Sheet metal parts are widely used in industries such as aviation, home appliances, electricity, fire protection, and instrumentation. As an important sheet metal forming method, the quality of the bending process directly affects the final forming quality and appearance of the product. At present, bending mainly adopts manual assistance, which has high labor intensity and low production efficiency. To solve the above problems, it is urgent to improve the automation, informatization, and intelligence level of the process. The replacement of manual labor by robots has become the main development trend of the industry in the future.
Existing production mode
In the bending process of thin plate parts, the traditional manual conveying method is used for loading and unloading the plates. The main problems are: if the workpiece sheet is a large-sized workpiece, the quality of the workpiece will be heavy, and the bending operation of this type of product is difficult to manually operate, requires high physical labor intensity, and has potential safety hazards.
process flow
A complete workflow mainly includes three stages: material retrieval, bending, and stacking, as shown in Figure 1. Firstly, place the boards to be processed and finished products on the placement table, and start the system; Secondly, the robot grabs the material from the loading device and places it in the alignment system; Then the robot grabs the sheet from the centering system, sends it to the Press brake, and the Press brake follows the bending. In multi bending, the robot rotates the arm to send another part to be bent to the Press brake for bending, and the Press brake will follow the bending again. Finally, the robot will grab and feed the bent workpiece into the finished product placement table, and stack it neatly.
System composition and unit design
Combined with the existing space around the CNC Press brake, complete the layout of the functional areas of automatic bending; It is mainly composed of six axis robot, end pickup (robot gripper), feeding device, finished product stacking device, Press brake (existing), turnover frame, plate positioning and centering unit (gravity centering platform), back finger displacement detection unit and electric control system.
Robot selection: Analyze the selected product object, based on factors such as the maximum workpiece sheet thickness, size, and weight, and comprehensively estimate the matching of the robot arm's range of motion and operating range size, the self weight of the gripper, the deviation of the center of gravity after grasping the steel plate, and the attenuation of the effective load at the end of the robot, and select a suitable six axis robot.
Design of end effectors: Based on the size of the workpiece and process requirements (single edge bending, double edge bending, or four edge bending), group and design the structure of the end effectors. The end pickup is mainly composed of a servo drive module, cylinder, and vacuum device. The suction cups are controlled in groups and equipped with a check valve to prevent the leakage of a single suction cup from affecting the adsorption effect of other suction cups.
Requirements for material loading and unloading mechanism: The unloading mechanism requires coarse positioning of the material stack, loading and unloading of materials of different specifications, effective separation when picking up materials by the end effector, and detection when the last piece of material is left on the material stack. Through the photoelectric sensor equipped on the material table, an alarm prompt should be given when there is no material.
Gravity centering platform and flipping system: The gravity centering platform includes a right angle frame, a gravity slide, and a positioning detection device. The material reaches the gravity centering mechanism and makes a brief pause. The material slides down to the right angle frame of the sliding table using the workpiece's own weight on the gravity sliding table, and then confirms the position of the plate through positioning detection sensors for the robot to accurately grasp the material. At the same time, a ball structure is adopted to reduce friction during sliding and avoid scratching the surface of the workpiece. The flip system can achieve the folding of materials on both sides during stacking.
The transformation of the Press brake: First, the communication transformation between the Press brake and the robot was implemented; The second is to reform the rear part of the Press brake. High precision displacement sensor and communication module are used on the rear gear to ensure the accuracy when the Press brake is pressed and bent. Realize full closed-loop automatic sheet metal alignment during the automated bending process.
Selection of suction cups: Due to complex movements such as flipping and following during the bending process, the material is often in a vertical or above position. When selecting suction cups, factors such as lateral friction and material hardness should be fully considered to minimize the deviation of the material from the suction cup and the deformation of the suction cup itself.
Safety protection device: A closed area is formed within the working range of the robot by safety barriers and related equipment. And equipped with a three color light prompt system as an auxiliary tool for the safety system; The master control can stop the machine in time and give an alarm prompt in case of various abnormal conditions such as the start and stop, failure, refueling, loading and unloading, and safety alarm of robots, Press brake and other equipment.