Patent Publication Number: US-11649577-B2

Title: Washing machine and manufacturing method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This present application claims the benefit of priority to Korean Patent Application No. 10-2019-0077240, entitled “WASHING MACHINE AND MANUFACTURING METHOD THEREOF,” filed on Jun. 27, 2019, the entire disclosure of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a washing machine that can be manufactured in a large capacity without deterioration in function, and a manufacturing method thereof. 
     BACKGROUND 
     In general, a washing machine is a machine that washes laundry by using an emulsifying effect of detergent, a frictional force of a water stream made by rotation of a washing blade, and an impact applied by the washing blade. Such a washing machine mainly uses an electric motor as a main power source, and as the washing, rinsing, and dehydration processes are performed using the action of detergent and water, contaminants in clothing are separated from the clothing. 
     Meanwhile, washing machines are divided into a cylinder type, an agitator type, and a pulsator type depending on the washing method. Among them, the cylinder-type washing machine includes a drum rotatably disposed within a tub and performs the washing process by putting water and detergent into the drum having laundry therein. 
     The capacity of such a cylinder-type washing machine is determined depending on the internal volume of the drum receiving laundry therein. Users tend to prefer a washing machine with a larger capacity, because they want to be able to easily wash bulky laundry such as bedclothes at home too. 
     However, when manufacturing such a large-capacity washing machine, the main parts thereof, such as the drum, are increased in size, and as such, there are factors to be considered in order to prevent functional deterioration of the washing machine from occurring. 
     For example, when a washing machine with a relatively large capacity is manufactured, defects such as cracks or creases can occur in a drum back which is coupled to a back surface portion of the drum. 
     Accordingly, there is a need to perform an appropriate process for reinforcement such that defects such as crack or creases are prevented from occurring in the process of manufacturing the drum back. 
     Here, there is a need to maintain the capacity of the drum to be relatively large through the shape of the drum back and to perform reinforcement against defects, such that a relatively large capacity of the washing machine is achieved. 
     In addition, an excellent washing performance for the laundry in the drum must be secured even when a relatively large-sized drum back is applied to the large-capacity washing machine. 
     In this regard, Korean Patent Registration no. 10-1054408 (hereinafter referred to as “related art 1”) discloses a structure of a drum of a washing machine. 
     Specifically, a forming portion having a drum expansion space and a bead formed in a front surface of the forming portion are disclosed in related art 1. 
     In the washing machine of related art 1, the forming portion is formed in a back surface of the drum in order to maximize the capacity of washing machine, and the bead is formed for reinforcing the forming portion. However, no reinforcement other than the reinforcement for the forming portion is considered in related art 1. Accordingly, in related art 1, there may be a part in the washing machine where defects can occur in the manufacturing process of the washing machine. 
     In addition, Korean Patent Registration no. 10-0598000 (hereinafter, referred to as “related art 2”) discloses a drum back of a cylinder-type washing machine. 
     Specifically, related art 2 discloses a feature of a first forming portion which protrudes forward in a portion thereof that faces a spider and a feature of a second forming portion formed in the first forming portion to be recessed backward. 
     However, the drum back of related art 2 is formed in such a shape that the first forming portion protrudes forward and only a portion of the first forming portion is recessed backward. Accordingly, the portion that is recessed backward in the first forming portion is relatively small, and thus there is a limit in terms of the capacity of the washing machine. 
     In addition, the second forming portion is recessed backward and is thus ineffective in physically contacting the laundry in the drum. Accordingly, there is a limit in improving washing performance of the washing machine. 
     As described above, existing large-capacity washing machines have several shortcomings, and the shortcomings should be appropriately resolved. 
     SUMMARY 
     The present disclosure is directed to addressing shortcomings associated with existing washing machines. 
     Specifically, an aspect of the present disclosure is directed to making appropriate reinforcement against defects that can occur in the process of manufacturing a drum back of a washing machine, such that the drum back of the washing machine is manufactured in a relatively large size. 
     Another aspect of the present disclosure is directed to manufacturing a drum back of a washing machine in a shape that enables reinforcement against defects and secures a relatively large capacity of a drum, so as to secure a relatively large capacity of a washing machine. 
