Publish Time: 2023-07-01 Origin: Site
As a high-efficiency equipment, CNC machine tools want to give full play to their 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 and determination should be carried out before programming. Reasonable processing technology to get the best processing plan.
The content of CNC turning process
The CNC turning process is the sum of the methods and technical means used when CNC lathes are used to process parts. Its main contents include the following aspects:
(1) Select and determine the CNC turning processing content of the parts;
(2) Carry out CNC turning process analysis on parts drawings;
(3) Selection and adjustment design of tools and fixtures;
(4) Design of procedures and steps;
(5) Calculation and optimization of machining trajectory;
(6) Compilation, verification and modification of CNC turning programs;
(7) First article trial processing and handling of on-site problems;
(8) Compilation of technical documents for NC machining process; in short, NC machining process has many contents, some of which are similar to ordinary machine tool processing.
CNC turning process analysis
Process analysis is the pre-process preparation work for CNC turning. Whether the process is formulated reasonably or not has an important impact on the compilation of the program, the processing efficiency of the machine tool and the processing accuracy of the parts. In order to compile a reasonable and practical processing program, the programmer is required not only to understand the working principle, performance characteristics and structure of the CNC lathe. To master the programming language and programming format, you should also master the workpiece processing technology, determine the reasonable cutting amount, and correctly select the tool and workpiece clamping method. Therefore, the general process principles should be followed and combined with the characteristics of CNC lathes, the CNC turning process analysis should be carried out carefully and in detail. Its main contents include: analyze the processing requirements and rationality of the parts according to the drawings; determine the clamping method of the workpiece on the CNC lathe; the processing sequence of each surface, the feed route of the tool, and the selection of the tool, fixture and cutting amount, etc.
1 Parts drawing analysis
Parts drawing analysis is the primary task of formulating NC turning process. Mainly carry out dimensioning method analysis, outline geometric element analysis, precision 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) Dimensioning Method Analysis
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 reference, process reference, measurement reference and programming origin. If there is no unified design basis for the dimensions in each direction on the part drawing, consider choosing a unified process basis without affecting the accuracy of the part. Calculation transforms each dimension to simplify programming calculations.
(2) Contour geometry analysis
When programming manually, it is necessary to calculate the coordinates of each node. During automatic programming, all geometric elements of the part outline must be defined. Therefore, in the analysis of part drawings, it is necessary to analyze whether the given conditions of geometric elements are sufficient.
(3) Accuracy and Technical Requirements Analysis
Analyzing the precision 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 correct and reasonable selection of processing methods, clamping methods, cutting tools and cutting parameters be carried out. wait. Its main content includes: analyzing whether the accuracy and various technical requirements are complete and reasonable; analyzing whether the machining accuracy of CNC turning in this process can meet the requirements of the drawing, if not, other processing methods are allowed to make up for it, and it should be reserved for the subsequent process. There is a margin; for the surface with position accuracy requirements on the drawing, it should be completed under one clamping; for the surface with high surface roughness, it should be cut at a constant linear speed (note: when turning the end face, the spindle should be limited maximum speed).
2 Selection of fixtures and tools
(1) Workpiece clamping and positioning
In the CNC turning process, it is possible to process all or most of the sub-machined surfaces after one clamping, and minimize the number of clamping times to improve processing efficiency and ensure 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 reference. In addition to the general-purpose three-jaw self-centering chuck, four-jaw chuck, hydraulic, electric and pneumatic clamps, CNC lathe fixtures also have a variety of special fixtures with good versatility. It should be chosen reasonably in actual operation. Metal processing WeChat, the content is good, it is worth paying attention to.
(2) Tool selection
The service life of the tool is not only related to the material of the tool, but also has a great relationship with the diameter of the tool. The larger the tool diameter, the greater the amount of cutting it can withstand. Therefore, when the shape of the part allows, using the largest possible tool diameter is an effective measure to prolong tool life and increase productivity. The tools commonly used in CNC turning are generally divided into three categories. That is, pointed turning tools, arc turning tools and forming turning tools.
① Pointed turning tool. Turning tools characterized by straight cutting edges are generally referred to as pointed turning tools. The tip of the tool is composed of linear main and auxiliary cutting edges, such as outer circular eccentric tools, end turning tools, etc. When this type of turning tool processes parts, the contour shape of the part is mainly obtained by the displacement of an independent tool tip or a linear main cutting edge.
② Arc-shaped turning tool. In addition to turning inner and outer circular surfaces, it is especially suitable for turning various smooth and connected forming surfaces. Its characteristics are: the shape of the blade constituting the main cutting edge is an arc with a small roundness error or line profile error, and each point of the arc edge is the tip of the arc-shaped turning tool, so the tool position is not in the circle. on the arc, and on the center of the arc.
③ Forming turning tool. That is to say, the contour shape of the machined part is completely determined by the shape and size of the turning tool blade. In CNC turning, the commonly used forming turning tools include small radius arc turning tools, groove turning tools and thread turning tools. In order to reduce the tool change time and facilitate tool setting, it is convenient to realize the standardization of machining. In CNC turning processing, indexable turning tools with machine clamps should be used as much as possible.
3 Selection of cutting amount
The cutting amount in CNC turning includes the amount of back cutting ap, the spindle speed S (or cutting speed υ) and the feed rate F (or feed rate f).
The selection principle of cutting amount, reasonable selection of cutting amount is very important to improve the processing quality of CNC lathe. When determining the cutting amount of the 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: during rough turning, first consider selecting the largest possible back engagement ap under the condition that the rigidity of the machine tool allows; secondly choose a larger feed rate f; finally determine a suitable one according to the allowable life of the tool. The cutting speed υ. Increasing the amount of back feed can reduce the number of tool passes and improve processing efficiency, and increasing the feed rate is conducive to chip breaking. When finishing the car, you should focus on how to ensure the processing quality, and improve the processing 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 processing speed as much as possible. The spindle speed S (r/min) can be calculated according to the cutting speed υ (mm/min) by the formula S=υ1000/πD (D is the diameter of the workpiece or tool/tool in mm), and can also be determined by looking up the table or based on practical experience.
4 Divide the process and plan the processing sequence
(1) The principle of process division
There are two commonly used division principles for machining parts on CNC lathes.
① Maintain the principle of precision. The process generally requires as much concentration as possible, and the rough and finish machining 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, after the processing parts that need to be processed by the same knife are completed, another tool should be used to process other parts, and the idle travel should be minimized at the same time.
(2) Determine the processing sequence
The processing sequence generally follows the following principles:
① Rough first and then refined. Carry out in the order of rough turning, semi-finishing turning and finishing turning, and gradually improve the machining accuracy.
② Close first and then far. The part close to the tool setting point is processed first, and the part far away from the tool setting point is processed later, so as to shorten the tool moving distance and reduce the idle travel time. In addition, turning near first and then far is also conducive to maintaining the rigidity of the blank or semi-finished product and improving its cutting conditions.
③ Inside and outside cross. For parts with both inner and outer surfaces to be processed, rough machining of the inner and outer surfaces should be carried out first, and then finishing of the inner and outer surfaces should be carried out.
④ Base first. The surface used as a fine reference should be machined first. The more accurate the surface of the positioning reference, the smaller the clamping error.