Safety and noise prevention in stamping production are two of the most difficult problems in the stamping industry, and they are also two major problems in occupational safety and health. Generally known as stamping safety technology. Its main task is to take various practical and appropriate methods and technical measures in accordance with the characteristics of stamping production and the needs of all aspects of the whole process of production in the stamping production process, and to eliminate the stamping workers and related personnel. Personal injury, eradication of equipment and mold accidents, reducing noise during the stamping process, and ensuring the safety and health of workers.
I. Review of stamping safety production
In recent years, with the rapid development of various types of electromechanical and home appliance manufacturing industries, especially the emergence and rapid growth of townships and private enterprises, sheet metal stamping process has become one of the leading processes in metal processing and manufacturing. Popularization and expansion. In the switch electrical appliances, instrumentation, hardware appliances, as well as automotive, motorcycle, agricultural machinery, telecommunications and toys, such as stamping work, the products of 40% to 70% of the products are stamping parts. With the development of the economy and the widening of the market, the amount of stamping work is increasing, and the safety of production is often neglected. Stamping accidents, especially personal injury accidents involving broken fingers, occur frequently.
CCTV reporters have conducted a survey on a county-level city in the province that is famous for producing switchgear, and disclosed that the two towns in the city have 5,000 cases per year. Hands and broken fingers should go to the hospital for replantation surgery. The hospitals in the city have gained a wealth of experience due to an average of 14 broken hands and replanted fingers every day. Their superb medical skills are well known in China. Most of the local factories that produce switchgear are private enterprises, attracting migrant workers from all over the country to go to work. Most of them go to work without training or training time. In order to obtain the maximum return with minimum investment, the private enterprise boss purchases old-fashioned or second-hand or even state-owned enterprise scrapped presses at a low price; using a simple open die with no guidance and no safety protection, it is completely stamped by manual feeding. Most of the migrant workers are migrant workers, with poor technical quality, lack of in-depth understanding of the structure and working characteristics of the punching machine and the die, and even know nothing about it. I have worked in the largest instrument factory in China for many years. I have witnessed the broken hand and broken finger accidents in the stamping workshop and the damage of imported molds and imported presses, and even the mold fastening screws and mold misalignment. A major equipment accident that caused the fracture of the imported 630kN pressure machine body.
The damage of the stamping noise to the body and mind of the stamping worker is manifested as a potentially gradual increase in hearing impairment. According to the relevant specifications and industrial hygiene standards, the author has repeatedly measured on site, except for mechanical presses with a tonnage less than 6.3t and a nominal pressure of 63kN or less. Most of the presses have a stamping noise that exceeds the national standard. The allowable value is 85dB (decibel). The instrument industry stamping workshop uses a nominal pressure of 100-1600kN, that is, a 10- to 160-ton mechanical press. The measured noise of the working place is 94-96 dB (decibel), and it is difficult to hear the opposite speech. Since the stamping noise is a comprehensive noise pollution caused by the superposition of mechanical noise, aerodynamic noise, and electromagnetic noise reverberation. In the operation of stamping and stamping equipment, the mechanical load caused by the alternating load of metal plates, rupture deformation and rigid impact and mechanical friction is mainly accompanied by the flow noise generated by the compressed air widely used in the stamping process, and the motor. Electromagnetic noise generated by the load of the electronic control system and the like are simultaneously generated in the stamping production. Therefore, the treatment of stamping noise should start from reducing and controlling the sound source, starting from changing the process, improving the equipment structure, and constructing the sound control work. It involves wide area, difficulty, long cycle, high investment and slow effect. To date, few companies have successfully managed stamping noise and met the standards. Most factories use anti-sound earplugs, earmuffs and anti-sound helmets for the stampers to protect them. Most online stampers are reluctant to wear a variety of soundproofing appliances. In addition to being unaccustomed, wearing them for a long time may cause discomfort and even cause physical discomfort. The use of breaks, rotation stations and other methods to shorten the continuous working time of workers in the noise field is one of the effective protection methods adopted by many factories for a long time.
Working in the noise field for a long time will cause hearing damage and even deafness. According to the international standard ISO recommended industrial noise allowable standard, work 5 days a week, 8 hours a day, the noise (continuous stability) strength does not exceed 85 ~ 90dB. When working in the noise field for less than 8h, the working time is reduced by half and the noise level is allowed to increase by 3 dB. Therefore, adhering to the break and rotation station is a good way to achieve noise protection.
