How to repair the casting defects?
I. Analysis of the status quo of the foundry industry (rate of repair rate)
At present, the production scale of China's foundry industry and the variety of castings are already in the forefront of the world. The strong industrial base provides a large number of castings (blanks and parts) for many industries.
In recent years, China's foundry industry has entered the ranks of world casting countries with many factories, large output and complete categories. At the same time, China's casting exports have grown rapidly. In the first three months of this year alone, China's steel and cast iron production reached 2,469,140 respectively. Tons, 1,040,613 tons, an increase of 13.32% and 12.54%. Export products have also evolved from simple pieces to more demanding castings with complex shapes. However, compared with the founding powers such as the United States, Japan, Germany and France, there is still a considerable gap.
The main manifestation is that China's castings are famous for their “oldâ€, “bigâ€, “black†and “roughâ€. The main reason is that there is a high rate of scrap in China's foundry industry. The scrap rate of ordinary cast iron parts in China is about 10%, the complexity and high-grade parts are about 10% to 15%, and the aluminum alloy die-casting parts are about 8% to 10%. At the same time, the defects mainly focus on the pores, blisters, etc. that appear on the surface or inside the casting. About 80% of the defects can be saved through repair. There are many reasons for the defects. In the process of process arrangement, material selection, casting mold design and production, casting molding, etc., if it is not scientific and rigorous design and implementation, it will lead to the emergence and improvement of the scrap rate.
With the development of the world economy, China has become a casting power, and casting production must take the road of sustainable development with high quality, high efficiency, low consumption and cleanliness. The fundamental approach is: castings are developed from low value-added products to medium and high-grade castings. This requires that the technical level of the entire casting must be improved, but the level of casting technology is a systematic project, subject to the reality, it is difficult to obtain a substantial increase in the short term. It is imperative to reduce the scrap rate of castings. As a result, the repairing benefits of castings have been increasingly valued by enterprises. Even well-known foreign-funded enterprises and large state-owned enterprises with strong technical strength have used the method of casting repair to make up for the shortage of existing casting technology. . Companies often take different approaches to saving defective castings because of their own circumstances.
Second, repair situation and equipment analysis
1. Casting glue:
It is the instinct choice for companies to repair castings. The main features are simple, convenient, low price and low requirements for employees. However, this method is only suitable for extensive castings, and the subsequent repairing is not possible, and the bonding strength is very low. This process is only suitable for simple and extensive castings, or for castings with lower added value. With the development of the foundry industry, caster glue is becoming less and less suitable for customer requirements.
2, welding repair:
Almost all foundries choose weld repair to solve casting defects encountered in production. The repair welding repair of castings is to use the welding consumables to match the metal materials of the casting materials to meet the basic mechanical performance standards required by the parent body. This requires various welding methods; the welding repair method is simple; the welding repair efficiency is high, the welding repair cost is low, the welding repair has little environmental pollution, and the subsequent processing after welding repair is simple, and only in this way can the casting manufacturer accept the approval and trust. At present, there are many types of welders in the welding of castings, which are generally the following:
2.1, welding machine
The electric welder is an indispensable equipment for the foundry. It uses the electrodes to ignite the arc when it is short-circuited instantaneously. The arc generated is used to melt the electrode and the welding consumables, and then cooled to achieve the purpose of combining them. It is the most traditional welding method, and is usually used for welding repair of cast iron and steel castings, or some traditional welding repair.
Advantages: It is suitable for working in a dry environment, does not require too much requirement, is relatively small in size, simple in operation, convenient to use, fast in speed, and firm in weld after welding, suitable for large-area weld repair welding. The metal material of the same kind (which can also be connected to different metals, but different welding methods) can be connected in a moment. The weld is heat-treated and has the same strength as the base material, and the seal is good.
