Analysis of common problems and solutions of stamping die&stamping parts

1. Scrap jumping
1) If the length of the punch is not enough, replace the punch according to the cutting edge of the punch to cut into a material thickness of the concave die plus 1mm
2) The gap of the concave die is too large, and the gap can be reduced by cutting in or by using the covering machine
3) The punch or template is not demagnetized. Use demagnetizer to demagnetize the punch or template
2. Scrap plugging
1) The blanking hole is small or offset, and the blanking hole is enlarged to make the blanking smooth
2) The blanking hole has a chamfer. Increase the blanking hole to remove the chamfer
3) The knife edge is not tapered, and the linear cutting taper or the reverse expansion hole reduces the length of the straight wall position
4) The straight wall position of the knife edge is too long, and the reverse side is drilled to shorten the straight wall position of the knife edge
5) The edge is broken, resulting in a large edge, and the material is blocked, and the edge is reground
3. Poor front
1) The edge of the blade is broken, resulting in excessive edge and regrinding the edge
2) The clearance between the punch and the die is too large, the wire is cut into the block, and the clearance is reset
3) Poor finish of concave die blade, polishing the straight wall position of blade
4) The clearance between the punch and the die is too small, so the die is saved again and the clearance is equipped
5) If the jacking force is too large, pull out the draper reversely and change the spring to reduce the jacking force
4. Uneven trimming
1) Positioning offset adjusting positioning
2) One-sided forming, material pulling and pressing force increase, and positioning adjustment
3) Design error, resulting in uneven tool connection, cutting edge insert
4) Feeding is not allowed to adjust the feeder
5) The feeding step calculation is incorrect. Recalculate the step and reset the tool position
5. The punch is easy to break
1) The closing height is too low, and the punch cutting edge is too long. Adjust the closing height
2) Improper material positioning causes the punching punch to cut one side, adjust the positioning or the feeding device to break due to uneven stress
3) The lower die scrap blocks the knife edge, causing the punch to break, and re-drill the large blanking hole to make the blanking smooth
4) The fixed part of the punch (splint) and the guide part are repaired or cut into the block again to make the punch move up and down smoothly (punch)
5) The punch is not well guided, which causes the punch to be forced on one side to re-repair the punch clearance
6) The cutting edge of the punch is too short, and it interferes with the punching plate to change the punch again, increasing the length of the cutting edge
7) The punch is not fixed well, and moves up and down. Fix the punch again so that it cannot move up and down
8) The punch edge is not sharp and regrind the edge
9) The surface of the punch is strained, and the stress is uneven during stripping. Replace the punch again
10) The punch is too thin, too long, and the strength is not enough. Change the punch type again
11) The punch hardness is too high, the punch material is not correct, change the punch material, and adjust the heat treatment hardness
6. Iron filings
1) Rebar dislocation Recalculate the rebar position or bending position
2) The bending clearance is too small, extrude iron filings to readjust the clearance, or grind the forming block, or grind the forming punch
3) Bending punch is too sharp to repair R angle
4) The material of the knife edge is too small. Reconnect the knife edge
5) The pressure bar is too narrow. Grind the pressure bar again
7. Poor sprouting
1) The center of the sprouting bottom hole does not coincide with the center of the sprouting punch to determine the correct center position, or move the position of the sprouting punch, or move it to the position of sprouting - edge high - edge low or even fracture dynamic pre-punching, or adjust the positioning
2) The gap of the die is uneven, resulting in sprouting - high side - low or even broken sprouting gap during repair
3) The sprouting bottom hole does not meet the requirements, resulting in the sprouting height and recalculation of the bottom hole diameter, and the pre-punching increases or reduces the diameter deviation, or even cracks
8. Poor molding
1) The forming die punch is too sharp, which causes the material to crack. The forming punch is trimmed with R angle, and the knife edge is properly trimmed with R angle
2) The length of the forming punch is not enough, resulting in the failure to calculate the correct length of the punch and adjust the actual length of the punch to meet the forming requirements
3) The forming punch is too long and the material at the forming part is deformed. It is very important to determine the correct length of the punch and adjust the actual length of the punch to meet the requirements until the punch breaks
4) The material at the forming part is not enough to cause tensile crack, calculate the expanded material, or repair the R angle, or reduce the forming height
5) Poor positioning, resulting in poor molding adjustment positioning or feeding device
6) The forming gap is too small to cause cracks or deformation
9. Bending dimension
1) The mold is not adjusted in place, resulting in angle error, resulting in size deviation, poor closing height or poor angle difference
2) Insufficient elasticity leads to poor angle, resulting in dimensional deviation. Replace the spring
3) The material does not meet the requirements, resulting in poor angle, resulting in size change of material or re-adjustment of gap deviation
4) The deviation of material thickness causes poor angle, which leads to the size deviation. The material thickness is determined, and the material is changed or the gap difference is readjusted
5) Improper positioning leads to size deviation Adjust the positioning to make the size OK
6) The design or processing error causes the repair welding and grinding between the bent male blocks, eliminates the gap between the blocks, and results in small bending size
7) The forming company has no R angle, and the bending height is too small under the angle and other normal conditions
8) The bending size on both sides is too large for compression reinforcement
9) One-sided bending and drawing cause dimensional instability, increase spring force and adjust positioning
10) The clearance is unreasonable, resulting in poor angle and dimension deviation. Repair the clearance
11) The height of the bending tool is not enough, and the bending punch is too short to close the bending tool, which increases the height of the bending tool, so that the bending punch can close into the position of the bending tool as much as possible, resulting in more bad angle
12) The bending speed is too fast, resulting in deformation of the bending root. Adjust the speed ratio and select a reasonable speed
