How to control the surface roughness when stamping the kitchenware with 8079 alloy aluminum round plates?

1. Introduction: Application Value of 1060 Aluminum Discs for Cookware and Significance of Roughness Control

1060 aluminum discs for cookware (Al content ≥99.6%, O temper elongation ≥35%) have become the mainstream base material for cookware such as flat pans, stockpots, and tableware due to their high purity, excellent ductility, easy stamping forming, and moderate cost. Notably, the surface roughness of cookware (typically measured by the arithmetic mean deviation of the profile, Ra) not only determines the appearance texture—surfaces with Ra >1.6μm tend to appear “hazy” or scratched—but also directly affects user experience:

• Cleanliness: Uneven surfaces with Ra >2.5μm easily trap oil stains and food residues, increasing cleaning difficulty;

• Corrosion resistance: Micro-depressions on rough surfaces tend to accumulate electrolytes (e.g., salt water, vinegar), accelerating the electrochemical corrosion of aluminum;

• Tactile feel: High roughness (Ra >3.2μm) on cookware handles and pot edges causes a “prickly” sensation, reducing user satisfaction.

According to the cookware industry standard QB/T 2421-2021 Aluminum and Aluminum Alloy Non-Stick Pans, the Ra of the inner food-contacting surface of cookware must be ≤1.6μm, and the outer surface ≤2.0μm. However, 1060 alloy has low strength (yield strength ≤95MPa) and high sensitivity to plastic deformation, making it prone to excessive roughness during stamping (Ra often reaches 2.5-3.8μm under unoptimized processes). To address this challenge, it is necessary to analyze influencing factors throughout the entire process and develop targeted control solutions.

2. Correlation Between the Properties of 1060 Aluminum Discs for Cookware and Stamping Roughness

Fundamentally, the pure aluminum properties of 1060 aluminum discs for cookware are a “double-edged sword”—high ductility adapts to complex cookware shapes (e.g., deep-drawn pot bodies), but low strength and plastic deformation characteristics also pose challenges for roughness control:

(1) Stamping Deformation Characteristics

1. Plastic flow-dominated deformation: 1060 alloy has no obvious yield plateau. During stamping, metal deformation is dominated by “uniform plastic flow”. If the local deformation rate difference exceeds 20%, “shear bands” are likely to form, manifesting as periodic surface unevenness (similar to “orange peel texture”), with an Ra increase of 0.8-1.2μm;

2. Surface vulnerability to wear: With low hardness (HV ≤30), when the friction coefficient between the mold and the aluminum disc exceeds 0.2, the surface metal of the disc is prone to “scratching and peeling”, forming scratches with a depth of 5-10μm and a sharp Ra increase of 1.5-2.0μm;

3. Sensitivity to oxide layers: Furthermore, if the natural oxide layer (2-5nm thick) on the surface of the aluminum disc is not removed before stamping, it will be pressed into the matrix under high pressure, forming “oxide inclusion protrusions” and causing local Ra >3.0μm.

(2) Key Influence Scenarios for Cookware Stamping

Across different stamping processes for cookware, the roughness risks vary significantly:

• Blanking process (trimming, punching): Dull mold edges or uneven gaps easily produce “burrs” (height 10-20μm), resulting in edge Ra >4.0μm;

• Deep drawing process (pot body deep drawing): Insufficient blank holder force causes material wrinkling (wrinkle height 5-8μm), or insufficient lubrication leads to mold adhesion of aluminum chips, forming “indentations” (Ra increase of 0.5-1.0μm);

• Bending process (handle bending): A bending radius smaller than 1.5 times the material thickness easily produces surface tensile cracks (width 2-3μm), resulting in local Ra >2.8μm.

3. Key Influencing Factors of Stamping Roughness for 1060 Aluminum Discs for Cookware

To systematically identify the root causes of excessive roughness, we break down the “raw material-mold-process-post-treatment” full process. The core influencing factors can be categorized into four types, with their weight ratios verified by orthogonal experiments (Table 1):

Table 1: Weight Ratio of Factors Influencing Stamping Roughness of 1060 Aluminum Discs for Cookware

Influence Link	Specific Factor	Weight Ratio (%)	Ra Impact Range (μm)
Raw Material Pretreatment	Initial roughness, oxide layer thickness	25	0.5-1.2
Mold System	Mold Ra, gap, edge condition	35	0.8-1.8
Stamping Process Parameters	Stamping speed, blank holder force, lubrication	30	0.6-1.5
Post-Treatment	Deburring, cleaning method	10	0.3-0.8

(1) Raw Material Pretreatment: The Basic Threshold

First and foremost, raw material pretreatment serves as the foundational barrier against excessive roughness:

1. Excessive initial roughness: When 1060 aluminum discs for cookware are not subjected to finish rolling after cold rolling, their initial Ra often reaches 3.2-4.5μm. Stamping can only slightly smooth the surface (Ra reduction ≤0.5μm), resulting in final roughness still exceeding standards;

2. Oxide layer and oil residue: Additionally, if rolling oil (mainly mineral oil) remaining on the aluminum disc is not degreased, it will cause local dry friction between the mold and the aluminum disc during stamping. When the oxide layer thickness exceeds 5nm, it will be pressed into the surface to form “hard particles”.

