Patent Publication Number: US-2022228309-A1

Title: Drum structure for laundry treatment device and method of manufacturing drum

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 10-2021-0007005, filed on Jan. 18, 2021, and Korean Patent Application No. 10-2021-0007006, filed Jan. 18, 2021, which is incorporated herein by reference for all purposes as if fully set forth herein. 
     TECHNICAL FIELD 
     The present disclosure relates to a drum structure for laundry treatment device and a method of manufacturing a drum. More specifically, the present disclosure relates to a drum structure for laundry treatment device and a method of manufacturing a drum that do not need to separately manufacture a drum front and a drum rear, do not require separate molds for the manufacture of the drum front and the drum rear, and can reduce the overall manufacturing cost. 
     BACKGROUND 
     Recently, air pollution due to pollutants such as fine dust, ultra-fine dust, and yellow sand has emerged as a serious problem. Such air pollution causes a problem of increasing the washing frequency of laundry by easily contaminating clothes that people wear in their daily life, and at the same time causes a problem of making it difficult to naturally dry the washed laundry in the air. 
     Hence, most homes have a washing machine that can easily and conveniently wash laundry such as clothes, bedding, etc., or a dryer that can easily and conveniently dry the washed laundry by applying hot air to the washed laundry, or a laundry treatment device such as a washer and dryer having both washing and drying functions. 
     A laundry treatment device generally includes a drum in which laundry is accommodated to perform washing or drying. The drum is generally formed in a cylindrical shape and is installed inside a main body of the laundry treatment device. 
     A conventional drum structure for laundry treatment device and a method of manufacturing a drum are disclosed in Korean Patent No. 10-0657465. 
     As illustrated in  FIG. 1 , a conventional drum structure for laundry treatment device includes a center drum  58 , a front drum  60 , and a back (rear) drum  70 , each of which is provided separately. The center drum  58 , the front drum  60 , and the back (rear) drum  70  have a structure in which they are coupled to each other. 
     More specifically, the conventional drum structure for laundry treatment device is configured such that bent portions are formed at a front end and a rear end of the center drum  58  formed in a hollow cylindrical shape through rolling of a metal plate; a perimeter portion  61  of the front drum  60  and a front end bent portion  56  of the center drum  58  are curled rearward so that the perimeter portion  61  of the front drum  60  surrounds the front end bent portion  56  of the center drum  58 ; after a perimeter portion  71  of the back (rear) drum  70  and a rear end bent portion  57  of the center drum  58  are curled forward so that the perimeter portion  71  of the back (rear) drum  70  surrounds the rear end bent portion  57  of the center drum  58 , the perimeter portion  61  of the curled front drum  60  and the front end bent portion  56  of the center drum  58  are spot welded to a hollow cylinder  55 ; and the perimeter portion  71  of the curled back (rear) drum  70  and the rear end bent portion  57  of the center drum  58  are spot welded to the hollow cylinder  55 . In this instance, an inlet side of the front drum  60  is generally hemming processed so that edges are overlapped and is formed in a folded shape, and thus strength reinforcement is achieved. 
     As illustrated in  FIG. 2 , a method of manufacturing a conventional drum for laundry treatment device comprises a hole forming step of forming a plurality of holes in a metal plate; a first bending step of bending both ends of the metal plate, in which the holes are formed, in opposite directions; a rolling step of rolling the portion other than both bent ends with a hollow cylinder and hanging one bent end on other bent end; a curling/seaming step of curling the one bent end and the other bent end, that hang each other, on the hollow cylinder and seaming the one bent end and the other bent end with the hollow cylinder; a second bending step S 50  of bending the curled/seamed one bent end, other bent end, and front and rear ends of the hollow cylinder; a front drum coupling step of welding with the hollow cylinder after a perimeter portion of a front drum and a front end bent portion of a center drum are curled rearward so that the perimeter portion of the front drum surrounds the front end bent portion of the center drum; and a rear drum coupling step of welding with the hollow cylinder after a perimeter portion of a rear drum and a rear end bent portion of the center drum are curled forward so that the perimeter portion of the rear drum surrounds the rear end bent portion of the center drum. In this instance, an inlet side of the front drum is generally hemming processed so that edges are overlapped and is formed in a folded shape, and thus strength reinforcement is achieved. 
