With the rapid development of the automotive industry, stamping technology, as the first of the four major automotive manufacturing processes, has also been developed rapidly. The larger the scale of automobile spare parts manufacturing, the more important is low cost and high output. The use of multi-station press greatly improves the efficiency of stamping production. However, due to the complexity of the multi-station press system, the security problems caused by the decentralization of working areas are also more and more worthy of our attention. In order to ensure safety and reliability, it is necessary to put forward higher requirements for the reasonable design of press safety system.
Press manufacturers are demanding higher and higher automation of equipment. Machines and equipment are becoming more and more complex and faster. Therefore, manufacturers are increasingly demanding for the safety of these machines. The safety function of press is widely used in industrial equipment in many developed countries and is required to be enforced. For example, in Europe, there are mandatory safety standards, and only equipment that meets the corresponding safety level can be put into operation. In the United States, high accident compensation is relied on to enforce the safety of equipment. Similarly, with the deepening of people’s understanding of equipment safety in our country, thermostatic element the safety of equipment is also receiving more and more attention.
The purpose of introducing safety control system into multi-station press is to provide a highly reliable means of safety protection, so as to avoid or eliminate the potential unsafe hazards of equipment to the greatest extent, ensure the safety of persons and equipment, and prevent the occurrence of malignant safety accidents. Safety PLC not only monitors the status of equipment in real time during start/stop, process disturbance and normal operation and maintenance, but also responds to the danger of equipment and outputs the correct signal to make the equipment shut down safely. The security controller system can continuously monitor the status of the device input by the original lock.
For example, emergency stop button, safety door switch, safety grating and so on, so as to make corresponding operation to the energy point or main circuit through the output module. Safety of the original device and safety circuit is the necessary condition for the equipment to ensure the corresponding safety level. It must be double-loop connection safety controller to achieve safety input for continuous monitoring. On the surface, ordinary devices can also ensure security under certain conditions, but when these devices are defective, they may lose the function of security protection and cause failure. For the safety control module (safety relay), because of the redundancy and diversity of the structure, as well as the use of self-monitoring, reliable electrical components, feedback loop and other safety measures, it can not only ensure the defect or external fault conditions, but also ensure the safety function, and timely fault detection. Thus, the normal operation of the whole control system is guaranteed to the greatest extent, and the safety of personnel and equipment is protected. At present, the most commonly used safety devices are safety PLC and safety relay. This kind of original device does not refer to the original without fault, but makes regular action when the fault occurs.
According to the industrial safety standards, safety devices must be controlled by double loops. Even if a line fails, it can still ensure that the equipment can run under unsatisfactory conditions or stop immediately and controllably. For a long time, the common relay may cause contact adhesion. Through safety relay and safety circuit, we can complement the abnormal defects to achieve the function of correct and low-error action. In other words, the lower the error and failure value, the higher the safety factor. Therefore, we need to design safety control systems with different functions to protect different levels of machinery. Multi-station press is widely used by automotive parts suppliers because of its high output rate and high reliability. The core device of the equipment consists of several working areas, such as uncoiling unit, feeding mechanism, press and feeding conveying part. Each area has two safety lifting doors or safety switches and a number of emergency stop buttons, and the periphery also needs a safety grating to protect the area of mode change and feeding. In addition, there are a large number of safety signals in the multi-station press, such as slider locking, two-hand control, press mode, clutch status, etc.
which need to be used as safety input to connect the safety control system of the press. Complex logic relationship runs through the whole safety control loop. According to the particularity of safety requirement of multi-station press, programmable safety relay and safety bus system are the most suitable solutions. Safety relay can be programmed logically by PC for input and output signals. Distributed security modules and security input signals scattered in the field can be centralized to the main station through the security bus for logical operation. Programmable safety relay is also called safety PLC. At present, PILZ brand is widely used. It consists of processing unit, output unit and bus unit. It has certain programmability. At the same time, it is very convenient to expand in the form of functional modules. The advantage of the safety relay is that the programmable safety relay’s safety circuit can be easily generated on the personal computer by using the graphic configuration tool. The program can be written directly to the programmable safety relay through the Ethernet communication interface on the function module. This complete loop can sense potential dangers and take necessary measures to reduce them. Safety relays are connected in series by two loops.
When the emergency stop is lifted, the machine can not be restarted abruptly. It needs the operator to confirm and reset the device before restarting it.
At the same time, if the safety circuit fails, the power supply and other energy input must be cut off immediately. Safety relays conforming to EN954-1 standard have mandatory guidance to prevent both normally open and normally closed contacts from working at the same time during contact cladding, which enables the safety relay itself to detect contact cladding and short circuit. Double contacts are used for all safety components in the safety circuit of multi-station press line. The safety controller should be synchronized when the components are in action. If the time difference between the two contacts is more than 500 ms, the system should prompt the alarm and can not start the equipment. On the contrary, the device can be started after the self-check of the safety circuit is completed, which can be confirmed by the operator. From another point of view, redundant input and strict time difference comparison can effectively avoid the possibility of starting and stopping equipment caused by signal disturbance. Moreover, programmable safety relay can monitor power, current, voltage, ground fault and phase sequence, which can ensure faster trial operation, minimum space, the highest safety level, excellent cost performance, and low storage cost of general power supply. Any automatic protection system should try its best to achieve the reliability and integrity of safety functions. In the design stage of equipment, it is necessary to realize that the higher the danger level, the higher the safety reliability and integrity required. According to international standards, this degree of integrity is defined as the “safety integrity level” (SIL). International standards EN954-1 and ISO13849 specify four levels of security integrity, four levels represent the highest level of integrity, and one level represents the lowest level of integrity. For each level of safety and integrity, design specifications are provided to reduce design errors. In many industrial fields, it is equally important to avoid the wrong stopping of the operation process. Therefore, the security system must be able to provide a high degree of security integrity and availability. If the operation process of multi-station press is well designed, there will be no danger. In order to improve the safety and reliability in use, the safety components must be checked regularly.
During regular inspection, the whole process test can be carried out for emergency stop, safety door switch, two-hand button, etc. Many faults can be detected by testing.
Safety performance of equipment is indispensable. Safety electrical components have gradually become a mature product. This paper introduces the composition of safety control system of multi-station press and the requirement of safety components. By using safety PLC and safety relay, the safety control system of multi-station press is established, which meets the safety needs of production and maintenance of multi-station press. The purpose of safety design is to minimize or eliminate dangerous points through necessary safety protection planning and appropriate technical choices. In order to avoid the subsidiary cost, improve the availability of the machine, and minimize the downtime, improve the safety of production. With people’s deep understanding of safety concept, it is believed that safety control will be more widely used in future industrial production.