(2) Mold System: The Carrier for “Copying and Amplifying” Roughness

Equally critical is the mold system, which directly transfers its surface characteristics to the aluminum disc and amplifies existing defects:

1. Insufficient mold surface precision: Specifically, when the mold Ra (e.g., for deep drawing molds, blanking molds) is ≥0.8μm, its surface texture will be “copied” onto the aluminum disc (pure aluminum has high ductility and easily conforms to the mold surface), resulting in a workpiece Ra ≈ mold Ra + 0.3-0.5μm;

2. Mismatched mold gaps: Furthermore, the reasonable gap for stamping 1060 aluminum discs for cookware is 8%-12% of the material thickness (e.g., 0.08-0.12mm for 1mm-thick discs):

• • Too small a gap (<8%): Metal flow is hindered, and mold edges squeeze the aluminum disc surface, forming “indentations” (Ra increase of 0.8-1.2μm);

• • Too large a gap (>12%): Tear burrs form at the aluminum disc edge (height 10-15μm), causing a sharp Ra increase of 1.5-2.0μm;

3. Mold wear and edge dulling: Moreover, if the mold is made of ordinary Cr12 steel (without chrome plating), the edge wear reaches 5-8μm after stamping 5,000 pieces, easily causing “scratches” on the aluminum disc surface and increasing Ra from 1.2μm to 2.5μm.

(3) Stamping Process: The “Control Core” for Metal Deformation Uniformity

Another key determinant lies in the stamping process parameters, which regulate metal flow and directly affect surface smoothness:

1. Unbalanced stamping speed: For instance, the optimal stamping speed for these aluminum discs is 50-150mm/s (adjusted according to cookware complexity):

• • Excessively high speed (>200mm/s): The metal flow rate exceeds the plastic deformation limit of 1060 alloy (dynamic recovery rate ≤150mm/s), causing local “shear instability” and forming orange peel texture (Ra increase of 0.6-1.0μm);

• • Excessively low speed (<30mm/s): Production efficiency decreases, and prolonged contact between the aluminum disc and mold increases oxidation risk;

2. Improper blank holder force: During the deep drawing process, in particular, the blank holder force must match the material flow demand (e.g., 5-10kN for 1mm-thick 1060 discs used in pot body deep drawing):

• • Insufficient blank holder force (<5kN): Material is prone to wrinkling (wrinkle height 5-7μm), with an Ra increase of 1.0-1.5μm;

• • Excessive blank holder force (>12kN): Friction between the aluminum disc surface and the blank holder increases, forming “striped scratches” (Ra increase of 0.8-1.2μm);

3. Insufficient lubrication: Notably, failure to use dedicated aluminum stamping lubricant or using it at low concentration leads to a friction coefficient >0.25, causing “adhesive wear” between the mold and the aluminum disc and forming irregular scratches (Ra increase of 1.2-1.8μm).

(4) Post-Treatment: The Final Polish for Roughness Reduction

Finally, post-treatment processes play a supporting yet non-negligible role, accounting for 10% of roughness variation:

1. Deburring process upgrading: Crude deburring methods (e.g., wire brushing) easily scratch the surface; instead, vibration grinding (abrasive: resin grinding blocks, grit 800#, grinding time 10-15min) avoids metal abrasive-induced damage;

2. Cleaning method: Residual abrasive particles or cleaning agents can adhere to the surface, so a multi-step cleaning process (hot water pre-wash → ultrasonic cleaning → pure water rinsing) is essential to prevent secondary contamination.

