UNIT-III
SHAPING, SLOTTING & PLANING MACHINES
shapers and planers & slotting machine tools which produce a flat surface. They are capable ofmachininga horizontal, vertical or inclined flat surface. They employ single-point cutting tools which are essentially similar to single-point cutting tools used on lathe. In both these machine tools, the cutting tool is subjected to interrupted cuts, the tools cuts in forward direction and is idle in the return direction
Types of shapers
1 According to type of mechanism used for ram:
a) Crank type b) geared type c) Hydraulic type
2. According to position & travel of ram:
a) Horizontal type b) Vertical type c) Traveling type
3. According to type of design of table:
a) standard shaper b) universal shaper
4. According to type of cutting stroke:
a) push type b) draw type
Working principle of shaper:
It consists of a hollow machine bed made of cast iron which rests on the ground. Inside the hollow portion the machine drive mechanism is housed. This mechanism is called slotted lever quick return mechanism and it drives a horizontal ram which reciprocates in the guide ways provided on the top surface of the machine frame. In the front face of the ram, a toolpost is fitted. This is a very special kind of tool post. It carries a slide which can be operated by a hand wheel and the entire tool post can be lowered or raised. Besides, the tool slide can be swiveled in a vertical plane and its inclination to the vertical (amount of swiveling) can be read off on a scale marked in degrees. The tool is inclined, when an inclined surface has to be machined. In the front portion of the base, a table is fitted. The table can be raised or lowered to vary its height. It can also bemoved horizontally to left or right. A vice to hold thework piece
is provided on the table top. Thetool does useful work i.e., cutting only in theforward stroke ofthe ram. It does not cut in return stroke i.e. it is idle during the return stroke of ram. In order that while returning, the tool may not rub andspoil thestrip of the metal machined in the forward stroke, a special device called the “clapper box” is provided in the tool post. It lifts the tip of the toolduring the return stroke.
Base: The base is a heavy cast iron casting which is fixed to the shop floor. It supports the body frame and the entire load of the machine. The base absorbs and withstands vibrations and other forces which are likely to be induced during the shaping operations.
Body (Pillar, Frame, Column):It is mounted on the base and houses the drive mechanism compressing the main drives, the gear box and the quick return mechanism for the ram movement. The top of the body provides guide ways for the ram and its front provides the guide ways for the cross rail.
Cross rail:The cross rail is mounted on the front of the body frame and can be moved up and down. The vertical movement of the cross rail permits jobs of different heights to be accommodated below the tool. Sliding along the cross rail is a saddle which carries the work table.
Ram and tool head:The ram is driven back and forth in its slides by the slotted link mechanism. The back and forth movement of ram is called stroke and it can be adjusted according to the length of the work piece to be-machined.
Shaper specifications:
· Maximum length of stroke or cut it can make ranges from- 175 to 900 mm.
· Drive- belt or individual motor drive
· Power input
· Floor space
· Weight of machine
· Cutting to return stroke
· Number & amount of feed
Shaper mechanism:
The shaper machine should be so designed that it can allow the ram holding the tool to move at a comparatively slower speed during the forward cutting stroke the cutting speed depending upon the type of material & machining conditions, whereas during the return stroke it can allow the ram to move at a faster rate to reduce the idle return time. This mechanism is know as Quick return mechanism
1. Crank & slotted link mechanism
2. Whit worth quick return mechanism
3. Hydraulic shaper mechanism
1. Crank & slotted link mechanism:
Since useful work is done onlyduring the forward stroke of ram, the mechanism driving theram is so designed that the return stroke iscompleted in much less time than the forward stroke. The slotted lever quick return mechanism isillustrated in Figs. 2(a) & 2(b)
The crank AB(of adjustable length R) rotates with a uniform angular speed. The crank pin B is in the shape of a die block which is free to slide inside the slot in the slotted lever OBC. This slotted lever is pivoted at O and the other end Cis connected to the ram by a short link arm as shown in Fig. 2 (a). When the crankAB rotates clockwise from positionAB1toAB2, the ram moves forward from left to right and when it rotates from positionAB2toAB1the ram returns back to its original position. Clearly the time taken to complete forward stroke is proportional to angle α (refer to Fig. 2 (b) and the return stroke is completed in less time which is proportional to angle β.
The ratio between the cutting time & return time may be determined by
Cutting time/ Return time
2. Whit worth quick return mechanism:
Shapers operations:
1. Machining vertical surface
2. Machining horizontal surface
3. Machining angular surface
4. Cutting slots, grooves & key ways
5. Machining irregulars surface
6. Machining splines or cutting gears
Work holding devices
1. Clamped in a vise
2. Clamped on the table
3. Clamped to the angle plate
4. Clamped on a v- block
5. Held between shaper index centers
Planning machines:
The planer is a machine tool designed to produce plane and flat surface on a work piece which is too large or too heavy. The work piece is securely fixed on a table called platen, and it reciprocates horizontally against a single edged cutting tool. The surface machined may be horizontal, vertical or at an angle.
Types of planning machines
1. Double housing planer
2. Open side planer
3. Pit type planer
4. Divided table planer
5. Edge or plate planer
1. Double housing planer:
It is the mostcommon type of planer. It consists ofmainly a massive bed on which thework table reciprocates, and two vertical columns or housing, one on each side ofthe bed. Each column carries a tool head that can be slide upand down onthe column.Across rail fitted between the two columns may carryone ortwo tool heads that can slide horizontally on the cross rail. All the tool heads canbe clamped in position, and can be used collectively orindividually depending on the requirements.
