The die casting injection process is a precisely orchestrated sequence of speed and pressure adjustments that transforms molten metal into high-quality parts. While it may seem like a single “injection” step, it actually unfolds in distinct stages—each designed to solve a specific challenge, from expelling air to preventing defects like shrinkage or flash. These stages vary slightly by equipment type (e.g., hot vs. cold chamber machines) and alloy (aluminum vs. zinc), but three mainstream classification systems dominate industry use: the 5-stage (theoretical), 3-stage (simplified), and 4-stage (modern machine) models. But what happens in each stage? How do they differ? And how to choose the right classification for your production? This article answers these questions with technical details, parameter benchmarks, and real-world applications.
1. Core Principles: Why Staged Injection Matters
Before diving into specific stages, it’s critical to understand the “why” behind staged injection. Molten metal behaves differently under varying speed and pressure—rushing it too fast causes turbulence (trapping air and oxide films), while moving it too slow leads to premature solidification (causing undercasting). Staged injection solves this by:
- Expelling air: Low-speed stages push air out of the pressure chamber and runners, avoiding bubbles in the final part.
- Preventing splashing: Gentle initial movement stops molten metal from splashing against mold walls (which creates cold shuts).
- Ensuring full filling: High-speed stages quickly fill complex cavities before the metal cools.
- Compacting metal: Final pressure stages eliminate shrinkage and boost part density.
Every stage works together to balance flow efficiency (filling the mold quickly) and defect prevention (avoiding air, cold shuts, or flash)—the key to consistent die casting quality.
2. Three Mainstream Stage Classifications: A Detailed Comparison
The industry uses three primary ways to divide the injection process, each tailored to different equipment and production goals. The table below breaks down each classification, its stages, key parameters, and ideal use cases:
| Classification | Stages | Key Objectives & Technical Details | Typical Parameters (Aluminum Alloys, Cold Chamber) | Ideal Application |
| 1. 5-Stage Division (Basic Theory) | 1. Preparation Stage | – Adjust initial machine state: Reset punch to starting position; preheat pressure chamber to 150–200°C.- Load molten metal into the pressure chamber (volume = part weight + 5–10% waste). | – Punch position: 0mm (starting point)- Pressure chamber temp: ±10°C tolerance | All die casting machines; used for training and process validation. |
| 2. Slow Sealing Stage | – Punch moves at low speed (0.1–0.3m/s) to seal the feeding port.- Push molten metal to the front of the pressure chamber—expels 80–90% of air. | – Speed: 0.1–0.3m/s- Travel distance: 50–100mm (covers feeding port) | Prevents air from being drawn back into the pressure chamber; critical for large parts. | |
| 3. Accumulation Stage | – Metal accumulates at the inner gate front, building “momentum” for high-speed filling.- Ensures a steady metal supply to avoid gaps during the next stage. | – Speed: 0.3–0.5m/s- Pressure: 5–10MPa (maintains flow without splashing) | Ideal for parts with thin walls (≤3mm); ensures uniform metal distribution. | |
| 4. Filling Stage | – Punch accelerates to high speed (2–5m/s) to fill the mold cavity quickly.- Key: Fill before the metal solidifies (typical filling time: 0.05–0.2s for small parts). | – Speed: 2–5m/s (varies by part thickness; faster for thinner walls)- Acceleration: ≤5m/s² (avoids turbulence) | All high-volume production; critical for complex parts with deep cavities. | |
| 5. Boosting & Holding Stage | – Apply high pressure (50–100MPa) via the booster mechanism to compact molten metal.- Maintain pressure during solidification (holding time: 10–20s) to eliminate shrinkage. | – Boost pressure: 50–100MPa- Holding time: 1.2× solidification time | Pressure-bearing parts (e.g., hydraulic valves); prevents sink defects. | |
| 2. 3-Stage Division (Classic Simplified) | 1. Slow Injection Stage | – Combines “slow sealing” and “accumulation” stages: Low speed (0.1–0.5m/s) pushes metal over the gate, expels air, and builds momentum.- Simplified for easy operation—reduces parameter setup time. | – Speed: 0.1–0.5m/s- Pressure: 5–15MPa | Small to medium-sized parts (e.g., 3C electronic components); used on older machines with limited parameter controls. |
| 2. Fast Injection Stage | – Same as 5-stage “filling stage”: High speed (2–5m/s) fills the cavity quickly.- Focus on cycle efficiency—common in high-volume production (e.g., zinc alloy hardware). | – Speed: 2–5m/s- Filling time: <0.2s (for parts <500g) | Zinc alloy parts (hot chamber machines); fast-cycle products (e.g., bathroom faucet handles). | |
| 3. Boosting Stage | – Merges “boosting” and “holding” stages: Apply high pressure (50–80MPa) and hold until solidification.- Simplified for operators to monitor—reduces human error. | – Pressure: 50–80MPa- Holding time: 8–15s | Non-critical parts (e.g., toy casings); low-skill production lines. | |
| 3. 4-Stage Division (Modern Machines) | 1. Slow Pressure Injection Stage | – Identical to 5-stage “slow sealing stage”: Low speed (0.1–0.3m/s) seals the port and expels air.- Adds real-time pressure monitoring to avoid metal leakage. | – Speed: 0.1–0.3m/s- Pressure: 5–10MPa (monitored via sensors) | Modern cold chamber machines; parts requiring strict air control (e.g., EV battery housings). |
