Die casting is becoming one of the most dependable methods in industrial technologies. Die casting is utilized to create a vast range of items that may be found in just about any industry or vertical you can think of.
Of course, like other metal fabrication methods, die casting goods will only be as excellent as the metals utilized in their manufacturing. The source metals will affect the finished product’s overall quality, durability, and visual look. This post will cover the many metals used in die casting and other vital things you need to know about the process.
Before getting into the best metals for die casting, let’s first speak a bit about the die casting process.
Table of Contents
What is Die Casting
To cast metal, die casting uses high pressure to force molten metal into a mold. It makes high-quality precision metal products that meet or exceed all specifications. Its capacity to generate detailed parts makes it excellent for the mass production of products. Die castings are created from non-ferrous metals such as zinc, aluminum, copper, magnesium, pewter, tin, and lead.
Die casting can be done in either a hot or cold chamber. The process used depends on the part and the type of metal. The cold chamber method is used with metals with a high melting point, like aluminum, copper, or brass alloys. Die casting in a hot chamber can only be done with metals that don’t melt when heated, like lead, magnesium, and zinc alloys.
Die casting is a fast and cost-effective way to make various shapes and parts. The parts that are made last a long time and can be made to look nice, giving designers many advantages and benefits.
Die casting is fast and makes complex shapes with close tolerances that don’t need extra work after they are made. There is no need to use more tools or change the shape. The final parts can stand up to heat and have high tensile strength.
Depending on the size and features, aluminum can hold tolerances of +/-.002″, while zinc can hold tolerances of +/-.0005″.
The Materials for Die Casting ( Die Casting Alloys )
Die casting is usually done with non-ferrous alloys that don’t contain iron. The low melting point and the strong mechanical properties are both caused by the non-ferrous part. It depends on the material being worked on and what properties are needed. So, there are no limits when it comes to choosing material. But here are a few well-known alloys:
Aluminum Alloys
Aluminum alloys have their own special qualities that make them helpful in making a wide range of things. On the one hand, aluminum alloy 380.0 is the most popular material used in die casting because of its unique properties. Aluminum Alloys 360, 390, and 413 are some other alloys. Below are the pros for the alumunum die casting. For more details, please check the article of <An Ultimate Guide for Aluminum Die Casting>
- Operates even in high temperatures
- Impressive corrosion resistance
- Lightweight
- Outstanding hardness and strength
- Full recyclability
- High electrical conductivity
- It keeps its shape even though its walls are thin
- Good strength-to-weight ratio and stiffness
- Corrosion resistant
- Excellent ability to block EMI and RFI
- Impressive finishing characteristics
- Diecast alloys can withstand the highest operating temperatures among all of them.
- Exceptional ability to transfer heat
- Full recyclability
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Zinc Alloys
Zinc alloys are strong, tough, firm, perform well, and are cost-effective. Because of this, they are an important part of the die-casting process. Their properties are similar to or better than those of aluminum, bronze, and magnesium alloys.
There are many ways to use zinc alloys. But the most common zinc materials for die casting are Zamak #2, #3, #5, #7, ZA8, and ZA27, which are known for the following:
- Made it easier to cast
- Cut down on cycle time
- Extended Die Life
- Ideal Mechanical Qualities
Magnesium Alloys
The process of diecasting can also be done with magnesium. It comes in many different alloys, but the most common one is AZ91D, which is known for being tough, durable, lightweight, and easy to cast. It is 75% lighter than steel and 33% lighter than aluminum, but it is still just as strong. Most hobbyists prefer magnesium because it is easier to cast into complex shapes with tight tolerances and less likely to rust.
Other Alloys
Brass, bronze, lead, and tin are some other alloys that can be used to make diecast parts.
Because of its high fluidity, tin was the first material used in die casting. It has a low melting point and wears down molds very little or not at all.
In the jewelry business, bronze (white bronze) is a suitable material for die casting. It has the same color as white gold and stainless steel alloys, but because its melting point is low, it can be used for die casting
The Process for Die Casting
Whether you use a hot or cold chamber, the standard die casting process is to inject molten metal under high pressure into a die mold. Here are the complicated steps of the process:
- Preparation & Clamping
- Transferring into a Chamber to be Injected into the Die
- Cooling and Hardening
- Ejection and Casting Out of the Die Cavity
- Cutting of Excess Material
Preparation & Clamping
The first step is to get the two halves of the die ready and clamp them together. Each half of the die is cleaned from the last injection and then oiled to make it easier for the next part to come out. The amount of time it takes to grease a part depends on how big it is and how many cavities and side cores it has.
Also, depending on the material, lubrication may not be needed after every cycle, but only after 2 or 3 cycles. After being oiled, the two halves of the die are closed and clamped together tightly inside the die-casting machine.
