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การแนะนำ: Why “Cracking” Has Become the Biggest Bottleneck in Aluminum Circle Forming

As the cookware and lighting industries continue to shift toward lightweight metal forming, ตัวเครื่องครัวที่ดึงออกมาลึก, หม้อชั้นในของหม้ออัดแรงดัน, แผ่นสะท้อนแสง, โป๊ะโคม, and storage vessels place increasingly higher demands on the formability of aluminum circles. อย่างไรก็ตาม, in daily production, แคร็ก, tearing, excessive earing, orange-peel texture, and edge breakage still occur frequently. These defects reduce yield rates by 20–40% in many factories, severely affecting output stability.

Manufacturers often ask:

• Why do aluminum circles with the same alloy and thickness perform differently during forming?
• Why do edges tend to crack first during deep drawing?
• Why does the arc (R-zone) crack suddenly during spinning?
• What is the systematic method to eliminate cracking from materials, annealing, dies, lubrication, and parameter control?

This article explains in engineering depth the mechanisms behind aluminum circle cracking, the material causes, process-related causes, and comprehensive solutions from an end-to-end production perspective.

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ส่วนหนึ่ง 1 — Why Do Aluminum Circles Crack During Deep Drawing or Spinning? (การวิเคราะห์กลไก)

1. Material-Related Causes

1. Alloy Composition Determines Deformation Capacity

Different aluminum alloys have very different stretchability:

Higher contents of Mn or Mg increase strength but reduce elongation, making cracking more likely.
ดังนั้น:

• 1050/1060 are the best alloys for deep drawing
• 3003 is usable only with well-controlled annealing
• 5052 is high strength but risky for deep drawing

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2. Non-uniform Mechanical Properties (Uneven Hardness or Thickness)

Cracking can occur when:

• Internal stress distribution is uneven
• Thickness deviation is large
• Edge hardness is significantly higher than the center
• Cold-work hardening remains due to insufficient annealing

ที่ edge area is the most common weak point.

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3. Coarse or Elongated Grains Cause Early Crack Initiation

Grain structure determines formability:

• Fine grains = excellent formability
• Coarse grains = higher brittleness, easier cracking
• Strong grain orientation leads to earing, stress concentration, and cracks

Typical metallurgical defects that increase crack risk:

• Coarse grains
• Elongated grains
• Strong rolling texture
• Excessive precipitates

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2. Process-Related Causes

1. Excessive Drawing Ratio (DR)

Deep drawing ratio (DR):
DR = blank diameter / cup diameter

• When DR > 2.1, aluminum circles are highly likely to crack.

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2. Restricted Material Flow = Forced Stretching = Cracking

Cracking happens when metal cannot flow smoothly into the die cavity.

Common reasons:

• Excessive blank-holder force
• Insufficient blank-holder force (causing wrinkles → later tearing)
• Poor lubrication (high friction → tearing)

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3. Improper Die Radius (R-Value)

A small R-angle is the No.1 reason for cracking.

• Small die radius → stress concentration → R-zone cracks in 90% of cases
• Tight punch-die clearance
• Abrupt transition angles

Recommended R values:

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4. Poor Lubrication Causes Tearing

Insufficient lubrication leads to:

• รอยขีดข่วน
• Galling
• Severe friction
• Tearing at the R-zone or walls

ใช้:

• High-pressure deep drawing oils
• Graphite-based lubricants
• Food-grade lubricants for cookware

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5. Spinning-Related Force Imbalance

Cracks in spinning commonly occur in:

• R-zone
• Bottom-to-wall transition area
• Flanging area

สาเหตุ:

• Excessive roller pressure
• Too fast feed rate
• High localized heating → work hardening
• Starting thickness too thin

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3. Equipment-Related Causes

1. Poor Machine Precision

• Eccentric ram
• Machine vibration
• Uneven force distribution
  → Cracking during forming.

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2. Worn Dies or Blank Holders

Wear introduces:

• Burrs
• รอยขีดข่วน
• Localized grabbing of metal

Leading to premature cracking.

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ส่วนหนึ่ง 2 — How to Prevent Cracking During Deep Drawing or Spinning

1. Material Control (The Most Important Factor)

1. Selecting the Right Alloy

Strengthened tempers (H14/H24) cannot be deep drawn.
ใช้ O-temper เท่านั้น.

