Molded material production method and molded material

Abstract

Provided are: a method for producing a molded material comprising tubular body and a flange formed at an end portion of the body; and a molded material produced thereby, which can prevent the flange of the molded material becoming unnecessarily thick, avoid the generation of wrinkles and buckling, and allow weight reduction of the molded material and size reduction of a base metal sheet. When producing the molded material by molding processes including at least one drawing-out process and at least one drawing process performed after the drawing-out process, a first drawing process is carried out on a region corresponding to the body while opening a die and a drawing sleeve, and an ironing process is carried out on a region corresponding to the flange while keeping a constant interval of a mold gap between the die and the drawing sleeve.

Claims

1. A method for producing a molded material, the molded material comprising a tubular body and a flange formed at an end portion of the body, the method comprising: performing at least one drawing-out process on a base metal sheet to form a first intermediate body from the base metal sheet, wherein the at least one drawing-out process is carried out using a first mold that comprises a punch and a first die having a pushing hole; performing one or more drawing processes performed after the at least one drawing-out process, completion of the one or more drawing processes resulting in the molded material from the first intermediate body, wherein a first drawing process of the one or more drawing processes is carried out using a second mold comprising a second die and a drawing sleeve; wherein the first drawing process is carried out on a region that corresponds to the body of the molded material upon the completion of the one or more drawing processes, while a gap between the second die and the drawing sleeve is open so that an outer edge of the first intermediate body is not sandwiched therebetween; wherein the first drawing process further includes an ironing process performed on a region that corresponds to the flange of the molded material upon completion of the one or more drawing processes, while keeping a constant interval of the gap between the second die and the drawing sleeve, the second die and the drawing sleeve sandwiching the region that corresponds to the flange; and wherein the second mold comprises a stopper and a lifter plate, and the constant interval of the gap is determined by a position of the stopper along an axial direction of the drawing sleeve.

2. The method for producing the molded material according to claim 1, wherein an ironing ratio of the ironing process is 35% or more and 50% or less.

3. The method for producing the molded material according to claim 1, wherein the constant interval of the gap is set to the same value as a thickness of the flange of the molded material.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a perspective view showing a molded material produced by a method for producing a molded material according to Embodiment 1 of the present invention.

(2) FIG. 2 is a sectional view taken along the line II-II in FIG. 1.

(3) FIG. 3 is an explanatory view illustrating a method for producing the molded material shown in FIG. 1.

(4) FIG. 4 is an explanatory view illustrating a mold used in the drawing-out process shown in FIG. 3.

(5) FIG. 5 is an explanatory view illustrating the drawing-out process performed with the mold shown in FIG. 4.

(6) FIG. 6 is an explanatory view illustrating a mold used in the first drawing process show in FIG. 3.

(7) FIG. 7 is an explanatory view illustrating a first drawing process performed with the mold shown in FIG. 6.

(8) FIG. 8 is a graph showing a thickness distribution of a molded material produced by a method for producing a molded material according to the present embodiment.

(9) FIG. 9 is an explanatory view showing the sheet thickness measured positions in the molded material shown in FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(10) Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1

(11) FIG. 1 is a perspective view showing a molded material 1 produced by a method for producing a mold material according to Embodiment 1 of the present invention. As shown in FIG. 1, the molded material 1 produced by the method for producing the molded material according to the present embodiment includes a body 10 and a flange 11. The body 10 is a tubular portion having a top wall 100 and a circumferential wall 101 that extends from an outer edge of the top wall 100. Depending on the orientation of the molded material 1 to be used, the top wall 100 may be referred to by other terms, such as a bottom wall. In FIG. 1, the body 10 is shown to have a perfectly circular sectional shape, but the body 10 may have another shape, for example, such as an elliptical sectional shape or angular tubular shape. The top wall 100 may be subjected to further processing. For example, a protrusion further projecting from the top wall 100 can be formed. The flange 11 is a sheet portion formed on an end portion (an end of the circumferential wall 101) of the body 10.

(12) FIG. 2 is a sectional view taken along the line II-II in FIG. 1. As shown in FIG. 2, a sheet thickness t.sub.11 of the flange 11 is lower than a sheet thickness t.sub.101 of the circumferential wall 101 of the body 10. The reason for this is that the ironing process is performed on a region of corresponding to the flange 11 of a base metal sheet 2 (see FIG. 3), as will be described in detail below. As used herein, the sheet thickness t.sub.11 of the flange 11 means an average value of the sheet thickness of the flange 11 from a lower end of a lower side shoulder portion Rd between the circumferential wall 101 and the flange 11 to an outer end of the flange 11. Similarly, the sheet thickness t.sub.101 of the circumferential wall 101 means an average value of the sheet thickness of the circumferential wall 101 from an upper end of the lower side shoulder portion Rd to a lower end of an upper side shoulder portion Rp.

