Discussion sur le processus d'usinage sur tour CNC

China’s industrial production system has gradually matured and is developing toward intelligence and digitalization. This paper takes the processing process and details of CNC lathe as the starting point clarifies the principle and characteristics of CNC processing, elaborates on the selection of comprehensive processing methods and the determination of processing solutions, analyzes the key points of CNC processing relying on actual cases, and enhances the development strategy of optimizing the quality of CNC processing, to lay a foundation for improving the quality of China’s CNC lathe machining technology.

The high-quality development of the industrial production system symbolizes the overall improvement of national living standards and the continuous improvement of China’s emerging technology system. Among them, CNC machining technology is established in mechanical production and industrial processing based on digital processing methods; it has a strong modernization characteristic, reducing labor costs and artificial pressure and greatly enhancing the scientific and rational industrial processing system. All-round analysis of the specific application process of CNC machining technology clear focus on the use of CNC lathes, helps to improve the quality of the development of China’s processing system.

1. The principle and characteristics of CNC processing analysis

(A) Processing principle and process analysis

CNC lathe processing parts usually need to use action instructions to control the operation of the lathe. On the one hand, it is necessary to control the sequence of actions; on the other hand, it is necessary to control the amount of displacement in each field. These control priorities also need to be analyzed in conjunction with different types of CNC lathes, such as the traditional ordinary CNC lathes need to be controlled directly by manual control to ensure that the lathe’s normal driving, stopping, phantom, spindle speed, switching the cutting fluid, and other processes, and automatic CNC lathes, as well as imitation machine tools in the application of the process of Automatic control, can be carried out through the system, such as a better-designed cam, leaning mold and block and other devices, can be detected through the analog, and determine the processing needs, automatic control, this process is more complex but can enhance the stability of the operation of the CNC lathe and the comprehensive benefits.
The use of CNC machine tools to process parts, you need to obtain the graphics of the parts in advance, process parameters, processing steps, key considerations, and other information, and then through the coding of the way in advance, will be input into the control system of the CNC machine tool, and then by the control system of the independent operation and processing, drive the servo mechanism to receive instructions to coordinate the various parts of the CNC lathe for action. In this process, the devices of the CNC lathe can replace the human brain and hands to realize automation and intelligent control, greatly enhancing the accuracy and scientific control of complex parts processing and improving the overall processing efficiency. Figure 1 shows a more complete CNC lathe processing principle process.

(B) CNC lathe processing characteristics

An all-around understanding of the processing characteristics of CNC lathes and application details for the enhancement of CNC machining upgrading and innovation diversity has a certain role in promoting. From the current application scenarios in CNC processing and benefits, CNC lathe processing has the following characteristics.
First of all, a strong degree of automation can greatly enhance the productivity of CNC machining; in addition to manual clamping of blanks, a series of other processing and control processes are automatically completed by the system, reducing labor and labor costs at the same time, but also to enhance the accuracy of CNC machining. Applicable to the current large-scale centralized product processing and full production line control.
Secondly, CNC lathe processing is highly adaptable, especially in processing complex parts. We only need to replace the tool fixture; through the system, automatic control will be able to realize automated management not need to carry out additional complex operations, which simplify the production process and enhance production efficiency has a very strong role in promoting.
Again, the CNC lathe processing can improve the processing accuracy to create a stable quality assurance; CNC lathe processing can be controlled in the accuracy of 0.005-0.01 mm or so, will not be affected by the complexity of the parts, and the production line of other factors affecting too much. In addition, most of the processing operation is completed by machinery, which can reduce the interference caused by human beings on the processing accuracy. In addition, the processing system of the CNC lathe is often set up with intelligent detection equipment, which can be combined with the various errors during processing for rapid detection and give the compensation plan and optimization measures, which has a very strong role in promoting the overall efficiency of parts processing. 
In addition, the CNC lathe machining process can also have a strong expandability, such as the ability to establish communication with the computer system; integrated management can be achieved, but also with a large number of CNC design software associated, such as the construction of CAD/CAM integrated system, can greatly enhance the CNC processing, design, operation, and maintenance management systematic, to realize the development of clusters.

2. The application of CNC lathe machining process system and detail analysis

(A) The choice of lathe

CNC lathe is suitable for the following types of processing parts: small batch production of parts or new products in the trial production of parts; parts of the shape and contour of the more complex, for the processing, has a higher precision requirement; through the ordinary machine tool processing will cost much time as well as cost; the need for multiple improvements and upgrades; the parts of their price are higher, in the processing process does not allow the occurrence of the situation of scrapping; the parts of a shorter production cycle, and urgently need to be processed. The production cycle is short and urgent production. CNC lathe processing can further improve the processing efficiency also to reduce unnecessary waste of resources, so the process of selecting a CNC lathe can be combined with the parts of their own processing needs and characteristics to determine the choice of ordinary lathe processing or CNC lathe processing, to ensure that the processing of the comprehensive quality.

