JPH04351230A - Warm bulging method for aluminum alloy sheet - Google Patents

Abstract

PURPOSE:To provide a warm bulging method for aluminum alloy sheet enabling improvement of bulging formability of the aluminum alloy sheet used as pressed part of body sheet, etc., for car. CONSTITUTION:The warm bulging process for aluminum alloy sheet has the peculiarity, in which, at the time of bulging the aluminum alloy sheet with a forming apparatus providing a punch 4 and a sheet holder 2 having a die used together with a bead, the forming is executed under condition of heating the contacting part of a blank 11 with the punch at the temp. lower than m.p. of the blank by 50 deg.C.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a stretch-forming method for stretch-forming aluminum alloy plates when manufacturing press-formed products such as automobile body sheets.

0002

[Conventional technology and its problems] In recent years, in the automobile industry,
As the need for weight reduction is increasing due to reasons such as energy conservation, fuel consumption regulations, and exhaust gas countermeasures, aluminum sheets or aluminum alloy sheets are being adopted as materials to replace steel sheets. However, among aluminum plates and aluminum alloy plates, those with a strength equivalent to mild steel plates have poor ductility and low r-value compared to mild steel plates, so it is necessary to heat the material to reduce deformation resistance. Various methods have been investigated for warm stretch forming to increase the As is well known, warm stretch forming is a process in which a workpiece is heated above room temperature to perform stretch forming, but the problem in doing so is how to improve stretchability. In order to solve such problems, studies have been made on heating conditions, lubrication conditions, mold materials, tool shapes such as punches and dies, etc. for stainless steel and the like. However, in warm stretch forming processing of aluminum alloy plates, heating conditions, mold materials, lubrication conditions, etc. have not yet been sufficiently studied.

0003

SUMMARY OF THE INVENTION The present invention was made in view of the above-mentioned circumstances, and establishes a warm stretch forming process that improves the limit stretch formability of aluminum alloy plates.

0004

[Means for Solving the Problems] The present invention provides a method for melting the portion of the blank where the blank and the punch come into contact when stretch-forming an aluminum alloy plate using a forming device equipped with a plate holder having a punch and a die and a bead. Claim 1 provides a warm stretch forming method for an aluminum alloy plate, characterized in that the forming process is carried out in a heated state at a temperature 50°C lower than the temperature, wherein the blank is rolled with a rolling roll having a roughened surface. and the center line average roughness Ra in the direction showing the largest value on the plate surface is 0.1 to 2.0.
μm, and the surface roughness is adjusted so that the average distance between peaks or valleys that is twice Ra or more is 50 μm or more. Claim 2 provides a warm stretch forming method for an aluminum alloy plate, characterized in that a lubricating medium such as mineral oil or a Teflon sheet is used.

[0005]

[Function] In general, the stretch forming limit is determined by the uniformity of strain distribution and deformation resistance, and the more uniform the strain distribution and the lower the deformation resistance, the higher the stretch forming limit. Therefore, by heating the contact area between the blank and the punch, the deformation resistance can be reduced.
The molding limit can be improved. It is preferable to heat the molding temperature to a temperature 50°C lower than the melting temperature of the blank.In warm stretch forming, it is preferable to set the molding temperature as high as possible, but when heating the molded blank with a heater, the set temperature and the actual temperature are Since errors and variations may occur between the two, the temperature was set at 50° C. lower than the melting temperature for safety reasons in order to prevent heating above the melting temperature. Further, according to claim 2 of the present invention, by using a lubricating medium at least on the surface of the blank that contacts the punch, the friction coefficient of the portion where the blank and the punch come into contact is reduced, and the area at risk of breakage is reduced. The forming limit can be improved by preventing strain from concentrating on the surface and spreading and distributing the strain uniformly to the surrounding area. Here, the surface roughness of the blank is determined by the centerline average roughness Ra of 0.1 to 2.0 in the direction showing the largest value on the plate surface.
The surface roughness is adjusted so that the average distance between peaks or troughs is 50 μm or more, which is 50 μm or more. This is because the retention during processing deteriorates, resulting in a reduction in the molding limit. Further, according to the method of claim 2, a more outstanding effect can be obtained from the synergistic effect of making the strain distribution uniform and reducing the deformation resistance.

