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metal stampings parts quality problems analysis and solutions

 

First, the common defects and reasons analysis punching member
Punching sheet metal using a mold to make separate stamping process.
Blanking member common defects: burr, workpiece surface warpage, dimensional tolerance.
1, burr
   In the sheet metal punching, resulting in varying degrees of glitches, in general it is difficult to avoid, but to improve the parts of the process, improved stamping conditions, it can reduce the glitch.
  Glitch causes are mainly the following aspects:
1.1 gap
Blanking gap is too big, too small or uneven can produce glitches. Effect of the gap is too big, too small or uneven the following factors:
a mold manufacturing error - Die parts processing does not comply with the drawings, floor parallelism bad and so on;
b mold assembly errors - guide portion gap, punch and die assembly misalignment and the like;
c press accuracy is poor - such as press guide gap is too large, parallel to the bottom surface of the slide with the table surface is not good, or the vertical stroke of the slide and the press table is not good, poor rigidity bench in blanking generated when the deflection, can cause changes in the gap;
d installation error - such as top and bottom surfaces of the die at the time of installation is not clean or fastening methods on a large die mold properly, the upper and lower mold die install a different heart (especially no pillar mold) caused by the working portion inclined;
e die structure is irrational - die and not enough work part rigidity, punching power imbalance;
d steel scoop curvature large - steel uneven.
1.2 blunt knife
Blunt edge wear or bite wounds can produce glitches. Factors Affecting blunt edge are:
a convex mold, bad state of the material and the surface treatment die, wear resistance is poor;
bad b die structure, poor rigidity, resulting in bite wounds;
When c-operation is not timely lubrication, wear faster;
d no time grinding blade mouth.
1.3 Blanking improper state
Such as blank (including intermediate parts) and punch or die a bad contact when positioning relative height improper trimming punching, also due to the workpiece height of less than positioning relative height, shape parts punching process and edge shape against posts and burrs.
1.4 Improper mold structure
1.5 material discrepancies craft regulations
Material thickness tolerance or serious wrong material (such as steel does) cause unreasonable relative gap leaving parts burrs.
1.6 parts of the process is poor - complex shape protruding or concave corners are easy due to excessive wear and burrs.
    Burrs, not only deformed after blanking process due to stress concentration and easy to crack, but also to the subsequent step stratified blank difficult. Burr easily handle large scratch; when welding two sheets bonded well, easy to wear welding, welding is not strong; it is easy to produce riveting riveting riveting gap or cause cracking.
    Therefore, there is a glitch allowed beyond extremely harmful. Burr that has been generated for filing is available, tumbling, electrolysis, chemical processing and other methods to eliminate.
2, warping uneven parts
    Tension in the material must first instant contact with the punch, die, and then cut, torn. Since the drawing, bending, lateral extrusion of various force, so that parts exhibition material appear wavy shape, parts resulting warpage.
    Reason parts warpage produced in the following areas:
2.1 Blanking large gap
  The gap is too large, the punching process, drawing parts, the bending force, prone to warping. Improved approach could be used in tightly pressed against punching punch and pressure plate, and to maintain a sharp edge, can receive good results.
2.2 die hole counter-cone
  Workpiece size at the time through a small portion of the outer periphery to the center of compression is necessary, resulting in bending.
Warp 2.3 parts structural shapes produced
  Parts of complex shape, the parts around on uneven shearing force, resulting in a force center from the surrounding, so parts warping. The solution is to increase the nip force.
2.4 warpage material internal stress generated
  The internal stress of the material during rolling is wound produced, after punching surface is moved, the part will warping. By leveler leveler when unwinding solving approach.
2.5 warpage due oil, air and produce poor contact
  When there is oil, air and other oppressed parts between die and parts, parts and parts, parts will be warped, especially thin, soft material easier to produce. But as evenly oiled, set the vent can eliminate warping phenomenon. Between the parts and the die surface debris is also easy in that article warpage.
  Contact surface will warp when punching bad.
