At Yonglihao Machinery, we provide die casting services for precision metal components. This guide focuses on how the metal die casting process works—step by step—so you can connect each stage to part quality, defects, and repeatability.
What Metal Die Casting Is?
Metal die casting injects melted metal into a steel die. This is done under high pressure. The process creates accurate and repeatable parts. The term “high pressure” is key. It is the force that drives fast filling and packs metal as it cools. This helps achieve tight tolerances.
Most die casting uses non-ferrous alloys. These include aluminum, zinc, and magnesium. The result is a near-net-shape part. It has a good surface finish and high consistency.
Key Elements Inside a Die Casting Setup
A die casting system has several “hidden” features inside the tool. These features guide metal flow and control trapped gas. Looking only at the outer mold halves misses where quality is decided.
- Die cavity & parting line: This defines the part’s shape. The parting line must stop metal from leaking.
- Runner / gate / sprue: This system routes metal into the cavity at a controlled speed.
- Overflow & vents (or vacuum ports): These give air and oxides a place to go.
- Cooling channels: They remove heat. This controls solidification and cycle time.
- Ejector pins + slides/cores: These release the part without damage after it solidifies.
In practice, the gating, venting, and cooling act as one system. They decide how the cavity fills, how air escapes, and how shrinkage is fed.
Step-by-Step: How the Die Casting Cycle Works
A die casting cycle closes and clamps the die. It then fills the cavity quickly. Pressure is increased as the metal freezes. Then it cools, opens, ejects, and is trimmed. Each step has a clear purpose. Defects start when control is skipped here.
Die Preparation
Die preparation involves cleaning, preheating, and applying lubricant. This helps the die surface release the part and stay thermally stable. A stable die temperature prevents issues like cold shuts and soldering. It also helps create consistent dimensions.
Lubricant also protects the die surface. It supports consistent ejection. Too much lubricant, however, can increase gas and cause porosity.
Clamping
Clamping seals the die halves while metal is injected. If the clamping force is too low, molten metal can create flash. Poor die alignment can also cause this.
This is why die fit and tie-bar condition are very important. They matter as much as the injection pressure.
Filling (Shot)
Filling injects molten metal through the shot system. It flows into runners and gates, then into the cavity. The goal is to fill the cavity completely before the metal freezes. This must happen without too much turbulence, which traps air.
Many machines use a speed profile. This means a controlled start, then a fast fill near the gate. This approach balances complete filling with the risk of trapped gas.
Intensification & Holding
After the cavity is full, the pressure is increased and held. This “packs” the metal. This intensification stage makes up for shrinkage as the metal hardens. It also improves density.
If intensification is too low or short, problems can occur. You might see shrinkage porosity or weak spots in thick sections.
Cooling
Cooling removes heat through the die and its cooling channels. This continues until the part is strong enough to eject. Uniform cooling reduces warping and size changes. Hot spots can lead to shrinkage defects in thicker areas.
Cooling time depends on the alloy and wall thickness. It is also tied to the die’s thermal balance. Over-cooling lowers output and can make parts stick.
Die Opening & Ejection
Once solid, the die opens. Ejector pins push the part off the ejector side. Draft angles, fillets, and ejector design all affect the release. They decide if the ejection is smooth or damaging.
Slides and cores pull back to release undercuts. Poor timing or not enough draft can cause drag marks and damage.
Trimming & Basic Finishing
Trimming removes runners, gates, and any flash. This step is part of the process loop. The scrap is often remelted and reused. This affects the melt practice and its cleanliness.
The part might need post-machining for holes or threads. Many die cast parts, however, only need trimming and light deburring.
Hot-Chamber vs Cold-Chamber
Hot-chamber and cold-chamber die casting are different. They differ in where the metal is melted. They also differ in how it enters the injection system. This changes the cycle time and which alloys can be used.
Hot-Chamber
Hot-chamber die casting keeps molten metal inside the machine. It injects the metal through a gooseneck submerged in the melt. This design allows for fast cycle times and stable feeding.
It works best for alloys with low melting points, like zinc. It is not good for many aluminum alloys due to heat and corrosion issues.
Cold-Chamber
Cold-chamber die casting melts metal in a separate furnace. The metal is then moved into a shot sleeve with a ladle. A plunger injects the metal into the die under high pressure.
This setup is good for aluminum alloys and materials with higher temperatures. The transfer step usually makes cycles slower. It is often used for larger parts and aluminum housings.
|
Item |
Hot-Chamber |
Cold-Chamber |
|---|---|---|
|
Where metal melts |
Inside machine |
In separate furnace |
|
Metal loading |
Automatic through gooseneck |
Ladle into shot sleeve |
|
Typical alloys |
Zinc, some Mg |
Aluminum, Cu alloys, some Mg |
|
Cycle time |
Faster |
Slower (transfer step) |
|
Best fit |
Small–medium parts, high volume |
Aluminum parts, wider alloy range |
The Few Process Variables That Decide Part Quality
Part quality depends on a few key things. These are temperature control, filling behavior, and packing pressure. Venting and cooling balance are also vital. If you can explain these five factors, you can explain most die casting results.
