Fluidity refers to the ability of the alloy liquid to fill the mold. The fluidity determines whether the alloy can cast complex castings. The eutectic alloy in aluminum alloy has the best fluidity.
There are many factors that affect the fluidity, mainly the composition, temperature and solid particles of metal oxides, metal compounds and other pollutants in the alloy liquid, but the external fundamental factors are the pouring temperature and pouring pressure (commonly known as pouring indenters).
In the actual production, under the condition that the alloy has been determined, in addition to strengthening the melting process (refining and slag removal), it is necessary to improve the casting technology (air permeability of the sand mold, exhaust gas of the metal mold and temperature), and improve the pouring temperature without affecting the quality of the casting to ensure the fluidity of the alloy.
Notes for die casting forming conditions:
Die casting machine, die casting alloy and die casting die are the three main elements of die casting production. The so-called die casting process is the organic comprehensive use of these three elements, so that the appearance, internal quality, good size in line with the drawing or agreement requirements of qualified castings, and even high quality castings can be produced steadily and rhythmically.
Material melting temperature, injection mold temperature and molten temperature;
Finally, the condition of die casting products should be trimmed to obtain perfect pieces. The selection principle of die casting mold working temperature:
1) The mold temperature is too low, the internal structure of the casting is loose, the air discharge is difficult, and it is difficult to form;
2) The mold temperature is too high, the internal structure of the casting is dense, but the casting is easy to be “welded” in the mold cavity, and the sticky mold is not easy to unload the casting. At the same time, too high temperature will cause the mold itself to expand, affecting the casting dimensional accuracy.
3) The mold temperature should be selected in the appropriate range, generally after the test is suitable, constant temperature control is better. Matters needing attention in die casting forming conditions can be simply summarized as the following two aspects:
- Material melting temperature, injection mold temperature and molten temperature;
The essence of pressure casting (referred to as die casting) is to make liquid or semi-liquid metal fill the die casting cavity at a high speed under the action of high pressure, and forming and solidification under pressure to obtain the casting method.
The characteristics of
High pressure and high speed filling die casting are two main characteristics of die casting. Its commonly used injection ratio pressure is from thousands to tens of thousands of kPa, even as high as 2×105kPa. The filling speed is about 10~50m/s, and sometimes even more than 100m/s. The filling time is very short, generally within the range of 0.01~0.2s. Compared with other casting methods, die casting has the following three advantages:
1.Good product quality
Casting dimension accuracy is high, generally equivalent to 6~7 grade, or even up to 4 grade; Good surface finish, generally equivalent to 5~8 level; The strength and hardness are high, and the strength is generally increased by 25~30% compared with sand casting, but the elongation is reduced by about 70%; Stable size, good interchangeability; Die – cast thin – walled complex castings. For example, the current minimum wall thickness of zinc alloy die casting is up to 0.3mm; Aluminum alloy casting up to 0.5mm; The minimum cast aperture is 0.7mm; The minimum pitch is 0.75mm.
2.High production efficiency
Machine productivity is high, for example, domestic JⅢ3 horizontal cold air die casting machine can die casting 600 ~700 times in an average of eight hours, small hot chamber die casting machine can die casting 3000~7000 times in an average of eight hours; Die casting mold has long life, a set of die casting mold, die casting bell alloy, life can reach hundreds of thousands of times, even millions of times; Easy to realize mechanization and automation.
3.Excellent economic effect
Due to the precise size of the die casting, the surface is glossy and clean. Generally no longer for mechanical processing and direct use, or processing volume is very small, so it not only improves the metal utilization rate, but also reduces a large number of processing equipment and man-hours; Casting price is easy; Other metal or non-metal materials can be combined with die casting. It saves both assembly time and metal.
Although die casting has many advantages, it also has some disadvantages which need to be solved.
1). Due to the high velocity of liquid metal filling cavity and unstable flow state in die casting, the general die casting method is used, which is easy to produce pores in the casting and cannot be heat treated;
2). It is difficult to die cast castings with complex concave;
3). High melting point alloy (such as copper, ferrous metal), die casting mold life is low;
4). It is not suitable for small batch production. The main reason is that the manufacturing cost of die casting mold is high, the production efficiency of die casting machine is high, and the small batch production is not economic.
Application scope and development trend of die casting
Die casting is one of the most advanced metal forming methods. It is an effective way to achieve less chip and no chip. It is widely used and develops rapidly. The size and weight of the casting depends on the power of the die casting machine. Due to the increasing power of the die casting machine, the casting size can be from a few millimeters to 1 ~ 2m; Weights can range from a few grams to tens of kilograms. Aluminum castings with diameter of 2m and weight of 50kg can be die-cast abroad.
Die casting is no longer limited to the automobile industry and instrument industry, and has gradually expanded to other industrial sectors, such as agricultural machinery, machine tool industry, electronics industry, national defense industry, computer, medical instruments, watches, cameras and daily hardware and dozens of other industries. Specific: auto parts, furniture accessories, bathroom accessories (bathroom), lighting parts, toys, shaper, tie clip, electrical and electronic parts, belt buckle, watch case, metal buckle, lock, zipper. And so on. In the aspect of die casting technology, new technologies such as vacuum die casting, oxygen die casting, precision die casting and the application of soluble core have appeared.
There will be a very good promotion for Chinese casting industry.
The development of
Die casting casting production, need to rely on die casting machine equipment to complete, die casting machine is the basis of die casting production, die casting equipment technology level determines the quality and level of die casting casting, so in order to promote the development of die casting industry must give priority to the development of die casting equipment. Is die casting power in our country, but in terms of production technology level and industrial equipment needs to be improved, our country’s development in foundry industry is pointed out in the 12th five-year plan: is the main task of the priority to the development of major technical equipment, including “big tonnage die-casting machine casting unit”, the goal is to provide equipment support for the die casting enterprise technology upgrades. The DEVELOPMENT OF die casting technology and equipment will help improve the level of die casting machinery and equipment, so as to improve the quality and technical level of casting, and promote the development of casting industry.
The status quo
At present, the competition in Chinese die-casting industry is still not standardized, which will affect the development of die-casting industry, the main problems include: first, some managers buy die-casting without the factory name site, printing well-known brands and certificates of pass manufacturers, which do serious harm to the reputation of qualified die-casting enterprises. Second, the renovation of die casting, part of the operators through the waste die casting repaint after the second sale, to the quality of the project to bring serious die casting safety hidden trouble.
The die casting industry in Europe and the United States is based on quality, reasonable interests, customer service, the establishment of enterprise reputation as the purpose, organization, education of staff, management of enterprises, with each die casting plan project, and its production process as the control and management unit, to control and ensure the quality and performance of each die casting. These factors caused the domestic industry and these developed countries there is still a big gap.
With the transfer of the casting industry to China, it not only expands the production capacity of the casting industry, but also improves the overall level of the casting industry, increases the popularity of Chinese casting industry, and increases the international market share of Chinese products. However, due to the neglect of the problems of industrial structure and production capacity in the development process of Chinese casting products, China’s casting industry has fallen into a difficult position.
Up to now, the overall marketing level of China’s die-casting enterprises is still in the primary stage of the world, without the establishment of brand, technological innovation ability, let alone the control of the industrial chain. For Chinese casting industry, only by changing ideas, innovative development and adjusting industrial structure can we get out of the difficulties gradually, which can make our casting industry develop better.