Disadvantages: During the use of the welding machine, a certain magnetic field will be generated around the welding machine. When the arc burns, it will generate radiation to the surroundings. There are infrared light, ultraviolet light and other light species in the arc, as well as harmful substances such as metal vapor and soot. Sufficient protective measures must be taken and a special welder is required to operate. It is not suitable for welding repair of high carbon steel. Due to the process of weld metal crystallization, segregation and oxidation, there are internal stresses, which are easy to crack after welding, resulting in hot cracks and cold cracks. The interior is prone to secondary defects such as pores and slag inclusions; the hardness on the solder joint is too high, and annealing heat treatment is generally required to meet the processing requirements. This determines that the welding machine can only repair some rough castings. Even if the precision castings are repaired, it needs to be preheated. After welding, annealing is required, and the welding compensation is cumbersome. This requires more advanced soldering equipment to make up for its shortcomings.
2.2, argon arc welding:
Argon arc welding is also called argon gas shielded welding. That is, an argon arc protective gas is passed around the arc welding to isolate the air outside the weld zone to prevent oxidation of the weld zone.
Precision castings (alloy steel, stainless steel precision castings), aluminum alloy die-casting parts are often welded by argon arc welding machine. Some mold manufacturing and repair manufacturers also use this welder to repair mold defects.
Advantages: high welding efficiency and higher precision than electric welding machines. There are many types of welding wire, and the most widely used stainless steel and aluminum alloy products. Can be used for welding, high strength.
Disadvantages: argon arc welding has a large area affected by heat, because D has too much impact on the casting, and the edge of the molten pool has traces. Welded steel parts have hard spots. Due to thermal influences, when hot-filled colored castings or thin-walled parts are welded, thermal deformation is likely to occur. The technical requirements are high. After repairing the workpiece, it often causes deformation, hardness reduction, blisters, local annealing, cracking, pinholes, abrasion, scratches, undercuts, or insufficient bonding strength and internal stress damage. Especially in the repair process of fine defects of precision casting parts, the surface is prominent. Compared with electrode arc welding, argon arc welding has a higher degree of damage to the human body. The current density of argon arc welding is large, and the emitted light is relatively strong. The ultraviolet radiation generated by its arc is about 5~ of ordinary electrode arc welding. 30 times, the infrared ray is about 1 to 1.5 times that of the electrode arc welding. The ozone content generated during welding is high. Therefore, try to choose a place with good air circulation, otherwise it will cause great harm to the body. This requires that argon arc welding needs to be in a special place, requiring special personnel to operate, greatly reducing its flexibility.
Third, cold welding repair
Cold welder: It can release the welding energy to a very small range (<1 mm2) in an instant (ms class), so that the flux is completely welded to the workpiece. During the welding repair process, the heat generated by the workpiece is extremely small, and the workpiece is in a normal temperature state as a whole, so that defects such as deformation, crack, and discoloration of the conventional welding can be avoided. After several years of development, the application direction and technology of the welding machine have been greatly developed, and it has already occupied a large share in the repair market.
According to the cold welder product classification: the placement machine and the traditional electric spark surfacing repair machine.
1, placement machine
Using the principle of instantaneous high-frequency discharge, the soldering piece (steel sheet, powder, solder powder or machining waste) (0.05-0.20mm) is pasted to the surface of the workpiece by high-frequency discharge or filled into the defect (such as sand hole), each time the thickness is pasted. The maximum equivalent is the thickness of the solder tab, and the soldering quality depends on whether the discharge is uniform. Suitable for workpiece wear and machining over-wound repair. The advantage is that the repaired casting has small color difference, basically does not generate internal stress, has no deformed undercut, and has small repair amount after welding, and can be directly processed.
Disadvantages: the welding speed is very slow, usually 2mm holes need 3-5 minutes, not suitable for large-scale repair; the hardness after repair is low, generally only about HB150, can only look at the high hardness castings; Low, because the additive is attached to the workpiece, it is easy to fall off after the lathe milling machine; the post-weld finish is low, and it is powerless for castings with smoothness after processing. Because it often uses copper rods to contact the refill, it is inevitable that copper scrap or Small pores can only repair some castings that are not too high in processing requirements.
2. Traditional EDM welding repair machine
Using the principle of spark transient high-frequency discharge, the nickel-based welding material or special welding material is applied to the surface of the workpiece in an ionic state, so that the welding material and the workpiece are metallurgically fused together. The surface of the workpiece generates minimal heat throughout the weld repair process. The welding torch uses a rotating electrode with a wire diameter ranging from 1.6 to 3.0 mm. Suitable for repair of casting defects. And the machine can achieve surface coating strengthening on the setting of power and discharge frequency. It can repair various metals such as steel, copper and aluminum.
