Como evitar casca de laranja ou babados no fundo de uma panela ao estampar discos de alumínio?

HW-A. Introdução: Core Impact of Stamping Defects on Pot Bottom Quality

Aluminum disc stamping (primarily using alloys 1060 e 3003) is a core process in pot bottom manufacturing for cookware. Orange peel texture formation during aluminum disc stamping and wavy edges are two high-frequency appearance defects: this orange peel defect manifests as irregular concave-convex patterns on the pot bottom surface (resembling orange peel, with surface roughness Ra > 1.6μm), while wavy edges refer to periodic wavy deformations at the pot bottom edge (wave height > 0.1milímetros, wave spacing 5-10mm). Among these two defects, this texture issue not only impairs product aesthetics (the appearance defect rate for high-end cookware must be controlled below 0.5%) but also reduces subsequent coating adhesion (coatings on orange peel textures tend to peel off). Portanto, targeted prevention from the root cause is essential.

HW-B. In-depth Analysis of Defect Causes: Synergistic Effects of Material, Processo, and Mold

This orange peel defect and wavy edges are not caused by a single factor but result from the combined effects of aluminum disc material properties, stamping process parameters, mold design, and lubrication conditions. The specific differences are as follows:

(UM) Core Causes of the Orange Peel Defect in Aluminum Disc Stamping

1. Imbalance Between Material Ductility and Grain State

• • Primeiro, the ductility index (elongation δ10) of aluminum discs is directly related to grain size: For alloy 1060, if grains are coarse (>50μm, without homogenization annealing), grain deformation during stamping becomes uneven—some grains are overstretched while others retain their original shape, formando “grain-level concavities and convexities” that ultimately lead to this orange peel defect;

• • Segundo, improper alloy temper exacerbates the issue: If alloy 3003 adopts the H14 hard temper (tensile strength σb = 150MPa) instead of the O temper (σb = 120MPa), insufficient ductility causes local stress concentration during stamping. Exceeding the material’s yield limit results in uneven plastic deformation, with tear-like patterns appearing on the surface, inducing such texture formation.

2. Uneven Distribution of Stamping Stress

• • Excessively high stamping speed (>30mm/s) is a key trigger: Aluminum discs have a short deformation time (<0.5é) inside the mold, preventing uniform stress transmission. The deformation rate difference between the edge and center exceeds 20%, and the central area undergoes plastic deformation first due to stress concentration, forming an orange peel-like “high center, low edge” shape that directly causes this defect;

• • Adicionalmente, insufficient blank holder force (<5kN) worsens the problem: The edge of the aluminum disc is prone to “unstable stretching” during stamping. The stretching amount of local areas exceeds 25% (the ultimate elongation of alloy 1060 é aproximadamente 30%), and irregular wrinkles appear on the surface when approaching the plastic limit, further developing into this orange peel issue.

3. Deterioration of Mold Surface Condition

• • Poor surface roughness of the mold punch (Rá > 0.8μm, sem cromagem) contributes significantly: Durante a estampagem, the friction coefficient between the aluminum disc and mold surface exceeds 0.3. Local areas experience “material sticking” due to excessive friction resistance, and aluminum material is scratched by protrusions on the mold surface, forming scratch-like patterns that exacerbate this texture defect;

• • Além disso, excessively high mold temperature (>50℃) is another critical factor: Continuous stamping (>500 pieces/hour) causes heat accumulation in the mold, raising the local temperature of the aluminum disc to 80-100℃. Uneven material softening (grain boundaries soften first) leads to grain boundary sliding during deformation, producing surface concavities and convexities that become a key inducer of this stamping defect.

(B) Core Causes of Wavy Edges

1. Mismatch Between Mold Clearance and Material Thickness

• • Excessively large punch-die clearance (>15% da espessura do material) is a primary cause: Taking a 1.5mm-thick 3003 aluminum disc as an example, if the clearance exceeds 0.225mm, the edge of the aluminum disc undergoes “free deformation” within the mold clearance and cannot be effectively constrained by the mold wall, forming waves;

• • Em contraste, uneven clearance (circumferential error >0.05milímetros) leads to directional defects: If the punch and die are not concentric during mold installation, the clearance is too small (<0.1milímetros) in one direction and too large (>0.2milímetros) in another. This causes uneven stress on the aluminum disc edge, with excessive stretching in areas with large clearance, forming directional wavy edges.

