Analysis and Discussion on repairing technology of

2022-08-21
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Analysis and Discussion on the repair technology of machine tool guide rail surface defects in the past 20 years

[Abstract]: This paper introduces several traditional welding repair methods for the repair of machine tool guide rail surface defects and analyzes the different characteristics of various methods to determine the reasons for the limitations of the repair of machine tool guide rail surface defects. At the same time, a new casting defect repair technology and its equipment, casting defect repair machine, have been carried out practical operation experiments and microstructure analysis of test bars, which shows that using casting defect repair machine to repair machine tool guide rail surface defects is in line with quality inspection standards. Further analysis shows that defect repair machine is a new technology worthy of promotion in casting defect repair

key words: repair of machine tool guide rail defects spray welding (brazing) arc welding new process casting defect repair machine

1, experimental purpose

through the welding results of several traditional welding repair processes in the defects of machine tool guide rail, analyze the reasons for the poor repair results of machine tool guide rail. Through the research on the repair results of the casting defect repair machine on the machine tool guide rail surface, it is determined that a new technology and process for repairing the machine tool guide rail surface, which is really feasible and has reached the forefront of the industry, will reduce the waste of energy for the country and increase benefits for enterprises

2. Welding repair results and analysis of traditional welding repair process

2.1 preparation before test:

2.1 number of defective guide rails: 4 pieces, material HT, number of defects of each guide rail ≥ 2, area of each guide rail defect s < 1000mm2, number of defects with depth h < 8mm is not less than 2, s > 1000mm2, number of defects with depth h < 8mm is not less than 2, heat treatment status: 3 pieces have not been surface quenched, 1 piece has been surface quenched

2.1.2 spray welding equipment, electric arc welding equipment, Nickel based welding powder F103 (C ≤ 0.15, 8.0 < Cr < 12, 2.5 < Si < 4.5, 1.0 < B < 1.7, Fe ≤ 8, the rest Ni =, cast iron welding rods: Z308, z248.

2.2 welding repair results and analysis

2.2.1 spray welding is carried out according to the spray welding process, preheat the guide rail surface to more than 150 ℃. After the preliminary spray of welding powder is completed, heat the spray surface to more than 900 ℃ -1200 ℃, so that the welding powder melts and forms a flat surface. Due to the long preheating and heating time, the workpiece has a large heating area, and the thermal stress With larger force, it is easier to produce cracks than arc welding, and the linear shrinkage has a greater tendency to produce cracks. As the crack tendency is affected by factors such as spray welding time and spray layer thickness, the size of defects is limited to a certain extent, and the defects of welding repair need to be cleaned up. Due to the high proportion of Fe in the powder, the color of the spray layer formed is more similar to that of the base metal than that of arc welding. However, due to a certain amount of Ni, it cannot be closer to the color of the base metal, and machining can be carried out after welding repair

2.2.2 electric arc welding: use cast iron electrode z248 to conduct welding repair according to the corresponding process. There are two kinds of welding repair processes. The first kind: conduct welding repair when preheating to 550 ℃ -650 ℃ before welding, and keep the temperature for hours after welding repair. The second kind: do not preheat the workpiece before welding, and keep the temperature for hours after welding. The welding repair quality of the two methods is not easy to guarantee, cracks and hard spots are easy to appear, and it is not easy to carry out machining after welding repair. Welding rods are cheap

use nickel based cast iron electrode Z308 to carry out welding repair according to the corresponding process. In addition to the heating hammering process, the gap between the welding layer and the welding layer should be stopped and cooled to below 60 ℃. There are few pores and cracks in the welding repair area, with good machinability, high bonding strength and no falling off. Due to the influence of oil absorption after machining of machine tool guide rail and blowing force of electrode, it is easy to produce undercut and form "welding repair trace". In addition, because the electrode contains a large amount of nickel element, The color of the welding repair area is very different from that of the base metal, and the welding rod is expensive

2.2.3 result analysis the traditional spray welding and arc welding processes are easy to produce cracks after welding repair, the workpiece is easy to be heated and deformed, and it is easy to have secondary pores. The common characteristics of the welding repair are the large difference between the metal color and the base metal, which is also the fundamental reason why the traditional welding repair process can not completely solve the defect repair of machine tool guide rail. The traditional welding repair process is not suitable for the repair of visible machined surfaces, but for the repair of non machined or invisible machined surfaces. The price of some welding repair materials is high, and the welding repair quality is not easy to be stable, which requires the operator to be skilled and experienced

3. Welding repair effect and analysis of casting defect repair machine:

3.1 production and analysis of test bar

3.1.1 prepare a piece Φ thirty × 200 test bar, material HT250, surface roughness Ra0.8, drill on the surface Φ The hole 5mm deep and mm deep shall be welded and repaired with akzqb-2000c casting defect repair machine. The repair material shall be 0.8 × 0.25mm thick metal sheet and 0.4mm thick HT250 iron filings

3.1.2 grind and polish the weld repair, and make metallographic analysis test pieces. The metallographic structure is shown in Figure 1 and Figure 2. In Figure 1, the base metal HT250 is on the left, and the 0.8 × 0.5 × 0.5 × 0.5 × 0.5 × 0.5 × 0.5 × 0.5 × 0.5 × 0.5 × 0.5 × 0.5 × 0.5 × 0.5 × 0.5 × 0.5 × 0.5 × 0.5 × 0.5 ×. There is no obvious boundary at the weld repair, the transition area is small, there is no carbide precipitation near the weld repair point, the metal structure at the weld repair is dense, and there is no crack. Conclusion: according to the macroscopic inspection, the metal color of the weld repair point is the same as that of the base metal near the weld repair point and the whole test bar at room temperature. The weld repair point with the repair material of 0.8 # is denser than the base metal. The density of the weld repair point with the same material is the same as that of the base metal. The metallographic structure analysis: there is no crack, the surrounding metallographic structure has not changed, there is no internal stress, and there is no hardening and softening

