Are strength and durability among your top priorities when fabricating components? If yes, structural die casting may be the best fit for you. Due to its remarkable results, it’s a top choice for several manufacturers building structurally sound and lightweight metallic products. Read on to find out all you need to know about this technique.
What Is Structural Die Casting?
Structural die casting is a form of die casting used in manufacturing various parts and components, with the focus being on the strength, structural integrity, and weight of the product.
The goal is to produce results similar to that of forging without having most of the common setbacks of casting. Hence, it’s common to use aluminum alloys for this process due to its innate properties. However, other elements may be suitable too.
Processes Involved In Structural Die Casting
These are the integral processes involved in creating components using this technique:
Prepare the Mold
Preparing the mold is an important part of the casting process, and is especially dependent on the designs of the part we intend to cast. In this step, the mold is heated and its inner walls are coated with a lubricant. This ensures that the cast products come off easily after cooling.
Melt the Metal Alloy
This step involves heating the metal alloy to get molten metal otherwise known as the cast. This heating happens in an industrial furnace, and the temperature of the furnace depends on the metal alloy in use. 
Injection
In this phase, we introduce the cast into the mold at a very high pressure. The high pressure ensures that the cast fills the mold uniformly to take its shape while eliminating gases and porosities that might be present.
Solidification and Cooling
This process involves gradually removing heat from the mold to allow the solidification of the molten metal. It is important to ensure there is proper structural integrity of the cast product. The rate of cooling also depends on the metal alloy and mold used.
Ejection
In the ejection phase, we carefully remove the solidified cast from the mold with the use of ejector pins. These ejector pins are specialized rods used in casting for pushing out the cast from the mold. This process is carried out with precision to prevent cracks and damage to the cast component.
Finishing and Inspection
Our main goal is to produce high-quality cast materials that meet the needs of our clients. Hence in this phase, we inspect the part to ensure there are no deformities. This step also involves all post-production processes we carry out to improve the quality of the cast components. This includes trimming, thermal treating, CNC machining, etc.
Types of Dies Suitable for Structural Die Casting
There are several dies available and suitable for use when carrying out structural die casting. We explore these in the following:
Single-Cavity Die
Single-cavity dies are molds with just one cavity, hence, they are only able to produce one cast product per production time. Since there is just one cavity, these molds are great choices for casting complex components where attention to detail is of the essence. It is also suitable for carrying out low-volume production.
Multi-Cavity Die
In a multi-cavity die, there are multiple identical cavities used in casting. This allows the production of more cast products at a time. Casting using a multi-cavity die allows for a shorter lead time, as manufacturers can produce more in less time. It is also the most ideal mold for carrying out high-volume production.
Combination Die
A combination die also has the ability to produce several cast products at a time. It has multiple cavities, but with different shapes, allowing for the production of parts. Its versatility makes it desirable for manufacturers that prioritize multiple operations at a time.
Trim Die
A trim die is a special kind of die with the machinery for trimming or removing the excess material from a cast product. This extra material is called flash. The type of die offers high levels of precision, making it suitable for parts with intricate designs and details.
Advantages of Structural Die Casting
This technique offers many benefits to manufacturers, some of which include the following:
Material Efficiency
Structural casting allows for excellent material management as there is little wastage in the casting process. Most types of casting also require little or no post-production processes; hence, materials are used more efficiently, making them desirable to manufacturers.
Strength and Durability
Structural die casting is popular for producing products with high tensile strength and the ability to resist wear and tear from corrosion, heat, chemicals, etc. It also offers us the choice of choosing different metal alloys to meet different needs.
Precision and Complexity
One major advantage of structural die casting over other manufacturing processes is that we can produce very complex parts with high precision. This is because the details of the mold are easily adjustable, and the cast automatically assumes the shape of the mold used.
Weight Reduction
This technique focuses on producing parts that are strong and lightweight. This is mostly because there is a wide range of metal alloys that are available for the manufacturing process. A perfect example is a high-grade aluminum alloy that offers high tensile strength and lightweight properties.
Economic With High Volumes
There is an array of dies to choose from when using this technique. Some of these dies, such as the multi-cavity, are labour and time saving. Overall, they are great for bulk productions and the investment to reward ratio will leave you at an advantageous position.
What Are the Different Variations of Structural Die Castings?
Low Pressure
In low-pressure die casting, the molten metal or the cast enters the mold cavity under low pressure. Because of the low pressure used in forcing the cast, there is a constant and uniform spread of the cast in the mold. This results in die casting structural parts that are strong and well-detailed. Low-pressure casting is also suitable for making large components having thinner walls.
Acurad
The name Acurad translates to accurate, reliable, and dense, and this type of die casting shows these qualities. It is similar to high-pressure casting and involves the use of special molds with intricate designs and details in producing high-quality parts with thin walls. Acurad casting also produces parts with an amazing finish, reducing the need for post-production modifications.
Pore Free
As the name suggests, pore-free casting is a form of casting we use in manufacturing parts that are devoid of porosities. We do this by first injecting an active gas like nitrogen into the mold, followed by the cast under high pressure. The high pressure displaces air from the mold, while the active gas reacts with the remaining air present and rises above the molten metal to be removed.