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2. Correct Annealing (Solves 80% of Cracking Problems)

Annealing target:

• Remove cold-work hardening
• Restore ductility
• Balance mechanical properties

Recommended:

Under-annealed:

• High edge hardness
• R-zone tearing
• Roller marks

Over-annealed:

• Coarse grains
• Orange-peel surface

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3. Thickness and Hardness Control

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2. Die Optimization

1. Proper R-Radius Design

ใช้:

• Punch R ≥ 4t
• Die R ≥ 6t

Where t = sheet thickness.

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2. Proper Clearance

Recommended:

• 1.08–1.12t for first draw
• 1.15–1.20t for redrawing

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3. Controlled Blank-holder Force

• Too much → restricted flow → cracking
• Too little → wrinkling → later tearing

Use hydraulic or CNC-controlled systems when possible.

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3. การหล่อลื่น & การรักษาพื้นผิว

Good lubrication reduces friction 3–5×.

Recommended:

• High-pressure deep-drawing oils
• Graphite lubricants
• Food-grade oils for cookware production

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4. Deep Drawing Parameter Optimization

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5. Spinning Parameter Optimization

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6. Using “Pre-forming + Deep Drawing” Combination

Steps:

• Pre-stretching
• Pre-bending
• Drawing in two stages
• Intermediate annealing

This reduces cracking by over 60%.

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ส่วนหนึ่ง 3 — Common Cracking Types and How to Diagnose Them

1. Edge Cracking (Most Common)

สาเหตุ:

• High edge hardness
• Insufficient annealing
• Thickness deviation

Solutions:

• Test edge hardness
• Ensure complete annealing
• Reduce blank-holder force

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2. R-Zone Cracking

สาเหตุ:

• Small R-radius
• High friction
• Stress concentration

สารละลาย:

• Increase die R
• Improve lubrication
• Reduce drawing speed

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3. Straight-Line Cracking

สาเหตุ:

• Strong rolling texture
• Grain elongation

สารละลาย: Change to better-quality material.

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4. Orange-Peel Surface Cracking

สาเหตุ:

• Over-annealing
• Coarse grains

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5. Spinning Cracks at Transition Zone

สาเหตุ:

• Imbalanced roller force
• Thin starting thickness

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6. Flanging Cracks

สาเหตุ:

• Large angle transition
• Insufficient thickness

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ส่วนหนึ่ง 4 — Complete Factory-Level Solution (From Coil to Final Product)

1. Raw Material (Aluminum Coil)

Key requirements:

• อัลลอย: 1050/1060-โอ, 3003-โอ
• Grain size: 50–100 μm
• Thickness tolerance: ±0.01 mm
• Hardness variation < 5HB

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2. Cleaning and Blanking

• Oil removal
• Scratch prevention
• High-precision circle cutting

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3. การหลอม

Ideal:

• 380–420°C
• 4 hours soaking
• Slow cooling

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4. Pre-forming Preparation

• Even lubrication
• Mold preheating
• Blank-holder inspection

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5. Deep Drawing

• First draw controls DR
• Anneal before second draw
• Fine-tune blank-holder force

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6. ปั่น

• Multi-stage forming
• Smooth roller surface
• Auxiliary heating when needed

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7. การตรวจสอบขั้นสุดท้าย

• Visual inspection
• Thickness mapping
• Forming height
• Expansion test

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ส่วนหนึ่ง 5 — Engineering Case Studies

Case 1 — 3003 Aluminum Circles Cracking in Deep-Drawn Cookware

ปัญหา:

• Edge hardness high by 10–15HB
• Under-annealed

สารละลาย:

• Increase annealing soak time
• Add intermediate annealing before second draw
• Reduce blank-holder force by 15%

Result:

• Crack rate reduced from 22% → 1.5%

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Case 2 — 1060 Circles Cracking in Spun Pressure Cooker Lid

ปัญหา:

• Uneven roller pressure at R-zone
• Starting thickness too thin

สารละลาย:

• Correct roller pressure curve
• Increase thickness 1.3 → 1.4 มม

Result:

• Crack rate reduced from 18% → 0.8%

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บทสรุป: A System-Level Strategy Is Required to Eliminate Cracking

Cracking during deep drawing or spinning is not caused by a single factor. It is the combined effect of:

• Material structure
• Annealing precision
• Die design
• การหล่อลื่น
• Process parameters
• Equipment accuracy

Only when these factors are optimized together can manufacturers fundamentally solve วงกลมอลูมิเนียม cracking in deep drawing and significantly increase yield rates.