4. Full-Process Control Solution for Stamping Roughness of 1060 Aluminum Discs for Cookware

Building on the above analysis of influencing factors, a collaborative control system is established across the “pretreatment-mold-process-post-treatment” four links. The core goal is to achieve cookware surface Ra ≤1.6μm (inner surface) and ≤2.0μm (outer surface):

(1) Raw Material Pretreatment: Laying the Foundation for Low Roughness

Starting with raw material pretreatment, we optimize the initial state of the aluminum disc to minimize inherent roughness:

1. Initial roughness control of 1060 aluminum discs:

• • Cold rolling process optimization: Adopt “rough rolling (reduction rate 50%-60%) + 2-pass finish rolling (single-pass reduction rate 15%-20%)”. The finish rolling roller surface is polished to Ra ≤0.2μm, ensuring the initial Ra of the aluminum disc ≤0.8μm (meeting the high-precision grade requirements of GB/T 26499-2011 Cold Rolled Aluminum and Aluminum Alloy Strip);

• • Surface cleaning process: Implement “alkaline degreasing (50-60℃, 5%-8% NaOH solution, soaking for 5-8min) → pickling (10%-15% HNO₃ solution to remove oxide layer, 3-5min) → pure water rinsing (3 times, water temperature 40-50℃) → hot air drying (60-80℃)”, ensuring surface oil residue ≤5mg/m² and oxide layer thickness ≤2nm;

2. Raw material storage protection: Use vacuum packaging or film-coated packaging to prevent moisture-induced oxidation of aluminum discs during storage. The storage period should not exceed 3 months (recleaning is required if exceeded).

(2) Mold System Optimization: Blocking the “Copying Path” of Roughness

Moving to mold system optimization, we enhance mold precision to avoid transferring defects to the aluminum disc:

1. Mold surface precision improvement:

• • Mold material selection: Use DC53 die steel (quenched hardness HRC62-65) for deep drawing molds and blanking molds, which has 30% higher wear resistance than traditional Cr12 steel and extends the mold roughness stability period (from 5,000 pieces to 15,000 pieces);

• • Surface treatment process: The mold forming surface undergoes “rough grinding (Ra ≤1.6μm) → fine grinding (Ra ≤0.4μm) → polishing (diamond polishing paste, Ra ≤0.2μm) → hard chrome plating (Cr layer thickness 5-8μm, Ra ≤0.1μm)”, ensuring no scratches or pitting on the mold surface;

2. Precision mold gap design:

• • Based on the thickness (t) of 1060 aluminum discs, the blanking mold gap is set to 0.08t-0.12t, and the deep drawing mold gap to 1.05t-1.1t (reserving material springback allowance). A laser micrometer (accuracy ±0.001mm) is used to detect gap uniformity, with a deviation ≤0.005mm;

3. Mold edge maintenance:

• • Initial edge grinding: The blanking mold edge is ground to a fillet of R=0.05-0.1mm (avoiding sharp edges scratching the aluminum disc), and the deep drawing mold punch to a fillet of R=3-5mm (adjusted according to cookware depth to reduce material tensile stress);

• • Online wear monitoring: After stamping 5,000 pieces, the edge wear is inspected with an optical microscope (50x magnification). If wear exceeds 5μm, the machine is shut down immediately for grinding and repair.

(3) Stamping Process Parameter Regulation: Achieving Uniform Deformation and Low Friction

Next, precise regulation of stamping process parameters ensures smooth metal flow and minimizes friction-induced defects:

1. Staged stamping speed optimization:

• • Blanking process: Speed of 80-120mm/s (fast cutting to reduce contact time between edges and aluminum discs);

• • Deep drawing process: Adjusted according to pot depth—80-100mm/s for shallow drawing (depth <30mm) and 50-80mm/s for deep drawing (depth 30-60mm) (slowing metal flow rate to avoid shear instability);

• • Bending process: Speed of 60-90mm/s (avoiding local excessive stretching);

2. Dynamic blank holder force adaptation:

• • Adopt a “variable blank holder force system”: Low force (5-6kN) in the initial deep drawing stage (when material just contacts the punch) to promote flow, increased force (8-10kN) in the mid-stage (when material enters the die) to prevent wrinkling, and reduced force (6-7kN) in the final stage (near forming completion) to reduce friction;

3. Dedicated lubrication system construction:

• • Lubricant selection: Use water-based dedicated aluminum stamping lubricant (containing extreme pressure additives and rust inhibitors, e.g., model AL-800) at a concentration of 8%-10% (viscosity 20-30mm²/s at 40℃ after dilution);

• • Lubrication method: Adopt “mold spraying + aluminum disc pre-coating” for the deep drawing process, ensuring a lubricating film thickness of 5-8μm on the forming surface (detected by a coating thickness gauge) to avoid dry friction.

