Die casting is one of the metal part-making methods. The two halves of die steel mold are cleaned and spray coated with oil; the machine then closes. Pressure exerted by the machine can be in the range of the hundreds of tons to well over 4000 tons. This force acts to keep the mold clamps flat, which is essential when the hot metal fills in under pressure.
It is hot liquid metal is injected into a hollow chamber. This happens in a span of a few seconds and under full pressure. A special system forces the liquid metal into every tiny detail of the mold.
The cooling cycle is the longest one in the process as it is necessary for the filling to solidify completely and to reach the final product. The cooling system of the mold also consists of tubes inside that have water or oil flowing through them.
The next step is to release the grip of the machine, which is already open. The push pins on one side then act to push the part out of the mold.
During this operation, workers can learn when it is done correctly. A clean, fast ‘thud’ sound is produced, at which point the part is freed. On the other hand, a scraping sound indicates poor oiling or design would be the reason for sticking. It shows why angles, as well as oil, are so very important for mold life.
Trimming is the last phase of the process. The part has not yet been removed completely. It still has internal channels attached to the mold. This is related to the main channel and the smaller channels that directed the metal to the part. There may also be a little amount of excess metal called ‘flash’.
Cutting this excess material is done in a trimming operation. A press with a cutting tool takes care of this efficiently with just one stroke of the cutter. Meanwhile, the rest of the parts are sawed or ground. The scrap metal cut off from this is recycled back to the furnace.
Hot Chamber vs. Cold Chamber: Select The Suitable Process
Not all die casting is the same. There are two major aspects which are hot chamber and cold chamber die casting. The decision is based on the type of metal that is going to be cast, therefore, it refers to this difference as it is necessary to understand how die casting works for different operations.
What Does Hot Chamber Die Casting Mean?
The hot chamber does blow the ejector mechanism right inside the bath of hot liquid metal. A curved tube feeds metal into the mold directly. With this setup, the metal doesn’t have to be relocated from a separate pot.
This method is useful for low-melting point metals the most. Those are zinc, tin, and magnesium. Hot chamber die casting is mostly used for these types of metals. However, no other types are applicable. High-temperate metals are likely to discharge the injection mechanism’s parts.
What is Cold Chamber Die Casting?
In this process, the melting pot is separate from the machine. Workers fill a tube with hot liquid metal from the pot, then close it off and use a hydraulic pusher to force the metal into the mold.
This process is used for the metals, for example, aluminum, brass, and copper, that melt at high temperatures. The injection system thus becomes less stressed as it does not have direct contact with the hot metal all the time. Consequently, the parts do not wear out so fast. This process of making strong aluminum parts is slower than hot chamber.
Table of Quick Comparison
| Features | Hot Chamber | Cold Chamber |
|---|---|---|
| Materials | Zinc, Magnesium, Tin, Lead | Aluminum, Brass, Copper |
| Melting Temp | Low | High |
| Speed of Cycle | Faster (15 or more shots/minute) | Slower (1-2 shots/minute) |
| Wear of Machine Parts | Higher (continuous metal contact) | Lower |
| Pressure Ratio | Lower | Higher |
| Task Examples | Decorative hardware, zippers | Car parts, engine blocks |
Design for Manufacturability (DFM): Helpful Hints for Achieving Die Casting Success
However, just knowing the die casting process isn’t enough. Making a good part will depend a lot on product design and what materials to choose. This is known as Design for Manufacturability or DFM. Adopting the expert suggestions below will save time and money, and you will achieve a better end product.
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Ensure Wall Thickness is Uniform: Make sure that parts will have uniform wall thickness all the way along. This measure helps the metal to cool evenly and be free from defects, such as weak points, and voids (porosity).
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Use Appropriate Draft Angles: The draft angle is a slight slope on a part wall. The slope is parallel to the parting line. This slope helps a lot to easy removal of the part. The minimum is one degree, but two to three degrees on most surfaces work much better. This will extend the life of the mold and improve the finish.
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Use Rounded Corners: Make sure to create rounded corners both on the inside and outside. This promotes the flow of hot liquid metal into the mold. Besides, it alleviates stress on the finished and the mold part. This way no cracks develop.
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Prevent Undercuts: An undercut is the detail that prevents the part from coming straight out of the mold. These features add the cost of complexity and extra parts in the die. By designing them out, you will save a lot on tools.
- Choose Parting Lines & Pin Marks Carefully: The joint of the two mold halves is the parting line, which is going to be left faint on the part. Push pins will also leave small round marks. Think about these marks beforehand. Try to place them on surfaces that are not visible to people.
