The machining accuracy is the extent in which the actual size, shape and position of the surface of the room after treatment comply with the ideal geometric parameters required by the drawing. The ideal geometric parameters are the average size of the dimensions; , etc. The difference between the actual geometric parameters of the part and the ideal geometric parameters is called the machining error.
1. The concept of treatment precision
Treatment accuracy is mainly used to produce the product level, and treatment accuracy and processing error are terms to assess the geometric parameters of the treatment surface. The machining precision is measured by tolerance levels. High treatment accuracy means a small processing error, and vice versa.
There are 20 levels of tolerance ranging from IT01, IT0, IT1, IT2, IT3 to IT18. have an average machining precision.
The real parameters obtained by any machining method will not be absolutely precise.
The quality of the machine depends on the quality of treatment of parts and the quality of the assembly of the machine.
The machining accuracy refers to the measure in which the real geometric parameters (size, shape and position) after the treatment of the part and the ideal geometric parameters are consistent. The difference between them is called treatment error. The size of the processing error reflects the precision of machining. The greater the error, the lower the machining accuracy, the smaller the error, the higher the machining precision.
2. Content linked to the precision of the treatment
(1) Dimensional precision
Referring to the measure in which the actual size of the part after treatment complies with the center of the room size tolerance.
(2) Precision of form
It refers to the extent in which the actual geometric shape of the surface of the transformed part complies with the ideal geometric shape.
(3) Position precision
Referring to the difference in real position accuracy between the relevant surfaces of the parts after treatment.
(4) Relationship between the other
Usually, when designing the machine’s parts and specifying the machining accuracy, attention must be paid to control the form error in position tolerance, which should be less than dimensional tolerance . In other words, the formation requirements of the large surface of precision parts or parts must be greater than the position of positioning precision, and the positioning requirements of position must be higher than the requirements of dimensional precision.
3. Adjustment method
(1) Adjust the process system
(2) Reduce the machine-tool error
(3) Reduce the transmission error of the transmission chain
(4) Reduce the wear of tools
(5) Reduce the constraint deformation of the process system
(6) Reduce thermal deformation of the process system
(7) Reduce residual stress
4. Causes of impact
(1) Treatment principle error
The error in the machining principle refers to the error caused by treatment using an approximate blade profile or an approximate transmission relationship. Machining errors occur mainly in wires, gears and complex treatment of curved surface.
In treatment, approximate treatment is generally used to improve productivity and the economy in principle that theoretical errors can meet the treatment requirements.
(2) Adjustment error
The error in setting a machine-tool refers to the error caused by an inaccurate adjustment.
(3) Machine-tool error
The machine-tool error refers to the manufacturing error, the installation error and the wear of the machine tool. It mainly includes the guidance error in the machine-tool guide rail, the rotation error of the machine-tool pin and the machine-tool transmission error.
5. Measuring method
The treatment accuracy uses different measurement methods as a function of different processing content and precision requirements. In general, there are the following methods:
(1) Depending on if the measured parameters are directly measured, they can be divided into direct measurement and indirect measurement.
Direct measurement: Measure the measured parameters directly to obtain the measured size. For example, use calipers or comparators to measure.
Indirect measurement: Measure the geometric parameters linked to the measured size and obtain the size measured after the calculation.
Obviously, direct measurement is more intuitive, while indirect measurement is heavier. Generally, when the size measured or the direct measurement cannot meet the precision requirements, an indirect measurement should be used.
(2) Depending on if the reading value of the measurement instrument directly represents the value of the measured size, it can be divided into absolute measurement and relative measure.
Absolute measurement: the reading value directly indicates the size of the measured size, such as measurement with a vernier stirrup.
Relative measurement: The reading value only indicates the difference in the size measured compared to the standard quantity. If you use a comparator to measure the diameter of the tree, you must first use a measurement block to adjust the zero position of the instrument, then perform the measurement. The size of the measurement block, which is a relative measure. In general, the relative precision of the measure is relatively higher, but the measure is more embarrassing.
(3) Depending on if the measurement surface is in contact with the measurement head of the measurement instrument, it is divided into contact and contactless measurement.
Contact measurement: The measurement head is in contact with the contact surface and has a mechanical measurement force. If you use a micrometer to measure the parts.
Contactless measurement: The measurement head is not in contact with the surface of the part to be tested. For example, use the projection method, light wave interference method to measure, etc.
(4) Depending on the number of measurement parameters, it is divided into a single measure and a complete measurement.
Measure in one element: each parameter of the part to be tested is measured separately.
Complete measurement: Measure complete indicators that reflect parts’ parameters. If you use a tool microscope to measure threads, you can measure the real average diameter of the wire, the half angle error of the dental type and the cumulative pitch error respectively.
The full measurement is generally more efficient and more reliable to ensure the interchangeability of parts. The unique measurements can determine the error of each parameter separately and are generally used for process analysis, process inspection and measurement of specified parameters.
(5) Depending on the role of measurement in the processing process, it is divided into active measurement and passive measure.
Active measurement: The part is measured during the processing process, and the results are directly used to control the processing process, thus preventing and controlling the generation of waste in a timely manner.
Passive measurement: measurements made after the treatment of the part. This type of measure can only determine if the parts treated are qualified, and it is limited to discovering and deleting the remains.
(6) Depending on the state of the part measured in the measurement process, it is divided in static and dynamic measurement.
Static measurement: the measurement is relatively static. For example, measure the diameter of a micrometer.
Dynamic measurement: During the measurement, the measurement surface moves in relation to the measurement head in the simulated working state.
Dynamic measurement methods can reflect the situation where parts are close to use and are the development management of measurement technology.
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