Technological analysis and tool design of machinin

Process analysis and tool design of steering arm spline taper hole machining

1

in the automobile steering mechanism manufactured by our factory, the steering arm and steering arm shaft are connected by taper spline. The product dimension (N-N section) of the steering arm spline taper hole is shown in Figure 1. The processing technology is divided into three processes: (1) pull out the straight hole spline groove with a triangular spline broach; (2) Extrude the spline hole with a coarse extruding knife with taper to form a certain taper; (3) Use the forming taper precision extruding knife to extrude the spline taper hole

figure 1

in the actual design of spline broach and coarse and fine extrusion cutter, due to the unreasonable large diameter, small diameter and tooth thickness of the spline after broaching determined by the process, the allowance of the workpiece spline on the large diameter and small diameter is uneven in the extrusion process, resulting in insufficient guiding length of the coarse extrusion cutter, and even non extrusion. The fine extrusion cutter can only be used for one-time extrusion. This leads to the reduction of the durability of the extrusion tool and the increase of the surface roughness of the workpiece. In order to ensure the strength of the tool tip and increase the durability of the tool, the operators on the production site often reduce the outer diameter of the tool (that is, widen the tool tip). When designing the spline plug gauge, only the tooth thickness tolerance of the workpiece is considered, and the wear of the major diameter of the tool spline is underestimated. When the spline plug gauge is used for inspection, the major diameter of the plug gauge is in contact with the major diameter of the extruded part spline, and the inspection pass gauge cannot pass, but at this time, the tooth width of the spline hole has actually reached the qualified size. In order to make the plug gauge pass the inspection, the operator often presses the extrusion knife down for an additional section. At this time, the tooth width of the processed spline hole is actually larger than the theoretical size. During assembly, due to the contact between the steering arm and the steering arm shaft, there is a gap on the tooth side, resulting in loose connection and affecting the product quality

2 process analysis

the major diameter taper of the spline given in the product drawing is 1:15, and the minor diameter bevel is 1 ° 48'56 ", which is converted into a taper of zn=1: (TG1 ° 48'56")/2=1:15.77385

according to the principle of tool grinding, the slot width of the extruding tool on each section perpendicular to the tooth root is equal. Because the taper of the slot bottom is small, the axial section of the extruding tool can be used to replace each section perpendicular to the tooth root. Therefore, when the measuring rods are the same, the measuring rod distance of each section is the same as the tool diameter, and the taper is also 1:15.77385. By analyzing the above process problems, it can be seen that the main reason for the problems lies in the incorrect process size of the spline broach. The correct process size should make the ratio of the machining allowance left in the extrusion process on the large and small diameter of the spline after broaching by the spline broach be 15.77385:15, and the ratio of the unilateral allowance on the spline tooth groove to the small diameter allowance be 1:1. In this way, on the one hand, it can ensure that the large, small diameter and tooth side of the spline tooth can contact with the large, small diameter and tooth side of the workpiece at the same time during the rough and fine extrusion processing, so as to realize the extrusion processing at three places at the same time, so as to ensure the surface processing accuracy of the workpiece and improve the durability of the tool at the same time; On the other hand, the coarse and fine extrusion tools can be designed with different taper (the taper of the fine extrusion tool is the same as that of the product), so as to eliminate the uneven extrusion amount when using the same taper tool, and make the design of the extrusion tool more convenient

for the design of the inspection tool, the large, small diameter and tooth side of the spline taper hole should be detected respectively, so that the detection error caused by the wear of the extrusion tool can be eliminated

3. determination of process parameters

in order to ensure that the small end of the workpiece can also be extruded, the large and small diameter of the spline broach should be determined based on the small end, that is, the pressure test site at the small end adopts camera real-time monitoring, which can realize the minimum extrusion allowance on the site of unmanned pressure test. The large and small diameter dimensions of N-N section given in the product drawing are: large diameter de=41.2mm, small diameter df=39.21 ~ 39.37mm. The diameter of the measuring rod is da=2.886mm. According to the given cogging width of 1.571 ~ 1.718mm, it can be deduced that the distance between measuring rods is ma=45.334 ~ 45.476mm. Based on this, it can be deduced and calculated that the large diameter, small diameter and measuring rod distance of the small end face are de=41/15=40.8mm； df=(39.21～39.37)-6/15.77385=38.83～38.99mm； Ma= (45.334 ~ 45.476) -6/15.77385=44.954 ~ 45.096mm (gauge rod diameter da=2.886mm)

from this, it can be determined that the major diameter dimension of spline in broaching process is deo=40.8mm. Considering that both broach and extruding knife are easy to wear with large diameter, the large diameter of the product can be increased to 41.35mm; In addition, in order to avoid interference between its small diameter and the inspection tool, the small diameter of the product is increased to 39.234mm. Therefore, the diameter of spline in broaching process is dfo=39.234- (41..8) 15/15.77385=38.71mm. The spline gauge distance in broaching process is mao=45.334- (41..8) 15/15.77385=44.82 Adopt LCD controller 1mm. According to the small diameter value of broaching process, the drilling process size of drilling process can be determined as φ 38mm。

