Application of CNC machine tools in automobile manufacturing

In addition to the advanced new product development methods, virtual manufacturing, simultaneous engineering and other advanced development technologies adopted by automobile manufacturers, it is also very important to benefit from the efforts of equipment suppliers that provide manufacturing equipment for automobile manufacturing, especially these equipment suppliers provide a variety of CNC machine tools, which allow automobile manufacturers to provide products that meet market demand at the fastest speed. In today's automobile production, the development cycle of new products is constantly shortening and the cost is constantly decreasing. According to data, automobile products that required a four-year development cycle ten years ago can be completed in only two years today.

Classification and characteristics of CNC machine tools

There are many types of CNC machine tools; from the major categories, there are special CNC machine tools and general CNC machine tools; from the processing types, there are CNC milling machines and machining centers for processing shells, CNC lathes and turning centers for processing shafts, cam CNC grinders, etc.; from the control requirements of processing, there are single-axis CNC belt polishers, five-link CNC gear cutting machines, and CNC hob grinders; from the complexity of control, there are simple CNC and multi-channel CNC; from the drive mode, there are stepper motors, DC servo motors, AC synchronous servo motors, AC asynchronous servo motors, and linear motors; from the spindle drive mode, there are DC spindle motors, AC spindle motors, and AC electric spindles; from the position feedback mode, there are full closed-loop feedback, semi-closed-loop feedback, open-loop control, etc.

Good flexibility of CNC machine tools. High adjustment and high processing precision have long been the focus of automobile manufacturers. They began to enter the field of automobile parts production in the 1960s. Due to its high cost, unsatisfactory system functions and efficiency, it has not been widely used. In the 1990s, with the intensification of market competition; multi-variety production to maximize the diversified needs of the market until the needs of every user are met has become the goal pursued by automobile manufacturers, and flexible manufacturing units with CNC machine tools as the main body have been widely used. There are two key development directions for CNC machine tools today:

High-speed CNC machine tools, high speed to achieve high efficiency. The current international level is spindle speed ≤25000rpm, acceleration and deceleration ≤2.5g, rapid movement ≤160m/min. To achieve this new level, the drive, mechanical transmission, mechanical structure and tool of CNC machine tools must be greatly improved. The spindle of the machine tool must use an electric spindle, and the main bearing generally uses ceramic bearings. The difficulty is cooling and lubrication, and the service life is generally 20,000h. The drive generally adopts linear motor plus linear guide (there are also hydrostatic guides). The 90m/min, 1g machine tool is also driven by a dual servo motor with a large pitch double ball screw pre-tensioning solution. The mechanical structure generally adopts a frame box structure. The tool adopts a high-hardness and high-heat-resistant tool, and the tool handle adopts an HSK handle.

The contradiction between flexibility and high efficiency is solved by specializing CNC machine tools or CNC special machine tools. At present, most European and American automobile production adopts an agile production system composed of high-speed machining centers. This system can produce 100% flexible mixed flow and multiple varieties. It consists of multiple flexible processing units called islands. Each island consists of multiple similar machine tools and manipulators that connect the machine tools. It uses a pallet with an electronic storage device to exchange information with the machine tool. It is worth noting that these equipment suppliers not only master the proprietary technology of equipment manufacturing, but also attach great importance to the development of automobile manufacturing process. They can provide users with turnkey projects and have their own system development capabilities. The reliability indicators of machine tools are extremely advanced, and the single machine start-up rate is over 98%. With this production system, the industrialization launch cycle of new products of automobile manufacturers is greatly shortened.

After more than 20 years of reform and opening up, CNC machine tools are increasingly widely used in the field of domestic automobile parts manufacturing. However, most of them are imported from Europe, the United States and Japan. The characteristics of European, American and Japanese machine tools are: good reliability and low failure rate; the design of the human-machine interface emphasizes humanization; with active measurement and compensation system; can provide processing units with automatic loading and unloading devices; modular design of machine tools. Although there are many domestic CNC machine tool manufacturers, from the perspective of variety, there are still more low-level general CNC lathes. For multi-axis CNC machining centers suitable for large-scale automobile engines, gearboxes, and chassis main parts, there are few varieties, and most of them have not undergone the test of mass production.

