Medium pressure die casting uses injection pressures of 4–20 megapascals (MPa) to inject molten aluminum into the die casting mold. It strikes a balance between low-pressure and high-pressure die casting methods, providing stronger mechanical properties, lower porosity, and greater dimensional accuracy. The process is particularly useful for producing complex, medium-volume die casting parts that require high precision without incurring excessive tooling costs or wear.
This article will explain what medium-pressure die casting is, how it works, its key advantages, how it compares to other die casting processes, and typical application scenarios. Let’s take a deeper look at why it may be the best choice for your next aluminum casting project.
What Is Medium-Pressure Die Casting?
A Bridge Between LPDC and HPDC
MPDC is somewhere between low-pressure die casting (LPDC) and high-pressure die casting (HPDC), combining the gentle injection method of LPDC with the fast production cycle of HPDC.
It offers better part integrity than LPDC, while causing less tooling wear than HPDC.
Pressure Range
The operating pressure of medium pressure die casting (MPDC) is 4 to 20 MPa.
This enables molten aluminum to fill the mold at a controlled speed and consistency, reducing turbulence during the flow process, thereby improving the casting quality of parts with complex shapes and sizes.
Working Principle of Medium-Pressure Die Casting
Mold Preheating
Medium-pressure die casting uses high-pressure resistant molds, which are preheated to 250–300°C to ensure uniform heat conduction after the molten aluminum enters the mold cavity.
Stable mold temperature is the prerequisite for achieving “pressure-holding solidification”, which can effectively prevent defects such as shrinkage cavities and cold shuts, and improve the consistency of finished die casting products.
Medium-Pressure Injection of Molten Aluminum
The molten aluminum is smoothly injected into the mold cavity from a sealed crucible under a pressure of 4–20 MPa.
This pressure can not only fill the mold quickly, but also avoid the turbulent air entrapment problem common in HPDC, and can effectively achieve a low porosity and high-density structure of the aluminium die casting components.
Controlled Filling and Solidification
After the injection is completed, the medium pressure is maintained until the solidification is completed to achieve dynamic shrinkage compensation.
This process improves the internal density of the casting and effectively avoids central looseness and micro-shrinkage cavities.
Demolding and Cooling
Medium pressure casting has a moderate injection speed (faster than LPDC and slower than HPDC), small mold temperature fluctuations, and low stress concentration during demolding.
The cooling process is easy to control, the dimensional shrinkage is uniform, and high-precision complex geometric structure castings can be stably achieved.
Main Advantages of Medium Pressure Die Casting
Balanced Pressure and Filling Speed
MPDC controls the injection pressure in the range of 4–20 MPa, and the filling speed is moderate, which is faster than LPDC to improve efficiency and lower than HPDC to avoid air entrainment and flash.
Stable filling reduces turbulence and can effectively reduce casting defects.
Better Mechanical Properties
Continuous pressure holding, filling, and solidification can effectively eliminate micro-shrinkage pores and central looseness, making the aluminium alloy die casting dense and uniform.
Test data shows that the tensile strength of MPDC castings is often higher than 240 MPa, and the fatigue life is also better than traditional LPDC parts.
Higher Dimensional Accuracy
MPDC can accurately control the injection speed, holding time, and mold temperature, and the die casting mold thermal balance is stable, so the casting dimensional accuracy is higher.
The tolerance of castings can be controlled within ±0.3 mm, which can effectively reduce the need for subsequent machining and improve overall production efficiency.
Extended Mold Life
MPDC has moderate injection speed and pressure, and will not repeatedly impact the mold surface like HPDC.
Under long-term operation, the mold has fewer fatigue cracks, and the service life is generally increased by 30-50%.
In addition, the medium-pressure system has low dependence on lubricants and cooling water, and the mold maintenance cycle is longer, and the cost in lower cost.
