The multi-station press is a special, automatic, CNC mechanical press used to stretch and form parts that cannot be stretched at one time or parts with complex shapes. It is especially suitable for the forming of complex and difficult-to-form parts that cannot be drawn at one time.
1 The development process of the multi-station press
1.1 The development of multi-station presses
Multi-station presses are mainly developed rapidly in developed countries such as the United States, Germany, Japan, Italy, and the United Kingdom.Among them, the American Baird company has a history of more than 170 years, and the German Schuler company exhibited the world’s first multi-station press at the Paris World Expo in 1900. In 1900, it began to produce small multi-station presses with a maximum tonnage of 32,000kN CNC multi-link multi-station press; Japan’s Asahi Seiki Industry Co., Ltd. introduced the multi-station press technology of Baird Company in the United States in 1964, and the British Baxter Company has produced multi-station presses for 60 years; Italy BMV Company Production of transfer presses since 1972; Hitachi Shipbuilding Corporation manufactured Japan’s first three-way transmission type 12000kN multi-link multi-station press in 1973, and its multi-station presses range from 5000kN to 60,000kN; Germany WEINGARTEN (WEINGARTEN) multi-station press size There are all specifications, and the large ones can reach 80000kN; the multi-station presses of Komatsu Corporation of Japan are as small as 2000kN and as large as 48000kN; companies such as German Wanjiaton, American VERSON (VERSON), and Danly (DANLY) are also the world’s largest manufacturers of multi-station presses. A well-known company for station presses.
The development of multi-station presses in China is relatively late, and the development speed is slow.
In August 1976, Jinan No. 2 Machine Tool Factory successfully trial-produced the first Z81-250 multi-station automatic press in China. The maximum station press has reached 50,000kN, and 16,000-32,000kN multi-link multi-station presses have been produced at present.In the early 1990s, Jinan Foundry and Forging Machinery Research successfully developed the J72 series of small and medium-sized multi-station presses;Qier Group cooperated with Hagel Automation GmbH of Germany in 2008 to produce CNC large-scale multi-station presses with a nominal pressure ranging from 10,000kN to 35,000kN, and its 25,000kN and 32,000kN multi-link multi-station presses have already undertaken orders in production. The former Shanghai Forging Machine Tool Factory, the former Yingkou Forging Machine Tool Factory and other enterprises produce multi-station presses. Jiangsu Xuzhou Forging Machine Tool Factory Group Co., Ltd. produces closed two-point 2500kN ~ 16000kN multi-station presses and closed four-point 6000kN ~ 12500kN multi-station presses. At present, more than ten units have been delivered to users, and more than ten units are under production.
1.2 Several development stages of multi-station presses and production lines
(1) 1969-1979. At this stage, the multi-station press production line is mainly composed of: feeding device + multi-station press + workpiece conveying belt. The drawing process is performed by the first station drawing pad installed in the base. This stage is the stage of development and marketing. The basic mechanism of the multi-station press has been established by summarizing, and the two-column and three-column multi-station presses have been designed and manufactured. After the market is promoted, it is well received by users. The maximum tonnage is 2700kN, the feeding stroke is 900-1500mm, and the maximum stroke times is 25min-1.It is suitable for pressing small covering parts such as the outer panel of the automobile bottom beam and the center pillar.
(2) 1980-1984. Its production line is mainly composed of: feeding device + double-action press + turning device + multi-station press + workpiece conveying belt. Features: The press is large-scale, and the double-action press is used, which makes the drawing process of deep-drawing cover parts easy to achieve, and expands the scope of the production line. On the other hand, the application of computer technology such as finite element analysis software has strongly promoted the development of press technology to large-scale, making the design and calculation of large-scale structural parts simpler, faster and more accurate. The stamping parts of the transfer press range from small, medium, large and even very large parts. The combined production line has a capacity of 2000kN double-action press and 2500kN multi-station press; the number of strokes is 14 min-1, the feeding stroke is 210mm, and the mold change time is 5min. With the development of large-scale presses, automation technology has also developed rapidly, especially the rapid development of quick-change and quick-adjustment technology of the three-coordinate feeding mechanism, which greatly shortens the mold change time. Due to the use of a double-action press, the use of loading and unloading manipulators and the drawing technology of internal and external sliders, the production cost is high, and the workpiece conveying distance is large. 9 pieces/min. At this stage, the feeding mechanism driven by the servo motor has been developed. Since the three-coordinate stroke can be independently adjusted steplessly, the process range has been significantly expanded, that is, the process range of the multi-station press has been extended from automobiles to motors, electrical appliances and metal products, thus establishing the Dominance in the field of forging equipment. The capacity of the multi-station press is also polarized. It can be designed and manufactured as small as 200kN and as large as 9000kN, and the mold change time is shortened to 4min..