Metal Temperature & Die Temperature
Hotter metal flows better. But if it is too hot, it can increase soldering and oxidation. The die temperature must be stable. If it’s too cold, it causes misruns. If it’s too hot, it increases flash and sticking.
Good practice aims for a “thermal window.” This is where the metal fills completely and solidifies in a predictable way.
Shot Speed Profile
Shot speed affects how the cavity fills before freezing. It also affects how much air gets trapped. Too much turbulence increases gas entrapment and porosity. This is especially true when venting is poor. A controlled speed profile is often better than just “maximum speed.”
Intensification Pressure & Hold Time
Higher intensification can improve density. But it also raises the risk of flash if clamping is not perfect. The hold time must match the freeze time at the gate. If not, the pressure cannot feed the shrinkage. This is a common reason why two shops get different results with the same alloy.
Venting / Vacuum
Air must leave the cavity before metal seals the vents. If vents are too small, blocked, or in the wrong place, gas stays inside. This forms porosity.
Vacuum die casting can help reduce trapped gas. But it still needs clean vent paths and correct timing.
Cooling Balance
Uneven cooling creates thermal differences. This leads to warpage and size changes. Hot spots also increase the risk of shrinkage voids in thicker areas.
If you are trying to fix repeatability issues, check the cooling balance first. It is often a “quiet” cause of problems.
Quick quality-control checklist :
- Is the die temperature stable from shot to shot?
- Are the vents and overflows clean and open?
- Is the shot profile controlled, not just “fast”?
- Does intensification last until the gate freezes?
- Is the cooling balanced, with no lasting hot spots?
Quick Troubleshooting
Most die casting defects are not a mystery. They are results of air management, sealing, feeding shrinkage, and temperature control.
Porosity
Porosity has two main causes. Gas gets trapped during filling. Or, shrinkage is not fed as the metal hardens. Gas porosity is often linked to turbulence and weak venting. Shrinkage porosity is linked to low packing pressure or poor feeding paths.
Fix direction: improve venting or vacuum. Soften turbulence with the shot profile. Ensure intensification and hold time match the gate freeze.
Flash
Flash happens when molten metal escapes. It leaks through the parting line or around inserts under pressure. It is usually a sealing problem first, then a pressure problem.
Fix direction: check die fit and alignment. Check clamping force and parting line support. Then, adjust injection and intensification pressures.
Cold Shut / Misrun
A cold shut or misrun happens when metal fronts meet after partially freezing. It also happens if the cavity never fills completely. This is often caused by low metal or die temperature. It can also result from a slow fill or a restrictive gate.
Fix direction: stabilize the die temperature. Adjust metal temperature. Improve the gating and flow path. Refine the shot speed profile.
|
Symptom |
Likely mechanism |
First control points |
|---|---|---|
|
Porosity |
trapped gas / shrinkage not fed |
venting/vacuum, shot profile, intensification & hold |
|
Flash |
die not sealing under pressure |
die fit, clamping, parting line support, pressure levels |
|
Misrun/cold shut |
freezing before complete fill |
die temp, metal temp, gating restriction, fill speed |
Conclusion
As manufacturing continues to evolve, so does die casting technology. Innovations in intelligent manufacturing and automation are bringing new possibilities to the die casting industry. Modern die casting machines increasingly integrate intelligent sensors and AI-driven control systems to monitor and adjust production parameters in real time, enhancing precision and efficiency. Additionally, the development of new materials, such as high-strength alloys and composites, is expanding die casting applications, enabling them to meet higher performance requirements.
At Yonglihao Machinery, we are committed to advancing die casting technology. We actively invest in state-of-the-art equipment and technologies to ensure our pressure die casting processes remain at the industry’s forefront. Meanwhile, we continuously enhance our team’s expertise to ensure we provide the highest quality service to our clients.
FAQ
What is the core working principle of metal die casting?
It works by forcing molten metal into a die at high speed and high pressure. The metal is then packed as it freezes. This pressure-driven filling allows for thin walls, detail, and repeatability.
Why does high pressure improve dimensional consistency?
High pressure helps reduce incomplete filling. It also compensates for shrinkage during solidification. With a stable die temperature and correct hold time, the part freezes in a more controlled, repeatable way.
When should I use hot-chamber vs cold-chamber die casting?
Use hot-chamber for low-melting alloys like zinc when you need fast cycles. Use cold-chamber for aluminum and higher-temperature alloys. This is best when material choice and part size are priorities.
What causes porosity in die cast parts most often?
Porosity most often comes from trapped gas or poor feeding during shrinkage. Start by checking vent cleanliness, shot turbulence, and intensification timing.
Which process settings usually give the fastest quality improvement?
Stabilizing die temperature and cleaning vents give the fastest wins. After that, refine the shot speed profile and intensification timing to match the gate freeze.
