China Quality parts Professional Precision machining,Precision parts processingMotor shaft, Bushings, rivets, special screws, nuts, etc.Precision partsProcessing. Products are widely used in automotive, communications, medical, watch, mobile phone, computer and other industries.
n the usual Precision machining process, parts are often unqualified due to some accuracy issues. Today, lets talk about Precision The accuracy of machining. 1 1.1 Processing accuracy and processing error Machining accuracy refers to the degree to which the actual parameters (size, shape and position) of the parts after processing are in accordance with the ideal parameters. It is impossible to make the actual processing exactly the same as the ideal part, and there will always be deviations of different sizes. The degree of deviation of the actual parameter after the part is processed from the ideal parameter is called the processing error. There is no way to avoid this, only ways to make the actual parameters of the machining accuracy close to the ideal parameters. 1.2 Original error The Precision machining process system (referred to as the process system) composed of CNC machine tools, tooling fixtures, cutting tools and workpieces will have various errors, These errors will be reflected as machining errors of the workpiece in various ways (or expanded or reduced) under various specific working conditions. The original errors of the process system mainly include the geometric error of the process system, the positioning error, the processing error caused by the mechanical deformation of the process system, the processing error caused by the thermal deformation of the process system, the deformation caused by the redistribution of the internal stress of the workpiece, and the principle error, Adjustment error, measurement error, etc. 1.3 Research methods of machining accuracy The method analysis calculation method and statistical analysis method of studying Precision machining precision. You can minimize the error as much as possible. 2 Process system assembly error 2.1 Geometric errors caused by CNC machine tools The forming movement of the cutting tool relative to the workpiece during processing is generally completed by a CNC machine tool. Therefore, the machining accuracy of the workpiece depends largely on the accuracy of the CNC machine tool. CNC machine tool manufacturing errors have a greater impact on workpiece processing accuracy: spindle rotation error, guide rail error and transmission chain error. The wear of CNC machine tools will reduce the accuracy of machine tools. Therefore, choosing a good CNC machine tool is also a way to reduce errors. Generally speaking, some CNC machine tools currently produced in China are far inferior to foreign CNC machine tools. In contrast, the machining errors of CNC machine tools produced in China Larger. Changzhou Quality parts company introduced Japans Tsushang CNC machine tool, which not only has high precision, but also has high working efficiency. 2.1.1 Spindle rotation error The spindle of the CNC machine tool is the benchmark for clamping the workpiece or tool, and transmits the motion and power to the workpiece or tool. The rotation error of the spindle will directly affect the accuracy of the workpiece. Therefore, it is also necessary to buy a good spindle. The spindle rotation error refers to the variation of the actual rotation axis of the spindle at each instant relative to its average rotation axis. It can be decomposed into three basic forms: radial circle runout, axial runout and angular swing. The main reasons for the radial rotation error of the main shaft are: the coaxiality errors of several sections of the main shaft journal, various errors of the bearings themselves, the coaxiality errors between the bearings, and the main shaft winding degree. However, their effect on the spindle's radial rotation accuracy varies with the processing method. The main reason for the axial movement is the verticality error of the end surface of the main shaft shoulder and the bearing end face of the main shaft. Different machining methods cause different machining errors caused by spindle rotation errors. When processing the outer circle and inner hole on the lathe, the radial rotation error of the spindle can cause the roundness and cylindricity errors of the workpiece, but it has no direct effect on the machining of the end face of the workpiece. The axial rotation error of the spindle has little effect on the processing of the outer circle and the inner hole, but it has a greater influence on the verticality and flatness of the processed end face. When threading, the main axis rotation error can cause periodic errors in the lead of the processed thread. Appropriately improve the manufacturing accuracy of the spindle and the box, select high-precision bearings, improve the assembly accuracy of the spindle components, balance the high-speed spindle components, and preload the rolling bearings, etc., which can improve the rotation accuracy of the machine tool spindle. 2.1.2 Guide rail error The guide rail is a benchmark on the machine tool to determine the relative position relationship of each machine tool component, and also a benchmark of the machine tool movement. The precision requirements of the lathe guide rails are mainly in the following three aspects: straightness in the horizontal plane; straightness in the vertical plane; parallelism (twisting) of the front and rear guides. In addition to the manufacturing error of the guide rail itself, the uneven wear and installation quality of the guide rail also make it an important factor that causes the error of the guide rail. Guide rail wear is one of the main reasons for the decline in machine tool accuracy. 