Die casting product sink—also called dent или shrinkage depression—is a prevalent surface defect characterized by smooth, sunken areas (0.1–2mm deep) that form in thick-walled sections of cast parts. It not only ruins product aesthetics (rejecting 5–8% of parts in mass production) but also weakens structural integrity: sinks in pressure-bearing components (НАПРИМЕР., Гидравлические клапаны) can cause leaks or even catastrophic failure. Unlike other defects (НАПРИМЕР., flow marks), sinks stem from systemic issues in design, процесс, or equipment—requiring targeted fixes rather than quick fixes. But what exactly triggers these sunken areas? How to diagnose their root causes accurately? And what long-term solutions prevent recurrence? This article answers these questions with data-driven insights and actionable strategies.
1. Types of Die Casting Product Sink: Identify Before Fixing
Not all sinks are the same—their location and severity reveal clues about their root cause. The table below classifies common sink types and their key traits:
| Sink Type | Morphological Features | Typical Occurrence Areas | Severity (1–5, 5=Critical) |
| Localized Thick-Wall Sink | Маленький, circular depressions (diameter 2–10mm); гладкие края | Thick-walled cores (НАПРИМЕР., engine block ribs), wall thickness transitions (10mm → 3mm) | 4 (weakens local strength; visible on functional surfaces) |
| Hot-Joint Sink | Irregular, elongated sunken areas; often connected to internal shrinkage | Intersections of multiple ribs (НАПРИМЕР., EV battery frame junctions) | 5 (indicates internal voids; unsafe for load-bearing parts) |
| Surface Layer Sink | Мелкий, widespread depressions (глубина <0.5мм); no internal defects | Большие плоские поверхности (НАПРИМЕР., automotive cover panels) | 2 (only affects aesthetics; no structural risk) |
| Post-Cooling Sink | Appears hours/days after demolding; caused by delayed solidification | Thick-walled parts (НАПРИМЕР., heavy-duty equipment brackets) | 3 (unpredictable; requires rework) |
2. Core Causes of Die Casting Product Sink: A 4-Dimension Analysis
Sink formation follows a clear causal chain: uneven solidification → volume shrinkage → lack of metal replenishment → surface depression. Below is a breakdown of the four key triggers, with quantitative thresholds:
А. Design Deficiencies (30–40% of Sinks)
Poor casting or mold design creates conditions for uneven cooling and shrinkage.
| Design Issue | Технические детали | Quantitative Impact |
| Severe Wall Thickness Difference | Thickness ratio >3:1 (НАПРИМЕР., 9мм против. 3мм) creates “hot spots”—thick areas solidify 2–3× slower than thin areas. | Shrinkage volume increases by 15–20% in thick sections; 80% of these cases develop sinks. |
| Unoptimized Hot Joints | Rib intersections without heat-dissipating structures (НАПРИМЕР., 3 ribs crossing at 90°) ловушка тепла. | Local temperature remains 50–80°C higher than surrounding areas; solidification delayed by 10–15 seconds. |
| Ineffective Sprue Systems | Inner gate located >50mm from hot joints; cross-sectional area <2× the part’s wall thickness. | Metal can’t reach shrinking areas in time—replenishment rate drops by 40–60%. |
Беременный. Process Parameter Mismatches (25–35% of Sinks)
Incorrect injection, температура, or timing settings fail to compensate for shrinkage.
| Parameter Issue | Key Problem | Data Threshold |
| Low Injection Specific Pressure | Pressure too low to push molten metal into shrinking gaps. | <50МПА (алюминиевые сплавы); <30МПА (цинковые сплавы) → 70% sink rate in thick parts. |
| Insufficient Holding Time | Mold opens before thick sections fully solidify; no time for metal replenishment. | Время выдержки <0.8× время затвердевания (НАПРИМЕР., 5s for a 10mm-thick part) → 60% post-demolding sinks. |
| Excessive Pouring Temperature | High temperature increases total shrinkage volume; gas content rises, exacerbating voids. | >720° C. (алюминиевые сплавы); >430° C. (цинковые сплавы) → shrinkage volume increases by 12–18%. |
В. Cooling System Failures (20–25% of Sinks)
Uneven mold cooling amplifies solidification differences.