(B) Processing methods and programs to determine

The choice of processing methods needs to be combined with the characteristics of different parts to analyze their own, to ensure that the processing accuracy and surface roughness meet the actual requirements, and also consider the economic benefits of processing and production efficiency to understand the operation of the production equipment. The determination of the processing program needs to adhere to the fulfillment of the following principles: First, the precision requirements of the parts must be higher than the surface processing requirements, usually to the surface roughing, semi-finishing, finishing, and other processes. Comprehensive these processing requirements, reasonable screening of the quality standards of the processing program, analysis of the situation of the CNC lathe, understanding the conditions of the blank, and enhancing the scientific nature of the processing. To ensure that the determination of the processing program meets the actual application requirements while conforming to the operating characteristics of the CNC lathe itself.

(C) Machining process division

1. Part clamping and positioning method as a standard for division.
Parts clamping and positioning, as the standard of process division, need to consider the type of basic structure of each part to analyze the actual requirements of the surface processing technology system; in the process of processing also need to consider different positioning methods. Conventional processing of parts in the form of the usual endomorphic positioning and the processing of parts in the form of the internal shape of the division through the shape of the positioning.
2. Classification based on the standard of machining fineness.
They are combined with the specific machining accuracy, deformation, stiffness, and other factors for the division of the process, usually based on roughing or fine machining as the basis for division, first roughing, then finishing. Different types of CNC lathes or tools can be selected in this process. Generally speaking, an installation period needs to ensure that each part and surface machining is completed once to avoid excessive replacement of tools and to shorten further the time of the empty stroke operation to reduce the positioning error and improve the accuracy of processing the main factors.
3. Divided by machining process as a standard.
A part of the parts needs to be processed through various machining processes, for example, both the milling plane and boring parts of the surface, according to the first milling plane after boring processing. Because according to this method of division of work, the step can improve the processing accuracy. Because the cutting force is larger when milling the plane, the parts are prone to deformation. The first milling plane, after boring, can restore the deformation phenomenon and reduce the oil and electricity type caused by the problem of precision degradation.
4. Divide by tool as a standard.
Suppose part of the CNC lathe table rotation time is less than the tool change time. In that case, you can use different tools through the standard for the division of the process, reduce the number of tool changes, and improve the overall processing and operational efficiency.

(D) The installation of parts and fixture selection

Installation of parts needs to adhere to the design of the benchmarks, process benchmarks, and programming calculations of the benchmarks for the unified analysis to ensure that the parameters are consistent to provide a fundamental guarantee for subsequent processing, to reduce the number of clamping further, and to strive for completion. The automatic control function of the CNC machine tool itself, to adjust the details and further reduce the degree of manual intervention, can enhance the processing accuracy.
Fixture selection needs to be analyzed in conjunction with specific processing characteristics, on the one hand, to ensure that the fixture coordinate direction and the coordinate direction of the machine tool are relatively unchanged; on the other hand, we should do a good job of coordinating the parts and detail control, mainly based on the coordinate system of the machine tool size. At the same time, it should also be adjusted to different production scenarios and needs. If the parts processing batch is small, you can use a combination of fixtures or adjustable fixtures to shorten further the time used in production and processing, but also effective cost savings; and the need for batch production, the use of special fixtures. Parts loading and unloading must be ensured during the reliable, fast, reduced downtime of the CNC lathe. A series of parts on the fixture cannot hinder the machine tool processing operations, so the fixture must be kept open to avoid affecting the tool.

(E) the choice of tools and cutting the amount of control

In selecting tools to choose high-quality materials, the most common material is carbide. In precision machining, you can choose to have stronger wear-resistant properties of ceramic and diamond tools with reasonable adjustment of the tool’s parameters.
The choice of cutting amount should be combined with different machining methods and needs to be adjusted. For example, the roughing process for processing requirements and standards is low, usually considering the production efficiency; the semi-finishing and finishing process, to ensure quality first, needs to consider the economic benefits of the cutting rate and processing costs. The determination of the depth of cut should be analyzed in conjunction with the CNC lathe, the tool, and the workpiece’s rigidity. Further, reducing the number of feeds is best; a time to complete the removal can greatly improve the processing efficiency. Cutting speed adjustment can be combined with productivity and different machining accuracy control; determine the feed rate adjustment, combined with the surface machining accuracy requirements and roughness requirements for control, but also need to consider the material properties of parts and tools. For example, the feed rate should be appropriately reduced for surface roughness requirements to be higher in the finishing conditions. For the maximum feed rate, you need to combine the rigidity of the machine tool and the operating performance of the feed system for standard settings while taking into account the pulse equivalent of the CNC system itself.

