Automotive cladding process issues

The good or bad surface quality of automotive cover parts will directly affect the quality of the body, so the dimensional accuracy and surface quality of the cover parts have high requirements. Body covering parts are not allowed to have wrinkles, scratches and other surface defects, and at the same time should have enough stable rigidity.

1.Dark pit

Dark pits are slight depressions or bumps that occur locally on the continuously protruding curved surfaces of the covering parts. Because of this defect is difficult to find direct visual observation, the body must be painted by light irradiation to show, so it is called dark pit.

Cause: sheet in the forming process, its deformation by the elastic deformation and plastic deformation. When the external force is withdrawn, the elastic deformation by the already born.

Formation of plastic deformation limitations, can not be fully restored, then formed in the stamping parts of the residual stress, and the shape and size of the stamping parts is the elastic deformation of the sheet material and plastic deformation of the integrated embodiment. The elastic deformation of bending causes the change of the radius of curvature of the workpiece at the place, forming a dark pit.

2. Wave

Wave is a slight wrinkle, similar to a certain area of continuous dark pits, mainly generated near the edge of the parts, such as the wing plate above the wheel cover, the door near the flap line. Causes: During the forming process, the flange surface part of the sheet is wrinkled due to instability under the action of tangential compressive stress, which is retained on the surface of the stamped part through the gap between the convex die and the concave die, forming a surface wave. In addition, due to the bending deformation of the material in the process of flanging, the outer part of the bent part is subjected to tensile stresses and the inner part is subjected to compressive stresses, and due to the moment effect of these stresses, the slight warping deformation generated after unloading is also reflected as the surface wave. The generation of waves is affected by product shape, material properties, mould structure and other factors. Especially when stretching the crimping circle design and mould gap is unreasonable and other factors will directly lead to the generation of waves.

3. Ribs are not clear

Ribs are not clear mainly because of the shape of the mould, poor dimensional accuracy, the mould is not pressed to the end, the positioning of the workpiece is inaccurate, etc., and hair pulling is mainly due to the state of the concave die corner is not good, and poor lubrication or insufficient hardness of the mould and other reasons.

4. Springback

To overcome the rebound, can be improved by using reasonable technology to improve the stress state of the plate in the forming process, but also through the selection of reasonable rebound angle, rebound radius, mould clearance and other mould process parameters to solve.

5. Insufficient stiffness

Body covering parts have a certain stiffness requirements, if the stiffness is not enough, the car will produce resonance phenomenon in the driving process, resulting in a lot of noise, and will make the covering parts premature damage. In the case of the shape of the cover, the structure of the dimensions are unchanged, the greater the plastic deformation of the automotive cover in the stamping and forming process, the better its rigidity. In general, the plastic deformation of automotive cover part blank should be more than 2%. The main countermeasures to overcome the lack of rigidity are: in product design, the design of aesthetic decorative strips, decorative bars, etc.; in the design of the tensile parts. Appropriate increase in the depth of the tensile parts, or the use of technology to supplement the depth of the tensile parts increased; in the mould design, the use of tensile rib, tensile threshold, etc.; stamping process to increase the crimping force, etc.. These measures are conducive to increasing the plastic deformation of the blank and improving the rigidity of the stamped part.

6. Wrinkle

Adopt to improve the radial tensile stress in the plate to eliminate wrinkles, can be increased by increasing the tensile rib, reducing the radius of the concave die round corner, adjusting the gap of the pressing surface and the stretching gap to increase the crimping force, to avoid the occurrence of wrinkles.

7. Rupture

For stamping parts with internal local forming, due to the deformation of two-way elongation deformation, if the external material can not be supplemented to the internal, the amount of plastic deformation is too large will produce rupture. The root cause is that the tensile deformation force is greater than the actual effective tensile strength of the material at the side wall crack.