- Oct 22, 2018 -
[1, positioning error]
One is: the benchmark does not coincide with the error. The basis on which the surface dimensions and locations are used to determine a surface is called the design basis. The basis on which the size and position after processing the surface to be machined in this process are determined on the process drawing is called the process reference. When machining a workpiece on a machine tool, several geometric elements on the workpiece must be selected as the positioning reference for machining. If the selected positioning reference does not coincide with the design basis, a reference misalignment error will occur.
The second is: positioning sub-manufacturing inaccuracy error. The components on the fixture are not absolutely accurate in their basic dimensions, and their actual dimensions (or locations) are allowed to vary within the specified tolerances. The workpiece positioning surface and the fixture positioning component together form a positioning pair. Due to the inaccurate manufacturing of the positioning pair and the matching gap between the positioning pairs, the maximum position variation of the workpiece is called an inaccurate error in positioning manufacturing.
[2, geometric error of the tool]
Any tool in the cutting process will inevitably wear out, and thus cause changes in the size and shape of the workpiece. Correct selection of tool materials and selection of new wear-resistant tool materials, reasonable selection of tool geometry parameters and cutting amount, proper use of coolant, etc., can minimize tool and size wear. If necessary, the compensation device can also be used to compensate for tool size wear.
[3. Lathe spindle rotation error]
The spindle rotation error refers to the amount of variation of the actual rotation axis of the spindle instantaneously with respect to its average rotation axis. The main reasons for the spindle radial rotation error are: the coaxiality error of several sections of the journal of the main shaft, the error of the bearing itself, the coaxiality error between the bearings, and the winding of the main shaft. Appropriately improve the manufacturing precision 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 pre-tension the rolling bearings. Both can improve the rotation accuracy of the machine tool spindle.
[4, adjustment error]
In each process of machining, the process system is always adjusted in this way. Since the adjustment cannot be absolutely accurate, an adjustment error is generated. In the process system, the mutual positional accuracy of the workpiece and the tool on the machine is ensured by adjusting the machine tool, tool, fixture or workpiece.
[5. Transmission chain error]
The transmission error of the transmission chain refers to the error of the relative motion between the first and last transmission elements in the internal transmission chain. Transmission error is the manufacturing and assembly error of each component of the drive chain, as well as the error caused by wear during use.
[6. Error caused by thermal deformation of the process system]
The thermal deformation of the process system has a great influence on the machining accuracy. Especially in precision machining and large-piece machining, the machining error caused by thermal deformation can sometimes account for 50% of the total error of the workpiece. Machine tools, tools and workpieces are subjected to various heat sources, and the temperature is gradually increased. At the same time, they also dissipate heat to the surrounding materials and spaces through various heat transfer methods.
[7. Track error]
The guide rail is the reference on the machine tool to determine the relative positional relationship of each machine tool component, and is also the benchmark for machine tool motion. The accuracy requirements of the lathe guide mainly have the following three aspects: straightness in the horizontal plane; straightness in the vertical plane; parallelism of the front and rear rails. In addition to the manufacturing tolerances of the guide rail itself, the uneven wear and installation quality of the guide rail is also the cause of the guide rail error.
[8, measurement error]
When the part is measured during or after machining, the accuracy is directly measured due to the measurement method, the accuracy of the gauge, and the workpiece and subjective and objective factors.
[9, personnel error]
The personnel error is the error caused by the supervisor's supervisory factors and the skill level of the operator.
[10. Errors caused by deformation of the process system]
One is: the rigidity of the workpiece. In the process system, if the workpiece stiffness is relatively low relative to the machine tool, the tool, and the fixture, the deformation caused by the insufficient rigidity of the workpiece under the action of the cutting force has a large influence on the machining accuracy.
The second is: the rigidity of the tool. The outer turning tool has a large rigidity in the normal direction of the machined surface (y), and its deformation is negligible. When the inner diameter of the hole is small, the rigidity of the shank is very poor, and the arbor is greatly deformed by force, which has a great influence on the precision of the machining hole.
The third is: the rigidity of the machine tool components.
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