This is a 100% technical article that summarizes the various defects of stamping parts produced by stamping factories, analyzes the causes and provides preventive measures. The content is practical and it is recommended to collect it! ! !
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Produce stamping waste
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reason
Raw materials are of poor quality;
Improper installation, adjustment and use of the die;
The operator did not feed the strips along the correct positioning or did not ensure that the strips were fed with a certain gap; due to long-term use of the die, the gap changed or its working parts and guide parts were worn;
Due to the impact and vibration of the die for too long, the fastening parts loosened, causing relative changes in the installation positions of the die; the operator was negligent and did not operate according to the operating procedures.
Countermeasures
Raw materials must comply with specified technical conditions;
All aspects stipulated in the process regulations should be fully and strictly observed;
The tooling equipment such as presses and dies used should be guaranteed to work in normal working conditions;
A strict inspection system has been established during the production process. The first stamped parts must be fully inspected and can be put into production only after passing the inspection. At the same time, inspections are strengthened, and when accidents occur, they must be dealt with promptly;
During the stamping process, the mold cavity must be kept clean, and the workplace must be organized and the workpieces after processing must be placed neatly.
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Punching parts burrs
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reason
The punching gap is too large, too small or uneven;
The cutting edge of the working part of the die becomes dull;
Due to long-term vibration and impact, the center lines of the punch and the die change, and the axes do not coincide, resulting in single-sided burrs.
Countermeasures
Ensure the processing accuracy and assembly quality of the convex and concave dies, ensure the verticality of the convex molds and withstand lateral pressure, and ensure that the entire punch mold has sufficient rigidity;
When installing the punch, be sure to ensure the correct clearance between the convex and concave dies and ensure that the convex and concave molds are firmly installed on the mold fixing plate. The end faces of the upper and lower dies must be parallel to the work surface of the press;
The press is required to have good rigidity, small elastic deformation, high rail accuracy and parallelism between the backing plate and the slider;
The press is required to have sufficient punching force;
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Warping deformation of punched parts
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reason
There is a gap force and a reaction force that does not produce a moment on the same line (warping deformation occurs when the gap between the convex and concave molds is too large and the cutting edge of the concave mold has a reverse taper, or the contact area between the ejector and the workpiece is too small).
Countermeasures
The blanking gap should be chosen reasonably;
A pressing plate (or supporting plate) should be added to the mold structure to make plane contact with the pressing plate and have a certain amount of pressure;
Check the die edge and if back taper is found, the die edge must be trimmed appropriately;
If the shape of the blanking part is complex and there are many inner holes, the shearing force will be uneven and the pressing force will increase. The strip should be pressed tightly before punching or a high-precision press should be used for punching;
The plate should be leveled before punching. If the warpage deformation still cannot be eliminated, the workpiece after punching can be leveled again through the leveling die;
Clean the stolen goods in the mold cavity regularly, lubricate the surface of the thin sheet, and provide oil vents on the mold structure.
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Decreased accuracy, dimensional changes
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reason
The positions of positioning pins, stopper pins, etc. have changed or are too worn;
The operator's carelessness caused the material to shift left and right when feeding;
The dimensional accuracy of the strip is low, too narrow and too wide, making it difficult to deliver the material to the designated location. The strip will shift forward and backward in the guide plate, resulting in a large deviation between the inner hole of the punched workpiece and the front and rear position of the outer shape.
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Unsatisfactory size and shape
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reason
Material rebound causes the product to fail;
The positioner is worn and deformed, causing the strip to be positioned inaccurately, and the positioner must be replaced with a new one;
In a non-guided bending die, 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 bent part to be unqualified;
The pressing device of the mold fails or does not work at all. The pressing force must be readjusted or the pressure spring must be replaced to make it work properly.
Countermeasures
Choose stamping materials with large elastic modulus and small yield point and relatively stable mechanical properties;
Add a correction process and use correction bending instead of free bending;
The material must be annealed before bending to soften the cold work hardened material before bending;
If shape deformation occurs during the stamping process and is difficult to eliminate; the slope of the punch and the die should be replaced 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, and reduce the contact area between the punch and the workpiece;
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bend offset
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reason
When the blank slides along the surface of the die during the bending process, it will encounter frictional resistance. If the frictional resistance on both sides of the blank is greatly different, the blank will shift to the side with greater frictional resistance.
