In the manufacturing of gears, which of the following processes is specifically classified as a gear finishing operation used to improve surface finish and accuracy of the gear teeth?

Introduction / Context:
Gear manufacturing involves several stages, starting from rough cutting of gear teeth and ending with finishing operations that improve accuracy and surface quality. The basic tooth form may be produced by processes like hobbing, shaping or milling, but to obtain smooth, quiet running gears with long service life, finishing operations are used. This question tests whether you can distinguish between gear generating processes and gear finishing processes in basic production engineering.

Given Data / Assumptions:

• We are concerned with gears and operations applied to their teeth.
• Options include burnishing, hobbing, shaping and milling.
• The term finishing operation refers to operations done after the basic tooth geometry has been created.
• The goal of finishing is to improve surface finish, accuracy and sometimes fatigue strength.

Concept / Approach:
Hobbing, shaping and milling are primarily generating or cutting operations used to produce the gear tooth form from a blank. They remove significant amounts of material and define the basic geometry of the teeth. In contrast, finishing operations, such as burnishing, grinding, honing and lapping, mainly refine an already formed surface. Burnishing is a cold working process in which a hardened roller or tool is pressed against the surface and moved over it. This plastically deforms the peaks into the valleys, improving surface finish and sometimes increasing surface hardness and fatigue life. In the context of gears, burnishing can be carried out on teeth as a finishing operation. Thus, burnishing is the correct answer among the options.

Step-by-Step Solution:
Step 1: Identify which processes are used mainly to create the gear tooth form from a blank. Step 2: Recognise that hobbing is a widely used generating process to cut the teeth using a hob tool. Step 3: Understand that shaping can also be used to generate gear teeth, especially for internal gears. Step 4: Note that milling can be used to cut individual gear teeth with a form or end mill, but it is still a rough cutting process. Step 5: Burnishing, on the other hand, does not primarily remove material; instead, it smooths and work hardens the surface by plastic deformation. Step 6: In gear production, burnishing can be applied after tooth cutting to improve surface finish and accuracy, making it a finishing operation. Step 7: Therefore, among the listed processes, burnishing is the one correctly classified as a gear finishing operation.

Verification / Alternative check:
Manufacturing references typically divide gear operations into roughing (such as casting and forging), cutting or generating (hobbing, shaping, milling, broaching) and finishing (grinding, honing, lapping, burnishing). When high precision and low noise gears are required, finishing operations are essential after basic tooth cutting. Burnishing is often mentioned as a finishing technique for both cylindrical surfaces and gear teeth, while hobbing, shaping and milling are clearly described as primary cutting processes. This literature support confirms that burnishing is the correct choice.

Why Other Options Are Wrong:
Hobbing is a gear generating process used to cut gear teeth from a blank and is not primarily a finishing operation. Shaping is also a generating or cutting process that forms gear teeth, especially for internal or special gears. Milling is a general machining process used to cut material and form the gear tooth but is not classified as a microscopic finishing process.

Common Pitfalls:
A common mistake is to assume that any machining process which gives a smooth surface is a finishing operation. However, in gear technology, the classification depends on whether the process primarily generates the shape or refines it. Learners should remember that hobbing, shaping and milling define the basic tooth geometry, while processes like grinding, honing, lapping and burnishing are used afterwards to perfect the teeth. Keeping this hierarchy in mind helps in quickly identifying burnishing as a finishing operation in exam questions.

Final Answer:
The gear finishing operation among the given choices is Burnishing.