Question

Continuous chips with built-up edge (BUE) are formed with

• A. Ductile work material, small uncut thickness, low cutting speed, larger rake angle
• B. Ductile work material, small uncut thickness, high cutting speed, larger rake angle
• C. Brittle work material, small uncut thickness, low cutting speed, smaller rake angle
• D. Brittle work material, small uncut thickness, high cutting speed, larger rake angle

Hint:

Continuous chips with BUE form in ductile materials at high cutting speeds, where increased temperature promotes adhesion to the tool, especially with a larger rake angle.

Answer 1

The Correct Option is B

Step 1: Understand chip formation and built-up edge (BUE).
In machining, chips are classified as continuous, discontinuous, or continuous with a built-up edge (BUE). A BUE forms when material from the workpiece adheres to the cutting tool’s edge, acting as a false cutting edge. This typically occurs under specific conditions involving the workpiece material, cutting parameters, and tool geometry. Step 2: Analyze the conditions for continuous chips with BUE.
Ductile work material: Continuous chips form with ductile materials (e.g., mild steel, aluminum) because they can undergo significant plastic deformation without fracturing. BUE is also more likely with ductile materials due to their tendency to adhere to the tool.
Small uncut thickness (depth of cut or feed): A smaller uncut thickness reduces the cutting forces and heat generation, but still allows for chip formation. It can contribute to BUE formation by increasing the likelihood of material sticking to the tool.
Cutting speed: High cutting speed increases the temperature at the tool-chip interface, which can promote adhesion of the workpiece material to the tool, leading to BUE formation. Low cutting speeds are less likely to cause BUE because the temperature is lower, reducing adhesion.
Rake angle: A larger (more positive) rake angle reduces the cutting forces and the heat generated, but it can also increase the likelihood of BUE by reducing the pressure that would otherwise prevent adhesion. Smaller rake angles increase cutting forces and heat, which may suppress BUE but lead to other chip types.
Continuous chips with BUE typically form with ductile materials under conditions that promote adhesion, such as high cutting speeds and larger rake angles. Step 3: Evaluate the options.
(1) Ductile work material, small uncut thickness, low cutting speed, larger rake angle: Low cutting speed reduces the temperature, making BUE less likely, as adhesion requires higher temperatures. Incorrect.
(2) Ductile work material, small uncut thickness, high cutting speed, larger rake angle: High cutting speed increases the temperature, promoting BUE formation, and the larger rake angle aligns with conditions for continuous chips in ductile materials. Correct.
(3) Brittle work material, small uncut thickness, low cutting speed, smaller rake angle: Brittle materials (e.g., cast iron) typically form discontinuous chips, not continuous chips with BUE. Incorrect.
(4) Brittle work material, small uncut thickness, high cutting speed, larger rake angle: Brittle materials are unlikely to form continuous chips, and BUE is less common with brittle materials. Incorrect.
Step 4: Select the correct answer.
Continuous chips with built-up edge (BUE) are formed with a ductile work material, small uncut thickness, high cutting speed, and larger rake angle, matching option (2).