13) The structure is unreasonable, the folding knife is not inserted into the fixed template, and the groove is milled again. When the folding knife is inserted into the template for stamping, the gap becomes larger
14) The hardness of the formed male heat treatment is not enough, resulting in the collapse of the pressing line or the flattening of the re-formed male pressing line
10. No unloading
1) Improper positioning or feeding Adjust the positioning or feeding device
2) The avoidance is not enough to polish the avoidance
3) The inner guide pillar is strained, which causes poor plate movement. Replace the inner guide pillar
4) The punch is pulled or the surface is not smooth. Replace the punch
5) Reasonably rearrange the position of the ejector pin
6) The jacking force is not enough, or the stripping force is not enough. Replace the jacking spring or stripping spring
7) The punch and splint do not fit smoothly. Repair the splint and splint to make the punch fit smoothly
8) The forming slide block is not smoothly matched. Trim the slide block and guide groove to make it fit smoothly
9) The heat treatment of the plate is not suitable, and the plate is deformed after stamping for a period of time. Grind the plate again to correct the deformation
10) The punch is too long or the length of the ejector pin is not enough. Increase the length of the ejector pin or replace it with a punch with appropriate length
11) The punch is broken and the punch is replaced
12) The template is not magnetized, and the workpiece is brought up to demagnetize the template

11. Unsmooth feeding
1) The mold is not aligned, resulting in that the belt is not in the same line with the feeder and the mold is not aligned with the mold or adjusted feeder
2) Leveling machine or material replacement for uneven belt
3) Non-discharging causes irregular feeding. Refer to non-unloading solutions
4) The positioning is too tight. Adjust the positioning
5) The guide pin is too tight or the straight wall position is too long. Adjust the guide pin
6) The punch is not fixed properly or is too long and interferes with the material belt. Replace the punch with proper length and fix it again
7) The ejector pin is too short, and the belt interferes with the molding block to adjust the length of the ejector pin to avoid interference
8) Improper arrangement of floating block position Adjust the floating block position
12. Poor riveting
1) The closing height of the mold is not correct. The riveting is not in place. Adjust the closing height
2) The workpiece is not placed in place, and the positioning deviation is adjusted
3) Before riveting, if the workpiece is defective, confirm the sprout hole, and refer to the solution for the defect of the sprout hole to confirm whether the riveting hole is chamfered. If there is no chamfer, increase the chamfer
4) The riveting punch is not long enough, and replace it with a punch with appropriate length
5) Confirm that the riveting punch does not meet the requirements and use the riveting punch that meets the requirements
13. Missing or installing
1) Careful wrong punch when assembling carelessly
2) The punch has no direction mark. Mark the punch with direction
14. Install the wrong screw
1) Do not know the thickness of the template. The thickness of the template is too long or too short
2) Not careful and experienced enough to select proper screws
15. Disassembly and assembly of mold
1) If the pin hole is not cleaned, clean the pin hole and pin. When removing the mold, the locating pin should be removed first. If it is easy to damage the mold, the screw should be used to guide it, and then the locating pin hole should be drilled
2) Do not damage the pin hole when the pin is knocked down due to incorrect assembly and disassembly procedures
16. Locating pin
1) When the hole wall is roughened and scratched, resulting in too tight mold assembly, carefully check whether the pin hole is roughened, otherwise the pin hole that cannot be punched out should be reamed again
2) The pin hole is out of position or there is no escape hole below. Add a locating pin escape hole
17. The spring is too long
1) Not paying attention to the depth of the spring hole, measuring the depth of the spring hole, calculating the compression amount of the spring, and selecting again can not be pressed down
2) Not careful enough, not experienced enough, suitable spring bottom dead center
Analysis of common problems of progressive stamping die (II)
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In the stamping production of progressive die, we must make a specific analysis of the bad stamping phenomenon, take effective countermeasures, and fundamentally solve the problems, so as to reduce production costs and achieve smooth production. The following is an analysis of the causes and countermeasures of the common stamping defects in production, for the reference of mold maintenance personnel.
1. Blanking
(1) Cause: A. Blade wear; B. The gap is too large and the effect is not obvious after trimming the blade; C. Blade angle collapse; D. Unreasonable up and down deviation or looseness of clearance; E. Upper and lower dislocation.
(2) Countermeasures: A. Study and repair the cutting edge; B. Control the machining accuracy of the male and female dies or modify the design clearance; C. Study and repair the blade; D. Adjust the blanking clearance to confirm the wear of the template hole or the processing accuracy of the molded part; E. Replace the guide part or reassemble the mold.
2. Chip jumping and crushing
(1) Cause: A. The clearance is too large; B. Improper feeding; C. The pressing oil drops are too fast and sticky; D. The mold is not demagnetized; E. The punch is worn and chips are pressed on the punch; F. The punch is too short and the length inserted into the female die is insufficient; G. The material is hard and the punching shape is simple; H. Emergency measures.
(2) Countermeasures: A. Control the machining accuracy of male and female dies or modify the design clearance; B. Trim the material belt and clean the mold in time when it is sent to the proper position; C. Control the amount of oil dripping of the stamping oil, or change the oil type to reduce the viscosity; D The mold must be demagnetized after research and repair (more attention should be paid to punching iron); E. Study and repair the punch blade; F. Adjust the length of the male die edge into the female die; G. Replace materials and modify design. Insert the punch edge into the end face, install and eject or repair the inclined plane or arc (pay attention to the direction). Reduce the fitting area between the end face of the punch edge and the scrap; H. Reduce the sharpness of the concave die edge, reduce the amount of research on the concave die edge, increase the surface roughness (coating) of the straight edge of the concave die, and use a vacuum cleaner to absorb waste. Reduce the impact speed and chip jumping.
