ã€Abstract】 In this paper, through the introduction of several traditional welding repair methods for the repair of machine tool guideway surface defects and the analysis of the different characteristics of various methods, the reasons for the limitations of machine guide rail surface defect repair are determined. At the same time, a newly emerged casting defect repair technology and its equipment—casting defect repairing machine—have been subjected to practical operation experiments and microstructure analysis of the test bar, which shows that the use of a casting defect repair machine to repair machine rail surface defects is in line with quality inspection. Standard, further analysis proves that the defect repair machine is a new technology worthy of promotion in casting defect repair.
Keywords: machine tool rail defect repair spray welding (brazing) new arc welding process defect repairing machine
1, the purpose of the experiment
Through the welding repair results of several traditional welding repair methods at the machine guide rail defects, the reasons for the poor repair results of the machine guide rails are analyzed. Through the research on the repair results of the casting defect repair machine on the guide surface of the machine tool, it is determined that a new technology and process that can be repaired on the guide surface of the machine tool can be used to reduce the energy waste for the country and increase the profits for the enterprise.
2. Welding repair results and analysis of traditional welding repair process
2.1 Preparation before the test:
2.1.1 Defective track number: 4 pieces, material HT200-400, defect quantity of each guide rail ≥ 2, defect area of ​​each rail S<1000mm2, depth of defect less than 8mm<8mm, S>1000mm2, The number of defects having a depth of h<8mm is not less than two. In the heat treatment state, three surfaces have not been quenched and one surface has been quenched.
2.1.2 spray welding equipment, 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 remaining Ni =, cast iron electrode: Z308, Z248.
2.2 Welding results and analysis
2.2.1 Spray welding is performed according to the spray welding process. Preheat the guide rail surface to 150°C or more. After the preliminary solder powder is sprayed, heat the sprayed surface to 900°C-1200°C or more to form a flat surface after melting the solder powder. Due to the long preheating and heating time, the workpiece has a large heated area and a large thermal stress. It is more prone to cracks than arc welding. At the same time, the line shrinkage tends to produce more cracks. Because the crack tends to be influenced by the spray welding time, the thickness of the sprayed layer and other factors, the size of the defect is limited, and the defects of the welding repair are required to be cleaned. Because the proportion of Fe contained in the powder is high, the spray layer formed is more arc welded than the mother. The color of the wood is more similar. However, due to the presence of a certain amount of Ni, it is not possible to get closer to the base metal, and it can be machined after welding.
2.2.2 Arc welding: welding with welding rod Z248 according to the corresponding process, welding repair process is divided into two kinds, the first one: preheating before welding to 550 °C -650 °C welding repair, thermal insulation after welding 5-8 Hours, second: No preheating before welding and 3-4 hours after welding. The welding quality of the two methods is not easy to guarantee, and it is prone to cracks and hard spots. It is not easy to perform machining after welding repair. Welding rods are cheap.
Using nickel-based cast iron electrode Z308 welding process according to the corresponding process, and the hammering process of the heated state, the welding layer and the welding layer should be paused and cooled to below 60 °C, the weld repair area with less pores, cracks, good machining, combined High strength, no fall off phenomenon, due to machine tool guide oil absorption and welding rod blowing effect, easy to produce undercuts, the formation of "welding traces", in addition to the electrode contains a lot of nickel, the welding area color and the parent material A big difference, and the welding rod is expensive.
2.2.3 Result Analysis Traditional spray welding and arc welding processes are prone to cracking after welding repair. The workpiece is susceptible to thermal deformation and secondary porosity is likely to occur. The difference between the metal color and the base metal of the welding repair site is a common feature. The traditional welding repair process cannot completely solve the root cause of machine rail defect repair. The traditional welding repair process is not suitable for the repair of visible processing surfaces, and is suitable for the repair of non-machined or invisible processing surfaces. The price of some welding repair materials is high, and the quality of welding repair is not easy to stabilize. Operators are required to have rich technology and experience.
3, welding defect repair machine repair effect and analysis:
3.1 Production and Analysis of Test Rods
3.1.1 Prepare a Φ30×200 test rod made of HT250 with a surface roughness of Ra0.8. Drill 4-5 Φ5mm deep 3-4mm holes in the surface and use the AKZQB-2000C casting defect repair machine. For welding repair, the fill material is 0.8# with a thickness of 0.25mm and HT250 iron with a thickness of 0.4mm.
3.1.2 Grinding and polishing the weld repairing section to produce a metallographic analysis test piece. The metallographic structure is shown in Fig. 1 and Fig. 2 . In Figure 1, the left side is the base material HT250, the right side is the 0.8# fill material, the left side of Figure 2 is the base material HT250, and the right side is the HT250 iron filings. There was no obvious line of demarcation at the weld repair site, a small transition area, no carbide precipitation near the weld repair site, and a dense metal structure at the weld repair site, and no cracks were observed. Conclusion: In the macroscopic inspection, near the welding repair point and the entire test bar at room temperature, the metal color of the welding repair point is the same as that of the parent metal, and the repair point of 0.8 # for the supplementary material is more dense than that of the parent material, and the repair material is the welding repair point of the same material. The same density of the base metal, metallographic analysis: no cracks, the surrounding metallurgical structure has not changed, no internal stress, no hardening, softening phenomenon.
