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Shandong Yishun CNC Machinery Co.,Ltd

Influence factors and control measures of Machining accuracy of NC machine tools

G3: the NC program, the first factor to consider is the initial point of programming.

According to the G3 integrated reports: General, programming related to the identified needs of the coordinate system operator according to the required machining characteristics and drawings were taken into account, in this one, programming the determination of origin is directly related to the final accuracy. In practice, programming determines the coordinate system should be based on programmable reference, design, process the principle of uniting, and only in this way can the tolerance conversion errors to a minimum and actual operation can be carried out in accordance with the following actions:

1) programming the origin should try to agree well with the benchmarks in the drawings. Design of spare parts will have the corresponding design benchmarks, will have the corresponding process in the processing of the benchmark, origin of programming should be consistent with these benchmarks.

2) at the time of calculation of the relevant data, and simplify as far as possible, avoid unnecessary dimensional chain computing processes reduce the occurrence of errors.

3) programming should as far as possible to choose the coordinate system in high accuracy parts on the surface.

1.2 impact on accuracy of data processing in the programming process and the control measures

CNC programming, data processing is mainly the contour accuracy of the parts as a whole have an important impact, in which the more important are some unknown program node and programming calculation of tolerances and conversion issues.

1) current CNC machine tool equipment and some advanced equipment can be carried out according to the machining parts automatic node coordinates, and most of the CNC machine tools still need artificial hand calculations. Usually use manual calculation of node coordinates is how to control the accuracy, under normal circumstances, there is 0.01~0.03mm between manual and computer errors, usually you can use the following methods to improve accuracy of the calculation: first, manual process of intermediate data should remain in the more than four decimal places, if computer calculations, should try to keep all of the decimals. Second, programming process in the size of adjustment main is according to NC machine of pulse equivalent to determine, so-called pulse equivalent is refers to Dang control system issued a instruction pulse Hou, corresponding of machine mobile equipment by produced of mobile volume, pulse equivalent is NC machine minimum of design and control units, say for pulse equivalent for 0.001mm of NC machine,, in calculation process in the, various calculation results should at least retained three bit decimal above.

2) when the parts dimensional tolerances in different parts have different or asymmetric phenomena, artificial methods of programming should be used for calculations. The whole process if you use the same tool, you should select the tolerance value to program, have reserved some space for errors and ensure accuracy. When the programming dimension tolerances when usually nominal size can be used for programming, so that the corresponding reducing amount of calculation.

1.3 impact on precision machining and control measures

CNC programming, processing route is an important part, and the accuracy and efficiency of NC machining process has a huge effect. How to choice of process route starts from the following aspects:

1) process, retract method on the outline of the parts plays an important role.

When directly on the parts of the surface, operation retract time, possibly due to tool the machine errors, speed mutations make parts of some small dents on the surface, so some high precision machining, inlet and exit should be avoided as much as possible on the surface. For those who have to operate on the surface, should choose arc cut in and out of form, and ARC radius should be larger than the radius of the cutter.

2) at the time of NC machine tool, in order to ensure the overall quality of the surface meets the accuracy requirements, usually processed by clockwise, but in the following cases should be processed using conventional milling methods: first, when the parts to be processed when the surface hardened layer or mortar, should choose a milling method for processing. Because if using Shun milling from parts of surface for cut processing, so surface of hardening layer and clip sand may will on tool caused damage, and using inverse milling of method, dang tool from surface cut out Shi, outside surface of hardening layer and clip sand on will was lift off, to avoid has tool by damage; second, in for some non-metal of processing Shi, especially some fiber material should as select inverse milling of method. Because from the surface into the climb may not be effective for staple fiber, thereby cutting surface of Burr, and milling processing methods can make some fines are effectively cut off material, processing section is smooth.

2 error on Machining accuracy of NC machine system and control measures

2.1 pitch error compensation

Error compensation technology that is called during processing in CNC machine tools, the real location of a specific axis records, and record results compare to precision measurements. In practice, on the shaft, select a certain amount of points, and errors are recorded in the running, input to the machine control system, in this way, different control system for axis movement and time of error control. The number of measurement points the more pitch error compensation technique of the effect more obvious, in the use of this technology should focus on the following issues:

1) CNC machine tools repeatability positioning accuracy is not high, this technology is difficult to be implemented; 2) this technology is based on the premise of the NC machine coordinate system; 3) reference point is to identify the important parameters of the NC machine coordinate system, so the choice of reference point error is zero.

2.2 opposite clearance error compensation

In CNC machining process, operation of the transmission chain has many gaps, and the reverse gap may cause the machine in reverse, when servo motor is running and the machine does not produce movement, which directly makes CNC machine tools to produce some error or machine oscillation. At the time of design of NC machine tool, should fully consider the backlash, but regardless of the improvement measures taken, there will inevitably be some gaps. In semi-closed-loop system of numerical control machine tool, through the above pitch error compensation technology, backlash on the machine in the process of recording, and its entry into the control system, so that when the reverse movement, the system automatically compensates the error operation. For closed-loop system of CNC machine tool, back backlash compensation can be implemented using parameters setting.

In short, in CNC machining process, there are many factors that affect their precision, in addition to the above mentioned factors, process design, tooling, operator skill level will have a certain impact on racing, in actual machining process, therefore, should consider the various aspects of the impact, can we truly achieve accuracy improve.

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