In high pressure die casting, first, you create a mold in the shape of the toy. Then, you melt metal until it’s liquid, like water. Using a big machine, you quickly force the hot, liquid metal into the mold with a lot of pressure. The metal cools down and becomes solid, taking the shape of the mold. Finally, you open the mold and pop out your brand new metal toy! That’s high pressure die casting in a nutshell.

HPDC is expected to grow $55.34 B by 2030. The causes of its rise are small to large volumes of industrial applications, such as car parts or electronics.

Learn more about this process and its relevant parameters, such as techniques, designs, optimization, etc., in this article.

Principles of High-Pressure Die Casting

The manufacturers start pressofusione ad alta pressione with some initial preparations. This preparation includes cleaning mold (posting and blowing) and locking it tightly (module lock). Then, they pour the molten metal into the container.

Injection systems mounted on the machinery pump the metal toward the mold at 10 MPa to 150 MPa. This system may pass through in three phases.

During filling, apply low pressure at the first phase, increase speed and pressure at the second phase, and maintain consistent pressure at the third phase.

The solidification step converts the molten particle into hard form. It shapes them according to the item profile. At last, manufacturers open the mold and remove the solid metal part.

Role of Molten Metal Characteristics

You should maintain viscosity and high fluidity in molten metal around 1-10 mPa·s and 20-50 cm flow distance, respectively. It will smoothly fill mold inside substances. Further, maintain a temperature of 20–30 °C above the melting point to adjust these parameters.

While speaking of melting points of metal, these vary. For example, aluminum has 660°C, zinc has 419.5 °C and magnesium has 650 °C. So they need steady heat.

Impact of Alloy Systems

The most common alloy types of HPDC are aluminum, magnesium, and zinc. But they are different in nature and attributes. For example, aluminum contains 2.7 g/cm³ density and is light in weight. You can use it for structural parts like engine blocks or gear housings.

Conversely, magnesium has a 1.7 g/cm³ density. It is also lighter. This is usually used for car seat frame kinds of parts.

While zinc has a 7.1 g/cm³ density and can cost you $1.80/kg. It is a good option for small or detailed parts like connectors and brackets.

Cooling Channels and Solidification Rate

Try to maintain the temperature of cooling channels in the mold at about 200-300 °C. This range is suitable to get optimal results. For example, it reduces thermal stress, improves grain structure and increases part strength and quality.

Additionally, applying faster cooling minimizes the grain size. It gives strength to parts and creates smooth surfaces.

For example, when manufacturers produce aluminum parts by applying a cooling rate of 250 °C, they witness that they have 20% higher tensile strength than slower cooling.

Shot Weight and Its Significance

Adding the right parameters of shot weight (metal amount) into the mold reduces defects. Typically, 80–95% of the mold cavity’s volume. You must measure the molten metal before injection.

Maintain the shot weight amount higher than the part weight around 2 to 3 times. Because overflows, runners or sprues can waste it.

HPDC Techniques for Improved Casting Quality

1.   Vacuum Casting

During vacuum casting, the die-casters melt the ingot in a furnace. They transfer this molten metal into a vacuum chamber using a plunger. The metal is then pushed toward the steel die under a vacuum level of 50–100 mbar. After cooling, you will get your near-net shape part by opening the mold halves.

Vacuum in the die cavity here eliminates air and certain defects. This is the built-in method. It minimizes air entrapment. That can weaken your material.

It is better than the traditional HPDC method. The setup of vacuum casting may cost you $200,000 and offer a cycle time per part of about 1-2 minutes.

2.   Squeeze Casting

In the squeezing method, the manufacturers first melt the metal in a crucible and then pour it into the die under high pressure (typically 100–150 MPa). They fill the entire section completely by pressing the punch.

This punch part helps in removing any presence or causing air gaps from the mold. Ejector pins mounted to the mold push out the molded part when it cools and solidifies.

Squeezing casting can make dense parts like engine blocks and gearbox housings. However, it needs a longer cycle time (2 to 4 minutes) and more investment up to $250,000. It fully utilizes liquid. You can use the squeezing casting method for strong parts like engine components.

3.   Semisolid Die Casting

For semi-solid die casting, prepare metal slurry using the gas-induced method. The slurry must be partially in liquid form and a partially solid fraction (30–70%). Then, charge this slurry via shot systems into the die.

The clamping systems of dies remain locked tightly until the metal is filed evenly and shapes the product.

Maintain the parameters, like processing temperature just below the melt’s melting point and pressers of 50 to 100 MPa.

The combination of casting and forging differentiates this process from vacuum and squeezing castings. It may require a $ 300,000 to $400,000 budget and take 1 to 3 per unit cycle.

You can use this process to make microstructure parts. Because this is best for giving them the needed strength and precision.