3. Chip blocking
(1) Cause: A. The leakage hole is too small; B. The leakage hole is too large, and the scraps roll; C. The blade is worn and the rough edge is large; D. The pressing oil drops are too fast and sticky; E. The surface of the straight edge of the die is rough, and the powder chips are sintered and attached to the edge; F. The material is soft; G. Emergency measures.
(2) Countermeasures: A. Modify the leakage hole; B. Modify the leakage hole; C. Blade trimming edge; D. Control the amount of oil dripping and change the oil type; E. Surface treatment, polishing and attention shall be paid to reducing surface roughness during processing; Change the material, F. Modify the blanking clearance; G. Trim the slope or arc (pay attention to the direction) on the end face of the punch edge, use a vacuum cleaner and add air at the blanking hole of the base plate.
4. Deviation size variation of blanking
(1) Cause: A. The tool edge of the male and female die is worn, resulting in burr (the shape is too large, and the inner hole is too small); B. Improper design size and clearance, poor machining accuracy; C. The blanking position punch and die insert are offset and the gap is uneven; D. The guide pin is worn and the pin diameter is insufficient; E. The guide element is worn; F. Improper adjustment of feeding distance, pressing and loosening of feeder; G. Improper adjustment of mold closing height; H. The material pressing position of the stripping insert is worn, and there is no material pressing (strong pressure) function (small punching caused by material pulling and turning); I. The unloading insert is too deeply pressed and the punching is too large; J. Mechanical property variation of stamping materials (unstable strength elongation); K. During punching, the punching force pulls the material and causes dimensional variation.
(2) Countermeasures: A. Study and repair the cutting edge; B. Modify the design and control the machining accuracy; C. Adjust its position accuracy and blanking clearance; D. Replace the guide pin; E. Replace the guide post and guide sleeve; F. Readjust the feeder; G. Readjust the closing height; H. Grind or replace the stripping insert, increase the strong pressure function, and adjust the pressing; I. Reduce the depth of strong pressure; J. Replace materials and control the quality of incoming materials; K. Trim the slope or arc (pay attention to the direction) at the end face of the punch edge to improve the stress condition during punching. When permitted, the blanking part is located on the unloading insert and equipped with a guide function.
5. Stuck
(1) Cause: A. The feeding distance, pressing and loosening of the feeder are not adjusted properly; B. The delivery distance changes during production; C. Feeder failure; D. The material is curved, the width is out of tolerance, and the burr is large; E、
Abnormal die stamping and sickle bending; F. The hole diameter of the guide material is insufficient, and the upper die pulls the material; G. Unsmooth material stripping up and down at the bending or tearing position; H. The stripper function of the guide plate is improperly set, and the material belt is attached; I. The material is thin and warped during feeding; J. The mold is improperly erected and has a large deviation from the perpendicularity of the feeder.
(2) Countermeasures: A. readjustment; B. Readjust; C. Adjustment and maintenance; D. Replace materials and control the quality of incoming materials; E. Eliminate the sickle bend of the material belt; F. Study and repair the convex and concave die of the punching guide hole; G. Adjust the force of the stripping spring, etc; H. Modify the material guide and put on the material belt; I. The upper and lower pressing and the upper and lower extruding safety switches are added between the feeder and the mold; J. Erect the mold again.
6. Material belt sickle bending
(1) Cause: A. Stamping burr (especially on the carrier); B. Material burr, no trimming of the mold; C. The depth of the punch is improper (too deep or too shallow); D. The punch is crushed and there are scraps in the mold; E. Local pressing is too deep or local damage is caused by pressing; F. Mold design.
(2) Countermeasures: A. Study and repair the cutting edge; B. Replace the material and add the trimming device to the mold; C. Re-adjust the depth of the punch; D. Clean the mold and solve the problems of chip jumping and crushing; E. Check and adjust the height and size of each stripping and die insert to be correct, and repair the damage position; F. The bending mechanism is used for adjustment.

7. Punch fracture and edge collapse
(1) Cause: A. It is caused by chip jumping, chip material blocking, clamping, etc; B. Improper feeding, cutting half of the material; C. The punch strength is insufficient; D. The big and small punch are too close to each other, and the material is pulled during punching and cutting, causing the small punch to break; E. The part of the punch and female die is too sharp; F. The blanking clearance is too small; G. There is no stamping oil or the used stamping oil is highly volatile; H. The blanking clearance is uneven and offset, and the convex and concave dies interfere; I. The precision of the stripping insert is poor or worn, and the precision guidance function is lost; J. The mold guide is inaccurate and worn; K. Improper selection of materials and hardness of male and female dies; I. The guide part (pin) is worn; M. Improper setting of gasket.
(2) Countermeasures: A. Solve the problems such as chip jumping, chip material blocking and clamping; B. Pay attention to feeding, trim the material belt and clean the mold in time; C. Modify the design, increase the overall strength of the punch, reduce the size of the straight edge of the female die, pay attention to the slope or arc of the end face of the punch edge, and cut the small part back; D. The length of the small punch is shorter than that of the large punch by more than one material thickness; E. Modify the design; F. Control the machining accuracy of the male and female dies or modify the design clearance, and properly increase the punching clearance of the small parts; G. Adjust the amount of oil dripping of stamping oil or change the oil type; H. Check the accuracy of each formed part, and adjust or replace it to control the processing accuracy; I. Research or replacement; J. Replace the guide post and guide sleeve, and pay attention to daily maintenance; K. Change the material and use the appropriate hardness; I. Replace the guide part; M. Correct. The number of shims should be as small as possible, and steel pads should be used. The gasket under the concave mold should be placed under the cushion block.
