the methods of machining gears can be classified into two primary categories gear generating and gear form cutting many of the process is used to machine gears may also be used to finish gears gear generating involves here cutting through the relative motion between a rotating cutting tool and the generating motion or rotation of the workpiece the primary geared generating processes include hobbing and shaping in hobbing gear teeth are progressively generated by a series of cuts using a helicaly fluted cutting tool called a hob both the hob and the gear blankl rotate as the hob is fed axially across the face of the blank
hubbing is the principal method for producing spur gears and helical gears and is also used to produce many special gear forms the. main limitation of hobbling is that it can only be used to produce external gears hobbling can be performed on a single gear blank but also allows for the stacking of work pieces to increase production rates.
shaping generates gear teeth by rotating the workpiece in contact with the reciprocating cutter the reciprocating cutter maybe a pinion shaped cutter a multi tooth rack shaped cutter or a single point cutter the pinion shaped cutters axis is parallel to the gear blank and begins cutting by reciprocating while feeding gradually into to the blank to a predetermined cutting depth the cuttar and gear blank rotates slowly at the same pitch circle velocity as the cutter enters and exits the cut incrementally generating the gear teeth.
rack shaped cutters typically have between six to twelve teeth that reciprocate into the gear blank once the rack cutter finishes a pass the cutter is disengaged and returns to a starting point to begin cutting again when shaping with a single point cutter the cutter reciprocate making successively deeper cuts until a predetermined depth is reached.
gear shapers are used to make internal gears shoulder gears and many other gear types that cannot be produced with hubbers shapers can also produce noninvolute shapes such as a cam and gear on the same shape gears form cutting typically involves the use of formed tooth cutters that had the desired gear shape or profile the primary gear form cutting processes include broaching and milling.
broaching is the fastest method of machining gears and is performed on many different machine types using a multi tooth cutting tool called a broach. the broach or the gear blank are pushed or pulled relative to each other to remove material. each tooth and the broaches generally higher than the preceding tooth as a result the death of cut increases with each tooth as the broken operation progresses the conventional method approaching he's used mainly to produce internal gears for external gears pub broachng is used pub broaching is performed on special machine tools having a hollow broach ing to assembly called the pub .
gear blanks are either pushed down pushed op holed up through the park could generate the gear teeth,
milling is a machining process that uses the relative motion between a rotating multi edge cutter and the workpiece to generate gear shapes. mill gears are typically produced using cutters that mill each gear to space individually to produce large course pitch internal or external spur bevil or helical gears.
a process called gashing can be used on heavy duty milling machines gashing involves plunging the rotating cutter into a blank for rapid metal removal after machining gears may require heatreatment to meet hardness requirements after heatreating gears usually require finishing nullify any distortion that may occur in some cases gears are machine and finished before heatreatment and then once processed surface finish to remove distortion from the heat treatment
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