Encyclopedia of Hole Processing Methods _ Aperture

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Original Title: History of Russian (Soviet) Fighter Development: MiG 25 Fighter When it comes to the fastest aircraft flying today

Original title: Encyclopedia of Hole Processing Methods There are many processing methods for inner hole surface, such as drilling, reaming, reaming, boring, grinding, broaching, grinding, honing and rolling. 1. Drilling Drilling a hole in a solid part of a workpiece with a drill bit is called drilling. The drilling belongs to rough machining, the achievable dimensional tolerance grade is IT13 ~ IT11, and the surface roughness value is Ra50 ~ 12.5 μm. Drilling has the following process features: 1. The drill bit is prone to deflection. When drilling on a drilling machine, it is easy to cause the axis of the hole to be offset and not straight, but the hole diameter has no significant change; when drilling on a lathe, it is easy to cause the hole diameter to change, but the axis of the hole is still straight. Therefore, the end face should be machined before drilling, and a cone pit should be pre-drilled with a drill bit or a center drill so that the drill bit can be centered. When drilling small and deep holes, in order to avoid the deviation and unstraightness of the axis of the hole, the workpiece should be rotated as far as possible. 2. The aperture is easy to enlarge. When drilling, the radial force of the two cutting edges of the drill is not equal, which will cause the aperture to expand; the cutting deviation of the horizontal lathe is also an important reason for the aperture to expand; in addition, the radial runout of the drill is also the reason for the aperture expansion. 3. The surface quality of the hole is poor. The drilling chips are wide and are forced to roll into a spiral shape in the hole, and when they flow out, they rub against the hole wall and scratch the machined surface. 4. Axial force is large during drilling. This is mainly caused by the chisel edge of the drill. Therefore, when the drilling diameter d d is 30 mm, the drilling is generally carried out in two times. Drill out (0.5 ~ 0.7) d for the first time, and drill to the required hole diameter for the second time. Because the chisel edge does not participate in the cutting for the second time, a larger amount of feed can be used, so that the surface quality of the hole and the productivity are improved. 2. Reaming Reaming is the further processing of a drilled hole with a reaming drill to enlarge the hole diameter, improve the accuracy and reduce the surface roughness value. The dimensional tolerance grade of reaming is IT11 ~ IT10, and the surface roughness value is Ra12.5 ~ 6.3 μm. It belongs to the semi-finish machining method of holes, which is often used as the pre-machining before reaming, and can also be used as the final machining of holes with low precision. The reaming method is shown in Figure 7-4. The reaming allowance (D-d) can be found in the table. The type of reamer varies with the diameter. Taper shank reamers with a diameter of Φ10 ~ Φ32 are shown in Fig. 7-5a. The reamer with diameter of Φ25 ~ Φ80 is a sleeve-type reamer, as shown in Figure 7-5 B. Expand the full text Compared with the twist drill, the structure of the reamer has the following characteristics: 1. The rigidity is better. Due to the small cutting depth of the back of the reamer, less chips, the shallow and narrow chip groove of the reamer, and the larger diameter of the drill core, the rigidity of the working part of a reamer is increased. 2. The guidance is good. The reaming drill has 3 to 4 cutter teeth, the number of edges around the cutter is increased, and the guiding effect is relatively enhanced. 3. The chip condition is good. The reaming drill has no chisel edge to participate in the cutting, the cutting is light and fast, the larger feed amount can be adopted, the productivity is higher, and the machined surface is not easy to be scratched due to less chips and smooth chip removal. Therefore, compared with drilling, reaming has higher machining accuracy and lower surface roughness, and can correct the axis error of drilling to a certain extent. In addition, the machine tool used for reaming is the same as that used for drilling. III. Reaming Reaming is a method of finishing a hole based on semi-finishing (reaming or semi-finishing boring). The dimensional tolerance grade of the reamed hole can reach IT9 ~ IT6, and the surface roughness value can reach Ra3.2 ~ 0.2 μm. There are two ways of reaming: machine reaming and hand reaming. Reamers are generally divided into machine reamers and hand reamers. As shown in figure 7-8. Machine reamers can be divided into reamers with shanks (straight shanks with a diameter of 1 ~ 20mm and taper shanks with a diameter of 10 ~ 32mm, as shown in Fig. 7-8 a, B and C) and reamers with sleeves (diameter of 25 ~ 80mm, as shown in Fig. 7-8 f). Hand reamers can be divided into integral type (as shown in Fig. 7-8 d) and adjustable type (as shown in Fig. 7-8 e). Reaming can be used not only to machine cylindrical holes, but also to machine conical holes with taper reamers (as shown in Figure 7-8g, H). 