This paper expounds the problems in the development of nibbling CAPP system, the reasonable selection of standard punches, the scientific matching of punches, the need for punches to meet process requirements and the optimization of blanking paths, and points out that the solution to these problems is to first simulate the stampings. Cut. Through blanking simulation, the CNC stamping process scheme and numerical control code will be optimized, which can effectively ensure the efficiency of blanking processing, make the blanking processing technology more scientific, standardized and optimized, and make a useful exploration in the simulation and processing.

Foreword

When traditional CNC nibbling press processing, its technological decision-making, such as whether the choice of punch is reasonable and whether the blanking result satisfies the production requirements, generally depends on the operator's experience to grasp, and the production effect is only checked through actual processing. This method has high requirements on the technical level of the first-line operators, and it takes a long time and has a high risk. Therefore, it is necessary to perform the pre-processing simulation of the blanking process through the nibble CAPP system before actual processing.

The blanking simulation of the Crush CAPP system mainly achieves the following goals: 1) Finding the best blanking program through simulation. One of the main basis for testing whether the brewing scheme is reasonable is the principle of maximizing the efficiency of blanking, that is, choosing a reasonable combination of punch types to complete the blanking process in the shortest time with the optimal path; 2) On the basis of simulation, The display, recording, management and transmission of blanking processing information are realized, and raw data information is provided for the automatic generation of the subsequent NC code processing of the system. This is also the key to realizing the integration of the CAPP/NC.

1 Blanking Simulation Constraints and Principles
The precondition for realizing the blanking simulation is to establish a scientific blanking simulation mathematical model and give reasonable boundary constraints for blanking. The constraints of blanking simulation can be divided into geometric boundary constraints and process constraints as a whole. Because the thickness of stamping parts can be ignored with respect to the length and width, the model can be regarded as two-dimensional, and the geometric boundary constraints are mainly rushed. Cutting geometry, punch shape, punch size, etc. The geometric model of the contour section of the round punch line is shown in Fig. 1.

Fig.1 Circular punch contour contour model

The process constraints of blanking simulation are mainly the blanking section cross-section mass, the punch movement step, the direction of movement (such as the punching of the inner contour of the punching system in this system clockwise, the outer contour of the punching counterclockwise), the punch movement boundary constraints, Jump constraints between different contour segments, etc.

To ensure the authenticity of the simulation, it is necessary to establish a scientific geometric model of blanking parts in the system environment. The blanking model is based on the size of the system graphics window. The actual size of the part is reduced or enlarged according to a certain proportion and displayed in the graphics window. The CAD information about the blanking part is passed to the CAPP system. There is discussion. In order to ensure the authenticity of the simulation, the proportions of coordinate origin transformation and graphic display should be processed. On the one hand, it is necessary to ensure that the outline elements of the blanking parts are displayed, and on the other hand, the ratio of the X and Y axes is not distorted. . Let the punching part have N contour segments, and make the boundary points of the contour, ie, the coordinates of the lower left corner and the upper right corner are (Xmin, Ymin), (Xmax, Ymax), then there are

Xi and Yi are respectively the endpoint abscissa and ordinate of the outline segment of the blank.

When the contour segment is an arc segment, since the starting point and the ending point of the arc are taken, the radius of curvature R of the arc is taken into consideration, and then Xi= Xi±R and Yi=Yi±R are taken before the extremum is taken. In order to ensure that the scaling ratio of the abscissa of the graph is consistent with the scaling of the ordinate, the following corrections can be made on the limit coordinates:

2 The realization of nibbling simulation
The system simulates square punches, round punches, and triangular punches with solid squares, solid rounds, and solid triangles, respectively, in punching simulations. After the punch type and size are selected, the selected punch size is used. According to the graphic display scale of the blanking profile, the drive command draws squares, triangles, or circles corresponding to the length of the side to simulate punches. For example, the command for drawing square punches is as follows:

Graphic window: Line Xi, Yi-Xi+1, Yi+1, vbBlack, BF

Among them, Xi, Yi, Xi+1, and Yi+1 indicate the dynamic coordinates of the upper left corner and the lower right corner of the punch movement respectively, and BF indicates that the graphics rendering effect is black solid.

The punch simulation also needs to address the control of the position and trajectory of the punch motion. The movement of the punch is performed along the contour of the blank, so the trajectory of the movement depends on the shape of the contour. Take the circular punch contour cutting segment as an example. The starting and ending angles of the arc segment in Figure 2 are α and β, respectively. The overall constraints of the punch movement are as follows:

Punch Center Circle: Arc with radius (Rr)
Starting and ending position of punch movement: starting angle ( pp - α), ending angle β

Punch motion step: Step S has the blanking cross-section quality, punch type size, punching contour segment size and other decisions (blank punching specific algorithm has been described in other articles, not repeat them here).

Punch motion speed: In order to improve the authenticity of punching simulation, it is also necessary to control the punch motion, that is, to add a reasonable time interval between drawing two motion punches, and manually adjust the interval according to the situation. . The following is the punch movement interval program. The variable "ms" represents the interval time and the unit is ms.