(13) FIG. 3 is an explanatory view illustrating the method for producing the molded material 1 shown in FIG. 1. The method for producing the molded material according to the present invention produces the molded material 1 by performing at least two molding processes on a flat base metal sheet 2. The at least two molding processes include at least one drawing-out process and at least one drawing process performed after the drawing-out process. In the method for producing the molded material according to this embodiment, the molded material 1 is produced by one drawing-out process and three drawing processes (first to third drawing processes). Various metal sheets, such as cold-rolled steel sheets, stainless steel sheets, and plated steel sheets based on these sheets, can be used as the base metal sheet 2.

(14) FIG. 4 is an explanatory view illustrating a mold 3 used in the drawing-out process shown in FIG. 3, and FIG. 5 is an explanatory view illustrating the drawing-out process performed with the mold 3 shown in FIG. 4. As shown in FIG. 4, the mold 3 used in the drawing-out process includes a die 30; a punch 31; and a cushion pad 32. The die 30 is provided with a pushing hole 30a into which the base metal sheet 2 is pushed together with the punch 31. The cushion pad 32 is disposed at an outer peripheral position of the punch 31 so as to face an outer end surface of the die 30.

(15) As shown in FIG. 5, in the drawing-out process, an outer edge portion of the base metal sheet 2 is not completely constrained by the die 30 and the cushion pad 32, and the outer edge portion of the base metal sheet 2 is drawn out until it escapes from the constraint applied thereto by the die 30 and the cushion pad 32. The entire base metal sheet 2 may be pushed together with the punch 31 into the pushing hole 30a and drawn out.

(16) Next, FIG. 6 is an explanatory view illustrating a mold 4 used in the first drawing process in FIG. 3, and FIG. 8 is an explanatory drawing showing the first drawing by means of the mold 4 in FIG. 7. With reference to FIGS. 6 and 7, the movement of the mold and the state of processing during the first drawing process will be described in detail.

(17) As shown in FIG. 6, the mold 4 used in the first drawing process includes a die 40; a punch 41; a drawing sleeve 42; a lifter plate 43; a killer pin 44; and a stopper 45. The die 40 is provided with a pushing hole 40a into which a first intermediate body 20 formed by the above drawing-out process is pushed together with the punch 41. The drawing sleeve 42 is disposed at an outer peripheral position of the punch 41 so as to face an outer end surface of the die 40.

(18) Referring now to the figure as shown on the left side of the dashed line in FIG. 6, the first intermediate body 20 is placed on an upper surface of the lifter plate 43, and an inner peripheral surface of the first intermediate body 20 is in contact with an outer peripheral surface of the drawing sleeve 42. At this time, although the die 40 begins to descend, the outer end surface of the die 40 is not in contact with the first intermediate body 20, so that the drawing process of the first intermediate body 20 is not started yet. The tip of the killer pin 44 provided on the outer end surface of the die 40 does not reach the upper surface of the lifter plate 43.

(19) Referring to the figure as shown on the right side of the dotted line in FIG. 6, the die 40 further descends to be in contact with the first intermediate body 20, whereby the drawing process begins. At this time, the tip of the killer pin 44 reaches the upper surface of the lifter plate 43, so that the die 40 descends and also pushes down the lifter plate 43. This will allow maintenance of the state where the flange tip of the first intermediate body 20 is not in contact with the upper surface of the lifter plate 43.

(20) Next, referring to the figure as shown on the left side of the dotted line in FIG. 7, the die 40 continues to further descend, and the drawing process for responding to the pushing hole 40a of the die 40 is carried out on the body of the first intermediate body 20. At this time, a tip of a killer pin 44 reaches the upper surface of the lifter plate 43 and pushes down the lifter plate 43 as the die 40 descends. Therefore, the tip of the flange of the first intermediate body 20 which is subjected to the drawing process is not in contact with the upper surface of the lifter plate 43 and is in an uplifting state. Although the body of the first intermediate body 20 is being pushed into the pushing hole 40a due to relative motion between the die 40 and the punch 41, the tip of the flange is uplifting, so that any compressive stress in the upward direction is not applied to the circumferential wall of the body. Further, the gap between the die 40 and the drawing sleeve 42 is open, and a region corresponding to an outer edge of the first intermediate body 20 does not reach a state where the region is sandwiched by the die 40 and the drawing sleeve 42.