1. Reaming mode The reaming allowance is very small. If the allowance is too large, the cutting temperature will be high, which will cause the reamer diameter to expand, resulting in the expansion of the hole diameter and the increase of chips, thus scratching the surface of the hole. If the allowance is too small, the tool marks of the original hole will be left, which will affect the surface roughness. Generally, the rough reaming allowance is 0.15 ~ 0.25 mm, and the fine reaming allowance is 0.05 ~ 0.15 mm. Low cutting speed shall be adopted for reaming to avoid built-up edge and vibration. Generally, f = 4 ~ 10 m/min for coarse reaming and f = 1.5 ~ 5 m/min for fine reaming. The feed rate of machine reaming can be 3 ~ 4 times higher than that of drilling, generally 0.5 ~ 1.5mm/R. In order to dissipate heat, remove chips, reduce friction, suppress vibration and reduce surface roughness, appropriate cutting fluid should be selected during reaming. Emulsion is commonly used for reaming steel parts, while kerosene can be used for reaming cast iron parts. As shown in Figure 7-9 a, if the axis of the reamer mounted in the tailstock sleeve is offset from the axis of rotation of the workpiece when reaming a hole on a lathe, the hole diameter will be enlarged. As shown in Fig. 7-9 B, if the axis of the reamer is offset from the axis of the original hole when reaming on the drilling machine, it will also cause the shape error of the hole. Machine reamers and machine tools are often connected by floating to prevent the enlargement of the hole diameter or the shape error of the hole during reaming. The floating Chuck used for the floating connection between the reamer and the machine tool spindle is shown in Fig. 7-10. The taper shank 1 of the floating Chuck is installed in the taper hole of the machine tool, the taper shank of the reamer is installed in the taper sleeve 2, the retaining pin 3 is used to bear the axial force, and the pin 4 can transmit the torque. Because there are large clearances between the tail of the taper sleeve 2 and the big hole, and between the pin 4 and the small hole,DHD Drill bit, the reamer is in a floating state. 2. Technological characteristics of reaming (1) The accuracy and surface roughness of reaming do not depend on the accuracy of the machine tool, but on the accuracy of the reamer, the installation method of the reamer, the machining allowance, the cutting parameters and the cutting fluid. For example, under the same conditions, the accuracy and surface roughness obtained by reaming on a drilling machine and on a lathe are basically the same. (2) The reamer is a finishing tool for sizing. Reaming is easier to ensure dimensional accuracy and shape accuracy than fine boring, and the productivity is higher, especially for small holes and slender holes. However, due to the small reaming allowance, the reamer is often floating connection, so it can not correct the axis deviation of the original hole, and the position accuracy of the hole and other surfaces needs to be guaranteed by the previous or subsequent processes. (3) The adaptability of reaming is poor. A reamer with a certain diameter can only process a hole with one diameter and dimensional tolerance class. If the tolerance class of the hole diameter needs to be improved, the reamer needs to be ground. The hole diameter of reaming is generally less than Φ80mm, usually less than Φ40mm. For stepped holes and blind holes, the manufacturability of reaming is poor. IV. Boring and turning Boring is the further machining of a drilled, cast, or forged hole with a boring cutter. Can be performed on a lathe, boring machine, or milling machine. Boring is one of the commonly used hole processing methods, which can be divided into rough boring, semi-fine boring and fine boring. For rough boring, the dimensional tolerance grade is IT13 ~ IT12, and the surface roughness value is Ra12.5 ~ 6.3 μm; for semi-fine boring, the dimensional tolerance grade is IT10 ~ IT9, and the surface roughness value is Ra6.3 ~ 3.2 