8. Bending deformation size variation
(1) Cause: A. The guide pin is worn and the pin diameter is insufficient; B. The bending guide element has poor accuracy and is worn; C. Bending punch and die wear (pressure loss); D. The mold is not enough; E. The material slips, the bending convex and concave dies have no guide function, and no pre-pressure is applied during bending; F. Poor mold structure and design size; G. The rough edge of the punched part causes poor bending; H. There are many gaskets added to the convex and concave moulds of the bending part, which causes the size instability; I. Variation of material thickness and size; J. Mechanical shape and energy variation of materials.
(1) Countermeasures: A. Replace the guide pin; B. Grind or replace again; C. Grind or replace again; D. Check and correct; E. Modify the design and add guide and preloading functions; F. Modify the design size, break down the bending, add bending shaping, etc; G. Study and repair the cutting edge of the blanking position; H. Adjust and use integral steel pad; I. Replace materials and control the quality of incoming materials; J. Replace materials and control the quality of incoming materials.
9. Height of stamping parts (when there are more than one the first mock examination)
(2) Cause: A. Rough edge of punched parts; B. The stamping parts are crushed and there are scraps in the mold; C. The convex and concave dies (bending position) are pressed or damaged; D. Turnover during punching and shearing; E. Wear and pressure loss of relevant pressing parts; F. The tear size of the relevant tear position is inconsistent, and the blade is worn; G. The pre-cutting depth of relevant vulnerable parts is inconsistent, and the convex and concave dies are worn or broken; H. The convex and concave dies of the relevant convex parts have broken edges or are seriously worn; I. Defects in mold design.
(2) Countermeasures: A. Study and repair the cutting edge of the blanking position; B. Clean the mold and solve the problem of chips floating; C. Re-research or replace new parts; D. Study and repair the punching knife edge, adjust or add strong pressure function; E. Check, implement maintenance or replacement; F. Repair or replace to ensure the consistent tearing and cutting conditions; G. Check the condition of pre-cutting convex and concave dies, and implement maintenance or replacement; H. Check the condition of male and female dies, and implement maintenance or replacement; I. Modify the design, add height adjustment or add reshaping station.
10. Improper maintenance
(1) Cause: A. The mold has no anti-dazzle function, and the assembly direction and dislocation (referring to different positions) are caused by negligence during mold assembly; B. The inserts that have offset the gap are not restored as they are.
(2) Countermeasures: A. Modify the mold and add the function of prevention against fooling; B. Make marks on the mold, and make necessary inspection and confirmation on the care belt after the mold is assembled, and make written records for easy inquiry.
In the stamping production, the daily maintenance of the die is very important, that is, the daily attention should be paid to check whether the press and die are in normal condition, such as the supply of stamping oil and the refueling of the guide part. The inspection before the mold is put on the machine, the inspection of the blade and the confirmation of the locking of each part can avoid many unexpected accidents. When repairing the mold, we must think first and then act, and carefully record and accumulate experience.
Analysis of common problems of automobile stamping die (III)
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1、 Deformation of flanging and shaping parts
In the process of flanging and shaping, the deformation of the parts often occurs. In the non-surface parts, the quality of the parts will not be greatly affected, but in the surface parts, as long as there is a little deformation, it will bring great quality defects to the appearance and affect the quality of the whole vehicle.
reason:
1. Due to the deformation and flow of the sheet metal during the forming and flanging of the parts, the deformation will occur if the pressing is not tight;
2. When the pressing force is large enough, the above situation will also occur if the pressing surface is uneven and there are gaps in some parts.
resolvent:
Increase the material pressing force. If it is spring material pressing, the method of adding spring can be used. For air cushion material pressing, the method of adding atmospheric cushion force is usually used;
If there is local deformation after increasing the pressure, the red lead can be used to find out the specific problem point and check whether there is local depression on the pressing surface. At this time, the method of welding the pressing plate can be used;
After welding, the press plate shall be matched with the lower surface of the mold.
2、 The blade breaks
In the process of using the die, the broken edge caused by various reasons will have a certain impact on the quality of the parts. It is one of the most common repair contents in mold repair. The repair steps for the broken edge of the blade are as follows:
1. According to the situation of the broken edge, if the broken edge is very small, it is usually necessary to grind the broken edge with a grinder to ensure that the welding is firm and it is not easy to break the edge again;
2. Use the corresponding welding rod for welding. At present, we use D332 welding rod to weld the edge. Before surfacing, the datum plane for repair must be selected, including clearance surface and non-clearance surface;
3. Trim the non-gap surface of the cutting edge (refer to the datum left in advance);
4. Draw a line against the transition piece. If there is no transition piece, rough grind the gap surface with the datum left in advance;
5. The gap surface can be repaired on the upper platform with the aid of clay. Be careful in the process of repair. Start the press as slowly as possible. If necessary, adjust the height of the mold to open it downward to prevent the blade from being damaged;
6. The blade gap should be reasonable. For the steel plate stamping die, the unilateral blade gap should be 1/20 of the sheet thickness. However, in the actual operation process, the size of the gap can be checked by the method of sheet metal test punching, as long as the burr of the workpiece after cutting meets the requirements. In general, the judgment standard of the burr size is that the height of the burr is not greater than 1/10 of the sheet metal thickness;
7. Check whether the clearance surface of the cutting edge is consistent with the shearing direction;
8. After the gap is prepared, use an oilstone to smooth the gap surface of the knife edge to reduce the friction between the plate and the knife edge in production and the resistance of waste falling.
