Die casting cold partitions (also known as cold shuts) are a prevalent and damaging surface defect that plagues metal forming processes. They occur when two or more streams of molten metal meet in the mold cavity but fail to fuse completely due to excessive cooling, leaving visible seams or even hidden cracks. This defect not only ruins the appearance of castings but also severely weakens their mechanical strength—for critical components like automotive brake calipers or hydraulic valves, cold partitions can lead to catastrophic failure, product recalls, and significant financial losses. This article systematically explores the nature of die casting cold partitions, their root causes, and a comprehensive solution framework to help manufacturers eliminate this issue and improve production quality.
1. Understanding Die Casting Cold Partitions: Definición, Características, and Risks
Before tackling the problem, it is essential to clearly define what die casting cold partitions are and recognize their potential impacts. Esta sección utiliza un Estructura de puntuación total to cover core concepts, con términos clave resaltados para mayor claridad.
1.1 Definición fundamental
Die casting cold partitions refer to a defect where molten metal, during the filling process, splits into multiple streams that cool down excessively before merging in the mold cavity. The cooled metal streams lose their fluidity and fail to form a homogeneous bond, resulting in a distinct separation line (seam) on the casting surface. Unlike minor surface scratches, cold partitions are not just cosmetic flaws—they often extend into the casting’s interior, creating weak planes that compromise structural integrity.
1.2 Características clave
You can identify die casting cold partitions through the following distinct traits, both visual and structural:
| Characteristic Category | Specific Traits | Detection Method |
| Surface Features | – Irregular, linear seams (often curved or zigzagged) with smooth, bordes redondeados- Dull, matte appearance along the seam (no metallic luster)- Localized depressions or grooves adjacent to the seam | Naked eye inspection (after surface cleaning) or 10x magnification lens; the seam is easily distinguishable from the surrounding metal |
| Structural Traits | – Incomplete fusion between metal streams (visible gap under microscopic examination)- Concentrated pores or shrinkage voids near the partition line- Reduced material density along the seam (compared to normal casting areas) | Metallographic analysis (sample sectioning and etching with 5% ácido nítrico); ultrasonic flaw detection to identify internal extensions of the partition |
1.3 Potential Risks
The presence of cold partitions poses significant risks to both the casting’s performance and the manufacturer’s operations:
- Mechanical Performance Degradation: Cold partitions act as stress concentration points. Tensile strength along the partition line can decrease by 25-40%, and fatigue life may be shortened by 50-70%. Por ejemplo, an aluminum alloy automotive suspension bracket with a cold partition may crack under normal driving loads, lo que lleva a riesgos de seguridad.
- Functional Failure: For pressure-bearing components (P.EJ., cilindros hidráulicos, inyectores de combustible), cold partitions can cause leakage. The incomplete fusion creates tiny channels that allow fluids or gases to escape, making the component unable to maintain the required pressure.
- Production Losses: Castings with cold partitions often require rework or scrapping. En producción en masa, incluso un 5% defect rate can increase production costs by 15-20% due to material waste, labor rework, and delayed delivery.
- Reputational Damage: If cold partition defects reach the market, they can lead to product recalls. A single recall of 10,000 defective parts can cost a manufacturer millions of dollars in replacement costs, legal fees, and lost customer trust.
2. Root Causes of Die Casting Cold Partitions: A Comprehensive Analysis
Die casting cold partitions are not caused by a single factor but by a combination of failures in temperature control, diseño de moldes, parámetros del proceso, y selección de materiales. La siguiente tabla utiliza un factor-causa-mecanismo estructura para identificar la fuente del problema, con ejemplos del mundo real como referencia práctica.