Advantages: easy to install, easy to operate, the general staff can operate with a little training. The welding repairing strength is high, the welding repairing parts are not annealed, no cracks, no deformation, no internal stress is generated, no hard points are processed at the solder joints, and the repairing speed is faster than the mounting machine, and the repairing precision is relatively high. And can be tested by X-ray inspection, penetration, stretching and so on. It has been accepted and used by many foundry manufacturers. In addition, there are some use values ​​in mold repair.
Disadvantages: Slow speed, 2mm cast iron takes about 3 minutes. Corresponding to the welding consumables, the cast iron parts can only be welded with nickel-based welding consumables (300/kg), and the welding consumables can only reach 80%. The color difference is relatively large, and the degree of bonding is low. Since the principle is high-frequency discharge, that is, granulated surfacing, the combination is relatively low compared with argon arc welding, and the denseness of the non-ferrous metal pig iron pieces is poor. The finish is not high, and the requirements for high-gloss castings cannot be met. Moreover, due to the design principle of the traditional cold welder, the power is generally around 2000w, and the internal electronic components are bare. In the environment of the foundry, the machine often fails, especially the electrode gun (the gas and electricity are separated, extremely vulnerable). It is a waste of energy and is not suitable for large-scale repair requirements of foundry manufacturers.
3, ESD-05 high efficiency, one machine multi-purpose type spark welding repair machine
ESD-05 adopts unique chopper soft switching technology, and the output control is accurate. In addition to the convenient operation of the traditional cold welding machine, the normal temperature welding repair, after the welding, the hand can be touched without internal stress, and the car grinding and milling can be directly processed. Beyond the characteristics. Its uniqueness:
3.1, accurate output control, internal integrated design, electronic components closed layout, unique motherboard structure design, thus avoiding the common faults of traditional EDM welding repair machine, the electrode gun adopts gas-electric integrated heat-dissipation design, greatly reducing failure rate. Combined with the principle characteristics of WS welding machine, semi-fusion welding (ion conversion plus "particle" conversion), so ESD-05 high-energy electric spark surfacing repair machine is only 600W power, but the speed and effect of welding repair It is several times the traditional electric spark welding repair machine 2000W. It is necessary to point out that the electric spark welding repair machine is not a traditional electric welder. The speed and effect are not determined by power. The key lies in the optimization design of the internal system.
3.2, the welding material is applicable to a wide range, the ordinary welding electrode can be used directly, such as 308, 208, 303, 506, etc., the argon arc welding electrode of non-ferrous metal or even the electrode made of its body material can be used. This greatly reduces the cost of use and labor of the foundry.
3.3, welding speed is fast, 2mm aluminum alloy only needs 10s, 2mm gray iron only takes 1 minute. Since ESD-05 uses a single point of output energy, each single point of the welding material is bonded to the substrate in a molten state to form a metallurgical bond, resulting in a strong bond bonding (semi-fusion property), especially overcoming The problem of poor compactness after the conventional electric spark welding repair has greatly improved the repairing efficiency of the foundry.
3.4. The problem of low welding and bonding of high-content magnesium alloys and copper alloys is generally considered to be impossible to weld. Because ESD-05 uses instantaneous high-energy output, it effectively solves the welding repair of high-conductivity metals such as copper and aluminum, and overcomes the shortcomings of common point spark surfacing.
3.5. The problem of chromatic aberration of phosphating after welding of ductile iron and gray iron has always been a problem. Since ESD-05 can use a variety of welding consumables, we have found a kind of welding consumables, which can make the welding of gray iron ductile iron. Phosphating has no chromatic aberration or small chromatic aberration. It can also make the gray iron parts weld after grinding, or the milling machine has no color difference or small color difference, and can also be polished with oil stone.
3.6. Disadvantages: The efficiency is still not as good as that of electric welding machine and argon arc welding machine.
ESD-05's high-efficiency, multi-purpose spark-sand weld repair machine is made more attractive to people with its outstanding advantages.
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Label: How to repair casting defects?
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