Automotive casting technology

Casting molding is the most flexible method for manufacturing complex parts. The application of advanced casting technology has brought new vitality to the manufacturing industry. Numerous software and the rapid development of computer technology makes it possible for the production of geometric shape, size, performance and other aspects of the castings meet the requirements of accurate and reliable information.

Automotive parts in about 15% to 20% for the use of different casting methods for the production of castings, these castings are mainly for the power system key components and important structural components. At present, the automobile industry in developed countries of the automobile castings production technology is advanced, product quality, high production efficiency, environmental pollution is small. Casting raw and auxiliary materials have formed a series and standardization, the entire production process has achieved mechanization, automation and intelligence. With the rapid development of automotive technology, the use of rapid molding technology, CAE technology, three-dimensional modeling, CNC technology and other technologies to shorten the casting production preparation cycle and reduce the risk of new product development to provide reliable support.

Automobile casting technology

1, casting process

Casting mainly sand casting and special casting two categories.

• Ordinary sand casting, the use of sand as a casting mold material, also known as sand casting, sand, including wet sand, dry sand and chemical hardening sand 3 categories, but not all sand can be used for casting. The advantage is lower cost, because the sand used for casting mold can be reused; the disadvantage is that the production of casting mold is time-consuming, the casting mold itself can not be reused, and must be destroyed to obtain the finished product.
• special casting, according to the molding material can be divided into natural mineral sand and gravel as the main modeling material for special casting (such as investment casting, mud casting, shell casting, negative pressure casting, solid casting, ceramic casting, etc.) and metal as the main casting material for the special casting (such as metal casting, pressure casting, continuous casting, low-pressure casting, centrifugal casting, etc.) two categories.

In the automotive field, the main application of the casting process has the following two categories:

1.1 gravity casting (GDC)

Gravity casting is a process in which the liquid metal is injected into the casting mold under the action of the earth's gravity, also known as gravity casting. The molten metal is poured into the mold and the molten metal occupies the space in the cavity under the force of gravity. If the part must be hollow, then a sand core is also required in the mold cavity. Sometimes, to ensure proper metal flow, the pouring unit may be tilted, and this is referred to as a "tilted GDC". Broadly speaking, gravity casting includes sand casting, metal casting, investment casting, vanishing mold casting, clay casting, etc. Among them, sand casting is most widely used in the automotive industry.

1.1.1 Sand casting

At present, for cast iron automobile parts, the most widely used is still wet sand molding, especially the emergence of static pressure or air impulse molding of air pre-fastening, reflecting more superiority - low energy consumption, low noise, less pollution, high efficiency, reliable operation.

Recently, foreign equipment manufacturers on the molding machine and continuous improvement, has appeared in the air punch compaction, airflow gain air punch plus compaction, static pressure plus compaction, active multi-contact compaction, molding extrusion compaction and other improvements to make the hardness of the sand more uniform.

With the development of high-power semiconductor components and computers, microelectronics technology, the use of electric servo systems instead of the usual molding line used in the hydraulic, pneumatic drive, so that the molding line to further accelerate the beat, and greatly improve the reliability of the operation, while significantly simplifying the hydraulic control system, so that the maintenance workload is also reduced accordingly.

Moulding line adopts double-cylinder type sand dropping machine, which can make the castings and sprues get pre-cleaning at the same time of sand dropping. Moulding line pouring often restricts the opening rate of the whole line, automatic pouring equipment should be used. Some manufacturers use air pressure pouring package and contact pouring process, is conducive to saving iron, quality assurance and protection of the sand box, the pouring process with the flow of pregnancy more, some use the type of pregnancy and filtration combined.

Casting process, for the use of sand core, depending on the conditions of each plant, respectively, the use of cold core box core, hot core box core or shell core system core, other sand cores, including crankcase core, cylinder cylinder barrel and the top of the core, front and rear of the front of the core, etc. Most of the use of cold core box core, in order to ensure the size of the precision and energy saving, the cold core box is becoming more and more widely used. Cold core making with ISO CURE triethylamine hardening method mostly (the United States has developed a more advanced ISO MAX).

