Gear Manufacturing Processes

Gear cutting methods can be classified as either forming or generating. In forming, the tool's shape is directly copied onto the workpiece. In generating, the final shape depends on both the tool and its motion relative to the workpiece.

In form cutting, the cutting tool has the same shape as the space between gear teeth. This method creates precise teeth when the cutter is accurately made and the tooth spaces are consistent, like in spur and helical gears.

A single-space cutter removes material in one pass, creating either one or all the spaces between teeth. Single-space cutters can be disk-type or end-mill-type milling cutters.

Single-space form milling with disk-type cutters is ideal for gears with large teeth. This is because the milling cutter's cutting action is more efficient for removing material than the tools used in generating processes.

The shape (profile) of an involute gear's teeth depends on the number of teeth on the gear. This means a different cutter is needed for each tooth count.

To simplify the process, there are commercially available sets of cutters for each gear pitch (tooth size). Each cutter is designed to cut a range of tooth numbers, providing flexibility.

Form cutting using commercially available cutters can produce satisfactory results for a range of tooth numbers within a gear pitch. A single cutter can be used for multiple gear teeth within a specific range.

A process where a tool, acting as a gear, shapes the teeth of a gear blank.

Two gears that mesh together to transmit power smoothly.

A specific tooth shape that allows gears of different numbers of teeth to mesh smoothly.

A specialized tool shaped like a screw with teeth cut in a helical pattern.

A straight, flat cutter that can generate gear teeth with a straight profile.

A smaller gear-shaped cutter used to create gear teeth.

A machine that uses a pinion-shaped cutter to shape gear teeth by a reciprocating motion.

A machine that uses a segment of a rack to shape gear teeth by a reciprocating motion.

A hob can have one, two, or three threads. The generating portion of the hob tooth on a single-thread involute hob usually has straight sides, resembling an involute rack tooth.

Hobbing involves rotating both the hob and the workpiece while simultaneously feeding the hob parallel to the workpiece axis. This continuous process cuts all the teeth in a single operation.

The same hobs and machines used for spur gears can be used for helical gears. The hob axis is tilted to ensure the hob and gear pitch helices are tangent.

Worm gears are typically cut with a hob, similar to spur and helical gears. The hob and workpiece axes are inclined at the shaft angle of the worm and gear set, usually 90 degrees.

Straight bevel gears are often rough-cut with a form cutter on indexing machines and then finished to the desired shape using a generator.

The feed rate in hobbing is the distance the hob moves parallel to the workpiece axis per revolution of the workpiece. It's determined by material, pitch, and desired finish.

Indexing gears control the rotation of the workpiece during hobbing, ensuring each tooth is cut correctly. These gears are independent of the feed gears.

While hobs are used for cutting gears, thread milling cutters are used for cutting worm threads. Grinding is often used for finishing worm threads after hardening.

The method used to generate straight bevel gears, similar to the rack-generating method used for spur gears, but using a cutter with one straight edge moving in the plane of the tooth of a crown gear.

The 'rack' equivalent for bevel gears; its pitch surface is a plane, and its teeth have straight sides.

The process of rotating the bevel gear slowly relative to the cutting tool during generation, similar to the tool's movement on a shaper.

The process of cutting spiral bevel gears, using a spiral cutter with blades protruding from its periphery, similar to the straight bevel gear cutting process.

A free-cutting gear finishing operation that uses a cutter with sharp-edged grooves to remove small amounts of metal, improving surface finish and profile accuracy of spur and helical gears.

A cutter with a series of sharp-edged rectangular grooves running from tip to root, used in gear shaving to improve tooth profile accuracy.

The process involves meshing the cutter and workpiece, causing relative movement along the teeth, with the cutter driving the workpiece, resulting in metal removal and improved surface finish.

Gear shaving is most effective on gears with hardness up to approximately 400 HB (42 HRC), not suitable for harder materials.

The technique used for finishing gears involves either forming or generating. In forming, a shaped grinding wheel is used. In generating, the wheel is shaped by rolling a master gear against a rack.

A disk-type grinding wheel is dressed to the desired shape using a diamond. A specific index plate is required for each tooth count and is used to accurately grind the gear.

A grinding wheel with a shape matching the gear's basic rack is used. A master gear meshes with a master rack, and the wheel's shape is generated as the master gear rolls on the rack.

A finishing process for spur and helical gears where metal is displaced under pressure, rather than removed, to create the tooth profiles.

There are two main types: those using rack or gear dies in a parallel axis arrangement, and those using worm-type dies at a 90° angle to the workpiece.

The process resembles thread rolling, where the dies press against the gear blank to create the tooth profile. The dies are aligned with the workpiece axis, and the blank rotates between them.

The blank rotates between two dies, one fixed, the other movable. The dies have the same number of teeth and are connected to run at the same speed. The movable die presses the blank into contact with the fixed die, forming the gear's profile.

When the moving die presses against the blank, it creates a matching tooth profile, ensuring proper meshing with other gears.