Explanation:

A built-up edge (BUE) is a common phenomenon that occurs during machining processes, particularly when machining ductile materials at low speeds. It refers to the accumulation of workpiece material on the cutting tool's edge, which alters the cutting conditions and affects the quality of the machined surface.

Reasons for the formation of a built-up edge:

1. Low cutting speeds: A built-up edge is more likely to occur at low cutting speeds due to the longer contact time between the tool and the workpiece. This prolonged contact allows for the transfer of workpiece material onto the tool's edge.

2. Ductile materials: Ductile materials have the tendency to adhere to the tool's cutting edge due to their plastic deformation characteristics. This adhesion occurs as a result of the high temperature and pressure generated during the cutting process.

3. Chemical affinity: Certain workpiece materials may have a chemical affinity for the tool material, leading to a stronger adhesion and the formation of a built-up edge. This is particularly common when machining materials such as aluminum or copper.

Effects of a built-up edge:

1. Increased cutting forces: The presence of a built-up edge creates an irregular cutting edge, resulting in increased cutting forces. This can lead to tool wear, reduced tool life, and poor surface finish.

2. Altered cutting conditions: The formation of a built-up edge changes the geometry of the cutting edge, causing variations in the cutting forces, cutting temperature, and chip formation. These alterations can affect the overall machining process and the quality of the machined surface.

3. Poor surface finish: The presence of a built-up edge can result in a rough or uneven machined surface due to the irregularities introduced by the adhesion of workpiece material onto the cutting tool.

Prevention and control:

1. Higher cutting speeds: Increasing the cutting speed can help reduce the formation of a built-up edge by minimizing the contact time between the tool and the workpiece.

2. Proper tool material and coating selection: Choosing a tool material and coating that have good resistance to adhesion can help reduce the formation of a built-up edge.

3. Effective chip evacuation: Ensuring proper chip evacuation during the machining process can help prevent the accumulation of workpiece material on the cutting tool's edge.

In conclusion, a built-up edge is formed while machining ductile materials at low speeds due to the prolonged contact time, plastic deformation characteristics of the workpiece material, and potential chemical affinity between the workpiece and tool material. It can have detrimental effects on the machining process, including increased cutting forces, altered cutting conditions, and poor surface finish. Preventive measures such as higher cutting speeds, proper tool material selection, and effective chip evacuation can help control the formation of a built-up edge.