2. Failure of the Lubrication System

• • Improper lubricant type disrupts the stamping process: Using mineral oil-based lubricants (viscosidade >100cSt) prevents uniform coverage of the mold surface during stamping. Insufficient lubrication in local areas (por exemplo, die cutting edge) causes a sudden increase in friction coefficient, and the aluminum disc edge is “dragged” and deformed, producing irregular wavy edges;

• • Notavelmente, uneven application further amplifies the issue: If there are “uncoated areas” (área >5%) during manual lubricant application, the aluminum disc directly contacts the mold in these areas. The friction resistance is 3-5 times higher than in lubricated areas, leading to differences in edge deformation rates and forming periodic wavy edges.

3. Excessive Thickness Tolerance of Aluminum Discs

• • Thickness deviation exceeding ±0.05mm (surpassing GB/T 3880.2 requirements) creates uneven deformation: Thicker areas require greater stamping force for deformation, while thinner areas are prone to overstretching. The stretching amount of thin edge areas (por exemplo, 1.4espessura mm) é 15-20% higher than that of thick areas (1.6milímetros), ultimately forming wavy edges;

• • Além disso, excessively large edge burrs (>0.1milímetros) induce local accumulation: If aluminum discs are not deburred after cutting, burrs are squeezed by the mold during stamping, causing local material accumulation and forming “burr-induced” wavy edges.

HW-C. Systematic Prevention Solutions: Full-Chain Optimization of Material, Processo, Mofo, and Lubrication

To address this orange peel defect and wavy edges, a prevention system must be established from three aspects: controle de origem, otimização de processos, and equipment assurance. The specific measures for preventing the orange peel issue are as follows:

(UM) Material Pretreatment: Laying the Foundation for Defect-Free Production

1. Precise Selection of Aluminum Disc Parameters

• • Alloy and temper: To avoid this orange peel defect, pot bottom stamping prioritizes alloy 1060-O (δ10 ≥30%, grain size 20-30μm) or 3003-O (δ10 ≥25%), and avoids H14/H18 hard tempers. For high-precision pot bottoms (por exemplo, high-end frying pans), aluminum discs undergo “homogenization annealing + laminação a frio,” with grain size controlled at 15-20μm (detected via metallographic microscope). This eliminates inducers of the texture issue from the perspective of material ductility and grain uniformity;

• • Thickness and tolerance: Based on pot bottom thickness requirements (por exemplo, 2milímetros), aluminum discs with thickness tolerance ≤±0.03mm and edge burrs ≤0.05mm (detected via laser thickness gauge and profilometer) are selected to ensure material uniformity, reduce uneven deformation caused by thickness differences, and indirectly prevent this stamping defect.

2. Pretreatment Process Optimization

• • Stress relief annealing eliminates residual stress: Cut aluminum discs undergo annealing at 180-200℃ for 1 hour to eliminate residual stress from cutting (residual stress ≤50MPa after annealing), avoiding stress superposition-induced uneven deformation during stamping and preventing this orange peel issue;

• • Surface cleaning reduces friction-related risks: Aluminum disc surfaces are cleaned with 95% alcohol before stamping to remove oil and dust (cleanliness meets ISO 16232 Aula 5), preventing increased local friction caused by impurities and reducing this texture defect induced by friction.

