Extract - Forming a sheet blank in a cup or box-like shell or workpiece in the form of such a shell into a deeper shell, resulting from the pulling of a part of the material on the mirror behind the contour of the cavity (cavity) of the die, located inside the contour. There are varieties of hoods - axisymmetric, non-axisymmetric and complex. Nonaxisymmetric stretching - an extraction of a non-axisymmetric shell, for example a box-like shell, having two or one plane of symmetry. Complex extract - a hood of a shell of complex shape, usually not having any plane of symmetry. Axisymmetric extractor - Extraction of the shell from an axisymmetric billet by an axisymmetric punch and a matrix (Figures 9.39, 9.40).
Fig. 9.39. The drawing of the drawing ( a ) and the type of the resulting blank ( b )
Fig. 9.40. Appearance of blanks after drawing ( a ) and cutoff of technological waste < strong> (b)
When drawing, the flat workpiece 5 is drawn by a punch 1 into the hole of the matrix 3. In the flange of the workpiece, significant compressive stresses occur that can cause creasing.
To prevent this, use clamps 4. It is recommended to use them for drawing from a flat workpiece with D d - d 1 = 225, where < i> D s - diameter of the flat workpiece; d 1 - diameter of the part or semi-finished product; δ is the thickness of the sheet. The process is characterized by the draw ratio m = d 1 /D s. To prevent tearing off the bottom, it should not exceed a certain value. Deep details, which in terms of strength can not be pulled into a single transition, stretch in several transitions. The value of the coefficient т is chosen according to the reference tables depending on the type and condition of the workpiece. For mild steel, the value t is 0.5-0.53 for the first drawing; for the second - 0,75-0,76, etc.
The pulling force of a cylindrical semi-finished product in a stamp with a clamp is determined approximately by the formula
where P 1 is the drawing force, ; P2 is the clamping force, ; n is a coefficient whose value is chosen according to the reference tables depending on the coefficient t; σв - the strength of the material; F 1 - the cross-sectional area of the cylindrical part of the semi-finished product, through which the drawing force is transferred; q is the specific drawing force; F 2 - contact area of the clamp and workpiece at the initial drawing point.
The value of q is chosen from the directories. For example, for soft steel it is 2-3; aluminum 0.8-1.2; copper 1-1.5; brass 1.5-2.
Depending on the type of semi-finished product, punches and dies can be cylindrical, conical, spherical, rectangular, shaped, etc. They are made with rounding of the working edges, the size of which affects the drawing force, the degree of deformation, the possibility of creasing on the flange. The dimensions of the punch and the matrix are chosen so that the gap between them is 1.35-1.5 times the thickness of the deformable metal. An example of a punch for obtaining cylindrical parts is shown in Fig. 9.41.
Fig. 9.41. Details of the die for drawing:
1 - body of the stamp; 2 - the body of the punch; 3 - punch
This form change, in which a part of the sheet preform, located along its closed or unclosed contour, under the action of the punch is displaced into the matrix, simultaneously stretched, rotated and converted into a bead. The formation of the bead from the region along the convex closed or open contour of the sheet preform is a shallow stretch, and along the rectilinear contour - bending.
There are two types of flanging-internal flanging of holes (Figure 9.42, a ) and external flanging of the outer contour (Figure 9.42, b ), which differ in character deformation and stress scheme.
Fig. 9.42. Examples of using the flanging operation:
a - holes; b - the outer contour
The process of flanging holes consists in the formation in a flat or hollow product with a pre-punched hole (sometimes without it) holes of a larger diameter with cylindrical sides (Figure 9.43).
Fig. 9.43. Internal flanging process
For several operations in a flat workpiece, it is possible to obtain holes with a flange of complex shape (Figure 9.44).
Fig. 9.44. Flanging a hole in a complex shape
Flapping holes allows not only to receive constructively successful forms of various products, but also to save stamped metal. At present, parts with a hole diameter of 3-1000 mm with a material thickness of 0.3-30.0 mm are obtained by flanging (Figure 9.45).
Fig. 9.45. Example of obtaining a part with inner and outer flanging
The degree of deformation is determined by the ratio of the diameter of the hole in the workpiece to the diameter of the bead along the middle line D (Figure 9.46).
Fig. 9.46. Scheme for calculating the diameter of the flanging hole
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