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Keywords: small-scale planer CNC transformation CNC system programming
The non-cylindrical surface with a small length can be processed by a CNC milling machine or by wire cutting (single piece production). However, when the non-cylindrical surface reaches a certain length, the above two methods are incapable or the processing cost is too high. Such as the series Roots vacuum pump and the rotor of the Roots blower (shown in Figure 1, the cross-sectional contour consists of multiple involutes, epicycloids and arcs, lengths above 300mm), the blades of the large water ring pump impeller model ( The cross-section contour consists of multiple straight lines and arcs with a length of 500mm or more. In order to adapt to the processing of cylindrical workpieces whose cross-section contours are complex curves, the author developed the IPC-based planer CNC system and carried out numerical control transformation on a small-sized planer of a vacuum pump manufacturer.
1 Mechanical transformation of small planer
The numerical modification of the small planer is to change the manual adjustment tool holder into a numerical control tool holder driven by a stepping motor. The Z stepping motor controls the movement of the tool holder in the vertical direction, and the X stepping motor controls the movement of the tool holder in the horizontal direction. . Install three proximity switches on the slide base near the slider, and fix a slider position marker block (iron block) on the slider that is parallel to the three proximity switches and that is close to the three switches during the movement. Both are used together for the detection of the direction and position of the slider. In addition, install a simple tool setting device on the slide table. After the load (friction force, moment of inertia, etc.) calculation, the stepping motor that drives the tool holder up and down (Z coordinate axis) and the left and right movement (X coordinate axis) are selected as 110BF003 and 130BF003 respectively. The pulse equivalent of these two coordinate movements is 0.01 mm.
2 planer CNC system hardware structure
The CNC system adopts PC bus and 486CPU industrial control machine with main frequency of 100MHZ as the host. It has a standard 16-bit data bus and flexible plug-in structure. It can optimize the structure according to system requirements. Planer CNC system hardware structure The CNC system uses the 8255A on the IO/TIMER (parallel I/O/Timer) interface board to control the motion of the two stepper motors, receiving the slide return and position sensor signals, and the tool post limit switch signal. , function selection switch signal, 8253 timer on the interface board is used for stepping motor interrupt service program, the clock frequency is 2MHz.
3 planer CNC system software
Planer CNC system software uses Windows operating system as the platform, adopts modular and structured C language programming. The interface of system software adopts Chinese menu structure, friendly man-machine interface and convenient operation. The specific structure is shown in Figure 4. The system software is mainly composed of three modules: programming, tool position adjustment and operation control, and multiple sub-modules are divided in each module.
3.1 programming module
A correct machining program must go through the following stages: programming, grammar checking, simulation and tool interference, and overcutting. In the CNC software system, the programming can be programmed in a variety of ways: graphical automatic programming, manual programming, and list curve programming. The data and processing program of the list curve file can be input through the keyboard through the floppy drive or through the full screen editor, or through the serial communication interface.
Graphic programming includes the following steps:
(1) The editing input of the contour curve first inputs the straight lines, arcs, and segments according to the direction of the curve through the interactive graphical operation interface.
After the curve is input, editing processing such as modification, enlargement, reduction, and symmetry can be performed.
(2) Find the offset curve for the curve edited above, and generate the equidistant curve, that is, the offset curve, according to the required tool nose radius.
(3) Automatic programming The offset curve is fitted with a straight line according to the specified accuracy requirements, and converted into a G code processing program.
(4) The simulation simulation runs the machining program in the simulation mode and dynamically displays the tool nose movement trajectory. If the machining program is correct, the simulated display will coincide with the previous offset curve.
The programming of the list curve is also performed under the graphical programming interface. First, the person list curve data file is read. According to the order of the points in the data file, the adjacent points are connected by a straight line and displayed. Then, based on this, spline fitting, smoothing and offset processing are performed, and then discrete lines are formed into small segments according to the accuracy requirement, and a machining program is automatically generated.
Interactive graphical programming and simulation runs make complex curve and list curve processing programs not only efficient, but also convenient, intuitive and reliable.
CNC system manager
Programming tool position adjustment operation control graphic programming
Manual programming list curve programming simulation run manually
Jog running automatic tool setting fast air run automatic operation
Jog run manually
3.2 Operation Control
The operation of the CNC system mainly includes the following modes: automatic operation, fast empty operation, manual operation and jog operation. [Page]
Automatic operation is the core part of the CNC system operation control, which runs according to the machining program. If the last instruction of the processing statement being executed is M32, the tool makes an intermittent feed motion according to the reciprocating motion signal of the slide table; if it is M33, it moves continuously, and the reciprocating motion signal of the slide table does not work for it, that is, Make a fast run. If the slide stops reciprocating during machining, the feed motion of the tool also stops. This function enables the worker to follow the operating habit of the planer and control the start and stop of the feed movement of the tool holder by controlling the start and stop of the reciprocating motion of the slide table.
The automatic running program consists of two parts: the foreground and the background. The background program completes the initialization of the parallel port 8255A and the timer 8253, decodes the instruction, controls the execution frequency of the interrupt service program (speed adjustment), pauses, single-segment and start control, and the processing track. The dynamic tracking display and the coordinate flip display; the foreground program is an interrupt service program, which mainly performs interpolation calculation, stepping motor operation control, lifting speed control, receiving the slide round trip and the position sensor signal. The intermittent feed motion of the tool is completed during the return stroke of the slide. The feed amount of the slide table to and from the tool can be set or modified by the function key. The minimum value is two pulse equivalents. Another function of the automatic running program is that when the "continuous" function key is pressed, the intermittent feed of the tool can be changed to continuous feed; when the function key is raised, the tool can resume intermittent feed. When roughing blanks, due to the uneven machining allowance, some places may be fed in the air. This function can quickly jump over here and greatly improve the machining efficiency.
Fast air run is also controlled by the machining program, but it is for continuous operation. It allows you to check the relative positional relationship between the tool and the workpiece blank to determine the tool height position for the initial machining. The fast air-running program is also composed of two parts, the front and the back. The structure of the fast-running program is similar to that of the automatic running program, except that the interrupt service program is not controlled by the round-trip motion of the sliding table.
When the selector switch is in the automatic running state, the jog function can only be used in the return stroke of the slide table, and the maximum displacement of the tool can be set continuously. This function facilitates tool position adjustment during machining. If the knife is too deep, the knife can be lifted without stopping the processing.
Depending on the selection, manual operation can also be controlled by the shuttle's reciprocating motion for intermittent motion. The manual function can be used for plane machining without programming. This method brings convenience to the plane processing.
4 Conclusion
The author used the self-developed planer CNC system to carry out numerical control transformation for a small gantry planer of a certain enterprise, successfully realized the processing of the series of water ring pump impeller blades and the mass production of series Roots vacuum pump rotors, which not only has high processing efficiency, but also The processing quality is stable and reliable. After continuous improvement and improvement in recent years, the CNC system has functions such as real-time machining control, automatic graphic programming, complex curve and list curve fitting, programming, tool wear compensation, automatic tool setting, simulation and machining track tracking display. . The planer CNC system is not only suitable for the numerical control transformation of small planer, but also for the numerical control transformation of other forms of planer.
Numerical control transformation of small planer
The numerical control transformation of the planer and its CNC system are introduced. The control system adopts an open PC bus structure on the hardware. The software adopts modular and structured design. The graphical interface is used on the operation interface. It has graphic programming, list curve programming, simulation running, automatic tool setting and tool wear compensation. Real-time machining control and dynamic tracking display.