Die casting is a part manufacturing method that is similar to injection molding, except that the primary material is non-ferrous metal alloys like aluminum, magnesium, or zinc. The molten material is injected into the cavity of a reusable mold called a die under high pressure. When the molten metal solidifies, it takes the shape of the mold.
Die casting is valuable for producing precise parts with smooth surfaces, thereby minimizing the amount of post-processing required. This technique helps manufacturers to produce large quantities of identical, complex parts or small-to-medium-sized metal parts at the lowest possible price per part.
How Die Casting Works
In theory, there are just three or four steps to die casting. However, in practical, each step comprises numerous other processes that involve many hours of work from skilled engineers. The steps are mold creation, casting (which can be further divided into metal injection and solidification), part ejection, and post-machining.
- Mold creation: The die, a permanent mold with a cavity designed to the shape of the desired part, is made using steel.
- Casting: Molten metal is manually or mechanically fed into the die cavity at high pressure. The metal is allowed to cool and harden within the die.
- Part ejection: The die is opened, and the hardened metal part is ejected.
- Post-machining: This is mostly required after the casting of net-shape parts. Precision machining will be required to cut out holes.
It is important to mention that there are two main types of die casting, namely Hot-chamber and Cold-chamber. The way they work is slightly different, particularly how the molten metal is delivered to the mold.
Hot-chamber die casting
This is a self-contained system where the machine contains heating equipment for bringing the metal to a molten state. The injection mechanism automatically sips the molten metal from the furnace into the die cavity. It is best for metals with low melting points, like tin, magnesium, and lead alloys. Hot-chamber is characterized by fast cycle times, which makes it a great choice for high-volume productions.
Cold-chamber die casting
These machines usually have a separate furnace where the heating is done, and the molten metal is manually ladled from the furnace to the injection system, where a hydraulic piston forcefully injects it into the die cavity. The separate furnace has a higher temperature, which allows for the molting of metals with higher melting points, e.g., aluminum, copper, and brass. Its cycle time is slower compared to the hot-chamber mechanism.
Reasons to Choose Die Casting
If your project involves the production of high volumes of complex and precise metal parts, die casting would be the best fit. It is particularly suited for manufacturers working on a tight budget. The technique makes the creation of parts with integrated functionality possible.
| Production expectation | What does die casting offer |
|---|---|
| High volume project | A hot-chamber is particularly efficient in the mass production of identical parts. |
| Precision with complex geometries | Forms intricate shapes with tight tolerance and thin walls, which is difficult to achieve with other methods |
| Durable parts | Die-cast parts maintain their rigidity, shape, and dimension over time |
| Great surface finish | The high pressure of die-cast parts leaves a smooth surface finish that requires minimal post-processing. |
| Lightweight parts | Die casting is perfect for working with high-strength, lightweight metals like aluminum, zinc, and magnesium. |
| Integrated features | Fastening elements like studs and bosses, cast-in threads, and cored holes for tapping can be integrated into the cast to make assembly simpler and lower costs. |
| Cost effective | In the long term, the technique pays for its initial tooling cost through high production rates. |
Applications of Die Casting
Die-cast parts can be found across a broad range of industries, including the structural parts of airplanes, the complex and precise engine blocks of automobiles, heat sinks of consumer electronics, and the list goes on. Its broad range of applications is due to the versatility of the process, detail, repeatability, and the long list of material options.
| Industry | Application |
|---|---|
| Automotive | Aluminum die casting is used for engine blocks, pistons, gears, and transmission cases. Die-cast zinc is used for power steering, brake, and fuel components Magnesium die casting is great for seat frames and panels |
| Aerospace | Critical components of aircraft and spacecraft benefit from the high strength-to-weight ratio and lightweight of die-cast aluminum. |
| Electronics | Used for making casing or housing for many electronic devices. Die-cast magnesium is popular for thin-walled shielding RFI/EMI components. |
| Construction | Window frames, door hardware, and building facades can be made with aluminum die casting. |
| Energy | Filtration parts, valves, wind turbine blades, and other energy components can be die-cast. |
| Home appliances | Parts of washing machines and refrigerators are made from aluminum die casting. |
| Medical | Components of monitoring devices, ultrasound systems, and surgical instruments are made using this technique. |
| Recreation | Toys like scaled models of cars are sometimes made from die-cast zinc alloys. |
| Machinery | Bodies of valves, pumps, and various machine parts are made using this technique. |
| Telecommunications | Computer parts, including heat sinks, are made through die casting |
Top 5 Materials for Die Casting
Aluminum, zinc, magnesium, copper, and lead alloys are the most commonly used materials for die casting. They bring unique properties to the project or confer beneficial properties to the product, including lightweight, machinability, corrosion resistance, and strength. The exact choice of material will depend on the project’s unique needs.
