How to select CNC machine tools?

How to select CNC machine tools?

With the development of modern manufacturing technology, it is a general trend for enterprises to choose CNC equipment. At present, the CNC equipment on the market can be described as a dazzling array, how to economically and reasonably choose the CNC equipment suitable for the enterprise, has been a topic of concern. This paper discusses the problems that should be paid attention to in the selection completely from the technical point of view.

For a manufacturing enterprise, the improvement of production capacity often starts from the production management, manufacturing process, production equipment and other aspects of technical transformation, and these parts are mutually affecting and restricting. In the choice of production equipment, CNC machine tool update, maintenance, procurement, etc., must take into account what kind of environment to use, how to manage, how to achieve the best economic results and so on.

The selection of manufacturing equipment is to serve the manufacture of some products, and the selected equipment may be used for a part of the process processing of the product parts, or may be used for all the process processing. The level of manufacturing first depends on the design of the process, it will determine what methods and means to process, which also determines the basic requirements for the use of equipment, which is also the basis for technical organization and management of production. The basic requirements of equipment selection should be determined according to what kind of technical level of equipment can be provided on the market to choose, for most small and medium-sized mass production manufacturing enterprises, the choice of CNC machine tools to replace old machine tools or enhance production capacity has been a development trend.

Comparing the performance of ordinary and CNC machine tools, CNC machine tools have strong ability to process complex surface parts and adapt to a variety of processing objects (strong flexibility); High processing quality, precision and efficiency; Suitable for CAD/CAM networking and integrated management of manufacturing and processing information; The equipment has the characteristics of high utilization rate and low normal operation cost.

The choice of CNC machine tools is a comprehensive technical problem, now whether domestic or foreign, can produce a variety of equipment. CNC machine tools after decades of development has evolved into a large family group, can complete a variety of processing and manufacturing requirements. How to choose the suitable equipment from a wide variety of expensive equipment, how to make these equipment play a full role in manufacturing and meet the future development of the enterprise, how to correctly and reasonably purchase accessories, tools, software technology, after-sales technical service and so on, so that the purchased equipment can achieve a better input ratio...... These problems are the majority of buyers must consider, and one by one to deal with the problem.

First, determine the typical machining workpiece "family"

Determining what parts to process is the first step in selecting equipment. 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, taking into account the long-term planning of product development. These parts are grouped and classified by group technology to determine the typical part family of the main processing object. In the classification, there are often many differences in the size of the parts, the shape of the parts is relatively large, and the processing hours of various parts greatly exceed the full load hours of the equipment, so it is necessary to further choose to determine the production program and the typical workpiece family that is close to the requirements. According to the appearance of the typical workpiece family can be divided into diamond type (box type), plate type, rotary type (disk, sleeve, shaft, flange) and special-shaped class; According to the processing accuracy requirements, it can be divided into ordinary grade and precision grade. The typical parts are clearly classified, and the basic processing equipment is more clear.

Second, the process specification design of typical parts family

After determining the machining parts, it is necessary to use the scientific point of view of CNC machining technology to carry out new planning and design of the process flow. This includes the transformation of the original process production process, exploring the feasibility of realizing new process methods, exploring the feasibility of realizing modern production management and logistics management, exploring the feasibility of using advanced tools to greatly improve production efficiency, exploring the reasonable preparation process of numerical control equipment and other equipment (ordinary, special aircraft) on the production line, etc. The aim is to get the best manufacturing process after using CNC machine tools. The following is a few typical parts of the reasonable processing technology.

☆ Shaft parts: face milling and center hole → CNC lathe (roughing) → CNC grinding machine (finishing);

☆ Flange and disc parts: CNC lathe (roughing) → turning center (finishing);

☆ Cavity mold parts: ordinary machine shape and base surface → CNC milling machine machining surface → high-speed CNC milling finishing → polishing or electroetching surface;

☆ Plate parts: biaxial milling machine or gantry milling machine processing large plane → ;vertical machining center processing all kinds of holes

☆ Box parts: vertical machining center on the bottom surface → horizontal machining center on the surrounding surface of the process surface.

Consider the following factors in arranging the process flow:

(1) Select the shortest processing process.

(2) CNC machine tools have considerable adaptability, but it is not universal, from the economic point of view, each part in the typical workpiece family has an economic batch, should be based on the use of more advanced technological means.

(3) Try to give full play to the various process characteristics of the machine tool, the pursuit of maximizing the comprehensive processing capacity of the CNC machine tool (multi-process concentrated process characteristics), should be configured in the production process with the least number of machine tools, the least amount of process equipment and fixtures.

(4) To consider the balance of the capacity of various equipment in the production line or production workshop. As the choice of a single CNC machine tool or the configuration of a production line, a single equipment can not completely package all the processing processes of a workpiece, there must be a process transfer with other equipment, the production capacity between the equipment should be balanced to meet the comprehensive requirements of the production beat. Therefore, the arrangement of the number of processes and the sequence of processing processes on each equipment should not only play the special advantages of each CNC machine tool, but also meet the accuracy requirements, but also consider the reasonable use of the process benchmark when the workpiece is rotated on each machine tool.

(5) The problem often encountered in the arrangement of CNC machining technology is the contradiction between the process concentration and the process processing principle. In the use of CNC machine tools, people generally adopt the process concentration principle of concentrating multiple processes on a machine tool, in order to pursue improved productivity, shorten the parts processing cycle, and even hope that the workpiece is all processed in a single loading card. However, in fact, for some complex and high-precision workpieces, due to thermal deformation during processing, workpiece deformation caused by internal stress, fixture clamping deformation, heat treatment requirements such as aging process factors and programmer operating factors, it is difficult to complete all processing at one time. In the basic process criteria, the gradual refinement of machining parts restricts the number of working procedures. It is an important content of CNC machining technology to properly deal with the contradiction between the two.

(6) In the arrangement of the typical workpiece family process flow, the manual adjustment and detection 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 according to their own technical equipment capacity, technical level and technical transformation investment, which determines the level of automation and functional requirements for the selection of CNC machine tools. The appropriate use of manual adjustment should be objectively considered to supplement the ability of the enterprise to achieve complete automation, and the exact positioning of the process capacity and equipment level of the enterprise.