Sheet Metal Stamping

Process Definition & Working Principle

Sheet metal stamping (also known as pressing) is a cold-forming manufacturing process in which flat metal sheets are converted into three-dimensional components. The process is driven by high compressive forces exerted by mechanical, hydraulic, or servo-driven presses using specialized tooling assemblies called stamping dies (consisting of a punch and a die cavity).

Physics and Mechanics of Stamping

The deformation of sheet metal is categorized into three primary mechanics depending on the operation:

1. Shearing Mechanics: Applied in cutting, blanking, and piercing/punching. As the punch penetrates the sheet metal, the shear zone undergoes four distinct mechanical phases:

   Kinematics, Axes, & Machine Configuration

   The configuration of a stamping press and its kinematics dictate deformation speeds, force distribution throughout the stroke, and process suitability.

   Press Types and Kinematic Behaviors

   1. Mechanical Presses (Crank and Eccentric):

      • Operating Principle: A flywheel stores energy and transfers it to the slider/ram via a crank, eccentric, or link-motion system.
      • Kinematics: The ram velocity follows a sinusoidal path: zero speed at Top Dead Center (TDC), maximum velocity near mid-stroke, and zero speed at Bottom Dead Center (BDC). The rated press capacity is only achieved near BDC.
      • Application: Excellent for high-speed blanking, piercing, and shallow forming in progressive dies (up to 1000 strokes per minute).

   2. Hydraulic Presses:

      • Operating Principle: Driven by high-pressure hydraulic cylinders with variable-displacement pumps.
      • Kinematics: Provide full tonnage capability at any point along the stroke. The ram velocity can be adjusted and held constant during deformation.
      • Application: Recommended for deep drawing and heavy-duty forming where deep penetration and constant speed are required.

   3. Servo Presses (Direct Drive):