Method of production of a part formed with an opening
This application is a continuation of application Ser. No. 451,961, filed 12/21/82, now abandoned. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a method of production of a part formed with an opening, such as a part of a fluid machine used as a fluid outlet port or a part of a fan serving as a mouth ring. 
     BACKGROUND OF THE INVENTION 
     As shown in FIGS. 1 and 2 in a prior art method a flat ring blank 2 is produced by punching a rectangular metal sheet 1 by a press. Then a part 3 formed with an opening 7 is produced by stretching the flange inwardly of the ring material 2 as indicated at 3a and shrink flanging outwardly thereof as indicated at 3b by a press. 
     In the method of production of the prior art, portions of the material or rectangular metal material 1 corresponding to four corners 4 and a portion 5 corresponding to the opening 7 are scrapped as waste material. Thus, the material has a very low yield and a large portion thereof is discarded as waste material. When the part 3 is formed by drawing, the stretch flange 3a has its thickness reduced in going from its base toward its end, thereby causing a reduction in strength. Meanwhile the shrink flange 3b has its thickness increased in going from its base toward its end, thereby causing an increase in weight. 
     SUMMARY OF THE INVENTION 
     This invention has as its object the provision of a method of production of a part formed with an opening capable of producing such part by minimizing waste of the material while imparting a uniform thickness to the part. 
     The outstanding characteristic of the invention enabling the aforesaid object to be accomplished is that a metal strip material has its outer peripheral portion rolled to have its thickness slightly reduced to wind the metal strip into a ring-shaped blank, and a flange is formed by drawing at least one of outer and inner peripheral portions of the ring-shaped blank. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a ring blank produced by punching by a method of the prior art for producing a part formed with an opening; 
     FIG. 2 is a sectional view of a part formed with an opening produced as a completed article by the method of the prior art; 
     FIG. 3 is a perspective view of an apparatus suitable for carrying into practice the method of production of a part formed with an opening comprising one embodiment of the invention; 
     FIG. 4 is a sectional view of the material used for producing a part formed with an opening by the method of the invention being subjected to rolling by the apparatus shown in FIG. 3; 
     FIG. 5 is a fragmentary plan view of the material used for producing a part formed with an opening by the method according to the invention being subjected to cutting; 
     FIG. 6 is a fragmentary plan view of the material used for producing a part formed with an opening by the method according to the invention being subjected to welding by electric spot welding; and 
     FIG. 7 is a sectional view in explanation of the operation of forming flanges in the ring-shaped blank formed of the material shown in FIGS. 4, 5 and 6 by the method according to the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings wherein like reference numerals are used throughout the various views to designate like parts and, more particularly, to FIGS. 3-6, according to these figures, a metal strip material 11, such as steel, aluminum, etc., having a width large enough to form a ring-shaped blank is wound in coil form and supported on an uncoiler 13. The metal strip material 11 is payed out of the uncoiler 13 and fed through a loop control means 14 to a roll bending machine 15 where it is rendered straight by a leveler 16 before reaching roll means 17 for effecting rolling. The roll means 17 comprises, as shown in FIG. 4, a rolling roll 18 of minor diameter supported in a vertical position, and a rolling roll 19 of major diameter supported in an inclined position, with the rolling roll 18 of minor diameter being formed with an inclined cutout 18a in its upper portion. The rolling rolls 18 and 19 of minor and major diameters are spaced apart from each other by a gap of a dimension such that the gap is smaller at its lower end than the thickness of the metal strip material 11, substantially equal thereto at a starting point of the cutout 18a, and larger in the cutout 18a. The metal strip material 11 is rolled in such a manner that a lower end of a portion below the cutout 18a of the rolling roll 18 is minimized in thickness and the thickness increases in going upwardly from the lower end with the metal strip material 11 being automatically bent inwardly and shaped into a ring-shaped blank. 
