Understanding the Gear Hobs in gear manufacturing processes

Manufacturing of gears requires critical tools. Gear hobbing is one such process that aids in the production of high-precision gears. This technique is used in various industries, including automotive, aerospace, robotics, and machinery. Here, gears are fundamental components in power transmission and motion control.

Gear hobbing offers numerous advantages, including accuracy, repeatability, and cost-effectiveness. In this article, we will explore the gear hobbing process, its principles, and the benefits it provides to different industries.

Working principle of gear hobs

The working principle of gear hobs is based on the process of gear hobbing, which is a machining technique used to create gears with accurate tooth profiles and spacing. Gear hobs are the cutting tools used in gear hobbing machines to perform this operation.

Gear hobs are made from high-speed steel and carbide. Due to this, the tool is hard but brittle. The hardness of the carbide or HSS tool allows to cut the gear teeth precisely. The design of the tool helps in producing a specific tooth profile.

Gear hobbing is a continuous cutting process while both the hob and the workpiece rotate. The hob and workpiece rotate in opposite directions. As they mesh together, the hob’s cutting teeth gradually engage with the workpiece, removing material and forming the gear teeth. After the profiling is done, the workpiece is removed from the machine and carried out for other processes.

Types of Gear Hobs

Gear hobs can be of various types and designs. The choice of gear hob type depends on the gear designs and capabilities of the machine tool. Some common gear hobs available in the market are as follows:

• • Spur Gear Hob: Spur gear hobs are the most common type and are used to cut straight-toothed spur gears. These gears have teeth that are parallel to the gear’s axis of rotation. Spur gear hobs have straight, parallel cutting teeth along the cylindrical body of the hob.
  • Helical Gear Hob: Helical gear hobs are designed to cut helical gears. The hob’s cutting teeth have a helical shape to match the desired helix angle of the gear.
  • Worm Gear Hob: Worm gear hobs are specialized hobs used to cut worm gears. The gears have helical teeth that mesh with a worm wheel.
  • Spline Hob: Spline hobs are used to cut splines, which are ridges or teeth on a shaft that mesh with a corresponding part.
  • Rack Hob: Rack hobs are used to cut racks, which are straight gears with infinite diameters. A rack hob has cutting teeth that are parallel to the hob’s axis and are used to generate straight rack teeth during gear hobbing.
  • Double Helical Gear Hob (Herringbone Gear Hob): Double helical gear hobs are used to cut double helical gears. These are also known as Herringbone gears as the profile matches the profile of a fish bone. These gears have two sets of helical teeth with opposite helix angles.

Each type of gear hob is carefully designed to cut gears with specific tooth profiles, angles, and shapes. The versatility of gear hobs allows for the efficient and precise production of a wide range of gear manufacturing.

Advantages of Gear Hobbing

• High Precision: Gear hobbing is known for its exceptional precision, resulting in gears with accurate tooth profiles and spacing. This precision ensures smooth and efficient gear engagement, reducing noise and wear.
• Cost-Effective: Gear hobbing is a cost-effective mass production method, as it allows for the simultaneous cutting of multiple gear teeth during each revolution of the workpiece. This leads to shorter production times and lower per-unit costs.
• Versatility: Gear hobbing machines can produce a wide range of gears, including spur gears, helical gears, worm gears, and splines, making the process highly versatile to meet various industry needs.
• Improved Surface Finish: The hobbing process typically results in excellent surface finishes on the gear teeth, reducing the need for additional finishing operations.

Disadvantages of gear hobbing

• Limited to Certain Gear Types: Gear hobbing works fine with straight or helical teeth. However, when it comes to machine internal gears, bevel gears with complex geometries, or gears with non-standard tooth profiles, hobbing is not preferred. For such gears, alternative manufacturing processes like gear shaping or grinding may be more suitable.
• High Tooling Costs: Gear hobbing requires specialized carbide or HSS cutting tools. The cost of these tools can be a significant investment.
• Material Limitations: Gear hobbing is most effective for cutting gears from relatively soft materials, such as steel, aluminum, or brass. Machining harder materials or heat-treated gears with traditional gear hobs can lead to increased tool wear and reduced tool life.

Types of Gear hobbing machines

The gear hobbing machines can be broadly classified into two categories:

• Horizontal type – the tool is mounted on the horizontal axis while the workpiece is mounted vertically.
• Vertical type – the hobbing head is mounted on the vertical axis whereas the workpiece is on the horizontal axis.

Other gear manufacturing processes

As already discussed Gear hobbing has limitations in producing certain types of gears. When it comes to different gear-forming processes, you can select from the below sets:

• Gear shaping – A formalized cutting tool is used to cut the shape of gear teeth
• Milling – a miller cutter on the arbor is used to give a profile of the gear teeth
• Grinding – grinding tool is used to grind the gear teeth and impart proper dimensions and surface finish

The future of Gear hobbing

The future of gear hobbing lies in advancing technology, including improved machine capabilities, AI-driven automation, and high-performance cutting tools. Gear hobbing will continue to be a preferred method for high-precision gear production due to its efficiency, versatility, and ability to meet the demands of various industries.