Guarantee of parallelism of two bolt holes of conn

2022-08-17
  • Detail

160F diesel engine connecting rod two bolt hole parallelism guarantee

1 overview

160f diesel engine connecting rod is composed of connecting rod body and connecting rod cap. The connecting rod body and the connecting rod cap are connected by bolts and nuts. Because the connecting rod is subjected to the action of rapidly changing dynamic load in the working process, and this dynamic load is transmitted to the two bolts and nuts of the connecting rod body and the connecting rod cap, in addition to the requirements for bolts and nuts, there are also relatively high requirements for the holes for installing these two bolts. According to the technical requirements for connecting rod assembly of 160F diesel engine, the parallelism of the two bolt holes in the two directions perpendicular to each other is 100mm long, because they can isolate oxygen, the tolerance is 0.15mm. The machining of two bolt holes is realized by using multiple axle boxes and jigs on the Z535 vertical drilling machine, and its structural diagram is shown in Figure 1. When machining the two bolt holes, the connecting rod is positioned with the end face and side face of the small head hole and the big head hole. First screw the screw 2, press the connecting rod cover towards the connecting rod body, and then rotate the plum blossom handle. The pressure block 3 pushes the connecting rod to make its side close to the retaining iron 4, press the handle 5 downward, the screw drives the nut to compress the open gasket 6, and tightly press the connecting rod on the positioning gasket 7, so as to realize the positioning and clamping of the connecting rod. Turn on the power and start the drilling machine. The spindle of the drilling machine transmits the rotating motion to the multi axle box, driving the drilling spindle on the multi axle box to drill the two bolt holes. In actual processing, the parallelism of the two bolt holes in the two directions perpendicular to each other cannot meet the technical requirements, especially in the plane perpendicular to the end face of the big head hole. Through the careful analysis of the structure of the multi axle box and the drilling jig and the repeated experimental research of the processing process, the factors affecting the parallelism error of the two bolt holes are found out, and the manufacturing and installation methods of the multi axle box and the drilling jig are determined to ensure the parallelism requirements of the two bolt holes in two directions perpendicular to each other

Figure 1

2 analysis of machining error of parallelism of two bolt holes

1) influence of machining accuracy of multi axle box

multi axle box is specifically connected with the clamp of drilling jig through guide rod. In this way, the machining accuracy of the two bolt holes of the connecting rod is determined by the mutual position accuracy of the drilling sleeve on the multi axle box drilling spindle and the drilling jig clamp. Through many measurements, it is found that the distance between the axis line of the drilling spindle and the guide rod is always greater than the distance between the center line of the corresponding drilling sleeve and the guide rod by about 0.12mm. At the same time, through the drilling of the multi axle box support shown in Figure 2, the coaxiality error of the bearing hole of the main shaft in the schematic diagram of the box parts shown in Figure 2 is large (resulting in the bending deformation or inclination of the drilling main shaft due to the different axes of the support bearing), which is mainly due to the inconsistency of the datum planes when machining the bearing holes on both sides, and the parallelism error of the two datum planes after milling is 0.10 mm

figure 2

2) influence of manufacturing error of drill sleeve

coaxiality error of drill sleeve the diameter of bolt hole is φ 8. Select the diameter of T10A drill sleeve hole as φ 7.8. The hole diameter of the drill sleeve is small. The drill sleeve is processed by drilling and reaming process, and then heat treatment. The heat treatment deformation is large, while the excircle is ground, which leads to the coaxiality error between the drill sleeve hole and the excircle

the accuracy of the size of the drill sleeve hole. Because there is a gap between the drill bit and the replaceable drill sleeve, the drill bit deflects when processing the bolt deep hole. The offset mainly depends on the maximum matching gap between the tool guide part and the drill sleeve and the depth of the bolt hole