Semi-Solid
In semi-solid casting, we pour the metal into the mold in its semi-solid form rather than in its liquid form. This technique is especially used when working with alloys of very high melting points such as copper and magnesium.
Semi-solid casting offers both benefits of casting and forging, such as high mechanical strength, smooth surface finish, improved grain structure, etc., making it suitable for use in the automotive and construction industries.
How to Minimize Defects in Structural Die Casting
Regulate and Control Injection
Using the right speed and pressure while introducing the cast into the mold cavity is relevant to avoid defects. This not only minimizes defects but also ensures all the products are consistent with each other.
Parameters
Different parameters are used when casting different components and are necessary for producing the best quality cast product. These parameters include the melting temperature, injection speed, injection pressure, cooling rate, etc.
Proper Cooling
The practice of proper cooling when carrying out structural casting drastically minimizes the occurrence of defects like cracks. This involves the use of special cooling channels that regulate the temperature of the mold allowing for even cooling and solidification.
Regular Maintenance
As with other forms of manufacturing, regular maintenance is important to ensure favorable outcomes. This includes cleaning the die regularly, checking for dents and cracks, optimizing the cooling systems, etc.
Extensive Operator Training
Engineers in charge of the die casting should have sufficient training and information to effectively perform different casting techniques. They should also be able to spot possible defects and make corrections when possible.
What Is “Skin Effect” in Structural Die Casting?
The Skin Effect is a common phenomenon we see during casting where the outer layer of metal in contact with the mold is stronger than at the core. This happens because the cast at the outermost layer cools and solidifies more quickly than at the core, making it more dense and stronger.
This die casting skin effect offers both benefits and drawbacks to manufacturers depending on the application. This effect can increase the overall strength and durability of the cast product, especially in cylindrical-shaped parts. This, however, makes the product more prone to internal defects like porosities and cracks, causing it to fall apart.
We can, however, manage this “Skin effect” by preheating the die, ensuring a cooler mold does not interfere with the rate of cooling of the outer layer. Post-casting modifications like annealing also improve the structural integrity of the entire product.
Limitations of Structural Die Casting
Environmental Impact
Structural die-casting negatively impacts the environment in different ways. This includes the generation of scrap metals, which are byproducts of the casting process. Casting also requires a steady input of high energy needed in heating the metal and in powering different machines. This results in harmful gases that are unfit for the environment.
High Start-up Cost
The materials, such as dies and casting machines used in structural casting, are very expensive, and so is a major limitation, especially for first-time manufacturers trying to start up. Coupled with this, first-time productions are usually associated with more wastage and additional costs.
Material Limitation
The casting process is mostly limited to the use of non-ferrous metals and their alloys because of their lower melting points, compared to ferrous metals with higher melting points. This significantly limits the products that are made using casting.
Limited Defect Control
Structural die casting, as with other types of casting, is more prone to structural defects including porosities, cracks, surface defects, etc.
Technological Advancements in Structural Die Casting
Lightweight Alloy Development
Previously, most structural die-casting operations were carried out using just aluminum and zinc alloys. However, there is now a wide range of materials, including alloys of magnesium and titanium, offering more varieties to manufacturers with different needs.
Automation
The use of robots and other automated sensors is becoming relevant in structural die-casting. It is especially important in quality control where there are possibilities of die casting defects. They will arrest the issue early, preventing future challenges that would be both financially and timely expensive.
3D Die Manufacturing
With the advent of 3D printing, dies with very intricate designs and patterns can now be 3D printed. This reduces the need for post-production modifications like CNC machining, leading to more material efficiency while remaining cost-effective.
High-Vacuum Die Casting
One major limitation of casting is the presence of porosities. However, you can use specialized high-power vacuums to reduce the amount of air present in the mold before pouring in the cast. This significantly reduces the presence of porosities, resulting in more structurally strong parts.
Advanced Cooling Systems
Advanced cooling systems in structural die casting focus on cooling the cast both rapidly and uniformly. This ensures the production of high quality materials while eliminating common defects commonly resulting from uneven cooling.
Common Applications of Structural Die Casting
Aerospace Industry
As mentioned above, structural die casting focuses on the production of lightweight yet strong materials. This makes it an excellent option for manufacturing components of aircraft with high strength-to-weight ratios, such as gears, engine parts, etc.
Construction and Architecture
Construction and architecture continually depend on materials with high tensile strength and resistance to fatigue. Structural die casting offers not only this but also the ability to customize aesthetic designs using different molds.
Industrial Machinery
Just as in the aerospace industry, structural die-casting produces high-quality strong materials capable of bearing loads under tension. This makes it suitable for making components such as gears, engine blocks, fasteners, etc.
Military Applications
Structural die casting finds heavy usage in military applications because of its mechanical properties, including its high tensile strength and resistance to fatigue that military equipment are constantly exposed to.
Conclusion
Structural die casting finds applications in several industries and offers a variety of benefits. This technique, however, relies on technical skills and the best quality of materials available. This is why you should trust Hmaking for all your structural die cast parts. Contact us now to get started.