μm; for fine boring,down the hole bit, it is IT 8 ~ IT 7, and the surfaces roughness value is Ra 1.6 ~ 0.8 μm. 1. Lathe hole Lathe holes are shown in Fig. 7-11. For holes without through holes or holes with right-angle steps (Fig. 7-11b), the turning tool can make longitudinal feed motion first, and then change to transverse feed motion when cutting to the end of the hole, and then process the inner end face. In this way, the inner end surface can be well connected with the hole wall. Turn the inner hole groove (Fig. 7-11d), insert the turning tool into the hole, first make the transverse feed, and then make the longitudinal feed after cutting to the required depth. The turning hole on the lathe is the rotation of the workpiece and the movement of the turning tool. The size of the hole diameter can be controlled by the cutting depth of the turning tool and the number of passes. The operation is more convenient. Lathe holes are mostly used to process the holes of disc sleeve and small bracket parts. 2. Boring machine boring There are three main ways for boring machine to bore holes: (1) The spindle of the boring machine drives the arbor and the boring cutter to rotate, and the worktable drives the workpiece to make longitudinal feeding motion, as shown in Fig. 7-12. The hole diameter bored in this way is generally less than about 120 mm. Figure 7-12 a shows the overhanging arbor, which should not be extended too long to avoid excessive bending deformation. It is generally used to bore holes with small depth. The arbor shown in Fig. 7-12 B is longer and is used to bore coaxial holes far away from the two walls of the box. And in ord to increase that rigidity of the cutter bar, the other end of the cut bar is supported in a guide sleeve seat of a rear upright post of the boring machine. (2) The spindle of the boring machine drives the arbor and the boring cutter to rotate and perform longitudinal feed motion, as shown in Fig. 7-13. In this way, the overhang length of the spindle increases and the rigidity decreases, so it is generally only used for boring holes with shorter length. And (3) that flat turntable of the bore machine drives the bore cutter to rotate, and the worktable drives the workpiece to do longitudinal feeding motion. For the above two boring methods, the size and tolerance of the hole diameter shall be guaranteed by adjusting the extension length of the cutter head, as shown in Fig. 7-14. Adjustment, trial boring and measurement are required, and formal boring can be carried out only after the hole diameter is qualified, which requires high operation technology. The flat turntable of the boring machine shown in Fig. 7-15 can move up and down with the headstock, and can also rotate itself. The radial tool rest in the middle part can make radial feeding motion and can also be in any required position. As shown in Fig. 7-16 a, the large hole can be bored by using the radial tool rest to make the boring tool in the eccentric position. This boring method is often used for holes above Φ 200mm, but the hole should not be too long. Fig. 7-16 B shows the boring of the inner groove. The flat rotary disc drives the boring cutter to rotate, and the radial tool rest drives the boring cutter to make continuous radial feed motion. If the tool tip extends out of the end of the arbor, the end face of the hole can also be bored. The boring machine is mainly used for boring the end faces of supporting holes, inner grooves and holes of large and medium-sized supports or boxes; the boring machine can also be used for drilling, reaming, reaming, milling grooves and milling planes. 3. Boring with milling machine Boring on a horizontal milling machine is performed in the same manner as shown in Figure 7-12 a. The boring cutter bar is installed in the taper hole of the spindle of the horizontal milling machine for rotary motion, and the workpiece is installed on the worktable for transverse feed motion. 