Gear cutting machines

Gear cutting machines

Gear cutting machines are tools that, as their name suggests, are used for the machining or manufacture of gears, starting from basic blanks or workpieces, such as cylinders or other shapes, made of materials such as steel or aluminium.

These machines use a sequence of drills or standardised bits to create, in compliance with adjusted pitch and circle parameters, the various cuts needed to obtain gears which, once finished, are intended for carrying out work or mechanical processes in other machines or equipment.

How gear cutting machines work

The cylinder, which is generally made of steel, although another rigid metal such as copper, bronze or aluminium may be used, serves as the starting workpiece. First, this shape is cut to obtain round discs which are subsequently machined as blanks, that is, as drilled or bored plates without teeth.

The process above is carried out as a preliminary step to a series of operations, needed to produce the final product, which are described below:

• Gear cutting: the discs or blanks undergo this process to create the functional teeth of the gear.
• Hardening: in this heat process the part is cooled in order to strengthen or harden the resulting part, thereby increasing its mechanical strength.
• Grinding: during this process the finish of the parts is perfected, both on their surface and on their teeth.

Types of gear cutting machines

Gear cutting machines are classified according to the process used in their production, divided into two main groups: by reproduction or forming, or by generation.

By reproduction or forming

In this case, the cutting edge is an exact replica of the gap between adjacent teeth, and for this it uses a large number of tools, because the gap between teeth varies with the module and the number of teeth.

These gear cutting machines are classified, broadly speaking, into two types of tools:

• Milling machine: a machine that uses a rotating module cutter, which is basically a standard special milling cutter, with teeth or edges very similar to the tooth gaps. This tool cuts into the cylinder taken initially as the base workpiece to carry out the machining process. This operation is repetitive, or patterned, and is known as part milling.
• Planing machine: a device that has a cutting edge positioned perpendicular to the direction of movement. The segment that performs the cutting or machining also matches the area of the tooth gap of the gear to be cut.

By generation

This type of gear cutting machine delivers great accuracy in the work done on the workpiece. It is practical and quiet in the machining process, as well as using consistently high speeds.

Its operation is based on the characteristics of the involute of the circle, which is nothing more than a plane curve in development. The teeth, which meet these same parameters, can be cut by rectilinear machines, while the tool in charge of making the cuts advances alongside the wheel and rotates about its own axis.

Gear cutting machines of the generation type can in turn be divided into the following types:

• With a hob: a gear cutting machine of this kind carries out a continuous process and is more accurate than the others. In this case, it uses as its tool a screw with straight teeth, while its axis is offset by the same amount as the lead angle of the screw helix. This method is one of the most widely used in industry.
• With a rack cutter: during this process or method, the machine produces both tooth profiles simultaneously, and for this it uses a rack-shaped tool with a module exactly matching the gear to be cut. The cut is made with reciprocating movements of the tool, in step with the axis of the cylinder taken as the base workpiece. Although it is not a continuous machining process and requires the tool to be repositioned, it is also one of the most common processes because of how widely it is used.
• With a pinion cutter: the machinery carries out a continuous machining process in which the cutting tool does not need to be repositioned. The cut is made by a wheel or thread with sharpened teeth, while it rotates on the cylindrical base that is the object of the cutting process. Making this generating pinion is complex, and any defects it may have are transferred to the workpiece being machined, since, in general, they are reproduced very easily.
• With planing: in this case the machine uses a flat-profile cutting tool, whose characteristic movement when machining the workpiece is reciprocating. Of all the gear cutting processes, this is one of the least used.

Other machines that may interest you

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Not sure which machine to choose? Talk to a Heller technician.