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Gear Manufacturing Process.pdf

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Gear Manufacturing ProcessGEARS IN AUTOMOBILE TRANSMISSIONS ?? A gear box transmits the engine power to the driving ?wheels with the help of different gearing systems. ?? Different gear combinations are used to give the smooth ?running, the lower fuel consumption, and the optimum ?driving comfort. ? Generally, passenger car transmissions are provided ?with 4-5 forward speeds and one reverse speed. ?? In front wheel models, hypoid gears have been replaced ?by helical gears. ?? parallel axes spur and helical gears are the main gears ?in automotive transmission. Gear Materials The materials of most of the gears used for transmitting reasonable ?torque and speed mainly need to be mechanically strong in shear and ?bending, sufficiently tough and resistant to wear, fatigue and chemical ?degradation. ?The material for any gear is selected based on, ?1) The working condition ie, power, speed and torque to be transmitted ?2) Working environment, i.e., temperature, vibration, chemical etc. ?3) Ease of manufacture ?4) Overall cost of material and manufacture RAW MATERIALS FOR TRANSMISSION GEARS ?? Alloy steels are most favoured gear material. ? Case hardening steels provide the ideal features ?required for gear material. ?? For gear teeth, the surface is to be hard with soft and ?tough core to provide wear and fatigue resistance. ?? Case hardening steels do have varying chemical ?composition, and are named accordingly, e.g. Chrome ?Steel, Low molybdenum steel, Chrome molybdenum ?steel, Nickel-chrome-molybdenum steel. Manufacturing Process ?? Because of growing ?demand manufacturers are ?now increasingly seeking ?machining tools and ?technology that can meet ?with the tough challenges. ?? Now produced in near-net ?shape, with a cut in ?production as well as ?labour costs and ?elimination or reduction of ?wastes. ?? greater freedom in the ?choice of materials. (Image of an assembly line in a Gear manufacturing unit)Gearbox 1.Gear case/housing 2.Shafts 3.Gears ?& Shift Gears ( spur, ?helical, ?internal) 4.Differential case 5. Straight, spiral, hypoid GearboxGears There are many different types of gears ?for transmitting motion, resulting in a wide variety of gear-making processes.Functions of the Gearbox Casing ? Provides structural support for the shaft bearings. This in turn ?helps in gear loading. ? Transfers the reaction of mechanical rotation (torque) to the ?other supporting structure of the gearbox or drive elements. ? Prevents the lubricant from spreading and also prevents the ?unwanted particles from coming inside. ? Provides safety provision and also reduces noise intensity. ? Reduces the amount of heat that generated due to the internal ?friction. ? It increases the external and visual qualities of the gearbox. Gearing arrangement in Gearbox ? Various components are: cycloidal, worm, bevel, planetary, spur and helical. ? Bevel gear is actually a gear wheel that is meshed with another bevel gear in such a way so ?that the shafts can form an angle, which is less than 180 degrees. ? Helical gears -- join shafts that are parallel. The involute teeth of the helical gears are cut ?at an angle to the axis of the rotation. If there are two mating helical gears in the gearing ?arrangement of the gearbox, then they must have equal helix angle but opposite hands. ? Spur gears - connect parallel shafts. They have curled teeth which are parallel to the shaft ?and may have either external or internal teeth. ? The planetary gears may present in total number of two and they are present either on or ?inside a large gear. ? Intense gear ratio is possible with these gears. ? Used when the ?intention is to turn the input in the same direction of the output. ?Planetary gears can be ?designed along with a set of planetary cones or with a gear set. ? Cycloidal gears are used in pair form and they are arranged in such a way so that the angle ?formed by them should be equal to 180 degrees. The formation of 180 provides balance to ?the load and these gears are driven by many crank shafts. Multiple shafts are present for ?sharing the load and to enhance the twisting state firmness. ? The worm gears are wrapped around a central axle and these have slant plane. This kind of ?gear consists one or more than one teeth and these teeth are present in the screwed thread ?form.Common Materials used for Gearboxes ? Steel ? Cast Iron ? Aluminum ? Stainless Steel ? Non-metallic Phenolic ? Tungsten ? Bronze? In a typical manufacturing cycle the gear blank goes through many processes ?from being transformed from the raw material to the final end product. Actually ?the gear blank is the work piece which is processed to give the final shape of ?gears. A lot of things goes into making a quality gear blank. Materials for Gear Blanks ? low carbon steel ?? high grade carbon steel ? Aluminum Gear Blanks ? Stainless Steel Gear Blanks ? Brass Gear Blanks. ?? Typical examples range from