Research on Flexible Manufacturing Technology of Commercial Vehicle Longitudinal Beam
Commercial vehicles have the characteristics of large load, high utilization rate and long average annual mileage. They are an important part of the automobile industry and play a pivotal role in the development of the national automobile economy. As the largest and most critical component in the field of commercial vehicles, the manufacturing level of commercial vehicle beams affects the service life, fuel economy, handling and safety of commercial vehicles.
The traditional longitudinal beam manufacturing mode is mainly based on stamping. The prominent problem is that the mold is frequently replaced during the production process, which causes a lot of production time to be wasted. At the same time, there are also insufficient flexible processing capabilities, long production preparation cycles, high mold investment costs, and longitudinal molds. Liang rebounds serious and other problems. With the intensification of market competition and the application of high-strength panels, customer needs are gradually showing the characteristics of customization, lightweight and individualization. Therefore, the development of flexible stringer manufacturing equipment and technology improves the intelligent level of production lines to meet the needs of large-scale While automating production, it can also take into account the small batch and multi-variety production mode, which has important promotion significance in the field of commercial vehicle chassis manufacturing.
Structural analysis of commercial vehicle longitudinal beams
According to the different capacity of commercial trucks, they can be divided into light, medium and heavy. Their frame structure characteristics are shown in Figure 1.
Light truck type longitudinal beams are mainly variable cross-sections. As shown in Figure 1(a), the sinking of the front section of the frame can greatly reduce the center of gravity of the vehicle, and the installation plane of the front suspension bracket of the cab will be about 10cm lower than that of the through beam. The height of the room above the ground is greatly reduced. The reduction in the height of the front and rear widths of the frame longitudinal beams makes the entire frame closer to the equal-strength beam structure, avoiding unnecessary steel waste in the parts of the front and rear sections of the frame that are less stressed, and it is also an effective measure to reduce weight.
Figure 1 Schematic diagram of commercial vehicle frame and longitudinal beam
Figure 2 Light truck longitudinal beam stamping line of a domestic vehicle manufacturer
The light truck type longitudinal beam has a cross-section width of 160-220mm, a length of 5-7m, and a material thickness of 4-6mm. The current mainstream manufacturing method of this type of stringer is still mainly stamping. As shown in Figure 2, a large press is used to complete the manufacturing process of the stringer with blanking punching dies and profiling dies. In order to meet the market demand of multiple varieties and small batches, large-scale press blanking and punching are gradually replaced by CNC flat punching and plasma cutting, thereby shortening the manufacturing cycle of the stringer and reducing the cost of molds.
Medium and heavy trucks gradually adopt the design idea of constant cross-section longitudinal beams, as shown in Figure 1(b) and Figure 1(c). The cross-sectional width of the longitudinal beam is 220-360mm, the length is 5-12m, and the material thickness is 5-10mm. Some domestic automakers generally adopt the stamping process for production, which facilitates the organization of production and also reduces the investment costs of stamping equipment and molds to a certain extent.
However, with the continuous improvement of vehicle lightweight requirements, the yield strength of longitudinal beam steel plates is also getting higher and higher. The tonnage of ordinary presses can no longer provide sufficient punching and forming pressure, and the purchase of larger tonnage presses will bring Come higher manufacturing costs. In addition, during the stamping and forming process of high-strength steel plates, affected by the performance of the sheet metal, cracks are easily generated in the stamping deformation zone, which seriously affects the product quality.
Stringer flexible manufacturing system
This article takes the longitudinal beam production line of a domestic commercial vehicle manufacturer as an example to discuss the composition of the longitudinal beam flexible manufacturing system. At present, the cross-sectional shape of the longitudinal beams of commercial vehicle chassis is mostly “U”-shaped, with a maximum length of 12000mm, a maximum width of 360mm, a maximum thickness of 12mm, and a yield strength of 350-700MPa.
The flexible manufacturing process of the stringer includes rolling (coil feeding, uncoiling, leveling, head cutting, rolling forming, online inspection, correction, follow-up cutting) → marking → CNC punching → robotic plasma cutting → calibration Straight → shot blasting → beam bending → transport to the storage area. In order to improve the level of automation, each process equipment is integrated through the logistics on-line system to achieve the goal of less human production.
Flexible roll forming
The first sequence of the production line adopts flexible rolling type gradual forming, which can effectively avoid the problems of springback and deformation and cracking of the sheet during the stamping process. At the same time, the production efficiency is high and the labor intensity is low. The flexible rolling equipment can automatically drive the forming roll by the motor according to the changes of the longitudinal beam product parameters (such as material thickness, length, cross-sectional size, etc.) to adjust the corresponding parameters of the equipment without changing the roll. Before the new specifications of the longitudinal beams are put into production, there is no need to prepare additional molds, which shortens the production preparation cycle and simplifies the product development process. When the normal production parameters change, the adjustment time of the rolling equipment (Figure 3) parameters is less than 5 minutes, which is much shorter than the replacement time of the stamping die.
