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Reciprocating machine tools shaper
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- 2. WORKING PRINCIPLE The toolheld in the tool holder mounted on the ram moves forwards and backwards in a straight line over the work piece rigidly held in a vice clamped over the work table.
- 3. WORKING PRINCIPLE Each timethe tool moves forward it cuts a slice of metal from the workpiece. Each time the tool moves backward the tool lifts clear of the workpiece.
- 5. Cutting stroke Returnstroke A - Work A - Work
- 6. PARTS OF SHAPINGMACHINE 1. Base. 2. Column or pillar 3. Cross rail. 4. Saddle. 5. Table. 6. Ram. 7. Tool head. 8. Drive mechanism
- 7. A - SwivelingHead G - Outboard clamp M - Bull Gear S - Crank pin B - Stroke position Adjustment H - Ratchet power cross feed N - Rocker arm T - Ram C - Ram clamp I - Cross feed Screw O - Drive Pinion U - Base D - Tool Holder J - Ways P - Stroke Adjustment for Ram V - Vertical feed E - Crossrail K - Elevating Screw Q - Scotch york W - Column or pillar F - Saddle L - Cross feed arm R - Link X - Pawl
- 9. 1. Base The baseof the shaper supports the column or pillar which supports all the working parts such as ram, work table, drive mechanism etc. Base is a heavy cast iron body.
- 10. 2. Column, Pillaror Body It is a ribbed casting of cellular construction. The top of the column carries the ram slideways. The crank and slotted link mechanism that drives the ram is contained within the column. The driving motor, the variable speed gearbox, levers, handles and other controls of shaper are also contained in the column.
- 11. 3. Cross rail Itcarries the horizontal table slideways and is mounted on the vertical slideways of the column. The cross rail can be raised or lowered by means of an elevating screw in order to suit different thicknesses of work. It also carries the table cross feed screw together with the pawl and ratchet intermittent drive mechanism.
- 12. 4. Saddle Saddle isattached to the cross rail and supports the table. If the table is removed, the work can be bolted or clamped to the T-slots in front of the saddle. Crosswise movement of the saddle causes the work table to move sideways.
- 13. 5. Table Thework table is a box shaped casting with T-slots in its upper surface and down one side. It also has a vee machined in the vertical side to carry cylindrical work.
- 14. 6. Ram Ram isa rigidly braced casting and is located on the top of column. The ram is driven back and forth in its slides by the slotted link mechanism.
- 15. 7. Tool head Thetool head can swivel from 0° to 90° in a vertical plane: The tool head can be raised a or lowered by hand feed for vertical cuts on the workpiece.
- 16. Direction of Movement A- Tool post B - Clapper box C - Tool Slide D - Protractor scale E - Ram
- 17. SPECIFICATIONS OF ASHAPERMaximum ram stroke 700mm Maximum tooloverhang840mm Distance between table surface and ram Maximum 400 mm Minimum 80 mm Dimensions of table working surface 700 mm * 450 mm Maximum travel of table Horizontal 700 mm Vertical 320 mm Horizontal feed per double stroke 0.25--5 mm Motor power 7 kw Overall dimensions 2785 * 1750 * 1780 mm
- 18. TYPES OF SHAPER (a)Design of work table as Standard shaper Universal shaper (b) Driving mechanism as Crank shaper Geared shaper Hydraulic shaper
- 19. (c) Direction oftravel of ram as Horizontal shape Vertical shape (d) Nature of cutting stroke as Push cut shaper Draw cut shaper
- 20. In astandard shaper the work table has only vertical and horizontal movements. Universal shaper has a work table-which may be swivelled around horizontal axes and also adjusted horizontally
- 21. Crank shaper Have acrank and slotted link mechanism to constitute the quick return motion in the driving mechanism. The crank changes the circular motion of the power source to the reciprocating motion of the ram or cutting tool.
- 22. Geared shaper Itis not commonly used. A geared shaper has got a rack under its ram. The rack (and hence the ram) is driven by a spur gear. Hydraulic shaper The drive is neither a crank nor gear, rather it is a hydraulic circuit. Though expensive, it is very efficient. The reciprocating movements of the ram are obtained by the application of oil pressure on the piston in a cylinder.