In order to improve the quality of the inner surface of the casting and the cleanliness of the inner cavity, the core should be coated with water-based paint instead of alcohol-based paint is conducive to anti-pollution. After coating, the use of microwave drying efficiency, energy saving, sand core quality is also better than the traditional drying with gas, natural gas. With KCY-CORE process, using the process holes opened on the sand core, the second filling of sand curing, so that a number of sand cores for a whole combination of sand core, and then the whole coating, drying, so that the casting dimensional accuracy can be greatly improved, the overall dimensional error <0.3mm.

In the sand system, there are old sand magnetic separation equipment, sand block crushing equipment and screening equipment and old sand cooling equipment to ensure the quality of old sand for reuse. Meanwhile, the new sand, coal powder, bentonite and other added materials are accurately quantized and fed according to the ratio determined by the process, and the amount of water is adjusted at any time according to the real-time control data to ensure the performance of the sand. There is also a closed-loop real-time control of the performance of the whole system sand or sand quality computer online expert system control. It should be noted that the sand system sand turnover is large, inert, sand performance adjustment should be judged by the trend, the use of predictive adjustment measures to ensure that the quality of the sand system is stable.

Common castings are: engine block, cylinder head, gearbox shell, intake manifold and so on.

1.2 Die casting

When the cross-section of the desired casting is quite complex, or the wall thickness of some specific places is very thin (such as Figure 3), only under the influence of gravity, it is not possible to ensure that the metal liquid completely fill the mold cavity. In this case, the metal liquid can be pressed into the mold cavity under pressure to ensure that the metal liquid can completely fill the mold cavity, the setting can be high-pressure die casting (HPDC) or low-pressure die casting (LPDC). The castings produced by the HPDC process have good dimensional consistency and similar tolerances of about +/-0.2mm. this precision is unattainable in GDC or even LPDC. With the rapid development of automobile technology, high-pressure die casting technology has also become one of the hot spots of current automobile casting.

1.2.1 High pressure casting

High pressure casting is under high pressure will liquid or semi-liquid metal quickly pressed into the casting, and under pressure crystallization solidification and obtain casting method. The main process of high pressure casting can be divided into: together, pressure shot, top out of three stages.

In the die casting process, the pressure injection parameters on the die casting porosity effect is quite big, must be reasonable adjustment. The use of closed injection end time control system, can realize no fly edge die casting. The inspection of die casting quality can adopt X-ray flaw detection, ultrasonic testing and so on.

Developed on the basis of high-pressure casting process, vacuum casting, oxygenated die casting, aimed at eliminating casting defects, improve internal quality, and expand the scope of application of die casting. Squeeze casting process, the melt in the pressure filling and solidification, has a smooth, no metal spatter, the liquid metal oxidation loss is small, energy saving, safe operation and reduce casting hole class defects, etc., in the aluminum alloy sub-frame and other high-performance aluminum alloy casting development and application of a wide range of applications.

• Vacuum die casting

In order to reduce or avoid the die-casting process gas with the metal liquid high-speed involved in the casting and make the casting produce porosity and loosening, die-casting before the casting mold vacuum die-casting is the most common. According to the size of the vacuum in the pressure room and cavity and vacuum die casting can be divided into ordinary vacuum die casting and high vacuum die casting.

The key to high vacuum die casting is to obtain a high vacuum in a very short period of time. Figure 6 for inhalation type high vacuum die casting machine working principle diagram, it adopts the vacuum inhalation of metal liquid to the pressure chamber, and then rapid injection, can obtain high vacuum die casting.

The principle of high vacuum die casting: before die casting work, first from the vacuum pipe will the whole pressure chamber and cavity in the air out, this vacuum process speed must be as fast as possible, make the crucible in the metal liquid and pressure chamber to produce a large pressure difference, so as to make the crucible in the metal liquid along the ascending liquid tube into the pressure chamber, and then ejection punches began to ejection.

• Oxygenation die casting

Oxygenated die casting is to fill dry oxygen into the pressure chamber and die casting mold cavity, in order to replace the air and other gases. Oxygenated die casting process schematic diagram shown in Figure 7.

Oxygenated die casting is only applicable to aluminum alloy. When the aluminum alloy liquid pressed into the pressure chamber and die-casting mold cavity and oxygen chemosynthesis reaction, the formation of AL2O3, the formation of uniformly distributed AL2O3 small particles (diameter of 1um or less), thus reducing or eliminating the air holes, improve the casting of the denseness. These small particles are dispersed in the castings, accounting for about 0.1%-0.2% of the total mass, and do not affect the mechanical processing.