How to deal with the defects of precision castings in general? Today, Cheng Mao will popularize it for everyone.

1. Analysis of the status quo of the foundry industry (yield rate repair ratio)

At present, the production scale of my country's foundry industry and the output varieties of castings are already in the forefront of the world. The strong industrial foundation provides a large number of castings (blanks and parts) for many industries.

In recent years, my country's foundry industry has entered the ranks of the world's major foundry countries with many factories, large output, and complete categories. At the same time, my country's casting exports have grown rapidly. In the first three months of this year, my country's steel casting and iron casting output reached 2,469,140 respectively. Tons, 1,040,613 tons, a year-on-year increase of 13.32%, 12.54%. Export products have also evolved from simple parts to more demanding castings with complex shapes. But compared with the founding powers of the United States, Japan, Germany, and France, there is still a considerable gap.

It is mainly manifested in the fact that my country's castings are famous for being'old, big, black, and rough', mainly due to the high scrap rate in my country's foundry industry. The scrap rate of ordinary iron castings in my country is about 10%, that of complex and high-grade parts is about 10% to 15%, and that of aluminum alloy die castings is about 8% to 10%. At the same time, the defects are mainly concentrated in the pores and blisters on the surface or inside of the casting. About 80% of the defects can be rescued by repairing. There are many reasons for the defects. In the process of process arrangement, material selection, casting mold design and production, casting molding, etc., if the design and implementation are not scientific and rigorous, it will lead to the emergence and increase of the rejection rate.

With the development of the world economy, my country has become a foundry power, and foundry production must follow the path of high-quality, high-efficiency, low-consumption, and clean sustainable development. The fundamental method is: the development of castings from low value-added products to medium and high-end castings. This requires that the technical level of the entire casting must be improved. However, the technical level of the casting is a systematic project, subject to the actual situation, it is difficult to achieve a substantial improvement in the short term. The most urgent task is to reduce the scrap rate of castings. As a result, the repair benefits of castings have been valued more and more by enterprises. Even well-known foreign-funded enterprises and large state-owned enterprises with strong technical strength have adopted casting repair methods to make up for the deficiencies of existing casting technology. . Companies often adopt different methods in saving defective castings due to their own circumstances. www.wxyszj.cn

2. Repair situation and equipment analysis

1. Caster glue:

It is an instinctive choice for companies to repair castings. The main features are simplicity, convenience, low price, and low requirements for employees. However, this method is only suitable for extensive castings. Generally, subsequent processing cannot be carried out at the repaired part, and the bonding strength and hardness are very low. Such a process is only suitable for simple and extensive castings, or castings with relatively low added value. With the development of the foundry industry, the caster glue is becoming less and less adaptable to the requirements of customers.

2. Welding repair:

Almost all foundries choose welding repair to solve the casting defects encountered in production. Welding repair of castings is the use of welding consumables that generally match the material of the castings with metal fillers, so as to meet the basic mechanical performance standards required by the parent body. This requires a variety of welding repair methods; simple welding repair methods; high welding repair efficiency, low repair welding costs, low environmental pollution to the environment, and simple follow-up treatment after welding repairs. Only in this way can it be accepted and trusted by the foundry. At present, there are many types of welding machines for welding and repairing castings in the market, generally including the following types:

2.1, electric welding machine

Electric welding machine is a necessary equipment for foundries. It uses the electrode poles to ignite the arc when the two poles of the electrode are short-circuited instantaneously, and the generated arc is used to melt the welding rod and the welding material, and after cooling to achieve the purpose of combining them. It is the most traditional welding method, generally used for repair welding of cast iron and cast steel, or some traditional welding repairs.

Advantages: suitable for working in a dry environment, does not require much, relatively small size, simple operation, easy to use, fast, strong after welding, suitable for large-area repair welding. It can instantly connect the same metal material (also can connect dissimilar metals, but the welding method is different) permanently. After heat treatment, the weld seam will have the same strength as the base metal and have a good seal.

Disadvantages: During the use of the electric welding machine, a certain magnetic field will be generated around the welding machine. When the arc burns, radiation will be generated to the surroundings. There are light species such as infrared and ultraviolet rays in the arc, and harmful substances such as metal vapor and smoke. Adequate protective measures must be taken at the time, and special electric welders are required to perform the operation. It is not suitable for welding repair of high carbon steel. Due to the crystallization, segregation and oxidation of the weld metal, there is internal stress, and it is easy to crack after welding, resulting in hot and cold cracks. It is easy to produce secondary defects such as pores and slag inclusions inside; the hardness of the solder joints is too high, and annealing heat treatment is generally required to meet the processing requirements. This determines that the electric welder can only repair some rough castings. Even if the repair of precision castings, preheating is required, and annealing treatment is required after welding, and welding repair is relatively cumbersome. This requires more advanced welding equipment to make up for its shortcomings.

2.2. Argon arc welding:

Argon arc welding is also called argon gas shielded welding. It is to pass argon arc protective gas around the arc welding to isolate the air from the welding area and prevent the oxidation of the welding area.

Precision castings (alloy steel, stainless steel precision castings), aluminum alloy die castings are mostly welded by argon arc welding machines. Some mold manufacturing and repairing manufacturers also use this welder to repair mold defects.

Advantages: high welding repair efficiency and higher accuracy than electric welding machines. There are many types of welding wire, and the most widely used in stainless steel and aluminum alloy products. It can be used for welding with high strength.

Disadvantages: Argon arc welding has a large heat-affected area, and because D has too much impact on the casting, there are traces on the edge of the molten pool. Welded steel parts have hard spots. Due to thermal influence, thermal deformation is likely to occur when welding non-ferrous castings or thin-walled parts. Operational technical requirements are high. After repair, the workpiece often causes defects such as deformation, reduced hardness, blisters, partial annealing, cracking, pinholes, abrasion, scratches, undercuts, or insufficient bonding force and internal stress damage. Especially in the repair process of small defects in precision castings, the surface is prominent. Compared with electrode arc welding, argon arc welding is more harmful to the human body. The current density of argon arc welding is large, and the light emitted is relatively strong. The ultraviolet radiation generated by its arc is about 5 to that of ordinary electrode arc welding. 30 times, infrared is about 1 to 1.5 times that of electrode arc welding. The ozone content produced during welding is higher. Therefore, try to choose a place with better air circulation for construction, otherwise it will cause great harm to the body. This requires argon arc welding to be performed in a special place and requires specialized personnel to operate, which greatly reduces its flexibility.

Three, cold welding repair

Cold welding machine: It can release welding energy in a very small range (GG lt; 1 square millimeter) in an instant (ms level), so that the repair material can be completely welded to the workpiece. During the welding repair process, the workpiece generates very little heat, and the workpiece is at a normal temperature as a whole, so the defects of traditional welding such as deformation, cracks, and discoloration can be avoided. After several years of development, the application direction and technology of welding machines have been greatly developed, and they have occupied a large share of the repair market.