     However, the conventional drum structure for laundry treatment device and the method of manufacturing the drum have a problem in that a mold for manufacturing the center drum, a mold for manufacturing the front drum, and a mold for manufacturing the back (rear) drum are individually required since the center drum, the front drum, and the back (rear) drum need to be separately manufactured. 
     The conventional drum structure for laundry treatment device and the method of manufacturing the drum also have a problem in that operations such as curling, seaming, and welding need to be performed to couple the separately provided center drum, front drum, and back (rear) drum with each other, and respective facilities are required to perform the operations. 
     The conventional drum structure for laundry treatment device and the method of manufacturing the drum also have a problem in that the manufacturing cost greatly increases due to the separate manufacturing and the coupling of the center drum, the front drum, and the back (rear) drum. 
     The conventional drum structure for laundry treatment device and the method of manufacturing the drum also have a problem in that the inlet side of the front drum needs to be hemming processed in order to reinforce the strength of the inlet side of the front drum, and an end of the inlet side of the front drum may be torn during the hemming processing. 
     PRIOR ART DOCUMENT 
     [Patent Document] 
     (Patent Document 1) KR10-0657465 B1 
     SUMMARY 
     An object of the present disclosure is to address the above-described and other problems. Another object of the present disclosure is to provide a drum structure for laundry treatment device and a method of manufacturing a drum that do not need to separately manufacture a drum front and a drum rear to thereby eliminate the need for separate molds for manufacturing the drum front and the drum rear and can reduce the overall manufacturing cost. 
     In order to achieve the above-described objects, in one aspect of the present disclosure, there is provided a drum structure for laundry treatment device comprising a drum center formed of a metal sheet in a cylindrical shape having a hollow, wherein the drum center includes a reduced drum portion formed by reducing both ends of the drum center, and a curved portion formed in the reduced drum portion. 
     The curved portion is continuously formed over an entire circumference of the reduced drum portion. 
     The curved portion is formed in a concave shape with respect to an outer circumferential surface of the reduced drum portion. 
     The curved portion is formed such that a plurality of curved portions are spaced apart from each other in parallel. 
     The drum center is formed by rolling the metal sheet and then welding both ends of the metal sheet, a welding line according to the welding of both ends of the metal sheet is formed on the drum center, and a reinforcement piece is attached to the welding line. 
     The reinforcement piece is welded to the reduced drum portion in a form perpendicular to the welding line. 
     In order to achieve the above-described objects, in another aspect of the present disclosure, there is provided a method of manufacturing a drum for laundry treatment device, the method comprising a rolling step of rolling a metal sheet in a hollow cylindrical shape; a welding step of welding both ends of the metal sheet to form a drum center; and a molding step of processing a reduced drum portion at both ends of the drum center. 
     The molding step comprises processing a curved portion at both ends of the drum center and processing the reduced drum portion. 
     The molding step comprises processing the curved portion and the reduced drum portion so that the curved portion is positioned in the reduced drum portion. 
     The curved portion supports the processing of the reduced drum portion. 
     The method further comprises, after the molding step, an attaching step of attaching a reinforcement piece to a welding line according to the welding of both ends of the metal sheet. 
     The attaching step comprises welding the reinforcement piece to the reduced drum portion in a form perpendicular to the welding line. 
     A drum structure for laundry treatment device and a method of manufacturing a drum according to the present disclosure have the following advantages. 
     The drum structure for laundry treatment device and the method of manufacturing the drum according to the present disclosure have an advantage in that a drum front and a drum rear do not need to be separately manufactured since a reduced drum portion serving as the drum front and the drum rear is formed at both ends of a drum center, and separate molds for the manufacture of the drum front and the drum rear are unnecessary. 
     The drum structure for laundry treatment device and the method of manufacturing the drum according to the present disclosure also have an advantage in that separate coupling operations such as curling, seaming, and welding are unnecessary since the reduced drum portion is formed in the drum center itself. 
     The drum structure for laundry treatment device and the method of manufacturing the drum according to the present disclosure also have an advantage in that the overall manufacturing cost can be reduced. 
     The drum structure for laundry treatment device and the method of manufacturing the drum according to the present disclosure also have an advantage of being able to prevent tearing of the reduced drum portion that may occur during a hemming processing by forming a curved portion of a simple structure instead of the hemming processing so as to reinforce a strength of the reduced drum portion. 