| Categoría de causa | Fallos específicos | Mecanismo de formación de defectos | Ejemplo del mundo real |
| Problemas de control de temperatura | 1. Baja temperatura de vertido del metal fundido (por debajo de la temperatura líquida de la aleación)2. Precalentamiento insuficiente del molde (Temperatura del molde por debajo del rango recomendado.)3. Pérdida excesiva de calor en el sistema de canales. (largo, corredores sin aislamiento) | 1. Low-temperature molten metal has high viscosity and loses fluidity quickly, failing to fuse when streams meet.2. A cold mold absorbs heat from the molten metal, causing rapid cooling of the metal stream surfaces.3. Largo, uninsulated runners allow the molten metal to cool down before reaching the cavity, resulting in cold stream fronts. | An aluminum alloy ADC12 casting plant set the pouring temperature at 650°C (10°C below the liquidus temperature of ADC12). Cold partition defects increased from 2% a 15% within a week, and the defective castings failed tensile tests. |
| Moho & Gating System Design Flaws | 1. Unreasonable runner layout (sharp bends, sudden cross-sectional changes)2. Improper inner gate placement (leading to chaotic metal flow and stream splitting)3. Inadequate exhaust (trapped gas prevents metal stream fusion) | 1. Sharp bends and sudden cross-sectional changes disrupt the molten metal flow, splitting it into multiple streams that cool independently.2. Poorly placed inner gates cause the metal to flow in conflicting directions, resulting in non-simultaneous filling and stream cooling.3. Trapped gas creates a barrier between metal streams, preventing them from merging even if they are still hot enough. | A zinc alloy toy manufacturer used a mold with a 90° sharp bend in the main runner. Cold partitions formed at the bend in 30% of castings. Redesigning the runner with a 15mm radius and adding an auxiliary gate reduced defects to 1.5%. |
| Discrepancias en los parámetros del proceso | 1. Slow injection speed (prolonging filling time and heat loss)2. Insufficient injection pressure (failing to push metal streams together for fusion)3. Excessive release agent application (creating a cooling barrier between metal streams) | 1. Slow injection extends the time the molten metal is in contact with the cold mold and runner walls, leading to excessive cooling of the stream fronts.2. Low injection pressure cannot overcome the resistance between cooled metal streams, preventing complete fusion.3. A thick release agent film acts as an insulator, reducing heat transfer between merging metal streams and inhibiting fusion. | An automotive parts supplier used an injection speed of 1.8 m/s for a 2mm-thick aluminum dashboard bracket. Cold partitions appeared in 22% of castings. Increasing the injection speed to 4.2 m/s and reducing release agent usage by 30% eliminated the defect. |
| Propiedades del material & Management | 1. Poor alloy fluidity (P.EJ., low silicon content in aluminum alloys)2. Contaminated raw materials (mixed with oxides, impurezas, or moisture)3. Improper return material ratio (high proportion of cold, oxidized return material) | 1. Alloys with low fluidity cool quickly and lose the ability to fuse, even if streams meet shortly after splitting.2. Oxides and impurities in the molten metal act as barriers between merging streams, preventing homogeneous bonding.3. A high proportion of cold return material lowers the overall temperature of the molten metal, increasing the risk of stream cooling before fusion. | A magnesium alloy casting plant mixed 40% unscreened return material (with oxide scales) into new ingots. Cold partition defects rose by 18%. Reducing the return material ratio to 20% and adding a 50μm ceramic filter cut defects to 3%. |
3. Systematic Prevention & Solution Strategies for Die Casting Cold Partitions
La eliminación de las particiones frías de fundición a presión requiere un “proceso completo, multidimensional” enfoque que aborda el control de la temperatura, diseño de moldes, optimización de procesos, y gestión de materiales. Esta sección utiliza un marco paso a paso con medidas viables y objetivos mensurables.
3.1 Paso 1: Optimize Temperature Control Throughout the Production Process
La temperatura es el factor principal que influye en la fluidez y fusión del metal fundido.. Estabilizar las temperaturas en todas las etapas es fundamental para evitar particiones frías.:
- Gestión de la temperatura del metal fundido:
- Establezca la temperatura de vertido entre 10 y 20 °C por encima de la temperatura líquida de la aleación. (P.EJ., 680-700°C para aleación de aluminio ADC12, 450-470°C para ZAMAK 5 aleación de zinc).
- Usar un double-furnace system: The main furnace (higher temperature) ensures complete melting, and the holding furnace (precise temperature control) maintains the molten metal at the optimal pouring temperature. Install online infrared thermometers (accuracy ±2°C) to monitor temperature in real time and trigger alarms if deviations exceed 5°C.
