Most popular high-speed machining center to replac

Replacing automatic lines with high-speed machining centers

more than a decade ago, it was still difficult to replace automatic lines with machining centers. However, today, this substitution has become a reality. In the late 1980s and early 1990s, the processing equipment used in mass production fields such as car engines were mainly automatic lines and modular machine tools. For example, in the engine production plant of Salzgitter, Volkswagen works in Germany produces four cylinder, five cylinder and six cylinder engines with (1~2.8) liter displacement, including prototypes. Automatic lines account for 60% of the processing equipment, and modular machine tools and machining centers account for 20% respectively. However, in the past few years, many machine tool plants have made full use of the great progress made in tool technology and drive technology. In the early 1990s, high-speed machining and the development of high-speed machining centers have significantly improved the production efficiency of machining centers. At the same time, due to economic globalization and personalized demand, the product variety is increasing day by day, and the flexibility of equipment has become an important factor in choosing processing equipment. Under such technology and market conditions, high-speed machining centers began to enter the field of mass production in the mid-1990s, breaking the monopoly of automatic lines and modular machine tools in these fields

at present, in the processing of cylinder head, cylinder block, gearbox and clutch housing of automobile engine, the flexible production line composed of high-speed machining center has largely replaced the automatic line and high-speed machining center, and has become the main equipment for the processing of automobile engine chassis

machining center and automatic line are two different types of machine tools. Initially, they have different application fields, and there is no competition between them. Technological progress and market changes have promoted the flexibility of automatic lines and processing, which has increased the demand for wood pulp to replace some waste paper imports, and the high-speed development of the center. As a result, the application fields of these two different types of machine tools are close to and overlap with each other, and the contradiction between the two characteristic parameters of productivity and flexibility is gradually disappearing

at present, in the field of medium and mass production, some workpieces can be processed by high-speed machining centers. For some workpiece processing that requires complex cutting tools and machine tools, more and more are turning to modular production systems. In such production systems, machining centers, automatic lines and modular machine tools can be integrated according to specific machining tasks, so as to make full use of the respective advantages of automatic lines and machining centers

at present, in the processing of cylinder head, cylinder block, gearbox and clutch housing of automobile engine, the flexible production line composed of high-speed machining center has largely replaced the automatic line and high-speed machining center, and has become the main equipment for the processing of automobile engine chassis

machining center and automatic line are two different types of machine tools. Initially, they have different application fields, and there is no competition between them. Technological progress and market changes have promoted the flexibility of automatic lines and the high-speed development of machining centers. As a result, the application fields of these two different types of machine tools are close to and overlap with each other, and the contradiction between the two characteristic parameters of productivity and flexibility is gradually disappearing

at present, in the field of medium and mass production, some workpieces can be processed by high-speed machining centers. For some workpiece processing that requires complex cutting tools and machine tools, more and more are turning to modular production systems. In such production systems, machining centers, automatic lines and modular machine tools can be integrated according to specific machining tasks, so as to make full use of the respective advantages of automatic lines and machining centers

flexibility and characteristics of automatic line

in order to adapt to the production of increasing varieties, in the late 1970s and early 1980s, many modular machine tool manufacturers successively developed various types of NC machining modules for flexible automatic line by using NC technology. These processing modules have single coordinate, double coordinate and three coordinate modules according to the number of their motion coordinates; According to the number of spindles, there are single spindle and multi spindle modules (turret multi spindle processing module). Because these modules are numerically controlled, when the flexible automatic line changes from processing one kind of workpiece in the variant varieties to processing another kind of workpiece, it can realize automatic tool change, automatic replacement of multiple axle boxes, automatic change of processing stroke, automatic change of working cycle, cutting amount and processing position by changing the numerical control program, so as to adapt to the variant variety processing

Figure 1 shows a flexible automatic line for processing eight kinds of gearboxes of heavy-duty trucks. The line adopts four two coordinate NC milling modules, six CNC turret multi axis machining modules and six column mobile three coordinate machining modules. The auxiliary stations include cleaning station and clamping workstation operated by robots. When the processing of one workpiece is converted to the processing of another workpiece, it is only necessary to call the NC program, tools and processing parameters of the workpiece to be processed through the code on the fixture and showing the determination of covestro to continue its investment in the Chinese market, without manual adjustment of machinery and other aspects