(B) Otimização de parâmetros de processo: Precise Control of the Deformation Process

1. Adjustment of Core Stamping Parameters (Focused on Preventing the Orange Peel Defect)

Parameter Type	Optimized Values for Preventing the Orange Peel Defect	Optimized Values for Wavy Edges	Principle Explanation
Stamping Speed	15-20mm/s	10-15mm/s	Reducing speed extends deformation time for uniform stress transmission, avoiding local stress concentration-induced orange peel texture
Força de suporte em branco	8-12kN (for φ200mm discs)	10-15kN	Sufficient blank holder force constrains edges to avoid unstable stretching, reducing inducers of the texture issue
Stamping Depth	Precisely set based on pot bottom curvature (por exemplo, 5milímetros)	Synchronous control of punch-die stroke (error ≤0.02mm)	Avoiding local overstretching prevents surface concavities and convexities that form the orange peel defect
Dwell Time	0.3-0.5é	0.5-0.8é	Dwell eliminates springback and stabilizes deformation, avoiding the texture issue caused by stress release

2. Mold Clearance and Alignment Control

• • Mold clearance: Set as “material thickness × (8%-12%)” (por exemplo, 0.16-0.24mm for 2mm aluminum discs). Circumferential clearance is detected via feeler gauges, with error ≤0.02mm;

• • Coaxiality calibration: After each mold installation, a laser alignment instrument detects the coaxiality of the punch and die, ensuring deviation ≤0.01mm to avoid edge deformation caused by uneven clearance and indirectly assist in preventing this orange peel defect.

(C) Mold Optimization: Enhancing Forming Stability (Focused on Inhibiting the Orange Peel Defect)

1. Mold Surface and Structural Design

• • Surface treatment reduces friction-induced defects: To reduce this orange peel defect caused by friction, the punch and die surfaces adopt a “chrome plating + polimento” processo, with a chrome layer thickness of 5-10μm and surface roughness Ra ≤0.2μm (detected via surface roughness tester). This reduces the friction coefficient to 0.1-0.15, avoiding scratches between aluminum material and the mold surface;

• • Fillet design disperses stress: The die cutting edge fillet radius R = 1.5-3mm (adjusted based on aluminum disc thickness—larger fillets for thicker materials) to avoid scratches from sharp edges. The punch top features a “micro-convex arc” projeto (curvature radius 500-800mm) to disperse central stress, eliminating this texture defect from the perspective of stress distribution.

2. Mold Temperature and Maintenance

• • Temperature control system stabilizes material properties: Thermocouples are embedded in the mold to monitor temperature in real time. When the temperature exceeds 40℃, a water cooling system (cooling water flow 5-10L/min) is activated to control the mold temperature at 25-35℃, avoiding uneven aluminum softening caused by overheated molds and preventing this orange peel defect;

• • Regular maintenance preserves mold performance: Depois de carimbar 5,000 pedaços, the mold surface is polished with metallographic sandpaper (800#) to remove stuck aluminum chips. The die cutting edge is replaced after stamping 20,000 pieces to avoid increased surface roughness due to wear and reduce the risk of this stamping defect.

(D) Atualização do sistema de lubrificação: Reducing Friction Interference

1. Lubricant Selection and Application

• • Type selection prioritizes compatibility: Water-based emulsified lubricants (por exemplo, chlorinated paraffin + emulsifier, viscosity 30-50cSt) are preferred for their combined lubricity and cleanability, avoiding mineral oil residues. For high-precision pot bottoms, um “lubrificante + boron nitride coating” combination can be used to further reduce the friction coefficient to 0.08-0.1, minimizing this orange peel defect caused by friction;

• • Application method ensures uniformity: An automatic spraying system (nozzle diameter 0.5mm, spraying pressure 0.3MPa) is used to form a uniform coating (thickness 5-10μm) on the aluminum disc and mold surfaces, alcançar 100% coverage. This avoids increased local friction due to missed coating and prevents this texture issue.

2. Post-Lubrication Treatment

• • Residual lubricant is blown dry with hot air (60-80℃) after stamping to avoid reduced subsequent coating adhesion caused by lubricant residues. For pot bottoms requiring anodization, alkaline cleaners (pH 8-9) are used to ensure no oil remains on the surface.

