Design and Application of a Fine Boring Hole Adjustable Fixture
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figure 1 
1. pressure plate 2. boring bar 3. pressure block 4. stop
5. Coupling block 6. Slider 7. Base plate 8. Clip-specific
9. Piston 10. Screw 11. Bolt 12. Mandrel
Fig. 2 The fine pin hole in the piston machining process of the internal combustion engine is the key process (Fig. 1), which is one of the quality control points. The accuracy of the pin hole's main position is formed here. Because of its high precision requirements, if the integral positioning cannot achieve the continuity of the adjustment, that is, it cannot be adjusted on a micro-meter basis as required, thereby making the eccentricity of the pin hole axis line, the height to the base surface, and the vertical axis of the piston shaft. It is more difficult to adjust the degree, and ultimately the desired finish quality is not obtained. Therefore, we designed and applied a split-type positioning and adjustable fixture, which can not only compensate for the lack of fixture manufacturing and assembly accuracy, but also adapt to the requirements of the production line for multiple varieties of production. The following describes its positioning method. 1 The characteristics of the adjustable fixture structure The fixture structure is shown in Figure 2. It is mainly composed of a pressing element 1, a clip specific part 8 and a positioning part. The diamond-shaped pin (not shown in the figure) is pushed into the rough pin hole from the left side to be positioned in the circumferential direction, and is to be withdrawn after the pneumatic platen is pressed. The positioning part consists of a pressure block 3, a stop rib 4, a coupling block 5, a slider 6, a bottom plate 7, and a mandrel 12. The slider and the base plate have a wedge angle a, and the spindle has an eccentricity e. Each part is specifically connected to the clamp by bolts. 2 Basic principle The basic principle of positioning is to use the amplifying effect of the stop rib radius is far greater than the eccentricity of the mandrel. The circumferential rotation of the arbour can change the distance between the pin hole shaft and the symmetrical center plane of the piston to accommodate the eccentricity of different types of pistons. Distances and requirements for improving the dimensional accuracy: micro-adjustment in the vertical direction using a beveling micro-motion mechanism, the height of the pin hole axis to the base surface is changed by the translation of the slider with a small angle inclination: relative rotation of the inclined mechanism The slider produces a small swing angle, which changes the parallelism of the axis of the pin hole with respect to the reference plane so as to adjust its verticality to the piston centerline. 
(a) 
(c) 
(b) Fig. 3 2 Positioning and adjustment method First of all, the initial state of the fixture must be set. Otherwise, the following mathematical formula will not be valid and the whole debugging process will be complicated. In order to simplify the process, we set the eccentric direction of the mandrel before the test, the direction of the wedge angle of the slider and the direction of the wedge angle of the bottom plate to be parallel to the feeding direction of the boring bar, which is easy to guarantee by the manufacturing and assembly precision. By pre-setting the initial state, the analytical model of the mathematical model can be established (Figure 3). In the figure, the 2 points are the positions of a certain defined point on the punctures during the test. After the A' point is moved on the A point, ∆1, ∆2, ∆3 respectively affect the eccentricity, affect the height of the base surface, and affect the verticality. The quantities, 分别 1 = esinq (1) ∆ 2 = Ltga (2) In accordance with the principle of relative motion, the rotation of the soleplate is equivalent to the simultaneous rotation of the simple slider and the puncture tire. Therefore, point A and its symmetry about the center line are moved by the dashed trajectory in the main view of Fig. 3c. Then there are: ∆3=R(1-cosb)tga (3) Where: q—the angle at which the mandrel turns L—the distance that the slider translates d—the lateral displacement at point A—the stop The radius of the top circle b—the angle rotated by the bottom plate. After the test, the measured error is substituted into equations (1), (2) and (3) for calculation, and coarse adjustment is performed according to the calculation results. The first step is to adjust the eccentricity of the pin hole axis: first remove the clamp 3, and then loosen the bolt 11 (the hexagon wrench can be removed without extending the coupling block). After turning the mandrel to the desired angle, tighten it. , should pay attention to maintaining the synchronization of other components: the second step is to adjust the height of the middle point of the pin hole axis to the base surface, that is, to turn the screw 10 to translate the slider: The third step is to adjust the verticality of the pin hole axis to the piston centerline: rotate The bottom plate shall keep the circumferential position of other components unchanged during rotation. Finally, the adjustment is completed by loading the clamp and fastening the other bolts and screws. If you are not satisfied with the accuracy of a certain size of positioning after adjustment, you can further fine tune the method. In the design it has been determined that a=1°, e=2mm and R=50mm. Assume that the measured values ​​of machining error after boring in the initial state are: eccentricity error ∆'1=0.856mm, ∆'2=0.017mm, and squareness error ∆'3=0.006mm. After conversion, ∆1=∆'1=0.856mm, ∆2=∆'2=0.017mm, and ∆3=∆'3/2=0.003mm. Substituting the above data into equations (1), (2), and (3) respectively yields the required adjustments: q=arcsin(∆1/e)=arcsin(0.856/2)=25°20'27" L=∆2 /tga=0.017/tg1°=0.97mm b=arccos[1-(∆3/Rtga)]=arccos[1-(0.003/50)tg1°]=4°45'7" (The above calculation results are ignored. 10-3 small quantity) In order to facilitate the operation of the production site commissioning personnel, omitting the cumbersome calculation process, we have plotted the correspondence between the processing error value and the required adjustment amount, and only need to use the interpolation method to check the table when adjusting. . As for the amount of adjustments that have been made during the adjustment, it can be confirmed by the use of table-making methods, graduation marks or other methods. Due to limitations in space, no further explanation is given here. 4 Conclusion The above-mentioned split type positioning adjustable fixture is compact in structure and cleverly designed. It can be applied to various kinds of piston processing by adjusting or replacing individual parts (such as stop tires). It not only realizes continuous adjustment of multiple quality characteristics, but also has comparative advantages. Strong versatility, significant gains in long-term production applications. In addition, this design idea has been promoted for milling, planing, and even turning. It has also achieved the desired results and has a good application prospect.