In the course of CNC lathe training, students have not yet mastered the performance of CNC machine tools. Therefore, they often skip the tool during processing and operation, causing tool damage, workpiece scraps, and machine tool chucks. And electric tool holder, seriously affect the accuracy of the machine tool and even hurt the operator.
With the development of science and technology, especially the widespread application of a series of numerical control simulation software such as Yulong, students can use the simulation software to program the numerical control machine tools, use the operation panel, set the tool, correct and correct the software before the actual operation. Machining and other simulation exercises.
Through virtual simulation, you can effectively check the programming and tool setting errors, and also check out possible collisions and dangers. It is extremely important to improve the student's CNC machine operation technology and maintain the safety of machine tools and equipment. But has it passed the simulation check program, can you safely execute the automatic machining program directly on the CNC machine tool? The answer is "No".
Through virtual simulation, it is mainly to observe the correctness of the overall machining contour and trajectory of the machine tool, and some specific details of processing, such as whether the cutting amount is reasonable, the tool setting and parameter input are correct, can only be experienced in actual machining. Therefore, the processing on the machine tool must still be prevented beforehand, and the hidden dangers such as “collisions” must be carefully and timely discovered and modified to remove them through the first piece processing. This article starts with the implementation of automatic processing, and talks about the methods and measures of collision prevention in specific operations.
"Three, two, one stop" CNC machine tool machining can be simply summarized into three major tasks: programming, tool setting and automatic machining. Whether the programming is correct, whether the selected cutting amount is reasonable, whether the tool setting and parameter input are accurate, will be reflected in the automatic processing. In order to prevent safety accidents, the key to implementing automatic processing is the first one, which is customarily called "first trial cutting processing", and discovers and corrects hidden error factors.
Therefore, it is necessary to "three see two and one stop" when performing automatic processing to prevent collisions and other safety accidents and ensure processing quality. "Three Looks" includes the following:
Take a look at the program. First see if the program name is correct. There are many programs stored in the system. Check the program names executed by the machine carefully. If the program name is incorrect, the program name to be executed should be recalled in the automatic mode, and the name of the program currently being executed by the current system should be displayed in a specific area on the screen. Then look at the program segment. The current machining program segment is displayed on the screen. You can determine whether the statement is correct and consistent with the current processing technology by looking at the program segment. You can learn whether the processing purpose of the current segment is in line with the execution of the machine by watching the current program segment. The processing purpose of this paragraph is consistent. If it is found that the tool position is wrong or the tool moving direction is inconsistent with the purpose of the block, the execution should be stopped immediately, then reset, manually retract the tool away from the workpiece, and then find the cause of the error.
Second look at the workpiece coordinates. The display will show the current machine tool coordinate system coordinates, workpiece coordinate system coordinates, and other values. During the execution of automatic machining, focus on the displayed workpiece coordinate values and remaining values. The workpiece coordinate value is the position of the tool tip relative to the workpiece, and the remaining value is the remaining distance from the tool tip to the block target point.
Third look at the position of the blade. The contour machined by a CNC machine tool is the trajectory required by the tool tip. Looking at the position of the tool tip is the position of the tool tip relative to the workpiece.
The "three views" in the process of processing are uniform. Especially the displayed workpiece coordinates and tool tip positions should be observed at the same time to see if the tool tip position is consistent with the actual workpiece coordinates, the distance between the tool tip and the workpiece and the remaining value displayed. If it matches, it will not collide with the workpiece or chuck.
If the position of the tool tip does not match the displayed value, stop executing the program immediately, then reset, stop and exit the tool, and check and analyze the cause of the error.
"Two musts" and one must be executed in a single stage. CNC machine tools have a single-segment "SBL" execution function. During the execution of automatic machining, the machining action is suspended after each execution of a block. To continue executing the program, press the cycle start key again to continue to the next block. Through single-segment execution, the operator is provided with sufficient time to look at the program, coordinates, and the tip of the knife to prevent collisions caused by program errors. Especially when changing tools, pay attention to whether the turning tool is retracted to the tool changing point and whether it will collide with the workpiece or chuck.
Second, low magnification. The control panel of the CNC machine tool has a feed speed adjustment knob or keys. Low magnification is mainly to reduce the feed rate of the tool during processing. The G00 feed rate is particularly emphasized here. Taking the Fanac system as an example, in the first piece processing, the tool tip is far away from the workpiece, and the fast override can be set to "100%". When the tool gradually approaches the workpiece, the rapid override should be on the "25%" or "F0" key. Decrease the tool feed speed, it is convenient for the operator to observe and compare whether the position of the tool tip is consistent with the displayed coordinates or the remaining value to prevent collision.