- Mold Preheating & Temperature Maintenance:
- Preheat the mold to the recommended temperature range: 180-250°C for aluminum alloys, 120-180°C for zinc alloys, and 220-280°C for magnesium alloys. Use mold temperature controllers with zone-specific heating to ensure uniform temperature distribution (deviation ≤±10°C).
- For large molds or complex cavities, install additional heating elements in cold spots (P.EJ., cavidades profundas, thin-walled sections) to prevent localized cooling of the molten metal.
- Runner & Gate Temperature Insulation:
- Insulate the runner system with ceramic sleeves (thermal conductivity ≤0.5 W/m·K) to reduce heat loss. For long runners (length >300mm), add electric heating tapes to maintain the runner temperature at 50-80°C below the molten metal pouring temperature.
3.2 Paso 2: Redesign Mold & Gating System for Smooth Metal Flow
A well-designed mold and gating system ensures that molten metal flows uniformly, avoiding stream splitting and cooling. Key improvements include:
- Runner System Optimization:
- Usar streamlined runner designs with gradual cross-sectional transitions (taper angle 1-3°) and large-radius bends (radius ≥10mm) to prevent flow disruption. The cross-sectional area of the runner should decrease gradually from the main runner to the inner gate (relación de reducción 1:0.8) to maintain consistent flow velocity.
- For complex castings with multiple cavities, adopt a balanced runner layout to ensure that molten metal reaches each cavity simultaneously. Use CAE simulation software (P.EJ., MAGMA, cualquier casting) to verify flow uniformity and adjust the runner size accordingly.
- Inner Gate Design & Colocación:
- Position inner gates to ensure that molten metal fills the cavity in a single, continuous stream. Avoid placing gates opposite each other (which causes conflicting flows) or at the end of long, narrow sections (which increases flow resistance and cooling).
- Optimize the inner gate dimensions: The gate width should be 3-5 times the gate thickness, and the gate length should be as short as possible (≤5 mm) to minimize heat loss. For thin-walled castings (<2milímetros), use fan-shaped inner gates to distribute the molten metal evenly.
- Exhaust System Enhancement:
- Agregar serpentine exhaust grooves (depth 0.1-0.15mm, width 5-8mm) en las últimas posiciones de llenado de la cavidad para eliminar el gas atrapado. El área transversal total del sistema de escape debe ser al menos 1/3 del área de la sección transversal de la puerta interior para garantizar una evacuación eficaz del gas.
- Para piezas fundidas complejas o de cavidades profundas, usar tecnología de escape al vacío (vacuum degree >90kPa) para eliminar las barreras de gas entre las corrientes de metal y promover la fusión.
3.3 Paso 3: Adjust Process Parameters to Promote Metal Fusion
La optimización de los parámetros de inyección garantiza que las corrientes de metal fundido se fusionen antes de enfriarse excesivamente.. Concéntrese en los siguientes ajustes:
| Parámetro del proceso | Medidas de optimización | Target Value (for Aluminum Alloy ADC12) |
| Velocidad de inyección | Adopt a “two-stage speed profile”:1. Initial slow speed (1-2 EM) to fill the runner and avoid splashing.2. Fast speed (4-6 EM) to fill the cavity quickly and reduce heat loss. | Total filling time ≤2 seconds for castings with a maximum dimension of 200mm |
| Inyección | Set the specific pressure to 80-120MPa to ensure that molten metal streams are pressed together for fusion. Increase pressure by 10-15% for complex castings with multiple flow paths. | Pressure should be maintained until the metal at the inner gate solidifies (tiempo de espera: 5-10 artículos de segunda clase) |
| Aplicación de agente de liberación | Utilice un producto poco volátil, agente desmoldante resistente a altas temperaturas (P.EJ., a base de grafito) y aplicarlo en una fina, película uniforme (espesor 5-10μm) utilizando un sistema de pulverización automático. Evite rociar demasiado. | El agente desmoldante debe cubrir completamente la cavidad del molde pero no formar gotas visibles ni capas gruesas. |
3.4 Paso 4: Strict Material Control & Management
El metal fundido de alta calidad con buena fluidez es esencial para evitar particiones frías. Implementar las siguientes medidas de control de materiales.:
- Optimización de la composición de la aleación:
- Seleccione aleaciones con buena fluidez para fundición a presión.: Para aleaciones de aluminio, ensure silicon content is 11-13% (ADC12) o 7-9% (A380); for zinc alloys, use ZAMAK 5 (con 4% aluminio) Para un mejor flujo. Add trace elements (P.EJ., 0.1-0.2% rare earth elements for aluminum) to improve fluidity by 15-20%.