     Yet another aspect of the present disclosure is directed to securing a certain level of washing performance in the drum to which a relatively large-sized drum back is applied, such that no functional deterioration occurs in a large-capacity washing machine. 
     Aspects of the present disclosure are not limited to the above-mentioned aspects, and other technical aspects not mentioned above will be clearly understood by those skilled in the art from the following description. 
     A washing machine and a manufacturing method thereof according to an aspect of the present disclosure are characterized by reinforcing portions of the washing machine that become vulnerable to defects in the process of forming a protruding portion and a recessed portion while a drum back is manufactured. Specifically, in the drum back, a coupling portion may be formed to protrude in a front direction of a drum, a first forming portion may be formed to be recessed in a back direction of the drum, and a reinforcement portion may be formed in a portion of the coupling portion that is adjacent to the first forming portion. 
     In addition, the washing machine and the manufacturing method thereof according to an aspect of the present disclosure are characterized in that even when the vulnerable portions are reinforced, the portion that is recessed in the back direction of the drum in the process of manufacturing the drum back may be maintained. Specifically, in the drum back, the first forming portion which is recessed in the back direction of the drum may be formed, and the reinforcement portion may be formed in a portion of the coupling portion that is adjacent to the first forming portion. 
     In addition, the washing machine and the manufacturing method thereof according to an aspect of the present disclosure are characterized in that friction between laundry in the drum and portions of the drum back that protrude in the front direction of the drum may increase. Specifically, the coupling portion may protrude in the front direction of the drum, and the reinforcement portion may additionally protrude from the coupling portion. 
     Furthermore, the washing machine and the manufacturing method thereof according to an aspect of the present disclosure are characterized in that the coupling portion may include a first surface formed to be inclined and a second surface extending from the first surface to be flush with a circumferential surface of the drum back, and the reinforcement portion may be formed on the second surface. 
     In addition, the washing machine and the manufacturing method thereof according to an aspect of the present disclosure are characterized in that a second forming portion may be formed in the first surface to be recessed in the back direction of the drum. 
     Furthermore, the washing machine and the manufacturing method thereof according to an aspect of the present disclosure are characterized in that the reinforcement portion may be formed between every two adjacent first forming portions from among a plurality of first forming portions. 
     In addition, the washing machine and the manufacturing method thereof according to an aspect of the present disclosure are characterized in that the reinforcement portion may be formed in such a shape that a cross section of the reinforcement portion includes an arc. 
     Furthermore, the washing machine and the manufacturing method thereof according to an aspect of the present disclosure are characterized in that the reinforcement portion may be formed in such a shape that a plane of the reinforcement portion becomes increasingly wider towards a circumferential surface of the drum back. 
     In addition, the washing machine and the manufacturing method thereof according to an aspect of the present disclosure are characterized in that the drum back may be formed as a one-piece body by changing a shape of a base sheet having a plate shape. 
     Furthermore, the washing machine and the manufacturing method thereof according to an aspect of the present disclosure are characterized in that the drum back may be formed by pressing the base sheet through a mold. 
     In addition, the washing machine and the manufacturing method thereof according to an aspect of the present disclosure are characterized in that the drum back may be formed by pressing both surfaces of the base sheet simultaneously. 
     Technical solutions of the present disclosure are not limited to the above-mentioned technical solutions, and other technical solutions not mentioned above will be clearly understood by those skilled in the art from the following description. 
     Hereinafter, the effects of the washing machine and the manufacturing method thereof according to the present disclosure will be described. 
     According to at least one of the embodiments of the present disclosure, since the coupling portion protrudes in the front direction of the drum, and the reinforcement portion is formed in a portion of the coupling portion that is adjacent to the first forming portion recessed in the back direction of the drum, appropriate reinforcement may be made for defects that can occur when the drum back of the washing machine is manufactured in a large size. 
     In addition, according to at least one of the embodiments of the present disclosure, since the first forming portion is formed to be recessed in the back direction of the drum, and the reinforcement portion is formed in a portion of the coupling portion that is adjacent to the first forming portion, the reinforcement against defects may be appropriately made, and at the same time, the drum back may be manufactured in a shape capable of securing a relatively large capacity of the drum. 