[0006]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings and the like. FIG. 1 shows an example of the warm stretch forming apparatus for aluminum plate material used in the present invention, in which 1 is a heater for heating the plate, 2 is a plate holder having a die and bead, 3 is a heater for heating a punch, 4 is punch, 5
is Steel plate, 6 is insulation material, 7 is cushion pin,
8 is a load cell for load detection, 9 is a bolster and a stand,
10 is a cushion, 11 is a blank, and 12 is a bead for preventing material from flowing into the flange portion. Note that the blank 11 in the present invention is an aluminum alloy plate. Further, the plate-top heater 1 is for heating the blank to a set temperature before forming, and is heated to the same temperature as the punch heater 3. The blank 11 is held between two plate holders, heated to a predetermined temperature by a first heater, and then molded at that temperature. Example 1 An experiment was conducted to examine changes in warm extensibility by changing the heating conditions and molding temperature. Experimental conditions △Blank material and plate thickness: Aluminum alloy plate material A5
182P-O-1mmt △Forming speed: 1mm/sec. △Lubrication conditions: Adhesive Teflon sheet on one side of the blank that comes in contact with the punch. Using the blank material and molding device with the above configuration, the punch and blank are heated to the prescribed temperature as shown in Table 1 below using a heater as shown in Figure 1. Heated. Next, the blank was set in a molding device, pressure was applied to the plate holder, stretch molding was performed at each molding temperature, and the limit height of stretch molding was determined. The results are shown in Table 1.

[0007]

[Table 1]

As is clear from Table 1, the No.
．． 1~No. 3, Comparative Example No. It can be seen that, compared to the case of RT (no heating) in No. 4, by increasing the forming temperature, the deformation resistance of the part where the blank and the punch are in contact decreases, and the limit stretch forming height increases. Furthermore, in the molding temperature range of the present invention, the critical overhang molding height increases as the molding temperature increases;
Comparative example No. The molding at a molding temperature of 600°C in No. 5 is 573, which is the solidus temperature of the blank in this example.
Because the temperature exceeded ℃, local melting occurred and molding became impossible. As described above, it can be seen that the limit overhang molding height is improved according to the range of molding temperature in the present invention. Example 2 Using blanks with different surface roughness and peak or valley spacing, experiments were conducted to examine changes in warm stretch formability due to differences in lubrication conditions. Experimental conditions △Blank material and plate thickness: Aluminum alloy plate material A5
182P-O-1mmt △Molding temperature: 300°C △Molding speed: 1mm/sec. △Lubrication conditions: Synthetic oil was applied to one side of the blank in contact with the punch.Using the blank material and molding apparatus configured as described above, stretch molding was performed in the same manner as in Example 1, and the limit stretch molding height was determined. The results are shown in Table 2.

[0009]

[Table 2]

As is clear from Table 2, No.
．． 1~No. It can be seen that Sample No. 4 has good lubricating oil retention, so the limit stretch forming height is large in all cases, and the formability is good. In contrast, comparative example No. 5 is Ra and L, No. No. 6 has Ra smaller than that of the present invention. It can be seen that Sample No. 7 has a larger Ra than the present invention, a smaller L, and poor lubricating oil retention, so that the limit stretch forming height in all cases is lower than that of the present invention example. Next, No. 8 is Ra and L
No. is within the scope of the present invention, but since no lubrication is required, No.
9 has small Ra and L and no lubrication, so
The limit overhang molding height has become smaller. In this way, the surface roughness within the range of the present invention provides good lubricant retention, and by using a lubricating medium, the deformation resistance at the contact area between the blank and the punch is reduced, and the limit overhang is reduced. It can be seen that the molding height increases.

[0011]

[Effects of the Invention] As explained above, according to the present invention,
Higher stretch moldability can be obtained compared to the case where stretch molding is simply performed, and this has a significant industrial effect.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a molding apparatus used in one embodiment of the present invention.

[Explanation of symbols]

1 Heater for heating the plate 2 Plate holder 3 having dice and beads
Punch heating heater 4 Punch 11 Blank

Claims (2)

[Claims] Claim 1: When stretch-forming an aluminum alloy plate using a forming device equipped with a plate holder having both a punch and a die and a bead, the contact area between the blank and the punch is kept at a temperature below 50°C lower than the melting temperature of the blank. A warm stretch forming method for an aluminum alloy plate, characterized by forming the aluminum alloy plate in a heated state. 2. The blank is rolled with a rolling roll having a roughened surface, and has a center line average roughness Ra of 0.1 to 2.0 μm in the direction showing the largest value on the plate surface, and Ra When stretch-forming an aluminum alloy plate whose surface roughness has been adjusted so that the average distance between peaks or valleys is 50 μm or more, at least the surface of the blank that comes into contact with the punch is coated with mineral oil or a Teflon sheet. 2. The warm stretch forming method for an aluminum alloy plate according to claim 1, wherein a medium having lubricating properties of (registered trademark) is used.