- Detail

Research on microcomputer GNC system of NC lathe

1 preface

the main advantage of NC machine tool is the high combination of efficiency and flexibility, which is mainly manifested in that NC machine tool can complete the processing of different parts, and only the control medium of the machine tool - NC code needs to be changed, which is exactly the difference between numerical control processing and other traditional processing. At present, the utilization rate of CNC machine tools in domestic enterprises is generally low. The reason for this situation is that CNC programming technology can not keep up with it. Many enterprises are still in the stage of manual programming, so there is an urgent need to change the current situation of CNC programming

after manual programming and computer-aided programming, the automatic programming technology of NC machining has entered the era of graphic programming. Graphic NC programming has become an essential part of cad/cam and the best way of NC programming. At present, there are few domestic software in this field, while foreign software is mostly in workstations, and there is not much use of microcomputers, and the software system cost is very high, which is not suitable for the actual situation of domestic enterprises. The operation interface is in foreign language, which is not convenient for engineering personnel to operate, and it needs to spend a lot of manpower and material resources to train. Therefore, there is an urgent need for a set of NC programming software suitable for domestic use

this system is a graphic NC programming software based on microcomputer and developed for domestic enterprises. After the user inputs the geometric information of the part (or opens the relevant data file), the system automatically generates the part graphics. Combined with the input processing information (blank size, cutting parameters, etc.), the system can carry out dynamic simulation processing, and automatically generate the g/m code of the NC lathe. This system is developed by using VB5.0. It is operated in pure Chinese. The interface is easy to understand and intuitive. It is suitable for ordinary engineering technicians. The system adopts the combination of pull-down menu, pop-up menu and toolbar to operate, which greatly facilitates the use of users

2 hardware composition of GNC system

a complete GNC system includes the whole process from information acquisition to processing instructions. Manual input (MDI) of NC code program sheet is troublesome, boring and has a high error rate. Connecting the computer system with the numerical control device of the machine tool can not only eliminate the manual operation, but also carry out real-time or time-sharing control of multiple machine tools at the same time, so it can be equipped with serial port and DNC interface for communication. The hardware structure of GNC system is shown in Figure 1, and the system structure is shown in Figure 2

Figure 1 GNC system hardware composition

Figure 2 GNC system structure

3 part geometry information input and graphics generation

part geometry information input includes determining the total number of lines of parts, the parameters of each segment and the connection characteristics between them. The generation of part geometry refers to that the system automatically generates part geometry on the screen according to the relevant information entered by the user

1) input the geometric information of the part under the initial prestress of 0.7 times the yield strength

after the user inputs the parameters of each section of the part from left to right and determines its connection characteristics, the system can accurately calculate the intersection coordinates between them and "remember" the relevant geometric information (such as the linear characteristics of each section, the order and inverse of the arc, whether the sections are tangent, etc.). If there is a non-circular curve (parabola, ellipse) in the part, the system uses the "variable spacing linear force, which also determines the structure of the tension machine" to calculate its node coordinate value, and stores the value in an array. After the geometric information is input, the system will put the obtained data into a file specified by the user for post-processing to replace the corresponding jaw and guide sleeve (the jaw and guide sleeve are marked)

processing method of non-circular curve (taking ellipse as an example):

this system adopts "variable spacing straight line approximation method", which has obvious advantages over the traditional "equal spacing method". The traditional "equidistant method" divides the interval of the non-circular curve into N parts on average, that is, the place with larger radius of curvature is also divided into sub intervals of the same size according to the place with smaller radius of curvature. This reaction to CNC machine tools is unnecessary to walk more tools, and the efficiency is very low. The variable spacing rule can deal with this problem better. The specific method is shown in Figure 3