- Conduct spectral analysis for each batch of raw materials to verify alloy composition. Reject batches with deviations exceeding ±0.5% from the standard.
- Materia prima & Return Material Management:
- Use clean, dry raw materials. Store ingots in a dry environment (relative humidity ≤60%) and preheat them to 120-150°C before melting to remove moisture.
- Screen return material with a 1mm mesh sieve to remove oxide scales, impurezas, and cold metal fragments. Limit the return material ratio to ≤30% (mixed with 70% new ingots) to maintain molten metal quality and temperature.
- Molten Metal Refining:
- Refine the molten metal using argon rotary degassing (15-20 minutos, argon flow rate 2-3L/min) to remove hydrogen and oxides. Use a ceramic filter (50-80μm pore size) to filter the molten metal before pouring to eliminate solid impurities.
4. On-Site Diagnosis & Emergency Treatment for Cold Partitions
Even with preventive measures, cold partitions may occasionally occur. This section provides quick-response steps to minimize production losses and restore normal operations.
4.1 Rapid Diagnosis
Follow this 3-step process to confirm the presence of cold partitions and identify the root cause:
- Inspección visual: Check the casting surface for linear seams with dull edges. Use a small hammer to tap the area around the seam— a dull, hollow sound indicates a cold partition (compared to a clear, resonant sound for normal metal).
- Microscopic Verification: Take a small sample from the suspected area, polish it, and etch it with 5% ácido nítrico. Under a 100x microscope, a cold partition will appear as a distinct gap or incomplete fusion line between metal grains.
- Parámetro & Process Review: Analyze recent production data to identify potential deviations:
- Did the molten metal temperature drop below the set range?
- Was the injection speed or pressure lower than normal?
- Did the mold temperature in the defect area fall below the target?
- Was there a change in the raw material batch or return material ratio?
4.2 Emergency Countermeasures
If cold partitions are detected, take the following immediate actions to resolve the issue:
- Temperature Adjustment: Increase the molten metal pouring temperature by 10-15°C (within the safe range) and raise the mold preheating temperature by 20-30°C. Prueba 10-20 samples to verify if the cold partitions are eliminated.
- Process Parameter Tweak: Increase the injection speed by 0.5-1 EM (up to the maximum safe speed for the mold) and raise the injection pressure by 10-15% to enhance metal stream fusion. Reduce the release agent application amount by 20-30% to avoid cooling barriers.
- Moho & Runner Maintenance: Limpie el sistema de canales y la cavidad del molde para eliminar incrustaciones de óxido residuales o fragmentos de metal frío.. Para moldes con curvas pronunciadas o escape deficiente, agregar temporalmente orificios de escape auxiliares (0.5-1diámetro mm) en las últimas posiciones de llenado para mejorar la evacuación de gases.
- Ajuste de materiales: Si la proporción de material de retorno es alta, reducirlo a 20% y agregar nuevos lingotes para mejorar la fluidez del metal fundido. Si la composición de la aleación no cumple con las especificaciones, ajustarlo añadiendo los elementos necesarios (P.EJ., silicio para aleaciones de aluminio) para restaurar la fluidez.
5. Yigu Technology’s Perspective on Die Casting Cold Partitions
En la tecnología yigu, Creemos que las particiones frías de fundición a presión no son solo un defecto de producción sino un reflejo de problemas sistémicos en el proceso de fabricación.. Muchos fabricantes se centran únicamente en tratar los síntomas. (P.EJ., aumento de la temperatura de vertido) sin abordar las causas profundas (P.EJ., diseño de molde defectuoso o calidad del material inconsistente), lo que lleva a defectos recurrentes y desperdicio de recursos.