4. Floating boring As mentioned above, lathe, boring machine and milling machine often use single-edged boring cutter. In batch or mass production, the floating boring cutter can be used for finish machining of holes with large diameter ( Φ 80mm), long hole depth and high precision. The adjustable floating boring block is shown in Figure 7-17. When adjusting, loosen the two screws 2 and turn the screw 3 to adjust the radial position of the cutter block 1 to the diameter and tolerance of the hole to be bored. The floating boring tool turns the workpiece on the lathe as shown in Fig. 7-18. During working, the arbor is fixed on the square tool rest, the floating boring tool block is installed in the rectangular hole of the arbor, and the automatic centering is realized by the balance of the radial cutting forces of the two cutting edges, so that the aperture error caused by the installation error of the tool block on the arbor can be eliminated. Floating boring is essentially equivalent to reaming, and its machining allowance, dimensional accuracy and surface roughness values are similar to those of reaming. The advantage of floating boring is that it is easy to ensure the processing quality stably, the operation is simple and the productivity is high. However, it can not correct the position error of the original hole, so the position accuracy of the hole should be guaranteed in the previous process. 5. Technological Characteristics of Boring Boring with single-edge boring tool has the following characteristics: (1) The adaptability of boring is strong. Boring can be carried out on the basis of drilling, casting and forging. A wide range of dimensional tolerance grades and surface roughness values can be achieved; almost all holes of various diameters and structural types can be bored except for very small and deep holes, as shown in Table 7-1. (2) Boring can effectively correct the position error of the original hole, but because the diameter of the boring bar is limited by the diameter of the hole, its rigidity is generally poor, and it is easy to bend and vibrate, so the control of boring quality (especially slender holes) is not as convenient as reaming. (3) The productivity of boring is low. Because boring requires multiple passes with small depth of cut and feed rate to reduce the bending deformation of the arbor, and boring on boring and milling machines requires adjusting the radial position of the boring cutter on the arbor, Borehole Drill Bits ,dth drill bits, the operation is complex and time-consuming. (4) Boring is widely used in the hole processing of various parts in single and small batch production. In mass production, boring dies are needed to bore the bearing holes of brackets and boxes. Five, pull the hole Broaching is an efficient finishing method. In addition to broaching round holes, through holes and inner keyways with various cross sections can also be broached, as shown in Fig. 7-19. The dimensional tolerance grade of broached round holes is IT9 ~ IT7, and the surface roughness value is Ra 1.6 ~ 0.4 μm. 1. Broaching can be regarded as the planing of multiple planing tools arranged in the order of height, as shown in Figure 7-20. The structure of the round hole broach is shown in Fig. 7-21, and the functions of each part are as follows: The handle is where the broaching tool is held by the broaching tool holder. The neck has the smallest diameter. When the broaching force is too large, it usually breaks here, which is convenient for welding repair. The transition cone guides the broach into the hole to be machined. The leading part ensures a smooth transition of the workpiece to the cutting part, and at the same time, it can check whether the hole diameter before pulling is too small, so as not to damage the first cutter tooth due to excessive load. The cutting part includes the rough cutting teeth and the fine cutting teeth, which are responsible for the main cutting work. The calibrating part is a calibrating tooth which is used for calibrating the aperture and smoothing the wall of the aperture. When the diameter of the cutting tooth is reduced after sharpening, the first few calibration teeth are ground into cutting teeth in turn. The rear guide part prevents the workpiece from drooping to scratch the machined surface and damage the cutter teeth when the cutter teeth of the broach are cut away from the workpiece. The horizontal broaching machine is shown in Figure 7-22. A hydraulic driving oil cylinder is arranged in the lathe bed, and a follow-up bracket and a tool holder are arranged at the right end of the piston pull rod to support and hold the broach. Before working, the broach is supported on the roller and the rear bracket of the broach, and the workpiece is inserted from the left end of the broach. When the tool holder holds the broach and moves to the left in a straight line, the workpiece is against the "support", and the broach can complete the cutting process. The linear motion of the broach is the main motion, and the feed motion is completed by the rise of each tooth of the broach. (1) Broaching round hole is shown in Fig. 7-23. The hole diameter of broaching is generally 8 ~ 125mm, and the length-diameter ratio of the hole is generally not more than 5. Generally, precise