Determination of the feeding route for the most po

2022-07-28
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Determination of NC turning feed route

the determination of machining route must first maintain the dimensional accuracy and surface quality of the machined parts, and then consider the simple numerical calculation, the shortest tool path and higher efficiency. Because the feed route of finish machining is basically carried out along the contour of its parts, the focus of determining the feed route is to determine the feed route of rough machining and empty stroke. The following will be analyzed in detail:

(1) the relationship between machining route and machining allowance

under the condition that CNC lathes have not reached universal use, generally, excessive allowance on blank parts, especially the allowance containing forged and cast hard skin, should be arranged to be machined on ordinary lathes. If it is necessary to process with a numerical control lathe, pay attention to the flexible arrangement of the program. Arrange some subroutines to cut the parts with excessive allowance first

① machining route for step cutting of large allowance workpieces

Figure 1 shows two machining routes for turning large allowance workpieces. Figure (a) is the wrong step cutting route, and figure (b) is the correct step cutting route by cutting in the order of 1 → 5, with equal allowance for each cutting. Because there is too much allowance left in machining according to figure (a) under the condition of the same back cutting amount

(a) (b)

Figure 1 ladder route for turning large surplus workpieces

according to the characteristics of NC machining, you can also abandon the commonly used ladder turning method and use the route of successively feeding the tool from the axial and radial direction and following the workpiece contour (as shown in Figure 2)

figure 2 two-way feeding and cutting route

② the end position of the tool during layered cutting

when there is a large amount of allowance on a surface and multiple layered cutting is required, From the second tool, you should pay attention to prevent the sharp increase of cutting depth when the tool reaches the end point. As shown in Figure 3, if 900 main deflection angle cutters are used to turn the excircle layer by layer, the reasonable arrangement should be that the cutting end point of each cutter is advanced by a small distance E (e.g. e=0.05 mm). If e=0, each tool terminates at the same axial position, and the main cutting edge may be impacted by instantaneous heavy load. When the main deflection angle of the tool is greater than 900, but still close to 900, it is also appropriate to make a layer by layer return arrangement. Experience shows that this is beneficial to prolong the service life of the rough machining tool

Figure 3 end position of the tool during layered cutting

(2) cutting in and cutting out of the tool

when machining on the NC machine tool, the cutting in and cutting out routes of the tool shall be arranged to make the tool cut in and cut out along the tangent direction of the contour as far as possible

especially when threading, the acceleration section must be set δ 1 and deceleration section δ 2 (as shown in Figure 4), so as to avoid affecting the stability of the pitch due to the lifting and lowering of the turning tool

Fig. 4 lead in distance and overrun distance during thread turning

(3) determine the shortest empty travel route

determine the shortest cutting route. In addition to relying on a lot of practical experience, it should also be good at analysis, supplemented by some simple calculations if necessary. Some design methods or ideas in practice are introduced as follows

① skillfully use tool setting points Figure 5 (a) is an example of the general situation of rough turning with rectangular circulation. The tool starting point a is set at a position far away from the blank in consideration of the convenient tool change during finishing machining, and the tool starting point is overlapped with its tool setting point, The routing of three tool rough turning is arranged as follows:

the first tool is a → B → C → D → a

this method greatly simplifies the operation process of verification. The second tool is a → e → f → g → a

the third tool is a → h → I → J → a

Figure 5 (b) is to skillfully separate the tool starting point from the tool setting point, and set it at point B in the figure. The three tool rough turning is still carried out according to the same cutting amount, The cutting route is arranged as follows: the empty travel between the starting point and the tool setting point is a → b

the first knife is B → C → D → e → b

the second knife is B → f → g → h → b

the third knife is B → I → J → K → b

obviously, the cutting route shown in Figure 5 (b) is short

Figure 5 skillfully use the tool starting point

(a) the tool starting point coincides with the tool setting point (b) the tool starting point separates from the tool setting point

② skillfully set the tool changing point in order to consider the convenience and safety of changing (turning) the tool. Sometimes, the tool changing (turning) point is also set far away from the blank (such as point a in Figure 5). Then, after changing the second tool, the empty travel route for finishing turning must be longer; If the tool change point of the second tool is also set at point B in Figure 5 (b), the empty travel distance can be shortened

③ reasonably arrange the "return to zero" route. In order to simplify the calculation process as much as possible, not easy to make mistakes, but also easy to check, programmers (especially the specific use of the initial impact testing machine (auto parts testing machine) in the automobile manufacturing process: Scholars) sometimes execute the "return to zero" (i.e. return to the tool setting point) command on the tool end point after each tool is processed, Make them all return to the tool setting point position, and then carry out subsequent procedures. This will increase the distance of the tool path and greatly reduce the production efficiency. Therefore, when reasonably arranging the "return to zero" route, the distance between the end point of the previous knife and the start point of the next knife should be minimized or zero, so as to meet the requirement that the cutting route is the shortest

(4) determine the shortest cutting feed route

cutting feed route is short, which can effectively improve production efficiency and reduce tool loss. When arranging the cutting feed route for rough machining or semi finishing machining, the rigidity of the machined parts and the processing technology should be taken into account at the same time, and do not lose sight of one or the other

Figure 6 is an example of the arrangement of several different cutting feed routes when rough turning the workpiece. Fig. 6 (a) shows the path of controlling the turning tool to move along the workpiece contour by using the closed compound cycle function of the NC system; Figure 6 (b) shows the "triangle" tool path arranged by using its program cycle function; Figure 6 (c) a "rectangular" tool path arranged to take advantage of its rectangular cycle function

figure example of cutting route

(a) cutting along the workpiece contour (b) "triangle" cutting (c) "Rectangle" cutting

for the above three cutting samples, they will certainly be clamped by the jaw to cut the feeding route. After analysis and judgment, it can be seen that the total sum of the cutting length of the rectangular circular feeding route is the shortest. Therefore, under the same conditions, the cutting time (excluding empty travel) is the shortest and the tool loss is small. In addition, the program segment format of rectangular circular machining is relatively simple, so this kind of feed route arrangement is widely used in the formulation of machining scheme. (end)

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