Die casting defects—from surface blemishes to internal cracks—cost manufacturers an average of 5–12% of annual production value (industry data). These flaws not only force rework or scrapping but also compromise part performance, especially for safety-critical components like automotive sensors or aerospace brackets. While processes like hot chamber die casting (for low-melting alloys) or cold chamber die casting (for high-melting metals) have unique defect risks, most issues stem from shared pain points: mold design flaws, parameter mismatches, or material inconsistencies. But what do these common defects look like? O que os causa? And how can you fix or prevent them? This article answers these questions with detailed classifications, Exemplos do mundo real, and actionable solutions.
1. Classification of Common Die Casting Defects: 5 Core Categories
Die casting defects are grouped by their location (surface vs. interno) and root cause. The table below breaks down 5 key categories, with defect characteristics, high-incidence areas, and visual cues:
| Categoria de defeito | Specific Defect | Principais características | High-Incidence Areas | Detection Method |
| Filling Defects | Undercasting | Metal liquid fails to fill the cavity; incomplete part shape or cavities. | End of castings, narrow deep cavities (Por exemplo, USB connector slots). | Inspeção visual; medição dimensional (part shorter than design). |
| Cold Separation | Low-temperature metal flows dock but don’t fuse; irregular linear gaps (may penetrate); often with flow marks or surface bubbles. | Thick-thin wall transitions (Por exemplo, Altas do sensor automotivo). | Inspeção visual; Teste ultrassônico (Ut) for hidden gaps. | |
| Marcas de fluxo | First-entering metal forms a thin layer; covered by subsequent metal, leaving flow-direction traces; partial sunken feel. | Grandes superfícies planas (Por exemplo, laptop hinge bases); near gates. | Inspeção visual; touch test (detects slight depressions). | |
| Surface Damage Defects | Abrasion (Strain) | Surface scars from metal adhesion or insufficient mold draft; severe cases have cracks. | Mold release direction (Por exemplo, cylindrical part edges). | Inspeção visual; magnifying glass (10×) for fine scars. |
| Pockmarks | Small pockmark-like areas; rough surface texture. | Caused by low mold/alloy temperature during filling. | Inspeção visual; testador de rugosidade da superfície (Rá >6.3μm indicates defects). | |
| Mesh Burrs | Mesh-shaped bulges and metal burrs; caused by mold thermal fatigue. | Mold parting surfaces (Por exemplo, zinc alloy faucet handles). | Inspeção visual; edge feel (detects sharp burrs). | |
| Abnormal Shape Defects | Depression (Encolhimento) | Concave areas on smooth surfaces; often with dimples. | Thick-walled areas or wall thickness transitions (Por exemplo, battery terminal bases). | Inspeção visual; Digitalização a laser (measures surface flatness). |
| Deformação (Deformação) | Overall/partial geometry mismatch with design; Por exemplo, bent brackets. | Peças de paredes finas (Por exemplo, Afotos de calor de LED); large flat components. | Teste dimensional (Por exemplo, calipers for bending angle); Cmm (Máquina de medição de coordenadas). | |
| Wrong Edge (Mismatch) | Relative displacement on both sides of the parting surface; step-like gaps. | Mold split lines (Por exemplo, toy car bodies). | Inspeção visual; feel test (detects step differences). | |
| Internal Quality Defects | Encolhimento & Loosening | Holes or loose tissue from solidification contraction; baixa densidade. | Thick-walled cores (Por exemplo, engine block ribs); wall thickness changes. | Detecção de falhas de raios X; Teste de densidade (lower than material standard). |
| Bolhas | Gas accumulation under the epidermis; bulging bubbles (may penetrate or be closed); easy to crack when stressed. | Near mold vents (Por exemplo, 3C part inner cavities). | X-ray testing; tratamento térmico (bubbles expand and become visible). | |
| Rachaduras | Filamentous gaps; cold cracks (no oxidation, frágil) or hot cracks (oxidized edges, Dukes). | High-stress areas (Por exemplo, part corners); Após o tratamento térmico. | UT testing; dye penetrant inspection (DPI) para rachaduras na superfície. | |
| Outros defeitos | Clarão (Fofo) | Excesso de flocos de metal nas bordas ou emendas; fino e quebradiço. | Mold parting surfaces, inserir lacunas (Por exemplo, juntas de ferragens para banheiro). | Inspeção visual; corte de borda (remove o excesso de material). |
| Impressão | Marcas irregulares de emenda do empurrador/inserto; Por exemplo, amolgadelas circulares de pinos ejetores. | Áreas de contato do empurrador (Por exemplo, parte inferior). | Inspeção visual; touch test (detecta irregularidades). | |
