Shaper machine tool
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Shaper Mechanism
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Transcript of Shaper machine tool
Shaper Mechanism
• Crank shaper: Shapers whose ram reciprocates with the help of a crank mechanism
• Geared shaper: The ram reciprocates with spur gear mechanism. this type of shaper carries a rack under the ram for to and fro motion.
• Hydraulic shaper: the movement of the ram is provided by hydraulic pressure
• Horizontal shaper: The ram reciprocates in horizontal direction.
• Vertical shaper: The ram reciprocates in vertical direction.
• It is also known as slotter.• Travelling head shaper: a shaper whose
reciprocating tool head is mounted on a bed in such a way that the head may be fed laterally on ways provided on the bed prior to each cutting .
• 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.
• Saddle: Sliding along the cross rail is a saddle which carries the work table. Crosswise movement of the saddle causes the work table to move side ways.
• Ram: 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 workpiece to be-machined.
• Tool head: The tool head in a dovetail at the front of the ram by means of T-bolts. It can swivel from 0 to 90 in a vertical plane.
• Tool head can be raised or lowered by hand feed for vertical cuts on the work pieces.
• Tool head holds tool. The tool head imparts the tool, necessery vertical and angular feed movement.
• The tool slide controls the feed in the cutting tool into the workpieces by a lead screw.
• The clapper box allows the cutting tool to lift on the return or idle stroke so that the tool is not dragged back through the uncut workpice and get damaged.
• Tool post carries the cutting tool.
The cutting speed depends on Type of material Machining condition
The return stroke allow the ram to move at a faster rate to reduce the idle time which is known as Quick Return Mechanism.
The reciprocating movement of ram and quick return mechanism of the machine are obtained from
(i) Crank and Slotted link mechanism (ii) Whitworth quick return mechanism (III) Hydraulic Shaper Mechanism
Crank and Slotted link mechanism•Slotted link mechanism is very common in mechanical shapers.•It is simple and compact. It converts rotary motion of the electric motor and gearboxinto the reciprocating motion of the ram.•The return stroke allow the ram to move at a faster rate to reduce the idle time which is known as Quick Return Mechanism, reducing the time waste during return stroke.
•Bull gear is driven by a pinion which connects to the motor shaft through gear box.
•The bull wheel has a slot. The crank pin A secured into this slot, at the same time it can slide in the slotted crank B.
As the bull gear rotate cause the crankpin A also to turn and side by side slides through the slot in the slotted crank B.
This makes the slotted crank to oscillate about its one end C.
This oscillating motion of slotted crank (through the link D) makes the ram to reciprocate.
The intermediate link D is necessary to accomdate the rise and fall of the crank.
The principle of Quick Return Mechanism
When the link is in position AP1, the ram will at extreme backward position of stroke
When the link position is at AP2, the extreme forward position Ram will have been reached
AP1 and AP2---- Tangent to the crank pin circle Forward cutting stroke takes place when the crank rotates
through an angle C1KC2 Return stroke ---- the crank rotates through angle C1LC2 It is seen that C1KC2 > C1LC2 The angular velocity of crank pin remains constant.
The ratio of cutting time and return time :
It varies from 2:1 and the practical limit 3:2Disadvantage:The cutting speed and return speed is not constant throughout the
stroke
1 2
1 2ReC KCCutting time
turntime C LC
Adjustment of the length of stroke
How the length of stroke in a crank shaper can be adjusted?Ans: The crank pin (11) is fastened to the sliding block (10) which
can be adjusted and the radius of its travel may be varied. The block (10) is again mounted upon the radial slide (16)
bolted to the centre of bull gear. The bevel gear (18) placed at the centre of the bull gear may
be rotated by a handle causing the bevel gear(17) to rotate The bevel gear (17) is mounted upon the small lead screw
(13) which passes through sliding block (10). The rotation between bevel gear (17) will cause the sliding
block (10) carrying the crank pin (11) to be brought inwards or outwards with respect to the centre of bull wheel.
Note :The closer the pin is brought to the centre of the bull wheel, the
smaller will be the stroke.Maximum stroke of the ram obtained when the crank pin is
shifted towards the farthest end of slide.
Adjustment of the position of stroke
The position of ram relative to the work can be adjusted by Rotating the hand wheel (5) the screw shaft (3) which is
fitted in the ram may be rotated through two bevel gears (6&7).
The ram block (8) which is mounted upon the screw shaft (3) acts as a nut.
When the machine is in operation, the clamping lever (4) is tightened upon the ram body (2) and the ram block, the screw shaft and ram block becomes as one unit.
To set the position of stroke, the clamping lever (4) is loosened and by rotating the hand wheel (5), the screw shaft (3) will rotates within the ram block.
