1. Produce stamping scrap
Poor quality of raw materials;
Improper installation, adjustment and use of the die;
The operator did not feed the strip along the correct positioning or did not guarantee that the strip was fed according to a certain gap;
Due to long-term use of the die, the gap changes or the working parts and guide parts of the die are worn;
Because the impact vibration time of the die is too long and the fastening parts are loose, the installation positions of the die change relatively;
The operator's negligence, did not operate according to the operating procedures.
The raw materials must conform to the specified technical conditions (strictly check the specification and brand of raw materials, and test and inspect the workpieces with high dimensional accuracy and surface quality requirements when conditions permit). )；
All links specified in the process specification should be strictly observed;
The press, die and other tooling equipment used shall be ensured to work under normal working conditions;
Strict inspection system has been established in the production process. The first part of stamping parts must be inspected comprehensively and can be put into production only after passing the inspection. Meanwhile, inspection inspection should be strengthened and accidents should be handled in time; > wechat of cutting-edge numerical control technology is good, remember to pay attention to it.
Adhere to the civilized production system, such as the workpiece and blank transmission must use the appropriate station equipment, otherwise it will crush and scratch the surface of the workpiece, affecting the surface quality of the workpiece;
In the stamping process to ensure that the mold cavity is clean, the workplace should be organized, and the processed workpiece should be placed neatly.
2. Burr of blanking parts
The blanking gap is too large, too small or uneven;
The cutting edge of the working part of the die becomes blunt;
Due to long-term vibration impact, the center line of punch and die changes, and the axes do not coincide, resulting in single side burr.
Ensure the machining accuracy and assembly quality of punch and die, ensure the perpendicularity of punch and bear the side pressure, and the whole die should have enough rigidity;
When installing the punch, it is necessary to ensure the correct clearance between the punch and the concave die, and make the punch and the concave die firmly installed on the die fixing plate. The end faces of the upper and lower dies should be parallel to the working table of the press;
It is required that the rigidity of the press should be good, the elastic deformation should be small, the accuracy of the track and the parallelism of the base plate and the slider should be high;
The press is required to have enough blanking force;
Allowable burr height of shearing section of blanking parts
Blanking plate thickness > 0.3 > 0.3-0.5 > 0.5-1.0 > 1.0-1.5 > 1.5-2.0
Burr height of new die test ≤ 0.015 ≤ 0.02 ≤ 0.03 ≤ 0.04 ≤ 0.05
Allowable burr height in production ≤ 0.05 ≤ 0.08 ≤ 0.10 ≤ 0.13 ≤ 0.15
3. Warping deformation of blanking parts
With clearance, the force and reaction do not produce torque in one line. (warpage occurs when the clearance between punch and die is too large, the edge of die has reverse taper, or the contact area between ejector and workpiece is too small).
The blanking clearance should be selected reasonably
In the die structure, it is necessary to increase the contact between the pressing plate (or carrier plate) and the plane of the pressing plate with a certain pressure;
Check the edge of the die. If the reverse taper is found, the edge of the die must be trimmed properly;
For example, because the shape of blanking parts is complex and there are many inner holes, the shearing force is not uniform, and the pressing force increases. Before blanking, press the strip or use a high-precision press for blanking;
The plate should be leveled before blanking. If the warpage can not be eliminated, the workpiece after blanking can be leveled again through the leveling die;
The dirt in the mould cavity is removed regularly, the surface of the sheet metal is lubricated, and an oil vent is arranged on the mould structure.
4. The accuracy of outer edge and inner hole of blanking parts is reduced, and the size is changed
The location of locating pin and retaining pin changes or the wear is too large
The operator's carelessness makes the feeding move forward and backward;
The size accuracy of the strip is low, too narrow and too wide feeding difficulties make it difficult to send to the designated place, the strip will shift back and forth in the guide plate, then the position deviation between the inner hole and the contour is large.
5. When the parts are bent, the size and shape are unqualified
The rebound of material causes the unqualified products;
If the positioner is worn and deformed, and the strip positioning is inaccurate, a new positioner must be replaced;
In the bending die without guide, when adjusting on the press, improper adjustment of the bottom dead center position of the press slider will also cause the shape and size of the bending parts to be unqualified;
If the pressing device of the die fails or does not work at all, the pressing force must be readjusted or the pressure spring must be replaced to make it work normally.
