Jiangsu Gaoyi Precision Machinery Equipment Co., Ltd. is a comprehensive manufacturer of CNC machining centers, gantry machining centers, horizontal machining centers, radial drilling machines, and other CNC automation equipment. Equipped with a one-stop service for machine tool sales, installation, debugging, and maintenance, we can design machine tool processing plans, develop process flows for customers, and provide free training on machine tool operations.

 

 

2、 Reasons for machining accuracy errors

1. Processing principle error

Processing principle error refers to the error generated by using approximate blade profiles or approximate transmission relationships for processing. The machining principle error often occurs in the machining of threads, gears, and complex surfaces.

For example, the gear hob used for machining involute gears, in order to facilitate the manufacturing of the hob, uses Archimedes basic worm or normal straight profile basic worm instead of involute basic worm, resulting in errors in the involute tooth profile of the gear. For example, when turning modular worm gears, due to the fact that the pitch of the worm gear is equal to the circumference of the worm gear (i.e. m π) where m is the modulus and π is an irrational number, the number of teeth in the replacement gear of the lathe is limited. When selecting the replacement gear, π can only be converted into an approximate fractional value (π=3.1415) for calculation, which will cause the tool to be inaccurate in the forming motion of the workpiece (spiral motion), resulting in pitch errors.

In machining, approximate machining is generally used to improve productivity and economy, provided that the theoretical error can meet the machining accuracy requirements (i.e., 10% -15% dimensional tolerance).

 

2. Adjustment error

The adjustment error of a machine tool refers to the error caused by inaccurate adjustment.

 

3. Manufacturing errors and wear of fixtures

The error of fixtures mainly refers to:

(1) Manufacturing errors in positioning components, tool guide components, indexing mechanisms, and clamping details;

(2) The relative dimensional errors between the working surfaces of the various components mentioned above after fixture assembly;

(3) Wear on the working surface of the fixture during use.

4. Machine tool error

Machine tool error refers to the manufacturing error, installation error, and wear of the machine tool. This mainly includes the guiding error of the machine tool guide rail, the rotation error of the machine tool spindle, and the transmission error of the machine tool transmission chain.

(1) Guiding error of machine tool guide rail

1) Guide rail guidance accuracy - the degree to which the actual motion direction of the moving part of the guide rail pair matches the ideal motion direction. Mainly including:

① The straightness of the guide rail in the horizontal plane Δ Y and straightness in the vertical plane Δ Z (bending);

② Parallelism (distortion) of the front and rear guide rails;

③ The parallelism or perpendicularity error between the guide rail and the spindle rotation axis in the horizontal and vertical planes.

2) The influence of guide rail guidance accuracy on cutting machining

Mainly considering the relative displacement between the tool and the workpiece in the error sensitive direction caused by guide rail errors. The error sensitive direction during turning is the horizontal direction, and the machining error caused by the vertical direction's guidance error can be ignored; The error sensitive direction during boring machining changes with the rotation of the tool; The error sensitive direction during planing is the vertical direction, and the straightness of the bed guide rail in the vertical plane causes surface straightness and flatness errors.

(2) Machine tool spindle rotation error

The rotation error of machine tool spindle refers to the drift of the actual rotation axis from the ideal rotation axis. Mainly including spindle end face circular runout, spindle radial circular runout, and spindle geometric axis inclination swing.

1) The influence of spindle end face circular runout on machining accuracy:

① No impact when machining cylindrical surfaces;

② When turning or boring the end face, there will be a perpendicularity error or flatness error between the end face and the cylindrical axis;

③ When machining threads, there will be pitch cycle errors.

2) The influence of spindle radial runout on machining accuracy:

① If the radial rotation error is manifested as a harmonic linear motion of its actual axis in the y-axis coordinate direction, the hole drilled by the boring machine is an elliptical hole, and the roundness error is the radial circular runout amplitude; And the holes produced by the lathe have little effect;

② If the geometric axis of the spindle undergoes eccentric motion, a circle with a radius equal to the distance from the tool tip to the average axis can be obtained for both turning and boring.

3) The influence of spindle geometric axis inclination angle swing on machining accuracy:

① A conical trajectory where the geometric axis forms a certain cone angle in space relative to the average axis, and from each section, it is equivalent to an eccentric motion of the geometric axis around the average axis, while from the axial perspective, the eccentricity values vary at different locations;

② The geometric axis swings in a certain plane, and from each cross-section, it is equivalent to the actual axis moving in a simple harmonic straight line in a plane, while from the axis, the amplitude of the jump varies in different places;

③ In fact, the tilt angle swing of the geometric axis of the spindle is the superposition of the above two.

(3) Transmission error of machine tool transmission chain

The transmission error of machine tool transmission chain refers to the relative motion error between the first and last transmission components in the transmission chain.

 

5. Deformation of process system under stress

The process system undergoes deformation under the effects of cutting force, clamping force, gravity, and inertial force, which disrupts the interrelationships between the components of the adjusted process system, leading to machining errors and affecting the stability of the machining process. Mainly considering machine tool deformation, workpiece deformation, and overall deformation of the process system.

(1) The influence of cutting force on machining accuracy

Considering only the deformation of the machine tool, for machining shaft parts, the force deformation of the machine tool causes the workpiece to form a saddle shape with thick ends and thin middle, resulting in cylindricity error. Considering only the deformation of the workpiece, for machining shaft type parts, the force deformation of the workpiece causes the workpiece to form a drum shape with thin ends and thick middle after machining. For machining hole type parts, when considering the deformation of the machine tool or workpiece separately, the shape of the workpiece after machining is opposite to that of the machined shaft type parts.

(2) The influence of clamping force on machining accuracy

When clamping workpieces, due to the low stiffness of the workpiece or improper clamping force, the workpiece undergoes corresponding deformation, resulting in machining errors.

 

6. Manufacturing errors and wear of cutting tools

The impact of tool errors on machining accuracy varies depending on the type of tool used.

(1) The dimensional accuracy of fixed size tools (such as drill bits, reamers, keyway milling cutters, and circular pullers) directly affects the dimensional accuracy of the workpiece.

(2) The shape accuracy of formed cutting tools (such as formed turning tools, formed milling cutters, formed grinding wheels, etc.) will directly affect the shape accuracy of the workpiece.

(3) The blade shape error of developed cutting tools (such as gear hobbing cutters, spline hobbing cutters, gear shaping cutters, etc.) can affect the shape accuracy of the machining surface.

(4) General cutting tools