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In the stamping process, product warpage (poor flatness) and dimensional errors are common quality issues. Resolving these challenges requires optimization across multiple dimensions, including material properties, die design, processing techniques, and equipment precision.

I. Methods to Resolve Product Warpage (Poor Flatness)

Warpage typically stems from residual internal stress, bending moments during processing, or uneven material deformation.

1. Material-Side Control:

• Use of Precision Levelers: For longitudinal curvature (Coil Set) or transverse curvature (Cross Bow) in coil stock, high-precision levelers with 19 or more rollers should be used for correction.
• Elimination of Internal Stress: Residual stresses generated during the rolling process are released during stamping. These can be eliminated through heat treatments such as annealing.

2. Die Design and Processing Techniques:

• Increased Blank-Holding Force and Counter-Pressure: During blanking, use a stripper plate to clamp the material tightly. Additionally, install a counter-pressure pad (ejected by springs or air cushions) in the lower die to provide support opposite to the punch. This effectively offsets the bending moments that cause warpage.
• Corrective Bending and Bottom-Dead-Center Coining: In bending processes, apply surface pressure (Coining/Striking) at the end of the stroke. This induces plastic flow in the deformation zone, significantly reducing springback and improving flatness.
• Reinforcement Ribs (Beads): For thin sheet parts, concave-convex strengthening ribs (beads) can be designed on flat areas to increase rigidity and prevent deformation from external forces.
• Optimization of Die Clearance: Excessive clearance increases the material’s tendency to stretch and bend, exacerbating warpage. Select a reasonable clearance based on material properties and maintain uniformity.
• Setting Up Correction Stages: For products already exhibiting warpage, a stippling/planishing (Hoshida) stage can be added in subsequent processes. This uses subtle protrusions on the surface to squeeze the material and restore flatness.

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II. Methods to Resolve Dimensional Errors

Dimensional errors are usually caused by die wear, variations in material thickness, inaccurate positioning, or springback phenomena.

1. Improving Positioning Accuracy:

• Application of Pilot Pins: In progressive dies, pilot pins must be installed to precisely calibrate the feeding position of the strip, preventing deviations in hole pitch or profile dimensions caused by feeding errors.
• Precise Guiding Systems: Use high-precision guide posts and bushings (such as ball bearing guides) and account for the elastic deformation of the die under stamping loads.

2. Counteracting Die Wear:

• Allowing for Wear Margins: During design, the piercing punch size should be set toward the upper limit of the tolerance band, while the blanking die size should be set toward the lower limit to compensate for future dimensional changes due to wear.
• Selection of Wear-Resistant Materials and Regular Grinding: Use carbide or high-quality tool steels, and perform regular grinding before the cutting edges become dull to maintain dimensional stability.

3. Controlling Dimensional Variations from Springback:

• Compensation Method Design: Pre-compensate for the material’s springback by adjusting the die angles, such as utilizing overbending designs.
• Fine-Tuning Die Mechanisms: Use height blocks (limit blocks) to fine-tune the bottom-dead-center height, or use replaceable shims to correct the processing stroke.

4. Material and Measurement Environment Management:

• Material Stratification Management: Address thickness tolerance fluctuations by categorizing materials by thickness for separate processing, or use servo presses equipped with automatic thickness compensation.
• Environmental Temperature Control: Dimensional measurement of precision parts should be conducted at a standard temperature (20°C) to avoid measurement errors caused by thermal expansion.

Through these measures, the deformation of stamped parts can be effectively controlled and dimensional accuracy improved, ensuring product interchangeability and functionality.