The unit remaining fixed in position, rotation of screw will cause the ram to move forward or backward respect the ram block according to the direction of rotation of hand wheel (5).
Thus the position of ram can be adjusted with respect to the work piece.
The clamping lever (4) must be tightened after the adjustment has been made.
Whitworth Quick return Mechanismy
x
• Crank PC revolves at uniform speed. During cutting stroke the point P travels from P1 to P2 through y.
• The ram is returned at high speed as the crank rotates from P1 to P2 through x.
• The ratio of cutting time and return time : Cutting time /return time=P1YP2/P1XP2
• The stroke length can be changed by varying the radius OA.
Difference between Crank and slotted link mechanism and whitworth quick return
• The slotted lever mechanism is used in Shaper machines for quick return mechanism; while whitworth mechanism is used in Slotting machine.
• The velocity of forward stroke in Crank and slotted lever mechanism remains same for different stroke length while the velocity of return stroke decreses for smaller stroke lengths.Thus for smaller stroke lengths Slotted lever serves no advantage over quick return.
Hydraulic Mechanism
Hydraulic shaper has the same major parts as the mechanical one. However, the ram is driven by a hydraulic cylinder.
The sppeds of the shaper ram and feeds of the work table are controlled by hydraulic mechanism. A lever operates Valve that varies the quantity of oil delived to the ram cylinder and therby governs the ram speed.
The ram moved forward and backward by a piston moving in a cylinder placed under the ram
The machine consists of a constant discharge oil pump, a valve chamber, a cylinder and a piston.
The piston rod is bolted to ram body. The oil under high pressure is pumped from the reservoir and is made to
pass through the valve chamber to the right side of oil cylinder exerting pressure on piston
Neutral circuit
Service Active
• This mechanism are suitable increasingly popular these days as of their bigger litheness, smooth process, capability to slip in case of excess, capacity to withstand obstructions with no damaging tool or machine and the option of change speed with the feed during process. This system can efficiently use as rapid return mechanisms. Shaper ram is on its forward cutting strokes with is moving as of right to left. Oil as of reservoir is passed through a filter with pump. Pump, drive by an electric motor, push oil in a stable amount with at reasonable pressure to control valve. Control valve is fixed by an indicator that indicates direction in which oil is moving. As of the control valve, oil can be delivering to each side of the piston.
Note: The quick return motion is effected due to the difference in
stroke volume of the cylinder at both ends The left end is smaller due to the presence of the piston rod As the pump is a constant discharge one, within a fixed
period , the same amount of oil will be pumped into the right or left hand side of the cylinder.
i. e the same amount of oil will be packed within a smaller stroke volume causing the oil pressure to rise automatically and increasing the speed during return stroke.
The length and position of stroke is adjusted by shifting the position of reversing dogs.
Advantages
The cutting and return speeds are partially constant throughout the stroke which permits the cutting tool to work uniformly during cutting stroke.
The reversal of ram is obtained quickly without any shock as the oil on the other end of cylinder provides cushioning effect.
Infinite number of cutting speed may be obtained from zero to the maximum value and control is easier.
With high rate of return speed, a greater number of cutting strokes may be available within the range of cutting speed
The relief valve ensure safety to the tool and the machine when the machine is overloaded.
Machining time for shaper
Let L = the length of stroke(m) of shaperVo=cutting speed in m/minVr=return speed in m/minf= feed per cycle in m
• Threfore, time for cutting stroke, tc=Length of the stroke/cutting speed
Speed)L(travelectanDisimeMachiningt
c
c VLt
• Similarly, time for return stroke
• Total time for one cycle T= tc+ tr
• Now, Shaping width W= width of the workpiece + distance the tool moves on either side of the workpiece to ensure that the full width of the workpice has been machined
• No. of cylce required to machine the workpice=W/f• Machining time Tm=No. of cycles x time per cycle
R
R VLt
TfWTm
• Q1-Calculate the time to machine 250mm long plate, 100mm wide. Tool clearance at each end of stroke is 30mm and 20mm repctively. Cutting speed is 10m/minute and return speed is 20m/min. feed is 1mm per cycle and the distance the tool moves on either side of the work in width direction is 10mm each.
• In Shaper machine, tool is having reciprocating motion and w/p is clamped on table which is stationary.
• It is mostly suitable for light duty operation. In Shaping large cutting force is transferred to tool.
• In Planer machine, tool is having stationary and w/p is clamped on table which is reciprocating motion.
• It is mostly suitable for Heavy duty operation. In planner large cutting force is transferred to table.
1- Light duty machine used for finishing of material object.
2- job is stationery whereas cutting tool is moving.
While PLANER is
1- Heavy duty machine used when more finishing is required.
2-job can be moved but cutting tool is stationery.
