CROSS-REFERENCE TO RELATED APPLICATION
This application claims the benefit of Taiwan Patent Application No. 103119745, filed on Jun. 6, 2014, which is hereby incorporated by reference for all purposes as if fully set forth herein.
BACKGROUND
1. Technical Field
The present invention relates to a drawing die provided with microstructures, and in particular, to a drawing die with a lower die of which surfaces are provided with sunken microstructures.
2. Related Art
Drawing forming is stamping a flat sheet metal (for example, a blank) by using a drawing die to form a required product shape. Please refer to FIG. 1A to FIG. 1D, which are structural flowcharts of processing a blank by using a drawing die in the prior art. FIG. 1E is a schematic view of stresses on parts of a finished product 20. FIG. 1A shows a drawing die 10 in the prior art, including a lower die base 11, a lower die 12, an ejection apparatus 13, a positioning plate 14, a blank holder 15, an upper die base 16, a punch 17, an punch fixing plate 18 and a blank 19. The lower die 12, which is secured on the lower die base 11, coordinates with the blank holder 15 to clamp the blank 19, and coordinates with the corresponding punch 17 to perform drawing processing on the blank 19. FIG. 1B shows a process in which the blank holder 15 descends following a stroke and collides with the blank 19 in a working process of the drawing die 10. FIG. 1C shows a process in which the punch 17 presses the blank 19 to form a shape in a drawing process. FIG. 1D shows a situation where the finished product 20 is ejected by the ejection apparatus 13 after the processing is completed. FIG. 1E is a schematic view of stresses on parts of the finished product 20 in a drawing process in which the blank 19 forms the finished product 20.
Please refer to FIG. 1C, FIG. 1D, and FIG. 1E again. In the foregoing drawing die 10, when the blank 19 of a sheet metal forms the finished product 20 in a cup shape or a barrel shape (the cup shape is used herein as an example), a drawing force Fa applied by the punch 17 on the blank 19 must overcome a strain force f1 required for the strain of the blank, a friction force f2 between the blank holder 15 and the blank 19, and a friction force f3 between the blank 19 and the lower die 12. Besides, when the punch 17 descends to perform forming and the blank 19 gradually forms the finished product 20, an outer edge surface 201 of the finished product 20 gradually shrinks; at the same time, the thickness of a top 202 of the finished product 20 gradually increases. When a blank pressing force Fb applied by the blank holder 15 on the top 202 of the finished product 20 is not sufficient to resist a circumferential compression stress on the top 202, the top 202 wrinkles Besides, the blank pressing force Fb affects the magnitude of the friction force between the blank holder 15 and the blank 19 and the magnitude of the friction force between the blank 19 and the lower die 12.
In another aspect, during the forming, a side wall 204 of the finished product 20 is subject to a drawing force of the punch 17; therefore, the thickness of the side wall 204 of the finished product 20 gradually decreases. When the stress of the side wall 204 exceeds the strength of a material of the side wall 204, an area, close to a bottom 205, of the side wall 204 cracks.
SUMMARY
An objective of the present invention is to provide a drawing die that reduces a friction force between a lower die and a blank so that the blank is of a more uniform thickness after forming a shape and improves formability.
To achieve the foregoing objective, a technical means of a drawing die with a lower die provided with microstructures in the present invention comprises: a lower die, where the lower die is secured on a lower die base, coordinates with a blank holder to clamp a blank and performs drawing processing on the blank by using a punch moving relative to the lower die, where a top working surface, a shoulder surface, and a side wall surface of the lower die comprise multiple microstructures sunken into the surfaces.
In an embodiment, the top working surface, the shoulder surface, and the side wall surface of the lower die comprise multiple microstructures sunken into the surfaces.
In an embodiment, a configuration pattern of the microstructures comprises an irregular pattern, an array pattern, a radial pattern, or a pattern comprising multiple annuluses.
In an embodiment, shapes of sunken surfaces of the microstructures comprise an irregular shape or a geometrical shape such as a triangle, a square, a trapezoid, an ellipse, a circle, or an annulus.
In an embodiment, shapes of sunken cross sections of the microstructures comprise an irregular shape or a geometrical shape such as a triangle, a square, a trapezoid, a semiellipse, or a semicircle.
