Die casting cold material is a common yet destructive defect that undermines the quality, desempenho, and appearance of castings. It forms when molten metal loses too much heat during filling, leading to reduced fluidity and incomplete mold cavity filling. This defect not only causes scrap rates to spike (até 20% in severe cases) but also poses safety risks for critical components like automotive engine parts or aerospace structural elements. To help manufacturers identify, prevent, and resolve this issue, this article systematically breaks down the nature of die casting cold material, its root causes, and a step-by-step improvement framework—backed by practical data and industry best practices.
1. Understanding Die Casting Cold Material: Definição, Manifestations, e Riscos
Before solving the problem, it’s essential to clearly define what die casting cold material is and how it impacts production. Esta seção usa um 总分结构 to cover core concepts, com termos-chave destacados para maior clareza.
1.1 Definição Fundamental
Die casting cold material refers to a defect where molten metal experiences excessive cooling (either in the melting stage, transfer process, or mold filling) before fully filling the mold cavity. This cooling reduces the metal’s fluidity, causing it to solidify prematurely or form irregular structures that fail to bond with surrounding metal. Unlike surface blemishes (Por exemplo, arranhões), cold material is often a “hidden threat”—it may appear as minor surface marks but hide internal flaws like shrinkage or pore clusters.
1.2 Typical Manifestations
You can recognize cold material through four observable signs, both on the surface and inside the casting:
| Observation Dimension | Specific Traits | Detection Method |
| Surface Features | – Duro, dull patches (no metallic luster)- Obvious flow lines or layered “striations”- Localized material shortage (small unfilled gaps) | Naked eye inspection (after sandblasting) or 5x magnification lens |
| Defeitos Internos | – Concentrated shrinkage voids (0.1-0.5mm diâmetro)- Aggregated pores (often near cold material areas)- Unmelted solid particles (residues from incomplete melting) | X-ray inspection or metallographic analysis (sample etching with 5% ácido nítrico) |
1.3 Key Risk Areas
Cold material is not random—it tends to form in specific parts of the casting, where heat loss is most severe:
- Thin-walled areas far from the gate: These sections have a large surface area-to-volume ratio, accelerating heat dissipation. Por exemplo, a 1mm-thick aluminum shell 100mm from the gate is 3x more likely to develop cold material than a 5mm-thick section near the gate.
- Deep cavity bottoms: Molten metal takes longer to reach these areas, and heat is trapped against the mold wall—cooling occurs before full filling.
- Low-temperature mold zones: Areas without proper preheating (Por exemplo, mold corners, sections near cooling water channels) act as “Afotos de calor,” rapidly cooling the metal.
2. Root Causes of Die Casting Cold Material: Uma análise abrangente
Cold material forms due to a combination of failures in temperature control, Design de molde, parâmetros de processo, e gerenciamento de materiais. A tabela abaixo usa um mecanismo fator-causa estrutura para identificar a origem do problema, with specific examples for clarity.
| Categoria de causa | Falhas Específicas | Mecanismo de formação de defeitos | Exemplo do mundo real |
| Molten Metal Temperature Control | 1. Incomplete melting (alloy not heated to process temperature)2. Holding furnace power shortage (temperature drops by 20-30°C)3. Unpreheated pressure chamber (room temperature vs. required 150-200°C) | 1. Unmelted particles remain in the metal, acting as “cold cores” that reduce overall fluidity.2. Cooled metal solidifies at the front of the flow, blocking subsequent filling.3. The cold chamber absorbs heat from the molten metal, causing front-end solidification in 2-3 segundos. | An aluminum alloy ADC12 casting plant used a faulty holding furnace—metal temperature dropped from 700°C to 650°C. Cold material defects increased from 3% para 18% em 1 semana. |
| Design de molde & Condition | 1. Poor runner design (sudden cross-sectional changes, sharp bends)2. Uneven mold temperature (cooling water too close to cavity: <5milímetros)3. Agente desmoldante excessivo (filme espesso >0.1milímetros) | 1. Runner irregularities increase flow resistance, prolonging filling time and heat loss.2. Cold mold areas cool the metal to below its liquidus temperature, stopping flow.3. Um filme espesso de agente desmoldante atua como isolante, preventing heat transfer from the mold to the metal (worsening cooling). | A zinc alloy toy manufacturer used a mold with a 90° sharp bend in the runner. Cold material formed at the bend in 25% of castings—redesigning to a 15mm radius reduced defects to 2%. |
| Process Parameter Mismatch | 1. Slow injection speed (<2 m/s for aluminum)2. Incorrect pressure holding timing (too early, compressing cold metal)3. Excessive pouring volume (residual cold material accumulates in the chamber) | 1. Slow flow extends the time the metal is in contact with the cold mold, accelerating cooling.2. Early pressure compresses partially solidified metal, creating layered cold material.3. Residual cold material from previous cycles mixes with new molten metal, reducing overall temperature. | An automotive parts plant used 1.5 m/s injection speed for a 2mm-thick aluminum bracket. 30% of parts had cold material—increasing speed to 4 m/s eliminated the defect. |
| Propriedades do material & Management | 1. Alloy composition deviation (low silicon in aluminum: <9% vs.. obrigatório 11-13%)2. Unscreened return material (mixed with oxide scales, impurezas) | 1. Low silicon reduces aluminum’s fluidity (silicon acts as a “flow enhancer”), making it more prone to cooling-induced solidification.2. Impurities and oxides act as nucleation sites for solidification, triggering premature cooling. | A magnesium alloy plant mixed 50% unscreened return material with new ingots. Cold material defects rose by 12%—reducing return material to 30% and adding a 50μm filter cut defects to 4%. |
3. Systematic Improvement Plan: From Prevention to Resolution
Eliminating cold material requires a “full-process” approach—addressing temperature control, Design de molde, parâmetros de processo, e gerenciamento de materiais. Esta seção usa um step-by-step framework with actionable measures and measurable targets.