(F) Machining route determination

Processing route determination needs to consider the surface roughness of the parts, the machining accuracy of these conventional standards, and at the same time to ensure that the numerical calculation has a higher efficiency to reduce the air travel to shorten the processing route comprehensively. The process route is to determine the process, combined with the parts machining allowance, tool rigidity, and machine performance to determine whether it is necessary to carry out a tool or need to carry out cutting through several tools. Different types of CNC lathes also determine the processing route; for example, the CNC milling process includes two methods: reverse milling and down milling, which can be adjusted according to their respective operating requirements.

3. The specific application of CNC lathe processing cases

A processing line needs to make a car with mechanical parts, parts of the material for 45# medium carbon hot rolled steel, without heat treatment and hardness treatment. The forming surface consists of cylindrical, conical, spherical, arc, and threaded surfaces; each surface has no precision or roughness requirements. Through the CNC lathe cutting can be completed processing, and the overall processing complexity is not high, but due to the number of machining surfaces are more, in order to further enhance the efficiency and accuracy of the processing, need to take into account the influencing factors during the machining period, and rationally carry out the process measures. Determination.

(A) Process Measures

Due to the processing of parts without surface roughness and precision requirements, conventional parts processing positions the surface roughness as a 7-level precision. Using a medium-precision CNC lathe, you can complete parts processing in the programming process to directly substitute specific parts processing dimensions. Due to the right side of the shaft section of the parts having two sections of the arc of the reverse, it can be processed through the equipment with mechanical clearance compensation; the complexity of the various surfaces of the molding of the connection for the medium degree of complexity, do not need indexable inserts, the use of conventional cemented carbide inserts can be completed operations.

(B) Positioning datum

Design benchmarks, positioning benchmarks, and process benchmarks three overlap in the corresponding processing before the benchmark end face to be processed first.
In machining, the main choice of a three-jaw self-centering chuck for clamping the manual clamping end; the excess must be inserted into the inner side of the spindle to process the four shafts. To further enhance the processing efficiency, it is necessary to remove the flat end face and the residual amount of the surface of the external round structure on the ordinary lathe and then place it on the CNC lathe for the processing of the structure of the ball, arc, chamfering, threading, etc., and finally cut off the edge by the cutting tool to complete the overall processing process. The machining route and feed route are shown in Figure 1.

Figure.1 Machining route and feed route
It should be noted that, due to the parts processing in the thread processing process, and threads are prone to cause damage to the surface, they need to be processed at the end of the process; the process of processing can be selected G92 thread cycle instruction programming, automatic control by the system to complete the processing, and finally cut off the use of cutting knife to cut off the machining of the completed part.

(C) Tool selection and detail control

The processing process of the tool material for carbide, after preliminary analysis to determine the parameters of control for sina = OC/OK = 6.5/7.5 = 0.866, a = 60 degrees, Kr is greater than 30, according to this line can significantly improve the overall efficiency and safety of processing.
Cutting the amount of control combined with conventional parts processing standards for adjustment, the roughing of the outer contour of the backstroke amount of control for 3 mm, precision turning allowance backstroke amount of control for 0.25 mm, thread roughing backstroke amount of 0.4 mm, and through the cycle of the sequential reduction of the precision turning allowance backstroke amount of 0.1 mm.

(D) Quality control details

• First of all, although the processing of CNC lathes reduces manual intervention, through the system, automatic control can be completed processing. Still, it is also necessary to create perfect quality control methods further to enhance processing accuracy and overall efficiency. One of the automatic programs is to enhance the quality control effect of the main factors. The choice of automatic programming methods will affect the final product effect. The current high-quality automatic programming program is usually CAXA programming and other methods as a representative of the new period of the level of computer applications and programming software development quality continues to improve, the automatic programming system is also maturing, the designers can be combined with different CNC lathe system Designers can combine the characteristics and performance of different CNC lathe systems, and reasonably select the programming software for processing, which can greatly enhance the accuracy of processing.
• Secondly, the operator must fully understand the operating skills and key knowledge of the CNC lathe, especially mastering the system and model differences of the CNC lathe itself, the system code and format, the operating panel, and other areas will have certain differences, only a clear understanding of the performance and characteristics of different CNC lathes, can lay a good foundation for the enhancement of processing accuracy.
• Finally, the need for authentic control of the program. Programs in the machine panel must be input after the first simulation so that the machining program in the CRT simulation processing displays the machining trajectory to see the movement of the machine tool and the simulation of the shape of the workpiece processed is correct. Through the program simulation, you can check whether the program is correct and reasonable to avoid accidents caused by program errors, thereby reducing the loss of equipment and tools to ensure personal safety and processing quality.

Author: Sun Ruirui