3、 Roughening
The blade breaking and roughening mainly occur in the processes of drawing, forming and flanging.
resolvent:
1. First, find out the corresponding roughening position of the mold by comparing the parts;
2. Push the corresponding position of the mold with an oilstone, and pay attention to the uniform size of the fillet;
3. Use fine abrasive paper to push the mold along the part for polishing, and the abrasive paper is more than 400.
4、 Trimming and punching strip material
The main reason for trimming and punching strip is that the pressing or discharging device of the die is abnormal during trimming or punching.
resolvent:
Find out the corresponding part of the mold according to the part of the part belt;
Check whether there is any abnormality in the die pressure discharge plate;
Repair welding shall be carried out for the corresponding parts of the pressing plate;
The welding repair parts shall be smoothed in combination with the parts, and the specific profile and process parts shall be prepared;
Test punch;
If the inspection is not the problem of the die pressing and unloading plate, you can check whether the tool block of the die is roughened.
5、 Waste cutting
In view of the phenomenon of continuous cutting of waste materials, the main reason is that the operators did not clean up the waste materials in time during the production process, resulting in the accumulation of waste materials, and finally caused the collapse of the waste knife under the pressure of the upper trimming knife block. The repair method is similar to the method of trimming and blade collapse, which will not be introduced in detail here, but only in the repair process
Pay attention to the height of the trimming tool block. If the trimming is too high, it will cause interference between the cutter block and the upper trimming cutter block, thus causing damage to the scrap cutter block again; If the repair is too low, the scrap will be cut continuously, so when repairing the scrap knife, not only the gap surface of the knife block should be considered, but also the height of the knife block is very important. Its repair is more difficult than the simple blade breaking. However, as long as the datum plane is selected before the repair, it can be easily repaired.

6、 Burr
When trimming, punching and blanking, parts are prone to excessive burr. The main reasons for burr are large gap between die edges and small gap between die edges:
When the gap is large: the bright band on the section is small or basically invisible, and the burr is characterized by thick and large, which is difficult to remove;
Small gap: there are two bright bands on the section. Due to the small gap, the burr is characterized by high and thin.
Repair method for large clearance:
1. The trimming and punching process adopts the method of trimming the female die without moving the male die, while the blanking process is based on the female die, that is, the size of the female die remains unchanged, and the male die is trimmed. The above differences are to ensure that the product size is not affected before and after repair;
2. Find out the part with large gap between the die edge and the workpiece;
3. Repair welding of this part with corresponding welding rod (D332) to ensure the hardness of the die edge;
4. Repair the blade gap (the method is the same as the method of blade breaking).
Repair method for small clearance:
1. The specific situation shall be adjusted according to the size of the die gap to ensure the reasonable gap. For trimming and punching dies, the method of placing the gap in the female die shall be adopted, while for blanking dies, the method of enlarging the male die shall be adopted, so as to ensure that the size of parts remains unchanged before and after repair;
2. After repair, measure the perpendicularity of the clearance surface between them, and test whether the blade gap meets the reasonable requirements with a plate.
For the punching die, if the punch or concave die is worn after burring, it can be replaced with corresponding standard parts. If there is no standard part, it can be manufactured by repair welding or mapping. In addition, it is particularly pointed out that for materials with poor welding performance such as alloy steel materials, special treatment shall be carried out before welding, such as preheating, otherwise the mold will crack.
7、 Punching waste blocked
Punching waste blocking is a common type of failure in the punching die. The causes may be as follows: the waste channel is not smooth, the waste channel has an inverted taper, and the waste is not cleaned in time.
reason:
1. The mold is not smooth, and there are processing lines on its surface;
2. The reverse taper of the mold causes the waste channel to be large and small, and the waste is blocked.
Repair method:
As long as side A and side B are smooth and equal in diameter, it can ensure that the waste will not be blocked.
Quality problems and countermeasures of common stamping parts (IV)
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1、 Common defects and cause analysis of blanking parts
Blanking is a stamping process that uses dies to separate sheet metal.
Common defects of blanking parts include burr, surface warpage of parts, and out-of-tolerance dimension.
1. Burr
In the blanking of sheet metal, it is difficult to avoid the burr of different degrees, but the burr can be reduced by improving the processability of the parts and improving the stamping conditions.
The main reasons for burr are as follows:
1.1 Clearance
Too large, too small or uneven blanking clearance can cause burrs. The following factors affect the excessive, small or uneven clearance:
A. Die manufacturing error - the processing of die parts does not conform to the drawing, the parallelism of the base plate is not good, etc;
B. Die assembly error - large gap of guide part, uneven assembly of male and female dies, etc;
C. Poor accuracy of the press - if the clearance of the press guide rail is too large, the parallelism between the bottom surface of the slider and the surface of the workbench is not good, or the perpendicularity between the slider stroke and the surface of the press table is not good, the rigidity of the workbench is poor, and the deflection occurs during blanking, all of which can cause the change of the clearance;
D. Installation error - if the surface of the upper and lower base plates of the die is not cleaned during installation or the fastening method of the upper die of the large die is improper, and the upper and lower dies of the die are not installed concentrically (especially the die without guide pillar), which causes the working part to tilt;
E. The structure of the die is unreasonable - the rigidity of the die and working part is not enough, and the punching force is not balanced;
D. Large camber of steel plate - uneven steel plate.
1.2 Blunt blade
Burrs can be produced when the cutting edge becomes blunt or gnawed.
The factors that affect the blunt edge are:
A. The material and surface treatment of the male and female die of the die are poor, and the wear resistance is poor;
B. The die has poor structure and rigidity, resulting in gnawing;
C. Failure to lubricate in time during operation and fast wear;
D. The blade was not sharpened in time.
1.3 Improper blanking status
If the blank (including the intermediate part) is not in good contact with the punch or the concave die, when the positioning relative height is improper for trimming and punching, the workpiece height will also be lower than the positioning relative height, and the workpiece shape and the edge shape will not conform during the blanking process, resulting in burrs.
1.4 Improper mold structure.
1.5 Material does not conform to process regulations
The material thickness is seriously out of tolerance or the relative clearance is unreasonable due to the wrong material (such as the wrong steel grade), which makes the workpiece burr.