2) Measures to reduce rebound:
The stamping material with large elastic modulus and small yield point is selected;
The correction process is added, and the correction bending is used to replace the free bending;
Before bending, the material should be annealed to soften the cold work hardening material before bending;
If it is difficult to eliminate the shape deformation in the stamping process, the angle between the punch and the die should be changed or trimmed, and the gap between the punch and the die should be equal to the minimum material thickness;
Increase the contact area between the die and the workpiece, reduce the contact area between the punch and the workpiece;
Adopt the method of "overcorrection" to reduce the impact of rebound.
6. The bending part of the bending part has cracks
In this area, the burr will be removed to eliminate the deformation of the burr;
The side with burr is placed on the inside of the bending area;
When bending the workpiece, it is better to make the bending direction perpendicular to the fiber direction of the material (rolling direction);
The bending radius should not be too small, and the fillet radius should be increased as far as the quality permits;
The surface of the bending blank should be smooth and clean without obvious bulge and scar;
During bending, the intermediate annealing process is used to eliminate the internal stress. After softening, there are few cracks
When bending, the large bending parts must be coated with lubricant to reduce the friction in the bending process.
7. Deflection of bending parts during bending
In the process of bending, when the blank slides along the surface of the die, it will be subject to friction resistance. If the friction resistance difference between the two sides of the blank is large, the blank will shift to the side with larger friction resistance. >Wechat of cutting-edge numerical control technology is good, remember to pay attention to it.
Symmetrical bending is adopted for the bending parts with asymmetric shape (the single-sided bending parts are cut after two pieces of symmetrical bending).
An elastic pressing device is added on the bending die so that the blank can be pressed to prevent movement during bending;
The inner hole and shape positioning form are adopted to make the positioning accurate.
8. Surface abrasion of bending parts
1) Causes and Countermeasures:
For copper, aluminum alloy and other soft materials for continuous bending, metal particles or dregs are easy to adhere to the surface of the working part, so that the parts appear larger scratch. At this time, we should carefully analyze the shape of the working part, lubricating oil and other conditions, so that the blank had better not appear particles and dregs, and even scratch;
When the bending direction is parallel to the rolling direction of the material, cracks will appear on the surface of the workpiece, which will reduce the surface quality of the workpiece. When bending in more than two parts, the bending direction and rolling direction should have a certain angle as far as possible;
When the burr surface is used as the outer surface for bending, the workpiece is easy to crack and scratch, so the burr surface should be used as the inner surface for bending;
The fillet radius of the die is too small, and impact marks appear in the bending part. Polishing the die and increasing the fillet radius of the die can avoid the scratch of the bending parts;
The clearance between punch and die should not be too small. Too small clearance will cause thinning and abrasion. In the process of stamping, the change of die clearance should be checked at all times;
When the depth of punch into the die is too large, the surface of the part will be scratched. Therefore, in the case of ensuring that it is not affected by springback, the depth of punch into the die should be appropriately reduced;
In order to make the parts meet the requirements of accuracy, the bending die is often used for pressing at the bottom. When bending, the spring, locating pin hole, supporting plate and return hole on the pressing plate will be pressed into indentation, so it should be adjusted.
9. The position of blank hole changes during bending
The position and size of the hole are not right (bending and tension thinning);
The holes are not concentric (bending height is not enough, blank sliding, springback, undulation on the bending plane);
The bending curve and the center line of the two holes are not parallel, and the part whose bending height is less than the minimum bending height presents an outward opening shape after bending;
The hole near the curve is easy to deform.
The position and size of the hole are not correct, the bending radius, bending angle and material thickness are strictly controlled, the neutral layer of the material is trimmed, the depth of the punch into the die and the proper uniformity of the punch and die are ensured;
The causes of the holes are not concentric and the measures are taken;
Ensure the right and left bending height is correct;
Correct the worn locating pin and locating plate;
Reduce the springback to ensure the parallelism and flatness of the two curved surfaces;
Change the process route, bend first and then punch.
It presents the outward opening shape
When bending, the minimum bending height h (H ≥ R + 2T, t material thickness R, bending radius) shall be ensured;
Change the shape of the processing parts, and remove the part less than the minimum bending height without affecting the use.
