Difficulty: Easy
Correct Answer: reducing
Explanation:
Introduction / Context:
Forging operations deliberately change a workpiece's shape by plastic deformation under compressive force. Among the basic operations are upsetting, drawing down, bending, and punching. Understanding what each does to cross-section and length is essential for process planning.
Given Data / Assumptions:
Concept / Approach:
Because plastic deformation conserves volume approximately, reducing one dimension necessitates an increase in another. In drawing down, repeated blows or press passes elongate the bar while decreasing its cross-sectional area. This is the opposite of upsetting, which shortens length while increasing area.
Step-by-Step Solution:
Take a bar of initial area A0 and length L0.Apply forging blows along the length to thin the section.With volume ~ constant, A0 * L0 ≈ A1 * L1. If A1 < A0, then L1 > L0.Therefore, drawing down reduces cross-section.
Verification / Alternative check:
Practical examples include making a tapered chisel shank or elongating a rod. The cross-section visibly decreases while length increases, confirming the definition.
Why Other Options Are Wrong:
Increasing or maintaining area contradicts the operation's goal; alternating or roughening describes surface treatment, not the fundamental geometric change.
Common Pitfalls:
Confusing drawing down with wire drawing (a different process using dies but also reduces section); mixing up upsetting vs. drawing; ignoring temperature control which affects flow resistance and surface quality.
Final Answer:
reducing
Discussion & Comments