| Cooling Issue | Технические детали | Impact on Sinks |
| Unreasonable Channel Layout | Cooling channels >20mm from thick sections; no targeted cooling for hot joints. | Temperature difference between thick/thin areas >40° C.; solidification asynchronized. |
| Blocked Cooling Channels | Scale/rust buildup (толщина >1мм) reduces heat transfer efficiency by 30–40%. | Local cooling rate drops from 15°C/s to <8° C/с; thick sections develop sinks. |
| Inconsistent Cooling Water Flow | Flow rate <2L/min for critical channels; pressure fluctuations >±0.2MPa. | Cooling unevenness increases by 25%; sinks appear in low-flow areas. |
Дюймовый. Operational Errors (5–10% of Sinks)
Human factors disrupt process stability.
- Premature Mold Opening: Mold opened 2–3 seconds before solidification completion (detected via thermocouples). Surface layers soften and collapse under internal shrinkage.
- Over-Spraying Release Agent: Thick agent layers (>10μm) insulate the mold surface, slowing heat dissipation in local areas.
- Incorrect Alloy Composition: High copper content (>4% in aluminum alloys) increases shrinkage rate by 10–15%; magnesium deficiency (<0.3%) reduces fluidity, hindering metal replenishment.
3. Systematic Solutions: From Design to Maintenance
Resolving sinks requires a holistic approach—fixing one link alone is ineffective. Ниже представлена пошаговая схема решения.:
А. Оптимизация дизайна: Eliminate Sink Risks Upfront
| Мера оптимизации | Детали реализации | Ожидаемый результат |
| Баланс толщины стенки | Ограничить соотношение толщины до ≤2:1; используйте постепенные переходы (склон 1:5) между толстыми/тонкими областями. | Образование горячих точек уменьшено на 70%; стабилизированный объем усадки. |
| Улучшение горячих соединений | – Добавьте «теплорассеивающие отверстия» (диаметр 3–5 мм) в местах пересечения ребер.- Используйте полые ребра (толщина стенки 2–3 мм) вместо цельных ребер. | Скорость локального охлаждения увеличилась на 40%; раковины с горячими соединениями, вырезанные 80%. |
| Модернизация литниковых систем | – Расположите внутренние ворота в пределах 30 мм от горячих швов.- Increase gate cross-sectional area to 2.5× the part’s wall thickness.- Add auxiliary feeders (volume 5–10% of the hot joint) для больших частей. | Metal replenishment rate improved by 50%; sink rate drops to <5%. |
Беременный. Process Parameter Fine-Tuning
The table below lists optimized parameters for common alloys, tailored to prevent sinks:
| Параметр | Алюминиевые сплавы (Холодная камера) | Цинковые сплавы (Горячая камера) | Monitoring Method |
| Injection Specific Pressure | 60–80MPa | 30–50MPa | Real-time pressure curve (deviation ≤±5MPa) |
| Время выдержки | 1.2× время затвердевания (НАПРИМЕР., 12s for 10mm-thick parts) | 1.0× время затвердевания (НАПРИМЕР., 8s for 8mm-thick parts) | Timer linked to mold temperature sensor |
| Pouring Temperature | 680–700 ° C. | 380–400 ° C. | Digital thermocouple (±2°C accuracy) |
| Температура формы | 200–220 ° C. (толстые секции); 180–200 ° C. (тонкие секции) | 150–170 ° C. (uniform across mold) | Infrared thermal imager (temperature difference ≤±5°C) |
В. Cooling System Upgrade
- Targeted Cooling: Install profiled cooling channels (shape matches part geometry) для толстых секций. Например, use spiral channels around 10mm-thick ribs to boost heat transfer by 35%.