| 2. Fast Injection Stage | – Same as 5-stage “filling stage”: High speed (2–6m/s) fills complex cavities.- Uses variable speed curves (e.g., J-shaped acceleration) to reduce turbulence. | – Speed: 2–6m/s- Acceleration: 3–5m/s² (smooth ramp-up) | Complex aluminum parts (e.g., automotive engine brackets); machines with AI parameter control. | |
| 3. Deceleration Stage | – Unique to modern machines: Slow the punch (from 2–6m/s to 0.5–1m/s) as filling nears completion.- Reduces impact on the mold (extending mold life) and minimizes flash (excess metal at parting lines). | – Deceleration rate: 2–4m/s²- End speed: 0.5–1m/s | High-precision parts (e.g., medical device components); molds with tight tolerances (±0.05mm). | |
| 4. Pressure Holding Stage | – Focus on uniform pressure application: Maintain 50–100MPa until the part’s surface solidifies.- Adds cooling channel synchronization (adjusts water flow to match solidification). | – Pressure: 50–100MPa- Holding time: 10–25s (varies by wall thickness) | Safety-critical parts (e.g., automotive steering knuckles); parts requiring high density (≥99.5%). |
3. Key Parameter Tuning: Optimize Each Stage for Defect Prevention
Even with the right stage division, poor parameter settings lead to defects. Below is a guide to tuning critical parameters for common alloys and defect risks:
A. Parameter Benchmarks by Alloy
| Alloy Type | Slow Stage Speed | Fast Stage Speed | Boost Pressure | Holding Time (10mm Thick Part) |
| Aluminum (Cold Chamber) | 0.1–0.3m/s | 2–5m/s | 50–100MPa | 12–18s |
| Zinc (Hot Chamber) | 0.2–0.4m/s | 1–3m/s | 30–50MPa | 8–12s |
| Magnesium (Cold Chamber) | 0.1–0.2m/s | 3–6m/s | 60–90MPa | 10–15s |
B. Defect-Specific Parameter Adjustments
If you’re facing common issues (e.g., bubbles, cold shuts), tweak stages as follows:
| Defect | Root Cause (Stage Issue) | Parameter Fix |
| Bubbles/ Porosity | Fast stage too fast (turbulence); slow stage didn’t expel air. | – Reduce fast stage speed by 0.5–1m/s.- Extend slow stage travel by 20–30mm (expels more air). |
| Cold Shuts | Fast stage too slow (metal solidifies mid-fill); slow stage too long. | – Increase fast stage speed by 0.3–0.8m/s.- Shorten slow stage time by 0.5–1s. |
| Shrinkage Sinks | Boost pressure too low; holding time too short. | – Increase boost pressure by 10–20MPa.- Extend holding time by 2–5s (1.2× solidification time). |
| Flash | Deceleration stage missing; fast stage too fast (excess metal squeezed into gaps). | – Add a deceleration stage (0.5–1m/s end speed).- Reduce fast stage speed by 0.5–1m/s. |
4. How to Choose the Right Stage Classification
Selecting the best stage division depends on three factors: equipment capability, part complexity, and production volume. Follow this decision tree:
- Equipment Age/Type:
- Older machines (pre-2010) with limited parameter controls: Use 3-stage division (simplified, easy to operate).
- Modern machines (post-2010) with AI and sensor integration: Use 4-stage division (leverages deceleration and real-time monitoring).
- Training or lab environments: Use 5-stage division (teaches core principles).
- Part Complexity:
- Simple parts (e.g., flat brackets): 3-stage division (no need for deceleration).
- Complex parts (e.g., EV battery housings with thin walls): 4-stage division (deceleration prevents flash).
- Critical parts (e.g., aerospace components): 5-stage division (granular control reduces defects).
- Production Volume:
- High volume (>100k parts/year): 3 or 4-stage (fast setup, low operator input).
- Low volume (<10k parts/year): 5-stage (flexible tuning for small batches).
5. Yigu Technology’s Perspective on Staged Injection
At Yigu Technology, we see staged injection as the “brain” of die casting—poorly tuned stages undo even the best mold designs. For automotive clients using cold chamber machines, our 4-stage AI-driven system (with real-time speed/pressure adjustment) reduced defect rates from 7% to <1.8%, cutting scrap costs by $40,000/year for a 100k-part batch. For zinc alloy hardware clients, our simplified 3-stage setup (pre-set parameters for common parts) reduced operator training time by 50%.
We’re advancing two key innovations: 1) Self-learning stage tuning (AI analyzes defect data to optimize speeds/pressures automatically); 2) Cross-alloy parameter libraries (pre-loaded settings for aluminum, zinc, and magnesium, reducing setup time by 70%). Our goal is to make staged injection accessible—turning complex parameters into intuitive, reliable controls that boost quality and efficiency for every client.
FAQ
- Can I skip stages (e.g., deceleration) to speed up cycle time?
Skipping stages risks costly defects. For example, skipping deceleration increases flash by 30–50% (requiring extra trimming time) and shortens mold life by 20% (due to excess impact). Instead, optimize existing stages: e.g., reduce slow stage speed by 0.1m/s (cuts 0.3s/cycle) without sacrificing air expulsion.
- Do hot chamber machines use the same stage classifications as cold chamber?
Hot chamber machines (for zinc/magnesium) often use simplified 3-stage division—they have shorter pressure chambers (less air to expel), so the 5-stage “accumulation” stage is unnecessary. However, modern hot chamber machines (post-2015) can use 4-stage division for high-precision parts (e.g., medical device components).
- How do I know if my stage parameters are optimized?
Use three tests: 1) Air detection: Check for bubbles via X-ray (porosity grade ≤2 per ASTM E446). 2) Fill test: Use a high-speed camera (1000fps) to confirm no splashing or turbulence. 3) Density test: Measure part density (≥99.2% for aluminum alloys). If all pass, your parameters are optimized.