What you must know about CNC lathe process analysis
CNC turning process is the sum of the methods and technical means used in the processing of parts using CNC lathes. Its main content includes the following aspects:
(a) select and determine the content of CNC turning processing of parts;
(B) the part drawings for CNC turning process analysis;
(C) the selection and adjustment of tools and fixtures design;
(iv) the design of processes and work steps;
(E) the calculation and optimization of machining trajectory;
(F) CNC turning program preparation, verification and modification;
(vii) the first trial processing and field problems;
(H) the preparation of CNC machining process technical documents.
CNC turning process analysis
Process analysis is the pre-process preparation work of CNC turning processing. Process development is reasonable or not, the preparation of the program, the machine tool processing efficiency and machining accuracy of the parts have an important impact. In order to prepare a reasonable and practical machining program, the programmer is required not only to understand the working principle, performance characteristics and structure of the CNC lathe, master the programming language and programming format, but also to master the workpiece processing process, determine the reasonable cutting amount, the correct choice of tools and workpiece clamping methods. Therefore, the general process principles should be followed and combined with the characteristics of CNC lathes, and the CNC turning process analysis should be carried out carefully and in detail.
Its main contents are: analyzing the processing requirements of the parts and their reasonableness according to the drawing; determining 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.
Part drawing analysis
Part drawing analysis is the first task of developing CNC turning process. Mainly dimensional labeling method analysis, analysis of contour geometric elements and analysis of precision and technical requirements. In addition, it should analyze the reasonableness of the part structure and processing requirements, and select the process benchmark.
1. Size labeling method analysis
The dimensioning method on the part drawing should be adapted to the processing characteristics of CNC lathe, with the same datum dimensioning or directly give the coordinate dimension. This labeling method is not only convenient for programming, but also conducive to the unification of design benchmark, process benchmark, measurement benchmark and programming origin. If there is no unified design datum for the dimensions in each direction on the part drawing, consider choosing a unified process datum without affecting the accuracy of the part. Calculate the conversion of each dimension to simplify the programming calculation.
2. Analysis of contour geometric elements
In manual programming, to calculate each node coordinates. During automatic programming all geometric elements of the part contour are defined. Therefore, during the part drawing analysis, the adequacy of the given conditions of the geometric elements is analyzed.
3. Analysis of accuracy and technical requirements
Only on the basis of the analysis of the dimensional accuracy and surface roughness of the part, can the processing method, clamping method, tool and cutting amount be selected correctly and reasonably. Its main content includes: analysis of the accuracy and the technical requirements are complete, whether reasonable; analysis of the process of CNC turning accuracy can reach the drawing requirements, if not, allow other processing methods to compensate, should be left to the subsequent process margin; on the drawing of the position accuracy requirements of the surface, should ensure that in a clamping completed; surface roughness requirements of the surface, should be used to constant linear speed Cutting (Note: when turning end surfaces, the maximum spindle speed should be limited).
Selection of fixtures and tools
1. Clamping and positioning of the workpiece
CNC turning machining as far as possible after a clamping can be processed all or most of the substitute surface, as far as possible to reduce the number of clamping, in order to improve processing efficiency and ensure machining accuracy. For shaft parts, usually the outer cylindrical surface of the part itself is used as the positioning reference; for sleeve parts, the inner hole is used as the positioning reference. In addition to the general three-jaw automatic centering chuck, four-jaw chuck, hydraulic, electric and pneumatic clamps, there are many kinds of special clamps with good generality. The actual operation should be reasonably selected. Metal processing micro letter, the content is good, worthy of attention.
2. Tool selection
The service life of the tool, in addition to the tool material, 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. So in the case of the shape of the part allows, the use of the largest possible tool diameter is an effective measure to extend tool life and improve productivity. The tools commonly used in CNC turning are generally divided into three categories, namely, pointed turning tools, circular turning tools and shaped turning tools.
(1) Pointed turning tools. The turning tool characterized by linear cutting edge is generally called pointed turning tool. Its tip is composed of linear main and secondary cutting edges, such as external offset, face turning tools. This type of turning tool processing parts, the contour shape of the parts mainly by an independent tip or a linear main cutting edge displacement to get.
(2) Arc turning tool. In addition to turning internal and external circular surfaces, it is especially suitable for turning various smoothly connected shaped surfaces. Its characteristics are: the shape of the cutting edge of the main cutting edge is a circular arc with small roundness error or line profile error, and every point of the arc edge is the tip of the arc turning tool, so the tool position point is not on the arc, but on the center of the arc.
(3) Forming turning tool. That is, the shape of the contour of the machined part is completely determined by the shape and size of the turning tool blade. In the CNC turning process, the commonly used shaping turning tools are small radius arc turning tools, grooving tools and thread turning tools. In order to reduce tool change time and facilitate tool setting, it is easy to realize the standardization of machining. In CNC turning processing, machine clampable indexable turning tools should be used as much as possible.
Cutting amount selection
The cutting amount in CNC turning machining includes the back draft ap, spindle speed S (or cutting speed υ) and feed speed F (or feed f).
The principle of choosing the cutting amount, the reasonable selection of cutting amount is essential to improve the machining quality of CNC lathe. To determine the cutting amount of CNC lathe must be based on the requirements specified in the machine tool manual, as well as the durability of the tool to choose, can also be combined with the actual experience to determine the analogy method.
The general selection principle is: when rough turning, first of all, consider choosing the largest possible back draft ap as much as the machine rigidity allows; secondly, choose a larger feed f; finally, determine a suitable cutting speed υ according to the allowable tool life; increasing the back draft can reduce the number of tool walks and improve machining efficiency, and increasing the feed is good for chip breaking. When fine turning, we should focus on how to ensure the machining quality and try to improve the machining efficiency on this basis, so it is appropriate to choose a smaller back draft and feed, and increase the machining 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 workpiece or tool mm), and it can also be determined by checking the table or according to practical experience.
Dividing the process and the proposed processing sequence
1. The principle of process division
In the CNC lathe processing parts, the common principles of the division of the process are two.
(1) maintain the principle of precision. The process is generally required to focus as much as possible, rough and finish machining will usually be completed in one clamping. In order to reduce thermal deformation and cutting force deformation on the shape of the workpiece, position accuracy, dimensional accuracy and surface roughness of the impact, then the rough and finish machining should be carried out separately.
(2) Improve the principle of production efficiency. In order to reduce the number of tool changes, save tool change time and improve productivity, the processing parts that need to be processed with the same tool should be completed, and then change another tool to process other parts, and the empty stroke should be reduced as much as possible.
2. Determine the processing order
Develop the processing sequence generally follows the following principles:
(1) first coarse and then fine. According to the order of coarse turning semi-finish turning fine turning, and gradually improve the processing precision.
(2) First near and then far. Parts close to the tooling point are machined first, and parts far from the tooling point are machined later, in order to shorten the tool travel distance and reduce the empty travel time. In addition, the first near and then far turning is also conducive to maintaining the rigidity of the blank or semi-finished products, to improve its cutting conditions.
(3) Inside and outside cross. Both the inner surface and the outer surface of the parts to be machined, the inner and outer surface of the roughing process should be carried out first, followed by the finishing process of the inner and outer surface.
(4) base surface first. The surface used as a fine reference should be processed first, the more accurate the surface of the positioning reference, the smaller the clamping error.