The hole near the bending curve is easy to deform, and the measures are put forward
In the design of bending parts, the distance x from the bending part to the hole edge should be greater than a certain value x ≥ (1.5-2.0) t, and the thickness of bending sheet should be ensured;
An auxiliary hole is designed in the bending part to absorb the bending deformation stress, which can prevent the hole deformation near the bending curve. Generally, the scheme of bending before punching is adopted.
10. After bending, the bending parts become thinner obviously
When the bending radius is too small relative to the plate thickness (R / T > 3), the bending radius is generally increased;
Multi angle bending makes the bending part thinner and larger. In order to reduce the thinning, single angle multi process bending method is used as far as possible;
When the sharp angle punch is used, the depth of the punch into the die is too deep, so that the thickness of the bending part is obviously reduced.
11. The flange of the drawing part is wrinkled during the drawing process1) Reason:
The blank holder force at the flange is too small to resist the excessive tangential compressive stress, resulting in the tangential deformation and the formation of wrinkles after losing stability. The material is thin and easy to form wrinkles.
Increase the blank holder force of blank holder and increase the thickness of material appropriately.
12. Causes and prevention of wall crack of drawing parts
The radial tensile stress of material in deep drawing is too large;
The radius of die fillet is too small;
Poor lubrication in deep drawing;
The plasticity of raw materials is poor.
The blank holder force is reduced;
Increase the radius of die fillet;
Proper use of lubricants;
Choose better material or increase annealing process.
13. The bottom of the drawing part is cracked
The fillet radius of the die is too small to make the material cut.
(generally occurs in the initial stage of deep drawing) increase the fillet radius of the die and make it smooth, and the surface roughness is smaller, generally RA < 0.2 μ M.
14. The edge of drawing parts is uneven and wrinkled
The blank is not in conformity with the center of punch and die, or the material thickness is not uniform, and the radius of die fillet and the gap between punch and die are not uniform (the radius of die fillet is too large, and the blank holder is separated from the blank holder in the final stage of deep drawing, so that the material blank holder which has not crossed the fillet can not be wrinkled, and then it is pulled into the die to form edge wrinkles.
The punch is repositioned, and the radius of the die fillet and the gap between the punch and the die are corrected to make them uniform before putting them into production (the wrinkle can be eliminated by reducing the radius of the die fillet or using the arc-shaped blank holder device).
15. Waist wrinkling when drawing conical or hemispherical parts
At the beginning of deep drawing, most of the material is suspended, and the blank holder force is too small, the die fillet radius is too large or too much lubricant is used. It makes the radial tensile stress smaller and makes the material lose stability and wrinkle under the action of tangential compressive stress.
Increase the blank holder force or adopt calendering rib structure, reduce the die fillet radius or slightly increase the material thickness.
16. There are draw marks on the surface of deep drawing parts
1) Causes and Countermeasures:
There is sharp indentation on the surface of punch or die, which causes the corresponding pull marks on the surface of the workpiece. At this time, the surface of the indentation should be polished or polished;
If the gap between punch and die is too small or uneven, the surface of workpiece will be scratched during deep drawing. At this time, the gap between punch and die should be trimmed until it is appropriate;
When the surface of the die fillet is rough and the workpiece surface is scratched during deep drawing, the die fillet radius should be polished;
When stamping, the surface of the punch die or material is not clean and mixed with impurities, which will crush the surface of the workpiece. Therefore, the surface of the punch and die must always be kept clean when drawing, and the blank must be wiped before drawing;
When the hardness of punch and die is low, the metal scraps attached on the surface of the punch and die will also cause the drawing marks on the surface of the drawing workpiece. Therefore, in addition to increasing the hardness of the punch and die surface, the punch and die surface should be inspected frequently during drawing, even if the metal scraps left behind are removed;
If the quality of lubricant is poor, the surface roughness of the deep drawing workpiece will be increased. In this case, the lubricant suitable for the deep drawing process should be used. If necessary, the lubricant should be filtered before use. In order to prevent impurities from mixing and damaging the surface of the workpiece.
17. The straight wall of the drawing part is not flat
1) Causes and Countermeasures:
There is no air hole designed and manufactured on the punch, so that its surface is deformed due to compressed air, resulting in unevenness. At this time, the air hole must be added;
The springback effect of the material will also make the surface of the deep drawing workpiece uneven. Finally, the shaping process should be added;
If the gap between punch and die is too large, the drawing is difficult to be flattened. At this time, the gap must be adjusted evenly.
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