1.6 Poor workmanship of parts
Sharp corners with complex shapes and protruding or concave corners are prone to burr due to excessive wear.
The generation of burr not only makes the deformation process after blanking easy to crack due to stress concentration, but also makes it difficult to layer the blank in the subsequent process. Large burr is easy to scratch the handle; During welding, the two steel plates are not well jointed, easy to be welded through and not firmly welded; During riveting, it is easy to produce riveting gap or cause riveting crack. Therefore, burr beyond the allowable range is extremely harmful. The burrs that have been produced can be eliminated by filing, polishing, electrolysis, chemical treatment and other methods.
2. The parts are warped and uneven
The material shall be stretched and bent at the moment of contact with the punch and die, and then cut and torn. Due to the effects of various forces such as deep drawing, bending and transverse extrusion, the parts exhibit wavy shape in the spreading, and the parts are warped.
The reasons for warpage of parts are as follows:
2.1 Large blanking clearance
If the gap is too large, the tensile and bending forces of the parts are large and easy to warp during blanking. The improvement can be achieved by pressing the punch and pressing plate tightly and keeping the sharp edge during blanking.
2.2 There is a reverse cone at the cavity of the female mold
When the workpiece passes through the small part, the outer circumference will be compressed towards the center, which will cause bending.
2.3 Warpage caused by structural shape of parts
When the shape of the workpiece is complex, the shear force around the workpiece is not uniform, so the force from the periphery to the center is generated, which makes the workpiece warp. The solution is to increase the pressing force.
2.4 Warpage caused by internal stress of material
The internal stress produced by the material during rolling and winding will move to the surface after blanking, and the workpiece will warp. The solution is to use the leveler to level the uncoiler.
2.5 Warpage due to oil, air and poor contact
When there is oil, air and other pressure between the die and parts, parts and parts, parts will warp, especially thin materials and soft materials. However, warpage can be eliminated by evenly oiling and setting vent holes. There are sundries on the surface between the parts and the die, which can easily warp the parts.
Poor contact surface will also cause warpage during blanking.
3. Dimensional accuracy out of tolerance
3.1 The manufacturing of die edge size is out of tolerance
3.2 The springback in the blanking process and the shape of the workpiece in the previous process are inconsistent with the shape of the supporting surface of the working part of the mold in the next process, which causes the workpiece to deform in the blanking process and produce elastic recovery after blanking, thus affecting the dimensional accuracy.
3.3 Poor plate shape.
3.4 Due to the improper adjustment of the previous process or the wear of the fillet, the principle of equal volume during deformation is broken, resulting in the size change after blanking.
3.5 Due to poor positioning during operation or poor design of positioning mechanism, the blank moves during blanking. Or the inaccurate positioning caused by the defects of the shear piece (prismatic degree, missing edge, etc.) can cause the size out-of-tolerance.
3.6 The punching sequence is incorrect.
2、 Common defects and cause analysis of bending parts
Common defects of bent parts include: inconsistent shape and size, bending crack, surface scratch, deflection and distortion, etc.
1. The shape does not conform to the size
The main reason is due to the impact and improper positioning. In addition to taking measures to reduce rebound, it is also important to improve the reliability of blank positioning. The following two measures are usually adopted;
1.1 Pressing blank
Use air cushion, rubber or spring to generate compression force, and compress the sheet before bending. To achieve this goal, the ejection height of the press plate or press bar should be slightly higher than the plane of the female die.
1.2 Reliable positioning method
There are two main forms of blank positioning, one is based on the shape and the other is based on the hole. The shape positioning is easy to operate, but the positioning accuracy is poor. The hole positioning method is not convenient to operate and has a narrow range of use, but the positioning is accurate and reliable. Under certain conditions, sometimes the initial positioning of the shape is used to control the blank within a certain range, and finally the final positioning of the hole position is used to absorb the advantages of both, so that the positioning is accurate and easy to operate.
2. Bending crack
There are many factors affecting crack generation, mainly including the following aspects:
2.1 Poor material plasticity.
2.2 The included angle between the bending curve and the direction of the rolling line of the sheet does not meet the requirements: during the layout, the bending curve should be perpendicular to the direction of the rolling line in the case of one-way V-shaped bending; When bending in both directions, the bending curve should be 45 degrees from the direction of the rolling line.
2.3 The bending radius is too small.
2.4 Poor quality of blank shear and blanking section - burr and crack.
2.5 The radius of the round corner of the male and female dies is worn or the gap is too small - the feed resistance increases.
2.6 Insufficient lubrication - high friction
2.7 The material thickness is seriously out of tolerance - feeding is difficult
2.8 Poor pickling quality
3. Surface scratch (pulling)
The main reasons for surface scratch are improper material selection of the working part of the mold, low heat treatment hardness, wear of the concave die fillet, poor finish, poor surface quality of the bending blank (rust, scab, etc.), excessive material thickness, unreasonable selection of the process plan, lack of lubrication, etc.
3、 Common defects and causes of large curved drawing parts
1. Drawing characteristics of large curved parts
1.1 Deformation characteristics
The deformation characteristics of large curved parts are as follows: the periphery is deep drawing, and the interior is bulging. The surface shape is supplemented by the external material of the pressing surface, while the internal material is extended to meet the requirements of bulging. At the same time, due to the different drawing depth and complex shape, the deformation part is unevenly distributed around. Therefore, it is very important to control the flow direction and velocity of materials. Local parts of large curved parts are easy to wrinkle and crack.
