Gear hobbing and gear shaping are the primary high-productivity subtractive manufacturing methods utilized to generate precise tooth profiles on cylindrical and conical workpieces.
Gear hobbing and gear shaping are the primary high-productivity subtractive manufacturing methods utilized to generate precise tooth profiles on cylindrical and conical workpieces. The physical principle of both processes is based on the kinematic generation method (generating action) through rolling, where the tool and the workpiece perform continuous, coordinated movements simulating the engagement of an actual gear pair.
Gear Hobbing: Gear hobbing is a continuous cutting process where the cutting tool, the hob, acts as a cutting worm, while the workpiece rotates as the corresponding worm wheel. The profile of the hob's teeth represents a rack in a given cross-section. As the hob rotates about its axis, its helical cutting edges move translationally relative to the workpiece, generating the involute profile of the teeth. The kinematics are based on the principles of a worm gear drive. The tooth profile is not directly copied from the tool's form but is generated as an envelope curve of the successive positions of the cutting edges during the synchronized rotation of the tool and the workpiece.
Modern CNC gear hobbing and shaping machines require highly precise multi-axis synchronization, executed via an Electronic Gearbox (EGB) within the CNC controller.
CNC Gear Hobber Axis Configuration: A typical 6-axis CNC gear hobbing machine consists of the following controllable axes:
The efficiency of gear machining is directly dependent on the design, geometry, and material of the cutting tool.
Hob Cutter Design: A hob is a multi-point tool with helical teeth, divided by longitudinal flutes (gashes) to form rake faces. These gashes can be straight (parallel to the tool axis for small lead angles) or helical (perpendicular to the thread spirals for larger lead angles).
Proper selection and optimization of process parameters are critical to maintaining the balance between productivity, tool life, and dimensional accuracy.
Fundamental Formulas:
| Category | Subtractive Manufacturing |
|---|---|
| Library | CNC machining |
Engineer, author of The Big Book of 3D Printing and additive manufacturing expert