(3) 1985-1992. Its production line consists of: depalletizing (unmanned feeding trolley) + automatic conveying + multi-station press + palletizing. The first station of the multi-station press is a numerically controlled hydraulic stretching air cushion, which completes the reverse stretching process of the workpiece. Its performance completely replaces the double-action press and reduces the manufacturing cost of the equipment.
(4) Before 2000. A new process (Crossbar) for the vacuum chuck to grab the workpiece is added to the three-coordinate device. The emergence of this technology is conducive to the production of large-scale, complex-shaped and low-rigidity covers. In addition, the Crossbar transfer press can simultaneously punch two parts in one stroke of the slide, increasing production efficiency by 50% to 100%. Another notable feature of this period is the application of microelectronic control technology, computer-aided operation and auxiliary maintenance system, which makes production and maintenance more convenient, and the market preparation time is further shortened. As long as the mold number is input, all relevant parameters can be adjusted automatically. The transmission line is simple and the anti-interference ability is strong. The application of fieldbus and other technologies makes the multi-station press to achieve a high degree of automation.
(5) By 2012, the multi-station press has developed to a higher level. It is usually composed of depalletizer, large press, three-coordinate workpiece conveying system and palletizing station, and some use robots instead of three-coordinate clamps for feeding. At present, the world has been able to produce 95000kN large-scale multi-station presses. Especially the closed multi-link multi-station press developed in recent years has realized one press and one production line, destacking device, heavy material detection, magnetic separation, oiling, three-dimensional feeding (or robot feeding), Finished product output, scrap output, etc., are readily available, representing the highest level of today’s forging machinery.
Schuler’s three-axis transfer system is particularly typical in the case of auxiliary machines for transfer press production lines. The Schuler Group has developed automation technology specifically for press production lines – crossbar manipulators and crossbar robots. The outstanding advantages of a press production line using a crossbar manipulator or a crossbar robot are compact structure and high efficiency. Optimum spacing between presses can be achieved compared to conventional manipulator or robot solutions. Due to the high flexibility of the crossbar manipulator and the crossbar robot, it is also one of the best choices for automating existing transfer press production lines. Figure 2 shows the Schuler triaxial transfer system installed on a Verson transfer press. Figure 3 shows the foreign multi-station press with suction cup end effector. Figure 4 shows the robot end picker for foreign presses.
2 Application of large-scale multi-station presses in the automotive industry
After the mid-1980s, the US General Motors Corporation took the lead in transforming the original single-machine stamping line with a large-scale application of multi-station presses. Leading European and American car manufacturers use large transfer presses and automatic crossbar presses to mass-produce body panels that meet the highest standards of precision and surface quality for contemporary automotive stampings. According to the statistics of the American Precision Forging Association, 70% of the more than 680 stamping lines of the three major automobile companies in the United States are multi-station presses; Japan has 24 multi-station presses in the 35 stamping lines in the United States, accounting for 69% of the total. %; Among the 250 stamping lines in Japan, there are more than 80 multi-station presses, accounting for 32%; after 1985, German BMW, Mercedes-Benz and Volkswagen developed new cars with almost all multi-station presses, and the United States also appeared Some automobile stamping plants that only use multi-station presses, some newly invested and renovated automobile plants and new automobile plants, this trend is more obvious. Figure 5 shows the transfer press used by Shanghai Volkswagen. Figure 6 is a multi-station press used by a foreign enterprise.
Large-scale multi-station presses used to be unique to industrialized countries. From the end of the 20th century to the beginning of the 21st century, my country has also developed and successfully developed multi-station presses. Domestic automobile enterprises have also successively used multi-station presses. In 2007, Jinan No. 2 Machine Tool Group Co., Ltd. provided Chery Automobile with a 25000kN large-scale multi-station mechanical press, and Chery became the first domestic enterprise to use a domestic large-scale multi-station press production line. At present, many enterprises have been equipped with multi-station press production lines, such as the 25,000kN multi-station press production line of Dongfeng Motor Corporation, the 31,000kN multi-station press production line of Dongfeng Die Stamping Technology Co., Ltd., and the 25,000kN and 32,000kN closed Type four-point multi-station press automatic stamping production line, Shanghai Internal Combustion Engine Company 12500kN, 25000kN multi-link press production line, Shandong Dongyue multi-link press production line, and multiple multi-station press production lines used by China FAW, etc. .