3) the influence of the tool

the rigidity of the tool affects the machining of bolt holes. The lengthened drill with small diameter is used, and its rigidity is poor. When drilling deep bolt holes, the axial cutting resistance of the drill bit is large, which is easy to bend and deflect the drill bit, resulting in serious distortion of the center line of the bolt hole

the grinding of the tool affects the two main cutting edges of the drill bit. When the edges are asymmetrical, the cutting force acting on the two main cutting edges is different, resulting in the deviation of the drill bit during machining, and then affecting the position accuracy of the centerline of the bolt hole

4) influence of processing technology

in order to improve production efficiency and take into account the small bolt hole diameter, the processing technology adopted by the factory in the processing of connecting rod bolt holes is drilling and reaming. The deviation of the center line formed by drilling bolt holes cannot be corrected by the reaming process. Therefore, the processing technology of bolt holes must be re formulated

5) influence of installation method

the multi axle box is connected with the spindle of the vertical drill through the sleeve, the drill jig is placed on the vertical drill workbench, and the multi axle box and the drill jig are connected by the guide rod. The multi axle box and the drill jig are installed separately or when the multi axle box is in contact with the upper end of the guide rod, the drill jig is installed. Although they are installed on the surface, the relative position of the multi axle box and the drill jig is also determined, But in fact, it is very difficult to move the multi axle box down along the guide rod, and it may even get stuck. When the guide sleeve is removed for inspection, it will be found that the inner hole of the guide sleeve is severely roughened, which is mainly caused by the change of the position of the drilling jig when it is installed on the workbench

in order to ensure the parallelism of bolt holes in two directions perpendicular to each other, effective measures must be taken to eliminate the effects of the above-mentioned errors

3 measures to improve the parallelism processing accuracy of the annual production capacity of 5000 tons of lithium ion cathode material and 200million watt hour power battery for the two bolt holes

1) after milling the multi axle box, the front and rear must be scraped (because the box is aluminum alloy, grinding processing cannot be used) to ensure the parallelism requirements of the front and rear. In addition, the benchmark machining hole system is selected according to the actual installation state of the multi axle box, which is processed in the order of the left guide hole, the main shaft hole and the right guide hole, and the guide holes and drill sleeve holes on the drilling jig are processed in the same order, so as to ensure the positional relationship between the holes on the multi axle box and the holes on the drilling jig

2) in order to improve the manufacturing accuracy of the drill sleeve, 40Cr is selected as the drill sleeve material, so as to reduce the heat treatment deformation. At the same time, the drill sleeve adopts the processing technology of drilling, expanding and grinding. Correct the deviation of the center line during drilling by reaming. After quenching, grind the inner hole of the drill sleeve first, and then locate and grind the outer circle with the inner hole, so as to ensure the coaxiality of the inner hole and the outer circle. According to the specially produced drill bit, the corresponding matching size of the inner hole of the drill sleeve is selected to minimize the gap between the drill sleeve and the drill bit and improve the guiding accuracy

3) reduce the axial force of drilling, reduce the bending of the bit, and reduce the deviation of the bit

· the grinding of the drill bit must be correct, and the two main cutting edges must be ground symmetrically

· use a small amount of cutting

· adopt special lubrication device and use coolant correctly (it can also remove the impact of chips on the positioning surface on the positioning accuracy)

3) the processing technology of bolt holes is changed to drilling, expanding and reaming. Reaming can correct the skew of the center line of the machined hole. Such technological measures are convenient to ensure the machining accuracy requirements of the bolt hole

5) use the tool to determine the relative position of the multi axle box to the drilling jig. First, install the tools that account for about 1.5% of the global cobalt reserves in the DRC into the drilling spindle on the multi axle box, then move the multi axle box, insert the tools into the drill sleeve of the drill jig to understand the functional characteristics of these machines, and then fix the drill jig on the machine tool workbench, so as to ensure the relative position of the multi axle box and the drill jig. By taking a series of measures mentioned above, the two bolts are finally ensured. (end)

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