Broaching machine

Machine tools and meterology

1. Module 3 Broaching process Gear manufacturing methods

2. BROACHING PROCESS It is a process of machining a surface with a special multipoint cutting tool called BROACH which has successively higher cutting edges in a fixed path

3. Specification of a broaching machine Maximum length of stroke Maximum force developed by the slide Type of drive for straight line motion Power rating of the electrical motor Speed and feed range Weight of the machine Floor space rquired

4. Different types of broaching tools

5. Types of broaching machines a) According to the nature and direction of primary cutting motion Horizontal broaching machine Vertical broaching machine Continous broaching machine According to the purpose Internal broaching machine External or surface broaching machine c) According to the method of operation Pull broaching machine Push broaching machine

6. d) According to the function Keyway broaching machine Burnishing broaching machine Spline broaching machine Round hole broaching machine Surface broaching machine e) According to the motion of the broach tool relative to the work Straight line motion broaching machine Stationary broach tool broaching machine

7. HORIZONTAL BROACHING MACHINES

8. VERTICAL BROACHING MACHINES Push down type Pull down type Pull up type

9. VERTICAL BROACHING MACHINES

10. CONTINUOUS BROACHING MACHINES These are used for high production rate of small parts Horizontal Vertical Rotary type

11. HORIZONTAL CONTINUOUS BROACHING MACHINE

12. Construction and Working : In this type of machine the work pieces are carried by an endless chain Work pieces are loaded by means of fixtures. Fixtures are mounted on the continuously moving chain or conveyor. Broach head does not move. It is the fixed member of the machine. Conveyor is made to rotate continuously by the two drums. Out of these two drums, one drum is given power, the other drum rotates freely. Chain connects these drums. Toothed wheel is mounted on each drum to drive the chain. Power driven drum rotates at constant speed by the electrical motor and gear drive. As the drum rotate, the work pieces pass under the broach tool and the broach tool removes the material.

13. BROACHING TOOL

14. BROACH TOOL - NOMENCLATURE

15. Types of broaching tools According to the method of operation Push broach Pull broach 2. According to the kind of operation Internal broach External broach 3. According to their construction Solid broach Built up of replaceable section Inserted tooth broach Overlapping teeth broach Progressive cut broach

16. Broaching tool materials High speed tool steels such as alloy steel and stainless steel TiN coated carbides Aluminium Brass 12L14

17. SPLINE BROACHING BROACHING OPERATIONS

18. Keyway Broacher

19. Basic principle of broaching

20. Like any other machining, broaching is also accomplished through a series of following sequential steps : • Selection of broach and broaching machine • Mounting and clamping the broach in the broaching machine • Fixing workpiece in the machine • Planning tool - work motions • Selection of the levels of the process parameters and their setting • Conducting machining by the broach.

21. Mounting blank in broaching machine

22. Different Types Of Broaches And Their Applications Broaches can be broadly classified in several aspects such as, • Internal broaching or External broaching • Pull type or Push type • Ordinary cut or Progressive type • Solid, Sectional or Modular type • Profile sharpened or form relieved type

23. Internal broaching and broaches Internal broaching tools are used to enlarge and finish various contours in through holes preformed by casting, forging, rolling, drilling, punching etc. Internal broaching tools are mostly pull type but may be push type also for lighter work. Pull type internal broaching tools are generally provided with a set of roughing teeth followed by few semi-finishing teeth and then some finishing teeth which may also include a few burnishing teeth at the end.

24. Internal broaching – tools and applications.

25. External broaching External surface broaching competes with milling, shaping and planing and, wherever feasible, outperforms those processes in respect of productivity and product quality. External broaching tools may be both pull and push type.

26. Typical external broaching (a) making slot (b) teeth of gear sector

27. Pull type and push type broache s During operation a pull type broach is subjected to tensile force, which helps in maintaining alignment and prevents buckling. Pull type broaches are generally made as a long single piece and are more widely used, for internal broaching in particular. Push type broaches are essentially shorter in length (to avoid buckling) and may be made in segments. Push type broaches are generally used for external broaching, preferably, requiring light cuts and small depth of material removal.

28. Ordinary – cut and Progressive type broach Most of the broaches fall under the category of Ordinary – cut type where the teeth increase in height or protrusion gradually from tooth to tooth along the length of the broach. By such broaches, work material is removed in thin layers over the complete form. Progressive – cut type broaches have their teeth increasing in width instead of height.