completely machined gear blank, with or without ?keyways. ?? Other options of gear blanks include saw cut stock, or even semi finished to ?meet the customers needs. ?? Today with the advancing technology the nonmetallic gear blanks are also used ?plastic gear blanks are very popular. Gear BlankGear Materials Type Material Outstanding features Applications Precision Rating ?Ferrous Cast Iron ?Low cost, good machining, high ?internal damping ?Big size, moderate power ?rating, Commercial gears ?Commercial quality ?Cast Steel Low cost, high strength ?Power Gears, medium ?rating ?Commercial quality ?Plain Carbon Steel Good machining, Heat treated ?Power Gears, medium ?rating ?Commercial to ?medium precision ?Alloy Steels ?Heat treated, high strength and ?durability ?Strict power requirements High precision ?Stainless Steel ?High corrosion resistance, ?nonmagnetic ?Low power rating Good Precision ?Non ?Ferrous Aluminium alloys ?Light weight, noncorrosive, good ?machinability ?Very light duty instrument ?gears ?High precision ?Brass alloys ?Low cost, noncorrosive, good ?machinability ?Low cost commercial ?equipment ?Medium precision ?Die cast alloys Low cost, low strength ?High production, low ?quality, commercial ?Low grade ?commercial ?Non ?Metallic Nylon ?No friction or lubricant, high water ?absorption ?Long life, low nose, low ?loads ?Commercial quality ?Delrin Wear resistant, long life Low loads Commercial quality Selection of Gear Materials ? Allowable bending and hertz stress ? Wear resistance ? Impact strength ? Water and corrosion resistance ? Manufacturing cost ? Size ? Weight ? Reliability ? Lubrication requirements ? No Moisture Absorption ? Dimensionally Stable ? Stress-Free structure ? Environmental and surface temperature- ?It has been found that if there is friction the surface temperature of the ?gear shows a tendency to rise.GEAR MANUFACTURING PROCESSES - IN GENERAL ?? Gear manufacturing processes can be grouped in two ?categories. ?? Category one relates to teeth cutting, finishing and all ?necessary operations related to gear tooth profiles, such as ?hobbing, shaping, shaving, honing, etc. ?? Category two relates to the rest of the conventional ?machining, such as, drilling, milling, grinding, etc. ?GEAR CUTTING ?? Gear hobbing and shaping are the most commonly used ?cutting processes used for generating the gear teeth. ?Basis for selection of either of the two depends on ?application: COMPARISON OF PROCESS CAPABILITIES OF ?HOBBING & SHAPING Steps in the Manufacturing ?Process of Gears ? Complex step right from selecting the right material to finally doing the ?finishing process for getting an optimum quality gear ? Gear blanks – rough machining ? Then, completely stress relieved to minimize the distortion due to carburizing. ?? Blanks subsequently undergo the finishing process. ?? Gear cutting process takes place giving allowance on the tooth flank for grinding. ? Grinding and other steps takes place. ?? Following are the steps in the gear manufacturing processes: ?? Inject Molded Gears ?? Powder Metal Gears ? Gear Blank ? Gear Cutting [Hobbing or Broaching or Shaping or Milling or ?Wire cut edm or form cutting] ?? Heat Treatment of Gears ?? Finishing ? Gear Grinding, Gear Deburring, Gear Shaving, Lapping, HoningManufacturing processTypical Gear Mfg process The typical ?gear-making ?process (for ?very ?accurate ?gears) ?involves both ?hobbing and ?shaving ?followed by grinding ?after heat ?treating.Form cutter The basic method of machining a gear using a form cutter (left) to mill out the space between ?the teeth using the form cutter (middle) or the stocking cutter (right) to machine the gear. ?(Courtesy of Brown and Sharpe Manufacturing Company.)Hobbing cutter(a) Three views of hob and gear blanks (small spur gear). ?(b) Hob. ?(c) Schematic of mechanism of a hobbing machine, shown hobbing a large spur gear.On the upper left, the method for cold forming gear ?teeth on a spline using three dies is shown. (Upper ?right) Worm gear being roll formed by means of two ?rotating rolling tools with typical worm made by ?rolling. (Lower left) Gear made by rolling. (Courtesy ?of Landis Machine Company.)Selecting the Correct Material ? A correct gear blank should have a correct wall thickness. ?This ensures the wall thickness between the tooth root ?diameter and outside diameter of the metal core is just ?right. ? Suitable core size selection of the gear blank: ?? Authentication of the bore dimensions including the keyway. ?? Making sure the top of the keyway does not intersect the ?metal core OD. ?? For optimal use, the metal core should be around half of the ?gear's OD.Knurled Core Advantages ? provide high torque transmission ? perform heat dissipation from the ?shaft to the metal through the ?gear teeth. ?? knurled core has virtually replaced ?conventional options like the ?hexagonal or the round notched ?metal core. ?? distinct advantage is the closer ?minimum wall thickness in context ?to both bore and root diameter, ?this is especially profound in ?border line