Холодное литье под давлением является распространенным, но разрушительным дефектом, который снижает качество., производительность, и внешний вид отливок. Он образуется, когда расплавленный металл теряет слишком много тепла во время заливки., приводит к снижению текучести и неполному заполнению полости формы.. Этот дефект не только приводит к резкому увеличению количества брака. (до 20% в тяжелых случаях) but also poses safety risks for critical components like automotive engine parts or aerospace structural elements. To help manufacturers identify, предотвращать, 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: Определение, Manifestations, и риски
Before solving the problem, it’s essential to clearly define what die casting cold material is and how it impacts production. В этом разделе используется Общая структура баллов to cover core concepts, ключевые термины выделены для ясности.
1.1 Фундаментальное определение
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 (НАПРИМЕР., царапины), 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 | Метод обнаружения |
| Surface Features | – Грубый, 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 |
| Internal Defects | – Concentrated shrinkage voids (0.1-0.5мм диаметр)- Aggregated pores (often near cold material areas)- Unmelted solid particles (residues from incomplete melting) | X-ray inspection or metallographic analysis (sample etching with 5% азотная кислота) |
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: Эти секции имеют большое соотношение площади поверхности к объему., ускорение отвода тепла. Например, алюминиевая оболочка толщиной 1 мм на расстоянии 100 мм от ворот в 3 раза более склонна к образованию холодного материала, чем секция толщиной 5 мм возле ворот.
- Дно с глубокими полостями: Расплавленному металлу требуется больше времени, чтобы достичь этих областей., и тепло удерживается стенками формы — охлаждение происходит до полного заполнения.
- Низкотемпературные зоны пресс-формы: Помещения без надлежащего предварительного подогрева (НАПРИМЕР., углы формы, участки возле каналов охлаждающей воды) действовать как “радиаторы,” быстрое охлаждение металла.
2. Root Causes of Die Casting Cold Material: A Comprehensive Analysis
Cold material forms due to a combination of failures in temperature control, дизайн плесени, process parameters, and material management. The table below uses a factor-cause-mechanism structure to identify the source of the problem, with specific examples for clarity.
| Категория причина | Specific Failures | Defect Formation Mechanism | Пример реального мира |
| 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 секунды. | 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% к 18% в 1 неделя. |
| Дизайн плесени & Condition | 1. Poor runner design (sudden cross-sectional changes, sharp bends)2. Uneven mold temperature (cooling water too close to cavity: <5мм)3. Excessive release agent (thick film >0.1мм) | 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. A thick release agent film acts as an insulator, 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. |
| Свойства материала & Management | 1. Alloy composition deviation (low silicon in aluminum: <9% против. необходимый 11-13%)2. Unscreened return material (mixed with oxide scales, примеси) | 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, дизайн плесени, process parameters, and material management. В этом разделе используется step-by-step framework with actionable measures and measurable targets.
3.1 Шаг 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:
- Принять 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.
- Install online infrared thermometers (accuracy ±2°C) to monitor metal temperature in real time—trigger an alarm if it drops below the lower limit (НАПРИМЕР., 670°C for ADC12).
- Transfer & Injection Stage:
- Использовать 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. (алюминий) или 180-220° C. (магний) using electric heating jackets—never start injection with a room-temperature chamber.
- Mold Preheating Stage:
- Набор gradient preheating temperatures based on alloy type: Aluminum molds → 200-250°C; Magnesium molds → 220-280°C.
- Использовать zone-specific heating (НАПРИМЕР., install additional heaters in cold spots like deep cavities) to ensure temperature uniformity (deviation ≤±10°C).
3.2 Шаг 2: Optimize Mold Design for Heat Retention & Flow
A well-designed mold minimizes heat loss and ensures smooth metal flow. Focus on these improvements:
- Runner Redesign:
- Replace sudden cross-sectional changes with Постепенные переходы (taper angle 1-3°) to reduce flow resistance.
- Использовать smooth curved runners (radius ≥10mm) instead of sharp bends—cut filling time by 30% and heat loss by 25%.
- Добавлять buffer grooves (volume 1.2x runner volume) at the entrance of thin-walled areas to stabilize flow and prevent front-end cooling.
- Thermal Balance Adjustment:
- Embed ceramic heat-insulating inserts (теплопроводность 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 (против. 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: Используйте mist sprayer to apply a thin, uniform film (thickness 5-10μm)—avoid excessive spraying that insulates the metal.