29. Progressive – cut type broaches; (a) single bar and (b) double bar type

30. (a) Solid, (b) Sectional and (c) Segmented broaches

31. ADVANTAGES AND LIMITATIONS OF BROACHING Major advantages • Very high production rate (much higher than milling, planing , boring etc.) • High dimensional and form accuracy and surface finish of the product • Roughing and finishing in single stroke of the same cutter • Needs only one motion (cutting), so design, construction, operation and control are simpler • Extremely suitable and economic for mass production

32. Limitations • Only through holes and surfaces can be machined • Usable only for light cuts, i.e. low chip load and unhard materials • Cutting speed cannot be high • Defects or damages in the broach (cutting edges) severely affect product quality • Design, manufacture and restoration of the broaches are difficult and expensive • Separate broach has to be procured and used whenever size, shape and geometry of the job changes • Economic only when the production volume is large.

33. Manufacturing of Gears

34. Basic Purpose of Use of Gears Gears are widely used in various mechanisms and devices to transmit power and motion positively (without slip) between parallel, intersecting ( axis) or non-intersecting non parallel shafts, • without change in the direction of rotation • with change in the direction of rotation • without change of speed (of rotation) • with change in speed at any desired ratio

35. Features of spur gears

36. Gears are broadly classified (a) According to configuration • External gear • Internal gear Configuration of (a) external and (b) internal gears

37. (b) According to axes of transmission Spur gears – transmitting rotation between parallel shafts o Straight toothed o Helical toothed ⎯ Single helical ⎯ double helical (herringbone)

38. Bevel gears – transmitting motion between intersecting shafts (axes) o Straight toothed o Helical toothed ⎯ Spiral bevel gear Helical toothed bevel gears are used for smoother and larger torque transmission.

39. Gears transmitting motion and power between non-parallel non-intersecting shafts o Worm and worm wheel o Spiral gears o Skewed or hypoid bevel gears

40. (c) According to pattern of motion • Rotation to rotation : wheel type gears • Rotation to translation or vice versa – e.g. rack and pinion o Straight toothed

41. Materials generally used for making gears are : Δ Ferrous metals – for high loads • Grey cast iron – preferred for reasonable strength and wear resistance, ease of casting and machining and low cost • Forged or rolled high carbon steels and alloy steels (Ni-Cr, Mo etc.) which are either fully hardened or surface hardened for use under high stresses and speed. Δ Non ferrous metals – for light load • Aluminium, bronze and brass are used for making gears having fine teeth and working at very light load – e.g., in equipments, toys etc. or against hard steel mating gears • Aluminium alloys like aluminium bronze, Zinc – Al. alloy etc. Δ Non-metals – widely used for light load, non-precision and noiseless operation. Polymers (plastics) : both themoplastic and thermosetting type and various composites (metals, graphite,

42. Size or major dimensions Dimensional features that are used to express or specify the gears are ; Δ For spur gears and worm wheels ⎯ number of teeth, z ⎯ module, m ⎯ helix angle, if any (θ) ⎯ width (b) Pitch Circle Diameter (PCD) = mZ / cos θ

43. • Gear geometry Some geometrical features also need to be mentioned while specifying gears, such as, Δ Pressure angle Δ Addendum and dedendum

44. • Special features If there be any special feature, that also has to be included with gear specification, such as ⎯ Tooth bevelling for safe handling ⎯ Tooth crowning for uniform wear and long service life ⎯ Tooth rounding for easy engagement

45. SAND CASTING Characteristics : • Cheaper low quality gear in small numbers • The tooling costs are reasonable • Poor Surface finish and dimensional accuracy • Due to low precision and high backlash, they are noisy. • They are suited for non- critical applications Applications: (without finishing operation) Toys , small appliances, cement-mixer barrels, Hoist gearbox of dam gate lifting mechanism, Hand operated crane etc., Materials: C I, cast steel, bronzes, brass, ceramics

46. DIE-CASTING Characteristics : • Better surface finish and accuracy (tooth spacing and concentricity) • High tooling costs • Suited for large scale production Applications: Applications: Instruments, cameras, business machines, washing machines, gear pumps, small speed reducers, and lawn movers. Materials: Zinc, aluminium and brass The gears made from this process are not used for high speeds and heavy tooth loading. Normally applied for small size gears.

