By Prof. Hong Shenzhang, Plastic Forming Technology and Equipment Research Institute, Shanghai Jiao Tong University

　　A press that uses a mechanical transmission as a working mechanism is called a mechanical press。In forging production, the commonly used mechanical presses are hot die forging crank presses, cutting and punching crank presses。The former is compared with the die forging on the hammer，High forging accuracy，Small processing allowance，The drawing Angle is small，Greatly solved the metal material，Simple operation，Easy to realize mechanization and automation，It is widely used in batch and large quantities of medium and small production;The latter can be selected as a special trimming press or a universal crank press，It is used in combination with die forging to cut edges and punch holes of die forging parts。

　　1.The working principle and structural characteristics of hot die forging crank press

　　In die forging production, hot die forging crank press is referred to as forging press, which is a relatively advanced die forging equipment。It relies on the rotation of the crank, through the crank connecting rod to make the slider for up and down reciprocating movement, using the pressure issued by the slider to produce plastic deformation of the blank to make a certain shape of forging。The motor releases energy through the flywheel, so the pressure of the slider basically belongs to the nature of static pressure, no vibration and noise when working, with the following characteristics

　　(1) The rigidity of the frame and crank connecting rod mechanism is large, and the elastic deformation is small when working。

　　(2) The slider has an elephant-nose structure with additional guidance, thereby increasing the guide length of the slider and improving the guide accuracy。

　　(3) With a wedge table to adjust the closing height of the forging press, it can avoid damage to the crank and connecting rod due to the "stuck" (or stuffy car) of the slider。

　　(4) With automatic charging device

　　Figure 5-2 shows the structure of the hot die forging crank press. The motor drives the crank shaft to rotate through the pulley, pinion, big gear (flywheel) and clutch, and then the slider moves reciprocally in the guide rail of the fuselage through the connecting rod. The upper die is fixed on the slider, and the lower die is fixed on the fuselage workbench。The guide rail ensures that the direction of movement of the slider is accurate, and there will be no horizontal misalignment between the upper and lower molds during work。When the clutch rotates in the electric vehicle, the crank slider mechanism can be moved or stopped。The action of the brake is closely coordinated with that of the clutch。After the clutch is disengaged, the brake works, stopping the crank slider mechanism in a certain position。

　　When working, step on the foot pedal and combine the clutch to produce。

　　Commonly used hot die forging crank presses can be divided into two categories according to the type of working mechanism: connecting rod type and wedge type。

　　The connecting rod type adopts the crank slider mechanism, while the wedge type adopts the wedge transmission mechanism, that is, the up and down movement of the slider is not directly driven by the connecting rod, but the wedge driven by the connecting rod is sliding, so as to achieve the up and down movement of the slider。

　　As shown in Figure 5-3, the mechanism of crank-connecting rod hot die forging crank press is composed of bed, crank connecting rod mechanism, balancer, transmission part, clutch part, control part, lubrication part and upper and lower charging part。

　　(1) The bed large forging press adopts a combined structure, that is, after the fuselage is divided into three sections, four tension bolts are heated and pre-tightened into a whole。The medium and small forging press adopts an integral cast or welded body, with side Windows on both sides of the body to adapt to the needs of the transfer of billets and workpieces。

　　(2) The crank connecting rod mechanism is composed of a crank connecting rod and a slider。The crank adopts eccentric type to ensure sufficient strength and stiffness。The connecting rod is integrated, short and thick with good stiffness。The slide block adopts the elephant trunk type, which is composed of the lower leading rail and the upper additional guide rail, lengthens the guide length, increases the supporting width of the connecting rod and the slide block, and improves the anti-inclination ability of the slide block。At the same time, under the same overturning moment, the lateral misalignment is reduced。The work of the balancer moves with the connecting rod slider at the same time, and the piston rod of the balancing cylinder is connected with the hammer head, and the balance cylinder on both sides can maintain balance when the slider moves due to the effect of air pressure 。

　　(3) Clutch braking part of the clutch and brake are mostly in the form of friction plates。Small forging presses also use band brakes。The clutch and brake are arranged at both ends of the spindle, and the entire motion system is in continuous operation except for the crank connecting rod system, so that a high number of strokes can be obtained。

　　(4) The transmission part is composed of a motor, a small belt wheel, a large belt wheel (flywheel), a drive shaft and the size of the gear。

　　(5) The operation part is mainly by electrical control and pneumatic control of the interlocking action or mechanical interlocking, to achieve the different work requirements of the forging press。

　　(6) The lubrication part is controlled by electrical machinery through the oil pump, oil distributor, pipeline and other parts of the oil system to the guide rail, connecting rod, crank and other lubricating parts of the equipment for oil supply lubrication。

　　(7) Mechanical transmission up and down anticipation device In order to improve the accuracy of forging, forging press is provided with an upper and lower charging mechanism。The top material is pushed down from the top as the slider rises, and the bottom material is pushed out from the bottom net through the CAM and lever system as the slider rises。Because the action is achieved by the mechanical transmission charging device, because the completion of the transmission mode can ensure that the charging stroke is strictly synchronized with the slider stroke, and the forging can be easily removed from the die chamber when the upper and lower die are opened。

　　(8) The work of the workbench is different from other die forging equipment。The forging press uses an adjustable (up and down position) wedge table。As shown in Figure 5-4, when the table needs to be adjusted, simply move the oblique wedge position on the side, and the wedge table can be moved along the inclined surface, thus fine-tuning the closing height of the press。It has a universal press that uses connecting rod to drive connecting rod length comparison, which can improve the stiffness of the working part。In addition, this form of table can also be used to release the overload "boring car" caused by the forging press and the failure of the slider "stuck"。

　　2.Operating rules for hot die forging crank presses

　　Because the hot die forging crank press is prone to clutch no action, brake failure, slider stuck or can not stop to the top dead point, as well as electrical failure and stuffy car faults, the general operation basic requirements are the same as the die forging hammer, but due to the different forms of equipment, the following points need to be done。

　　(1) overload production is not allowed, that is, the maximum deformation force of the forging must be less than the nominal pressure of the forging press to ensure the safe operation of the forging press。

　　(2) When the compressed air pressure is lower than the specified value of the equipment, the equipment is not allowed to start。

　　(3) Check the wear of the friction materials of the clutch and brake regularly according to the regulations。

　　(4) Regularly check whether the minimum allowable clearance between module and guide rail meets the requirements。

　　(5) Whether the safety device of the testing equipment is safe and reliable;Installation and debugging mold pay attention to the workbench can not be lowered to the dead point;In addition, the slider must be in an upward motion position。

　　(6) When the equipment is stopped, the slider must be stopped at the bottom dead point to ensure that the guide rail is not eroded by dust and dirt, and turn off all electrical switches and compressed air。

　　3.Common faults and repair measures of hot die forging crank press (see Table 5-2)