In gear manufacturing, gear lapping is an operation that is usually carried out after heat treatment in order to improve tooth accuracy and surface finish. At which stage of the process is gear lapping normally performed?

Introduction / Context:

Gear lapping is a fine finishing process used in gear manufacturing to improve the accuracy and smoothness of gear tooth surfaces. This question tests whether you know at what stage in the overall process gear lapping is normally performed and why it is linked with heat treatment operations.

Given Data / Assumptions:

• We are dealing with the manufacturing sequence of gears.
• Gears are usually cut, then heat treated, and finally finished.
• Gear lapping is used to improve tooth surface finish and correct small errors.

Concept / Approach:

Heat treatment of gears, such as carburising and quenching, is done to increase hardness and wear resistance. However, heat treatment often causes small distortions and changes in tooth geometry. A finishing operation is therefore needed after heat treatment to correct minor errors. Gear lapping uses an abrasive compound between the gear and a lapping master to smooth high spots and improve contact pattern and noise behaviour.

Step-by-Step Solution:

Verification / Alternative check:

If gear lapping were done before heat treatment, any distortions produced during heating and quenching would ruin the carefully lapped surface. Since the goal is accurate contact in the final hardened gear, lapping must logically follow heat treatment.

Why Other Options Are Wrong:

Option A: For gear reconditioning of worn out gears is an occasional application, but the standard textbook definition refers to lapping as a finishing step in new gear manufacture after heat treatment.

Option B: Prior to heat treatment is incorrect because the finish would be lost due to distortion during heat treatment.

Option D: During rough cutting or hobbing of the gear is wrong because lapping is a fine finishing process, not a rough machining operation.

Common Pitfalls:

A common confusion is to think that all finishing processes occur before heat treatment. In precision gears, however, key finishing operations like grinding and lapping are placed after heat treatment to correct its side effects. Mixing up this sequence can lead to wrong answers.

Final Answer:

The correct stage is after heat treatment to correct errors and improve finish.