Your Quick Guide of Metal Casting

metal casting

Metal casting is the main supplier of blanks and parts for the machinery manufacturing industry. Castings in mechanical products accounted for a large proportion, such as internal combustion engine key parts (eight or nine) are castings, accounting for 70%-90% of the total mass, the quality of castings in the car accounted for 19%.

In the fast-changing world, casting is the most widely used metal processing technology. Knowledge about metal casting is important no matter what industry you are in.

What is metal casting

Metal casting refers to the molten metal liquid poured into the molds for metal casting, when the metal liquid cools and solidifies to obtain the blank or parts of the process called metal casting. The history of metal casting is very long, which means that this metal casting process has been tested over a long period of time and has been quite perfect and mature, and many metal casting products in our life are manufactured using this process. For example engine blocks for cars, lamp posts, wind turbines, bicycle pedals, etc. Let’s learn more about the metal casting process.

metal casting process

Designing a pattern and making a metal casting mold

You need to first design a pattern to determine the shape of the mold, such as a 3D printing model or CNC prototype of the object. The mold can be made of wax, plastic, sand, or even wood, and it needs to take into account the shrinkage that occurs when the metal cools, as well as the workability of the structure of the part based on precise calculations. Finally, gates are placed at the appropriate locations in the mold to allow the molten metal to flow evenly and smoothly into the mold.

Selection of metal materials

The main alloys often used in casting are aluminum, copper, and in the case of precious metals commonly used in the jewelry industry are gold, silver, copper, and platinum. These metals are mechanically capable of meeting the requirements of metal cast parts, they are a mixture of several elements, strong and durable.

Melting metal material

The metal casting molding process is like, playing at the beach and leaving footprints on the sand by yourself, which can be simply understood as your feet are the model and the footprints are the mold of your feet.

The molding process is a multi-step process, this process will use the metal casting sand, the sand, and the model into the sandbox, tightly press the sandbox, so that the sand and the model closely fit, the purpose is in the sand around the model to form the geometry of the casting, the model is removed, the geometric features of the model is perfectly copied, the mold is thus created. If a reusable mold is needed, a durable and indestructible metal mold can be made.

Pouring into the mold

Pouring or injecting the heated molten metal into the mold. For example, in gravity casting, the molten material can be poured directly into the mold downward by gravity; however, in high-pressure die metal casting, the molten material can only passively enter the mold under high pressure, and in addition, high closing forces are required to keep the mold secure.

Removing the mold

The most troublesome part of this process is the separation of the sand from the complete and clean casting, a process we generally call sand removal. The mold is vibrated to shake off the metal casting sand that is clinging to the casting. The shaken sand is then collected and cooled for recycling. The surface of the casting should not be covered with too much sand, which will cause defects on the surface of the casting and is not conducive to making full use of the sand.

Some companies with good conditions also use sand conditioners to remove and cool the sand, as well as evaporate water vapor to speed up the process of separating the sand from the casting. Some metals need to be quenched in water after solidification because water will help remove mold. For reusable molds for metal, castings are removed by automated ejector pins, so some ejector pin marks will be left on the back of the casting.

Completion of metal casting

The metal casting project in the final step is trimmed and cleaned. During the trimming process, all molding material is removed from the object, and the metal casting is ground and polished, for example, by cleaning in water to remove residual mold material, removing casting gate marks, and rough protruding edges.

Different types of metal casting

Metal casting can be divided into two kinds one is consumable mold casting, the other is non-consumable mold metal casting.

Expendable mold casting

Sand casting

Sand casting diagram

This casting method is very common and relatively simple because the metal casting sand is particularly cheap, it can also withstand the heat, the process is completed, it is easier to remove the surface of the sand, but the surface of the sand casting is usually very rough, it is difficult to achieve high accuracy in dimensional tolerances, so sand casting is more suitable for the production of large and simple parts, such as roadside fences, iron pots commonly used at home or car engine parts.

Metal casting can be divided into two kinds one is consumable mold casting, the other is non-consumable mold metal casting.

