Based on the study of the method of CNC grinding of spiral teeth cutters, the method of obtaining geometric parameters of helical cutting edge is proposed. The design and development of the software and hardware of the economical CNC tool grinding machine control system for the sharpening of helical teeth cutters are presented. Technology was introduced.
1 Introduction
Helical tools are helical cutting tools with cutting edges, such as cylindrical milling cutters, end mills, and spiral groove reamers. The sharpening of this kind of tool is generally done by the process operator manually on the tool grinding machine with the help of accessories. According to the spark, it is judged whether the grinding wheel is in contact with the tool tooth or not, and the amount of the back knife is grasped by hand, and one tool must be sharpened once. Therefore, the operator's requirement is high, and it is difficult to ensure the sharpening quality, and the sharpening efficiency is also not high. The author studied the CNC grinding method of spiral teeth cutters, and designed a small-scale economical CNC tool grinder based on this, which can solve the problem of CNC sharpening of spiral teeth cutters with unknown parameters.
2 CNC Tool Grinding Machine Drive System
In the transmission diagram of the mechanical part of the CNC tool grinding machine, the Y and Z axes are the horizontal and vertical movements of the table; the X axis is the movement of the grinding head; the C axis is the rotation of the tool (workpiece). Through the manual adjustment of the rotation of the grinding head around the X axis; the grinding wheel and the tool up and down; the tool gearbox rotates in the horizontal plane.
3 control system hardware structure
The hardware structure of the control system uses a microcontroller 8031 ​​as the CPU, through which the lower 7 bits of the P2 port and the 32 KB EPROM 27256 outside the P0 port store the system program. The lower 3 bits of the P2 port and the 2 KB RAM 6116 outside the P0 port store data, and the upper 5 bits of the P2 port are used for the address. Decode to strobe the LED display circuit, interface chip (8155, 8255), data memory (6116) and latch (273), P1 port is connected to stepper motor manual control circuit, stepper motor drive pulse signal from P0 The port output is sent to the stepper motor driver via the latch (273); the 8155's PA port is connected to the system program's start, pause button, and operating modes (parameter input method, measurement method, tool setting method, and automatic method). The port is used to measure helical screw tooth measurement signals and other auxiliary function signals. The PC port is used to output auxiliary function signals. The 8155's PA port and PC port are connected to the keyboard's row and column lines, respectively. The PB port's grinding and cutting tool type selector switch .
4 helical tooth geometry measurement
In CNC grinding, the relationship between the axial feed and the circumferential feed of the tool needs to be determined. Due to the production, the helix angle β and the lead of the helical tooth tool are generally unknown, so before grinding, it is necessary to test The relevant parameters of the spiral teeth. For this purpose, the helical teeth are spread out in a straight line. Set the length of axial feed (including grinding length l1, cutting edge length l2 and grinding length ll) to l, then it corresponds to the circumferential feed arc length (including grinding arc length s1, cutting edge arc length s2 and grinding arc length S3) is s0, in order to determine the arc length s, the geometric parameters of a helix can be measured first, and then the arc length can be obtained based on similar triangles.
For this purpose, before the sharpening, a measuring head is mounted on the grinding head. The measuring circuit of the measuring head and the tool together form a closed circuit. During measurement, in the measurement mode, using the manual function, the measuring head is first brought into contact with the tool teeth, and then the tool is moved or rotated in a straight line, and the measuring head is moved relative to the tool in a trajectory of 1 or 2, and the control system automatically records the result. The tool linearly moves the number of steps Z1 and the number of rotation steps C1, and converts the feed length input from the operation panel into the step number of the stepping motor Ze according to the pulse equivalent of the Z axis, using the measured geometrical relationship between Z1 and C1, The number of C-axis rotation steps Ce is calculated, and (Ze, Ce) is the end point coordinate of the straight line, and the two-axis linkage linear interpolation is performed by the linear movement of the tool and the rotation operation.
In order to prevent the measurement overtravel error in the C direction (due to the lack of a pulse equivalent between the cutter tooth and the measuring head, the error is less than one pulse equivalent), the accuracy of the spiral lead is affected. On the one hand, the step size should be reduced as much as possible. The arc length equivalent δ of the motor per step. Use a stepper motor with a small step angle, and use a small transmission ratio to reduce the δ value when sharpening a larger diameter tool.
On the other hand, increasing the Z-direction measurement length can also reduce the influence of the C-direction overtravel error on the lead accuracy of the helix.
5 Control System Software
The software adopts a modular structure, and the execution of the module depends on the mode switching state on the operation panel. After the system main program completes the initialization of the I/O ports and resets the data storage units, it enters one of them according to the status of the mode switch. Its main operating modes are as follows:
(1) Parameter input method. According to the system prompt, input the parameters such as the number of teeth, the rotation of the teeth, the feed length, the grinding allowance, the number of feeds, the feed rate, and the lower limit of the Z axis and C1min of the Z axis and C axis. .
(2) Measurement method. The measuring program flow utilizes the manual functions of the Z-axis and the C-axis so that the tooth contacts the measuring head and determines the starting point for the measurement. During the measurement, the system determines the axial and circumferential feed direction of the tool according to the rotation of the tool teeth. When the measured value reaches or exceeds the preset Z1min and C1min, press the C key to turn the cutter tooth to the measuring head. Once the two are in contact, the Z-direction and C-direction key presses are invalid, to avoid artificial overtravel errors and damage measurements. The device then completes the calculation and returns to the main program.
(3) Tool setting method. To sharpen the front and back flank, first turn the grinding wheel dial so that the spark at the contact point is consistent with the tangential direction of the point. In the manual mode, the tool setting point is adjusted. At this time, the system automatically records the tool movement from the start point to the tool point. Step number Z2, then set the mode switch to tool setting mode. After the tool setting program is started, the system firstly takes out the internally recorded parameters Z1, C1, and Z2. According to the calculation of the tool's return starting point, the number of tool rotation steps C2, and finally (Z2, C2) as the starting point, performs linear interpolation, and the tool is returned. To the sharpening starting point (0,0).
(4) Automatic mode. In the flowchart of the automatic sharpening program, i is the number of feeds for sharpening each tooth; n is the number of teeth.
In the cycle, the cutter teeth are used for internal circulation, and the number of feeds is external, that is, each feed is performed once, and all the cutters are sharpened again, so that the cutter teeth are heated and deformed uniformly, and the grinding margin is the same, which can guarantee the sharpening of the cutter. The teeth are on the same circumference. When the number of division steps m is decimal, rounding is performed and the decimal number is added to the next indexing step.
6 Conclusion
(1) The use of a numerically controlled circular edge grinder can reduce the influence of the grinding temperature on the sharpening accuracy. The sharpening accuracy is higher than that of manual sharpening, and the quality is stable.
(2) All the teeth of a knife can be sharpened after the measurement, and the sharpening efficiency and automation are high.
(3) Batch sharpening, no need to repeat measurement, just select the same clamping reference, the operation is simple and convenient.
(4) Applies only to sharpening of the equally divided spiral tooth cutter.