Some large-scale enterprises and factories with a single product variety and production scale exceeding and exceeding the scale of economic production, the stamping workshop (sub-factory) has strict production management rules and regulations, workers have high technical quality, can strictly abide by the safety production regulations and process procedures, and use There are many new types of stamping equipment with good technical performance. The number of multi-station continuous molds and automatic and semi-automatic dies is large, the degree of mechanization of the stamping process is high, and the safety production situation is generally good. These enterprises have relatively stable stamping parts and large output. The number of stampings and even the operators of each press are rarely changed. It is easy to use various safety devices. The workers are very skilled in operation, and there are few misoperations and lags. Operation, security incidents are much less.
Second, the hidden dangers of stamping safety production and elimination measures
The personal injury that occurs during the stamping production process is mostly a finger accident. The die is loaded onto the press and stamped at the rated rate. When the press is punched down, if the operator does not remove the hand, arm, and head from the mold (work) danger zone in time, the crushing and crushing accident will occur when the upper and lower molds are closed. The operator's hand, arm and head extend into the dangerous area of ​​the mold. During the non-stop stamping process, the punch, the feeding, the unloading, the removal of the waste along the edge, the placement of the blank to the appropriate mold position, and the cleaning of the mold are eliminated. There are safety hazards in the residue, the removal of the molded parts from the mold, and the lubrication of the mold.
The fundamental way out for stamping safety production lies in the mechanization and automation of the stamping process. The above safety hazards can be eliminated by automatic or semi-automatic stamping; the protection device is installed on the die structure, and the protection mechanism is installed on the ordinary press machine to eliminate the safety hazard. The following technical measures are recommended for safety protection.
(1) Replace the traditional sequential multi-mode stamping process with multi-station continuous stamping technology, and replace the single-process punch with multi-station continuous die to create conditions for mechanization and automation of the stamping process. Multiple sets of single-process dies are eliminated with a multi-station continuous die. The multi-station continuous die feeding operation is outside the danger zone of the mold, and there is no safety risk when the intermediate semi-finished blank is manually fed into the mold and placed in place.
(2) Design, manufacture and use safe dies. The so-called safety die is to consider in the die structure design that no part of the operator's body can enter the mold danger zone. If the operator's fingers intentionally or unintentionally enter the mold danger zone, they will not press their hands. It is more common to install a protective grille (cover) and a mounting limit post (sleeve) outside the mold danger zone. In addition, during the operation of the mold, the guide post and the guide sleeve of the upper and lower mold bases are not disengaged, and the punch does not fall off the guide plate (discharge plate). The fixed discharge guide type die is commonly called the guide plate die and the guide column die plate elastic pressure guide plate die have good operation safety, and belong to the safety die.
(3) Select the press with the appropriate technical performance according to the needs of the stamping process. Different stamping process operations have different technical requirements for presses. The ordinary mechanical press has two types of C-shaped open type and O-shaped closed type according to the frame structure. Domestic small and medium-sized mechanical presses, with nominal pressures ranging from 40 to 4000 kN, are C-type open frames, including: J11, J12, J21, J23 series and modified J11 open single-column fixed table eccentric presses. J12 open single column movable table eccentric press, J21 open double column fixed table press, J23 open double column tilting press. O-frame presses are large and medium tonnage closed single-point, double-point, four-point presses with a nominal tonnage of 1600 to 30 000 kN. The largest amount of domestic use and the largest domestic holding capacity are small and medium-sized open-type presses, while the closed-type large and medium-sized presses are mainly used for the production of automobile cover parts and the production of large-scale stamping parts for large agricultural machinery, ships and vehicles.
In the small and medium-sized C-type open-type presses, the J11 and J12 series eccentric presses have adjustable slider strokes, which can be selected according to the needs of the working stroke of the slider according to the stamping operation. For example, the blanking of the sheet requires a small working stroke, while the drawing requires a large stroke. The small working stroke makes the distance from the punch to the die small and safe to operate. The J21 and J23 series are crank presses, and the slider stroke is large and not adjustable. The operator must be extra careful. However, the eccentric press main shaft is longitudinally disposed, and the shaft end is concentratedly carried, and the rigidity is poor, and is only suitable for thin plate and small-sized punching. The crankshaft presses are all double-column, the main shaft is transversely placed, and the main shaft between the columns is uniformly distributed, and the rigidity is better than that of the eccentric press. Therefore, the J21 and J23 series presses have a wider range of adaptability.
The C-type frame open type press has large elastic deformation and unevenness. The front opening of the worktable is large and the rear side of the worktable is small. According to the measured average elastic load of the load, it is 10 times of the closed press, about 0.01mm/10kN. Therefore, the open press of the C-frame is not suitable for punching operations such as volume stamping and extrusion.