3.2.1 Preparation before welding: Number of guide rails: 4 pieces; Material: HT200-HT400; Heat treatment state: 2 pieces of surface quenched, hardness HRC 50-56; 2 pieces without surface hardening, hardness HB170-230, Φ1-Φ6mm Deep 3-4mm defect number. AKZQB-2000C casting defect repairing machine 1 sets of 0.8#, Φ0.8mm metal wires and HT200 iron filings.
3.2.2 Welding effect and analysis: Using AKZQB-2000C casting defect repairing machine, the 0.8mm Φ0.8mm wire and the HT200 iron filings are used as the supplementary material to weld and repair the quenched and unquenched guideway surface defects. After polishing and polishing, macroscopically detect the welding effect. The metal color of the welding point is the same as that of the parent metal, no undercut, no burn marks, near the welding repair point and the entire workpiece at room temperature. The on-site inspection of weld repairs using a 30-times magnifying glass and hardness tester showed that there was no clear line of demarcation, the welding repair metal was dense, crack-free, and non-blisted, and the 0.8# filler weld repair hardness HB180-220, HT200 filler weld repair The point hardness is HB210-240, and the hardness of HB160-210 is near the repair point of the unquenched rail surface. Hardness of the quenched rail near the welding point HRC51-56, no annealing, softening phenomenon, qualified by the detection of the flaw detector.
3.2.3 Welding repair conclusion: The defect repairing machine is used to repair the defects at the normal temperature, no stress, no cracks, no undercuts, no traces of weld repair, dense weld metal, no annealing and softening. No hard spots, no hardening, can be machined. The metal color of the welding repair site is the same as that of the base metal. It meets the quality inspection requirements for the repair of surface defects. The casting defect repairing machine utilizes the principle of resistive heat generation to instantly melt the filler material at the defect, and has high bonding strength and no possibility of shedding. The diameter of the welding repair point can reach Φ1.5mm, and the number of welding repair points can be completed up to 25 times per second. The thickness of the solder fillet is 0.4mm, which is suitable for welding and repairing various defects such as processed surface and non-processed surface. The length of welding repair depends on the size of the defect, and the cost is low and the defective casting has no meaning of welding. According to the performance requirements of the repair welding point, the filler material can be selected from different materials, such as silk, sheet, and iron filings. It is not exclusively for materials, and it is easy to obtain and the price is low.
4 Conclusion:
Traditional spray welding, arc welding and other processes, there are certain limitations on the defect repair of castings, spray welding processability is good, but easy to produce cracks, thermal deformation, annealing and other phenomena, the color is too different from the mother, combined The principle is mechanical bonding, and the bonding strength is lower than that of arc welding. Arc welding welding effect is directly related to the choice of welding rod, Z308's machinability and crack generation is not good, but the difference between the welding traces and the color and the mother is difficult to eliminate, and the price is high; Z248 and other ordinary cast iron electrode Both the workability and the crack yield were not good. In the traditional welding repair process, the pre-weld heating and post-weld insulation of the castings also cause some inconvenience for the welding of large castings. The overall analysis, some problems in the traditional welding repair process make the casting defects can not be completely repaired, different parts Different quality requirements should be selected according to the actual situation. For the machine tool guide rail defect repair, experiments have shown that in the non-processing surface should be carefully selected, the processing surface should be avoided.
The use of casting defect repair machines to repair the defects of castings is a new technique. During the repair process, the castings do not increase in temperature, do not deform, and no cracks are produced. The metal in welding repair points is dense, and hard spots and annealing are not generated. Perform any machining. The selection of filler materials is not limited by the material. The selection of different materials for the material can achieve the unity of welding point performance, color, and matrix. The supplement material and the parent metallurgical combination have high bonding strength and do not produce shedding. The welding repair quality conforms to the quality inspection standard of the casting product and is a new technology worthy of wide promotion. The defect repair of the machine tool guide rail has proved that it can be widely used. Can meet the requirements of its quality inspection standards. However, the welding repair process of the casting defect repairing machine is a process of repeated melting and accumulation of the Φ1.5-Φ1.2mm welding point. In the process of large-area defect repair, the repair efficiency is the only factor that restricts its widespread application.
According to the specific conditions of the casting, defects in a certain range can be directly applied to the welding repair machine for the defect repairing machine. For large defects, we also recommend the composite application of the traditional welding repair process and the casting defect repair machine, that is, the use of a casting defect repair machine to solve the traditional The appearance of surface cracks, surface processability and color differences in the welding repair process make it possible for the majority of castings to have weldable repairs, and ultimately solve the problem of repairing casting defects. In short, the correct application and promotion of casting defect repair machines to repair casting defects have a practical significance in reducing waste remelting caused by casting defects, increasing economic benefits for enterprises, and reducing energy consumption for the country!
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