     A portion of the metal strip material 11 corresponding to the cutout 18a of the rolling roll 18 becomes wrinkled as indicated at 11a. The amount of a bend formed in the metal strip material 11 may vary in dependence upon the manner in which the strip 11 is deformed in a thickness direction, but the amount shows variations of a large value when the initial thickness of the strip 11 is not uniform. This makes it necessary to provide a guide 20 of a predetermined arcuate shape at the outlet of the roll means 17 to effect adjustments. The metal strip material 11 bent into a ring-shaped blank is fed to cutting means 21. An encoder 22, for converting a signal representing a number of revolutions to a signal representing a length, is located anterior to the cutting means 21 in contact with an outer peripheral surface of the strip material for measuring the circumferential length of the strip material 11 that has been fed. When the metal strip material 11 has been fed for a length large enough to form the ring-shaped blank, the encoder 22 supplies a signal to the cutting means 21 to cut the metal strip material 11. When cutting of the metal strip material 11 is effected, the strip 11 is stamped to remove a small portion 11b (hatched portion) to be discarded as a scrap, as shown in FIG. 5. At this time, a projection 11c for welding is formed at one end portion of the severed strip 11. Then the projection 11c is joined by an electric spot welding machine 23 shown in FIG. 3 to the other end portion in such a manner that, as shown in FIG. 6, the projection 11c alone is superposed on the other end portion and end face portions 11d and 11e except for the end face of the projection 11c are abutted against the end face 11f of the other end portion. The spot welding is shown in FIG. 6 at 11g. Thereafter the ring-shaped blank is drawn by means of a press 24 shown in FIG. 3 to form a stretch flange 25a on its inner side 11h and a shrink flange 25b on its outer side 11i indicated by phantom lines, to provide an article 25 as shown in FIG. 7. The stretch flange 25a is formed by removing the wrinkle 11a of the blank 11 and elongating the material of the blank 11, so that the thickness of the article 25 becomes unified and all the portions thereof become equal in thickness to its central portion 25c. The shrink flange 25b is formed while the material itself is compressed to have its thickness increased to a value equal to that of the central portion 25c. 
     By the method of production of a part formed with an opening described hereinabove, the metal strip material 11 is formed into a ring-shaped blank by rolling the output peripheral portion of the strip 11 in a manner to reduce its thickness slightly, and at least one of the inner and outer peripheral portions of the ring-shaped blank is drawn to form flanges 25a and 25b. Thus, almost all the material of the metal strip material 11 can be utilized to provide the article 25 formed with an opening. The method according to the invention enables a part formed with an opening to be produced without wasting the material and makes it possible to economize on material cost. The article 25 formed with an opening according to the invention is free from the defect of being low in strength or heavy in weight because the flanges 25a and 25b have the same thickness as the central portion 25c of the article 25. 
     The metal strip material 11 is wound in coil form on the uncoiler 13 and has loops removed by the loop control means 14 and straightened by the leveler 16 before being rolled. This makes it possible to produce the article 25 formed with an opening continuously and automatically on a mass production basis. 
     When the metal strip material 11 has its outer peripheral portion rolled and has its thickness slightly reduced by rolling to provide a ring-shaped blank, the wrinkle 11a on the inner side of the strip material 11 is removed while the inner peripheral surface is drawn by means of a press to form the stretch flange 25a. This makes it possible to render the thickness of the stretch flange 25a equal to that of the central portion 25c of the article 25. 
     When the ring-shaped blank formed from the metal strip material 11 is cut, the projection 11c for welding is formed at one end portion of the ring-shaped blank and superposed on the other end portion of the blank and the overlapping is subjected to welding by electric spot welding before the flanges 25a and 25b are formed by drawing. This enables improved dimensional accuracy to be obtained. 
     The meritorious effects achieved by the invention include the following. The method according to the invention enables almost all the material of the metal strip material 11 to be utilized in producing the article 25 formed with an opening. Thus, waste of the material can be minimized, making it possible to economize on material cost. Since the article 25 has a uniform thickness, the article 25 is free from the defects of low strength or heavy weight.