     In addition, according to at least one of the embodiments of the present disclosure, since the coupling portion protrudes in the front direction of the drum, and the reinforcement portion additionally protrudes from the coupling portion, a certain level of washing performance in the drum to which a relatively large-sized drum back is coupled may be secured. 
     In addition, according to at least one of the embodiments of the present disclosure, since the coupling portion includes a first surface formed to be inclined and a second surface extending from the first surface to be flush with a circumferential surface of the drum back, and the reinforcement portion is formed on the second surface, it may be possible to appropriately reinforce a vulnerable portion of the drum back, which is neither protruded nor recessed in the process of molding the drum back and is thus affected by forces in both directions. 
     Furthermore, according to at least one of the embodiments of the present disclosure, since the second forming portion is formed in the first surface to be recessed in the back direction of the drum, a relatively large capacity of the drum may be secured. 
     In addition, according to at least one of the embodiments of the present disclosure, since the reinforcement portion is formed between every two adjacent first forming portions from among a plurality of first forming portions, the reinforcement may be uniformly made on the entire plane of the drum back. 
     Furthermore, according to at least one of the embodiments of the present disclosure, since the reinforcement portion is formed in such a shape that the cross section of the reinforcement portion includes an arc, even when the cross section of the reinforcement portion is relatively large, a certain degree of rigidity may be secured. 
     In addition, according to at least one of the embodiments of the present disclosure, since the reinforcement portion is formed in such a shape that the plane of the reinforcement portion becomes increasingly wider towards the circumferential surface of the drum back, the reinforcement effect at a portion of the circumferential surface of the drum back may be further improved. 
     In addition, according to at least one of the embodiments of the present disclosure, since the drum back is formed as a one-piece body by changing the shape of the base sheet having a plate shape, there is no separately joined portion in the drum back, and thus a portion vulnerable to structural deformation may be minimized. 
     Furthermore, according to at least one of the embodiments of the present disclosure, since the drum back is formed by pressing the base sheet through the mold, a large quantity of the drum backs may be molded in the same size. 
     In addition, according to at least one of the embodiments of the present disclosure, since the drum back is formed by pressing both surfaces of the base sheet simultaneously, the molding process may be relatively simple, and the defects that can be caused by a multi-stage compression molding process may be minimized. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other aspects, features, and advantages of the invention, as well as the following detailed description of the embodiments, will be better understood when read in conjunction with the accompanying drawings. For the purpose of illustrating the present disclosure, there is shown in the drawings an exemplary embodiment, it being understood, however, that the present disclosure is not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the present disclosure and within the scope and range of equivalents of the claims. The use of the same reference numerals or symbols in different drawings indicates similar or identical items. 
         FIG.  1    is an exemplary perspective view of a washing machine according to an embodiment of the present disclosure. 
         FIG.  2    is an exemplary cross-sectional view of a washing machine according to an embodiment of the present disclosure. 
         FIG.  3    is an exploded perspective view of main parts of a washing machine according to an embodiment of the present disclosure. 
         FIG.  4    is a perspective view of a drum back in a washing machine according to an embodiment of the present disclosure. 
         FIG.  5    is a front view of a drum back in a washing machine according to an embodiment of the present disclosure. 
         FIG.  6    is a cross-sectional view of  FIG.  5    taken along the line from A to A′. 
         FIGS.  7  and  8    are exemplary views of a process of manufacturing a drum back of a washing machine according to an embodiment of the present disclosure. 
         FIG.  9    is a flowchart illustrating a manufacturing method of a washing machine according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Advantages and features of the present disclosure and methods for achieving them will become apparent from the descriptions of aspects herein below with reference to the accompanying drawings. However, the present disclosure is not limited to the aspects disclosed herein but may be implemented in various different forms. The aspects are provided to make the description of the present disclosure thorough and to fully convey the scope of the present disclosure to those skilled in the art. It is to be noted that the scope of the present disclosure is defined only by the claims. 
     The shapes, sizes, ratios, angles, the number of elements given in the drawings are merely exemplary, and thus, the present disclosure is not limited to the illustrated details. Like reference numerals designate like elements throughout the specification. 
     The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
     When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments. 
     Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     The term “or” as used herein is to be interpreted as an inclusive or meaning any one or any combination. Therefore, “A, B or C” means any of the following: “A; B; C; A and B; A and C; B and C; A, B and C”. An exception to this definition will occur only when a combination of elements, functions, steps or acts are in some way inherently mutually exclusive. 
     Hereinafter, preferable exemplary embodiments of the present disclosure will be described in detail referring to the attached drawings. In the following description, known functions or features will be omitted in order to clarify the gist of the present disclosure. 
       FIG.  1    is an exemplary perspective view of a washing machine according to an embodiment of the present disclosure.  FIG.  2    is an exemplary cross-sectional view of a washing machine according to an embodiment of the present disclosure.  FIG.  3    is an exploded perspective view of main parts of a washing machine according to an embodiment of the present disclosure. 
     As illustrated in  FIGS.  1  to  3   , a washing machine  1000  according to an embodiment of the present disclosure may include a drum  100  and a drum back  200 , and may further include a spider  300 , a drum cover  500 , a shaft  600 , a motor  700 , a tub  800 , and a housing  900 . 
     The housing  900  may be a part that forms the main exterior of the washing machine  1000 , and the above components of the washing machine  1000  may be installed within the housing  900 . Here, the housing  900  may be subdivided into a base, a cabinet, a top cover, and a cabinet cover. 
     A laundry entrance through which laundry  10  can be placed into the washing machine  1000  may be formed in one surface of the cabinet cover of the housing  900 , and a door  910  for opening and closing the laundry entrance may be installed. 
     A tub  800  for holding washing water therein may be installed within the housing  900 , may be placed on a damper installed in the base of the housing  900 , and may be connected to a spring installed in the cabinet as if hung by the spring. As a result, the tub  800  may be supported by the damper and the spring in such a manner that the tub  800  is buffered by the damper and the spring. 
     The tub  800  may have a structure of a cylinder lying on one side thereof. The drum  100  may be disposed within the tub  800 , and the motor  700 , which is a driving means for rotating the drum  100 , may be installed on a back surface of the tub  800 . 
     The drum  100 , as a part for receiving the laundry  10 , may be formed, like the tub  800 , in a structure of a cylinder lying on one side thereof such that a lower portion of the drum  100  is submerged in washing water within the tub  800 , and may be rotatably positioned inside the tub  800 . 
     A plurality of through holes may be formed in a circumferential portion of the drum  100  such that washing water or air flows in through the through holes, and a lifter for lifting and falling the laundry  10  may be mounted in an inner circumferential surface of the circumferential portion of the drum  100 . 
     Meanwhile, the drum  100  may be formed of a single cylindrical member or formed of two members separated into front and back parts. Or, the drum  100  may be formed of three members including a drum cover  500  coupled to a front surface portion of the drum  100  and a drum back  200  coupled to a back surface portion of the drum  100 . 
     Hereinafter, for convenience of description, the description will be made based on the drum  100  formed of three members, and here, the drum  100  may refer to a portion of the drum  100  excluding the drum cover  500  and the drum back  200 , that is, to a body portion of the drum  100 . 
     The drum back  200  may be a part coupled to the drum  100  so as to cover the back surface portion of the drum  100 , and the drum  100  and the spider  300  may be coupled to each other through the drum back  200 . Here, the drum back  200  may be formed in the shape of a disk, and a protruding portion and a recessed portion may be formed in the drum back  200  as needed. 
     The spider  300  may be a part coupled to the back surface of the drum back  200  so as to transfer rotational force to the drum  100 , and may include a shaft fixing portion  310  to which a shaft  600  is coupled and a plurality of leg portions  320  formed to protrude from the shaft fixing portion  310  in a radial direction. 
     For example, the spider  300  may include the plurality of leg portions  320  radially extending from a rotational axis of the spider  300 , and may be formed in a rotationally symmetric shape as a whole about the rotational axis. 
     In addition, each of the plurality of the leg portions  320  may be coupled to the back surface of the drum back  200  by means of a fastening means such as a bolt. 
     The shaft  600  may be installed to pass through a back surface of the tub  800 , wherein a front end of the shaft  600  may be coupled to the shaft fixing portion  310 , and a rear end of the shaft  600  may be coupled to the motor  700 . Accordingly, rotational force generated in the motor  700  may be transferred to the spider  300  through the shaft  600 , and the drum  100  may be rotated through the drum back  200  coupled to the spider  300 . 