All domestically produced ordinary presses are not equipped with any personal safety protection devices. However, various special presses are different. For example, all kinds of special precision punching presses for precision punching are mostly NC or CNC automatic hydraulic fine punching machines, with automatic feeding, automatic straightening, automatic thickness measurement and lubrication. system. The precision die is mounted in a closed space with a stamping noise of less than 85dB. The automatic monitoring and protection system will monitor the whole process of the fine punching, and will automatically stop and alarm when the accident occurs. This equipment can also be used for ordinary stamping production and is a safe and ideal stamping equipment. However, the requirements for materials and supporting technologies are high and the cost is high.
(4) Install a safety protection device on the press. When the operator enters the danger zone, the operator can directly protect the personal safety. Since the 1960s, various types of press safety protection devices have been developed in various parts of the country, including mechanical, electronically controlled, inductive, infrared (light) and air curtain.
Mechanical safety protection devices mainly include fence type, lever push type, and rope handle type. The fence type is to install a movable or folding fence cover outside the slider, which is suitable for the single-process open mold without the mold frame. Before the upper mold is punched out from the fence cover, the lower mold cover is placed by the fence cover so that the hand cannot enter the mold working area. The pusher and pull handles use a set of levers mounted on the press at the appropriate position on the operator's wrist to force the operator's arm to be pulled out of the mold danger zone (outside the press table). Such safety protection devices are inconvenient to operate, affect the operation of the line of sight, and strong push-pull arms make it difficult for the operator to adapt, etc., especially to install auxiliary mechanisms on the equipment, the general factory does not allow, and does not have the conditions, so far Very few manufacturers have adopted it.
The electronic control safety protection device mainly includes a multi-contact switch, a two-hand switch, a foot switch cover, a push plate linkage switch, a photoelectric protection device and an inductance control switch. When multi-person operation, multi-contact switch is adopted, only the presser will press the switch, the press will start; use the two-hand switch to make the operating hands leave the mold working area; the foot switch can be installed to prevent accidental pressing of the switch The push-plate linkage switch is provided with a push plate in front of the workbench. The operator's hand must enter the work area and must push the push-pull plate off. The hands are separated from the danger zone, and the push-plate automatically sets the switch on, so that the press can be started. In addition to the push-plate linkage switch, the other electronic control methods are more suitable. It is still widely adopted by most manufacturers, and some have been adopted by the press manufacturer, such as two-hand switch.
It is worth mentioning that the light protection device, commonly known as the photoelectric protection device. It is usually installed on both sides of the press table: one side is equipped with a light projector and the other side is equipped with a receiver. In the danger zone of the workbench, a light layer is formed, and the light is stopped when the hand enters the danger zone and the light is blocked. The effect of such a device is acceptable. It only takes up the two operating surfaces on the left and right sides of the workbench, which causes inconvenience to the operation, higher manufacturing and maintenance costs, and is rarely used so far.
The air curtain type protection device similar to the principle of the light protection device is provided with two rows of holes correspondingly arranged on the front side of the press table, and the compressed air is sprayed from the bottom to the top to form a dense and continuous air curtain, and the receiver in the upper side tube is installed. When the air curtain is disconnected, the switch is cut off by its own weight to stop the press. This kind of device is suitable for large countertops and large-tonnage presses with gas source, and the cost and operation consumption are very large.
Third, the challenges and prospects of stamping safety production
People-oriented, sustainable development, and the concept of scientific development concept, the embodiment of the stamping industry should be implemented in two aspects of safe production and reduction of stamping noise pollution. The factors affecting the safe production of stamping and the control of stamping noise are various. The decisive factor is the technical quality of the staff engaged in stamping, including on-site stamping technicians, stamping workers, adjustment workers, die designers, and workshop managers. The production conditions on site are an important factor, such as the basic technical performance and technical state of stamping equipment, the rationality and advancement of stamping process design, the type and quality of stamping materials, the quality and hardness of die structure and technical functions, and manufacturing quality. Among them, the performance and technical state of the stamping equipment, the advantages and disadvantages of the die structure, and the technical level of the operator are particularly important. The above points are related to all aspects, so ensuring the safety of stamping production and preventing the pollution of stamping noise are manifested in the stamping production and the operation of the stamping machine, but also closely related to the equipment, mold, materials and management, and all parties need to work together. Guaranteed.
