At present, the front pin hole of the automobile front axle generally adopts a lock pin structure. The advantage of this structure is that it is easy to assemble and easy to replace parts. During the operation of the car, the maximum force is at the main pin hole and the leaf spring seat, and the front axle of the car is used as a security component. Once an accident occurs, the car may be destroyed. According to the bench test experience, 50% of the breaks start from the lock pin hole. Therefore, the main pin hole with the locking pin structure affects the strength of the entire front axle, and the intersection of the main locking pin holes during machining is difficult to control. There are also some models in which the front axle pin hole of the car does not have a locking pin hole, and the assembly adopts an interference fit, and the method of pressing or freezing the kingpin is used. The structure can improve the strength of the front axle, but it has higher requirements on the diameter of the main pin hole and the diameter of the kingpin, and is not conducive to the replacement of the parts. To this end, the company designed a tapered main pin hole structure (see Figure 1), which does not affect the strength of the entire front axle, and facilitates the replacement of parts. It requires color inspection, the contact area is ≥70%, the surface roughness value Ra=2.5μm, and the surface roughness is ≤0.5mm. This paper mainly discusses the processing scheme of the main pin hole taper for reference. During the reaming process, there is a large axial yaw force, and the locating pin is only φ25mm. It is difficult to withstand such a large axial force, which will cause the tapered main pin hole to be out of round, and the contact area will not reach 70% of the pattern requirement. . Therefore, there is an auxiliary support at the front of the fist (see Figure 2). The auxiliary support effectively reduces axial turbulence during machining and ensures roundness and tapered contact area of ​​the main pin hole. Hex Bolts,Allen Screw,Allen Bolt,Hex Head Bolt Nantong Romax Hardware Co.,Ltd. , https://www.hardwarehouse.cn
Figure 1 Car front axle main pin hole taper hole structure
Device Selection
Our main hole processing equipment mainly has horizontal special boring machine, model is GHC-U200046; vertical machining center, model is VB-825A. If the horizontal boring machine is used, the equipment needs to be modified, and a numerical control flat suspension device is added. The flat suspension plate and the longitudinal movement of the table can work together to process the taper hole. Through the on-site investigation of the equipment, it is found that the system is incompatible with the system of the CNC flat suspension plate due to the aging of the device, and the hole is not rounded to ensure the contact area of ​​the hole, so the horizontal special boring machine cannot process the main pin hole. The vertical machining center can complete the milling, boring, drilling, tapping and other processes, the clamping is convenient, the operation is easy, the processing condition is easy to observe, the debugging procedure is easy, and the application is wide. Therefore, the vertical machining center VB-825A is selected, the X, Y and Z strokes are 1400mm, 825mm, 700mm, the spindle speed is 4000r/min, and the cutting feed rate is 1~5000mm/min.
Conical main pin hole processing scheme
In combination with the actual situation of the VB-825A, it is determined by the tool manufacturer to determine the taper hole processing using a 1:10 shaped taper reamer. Through analysis, it is determined that the taper hole processing is divided into four processes: U-drilling, semi-finishing, fine-bending and straight-hole. After the reaming, it was found that the surface roughness of the φ47+0.5 0mm hole could not meet the requirements of the pattern, so the straight hole process was added to ensure the surface roughness requirement.
Analysis of clamping methods and fixtures
During the processing, a double pin positioning is adopted, that is, the leaf spring surface and the two positioning holes are positioned, and the hydraulic clamp is used to press the back plane of the leaf spring. An angle panel is mounted on the leaf spring surface to meet the requirements of the front axle back rake angle and the camber angle.
In order to ensure the coaxiality of the rough hole and the reaming hole, the unevenness of the reaming hole is avoided, the diameter of the taper hole is out of tolerance, and the surface roughness value does not meet the requirements of the pattern. The fixture needs to be clamped once, and the fixture body is fixed on the device. Allow to move.
