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By jett NG | 03 September 2021 | 0 Comments

Possible cause of CNC knife collision|www.easoar-soon.com

                                 Possible cause of CNC knife collision|www.easoar-soon.com


From the point of view of maintaining accuracy, the tool and the machine tool or the workpiece are never allowed to collide in the use of CNC machine tools. This article will list the main reasons for CNC knife collision from four angles, and put some messy reasons into the fifth category.




Cause one: The operation is omitted


1. Forget to lock the machine


Because CNC machining center is the use of software to lock, in the simulation of processing, when the press the automatic operation button in the simulation interface and can not directly see whether the machine has been locked. Simulation is often not on the knife, if the machine is not locked operation, easy to happen. So before the simulation processing should be to the operation interface to confirm whether the machine is locked.




2. Forget to turn off the no-run switch


In order to save time during program simulation, the empty run switch is often turned on. Empty operation means that all the moving axes of the machine are running at G00 speed. If the running switch is not turned off in the processing time and space, the machine tool ignores the given feed speed, and runs at the speed of G00, resulting in knife hitting and machine accident.




3. There is no return to the reference point after empty run simulation


While the machine tool is locked and stationary during the verification process, the tool is in simulated operation relative to the workpiece (absolute and relative coordinates are changing), when the coordinates do not match the actual position. The zero point coordinates of the machine should be consistent with the absolute and relative coordinates by returning the reference points. If no problems are found after the verification procedure, the machining operation will result in tool collision. The direction of the override is wrong.




4. Forget to call the tool


For the lathe, the need to call the tool offset value, if there is no tool call, run the program section of the tool may not be the tool, it is very likely to cause different tool collision accident. Of course, in the machining center, CNC milling machine must first call the coordinate system such as G54 and the cutter length compensation value. Because each knife length compensation value is different, if not called may also cause collision.




Cause two: The program was written incorrectly


Programming errors are also an important cause of collision. Including: process arrangement error, process to undertake the relationship is not considered carefully, parameter setting error and so on. Common mistakes include the following:


1, the coordinates are set as the bottom is zero, but in reality, the top is zero;


2, the safety height is too low, resulting in the tool can not be completely lifted out of the workpiece;


3, the second opening coarse allowance is less than the previous knife.



Cause three: The program single note is incorrect


Procedures shall be as detailed as possible, and changes in procedures shall be based on the old for new principle: the old procedures shall be destroyed.


Program note error caused by the collision knife, specific but not limited to the following:


1. The single side bumping number is written in the four sides;


2. The clamping distance of the vise or the protruding distance of the workpiece is marked incorrectly;


3. The extended length of the cutter is unknown or wrong.




Cause four: Tool measurement error


Tools should be measured in a scientific way and with as accurate instruments as possible. In practical operation, pay attention to the length of the knife to be longer than the actual depth of 2-5mm. In addition, too short tool loading, tool data input did not consider the tool bar are the causes of knife collision.




Other reasons


In addition to the above four common causes of CNC collision, there are also some scattered errors that may lead to collision. These include:


1. The blank exceeds the expectation and does not conform to the blank set by the program;


2, the workpiece material itself has defects or hardness is too high;


3, the program setting does not consider the clamping factor, pad factor;


4. Machine failure, wrong knife selection and so on.




Operation specification and precautions


Before sorting out operation specifications and matters needing attention, we should first have a specific understanding of CNC operation process. The following figure is the operating process of the comb, it is worth mentioning that check proofreading, trial and cut stage is essential, must not be in a hurry and miss any process.




CNC operation flow chart


Based on the above process, CNC operation can be divided into three stages: preparation stage (including review of drawings, clamping and proofreading), processing stage, and cleaning stage (including cleaning and inspection). At each stage, there are specific operating specifications and matters needing attention. The following will be from each stage, the matters needing attention and operating specifications one by one.


First, the preparation stage


1, the data of the processing diagram should be clear enough, and the workpiece has the qualified mark of the quality department. After receiving the program, check the workpiece datum with the drawing datum.




2. Check whether the tool is clamped after installation; The tools used to adjust the cutting tools must not be left in the machine. There are many specific specifications in the process of clamping tools, such as: clamping to be firm, not too short handle; The length of the cable cutter is determined according to the single depth of the program, generally slightly longer than the processing depth of 2mm, etc.








3, check the working state of chuck clamping; The machine door must be closed before the machine is started.




Two, processing stage


1. Do not touch the knife compartment and iron filings with your hands. Iron filings must be cleaned with a brush or iron hook; Do not in any way touch the main shaft or other parts when it is in operation.


When the lathe is running, it is forbidden to change speed. Operator shall not leave the post, if there is any abnormal shutdown of the machine in time.




2, in the process of processing, do not open the machine protective door. When the machine is running, always check the temperature and sound of the spindle. If the temperature is too high or abnormal sound, it should be reported to the supervisor immediately.




3. Program operation matters: Accurate knife setting; The cursor should be placed in the main program header; Add an appropriate amount of coolant; Be ready to press the stop button in case of emergency.


4, in the process of processing, pay attention to the wear condition of the tool, appropriate replacement of the cutter or tool. After replacing the cutter, pay attention to whether the boundary between phases of processing is consistent.




Third, the aftermath stage


1, after the completion of processing, we should first confirm that each procedure and each instruction required by the procedure list has been completed.


2, check whether the shape of the workpiece meets the requirements, and check whether there are abnormalities in each position of the workpiece.




3. Check the status of lubricating oil and coolant, and add or replace it in time.


4. Turn off the power supply and the total power supply on the operation panel of the machine in turn.

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