pre-machining is not required before broaching, and broaching can be carried out after drilling or rough boring. If the end face of the workpiece is not perpendicular to the axis of the hole, the end face is attached to the spherical washer of the broaching machine, and under the action of the broaching force, the workpiece rotates slightly together with the spherical washer, so that the axis of the hole is automatically adjusted to be consistent with the axis direction of the broach, and the broach can be prevented from being broken. (2) Broach the internal keyway as shown in Figure 7-24 a. The keyway broach is flat, and the upper part is provided with cutter teeth. The correct position of the workpiece and the broach is ensured by the guide element. The cylinder 1 of the broach guide element (Fig. 7-24 B) is inserted into the hole at the end of the broaching machine, the cylinder 2 is used to receive the workpiece, and the groove 3 is used to receive the broach. 2. Process characteristics of broaching (1) During broaching, multiple teeth of the broach work at the same time, and the rough and finish machining is completed in one stroke, so the productivity is high. (2) The broaching tool is a fixed-size tool with calibration teeth for calibration and finishing; the broaching machine adopts a hydraulic system with stable transmission, very low broaching speed (= 2 ~ 8 m/min), thin cutting thickness, and no built-up edge, so the broaching can obtain higher processing quality. (3) Broaches are complex to manufacture and expensive, and one broach is only suitable for holes or keyways of one size, so broaching is mainly used for mass production or mass production of finalized products. (4) Step holes and blind holes cannot be processed by broaching. Because of the working characteristics of the broaching machine, the holes of some complex parts are not suitable for broaching, such as the holes on the box. 6. Grind the hole Hole grinding is one of the finish machining methods of holes, which can achieve the dimensional tolerance grade of IT8 ~ IT6 and the surface roughness value of Ra 0.8 ~ 0.4 μm. Hole grinding can be performed on an internal grinder or a universal external grinder, as shown in Figure 7-25. A grinding wheel with a concave conical surface at the end can be used to grind the hole and the shoulder surface in the hole in one clamping, as shown in Figure 7-26. Compared with grinding the outer circle, hole grinding has the following disadvantages: (1) The surface roughness value of the grinding hole is generally slightly larger than that of cylindrical grinding, because the rotating speed of the commonly used internal grinding head is generally not more than 20000 R/min, and the diameter of the grinding wheel is small, so its circumferential speed is difficult to reach 35 ~ 50 m/s of cylindrical grinding. (2) The control of grinding accuracy is not as convenient as cylindrical grinding. Because the contact area between the grinding wheel and the workpiece is large, the calorific value is large, and the cooling condition is poor, the workpiece is easy to burn; especially the grinding wheel spindle is slender and has poor rigidity, which is easy to produce bending deformation and cause internal conical error. Therefore, it is necessary to reduce the grinding depth and increase the number of polishing strokes. (3) Low productivity. Because the diameter of the grinding wheel is small, the wear is fast; and the coolant is not easy to wash away the chips, so the grinding wheel is easy to be blocked and needs to be repaired or replaced frequently, which increases the auxiliary time. In addition, the reduction of grinding depth and the increase of polishing times will inevitably affect the productivity. Therefore, hole grinding is mainly used for the finish machining of high-precision holes and hardened holes that are not suitable or impossible for boring, reaming and broaching. VII. Precision machining of holes 1. Fine boring Fine boring and boring methods are basically the same, because the original use of diamond as a boring tool, it is also called diamond boring. This method is often used for the final machining of holes in sleeve parts made of non-ferrous alloys and cast iron, or as a preparatory machining before honing and rolling. The hole with high precision and good surface quality can be obtained by fine boring, and the economic precision of the machining is IT7 ~ IT6, and the surface roughness value is Ra 0.4 ~ 0.05 μm. At present, cemented carbide YT30, YT15, YG3X or synthetic diamond and cubic boron nitride are widely used as materials for fine boring