A type of cam used in a device manufactured by the China Air-to-Air Missile Research Institute has been modeled since the 1990s. From the initial trials and manual repairs and installed tests, a relatively ideal model is obtained. After processing, a certain amount of roughing is left according to the pattern, and then the operator performs the mold processing and repair according to the model. Smooth the cam surface. The problem that exists is that the processing is difficult, the technical level of the operator is high, the processing cycle is long, the precision is low, and the scrap rate is high. With the popularity of CNC machine tools and wire cutting equipment, the necessity and advantages of using wire cutting or CNC machining are increasing.
First, the original design requirements and processing methods of the cam
1. Original pattern data and technical requirements of the cam
The original pattern data of the cam is shown in Figure 1. The pattern requirements are: 355°～185° is the arc of R55, 185°～235° is the transition section, 235°～305° is the arc of radius R37, 305°～ 355° is the transition section. The transition section is 5° average, and each feature point is connected by a spline curve.
Figure 1 cam original pattern
2. Wire cutting processing trial and problem analysis
The software used in our wire-cutting machine is CAXA's electronic drawing board. The drawing is required according to the pattern. The transition section is to make the feature points first, and then the splines are connected to the two arcs through the feature points, so that the molybdenum wire The trajectory curve is formed. After the trial of the upper embryo, the surface of the cam profile was found to be ribbed and not smooth. The reason is analyzed: firstly, the value of the characteristic point of the original cam transition curve is not suitable, because the original pattern is drawn earlier, which is a hand-drawn spline curve, which causes the value of the characteristic point on the curve to have a large error; the second is the arc and the spline curve. Directly connected, there is no guarantee of tangency, so the ribs and ribs at the seam are more obvious. In addition, the insufficiency of wire cutting processing is that the coordination of surface roughness and processing efficiency cannot be satisfied.
3. Analysis of machining cam for CNC milling machine
If the CNC milling machine equipped with the numerical control indexing head is used instead of the original master processing method and wire cutting, the machining efficiency is not greatly improved, the technical level requirement for the operator is lowered, and the machining precision and the surface smoothness requirement can be improved.
However, because the cam CNC machining program is generally manually programmed, the disadvantage is that the CNC milling machine software compiles with linear interpolation, and the feature points are connected by straight lines. Due to the limitations of the manual programming method, sufficient coordinate points cannot be obtained, which leads to machining. The rear cam profile has a certain deviation, resulting in a ridge on the cam surface. The original pattern is indexed at intervals of 5°, and the interval is large. The data cannot be directly used. If the programmer manually interpolates the cam contour, the programming is complicated, the workload is too large, and the data calibration is difficult and error-prone. If the files recognized by the CNC milling machine can be obtained by software, the programming process will be greatly simplified.
Second, the use of Pro / ENGINEER wildfire 2.0
For the comprehensive comparison of traditional wire cutting and CNC milling machine processing methods, as well as the analysis of wire cutting prototype samples, it is decided to make full use of Pro/ENGINEER Wildfire 2.0 and Excel software to complete the cam data perfection, software simulation and automatic generation of CNC milling machine can be identified and used. Data sheet.
1. Raw data analysis and correction using Pro/ENGINEER
According to the results of the wire cutting trial, we initially concluded that the original data values ​​are not appropriate. To verify this inference, we decided to perform a 3D simulation in Pro/ENGINEER Wildfire 2.0 based on the cam pattern.
After entering the software, click File, New, select New Part, enter CAM001 in the name and enter the drawing mode, then click to stretch the feature and enter the sketching environment. In the sketching environment, drawing according to the design pattern, first make the inner hole φ55 and the two arcs of the size of R55 and R37, and then give a total of 18 feature points of the transition section 5° according to the figure. Then make two spline curves through the end points and feature points of the large and small arcs, so that the stretching is generated by the sketch, as shown in Figure 2. After clicking OK, the solid stretch is performed, and the tensile thickness dimension 10 is input to obtain a three-dimensional model as shown in FIG.
Figure 2 cam grass drawing
Figure 3 Original cam 3D view
It can be clearly seen from Fig. 3 that the cam surface has obvious irregularities and is not smooth, especially when the transition between the excessive section and the arc is clearly edged, which is very close to the cam profile processed by the wire cutting.
According to the simulation effect and the working timing requirements of the cam, it is decided to use the Pro/ENGINEER software to perform numerical fine-tuning under the premise of ensuring the timing of the arc segment, so that the cam surface is smoother. The value of the obvious concave and convex part is adjusted, and the spline curve and the arc connection point are added to the tangent relationship, and the modified pattern and the three-dimensional model are shown in FIG. 4 and FIG.
Figure 4 Figure after modifying the feature points
Figure 5 3D image of the corrected cam
It can be clearly seen from Fig. 5 that the corrected three-dimensional effect of the cam is very close to the ideal value, and the surface is smooth. The next step is how to convert the data into a text coordinate format recognizable by the CNC milling machine and correct it.
1. Correct selection of teeth
1) Before use, confirm whether the mechanical properties of the product meet the customer's requirements (such as the tensile strength of the Bolt and the safe load of the nut).
2) The length of the bolt should be selected properly, with 1-2 pitch exposed after tightening.
3) Before use, the thread should be kept clean.
2. How to use dental strips correctly
1) When tightening the teeth, pay attention to that the direction of force applied by the wrench should coincide with the axis of the screw, and do not tilt.
2) In the process of tightening, the force should not exceed the safety torque, and should be uniform. Try to use the torque wrench or socket.
3) Locking too fast will lead to locking, it is recommended not to use electric or pneumatic wrench.
4) Keep the thread clean. In order to ensure the smooth fit of screw and nut, it is recommended to put the product in a clean container and do not place it at will.
3. Standard of tooth bar maintenance
1) If there is slight damage to the removed tooth, screw and nut, the die and tap shall be used for repair.
2) The removed and repaired teeth, Screws and Nuts shall be maintained by means of oil bubble or lubricating oil, and shall be placed in order according to specifications, models and purposes.
4. Scrap standard
The bolts with obvious crack, broken thread, sliding, disorderly thread, screw tensile deformation, shear trace, etc. which can not be repaired by the on-site leader can be scrapped.
5. Specification parameters of tooth strips
Texture of material:
304/316
Product standard:
DIN975
Surface treatment:
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