1. Aluminum alloys for die casting
This is the predominant metal used with this molding technique. They are lightweight and the primary choice for complex, polished parts because they offer great dimensional stability. Other properties they confer on the product include temperature and corrosion resistance, as well as electrical and thermal conductivity. Below are the different aluminum variants and their properties.
| Aluminum alloy | Properties |
|---|---|
| A380 | General-purpose aluminum alloy with excellent fluidity and good mechanical properties (durability and strength) |
| A390 | High strength, dimensional stability at high temperatures, wear resistance, and low thermal expansion. Used for die casting automotive engine blocks |
| A413 | Excellent pressure tightness, good wear resistance, high strength, and excels in the casting of complex shapes for demanding environments. |
| A443 | Aluminum alloy with 5% silicon. It possesses excellent corrosion resistance, high ductility, and good machinability. Its low strength makes it useful in ornamental components where corrosion resistance and ductility are more important than strength. |
| A518 | Aluminum-magnesium alloy with excellent ductility and finishing. It has superior corrosion resistance compared to A380, but lower die-filling capacity and castability |
2. Zinc alloys for die casting
Zinc alloys have great castability, particularly in a hot-chamber. They offer numerous benefits to the products, including ductility, impact strength, and suitability for plating with other materials. It is usually alloyed with copper, aluminum, or magnesium to achieve unique properties. Commercially available zinc alloys used in die casting are listed in the table below.
| Zinc alloy | Properties |
|---|---|
| Zamak 2 | A zinc-aluminum alloy with 3% copper content, known for its high strength and hardness. It offers good vibration damping, easy post-processing, and wear resistance. |
| Zamak 3 | Contains 4% aluminum and traces of copper and magnesium. It has superior castability and long-term dimensional stability. |
| Zamak 5 | Zinc-aluminum alloy with added copper that offers enhanced hardness and strength compared to Zamak 3, while sacrificing ductility |
| Zamak 7 | A modification of Zamak 3 with lower magnesium content, leading to better ductility and casting fluidity. A small amount of nickel is added to reduce intergranular corrosion and control impurities. It is ideal for casting thin-walled components |
3. Magnesium alloy for die casting
Magnesium alloy is lighter than aluminum and brings the extra benefit of being highly machinable. This makes it the best metal choice for products that require additional details. These alloys work best with a hot-chamber. It is often alloyed with silicon, manganese, zinc, and aluminum. The common magnesium alloys used in die casting are highlighted below.
| Magnesium alloy | Properties |
|---|---|
| AZ91D | Contains around 1% zinc and 9% aluminum and offers good corrosion resistance, high strength, and excellent castability |
| AM20 | Offers high impact strength and ductility. It contains manganese and aluminum, making it lightweight for mechanical and structural components. |
| AM50A | Has excellent ductility, castability, good strength, and superior energy-absorbing properties. Primarily used in automobiles for steering wheels, seat frames, and brackets. |
| AM60B | Offers excellent toughness and ductility, and is mostly used for automotive steering wheels and seat frames. It has moderately low tensile strength compared to others. |
| AS41B and AE42 | Rare earth allows for enhanced temperature resistance, as well as good corrosion and creep resistance, and ductility |
4. Copper alloy for die casting
Copper alloys are mostly used for parts where toughness is the primary goal because of their high strength, corrosion resistance, hardness, and dimensional stability. These properties make them suitable for marine components, auto parts, bearings, and faucets.
| Copper alloy | Properties |
|---|---|
| C87600 (silicon bronze) | An alloy of 88% copper and silicon. It has very low electrical conductivity and fairly low thermal conductivity. |
| C93200 (high-leaded tin bronze) | Composed of copper, lead, tin, and zinc. It possesses excellent wear resistance, is resistant to corrosion by seawater and brine and has great machinability. Balances toughness and strength, making it great for gears, bushings, and bearings |
5. Lead alloys for die casting
Lead-based alloys for die casting are mainly lead-antimony (Pb-Sb) or tin-antimony-lead (Sn-Sb-Pb). Their most desirable properties are high fluidity and low melting points, which make them suitable for casting parts with intricate details. Notwithstanding its excellent malleability, its use in die casting is usually limited to gears, weights (due to its high density), and specialized parts (like print wheels for postage meters) because of its high density, softness, and potentially lower mechanical properties compared to other die casting metals.