Application and shortcomings

In the past 20 years, my country's machine tool design and modeling have made great progress. If you look at the appearance of the machine tool statically, there is not much difference from similar foreign products. However, to adapt to the production of large quantities of automobile parts, the machine tool needs to have high reliability. There are two main aspects that affect the reliability of machine tools. One is the design quality of the machine tool; the other is the process quality of the processing and assembly of machine tool components and assemblies. In a sense, process quality has a greater impact on the reliability of machine tools. Domestic machine tool manufacturers pay more attention to product design quality, and generally adopt joint ventures or imitate foreign products. However, the manufacturing process quality, which has a greater impact on the reliability of machine tools, has been ignored. As a result, some of our manufacturers have completed prototypes for many years, and the machine tools sold have constant minor problems, high failure rates, or precision that does not meet contract requirements, poor service, and very low user satisfaction. Therefore, the developed products have not formed economic benefits and achieved large-scale sales. What I want to emphasize is that paying attention to process quality control, standardizing manufacturing processes, quality monitoring, and continuous improvement of product quality are the prerequisites for obtaining high-reliability machine tools. In addition, it is also necessary to establish machine tool design and manufacturing standards that are synchronized with international advanced machine tool manufacturers. In the early 1980s, my country introduced some standards for special machine manufacturing from Schüller Wheeler Company. Through digestion and absorption, it has produced relatively excellent domestic combination special machine and automatic line production enterprises such as Dongfeng Equipment Manufacturing Plant and Dalian Machine Tool Plant. However, while introducing technology, we did not immediately promote technological innovation, did not establish complete technical standards through introduction, and maintained synchronous development. As a result, when Western countries were upgrading their equipment to CNC flexible equipment in the early 1990s, we were still spending manpower and material resources to improve the level of special machine manufacturing. At present, most domestic CNC machine tool manufacturers adopt the strategy of introducing one or several models through joint ventures or cooperation with foreign countries, which cannot form a series of products, making auto parts manufacturers lack of choice; today's automakers implement turnkey projects for industrialization in order to reduce costs and shorten development periods, while domestic suppliers lack the ability to develop automotive parts manufacturing processes. Most of them lack the experience of providing agile manufacturing systems for important automotive engine parts such as cylinder blocks, cylinder heads; crankshafts, connecting rods; camshaft parts lines, and lack the ability to develop supporting auxiliary machines and system connection design capabilities.

Views and suggestions

In order to enable domestic CNC machine tools to enter the automotive manufacturing industry on a large scale as soon as possible, I believe that domestic CNC machine tool manufacturers should focus on improving their own capabilities, mainly in the following aspects:

It is necessary to establish their own automotive parts manufacturing process capabilities and develop products according to the requirements of automotive parts manufacturing. Gradually form serialized and modular CNC machine tool products to meet the needs of automobile parts manufacturing and production.

Pay attention to the development of production line equipment (conveying devices, pallets, etc.). As the main supplier of automobile parts processing lines, CNC machine tool manufacturers should not only pay attention to the design and manufacture of the main machine, but also attach great importance to the development of various elements that constitute modern agile flexible units, such as manipulators, conveying devices, etc. Because the reliability of these devices affects the start-up rate of the production line. And the start-up rate is very important for the large-scale production of the automobile industry.

Have the supporting capacity of the whole line auxiliary equipment. Due to the requirements of turnkey projects, as a contractor, you should also pay attention to establishing your own long-term partner for the whole line contracting project, such as special cleaning machines, because the ability of supporting equipment manufacturers also affects the whole line acceptance capacity.

Improve the automation design capability of the whole line. Modern automobile parts manufacturing has entered the era of agile production. The rationality of the design of the automation information system determines the normal operation of the production system. It is the application of high-tech technology in automobile parts manufacturing. It is the core competitiveness of modern CNC machine tool system suppliers.

Establish an effective user problem feedback mechanism; establish a user-first concept and establish a fast service system; automobile production is a large-scale mass production, and the maintenance and repair of production equipment must be timely. Timely and effective service enhances the competitiveness of enterprises; at the same time, it is conducive to the improvement of machine tool product quality.

Pay attention to the reliability design of machine tools. The reliability of machine tools is mainly guaranteed by a reliable machine tool manufacturing system. It is necessary to pay attention to the quality control of the manufacturing process; ensuring the consistency of the manufacturing process is very important for the machine tool manufacturing industry.

Take advantage of the favorable opportunities of opening up and international exchanges; absorb and digest, and establish machine tool standards that are synchronized with the international standards.

Pay attention to exchanges and cooperation with CNC system manufacturers, and develop CNC systems with their own intellectual property rights in a timely manner. The CNC system should be open and can meet the needs of automobile parts manufacturing to the greatest extent.

Establish a reliable machine tool manufacturing system, abide by contracts, and pay attention to delivery time.