Time to read: 6 min
Low-pressure die casting (LPDC) is a permanent-mold process frequently used for casting high-quality aluminum products. It occupies a middle ground between gravity-fed and high-pressure die casting in terms of tooling cost, process speed, and mechanical and metallurgical quality.
What Is Low-Pressure Die Casting?
Low-pressure die casting is a casting process that uses permanent molds (dies) and applies a low positive pressure of 0.3–1.5 bar to slowly push molten metal into the dies. The controlled, low pressure minimizes turbulence and air entrapment as the metal fills the mold. This casting approach is valued for its ability to produce cast components with minimal porosity and heat-treatable properties.
The technique is most commonly used with aluminum alloys, since LPDC suits metals with relatively low melting points. This is because it is easier to keep a low-melting-point alloy hot enough to remain liquid in the crucible as the mold slowly fills. Low-pressure die casting uses permanent molds which can be manufactured with multiple cavities to increase the number of parts made per injection. Reusable tooling also decreases the tendency for part-to-part and run-to-run variation. The higher metallurgical quality of LPDC castings outweighs the additional time required compared to HPDC, making it a viable production method.
How the Low-Pressure Die-Casting Process Works
Step 1: Melt Preparation and Mold Preheat
The first step in the LPDC process is to prepare the molten alloy (e.g., A356). The metal is heated in a crucible to about 150°C above its melting point. The melt must then be degassed, primarily to release trapped hydrogen. Hydrogen gas within the melt will cause porosity in the finished casting. Rotary degassing or bubbling an inert gas (such as argon or nitrogen) through the molten metal allows hydrogen to diffuse into the gas and be released.
Temperature control of both the molten metal in the crucible and the receiving molds is important. If the melt temperature is too low, the die may not be completely filled before the metal begins to solidify. If the temperature is too high, there may be shrinkage after casting. For that reason, the melt needs to be controlled to a particular temperature, typically within the range of 700-730°C for alloys like A356. The dies are also typically preheated to 200-350°C.
Molten metal degassing
Step 2: Pressurized Filling
The next step is to fill the mold (die). This is accomplished by applying pressure to the holding chamber below the die using nitrogen gas. Pressurizing this chamber pushes the molten aluminum up through the riser tube and into the mold. The key advantage of low-pressure die casting is that the low gas pressure allows the filling to be done slowly, with little turbulence. This reduces the potential for trapped air, oxide formation, and porosity, resulting in a higher quality casting.
Step 3: Solidification Under Pressure
Once the die has been carefully filled, the pressure in the holding chamber is maintained during cooling. This sustained pressure helps to reduce porosity caused by shrinkage.
Step 4: Ejection and Finishing
Once cooling is complete, the part is ejected from the dies. At this point, any required finishing steps can be carried out. Usually, this includes trimming of excess material at the die interface and vents, as well as some machining.
A key aspect of LPDC is that the resulting castings can be heat-treated to improve mechanical properties. Low-pressure die casting provides parts with much lower porosity than high-pressure die casting. Therefore, the LPDC parts can be heat-treated, whereas the HPDC parts have larger volumes of trapped gas and are more complex and risky to heat-treat.
Advantages of Low-Pressure Die Casting
LPDC offers several advantages over high-pressure die casting. The primary advantage is that a much lower volume of gas is trapped during the slow filling of the die, delivering the following benefits:
- Lower rate of defects
- Improved surface finish
- Better mechanical properties
- Ability to heat treat parts to improve mechanical properties
- Good dimensional accuracy
Why LPDC Improves Mechanical Properties
Parts produced with LPDC tend to have better mechanical properties than those produced with HPDC because the lower applied pressure results in a slower, more controlled filling of the mold. This produces less turbulence as the molten metal flows in. The lower turbulence in LPDC mold filling leads to less gas entrapment than in high-pressure die casting, resulting in much lower porosity in the finished part.
Lower porosity is the primary advantage that underpins the other benefits. The parts have higher density and better, more consistent mechanical properties, resulting in improved fatigue resistance and overall performance. The more limited gas entrapment in LPDC castings also means that the parts are more suitable for heat treatment for stress relief, or to otherwise develop a more desirable microstructure.