Popularly Used Materials in Die Casting
The die-casting process is powered mainly by non-ferrous metals. Non-ferrous metals are those containing no iron at all. It is their unique properties such as strength, weight, and cost that often dictate the choice of material for the job. By using different alloys of metals, many distinct metal components can be manufactured.
Aluminum Alloys (e.g., A380)
Aluminum is the predominant die casting material. It is not only lightweight, but it also provides strength and good resistance to rust. Besides, it performs well in high-heat environments. Constructions of vehicle engine blocks and electronic cases are common applications.
Zinc Alloys (e.g., Zamak 3)
Zinc is a metal that is very simple to mould. It has an exceptional liquid flow which permits very thin walls and detailed features. Zinc also provides a first-rate surface finish which is easy to be coated or painted. It is mainly seen in decorative hardware and car door handles.
Magnesium Alloys (e.g., AZ91D)
Magnesium is the lightest widely used structural metal. It has an impressive strength-to-weight ratio. This is why it is widely employed in applications where weight-saving matters. Such tasks include car steering wheels and laptop cases.
Brass & Copper Alloys
Copper and brass alloys are often not used as they are harder on machines and they need a higher melting point. On the other hand, they provide hardness and rust resistance. Also, they are good conductors of electricity. Some of their common applications include plumbing fittings and electrical parts.
Die Casting vs. Other Manufacturing Processes
Learning how die casting works additionally includes the information of when to use it. Below is the comparison to other methods of forming.
Die Casting vs. CNC Machining
Die casting is the most efficient option for producing a large number of identical parts. The upfront cost of mold making is high, but per-part cost drops significantly with high quantity production.
On the other hand, CNC machining is excellent for the production of small quantities of parts, prototypes, and components that need a very tight tolerance. No tooling cost is there in CNC machining, but it is much higher due to the individual cutting of parts. Services like CNC machining are ideal for such situations. Many companies, when it comes to sourcing consider China CNC machining services because of their low cost.
Die Casting vs. Sand Casting
Die casting uses a steel mold that is in use many times. This feature ensures high accuracy and a smooth surface finish. It is capable of making complex and thin-walled parts.
Instead of using a sand mold for each part, the sand casting method utilizes temporary sand molds. As a result of this, it’s better suited for very large parts and has a lower tooling cost. Nevertheless, the parts have lower precision and a much rougher surface. The majority of them require more work after casting.
Conclusion: Significance of Knowing the Die Casting Mechanism
Die casting is a robust manufacturing process. The formation of precise, complex parts with hot liquid metal is fast, and that’s the leading edge. The five-cycle process is the functioning secret. We have noted the distinction between cold and hot chamber machines, and their differences in operation. Further, we have emphasized the significance of proper designs.
This is the initial knowledge that you can build upon to enhance the features of your parts and reduce costs. You may subsequently use this energy through the die casting process by letting the parts be the way they should be. Thus, you achieve speed, quality, and good value all in one. To get professional support for your upcoming project, please check out the offering of Mekalite.
Frequently Asked Questions (FAQ)
What is the primary advantage of die casting with high pressure?
The primary benefit is the ability to make a vast number of parts with very high accuracy. Hence, it also creates intricate designs and a very smooth surface finish. This sometimes eliminates the need for further processes after casting. The high pressure makes sure that each minute detail of the mold will be filled with hot liquid metal.
How long does a die casting tool (mold) last?
The longevity of die casting tools is subjective and depends upon factors like the type of materials used for casting, complexity of the design, and maintenance given. In the case of aluminum, a mold can last around 80,000 to 150,000 cycles. For less abusive materials such as zinc, a carefully maintained mold could be used for over a million cycles.
Is steel or iron appropriate for die casting?
No, the die casting process is strictly limited to non-ferrous metals like aluminum, zinc, and magnesium which makes it unsuitable for steel and iron die-casting. They melt at excessively high temperatures. Consequently, they would damage or destroy the hardened steel molds that are used in the process quickly.
What does the term porosity mean while die casting?
Porosity refers to the existence of tiny airspaces or bubbles in the casting material. It mainly happens due to two reasons. Gas porosity originates from the release of gases or from air being trapped in the liquid before it moves to the die area. The second, shrinkage porosity, happens when cooling conditions are uneven. Proper mold design, injection control, and temperature management are key to reducing it.
Is die casting a costly process?
Die casting is expensive at the outset due to mould making, which also is known as tooling. But, for producing thousands or millions of parts, the cost per part becomes extremely low. This makes it one of the most cost-effective ways to make things for mass production.