Since the vertical end of the fist end face and the king pin hole is 0.05 mm and is a special characteristic, the size must be secured. The main pin hole and the fist end face must be clamped once and processed at one time. Using the vertical machining center tool change system, after the milling of the main pin hole plane, the reamer is taken to perform the hinge main pin hole, which fully ensures the verticality of the fist end face and the king pin hole.
Because the end face of the fist is more long (350mm) from the positioning plate when clamping, the cutting force is larger when reaming, which will cause the vibration of the end face of the fist, and the end face of the main pin hole will produce the vibration pattern. Therefore, the upper end surface of the front shaft needs to have V-shaped auxiliary support (see Figure 2 auxiliary support 1) to improve the surface quality of the main pin hole. 
Figure 2 hinged taper pin hole clamp
Tool requirements
1) The hardness of the coarse-jointed cutter must meet the requirements to ensure that there is no hard layer after processing, and the residual amount after the thick hinge is uniform, and the surface roughness value Ra<6.3μm. The precision reamer should be consistent with the taper of the kingpin hole so that the hinged hole can meet the pattern requirements. In addition, the rough and fine reamer must carry out the tool life management. After processing a certain number of parts (10 pieces of fine reamer for our company and 12 pieces of coarse reamer), it is necessary to replace the new tool in time , implement forced tool change management, and effectively ensure the hinge. The quality of the hole.
2) The chipping groove should be set on the reamer to ensure that the chips are discharged in time during the reaming process. According to the actual situation of the product, the distance between the chip flutes is 140mm and the number of teeth is three; the flutes are left-handed and the pitch is 12mm, and the adjacent two flutes are staggered. The cutting edge of the tool is left-handed and the angle of rotation is 30°.
3) Since the cutting force is relatively large during the reaming process, the tool adds five cooling holes to ensure that the tool is sufficiently cooled during the machining process to improve the processing quality.
Reasonable choice of cutting three elements
1) In order to ensure the coaxiality of the reaming hole, through the on-site continuous technical trial production, the subsequent allowance of the rough drill is 2mm, and the margin of the semi-finished hinge is 0.5mm.
2) Due to the large amount of rough drilling, the cutting force is relatively large during the machining process, and it is difficult to use a large rotating speed. The rough drill adopts HDD1-145 U drill, the spindle speed is n=650r/min, and the feed rate is f=22mm/r.
3) The semi-finishing reamer is K23D1-280, the spindle speed is n=60r/min, and the feed rate is f=3mm/r.
4) The reaming reamer is HDD1-141, the spindle speed is n=60r/min, f=0.5mm/r.
Precautions
1) In order to ensure product quality, the first three items should be inspected for coloring to check whether the contact area meets the requirements.
2) When clamping the parts, ensure that the positioning surface must be clean and free of debris, and accurately position the positioning holes into the positioning pins to check whether the workpiece is clamped.
3) Strictly process according to the parameters of product quality and process specifications, and carefully implement the process three-check system.
4) When the locating pin wear gap on the fixture is large, it should be replaced in time. Defective products appearing during the self-test should be recorded, and at the same time be identified and stored in isolation.
5) In order to improve the surface quality of the processing, the cutting fluid needs to be continuously supplied during the processing to ensure timely cleaning of the chips.
Conclusion
Through the above practices, the qualification rate of the front axle tapered main pin hole processed by our company for Volvo is basically stable at 99.85%, and the cone hole coloring rate is 83%-95%, which satisfies the customer's demand and achieves a good quality reputation and economy. benefit.
The front axle of the car is one of the important load-bearing components of the car. The two ends are equipped with wheels, which are connected to the frame or the load-bearing body through the suspension, and are used to transmit the vertical force, longitudinal force and lateral direction between the frame and the suspension. force. In addition, the front axle also has to withstand the braking torque and side slip torque transmitted by the suspension, so it has high requirements on strength, fatigue reliability and rigidity.