Figure 3 Flexible rolling equipment
Longitudinal beam three-dimensional punching
The number of holes on the longitudinal beams is generally 200 to 500, distributed on the ventral surface and the wing surface. The level of flexibility of the production line is also reflected in the hole processing. In order to meet the three-dimensional flexible punching of stringers, five main machines and three-sided punching (Figure 4) are used to complete the hole punching process. When the longitudinal beam is on the feed conveyor raceway, the U-shaped opening is downward. The feed direction of the longitudinal beam is the X axis, the reference of the X axis is the front end face of the longitudinal beam wing surface, and the horizontal direction perpendicular to the X axis is the Y axis. The wing surface of the beam can be taken as the Y reference, and the axis perpendicular to the horizontal plane is The Z axis, the Z axis reference is the upper surface of the beam, as shown in Figure 5.
Figure 4 Three-dimensional punching equipment
Figure 5 Schematic diagram of the longitudinal beam coordinate system
The hole position tolerance of the punched parts: the position tolerance of the hole group is ±0.2mm/300mm, the tolerance of the hole center distance is ±0.5mm/12000 mm, and the tolerance of the hole edge distance is ±0.5mm. During the whole punching process, the CNC punching program is automatically switched, and the production efficiency is high.
Another three-dimensional processing technology for longitudinal beam holes is to use numerical control drilling equipment and special fixtures to form a drilling production line. The drilling equipment does not interfere with each other and can meet the needs of simultaneous drilling. Before drilling, you can first assemble the longitudinal beam and the inner reinforcement plate into an assembly. After fixing with a clamp, use the holes on the longitudinal beam as a guide and drill the holes on the inner reinforcement plate. This method can effectively ensure the longitudinal beam It is absolutely consistent with the aperture and position of the two parts of the reinforcing plate.
Robot 3D cutting
The robot plasma cutting is shown in Figure 6, and completes the cutting work of the front and rear ventral surface of the longitudinal beam, the airfoil surface, and the circular holes and special-shaped holes with a diameter greater than 60mm. During the cutting process, the system issues a feeding instruction → automatic transmission system feeding → feeding to the beam head cutting position → automatic pressing → cutting front shape (wing surface, ventral surface or oblong hole) → robot, pressing and grounding mechanism return to the original position → Feed the material to the beam tail cutting position→automatic pressing→cutting the shape of the rear end→releasing and discharging→the next cycle.
Figure 6 Robot plasma cutting
The flatness of the cutting surface should not exceed 1.2mm, the depth of the cut pattern should not exceed 210μm, and the cutting surface should be smooth and free of cutting edges. The size tolerance of cutting parts is ±1mm, and the tolerance of airfoil length cutting size is ±2mm.
The CNC bending production line is a special equipment designed and manufactured for the front width and rear narrow structure of the longitudinal beams of medium trucks and heavy trucks. Compared with the forming by stamping, this equipment solves the problem of flexibility required for production, so that only a small amount is needed. The adjustment can meet the forming needs of different longitudinal beams and inner reinforcing plates, as shown in Figure 7.
Figure 7 CNC bending production line
The production line can realize flexible bending actions of multi-variety, multi-angle longitudinal beams and inner reinforcing plates. There is no need to replace molds during the production process, with high degree of self-adaptation and high production efficiency. During the forming process, the wrinkling generated in the deformed area is significantly better than traditional mold forming, and it is widely used in the domestic commercial vehicle manufacturing field.
Intelligent marking and identification system for production line
In order to track the flow of the longitudinal beams between the various processes, the coding, identification, detection and control system of materials are generally used to realize the automatic collection and identification of logistics information. The marking and identification system is composed of a marking machine and a marking recognition device. It is used to mark and identify materials, and in the process of material circulation, the identification device is used to identify the markings printed on the materials, and the overall control software and each material The memory information of the management unit is compared to ensure accurate information transmission.
The production of the longitudinal beams of this project is mainly composed of flexible roll forming, three-dimensional punching, three-dimensional robotic cutting, CNC bending and other processes. The material management control system uses an intelligent marking machine to code each material from the rolling blanking. Marking and coding include QR code and digital code.
When each workpiece passes through various process equipment, the QR code on the workpiece is identified by the barcode reader installed on the device, and the identified workpiece information is fed back to the material control unit PLC, which not only verifies the workpiece logistics, but also It also tracks the processing process of the workpiece, and realizes real-time monitoring and tracking of the workpiece logistics. If the workpiece has quality problems in the downstream assembly process, the quality of the workpiece processing process can be traced.
Production line logistics control system
In order to fully balance the production cycle of the equipment in the various processes of marking, punching, cutting, and bending, increase the overall processing speed of the production line, and solve the contradiction of uneven work stations, the production line logistics control system (Figure 8) is configured, which is based on the production equipment The priority of the request, the processing capacity of the equipment, and the balanced production are used to schedule the operation plan at the process level and the equipment level. This kind of scheduling is based on limited capacity scheduling, and accurately calculates the start time, completion time, preparation time, queuing time and moving time of the process by considering the interleaving, overlap and parallel operations in production to ensure that it will be appropriate at the right time The materials are sent to the appropriate equipment and the overall productivity is increased by more than 50%.