4 cutter design

drill bits for drilling process can be selected φ 38mm standard drill bit

broach is used in broaching process according to the hole diameter before broaching φ 38mm. The minor diameter of the tool calibration tooth is φ 38.71mm, with major diameter of φ 40.8mm, the distance between measuring rods is 44.81mm, and the design process is short

the difficulty of tool design lies in the extrusion tool used in the extrusion process. Because the extrusion allowance is large, the use of one-time extrusion method will reduce the tool durability, so the use of two-time extrusion method. The taper on the big 6 and small diameter of the fine extrusion tool used is the same as that of the product, which is 1:15 and 1:15.77385 respectively (the taper of the measuring rod distance is the same as that of the small diameter); In order to ensure that the rough extrusion tool has a long insertion guide length and ensure the extrusion accuracy of fine extrusion, the taper of the rough extrusion tool is different from that of the fine extrusion tool

the processing position of the coarse and fine extrusion cutter is shown in Figure 2. Because the allowance left after the previous broaching process has met the taper requirements of 15:15.77385, the extrusion knife can be guaranteed to contact on the large, small diameter and tooth thickness at the same time in any machining section. Therefore, the key to the design is to determine the insertion guide length of the extrusion knife, and the key to determine the extrusion length is to determine the large and small diameter taper of the coarse extrusion knife

figure 2

take the N-N section of the product drawing as the design reference section, and X is the distance between the section in contact with the broached hole end and the reference section after extrusion; Y is the distance between the section in contact with the fine extrusion knife and the coarse extrusion knife after extrusion and the reference section after extrusion. Set the large diameter taper of the rough extruding tool as ZCW and the small diameter taper as zcn

on the outer cone, the major diameter of the rough extrusion knife of section a is dwa=deo=40.8mm; The major diameter of the rough extrusion cutter of section C is dwc=dwa+ (30-x)/zcw; The major diameter of the fine extrusion cutter of section B is djb=de+y/zjw=41.35+y/15. Because dwc=djb, there is

deo+ (30-x)/zcw=de+y/zjw (1)

the same principle. On the inner cone, there is

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 the two is taken.)

according to figure 2, the sectional area of extrusion allowance on the large diameter (one side) is

sofde=0.5 × 36(of+de)=0.5 × zero point five × 36[(de-deo-6/Zjw)+0.5 × 36/zjw]=9 (de deo + 12/zjw)

the extrusion allowance sectional area (one side) of the rough extrusion cutter on the large diameter is

sace=0.5 × ae × Ce=0.5 (30-x) [0.5 (30-x)/zcw]=0.25 (the international competition held in Xingtai area caused the local coking plant to limit production-x) 2/ZCW

take the total extrusion allowance as K times of the rough extrusion allowance, that is, softe=ksace, then there is

9 (de deo+12/zjw) =0.25k (30-x) 2/ZCW (3)

similarly, you can get

9 (DF dfo+12) on the inner cone./zjn) =0.25k (30-x) 2/zcn (4)

solve equations (1) to (4) simultaneously, and ZCW, zcn, x, y can be solved. Considering the distribution ratio of the extrusion allowance of the rough extrusion tool and the fine extrusion tool, take k=2.5, that is, the ratio of the extrusion allowance of the rough extrusion tool and the fine extrusion tool is 1:1.5. Finally, it can be solved: zcw=21, Zcn=22.41673，x=1.2，y=12。 Thus, the design parameters of the extrusion cutter on the large end face can be obtained

5 process correction method

since the current process cannot be changed significantly temporarily, the drill bit used in drilling process and broach used in broaching process cannot be changed; In the extrusion process, the fine extrusion knife basically meets the product processing requirements, so the only way to solve the above process problems is to correct the coarse extrusion knife. There are two methods to correct the rough extruding knife:

1) use the rough extruding knife with the same taper of large and small diameter as the fine extruding knife (in fact, the section of the fine extruding knife extending to the small end). This method can obtain a longer insertion guide length, but the extrusion allowance of rough extrusion is small, and there is still the problem that the extrusion knife cannot contact on the large, small diameter and tooth side at the same time when extruding with the fine extrusion knife

2) modify the parameters of the above design method, that is, by changing the parameter values of De, deo, DF, DFO, etc., a coarse extrusion tool with a different taper from the fine extrusion tool can be designed. This method can make a large extrusion allowance during rough extrusion, and ensure that the fine extrusion knife can contact on the large, small diameter and tooth side at the same time during extrusion, but there are also uneven extrusion amounts on the large, small diameter and tooth side, that is, the k values in formula (3) and formula (4) are different, so different K values should be selected respectively, and the insertion guide part of this method is short during rough extrusion

according to the above analysis, we adopted method (1) in the actual process correction, that is, the coarse extrusion knife adopts the same taper as the fine extrusion knife on the large and small diameter, which is convenient for manufacturing, and the fine extrusion knife can be changed into the coarse extrusion knife after wear, which can save the cost of the knife. (end)