1.2 Sufficient and stable blank holder force
Large curved parts require not only certain drawing force, but also sufficient and stable blank holder force in the process of drawing. Such parts are often spatial surfaces with large contour size and deep depth, so the deformation force and blank holder force are both large. On the ordinary single-acting press with air cushion, the blank holder force is only about 1/6 of the nominal tonnage, and the blank holder force is also unstable, which is difficult to meet the process requirements of such parts. Therefore, in mass production, the drawing of such parts is carried out on the double-acting press. The double-action press has two sliders for drawing and blank holding, namely the inner slider and the outer slider. The blank holding force can reach more than 40% - 50% of the total drawing force, which can meet the requirements of uneven deformation distribution around the workpiece, and the blank holding force is stable, and it is easy to obtain the drawing part with good rigidity.
1.3 The drawing parts must have sufficient rigidity
Most of these parts are used as mechanical shells, which require sufficient rigidity (no vibration and noise will occur in use) and dimensional stability (ensure welding and assembly quality). This requires that all parts of the material should be subjected to uniform tensile stress (the most ideal is the two-way tensile stress state) during the drawing process, and the tensile stress should exceed the yield limit, but be lower than the strength limit, so that the elastic recovery of the workpiece can be reduced to the minimum, so that the shape will not be distorted, and at the same time will not be broken.

2. Common defects and cause analysis
Common defects of large curved surface deep drawing parts include cracks and cracks, wrinkles and wrinkles, unclear edges, poor stiffness, surface scratches, surface roughness and slip lines.
2.1 Cracks and cracks
Cracks and cracks are mainly caused by the tensile stress of local blank exceeding the strength limit. The specific reasons for the impact are:
2.1.1 The stamping performance of the material does not meet the process requirements.
2.1.2 Sheet thickness out-of-tolerance - when the sheet thickness exceeds the upper deviation, the area with small local clearance is jammed when feeding, and the stamping deformation is difficult, and the material is not easy to be pulled through the concave die. When the thickness of the sheet exceeds the lower deviation, the material becomes thinner, the compressive stress on the unit area of the cross section increases, or because the material becomes thinner, the resistance decreases, and the sheet material flowing into the die is too much to form wrinkles first. At this time, the material is not easy to flow and is pulled apart.
2.1.3 Poor surface quality of materials - stress concentration caused by scratches and increased resistance after corrosion.
2.1.4 The feeding resistance of the pressing surface is too large - the blank shape is large, the gap between the pressing rib and groove is small, the radius of the female die fillet is too small, the outer slider is adjusted too deep, the drawing rib is too high, and the smoothness of the pressing surface and the radius of the female die fillet is poor.
2.1.5 The local drawing amount is too large, and the drawing deformation exceeds the material deformation limit.
2.1.6 During the operation, the blank is put aside, resulting in too large pressing on one side and too small pressing on the other. The oversized side is difficult to feed, causing cracking; Too small side, too much feed, easy to wrinkle, difficult to feed after wrinkle, resulting in cracking.
2.1.7 If the lubricant is not applied according to the process regulations, the resistance will increase, resulting in difficulty in feeding and cracking.
2.1.8 Improper installation of the die or poor accuracy of the press may cause the gap deflection and uneven feeding resistance.
2.2 Wrinkles and wrinkles
Wrinkles are mainly caused by instability caused by local blank compression and local material accumulation caused by uneven material flow. Specific aspects are as follows:
2.2.1 The stamping process of the parts is poor, the stamping direction and the shape of the pressing surface are not properly determined, and it is difficult to control the flow speed of the material, causing wrinkles.
2.2.2 The feeding resistance of the pressing surface is too small, and the feeding is too much and wrinkled. At this time, the external slider pressure can be adjusted or the local shape of the drawing blank can be changed, and the pressing area can be increased to eliminate, or the drawing rib can be increased locally to increase the feeding resistance.
2.2.3 The contact of the pressing surface is not good, and it is loose inside and tight outside when it is serious. After the material passes through the outer tight area, the pressing ring will lose its pressing effect, resulting in excessive feeding and wrinkles. At this time, the pressing surface shall be reground to ensure full contact and allow slight tightness inside and looseness outside.
2.2.4 Excessive oil lubrication.
2.2.5 Improper adjustment of the outer sliding block causes tilting, uneven pressure of the pressing surface at all places, and wrinkling at loose places.
2.3 Unclear edges and lines
The edges and lines of the parts shall be clear when viewed from the outside. If the pressure of the press is not enough, during the deep drawing process, when the material deformation process ends, there is not enough dead pressure, and the edge line is not clear. In addition, poor guide of the die, uneven clearance of the working part, or incorrect installation (tilting) of the male and female dies, and poor parallelism of the press can also cause unclear edges.
2.4 Poor rigidity
The main reason for the poor rigidity is that the feed resistance of the pressing surface is too small and the plastic deformation of the material is not enough. At this time, it can be considered to increase the drawbar or change the circular drawbar to the ridge drawbar to increase the feed resistance. This is also the reason why the rigidity of the parts drawn by single-acting press is worse than that drawn by double-acting press.
2.5 Surface scratch (strain)
The surface scratches are usually caused by the following reasons: the smoothness of the fillet part of the concave die is not enough, so that the material is scratched during the drawing process, and it is possible to make the material adhere to the concave die and form scratches; Because dirt falls into the die or the drawing oil is not clean, the surface of the part will also be scratched; If the pressing surface is composed of inserts, scratches will also be caused due to poor combination of inserts; Because the process supplement part is too small, the scratches through the die mouth are not cut off.
2.6 Surface roughness and slip line
The defect of rough surface is caused by excessive grain size of the material itself.
Aluminum alloy sheet stamping
Analysis of stamping defects and solutions (V)
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Some stamping defects often occur in the process of aluminum alloy sheet stamping production. These defects are slight and serious, and serious defects directly lead to the parts being unusable and scrapped. Since the stamping parts are produced in large quantities, the problems will be the loss of batches, so it is necessary to understand the various defects caused by stamping, analyze the causes of the possible defects, and put forward corresponding countermeasures for prevention.