Low-Pressure Die Casting (LPDC) vs. High-Pressure Die Casting (HPDC)
The table below compares the two die-casting processes, LPDC and HPDC, highlighting differences across several performance and production metrics.
Comparison of LPDC and HPDC
| Feature | LPDC | HPDC |
| Filling pressure | Low | Very high |
| Porosity | Lower | Higher* |
| Mechanical properties | Better | Moderate |
| Cycle time | Slower | Faster |
| Thin-wall capability | Moderate | Excellent |
| Heat treatability | Often suitable | Often limited* |
| Production speed | Medium | Very high |
LPDC is selected when high-quality parts with good mechanical performance are required, whereas HPDC is chosen for high-volume production applications. Both processes have strengths when utilized in suitable applications. LPDC can have a higher percent yield than HPDC, but this varies depending on the design and processing.
*Vacuum-assisted HPDC is becoming increasingly common and improves heat treatability by reducing internal porosity, which can cause blistering and distortion under high temperature.
Limitations of LPDC
Although we have focused on its advantages, LPDC does have some obvious limitations, as with any production process:
- LPDC has a relatively slow cycle time, so it is not well suited to high-volume production of commodity parts.
- Minimum wall thickness is not as thin as for HPDC.
- LPDC requires more complex equipment and tooling than gravity casting, though equipment needs and tooling costs are still lower than for HPDC.
Materials Used in Low-Pressure Die Casting
LPDC is most commonly used for the casting of aluminum alloys. Aluminum alloys have the advantage of a high strength-to-weight ratio. They are also broadly corrosion-resistant, forming a natural oxide layer, which can be further enhanced by anodization. These alloys are easily castable because of their low melting point and viscosity. Many aluminum alloys, depending on their composition, can also be heat-treated.
Common Alloys Used in LPDC
| Alloy | Relative Properties | Typical Uses |
| A356 | Most common (~7% Si, 0.35% Mg) | Wheels and housings |
| A357 | Higher magnesium, higher strength, lower ductility | Higher-strength structural and safety-critical parts such as suspension components |
| AlSi10Mg | Higher silicon, better flowability for complex parts | Structural applications and complex geometries such as engine components |
Other alloys with relatively low melting points can also be cast using LPDC. For example, magnesium alloys (such as AM 50 and AM60) and copper alloys (tin bronzes) can be cast using this production approach.
Design Guidelines for LPDC Parts
There are a few simple principles that should be kept in mind when designing parts for LPDC:
- LPDC works best when designs minimize abrupt thickness changes that can create uneven cooling and shrinkage defects.
- Plan for uniform wall thicknesses throughout.
- Consider how cooling and solidification will be controlled to avoid isolated hot spots. Design intent should consider that LPDC favors bottom-up solidification.
- Use sufficient draft angles for ejection from the die, and include ribs for structural stiffness.
- Include fillets and smooth transitions to avoid stress concentrations, and consider allowances for machining.
Learn more DFM tips in our Die Casting Design Guide.
When to Choose Low-Pressure Die Casting
LPDC is a strong fit for your project in the following cases:
- When mechanical performance is important, such as for automotive wheels, suspension knuckles, and control arms.
- When you expect to need to apply heat treatment to improve mechanical properties.
- When low porosity is required, particularly for pressure-tight and leak-sensitive applications, such as pump housings and fluid containment systems.
- When surface finish is important.
- When dimensional accuracy and consistent density are required, such as rotating components and structural automotive parts.
- When production volumes are medium-to-high.
Do you need help determining whether LPDC is right for your part? Talk with Fictiv’s manufacturing experts.
If your project doesn’t meet these requirements, you could consider alternative manufacturing processes:
- HPDC if mechanical performance, porosity, and heat treatment are not as critical.
- Gravity casting if the parts have thick walls, with a medium volume production run
- CNC machining if production volumes are low or higher precision is needed.
- Sand casting if the product is very large and requires less precision.
Learn more about other casting methods and how to transition from low-volume machining in our Scaling CNC to Casting Guide.
How Fictiv Supports Die Casting
Beyond experience with the die casting process, Fictiv has broader expertise, including DFM support and materials knowledge. Fictiv partners with you from the beginning, with prototype-to-production scaling experience and a manufacturing partner network that can assist at each stage, including secondary machining.
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