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- 24. Oil ispumped to Right side of Cylinder Piston moves Left Hand Side, Forward Stroke Shaper dog hits the reversing lever Reversing lever alters valve position Oil is now pumped to Left side of Piston Piston moves Right Side, return Stroke Oil on the Right side of Piston goes to reservoir At the end of Return stroke another trip dog hits reversing lever, reversing lever changes direction of stroke of Piston Thus the Cycle is repeated
- 25. QRM is obtaineddue to the difference in stroke volume volume on Left side of piston is small due to presence of piston rod. Right side volume is larger ( absence of piston rod). Pump pumps same amount of oil both sides. As volume is small on Left side, pressure increases causing Speed of ram to increase in return stroke
- 26. ADVANTAGES OF HYDRAULIC SHAPER Cutting tool works uniformly during cutting stroke. Reverse stroke is obtained without any shock More no. of cutting speeds are obtained Good control on cutting speed Relief valve ensures safety i.e. Machine is not overloaded
- 27. Horizontal shaperhas a ram which reciprocates in the horizontal plane only and are very commonly used to produce flat surfaces. Vertical shaper (also known as slotter) has the ram which reciprocates in vertical plane. It possesses a rotary work table. used to generate internal surfaces, keyways, grooves, slots
- 28. Push cutshapers are of the horizontal push cut type. In this type, cutting occurs as the ram pushes the tool across the workpiece. Draw cut shapers are used primarily in tool and die shops. Cutting is done during the return stroke as the tool is set in a reversed direction to that of the standard shaper. It can take heavy cuts with 'less vibration and strain on the work table.
- 29. SHAPER FEED MECHANISM The feeds of a shaper are usually obtained by means of a pawl and ratchet actuating the feed (lead) screw The driving disc is linked by connecting rod to the rocker arm which carries a spring loaded reversible pawl. As the disc rotates it causes pawl to oscillate about the centre of the feed screw.
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- 31. By offsettingthe driving pin on the slotted disc, the rocker arm is made to oscillate sufficient to move the pawl over one or more teeth of ratchet and so transmit intermittent motion to the Crossfeed lead screw which moves the work table.
- 32. To reversethe direction of table traverse, the pawl is lifted and turned round so that it moves the ratched wheel in the opposite direction. When no feed is required, the pawl is lifted and turned through 90° so that the pin is out of the groove and the pawl is held clear of the ratchet.
- 33. SHAPER OPERATIONS (a) Horizontalshaping (facing top job surface). (b) Vertical shaping (facing side), (c) Shaping of grooves, slots, steps and keyways (d)Angular shaping (Dovetail cutting) (e) Cutting of splines and gear teeth. (f) Irregular cutting.
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- 36. WORK HOLDING DEVICES (i)Vices (ii) Parallel strips (iii) Clamps (iv) Jack (v) Angle plate (vi) Vee blocks (vii) Stop pins and toe dogs (viii) Centres.
- 37. WORK HOLDING DEVICES Shaper Vice Parallel Strips Stop pins and Toe Dogs
- 38. ADJUSTING THE LENGTHOF THE STROKE The closer the pin is brought to the centre of the bull wheel, smaller will be the stroke. Maximum stroke of the ram is obtained when the crank pin is shifted towards the farthest end of the slide. 1. Crank pin Short stroke Long stroke
- 39. ADJUSTING THE POSITIONOF STROKE Clamping lever is loosened and by rotating the hand wheel, screwed shaft will rotate within the ram block. Rotation of the screwed shaft will cause the ram to move forward or backward. Thus position of the ram is adjusted to desired position. Now the clamping lever is
- 41. QUICK RETURN MECHANISM Sincereturn stroke does no cutting, the ram should move faster during return stroke. The shaper drive system incorporates quick return mechanism enabling the ram to move faster during return stroke Thus minimizing the (idle time) Quick Return time.
- 42. SHAPER DRIVE MECHANISMS Slotted link quick return mechanism Whitworth quick return mechanism Hydraulic quick return mechanism
- 43. CRANK AND SLOTTEDLINK A - Clamping nut B - Ram C - Link D - Crankpin E - Slotted crank F - Bull Wheel G - Slot A - Path of crankpin B - Length of stroke C - Cutting stroke D - Idle or return
- 44. When thebull wheel rotates, the crank pin rotates and also slides through the slot in the slotted crank. This makes the crank to oscillate about its one end E. This oscillating motion of the crank makes the ram to reciprocate. Rise and fall of the crank is taken care by the lever ‘C’
- 45. The positionof the crank pin in the slot in the bull wheel decides the length of the stroke of the shaper. The further it is away from the centre of bull wheel, the longer is the stroke.