3.1 Etapa 1: Build a Precise Temperature Control System
Temperature is the root of cold material—stabilizing it across all stages is critical. Key measures include:
- Melting Stage:
- Adopt a double-furnace process: Use a main furnace (720-750° c) for full melting and an auxiliary furnace (680-710° c) for precise temperature adjustment to the upper limit of the process window.
- Instalar online infrared thermometers (accuracy ±2°C) to monitor metal temperature in real time—trigger an alarm if it drops below the lower limit (Por exemplo, 670°C for ADC12).
- Transfer & Estágio de injeção:
- Usar heated transfer ladles (equipped with 5kW electric heaters) to maintain metal temperature during transport—reduce heat loss to <5° c.
- Preheat the pressure chamber to 150-200° c (alumínio) ou 180-220° c (magnésio) using electric heating jackets—never start injection with a room-temperature chamber.
- Mold Preheating Stage:
- Definir gradient preheating temperatures based on alloy type: Aluminum molds → 200-250°C; Magnesium molds → 220-280°C.
- Usar zone-specific heating (Por exemplo, instale aquecedores adicionais em pontos frios, como cavidades profundas) para garantir uniformidade de temperatura (desvio ≤±10°C).
3.2 Etapa 2: Optimize Mold Design for Heat Retention & Flow
Um molde bem projetado minimiza a perda de calor e garante um fluxo suave do metal. Concentre-se nessas melhorias:
- Redesenho do corredor:
- Substitua mudanças transversais repentinas por transições graduais (ângulo de conicidade 1-3°) para reduzir a resistência ao fluxo.
- Usar corredores curvados suaves (raio ≥10mm) em vez de curvas acentuadas - reduza o tempo de enchimento em 30% e perda de calor por 25%.
- Adicionar ranhuras de buffer (volume 1,2x volume do corredor) at the entrance of thin-walled areas to stabilize flow and prevent front-end cooling.
- Thermal Balance Adjustment:
- Embed ceramic heat-insulating inserts (condutividade térmica 0.5 W/m · k) in thin-walled or deep cavity parts—slow heat dissipation by 50%.
- Adjust cooling water channel spacing: Keep channels ≥8mm from the cavity surface (vs.. common 5mm) to avoid over-cooling.
- Mold Surface Maintenance:
- Polish the cavity surface to Ra ≤0.8 μm (using diamond grinding wheels) to reduce friction and heat loss from metal-mold contact.
- Control release agent application: Use um mist sprayer to apply a thin, filme uniforme (espessura 5-10μm)—avoid excessive spraying that insulates the metal.
3.3 Etapa 3: Dynamically Adjust Process Parameters
Process parameters must match the mold and material to avoid cold material. Key optimizations:
| Parâmetro | Adjustment Measures | Target Value (Aluminum ADC12) |
| Injection Speed | Adotar “fast-slow-fast” three-stage speed: 1. Initial fast (4-6 EM) to reach the cavity quickly.2. Middle slow (2-3 EM) for thick areas.3. Final fast (3-5 EM) for thin walls. | Filling time ≤2 seconds for parts <200mm de comprimento. |
| Pressure Holding | Start pressure holding 0.2-0.3 segundos after cavity filling (not earlier)—use cavity pressure sensors to trigger timing. | Pressão de retenção: 80-120MPA; tempo de espera: 70-80% do tempo total de solidificação. |
| Derramando Volume | Calcule o volume exato de vazamento único usando a fórmula: Volume = (Volume de transmissão + Volume do corredor) × 1.05 (fator de segurança). | Evite resíduos de material frio na câmara – limpe a câmara após cada 50 tiros. |
3.4 Etapa 4: Strict Material & Ingredient Management
A má qualidade do material agrava o material frio – aumente o controle com estas etapas:
- Controle de composição de liga:
- Estabeleça um banco de dados de liga e conduta análise espectral para cada lote de matérias-primas - certifique-se de que o conteúdo de silício no ADC12 seja 11-13%, magnésio em AZ91D é 0.7-1.0%.
- Adicionar elementos que melhoram o fluxo se necessário: Para alumínio, adicionar 0.1-0.2% elementos de terras raras (cério, lantânio) para melhorar a fluidez 15-20%.
