1 question raised
In the steering mechanism of the automobile manufactured by our factory, the steering arm and the steering arm shaft are connected by a taper spline. The product size (NN profile) of the steering arm spline taper is shown in Figure 1. The processing process is divided into three processes: (1) using a triangular spline broach to pull out the straight hole spline groove; (2) using a tapered squeeze knife to squeeze the spline hole to form a certain taper; (3) The spline taper hole is extruded by a forming taper.
In the actual design of the spline broach and the coarse and fine squeezing knives, the large diameter, the small diameter and the tooth thickness of the spline after the broaching determined by the process are unreasonable, so that the spline of the workpiece is in the large diameter during the squeezing process. The unevenness of the margin and the small diameter leads to insufficient guiding length of the rough squeezing knife, and even the case of squeezing does not advance, and can only be formed by one-time extrusion squeezing. This results in reduced durability of the extrusion tool and an increase in the surface roughness of the workpiece. In order to ensure the strength of the tool tip and increase the durability of the tool, the production site operator often reduces the outer diameter of the tool (ie widens the tool tip). When designing the spline plug gauge, only the tolerance of the tooth thickness of the workpiece is considered, and the wear of the large diameter of the cutter spline is not enough. When the spline plug gauge is used for inspection, the large diameter of the plug gauge is in contact with the spline of the workpiece after the extrusion, and the inspection pass can not be passed, but at this time, the spline hole width of the spline hole has actually reached the qualified size. In order to pass the plug gauge inspection, the operator often presses the squeegee down a more time. At this time, the spline hole width of the spline hole is actually larger than the theoretical size. During assembly, due to the formation of the tooth tip contact between the steering arm and the steering arm shaft, a gap is generated on the tooth side, resulting in a tight coupling, which affects product quality.
2 Process analysis The product diagram shows a large diameter taper of 1:15, a small diameter bevel of 1°48'56", and a taper of Zn=1:(tg1°48'56")/2=1: 15.77385.
According to the principle of tool grinding, the width of the squeegee is equal in each section perpendicular to the root. Since the bottom taper is small, the shaft section of the squeegee can be used instead of the section perpendicular to the root. Therefore, in the case where the measuring rods are the same, the gauge bars of the respective sections are the same as the tool diameter, and the taper is also 1:15.377384. Analysis of the aforementioned process problems shows that the main cause of the problem is that the given spline broach process size is incorrect. The correct process size should be such that the ratio of the machining allowance left to the extrusion process after the spline broach is broached on the large and small diameter of the spline is 15.77385:15, and the unilateral retention and diameter on the spline tooth groove The ratio of the retention is 1:1. In this way, on the one hand, it can ensure that the two large and small knives can be simultaneously contacted with the large, small diameter and flank of the workpiece on the large, small diameter and flank sides of the spline teeth, so that three simultaneous extrusion processes can be realized. In order to ensure the surface machining accuracy of the workpiece, and at the same time improve the durability of the tool; on the other hand, the coarse and fine extrusion knives can be designed with different taper (where the taper of the precision boring tool is the same as the product taper) to eliminate the use of the same taper tool. The resulting amount of extrusion is uneven and the design of the squeegee is more convenient.
For the design of the gage, the detection of the large, small diameter and the flank of the spline cone should be realized separately, so as to eliminate the detection error caused by the wear of the extrusion tool.
3. The process parameters are determined to ensure that the small end of the workpiece can also be extruded. The small and small ends should be used as the reference to determine the large and small diameter of the spline broach, that is, the minimum squeeze margin at the small end. The large and small diameter dimensions of the NN section given in the product diagram are: large diameter de = 41.2 mm, and small diameter df = 39.21 to 39.37 mm. Its measuring rod diameter is da=2.886mm. According to the given cogging width of 1.571 to 1.718 mm, the calculated bar spacing can be derived from Ma=45.334 to 45.476 mm. Based on this, it can be deduced that the large, small diameter and the gauge bar distance of the small end face are: de=41.2-6/15=40.8mm; df=(39.21～39.37)-6/15.77385=38.83～38.99mm; Ma = (45.334 - 45.476) - 6 / 15.77385 = 44.954 - 45.096 mm (measured bar diameter da = 2.886 mm).
Thus, it can be determined that the large diameter of the broaching process spline is deo=40.8 mm. Considering that both the broach and the squeezing knife have large diameters and are easy to wear, the large diameter of the product can be increased to 41.35 mm; in addition, in order to avoid interference between the small diameter and the inspection tool, the product diameter is increased to 39.234 mm. . Therefore, the size of the spline diameter of the broaching process is dfo=39.234-(41.35-40.8)15/15.77385=38.71 mm. The distance of the spline of the broaching process is Mao=45.334-(41.35-40.8)15/15.77385=44.81mm. According to the small diameter value of the broaching process, the drilling process size of the drilling process can be determined to be f38 mm.