Investment casting (lost wax casting)

Investment casting

Investment casting is also known as a lost wax casting, this method is to cover and wrap the outside of the model made of wax with refractory material, then heat the model and let the wax flow out so that you can get a molded shell with the same high-temperature resistant material as the wax mold, then the molten metal is injected into the mold, and after the solution cools, the metal model is finished.

Disappearing mold casting

Disappearing mold casting diagram

The process is in accordance with the requirements of the process, the first production bubble model, and then in the model’s surface coated with special high-temperature resistant paint, dry in the sandbox, according to the process requirements filled with dry sand, the use of three-dimensional vibration tightening, extraction of air to the vacuum state casting metal liquid, at this time the model vaporization disappeared, the metal liquid replacement model, reproduce the bubble model of the same casting.

Non-consumable mold castings

Centrifugal Casting

Centrifugal Casting

Centrifugal casting is the technology and method of injecting a metal solution into a high-speed rotating mold, and the molten metal is covered with the whole mold under the action of strong centrifugal force, and waiting for the metal solution to cool down to form the casting. Because the effect of centrifugal force is very strong, the inclusions and gases inside the mold are easily discharged, and the cooling is generally from the outside to the inside, the casting is very fine in an organization and the mechanical properties are close to the forging process.

die metal casting

die metal casting

This process is more like plastic injection molding. First, two metal steel molds need to be prepared as cavities for the molten metal, and then the molten metal is pressed into the cavities under high pressure, and then the fine arts can be manufactured. Die metal castings generally have an excellent surface finish, but the cost of custom cavities is higher, so this process is more suitable for high volume production because the metal cavities can be used multiple times.

Gravity Casting

metal casting process

Gravity casting predates other metal casting processes, it is a reusable metal mold casting metal method also known as casting. As the name implies, gravity casting relies on gravity to turn the metal solution from top to bottom to cover and fill the mold, rather than relying on pressure. This mold must be heated prior to casting and the material is usually made of iron, which has low thermal fatigue.

Pros and Cons of metal casting

A combination of the above characteristics of various casting processes, metal casting can be concluded that the following pros and cons.

Pros

1. It can produce the arbitrarily complex shapes of the parts, especially the internal cavity shape complex parts.
2. It is Very adaptable, the metal material is not limited, the size of the casting is almost unlimited.
3. Wide source of manufacturing materials, high recovery rate, low investment in equipment
4. Excellent bearing quality, suitable for mass production, and can produce thick-walled parts.

Cons

1. The production procedure of casting is more complicated and difficult to control. The surface finish may produce defects such as porosity, shrinkage, slag holes, cracks, poor fusion, sand holes, etc.
2. The dimensions of the castings deviate, and the dimensions are not as accurate as CNC machining.
3. For casting workers, the casting equipment is more dangerous, the working environment is poor, high temperature, dust, and labor intensity.

The application of Metal Casting

Disappearing mold casting

Power station equipment

Power station equipment is a high-tech product, the reliability of the parts has very strict requirements because the parts need to operate continuously for a long time under high load, thermal power stations and nuclear power station equipment in many parts also need to withstand high temperature and high-pressure steam corrosion. Cast steel parts can meet these requirements to the maximum extent possible, widely used in power station equipment.

Railway locomotives and vehicles

Railroad safety is of paramount importance, so some key components of locomotives and vehicles, such as wheels, side frames, shaking pillows, hooks, etc., are the traditional cast steel parts.

Construction, construction machinery and other vehicles

Most parts of construction machinery and engineering machinery are subjected to high loads or need to withstand impact wear, a large part of which are metal casting parts, such as the active wheel in the action system, load-bearing wheel, rocker arm, track plate, etc. General automobiles rarely use cast steel parts, but special off-road vehicles and heavy trucks also use a lot of cast steel parts in the action part.

Conclusion

Metal casting in the manufacturing industry has a wide range of uses, especially in construction and transportation, but also it is a very inexpensive method, its history is also very long, after the test of history, metal casting services are increasingly available to meet the different production requirements.

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