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Comparing the performance of ordinary and CNC machine tools, CNC machine tools have strong ability to process complex surface parts, adapt to a variety of processing objects (strong flexibility); high processing quality, precision and processing efficiency; adapt to CAD/CAM networking, suitable for manufacturing and processing information integration management; high equipment utilization rate, low normal operation cost and other characteristics.
How to choose CNC machine tools is a comprehensive technical issue. How to choose suitable CNC machine tools from a wide variety of expensive equipment, how to make these equipment fully play a role in manufacturing and meet the future development of the enterprise, how to correctly and reasonably purchase accessories, tools, software technology, after-sales technical services, etc. that match the main machine, so that the purchased equipment can achieve a better investment ratio… These issues are all issues that the majority of purchasers must consider and deal with one by one.
1.Determine the typical processing workpieces of CNC machine tools
Determining what kind of parts to process is the first step in selecting CNC machine tools. According to the needs of technological transformation and production development, enterprises determine which parts and processes are ready to be completed with new processing equipment, and take into account the long-term planning of product development. Use grouping technology to group and classify these parts, and determine the typical part family of the main processing objects. In the classification, we often encounter problems such as large differences in part specifications and shapes, and the processing hours of various parts greatly exceeding the full-load hours of the equipment. Therefore, we need to further select and determine the typical workpiece family whose production program is relatively close to the requirements. The typical workpiece family can be divided into diamond type (box type), plate type, rotating body type (disc, sleeve, shaft, flange) and special-shaped type according to the appearance; according to the processing accuracy requirements, it can be divided into ordinary grade and precision grade. The classification of typical parts is clear, and the basic processing equipment is also clear.
2.Process specification design of typical part family
After determining the processing parts, it is also necessary to use the CNC processing technology point of view to plan and design the process flow in a new way, including the transformation of the original process production process, the exploration of the feasibility of realizing new process methods, the exploration of the feasibility of realizing modern production management and logistics management, the exploration of the feasibility of using advanced tooling to greatly improve production efficiency, and the exploration of the reasonable configuration process of CNC equipment and other equipment (ordinary and special machines) on the production line. The purpose is to obtain the best process manufacturing process after using CNC machine tools. The following are the reasonable processing processes of several typical parts.
Shaft parts: milling end face and drilling center hole → CNC lathe (rough machining) → CNC grinder (finishing);
Flange and disc parts: CNC lathe (rough machining) → turning center (finishing);
Cavity mold parts: ordinary machine tool machining shape and base surface → CNC milling machine machining surface → high-speed CNC milling finishing → polishing or electro-etching surface;
Plate parts: double-axis milling machine or gantry milling machine machining large plane → machining various holes on vertical machining center;
Box parts: machining bottom surface on vertical machining center → machining all process surfaces on horizontal machining center.
Consider the following factors in arranging the process flow:
(1) Select the shortest processing process flow.
(2) CNC machine tools have considerable adaptability, but they are not omnipotent. From an economic point of view, each part in a typical workpiece family has an economic batch, and more advanced process means should be used based on the economic batch.
(3) Try to give full play to the various process characteristics of CNC machine tools, and strive to maximize the comprehensive processing capabilities of CNC machine tools (process characteristics of multi-process concentration). The minimum number of machine tools, the minimum process equipment and fixtures should be configured in the production process.
(4) Consider the balance of various equipment capabilities of the production line or production workshop. As the choice of a single CNC machine tool or the configuration of a production line, a single device cannot completely cover all the processing procedures of a workpiece. There must be process transfers with other equipment. The production capacity between the equipment must be balanced to meet the comprehensive requirements of the production rhythm. Therefore, the number of processes and the sequence of processing procedures on each device should not only give full play to the characteristics of each CNC machine tool and meet the precision requirements, but also further consider the reasonable use of the process benchmark when the workpiece on each machine tool is transferred.
(5) The problem often encountered in arranging CNC processing technology is the contradiction between process concentration and the principle of gradual refinement of process processing. In the use of CNC machine tools, people generally adopt the principle of process concentration to complete multiple processes on one machine tool, in order to pursue improved productivity, shorten the part processing cycle, and even hope that the workpiece can be fully processed in one clamping. However, in fact, for some complex workpieces with high precision requirements, it is difficult to complete all the processing in one clamping due to process factors such as thermal deformation during processing, workpiece deformation caused by internal stress, clamping deformation of workpieces, and time requirements for heat treatment, as well as programmer operation factors. The requirement for gradual refinement of processed parts in the basic process criteria restricts the number of process concentrations. Properly handling the contradiction between the two is an important part of CNC processing technology.
(6) In the arrangement of the process flow of a typical workpiece family, the manual adjustment and inspection of each machine tool and production line should be properly arranged, that is, the influence of manual intervention. Enterprises should determine the degree of manual intervention in the process flow based on their own technical equipment capabilities, technical level, and the intensity of technical transformation investment, which determines the automation level and functional requirements for the selected CNC machine tools. It should objectively consider the appropriate use of manual adjustment to supplement the ability of the enterprise to achieve full automation and accurately position the process capabilities and equipment level of the enterprise.