2. Open side planer:
Open side planer consists of only one vertical column or housing on which the cross rail is mounted. The column and the cross rail carry single and double tool heads respectively. This type of machine permits machining of wide work piece.
3. Pit type:
Apit type planer differs from otherplaner in the sense that, the table and the work piece resting on it remain stationary and the tool reciprocates across the work surface. This typeof machine is preferred for very large work, where the weight ofthe work piece and the tool required table would make reciprocating movement difficult. The job is either mounted on a stationary table, or on the floor inside a pit, and hence the name pit type planer. One or two tool heads can be mounted on the cross rail and two side tool posts the housings, if required. The entire unit travelsalong the horizontal ways and fro and, thus the tool moves past the work surface during operation.
4. Edge or plate planer:
This type of machine is used formachining the edges of heavy work pieces. The work piece is clamped on the bed and the side mounted carriage supporting the cutting tool is reciprocated along the edge of the work piece. Cutting can take place during both directions of carriage travel.
5. Divided table planer:
It is also called tandem planer and consists of two worktables, which may be reciprocated togetheror separately. Itis quite wellknown that, mounting and setting of work pieces on the worktable consumes more time thereby restricting the machine for continuous mass production applications. In such cases, divided tableplanercan be used, where in, one worktable can be used for setting up a new work piece, while the second worktable carrying work piece is being machined. The two tables can be joined together to hold large work piece.
Planing Machine parts:
Construction: The main parts of the double Housing Planer machine is Bed and table, Housings, Cross rail, Tool heads, Driving and feed mechanism.
Bed and table: The bed is a long heavy base and table made of cast iron. Its top surface is flat and machined accurately. The flat top surface has slots in which the work piece can be securely clamped. The work piece needs rigid fixing so that it does not shift out of its position. The standard clamping devices used on planer machine are: Heavy duty vice, T-holders and clamps, angle plate, planer jack, step blocks and stop. The table movement may be actuated by a variable speed drive through a rack and pinion arrangement, or a hydraulic system.
Housings: The housings are the rigid and upright column like castings. These are located near the centre on each side of the base.
Cross rail: The cross rail is a horizontal member supported on the machined ways of the upright columns. Guide ways are provided on vertical face of each column and that enables up and vertical movement of the cross rail. The vertical movement of the cross rail allows to accommodate work piece of different heights. Since the cross rail is supported at both the ends, this type of planer machine is rigid in construction.
Tool heads: Generally two tool heads are mounted in the horizontal cross rail and one on each of the vertical housing. Tool heads may be swiveled so that angular cuts can be made.
Driving and feed mechanism: The tool heads may be fed either by hand or by power in crosswise or vertical direction. The motor drive is usually at one side of the planer near the centre and drive mechanism is located under the table.
Planer mechanism :
Two important mechanism of a planer are
1. Table drive mechanism
2. Feeding mechanism
Different mechanism used to drive the table.
1. Open & belt drive mechanism
2. Receivable drive mechanism
3. Hydraulic drive mechanism
Planer operations:
1. Planing flat horizontal surfaces
2. Planing vertical surfaces
3. Planing at an angle & machining dovetails
4. Planing slots & grooves
1. Horizontal surfaces:
While machining horizontal surface, the work is given a reciprocating movement along with the table & the tool is fed crosswise to complete the cut. Both the rail heads may be used for simultaneous removal of the metal from two cutting edges.
2. Vertical surfaces:
The vertical surface of a work is planed by adjusting the saddle horizontally along the cross rail until the tool is in a position to give the required depth f cut. The vertical slide is adjusted perpendicular to the planer table & the apron is swiveled in a direction so that the tool will swing clear out of the machined surface during the return stroke.
3. Planing at an angle & machining dovetails
For dovetail work, cutting v- grooves etc., the tool head is swiveled to the required angle &the apron is then further swiveled away from the work to give relief to the tool cutting edges during return stroke.
4. Planing slots & grooves
Slots or grooves are cut by using slotting tools. The operations are similar to that of a shaper.
Slotting machines:
The slotting machine is a reciprocating machine tool in which, the ram holding the tool reciprocates in a vertical axis and the cutting action of the tool is only during the downward stroke.
Construction:
The slotter can be considered as a vertical shaper and its main parts are:
1. Base, column and table
2. Ram and tool head assembly
3. Saddle and cross slide
4. Ram drive mechanism and feed mechanism.
The base of the slotting machine is rigidly built to take up all the cutting forces. The front face of the vertical column has guide ways for Tool the reciprocating ram. The ram supports the tool head to which the tool is attached. The workpiece is mounted on the table which can be given longitudinal, cross and rotary feed motion.
The slotting machine is used for cutting grooves, keys and slotes of various shapes making regular and irregular surfaces both internal and external cutting internal and external gears and profiles .The slotter machine can be used on any type of work where vertical tool movement is considered essential and advantageous.
Types of slotting machines
1. Puncher slotter
2. Precision slotter
Puncher slotter:
It is a heavy , rigid machine designed for removal of large amount of metal from large forging or casting. It may be as long as 1800 to 2000 mm. It is usually driven by spiral pinion meshing with rack teeth cot on the under side of the ram. It is driven by an electric motor.