cases.The following image ?shows the different ?types of cores:Gear Cutting ? Gear Hobbing ? Gear Shaper cutterHobbing ? Hobbing is a sort of generating process, ?where the metal is gradually removed for a ?gear teeth to evolve out. ?? In this process there is simultaneous rotation ?of a hobbing cutter and gear blank for ?transferring the hob's profile on to the gear ?blank. Hobbing Cutters ? Involute Gear Hob ? Involute Spline ? Sprocket Hobs ? Worm Wheel Hobs ? Serration HobGear HobbingGear HobbingGear Hobbing MachineGear Hobbing ? Gear hobbing is considered to be the most productive and viable of ?all a generating process. ? With Gear hobbing process toothed wheels of gears are ?manufactured with high quality and gives excellent performance. Hobbing is only used to produce spur and worm gears. Internal ?gears or shoulder gear cannot be worked up in Hobbing process. ?? The hob is applied for generating the involute teeth. The hob is ?essentially a cylindrical tool which is positioned straight. ? In hobbing process the hob as well as the workpiece rotate ?continuously displaying a rotational relationship. A thread having the ?similar cross section as that of rack tooth is helically wound around ?the Hob. The Hob is then subsequently rotated. ?? The gear blank is fed onto the hob based on the depth of cut. The ?helix pattern of a rotating hob is identical to that of a moving rack. ?? Gear hobbing is an efficient process however it comes with ?complicated process kinematics, and some how difficult tool wear ?mechanisms.Advantages of Gear Hobbing ?Process ? High productivity ?rate ?? Economical and ?efficient operation ?? Accuracy ?? Close tolerances ?? Versatility of ?operations ?? Smooth finishes Gear Hobbing Machines ? There are different varieties of Gear ?Hobbing Machines. These machinces ?are used in effective production of ?accurate Spur, Helical, Worm Gears, ?Sprockets etc. These machines are ?manufactured with certain features ?such as follows: ?Gears and shafts of Alloy Steel. ?? Oil reservoirs, to ensure proper ?lubrication of gears and bearings. ?? Bed and Column of Close Grain Casting, ?perfectly ribbed with 'V' type guide ?ways. ?? Oil reservoirs provided to ensure ?through lubrication of gears and ?bearings. ?? Indexing Worm Wheel made of high ?grade Bronze material. Involute Gear Hob ? They can generate ?gears with maximum ?precision. They are ?used when there ?would be no tooth ?finishing operation ?afterwards and ?there is need for ?better precision ?before tooth shaving ?operations.Involute Spline ? They have an unique ?stud tooth depth to ?cut all types of ?standard or ?nonstandard involute ?SplinesSprocket Hobs ? They are used for ?cutting roller chain ?sprockets for a ?range spanning from ?1/4th inch-3 inch ?pitch. Can be ?produced in single or ?multi start.Worm Wheel Hobs ? They are designed ?for plunge cutting. ?The Worm wheel ?hobs are unique in a ?way, they match the ?wormshaft with ?sharpening allowance. ?They can be of ?shank or shell type.Serration Hob ? They are designed ?for cutting the ?serrations as per job. ?They give high ?accuracy.Gear Shaper Cutter A Gear shaper cutter is essentially a gear that has a ?teeth, which is relieved for providing appropriate ?cutting edges and clearances. The stroking, along with ?related rotation of the Gear shaper cutter and the ?workpiece translates into a molding-generation ?process. Shaper cutter are one of the best process ?to produce gears. This technology is a very suitable ?replacement for hobbing which is sometimes not ?possible due to problems of accessibility.Gear Shaper (Top) Generating action of a ?Fellows gear shaper cutter. ?(Bottom) Series of photographs showing various ?stages in generating one tooth in ?a gear by means of a gear shaper, action taking place from ?right to left, corresponding to ?the diagram above. One tooth of the cutter was painted white. ?(Courtesy of Fellows Gear ?Shaper Company.)Gear Shaper This machine tool is a gear shaper. The blank is ?rotating while the cutter is reciprocating vertically, as shown in the inset. The tool is very ?complex and is shown in detail below. (Courtesy ?Fellows Gear Shaper Company.)Gear Shaper This machine tool is a gear shaper. The blank is ?rotating while the cutter is reciprocating vertically, as shown in the inset. The tool is very ?complex and is shown in detail below. (Courtesy ?Fellows Gear Shaper Company.)There are following types of Gear ?Shaper cutter available…….Disc Type Shaper Cutter ? Disc type cutters are ?effective for cutting ?any type of gear. ?Internal, external, spur, ?helical etc. They are ?also effective for ?cutting sprockets, ?splines, serrations or ?other types of involute ?forms. Popular cutters ?have bore diameters ?between 10mm-120mm ?or ?“ to 4“.Shank Type Cutters ? They are essentially ?designed to cut ?internal gears, both ?spur and helical. Can ?also be designed for ?externals. These are ?full form generated ?cutters whatsoever be ?the pitch circle ?diame

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