tools. In order to achieve high precision and small surface roughness and reduce the influence of cutting deformation on the machining quality, the diamond boring machine with high rotary precision and rigidity is used, and the cutting speed is high (200m/min for steel cutting, 100m/min for cast iron cutting; 300m/min for cutting aluminum alloy), the machining allowance is small (about 0.2 ~ 0.3mm), and the feed rate is small (0.03 ~ 0.08mm/R) to ensure the machining quality. For the size control of fine boring, a fine adjustment boring cutter head is used. Fig. 7-27 shows a fine adjustment boring cutter with a vernier dial. An indexable blade 5 is clamped on the arbor 4. The arbor 4 is provided with a precise small-pitch thread. The nut of the dial 3 and the arbor 4 form a precise screw and nut pair. During fine adjustment, the clamping screw 7 is half loosened, the dial 3 is rotated, and the cutter bar 4 is guided by the key 9, so that the cutter bar can only move in a straight line to realize fine adjustment, and finally the clamping screw is locked. This fine boring tool has a scale value of up to 0.0025 mm. 2. Honing Honing is a high efficiency finishing method for hole machining with oilstone strip, which needs to be carried out on the basis of grinding or fine boring. The machining precision of honing is high, the dimensional tolerance grade after honing is IT7 ~ IT6, and the surface roughness value is Ra 0.2 ~ 0.05 μm. Honing has a wide range of applications, such as iron castings, hardened and unhardened steel parts and bronze, but it is not suitable for processing plastic metals which are easy to block oil stones. The honing hole diameter is Φ5 ~ Φ500mm, and it can also process deep holes with L/D 10, so it is widely used in processing the cylinder of engine, the oil cylinder of hydraulic device and the holes of various gun barrels. Honing is a grinding process with low speed and large area contact, and its principle is basically the same as that of grinding. The grinding tool used in honing is a honing head composed of several very fine oilstone strips. During honing, the oilstone of the honing head has three motions: rotary motion, reciprocating linear motion, and radial motion to apply pressure, as shown in Figure 7-28 a. Rotation and reciprocating linear motion are the main motions of honing. The combination of these two motions makes the cutting tracks of the abrasive particles on the inner surface of the hole cross without repeating, as shown in Fig. 7-28b. The radial pressing motion is the feed motion of the oilstone, and the greater the applied pressure, the greater the feed amount. During honing, the contact area between the oilstone and the hole wall is large, and there are many abrasive grains participating in the cutting, so the cutting force applied to each abrasive grain is very small (the vertical load of the abrasive grain is only 1/50 ~ 1/100 of that of grinding), and the cutting speed of honing is low (generally below 100m/min, only 1/30 ~ 1/100 of that of ordinary grinding). A large amount of cooling liquid is applied in the honing process, so that less heat is generated in the honing process, the surface of the hole is not easy to burn, and the processing deformation layer is extremely thin, so that the processed hole can obtain high dimensional accuracy, shape accuracy and surface quality. In order to make the oilstone evenly contact with the hole surface and cut off the small and uniform machining allowance, the honing head has a small amount of floating relative to the workpiece. The honing head is connected with the machine tool spindle in a floating way. Therefore, honing cannot correct the position accuracy and straightness of the hole. The position accuracy and straightness of the hole should be guaranteed in the process before honing. 3. Grind Grinding is also a common method of hole finishing, which needs to be carried out after fine boring, fine reaming or fine grinding. After lapping, the dimensional tolerance grade of the hole can be improved to IT6 ~ IT5, the surface roughness value is Ra0.1 ~ 0.008 μm, and the roundness and cylindricity of the hole are also improved accordingly. The lapping tool material, lapping agent, and lapping allowance used for lapping the hole are similar to those used for lapping the outer circle. The grinding method of sleeve part hole is shown in Figure 7-29. The lapping tool in the figure is an adjustable lapping rod, which consists of a taper mandrel and a lapping sleeve. The diameter can be adjusted within a certain range by screwing the nuts at both ends. Grooves and notches in the