Die casting product sink—also called dent or 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 (e.g., hydraulic valves) can cause leaks or even catastrophic failure. Unlike other defects (e.g., flow marks), sinks stem from systemic issues in design, process, 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 | Small, circular depressions (diameter 2–10mm); smooth edges | Thick-walled cores (e.g., 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 (e.g., EV battery frame junctions) | 5 (indicates internal voids; unsafe for load-bearing parts) |
| Surface Layer Sink | Shallow, widespread depressions (depth <0.5mm); no internal defects | Large flat surfaces (e.g., 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 (e.g., 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:
A. Design Deficiencies (30–40% of Sinks)
Poor casting or mold design creates conditions for uneven cooling and shrinkage.
| Design Issue | Technical Details | Quantitative Impact |
| Severe Wall Thickness Difference | Thickness ratio >3:1 (e.g., 9mm vs. 3mm) 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 (e.g., 3 ribs crossing at 90°) trap heat. | 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%. |
B. Process Parameter Mismatches (25–35% of Sinks)
Incorrect injection, temperature, 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. | <50MPa (aluminum alloys); <30MPa (zinc alloys) → 70% sink rate in thick parts. |
| Insufficient Holding Time | Mold opens before thick sections fully solidify; no time for metal replenishment. | Holding time <0.8× solidification time (e.g., 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 (aluminum alloys); >430°C (zinc alloys) → shrinkage volume increases by 12–18%. |
No comments:
Post a Comment