Die casting flow marks are common surface defects in die casting production—characterized by linear grooves, color difference bands, или неровная текстура along the metal flow direction. They typically appear in deep cavities, thin-walled areas, or near gating systems, reducing product aesthetics and even weakening structural strength. Для производителей, flow marks lead to rework rates of 3–5% (Среднее значение в отрасли) and extended production time. But what causes these marks? How to diagnose their root causes accurately? And what systematic solutions work for long-term prevention? This article answers these critical questions with data-driven insights.
1. Core Causes of Die Casting Flow Marks: A 5-Dimension Analysis
Flow marks arise from imbalances in the die casting process, охват мужчина, машина, материал, метод, и окружающая среда (the 5M framework). Below is a detailed breakdown of key triggers and their quantitative thresholds:
А. Filling Dynamics Imbalance (Машина & Метод)
The most common cause—when molten metal flows unevenly and cools prematurely.
- High Gate Speed: When inner gate speed exceeds 40РС (critical value for aluminum alloys), the metal front splits into turbulent streams. These streams cool quickly, forming oxide film fragments that deposit as flow marks.
- Short Filling Time: Для тонкостенных деталей (толщина <2мм), filling time < 0.03s/mm² leads to incomplete fusion of metal streams.
- Poor Gate Angle: An inlet angle > 15° relative to the cavity axis creates eddy currents. These currents trap air and cold metal, leaving linear marks on the final part.
Беременный. Mold Thermal Balance Failure (Машина & Среда)
Uneven mold temperatures disrupt metal flow and curing. The table below maps abnormal temperature effects to specific locations:
| Mold Location | Abnormal Temperature Phenomenon | Data Threshold | Impact on Flow Marks |
| Gating System | Insufficient preheating | <150° C. (aluminum alloy starting value) | Accelerates cold barrier formation—metal cools before filling the cavity |
| Core/Insert | Local overheating | >Mold average temperature +30°C | Causes metal backflow stagnation—warm and cold metal mix, creating color bands |
| Exhaust Slot | Temperature gradient mutation | Temperature difference >50° C. | Sudden flow direction changes—metal piles up unevenly, forming groove-like marks |
В. Material Abnormalities (Материал)
Impure or unstable molten metal increases flow mark risk:
- Excess Iron Content: Fe > 1.2% (в алюминиевых сплавах) causes precipitation of the β-Al5FeSi phase. This hard phase disrupts metal flow, leaving scratch-like marks.
- Magnesium Fluctuation: Mg content deviation of ±0.1% changes metal viscosity by 15–20%. Uneven viscosity leads to inconsistent flow rates and surface unevenness.
- High Gas Content: Hydrogen content > 0.3мл/100г Ал exacerbates turbulence. Trapped gas bubbles burst during cooling, creating small pits that appear as flow marks.
Дюймовый. Process Parameter Mismatch (Метод & Man)
Incorrect parameter settings amplify flow mark issues:
- Uncontrolled Low-Speed Stage: Not using a J-shaped speed curve (acceleration >5m/s²) in the initial filling stage causes sudden metal surges.
- Boost Trigger Delay: Failing to build up pressure when reaching 85% of the set threshold leads to incomplete cavity filling and cold flow lines.
- Insufficient Holding Time: Время выдержки < 0.7× set time (adjusted for shrinkage) results in uneven metal solidification and surface defects.
2. Step-by-Step Solution Framework: From Diagnosis to Prevention
Solving flow marks requires a systematic approach—starting with root cause diagnosis, followed by targeted improvements and long-term monitoring.
А. Defect Diagnosis: Compare Flow Marks to Similar Defects
Первый, distinguish flow marks from cold isolation and vortex spots (common misdiagnoses). The table below helps identify the correct defect type:
| Тип дефекта | Morphological Characteristics | Main Root Cause | Key Diagnosis Tool |
| Потоки | Линейный, continuous grooves/color bands along metal flow | High gate speed; uneven mold temperature | High-speed camera (tracks metal flow during filling) |
| Cold Isolation | Intermittent, disconnected traces (looks like “трещины”) | Low metal temperature; slow filling speed | Thermocouple (measures molten metal temperature) |
| Vortex Spots | Swirling moire patterns; often near gates | Poor gate design (угол >15°); eddy currents | CFD fluid simulation (visualizes flow turbulence) |
Беременный. Targeted Improvement Plans (3 Key Areas)
Once flow marks are confirmed, implement these data-backed fixes:
1. Mold Optimization
| Improvement Direction | Implementation Key Points | Effectiveness Verification Method |
| Gate System Reconstruction | – Replace open sprue with closed sprue (reduces turbulence).- Add diversion ribs with angle ≤7° (guides uniform flow). | High-speed camera: Check if metal flows smoothly without splitting |
| Temperature Control Upgrade | – Install conformal cooling water pipes (spacing ≤D/3, where D=pipe diameter).- Use gradient preheating (5–8°C temperature drop from inlet to outlet). | Infrared thermal imager: Ensure mold temperature variation <±5°C |
| Exhaust System Strengthening | – Add vacuum exhaust ducts (Φ8–12mm) to remove trapped air.- Install dynamic backpressure valves (response time <0.1с) to stabilize flow. | Barometric pressure sensor: Monitor cavity negative pressure (цель: -0.08MPA к -0.1МПА) |
2. Оптимизация параметров процесса
Adjust injection and holding parameters using the table below—tailored for aluminum alloys (the most common die casting material):
| Стадия процесса | Key Parameter Settings | Monitoring Indicators |
| Start-Up Stage | Initial speed (V_start) = 0.3m/s; duration (t1) = 0.2s | Acceleration ≤8m/s² (avoids sudden surges) |
| Acceleration Stage | Jerk (Дж) = 15m/s³; maximum speed (V_max) = 35m/s (≤40m/s critical value) | Peak pressure fluctuation <±5bar (ensures stable flow) |
| Filling Stage | Удерживание давления (P_hold) = 85% of set pressure; duration (t2) = 0.05s/mm (часть толщины) | Real-time pressure curve: Ensure smooth, no sudden drops |
| Boost Stage | Давление наддува (P_boost) = Set pressure +50bar; duration (t3) = 3–5s | Рентгеновская дефектоскопия: Shrinkage porosity grade ≤2 (ASTM standard) |
| Holding Stage | Время выдержки (T_hold) = 0.8× solidification time (τ) | Thermocouple: Monitor core temperature (no sudden drops) |
3. Material Quality Control
- Composition Precision: Enforce aerospace-grade standards: Fe ≤0.9%, Mn ≤0.3%, Ti ≤0.15% (reduces β-Al5FeSi precipitation).