3 Advantages and specifications of large multi-station presses
The large-scale multi-station press integrates machinery, electronics, automation and detection technology. It is fully automatic, intelligent, and safe to operate. It has low comprehensive cost of stamping parts, high labor productivity, high quality of parts, and no handling bumps between workpieces. It can meet the needs of mass production in the automotive industry. A multi-station press production line is used to replace a stamping line composed of 5-6 presses. Compared with the stamping production volume of the same scale, the most advanced multi-station press can reach 16-25min-1, which is a manual feeding line. 4 to 5 times that of the single-machine connection automated production line. Equipment investment can be reduced by 20% to 40%, energy consumption can be reduced by 50% to 70%, the comprehensive cost of stamping parts can be reduced by 40% to 50%, and a lot of production area and equipment investment can be saved, the number of workers is reduced, and the safety performance is high. Every key part and every work station is equipped with a detection point. If there is a fault, it can be stopped quickly to ensure the safety of personnel and molds to the greatest extent. The tonnage of the multi-station press is determined according to the user’s requirements, showing irregularity, especially the large tonnage such as 93000kN, 80000kN, 73000kN, 63000kN, 59000kN, 50000kN, 46000kN, 42000kN, 40000kN, 32000kN, 30000kN, 27000kN, 2500 12000kN, etc., the multi-station presses below 10000kN show regularity. Therefore, the tonnage of the large multi-station press is determined according to the user’s process requirements.
4 Large-scale multi-station press automatic production line process
4.1 The feeding gripper rule of the multi-station press
The slider of the multi-station press reciprocates up and down, and each stroke completes a stamping process. The movement law of the gripper (three-dimensional): clamp the workpiece → pick up and rise → advance to the next station → lower → release the workpiece → return to the previous station (as shown in Figure 7), complete the feeding action, and enter the next station. One delivery. The movement law of the gripper (two-dimensional): clamp the workpiece → advance to the next station → release the workpiece → return to the previous station, complete the feeding action, and enter the next feeding.
4.2 Classification of multi-station feeding systems Multi-station feeding systems are roughly divided into three categories: mechanical feeding, electronic feeding and combined feeding.
Mechanical feeding is accomplished through a direct connection to the press drive system, and the stamped parts are moved from one station to another. The power output device on the press beam transmits energy from the top of the press to the ground, and a large mechanical cam driven by a follower is installed on the feeding mechanism, and the rotation of the cam drives the mechanical feeding action.
Electronic multi-station feeding is to replace the mechanical power output device with a servo motor. With the help of a gearbox and a transmission shaft, the servo motor is connected to the feeding system and works under the control of a computer. Action coordination is accomplished by electronic signals exchanged between the press and the controller. The trajectory of the electronic feed is completed by a computer program. That is to say, the movement trajectory of the electronic feeding device can either follow the movement trajectory of the mechanical feeding, or it can be programmed according to a specific workpiece in order to optimize its movement trajectory.
Some actions of the combined feeder are done by mechanical systems, while others are done by electronic systems. The structure of its feeding device varies from factory to factory. Although the device is used more in some stamping industries, its use in body shops is limited.
4.3 Multi-station feeding action
There are three types of multi-station feeding actions: Tri-axial feeding, Crossbar feeding and Multi-mote feeding.
Plywood feeding method. The splint is hung on the upper part of the mold area, and the suction cup is installed on the splint, and the workpiece is picked up by the suction cup. The splint type feeding device can transfer the workpiece from one station to another by means of electronic multi-station feeding lifting and conveying. When the splint feeding device is used, the feeder does not move at the bottom dead center of the stroke.But two non-contact parts can be transported using suction cups. Multi-mode feeding. Multi-mode (M-ul-ti-mote) three-coordinate and adjusted clamp end effectors are only possible under electronic feeding conditions.
Plywood combined feeding. This kind of feeding is a combination of three-coordinate and splint feeding in one press, so it is called multi-mode feeding. One set of feeding rods is equipped with clamps for the three-coordinate feeding device, and the other set of feeding rods three-coordinate feeding method is to transfer the stamping parts in the press through three different actions. Mechanical clamps mounted on the front and rear of the feed bar transfer the stamped parts between the press stations. The clamping action is that a set of clamps (end pickers) feed the stamped part into the die cavity, and then another set of clamps picks up the stamped part from the die area. The lifting action lifts the stamped part from the die, and the conveying action puts the stamping part into the next die area. The three-coordinate feeding device repeats the above actions in reverse order, the stamping part is put into the mold, and the clamp (end picker) is retracted from the mold. After retracting, the multi-station feeding device returns to the previous die area. At this time, the slider is in the process of descending, and the mold is closed. The three-coordinate feeding device can be either mechanical or electronic. The three-coordinate feeding is divided into a clamp end effector (Fig. 7) and a suction cup end effector (Fig. 8). The cross bar installation is divided into left and right column installation (Figure 9) and front and rear column installation (Figure 10). Choose according to different processes of different users. Configured with a splint-type feeder. Change the mode, the two feeding methods can be interchanged. The computer-controlled motion track, time curve and workpiece program can be modified. Front and rear feed rods are interchangeable.The conversion between the above two methods can be completed in less than 5 minutes.