       FIG.  4    is a perspective view of a drum back in a washing machine according to an embodiment of the present disclosure.  FIG.  5    is a front view of a drum back in a washing machine according to an embodiment of the present disclosure.  FIG.  6    is a cross-sectional view of  FIG.  5    taken along the line from A to A′. 
     As illustrated in  FIGS.  4  to  6   , in the washing machine  1000  according to an embodiment of the present disclosure, the drum back  200  may include a coupling portion  210 , a first forming portion  220 , and a reinforcement portion  230 , and may further include a second forming portion  400 . 
     The coupling portion  210  may be a portion that is formed to protrude in a front direction of the drum  100 , and may be formed to be rotationally symmetric about a central shaft  205 . 
     Here, the coupling portion  210  may be formed to protrude in the front direction of the drum  100  at a portion of the drum back  200  to which the spider  300  is coupled so as to correspond to a shape of the spider  300 . The coupling portion  210  may be formed to correspond to the shapes of the shaft fixing portion  310  and the leg portions  320  of the spider  300 . That is, the protruding degree of the coupling portion  210  in the front direction of the drum  100  may correspond to the angle formed by the shaft fixing portion  310  and the leg portions  320  of the spider  300 . 
     For example, as illustrated in  FIG.  3   , in the spider  300 , the shaft fixing portion  310  may be formed to protrude the most, and three leg portions  320  may be formed to be inclined from the shaft fixing portion  310 . 
     Here, as illustrated in  FIGS.  4  to  6   , a central area of the coupling portion  210  of the drum back  200  that comes into contact with the shaft fixing member  310  may protrude the most towards a front of the drum  100 , and an area of the coupling portion  210  that comes into contact with the leg portions  320  may be formed to protrude from the central area along three inclined surfaces. 
     The first forming portion  220  may be formed to be recessed in a back direction of the drum  100  at an area of the drum back  200  excluding the coupling portion  210 . In addition, in a case where a plurality of first forming portions  220  are formed, the plurality of first forming portions  220  may be rotationally symmetric about the central shaft  205 . In some examples, the first forming portion  220  may be referred to as a first recess portion. 
     Here, the first forming portions  220  may be portions that are formed to be recessed in the back direction of the drum  100  at areas to which the spider  300  is not coupled, and the first forming portions  220  may thus be formed at areas surrounded by the shaft fixing portion  310  and the leg portions  320  of the spider  300 . 
     That is, the first forming portion  220  may be formed to protrude in a direction opposite to the protruding direction of the coupling portion  210  at an area of the drum back  200  excluding the area where the coupling portion  210  is formed. 
     For example, as illustrated in  FIGS.  4  to  6   , the first forming portion  220  may be formed to be recessed at an area surrounded by two adjacent leg portions  320  and a circumferential surface of the drum back  200 . 
     Here, through holes may be formed in the first forming portion  220  such that washing water or air can flow in through the drum back  200 . 
     The reinforcement portion  230  may be a portion that is formed to additionally protrude in the front direction of the drum  200  at an area of the coupling portion  210  that is adjacent to the first forming portion  220 , and may reinforce a portion that is vulnerable to defects occurring when said protruding and recessed portions are formed in a molding process. 
     Specifically, when the protruding portion and the recessed portion are formed in the drum back  200 , there is a possibility of defects such as cracks or creases occurring in a boundary between the protruding portion and the recessed portion. 
     In particular, in a case where the drum  100  is manufactured in a relatively large size, and thus the drum back  200  is also manufactured in a relatively large size, the boundary between the two portions may be even more vulnerable to such a defect. 
     Accordingly, for reinforcing the vulnerable portions, there is a need to attach an additional reinforcing member to the drum back  200  or form the vulnerable area with a material having a greater rigidity. However, for such a reinforcement, an additional process for reinforcement should be performed aside from the process of manufacturing the drum back  200 , which may make the manufacturing of the drum back  200  more complicated. 
     Therefore, such defects may be more effectively prevented from occurring by forming the reinforcement portion  230 , which is formed in a protruding shape in the process of manufacturing the drum back  200  and enables structural reinforcement of the drum back  200 . 
