In sheet metal blanking operations, why is a deliberate ‘‘shear’’ (inclination) provided on punches and/or dies—what is the principal objective of adding this shear to the cutting tools?

Introduction / Context:

Blanking and piercing involve shearing sheet stock with a punch and die. The instantaneous force can be very high if the entire perimeter shears at once. To manage machine capacity and tool life, toolmakers often apply an angular offset—‘‘shear’’—to the punch face or die face so that cutting engagement is progressive rather than simultaneous around the whole edge.

Given Data / Assumptions:

• Conventional presses operating within rated tonnage.
• Carbon steel or similar sheet materials of moderate thickness.
• Standard clearances and lubricants in use.

Concept / Approach:

Providing shear staggers the contact along the cutting edge so that only a small arc length is in peak shear at any instant. This reduces the maximum press load (tonnage) substantially, even though the overall work (energy) is similar. It may slightly affect edge characteristics but is primarily a load-management and shock-reduction measure that protects the press and tooling.

Step-by-Step Solution:

Verification / Alternative check:

Press tonnage calculations show that required peak tonnage ≈ perimeter × thickness × shear strength; with shear, the effective simultaneous perimeter reduces, lowering peak tonnage while keeping energy similar (force integrated over stroke).

Why Other Options Are Wrong:

• Perfectly straight blanks / zero warping: shear does not guarantee zero distortion; fixturing and clearances matter.
• Mirror-finished edge: finish depends on clearance, material, and die condition; shear alone does not polish edges.
• Die alignment not critical: alignment remains critical to avoid uneven wear and burrs.

Common Pitfalls:

• Expecting shear to improve surface finish dramatically; its primary role is peak load reduction and shock mitigation.
• Applying excessive shear that causes unacceptable angular edges or dimensional error.

Final Answer:

press load is reduced