Die Casting vs. Other Methods and When to Choose What
Sand casting, investment casting, permanent mold casting, and centrifugal casting are the other possible alternatives to die casting. The presence of these alternatives can make it harder for manufacturer to decide the method that is best for their project. However, choose die casting if your project must meet the following criteria:
- Requires high-volume production of hundreds or thousands of identical parts
- Involves the production of complex shapes, like near-net-shape, with thin walls
- Requires high precision with excellent dimensional accuracy and consistency
- Needs the part to have a smooth surface finish
- Involves the use of different metal alloys
The table below shows how die casting compares to other casting methods and will guide you in choosing the right method for your project.
| Type of casting | Die casting | Sand casting | Investment casting | Permanent mold casting | Centrifugal casting |
|---|---|---|---|---|---|
| Production volume | High | Low | Low | Medium to high | High |
| Part size | Small to medium | Large | Large | Large | Very large |
| Complex designs | √ | √ | √ | × | × |
| High Precision | √ | × | √ | √ | √ |
| Smooth surface finish | √ | × | √ | √ | √ |
| Low budget | √ | √ | × | √ | √ |
Avoid These Costly Die Casting Mistakes
Numerous die casting design mistakes can be costly to the manufacturer. These mistakes can lead to defective products or products that will require higher post-processing to fix. One of the most common mistakes is a pit defect. This is a small cavity or void that can result from design flaws, including trapped air, inadequate venting, or uneven wall thickness.
Trapped air is often a sign of poorly sized or placed gates, which can lead to turbulence. Also, when part designs are too complex, it may hinder proper metal flow and cooling. To solve this problem, you must understand the flowability of each material and only use metals with excellent flowability for highly complex designs. Here is a checklist of design-related mistakes you must avoid:
- Sharp changes in wall thickness, which cause uneven cooling, shrinkage cavities, and other defects
- Insufficient draft angles, which cause parts to stick to the mold
- Creating parts with too complex design geometries
- Poor venting facilitates the trapping of air, leading to incomplete filling.
- Failing to account for metal shrinkage during solidification can lead to inaccurate dimensions.
There are also costly process-related mistakes that would hurt your production, including inadequate cooling, poor temperature control, unoptimized metal flow speed, and the use of insufficient or low-quality mold release agents. Performing filling and solidification simulations during the design process can help you identify these potential problems.
Factors To Consider When Choosing The Suppliers
By collaborating with a supplier early on in the project, you can leverage their expertise to overcome some of the common die casting pitfalls. Here is a supplier negotiation script that will help you choose the right partner.
| Factors to consider | Questions to ask |
|---|---|
| Design for Manufacturing (DFM) | Can the supplier help with optimizing your design for cost-effectiveness without killing quality? |
| CAD/CAM | Can the supplier create new designs using CAD/CAM? |
| Prototyping | Is the supplier willing to provide prototypes for testing? |
| Material Expertise | Can they guide you on the best material to meet the desired tolerance, strength, and surface finish of your part? |
The Megacasting Revolution in Electric Vehicles
The transition from gasoline to electric vehicles has had a significant impact on the die casting industry. Instead of the traditional welded small parts, EV makers are demanding large, single-piece cast components using high-pressure die casting.
Megacasting revolution has come with additional benefits, including simplifying assembly, cost savings, reduction of overall weight of parts, improved structural integrity, and faster production times. Tesla is one of the pioneers of this innovation with their “Gigacasting” factories.
The adoption of megacasting is making EVs more efficient and affordable by reducing part counts and complexity. For example, the weight reduction achieved through megacasting directly leads to better energy efficiency, which allows EVs to cover a longer distance on a single charge. Therefore, megacasting indirectly contributes to the reduction of range anxiety, which has always been a major obstacle to EV adoption.
How to choose a supplier
Several factors will come into play when it is time to choose a die casting supplier, starting with location. Due to uncertain geopolitics, you need to work with a supplier that will help you navigate supply chain disruptions on one hand and balance cost with performance on the other hand. The important factors to consider when choosing a supplier include:
- Define your goals: Before searching for a supplier, you need to map out what you need, including material, size, precision, and volume of the parts.
- Choose a location: Once you have a clear goal, determine a preferred supplier location that will be beneficial in both labor costs and logistics.
- Evaluate technical capabilities: To further trim your list of possible suppliers, evaluate their offering, including DFM, machining, testing labs, in-house tooling, and equipment automation.
- Verify their experience: Having sophisticated equipment is good, but knowing how to use it to achieve results is ultimate. Check the supplier’s certification and see what current or past clients are saying about them.
- Production capacity: Ensure the supplier can scale to handle your intended production volume to meet demand.
- Assess their communication efficiency: Working with a supplier that proactively communicates about the progress of the project will help you avoid misunderstandings and quickly fix issues as they arise.
In addition to meeting the criteria above, always choose a supplier like First Mold that has the capacity to effectively manage the entire process from alloy selection to tooling, finishing, and assembly.
FAQ
It is the process of forcing molten metal alloy under high pressure into steel dies to form shapes upon solidification.
Non-ferrous metals, including aluminum, zinc, magnesium, lead, tin, and copper, can be formed using this technique.
The two main types are the hot-chamber and cold-chamber, which define how the molten metal alloy is delivered to the die.
Die casting offers several benefits to manufacturers, including high production volume at the lowest possible price per part, sustainability through the use of recyclable materials, and improved part functionality.
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