The traditional method of machining crankshaft holes is to use a combined boring tool on a special processing machine. Each blade corresponds to the corresponding processing position to finish the crankshaft hole. When processing, it is necessary to use auxiliary support for the boring tool. This processing method is generally not applicable. On the machining center. The flexible production line of the cylinder block mainly uses a machining center. In the actual processing process, because the crankshaft hole is a large depth to diameter ratio hole, the hole length is more than 400mm. And, the overhang is often long, the rigidity is poor, it is easy to cause vibration, it is difficult to ensure the dimensional accuracy and shape accuracy of the bored hole. The U-turn boring process can solve the above problems well.

The so-called turning boring is a long hole machining method in which the tools are bored from the two end surfaces of the part on the horizontal machining center. The turning boring process of the workpiece is clamped once and the table is rotated 180 °. The essence of this method is Reduce the length of feed. U-turn boring avoids the auxiliary support and the restriction on the rotation speed of the boring shaft, which can increase the cutting speed; the boring bar has short overhang and good rigidity, which can improve the accuracy of boring and is convenient for workers. 

Because the axes of the two boring holes cannot be absolutely coincident during processing, the index error of the table rotation of 180 °, the table movement error and the straightness error of the feed motion can directly lead to the coaxiality error of the hole axis. Therefore, controlling the coaxiality error of U-turn boring is the key to control the machining accuracy. In order to ensure the processing accuracy, the precision of the processing equipment needs to be improved, and the positioning accuracy and repeated positioning accuracy of the worktable and the spindle are required to be high. In addition, we can take measures in the process to eliminate or reduce these adverse factors that affect the coaxiality, so as to improve the coaxiality accuracy of the boring of the U-turn. Using a high-precision and high-efficiency machining center combined with the U-turn boring process to process a variety of long holes and coaxial hole systems can better take advantage of the U-turn boring process.

For crankshaft holes that require higher machining accuracy, honing processing technology is also required, that is, the tool rotates into the crankshaft hole, and honing processing is repeated. The honing process is as follows: coarse honing is used to remove the remaining amount, eliminate fine boring marks, improve the shape accuracy of the hole, and reduce the surface roughness of the hole; fine honing is used to further improve the dimensional accuracy and shape accuracy of the hole, and reduce the surface roughness, A uniform cross-texture is formed on the surface of the cylinder bore; flat-top honing is used to remove the peaks of the net groove marks, form a flat-top surface, establish a flat-top net structure on the surface of the hole, and improve the support rate of the surface of the hole. The honing of crankshaft holes is horizontal processing. Considering the accuracy requirements of F and B cylinder crankshaft holes, there is no need to honing the crankshaft holes, and no honing equipment is required.