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The combined boring machine developed is specially designed to repair the spindle hole of the locomotive engine body. The machining workpiece of the special boring machine is mainly used to repair and process the spindle hole of the engine body of Beijing 12V240 locomotive, taking into account the processing of the Dongfeng type and other body spindle holes.
The external dimensions of the Beijing locomotive engine body are: 2 XI385mm XI068mm, and the weight is 2712kg, which brings certain difficulties to lifting, positioning and clamping. There are 7 spindle holes on the body, and the coaxiality is required on the same axis. 08mm, the surface roughness of the hole is required to be 艮=1.6fim, the body material is 45 high-quality carbon structural steel, and the cutting allowance of the hole surface is <.15mm. The user proposes to repair one piece per day as much as possible, which is not high in productivity.
1 Selection of positioning reference and clamping method The structure of the engine body spindle hole is as shown.
The combined boring machine is generally a multi-knife machining with concentrated operations, which not only has a large cutting load, but also changes the direction of the workpiece. Therefore, the correct selection of the positioning reference and clamping position is an important condition to ensure the machining accuracy. For the blank reference selection, the uniformity of the machining allowance should be considered; for the selection of the smooth positioning reference, the positional relationship between the base and the machining part should be considered, which is beneficial to ensure the machining accuracy. The positioning of the clamping part should be selected with sufficient clamping force to minimize the deformation of the workpiece and the fixture can be easily guided and passed through the tool.
The positioning of the body on the combined trampoline is based on the principle that the process reference coincides with the design basis. The bottom surface is the positioning surface in the 7 direction, and the inner surface of the rear side boss of the body is the positioning surface in the X direction. The positioning of the body on the trampoline can be achieved by setting corresponding positioning blocks on the surface of the trampoline. The clamping adopts 8 pressure plates, 4 in front and rear, and the workpiece is fixed on the machine tool by bolts and nuts by using the bosses at the bottom of the body. The positioning of the mast relative to the main shaft hole of the machine adopts the expansion type self-finding positioning guide sleeve. The outermost I and W holes of the body are used as the positioning reference, and the I, B, IV, V, W5 holes can be processed at one time. Then, using the other two holes of the five holes as the positioning reference, two holes of I and VI are processed. This mutual reference positioning scheme can ensure that the seven holes processed reach the coaxiality requirement.
2 Combination type of boring machine and key combination of technology The configuration of boring machine should be determined according to the structural characteristics, processing requirements, process plan and productivity of the parts to be machined, due to process arrangement, different configurations of power components, number of parts installed and work. A number of configuration schemes can be generated depending on the number of bits. Different configuration schemes have an impact on the complexity, generalization degree, structural processability, machining accuracy, possibility of machine tool re-adjustment and economic effects of the combined machine tool. In order to realize the process plan of the engine body spindle hole, and considering the requirements of economy and processing efficiency, the combined machine tool configuration as shown is adopted. The boring bar and the power head are connected by a floating joint to prove the torque transmission, thereby reducing the requirement of the workpiece for positioning accuracy. The combined boring machine is fixed by a worktable and the power head is operated in an axial feed mode.
The key technical points in the design of the special combination boring machine for the locomotive engine body spindle hole machining are as follows.
Positioning issues include the positioning of the engine block at the machine and the positioning of the shank relative to the spindle bore. Since the driving of the boring power head arbor in this scheme adopts the floating joint connection mode, the positioning requirement of the workpiece on the machine tool is greatly reduced, and the positioning block can be set on the bed surface according to the original positioning standard of the machine body to meet the requirements. The positioning of the arbor relative to the spindle hole adopts the expanding self-finding positioning guide sleeve, which is satisfied by the machining precision of the guide sleeve, and the matching gap between the guide sleeve and the arbor is selected to meet the positioning requirement.
Deflection of the extra-long mast The arbor will produce a certain degree of deflection under the influence of gravity and affect the machining accuracy. We use hollow shank to reduce deflection; and add elastic floating support in the middle of the mast, the elastic force is 2/3 of the weight of the shank. In addition, the radial force generated by the cutting causes the shank to have deflection and error In this regard, we use empirical data to correct the tool, reduce or eliminate the error.
