Technological characteristics of cnc turning processing

CNC turning processing mainly includes process analysis, programming, tool mounting, workpiece mounting, tool setting, rough machining, semi-finishing and finishing. The process analysis of CNC turning is the guarantee for the smooth completion of CNC turning processing.

The purpose of the use of CNC lathes is to process qualified parts, but the processing of qualified parts must rely on the formulation of reasonable processing techniques. This article compares the unreasonable process analysis of current CNC lathe users, and tells the sequence of reasonable process analysis.

The CNC turning process is the sum of the methods and technical means used when machining parts with a CNC lathe. Its main content includes the following aspects:
1. Select and determine the CNC turning processing content of the part;
2. Analyze the CNC turning processing technology of the part drawings;
3. Selection and adjustment design of tools and fixtures;
4. Selection of cutting amount;
5. Process and process design;
6. Calculation and optimization of processing trajectory;
7. Compile technical documents of CNC machining technology.

Most users choose and determine the contents of CNC turning processing of parts, analysis of parts diagrams, selection of fixtures and tools, selection of cutting parameters, division of procedures and drafting of processing sequences, calculation and optimization of processing trajectories, and preparation of technical documents for CNC processing technology The sequence of the process analysis.

The process and design of the entire part are the most important part of the process analysis. The design of the process and the process is directly related to whether the parts that meet the requirements of the part shape and position tolerance can be processed. Unreasonable design of processes and steps will directly cause the geometric tolerances of parts to fail to meet the requirements. In other words, it is the process, and the unreasonable design of the process steps will directly lead to the defective product.

analyse problem
At present, users of CNC lathes have a very high level of operation and can independently solve many operational problems, but their theoretical level is not very high, which is the main reason for the unreasonable sequence of process analysis.

Another reason for the unreasonable sequence of process analysis is that the company has insufficient tools and equipment.

Solve the problem
In fact, after analyzing the phenomenon and reasons of the unreasonable process analysis sequence, it is very easy to solve the problem. The work that needs to be done only needs to slightly adjust the analysis sequence of the parts.

The reasonable process analysis steps should be:
(1) Select and determine the CNC turning processing content of the part;
(2) Analyze the CNC turning processing technology of the part drawings;
(3) Design of procedures and steps;
(4) Selection and adjustment design of tools and fixtures;
(5) Selection of cutting amount;
(6) Calculation and optimization of processing trajectories;
(7) Compile technical documents of CNC machining technology.

CNC Turning processing

(1) Part drawing analysis

The analysis of the part drawing is the primary task of the CNC turning process. Mainly carry out dimensioning method analysis, contour geometric element analysis, accuracy and technical requirement analysis. In addition, the rationality of the part structure and processing requirements should be analyzed, and the process benchmark should be selected.

1. Choose a benchmark
The dimensioning method on the part drawing should be adapted to the processing characteristics of the CNC lathe, and the dimensions should be marked on the same basis or the coordinate dimensions should be given directly. This marking method is not only convenient for programming, but also conducive to the unification of design benchmarks, process benchmarks, measurement benchmarks and programming origin.

2. Node coordinate calculation
In manual programming, the coordinates of each node must be calculated. During automatic programming, all geometric elements of the part contour should be defined.

3. Analysis of accuracy and technical requirements
Analyzing the accuracy and technology of the processed parts is an important part of the process analysis of the parts. Only on the basis of analyzing the dimensional accuracy and surface roughness of the parts, can the processing method, clamping method, tool and cutting amount be selected correctly and reasonably Wait.

(2) Design of process and working steps

1. The principle of process division

In the machining of parts on CNC lathes, there are two principles for the division of processes commonly used.

(1) The principle of maintaining accuracy. The working procedure is generally required to be as concentrated as possible, and the roughing and finishing are usually completed in one clamping. In order to reduce the influence of thermal deformation and cutting force deformation on the shape, position accuracy, dimensional accuracy and surface roughness of the workpiece, rough and finish machining should be carried out separately.

(2) The principle of improving production efficiency. In order to reduce the number of tool changes, save tool change time, and improve production efficiency, the machining parts that need to be processed with the same tool should be completed, and then another tool should be used to process other parts, and the idle stroke should be minimized.

2. Determine the processing sequence

The formulation of the processing sequence generally follows the following principles:

1) First rough and then refined. Follow the order of rough turning, semi-finishing turning and finishing turning to gradually improve the machining accuracy.

2) Near first and then far away. The parts close to the tool setting point are processed first, and the parts far away from the tool setting point are processed later in order to shorten the tool movement distance and reduce the idle travel time. In addition, turning near and far is also beneficial to maintain the rigidity of the blank or semi-finished product and improve its cutting conditions.

3) Crossing inside and outside. For parts that have both inner and outer surfaces to be processed, the rough machining of the inner and outer surfaces should be carried out first, and then the inner and outer surfaces should be finished.

4) The base surface goes first. The surface used as a precision datum should be processed first. The more accurate the surface of the positioning datum, the smaller the clamping error.

(3) Selection of fixtures and tools

1. Clamping and positioning of the workpiece
In CNC turning processing, all or most of the machining surfaces can be processed after one clamping as much as possible, and the number of clampings can be reduced as much as possible to improve the processing efficiency and ensure the processing accuracy.
For shaft parts, the outer cylindrical surface of the part itself is usually used as the positioning reference; for sleeve parts, the inner hole is used as the positioning base. In addition to the general three-jaw automatic centering chuck, four-jaw chuck, hydraulic, electric and pneumatic fixtures, CNC lathe fixtures also have a variety of special fixtures with better versatility. It should be selected reasonably in actual operation.

2 Tool selection
The service life of the tool is not only related to the tool material, but also has a great relationship with the diameter of the tool. The larger the diameter of the tool, the larger the cutting amount it can withstand. Therefore, when the shape of the part is allowed, the use of the largest possible knife and diameter is an effective measure to prolong the life of the tool and increase the productivity. Tools commonly used in CNC turning are generally divided into three categories. Namely, pointed turning tool, arc turning tool and forming turning tool.

(4) Selection of cutting parameters

The cutting parameters in CNC turning include the amount of back tool ap, the spindle speed S (or cutting speed v) and the feed speed F (or feed f).

The selection principle of cutting parameters, reasonable selection of cutting parameters is very important to improve the machining quality of CNC lathes. When determining the cutting amount of a CNC lathe, it must be selected according to the requirements specified in the machine tool manual and the durability of the tool. It can also be determined by analogy in combination with actual experience.

The general selection principle is:
When rough turning, first consider choosing the largest possible back-grabbing amount ap when the rigidity of the machine tool allows; secondly, choosing a larger feed amount f; and finally determining an appropriate cutting speed according to the allowable life of the tool. Increasing the amount of back-grabbing can reduce the number of passes and improve the processing efficiency. Increasing the feed rate is conducive to chip breaking.

When finishing turning, it is important to consider how to ensure the machining quality and to improve the machining efficiency as much as possible on this basis. Therefore, it is advisable to choose a smaller back-cutting amount and feed rate to increase the machining speed as much as possible. The spindle speed S (rimin) can be calculated from the formula S-01000/D (D is the diameter of the workpiece or tool/tool in mm) according to the cutting speed (mm/min), or it can be determined by looking up a table or based on practical experience.

in conclusion
As a kind of high-efficiency equipment, CNC machine tools want to give full play to its high-performance, high-precision and high-automation characteristics. In addition to mastering the performance, characteristics and operation methods of the machine tool, detailed process analysis should be carried out before programming. And determine the reasonable processing technology to get the best processing plan.