Abstract: The influence of the fillet radius and shape on the finished ferrule in the design and machining of the overrun groove of cylindrical roller bearing is analyzed. Taking the overrun groove of NU1006 cylindrical roller bearing as an example, the cutters with different M and R values are compared and analyzed. Based on the changes of width, depth and angle, the optimal method of overrun groove parameters is determined, which has obvious improvement effect on the overrun groove of small size section.
Cylindrical roller bearings have a wide range of applications, and the processing technology of their rollers and raceways has been very mature, but there are still some areas for improvement in the processing of overrun grooves with rib rings. The design of the size and shape of the overtravel groove has a great influence on the processability of the overtravel groove and the quality of the ferrule. The following takes NU1006 cylindrical roller bearing outer ring overrun groove as an example to analyze the advantages and disadvantages of the same coordinate size and different shapes of overrun grooves in processing, and obtain a better design method, which is extended to the processing of other types of bearings. middle.
1 Influence of the shape of the overrun groove on the ferrule
The NU1006 cylindrical roller bearing has double ribs on the outer ring and no ribs on the inner ring. The bearing design uses cylindrical rollers of Φ6mm×6mm. Figure 1 is the finished drawing of the outer ring overtravel groove. According to “Design Method of Reinforced Cylindrical Roller Bearing”, only M2max, Mmax and M1max dimensions are given for the overtravel groove, and the curvature radius of the groove bottom fillet and the arc two are not specified. The angle of the side hypotenuse. The dimensions of the outer ring overtravel groove can be obtained by looking up the table: M2max=0.4mm, Mmax=0.5mm, M1max=0.6mm.
The over-travel groove is cut with a forming turning tool during the turning process. The shape and size of the over-travel groove mainly depend on the shape and size of the turning tool. The drawing for the machining of overtravel grooves shall not only calculate the coordinate dimensions of the machining overtravel grooves according to the specific dimensions marked in the finished product drawing plus the machining allowance, but also give the radius of curvature R of the arc and the tangents on both sides of the arc angle, which provides a basis for the processing and inspection of the overrun groove.
In order to ensure the effective size of the over-travel slot, the maximum coordinate value is taken in the process, and the machining size of the over-travel slot car is shown in Figure 2. The drawing process is as follows: according to the dimensional coordinate values found in Figure 1, the overrun groove diagram of the finished part is made, and the intersection of the raceway and the rib is the center of the overrun groove arc. Make a corresponding parallel line according to the machining allowance of the raceway and rib. The intersection of the parallel line and the extension line of the rib is C, and the intersection with the extension line of the outer raceway is D; For strength, take the transition fillet R between points C and D as 0.5mm; connect AC and BD to obtain the shape and size of the overrun groove of the outer ring.
It can be seen from the figure that the angle between OA and AC is 43°21’52”, the angle between OB and BD is 32°0’19”, and the angle between AC and BD is 14°37’48”. The point is the vertical line of BD, and the length of the vertical line segment is 0.9mm measured by drawing; the vertical line segment of the tangent to the fillet R (0.5mm) is made through the point B, and the length of the vertical line segment is measured to be 1.34mm.
It can be seen from Figure 2 that during the machining process, the points C and D are subjected to large forces, and the cutter head is easy to wear. During lathe machining, the length of the cutter head increases due to the addition of the allowance, which is easy to be brittle, resulting in difficult to guarantee the machining quality of the overrun groove and low machining efficiency; the angle between OA and AC and the angle between OB and BD are more If it is small, the deviation of the machining allowance between the rib and the raceway will have a greater impact on the size of the overrun groove of the finished product; an excessively deep overrun groove will also affect the strength of the ferrule.
2. Comparison of improvement methods for overtravel groove shape
In order to improve the cutting state of C and D, the transition fillet curvature of the overrun groove and the angle of the hypotenuse on both sides of the arc are changed. Make the transition fillet R=0.35mm for L1 and L3, and make the tangent to the fillet through points A and B respectively. The tangent points are C and D respectively. Connect AC and BD to obtain the shape and size of the overrun groove of the outer ring. .
After changing the transition fillet, the length of the cutter head is shortened compared with the original method, the C and D points have no sharp corners, the fillet is tangent to the hypotenuse, and the tool strength is increased. However, the shape of the original tool is destroyed, the arc of the tool tip is too small to be sharpened, and the tool tip is easily damaged (such as chipping). Cracks appear after ring quenching. Therefore, the size and shape of the overrun slot need to be improved again.
Take the tool nose arc R = 0.45mm, the same as the drawing method in Figure 3, to obtain the shape of the overrun groove as shown in Figure 4. During the machining process, points C and D are tangent to the transition arc, which can improve the tool strength at the tangent point, and the depth of the overrun groove is slightly reduced.
The shapes of the overrun grooves when M=0.3mm, R=0.3mm and M=0.3mm and R=0.4mm are further made, as shown in Figure 5 and Figure 6 respectively. The comparison of tool width, tool depth and angle under different values of overrun groove depth M and tool nose arc curvature radius R is shown in Table 1. The drawing comparison is shown in Figure 7 and Figure 8.
It can be seen from Table 1 and Figure 7 and Figure 8 that when M=0.5mm,
Method 3 has the largest knife width and the largest included angle between OA, AC, OB, and BD. Therefore, the deviation of the raceway and rib allowance has the smallest influence on the overrun groove of the finished product, and it is not easy to cause the phenomenon of “leftover edge”. The size of the groove is relatively uniform; when M=0.3mm, method 5 is wider than method 4, and the included angle between OA, AC, OB, and BD is also large, which can effectively improve the strength of the tool and the tool durability is better. When M1 and M2 are determined, the smaller the value of M under the premise of meeting the needs of the machining process, the smaller the depth of the tool and the higher the strength. It can be seen that method 5 is relatively good. When M, M1, M2 are determined, since M2<M1, take the transition fillet R close to (M+M2)/2, and pass the two points A and B as the tangent of the fillet. At this time, the tool arc and the hypotenuse transition smoothly. , the tool wear is small. The closer the transition fillet R is to (M+M2)/2, the wider the tool and the better the strength. Less tool damage, less time for tool sharpening, installation and machine adjustment, and increased efficiency. In recent years, with the development of technology, the development trend of the overrun groove of cylindrical roller bearings is that the size is getting smaller and smaller, and the groove depth is getting shallower.
Through the improvement, the tool tip wear (side grinding) is reduced, the heat dissipation is good, and the strength of the tool root is increased, which avoids the influence of the over-travel groove being too deep or too shallow on the ferrule, the workpiece processing quality is stable, and the efficiency is improved. During the machining of the overrun groove in the outer ring of the NU1006 cylindrical roller bearing,
Method 5 improves the processing efficiency by 30% to 50% compared with the original grinding wheel overtravel groove design method, and the service life of the tool is also doubled. The improved overtravel groove design method has greater advantages in the smaller size section, but is not much different from the original design scheme in the large size section, because the tool strength of the large size section is larger, and the structural size The intensity change is not very noticeable when changing, but it still improves overall. In addition, in the improved method of overtravel groove machining, the angle between the two cutting edges of the shaped tool is increased, the length of the tool is reduced, and the tool circle
The design ideas of smooth transition between arc and hypotenuse and avoiding sharp corner cutting can not only be applied to small-sized grinding wheel overtravel grooves, but also can be applied to other small-structure forming turning processes, such as bearing sealing grooves, oil grooves, etc. structural design.