Die casting flow marks are common surface defects in die casting production—characterized by linear grooves, color difference bands, ou une texture inégale 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. Pour les fabricants, flow marks lead to rework rates of 3–5% (moyenne de l'industrie) and extended production time. But what causes these marks? Comment diagnostiquer avec précision leurs causes profondes? 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, étendue homme, machine, matériel, méthode, et environnement (the 5M framework). Below is a detailed breakdown of key triggers and their quantitative thresholds:
UN. Filling Dynamics Imbalance (Machine & Méthode)
The most common cause—when molten metal flows unevenly and cools prematurely.
- High Gate Speed: When inner gate speed exceeds 40MS (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: Pour les pièces à parois minces (épaisseur <2MM), temps de remplissage < 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.
B. Mold Thermal Balance Failure (Machine & Environnement)
Uneven mold temperatures disrupt metal flow and curing. The table below maps abnormal temperature effects to specific locations:
| Mold Location | Abnormal Temperature Phenomenon | Seuil de données | Impact on Flow Marks |
| Système de portail | 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 |
C. Material Abnormalities (Matériel)
Impure or unstable molten metal increases flow mark risk:
- Excess Iron Content: Fe > 1.2% (in aluminum alloys) 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 > 0.3ml/100g Al exacerbates turbulence. Trapped gas bubbles burst during cooling, creating small pits that appear as flow marks.
D. Inadéquation des paramètres de processus (Méthode & 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.
- Temps de maintien insuffisant: Temps de maintien < 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.
UN. Diagnostic des défauts: Compare Flow Marks to Similar Defects
D'abord, distinguish flow marks from cold isolation and vortex spots (common misdiagnoses). The table below helps identify the correct defect type:
| Type de défaut | Morphological Characteristics | Main Root Cause | Key Diagnosis Tool |
| Marques de flux | Linéaire, 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 “fissure”) | Low metal temperature; slow filling speed | Thermocouple (measures molten metal temperature) |
| Vortex Spots | Swirling moire patterns; often near gates | Poor gate design (angle >15°); eddy currents | CFD fluid simulation (visualizes flow turbulence) |
B. Targeted Improvement Plans (3 Domaines clés)
Once flow marks are confirmed, implement these data-backed fixes:
1. Optimisation des moules
| 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). | Imageur thermique infrarouge: 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 <0.1s) to stabilize flow. | Barometric pressure sensor: Monitor cavity negative pressure (cible: -0.08MPA à -0.1MPA) |
2. Optimisation des paramètres de processus
Adjust injection and holding parameters using the table below—tailored for aluminum alloys (the most common die casting material):
| Étape du processus | Paramètres des paramètres clés | 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 (J.) = 15m/s³; maximum speed (V_max) = 35m/s (≤40m/s critical value) | Peak pressure fluctuation <±5bar (ensures stable flow) |
| Filling Stage | Pression de maintien (P_hold) = 85% of set pressure; duration (t2) = 0.05s/mm (épaisseur) | Real-time pressure curve: Ensure smooth, no sudden drops |
| Boost Stage | Pression de suralimentation (P_boost) = Set pressure +50bar; duration (t3) = 3–5s | Détection des défauts aux rayons X: Shrinkage porosity grade ≤2 (ASTM standard) |
| Holding Stage | Temps de maintien (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 (400RPM) + online degassing unit to reduce hydrogen content to <0.2ml/100g Al.
C. 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. Se concentrer sur:
- Nombre de Reynolds (Concernant): Ensure Re <4000 (avoids severe turbulence).
- Weber number (Nous): 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 & Opération
- Mold Health Management:
- Mandatory maintenance after 80,000 injections.
- Plasma cleaning every 500 cycles (removes oxide buildup).
- Laser interferometer calibration (accuracy ±1μm) for key dimensions monthly.
- SOP Compliance:
- 17 mandatory inspection points (Par exemple, release agent spray amount = 0.8g/m²).
- First-article triple inspection: Appearance → size → internal quality.
- Mold temperature calibration (deviation <±3°C) before/after shifts.
3. Yigu Technology’s Perspective on Die Casting Flow Marks
À la technologie Yigu, we view flow marks not just as surface defects, but as indicators of process inefficiencies. Pour les clients automobiles, our integrated solution—combining conformal cooling molds, AI-driven parameter control, and real-time gas monitoring—reduced flow mark rates from 4.2% à <0.8% (1/5 of the industry average). Pour les pièces aérospatiales, our material genome engineering (Fe ≤0.8%, precise degassing) eliminated β-Al5FeSi-induced marks, meeting AS9100 standards.
We’re advancing two innovations: 1) Self-adaptive PID regulators (response time <10ms) that adjust gate speed dynamically; 2) Bases de données de défauts basées sur le cloud (labeling flow mark characteristics with >0.5% incidence) pour la maintenance prédictive. 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%.
FAQ
- Can flow marks be repaired after production, or must defective parts be scrapped?
Minor flow marks (shallow grooves <0.1MM) can be repaired via mechanical polishing (with 800-grit sandpaper) ou gravure chimique (pour alliages d'aluminium). Severe marks (profondeur >0.2MM) require scrapping—repairing would weaken structural strength. We recommend fixing the root cause (Par exemple, adjusting gate speed) instead of relying on post-production repairs.
- How long does it take to implement a full flow mark solution, and what’s the ROI?
A phased implementation (1st phase: mold temperature control + optimisation des paramètres; 2nd phase: surveillance intelligente) takes 8–12 weeks. For a mid-sized die caster (10,000 parties/jour), the ROI is ~6 months—savings from reduced rework (3–5% of parts) 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 (≤0,1 mm) are mostly cosmetic, deeper marks (>0.1MM) or those caused by oxide films/ gas traps reduce tensile strength by 5–10% (tested on aluminum alloys). For safety-critical parts (Par exemple, Composants du châssis automobile), even minor flow marks can be a failure risk—thus, prevention is critical.