     The drum structure for laundry treatment device and the method of manufacturing the drum according to the present disclosure also have an advantage of being able to prevent bursting of a welding line due to rotation, vibration, etc. of the drum center since a reinforcement piece is attached to the welding line by welding of a metal sheet. 
     The drum structure for laundry treatment device and the method of manufacturing the drum according to the present disclosure also have an advantage of being able to prevent bursting of the welding line since the reinforcement piece is welded to the reduced drum portion such that the reinforcement piece is perpendicular to the welding line. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the disclosure and are incorporated in and constitute a part of the disclosure, illustrate embodiments of the disclosure and together with the description serve to explain the principle of the disclosure. 
         FIG. 1  is a cross-sectional view illustrating a conventional drum for laundry treatment device. 
         FIG. 2  is a flow chart illustrating a method of manufacturing a conventional drum for laundry treatment device. 
         FIG. 3  is a front perspective view illustrating a drum for laundry treatment device according to an embodiment of the present disclosure. 
         FIG. 4  is a cross-sectional view taken along a portion A-A of  FIG. 3 . 
         FIG. 5  is an enlarged view illustrating a portion B of  FIG. 4 . 
         FIG. 6  is a plane view of  FIG. 3 . 
         FIG. 7  is an enlarged view illustrating a portion C of  FIG. 6 . 
         FIG. 8  is a plane view schematically illustrating that a metal sheet is prepared in a method of manufacturing a drum for laundry treatment device according to an embodiment of the present disclosure. 
         FIG. 9  is a plane view schematically illustrating that a metal sheet of  FIG. 8  is rolled in a hollow cylindrical shape. 
         FIG. 10  is a plane view schematically illustrating that both ends of a metal sheet rolled in a hollow cylindrical shape in  FIG. 9  are welded to form a drum center. 
         FIG. 11  is a plane view schematically illustrating that a curved portion and a reduced drum portion are formed at both ends of a drum center of  FIG. 10 . 
         FIG. 12  is a plane view schematically illustrating that a reinforcement piece is attached to a welding line by welding the reinforcement piece to a reduced drum portion of  FIG. 11 . 
         FIG. 13  is a flow chart illustrating a method of manufacturing a drum for laundry treatment device according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. 
     Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. It will be noted that a detailed description of known arts will be omitted if it is determined that the detailed description of the known arts can obscure the embodiments of the disclosure. 
     The terms disclosed herein are used to merely refer to a specific embodiment and does not intend to limit the present disclosure. A singular expression can include a plural expression as long as it does not have an apparently different meaning in context. In the present disclosure, terms “include” and “have” should be understood to be intended to designate that illustrated features, numbers, steps, operations, components, parts or combinations thereof are present and not to preclude the existence of one or more different features, numbers, steps, operations, components, parts or combinations thereof, or the possibility of the addition thereof. 
     When any component is described as “being connected” or “being coupled” to other component, this should be understood to mean that another component may exist between them, although any component may be directly connected or coupled to the other component. 
       FIG. 3  is a front perspective view illustrating a drum for laundry treatment device according to an embodiment of the present disclosure.  FIG. 4  is a cross-sectional view taken along a portion A-A of  FIG. 3 .  FIG. 5  is an enlarged view illustrating a portion B of  FIG. 4 .  FIG. 6  is a plane view of  FIG. 3 .  FIG. 7  is an enlarged view illustrating a portion C of  FIG. 6 . 
     As illustrated in  FIGS. 3 to 7 , a drum structure for laundry treatment device according to an embodiment of the present disclosure includes a drum center  100  formed of a metal sheet in a cylindrical shape having a hollow  101 . The drum center  100  may include a reduced drum portion  110  formed by reducing both ends of the drum center  100 . 
     As illustrated in  FIG. 3 , the drum center  100  may be formed in a cylindrical shape having a hollow  101  penetrating in a front-rear direction. 
     The drum center  100  is configured to accommodate laundry requiring washing or drying. The drum center  100  may be formed in a cylindrical shape having the hollow  101  by rolling a rectangular metal sheet with a rolling machine so that both ends of the rectangular metal sheet are in contact with each other, and then welding, i.e., butt welding the contacting both ends of the metal sheet using the both ends as a joint. 
