Figure 1 Hydraulic cylinder parts
Fig. 2 Workholding
Figure 3 Processing
Figure 4 floating boring knife
1. Floating trowel 2. Guide block 3. Seal ring 4. Compression nut Fig. 5 Rake-head structure
Figure 6 hob
Figure 7 Wave phenomenon
I. Overview Supporting the hydraulic cylinder is an important component of the crane. The reliability of the hydraulic cylinder is related to the safety of the crane when it is lifted. Therefore, the technical requirements of the support hydraulic cylinder are high, and it is reflected in the high requirements for precision machining of the parts. The cylinder block is an important part of the hydraulic cylinder. It is composed of welded joints and flange plates on the cylinder tube. As shown in Figure 1, the materials used for the steel pipes, joints and flanges of the cylinder block are 45 steel. The inner diameter of the workpiece blank is Ø210mm, the outer circle is Ø300mm and the length is 740mm. Due to the small bore size of the cylinder body, the used boring bar is fine, the chips are not easily discharged, the heat radiating ability is poor, and the tool is easily worn, which brings certain difficulties to the machining. Therefore, appropriate processes should be used for processing. Second, the problems appearing in the inner hole processing In the processing process, the hole in the cylinder bores the following problems. The centerline of the bore is skewed and the wall thickness of the cylinder is not uniform. There are different diameters at the two ports of the cylinder bore. The surface of the inner hole is uneven, and the surface roughness does not meet the requirements. Third, the selection of the process benchmark cylinder must go through the following procedures: rough center frame base → coarse wheel outer circle, inner hole → welding flange → draw 6-Ø20 hole line → drill hinge 6-Ø20 → with column pin And welding → annealing → precision car flange positioning surface → rough boring → semi-finished boring → fine boring → rolling → hole in the car hole → drilling. In order to eliminate the problem of internal stress and non-uniformity of the hardness of the material due to the combination welding of the cylinder block, the cylinder must be subjected to stress relief annealing in order to reduce the deformation of the workpiece. The key process in these processes is the keyhole to the roller bore. In order to ensure that the wall thickness of the workpiece after rolling and rolling is even, and to achieve the required technical requirements, the flange surface and the center frame base surface are used as the reference for the subsequent bore and rolling, and the inner hole groove processing. Benchmarking principles. Fourth, the analysis of some issues affecting the quality of processing and solutions The following analysis of the boring hole to the rolling hole and other processes in the process of the problem. In rough, semi-finished, fine boring and rolling, the equipment used is TZ120A deep hole drilling boring machine. The workpiece clamping method is shown in Figure 2. In order to eliminate the large amount of cutting heat generated during machining, it is easy to remove the chips and lubricate the tool block and the guide block. The oil pump output from the gear pump must have a certain pressure and flow rate. The through holes in the boring bar and the boring tool body are small. Holes flow out, cooling the cutter head while swarfing the chips from the unmachined surface. To make chip removal easy, the chips should be C-shaped. Rough and semi-finishing In the rough and semi-finishing process, in order to reduce the radial force Fy at the time of boring and to make the cutting speed faster and the depth of cut greater, a cemented carbide with a main angle of 75° should be used. Knife, in order to ensure the ideal cutting process, when boring the long cylinder with small bore diameter, due to the thin boring bar and poor rigidity of the system, a reasonable amount of cutting should be used. When rough, the machine speed is 30r/min, the feed rate is 7.5mm/min, the cutting depth is 1.5mm, the inner hole size is controlled at Ø218mm, the semi-finishing machine, the machine speed is 30r/min, the feed rate is 10.6 Mm/rnin, depth of cut is 0.75mm, inner diameter is controlled to be around Ø219.5mm. The reason for the uneven wall thickness of the inner hole is caused by the deviation of the centerline of the inner hole and the countermeasures. In the semi-finishing process, when the body size meets the requirements of the existing technology, the gap between the body guide block and the inner hole is 0.10mm. In the case of boring, due to the poor stiffness of the boring bar, the tool will produce a slight displacement under the action of cutting resistance. Although under the control of the mandrel guide block, the size of the bored hole is correct, but the center line must be deflected by 0.10 mm at the entrance, resulting in a wall thickness difference of 0.20 mm. When the