When G01 feeds, first turn the override knob to zero, and then slowly release it to increase the speed. At the same time, observe the condition of the tool, chip and workpiece surface, and adjust the override at any time. Especially for inner hole processing, it is necessary to prevent the wrong direction of entering or retracting the tool, or the phenomenon of cutting or collision. "One stop" accurately says that there should be multiple pauses in the automatic processing process. By pausing, the operator can have enough mental preparation to observe and compare the position of the tool tip and the display of the screen coordinates, especially when the chips are wound on the workpiece or the tool, they can press the cycle stop key to prevent errors during operation due to confusion. "Three points and one line" "Three points and one line" is the key content to determine the processing route in programming. "Three points" are the starting point, contour start point and contour end point. "One line" is the contour line to be processed (as shown). With reference to the Fanac system, for example, machining of outer contours, the starting point is the starting point of the cutting process of the tool. When programming, G00 quickly reaches this point and starts G01 machining. Many students use G71, G72, G73, G92 and other cycle instructions to set the starting point unreasonably. As a result, the tool and the workpiece are damaged during the retraction process, causing danger. Therefore, the setting of the starting point must be correct, the starting point must be outside the range of the workpiece blank, the X coordinate is greater than the blank 2mm, and the Z coordinate is 2 to 3mm beyond the end face of the blank. If the blank size error is relatively large, this point should be farther from the blank range to prevent collision of the tool with the workpiece when the tool G00 is fast-forwarded. The contour starting point corresponds to the P parameter in the G71 and G73 machining cycles. In this block, only the X coordinate is written, and the system defaults to the Z coordinate. In the execution of the machining, the tool should be vertically lowered outside the contour, otherwise a program error alarm will occur during system execution. The contour end corresponds to the Q parameter in the machining cycle. The X coordinate of this point must be greater than or equal to the diameter of the blank, but it must be smaller than the X coordinate of the starting point of the machining, otherwise a cutter or even a collision accident will occur when G71 is retracted. The Z coordinate of the end point should be the leftmost end of the outline. The relationship between the start and end points of the contour and the starting point. The start and end points of the contour go left and right, and X goes up and down. The starting point is outside the range of the blank. The X direction is higher than the contour end point and the contour start point is flush with the Z direction. No matter what kind of CNC system or different cutting cycle, the position of these three points must be paid attention to, and analyzed carefully to prevent problems during processing. The "first line" is the line from the start point to the end point. The G01, G02, and G03 instructions are mainly used to prepare corresponding processing programs according to each individual geometric element (that is, straight lines, diagonal lines, arcs, etc.) to form a processing program. Each program is a program block. In the preparation of the processing program, the minimum number of program segments should be used to process the part. This can make the program concise, reduce the probability of error, and improve the efficiency of programming. As CNC lathe devices generally have the functions of linear and circular interpolation operations, in addition to non-circular curves, the number of blocks can be obtained from each program determined by the geometric elements that constitute the part, that is, the process route. At this time, the least used program should be considered. The principle of paragraph preparation. Select the correct G command. The shape of the contour line must be unidirectionally increasing or decreasing (inner hole machining). In the X direction, the G71 machining cycle is generally used. Therefore, the shape of the contour line should be stepwise unidirectionally increasing. It can be observed through simulation that the G71 cycle does not recognize the cavity, no matter how deep the concave shape is, the last tool is turned out. If a sharp knife is used, the depth of some small undercut grooves is less than 2mm, which can be machined directly. Otherwise, the cavity must be isolated, programmed separately, and the tool selected and processed separately. If the contour of the workpiece has a straight step, note that in the G71 cycle, there is generally no finishing allowance in the Z direction to prevent the tool from cutting or boring during the G70 cycle. If the dimensional accuracy of the step is high, a margin of 0.2 ～ 0.3mm can be reserved in the contour programming, and the step surface processing can be performed separately to ensure the dimensional accuracy and surface accuracy of the workpiece. After inputting the "one complement and three adjustments" program, "tell" the machine tool parameters and the workpiece coordinate system through tool setting. During the tool setting process, it is necessary to prevent the following factors from causing collision or waste during processing: one is the tool installation height, that is, the tool is installed too high or too low, and the tool tip is not aligned with the workpiece rotation center; the second is the trial cutting measurement error, especially It is the measurement of the inner hole diameter; the third is the error in the parameter input process, for example, the T1 tool parameters are incorrectly input to the T2 tool parameter position; the fourth is the unreasonable selection of the cutting amount and the poor surface roughness of the workpiece; the fifth is the input size Method: Generally, when programming most dimensional deviations in a unified manner, directly input the basic dimensions, instead of uniform dimensions, and enter the intermediate value of the dimensional deviations. Sixth, there is a problem with the machine tool (rail). "One complement" means that after the tool is aligned, the X offset value in the tool parameters is compensated by 0.5 to 1 mm or more (outside contour machining as an example). Generally, the Z direction offset does not allow the size. The Fanac CNC system can directly use the "+ Input" soft key under the display screen to compensate 0.5 ~ 1mm. Siemens 802C can also use G158 zero offset command to compensate for the size, and then execute automatic processing. After the processing of the first part of "Three Tuning", accurately measure the dimensions of each step, head and head error, etc., and calculate the difference or allowance as the basis for tool offset compensation, and then "one tuning" the tool parameters, and give up Compensate the value again. The size of the "two-tune" program coordinate value for the size head error and the tool compensation parameter cannot be solved to ensure the processing size. The "three-adjust" cutting amount (spindle speed, feed speed, cutting depth) is adjusted according to the override during processing. Then perform one or two finishing cycles again, which can prevent the generation of waste products and ensure the processing quality.