3.2 welding repair effect and analysis of guide rail defects

3.2.1 preparation before welding repair: number of guide rails: 4; Therefore, the material is more durable: ht200-ht400; Heat treatment state: 2 pieces of surface quenching, hardness hrc50-56; 2 pieces without surface quenching, hardness Hb, with Φ 1- Φ 6mm; There are several mm deep defects. One akzqb-2000c casting defect repair machine, with 0.8 # Φ 0.8mm wire and HT200 iron filings

3.2.2 welding repair effect and analysis: akzqb-2000c casting defect repair machine is used, and the repair material is 0.8 # Φ 0.8mm metal wire and HT200 iron filings are used to weld and repair the quenched and unhardened guide rail surface defects respectively. After grinding and polishing, the welding and repair effect is tested macroscopically. The metal color of the welding and repair point is the same as that of the base metal, and there is no undercut and burn mark. The temperature near the welding and repair point and the whole workpiece is normal. The welding repair was tested on site with a 30x magnifying glass and a hardness tester. The results showed that there was no obvious boundary, the metal at the welding repair point was dense, without cracks and sand holes, the hardness of the 0.8 # repair material welding repair point was Hb, the hardness of the HT200 repair material welding repair point was Hb, and the hardness near the welding repair point on the surface of the unhardened guide rail was Hb. The hardness near the weld repair point of the quenched guide rail is HRC, no annealing and softening are found, and it is qualified through the flaw detection agent

3.2.3 welding repair conclusion: the casting defect repair machine is used to weld the defect. The matrix is in the normal temperature state, without stress, crack, undercut, welding repair trace, dense welding metal, annealing, softening, hard spot and hardening. It can be machined. The metal color of the welding repair is the same as that of the base metal, and the existence of pores is not allowed. It meets the quality inspection requirements of defect repair on the machined surface. Using the principle of resistance heat generation, the casting defect repair machine instantly melts the repair material at the defect, with high bonding strength, no possibility of falling off, and the diameter of the welding repair point can reach Φ 1.5mm, the number of welding repair points can reach 25 times per second, and the thickness of the welding strip can reach 0.4mm. It is suitable for repairing all kinds of defects such as machined and non machined surfaces. The length of welding repair time depends on the size of defects, and castings with low cost and large defects have no welding repair significance. According to the performance requirements of the welding repair point, different materials of wire, sheet and iron filings can be selected for the repair material. It is not a special material, which is easy to obtain and the price is low

4. Conclusion:

the traditional spray welding, arc welding and other processes have certain limitations on the defect repair of castings. The machinability of spray welding is good, but it is easy to produce cracks, thermal deformation, annealing and other phenomena. The color is too different from the parent body. The bonding principle is mechanical bonding, and the bonding strength is lower than that of arc welding. The repair effect of arc welding is directly related to the selection of welding rods. The machinability and non generation of cracks of Z308 are good, but the difference between the repair trace and color and the parent is difficult to be eliminated, and the price is high; Z248 and other ordinary cast iron electrodes have poor machinability and crack productivity. The pre welding temperature rise and post welding heat preservation of castings in the traditional welding repair process also cause some inconvenience to the welding repair of large castings. Overall analysis, some problems in the traditional welding repair process make the defects of castings unable to be completely repaired. Different parts and different quality requirements should be selected and applied according to the actual situation. In view of the defect repair of machine tool guide rail parts, experiments have proved that it should be carefully selected on the non machined surface and avoided on the machined surface

using the casting defect repair machine to repair the defects of castings is a new technology. During the repair process, the castings do not rise in temperature, do not deform, do not produce cracks, the metal at the weld repair point is dense, do not produce hard spots, and do not have annealing phenomenon, so any machining can be carried out. The selection of filler materials is not restricted by materials. Through the selection of filler materials of different materials, the unity of the performance and color of the weld repair point and the matrix can be achieved. The filler material and the matrix are metallurgically combined, with high bonding strength and no falling off. The welding repair quality meets the quality inspection standard of casting products. It is a new technology worthy of wide promotion. For the defect repair of machine tool guide rail, practice has proved that it can be widely used and meet the requirements of its quality inspection standard. However, the welding repair process of the casting defect repair machine is Φ 1.5- Φ In the process of repeated melting and accumulation of 1.2mm weld repair points, the repair efficiency is the only factor that restricts its wide application in the process of large-area defect repair

according to the specific situation of castings, defects of a certain size within a certain range can be directly repaired by casting defect repair machine. For large defects, we also recommend the composite application of traditional welding repair process and casting defect repair machine, that is, using casting defect repair machine to solve the problems of surface cracks, surface machinability and color differences in traditional welding repair process, so that the majority of castings can be repaired by welding, Finally, the repair of casting defects is completely solved. In short, the correct application and promotion of casting defect repair machine to repair casting defects has practical significance in reducing the remelting of waste products caused by casting defects, increasing economic benefits for enterprises and reducing energy consumption for the country

Author: Yuan Zhidong (1969 -) male, Qiqihar, Heilongjiang Province research direction: casting technology and quality (end)

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