(21) According to the figure as shown on the right side of the dotted line in FIG. 7, the die 40 further continue to descent, so that the lower surface of the lifter plate 43 will be brought into contact with the stopper 45 provided on the outer peripheral surface of the drawing sleeve 42. The lower surface of the lifter plate 43 is brought into contact with the stopper 45 provided on the outer peripheral surface of the drawing sleeve 42, whereby, hereafter, the drawing sleeve 42 will descend in synchronization with the die 40. Further, the interval of the mold gap between the die 40 and the drawing sleeve 42 will be constant. In this case, since the interval of the mold gap is provided so as to be equal to the thickness of the flange 11 of the final molded material 1, the region corresponding to the flange 11 of the final molded material 1 can be subjected to an ironing process.

(22) Thus, according to the method for producing the molded material of the present invention, in the first drawing process, the timing for starting the ironing process on the region corresponding to the flange 11 of the final molded material 1 can be determined based on abutting of the lifter plate 43 against the stopper 45.

(23) Further, the interval of the mold gap between the die 40 and the drawing sleeve 42 can be determined by the position of the stopper 45 along the axial direction of the drawing sleeve 42.

(24) As shown on the right side of the dotted line in FIG. 7, when the drawing process is carried out on the body of the first intermediate body 20 in the first drawing process, the diameter of the flange does not change. Therefore, in this case, the gap between the die 40 and the drawing sleeve is open so that the outer edge of the first intermediate body 20 is not sandwiched. This will allow suppression of a decrease in the thickness of the circumferential wall of the body.

(25) On the other hand, as shown on the right side of the dotted line in FIG. 7, when the drawing process is carried out on the outer edge of the first intermediate body 20, the diameter of the flange is decreased. In this case, generation of wrinkles and/or buckling can be prevented by molding the region corresponding to the flange while keeping the constant interval of the mold gap between the die 40 and the drawing sleeve 42.

(26) It should be noted that before the lifter plate 43 abuts against the stopper 45, the die 40 and the drawing sleeve 42 will sandwich the region corresponding to the flange 11 of the final molded material 1 in the first intermediate body 20. At this time, sufficient upward pressure must be applied to the drawing sleeve 42 such that the drawing sleeve 42 does not descend until the lifter plate 43 abuts against the stopper 45. Specifically, this can be achieved by providing an urging member 46 such as a spring at a lower portion of the drawing sleeve, and then adjusting its strength, or the like.

(27) The second drawing process and the third drawing process shown in FIG. 3 can be carried out using a conventional mold (not shown). In the second drawing process, the drawing process is further performed on a region of a second intermediate body 21 (see FIG. 3) formed in the first drawing process, the region corresponding to the body 10. The third drawing process corresponds to a re-striking process, in which the ironing process is performed on a region of a third intermediate body 22 (see FIG. 3) formed in the second drawing process, the region corresponding to the body 10.

(28) In the first to third drawing processes, shrinkage occurs in the region corresponding to the flange 11, and an increase in the thickness occurs in this region. Therefore, the ironing ratio in the first drawing process may be set so as to be equal to or less than the thickness of the flange 11 of the final formed material 1, taking an increased amount of the thickness into account. It should be noted that the ironing ratio can be adjusted as needed by changing the interval of the mold gap between the die 40 and the drawing sleeve 42 in the drawing process. By sufficiently reducing the sheet thickness of the region corresponding to the flange 11 in the first drawing process, the sheet thickness t.sub.11 of the flange 11 can be decreased as compared with the sheet thickness t.sub.101 of the circumferential wall 101 of the body 10, in the final molded material 1.

Examples

(29) Next, Examples will be described. The present inventors prepared a round sheet having a thickness of 1.8 mm and a diameter of 116 mm and formed by conducting ZnAlMg plating on a common cold-rolled steel sheet, as the base metal sheet 2. The drawing-out process was then carried out under the following processing conditions. Here, the ZnAlMg alloy plating was applied onto both surface of the steel sheet, and a plating coverage was 90 g/m.sup.2 for each surface. Here, the ironing ratio was set by changing the interval of the mold gap between the die 40 and the drawing sleeve 42 by adjusting the position of the stopper 45 attached to the drawing sleeve 42. Ironing ratio of region corresponding to flange 11: 50% to 60%; Tip angle of die 40: 45; Shoulder radius of drawing sleeve 42: 5 mm; Press oil: TN-20; and Material of die and punch: SKD 11 (HRC 60).

(30) <Evaluation of Ironing Ratio>

(31) Table 1 shows a relationship between the ironing ratio and the flange molding evaluation. Here, the average thickness of the flange of the first intermediate body was 2.0 mm.