47. INVESTMENT CASTING OR LOST WAX PROCESS Characteristics: • Reasonably accurate gears • Applicable for a variety of materials • Refractory mould material • Allows high melt-temperature materials • Accuracy depends on the original master pattern used for the mold. Materials: • Tool steel, Nitriding steel, Monel, Beryllium copper. • The process is used only if no other process is suitable since production cost is high.

48. Helical gears and combination of gears

49. Form milling by end milling cutter

50. Rack generation

51. Setup for Gear Shaping Machine

52. Manufacture of Gears Stages generally are : ⎯ Preforming the blank without or with teeth ⎯ Annealing of the blank, if required, as in case of forged or cast steels ⎯ Preparation of the gear blank to the required dimensions by machining ⎯ Producing teeth or finishing the preformed teeth by machining ⎯ Full or surface hardening of the machined gear (teeth), if required ⎯ Finishing teeth, if required, by shaving, grinding etc. ⎯ Inspection of the finished gears.

53. Preforming Gear Blanks Casting Sand casting Metal mould casting Die casting Investment casting Shell mould casting Centrifugal casting Manufacture of gears by rolling Powder metallurgy Blanking in Press tool Plastic moulding Extrusion process Wire EDM

54. Production of Gear Teeth by Machining Preformed blanks of approximate shape and irregular surface are machined to desired dimensions and finish and then the teeth are produced generally by machining and occasionally by rolling. Full gears with teeth are made by different processes and then finished by further machining and / or grinding Accurate gears in finished form are directly produced by near – net – shape process like rolling, plastic moulding , powder metallurgy etc., requiring slight or no further finishing.

55. Gear teeth are produced by machining based on ο Forming – where the profile of the teeth are obtained as the replica of the form of the cutting tool (edge); e.g., milling, broaching etc. ο Generation – where the complicated tooth profile are provided by much simpler form cutting tool (edges) through rolling type, tool – work motions, e.g., hobbing , gear shaping etc.

56. Methods of production of gear teeth by machining on Forming principle Shaping, planing and slotting Milling Parallel multiple teeth shaping Broaching

57. Gear teeth can be produced by both disc and end mill type form milling cutter

58. Fast production of teeth of spur gears

59. Production of gear teeth by machining on Generation principle Generation method is characterised by automatic indexing and ability of a single cutter to cover the entire range of number of teeth for a given combination of module and pressure angle and hence provides high productivity and economy.

60. Sunderland method using rack type cutter Rack type HSS cutter (having rake and clearance angles) reciprocates to accomplish the machining (cutting) action while rolling type interaction with the gear blank like a pair of rack and pinion.

61. Gear shaping Gear shaping is similar to the rack type cutting process, excepting that, the linear type rack cutter is replaced by a circular cutter

62. Gear Hobbing HSS or carbide cutter having teeth like gear milling cutter and the gear blank apparently interact like a pair of worm and worm wheel.

63. Having lesser number (only three) of tool – work motions, hobbing machines are much more rigid, strong and productive than gear shaping machine. But hobbing provides lesser accuracy and finish and is used only for cutting straight or helical teeth (single) of external spur gears and worm wheels. Gear Hobbing

64. Hob teeth are shaped to match the tooth space and are interrupted with grooves to provide cutting surfaces It rotates about an axis normal to that of the gear blank, cutting into the rotating blank to generate the teeth Most accyrate of the roughing processes since no repositioning of tool or blank is required and each tooth is cut by multiple hob-teeth, averaging out any tool errors Excellent surface finish is achieved by this method and it is widely used for production of gears Gear Hobbing

65. Setup for Gear Hobbing Machine

66. Manufacture of bevel gears In manufacture of bevel gears, first the blanks are preformed by casting or forging followed by machining to desired dimensions in lathes or special purpose machine. Then the teeth are produced in the blank by machining.

67. Straight toothed bevel gear o Forming by milling cutter – low productivity and quality hence employed for production requiring less volume and precision o Generation – high accuracy and finish, hence applied for batch to mass production. In generation process, the inner flanks of two adjacent teeth are developed with involute profile by the straight teeth of the cutters under rolling action.

