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Which error has great influence on machining accuracy of workpiece

ABIS Mold Technology Co.,Ltd Updated: Oct 16, 2018

            Which error has great influence on machining accuracy of workpiece

Geometric error of machine tool

   In machining, the forming motion of the cutter relative to the workpiece is generally completed by the machine tool. Therefore, the machining accuracy of the workpiece largely depends on the accuracy of the machine tool.The manufacturing error of machine tool has great influence on the machining accuracy of workpiece.The wear and tear of the machine will reduce the working accuracy of the machine.

(1) rotation error of spindle

   The spindle of machine tool is the base of clamping workpiece or cutter, and the movement and power are transmitted to the workpiece or cutter.

   The principal axis rotation error refers to the actual axis of rotation at each moment of the principal axis relative to its average axis of rotation.It can be decomposed into three basic forms: radial circular runout, axial channeling and Angle swing.

    The main reasons for the radial rotation error of the main shaft include: the coaxiality error of several parts of the main shaft journal, various errors of the bearing itself, the coaxiality error between the bearings, and the spindle winding.But their effect on the accuracy of radial rotation of spindle.The size varies with the processing mode.

, for example, sliding bearing used in the structure of the axis on the lathe turning round, the effect of cutting force F direction can think broadly unchanged, under the action of cutting force F, in different parts and main journal bearing inside diameter of contact, a fixed part at this time of the main journal had a greater influence on the roundness error of the spindle rotation accuracy, and the bearing inner diameter of the influence of roundness error of the spindle rotation accuracy is limited;On boring machine boring, because of the cutting force F direction along with the spindle turning and turning, in under the action of the cutting force F, spindle is always a fixed part with its journal and different parts of the bearing inner surface contact, therefore, the bearing inner surface of the roundness error of the spindle rotation accuracy, while the effect of main journal roundness error is not big.

(2) radial circular runout of the main shaft when using sliding bearing

   The main cause of axial channeling is the vertical error of the spindle axis facing the spindle axis at the spindle shoulder end and bearing bearing end.

   The machining error caused by spindle rotation is different with different machining methods.When machining the outer circle and inner hole on the lathe, the radial rotation error of the spindle can cause the roundness and cylindrical error of the workpiece, but has no direct influence on the end face of the workpiece.The axial rotation error of the principal axis has little influence on the processing of the outer circle and inner hole, but has great influence on the perpendicularity and planeness of the end face.In the process of thread, the principal axis rotation error can cause the lead of the thread to produce periodic error.

   Properly improve the manufacturing precision of the spindle and box, select high-precision bearing, improve the assembly precision of the spindle, balance the high-speed spindle and preload the rolling bearing, etc., which can improve the rotation precision of the machine tool spindle.

(3) guide error

   The guide rail is the reference for determining the relative position relation of each machine part on the machine tool as well as the reference for machine motion.The precision requirement of lathe guide has the following three aspects: the straightness in the horizontal plane;The straightness within the vertical plane;The parallelism (distortion) of the front and rear guides.

   The straightness error of horizontal lathe guide in horizontal plane will be directly reflected in the normal direction (sensitive direction of machining error) of the surface of the workpiece, which has the greatest influence on machining accuracy.The straightness error of horizontal lathe guide within vertical plane is less than 2, which can cause the shape error and size error of the workpiece.But the effect of al 2 on machining accuracy is much less than that of al 1.If sag 2 reduces the blade tip from a to b, it is not difficult to calculate the variation of workpiece radius R.

   When the parallelism error (distortion) exists in the current rear guide rail, the tool holder will swing when it moves, and the trajectory of the tool tip is a space curve, which makes the workpiece produce shape error.After the current rear guide has a deflection error of s-3, the s-y is approximately (H/B) s-3 can be obtained by geometric relations.The H/B of general lathe is 2/3, and the parallelism error of the guide rail before and after the lathe greatly affects the machining accuracy.

(4) straightness error of horizontal lathe guide

   In addition to the manufacturing error of the guide itself, the uneven wear and installation quality of the guide also make the important factors causing the error of the guide.Guide wear is one of the main reasons for the decrease of machine accuracy.

(5) error of transmission chain

   Transmission chain error refers to the error of relative motion between transmission components at both ends of the transmission chain.The Angle error of transmission chain end element is usually used to measure.

2. Geometric error of cutter

   The influence of cutter error on machining accuracy varies with the type of cutter.The machining accuracy of the workpiece is directly affected by the manufacturing error of the cutter when the cutter of the fixed size is formed.However, the manufacturing error has no direct influence on the machining accuracy of the workpiece.

   Any cutting tool in the process of cutting, it is inevitable to produce wear and thereby cause the workpiece size and shape change.Proper selection of cutting tool material and new wear-resistant cutting tool material, reasonable selection of geometric parameters of cutting tool and cutting dosage, correct cutting tool grinding, and correct use of cooling fluid can effectively reduce the size of the tool wear.If necessary, the tool size can be automatically compensated with a compensation device.

3. Geometric error of fixture

   When the jig is used, the workpiece is equivalent to the cutter and the machine tool in the correct position. Therefore, the manufacturing error of the jig has a great influence on the machining accuracy of the workpiece (especially the position accuracy).For example, in the jig of drill press in the right drawing, the distance error between the drill sleeve axis line f and the positioning plane c of the jig affects the accuracy of the workpiece hole a to the bottom surface B dimension L.The parallelism error between the axis line f of drill sleeve and the positioning plane c of the fixture affects the parallelism between the axis line a of the workpiece hole and the base surface B.The perpendicularity error of the positioning plane c and the bottom d of the clamping concrete bottom affects the dimensional accuracy and smoothness between the workpiece hole pivot line a and the bottom B.The diameter error of drill sleeve hole will also affect the dimension accuracy and smoothness of workpiece hole a to bottom B.

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