Gear Hobbing

Gear Hobbing Prepared by Nabeel Ali Naqvi & Asif Jelani

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Preamble Hobbing IntroductionTypes of HobbingHobbing ProcessHobbing machine and SettingCalculation of Machine ConstantIndexing GearFeed GearGear data requiredNo. of TeethDP/ModuleO/Dia. of Gear to be GeneratedDepth of Tooth to be GeneratedPAHob Cutter SelectionHob NomenclatureSingle Start/Double Start Gear Type to be Generated (Spur or Helical) (RH of LH)Module or DPPressure Angle of WPLead of Helix of CutterCutting Depth

Gear HobbingGear hobbing is a multipoint machining process in which gear teeth are progressively generated by a series of cuts with a cutting tool known as hob.Both the hob and the workpiece revolve constantly as the hob is fed across the face width of the gear. blank.

Gear HobbingA machining process for making gears, splines and sprockets on a hobbing machine, which is a special type of milling machine. Compared to other gear forming processes it is relatively inexpensive but still quite accurate, thus it is used for a broad range of parts and quantities.Types of Hobbing MachineThere are two main types of hobbing machine.

Vertical Hobbing Machine.Horizontal Hobbing MachineMain Parts of Hobbing machine

Mandrel ArborTail stoke

Electric feed

Electric Panel

Depth of cut

Scale: 1 small division=0.025 mmCutter shifting mechanism

On completion of 1 revolution of W.P, cutter shifts 0.5mm Electric systemCutter motorHydraulic motorCoolant motorLubrication motorFeed motorRapid motor Electric system

Oils for HobbingCutting oil: Neat metalHydraulic oil: 68Lubrication oil: Gear oil 100Process

Hobbing machine uses two non-parallel spindles, one mounted with a blank work piece and the other with the hob. The angle between the hob's spindle and the work piece's spindle varies, depending on the type of product being produced. For example, if a spur gear is being produced, then the hob is angled equal to the helix angle of the hob; if a helical gear is being produced then the angle must be increased by the same amount as the helix angle of the helical gear. The two shafts are rotated at a proportional ratio, which determines the number of teeth on the blank; for example, if the gear ratio is 40:1 the hob rotates 40 times to each turn of the blank, which produces 40 teeth in the blank.

ProcessThe hob is then fed into work piece until the correct tooth depth is obtained. Finally the hob is fed into the work piece parallel to the blank's axis of rotation.

Gear hobbing Schematic Diagram

Process CharacteristicsIt is a gear generating process that uses a hob cutter

Cutters and blanks rotate in a timed relationship

Maintains a proportional feed rate between the gear blank and the hob

Cuts several teeth on a progressive basis used for high production runs

EquipmentModern hobbing machines, also known as hobbers, are fully automated machines that come in many sizes, because they need to be able to produce anything from tiny instrument gears up to 10 ft (3.0 m) diameter marine gears. Each gear hobbing machine typically consists of a chuck and tailstock, to hold the work piece or a spindle, a spindle on which the hob is mounted, and a drive motor.Gear data required for Hobbing No of teethD.P/ModuleOuter diameterDepth of Tooth to be GeneratedPressure Angle Criteria for Machine SelectionCentre distance of Machine (Distance between Arbor & Mandrel)Mandrel Diameter Indexing Cutter selectionD.P- According to gear to be cut Single start/Double startPressure Angle of WPRight hand/Left handLead angle of CutterCutter depth