- Gerenciamento de devolução de materiais:
- Material de retorno da tela com um 1peneira de malha mm para remover incrustações de óxido e impurezas.
- Limitar a proporção de material devolvido a ≤30% (misture com 70% novos lingotes)—proporções mais altas reduzem a fluidez e aumentam o risco de material frio.
- Refino & Desgaseificação:
- Usar desgaseificação rotativa de argônio (15 minutos, 2Fluxo de argônio L/min) reduzir o teor de hidrogénio para <0.15ml/100g Al – isso também remove pequenas inclusões de óxido.
- Deixe o metal fundido representar ≥15 minutos after refining to allow slag to float—skim off slag before pouring.
4. On-Site Diagnosis & Emergency Treatment
Even with preventive measures, cold material may occur. This section provides quick-response steps to minimize production loss.
4.1 Rapid Diagnosis
Follow this 3-step process to confirm cold material and identify the root cause:
- Inspeção visual: Check for rough, dull patches or flow lines—tap the area with a small hammer: a dull sound indicates internal cold material (vs.. a clear ring for normal metal).
- Microscopic Check: Take a small sample from the defective area and polish it—if unmelted particles or layered structures are visible under 100x magnification, it’s confirmed cold material.
- Parameter Review: Check recent data logs:
- Did molten metal temperature drop below the process range?
- Was injection speed slower than usual?
- Did mold temperature in the defect area fall below the target?
4.2 Emergency Countermeasures
If cold material is detected, take these immediate actions to restore production:
- Temperature Adjustment: Increase molten metal temperature by 10-15° c (Por exemplo, from 680°C to 695°C for ADC12)—test 10-20 samples to verify improvement.
- Chamber Cleaning: Stop production and clean the pressure chamber with a steel brush to remove residual cold material—preheat the chamber to 200°C before restarting.
- Parameter Tweak: Increase injection speed by 0.5-1 EM (within the safe range) to reduce filling time—avoid exceeding 8 EM (which causes turbulence).
- Mold Touch-Up: Apply a small amount of high-temperature release agent (à base de grafite) para zonas frias do molde – isso reduz temporariamente a perda de calor até que a manutenção completa do molde seja possível.
5. Yigu Technology’s Perspective on Die Casting Cold Material
Na tecnologia Yigu, acreditamos que o material frio não é apenas um “defeito de produção” mas a “aviso do sistema”—sinaliza falhas no controle de temperatura, Design de molde, ou gerenciamento de processos. Muitos fabricantes tratam apenas o sintoma (Por exemplo, aumentando a temperatura do metal) sem abordar a causa raiz (Por exemplo, um forno de retenção defeituoso), levando a defeitos recorrentes.
Recomendamos um estratégia de prevenção baseada em dados: Instale sensores IoT para monitorar a temperatura, velocidade de injeção, e condição do molde em tempo real - construa um “cold material risk model” that predicts defects 1-2 hours in advance. Por exemplo, our system alerts operators if mold temperature in a deep cavity drops by 15°C, allowing adjustment before defects form.
We also advocate Dfm (Design para fabricação) reviews: Our engineers work with clients to optimize casting design (Por exemplo, thickening thin-walled areas near cold spots) and mold structure (Por exemplo, adding buffer grooves) before production—this cuts cold material defects by 60-70% in the first batch. By combining real-time monitoring with proactive design, cold material can be controlled to a rate of <2%.
6. Perguntas frequentes: Common Questions About Die Casting Cold Material
1º trimestre: Can cold material defects be repaired, or must the casting be scrapped?
Minor cold material (surface-only, no internal voids) can be repaired via argon arc welding (use matching alloy filler, current 80-100A) followed by grinding to restore surface smoothness. No entanto, castings with internal cold material (encolhimento, pores) or cold material in load-bearing areas should be scrapped—repairs cannot restore structural integrity, and these parts may fail under stress.
2º trimestre: How to distinguish cold material from other similar defects like cold shuts?
Cold material and cold shuts both involve premature cooling, but they differ in three key ways: 1. Localização: Cold material forms in thin-walled/far-from-gate areas; cold shuts form at the meeting point of two metal flows. 2. Structure: Cold material has unmelted particles or layers; cold shuts have a clear “costura” with no particles. 3. Impacto: Cold material causes internal weakness; cold shuts mainly affect surface appearance (if no internal separation).
3º trimestre: Does cold material affect the mechanical properties of the casting?
Yes—cold material significantly reduces mechanical performance. Por exemplo, an aluminum ADC12 casting with cold material has: 1. Resistência à tracção reduced by 20-30% (from 310MPa to 220MPa). 2. Alongamento dropped by 50% (de 3% para 1.5%). 3. Vida de fadiga shortened by 60-70% (fails after 50,000 Ciclos vs.. 150,000 cycles for normal castings). Isso torna as peças de material frio inadequadas para aplicações críticas, como componentes de motores automotivos ou suportes aeroespaciais..