3, the dimensional accuracy of ultra-poor
3.1 mold manufacturing cutting edge dimension tolerance
3.2 blanking during rebound, the bearing surface shape and the shape of the part under the procedures of the working portion of the mold processes are inconsistent, so the workpiece deformation in stamping process, resulting in elastic recovery after punching is complete, thus affecting dimensional accuracy.
3.3 Flatness bad.
More than 3.4 parts due process procedures on improperly adjusted or rounded wear, deformation undermine the principle of equal volume, causing a change in size after punching.
3.5 Due to the positioning operation is not good, or bad positioning mechanism designed, punching process occurs traverse rough. Or defects due to shear member (prism degree, lack of edge, etc.) caused by positioning allowed, can cause size tolerance.
3.6 punched the wrong order.
Second, common defects and reasons analysis of bending member
Bent piece of common defects: match the shape and size, bending crack, surface scratches, deflections and distortions.
1, does not match the shape and size
The main reason is due to improper and positioning will play. The solution in addition to taking measures to reduce the rebound, the enhancement of the reliability of the rough positioning is also important, usually two measures;
1.1 pressing blank
      Using air cushion, rubber or spring pressing force generated at the very beginning before bending sheet metal pressing. For this purpose, the pressure plate or pressure feed rod ejection height should be made slightly higher than the flat die.
1.2 reliable positioning method
      Positioned mainly in the form of rough appearance as a reference and as a reference to the two holes. Shape positioning easy to operate, but the positioning accuracy is poor. Hole positioning operation is not convenient, use a narrow range, but the positioning is accurate and reliable. Under certain conditions, sometimes early positioning shape, resulting in a large blank control within a certain range, the last hole final positioning, learn the advantages of both, so that the positioning that is accurate and easy to operate.
2. bending crack
    Factors affecting the cracks are many, mainly in the following aspects:
2.1 Plasticity poor.
2.2 curved line and the angle between the direction of sheet metal embossing does not comply
  When nesting, unidirectional V-shaped bend, the bending line should be perpendicular to the direction of the emboss; bidirectional bent, curved lines and emboss direction is preferably 45 degrees.
2.3 bend radius is too small.
The difference between 2.4 and punching rough cut section quality - burr, crack.
2.5 punch fillet radius wear or gap is too small - feed resistance increases.
2.6 Lubrication enough - larger friction
2.7 serious tolerance material thickness dimension - difficult feed
2.8 Pickling poor quality
3, the surface wipe (pull) injury
      The main reason is mold surface scratches work part improper selection, low heat hardness, die radius wear, poor finish, poor quality curved rough surface (rust, scarring, etc.), material thickness tolerance, unreasonable plan selection process lack of lubrication.
4, deflection and distortion
Third, the common pitfalls of large surface drawing parts and cause analysis
1, large parts of the drawing surface characteristics
1.1 Deformation Features
       Large parts of the surface deformation characteristics are: perimeter of the drawing, there bulge formed inside stars. Surface shape is by external binder material to supplement, while the interior is by bulging material extends to meet the requirements. At the same time due to the depth of drawing different, complex shape, the deformable portion surrounding unevenly distributed. Thus, the flow and velocity control material is extremely important. Large parts of both localized surface wrinkle easily, and easy to crack.
1.2 to have a stable enough BHF
      Large curved parts not only requires a certain drawing power, but also requires a sufficiently stable BHF in its drawing process. Such articles tend to be larger overall size, depth deeper space surface, so the required deforming force and BHF are larger. On an ordinary single-action press with cushion, BHF only about 1/6 of the nominal tonnage and BHF is not stable, it is difficult to meet the technological requirements of these parts, and therefore
  In the mass production of such parts of the drawing are performed on double-action press. Double-action press having a drawing and two sliders pressure side, namely the inner and outer slider slider, BHF can reach more than 40% -50% of the total drawing force, can not meet the parts surrounding strain distribution all the requirements, and BHF stable, easy to get a good stiffness drawing parts.