3.3 Шаг 3: Dynamically Adjust Process Parameters
Process parameters must match the mold and material to avoid cold material. Key optimizations:
| Параметр | Adjustment Measures | Целевое значение (Aluminum ADC12) |
| Injection Speed | Усыновить “fast-slow-fast” three-stage speed: 1. Initial fast (4-6 РС) to reach the cavity quickly.2. Middle slow (2-3 РС) for thick areas.3. Final fast (3-5 РС) for thin walls. | Filling time ≤2 seconds for parts <200мм в длину. |
| Удержание давления | Start pressure holding 0.2-0.3 секунды after cavity filling (not earlier)—use cavity pressure sensors to trigger timing. | Удерживание давления: 80-120МПА; время выдержки: 70-80% of total solidification time. |
| Pouring Volume | Calculate the exact single pouring volume using the formula: Volume = (Casting Volume + Runner Volume) × 1.05 (safety factor). | Avoid residual cold material in the chamber—clean the chamber after every 50 выстрелы. |
3.4 Шаг 4: Strict Material & Ingredient Management
Poor material quality exacerbates cold material—tighten control with these steps:
- Alloy Composition Control:
- Establish an alloy database and conduct spectral analysis for each batch of raw materials—ensure silicon content in ADC12 is 11-13%, magnesium in AZ91D is 0.7-1.0%.
- Добавлять flow-enhancing elements При необходимости: Для алюминия, добавлять 0.1-0.2% rare earth elements (Cerium, lanthanum) to improve fluidity by 15-20%.
- Return Material Management:
- Screen return material with a 1mm mesh sieve to remove oxide scales and impurities.
- Limit return material proportion to ≤30% (mix with 70% new ingots)—higher ratios reduce fluidity and increase cold material risk.
- Переработка & Дегазация:
- Использовать argon rotary degassing (15 минуты, 2L/min argon flow) to reduce hydrogen content to <0.15ml/100g Al—this also removes small oxide inclusions.
- Let the molten metal stand for ≥15 minutes 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. В этом разделе представлены 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:
- Визуальный осмотр: Check for rough, dull patches or flow lines—tap the area with a small hammer: a dull sound indicates internal cold material (против. 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. (НАПРИМЕР., 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 РС (within the safe range) to reduce filling time—avoid exceeding 8 РС (which causes turbulence).
- Mold Touch-Up: Apply a small amount of high-temperature release agent (graphite-based) to cold mold zones—this temporarily reduces heat loss until full mold maintenance is possible.
5. Yigu Technology’s Perspective on Die Casting Cold Material
В Yigu Technology, we believe cold material is not just a “production defect” но “system warning”—it signals failures in temperature control, дизайн плесени, or process management. Many manufacturers only treat the symptom (НАПРИМЕР., increasing metal temperature) without addressing the root cause (НАПРИМЕР., a faulty holding furnace), leading to recurring defects.
Мы рекомендуем data-driven prevention strategy: Install IoT sensors to monitor temperature, скорость впрыска, and mold condition in real time—build a “cold material risk model” that predicts defects 1-2 hours in advance. Например, our system alerts operators if mold temperature in a deep cavity drops by 15°C, allowing adjustment before defects form.
We also advocate DFM (Дизайн для производства) reviews: Our engineers work with clients to optimize casting design (НАПРИМЕР., thickening thin-walled areas near cold spots) and mold structure (НАПРИМЕР., 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. Часто задаваемые вопросы: Common Questions About Die Casting Cold Material
1 квартал: 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. Однако, отливки с внутренним холодным материалом (усадка, поры) или холодный материал в несущих зонах следует утилизировать — ремонт не может восстановить целостность конструкции., и эти детали могут выйти из строя под нагрузкой.
2 квартал: How to distinguish cold material from other similar defects like cold shuts?
Холодный материал и холодные затворы влекут за собой преждевременное охлаждение., но они различаются по трем ключевым аспектам: 1. Расположение: Холодный материал образуется в тонкостенных/далеко от ворот зонах.; Холодные швы образуются в месте встречи двух потоков металла. 2. Структура: Холодный материал имеет нерасплавленные частицы или слои.; холодные закрытия имеют ясность “шов” без частиц. 3. Влияние: Холодный материал вызывает внутреннюю слабость; холодные затворы главным образом влияют на внешний вид поверхности (если нет внутреннего разделения).
Q3: Does cold material affect the mechanical properties of the casting?
Да — холодный материал значительно снижает механические характеристики. Например, алюминиевое литье ADC12 с холодным материалом имеет: 1. Предел прочности уменьшено на 20-30% (от 310МПа до 220МПа). 2. Удлинение зашел 50% (от 3% к 1.5%). 3. Усталостная жизнь сокращено на 60-70% (терпит неудачу после 50,000 Циклы против. 150,000 циклы для обычных отливок). Это делает детали из холодного материала непригодными для критически важных применений, таких как детали автомобильных двигателей или кронштейны для аэрокосмической отрасли..