1. Process arrangement
The whole process of turbocharger wear-resistant transmission connecting rod is as follows:
1.1 Division of processing stages and arrangement of processing sequence
The connecting rod is a kind of work piece with poor rigidity, which is easy to bend under the action of external force; In the process of connecting rod machining, the amount of pore machining is the largest, usually by cutting, and cutting will increase its own stress, make the connecting rod deformation. Therefore, when processing the connecting rod, each process needs to be separated. So that the deformation in each process can be corrected in the next process, and finally meet the basic requirements of the parts. Connecting rod process includes rough machining process, semi finish machining process and finish machining process. When arranging the machining process, it is necessary to locate the datum before proceeding to the next process.
1.2 Selection of positioning datum
Because the connecting rod is of irregular shape, in order to locate it, it is necessary to select the positioning datum plane according to the actual situation. Generally, the large and small end faces of the connecting rod are not on the same plane, which makes it easy to produce errors in positioning. Therefore, choosing the boss as the auxiliary datum plane can effectively improve the stability of positioning.
1.3 Determination of reasonable clamping method
The rigidity of the connecting rod is poor, and it is easy to be affected by the clamping force. In the process of clamping, we should pay attention to the size and direction of the force, so as to prevent the deformation of the connecting rod caused by too high clamping force and reduce the accuracy of the connecting rod processing. In the production process of connecting rod, the end face of the fixture needs to be rough milled. The fixture designed in this way can ensure that the clamping force is parallel to the end face. Because the rigidity of the two end faces is relatively large, even if the connecting rod is deformed due to the clamping force, the two ends of the connecting rod can be parallel to the end face of the fixture, Slight deformation has little effect on the parallelism between the end face and the connecting rod. Moreover, the clamping force acts on the positioning fixture through auxiliary elements, which can effectively prevent the connecting rod from bending in the process of processing.
1.4 Processing method of main surface
The datum plane of connecting rod processing is determined according to the two end faces of connecting rod. In the production process of connecting rod, the process of refinement, inspection and reprocessing should be repeated to ensure the positioning accuracy of connecting rod after processing. But the efficiency of this production method is very low, not suitable for mass production, so in the process of mass production, or more use of grinding method.
When milling the two end faces, the axis of the connecting rod should be kept symmetrical with the end face, and the rod body should be fixed. The common milling methods are as follows: 1. Two hard end milling cutter heads are installed on the special milling machine, and the workpiece is clamped. Under the drive of the feeding mechanism of the workbench, the workpiece is rough milled, The other end face is processed by rotation; ② The milling cutter in different directions on the multi axis gantry milling machine is used to process the tool automatically, so as to complete the milling of two end faces.
In the process of grinding, the grinding wheel is usually moved and rotated to make the grinding wheel contact with the end face for grinding. In the mass production of connecting rod, the two end faces and the reverse direction of the grinding wheel can be grinded at the same time, so as to ensure the parallelism of the end face and greatly improve the grinding efficiency.
2. Processing of large and small head holes
In the process of connecting rod processing, the most delicate process is the processing of large and small end holes of connecting rod. The process is very complex and demanding, and it is the key factor to determine the quality of connecting rod.
The general processing procedure is to process the large and small head holes respectively, and then combine them for fine processing.
Due to the small size of the small head hole, it is impossible to set the preset hole in the forging process. Therefore, the small head hole is usually processed by drilling. The size of the big head hole is relatively large, so the forging of the preset hole can be completed in the process of forging, so the forging of the big head hole is more complex than that of the small head hole, and it needs to go through the whole process from rough boring to fine boring.
In order to maintain the machining accuracy of large and small head holes, boring is usually used in the machining process. When the large and small head holes are inclined in the machining process, the boring can be corrected to ensure the positioning accuracy between the hole and the surface. Because the hole diameter of the connecting rod is relatively small, the size of the boring bar will not affect the processing of large and small head holes.
In the process of large and small head hole fine boring, the double axis method is usually used to process, so as to improve the processing efficiency of large and small head hole fine boring. In order to reduce the surface roughness of large and small head holes, it is necessary to finish them to ensure the processing quality.
3. Positioning datum selection
According to the connecting rod machining process specification, in the process of clamping the workpiece, it is necessary to select the positioning datum, which affects the dimensional accuracy of machining and is the first step of connecting rod machining process. In most cases, the quality of the connecting rod depends on the correctness of the positioning datum. Therefore, positioning datum is the key content of connecting rod processing technology.
The selection standard of positioning datum is to select each base point which can determine the shape of connecting rod.
When selecting the positioning datum, it is necessary to ensure the machining accuracy of the workpiece. Therefore, multiple choices should be made for the positioning datum. From the perspective of economy and reliability, the following selection methods are generally adopted:
In the selection of precise datum, in addition to ensuring the machining accuracy, the convenience of workpiece installation should also be considered, as shown in the figure.
① Because the connecting rod needs to process each processing surface one by one in the process of processing, it needs to be repeatedly installed in the combination process to reach the standard size. Therefore, in order to ensure the overall accuracy of the connecting rod, a unified positioning datum should be established, so that most processes can be carried out on the same datum plane.
② Because the connecting rod is easy to be affected by external forces, resulting in the position accuracy deviation of each processing surface, so in the process of selecting the datum plane, the datum plane with accurate positioning should be selected as the standard.
③ The datum plane can be selected according to the standard on the drawing. So as to ensure that the actual positioning datum is consistent with the design standard, so as to reduce the size error.