- High-Pressure Cooling: Apply 0.8–1.2MPa high-pressure water to hot joints; this thickens the quench layer by 0.5–1mm, accelerating solidification.
- Regular Maintenance: Clean cooling channels every 500 cycles with descaling agents; replace corroded pipes (flow rate restored to ≥2L/min).
Дюймовый. Advanced Technologies for High-Risk Parts
For critical components (НАПРИМЕР., аэрокосмические скобки), use these cutting-edge solutions:
- Local Extrusion Technology: Integrate hydraulic extrusion pins (diameter 5–10mm) в форме. Apply 80–120MPa pressure during the semi-solid stage (solid fraction 60–70%) to push metal into shrinkage gaps—eliminates hot-joint sinks by 95%.
- Solidification Simulation: Use MAGMA or Flow-3D software to predict shrinkage areas. Например, a simulation of an EV battery frame identified a hot joint sink risk, prompting a design tweak that cut defects by 70%.
- Profiling Weight Reduction: Hollow out thick sections (НАПРИМЕР., 10mm → 5mm with internal ribs) to reduce heat accumulation. This lowers shrinkage volume by 25% сохраняя силу.
4. Defect Remediation: Fix Existing Sinks
For parts with minor sinks (not critical for safety), use these repair methods:
| Sink Severity | Repair Method | Детали реализации |
| Minor (глубина <0.5мм) | Механическая полировка | Use 800–1200-grit sandpaper to smooth the surface; follow with buffing (Раствор <1.6мкм). |
| Умеренный (depth 0.5–1mm) | Filler Repair | Apply aluminum/zinc alloy putty (matching the part’s composition); cure at 80–100°C for 30 минуты. |
| Severe (глубина >1мм) | Сварка + Обработка | Use TIG welding to fill the sink; machine to restore dimensions (Допуск ± 0,1 мм). Only for non-load-bearing parts. |
5. Yigu Technology’s Perspective on Die Casting Product Sink
В Yigu Technology, we see sinks as a “design-process mismatch”—not just a surface defect. For automotive clients producing engine blocks, our integrated solution (profiled cooling channels + local extrusion) reduced hot-joint sinks from 12% к <1.2%. For EV battery frame manufacturers, our solidification simulation tool identified sink risks upfront, cutting mold rework costs by 40%.
We’re advancing two key innovations: 1) AI-driven cooling control (adjusts water flow in real time based on mold temperature data); 2) Self-heating auxiliary feeders (maintain molten metal temperature to replenish shrinkage). Our goal is to help manufacturers shift from “defect repair” to “defect prevention”—turning sink elimination into a cost-saving advantage that boosts yield rates by 15%.
Часто задаваемые вопросы
- Can sinks be detected before demolding to avoid wasting materials?
Yes—use real-time monitoring tools: 1) Mold temperature sensors (alert if thick sections stay >300°C after set holding time); 2) Датчики давления (detect pressure drops in hot joints, indicating insufficient replenishment); 3) Ultrasonic testing during solidification (identifies internal shrinkage that will become surface sinks). These tools reduce wasted parts by 60%.
- Do sinks only affect aluminum/zinc alloys, or other die casting materials too?
All die casting materials are at risk, but severity varies: Magnesium alloys (скорость усадки 4.5%) are more prone to sinks than zinc alloys (скорость усадки 2.5%). Медные сплавы (высокая точка плавления) require stricter cooling control—sinks often form in thick sections if mold temperature exceeds 250°C. The solutions (design balance, pressure control) apply universally, but parameters must be tailored to each alloy.
- Is it cheaper to fix sinks during design or after production?
Fixing during design is 5–10× cheaper. A design tweak (НАПРИМЕР., adjusting rib thickness) расходы \(500- )1,000 but prevents \(5,000- )10,000 in post-production rework/scrap for a 10,000-part batch. We recommend investing in solidification simulation upfront—this identifies 90% of sink risks before mold manufacturing.