(1) The structural defects and safety hazards of domestic small and medium-sized mechanical presses are one of the major challenges facing stamping safety production. Most of the domestic small and medium-sized open-type presses use a rotary key or a pin-type rigid clutch. The slider can only stay at the upper and lower dead points, and can not stop at any point in the middle of the stroke. Once the press clutch is turned on, the slider completes a stroke. If the press starts and closes the clutch, the slider will find an emergency stop when it is in the process of going down. It can only be stopped after the slider is punched, and it can pass the bottom dead center and return to the top dead center to stop. Most accidents occur in the moment when the slider needs to stop at any position before the down stamping and cannot stop. Any safety device installed on such a press cannot be protected during the working stroke of the stamping. The closed presses of the domestic O-frames use electro-pneumatic friction or more advanced flexible clutches to allow the press slider to stop at any position. If the clutch is turned on, the slider starts to press down, and there is an unexpected situation that requires emergency stop. The protection device or the electric control switch issues a command, and the slider can stop at any required position through the inching stroke and the click stroke, eliminating the open type. An inevitable accident on the press.
Changing the small and medium-sized C-shaped open-end press to a flexible clutch-brake and increasing its slider stroke adjustment device will make the structure of the press more complicated, and the cost will increase by about 50%, but it is convenient and convenient to use. Safety, can install a variety of safety protection devices, to achieve the safety of the whole process of stamping, will reduce a lot of hand broken finger accidents, is a great good for the benefit of the stamping workers.
(2) The fracture, deformation and looseness of the screw are a major safety hazard in the assembly, installation, trial mode and long-time stamping of the die. The die assembly, that is, the installation on the punching machine, adopts a tight threaded coupling structure, and the tight threaded joint is clamped by the frictional force generated between the nut and the coupling after the screw (bolt) is moderately tightened. Moderate tightening, so that the screw produces a certain pre-tightening force, it is possible to ensure the friction required for the tight thread connection. The screw is not in place, the pre-tightening force is not enough, and the friction is small. When the shock is shocked for a long time, it will loosen; if the thread is tightened too much, the screw will deform and even break. In the tight threaded coupling assembly, the thread of a certain specification needs to be properly tightened with the rated torque to ensure a proper threaded connection in place. It is not uncommon for the M10 and below screws to be twisted and broken during die repair and assembly; the loosening of the die with the M12 and above screws in use sometimes occurs. It is not uncommon to have a mold accident or equipment accident because the screw is loose. So far, many factories and even some large enterprises' stamping workshops and mold manufacturing factories still use dead wrenches, adjustable wrenches, socket wrenches, even pliers, screwdrivers, etc. in the assembly, repair and installation of the die, completely tightened by hand and experience. Screw. In the installation of the die on the press table, in order to increase the torque, some people put long tubes on the rigid handle to tighten the nuts and screws; due to physical strength, gender, and different ways of tightening the screws, use different wrenches. The tightening torques that can be applied vary widely and are unlikely to meet the requirements for tight threaded connections. Especially when installing the die, if the tightening screws on both sides of the die are different in tightening, they will be misaligned during the punching, which will cause an accident. Therefore, when assembling, adjusting, and installing the die, a torque wrench must be used to tightly control the tightening torque. When the tightening torque is exceeded, the wrench will alarm and automatically slip and no longer apply torque.
(3) Vigorously promote the application of multi-station continuous stamping technology, reform the backward process of traditional sorting multi-die punching of various sheet metal stamping parts; set the feeding mechanism on the multi-station continuous mold to realize semi-automatic or fully automatic stamping. Temporary and difficult to realize multi-station continuous stamping of a complex three-dimensional forming part, when it must be punched by a single process die, should be punched on a press equipped with a safety device. The operator must use a special hand tool to feed a single sheet or process piece into place and out of the mold, and should not directly touch and feed it.
(4) For the new product sample test, batch test and small batch production of multi-type sheet metal stamping parts, it is recommended to use CNC rotary head press (NC and CNC punching center) for punching and die forming, using various simple economics. The die should be protected by reliable safety.
(5) Vigorously promote the application of universal feeding devices of various structural forms. It is recommended that the relevant departments of the industry organize the universal feeding device of the design standard and organize the production into a series of specifications to be introduced to the market. In particular, some commonly used mature structures, such as hook, roller, knives, pinch and friction. The use of a feeding device promotes the mechanization and automation of the stamping process and eliminates many personal injury accidents that should not occur.
(6) In order to prevent the stamping of personal injury accidents and reduce the stamping noise, it is recommended that the press manufacturers and relevant departments of the industry organize the production of NC and CNC hydraulic or mechanical fully automatic multi-functional presses with Chinese characteristics. The machine should be equipped with automatic feeding, straightening system, automatic detection and lubrication system, closed and transparent workbench, automatic adjustment and display system for slider stroke, automatic output and waste cutting system, press and mold protection system, and Run the fault parking alarm system. The press can be continuously stamped with sheet metal strips, strips or coils. It is similar in structure and function to NC and CNC full hydraulic fine punching machines, and is used for mass production of small and medium-sized stamping parts. Although the cost of this press is high, it can ensure the safety of stamping and avoid excessive noise pollution.
