1. Fine boring
Fine boring and boring methods are basically the same. Since diamonds were originally used as boring tools, they are also known as konjac. This method is commonly used for final machining of holes in sleeve parts made of non-ferrous metal alloys and cast iron, or as pre-machining before honing and rolling. Fine boring can obtain holes with high precision and good surface quality. The economic precision of machining is IT7~IT6, and the surface roughness is Ra0.4~0.05μm.
Carbide YT30, YT15, YG3X, or synthetic diamond and cubic boron nitride are commonly used as materials for fine boring tools. In order to achieve high precision and smaller surface roughness values ​​and reduce the influence of cutting distortion on machining quality, a diamond boring machine with high turning accuracy and high rigidity is used, and a high cutting speed is selected (cutting steel is 200m/min; cutting iron is 100m/min; cutting aluminum alloy is 300m/min), the processing allowance is small (about 0.2~0.3mm), and the feed amount is small (0.03~0.08mm/r) to guarantee the processing quality. The fine boring hole size control uses a fine-tuning boring head. Figure 7-27 shows a fine-tuning trowel with a vernier dial. The arbor 4 has an indexable insert 5, and the shank 4 has precision. The small pitch thread, the nut of the dial 3 and the knife bar 4 form a precise screw nut pair. During the fine tuning, half loosen the clamping screw 7 and turn the dial 3, because the knife bar 4 is guided by the key 9, so the knife bar can only be moved linearly to achieve fine adjustment, and finally the clamping screw is locked. This fine-tuning trowel can reach a value of 0.0025mm.
2. Honing
Honing is a high-efficiency finishing method for hole machining with whetstones, which needs to be performed on the basis of grinding or boring. Honing has high machining accuracy. After honing, the dimensional tolerance grade is IT7~IT6, and the surface roughness is Ra0.2~0.05μm.
Honing has a wide range of applications and can be used to machine cast iron parts, hardened and unhardened steel parts, and bronzes, but it is not suitable to process plastic metal that can easily block oilstones. The hole diameter of the honing process is Φ5~Φ500mm, and it can also process deep holes with L/D > 10, so it is widely used for machining engine cylinders, hydraulic cylinders, and holes of various barrels.
Honing is a low-speed, large-area contact grinding process that is basically the same as the grinding principle. The grinding tool used for honing is a honing head made up of several fine-grained stone bars. When honing, there are three kinds of movements of the whetstone whetstone: rotary motion, reciprocating rectilinear motion and radial motion of applied pressure, as shown in Figure 7-28a. Rotary and reciprocating rectilinear motions are the main motions of honing. The combination of these two types of motion makes the cutting trajectory of the abrasive grains on the whetstones on the inner surface of the hole cross-cut without repeating meshes, as shown in Fig. 7-28b. Radial pressurization is the feeding motion of Whetstone. The greater the pressure is applied, the greater the feed amount.
During the grinding, the contact area between the whetstone and the wall of the hole is large, and many abrasive grains participate in the cutting. Therefore, the cutting force applied to each abrasive grain is very small (the vertical load of the abrasive grain is only 1/50~1 of the grinding. /100), The cutting speed of honing is low (usually less than 100m/min, only 1/30~1/100 of ordinary grinding), and a large amount of coolant is applied during the honing process. Therefore, the honing process generates heat. Less, 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 Whetstone evenly contact with the hole surface, small and uniform machining allowance can be cut out, the honing head has a small amount of floating relative to the workpiece, and the honing head is floatingly connected with the spindle of the machine tool, so the honing cannot correct the positional accuracy of the hole and The straightness of the hole, hole position accuracy, and hole straightness should be guaranteed during the honing process.
3. GrindingGrinding is also a kind of finishing method commonly used for holes. It needs to be done after finishing, finishing or grinding. After grinding, the dimensional tolerance grade of the hole can be increased to IT6~IT5, the surface roughness is Ra0.1~0.008μm, and the roundness and cylindricity of the hole are also increased accordingly.
The lap materials, abrasives, and polishing allowances used for the polishing holes are similar to those for grinding the outer circle.
The sleeve part hole grinding method is shown in Figure 7-29. The lap in the figure is an adjustable grinding rod consisting of a taper rod and a grinding sleeve. Twist the nuts at both ends to adjust the diameter within a certain range. The grooves and notches in the sleeve are so designed that the sleeve can be uniformly opened or contracted during the adjustment and the abrasive can be stored.
Before grinding, put on the workpiece, put the grinding rod on the lathe, apply the abrasive, adjust the diameter of the grinding rod to make it have appropriate pressure on the workpiece, and then it can be ground. During grinding, the grinding rod rotates and the workpiece is moved back and forth.
Fixed abrasive rods are often used in single-piece production. The grooved grinding rod (Fig. 7-30a) facilitates the storage of abrasives for coarse grinding and the smoothing grinding rod (Fig. 7-30b) is generally used for lapping.