The die needs to be hit hard enough so that it stays closed while the metal is injected. How long it takes to close and clamp the die depends on the machine. Bigger machines with stronger clamping forces will take longer. This time can be guessed based on how long the machine takes to dry.
Transferring into a Chamber to be Injected into the Die
The molten metal, which is kept at a certain temperature in the furnace, is then moved to a chamber where it can be injected into the die. How the molten metal is moved depends on the type of die-casting machine, whether it is a hot chamber machine or a cold chamber machine.
After being moved, the molten metal is forced into the die at high pressure. Most of the time, the injection pressure is between 1,000 and 20,000 psi. This pressure is what holds the molten metal in place within the dies as it cools and solidifies. The shot is the amount of metal that is injected into the die.
The injection time is how long it takes for all of the channels and holes in the die to be filled with molten metal. This time is very short, usually less than 0.1 seconds, so that no part of the metal solidifies too quickly.
The thermodynamic properties of the material and the wall thickness of the casting can help figure out the right injection time. If the wall thickness is bigger, the injection time will need to be longer. When a cold chamber die casting machine is used, the injection time must also include the time it takes to manually pour the molten metal into the shot chamber.
Cooling and Hardening
When molten metal is injected into the die, it will start to cool down and harden as soon as it gets inside. The final shape of the casting is made when the whole space is filled and the molten metal cools. The die can’t be opened until the casting has had enough time to cool and become solid.
Several thermodynamic properties of the metal, the maximum wall thickness of the casting, and the complexity of the die can help figure out how long it will take to cool. If the wall is thicker, it will take longer to cool. Because there is more resistance to the flow of heat, the die needs more time to cool because of its complicated shape.
Ejection and Casting Out of the Die Cavity
After a certain amount of time has passed for the casting to cool, the die halves can be opened and the casting can be pushed out of the die cavity by an ejection mechanism. The time required to open the die can be roughly calculated based on the machine’s dry cycle time.
The ejection time is based on how big the casting envelope is and includes the time it takes for the casting to fall out of the die. Because the part shrinks and sticks to the die as it cools, the ejection mechanism has to use some force to get the part out of the die. After the casting is taken out, the die can be closed with a clamp, and ready for the succeeding injection.
Cutting of Excess Material
As the casting cools, the substance in the die’s channels will solidify and adhere to the surface. This extra material and any flash must be cut away from the casting. This can be done by hand by sawing or cutting, or with a trimming press.
The size of the casting envelope can be used to estimate how long it will take to cut away the extra material. The scraps left over from this cutting are either thrown away or used again in the die-casting process.
Before recycled material can be mixed with non-recycled metal and used again in the die-casting process, it may need to be reconditioned so that it has the right chemical make-up.
The Types Of Die Casting Process
All types of die casting are made with the same goal in mind – to pour molten metal into a mold. Depending on the type of metal being melted, the part’s shape, and the part’s size, different diecasting processes can produce better results than other methods. Die casting has 6 different types as below:
- Hot Chamber Die Casting
- Cold Chamber Die Casting
- Low-pressure die casting
- Semi-solid die casting
- Squeeze die casting
- Vacuum die casting
Hot Chamber Die Casting Process
Hot-chamber die casting is the more common of the two main diecasting processes, also called hot casting or gooseneck casting. The cylinder chamber of the injection mechanism is immersed in the molten metal throughout this procedure. A gooseneck metal feed system feeds the molten metal into the die cavity. With this method, parts can be made at a faster rate than with the cold-chamber method.
Direct immersion in the molten bath makes mold injection quick and easy, making the metal more likely to corrode. Because of this, the hot-chamber die-casting process works best with metals with low melting points and easy to flow. Lead, zinc, copper, and magnesium are all good choices for the hot-chamber diecasting process.
Cold Chamber Die Casting Process
Die casting with a cold chamber is much like die casting with a hot chamber. Melted metal is poured automatically or by hand into the injection system, which is made, so that machine corrosion is kept to a minimum instead of production speed. The injection mechanism doesn’t have to be put into the molten metal bath.
The cold-chamber process is a great alternative to the hot-chamber process when the immersion design of the hot-chamber process isn’t good enough for an application. One of these uses is casting metals with high melting temperatures, like aluminum and aluminum alloys.
Low-Pressure Die Casting Process
Low-pressure die casting is best for making aluminum parts that are the same on both sides of an axis of rotation. Low-pressure die casting is often used to make things like wheels for cars. In this process, the mold is placed vertically above the molten metal bath and connected to it by a riser tube.
When between 20 and 100kPa of pressure are put on the chamber, the metal is pulled up and into the mold. It is because there are no feeders used in this low-pressure aluminum casting process that it is able to produce such high casting yields.