Fig. 3 variable spacing straight line approximation method

according to the known parameter equation, the expression of y = f (x) is obtained: (x-xc) 2/r12+ (y-yc) 2/r22=1, the specified interval se is divided into N parts, Xi is calculated according to the obtained spacing DX, and a series of (Xi, Yi) can be calculated by substituting the obtained Xi into y = f (x), that is, the end coordinates of each line segment, and the linear program segment is compiled with this coordinate value or the corresponding tool center coordinate value. Calculate to point P, if it is found that it does not meet the accuracy requirements, divide the PE interval into finer parts and proceed in turn until all the accuracy requirements are met

the error test method is shown in Figure 3. Mn is an approximation line segment after trial calculation. M'n 'is parallel to Mn and the distance to Mn is d (given by the user). The equation of Mn and M'n' can be obtained:

m n:ax+by+c = 0

m'n':ax+by=c ± d[(a2+b2)]

solve the simultaneous equation. When m'n'and (x-xc) 2/r12+ (y-yc) 2/r22=1 intersect, it indicates that it is necessary to subdivide the interval again to reduce the value of DX (A2 + B2)]

.That is, increase the number of intervals n) until there is no intersection between them

The allowable value ofd is generally 1/5 or 1/10 of the part tolerance. The system recommends that the allowable value of d be within 0.001mm

2) generation of part geometry

vb (Zibo Municipal government provides nearly 2000 square meters of office space for start-ups in the first high building of Zibo Visual Basic) provides relatively rich drawing instructions, so it can easily generate part graphics when knowing relevant parameters. Lines and arcs use the line and circle commands directly. When encountering a non-circular curve, the nodes of the non-circular curve will be obtained by using the variable spacing straight line approximation method, and then connected by straight lines in turn, the non-circular curve can be approximately obtained

4 NC machining simulation

when simulating machining, the user needs to input the blank size, the starting point of the machine tool, the tool compensation value and the lead screw clearance compensation value, the cutting parameters (cutting depth, cutting speed, feed rate), the position of the NC code in the machine tool storage unit and other information in turn according to the system prompt

considering that the machining process of the lathe is complex and the turning parts are ever-changing, it is difficult to program in every fixed way, and include as many situations as possible. The system divides lathe parts into two categories: stepped shaft and typical parts (basically able to solve the processing of common shape parts)

step axis refers to the type of descending from left to right in a strict sense. According to the input processing information, combined with the geometric information of the part, the system automatically formulates the processing route for simulated processing, and automatically generates the corresponding g/m code

typical parts refer to the five types of metal shapes to be removed, as shown in Figure 4. If it is a typical part, the processing route needs to be customized. Select the feature type of rough machining, and enter the coordinate value of the corresponding point (marked in the figure) as required. The input of coordinate value should comprehensively consider the blank size, part size and finishing allowance, and the system will provide the information of intersection coordinates in the part. The system simulates processing according to the order selected by the user, and generates the corresponding g/m code

Figure 4 five types of metal shapes to be removed

in order to facilitate observation, a two-dimensional figure similar to the tool shape is used to replace the tool in the dynamic simulation process, and the blank outline and the cut part are given different colors, so it is like cutting with a knife, which is vivid, as shown in Figure 5

Figure 5 dynamic simulation diagram

5 generation of NC code

the straight line or arc data generated by the NC trajectory in the processing process will be simulated, and the processing arc or straight line program segment will be generated according to the processing route and the control input format requirements of the machine tool used. The specific steps are as follows: first, determine whether to process straight-line segments or arc segments. This information has been obtained when inputting the geometric information of the part. When processing straight-line segments or non-circular curve segments (approximated by straight lines), G01 code is output; If machining an arc, you need to judge whether the arc is clockwise or counterclockwise, and output G02 and G03 codes respectively. Then combine the information of tool location (coordinate values of X and z) and cutting parameters, and put these information into a file specified by the user in turn to get the NC code

6 conclusion

this system conforms to the development trend of NC automatic programming. It can deal with the programming problems of NC Lathe on microcomputer, automatically generate g/m code, and has simple operation and intuitive interface, which is suitable for ordinary engineering and technical personnel. At present, the system has been used in CNC lathes, and has good economic benefits and practical application prospects. (end)

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