Aluminum alloy casting is a die-casting product with high precision and high metal utilization rate. It is closely related to the automotive industry. We can't help asking, why does the automotive industry favor aluminum alloy die castings so much?
In recent years, China's economic development and social progress have driven the development of many industries, and the automotive industry is the representative. The number of private cars has increased, and the demand for cars has greatly increased, putting the industry into an unprecedented state of development. In the process, aluminum alloy die castings also successfully entered the eyes of car manufacturers, becoming the best choice for many car manufacturers.
There are three types of die castings that the automotive industry can choose from, mainly aluminum alloy castings, magnesium alloy castings, and carbon fiber. Among them, aluminum alloy die-casting has good recycling performance, large aluminum reserves and low sales prices have also successfully reduced the cost of automobile production, and China has a relatively mature aluminum alloy casting production process. Based on the above, there are also reasons for the automotive industry to choose aluminum alloy castings instead of the other two materials.
In the process of producing aluminum alloy castings, due to improper operation, improper selection of materials, etc., a variety of quality problems may occur in aluminum alloy die castings, including net burrs. What is going on?
The network burrs appearing in aluminum alloy castings include network traces, network patterns, and crack burrs. The main manifestations are the network-like raised marks and metal thorns formed on the surface of the die casting. The occurrence of net burrs in aluminum alloy die castings may be due to the excessively fast metal flow rate and flushing of the front wall; it may be that the surface roughness Ra of the mold cavity is too large; it may be that the temperature difference between the hot and cold temperatures of the mold is too large; Process errors; it may be that the pouring temperature of the alloy liquid is too high and the mold is not warmed up enough; it may be caused by cracks on the surface of the mold cavity; the heat conduction is concentrated near the gate area; the friction resistance is large; and the erosion by the hot-melt metal is strong , Cold and heat altered violently, generating enthusiasm and forming cracks.
Now that we have found the cause of the net burr on the aluminum alloy die castings, the next step is the solution. Workers need to correctly design the pouring system to meet the premise of good forming, and use a small injection speed as much as possible; improve the surface quality of the mold cavity and reduce the value of Ra; try to reduce the pouring temperature of the alloy liquid; fully predict the mold before casting Heat to make it reach the working temperature range; correct selection of mold materials and reasonable heat treatment process; regular annealing of the inserts to eliminate stress.
During the processing and production of aluminum alloy castings, due to many factors such as technology, molds, raw materials, etc., there will be a variety of quality problems in aluminum alloy die castings. We will also introduce solutions to these quality problems.
Carbon deposits. What is carbon deposition? It is the dark oxide on the surface of the aluminum alloy casting, which can usually be removed by wiping it with 0 # emery cloth. This kind of problem can usually be checked by visual inspection. The problem of carbon deposits in aluminum alloy die castings is because after the mold is continuously produced, release agents or other impurities are accumulated in the mold and adhere to the product surface. In order to avoid the problem of carbon deposits in the die castings, we recommend that the processing unit clean the molds regularly to keep them clean.
Lack of or fleshy meat. This problem is easy to check out. If there is more or less part of the surface of the die casting, it is a problem of fleshy or lack of meat. This is because after the mold is continuously produced, cracks or other failures occur, which will cause the surface of the aluminum alloy die-casting to be short or fleshy. How to solve this problem? It's simple, repairing the mold is all you need.
High-pressure and high-speed filling die-casting aluminum molds are two major characteristics of die-casting aluminum. Its common shot-to-shot specific pressure is from a few thousand to tens of thousands of kPa, even up to 2 × 105kPa. Filling speed is about 10 ~ 50m / s, and sometimes even more than 100m / s. The filling time is very short, generally in the range of 0.01 ~ 0.2s.
Advantage
1. Good product quality: castings have high dimensional accuracy, which is generally equivalent to 6-7, or even up to 4; surface finish is good, generally equivalent to 5-8; strength and hardness are higher, and strength is generally 25% higher than sand casting ~ 30%, but the elongation is reduced by about 70%; the size is stable and the interchangeability is good; it can die-cast aluminum thin-walled complex castings. For example, the current zinc alloy die-cast aluminum parts can have a small wall thickness of 0.3mm; aluminum alloy cast parts can reach 0.5mm; the small cast hole diameter is 0.7mm; and the small pitch is 0.75mm.
2. High production efficiency: high machine productivity. For example, the domestic JⅢ3 horizontal cold air die-casting aluminum machine can die-cast aluminum 600 to 700 times in eight hours on average, and the small hot-chamber die-casting aluminum machine can die-cast aluminum 3,000 to 7000 times every eight hours. The die-casting aluminum mold has a long life. One pair of die-casting aluminum molds and die-casting aluminum bell alloys have a service life of hundreds of thousands or even millions of times. It is easy to realize mechanization and automation.
3. Excellent economic effect: Due to the precise dimensions of the die-cast aluminum parts, the surface is smooth and smooth. Generally no longer use mechanical processing and directly use, or the processing volume is small, so it not only improves the metal utilization rate, but also reduces a lot of processing equipment and man-hours; the castings are cheap; the combined die-casting aluminum can be used for other metal or non-metal materials . Save both assembly man-hours and metal.