Dimensional Accuracy and Surface Roughness of the Workpiece The dimensional accuracy of the workpiece depends on the manufacturing accuracy of the arbor, the rigidity of the shank system, the rotation accuracy of the guide sleeve, and the positional accuracy of the knives. The surface roughness depends on the rigidity of the toolholder system, the geometry of the tool and the reasonable amount of cutting. The degree of concentricity depends on the quality of the guide sleeve and the support. Therefore, using a high-powered power head, selecting a better material and increasing the number of support of the tool holder to increase the rigidity; optimizing the geometric parameters of the tool and the amount of cutting, improving the cutting conditions, and achieving the purpose of improving the machining accuracy.
3 Technical measures taken 3.1 Positioning and guiding of the tool holder When the special combined boring machine is machined, the shank needs to be positioned and guided during the machining process. Therefore, first use the outermost I and M2 holes of the body as the positioning reference, and process the other 5 holes, and then use any two holes of the processed 5 holes as the positioning reference to process the I and VE 2 holes. To meet the principle of mutual benchmarking.
In the mast assembly, there is an expansion type self-finding positioning guide sleeve on the left and right sides, which functions to ensure the correct position of the tool for the workpiece and the support rigidity of the lifting tool system. The positioning guide sleeve is composed of a tension sleeve, a tapered sleeve, and a left and right fastening nut. Before the mast is loaded with the main shaft hole of the machine body, put the tension sleeve into the spindle hole of the engine body, then put the taper sleeve on the cutter bar, then put the cutter bar together with the taper sleeve into the tension sleeve, and tighten it tightly. The nut is forced to force the tension sleeve to move and clamp the taper sleeve to achieve automatic centering of the knife bar. When it is necessary to disassemble, reverse the sequence, the conical sleeve can be pulled out together with the cutter bar.
3.2 The connection between the mast and the boring head In order to reduce the influence of the position error of the mast and the vibration of the mast on the machining accuracy, the arbor is made to avoid the different axes of the mast and the guide sleeve while using the guiding device. "Influencing machining, the mast and the boring head are connected by a floating joint. The force between the arbor and the floating chuck is transmitted by the key, and the axial locking is the locking screw. Since the bowl seat and the flange and the rear joint have a certain gap in the radial direction, the mast can use the ball as a fulcrum to make a small amount of floating.
3.3 Auxiliary support mast assembly is a key component of the combined boring machine. The shank for the special combination boring machine is very long. When machining 1, 11, condition, and \ (15 holes, I and W2 holes are used as the positioning reference. The span of the rod reaches 2280mm. Due to the influence of the self-weight and cutting force of the arbor, the arbor will have a certain curvature. In order to reduce the influence of the shank bending on the machining accuracy, the auxiliary support is adopted. The auxiliary support can pass the bolt and the wedge. The block adjusts the height, and the auxiliary support is in contact with the mast by two (or two rows) rolling bearings which are mutually U-shaped. The support under the rolling bearing is supported by the spring, which realizes the floating contact between the rolling bearing and the mast, and the spring force of the spring is determined. For the weight of the mast 2/3. 3.4 How to install the mast: The mast and the boring head are connected by a floating joint and are detachable. When repairing the spindle hole of the machine, the body should be positioned on the trampoline. Tightly, then the mast is worn by the left end of the trampoline and connected to the boring head through the floating joint. Because the mast is long and the weight is large, it is impossible to fully advance the mast to the main shaft hole. In order to solve this problem, three mounting supports are used in the design. When the mast is installed, the mast is first lifted by the crane and placed on the two mounting supports at the left end, because the rolling bearing and the mast are mounted on the mounting support. The contact can be easily pushed into the spindle hole of the human body and passed through the spindle hole and placed on the mounting support on the right side. The mounting support can also be adjusted by bolts and wedges to achieve coaxial connection between the mast and the boring head.
4Practical results The finite element analysis of the combined trampoline and key components was carried out using I-DEAS software, which was verified and met the requirements. And the special combination trampoline has undergone actual processing test, which proves that it can fully meet the technical requirements put forward by the user.
Wang Yucheng, Shao Min. The basic principles and numerical methods of the finite element method. Beijing: Tsinghua University Press, 1997. Wang Fuxing, Wang Shugui Material Mechanics Course. Beijing: China Light Industry Publishing Dai Wei. Metal cutting machine tools. Beijing: Mechanical Industry Press. 1994. Li Kaifo. Overview of the machine tool industry. Beijing: Mechanical Industry Press, 1993. Xie Jiaxuan. A concise manual for the combination of machine tools. Beijing: Mechanical Industry Publishing