Basic Mechanical Properties Relevant to Forming
In the fully annealed (soft O‑state) condition, pure copper exhibits ideal forming properties:
Tensile strength: 200–240 MPa
Yield strength: ~70–90 MPa
Elongation (A50mm): 45%–55%
Hardness: 35–60 HV
Reduction of area: >70%
These values confirm that pure copper is soft, low‑strength, and highly deformable. It can withstand large plastic strains during stamping and drawing without cracking or necking. Its low yield ratio makes it easy to initiate flow under punch pressure, reducing springback and improving dimensional consistency in stamped parts.
Stamping Performance of Pure Copper
Pure copper is among the most formable metals for blanking, bending, coining, and progressive stamping.
Blanking and piercing: Low cutting force required; smooth shear surfaces with minimal burr. Tool wear is low because copper is soft and adhesive‑abrasive only under poor lubrication.
Bending and flanging: Can achieve small bending radii (down to ~0.5× thickness) without fracture. It shows almost no cold brittleness at room temperature, supporting sharp bending and hemming.
Complex stamping: Suitable for intricate geometries in progressive dies. Uniform deformation reduces wrinkling and tearing compared to higher‑strength alloys.
The main drawback is its softness: parts are prone to scratching, denting, and distortion during handling and ejection. Lubrication and tool surface finish are critical for surface quality.
Deep Drawing Performance of Pure Copper
Deep drawing is the process where pure copper excels most.
Limit drawing ratio (LDR): Typically 2.0–2.3 for annealed sheet, meaning it can form relatively deep cups in a single draw.
Deformation behavior: Material flows smoothly from the flange toward the die cavity. High ductility delays localized necking and fracture at the punch radius.
Springback: Very low due to low yield strength, so drawn parts maintain shape and wall uniformity.
Thinning: Wall thickness reduction is moderate and predictable, supporting thin‑wall deep‑drawn vessels and housings.
Pure copper's high thermal conductivity also dissipates heat generated during deformation, stabilizing friction and preventing local overheating or galling.
Effects of Work Hardening and Heat Treatment
Pure copper work hardens moderately during cold forming.
After moderate cold deformation, strength rises to 300–350 MPa, while elongation drops to 20%–30%.
After heavy cold working, strength can exceed 400 MPa with elongation below 15%, making further forming difficult.
Interstage annealing at 350–500°C fully restores ductility. Proper annealing eliminates residual stress, refines grains, and maximizes formability for multi‑stage drawing. Over‑annealing may cause grain growth and slight surface roughening.
Practical Advantages and Limitations
Advantages
Outstanding room‑temperature formability for deep drawing and complex stamping
Low flow stress reduces press load and die stress
Excellent ductility minimizes cracking in high‑strain regions
Low springback improves dimensional accuracy
Good surface finish with proper lubrication
Limitations
Low strength means parts are easily deformed in handling
Moderate work hardening requires annealing in multi‑stage processes
Can be prone to galling on tools without suitable lubricants
Not recommended for high‑stress structural parts without subsequent strengthening
Summary
Pure copper, especially in the soft annealed temper, is a premium material for stamping and deep drawing. Its high ductility, low strength, and FCC structure enable extensive plastic deformation, making it suitable for deep, complex, thin‑wall components. Process efficiency relies on material temper, lubrication, die design, and controlled annealing to counteract work hardening. With proper parameters, pure copper delivers consistent, high‑quality formed parts for electrical, thermal, and decorative applications.