2.1.3 Transmission chain error Transmission chain error refers to the error of relative motion between the transmission elements at both ends of the transmission chain. It is generally measured by the rotation angle error of the end element of the transmission chain. 2.1.3 Transmission chain error In the cutting process of any tool, it is inevitable to wear, and thus cause the workpiece size and shape to change. The correct selection of tool materials and the selection of new wear-resistant tool materials, the rational selection of tool geometric parameters and cutting dosage, the correct sharpening of tools, and the correct use of coolants, cutting fluids, etc. can effectively reduce the size of the tool. If possible, a compensation device can also be used to automatically compensate for tool size wear. I believe that if you want to make high-precision parts, this device still needs to be installed. 3 Positioning error 3.1 Reference misalignment error The reference used to determine the size and position of a surface on a part drawing is called a design reference. The reference used to determine the size and position of the processed surface on the process drawing is called the process reference. In general, the process basis should coincide with the design basis. When processing the workpiece on the machine tool, several geometric elements on the workpiece must be selected as the positioning datum (or measurement datum) during processing. If the selected positioning datum (or measurement datum) does not coincide with the design datum, a datum difference will occur. Coincidence error. The reference misalignment error is equal to the maximum variation of the positioning reference relative to the design reference in the process dimension direction. When doing this process, the masters in the factory will draw the picture, which is much more reliable. 3.2 Inaccurate errors in positioning pair manufacturing The correct position of the workpiece in the fixture is determined by the positioning elements on the fixture. The positioning elements on the jig cannot be manufactured with absolute accuracy according to the basic dimensions. Their actual dimensions (or positions) are allowed to vary within the specified tolerances. At the same time, the positioning reference plane on the workpiece will also have manufacturing errors. The positioning surface of the workpiece and the positioning elements of the fixture together form a positioning pair. The maximum positional variation of the workpiece due to the inaccurate manufacturing of the positioning pair and the matching gap between the positioning pairs is called the inaccurate error of the positioning pair manufacturing. 4 Error caused by deformation of the process system 4.1 Workpiece stiffness If the rigidity of the workpiece in the process system is lower than that of the machine tool, tool, and fixture, under the action of the cutting force, the deformation of the workpiece due to insufficient rigidity will have a greater impact on the machining accuracy. The maximum deformation can be calculated according to the mechanics of the material Relevant formula estimates. 4.2 Tool rigidity The rigidity of the external turning tool in the normal (y) direction of the machining surface is very large, and its deformation can be ignored. When boring an inner hole with a small diameter, the rigidity of the shank is very poor, and the deformation of the shank's force will greatly affect the accuracy of the hole processing. The arbor deformation can also be estimated according to the relevant formula of material mechanics. 4.3 Stiffness of machine tool components Machine tool components are composed of many parts, and there is no suitable simple calculation method for the stiffness of machine tool components. At present, the experimental method is mainly used to determine the stiffness of machine tool components. The deformation is not linear with the load, the loading curve and the unloading curve do not coincide, and the unloading curve lags the loading curve. The area contained between the two curves is the energy lost in the loading and unloading cycle, which is consumed by the work of friction and contact deformation work; after the first Times is unloaded, the deformation cannot be recovered from the starting point of the first Times loading, This shows that there is residual deformation. After multiple Times loading and unloading, the starting point of the loading curve coincides with the end point of the unloading curve, and the residual deformation gradually decreases to zero; the actual stiffness of the machine tool components is much smaller than what we estimate by the entity. 5 Errors caused by thermal deformation of the process system The thermal deformation of the process system has a greater influence on the processing accuracy, especially in precision machining and large parts processing, the processing error caused by thermal deformation can sometimes account for 40% to 70% of the total error of the workpiece. Machine tools, tools, and workpieces are gradually heated by various heat sources, and they also radiate heat to surrounding materials and spaces through various heat transfer methods. When the amount of heat introduced per unit time is equal to the amount of heat dissipated, the process system reaches thermal equilibrium. Choosing a good heat treatment is also very important. If you do not have this technology in your own factory, you must outsource processing. When outsourcing processing, you must find a suitable heat treatment plant. 6 Conclusion: ways to improve processing accuracy The phrase "reducing the original error; transferring the original error; sharing the original error; equalizing the original error; error compensation" is the best summary of how to reduce the error and improve the accuracy. This article Address:https://www.professionalmanufacturing.com/shownews.asp?id=75