At present, China's foundry industry has great advantages in terms of technology, quality and price compared to Southeast Asia and the Middle East, and its export prospects are very promising. When foreign-funded enterprises enter China, the re-sale and export of their castings will also become an important part of China's casting exports. As China's foundry production costs are much lower than abroad, with the gradual improvement of casting technology and quality improvement, not only can it reduce the import of castings, but it is also possible to gradually open up export markets and export more casting products to foreign countries
In order to promote the development of the foundry industry, the scale of precision casting enterprises is within a reasonable range. By 2015, the number of precision casting companies will be reduced from 30,000 to about 20,000, and to 10,000 by 2020. At the same time, the energy consumption of casting will be greatly reduced, and 30% of enterprises will reach the level of developed industrialized countries. Waste and exhaust emissions meet national or local standards; on the basis of the "Eleventh Five-Year Plan", energy conservation and emission reduction targets have reached a 10% reduction in energy consumption and a 15% reduction in emissions. Implementation of "Access Conditions for China's Precision Casting Industry", closure of wasteful resources Enterprises that pollute the environment and do not have the conditions for safe production.
Casting is a kind of metal thermal processing technology that humans have mastered relatively early. The smooth and coordinated development of China's manufacturing industry largely depends on the development of the domestic foundry industry.
At present, the development situation of China's fork casting industry is very good, and the development of related industries is in full swing, which provides a potential market demand for the development of the casting industry.
Fork casting enterprises should pay attention to the market expansion of key industries related to casting, seek for larger target markets and development space, and focus on meeting important market needs for the development of the casting industry. It is the key to the rapid development of the foundry industry to find the right sales channels and promote the development of foundry production.
At present, our government is vigorously promoting green casting. The low-carbon economy, this general economic policy, has an important role in promoting the development of green casting in China. It has made governments at all levels pay close attention to the progress of the casting industry in the direction of green casting, and vigorously promote the foundry industry to be green .
The green economy is a new concept of development. New development goals, new economic structure and new development methods. The traditional foundry industry is an industry with high energy consumption, low output, and high pollution. Therefore, it is of great significance for China to develop a green economy to rectify the foundry industry and make it green. However, the inertia of enterprises in the industry inertia, and the active transformation of green production by the foundry industry is far from achieving the goal of green casting. This requires the introduction of government forces, and the government must give full play to macro-control measures. Formulate various measures to promote green production in the foundry industry, vigorously support the green production of the foundry industry, and guide it on the road to green development.
The forks in machinery are generally divided into fork claws, fork shafts and fork handle seats. It is mainly to slide the sliding gear and change its position on the gear shaft, it can move up and down or left and right to achieve different speeds. Or it is the control of the clutch in mechanical products, such as the structure of the end face coupling teeth, the structure of the inner and outer teeth, all need to use a fork to control a part of it to achieve the combination and separation. Another is that the control of electrical appliances in mechanical products also requires a fork to achieve the closing and opening of the switch. Generally, there is a card switch on each side of the electrical box. .
1. Make sure the car starts smoothly
This is the primary function of the clutch. Before the car starts, it is natural to start the engine. When the car starts, the car gradually accelerates from a completely stationary state. If the drive train (which links the entire car) is rigidly connected to the engine, the car will suddenly move forward as soon as the transmission is in gear, but will not start. This is because when the car moves from standstill to forward, it generates a large inertial force, which causes a large resistance torque to the engine. Under this moment of inertia resistance, the engine's speed drops sharply below the minimum stable speed (generally 300-500 RPM) in an instant, and the engine will stop working and the car will not start.
Therefore, we need the help of a clutch. After the engine starts and before the car starts, the driver first depresses the clutch pedal, disengages the clutch, disengages the engine from the drive train, puts the transmission in gear, and then gradually releases the clutch pedal to gradually engage the clutch. During the engagement process, the engine's blocked torque gradually increases, so you should gradually step on the accelerator pedal at the same time, that is, gradually increase the fuel supply to the engine, so that the engine speed is always maintained at the minimum stable speed without stopping. At the same time, due to the increasing degree of tightness of the clutch engagement, the torque transmitted by the engine to the driving wheels via the driveline gradually increases. When the traction is sufficient to overcome the starting resistance, the car starts to move from standstill and gradually accelerates to ensure that the driveline shifts. Work smoothly.
2. Realize smooth shifting
In the process of driving a car, in order to adapt to changing driving conditions, the drive train often needs to be changed to work in different gears. To realize gear shifting of a gear type transmission, generally, a gear or other gear shifting mechanism is shifted to push out one gear pair of the original gear position for transmission, and then bring the gear pair of the other gear position into operation. Before changing gears, you must step on the clutch pedal to interrupt the power transmission, so that the meshing pair of the original gear can be disengaged. At the same time, the speed of the meshing parts of the meshing pair of the new gear can be gradually synchronized. Reduced to achieve smooth shifting.
3. Prevent overloading of the drive train
When the car is in emergency braking, if there is no clutch, the engine will reduce the speed sharply due to the rigid connection with the drive train, so all moving parts in it will generate a large moment of inertia (its value may greatly exceed that emitted by the engine during normal operation Maximum torque), causing the drive train to exceed its load carrying capacity and cause damage to the machine. With a clutch, this danger can be eliminated by relying on the possible relative movement between the clutch's active and driven parts. Therefore, we need a clutch to limit the maximum torque experienced by the drive train and ensure safety.
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