     In this instance, both ends of the metal sheet may be welded by a laser welding machine to form the cylindrical drum center  100 . 
     In the drum center  100 , a welding line L according to the welding of both ends of the metal sheet may be formed to extend along an axial direction of the drum center  100 . 
     The drum center  100  may be installed inside a main body (not shown) of a laundry treatment device which is usually called a cabinet. The drum center  100  can rotate as a belt (not shown) mounted on belt mounting portions  105  and  107  to be described later operates by a motor (not shown). 
     The drum center  100  may include the reduced drum portion  110 . 
     As illustrated in  FIGS. 3 to 5 , the reduced drum portion  110  is a portion that is reduced so that a diameter of the drum center  100  decreases, and may be formed at both ends of the drum center  100 . 
     More specifically, the reduced drum portion  110  may be formed in a symmetrical shape at a front end (front side in  FIG. 3 ) and a rear end (rear side in  FIG. 3 ) of the drum center  100 . The reduced drum portion  110  may be formed by reduction processing using a molding machine so that a diameter of each of the front end and the rear end of the drum center  100  is smaller than a central portion of the drum center  100  between the front end and the rear end of the drum center  100 . 
     In this instance, the reduced drum portion  110  may be formed up to an end of a front side of the drum center  100  at one position of a front side on an outer circumferential surface of the drum center  100 , and may be formed up to an end of a rear side of the drum center  100  at one position of a rear side on the outer circumferential surface of the drum center  100 . 
     The reduced drum portion  110  is integrally formed with both ends of the drum center  100  formed of a single metal sheet, and thus the reduced drum portion  110  itself at each of the front and rear ends of the drum center  100  can serve as a drum front and a drum rear in an existing drum structure. Therefore, a drum structure for laundry treatment device according to an embodiment of the present disclosure does not need to separately manufacture the drum front and the drum rear, and hence can have an advantage in that an individual mold is not required for the manufacture of the drum front and the drum rear. 
     In the drum structure for laundry treatment device according to an embodiment of the present disclosure, since the reduced drum portion  110  is formed in the drum center  100  itself formed of a single metal sheet, there is an advantage in that it is not necessary to couple the drum front and the drum rear to the drum center  100  through separate coupling operations such as curling, seaming, and welding. 
     An open surface of the reduced drum portion  110  formed at the front end of the drum center  100  may be an entrance through which laundry can be put into or taken out of the drum center  100  when washing or drying laundry. 
     The drum center  100  may include a curved portion  103  formed in the reduced drum portion  110 . 
     As illustrated in  FIGS. 3 to 5 , the curved portion  103  is configured to reinforce an overall strength of the reduced drum portion  110 . The curved portion  103  may be formed in a symmetrical shape at the front end reduced drum portion  110  and the rear end reduced drum portion  110  to replace separate hemming processing for the strength reinforcement. 
     The curved portion  103  may have an arc-shaped cross-sectional shape and may be continuously formed over an entire circumference of the reduced drum portion  110 . The curved portion  103  may be formed in a circular ring shape when viewed as a whole. 
     The curved portion  103  may be formed at both ends of the drum center  100  by the molding machine together when the reduced drum portion  110  is formed at both ends of the drum center  100 . 
     That is, the curved portion  103  and the reduced drum portion  110  may be formed together on an entire circumference of each of the front end and the rear end of the drum center  100 . In this instance, the reduced drum portion  110  may be formed such that the curved portion  103  is positioned on the reduced drum portion  110 . 
     The curved portion  103  positioned on the reduced drum portion  110  is spaced apart from a flange-shaped edge portion  109  formed at an end of the reduced drum portion  110 . 
     The curved portion  103  and the reduced drum portion  110  may be molded by the molding machine capable of both the processing of the curved portion  103  and the processing of the reduced drum portion  110 . 
     In addition to reinforcing the strength of the reduced drum portion  110 , the curved portion  103  is a structure that can be held by a roller of the molding machine so as to support the reduced drum portion during the processing of the reduced drum portion  110  using the molding machine, and can serve to support the processing of the reduced drum portion  110 . 
     The curved portion  103  may be formed in a concave shape with respect to an outer circumferential surface of the reduced drum portion  110 , and may be formed in a convex shape with respect to an inner circumferential surface of the reduced drum portion  110 . 