The manifestations of parts defects that are prone to occur during stamping are as follows:
1、 Burr
It refers to the part of the punching notch surface higher than the material, which is the industrial aluminum profile occurring along the punching direction, and may also be produced after extrusion. The burr is generally controlled within 0.1mm, which is a normal and common phenomenon of stamping.
Cause analysis:
1. The die edge is worn. The material cannot be cut off at one time due to the wear of the edge during stamping. The cutting process is accompanied by the phenomenon of drawing. The metal itself has tensile elongation, and the material is drawn, resulting in burr.
2. The gap between the male and female dies is too large, and there is still a certain space for the material to be pressed. The male die cannot break the material at one time, and the material is drawn to produce burrs.
3. The clearance between the male and female dies is not reasonable, and the edge of the male and female dies is offset. During stamping, the gap between one side is too large to produce burrs, and the other side is worn.
4. The material is too soft, and the gap between the male and female dies cannot overcome the burr caused by the material drawing rate during stamping.
5. The product is extruded and burred due to improper positioning.
2、 Crush injury
It refers to that there is foreign matter in the mold or the mold scrap jumps out and is pressed on the product.
Cause analysis:
1. The blanking hole of the die is too large, and the blanking hole is brought out between the punch and the scrap under vacuum stress during stamping, and jumps onto the die, resulting in crushing when the product is re-printed.
2. The product burrs and scraps fall onto the mold.
3. It is generated when there are sundries left on the material surface.
4. Other scraps fall into the mold for some reason.
3、 Poor size
For some reason, the size of the stamped parts does not meet the requirements.
Cause analysis:
1. It is caused by poor mold design or processing and assembly, which often occurs during the first production and use of the mold.
2. The height adjustment position of the die during die setting is inconsistent, and the die cannot be in place during stamping, resulting in the size inconsistency. The die height changes during stamping due to the industrial aluminum profile or the die head is not locked after adjusting the die.
3. The mold positioning is loose, and the parts are offset during positioning, which is caused by stamping.
4. It is caused by poor operation, improper positioning and increased die clearance during stamping.
4、 Product scratch
Cause analysis:
1. The material body is scratched, which is not noticed during production.
2. The product was not effectively protected during the process and was scratched during turnover.
3. Unreasonable turnover mode and non-standard product placement.
4. The surface of raw materials is not clean, with dust and other particles.
5、 Missed process
The process omission caused by industrial aluminum profile due to negligence or other reasons during product processing results in defective parts.
Cause analysis:
1. During production, the semi-finished products are lack of identification, and the operators do not know the process sequence, but use the semi-finished products with missed punching process.
2. Operators do not pay attention when working, and the products flow to the next process before washing.
3. During the rest time, the stamping personnel did not complete the products that were not punched in the mold. When the industrial aluminum profile was produced again, they thought it was finished, and the unconfirmed status flowed to the next process.
6、 Poor flatness
Cause analysis:
1. The material is uneven and there is a certain internal stress inside, which makes it difficult to overcome during stamping and shaping.
2. The parallelism between the upper mold and the lower mold is poor after the mold is erected, and the leveling effect cannot be achieved.
3. When the material is coiled, it is not leveled, and it is difficult to achieve the purpose of leveling at one time when the die is pressed.
4. The structure of the pressed part is large, and the uneven force of the upper die causes arc deformation.
These are the defects that often occur in the stamping process. These defects can be prevented as long as the corresponding countermeasures are found.
The following is mainly about the countermeasures adopted in different production stages:
1、 First inspection stage
1. During the confirmation of the first article of the frame mold production, the drawings or samples were not carefully checked, and only the main dimensions were measured, resulting in the neglect of inspection for other problems.
2. The shift handover did not clearly hand over the mold condition, and mistakenly considered it acceptable during the first inspection, but neglected the inspection, resulting in poor production batch.
3. After mold repair, the first article only confirms the maintenance problems, neglecting the confirmation of other quality problems.
Countermeasures taken:
a) In the first article, special attention shall be paid to checking the conformity of the sample and the drawing, including identification, typeface, and stamping confirmation.
b) Handover records shall be kept for the shift handover, and the existing abnormal molds shall be directly handed over or the samples shall be explained.
c) After mold repair, pay attention to check the hole position and relevant dimensions to prevent wrong installation of industrial aluminum profiles, reverse installation or missing punch.
2、 The reproduction stage of products that have not been produced for a long time
1. Since it has not been produced for a long time, it is unfamiliar with the product quality standards and prone to control omissions.
2. The mold has not been produced and maintained for a long time, which can not meet the quality requirements and is prone to many problems.
3. The operators are unfamiliar with the mold production operation and are prone to poor operation.
Countermeasures taken:
a) When such products are produced, they should be handled according to the status of new products to solve the problems of control in production.
b) When it is put into production, it shall be controlled as a key point, and it can be produced as a mature product only after it is stable.
c) When putting into production, it is required to educate and train operators to make them understand the operation methods before production.
3、 Product design change stage
1. Inaccurate information source and insufficient content transmission lead to the problem of change confirmation negligence.
2. The switching method of new and old products is not clear, and the old products are not handled thoroughly.
3. The changed product standard was not formulated in time, and the control was omitted.
Countermeasures taken:
a) The correct department and approval authority shall be clarified for the information source, which shall be transmitted in the form of documents.
b) New and old products shall be properly identified and isolated, and the handling method shall be notified to relevant departments in the form of documents for implementation.
c) It is necessary to prepare the change product standard in advance. It is necessary to conduct early guidance or training for the standard at the product sample delivery stage.