The cold-chamber process is a great alternative to the hot-chamber process when the immersion design of the hot-chamber process isn’t good enough for an application. One of these uses is casting metals with high melting temperatures, like aluminum and aluminum alloys.
Vacuum Die Casting Process
Vacuum pressure casting, or VPC, is a relatively new method of die casting that makes parts stronger and less porous. This process is like low-pressure die casting, but the diecast mold and molten metal bath are in the wrong places. The chamber of the cylinder can be made into a vacuum, which forces the molten metal into the mold cavity. With this design, there is less turbulence, and less gas gets in. Vacuum die casting is beneficial for parts that will be heated after they are cast.
Semi-Solid Die Casting Process
Semi-solid die casting or “Thixoforming” is another way to get the dense material with the fewest holes. The piece of work is cut into smaller pieces by a machine, which is then heated. Once the metal has reached the point where it is halfway between solid and liquid, it is forced into the mold cavity by a shot sleeve, where it hardens. This will help make things more accurate. Most of the time, the semi-solid die-casting process makes parts out of non-ferrous metals like magnesium and aluminum alloy.
Squeeze Die Casting Process
Squeeze casting was made as a way to cast metals and alloys that don’t flow very easily. In this process, molten metal fills an open die, which is then squeezed shut, forcing the metal into the recesses of the mold. The squeeze casting process makes very dense products and works well with the heat-treating process that comes next. Most of the time, the process is done with molten aluminum, and it is used in places where fiber reinforcement is needed.
The Machines for Die Casting
The two popular die casting machines are the hot chamber die casting machine and the cold die casting machine
Hot Chamber Die Casting Machine
The hot chamber machine has a pressure chamber attached to the mold cavity. The molten metal can flow to the pressurized compartment constantly. When the chamber’s cylinder reverts to an unpressurized condition, molten metal is injected into the casting die.
Metal is melted in a crucible that is attached to the machine and contains the piston mechanism used for hydraulic injection into the mold. Some hot chamber die casting machines employ pressurized air to directly press metal into the mold, the piston mechanism is not needed.
The injection mechanism is immersed in the molten metal, thus it’s vital to avoid chemical attack or erosion to the submerged injection system. A hot chamber die casting machine is generally used for casting zinc, tin, and other alloys with a low melting point.
Advantages of Hot Chamber Die Casting Machine
- Increase productivity
- Can produce intricate castings
- Recommended for zinc die casting parts
- Close dimensional tolerance
- Surface finish is improved
Cold Chamber Die Casting Machine
In a cold chamber machine, the molten metal from the holding furnace is scooped into the sleeve of the cold chamber after closing the mold. After the metal has been pressed into the die, the mold is opened and the casting is injected. The metal is burned away from the machine and then fed into the compression area. Vertical cold chamber die casting machines and horizontal cold chamber die casting machines are the two broad categories based on the orientation of the compression piston.
Vertical cold chamber die-casting machines have a furnace where molten metal is removed and deposited into a compression chamber. The compression piston forces the metal into the mold, while the other piston forces the excess out.
On a horizontal cold chamber die casting machine, the piston moves in a horizontal plane rather than up and down. As a rule, horizontal die casting machines are used today. Metals with a high melting point, such copper alloy, can be die-cast using a cold chamber die casting equipment.
Advantages of Cold Chamber Die Casting Machine
- Reduced corrosion risk.
- Can be utilized to make massive parts.
- Can cast copper, aluminum, and their alloys.
The Applications Of Die Casting
Die casting is a process that can be used to make different parts and pieces that are both unique and very useful. Here are some ways the process can be used:
Industrial and Consumer Products
The method can be used to make things like heat sinks, sink faucets, connector rods, compressor pistons, and so on.
Automotive Products
This method makes gears, small engines, cylinders, transfer cases, gladhands, and other parts for the auto industry.
Aerospace Components
Die casting is a cheap way to make metal parts that are strong and light and meet the high standards of the aerospace industry.
The Advantages Of Die Casting
Die casting is the best way to make things out of metal because it is easy to use and doesn’t cost much. But there are also other reasons to use the process: Here are some good things about die casting.
High-Precision in All Dimensions
The first 2.5 centimeters are measured to within 0.1 mm, and each subsequent centimeter is measured to within 0.02 mm.
Smooth Surfaces
The surface quality and dimensional stability of die castings are exceptional. Die-cast parts are often smoother and thinner than sand-cast parts, and their walls are thinner as well. Surfaces made using sand casting tend to be the roughest.
Production Rate
The cavitation rate, determined by the number of mold cavities, determines how quickly an item may be mass-produced. At a rate of 200-300 shots per hour, a single mold can crank out quite a few products quickly. The number can easily reach the thousands if the pieces are made smaller.
Detailed Parts
Produces exact copies of any design, right down to the minute details, using extremely thin walls and framework.
