Beijing Auto and Motorcycle Joint Manufacturing Company Equipment Factory (100022) Yang Zongzheng CAD/GAM technology is increasingly being promoted and applied. CAD can be more fully effective through CAM. Units with tight funds can develop CAM-specific software on their own, and the algorithm language to be used should be selected according to the requirements of convenience, reliability, accuracy, practicality, low cost, and less critical of hardware and operating system. I chose the BASIC language according to the situation of this unit. In this paper, the programming of CNC milling car body blanking edge is taken as an example. The method and self-made software are also suitable for the programming of CNC milling through the sparse point smooth curve profile (non-punching edge) in the plane.

In order to manufacture the blanking die in the complete set of molds for automotive body stamping parts, the mold designer often specifies some sparse points in the plane, and the punching cutting edge curve must pass through these points, without giving the cutting edge curve by which line segment. It consists of a non-circular curve composed of arcs or by what kind of equation.

In order to facilitate the manufacture of the blanking edge (cylinder) and to ensure its quality and precision, it is often necessary to use CNC milling. The general CNC milling machine has only line segment and circular interpolation functions, and there is no non-circular curve interpolation function. In other words, the segments of the cutting edge curve should not be line segments or arcs, and should not be other.

If the cutting edge curve is not smooth and there is a sharp corner somewhere, when milling one of the convex and concave molds, the "旮旯" that cannot be milled is inevitably left.

This will add trouble to the manufacturing molds. It is also not conducive to ensuring uniform punching clearance between the convex and concave molds, and affecting the mold quality. Therefore, a smooth cutting edge curve should be used. The radius of curvature of the curve should be larger than the radius of the milling cutter. The curvature change is preferably continuous and relatively uniform. Once the blanking die cutting edge (two-dimensional curve) is solved, the CNC milling edge cutting die cutting edge (three-dimensional curve) is not difficult to solve by flexible operation of the milling cutter axial movement.

This paper gives a method for finding the two-dimensional edge curve, and edited the corresponding software.

Let the position of 4 or more sparse points, such as 8 sparse points, have been given for increasing the X coordinate value in the given XY plane. Now try to find a smooth curve with continuous curvature changes of these 8 points. It can be known from the curvature formula that as long as the second derivative is a continuous function, the curvature is a continuous function. For each of the eight points, the function of the curve between the two points is a third-order polynomial. Thus, there are a total of 28 coefficients and constants, which are to be determined.

The curve between points 2 and 3 should pass through points 2 and 3. The curve between points 7 and 8 should pass points 7 and 8. Thus, 14 equations can be listed at the 2nd point, the left and right first-order derivative values ​​should be equal; the left and right second-order derivative values ​​should also be equal.

This is also true at points 3, 4, 5, 6, and 7. Thus, 12 equations can be listed. A boundary condition can be specified at the first point, for example, the boundary condition is that the second derivative value is zero. The same is true at the 8th point. In this way, two equations can be listed.

Combine the above 28 equations. I used the Gaussian principal to eliminate the software, and the computer automatically solved the 28 pending values. Then we get the 7-segment curve described by the 3rd degree polynomial respectively.

These seven segments together make up the entire curve required, which passes through the eight points and is smooth and the curvature is continuously variable.

With my software, you can easily calculate the coordinates of enough points on this curve. Then use another software I compiled to calculate the coordinate data of a series of positions that the center of the milling cutter should pass through when calculating the contour of the curve.

These have been verified in the CNC milling machine of our factory, which is correct and has been used in production.

Medium, then change the suffix name of the file to . LSP, if the application is automatically loaded after each CAD window is opened, add the following statement to ACADR14.LSP: (autoload command name can be. ()