In an embodiment, sunken spaces of the microstructures may be exposed to air or may be filled with lubricating oil.
In an embodiment, a surface, which touches the blank when drawing is performed, of the lower die comprises multiple microstructures sunken into the surface.
The present invention includes the following features: different from a conventional structure of a lower die, a lower die with sunken microstructures provided in the present invention can use a blank holder and a punch to press a blank when the blank holder clamps the blank and the punch performs drawing forming processing on the blank, so that the blank is in close contact with the microstructures of the lower die and is drawn on surfaces provided with the microstructures; because the surfaces, on which the microstructures are distributed, of the lower die reduce a friction force between the blank and the lower die, a drawing force of the punch is reduced, so as to reduce variations in the thickness of a finished product formed by the blank (that is, the finished product is of a uniform thickness), thereby improving formability of a drawing die.
BRIEF DESCRIPTION OF THE DRAWINGS
The disclosure will become more fully understood from the detailed description given herein below for illustration only, and thus are not limitative of the disclosure, and wherein:
FIG. 1A to FIG. 1D are structural flowcharts of processing a blank by using a drawing die in the prior art;
FIG. 1E is a schematic view of stresses on parts of a finished product in a process in which a blank forms the finished product;
FIG. 2 is a schematic structural view of a profile of a drawing die with a lower die provided with microstructures before drawing is performed according to an embodiment of the present invention;
FIG. 3 is an enlarged view of a part in FIG. 2;
FIG. 4 is a schematic structural view of a profile of a drawing die with a lower die provided with microstructures when drawing is performed according to an embodiment of the present invention;
FIG. 5 is an enlarged view of a part in FIG. 4;
FIG. 6A to FIG. 6D are schematic views of configuration patterns of different pattern embodiments of microstructures formed on surfaces of a lower die according to the present invention;
FIG. 7A to FIG. 7G are schematic views of different shape embodiments of sunken contours of microstructures formed on surfaces of a lower die according to an embodiment of the present invention; and
FIG. 8A to FIG. 8F are schematic views of different shape embodiments of sunken cross sections of microstructures formed on surfaces of a lower die according to an embodiment of the present invention.
DETAILED DESCRIPTION
Embodiments of the present invention are described as follows with reference to the accompanying drawings.
Please refer to FIG. 2 and FIG. 3 first. A drawing die 30 in this embodiment includes a lower die 31, where the lower die 31 is secured on a lower die base 32, and a positioning plate 34 used for positioning a blank W of which a sheet metal is to be processed is disposed on the lower die 31; a punch 33 is secured on an punch fixing plate 332 on a bottom of an upper die base 331; and a blank holder 35 capable of moving with the punch fixing plate 332 is disposed between the punch 33 and the lower die 31. The lower die 31 can coordinate with the punch 33 moving relative to the lower die 31, to perform drawing processing on the blank W. The lower die 31 includes a die cavity 311, a top 312 on a periphery of the die cavity 311, a shoulder 313 adjacent to the top 312, and a die cavity side wall 314 adjacent to an other side of the shoulder 313. A top working surface 3121 (a part of the top 312) in contact with the blank W of the lower die 31 and a shoulder surface 3131 include multiple microstructures 40 sunken into the surfaces. In another embodiment, further, a side wall surface 3141 of a part of the die cavity side wall 314 also includes sunken microstructures 40′.
Please refer to FIG. 4 and FIG. 5 then. When the drawing die 30 performs drawing, the punch 33 moves downward into the die cavity 311, so as to draw the blank W placed on the lower die 31. At this time, the blank W is in a position which is limited by the positioning plate 34 and covers the die cavity 311, where the blank is to be drawn in this position. When the punch 33 moves downward to act on the blank W above the die cavity 311, because the blank W on the periphery of the die cavity 311 is clamped by a blank holder 35, which descends earlier, in coordination with the secured lower die 31, when the punch 33 continues to push the blank W downward, the blank W strains due to the drawing, so as to form a cylindrical side wall. By using the microstructures 40 on the top working surface 3121 and the shoulder surface 3131 (and the microstructures 40′ on the side wall working surface 314) of the lower die 31, a friction force f3′ between the lower die 31 and the blank W can be reduced, thereby reducing a drawing force required for shaping the blank W by the punch 33. In this way, the drawing force applied on the blank W by the punch 33 decreases, and an acting force that reduces the thickness of the blank is reduced at the same time, so that the side wall is of a more uniform thickness T and the drawing die 30 has good formability.
