Abstract: This paper analyzes and studies the laser hardening principle, process and computer control methods of engine components and crankshafts in key parts of automobile overhaul. Next page cast iron stainless steel valve Valve Machine,Valve Company,Value Valve Jiekelong Precision Manufacturing Co., Ltd. , http://www.nbcoupling.com
1 Introduction
Laser surface modification technology is a high-tech integration of light, machine and electricity that developed rapidly after the emergence of high-power lasers in the 1970s. The process has the advantages of good hardening effect, high degree of automation, simple operation, low energy consumption, high efficiency, minimal deformation of the workpiece, and basically no waste. The use of a laser to treat the surface of the part can change the physical structure, chemical composition and metallographic structure of the part surface, thereby changing the physical, chemical and mechanical properties of the part surface, such as anti-wear, corrosion and fatigue resistance, effectively solving Many conventional heat treatments are currently difficult to solve or solve the problem of poor surface properties of parts. As a result, rapid progress has been achieved in countries around the world. For example, the AVCOEVETT Institute has surface hardened the gray iron camshaft of Ford, with a maximum deformation of <0.13mm. At the same time, the institute also heat-treated the journal and the neck of the diesel ductile iron crankshaft with a hardness of 55-62HRC. The treated crankshaft does not need to be straightened, which reduces the cost of crankshaft heat treatment by 20% and achieves good results. effect.
China's laser surface hardening technology has only entered the use stage in recent years, but it is still blank in some fields. This paper describes the multi-function laser machine and its control system jointly developed by the author and Qingdao Zhongfa Laser Technology Co., Ltd. in the engine block of the automobile. Application of laser surface hardening of cylinder liners and crankshafts.
2 laser surface hardening principle
Laser surface hardening is also known as laser heat treatment. The principle is that the laser beam is used as a heat source to illuminate the surface of the engine to be strengthened, and the surface thereof is rapidly heated to above the metal phase transition temperature. When the laser leaves, the heat of the high temperature surface is rapidly transferred to the metal matrix to form self-quenching, so that after treatment The surface layer forms a cryptocrystalline martensite having a high hardness, thereby improving the surface hardness, wear resistance and service life of the part.
3 Laser equipment and technology
3.1 Laser equipment Laser surface hardening equipment includes three parts: 1.5kW CO2 laser generator, multi-function laser processing machine and computer control system.
3.2 Conventional methods and defects of automobile engine overhaul When the engine is overhauled, it is mainly treated by boring cylinder and grinding shaft. After repeated grinding of the cylinder wall, the surface hardness is reduced. Because the crankshaft journal is round due to grinding loss, it is generally necessary to re-grind the shaft and change. bush. The surface hardness of the crankshaft journal is reduced after repeated grinding and cannot meet the requirements for use. Therefore, the engine overhaul period after the conventional method is processed becomes short.
3.3 Laser processing of automotive engine overhaul The laser processing of automotive engine overhaul is a conventional overhaul process plus laser processing. Laser heat treatment is generally arranged after semi-finishing. Since the reflectivity of the metal to the CO2 laser with a wavelength of 10.6 μm is as high as 80% or more at normal temperature, the smooth surface of the polished surface is more reflective, and the reflection of the laser will cause a large amount of energy loss. Therefore, the pre-applied absorbing coating is required before the laser heat treatment. The layer method is used to increase the absorption rate of the laser on the surface of the part. The coating can absorb the far-infrared part of the electromagnetic wave, and various metal or non-metal oxides, graphite, carbon ink, phosphate, etc. are all good coating materials.
When the crankshaft is heat-treated, it is mounted on the machine table and clamped with two chucks. The diameter of the laser spot is adjusted to 2~3mm, and the power density is uniform, so that the hardness on the hardened strip of a certain width is uniform.
The laser head is mounted on a bracket that is mounted on the machine cross member, thereby enabling movement of the laser head in the up and down direction and horizontal movement. The laser beam is positioned above the crankshaft journal, the stepping motor on the table drives the crankshaft to rotate, and the laser head moves in the horizontal direction, and the carriage moves along the beam, thereby scanning a shape scan on the surface of the crankshaft in the width direction. Line (line type is controlled by microcomputer). The coverage of the hardened zone on the journal (hardened area ratio) is generally 30% to 50%. The rotation of the crankshaft, the horizontal movement of the laser head and the combined motion are automatically controlled by the program control system.
When the cylinder is heat treated, it is mounted on the rotating table at the bottom, the cylinder rotates, and the laser head moves up and down.
The process parameters of the laser hardening process mainly include scanning speed, hardening area ratio, hardening depth and machined surface roughness. These parameters depend on the laser power density, scanning speed, material type, and surface coating characteristics. The microstructure of the laser hardened strip has two to four layers, depending on the laser processing specification and material composition. At high speeds of heating and cooling, "white highlights" are generally observed on the surface of steel.
Since the laser beam is scanned on the inner wall of the cylinder according to a certain geometrical trajectory, the laser-treated hardened belt constitutes a hard skeleton; in the place where the laser is not processed, when the engine is working, the oil is first slightly worn to form an oil storage structure. Such a hard and soft combined cylinder inner wall not only improves wear resistance, but also has good tensile strength. The piston ring works under good lubrication conditions and its service life is greatly improved. The same principle applies to the crankshaft journal.
3.4 Experimental comparison and wear amount (1) The comparison between the untreated cylinder and the laser-processed cylinder car sports car is shown in Figure 1.