In accordance with the above boundary conditions, a solid circle is gradually drawn to complete the blanking simulation of the arc contour. The core of punching simulation is to dynamically draw the solid figure of the punch according to the boundary conditions of the blanking section contour, the punching process judgment conditions and the punch contour according to the set punch moving speed. Among them, the boundary profile of the blanking part, punch shape and size control the movement path of the punch. The blanking step controls the punch to dynamically draw the forward distance for each movement of the punch, and combines the two to control the punch in the contour section. There are no overshoots and undershoots.

Figure 2 Circular punch punching arc segment contour model

In the punching process, the wear of the punch will cause its size to change with time. In the case of the unchanged cross-section quality of the blank, the wear of the punch will directly affect the change of the blanking step. Affect the authenticity of the simulation. There are two methods for dynamic adjustment in simulation punching. One is to establish the mathematical model of punch size wear. The system automatically adjusts the size of the punch according to the length of the punch processing; the second is the man-machine interaction adjustment, that is, according to a period of time. In the case of changes in the size of the inner punch, the blanking step parameters were manually adjusted and the former was adopted in this system.

The flow chart of system simulation punching is shown in Figure 3.

Fig. 3 Nibble simulation flow chart

3 Contour-section simulation of the first and last decision in blanking

In the simulation punching, the factors constraining the trajectory of the punches mainly include blanking profile, blanking cross-section quality, standard punch type, punch size, blanking type (punching, blanking, etc.).

After the blanking step is determined, the simulation movement of the punch in the middle part of the contour section of the blanking part is performed along the contour section. Generally, no problem occurs, and the emphasis is on controlling the start and end of the contour section of the blanking part. In order to ensure that the punch does not overshoot (the punch is out of the contour range, the part that should be retained is punched out) and the undershoot phenomenon (the punch motion is not in place, so that the stamped part is retained). The exact decision of the starting position is also the guarantee for correct jump of the punch between different contour segments.

There are two methods for punching the contour segment of the blanking part. The first is that the system dynamically monitors the center coordinate of the punch and the end coordinate distance of the contour segment of the blank to control the punching step distance and die at the end of the die. The correct jump; the second is to calculate the maximum number of blanking strokes (arc contours in arc) according to the punch step size and contour size, and perform special processing in the final blanking station. Intermediate data of this method Small in size and high in efficiency. The disadvantage is that there are certain errors in the calculation of blanking step length, blanking contour length, etc. When these errors are accumulated to a certain value, misjudgment may occur. However, due to the fact that operators have the opportunity to make timely adjustments according to the blanking simulation before actual production, the reliability of this method is greatly improved. The system uses the latter to decide.

When the system determines the punching inner contour during development, the punch moves in the clockwise direction, that is, the punch always moves along the right side of the contour section; when punching the outer contour (blank), it runs counterclockwise, The punch always moves along the left side of the contour line. For the closed contour of the same shape, the starting point and the end point of the contour section of the punching inner contour are exactly the end point and the starting point of the punching outer contour. When the last judgment of the punching contour section is judged, the judging and constraining points of the inner and outer contours are just opposite. .

4 Nibble Simulation of NC Code Generation

The generation of NC code, in addition to solving the problem of data transfer interface between the CNC system, must also provide necessary original information, including die type, die size, die movement trajectory and other process information. A custom structure and a dynamic array are defined in the transmission of punch data information.

Taking a circular punch as an example to simulate punching arcs, as shown in Fig. 2, the dynamic X and Y coordinate information of the punch center is extracted as

Among them, R, r are the radius dimension of contour segment and punch respectively, m is the number of punch motions in simulation punching, draws(i) is defined as the following graphic information data custom structure data type:

Public draws() As pic_datas Defines the array draws() as the data type of the graphic information

According to the above definition, the NC code generation module of the system continuously records the simulation data information of the dynamic trajectory generated by the punch during the movement through a custom structure:

ILength = UBound(Position)
ReDim Preserve Position(ILength + 1_
Position(ILength) = punc

Through the above-mentioned procedure, the main analog data information is passed to the numerical control code generation module to prepare the original data for automatic generation of the numerical control code to be performed below.

Figure 4 Simulation NC code automatically generated interface

The punch control system obtains punch information and machining trajectory. After the post-processing system converts the machining file into a numerical control system, the accepted NC command program is sent to the NC program library. The DNC system transfers the NC program to the punch press and controls the punch. Punching processing. The system automatically generates the NC code interface as shown in Figure 4. The system is mainly based on the following variables when processing:

1) MAX_LENGTH denotes the maximum distance between two holes for continuous punching. If this distance is exceeded, the punching shall be suspended and the punching shall be performed after the positioning is correct.
2) MIN_LENGTH denotes the minimum distance between two holes for continuous punching. If the distance is less than this distance, the punching must be suspended;
3) NCC STEP one indicates the maximum distance between two stations for continuous punching.

5 Concluding remarks
In the CNC nibbling process decision-making, whether the punch type and size selection is reasonable, whether the punch collocation is scientific, and whether the punch trajectory is optimized will directly affect the punching efficiency. The nibbling simulation system implements dynamic simulation of the blanking process before actual processing, and provides the necessary raw data for the production of CNC machining. It has made some beneficial attempts in the nibbling of the blanks.

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