1.3 drawing parts must have sufficient rigidity
      Most of the mechanical parts such as housing, requires sufficient stiffness and dimensional stability (in use tremors and noise does not occur) (ensure the welding, assembly quality). This requires the drawing process, to various parts of the material subjected to a uniform tensile stress (ideally two-way tensile stress state), and so the tensile stress exceeds the yield limit, but lower than the ultimate strength, elastic parts reduced to reply minimum, the shape distortion Buzhi Yu, but still will not break.
2, common defects and cause analysis
      Large surface drawing parts common defects: cracks and breakage, wrinkles and creases, the ridge is unclear, stiffness difference, surface scratches, surface roughness and slip lines.
2.1 crack and rupture
      The main reason for the crack and rupture is produced by rough due to local tensile stress exceeds the strength limit due. Cause specific effects are:
2.1.1 stamping performance material does not meet the technical requirements.
2.1.2 sheet thickness tolerance - when the sheet thickness exceeds the upper deviation, when local gap small area feed stuck, stamping deformation difficult material easily through the inner die and pulled off the premises. When the sheet thickness exceeds deviation, thinner material, stress cross-section per unit area increases, or due to thinning of the material, the resistance is reduced, excessive inflow of sheet metal and die within the first formation of wrinkles, this , the material flows easily pulled crack.
2.1.3 Materials poor surface quality - Scratch cause stress concentration, increased corrosion resistance after.
Feed resistance 2.1.4 binder is too large - rough shape large and small muscle groove binder gap, die radius is too small, too deep outer slide tone, drawbead too high, binder and die radius poor finish.
2.1.5 partial drawing is too big, deep drawing deformation than material deformation limit.
2.1.6 In operation, put the rough side, while causing the binder is too large, while the binder is too small. Oversized feed side is difficult, resulting in cracks; too small side, feed too much, easy to wrinkle, wrinkle backward material difficulties, causing rupture.
2.1.7 not coated according to the process prescribed lubricant, after resistance increases, resulting in feeding difficulties and cracking.
2.1.8 improper installation or press die poor accuracy, causing deflection gap, resulting in uneven feed resistance.
2.2 wrinkles and creases
    The main reason for wrinkles because of local instability and compression caused by rough material flows caused by uneven local material accumulation and wrinkles. There are several specific aspects of the following:
2.2.1 poor parts stamping process, stamping direction and shape is determined improper binder, it is difficult to control the speed of material flow, causing wrinkles.
Feed resistance 2.2.2 binder is too small, feed excessive wrinkling. Then adjust the pressure outside the slider or change local shape drawing blank, increasing the area to remove the binder, or a local increase drawbead to increase the feed resistance.
2.2.3 binder surface contact is not good, serious form outside the tight loose inside. Materials through the region outside the tight ring binder material effect on the loss of pressure, resulting in excessive feed, resulting in wrinkles. This time to reground binder, to ensure full access, allowing slightly in the tight loose.
2.2.4 oiled excessive lubrication.
2.2.5 outside slider to adjust properly, causing inclined to make the entire binder uneven pressure, place loose wrinkle easily.
2.3 ridgeline unclear
    Article observed from the outside, requiring clear the ridge. If the press pressure is not enough, then deep drawing, when the material deformation process is terminated, can not get enough pressure pier dead, the ridgeline unclear. In addition, the guide die poor, uneven work part of the gap, or the punch and die is not properly installed (tilt), parallelism can also cause bad press ridgeline unclear.
2.4 poor rigidity
    In addition to forming a rigid main reason for poor process is bad parts, the main binder is feed resistance is too small, not enough to cause plastic deformation of the material. Then you can consider increasing drawbead or Circular drawbead to sill drawbead to increase the feed resistance. This is also the reason single-action drawing presses out of parts of the stiffness ratio double action press drawing out parts bad.
2.5 surface scratches (strain)
      Surface scratches usually caused by the following reasons: die fillet portions finish is not enough, so in the process of drawing material from being scratched, and it is possible to make the material adhere to the die to form scratches; the dirt falls die or drawing oil is not clean, it will scratch the workpiece surface; if the binder is composed by the insert, since the combination of inserts bad, can also cause scratches; the addendum is too small, It is not cut by the die orifice scratches.

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