Deep drawing is a stamping and forming process in which a flat sheet is formed into an open hollow part through a concave die under pressure of a convex die. In all types of sheet metal components, deep drawing is often used for the processing of various cylindrical parts, hemispheres and parabolic heads of larger size or thicker material.
The process and requirements of deep drawing
Generally speaking, the deep drawing process must be completed by pressure of the hydraulic press through the deep drawing die. In general, cold processing is used, only for the shape size or deformation of the thicker plate material, deep drawing forming is used for hot processing.
Deep drawing process
The following diagram is the diameter of D, the thickness of t round flat plate blank placed in the concave die positioning hole, deep drawing into the cylinder-shaped parts of the drawing process.
Deep drawing process, due to deep drawing force F and convex, concave die gap between Z to form a bending moment, convex die downward contact with the plate material after downward pressure, so that the plate material bending concave, and in the convex, concave die rounded guide pulled into the concave die hole, the plate material slowly evolved into the bottom of the cylinder (convex die under the central part of the plate material), simple wall (pulled into the hole in the circular part of the plate material), convex edge (not pulled into the hole in the circular part) three major parts; with the convex die As the convex die continues to fall, the bottom of the simple is basically unmoved, the ring-shaped flange is constantly shrinking to the hole and is pulled into the concave die hole to turn into a cylinder wall, so the simple wall gradually increases in height, the flange gradually shrinks, and finally the flange is all pulled into the concave die hole to turn into a simple wall, then the drawing process ends. The round plate material becomes an open hollow circle with a diameter of d1 and a height of h.
Deep drawing deformation analysis
According to the deep-drawing deformation process can be understood: deep-drawing process is the ring-shaped flange gradually shrinkage to the concave die hole flow transfer into the process of the cylinder wall. Deep drawing process is a relatively complex plastic deformation process. Each part of the blank according to its deformation can be divided into several regions.
⒈The bottom of the cylinder (small deformation area) convex die bottom down contact to the central area of the plate material round part of the simple bottom, in the process of deep drawing, this area always maintain a flat shape, surrounded by uniform radial tension, can be considered as no plastic deformation or very small plastic deformation area, the bottom material will be convex die force to the cylinder wall, so that it produces axial tensile stress.
⒉ Flange part (large deformation area) above the concave die ring area that is the flange, is the main deformation area when deep drawing. Deep drawing, the flange part of the material due to the role of deep drawing force produces radial tensile stress σ1, in the direction of shrinkage flow to the concave die hole, the material squeezed each other to produce tangential compressive stress σ3. Its role and will be a fan-shaped part of the blank F is pulled through an imaginary wedge-shaped slot and becomes similar to the deformation of F2, see the following chart.
When the flange is large and the sheet is thin, the flange part will lose stability and arch due to tangential compressive stress when drawing, forming the so-called "wrinkling phenomenon", so the crimping ring is commonly used to crimp the flange.
⒊ Barrel wall (force transfer area) This is the deformation area, by the flange part of the material by tangential compression, radial stretching shrinkage flow transfer, basically no longer occurs large deformation. In continue to deep drawing, play the role of convex die deep drawing force transfer to the flange, simple wall material in the process of transferring deep drawing force itself to bear the role of one-way tensile stress, longitudinal slightly elongated, the thickness is slightly thinner.
⒋concave die corner part (transition zone) flange and simple wall intersection transition part, where the material deformation is more complex, in addition to the same characteristics as the flange part that is subject to radial tensile stress and tangential compressive stress, force, in addition to the role of concave die corner extrusion and bending role and the formation of thick compressive stress.
⒌convex die corner part (transition area) simple wall and simple bottom intersection transition part, radial and tangential to bear the role of tensile stress, thick to the role of extrusion and bending by the convex die corner and compressive stress, deep drawing process, the radial elongation, the thickness of some thinning, the most serious thinning occurs in the convex die corner and the wall of the barrel, the beginning of deep drawing, it is in the convex, concave die between, need to transfer the material less, by the deformation The degree of small, cold hardening degree is low but also not convex die corner at the useful friction, need to transfer the area of deep drawing force and smaller. Therefore, this place becomes the most likely to break when deep drawing "dangerous section".
Variation of wall thickness of deep-drawing parts
Uneven wall thickness of deep-drawing parts can be seen in the following figure. The following figure is the change of wall thickness of carbon steel elliptical head deep drawing, the following figure b is the change of wall thickness of flanged cylinder parts deep drawing with crimp ring.
Process requirements of deep drawing processing
The use of deep drawing process can complete the processing of complex shape parts, get the cylinder, stepped, conical, square, spherical and various irregular shapes of thin-walled parts. However, the precision of deep-drawing processing is related to many factors, such as the mechanical properties of the material and material thickness, mold structure and mold precision, the number of processes and the sequence of processes, etc. The manufacturing accuracy of the deep-drawing parts is generally not high, the appropriate accuracy in the IT11 level below, at the same time, due to the impact of deep-drawing deformation performance, the process of deep-drawing parts is good or bad, directly affect the parts can be processed with the most economical and simple method, and even affect the parts can be processed with deep-drawing method. Deep drawing parts of the process requirements are as follows.
⒈The shape of the deep-drawing parts should be as simple and symmetrical as possible. In the design of deep-drawing parts, should be combined with the processing of deep-drawing parts, as far as possible to use easier to form and can meet the requirements of the form. The following chart is the classification of the degree of ease of deep-drawing forming. All kinds of deep-drawing parts in the figure, its forming difficulty from top to bottom in increasing order. The difficulty of the same type of deep-drawing parts increases from left to right. Where: e indicates minimum straight edge length, f indicates the maximum size of the deep-drawn part, a indicates the short axis length, b indicates the long axis length.
⒉ For cylindrical deep-drawing parts with flange, the most suitable flange is in the following range when deep-drawing with crimping ring: d+12t≤d convex≤d+ 25t
where d - diameter of the round simple part, mm.
T - thickness of the material, mm.
d convex - flange diameter, mm.
⒊ The drawing depth should not be too large (i.e. H should not be greater than 2d). When one time can be pulled into, its height is best: no flange round simple pieces: H ≤ (0.5 ~ 0.7) d
⒋ on the cylinder drawing deep parts, the bottom and wall part of the corner radius r convex should meet r convex ≥ t, flange and wall between the corner radius r concave ≥ 2t, from the conditions conducive to deformation, the best to take r convex ≈ (3 ~ 5) t, r concave ≈ (4 ~ 8) t. If r convex (or r concave) ≥ (0.1 ~ 0.3) t, can increase the shaping.