Jiangsu GOING 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.

 

 

Processing accuracy is mainly used to evaluate the degree of product production, and both processing accuracy and processing error are terms used to evaluate the geometric parameters of the processed surface. The machining accuracy is measured by tolerance level, and the smaller the level value, the higher the accuracy; The machining error is represented by numerical values, and the larger the value, the greater the error. High machining accuracy means small machining errors, and vice versa. There are a total of 20 tolerance levels from IT01, IT0, IT1, IT2, IT3 to IT18. IT01 represents the highest machining accuracy of the part, while IT18 represents the lowest machining accuracy. Generally, IT7 and IT8 are of medium machining accuracy.

 

The actual parameters obtained by any machining method will not be absolutely accurate. From the perspective of the function of the part, as long as the machining error is within the tolerance range required by the part drawing, it is considered to ensure machining accuracy.

 

The quality of a machine depends on the machining quality of the parts and the assembly quality of the machine. The machining quality of the parts includes two major parts: machining accuracy and surface quality.

 

Mechanical machining accuracy refers to the degree to which the actual geometric parameters (size, shape, and position) of a part after machining match the ideal geometric parameters. The difference between them is called machining error. The magnitude of machining error reflects the level of machining accuracy. The larger the error, the lower the machining accuracy, and the smaller the error, the higher the machining accuracy.

 

1、 Methods for adjusting machining accuracy

1. Reduce machine tool errors

(1) Improving the manufacturing accuracy of spindle components

1) The rotational accuracy of bearings should be improved:

① Select high-precision rolling bearings;

② Adopting high-precision multi oil wedge dynamic pressure bearings;

③ Adopting high-precision hydrostatic bearings.

2) The accuracy of accessories related to bearings should be improved:

① Improve the machining accuracy of the box support hole and spindle journal;

② Improve the machining accuracy of the surface that matches the bearing;

③ Measure and adjust the radial runout range of the corresponding components to compensate or offset errors.

(2) Proper preloading of rolling bearings

① Can eliminate gaps;

② Increase bearing stiffness;

③ Uniform rolling element error.

(3) Make the spindle rotation accuracy not reflected on the workpiece.

 

2. Adjusting the process system

(1) Trial cutting method adjustment

By trial cutting, measuring dimensions, adjusting the cutting tool's feed, cutting through the cutting path, and repeating this process until the desired size is achieved. This method has low production efficiency and is mainly used for single piece and small batch production.

(2) Adjustment method

Obtain the required dimensions by pre adjusting the relative positions of the machine tool, fixture, workpiece, and tool. This method has high productivity and is mainly used for large-scale production.

 

3. Reduce tool wear

Before the tool size reaches the stage of sharp wear, it is necessary to regrind the tool.

 

4. Reduce transmission chain transmission errors

(1) The number of transmission components is small, the transmission chain is short, and the transmission accuracy is high;

(2) The use of deceleration transmission is an important principle to ensure transmission accuracy, and the closer the transmission pair is to the end, the smaller its transmission ratio should be;

(3) The precision of the end piece should be higher than that of other transmission parts.

 

5. Reduce the stress deformation of the process system

(1) Improve the stiffness of the system, especially the stiffness of weak links in the process system

1) Reasonable structural design

① Minimize the number of connecting surfaces as much as possible;

② Prevent the occurrence of local low stiffness links;

③ The structure and cross-sectional shape of the foundation and support components should be reasonably selected.

2) Improve the contact stiffness of the connecting surface

① Improve the quality of the joint surfaces between parts in machine tool components;

② Apply preload to machine tool components;

③ Improve the accuracy of the workpiece positioning reference plane and reduce its surface roughness value.

3) Adopting reasonable clamping and positioning methods

(2) Reduce load and its changes

1) Reasonably selecting tool geometry parameters and cutting parameters to reduce cutting force;

2) Group the rough embryos and try to make the machining allowance of the adjusted rough embryos as uniform as possible.

 

6. Reduce residual stress

(1) Increase heat treatment processes to eliminate internal stress;

(2) Reasonably arrange the process of production.

 

7. Reduce thermal deformation of the process system

(1) Adopting reasonable machine tool component structures and assembly standards

1) Adopting a thermally symmetrical structure - in the gearbox, the shafts, bearings, transmission gears, etc. are symmetrically arranged, which can make the temperature rise of the gearbox wall uniform and reduce the deformation of the gearbox;

2) Reasonably select the assembly benchmark for machine tool components.

(2) Reduce heat generation from heat sources and isolate heat sources

1) Using smaller cutting amounts;

2) When high precision is required for parts, separate the rough and fine machining processes;

3) Separate the heat source from the machine tool as much as possible to reduce thermal deformation of the machine tool;

4) Improve the friction characteristics of non separable heat sources such as spindle bearings, screw nut pairs, and high-speed moving guide rail pairs from the aspects of structure and lubrication, reduce heat generation, or use insulation materials;

5) Adopting forced air cooling, water cooling and other heat dissipation measures.

(3) Equilibrium temperature field

(4) Accelerate to achieve heat transfer equilibrium

(5) Control environment