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Gear Making
Workshop Technology
Mansoor Ghazi, Department of Mechanical EngineeringCollege of E&ME, NUST Pakistan
What Is A Gear ?
• A rotating machine part/element with teeth cut into it which is used to:– Transmit torque or– Alter velocity or– Change direction of motion or– Perform any combination of above functions
• A gear meshes with another gear(s) to form a transmission system.
• Relative motion between gears take place due to meshing of gear teeth.
Conventional Manufacturing ProcessesConventional Manufacturing Processes
Gear Cutting
Hobbing
Shaping
Planning
Milling
Gear Forming
Casting
Forging
Gear Finishing
Grinding
Shaving
Overview of Gear Manufacturing
• Gear cutting processes involve cutting the teeth onto a blank gear with help of shaped cutters.
• Gear forming processes are employed to produce gears without material removal. Used for mass production of low criticality gears.
• Gear finishing processes are employed after gear forming or cutting. These processes are used to impart required finishing before gear assembly.
• Majority of gears are made of carbon and low-alloy steels.
Gear Hobbing
• Relatively inexpensive yet fairly accurate, hobbing employs helical cutters to cut teeth into a blank gear.
• The helical cutter called ‘hob’ rotates on an axis perpendicular to the axis of blank gear.
• The hob moves radially to the depth of teeth and is then fed axially along the width of the gear teeth.
• The hob and blank gear rotate in constant timed relation with each other that determines the number of teeth being cut into the gear.
Gear Shaping
• A gear of desired teeth profile is used to cut similar shaped teeth into the blank gear.
• The cutting gear rotates along with the blank gear while simultaneously reciprocating parallel to the cut teeth.
• Unlike hobbing, shaping is capable of producing internal gears.
• Worm gears cannot be produced with shaping.
Fundamentals
• Gear forming processes include:– Casting– Forging– Roll Forming– Stamping– Powder Metallurgy– Extrusion
• Gear forming processes are employed to mass produce relatively smaller size gears with appreciable accuracy and mechanical properties.
• Gear finishing processes are used to impart surface finishing to generated and formed gears.