of a vertical shaper, also called a slotter.

Clapper box Crossrail

Bed

Drive motor Column or housing Side head

Table Bed Vee ways

FIGURE 7.5: Schematic illustration of a double-housing planer.

Chap 7: Shaping & Planing

with either cast iron weights or

hydraulic cylinders, in order that they

may be moved easily and positioned

accurately After being positioned, they

are clamped in place

Railheads: The two railheads can be

moved left or right across the crossrail,

each controlled by a separate lead

screw, which can be turned by hand but

usually by power feed The railhead can

be rotated, and vertically adjusted for

depth of cut, the same as the shaper

heads They also have a clapper box

(often with power lift) like the shaper

Sideheads: The sideheads are

inde-pendently moved up or down by hand or

by power feed and can also be rotated

and moved in or out for depth of cut

Table: The table is a heavy casting

which carries the work past the cutting

heads It runs on V- or flat ways The

table is driven either by a very long

hydraulic cylinder or by a pinion gear

driving a rack which is fastened under

the center of the table The motor

dri-ving the pinion gear is the reversible

type with variable speed

Bed: The bed of the planer must be a

weldment or casting twice as long as the

table Thus a 12-ft table requires a

24-ft bed The gearing of hydraulic

cylin-ders for driving the table is housed

under the bed

Toolholders: Planers use high speed

steel or carbide tipped cutting tools

sim-ilar to those used on shapers However,

since planers make heavy cuts, their

tools are much larger Rake relief

angles are similar to those used on

lath-es for cutting cast iron or steel, although

relief angles are often only 3 to 5

degrees, because all cuts are on flat

sur-faces

Work Holding: Holding the work

while machining such heavy cuts at 60

to 100 feet per minute requires

consid-erable force; therefore, the workpieces

must be solidly fastened to the table

Because the reversal of direction occurs

quite rapidly, the work must be

espe-cially well braced at the ends The table

has T-slots, both lengthwise and across,

in which heavy bolts and clamps may be used Sometimes holes are drilled in the table so that large pins can be used to prevent the workpiece from going off the table when the machine reverses

Planer Size: The size of planers is often referred to as a 30 inch planer or a

60 inch planer This specifies the approximate width of the table which ranges from 30 to 72 inches A more complete specification is:

Width of table x height under rail

x length of table (For example: 48 inches x 48 inches

x 14 feet) The width and height are usually, but not always, the same Table length is often made to order and may be as short

as 8 feet, or as long as 20 feet or more

The drive may be 15 HP on the smaller planers, and 100 HP or more on the larger models

Mechanical and hydraulic power can

be used for planers Uniform cutting speed is attained throughout the cutting stroke Acceleration and deceleration of the table takes place in a short distance

of travel and does not influence the time

to machine

Double-housing Planers: Double-housing planers consist of a long heavy base on which the table reciprocates

The upright housing near the center on the side of the base, supports the cross-rail on which the tools are fed across the work Figure 7.5 illustrates how the tools are supported both above and on the sides, and their adjustment for angle cuts They are fed by power in either a vertical or a crosswise direction

Open-sided Planers: Open-sided planers have the housing on one side only The open side permits machining wider workpieces Most planers have one flat and one double V-way, which allows for unequal bed and platen expansions Adjustable dogs at the side

of the bed control the stroke length of the platen

Planers are often converted to

planer-mills, for more efficient machining 7.3.1 Comparison of Shapers and Planers

Although both the planer and the shaper are able to machine flat surfaces, there

is little overlapping in their application They differ greatly in construction and

in the method of operation The planer

is especially adapted to large work: the shaper can do only small work On the planer the work is moved against a sta-tionary tool: on the shaper the tool moves across the work, which is sta-tionary On the planer the tool is fed into the work; on the shaper the work is usually fed across the tool The drive on the planer table is either by gears or by hydraulic means The shaper ram also can be driven in this manner, but many times a quick-return link mechanism is used

Most planers differ from shapers in that they approach more constant-veloc-ity cutting speeds Tools used in shaper and planer work are single point as used

on a lathe, but are heavier in construc-tion The holder is designed to secure the tool bit near the centerline of the holder or the pivot point rather than at

an angle as is customary with lathe tool-holders

Cutting tools for the planer operation are usually tipped with high-speed steel, cast alloy, or carbide inserts High speed steel or cast alloys are commonly used in heavy roughing cuts and car-bides for secondary roughing and fin-ishing

Cutting angles for tools depend on the tool used and the workpiece

materi-al They are similar to angles used on other single-point tools, but the end clearance does not exceed 4 degrees Cutting speeds are affected by the rigid-ity of the machine, how the work is held, tool, material, and the number of tools in operation Worktables on plan-ers and shapplan-ers are constructed with T-slots to hold and clamp parts that are to

be machined