- 46. The cuttingstroke of the ram is completed while the crank pin moves from A to A1 and the slotted link goes from left to right. Similarly, during return stroke crank pin moves from A1 to A and the link changes its position from right to left.
- 47. Since thecrank pin rotates with uniform velocity and angles of A1A is smaller, it is obvious that the idle return stroke is quicker than the forward cutting stroke and hence the slotted link mechanism is known as quick return mechanism. Cutting time/Idle time = angles of AA1/angles of A1A
- 50. WHITWORTH QUICK RETURN MECHANISM 1.Driving pinion 2. Crank pin 3. Sliding block 4. Crank plate 5. Pivot for crank plate 6. Connecting rod 7. Connecting pin for ram 8. Ram 9. Pin
- 51. Bull gearrotates at constant speed. Crank pin 2 with the sliding block 3 will rotate on a crank circle of radius A2 and the sliding block 3 will cause the crank plate to rotate about the point 5 with a variable angular velocity.
- 52. Rotary motionof the crank pin 9 will be converted in to reciprocating motion of the ram. When the pin 2 is at position C, the ram will be at the extreme backward position. At position B, ram is at the forward position.
- 53. Length ofthe stroke is adjusted by shifting the position of pin 9 closer or away from pivot 5 Position of stroke may be altered by shifting the position of pin 7 on the ram.
- 54. DIFFERENCE BETWEEN THE TWOQRM In whitworth the slotted or driven member is inside of the crank pin circle, whereas in crank and slotted link, the pivot is outside of the crank pin circle. As a result of this difference, part 4 in ww, has a continuous rotary motion, while slotted link E swings through a definite angle
- 55. DIFFERENCE BETWEEN THE TWOQRM On entering the cut, the highest pressure on the tool and the slowest speed is available. On entering the cut the maximum pressure is holding the ram down in its slides and so steadying the ram when most necessary.
- 56. The slottedlink motion is directly opposite to all the three points enumerated above
- 57. Machining time L= Length of the cutting stroke in mm M = Ratio between return time to cutting time n= Number of double strokes of the ram per minute or RPM of the bull wheel v= Cutting speed in m/min
- 58. CUTTING SPEED, FEED,DEPTH OF CUT CUTTING SPEED = Length of the cutting stroke in mm/1000 (m/min) ------------------------------------------------- Time required by the cutting stroke in min Time taken by the cutting stroke = L / (1000 x v) Time taken by the return stroke = m x cutting stroke time = (m x L)/(1000x v) Time taken to complete = cutting stroke + return stroke time one double stroke )1( 1000 m v L
- 59. Machining time Number ofdouble strokes per minute (n) = Total number of double strokes to complete the job = B / S B = breadth of the work in mm, S = feed in mm/double stroke Total time taken to complete the cut = Time to complete one double stroke x number of double strokes )1( 1000 mL v n )1( 1000 m Sv BL
- 60. ADVANTAGES OF SHAPERS The single point tool used is in-expensive Setup of shaper is very quick Thin jobs can be easily machined because of lower cutting forces
- 61. Problem 1… Ina shaper, the length of stroke is 200mm, number of double strokes per minute is 30 and the ratio of return time to cutting time is 2:3 (normally). Find the cutting speed
- 62. Solution V =length of the cutting stroke / Time taken by the cutting stroke m=2/3 V=30x200(1+2/3) -------------------- = 10m/min 1000
- 63. Problem 2… Findthe time required for taking a complete cut on a plate 600 x 900mm, if the cutting speed is 9m/min. The return time to cutting time ratio is 1:4 and the feed is 3mm. The clearance at each end is 75mm.
- 64. Solution In ashaper a stroke length of more than 900mm is not ordinarily available so the work is placed on the table to take a cut of 600mm plus the clearances. Total length of the stroke = 600 + 75 + 75 = 750mm m=1/4 , v=9m/min 750x900 -------------(1+1/4)=31.25min 1000x9x3 )1( 1000 m Sv BL
- 65. Problems…. Find thecorrect number of strokes per minute to use on a shaper cutting a m.s piece 250mm long and 150mm wide. The cutting speed is 20mpm for HSS tool. If a feed of 1mm be used then how much time will be taken in machining one surface of job. What will be the machining time if carbide tool be used to cut at 100mpm.