Easy to Insert Add On
It is simple to incorporate threaded bearings, inserts, and additional components.
High Strength and Durability
Products made by die casting have great mechanical properties. When the liquid metal hardens under a lot of pressure, it looks fine, compact, and crystalline. Die-cast parts are strong and hard, and they are rigid. Also, they last longer and conduct electricity well.
Cost-Effective for Mass Production
Die-cast parts often need less machining because the surface is usually smooth, and the mechanical features are good. In some cases, there wasn’t even any machining. Because of this, less money needs to be spent on extra operations. Die casting is cost-effective because it can save money on post-processing costs.
Die-casting machines, molds, and other types of related equipment are very expensive. But making a lot of things at once helps spread costs out more evenly, which makes die casting a cheap way to make things.
High Dimensional Tolerance
Die casting makes parts that last a long time and are the right size. Even when the parts are exposed to harsh conditions, they stay the same size over time. Die casting is used to make parts for machines that are hard to make and require a high level of precision and accuracy.
The Disadvantages Of Die Casting
High Production Cost
Each mold must be made with great accuracy, which takes hours to make, shape, and form.
Requires a Very High Degree to Burn
Furnaces have to burn at thousands of degrees, which costs a lot of money and makes pollution that has to be cleaned up with air filters.
Requires Metal with High Fluidity
Only metals that flow easily can be used, which changes the kinds of parts that can be made.
What Affects the Cost of Die Casting?
In general, die casting is a low-cost way to make things. However, the cost depends on several things. Here are a few things you can consider when figuring out how to make your diecast project cost the least.
- The Material Used in Die Casting
- Tooling Costs
- Cost Of Mold Production
- Cost of After-Processing & Secondary Operations
- The Cost For Finishing
The Materials Used in Die Casting
The price of die casting depends a lot on the materials you choose. Some things are expensive to buy. Also, the cost of materials for die casting is generally going up, even though it seems to go up and down a lot.
Tooling Costs
The cost of tools and die casting are two of the most important things affecting production costs. Tooling costs can be high, depending on how you make things, what technology you use, how you make molds, and how you take care of them.
Cost of Mold Production
How the mold is made determines how much it will cost. For instance, when CNC machining is used, the capabilities and benefits of the process will add to the high cost of the mold.
Cost of After-Processing and Secondary Operations
The cost of die casting will also depend on things like trimming and other after-processing. So, the secondary operations’ size, efficiency, and effectiveness will play a big role in how much they cost.
The Cost for Finishing
The cost of finishing also depends on the method you choose. For example, the finishing cost will be higher with electroplating than with painting.
Surface Finishing Options for Die Casting Parts
The diecast should have a good surface finish that makes it last longer, keeps it safe, or looks better. Die cast parts can be finished in a number of different ways. But your choices depend on the size of the parts you’re casting and the alloy you’re using.
- Powder Coating
- Plating
- Painting
- Antiquing
- Ceramic Coating
Powder Coating
Powder coating is another common way to give your die-cast part a decorative finish. It is done by putting charged particles on the surface of the part made by die casting. This process is the best because it hides small flaws on the surface of the die-cast, makes it easier to control the thickness, and makes it uniform.
After the process, the product is strong, hard, and resistant to corrosion and scratches. Powder coating is good for the environment because it doesn’t make any dangerous toxic waste.
Plating
Plating can be done with or without electricity, which is a good and inexpensive way to finish a die-cast. As an option, the thin layer of finish is made of ceramic. So, you have to prepare the surface before you can use it.
Electroless plating is a way to plate a diecast part without electricity. The diecast part is put in a chemical with properties that shrink it. The chemical reacts with other minerals builds up on the die-cast.
It’s the same with electroplating. Catalysis, however, happens when an electric current flows through the electrolyte instead of minerals. Both ways are great from an aesthetic point of view, even though some people who like sheet metal use it to make some parts more conductive.
Painting
Painting is the most common way to finish a surface, and it works well for many different kinds of materials. It can be for extra protection or to look better.
The process involves putting on lacquers, paints, or enamel in a way that considers the metal. Before adding, clean the metal’s surface to get rid of dirt and oil (this also helps the paint stick), then paint the metal with a primer and the main paint.
Antiquing
This method of finishing the surface gives the cast an old look and is mostly used for zinc casting. The casting is electroplated with copper or other alloys, and a colored material like copper sulfide is put on top. The casting is “relieved,” which means that some of the colored layers are taken off to reveal the copper layer underneath, and then it is treated to keep it from rusting.
Ceramic Coating
Ceramic coating is a way to make something look nicer. It is done by adding ceramic in a solution to the outer part. The process makes a thin layer that is like what happens when something is anodized. So, procedures for preparing the surface are essential before they are used.