| Manchas coloridas | Manchas heterocromáticas (Por exemplo, preto, marrom); causado por carbonetos de tinta ou óleo de punção. | Superfície de peças decorativas (Por exemplo, invólucros de brinquedos de liga de zinco). | Inspeção visual; limpeza com solvente (testa se as manchas são removíveis). | |
| Camadas (Aperto) | Camadas de metal óbvias dentro da peça; rebarbas espessas em superfícies de partição. | Caused by multiple metal flow layers not fusing. | Sectioning inspection; X-ray testing (shows layer boundaries). |
2. Causas de raiz: Why Defects Happen (3 Key Links)
Most die casting defects trace back to failures in Design de molde, parâmetros de processo, or material quality. Below is a detailed breakdown of causes for high-frequency defects:
UM. Mold Design Flaws (30–40% of Defects)
Mold issues create inherent risks for filling, superfície, and shape defects:
- Insufficient Draft Angle: Draft <1° (for zinc alloys) causes metal adhesion, leading to abrasion (strain) and deformation.
- Poor Gate/Exhaust Design: Small gate size (Por exemplo, <1mm for thin parts) slows filling, causing undercasting; blocked exhaust grooves (profundidade <0.2milímetros) trap gas, leading to bubbles.
- Uneven Cooling Channels: Cooling channel spacing >20mm creates temperature gradients (>30°C), causing cold separation and shrinkage depressions.
- Fadiga térmica: Mold used >100,000 shots without maintenance develops cracks, leading to mesh burrs and layering.
B. Process Parameter Mismatches (40–50% of Defects)
Incorrect settings during casting amplify defect risks—especially for filling and internal defects:
| Defeito | Key Parameter Cause | Quantitative Thresholds (Ligas de zinco) |
| Undercasting | Low injection pressure/speed; low alloy temperature. | Pressão <5MPA; velocidade <0.5EM; temperatura <380° c. |
| Cold Separation | Velocidade de enchimento lenta; large temperature drop between metal and mold. | Velocidade <0.8EM; temperatura do molde <150° c (alloy temp 400°C). |
| Bolhas | High injection speed (turbulência); insufficient holding pressure. | Velocidade >2EM; holding pressure <8MPA. |
| Shrinkage Depression | Short holding time; low holding pressure. | Tempo de espera <5é; pressão <10MPA. |
| Deformação | Uneven cooling time; mold opening too early. | Tempo de resfriamento <3é (partes finas); abertura do molde <2s after solidification. |
C. Material Quality Issues (10–20% of Defects)
Impure or unstable materials introduce internal and surface defects:
- Alloy Impurities: Iron content >1.2% (ligas de zinco) causes hard particles, leading to pockmarks and cracks.
- Moisture/Gas Content: Hydrogen content >0.3cc/100g (ligas de alumínio) creates bubbles during solidification.
- Oxide Slag: Unfiltered molten metal (slag content >0.5%) causes layering and shrinkage loosening.
3. Solution Framework: Consertar & Prevent Defects
Resolving die casting defects requires targeted fixes for root causes—follow this 3-step approach for long-term results:
UM. Targeted Fixes for High-Frequency Defects
For common defects, use these proven solutions tailored to cause and defect type:
| Defeito | Immediate Fix | Prevenção de longo prazo |
| Undercasting | Aumentar a pressão da injeção (by 2–5MPa) ou velocidade (by 0.2–0.5m/s); raise alloy temperature (by 10–15°C). | Optimize gate size (match to part thickness: gate width = 2× part thickness); clean exhaust grooves weekly. |
| Cold Separation | Preheat mold to 180–200°C (ligas de zinco); increase alloy temperature (by 15–20°C); use a larger gate. | Add diversion ribs (angle ≤10°) to guide uniform flow; install mold temperature controllers (±5°C tolerance). |
| Bolhas | Reduzir a velocidade de injeção (by 0.3–0.5m/s); estender o tempo de retenção (by 2–3s); add vacuum exhaust (vacuum degree ≥90kPa). | Use inert gas protection (argon/nitrogen) durante o derretimento; filter molten metal with 20-ppi ceramic foam filters. |
| Shrinkage Depression | Increase holding pressure (by 3–5MPa); estender o tempo de retenção (by 3–5s); add local cooling channels (near thick walls). | Otimize o design da peça (reduce wall thickness difference to ≤2:1); use risers for thick-walled areas. |
| Abrasion (Strain) | Cavidade de molde polonês (RA ≤1,6μm); increase draft angle to 1.5–2°; apply mold release agent (afinar, uniform layer). | Use wear-resistant mold materials (Por exemplo, H13 steel for hot chamber dies); coat cavity with TiN (nitreto de titânio) for zinc alloys. |
B. Mold Optimization: Build Defect-Resistant Designs
- Ângulo de rascunho: Ensure minimum draft of 1° for zinc alloys, 2° for aluminum alloys (prevents abrasion).