     That is, the curved portion  103  may have a concave shape when viewed from the outside of the reduced drum portion  110 , and may have a convex shape when viewed from the inside of the reduced drum portion  110 . The curved portion  103  is formed to protrude from the reduced drum portion  110  to the radial inside. 
     The curved portion  103  may include a concave surface  103   b  that is an outer surface directly connected to the outer circumferential surface of the reduced drum portion  110  and a convex surface  103   c  that is an inner surface directly connected to the inner circumferential surface of the reduced drum portion  110 . A concave groove  103   a  that becomes deeper as it goes toward the center of the bottom may be formed inside the concave surface  103   b.    
     The concave surface  103   b  and the convex surface  103   c  may be formed in an arc-shaped curved surface in which an axial (front-rear direction) width of the curved portion  103  increases as the concave surface  103   b  and the convex surface  103   c  go toward the radial outside of the curved portion  103 . A connection portion between the concave surface  103   b  and the outer circumferential surface of the reduced drum portion  110  may be formed to be round, and a connection portion between the convex surface  103   c  and the inner circumferential surface of the reduced drum portion  110  may also be formed to be round. 
     That is, the curved portion  103  can be formed so that the curved portion  103  itself and the connection portion between the curved portion  103  and the reduced drum portion  110  are not sharp. Thus, when a load due to rotation or vibration of the drum center  100  is applied to the curved portion  103 , it is possible to evenly distribute the load, and hence it is possible to prevent a crack from occurring in a specific part in advance. 
     A plurality of curved portions  103  may be formed in the reduced drum portion  110 , and the plurality of reduced drum portions  110  may be spaced apart from each other in parallel with a part of the reduced drum portion  110  interposed therebetween. 
     A part of the reduced drum portion  110  may be interposed between two adjacent curved portions  103  of the plurality of curved portions  103  and may be connected to the two adjacent curved portions  103 . When viewed as a whole, the plurality of curved portions  103  and the part of the reduced drum portion  110  interposed between the two adjacent curved portions  103  may be formed to be uneven and may be provided to have a waveform shape such as a wave shape. 
     The curved portion  103  formed in the reduced drum portion  110  reinforces the strength of the reduced drum portion  110  without the separate hemming processing, and thus, can prevent tearing of the reduced drum portion  110  and splaying of the welding line L that may occur when the hemming processing is performed on the reduced drum portion  110 . 
     During the processing of the curved portion  103 , the belt mounting portions  105  and  107  may be formed on the outer circumferential surface of the drum center  100 . 
     As illustrated in  FIGS. 3, 4, and 6 , the belt mounting portions  105  and  107  are portions on which a belt (not shown) for rotating the drum center  100  is mounted, and may be processed together when the curved portion  103  is processed. 
     The belt mounting portions  105  and  107  may be formed on the outer circumferential surface of the drum center  100  in the form of a rectangular groove corresponding to a cross-section of the belt (not shown), and the plurality of belt mounting portions may be spaced apart from each other in the drum center  100 . 
     The plurality of belt mounting portions  105  and  107  may have different widths (front-rear widths) in the axial direction of the drum center  100  corresponding to the mounted belt (not shown), and may have the same width. 
     In the present embodiment, the belt mounting portions  105  and  107  may be continuously formed as one body along the entire circumference of the outer circumferential surface of the drum center  100  in the central portion of the drum center  100 , and may be continuously formed along the entire circumference of the outer circumferential surface of the drum center  100  at the separated front and rear sides of the drum center  100 , respectively. The belt mounting portion  105  formed in the central portion of the drum center  100  may be formed to have a front-rear width greater than the two belt mounting portions  107  spaced apart from the belt mounting portion  105 . 
     Hence, a belt (not shown) having a front-rear width greater than the two belt mounting portions  107  spaced apart from the belt mounting portion  105  may be mounted on the belt mounting portion  105  formed in the central portion of the drum center  100 . 
     A reinforcement piece  120  may be attached to the welding line L formed in the drum center  100 . 
     As illustrated in  FIGS. 6 and 7 , the reinforcement piece  120  is a rectangular metal piece and may be attached to span the welding line L in order to prevent bursting of the welding line L due to rotation, vibration, etc. of the drum center  100 . 
     The reinforcement piece  120  may be attached to the reduced drum portion  110  formed on the drum center  100  through welding. 