This article was published in Metalworking, Thermal Processing, Issue 19, 2009
I. Review of stamping safety production
In recent years, with the rapid development of various types of electromechanical and home appliance manufacturing industries, especially the emergence and rapid growth of townships and private enterprises, sheet metal stamping process has become one of the leading processes in metal processing and manufacturing. Popularization and expansion. In the switch electrical appliances, instrumentation, hardware appliances, as well as automotive, motorcycle, agricultural machinery, telecommunications and toys, such as stamping work, the products of 40% to 70% of the products are stamping parts. With the development of the economy and the widening of the market, the amount of stamping work is increasing, and the safety of production is often neglected. Stamping accidents, especially personal injury accidents involving broken fingers, occur frequently.
CCTV reporters have conducted a survey on a county-level city in the province that is famous for producing switchgear, and disclosed that the two towns in the city have 5,000 cases per year. Hands and broken fingers should go to the hospital for replantation surgery. The hospitals in the city have gained a wealth of experience due to an average of 14 broken hands and replanted fingers every day. Their superb medical skills are well known in China. Most of the local factories that produce switchgear are private enterprises, attracting migrant workers from all over the country to go to work. Most of them go to work without training or training time. In order to obtain the maximum return with minimum investment, the private enterprise boss purchases old-fashioned or second-hand or even state-owned enterprise scrapped presses at a low price; using a simple open die with no guidance and no safety protection, it is completely stamped by manual feeding. Most of the migrant workers are migrant workers, with poor technical quality, lack of in-depth understanding of the structure and working characteristics of the punching machine and the die, and even know nothing about it. I have worked in the largest instrument factory in China for many years. I have witnessed the broken hand and broken finger accidents in the stamping workshop and the damage of imported molds and imported presses, and even the mold fastening screws and mold misalignment. A major equipment accident that caused the fracture of the imported 630kN pressure machine body.
The damage of the stamping noise to the body and mind of the stamping worker is manifested as a potentially gradual increase in hearing impairment. According to the relevant specifications and industrial hygiene standards, the author has repeatedly measured on site, except for mechanical presses with a tonnage less than 6.3t and a nominal pressure of 63kN or less. Most of the presses have a stamping noise that exceeds the national standard. The allowable value is 85dB (decibel). The instrument industry stamping workshop uses a nominal pressure of 100-1600kN, that is, a 10- to 160-ton mechanical press. The measured noise of the working place is 94-96 dB (decibel), and it is difficult to hear the opposite speech. Since the stamping noise is a comprehensive noise pollution caused by the superposition of mechanical noise, aerodynamic noise, and electromagnetic noise reverberation. In the operation of stamping and stamping equipment, the mechanical load caused by the alternating load of metal plates, rupture deformation and rigid impact and mechanical friction is mainly accompanied by the flow noise generated by the compressed air widely used in the stamping process, and the motor. Electromagnetic noise generated by the load of the electronic control system and the like are simultaneously generated in the stamping production. Therefore, the treatment of stamping noise should start from reducing and controlling the sound source, starting from changing the process, improving the equipment structure, and constructing the sound control work. It involves wide area, difficulty, long cycle, high investment and slow effect. To date, few companies have successfully managed stamping noise and met the standards. Most factories use anti-sound earplugs, earmuffs and anti-sound helmets for the stampers to protect them. Most online stampers are reluctant to wear a variety of soundproofing appliances. In addition to being unaccustomed, wearing them for a long time may cause discomfort and even cause physical discomfort. The use of breaks, rotation stations and other methods to shorten the continuous working time of workers in the noise field is one of the effective protection methods adopted by many factories for a long time.
Working in the noise field for a long time will cause hearing damage and even deafness. According to the international standard ISO recommended industrial noise allowable standard, work 5 days a week, 8 hours a day, the noise (continuous stability) strength does not exceed 85 ~ 90dB. When working in the noise field for less than 8h, the working time is reduced by half and the noise level is allowed to increase by 3 dB. Therefore, adhering to the break and rotation station is a good way to achieve noise protection.
Some large-scale enterprises and factories with a single product variety and production scale exceeding and exceeding the scale of economic production, the stamping workshop (sub-factory) has strict production management rules and regulations, workers have high technical quality, can strictly abide by the safety production regulations and process procedures, and use There are many new types of stamping equipment with good technical performance. The number of multi-station continuous molds and automatic and semi-automatic dies is large, the degree of mechanization of the stamping process is high, and the safety production situation is generally good. These enterprises have relatively stable stamping parts and large output. The number of stampings and even the operators of each press are rarely changed. It is easy to use various safety devices. The workers are very skilled in operation, and there are few misoperations and lags. Operation, security incidents are much less.