Suitable for Complex Structures
The controlled flow rate and medium-pressure system can reliably fill mold cavity areas with thin walls (<2.5 mm), deep cavities, or closed structures.
Compared with the problem of insufficient filling of LPDC or the problem of HPDC exploding the mold, MPDC takes into account both filling integrity and mold safety, and is the preferred process for complex structural castings.
Comparison of MPDC, LPDC, and HPDC
|
Feature |
LPDC | MPDC | HPDC |
| Pressure | 0.1–2 MPa | 4–20 MPa |
>20 MPa |
|
Fill Rate |
Slow | Moderate | Very Fast |
|
Surface Quality |
Good | Better |
Best |
| Porosity Level | Higher | Lower |
Lowest |
|
Dimensional Accuracy |
Moderate | Good | Excellent |
| Mold Wear | Low | Medium |
High |
|
Part Cost |
Low | Medium | High |
| Ideal Volume Range | Low–Medium | Medium |
High |
Injection Pressure
The injection pressure of MPDC is between 4–20 MPa, which is much higher than the 0.1–2 MPa of LPDC and is sufficient to efficiently fill complex molds.
But at the same time, it is lower than the 20–120 MPa of HPDC to avoid turbulence, air entrapment, and mold impact caused by high speed.
Production Cycle and Output
The typical LPDC cycle is 2–5 minutes/piece, MPDC is 1–3 minutes/piece, and HPDC can reach 30–60 seconds/piece at the fastest.
MPDC improves production capacity while maintaining good process controllability, and is suitable for medium-volume orders of 10,000 to 50,000 pieces per year.
Surface Quality and Defect Rate
The surface roughness of MPDC castings can reach Ra 3.2–6.3 μm, which is better than LPDC (Ra 6.3–12.5 μm) and close to HPDC (Ra 1.6–3.2 μm).
At the same time, due to the smooth filling process, MPDC is significantly better than LPDC in controlling defects such as cold shut, pores, and inclusions.
Cost Factors
The mold and operating costs of MPDC are usually between LPDC and HPDC.
Compared with LPDC, it can bring better mechanical properties and finished product consistency; compared with HPDC, it can avoid a high initial investment.
For projects with limited budgets but certain quality requirements, MPDC is the preferred process solution that takes into account both performance and cost.
Typical Applications of Medium-Pressure Die Casting
Automotive Structural Parts
MPDC is suitable for parts with uneven wall thickness and complex structures, such as chassis brackets and engine housings.
Compared with LPDC, it has better mechanical properties, and compared with HPDC, it has less mold wear and lower cost, which is the preferred solution that takes into account both strength and economy.
Aerospace Parts
Structural parts such as support seats and frame joints have high requirements for dimensional accuracy and density.
MPDC can achieve low porosity and good structural consistency through stable medium-pressure injection and pressure-holding solidification.
It is more suitable for load-bearing parts than LPDC and more economical than the HPDC solution.
Industrial Equipment Parts
Parts such as pump bodies, valve shells, gear chambers, etc., often have complex structures and moderate batches.
They require high mechanical stability but are not suitable for frequent mold changes.
MPDC strikes a balance between mold life and precision, and is particularly suitable for periodic orders and small batches of multiple varieties.
Customized Aluminum Castings
Custom aluminum castings for OEMs often involve complex cavities, reinforcing ribs, or closed structures, and the batch is not enough to spread the HPDC mold cost.
MPDC can stably fill complex cavities at 4–20 MPa to ensure structural integrity, and is suitable for product development, trial production, and medium-batch conversion stages.
Conclusion
Medium-pressure die casting achieves the best balance in strength, precision, and efficiency.
It combines the low cost of LPDC and the high efficiency of HPDC, with fewer casting defects and more stable performance.
As a professional aluminum alloy die casting manufacturer, CEX Casting provides high-quality, customized aluminum alloy die casting solutions.
Welcome to contact us to discuss the needs of your next aluminum die casting project.