(4) Refined Post-Treatment Process: Correcting Defects and Stabilizing Roughness

Last but not least, refined post-treatment processes eliminate residual defects and stabilize surface quality:

1. Deburring process upgrading:

• • Edge burrs: Use vibration grinding (abrasive: resin grinding blocks, grit 800#, grinding time 10-15min) to avoid scratching by metal abrasives;

• • Micro-protrusions on inner surfaces: Use ultrasonic deburring (power 500W, frequency 28kHz, time 3-5min) to peel off micro-impurities via ultrasonic vibration;

2. Collaborative cleaning and passivation:

• • Cleaning process: “Hot water pre-washing (50-60℃ to remove residual lubricant) → ultrasonic cleaning (40kHz, cleaning agent concentration 3%-5%, time 5-8min) → pure water rinsing (3 times, resistivity >15MΩ·cm) → hot air drying (70-80℃, air speed 2-3m/s)”;

• • Surface passivation: After cleaning, perform chromate passivation (concentration 2%-3%, temperature 25-30℃, time 2-3min) to form a 5-10nm-thick passivation film—not only improving corrosion resistance but also filling micro-depressions on the surface, reducing Ra by an additional 0.2-0.3μm.

5. Experimental Verification: Effectiveness Test of the Control Solution

To empirically validate the effectiveness of the proposed full-process control system, a cookware enterprise conducted comparative experiments using 1060 aluminum discs for cookware (φ300mm×1mm, O temper) to stamp flat pans (inner surface Ra requirement ≤1.6μm). Two groups were set up: an “unoptimized group” (traditional process) and an “optimized group” (full-process solution). The test results are as follows:

Table 2: Surface Roughness Comparison of Flat Pans Stamped from 1060 Aluminum Discs for Cookware

Test Item	Unoptimized Group (Traditional Process)	Optimized Group (Full-Process Solution)	Industry Standard Requirement
Initial Ra of Aluminum Disc (μm)	3.2	0.7	≤1.0
Ra of Mold Forming Surface (μm)	0.9	0.1	≤0.2
Ra of Inner Surface After Stamping (μm)	2.8	1.1	≤1.6
Ra of Outer Surface After Stamping (μm)	3.5	1.7	≤2.0
Burr Height (μm)	12	3	≤5
Orange Peel Texture Rate (%)	45	5	≤10

From the data in Table 2, it is evident that the optimized group outperforms the unoptimized group across all key metrics: inner surface Ra is reduced by 61%, burr height by 75%, and orange peel texture rate by 89%, fully meeting industry standards.

(1) Long-Term Stability Test

Beyond short-term performance, long-term stability is critical for industrial scalability. During continuous stamping of 10,000 flat pans, the inner surface Ra of the optimized group fluctuated within 1.0-1.3μm (deviation ≤0.3μm), and the mold edge wear was only 3μm. In contrast, the unoptimized group exhibited 12μm mold wear after 10,000 pieces, with inner surface Ra increasing to 2.2μm. This confirms the long-term reliability of the optimized process.

(2) User Experience Feedback

Complementing technical measurements, user experience feedback further validates practical value. The optimized cookware surface had “no obvious scratches or haze”, oil residue during cleaning was reduced by 60% (detected by the weighing method), and user satisfaction increased from 75% to 92%. These results confirm that roughness control directly enhances end-user acceptance.

6. Conclusions and Outlook

In summary, surface roughness control for stamping 1060 aluminum discs for cookware must follow the principle of “full-process collaboration”:

1. Core logic: Based on the “high ductility, low strength” characteristics of 1060 pure aluminum, the Ra target of ≤1.6μm is achieved through four synergistic steps: initial roughness control of raw materials (Ra ≤0.8μm), mold high precision (Ra ≤0.1μm), adaptive process parameters (speed 50-120mm/s, variable blank holder force), and refined post-treatment;

2. Key control points: Notably, two factors are most influential—mold surface precision (35% weight) and stamping lubrication (30% weight)—requiring priority resource allocation in industrial applications.

Looking ahead, three directions can further advance roughness control technology:

1. Intelligent monitoring: Develop a “laser confocal online roughness detection system” to provide real-time Ra feedback after stamping, enabling dynamic adjustments to mold gaps or lubrication amounts and reducing reliance on manual inspection;

2. Mold coating upgrading: Replace hard chrome with diamond-like carbon (DLC) coatings to further reduce the mold friction coefficient from 0.15 to 0.08, minimizing scratch risks and extending mold life;

3. Lubricant-free stamping technology: Develop nano-scale MoS₂ lubricating films on the surface of 1060 aluminum discs to replace traditional lubricants, eliminating cleaning residue issues and reducing environmental impact.

Ultimately, the core principle of effective roughness control is recognizing it as a “systematic project”—not isolated link optimization. Balancing precision, efficiency, and cost ensures the process meets both technical standards and market demands for high-quality cookware.