In an embodiment, the top working surface 3121, the shoulder surface 3131, and the side wall surface 3141 of the lower die 31 include multiple sunken microstructures (40 and 40′) (as shown in FIG. 3).
Please continue to refer to FIG. 6A to FIG. 6D. In an embodiment, a configuration pattern of the microstructures 40 formed on the top working surface 3121 and the shoulder surface 3131 and the microstructures 40′ formed on the side wall surface 3141 includes an irregular pattern (as shown in FIG. 6A), an array pattern (shown in FIG. 6B), a radial pattern (shown in FIG. 6C), or a pattern including multiple annuluses (shown in FIG. 6D).
Please refer to FIG. 7A to FIG. 7G. In an embodiment, shapes of sunken contours of the microstructures (40 and 40′) formed on the top working surface 3121, the shoulder surface 3131, and the side wall surface 3141 include an irregular microstructure 40a (as shown in FIG. 7A) or a geometrical shape such as a triangular microstructure 40b (as shown in FIG. 7B), a square microstructure 40c (as shown in FIG. 7C), a trapezoid microstructure 40d (as shown in FIG. 7D), an elliptic microstructure 40e (as shown in FIG. 7E), a circular microstructure 40f (as shown in FIG. 7F), or an annular microstructure 40g (as shown in FIG. 7G).
Please refer to FIG. 8A to FIG. 8E then. In an embodiment, shapes of sunken cross sections of the sunken microstructures (40 and 40′) on the surfaces of the lower die 31 include an irregular microstructure 401 (as shown in FIG. 8A) or a geometrical shape such as a triangular microstructure 40II (as shown in FIG. 8B), a square microstructure 40III (as shown in FIG. 8C), a trapezoid microstructure 40IV (as shown in FIG. 8D), a semielliptical microstructure 40V (as shown in FIG. 8E), or a semicircular microstructure 40VI (as shown in FIG. 8F).
As shown in FIG. 8E and FIG. 8F, in an embodiment, sunken spaces of the microstructures 40V may be exposed to air, so that the spaces are filled with air (FIG. 8E), or sunken spaces of the microstructures 40VI are filled with lubricating oil L (shown in FIG. 8F).
It must be made clear that in the foregoing embodiments, contour diameters and sinking depths of the sunken “microstructures” formed on the surfaces of the lower die and provided in the present invention and intervals between the microstructures depend on a size, a structure, and precision of a to-be-formed finished product, a size, a structure, and precision of the drawing die corresponding to the finished product, a feature of a material of the used board, and the like. However, on a premise that no nick or scratch is caused on a surface of the processed board, all contour sizes, contour intervals, and sinking depths fall within the scope of the microstructures which the present invention defines and claims to protect.
Compared with the prior art, the present invention has the following advantages: a lower die with sunken microstructures provide in the present invention can use a blank holder and a punch to press a blank when the blank holder clamps the blank and the punch performs drawing forming processing on the blank, so that the blank is in close contact with the microstructures of the lower die and is drawn on surfaces provided with the microstructures; because the surfaces, on which the microstructures are distributed, of the lower die can reduce a friction force between the blank and the surfaces of the lower die, a drawing force of the punch is reduced, so as to reduce variations in the thickness of a finished product formed by the blank (that is, the finished product is of a more uniform thickness), thereby improving formability of a drawing die.
In conclusion, the foregoing is merely preferred implementation manners or embodiments presenting the technical means adopted in the present invention to solve the problem, and is not intended to limit the implementation scope of the patent of the present invention. That is, all equivalent variations and modifications in accordance with the idea in the application scope of the patent of the present invention or made according to the scope of the patent of the present invention are covered by the scope of the patent of the present invention.
Patent Application
20150352628