The large holes of the housing or cylinder type parts can be drilled or modified on the simple equipment when it needs to be ground. The grinding rod is used for simultaneous rotation and axial movement, but the grinding rod and the spindle of the machine tool need to be floating. Otherwise, when the axis of the grinding rod and the axis of the hole are deflected, the shape error of the hole will occur.
4. Rolling
The hole rolling principle is the same as that of a rolling outer circle. Due to the high rolling processing efficiency, rolling technology has been used in recent years to replace the honing process. After the aperture rolling, the dimensional accuracy is within 0.01mm, the surface roughness is Ra0.16μm or less, the surface is hardened and wear-resistant, and the production efficiency is several times higher than that of honing.
Rolling has a great sensitivity to the quality of castings. For example, the hardness of the casting is uneven, the surface is loose, defects such as pores and trachoma have a great influence on rolling. Therefore, the casting oil cylinder can not use rolling process but choose honing. For hole finishing of hardened sleeves, rolling is not recommended.
Figure 7-31 shows a rolling head for a machining hydraulic cylinder. The conical roller 3 on the surface of the rolling head is supported on the taper sleeve 5, and the taper roller and the workpiece have an inclination of 0.5 DEG to 1 DEG during rolling. The corners allow the workpiece to gradually recover elasticity and prevent the surface of the workpiece hole wall from becoming rough.
Before the hole is rolled, the radial dimension of the rolling head is adjusted by adjusting the nut 11 , and the adjusting nut can be moved in the axial direction relative to the mandrel 1 and pushed to the left to push the transition sleeve 10, the thrust bearing 9 and the bushing 8 The collar 6 is passed through the pin 4 so that the conical roller 3 is moved to the left along the surface of the sleeve, with the result that the radial dimension of the roller head is reduced. When the adjusting nut is moved to the right, the bush is pressed by the compression spring 7, and the transition sleeve is always pressed against the left end surface of the adjusting nut through the thrust bearing. When the bush is moved rightward, the collar is driven, and the cover is used to make the cone. The rollers also move axially to the right, increasing the radial dimension of the roller head. The radial dimension of the rolling head should be determined according to the rolling interference of the hole. Usually, the rolling interference of the steel is 0.1~0.12mm, and the diameter of the rolling increases 0.02~0.03mm.
Radially-adjusted rolling head, in the rolling process, the axial force of the conical roller acts on the thrust bearing through the pin, ferrule, bushing, and finally the transition sleeve, adjusting nut and spindle Pass to the arbor connected to the M40×4 thread on the right end of the rolling head. After the rolling is completed, when the rolling head is withdrawn from the hole, the conical roller is subjected to a leftward axial force. This force is transmitted to the cover plate 2 via the collar and the bushing compresses the compression spring and moves to the left. The diameter of the roller head is reduced to ensure that the roller head does not damage the already rolled hole wall when it is withdrawn from the hole. After the rolling head is withdrawn from the hole, it is reset under the action of the spring force so that the radial dimension can be restored to the original value.
Rolling dosage: usually choose rolling speed v=60~80m/min; feed rate f=0.25~0.35mm/r; cutting fluid uses 50% vulcanized oil plus 50% diesel or kerosene.
Eight, hole processing program and its choice
The above describes the common machining methods, principles, and achievable precision and surface roughness of hole machining. However, to achieve the design requirements of the hole surface, generally only one kind of processing method is not available, but it is often necessary to sequentially combine several processing methods, that is, to select a reasonable processing plan. Table 3-15 shows the hole processing plan. The selection of the machining plan should take into consideration the structural shape, size, material and heat treatment requirements, and production conditions of the parts.
For example, in Table 3-15, the technical requirements can be basically the same for the serial number 5 “drilling-diverging-hinge†and the serial number 8 “drilling-diverging-pullingâ€. However, the processing plan shown in the serial number 8 should be mass-produced. The use of more reasonable. In addition, the technical requirements of the serial number 11 "Rough boring (expanding)-semi-precision boring (fine-expanding)-fine boring (hinge)" and No. 13 "rough boring (expanding)-semi-finishing-grinding" are achieved. It is also basically the same, but if the surface of the inner hole is quenched, only the grinding hole scheme (ie No.13) can be used, and when the material is non-ferrous metal, the scheme shown in No.11 is appropriate. For example, if the workpiece is not hardened, the two are The solutions can all be adopted. At this time, the processing plan can be decided according to the production site equipment. Also, as shown in the serial number 16, there are three kinds of processing solutions. For example, for large mass production, the “drilling-(expanding)-pulling-refining†option can be selected. If the bore diameter is small, “drilling-(expanding)-roughness†can be selected. "Hinge-finishing-finishing" option, if the aperture is larger, you can choose "rough-half-finishing-finishing-finishing" processing plan.
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