Stamping accuracy analysis of the hottest ordinary

Analysis of stamping accuracy of ordinary all steel stamping die (III)

3. Systematic error

the error caused by the stamping die feeding, blocking and positioning system in the stamping process is the systematic error. It makes the punching error fluctuate within a certain range according to the different feeding methods and feeding devices, the different stopping and feeding distance and position, and the different structure of the positioning device. If the blanking and positioning system of the die is designed and matched properly, the excessive feeding error caused by poor feeding mode or improper selection of feeding device can be reduced

the material fed into the die generally depends on the stopper pin or side edge stopper to stop the material and limit. Composite blanking dies, integrated composite dies and single stamping dies often use cylindrical heads or hook heads to fix the retaining pins, and single station composite dies also use movable retaining pins. The multi station continuous die uses the initial (temporary) stop pin and is matched with the fixed stop pin, side blade and guide pin to limit the feeding. When the molding material touches the stopper pin, it stops feeding and reversely retreats to form a gap with the stopper surface of the stopper pin. The size of this gap is related to the pushing (pulling) force of feeding. If the feeding force is large, the gap will be larger, but no matter the size of this gap, there will be a negative difference of 0.5mm in the feeding feed distance. The error will be larger if the movable retaining pin and the initial (temporary) retaining pin are used. If overlapping edge layout is adopted, the overlapping width can compensate the feeding error, so it has no effect on the punching accuracy of single die and single station composite die. However, for the shape and position accuracy of stamping parts of multi station continuous die and multi station continuous composite die, especially the inner hole (inner shape) has the most obvious influence on the coaxiality of the outer contour. In order to reduce this coaxiality deviation, a guide pin is usually installed on the end face of the blanking punch or a process guide positioning hole is set on the lap edge. Because the station layout of multi station continuous die is punching first and then blanking or forming, the guide pin is inserted into the punched hole shape in the subsequent station of punching first and then punched. For the medium hard steel plate with the material thickness of T 1 ~ 4mm, the guide pin can reduce the feeding error to 0.04 ~ 0.20mm, and the T value is large, and the error is also large

4. Accidental error

some unexpected or sudden situations in the stamping process make the stamping parts produce new errors, which further reduce the precision of the stamping parts from time to time, and it is difficult to prevent. This kind of accidental error is often caused by occasional mistakes in operation, local and macroscopic defects of materials, sudden loosening or damage of mold parts, accidental failure of stamping equipment, and interference and impact of accidental events in the workplace, resulting in the increase of stamping error

the use of various types of compound die stamping has high technical requirements for the operator. The size and surface quality of raw materials and blanks must be inspected before stamping. It is not uncommon to have strip thickness differences and out of tolerance caused by the same plate difference. Strip size out of tolerance and burrs are too large, and there are scratches, bumps, bumps, and rust scabs on the surface. Once missed inspection and not eliminated in time, the stamping accuracy will inevitably be reduced. Lubrication is particularly important in compound die stamping. Excessive, uneven or missing coating of lubricant on materials and dies can cause fluctuations in the dimensional error of stamping parts. As for the overlapping punching of thin materials, the pressing injury of punching parts and the joint operation command system are the top priorities. "Bumping, uneven feeding force will punch the edge into the blade or die cavity, and the punching parts will press the punching parts without leaving the die or the working face of the die. These operational errors can be reduced as long as the operation is careful

up to now, the two ends of the tightening sample should be processed as smoothly as possible. So far, dead wrenches, loose wrenches, socket wrenches and screwdrivers are mostly used in domestic assembly and repair of stamping dies, but it is difficult to achieve the reasonable pre tightening force required for screw connection. Tight thread connection is the main component connection type of stamping die. For dies that are subjected to high-speed, high-pressure, strong vibration and continuous severe alternating dynamic loads, loosening of threads in work is fatal! The tightening torque of the screw is not enough, and the screw of the die will loosen due to vibration after long-term operation; Too much tightening torque will deform, stretch or even break the screw. Due to the differences of workers' gender and physical strength, different people with the same thread have different tightening degrees, and the appropriate tightening torque is certain. It is not uncommon to cause die damage or even equipment accidents due to loose or broken screws on the die. Therefore, torque wrench should be used to tighten the screws on the die for assembly or repair of the die to ensure the reliability of tight thread connection. Due to improper tightening of screws, the split edge is loose and staggered in the stamping process, the insert is loose, the die handle is loose and rotates, the unloading plate falls off, and the pressing plate for fixing the stamping die is moved or loosened, which not only changes the stamping size, but also can cause accidents