68. Manufacture of bevel gears

69. Manufacture of BEVEL gear

70. TYPES OF BEVEL GEARS

71. Manufacture of Spiral gears Two common production methods of spiral bevel gears in gear industry are face-milling and face- hobbing

72. During the tooth generation process, in the face-milling technique , the cutting wheel interacts with one tooth space and is then indexed to the next location. The process continues until all tooth spaces are finish cut to the required depth. In the face- hobbing technique individual cutting blades interact with different tooth spaces. Face- hobbing is a continuously indexing tooth generation process, where all the teeth are cut a little at a time, until all the teeth are finished to the final desired depth. With the face hobbing process, the curve in the lengthwise direction of the tooth is an extended epicycloid and is a function of the relative roll between the workpiece and the cutter.

73. Spiral bevel gears are cut with a generating machine that uses a series of cutting blades mounted on a circular tool holder. The tooth profiling between the cutter and the generating tooth does not require any rotation of the generating gear

74. Manufacture of worm Screw like single or multi-start worms (gears) made of steel are generally made by machining like long thread milling or by cold rolling like thread rolling followed by heat treatment for surface hardening and finishing by grinding.

75. Gear Errors Forming principle – Gear errors due to ( i ) Incorrect profile of the cutting (ii) Incorrect positioning of the tool with respect to the tool (iii) Incorrect indexing of the blank Generation principle – Gear errors due to ( i ) Errors in the manufacture of the cutting tool (ii) Errors in the positioning of the tool with respect to the work (iii) Error in the relative motion during the generating

76. Gear Finishing Gear shaving Gear grinding Burnishing Lapping Honing

77. Methods of gear teeth finishing Gear teeth, after preforming and machining, are finished generally by; For soft and unhardened gears • gear shaving • gear rolling or burnishing For hard and hardened gears • grinding • lapping For soft but precision gears • shaving followed by surface hardening and then lapping

78. Gear shaving Teeth of straight or helical toothed external spur gears and worm wheels of moderate size and made of soft materials like aluminium alloy, brass, bronze, cast iron etc. and unhardened steels are mostly finished by shaving process. Finishing action of shaving cutters work apparently as a spur gear, rack or worm in mesh with the conjugate gears to be finished. All those gear, rack or worm type shaving cutters are of hard steel or HSS and their teeth are uniformly serrated to generate sharp cutting edges. While interacting with the gears, the cutting teeth of the shaving cutter keep on smoothening the mating gear flanks by fine machining to high accuracy and surface finish.

79. Shaving is similar to gear shaping, but uses accurate shaving tools to remove small amounts of material from a roughed gear to correct profile errors improve surface finish Gear Shaving

80. For such minute cutting action, the shaving teeth need an actual or apparent movement relative to the mating teeth along their length.

81. Gear shaving cutters

82. Gear rolling or burnishing In this method the machined gear is rolled under pressure with three hardened master gears of high accuracy and finish. Minute irregularities of the machined gear teeth are smeared off by cold plastic flow, which also helps in improving the surface integrity of the desired teeth.

83. Gear teeth grinding Grinding is a very accurate method and is, though relatively expensive, more widely used for finishing teeth of different type and size of gears of hard material or hardened surfaces. Properly formed and dressed wheel finishes the gear teeth flanks by fine machining or abrading action of the fine abrasives. Like gear milling, gear grinding is also done on two principles Forming Generation, which is more productive and accurate

84. Gear Lapping Principle:- It is the process of refining the gear element after the heat treatment. Process is done by rotating the gear and the lap tool as inter meshing gears, with abrasive compound forced between the teeth. • It is the process used for improving surface finish by reducing roughness, waviness & other irregularities on the surface. • Material for lapping tool can be natural or artificial abrasives depending on work piece material. • Lubricant is used to hold or retain the abrasive grains during operation.

85. Lapping operation is done two methods 1. Hand lapping:- Work piece is held in hand & the motion of the other enables the rubbing of two surfaces in contact, this method is used for press dies, valve seats etc. 2. Machine lapping:- It is done to obtain highly finished surfaces on work piece, like ball and roller bearings , engine parts.

86. LAPPING

87. Gear Honing Principle • It is a super finishing operation used for previously machined surfaces. • It is used for finishing internal cylindrical surfaces, drilled or bored holes the tool is called as Hone which is made out of bonded abrasive stone made in the form of stick. • The tool moves back & fourth while rotating about its axis.

88. HONING