length of the workpiece is 736mm, the wall thickness difference will increase to 1.14mm. Since the machining allowance between semi-finishing and finish boring is 0.50 mm, it is impossible to correct the difference in wall thickness due to centerline deflection after boring. The measure to solve this problem is: The gap between the guide sleeve and the body guide block should be determined to be about 0.02mm. In this way, the tool will not be offset and the cylinder wall thickness will be solved. The reason why the size of one end of the workpiece after the semi-finishing process is correct and the other end is oversized is that in the semi-finishing process, although the inlet end dimensions measured during the test run are within the tolerance range, the closed end cutting is performed on the workpiece. The measurement cannot be performed during the processing. When the boring is completed and the measurement is performed, it may be found that the size of the outlet end of the cylinder tube is excessively poor, so that there is no machining allowance in the fine boring and the waste product is prone to occur. As shown in Figure 3, the reason for the waste product is that the center line of the boring bar forms a angle with the centerline of the boring tool head. Due to deflection, when the workpiece is boring, the boring head is in a wobbling state. In this way, the longer the inner bore is machined, the larger the skew oscillation and the larger the outlet end size. The solution to this problem is to match the centerline of the boring bar with the center line of the boring bar in the design of the boring head, without forming a horn. This solves the problem of different port sizes. In order to make the accuracy of the rolling cylinder block to the design requirements of the pattern, semi-finishing shall be followed by a secondary floating boring and the boring tool shall be an adjustable floating boring tool. As shown in Figure 4. The cutter head has a guide angle of 1°30' to 2° and has a flat wiper with a small back angle, ie a=4° to 6°. In this way, the boring action acts as a squeezing action, so that the surface roughness of the inner hole reaches Ra 1.6 μm, and the precision reaches IT7 level. Since the boring block floats and the workpiece is in rotation, the block has automatic neutrality and good guidance. The boring head structure is shown in Fig. 5. The guide block in the figure is nylon and has certain elasticity. Using this material as a guide block can avoid scratching of the processed surface while maintaining the necessary guiding requirements. When adjusting the guide block, the guide block should be adjusted slightly larger than the block size. In this way, the amount of interference can be automatically abraded during boring while maintaining a more accurate guiding accuracy. In production practice, we use the test method. In the first floating boring, the optimum rotation speed is 30r/min, the feed rate is 15mm/min, the cutting depth is 0.2mm, and the inner hole size is controlled at Ø219.9±0.01mm. The second time is fine. The optimum rotation speed is 30r/min, the feed rate is only 7.5mm/min, the cutting depth is 0.05mm, and the inner hole size is controlled at Ø220+0.03+0.05mm. The actual operation shows that this cutting amount is more appropriate, and lays a solid foundation for the subsequent rolling processing. Rolling process shown in Figure 6, in order to make the hole in the cylinder to meet the design requirements after rolling, according to the material and structure size rolling, the rolling interference used should be between 0.02 ~ 0.04mm. The roller used is an adjustable size ball roller. In the rolling process, the feed amount is too large and the rolling density is not enough in a unit time. Therefore, the rolled inner hole will have a rough surface, ie, a waviness phenomenon, as shown in FIG. 7 . To further make the bore in the cylinder more smooth, the first rolling speed is generally 70 r/min, and the rolling feed is 15 mm/min. The second rolling reduces the feed to 7.5 mm/min. As a result, the bore surface roughness in the cylinder has reached the technical requirements. This will increase the number of rolling times per unit of time, rolling density will increase, so as to overcome the wave phenomenon, improve product quality. Rolling process is the middle of the spherical roller R-shaped corner of the workpiece surface forced into the plastic surface deformation of the workpiece. Lubrication and cooling in the rolling process are the same as those in fine boring. V. Concluding remarks This paper proposes a reasonable and feasible process route and method by analyzing the process selection and rough point, semi-finishing, fine boring and rolling process of the supporting cylinder bore in the hydraulic cylinder. The cylinder processing quality has a reference effect on the processing of the same type of hydraulic cylinder bore.
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