4 Tool design The drill bit can be selected with a f38mm standard drill bit.
The broaching process uses a broach to pull the front aperture to be f38mm, the tool calibration tooth diameter is f38.71mm, the large diameter is f40.8mm, and the gauge bar distance is 44.81mm. The design process is slightly.
The difficulty in tool design is the extrusion tool used in the extrusion process. Due to the large amount of extrusion, the one-shot method reduces the durability of the tool, so the two-extrusion method is used. The taper on the large and small diameters of the precision knives used is the same as the taper of the product, which are 1:15 and 1:15.773,384 respectively (the gauge taper is the same as the taper of the small diameter); to ensure the long insert guide length and ensure the fineness of the rough knives The extrusion precision of the extrusion process, the rough extrusion knife adopts a taper different from the precision extrusion knife.
The processing position of the coarse and fine extrusion knives is shown in Fig. 2. Because the margin left after the broaching process has satisfied the taper requirement of 15:15.77385, the cutting knives can ensure the simultaneous contact of the knives on the large, small diameter and tooth thickness in any processing section. Therefore, the key to the design lies in The insertion guide length of the extrusion knife is determined, and the key to determining the extrusion length is to determine the large and small diameter taper of the rough extrusion knife.
Taking the NN section of the product drawing as the design reference section, x is the distance between the section of the rough extrusion knives and the boring hole end after the extrusion is completed and the reference section; y is the extrusion of the squeezing knives and the rough squeezing knives The distance between the contact section and the reference section after the extrusion is completed. The roughing cutter has a large diameter taper of Zcw and a small taper of Zcn.
On the outer cone, the large diameter of the A section is dwa=deo=40.8mm; the large section of the C section is dwc=dwa+(30-x)/Zcw; the diameter of the section C is djb =de+y/Zjw=41.35+y/15. Because dwc=djb, so there is
Deo+(30-x)/Zcw=de+y/Zjw (1)
Similarly, there is on the inner cone
Dfo+(30-x)/Zcn=df+y/Zjn (2)
(The calculation result on the measuring rod distance is the same as that on the inner cone, and only one of them is taken.)
From Figure 2, the cross-sectional area of ​​the squeeze (single side) on the large diameter is
Sofde=0.5×36(of+de)=0.5×0.5×36[(de-deo-6/Zjw)+0.5×36/Zjw]=9(de-deo+12/Zjw)
The squeeze cross-sectional area (one side) of the rough squeeze knife on the large diameter is
Sace=0.5×ae×ce=0.5(30-x)[0.5(30-x)/Zcw]=0.25(30-x)2/Zcw
Take the total squeeze margin as K times the rough squeeze margin, ie Sofde=KSace, then
9(de-deo+12/Zjw)=0.25K(30-x)2/Zcw (3)
In the same way, it can be obtained on the inner cone.
9(df-dfo+12/Zjn)=0.25K(30-x)2/Zcn (4)
By solving the equations (1) to (4) in parallel, Zcw, Zcn, x, y can be solved. Considering the proportion of the extrusion allowance of the rough squeezing knife and the fine squeezing knife, K=2.5, that is, the ratio of the extrusion squeezing of the rough squeezing knife to the squeezing knives is 1:1.5. Finally, it can be solved: Zcw=21.3333454, Zcn=22.41673, x=1.2, y=12. From this, the design parameters of the extrusion knives on the large end faces can be obtained.
5 Process correction method Since the current process cannot be changed greatly for the time being, the drill for the drilling process and the broach for the broaching process cannot be changed; in the extrusion process, the precision extrusion knife basically meets the product processing requirements, so the solution is solved. The only way to deal with the aforementioned process problems is to correct the roughing knives. There are two ways to correct the rough knives:
It adopts a rough extrusion knife with the same taper of the large and small diameter of the precision squeezing knife (actually a section of the squeezing knives extending to the small end). This method can obtain a long insertion guide length, but the rough extrusion allowance is small, and when squeezed with a precision knife, there is still a problem that the extrusion knife cannot be simultaneously contacted on the large, small diameter and the flank.
The parameter modification of the above design method, that is, by changing the parameter values ​​of de, deo, df, dfo, etc., a rough extrusion knife different from the taper of the precision extrusion knife can be designed. The method can make a large squeeze margin when roughing, and can ensure simultaneous contact on the large, small diameter and the flank when the squeeze knife is squeezed, but there are also large and small diameters and the amount of squeeze on the flank. In the case of unevenness, that is, the values ​​of K in the equations (3) and (4) are not equal, different K values ​​should be selected respectively, and the insertion guide portion is shorter when the method is squeezed by the rough extrusion knife.
According to the above analysis, we have adopted the method (1) in the actual process correction, that is, the rough extrusion knife adopts the same taper as the fine extrusion knife on the large and small diameters, which is convenient for manufacturing, and the fine extrusion knife can be changed into a rough extrusion knife after being worn. Use, can save tool costs.
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