Quality Control Points in Drawing Die Forging and Forming Process

Quality Control Points in Drawing Die Forging and Forming Process

The forging and forming process of alloy drawing die blanks is a critical upstream stage that determines the final die performance, microstructure uniformity, crack resistance, and service life. Poor control in this stage often leads to irreversible defects such as internal voids, non-uniform carbide distribution, and early fracture during drawing.

Raw Material Quality Control

The foundation of die forging quality is raw material selection and inspection.

Key control points include:

• Chemical composition consistency (WC, Co, alloying elements)

• Powder purity and impurity control

• Oxygen and carbon balance in carbide systems

• Particle size distribution uniformity

Impurities or inconsistent powder quality can cause porosity, weak grain bonding, and structural instability after sintering.

Powder Mixing Uniformity Control

Before forming, WC and binder powders must be uniformly mixed.

Quality risks include:

• Binder segregation

• WC agglomeration

• Uneven particle distribution

Proper mixing ensures:

• Stable microstructure after sintering

• Uniform mechanical properties

• Reduced risk of localized weak zones

Pressing Density Control

During forming, powder compaction must achieve uniform green density.

Key control requirements:

• Uniform pressure distribution

• Avoidance of density gradients

• Controlled compaction speed

Uneven density leads to:

• Differential shrinkage during sintering

• Internal cracks

• Geometric distortion of die blank

Green Body Defect Inspection

After pressing, the green compact must be inspected for:

• Surface cracks

• Edge chipping

• Lamination defects

• Density inconsistency

Defective green bodies will amplify flaws during sintering and machining.

Dimensional Accuracy Control of Formed Blank

Forming precision determines machining allowance and final accuracy.

Key factors:

• Mold precision and wear condition

• Pressing force stability

• Elastic recovery behavior

Dimensional deviation at this stage increases downstream machining difficulty.

Die Forging Temperature Control (for Steel Die Bodies)

For alloy steel die bodies used in supporting structures:

• Heating temperature must be strictly controlled

• Overheating leads to grain coarsening

• Underheating results in incomplete deformation

Proper thermal control ensures uniform grain refinement and improved toughness.

Deformation Uniformity Control

During forging, material flow must remain stable.

Common problems include:

• Uneven deformation flow

• Local stress concentration

• Folding or internal defects

Uniform deformation ensures continuous grain flow and improved fatigue resistance.

Grain Flow Direction Optimization

Forging should align grain flow with stress direction.

Benefits:

• Improved fracture resistance

• Higher fatigue strength

• Better load-bearing capacity

Improper grain flow leads to early crack propagation under drawing stress.

Internal Defect Control

Forging must eliminate or prevent:

• Porosity

• Inclusion clusters

• Internal micro-cracks

Non-destructive inspection methods include:

• Ultrasonic testing

• X-ray inspection

Internal defects severely reduce die lifespan.

Surface Quality Control After Forging

Surface condition affects subsequent machining quality:

• No forging cracks

• No oxide scale defects

• No surface folding

Poor surface quality increases grinding difficulty and defect risk.

Cooling Rate Control After Forging

Cooling affects final microstructure:

• Rapid cooling → higher hardness, risk of internal stress

• Slow cooling → improved toughness, lower residual stress

Controlled cooling ensures balanced mechanical properties.

Residual Stress Management

Forging introduces internal stress that must be controlled.

Methods:

• Post-forging annealing

• Stress relief heat treatment

• Controlled cooling environment

Residual stress can cause dimensional instability during machining or sintering.

Common Forging Defects in Die Blanks

Typical defects include:

• Internal voids

• Cracks from improper deformation

• Density gradients

• Grain coarsening

• Folding defects

These directly affect die performance after processing.

Quality Inspection Methods

Key inspection techniques include:

• Ultrasonic flaw detection

• Metallographic analysis

• Hardness testing

• Dimensional measurement

• Microstructure evaluation

Process Optimization Strategies

Powder Pre-Treatment Optimization

Improve purity and uniformity before forming.

Controlled Pressing Technology

Use isostatic pressing to improve density uniformity.

Precision Mold Design

Ensure uniform stress distribution during forming.

Forging Simulation Analysis

Use FEM simulation to optimize deformation paths.

Heat Treatment Integration

Combine forging with proper annealing to stabilize structure.

Conclusion

Quality control in the forging and forming process of alloy drawing dies is essential for ensuring microstructural integrity, dimensional accuracy, and long-term durability. Key control points include raw material quality, powder uniformity, pressing density, deformation behavior, grain flow optimization, and residual stress management. Effective process control significantly improves die performance and reduces failure risk in later manufacturing stages.

References

1. ASM International, Powder Metallurgy and Forging Handbook

2. ASM International, Tool Materials Handbook

3. George E. Dieter, Mechanical Metallurgy

4. J.R. Davis, Tool Materials, ASM International

5. Bhushan, B., Introduction to Tribology