Second, the hidden dangers of stamping safety production and elimination measures
The personal injury that occurs during the stamping production process is mostly a finger accident. The die is loaded onto the press and stamped at the rated rate. When the press is punched down, if the operator does not remove the hand, arm, and head from the mold (work) danger zone in time, the crushing and crushing accident will occur when the upper and lower molds are closed. The operator's hand, arm and head extend into the dangerous area of ​​the mold. During the non-stop stamping process, the punch, the feeding, the unloading, the removal of the waste along the edge, the placement of the blank to the appropriate mold position, and the cleaning of the mold are eliminated. There are safety hazards in the residue, the removal of the molded parts from the mold, and the lubrication of the mold.
The fundamental way out for stamping safety production lies in the mechanization and automation of the stamping process. The above safety hazards can be eliminated by automatic or semi-automatic stamping; the protection device is installed on the die structure, and the protection mechanism is installed on the ordinary press machine to eliminate the safety hazard. The following technical measures are recommended for safety protection.
(1) Replace the traditional sequential multi-mode stamping process with multi-station continuous stamping technology, and replace the single-process punch with multi-station continuous die to create conditions for mechanization and automation of the stamping process. Multiple sets of single-process dies are eliminated with a multi-station continuous die. The multi-station continuous die feeding operation is outside the danger zone of the mold, and there is no safety risk when the intermediate semi-finished blank is manually fed into the mold and placed in place.
(2) Design, manufacture and use safe dies. The so-called safety die is to consider in the die structure design that no part of the operator's body can enter the mold danger zone. If the operator's fingers intentionally or unintentionally enter the mold danger zone, they will not press their hands. It is more common to install a protective grille (cover) and a mounting limit post (sleeve) outside the mold danger zone. In addition, during the operation of the mold, the guide post and the guide sleeve of the upper and lower mold bases are not disengaged, and the punch does not fall off the guide plate (discharge plate). The fixed discharge guide type die is commonly called the guide plate die and the guide column die plate elastic pressure guide plate die have good operation safety, and belong to the safety die.
(3) Select the press with the appropriate technical performance according to the needs of the stamping process. Different stamping process operations have different technical requirements for presses. The ordinary mechanical press has two types of C-shaped open type and O-shaped closed type according to the frame structure. Domestic small and medium-sized mechanical presses, with nominal pressures ranging from 40 to 4000 kN, are C-type open frames, including: J11, J12, J21, J23 series and modified J11 open single-column fixed table eccentric presses. J12 open single column movable table eccentric press, J21 open double column fixed table press, J23 open double column tilting press. O-frame presses are large and medium tonnage closed single-point, double-point, four-point presses with a nominal tonnage of 1600 to 30 000 kN. The largest amount of domestic use and the largest domestic holding capacity are small and medium-sized open-type presses, while the closed-type large and medium-sized presses are mainly used for the production of automobile cover parts and the production of large-scale stamping parts for large agricultural machinery, ships and vehicles.
In the small and medium-sized C-type open-type presses, the J11 and J12 series eccentric presses have adjustable slider strokes, which can be selected according to the needs of the working stroke of the slider according to the stamping operation. For example, the blanking of the sheet requires a small working stroke, while the drawing requires a large stroke. The small working stroke makes the distance from the punch to the die small and safe to operate. The J21 and J23 series are crank presses, and the slider stroke is large and not adjustable. The operator must be extra careful. However, the eccentric press main shaft is longitudinally disposed, and the shaft end is concentratedly carried, and the rigidity is poor, and is only suitable for thin plate and small-sized punching. The crankshaft presses are all double-column, the main shaft is transversely placed, and the main shaft between the columns is uniformly distributed, and the rigidity is better than that of the eccentric press. Therefore, the J21 and J23 series presses have a wider range of adaptability.
The C-type frame open type press has large elastic deformation and unevenness. The front opening of the worktable is large and the rear side of the worktable is small. According to the measured average elastic load of the load, it is 10 times of the closed press, about 0.01mm/10kN. Therefore, the open press of the C-frame is not suitable for punching operations such as volume stamping and extrusion.
All domestically produced ordinary presses are not equipped with any personal safety protection devices. However, various special presses are different. For example, all kinds of special precision punching presses for precision punching are mostly NC or CNC automatic hydraulic fine punching machines, with automatic feeding, automatic straightening, automatic thickness measurement and lubrication. system. The precision die is mounted in a closed space with a stamping noise of less than 85dB. The automatic monitoring and protection system will monitor the whole process of the fine punching, and will automatically stop and alarm when the accident occurs. This equipment can also be used for ordinary stamping production and is a safe and ideal stamping equipment. However, the requirements for materials and supporting technologies are high and the cost is high.
