Standard Test Method for Ball Punch Deformation of Metallic Sheet Material
APP-E643Always apply a standardized, high-pressure grease lubricant uniformly to the punch apex to guarantee pure, friction-free stretch-forming dynamics.
Challenge & Testing Gap
Insufficient or non-uniform blank clamping forces allow the sheet metal to draw into the die cavity, converting a pure stretch-forming test into a mixed drawing event and artificially inflating dome height metrics.
The Solution
Utilize a precision hydraulic stretch-forming sub-press assembly with a calibrated blank-holder ring and a polished, hemispherical ball penetrator.
Mechanics & Specimen Behavior
Primary Mechanics
Direct mechanical ball punch stretch-forming deformation driven perpendicular to a securely constrained metallic sheet boundary until breakthrough fracture.
Specimen Details
Square blank measuring 90mm x 90mm or strip stock with a minimum width of 90mm, clean and free of surface scaling.
Mechanical Ratios & Properties
Standardized punch diameter (20mm for Erichsen type) matched to specific die clearances to force pure out-of-plane dome stretching.
Expert Engineering Commentary
Core Problem Identification
Frictional stick-slip anomalies between the punch surface and the sheet face, which shifts the fracture initiation zone away from the apex.
Root Cause Analysis
Inadequate lubrication on the penetrator tip, or worn die surface radii that introduce severe asymmetrical localized friction fields.
Hardware Specific Solutions
Universal materials frame or dedicated ductility tester equipped with a 100kN hydraulic clamping sub-press and a high-resolution linear displacement transducer.
Analysis & Calculation Standards
Event & Failure Detection
Blank clamping force stabilization, initial dome stretching inflection points, and catastrophic peak-load through-thickness fracture drops.
Required Calculations
Ball Punch Deformation Height (Erichsen / Olsen Value), Peak Punch Force, Total Displacement at Fracture, Failure Morphology Code.
Statistical Outputs
Lot validation reports compiling mean stretch height boundaries, standard deviation metrics, and ductile-vs-brittle fracture face classifications.
High-velocity telemetry capture logging punch force vs. travel depth at 1000Hz to catch the exact micro-second of peak-load ductile tearing.
Additional Commentary
ASTM E643 provides a direct, highly practical simulation of sheet metal press-forming operations, yielding a definitive index of a material’s biaxial ductility.
Set the automated test termination trigger to stop the crosshead immediately upon a 5% load drop to preserve the crack morphology for fracture analysis.
Common Pitfalls
Allowing the blank-holding force to fluctuate during the test stroke, which permits material drawing and invalidates the dome height value.