Using an end mill to machine a workpiece on a CNC machine tool, it can be clearly seen that the tool center movement gauge does not coincide with the contour of the workpiece. This is because the workpiece contour is formed by the movement envelope of the end mill.
The center of the end mill is called the cutter location (4, 5 coordinate CNC machine tool is called cutter location vector), and the motion locus of the cutter location represents the trajectory of the cutter. In NC machining, programs are programmed according to the contour size of the workpiece or programmed according to the trajectory dimension of the tool location. This should be handled according to the specific situation.
In the full-function CNC machine tool, the CNC system has tool compensation function, which can be programmed according to the workpiece contour size. After the tool compensation is established and executed, the CNC system automatically calculates and the tool position is automatically adjusted to the tool movement path. By directly using the workpiece size to compile the machining program, the tool wears, and the replacement machining program does not change. Therefore, the use is simple and convenient.
Economical CNC machine tools are simple in structure, low in price, and have a certain amount of ownership in production enterprises. In the economical CNC machine tool system, if there is no tool compensation function, the machining program can only be programmed according to the trajectory size of the tool location. This requires that the trajectory size of the tool location should be calculated based on the workpiece contour size and tool diameter. Therefore, the calculation volume is large and complex, and the tool wear and replacement need to recalculate the trajectory size of the tool location and reprogram the machining program.
Tool compensation in full-function CNC machine tool system:
1. CNC lathe tool compensation CNC lathe tool compensation includes tool position compensation and tool arc radius compensation. In the machining program, it is specified by the T function. The first two XX in T***X are the tool number, and the last two XX are the tool compensation number, such as T0202. If the tool compensation number is 00, the tool offset is cancelled.
(1) Tool position compensation Tool wear or tool position change caused by reinstallation of the tool. After the tool position compensation is established and executed, the machining program does not need to be reprogrammed. The method is to measure the position of each tool and input it into the specified memory. After the program executes the tool compensation command, the actual position of the tool replaces the original position.
If there is no tool compensation, the tool moves from 0 to 1 point. The corresponding block is N60G00C45X93T0200. If the tool compensation is X=3 and Z=4, it will be stored in the corresponding compensation memory. After the tool compensation is executed, the tool will be from 0 point. Move to 2 instead of 1 and the corresponding block is N60G00X45Z93T0202.
(2) Tool arc radius compensation When programming a CNC lathe, the tool nose is regarded as a point (imaginary point P), but in fact, in order to improve the tool life and reduce the surface roughness of the workpiece, the vehicle The tip of the knife is ground to a radius with a small radius (blade tip AB arc), which will inevitably result in a shape error of the machined workpiece. On the other hand, the position of the tool nose arc, the shape of the turning tool will also have an impact on the workpiece machining, and these can be solved by tool arc radius compensation. The shape and position parameters of the turning tool are called the tool nose orientation and are represented by parameters 0 to 9. P point is the theoretical tool tip point.
(3) Tool compensation parameters Each tool compensation number corresponds to four parameters of tool position compensation (X and Z values) and tool arc radius compensation (R and T values), and is input to the corresponding memory before machining and displayed on the CRT. . In the automatic execution process, the numerical control system automatically corrects the position error of the tool according to the values of X, Z, R, and T in the memory and automatically performs the tool nose arc radius compensation.
2. CNC system of machining center, CNC milling cutter compensation machining center, and CNC milling machine. Tool compensation functions include tool radius compensation, included angle compensation, and length compensation tool compensation functions.
(1) Tool radius compensation (G41, G42, G40) The tool radius value is stored in the memory HXX in advance, and XX is the memory number. After executing tool radius compensation, the CNC system automatically calculates and automatically compensates the tool according to the calculation result. The tool radius left compensation (G41) means that the tool is offset to the left of the programmed machining path movement direction, and the tool radius right compensation (G42) means the tool deviation is programmed to the right of the machining path movement direction. Cancel tool radius compensation with G40, cancel tool radius compensation can also be used H00.
It should be noted during use: when creating or canceling tool compensation, the G01 or G42 command must be used for the G41 or G42 command block. G02 or G03 must not be used. When the tool radius compensation takes a negative value, the functions of G41 and G42 are used. exchange.
Tool radius compensation has two compensation modes: B function and C function. Since the B function tool radius compensation only performs tool compensation calculation according to the program of this paragraph, it can not solve the transition problem between the program segments. It is required to process the contour of the workpiece into a fillet transition. Therefore, the craft corner of the workpiece is not good, and the C function tool radius is The compensation can automatically handle the transfer of the tool center trajectory of the two blocks. It can be programmed exactly according to the contour of the workpiece. Therefore, almost all modern CNC machine tools use C function tool radius compensation. At this time, the following two program segments that require the establishment of a tool radius compensation block must have displacement instructions (G00, G01, G02, G03, etc.) for the specified compensation plane, otherwise the correct tool compensation cannot be established.
(2) Inclusion angle compensation (G39) The intersection between the two planes is the included angle. Over-cutting may occur, resulting in machining error. The angle compensation (G39) can be used to solve this problem. When using the angle compensation (G39) instruction, it should be noted that this instruction is not modal and is valid only within the instruction block. It can only be used after the G41 and G42 instructions.
(3) Tool length offset (G43, G44, G49) The tool length offset (G43, G44) command can compensate the change in the tool length at any time without changing the program, and the compensation amount is stored in the memory of the H code command. G43 indicates that the amount of compensation in the memory is added to the coordinates of the end point of the program instruction. G44 indicates the subtraction. To cancel the tool length offset, G49 or H00 can be used. In segment N80G43Z56H05 and in, if the value in the 05 memory is 16, then the end point coordinate value is 72mm.
The value of the amount of compensation in the memory can be pre-stored in the memory with MDI or DPL. The block instruction G10P05R16.0 can also be used to indicate that the compensation amount in memory No. 05 is 16 mm.
Calculation of tool trajectory in economical CNC machine tools:
The economical CNC machine tool system, if there is no tool compensation command, can only calculate the trajectory size of the tool location, and then press this to program or perform local compensation processing.