Figure 1: flexible automatic line for processing gearbox

(German Chemnitz Machinery Research Institute)

flexible automatic line, like rigid automatic line, is also a rigid connected multi station automatic processing equipment. The variants processed by flexible automatic line must be highly similar in the geometric shape and processing technology of workpieces, and these workpieces should be determined in the design of automatic line, because the detection of steel plates shows this, The flexibility of flexible automatic line is still limited. Due to the complementary relationship between all processing stations on the flexible automatic line, when a machine tool on the automatic line fails, the whole line will be stopped, resulting in a decline in the utilization rate of equipment. Even in the best case, the utilization rate of the automatic line is only 70%

at present, for example, in the automotive industry, the cylinder block, cylinder head and gearbox of engines are not only of many varieties, but also tend to be replaced by new products in about 6 years, which requires that the processing equipment not only adapt to the processing of the determined variant varieties, but also adapt to the processing of the workpiece that has not been determined and needs to be developed in the future. Obviously, the flexible automatic line is difficult to meet such requirements because of its structural characteristics

high speed of machining center

in the early 1980s, the maximum speed of the spindle of the machining center was only 4000r/min, and the maximum speed of the spindle movement was about 20 m/min. However, in the following (7-8) years, due to the great progress of drive, spindle bearing and control technology, high-speed machining center came out. At present, the spindle speed of high-speed machining centers has generally reached (15000 ~ 24000) r/min, the shaft acceleration has reached (1 ~ 2) g, the shaft moving speed has reached (80 ~ 120) m/min, and the interval between two cuts (chip to chip time) has reached (2.6 ~ 4.6) seconds. In this way, this kind of machining center can use high-efficiency tools to process efficiently with high cutting speed and feed speed, which greatly shortens the basic time. For example, the processing time of rough boring the cylinder hole of grey cast iron cylinder block with a diameter of 86mm and a depth of 135mm is only 1.8 seconds (the feed speed is 4500mm/min); Drill and mill M16 on aluminum alloy clutch housing × It takes only 1.2 seconds for a threaded hole with a depth of 1.5 and 22mm

due to the increase of axis acceleration and moving speed of high-speed machining center, the auxiliary time is also shortened. However, for most machining tasks, the proportion of auxiliary time in the processing process time can reach (50 ~ 70)%, Such a high proportion of auxiliary time is mainly generated by the tool change process [the tool exits the processing position - the spindle stops at the specified angular position - the spindle moves to the tool change position - the tool change (perhaps the automatic inspection of the tool) - the tool magazine moves (directly change the tool) or the manipulator changes the tool - blow out the tool handle - tighten the tool handle - the spindle starts to the working speed - the spindle tool is re cut], Reducing the number of tool changes is an important way to shorten the auxiliary time. Especially in medium and large-scale production, high-speed machining centers can usually adopt multi workpiece fixtures (clamping multiple identical workpieces on polyhedral fixtures), composite tools (centralizing multiple different machining processes on one tool) and multi-functional tools (realizing the machining of multiple processes with one tool) to reduce the number of tool changes, so as to shorten the auxiliary time. The significant shortening of basic time and auxiliary time makes the high-speed machining center reach the high level of modular machine tools and automatic lines in terms of production efficiency, creating conditions for the high-speed machining center to enter the field of mass production

flexible production lines and hybrid production systems

at present, flexible production lines (consisting of high-speed machining centers) and hybrid production systems (consisting of high-speed machining centers and automatic lines) have been widely used in the processing of cylinder blocks, cylinder heads and clutch shells of automotive engines. According to the current technical level, the annual optimal number of processed cylinder heads using hybrid production systems can reach (300 ~ 350) million, The annual optimal number of clutch shells processed by flexible production line is (350 ~ 400) thousand (Fig. 2 and Fig. 3)

Figure 2: comparison of single piece cost of processing clutch housing with flexible production line (xhc241 high speed machining center) and automatic line

(green area indicates that it is appropriate to use high-speed machining center; red area indicates that it is appropriate to use automatic line)

Figure 3: comparison of investment cost between high-speed machining center and automatic line for processing clutch shell

flexible production line is composed of several high-speed machining centers connected by a conveying system that transmits workpieces in a certain direction, and the conveying system often adopts rolling conveyor belt to realize continuous conveying of workpieces, The conveyor belt also plays the role of intermediate storage of workpieces, which is conducive to improving the utilization of machine tools. The high-speed machining centers on the production line are arranged in sequence according to the predetermined production process flow. At least two high-speed machining centers of the same specification and model that can be replaced each other are arranged on each processing unit for parallel processing. In this way, when one machining center fails and stops, the other machining center can still continue processing, so as to avoid the pause of the whole production line. Therefore, the utilization rate of this flexible production line can be as high as (90 ~ 95)%

the modular structure and multiple processing equipment configuration of the flexible production line enable the production line to be built in stages. Because the prediction of the annual sales volume of new products is often not necessarily correct, users of the system that is put into operation for the first time can not rush to make a lot of equipment investment, and in the future, they can also expand the scale of the production line according to the increase of market demand for products (Figure 4), which is undoubtedly conducive to improving the economic benefits of investment. However, the automatic line is on the contrary. When the project is determined, the scale of its equipment and its total investment are determined

Figure 4: hybrid production system for machining cylinder head (ex-cell-o company)

from Figure 4, it can be seen that automatic lines are used to process valve seat, guide hole and camshaft hole, and the machining center is used to process other parts of cylinder head. The number of machining centers can be expanded according to the increase of market demand for products. The high-speed machining centers used are xhc241 of one model and specification. In this way, it is beneficial to improve the economy of use, because these machining centers have similar operation, maintenance and repair,