As long as any CNC machining can be fully expressed by macro programs, even if it is complicated, the program length is very limited. It can be said that any reasonable and optimized macro program will rarely exceed 60 lines and be converted into bytes. 2KB. On the one hand, the macro program is inherently short and fine, even the cheapest machine tool CNC system, its internal program storage space will be a little smaller than 10KB (the FANUC 0i system standard configuration is generally 128KB or 256KB, other common CNC systems are also This is roughly the same), completely accommodates any "huge" macro program, so there is no need to consider the impact of the transfer speed of the machine and the external computer on the actual processing speed (in fact, there is no CNC system or DNC software support to run in DNC mode) Macro program for online processing).
On the other hand, in order to describe the complicated machining motion, the macro program will inevitably use the various command codes inside the CNC system to the maximum extent, such as the linear interpolation G01 command, the arc (spiral) interpolation G02/G03 command, etc. Therefore, when the machine tool executes the macro program, the computer of the numerical control system can directly perform the interpolation operation, the calculation speed is extremely fast, the servo motor response is fast, the machine tool reacts quickly, and the processing efficiency is extremely high.
For programs generated by CAD/CAM software, the situation is much more complicated! In the following, the author will combine the experience and experience of using CAD/CAM software for many years, and carry out a more in-depth and detailed explanation.
First of all, the programs generated by CAD/CAM software are usually quite large, and it is very easy to break through the limitations of the internal program storage space of the machine numerical control system (in layman's terms, the system can't fit the program), so in general, except for the relatively simple hole system. In addition to machining, 2D contouring or pocket processing, most of the other programs have to be processed online in DNC mode. Obviously, the transmission speed between the machine and the computer becomes the first "bottleneck" factor affecting the processing speed. In addition to the built-in hard drives of machine tools, or the new CNC machine tools (mainly high-speed machine tools) that are networked in the form of FDDI or Ethernet between the machine and the computer, CNC milling is currently used for CNC programming using CAD/CAM software. Most of the machining centers use the serial communication of the RS232 port to realize the online processing of DNC.
Most mainstream mid-range CNC systems, such as FANUC 0M, 0i, Mitsubishi M52, M64, Siemens 8021), 810D, etc., the maximum transmission speed of the RS232 port supported by the system (that is, the Baud rate) is basically 19,200. Most DNC ​​software (such as V24, PCIN, AIC, etc.) support the maximum baud rate is not too red 19200 ~ 38400, even if working at the baud rate of 19200, when the calculation accuracy is higher, the feed rate, the value Larger (such as F1800 ~ F2500), the program transmission speed is often; can not keep up with the machine's beat, in the actual processing can see the machine feed; the movement has obvious intermittent, hysteresis, for the FANUC system, even open DNC buffering, or setting C51.1 parameters, is also difficult to make a big difference.
Experience has proved that due to the limited anti-interference ability of RS232 port communication, the transmission effect actually involves whether the transmission line is well shielded, whether the length is moderate, whether the grounding of the machine tool and the computer is good, etc. The higher the baud rate, the more unstable the transmission. In practice, it is often forced to limit it to 9600 or even lower, so that the processing efficiency of DNC online mode is more favorable.
Secondly, from the user's level of use, it is very easy to use CAD/CAM software to generate the tool path and program. However, if the CAD/CAM software calculates the principle of the tool path, it knows that it has certain drawbacks. In CAD/CAM soft, whether it is a construction rule or an irregular surface, there is a mathematical operation process, and there must be calculation errors and processing. When generating a 3D machining tool, the software is based on you. The selected machining mode, the set machining parameters, and the set machining error (or the calculation accuracy of the surface) are combined to make the tool and the machining surface contact point (intersection point or tangency point) move point by point. In essence, it is actually the process of approximating the surface along a straight line in each of the allowed error values.
Performance comparison between CNC milling macro program and CAD/CAM software generation program (2)
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