     As described above, in the washing machine  1000  according to this embodiment of the present disclosure, appropriate reinforcement can be made for defects that can occur when the drum back  200  of the washing machine  1000  is manufactured in a relatively large size, since the coupling portion  210  protrudes in the front direction of the drum  100 , and the reinforcement portion  230  is formed at an area of the coupling portion  210  that is adjacent to the first forming portion  220  which is recessed in the back direction of the drum  100 . 
     In addition, since the first forming portion  220  which is recessed in the back direction of the drum  100  is formed, and the reinforcement portion  230  is formed at an area of the coupling portion  210  that is adjacent to the first forming portion  220 , reinforcement against defects can be made, and at the same time, the drum back  200  can be manufactured in a shape capable of securing a relatively large capacity of the drum  100 . 
     Specifically, the first forming portion  220  may be formed to be recessed in the back direction of the drum  100 , and thus the inner space of the drum  100  may be enlarged by the recessed volume of the first forming portion  220 . Accordingly, the first forming portion  220  itself may have an effect of increasing the capacity of the drum  100 . 
     Here, if the reinforcement portion  230  is formed in the first forming portion  220 , the capacity of the drum  100  may be reduced by the volume of the reinforcement portion  230 , which may be a disadvantage in terms of the capacity. 
     Accordingly, when the reinforcement portion  230  is formed on the coupling portion  210  while the shape of the first forming portion  220  is maintained, the reinforcement against defects may be made, and at the same time, a relatively large capacity of the drum  100  may be secured. 
     In addition, in the washing machine  1000  according to this embodiment of the present disclosure, as the coupling portion  210  protrudes in the front direction of the drum  100 , and the reinforcement portion  230  additionally protrudes from the coupling portion  210 , a certain level of washing performance may be secured in the drum  100  coupled to a relatively large-sized drum back  200 . 
     Specifically, one of various factors that determine the washing performance for the laundry  10  in the drum  100  may be a degree of friction between the drum  100  and the laundry  10 . That is, more friction between the laundry  10  in the drum  100  and the drum  100  may lead to an improved washing performance. 
     Accordingly, the degree of friction between the laundry  10  and the drum  100  may be further increased by forming the reinforcement portion  230  to additionally protrude in the front direction of the drum  100 . On the contrary, if the reinforcement portion  230  is formed to be recessed in the back direction of the drum  100 , it may be possible to make reinforcement against defects, but it may be difficult to secure a certain level of washing performance. 
     Accordingly, by forming the reinforcement portion  230  to protrude in the front direction of the drum  100 , the reinforcement against defects may be made, and at the same time, the washing performance may be improved. 
     In the washing machine  1000  according to this embodiment of the present disclosure, the coupling portion  210  may include a first surface  211  formed to be inclined from a center of the drum back  200  and a second surface  213  extending from the first surface to the circumferential surface of the drum back  200  to be flush with the circumferential surface, and the reinforcement portion  230  may be formed on the second surface  213 . 
     That is, as illustrated in  FIGS.  4  to  6   , the first surface  211  may be formed to be inclined in a central area of the drum back  200 , and the second surface  213  may be formed to be level in a peripheral area of the drum back  200 . 
     When the drum back  200  is formed in the shape described above, the spider  300  coming into close contact with the back surface of the drum back  200  along an inclined surface of the drum back  200  may be able to more firmly support the drum back  200 . 
     However, when the coupling portion  210  is formed to include the first surface  211  and the second surface  213  for said reason, the second surface  213  may be maintained in an original shape thereof where the second surface  213  neither protrudes nor is recessed. 
     Accordingly, when a molding process for forming a recess in the first forming portion  220  and forming a protrusion in the first surface  211  is performed, the second surface  213  may be affected by all forces applied from both directions. As a result, the second surface  213  may be most vulnerable to defects. 
     That is, in the washing machine  1000  according to this embodiment of the present disclosure, the coupling portion  210  may include the first surface  211  formed to be inclined and the second surface  213  extending from the first surface to the circumferential surface of the drum back  200  to be flush with the circumferential surface, and the reinforcement portion  230  may be formed on the second surface  213 . Accordingly, a vulnerable portion of the drum back  200 , which neither protrudes nor is recessed and is thus affected by the forces in both directions, may be appropriately reinforced. 