(4) Install a safety protection device on the press. When the operator enters the danger zone, the operator can directly protect the personal safety. Since the 1960s, various types of press safety protection devices have been developed in various parts of the country, including mechanical, electronically controlled, inductive, infrared (light) and air curtain.
Mechanical safety protection devices mainly include fence type, lever push type, and rope handle type. The fence type is to install a movable or folding fence cover outside the slider, which is suitable for the single-process open mold without the mold frame. Before the upper mold is punched out from the fence cover, the lower mold cover is placed by the fence cover so that the hand cannot enter the mold working area. The pusher and pull handles use a set of levers mounted on the press at the appropriate position on the operator's wrist to force the operator's arm to be pulled out of the mold danger zone (outside the press table). Such safety protection devices are inconvenient to operate, affect the operation of the line of sight, and strong push-pull arms make it difficult for the operator to adapt, etc., especially to install auxiliary mechanisms on the equipment, the general factory does not allow, and does not have the conditions, so far Very few manufacturers have adopted it.
The electronic control safety protection device mainly includes a multi-contact switch, a two-hand switch, a foot switch cover, a push plate linkage switch, a photoelectric protection device and an inductance control switch. When multi-person operation, multi-contact switch is adopted, only the presser will press the switch, the press will start; use the two-hand switch to make the operating hands leave the mold working area; the foot switch can be installed to prevent accidental pressing of the switch The push-plate linkage switch is provided with a push plate in front of the workbench. The operator's hand must enter the work area and must push the push-pull plate off. The hands are separated from the danger zone, and the push-plate automatically sets the switch on, so that the press can be started. In addition to the push-plate linkage switch, the other electronic control methods are more suitable. It is still widely adopted by most manufacturers, and some have been adopted by the press manufacturer, such as two-hand switch.
It is worth mentioning that the light protection device, commonly known as the photoelectric protection device. It is usually installed on both sides of the press table: one side is equipped with a light projector and the other side is equipped with a receiver. In the danger zone of the workbench, a light layer is formed, and the light is stopped when the hand enters the danger zone and the light is blocked. The effect of such a device is acceptable. It only takes up the two operating surfaces on the left and right sides of the workbench, which causes inconvenience to the operation, higher manufacturing and maintenance costs, and is rarely used so far.
The air curtain type protection device similar to the principle of the light protection device is provided with two rows of holes correspondingly arranged on the front side of the press table, and the compressed air is sprayed from the bottom to the top to form a dense and continuous air curtain, and the receiver in the upper side tube is installed. When the air curtain is disconnected, the switch is cut off by its own weight to stop the press. This kind of device is suitable for large countertops and large-tonnage presses with gas source, and the cost and operation consumption are very large.
Third, the challenges and prospects of stamping safety production
People-oriented, sustainable development, and the concept of scientific development concept, the embodiment of the stamping industry should be implemented in two aspects of safe production and reduction of stamping noise pollution. The factors affecting the safe production of stamping and the control of stamping noise are various. The decisive factor is the technical quality of the staff engaged in stamping, including on-site stamping technicians, stamping workers, adjustment workers, die designers, and workshop managers. The production conditions on site are an important factor, such as the basic technical performance and technical state of stamping equipment, the rationality and advancement of stamping process design, the type and quality of stamping materials, the quality and hardness of die structure and technical functions, and manufacturing quality. Among them, the performance and technical state of the stamping equipment, the advantages and disadvantages of the die structure, and the technical level of the operator are particularly important. The above points are related to all aspects, so ensuring the safety of stamping production and preventing the pollution of stamping noise are manifested in the stamping production and the operation of the stamping machine, but also closely related to the equipment, mold, materials and management, and all parties need to work together. Guaranteed.
(1) The structural defects and safety hazards of domestic small and medium-sized mechanical presses are one of the major challenges facing stamping safety production. Most of the domestic small and medium-sized open-type presses use a rotary key or a pin-type rigid clutch. The slider can only stay at the upper and lower dead points, and can not stop at any point in the middle of the stroke. Once the press clutch is turned on, the slider completes a stroke. If the press starts and closes the clutch, the slider will find an emergency stop when it is in the process of going down. It can only be stopped after the slider is punched, and it can pass the bottom dead center and return to the top dead center to stop. Most accidents occur in the moment when the slider needs to stop at any position before the down stamping and cannot stop. Any safety device installed on such a press cannot be protected during the working stroke of the stamping. The closed presses of the domestic O-frames use electro-pneumatic friction or more advanced flexible clutches to allow the press slider to stop at any position. If the clutch is turned on, the slider starts to press down, and there is an unexpected situation that requires emergency stop. The protection device or the electric control switch issues a command, and the slider can stop at any required position through the inching stroke and the click stroke, eliminating the open type. An inevitable accident on the press.