(32) TABLE-US-00001 TABLE 1 Ironing Ratio Mold Gap (%) (mm) State of Flange Molding Evaluation 50 3.0 Wrinkles, Buckling x 35 2.7 Good 20 2.4 Good 0 2.0 Good 20 1.6 Good 35 1.3 Good 50 1.0 Good 60 0.8 Cracking x
Average Sheet Thickness of First Intermediate Body: 2.0 mm

(33) When the interval of the mold gap was 3.0 mm, the ironing ratio was 50%. In this case, a gap of a closest portion between the die and the drawing sleeve was larger, so that wrinkles and buckling were generated in the flange. Further, when the interval of the mold gap was 0.8 mm, the ironing ratio was 60%, and cracking occurred during the molding so that the molding was not possible. Only in the range of the ironing rate of from 35% to 50%, the molding was possible without wrinkles, buckling and cracking.

(34) <Ironing Ratio>

(35) The ironing ratio is as represented by the following equation (1). Here, a value of the sheet thickness of the flange of the first intermediate body can be used as the sheet thickness before ironing, and a value of the interval of the mold gap can be used as the sheet thickness after ironing.

(36) $\begin{array}{cc}\mathrm{Ironing}\mathrm{Ratio}\left(\%\right)=\frac{\begin{array}{c}\mathrm{Sheet}\mathrm{thickness}\mathrm{before}\mathrm{ironing}-\\ \mathrm{Sheet}\mathrm{thickness}\mathrm{after}\mathrm{ironing}\end{array}}{\mathrm{Sheet}\mathrm{thickness}\mathrm{before}\mathrm{ironing}}100& \left(1\right)\end{array}$

(37) <Sheet Thickness of Flange>

(38) Next, FIG. 8 is a graph showing the sheet thickness distribution of the molded material produced from the first intermediate body. FIG. 9 is an explanatory view showing the sheet thickness measured positions in FIG. 8.

(39) When the drawing process, among the first drawing process, is carried out on the region corresponding to the body of the molded material, the gap between the die and the drawing sleeve is opened so as not to sandwich the material, thereby suppressing a decrease in the sheet thickness of the circumferential wall. It is thus found that at the timing when the drawing process progresses and the region corresponding to the flange of the molded material reaches the closest portion between the die and the drawing sleeve, the interval of the mold gap between the die and the drawing sleeve is hereafter kept constant to carried out the molding, so that the sheet thickness of the flange of the final molded material can be decreased. When the molded material which was subjected to the drawing-out process involving the ironing process (Inventive Example) and the molded material subjected to the conventional common drawing process (Comparative Example) had the same external dimensions, the weight of the Inventive Example was about 10% less than the weight of the Comparative Example.

(40) When the drawing-out process involving the ironing is carried out, the region corresponding to the flange 11 of the first intermediate body 20 is stretched. In order to form the molded material subjected to the drawing-out process involving the ironing (Inventive Example) and the molded material subjected to the conventional common drawing process (Comparative Example), both of which have the same external dimensions, either a smaller base metal sheet 2 may be used taking into consideration, in advance, an amount of stretching the region corresponding to the flange 11, or an unnecessary portion of the flange 11 may be trimmed.

(41) In such a method for producing the molded material and the molded material produced thereby, the drawing process involves an ironing process performed on the region corresponding to the flange 11 of the first intermediate body 20 by pushing the first intermediate body 20 together with the punch 41 into the pushing hole 40a. Therefore, the wrinkles and/or buckling can be prevented, the sheet thickness of the flange 11 can be prevented from becoming unnecessarily thicker, and the weight of the molded material 1 can be reduced. This configuration is particularly useful for applications in which weight reduction of the molded material and size reduction of the base metal sheet are required, such as motor cases.

(42) Further, the ironing ratio of the ironing process performed during the drawing process is 35% or more and 50% or less, and therefore the generation of wrinkles, buckling and cracking can be avoided.

(43) Furthermore, when the drawing process is performed on the region corresponding to the body, the gap between the die 40 and the drawing sleeve 42 is opened so as not to sandwich the material, thereby suppressing a decrease in the sheet thickness of the circumferential wall, and at the timing when the region corresponding to the flange of the first intermediate body reaches the closest portion between the die 40 and the drawing sleeve, the molding is carried out while keeping the constant interval of the mold gap between the die 40 and the drawing sleeve 42, whereby the generation of wrinkles and/or buckling in the region corresponding to the flange can be avoided.

(44) Further, although the present embodiment illustrates that the three drawing processes are performed, the number of the drawing processes may be changed, as needed, according to the size and required dimensional accuracy of the molded material.

DESCRIPTION OF REFERENCE NUMERALS

(45) 1 molded material 10 body 100 top wall 101 circumferential wall 11 flange 2 base metal sheet 20 first intermediate body 3 mold 30 die 30a pushing hole 31 punch 31a width variation portion 40 die 40a pushing hole 41 punch 42 drawing sleeve 43 lifter plate 44 killer pin 45 stopper 46 urging member