single station composite punching green flame retardant nylon is increasingly valued by the market. When using compressed air to blow off the punching parts or using a special unloading device to unload the parts, it must be ensured that the time for the punching parts to unload from the working surface of the punching die is less than 50% of the reciprocating stroke time of the slider of the punching machine before continuous automatic punching can be carried out. There are punching dies with process working stations such as deep drawing, bending and punching, thinning and deep drawing, And it is not suitable to make the number of slide stroke n 120 times/min. Otherwise, due to the time lag between the punching part being pushed out of the die cavity and leaving the working face of the die, it is often too late to push the punching part out of the die, resulting in friendly man-machine interface, crushing, bumping and even damage

when stamping with multi station continuous compound die, the error between the tail of the strip and the joint and the width of the strip is large, resulting in feed deflection, the height of the stopper pin is too small, as well as the activity of the hook stopper pin, the retention of foreign matters in the die cavity, and the dirt and rust are not eliminated in time, which will increase the stamping error. Equipment factors affecting the precision of sheet metal blanking parts

1. The impact of the dynamic accuracy of the open press on the blanking accuracy of the blanking die

the structural design of the die should fully consider the structural type, technical state and dynamic accuracy of the matching press. For punching small and medium-sized sheet metal stamping parts, domestic open presses with nominal pressure PG 2500kN are mostly used in China, including:

(1) j11, j12 series and their modified and improved design of open single column fixed table and movable table presses. Its nominal pressure PG 2500kN

(2) J21 series and its modified and improved design of open double column fixed table press. Its nominal pressure is PG 2500kN. Recently, large tonnage of PG 4000kn has been produced in China, but it is not used much

(3) J23 series and its modified and improved design of open double column tilting press. Its nominal pressure is mostly PG 1000KN

according to the industrial standard jb/t "accuracy of open press", the factory accuracy of open press with nominal pressure PG 2500kN must meet the specified test items and tolerances. Many factories have used domestic open presses for stamping small and medium-sized stamping parts for many years, and extended service is quite common. Its static accuracy is far lower than that of equivalent items, and the measured errors exceed the table tolerance. The ex factory accuracy has long been lost, and the dynamic accuracy after actual operation and bearing is lower. Because domestic open press adopts C-frame, its accuracy is far inferior to that of O-frame closed press. According to the actual measurement, the average elastic deformation of the C-shaped frame after bearing is 0.01mm/10kn, which is 10 times that of the O-shaped frame, and it is uneven; The opening of the C-shaped frame is large at the front and small at the back of the workbench. The dynamic accuracy of the open press will be seriously deteriorated when heavy blanking force is used to blanking medium and heavy plates. Measured under normal production conditions, the dynamic accuracy of the domestic open press, which is reflected in the displacement deviation on the cutting edge of the blanking die, can reach about 0.1 ~ 0.15mm. For example, the unilateral blanking gap C of the stamping die is usually taken as c=5%t according to the common blanking parts of instrument products, so the above displacement deviation is equal to the blanking gap of the blanking die of the blanking part with a material thickness of 2 ~ 3mm, that is, t=2mm, c=5%t=0.1mm; t-3mm； C=5%t=0.15mm, therefore, when punching a blanking part with t ＜ 3mm on an open press with an unguided open blanking die, whether it is punching, blanking, or notching, notching, the edge of the die may collide and gnaw, at least uneven wear will occur, reducing the service life of the die. When t ＞ 3mm, although punching is barely possible, the operation is very dangerous