GEAR HOBBING PROCESS

(32) Rishabh Jadhav,  (33) Sakshi Jadhav,  (45)Ameya Joshi,  (46) Ranbeer Kadam,  (47) Sonal Kadam

Guide: Dr. Ramkrishna Bharsakade


Hobbing

On a hobbing machine, a unique kind of milling machine, hobbing is a machining operation used to cut gears, splines, and sprockets.

Fig: 1

             Through a series of cuts performed with a cutting device known as a hob, the gear's teeth or splines are gradually carved into the material (a flat, cylindrical piece of metal)


Working Of Gear Hobbing

  • The process of Gear hobbing, the gear is cut by a generating process in which the gear blank and the cutter  is rotated at the same time along with a fixed gearing ratio between hob and gear blank.
  • Gear blank is fed into the revolving hob throughout this procedure until the necessary depth is obtained. Until all of the teeth are formed, the hob is fed through the blank's face.
  • When hobbing a spur gear, the hob teeth are positioned parallel to the blank's axis of rotation. The axis of the hob is placed over an angle to create the proper helix for helical teeth bobbing. Worm gears are made by setting the hob's axis at an angle to provide the right helix. Worm gears are created by setting the hob's axis at the proper angle to the gear blank.

Gear Hobbing Process

Fig: 2

1. 

  1. It is a gear generation process; in this process gear blank is roll with a rotating cutter called as hob.
  1. A multi-point cutting instrument called a gear hob is used for gear hobbing. It resembles a worm gear with several straight flutes running parallel to its axis around its perimeter.

  1. These flutes are so shaped that by giving a proper angle to them, these works as cutting edges.
  1. In gear hobbing operation the gear is rotated at a suitable rpm and simultaneously fed to the gear blank; The gear blank is also kept revolving.
  1. Gear hobbing used to make variety of gears like spear gear, worm & worm wheel, helical, hearing bone, splines and gear sprockets.


Types of Hobbing process
According to the hob's feeding directions for cutting gears, the gear hobbing operation is divided into many categories.

  1. Hobbing with Axial Feed

    In this process, the hob is in fed parallel to the axis with respect to the gear blank on the face side.
    Used in the manufacture of spur gears and helical gears.

  2. Hobbing with Radial Feed

    In this process, the hob and gear blank are set perpendicular to each other. The rotating hob is fed radially with respect to the gear blank or perpendicular to the axis of the gear blank.
    This process is used to manufacture worm gear.

  3. Hobbing with Tangential Feed

    Also used to cut teeth in worm gears.
    In this case, the hob is held so that its axis is horizontal but perpendicular to the blank axis.
    The hob is set to the entire tooth depth and then advances axially. The hob is tangentially fed to the surface of the gear blank    .


Five common elements in all gear hobbing machine

  • Work spindle that rotates workpieces

  •         Cutting spindles that rotate cutting tools, hobbing

  •         Devices that rotate work spindles and cutting spindles at accurate ratios according to the number. Number of teeth Number of gears and threads of hob.

  •        Means for crossing the hob across the face of the workpiece

  •        A means for adjusting the center distance between the hob and workpiece of different sized workpieces Workpieces and Hobbs


Advantages of gear hobbing

  • High Speed – The process is relatively fast. The speed is due to a very accurate and automated process.

  • High Precision – The entire process is an accurate to produce the best possible gears in the process.

  • Versatility – it can be used to manufacture spur gears, as well as to make helical gears, ratchets, splines, worm gears and cycloid gears.

    Its production cycle time is lower, i.e., faster production rate

  • This process can accommodate a variety of batch sizes (small to large).

  • Hob is a multipoint cutting tool because it has multiple cutting edges working at once, which gives it enough time to dissipate the heat produced. As a result, cutting tool overheating is prevented.

  • By gear hobbing  a special type of gear named herringbone gear cam be generated.


Disadvantages

  •          It cannot generate the internal gears.

  •      Splines and serrations are not suitable for hobbing

  •      Bevel gear cannot be manufactured by this process.




































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