Limitations and Challenges

1. Colata sotto vuoto: This process costs high investments of around $200,000. You may face difficulties in creating thin-walled components with this technique. Because it does not support thickness below 3 mm. Moreover, you cannot make a highly intricate part. For example, parts that include undercuts or sharp corners and whose complexity exceeds 7-8 on a 10-point scale cannot be obtained via vacuum casting.
2. Squeeze casting: It makes your production cycle slower by up to 20-30% than vacuum casting. The squeeze casting is costly for small-run industries (setup costs around $250,000). Also, this process cannot produce thin-walled parts below 4 mm thickness. Further, it does not let you produce complex shapes, like intricate lattice structures.
3. Semisolid die casting: The semisolid process is costlier than both vacuum and squeeze casting. It is limited to specific alloys suitable for semisolid states. Additionally, it demands hard struggles from you if you want to make parts with thicknesses below 5 mm. Semisolids also do not facilitate extreme geometries exceeding a complexity level of 9 on a 10-point scale.

Die Design and Manufacturing for HPDC

Factors Influencing Die Life

You should know that thermal cycling occurs with temperature changes of 200-400 °C. It causes cracks.

Likewise, if you push the metal at speeds over 50 m/s, it wears the surface. That leads to erosion.

Some other factors that occur in metals over time include corrosion, rust, strength, and weakness. These impacts happen because their metals often contain more than 2% chlorine. It reduces die life by 30–50%.

Importance of Venting and Cooling

Optimize venting systems to reduce air escapes during casting. These settings must maintain airflow rates of 100-150 cm³/s.  Avoid overheating and maintain the die temperature process. For this, set the cooling channels between 200°C and 250°C.

Additionally, an overlooked issue, such as thermal stress, occurs when you fail to regulate temperature differences that exceed 50 °C. That causes cracking and warping in the die.

Gating and Risering

Gating acts as the pathway in die. they control the flow of liquified metals with runners thickness of  5-10 mm. Meanwhile, the risers in machining setups are there to fill die substances evenly. It uses a diameter of 20–30 mm. The improper alignment of these factors can cause porosity in products.

Die Materials for Different Alloys

This is the most important aspect here to consider. Try to choose the strongest alloy for making a die while keeping in mind the produce metal being cast. For example, steel, copper, or aluminum.

However, steel is mostly used in dies because it is strong and can bear high temperatures. Copper is a good metal that can transfer heat efficiently in parts. Aluminum is always available to make light parts.

Die Manufacturing Processes

You can make dies using two methods. Among them, one is Electrical Discharge Machining (EDM), and the other is lavorazione CNC di precisione.

The EDM process is suitable for making dies with cuts that are as minimal as 0.01 mm. It vaporizes material using electrical discharges.

With CNC, the manufacturers integrate automated tools to make complex shape dies. This process is good for prototypes and shapes with tolerances up to 0.1 mm.

Die Coatings

Do you know applying coatings like ceramic or electroplating on a die can improve its life by 30–50%? You can do ceramic coatings on parts that are supposed to be exposed to over 300 °C. However, electroplating can increase the durability of the surface and the finishing of dies.

Process Optimization and Control in HPDC

Part Analysis

Analyze the part and check the practicality of the casting design. Focus on its wall thickness (typically 2–5 mm) and draft angles ( 1-3 degrees) for smooth ejection. This phase demonstrates the actual error areas and stress points to you.

Parting Surface

Keep the parting surfaces flat, or make sure it follows natural contours. This will decrease flash and allow easy removal of the casting. It also reduces machining time by 20–30%.

Mold System Design

The main components of mold designs can be gates, runners, and vents. Optimize them for uniform flow. For example, runner length (100-200 mm) and gate thickness (5-10 mm) can make your output defect-free production.

Optimization of Process Parameters

Process parameters include injection velocity (4-6 m/s for uniform filling), holding pressure (500-800 bar), and cooling rate (20-50 °C/s). You must set them appropriately to make parts with accurate dimensions and be error-free.

2D Documentation and Manufacturing

2D technical drawings help you to follow design details and minimize defects. For this, manufacturers use CNC machining and EDM for dies. That way,  they can achieve tolerances up to 0.01 mm.

HPDC Simulation

In HPDC, computational fluid dynamics (CFD) simulation and finite element analysis (FEA) are useful. They can handle thermal, flow, and stress in mold designs. Moreover, you can decrease lead times with them by around 40%. They further improve the first-time quality.

Adaptive Control and SPC

Adaptive control systems include AI algorithms. You can modify process settings dynamically with them. Also, it helps you reduce material waste by 20–30%, reduce production costs, and improve quality.

Similarly, using statistical process control (SPC), you can monitor and control production. It helps manufacturers make consistent outputs by analyzing data trends. They can also remove variability in critical parameters.

Real-Time Process Control

You can now adjust the settings during casting via sensors and actuators. Thermocouples measure the temperature of metals (200°C-450°C).

Transducers convert physical quantities of injection pressure (500–1200 bar) into electrical signals. Hence, adopting real-time process control allows you to maintain parameters instantly.

Conclusione:

Manufacturers use the high-pressure die-casting method to make parts with good details. It is the fastest technique. That can convert molten aluminum, zinc, or magnesium metal into various-shaped application parts. However, developing a perfect die is important. Because it has a direct impact on the final output results. So try to use advanced tools like AI, FEA, CFD, etc., to instantly adjust the parameters of HPDC.