     More specifically, the reinforcement piece  120  may be disposed on the outer circumferential surface of the reduced drum portion  110  so that the reinforcement piece  120  is interposed between the edge portion  109  and the curved portion  103 . At the same time, the reinforcement piece  120  may be disposed such that its longitudinal direction is perpendicular to the welding line L, and may be attached to the reduced drum portion  110  while spanning the welding line L by being welded to the reduced drum portion  110 . 
     In this instance, the reinforcement piece  120  may be spot-welded at a plurality of welding points S through a spot welding machine. 
     Hence, the reinforcement piece  120  can prevent bursting of the welding line L due to the rotation, vibration, etc. of the drum center  100  and reinforce the strength of the reduced drum portion  110  together with the curved portion  103 . 
     Hereinafter, a method of manufacturing a drum for laundry treatment device according to an embodiment of the present disclosure is described with reference to drawing. 
       FIG. 8  is a plane view schematically illustrating that a metal sheet is prepared in a method of manufacturing a drum for laundry treatment device according to an embodiment of the present disclosure.  FIG. 9  is a plane view schematically illustrating that a metal sheet of  FIG. 8  is rolled in a hollow cylindrical shape.  FIG. 10  is a plane view schematically illustrating that both ends of a metal sheet rolled in a hollow cylindrical shape in  FIG. 9  are welded to form a drum center.  FIG. 11  is a plane view schematically illustrating that a curved portion and a reduced drum portion are formed at both ends of a drum center of  FIG. 10 .  FIG. 12  is a plane view schematically illustrating that a reinforcement piece is attached to a welding line by welding the reinforcement piece to a reduced drum portion of  FIG. 11 .  FIG. 13  is a flow chart illustrating a method of manufacturing a drum for laundry treatment device according to an embodiment of the present disclosure. 
     For reference, a welding line L illustrated in  FIGS. 10 to 12  is substantially the same as the welding line L shown by the line in  FIG. 3 , but is indicated by dot hatching to be distinguished from both ends  11  of a metal sheet shown by the line in  FIG. 9 . 
     As illustrated in  FIGS. 8 to 13 , a method of manufacturing a drum for laundry treatment device according to an embodiment of the present disclosure may comprise a rolling step S 10  of rolling a metal sheet  10  in a hollow cylindrical shape; a welding step S 20  of welding both ends  11  of the metal sheet  10  to form a drum center  100 ; and a molding step S 30  of processing a reduced drum portion  110  at both ends of the drum center  100 . 
     The method of manufacturing the drum for laundry treatment device according to an embodiment of the present disclosure may first perform the rolling step S 10 . 
     As illustrated in  FIGS. 8, 9 and 13 , the rolling step S 10  may comprise preparing a rectangular metal sheet  10  using a rolling machine to roll the metal sheet  10  in a hollow cylindrical shape. 
     As described above, the both ends  11  of the metal sheet  10  rolled in the rolling step S 10  may be formed in a hollow cylindrical shape in contact with each other to form a joint. 
     That is, in the rolling step S 10 , the metal sheet  10  provided in a rectangular shape illustrated in  FIG. 8  may be formed as the hollow cylindrical metal sheet  10  in which the both ends  11  contact each other as illustrated in  FIG. 9 . 
     After the rolling step S 10 , the welding step S 20  may be performed. 
     As illustrated in  FIGS. 9, 10 and 13 , the welding step S 20  may comprise butt weld the contacting both ends  11  of the metal sheet  10  rolled in the hollow cylindrical shape after the rolling step S 10  using a laser welding machine to form a drum center  100 . 
     As described above, the metal sheet  10  welded in the welding step S 20  may be coupled along a welding line L and may be formed as the cylindrical drum center  100  having a hollow. In this instance, the welding line L may be formed in a straight line on an outer circumferential surface of the drum center  100  along an axial direction of the drum center  100 . 
     That is, in the welding step S 20 , the hollow cylindrical metal sheet  10  in which the both ends  11  contact each other as illustrated in  FIG. 9  may be formed as the cylindrical drum center  100  having a hollow illustrated in  FIG. 10 . 
     After the welding step S 20 , the molding step S 30  may be performed. 
     As illustrated in  FIGS. 10, 11 and 13 , the molding step S 30  may comprise integrally processing a reduced drum portion  110  at both ends of the cylindrical drum center  100  having the hollow using a molding machine. 