- Grain Refinement: Add Al-5Ti-1B master alloy (0.2–0.3% of total material) to improve metal flowability.
- Degassing Process: Combine rotary blowing + graphite rotor (400об/мин) + online degassing unit to reduce hydrogen content to <0.2мл/100г Ал.
В. Intelligent Prevention & Long-Term Monitoring
To avoid recurrence, implement these smart systems and protocols:
1. Digital Twin Rehearsal
Use software like MAGMA or Flow-3D to simulate filling processes. Focus on:
- Reynolds number (Re): Ensure Re <4000 (avoids severe turbulence).
- Weber number (Мы): Maintain We <5 (prevents jet fracture).
- Coanda effect: Adjust gate design to avoid boundary layer separation.
2. Real-Time Monitoring System
Install sensors to track critical parameters 24/7:
- Ultrasonic thickness monitor (accuracy ±1μm): Detects uneven filling early.
- Fiber Bragg grating strain sensor (resolution 0.1με): Monitors mold deformation (causes flow marks).
- Spectrometer: Measures online gas escape rate (prevents gas-induced marks).
3. Standardized Maintenance & Операция
- Mold Health Management:
- Mandatory maintenance after 80,000 injections.
- Plasma cleaning every 500 цикл (removes oxide buildup).
- Laser interferometer calibration (accuracy ±1μm) for key dimensions monthly.
- SOP Compliance:
- 17 mandatory inspection points (НАПРИМЕР., release agent spray amount = 0.8g/m²).
- First-article triple inspection: Внешний вид → размер → внутреннее качество.
- Калибровка температуры пресс-формы (отклонение <±3°С) до/после смены.
3. Yigu Technology’s Perspective on Die Casting Flow Marks
В Yigu Technology, мы рассматриваем следы текучести не только как поверхностные дефекты, но как индикаторы неэффективности процесса. Для автомобильных клиентов, наше комплексное решение — объединение конформных охлаждающих форм, Управление параметрами на основе искусственного интеллекта, и мониторинг газа в реальном времени — снижение скорости потока с 4.2% к <0.8% (1/5 среднего показателя по отрасли). Для аэрокосмических частей, наша генная инженерия материалов (Фе ≤0,8%, точная дегазация) устранены следы, вызванные β-Al5FeSi, соответствие стандартам AS9100.
Мы продвигаем две инновации: 1) Self-adaptive PID regulators (response time <10ms) that adjust gate speed dynamically; 2) Cloud-based defect databases (labeling flow mark characteristics with >0.5% incidence) for predictive maintenance. Our goal is to help manufacturers turn flow mark prevention into a competitive advantage—cutting rework time to <15 minutes per defect and boosting production efficiency by 20%.
Часто задаваемые вопросы
- Can flow marks be repaired after production, or must defective parts be scrapped?
Minor flow marks (shallow grooves <0.1мм) can be repaired via mechanical polishing (with 800-grit sandpaper) или химическое травление (для алюминиевых сплавов). Тяжелые следы (глубина >0.2мм) требуют сноса — ремонт ослабит прочность конструкции.. Рекомендуем устранить причину (НАПРИМЕР., регулировка скорости ворот) вместо того, чтобы полагаться на постпроизводственный ремонт.
- Сколько времени занимает внедрение решения по полной маркировке потока?, и какова рентабельность инвестиций?
Поэтапное внедрение (1первый этап: контроль температуры пресс-формы + оптимизация параметров; 2й этап: интеллектуальный мониторинг) занимает 8–12 недель. Для литейной машины среднего размера (10,000 частей/день), окупаемость инвестиций составляет ~6 месяцев — экономия за счет сокращения переделок (3–5% деталей) and faster production outweighs investment in molds/sensors.
- Do flow marks affect the mechanical properties of die cast parts, or are they only cosmetic?
While shallow flow marks (≤0.1mm) are mostly cosmetic, deeper marks (>0.1мм) or those caused by oxide films/ gas traps reduce tensile strength by 5–10% (tested on aluminum alloys). For safety-critical parts (НАПРИМЕР., Компоненты автомобильного шасси), even minor flow marks can be a failure risk—thus, prevention is critical.