Changing the small and medium-sized C-shaped open-end press to a flexible clutch-brake and increasing its slider stroke adjustment device will make the structure of the press more complicated, and the cost will increase by about 50%, but it is convenient and convenient to use. Safety, can install a variety of safety protection devices, to achieve the safety of the whole process of stamping, will reduce a lot of hand broken finger accidents, is a great good for the benefit of the stamping workers.
(2) The fracture, deformation and looseness of the screw are a major safety hazard in the assembly, installation, trial mode and long-time stamping of the die. The die assembly, that is, the installation on the punching machine, adopts a tight threaded coupling structure, and the tight threaded joint is clamped by the frictional force generated between the nut and the coupling after the screw (bolt) is moderately tightened. Moderate tightening, so that the screw produces a certain pre-tightening force, it is possible to ensure the friction required for the tight thread connection. The screw is not in place, the pre-tightening force is not enough, and the friction is small. When the shock is shocked for a long time, it will loosen; if the thread is tightened too much, the screw will deform and even break. In the tight threaded coupling assembly, the thread of a certain specification needs to be properly tightened with the rated torque to ensure a proper threaded connection in place. It is not uncommon for the M10 and below screws to be twisted and broken during die repair and assembly; the loosening of the die with the M12 and above screws in use sometimes occurs. It is not uncommon to have a mold accident or equipment accident because the screw is loose. So far, many factories and even some large enterprises' stamping workshops and mold manufacturing factories still use dead wrenches, adjustable wrenches, socket wrenches, even pliers, screwdrivers, etc. in the assembly, repair and installation of the die, completely tightened by hand and experience. Screw. In the installation of the die on the press table, in order to increase the torque, some people put long tubes on the rigid handle to tighten the nuts and screws; due to physical strength, gender, and different ways of tightening the screws, use different wrenches. The tightening torques that can be applied vary widely and are unlikely to meet the requirements for tight threaded connections. Especially when installing the die, if the tightening screws on both sides of the die are different in tightening, they will be misaligned during the punching, which will cause an accident. Therefore, when assembling, adjusting, and installing the die, a torque wrench must be used to tightly control the tightening torque. When the tightening torque is exceeded, the wrench will alarm and automatically slip and no longer apply torque.
(3) Vigorously promote the application of multi-station continuous stamping technology, reform the backward process of traditional sorting multi-die punching of various sheet metal stamping parts; set the feeding mechanism on the multi-station continuous mold to realize semi-automatic or fully automatic stamping. Temporary and difficult to realize multi-station continuous stamping of a complex three-dimensional forming part, when it must be punched by a single process die, should be punched on a press equipped with a safety device. The operator must use a special hand tool to feed a single sheet or process piece into place and out of the mold, and should not directly touch and feed it.
(4) For the new product sample test, batch test and small batch production of multi-type sheet metal stamping parts, it is recommended to use CNC rotary head press (NC and CNC punching center) for punching and die forming, using various simple economics. The die should be protected by reliable safety.
(5) Vigorously promote the application of universal feeding devices of various structural forms. It is recommended that the relevant departments of the industry organize the universal feeding device of the design standard and organize the production into a series of specifications to be introduced to the market. In particular, some commonly used mature structures, such as hook, roller, knives, pinch and friction. The use of a feeding device promotes the mechanization and automation of the stamping process and eliminates many personal injury accidents that should not occur.
(6) In order to prevent the stamping of personal injury accidents and reduce the stamping noise, it is recommended that the press manufacturers and relevant departments of the industry organize the production of NC and CNC hydraulic or mechanical fully automatic multi-functional presses with Chinese characteristics. The machine should be equipped with automatic feeding, straightening system, automatic detection and lubrication system, closed and transparent workbench, automatic adjustment and display system for slider stroke, automatic output and waste cutting system, press and mold protection system, and Run the fault parking alarm system. The press can be continuously stamped with sheet metal strips, strips or coils. It is similar in structure and function to NC and CNC full hydraulic fine punching machines, and is used for mass production of small and medium-sized stamping parts. Although the cost of this press is high, it can ensure the safety of stamping and avoid excessive noise pollution.
This article was published in Metalworking, Thermal Processing, Issue 19, 2009
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