     The molding step S 30  may further comprise processing a curved portion  103  together with the reduced drum portion  110  at both ends of the cylindrical drum center  100  having the hollow using the molding machine. 
     More specifically, in the molding step S 30 , after the hollow of the drum center  100  is inserted into the molding machine, the curved portion  103  may be processed to have a concave cross section of an arc shape over the entire circumference of a front end of the drum center  100 . The molding step S 30  may also process the reduced drum portion  110  having a diameter smaller than a diameter of the drum center  100  at the front end of the drum center  100  including a processing position of the curved portion  103 . Then, after the hollow of the drum center  100  is inserted into the molding machine with the drum center  100  inverted, the curved portion  103  may be processed to have a concave cross section of an arc shape over the entire circumference of a rear end of the drum center  100 . The molding step S 30  may also process the reduced drum portion  110  having a diameter smaller than a diameter of the drum center  100  at the rear end of the drum center  100  including a processing position of the curved portion  103 . 
     Hence, the curved portion  103  and the reduced drum portion  110  may be formed in a symmetrical shape at the front end and the rear end of the drum center  100 , and the curved portion  103  may be formed to be positioned on the reduced drum portion  110 . 
     Belt mounting portions  105  and  107  may be processed at the outer circumferential surface of the drum center  100  during the processing of the curved portion  103 . 
     Since the strength of the front end and the rear end of the drum center  100 , i.e., the front end reduced drum portion  110  and the rear end reduced drum portion  110  of the drum center  100  is reinforced by the formation of the curved portion  103 , the strength reinforcement through separate hemming processing is unnecessary. 
     Further, in the molding step S 30 , a role of a structure that can be held by a roller of the molding machine so as to support the reduced drum portion during the processing of the reduced drum portion  110  is performed by the curved portion  103 , and thus the curved portion  103  can support the processing of the reduced drum portion  110 . 
     As above, the drum center  100 , in which the curved portion  103  and the reduced drum portion  110  are molded at each of the front end and the rear end of the drum center  100  formed in the molding step S 30 , may be formed. 
     That is, in the molding step S 30 , the cylindrical drum center  100  having the hollow illustrated in  FIG. 10  may be formed as the drum center  100  in which the curved portion  103  and the reduced drum portion  110  are formed at both ends as illustrated in  FIG. 11 . 
     After the molding step S 30 , an attaching step S 40  may be performed. 
     As illustrated in  FIGS. 11 to 13 , the attaching step S 40  may comprise attaching a rectangular reinforcement piece  120  to a welding line L of the drum center  100  in which the curved portion  103  and the reduced drum portion  110  are formed at both ends using a spot welding machine. 
     More specifically, in the attaching step S 40 , the reinforcement piece  120  may be disposed on the outer circumferential surface of the reduced drum portion  110  so that the reinforcement piece  120  is interposed between an edge portion  109  formed at an end of the drum center  100  and the curved portion  103 . At the same time, the reinforcement piece  120  may be disposed such that its longitudinal direction is perpendicular to the welding line L, and then spot welding may be performed to form a plurality of welding spots in the reinforcement piece  120  and the reduced drum portion  110 . Hence, the reinforcement piece  120  may be attached to the reduced drum portion  110 . 
     Since the reinforcement piece  120  is spot welded to the reduced drum portion  110  in a state of spanning the welding line L and is attached to the reduced drum portion  110 , the reinforcement piece  120  can prevent bursting of the welding line L due to rotation and vibration of the drum center  100  generated during the washing or drying process and can reinforce the strength of the reduced drum portion  110  itself. 
     As above, as the reinforcement piece  120  is attached in the attaching step S 40 , the method of manufacturing the drum for laundry treatment device according to an embodiment of the present disclosure can be completed. 
     That is, in the attaching step S 40 , the drum center  100  in which the curved portion  103  and the reduced drum portion  110  are formed at both ends as illustrated in  FIG. 11  may be formed as the drum center  100  in which the reinforcement piece  120  is attached to the reduced drum portion  110  while spanning the welding line L as illustrated in  FIG. 12 . 
     Although the embodiments have been described with reference to a number of illustrative embodiments thereof, numerous other modifications and embodiments may be devised by those skilled in the art that will fall within the scope of the principles of the present disclosure. In particular, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.