HW-D. Defect Detection and Quality Verification: Ensuring Prevention Effectiveness (Focused on the Orange Peel Defect)

(UM) Online Detection: Real-Time Interception of the Orange Peel Defect

1. Visual Inspection System

• • An industrial camera (2-megapixel, shooting frequency 50 frames/s) is installed at the stamping machine outlet, paired with an AI algorithm (recognition accuracy ≥99.5%) to detect the pot bottom surface in real time. For this orange peel defect, concave-convex areas with Ra > 1.6μm are identified via grayscale differences; for wavy edges, waves with height >0.1mm are identified via edge profile analysis;

• • When this texture defect is detected, the system automatically triggers an alarm and pauses stamping to avoid batch defects.

2. Dimensional and Morphological Detection

• • A laser profilometer (precisão ±0,001mm) detects the pot bottom edge to record the wave height and spacing of wavy edges. A surface roughness tester (sampling length 2.5mm) measures the surface to ensure Ra ≤1.2μm (Ra ≤0.8μm for high-end pot bottoms), directly verifying the prevention effect of this orange peel defect;

• • One sample per 100 pieces is subjected to metallographic analysis to check grain deformation uniformity, ensuring no obvious coarse grains or stress-concentrated areas and eliminating hidden risks of this stamping defect at the micro level.

(B) Offline Verification: Ensuring Long-Term Stability

1. Teste de adesão: Anodização (film thickness 10-12μm) is performed on stamped pot bottoms, followed by a cross-cut test per GB/T 9286 (cut spacing 1mm). No coating peeling after tape peeling (adhesion grade ≥4B) verifies effective control of this orange peel defect;

2. Heating Uniformity Test: The pot bottom is heated on an induction cooker (power 2000W) para 10 minutos, and an infrared thermal imager detects the surface temperature distribution. A temperature difference ≤5℃ (typically ≤3℃ for pot bottoms with qualified wavy edge prevention) ensures uniform heating.

HW-E. Casos de aplicação na indústria: Practical Verification of Prevention Effects (Focused on Resolving the Orange Peel Defect)

1. Supor Wok Bottom Production Line (Alloy 1060-O Aluminum Discs, φ280mm)

• • Original Issue: Stamping speed 25mm/s, blank holder force 6kN, this orange peel defect rate 8%, wavy edge defect rate 5%;

• • Optimization Measures: ① Reduced stamping speed to 18mm/s and increased blank holder force to 10kN to improve stress distribution; ② Adjusted mold clearance from 0.25mm to 0.2mm and chrome-plated the surface to Ra = 0.15μm to reduce friction; ③ Adopted an automatic water-based lubricant spraying system to ensure uniform lubrication;

• • Efeito: This texture defect rate reduced to 0.3%, wavy edge defect rate reduced to 0.2%, meeting high-end product line requirements.

2. ZWILLING Frying Pan Bottom Production Line (Alloy 3003-O Aluminum Discs, φ240mm)

• • Original Issue: Aluminum disc grain size 40-50μm, mold temperature exceeding 50℃, severe orange peel defects;

• • Optimization Measures: ① Subjected aluminum discs to homogenization annealing at 200℃ for 1.5 hours to reduce grain size to 20-25μm and improve ductility uniformity; ② Installed a water cooling system for the mold to control temperature at 30℃, avoiding uneven aluminum softening;

• • Efeito: This orange peel defect was completely eliminated, surface roughness Ra reduced from 2.0μm to 0.8μm, and coating adhesion grade reached 5B.

HW-F. Conclusions and Future Trends

The prevention of this orange peel defect in aluminum disc stamping core lies in achieving synergy between “material uniformity, precisão do processo, mold stability, and lubrication effectiveness.” No futuro, with the application of intelligent technologies, prevention solutions will be further upgraded: ① Introduce AI parameter self-adjustment systems (automatically optimizing stamping speed and blank holder force based on real-time detection data of this texture issue); ② Adopt “digital twin” technology to simulate the stamping process and predict risks of this specific defect in advance; ③ Develop new nanolubricants (por exemplo, graphene-based lubricants) to further reduce the friction coefficient, pushing the defect rate of this orange peel issue toward “zero.”
Geral, defect-free control of this stamping defect requires breaking the mindset of “single-link optimization” and establishing a full-chain quality control system. Precise control at every step—from material incoming inspection to finished product testing—ensures both the appearance and performance of pot bottoms meet standards.