According to the above principles, in the process of machining the large and small end faces of the connecting rod, it is necessary to process the positioning datum plane first, and ensure that the positioning datum plane has high accuracy.
When locating the datum plane, the big and small end faces of the fixture are usually used as the datum plane. If the distance between the big and small end faces is large, it can be used as the guide datum plane. If the distance between the big and small end faces is small, it can be used as the thrust datum plane.
This kind of positioning method effectively unifies the selection of connecting rod on the datum plane
① So that most of the processes can use a unified selection standard, so as to reduce the error caused by datum conversion, and provide convenience in the machining surface of the same accuracy requirements, so that the axis parallelism of the connecting rod can meet the standard requirements.
② In the design process of small end hole, the end face of the end hole is usually taken as the design reference, and the error of the small end hole designed in this way is basically zero.
③ It reduces the difficulty in the process of process design, improves the efficiency of fixture design, saves processing time and reduces the production cost of fixture. In the process of processing the small end hole, the telescopic short pin is usually used to locate the small end hole. After the positioning is completed, the short pin is taken out.
4. Determination of reasonable clamping method
The rigidity of the connecting rod is poor, and it is easy to produce elastic deformation under the action of the clamping force. If the accuracy test is completed under the clamping state, the accuracy of the workpiece will be greatly affected after loosening. Therefore, when selecting the positioning datum, the action point of the clamping force should be considered, so as to ensure the accuracy of the connecting rod accuracy.
When determining the action point of the clamping force, it is necessary to ensure that the clamping force has the least influence on the deformation of the workpiece.
The selection of the force point of the clamping force can not offset the positioning point of the workpiece. If there is a problem in the selection of the force point, the workpiece will have an error in positioning. Usually, the workpiece will produce vibration when cutting, and the force produced by vibration will affect the clamping force. If the clamping force is too small, it will make the workpiece offset under the action of vibration force. If the clamping force is too large, it will cause the positioning point error of the workpiece. Therefore, the clamping force should be close to the machining surface to reduce the impact of vibration on the workpiece error.
Because the connecting rod is a kind of workpiece with poor rigidity, it is easy to produce deformation, so the focus of clamping force should select the part with strong rigidity, avoid selecting the soft part, prevent the deformation of connecting rod, and ensure the machining accuracy of connecting rod.
5. Machining of two end faces of connecting rod
The machining accuracy of the connecting rod end face is related to the coaxiality of the connecting rod big and small end holes. In the process of machining, it is necessary to select the appropriate force point to avoid the deformation of the connecting rod caused by the clamping force, thus affecting the positioning datum.
6. Machining of large and small end holes of connecting rod
The accuracy of positioning datum is determined by the machining of connecting rod big and small ends. In the process of connecting rod hole machining, the boss is usually used as the positioning reference. When boring process, we need to select the appropriate fixture, through the hydraulic or manual way for positioning processing.
7. Processing of connecting rod bolt hole
Bolt is the main part of connecting rod body and cover. Therefore, the bolt is subject to great force, and its quality requirements are very high. When there is a problem with the bolt, it will cause poor contact between the connecting rod body and the cover, which will lead to major accidents. Therefore, when processing the bolt, it is necessary to carefully identify the quality of the bolt, so that the bolt can meet the corresponding requirements.
8. Milling process of connecting rod body and cover
The milling process of connecting rod body and cover should meet the requirements of reliability, so as to prevent the deformation of connecting rod cover. To meet the requirements of reliability, it is necessary to reduce the clamping degree of connecting rod body and cover in the milling process, and ensure that the pressing plate and pin are symmetrical, so as to improve the stability of connecting rod body and cover.
9. Machining small head hole
Small head hole processing is divided into three stages. This can reduce the stress produced in the cutting process. Thus, a large amount of metal materials can be cut off in the process of machining, and the machining accuracy of small head hole can be improved.
10. Finish boring big head hole
The boring of large end hole needs to be carried out on milling machine, which can improve the machining accuracy of connecting rod hole, and the automatic operation can also reduce the labor cost.
11. Small bore press in bushing
When the bushing is pressed into the small head hole, professional tools are needed to improve the reliability between the small head hole and the bushing.
12. Boring small head bushing hole
When positioning the connecting rod body of boring small end, it is necessary to position the boss and small end, so as to ensure the machining accuracy of connecting rod.
13. Honing big end hole
Honing is an efficient processing method, and the honing accuracy is very high. When grinding the big end hole of connecting rod, the coaxiality must be within 4 μ On the other hand, the honing surface needs a higher support rate, so as to extend the service life of the big head hole. In addition, the honing speed is lower, so that the heat of the workpiece is smaller, so as to reduce the deformation degree of the connecting rod.
Because the connecting rod hole needs to contact with the honing head in honing, and the honing head needs to rotate and reciprocate in honing, the honing stone is often made of wear-resistant materials. The precision of honing head determines the precision of connecting rod hole. Horizontal honing machine is used in this process.
14. Process practice effect of new connecting rod
In order to deeply analyze the new connecting rod technology in this paper, it is compared with the common manufacturing technology of lathe. The cost ofis low and the product performance is good, but the rejection rate is high. The products produced by die forging process have good performance but high cost. Powder forging process has high material utilization rate, but high production cost. Based on the new connecting rod process proposed in this paper, the cost, product performance, precision and material utilization are optimized, and the product quality needs to be further optimized.