4.4 New Developments in Feeding Methods
In the past, when press users purchased a multi-station press, they generally had two choices: according to the application, buy a three-coordinate feeding press or a splint feeding press. Due to the huge investment of multi-station presses, users cannot purchase presses of these two methods at the same time. In actual use, for some workpieces, the use of a three-coordinate feeding press is more efficient, while for other workpieces, the use of a splint-type feeding press is more efficient. The multi-mode feeding method solves the single problem of the press process and expands the scope of the process, which is a new development of the feeding method. However, the multi-mode feeding method is not suitable for mechanical feeding, which is caused by the inherent limitations of mechanical feeding.
Another new development in multi-station feeding is real-time orientation adjustment or dynamic orientation adjustment. Stamping plants currently use large clamp-type transfer presses to produce stamped parts that were previously produced on press lines. When processing large stamping parts, it is necessary to adjust the orientation of the stamping parts from one station to the next. In the past, the splint-type multi-station press was equipped with an intermediate station between each station, and the material was placed on the double-station unstacking table. conveyed to the magnetic conveyor. After centering and positioning, the magnetic conveyor belt sends the sheet to the waiting station, and the double-arm multi-station servo feeding system takes the material and sends the sheet to the first press station. After stamping, the workpiece is taken out from the first press station through the double-bar high-speed compact crossbar feeding mechanism, and sent to the next press station together with the second sheet after centering, and this process is repeated to the end a process. Then, the stamping parts completed by the last press station are taken away by the servo crossbar feeding mechanism and placed on the discharge conveying system, slid into the material box, and officially packed by manual inspection.
4.6 Feeding distance and number of stations
The feeding step distance (X axis) of the multi-station press reaches 2300mm, the vertical lifting distance (Y axis) reaches 430mm, and the opening and closing stroke (Z axis) reaches 350mm. The number of stations of the multi-station press is usually 4 to 6 stations, and now it has increased to 20 stations.
4.7 Features of press multi-station automatic feeding production line
①The punch multi-station automatic feeding production line is suitable for the secondary processing of strips, sheets, sheets and semi-finished products of stamping and drawing parts.
- ②The feeding mode adopts three transmission modes according to different product characteristics: pneumatic transmission, servo transmission, and pure mechanical structure transmission.
- ③The internal production of the machine is equipped with an automatic detection system, which ensures the production between the equipment and the mold Safety.
- ④The multi-station flexible mechanical arm combined with the copying manipulator makes the feeding more stable and accurate.
- ⑤It is easy to adjust and have strong interchangeability when used with multi-station molds.
- ⑥With a mobile worktable, it is convenient to replace the mold.
5 Production of auto parts in multi-station presses
Generally speaking, automobile body stamping parts are divided into oversized parts, large parts, medium parts, small and medium parts, and small parts. Among them, there are few oversized parts, the large parts account for nearly 15% of the entire body stamping parts, the medium parts are 30%, the medium and small parts are 55%, and the small parts are very few. Among these parts, 30%~40% of oversized parts can use multi-station, 60%~70% of large parts, and 80% of medium parts. It can be seen that the application of multi-station presses in the automotive industry is very extensive. of. The stamping tonnage required for these parts is relatively large, the oversized parts are more than 2700t~4000t, and the maximum can reach 9300t; the large parts are 1500t~2700t; the medium and small parts are 300t~1250t. In fact, the worktable and station spacing are closely related to the main parameters of the multi-station press, and are also related to the size and material of the processed parts.
6 Development prospects of large-scale multi-station presses in my country
As one of the “four major technological equipments” manufactured by my country’s pillar industry, the automobile industry, CNC large-scale multi-station presses have been included in the 16 A major special project—“High-end CNC machine tools and basic manufacturing equipment” is a key development product of a major national science and technology project. Therefore, large and heavy-duty multi-station presses have high manufacturing technology and high added value, and belong to the national policy encouragement project. The achievements made by Jinan No. 2 Machine Tool and Qiqihar No. 2 Machine Tool in the technology of large-scale multi-station heavy-duty presses will greatly accelerate the pace of localized development of high-end heavy-duty CNC equipment in my country. The rapid development of Xu Ding on medium and small tonnage multi-station presses will contribute to the localization of multi-station presses in China, and will also provide equipment guarantees with world-leading levels for the development of my country’s automobile industry. Domestic forging enterprises have rapidly ranked among the top in the world in the design and manufacture of large-scale CNC stamping automation equipment, and have the strength to widely participate in international competition, which will rapidly change the domestic and foreign market structure of large and heavy stamping equipment. Due to the increase of labor costs, the increase of auxiliary costs such as electricity bills, the fierce market competition, the reduction of profits, and the need for low-carbon economy and energy saving and consumption reduction, the demand for multi-station presses will increase sharply in the future. Its economic benefits are significant and the market prospects are promising.
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