CNC machining tool and its treatment affects the precision of machining parts, also affects the operation of CNC machine tools. This is the tool error of CNC machine tool and put forward improvement measures.
1 process error in NC machining process
(1) programming error: the main interpolation error of NC programming system of NC, mainly due to the linear or arc near the part outline of avoidance. This is an important factor affecting the part machining precision. Can be resolved by increasing the number of interpolation nodes, but will increase the programming effort.(See the new fault detection and solution of NC cutter)
(2) the tool nose arc error: hole, outside or at the end in the cutting, bead does not affect the size, shape, but in processing cone caused by, or under the influence of tool nose arc when arc gouging or undercutting. This error can be determined by measuring tool nose RADIUS, cutting tool radius compensation function is used to eliminate errors.
(3) measurement errors: mainly are gauges accuracy and operation methods, leadto the measured size is not accurate. This error can be made up.
(4) the tool setting error: this error is primarily produced in the process of knives,cutter moved to the point where under the influence of feed override value of theoperating system. Solution ratio is a reasonable choice for trimming, especially when close to the knife-point position of the tool minimum block feed trimming toolused when precise positioning at knife point.
(5) the systematic error of machine tool: tolerances of form and position affected by the machine itself, this tolerance is generally not adjustable; servo unit, repeat positioning error drive, mainly by the system of machine tool pulse equivalent size,uniformity and transmission line effects; these errors is very small and stable, should be taken into account only in precision machining.
2 setting method
CNC machining tool and its treatment affects the precision of machining parts, also affects the operation of CNC machine tools. So-called knife is made in the workpiece coordinate system tool cutter location point (the point), under the control of numerical control program, cut out from the tool surface relative to the Datum has the correct size, thus ensuring the machining accuracy. In NC machining, the basicmethod tries to knife cuts, Cutter knife, using ATC on knives and automatic knives.
2.1 trial cuts
Position detection device based on numerical control machine tool using differenttest methods are both relative and absolute. In relative type try cut method on knife in the, can used three species method: a is with measuring (as plate feet,) directly measurement, alignment on knife size, this on knife method simple but not precise; II is through knife bit points and positioning block of work face align Hou, moved open tool to on knife size, this method of on knife accuracy depends on knife bit points and positioning block work face align of precision; three is will artifacts processing surface first light a knife, measured artifacts size, indirect is out on knife size, this method most precise. Absolute trial cuts on sword, benchmark tool is needed, then with the direct or indirect method to detect other tools of Cutter locationpoint benchmark deviations between the knife, as the other tools setting tool offset value. The above trial cuts, a "test--measure--adjusting (compensation)" mode, so take up more time machine, less efficient, but because the method is simple, auxiliary equipment required less widely used type low grade CNC machine tools.
2.2 tool detection tool
Tool instrument into tool touch sensor within the machine tool and machine tool apparatus two. Machine tool Tester is the tool installed directly on the machine in afixed position (lathes, tools directly on the holder or through the tool holder installtool holder), this method is used for turning such numerical control machine tools.Machine tool apparatus must pass holders mounted on a turret, (lathe), together with the knife holder together, outside of the machine tool calibration well in advance, then packed the knife machine tool can be used on, this method is mainly used for boring and milling CNC machine tools, machining centres. Knife tool need additional apparatus using auxiliary equipment, high costs, handling tools effort, butsaves machine tool time, improve the accuracy of tool, commonly used for high precision numerical control machine tools.
2.3 ATC tool
AIC tool is used on the machine tool microscope method of tool length is calculated automatically. Since there is no tool microscope and tool-setting process is manual and Visual, so there is still a certain degree of tool setting error. Tool instrument than just tool should facilitate easy loading and unloading. Automatic tool detection tool used CNC equipment, accurately measure the length of each coordinatedirection of the tool automatically, automatic correction tool offset value, and workpieces directly without having to pause. Compared with the previous setting method, this method reduces tool setting error, tool precision and efficiency is improved, but required by the knife detection sensor and cutter position point detection system of automatic tool systems and CNC systems must have tool to automatically detect accessibility, complex system, investment, generally used for high-end CNCmachine tools.
2.4 automatic tool
Automatic tool used CNC device detection tool automatic correction tool offset value function, automatic precision to measure the length of each coordinate direction of the tool and the workpieces directly without having to pause. Also known as automatic tool tip check function:
Once after installing the artifacts in the machining center, requires knife multi tool in processing multiple surfaces of the workpiece. In order to improve the tool precision and efficiency, the General machine tool equipment to knives, ATC tool and automatic methods, machine tool to instrument widely used in mid-range Keng milling machining center. Instrument using a knife to knife, usually choose a good basemandrel at the surface, to determine the origin of the workpiece and select a convenient tool, the dynamic (Swivel) tool.
3 processing error causes and measures taken
To sum up, tool setting error due to:
(1) when using trial cuts on a knife, tool setting error comes mainly from after a tryto cut the workpiece measurement error and the operation of Visual error.
(2) when using the tool instrument, when the tool mirrors and automatic tool, erroris not due to instrument manufacturing, installation and measurement error, usingthe poor skills of the instrument may cause errors.
(3) when the measuring tool is carried out in a static, and the process is dynamic,while under the influence of cutting force and vibration force, produced and preset dimensions inconsistencies. The size of this error depends on the quality of the tool and the dynamic stiffness.
(4) in setting process, most of the time you want to perform "machine returning reference point for" operation zero-point drift may occur during this process and lead to zero error resulting in tool setting error.
(5) within the machine tool has a measuring device, the size of the smallest unit ofmeasure is associated with the error. Generally speaking, the smallest unit of measurement devices measurement error, the smallest unit of measurement error is small for small measuring device.
The main measures to reduce tool setting error:
(1) when using trial cuts on a knife, operations carefully. Tool after tool according to the workpiece size and programming errors to fix the cutter compensation valuebetween size, also the machine tools repeatability positioning accuracy on the knife accuracy of Cutter location point the installation height of the effect on the precision of knife.
(2) when using the instrument for a knife, should pay attention to equipment manufacture, installation and measurement accuracy. The correct method to master theuse of the instrument.
(3) when you select the tool you want to pay attention to the quality of the tool and the dynamic stiffness.
(4) check the zero drift of NC machine tools on a regular basis, pay attention to the timely adjustment of machine tools.
Through the use of test method and the method of approximate evaluation method of parts machining, processing five parts of each method. Its axial dimensions were measured with a radial dimension (10), and the average absolute value of deviation, averages a set of artifacts that illustrate the tool-setting error.
If the axial dimension high precision parts, do not use the manual test tool for measuring, because when human error is inevitable, available system automatic measurement method for test cutting tool, but also to see if the system measurement accuracy with the need to ensure accuracy. If component radial dimensions are higher, try not to use the method of approximate evaluation on knife, this knife is difficult to ensure accurate alignment cutlery Center of rotation of the workpiece. But the knife part of error of axial dimensions will not be much because the axial dimensions of the cutter is automatically measured, avoiding human error involved.
