I. Introduction The camshaft is a key transmission comp […]
The camshaft is a key transmission component in the engine and has high performance requirements. At present, there are three main production processes for camshafts, namely cutting, die forging, and cross wedge rolling. The mechanical cutting processing method has shortcomings such as low production efficiency, low material utilization rate, and metal fibers being cut off, but because it does not require large-scale special equipment, the process is simple. The die forging method can ensure that the metal fibers of the forging are continuous, the quality of the forging is guaranteed, and it has a considerable production efficiency. However, there is flash during the die forging, and the material utilization rate is not high. The material utilization rate is roughly the same as that of the cutting method. Most domestic engine manufacturers still use the above two methods to produce. The cross wedge rolling process is a new process for the production of shaft forgings developed in the 1960s. It has many advantages such as high efficiency and material saving. After the efforts of many scholars and manufacturers, it has been widely used in production in recent years. Applications. There are more than 100 varieties of forgings produced by this process, and they are playing an increasingly important role in the forging industry.
2. Technological analysis of cross wedge rolling of camshaft
The camshaft rolling blank is close to the limit section reduction rate of 75% for one rolling of the cross wedge rolling process. The part that needs to be rolled is the right-angle shoulder in the narrow gear, and the narrowest part of the gear width is only 15mm. The calculation of the interception curve of the right-angle shoulder in the narrow gear is essentially the same as the calculation of the interception curve of the conventional right-angle shoulder. Therefore, the design and calculation of the truncation curve of the right angle shoulder in the narrow gear has become the key technology of camshaft rolling. The total length of the camshaft blank is 770mm, and the straightness is required to be 1mm. This piece is an ultra-long precision cross-wedge rolled piece. Therefore, the camshaft is a difficult-to-form part among the cross-wedge rolling parts, and the process is difficult.
3. Design points of cross wedge rolling die
1. Determination of rolling plan
The maximum diameter of the rolled piece is 60mm, but the total length and the part to be rolled are relatively large, so a large-sized cross wedge rolling mill must be selected. This process adopts a H1000mm cross wedge rolling mill. In order to ensure that the mold design has a long enough roll surface to use, the center distance is 1031.47mm. The total number of V6 camshaft concave shoulders to be rolled on the camshaft is 18. In order to ensure the synchronization of deformation during rolling and the balance of rolling force on both sides, the wedge-up position is selected at the middle stage with a width of 17mm. way rolled.
2. Calculation of process and mold parameters
Since there are as many as 18 concave gears to be formed, the roll surface of the H1000mm cross wedge rolling mill is limited. In order to minimize the length of each wedge, the forming angle and the wedge spread angle of the die should be large, the forming angle α should be 30°, and the wedge The spread angle β is 9.42°, the length of the wedge section is calculated according to the formula L1=0.5(d0-d1)cotαcotβ, the wedge spread section is calculated according to the formula L2=Bcotβ, the calculated total length of the mold is 2938.23mm, and the length of the feeding section is 120mm.
3. Design of the feeding mechanism
The H1000mm cross wedge rolling mill is a split type. The rolling mill has no clutch and brake system. The rotation of the roll is driven by the universal joint to continuously rotate. The feeding method can only use axial feeding. For this reason, there is a 75mm wide and 50mm deep trough in the front part of the upper mold. Whether the feeding mechanism can accurately and timely send the blanks to the trough is also the success of the process. one of the key issues. Due to the limitation of equipment and process conditions, the length of the feeding section cannot be made too large. The length of the feeding section is 120mm, and the rotational speed of the roll is 6r/min. Under these conditions, it is difficult for the feeding mechanism to accurately and smoothly feed the blank into the hopper. In the middle, sometimes it is easy to get stuck, and in severe cases, the mold or equipment can be damaged. The discharge chute in the upper mold does not work for discharge, so consider using the length of this section to achieve smooth feeding. The specific method is to seal the discharge section in the upper mold with steel plates, so that the blank is not directly fed into the holding tank, but has a sliding time on the mold before being sent into the holding tank, so as to realize the smooth feeding of the blank. Enter.
4. Design of the truncated curve of the shoulder with a large section reduction rate and a narrow profile with a straight inner angle
When the cross wedge rolling process forms the right inner angle shoulder, a special curve must be machined in the corresponding part of the mold, which is called the truncation curve. There are many calculation methods for the conventional truncation curve with a wide enough width. Although various algorithms have different degrees of simplification in the calculation, the calculation results can mostly meet the engineering requirements. The cross wedge rolling process of shafts with large section reduction rate is prone to diameter reduction defects during rolling. Therefore, to achieve large section reduction rate rolling, the generation of diameter reduction must first be avoided, and the method of eliminating diameter reduction also directly affects Design calculations to truncate curves. If the truncation curve of the right-angle shoulder in the narrow gear is calculated according to the conventional method, the truncation curve will extend to the wedge section, or even cut off the wedge tip, which is impossible in practice. Therefore, the forming law of the narrow-gauge right-angle shoulder with large section reduction rate is essentially different from that of the conventional right-angle shoulder, and the calculation model of the truncation curve is also completely different. In the debugging of the mold, a more accurate calculation method of the truncation curve has been found. The truncation curve calculated by this method can get satisfactory results with only a little grinding, thus greatly reducing the mold repair time and shortening the debugging cycle.