Countermeasures
Asymmetrically shaped bent parts are formed by symmetrical bending (single-sided bent parts are formed by bending two pieces symmetrically and then cutting);
Add an elastic pressing device to the bending die to hold the blank to prevent movement during bending;
The inner hole and outer shape positioning methods are used to make the positioning accurate.
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Scratches on the surface of parts
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Causes and Countermeasures
When soft materials such as copper and aluminum alloys are continuously pressed and bent, metal particles or residues tend to adhere to the surface of the working part, causing large abrasions or even scratches on the workpiece;
When the bending direction is parallel to the rolling direction of the material, cracks will occur on the surface of the workpiece, which will reduce the surface quality of the workpiece. When bending at more than two locations, try to ensure that the bending direction has a certain angle with the rolling direction;
The radius of the die fillet is too small, and impact marks appear on the bending part. Polish the die and increase the radius of the die's corners to avoid scratches on the bent parts;
The gap between the convex and concave molds should not be too small, otherwise it will cause thinning and scratches. During the stamping process, always check the changes in the gap of the mold;
If the depth of the punch entering the concave mold is too large, the surface of the part will be scratched. Therefore, the depth of the punch entering the concave mold should be appropriately reduced while ensuring that it is not affected by springback;
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hole position changes
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reason
The position and size of the hole are wrong (thinning due to bending and tension);
The holes are not concentric (the bending height is not enough, the blank slides and rebounds, and the bending plane appears undulations);
The bending line and the center line of the two holes are not parallel and the bending height is less than the minimum bending height. After bending, the part shows an outward opening shape;
Holes close to bending lines are prone to deformation.
Countermeasures
Measures for causes of hole inconsistency:
Make sure the left and right bending heights are correct;
Correct worn positioning pins and positioning plates;
Reduce springback and ensure the parallelism and flatness of the two curved surfaces;
Change the process route and perform bending correction first and then punching.
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The curved part becomes thinner
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Countermeasures
If the bending radius is too small relative to the plate thickness (r/t>3 right-angle bending), generally increase the bending radius;
Multi-angle bending makes the bending part thinner and larger. In order to reduce thinning, try to use a single-angle multi-process bending method;
When using a sharp-corner punch, the punch enters the die too deeply and the thickness of the bending part is significantly reduced.
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stretch wrinkles
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reason
The flange holding force is too small and cannot resist the excessive tangential compressive stress; it causes tangential deformation, resulting in loss of stability and formation of wrinkles. Thinner materials are also more prone to wrinkles.
Countermeasures
Increase the blank holder force of the blank holder and increase the thickness of the material appropriately.
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The wall is torn apart
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reason
The radial tensile stress the material bears during deep drawing is too large;
The die fillet radius is too small;
Poor deep drawing lubrication;
The raw material has poor plasticity.
Countermeasures
Reduce the blank holder force;
Increase the die fillet radius;
Use lubricants correctly;
Choose materials with better quality or add inter-work annealing process.
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Rugged edges
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reason
The blank does not match the center of the convex and concave molds or the material thickness is uneven, as well as the concave mold fillet radius and the gap between the convex and concave molds are uneven (the concave mold fillet radius is too large, and it breaks away from the blank holder in the final stage of drawing, so that the fillet has not yet been crossed. After the material is not wrinkled by the edge ring, it is pulled into the die to form edge wrinkles.
Countermeasures
Reposition the die, correct the radius of the die fillet and the gap between the convex and concave dies to make them even in size before putting them into production (wrinkles can be eliminated by reducing the fillet radius of the die or using an arc-shaped edge ring device).
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Wrinkles at the waist
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reason
At the beginning of deep drawing, most of the material is in a suspended state, and the blank holder force is too small, the die fillet radius is too large, or too much lubricant is used. The reduction of radial tensile stress causes the material to lose stability and wrinkle under the action of tangential compressive stress.
Countermeasures
Increase the blank holder force or adopt a rolling bead structure, reduce the die fillet radius or slightly increase the material thickness.
