The Fundamentals of Gear Chamfering and Deburring

Posted on Dec 19, 2020

Gear Chamfering

Chamfering and deburring of gears are particularly crucial prior to the hard gear finishing process. This is especially true for honing, where hardened burs and excessive stock can significantly diminish the tool life, thereby increasing the cost per piece significantly. These conditions can occur as well when the finishing process is threaded wheel grinding.

What Is Gear Chamfering?

Many gear manufacturers have been put to cope with premature transmission failure, less-than-optimal efficiency, or unbearable noise which is resulted from the application of transmission gears operating with anything less than a flawless tooth flank.

For these manufacturers, generating a chamfer to meet customer specifications for size, shape, and angle is of utmost importance in order to minimize the potential for sharp, brittle edges after heat treatment, as well as to avoid material plus conditions in the tooth flank prior to hand finishing operations. Gear chamfering and deburring is often an undervalued process in gear production. However, it has a positive impact on the usage characteristics of the workpiece. The process is also used for improving the ratings of gear shifting in vehicles. In the next section, we’ll explain the intricate tools required for chamfering, rolling, and cutting action for deburring.
 

Why Is Gear Chamfering Required?

Gears need to be chamfered and deburred using high quality and controlled process for the following reasons:

To avoid breakage: Excessive carburizing along the tooth edges can often lead to breakage as the gear is running.
To avoid damaging gears and bearings: Gear chamfering and deburring are required to remove burs. If the burs are not removed, they may chip off during the running cycle and damage both the gears and bearings.
To avoid poor tool life in the finishing processes: Gear chamfering and deburring is a required process to prolong the tool life expectancy in the finishing process.
Safety: The risk of tool handling injuries can be greatly reduced when the sharp burs are removed with the gear chamfering and deburring procedure.

Moreover, there are essentially four types of gear chamfering: 

Type A: Gear chamfering is undergone in only one flank with a constant size along with the profile.
Type B: Gearing chamfering is undergone in both flanks with a constant size along with the profile.
Type C: Gear chamfering is undergone with a chamfer in root diameter.
Type D: Gear chamfering is undergone without chamfer in root diameter.

Sometimes, a further rolling operation is also needed (refer to the Chamfer Rolling section below).
 

:: Read More: What Is a Bar End Chamfering Machine?

The Benefits of Gear Chamfering

Chamfering and deburring of gears are particularly crucial prior to the hard gear finishing process. This is especially true for honing, where hardened burs and excessive stock can significantly diminish the tool life, thereby increasing the cost per piece significantly. These conditions can occur as well when the finishing process is threaded wheel grinding. 

Another benefit of chamfering and deburring is to help diminish the health and safety risks that can result from operators handling parts with sharp burs. Many manufacturers offer highly desirable chamfering and deburring solutions with hobbing and deburring machines in response to the potential risks, allowing users to apply optimal chamfering technology for their particular lines of applications using forming or cutting technologies – up to and including truck-sized gears.
 

Gear Chamfering Tools: Plastic Deformation & Compression Tools

Advanced gear chamfering tools utilize compression to allow chamfers to be created on the edge. The pressure and the deformation of the material may alter the structure of the metal. Think of chamfering tools as taper gears, with a width of approximately 10-15 mm, and are normally very well finished with a mirror-like surface in order to prevent early wear.  

The key advantages of chamfering with these tools include:

1. Stronger gear tooth thanks to the optimum material flow.
2. Chamfer angles that are made more accurate.

The angles of the chamfers are defined by the tool drawing, but the size is based on the rolling time and the pressure of the tool against the gear. If the contact time between the tool and piece increases, the chamfer becomes larger. The pressure which defines the deformation force is created with a pneumatic cylinder. This method guarantees an “elastic force” that prevents breakage.
 

Chamfer Rolling Operation

Chamfer rolling is a forming process applied mostly for smaller gears up to module 5 mm, which creates chamfers along the tooth edge by pressing material. The pressed material forms a burr on the face side of the gear and a smaller one on the tooth flank. 

While the gear face burr is removed by single blades, deburring discs, or file discs, the flank burr requires special chamfer rolling tools with burnishing functionality or removal by an additional hob cut downstream in advance of a subsequent hard finishing operation. Gears require a rolling operation after chamfering because of the plastic deformation caused by this operation and to eliminate the burs or swellings that form on the material. While burs on the gear surface may be removed by deburring machines or tools, the ones on the lead can remain. These burs, usually in a span from 0.05 to 0.07 mm, cause problems in subsequent grinding phases and can put the grinding wheel at risk. At this point a rolling operation on the gears becomes necessary. Gears that are rolled and chamfered are tested after heat treatment. Cracks will not form in the rolled area. The structure will be normal and conforms to all structural characteristics of the material.
 

Summary

Gear chamfering and deburring is no doubt the key process technology in the automotive industry for achieving smooth gear transmission wherein the ability to produce strong and accurate chamfers is very important. For gears that are finished subsequently, a chamfer rolling operation can be integrated with gear chamfering and deburring as mentioned above. Multiple configuration options in tooling enable a solution for a wide range of automotive gears.

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