lapping sleeve to allow the sleeve to open or contract evenly during adjustment and to store the lapping compound. Fixed grinding rods are mostly used for single piece production. The grooved grinding rod (as shown in Fig. 7-30a) is convenient for storing grinding agent and is used for rough grinding; the smooth grinding rod (as shown in Fig. 7-30b) is generally used for fine grinding. Before grinding, cover the workpiece, install the grinding rod on the lathe, apply the grinding agent, adjust the diameter of the grinding rod to make it have appropriate pressure on the workpiece, and then grind. During grinding, the grinding rod rotates and the workpiece is held by the hand to move back and forth. The large holes of the shell or cylinder parts can be ground on the drilling machine or modified simple equipment, and the grinding rod can rotate and move axially at the same time, but the grinding rod and the machine tool spindle need to be connected in a floating way. Otherwise, when the axis of the grinding rod is deviated from the axis of the hole, the shape error of the hole will be generated. 8. Rolling the inner hole The actual pressing amount of the rolling processing part is very small, and the processing is carried out by the self-positioning of the processing surface of the part, so the surface roughness of the part can be reduced and the dimensional accuracy can be improved, but the shape deviation of the part will not be significantly improved, so the accuracy of the rolling processing part is mainly determined by the accuracy and surface roughness of the pre-processing (turning) before the rolling. Rolling processing is chipless processing, no heating phenomenon, the finished size is the forming size, and the processing size is easy to control. The surface layer of the part processed by rolling generates residual compressive stress and cold hardening, the fatigue strength of the part can be improved, and the production efficiency is high. However, the rolling tool shall be made. The surface quality of the rolling process has the following effects on the performance of the workpiece: ① Influence on wear resistance. Surface roughness has a great influence on the initial wear of friction pairs, but it is not the case that the smaller the roughness is, the more wear-resistant it is. Under certain working conditions, there is always an optimal parameter value for the surface of the friction pair, which is about 0.32 ~ 1.25? μm. ② Effect on fatigue strength. Under the action of alternating load, the uneven surface and defects of the workpiece are easy to cause stress concentration and fatigue cracks, resulting in fatigue failure. For some important parts under alternating load, such as the junction of crank and journal of crankshaft, finishing processing should be carried out to reduce its surface roughness and improve fatigue strength. ③ Influence on corrosion resistance. The rougher the workpiece surface is, the easier it is to accumulate corrosive substances; the deeper the valley is, the stronger the penetration and corrosion are. Therefore, reducing the surface roughness value of the part can improve the corrosion resistance of the part. ④ Influence on coordination property. Rough fitting surface will increase the fitting clearance after the fitting parts are worn, change the fitting nature, reduce the fitting accuracy and stiffness, and affect the stability and reliability of operation. Therefore, it is necessary to define a smaller surface roughness parameter value for the surface with matching requirements. Rolling auxiliary processing technology is a new processing technology which is gradually developed with the development of mechanical processing. Surface rolling is an auxiliary surface modification method, which has the advantages of small elastic pressure, small friction force, further reduction of surface roughness Ra value, significant improvement of surface hardness and increase of surface wear resistance, so it has attracted more and more technical personnel's attention and favor. For a new processing technology, technicians pay more attention to the excellent properties of materials obtained by this technology, but seldom involve the selection of process parameters and their impact on the processing quality. In surface rolling technology, the final surface condition is directly determined by the processing parameters such as spindle speed,Tapered Rock Bit, axial feed, processing times, static pressure and lubrication. Return to Sohu to see more Responsible Editor:. wt-dthtools.com

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