- Exhaust System: Add exhaust grooves (depth 0.1–0.2mm, width 5–10mm) at final filling zones; para peças complexas, use vent pins (diameter 0.5–1mm).
- Canais de resfriamento: Space channels 15–20mm apart; align with thick-walled areas (Por exemplo, 5mm from 10mm-thick walls) to reduce temperature gradients.
- Gate Design: Use fan gates for large flat parts (ensures uniform filling); use pinpoint gates (diameter 0.8–1.2mm) for small 3C components.
C. Controle de processo: Stabilize Parameters
- Controle de temperatura:
- Alloy temperature: 380–420 ° C. (ligas de zinco), 680–720°C (ligas de alumínio); use a digital thermostat (±5°C tolerance).
- Temperatura do molde: 150–200 ° C. (ligas de zinco), 200–250 ° C. (ligas de alumínio); monitor with infrared thermal imagers.
- Injection Parameters:
- Elenco de morrer de câmara quente (zinco): Pressure 10–20MPa, speed 0.5–1.5m/s.
- Cold chamber die casting (alumínio): Pressure 30–80MPa, speed 2–5m/s.
- Verificações de qualidade:
- First-part inspection: Verifique as dimensões, superfície, and internal quality (X-ray for critical parts) at the start of each shift.
- Controle de processo estatístico (Spc): Track parameters (temperatura, pressão) and defect rates; set control limits (Por exemplo, ±10% for pressure).
4. Yigu Technology’s Perspective on Common Die Casting Defects
Na tecnologia Yigu, we view defects not as failures, but as opportunities to optimize processes. For hot chamber die casting clients (zinc alloy 3C parts), our AI-driven parameter control system—combining real-time temperature monitoring and adaptive pressure adjustment—reduced filling defects (undercasting, cold separation) de 8% para <1.5%. For cold chamber clients (aluminum automotive parts), our vacuum-assisted exhaust and ceramic foam filtration cut bubble and shrinkage rates by 60%.
We’re advancing two key solutions: 1) Digital twin simulation (MAGMA software) to predict filling defects before mold production; 2) Wear-resistant mold coatings (Tialn) that extend mold life by 50%, reducing mesh burrs. Our goal is to help manufacturers shift from “defect repair” to “defect prevention”—cutting scrap rates to <2% and boosting production efficiency by 15%.
Perguntas frequentes
- Can surface defects like flow marks or pockmarks be repaired after casting?
Yes—minor flow marks can be removed by mechanical polishing (800–1200-grit sandpaper) or chemical etching (para ligas de alumínio). Pockmarks may require putty filling (para peças não críticas), but severe cases need scrapping. We recommend fixing root causes (Por exemplo, adjusting injection speed) instead of relying on post-repair.
- Why do internal defects like bubbles or shrinkage often go undetected until later?
Internal defects are hidden under the surface—they may only appear after heat treatment (bubbles expand) or stress testing (cracks form). To detect them early, use X-ray flaw detection for critical parts (Por exemplo, Sensores automotivos) and density testing (ensure ≥99.5% density for aluminum alloys).
- Do common defects differ between hot chamber and cold chamber die casting?
Yes—hot chamber (zinco) is prone to surface defects (abrasion, pockmarks) due to mold adhesion and low pressure; cold chamber (alumínio) faces more internal defects (bolhas, encolhimento) due to high-temperature metal and turbulent filling. Our solutions are tailored: for hot chamber, we optimize draft and mold release; for cold chamber, we focus on vacuum and filtration.