     The second forming portion  400  may be a portion that is formed in the first surface  211  to be recessed in the back direction of the drum  100 , and may thus additionally secure the capacity of the drum  100  on the first surface  211  which is relatively resistant to defects. In some examples, the second forming portion  400  may be referred to as a second recess portion. 
     That is, the inner space of the drum  100  may be additionally enlarged by the recessed volume of the second forming portion  400 , and thus the second forming portion  400  may have an effect of additionally increasing the capacity of the drum  100 . 
     That is, in the washing machine  1000  according to this embodiment of the present disclosure, since the second forming portion  400  is formed in the first surface  211  to be recessed in the back direction of the drum  100 , a relatively larger capacity of the drum  100  may be secured. 
     In the washing machine  1000  according to this embodiment, the first forming portion  220  may be a plurality of first forming portions  220  that are separated from each other by the coupling portion  210 , and the reinforcement portion  230  may be formed between every two adjacent first forming portions  220 . 
     For example, as illustrated in  FIGS.  4  and  5   , the first forming portions  220  are formed respectively at three areas of the drum back  200 , and the first forming portions may be separated from each other by the coupling portion  210 . In addition, reinforcement portions  230  may be formed respectively at areas in the coupling portion  210  between every two adjacent first forming portions  220 . 
     That is, in the washing machine  1000  according to this embodiment, since the reinforcement portions  230  are formed between every two adjacent first forming portions  220  from among the plurality of first forming portions  220 , the reinforcement may be uniformly made on the entire plane of the drum back  200 . 
     In the washing machine  1000  according to this embodiment, the reinforcement portion  230  may be formed in such a shape that a cross section thereof includes an arc protruding from the second surface  213 . 
     That is, as illustrated in  FIG.  6   , the reinforcement portion  230  may be formed in such a shape that a cross section of the reinforcement portion  230  includes an arc where a center of the arc protrudes the most and a portion of the arc away from the center protrudes relatively less, and thus a line from the center to the portion away from the center forms a curve. 
     Accordingly, even when the reinforcement portion  230  is formed in such a shape that the cross section of the reinforcement portion  230  is relatively large, the reinforcement against defects may be made well in the vulnerable portion by an arch effect. 
     Meanwhile, the reinforcement portion  230  may be formed in such a manner that the center of the arc is positioned at the most vulnerable area of the drum back  200  by performing a structural analysis or the like. 
     That is, in the washing machine  1000  according to this embodiment, since the reinforcement portion  230  is formed in such a shape that the cross section thereof includes an arc, a certain degree of rigidity may be secured even when the cross section thereof is relatively large. 
     In particular, rigidity may be reinforced in a circumferential direction or in a radial direction depending on a direction in which the cross section of the reinforcement portion  230  including an arc is formed. 
     Here, the reinforcement portion  230  may be formed in such a manner that a protruding plane of the reinforcement portion  230  becomes increasingly wider towards the circumferential surface of the drum back  200 . 
     That is, referring to  FIG.  5   , the reinforcement portion  230  may be formed in such a shape that a length (d 1 ) of the reinforcement portion  230  at a side of the circumferential surface of the drum back  200  may be greater than a length (d 2 ) at a side of the center of the drum back  200 , on a plane of the reinforcement portion  230 . 
     As the drum back  200  is formed in a disk shape as a whole, a surface area covered by the reinforcement portion  230  may become increasingly larger towards the circumferential surface of the drum back  200 . Accordingly, it may be preferable to form the reinforcement portion  230  in such a shape that the size of the reinforcement portion  230  becomes increasingly greater towards the circumferential surface of the drum back  200 . 
     That is, in the washing machine  1000  according to this embodiment, since the reinforcement portion  230  has a shape in which the plane of the reinforcement portion  230  becomes increasingly wider towards the circumferential surface of the drum back  200 , the effect of reinforcement for a portion of the circumferential surface of the drum back  200  may be further improved. 
       FIGS.  7  and  8    are exemplary views of a process of manufacturing a drum back of a washing machine according to an embodiment of the present disclosure. 
     As illustrated in  FIGS.  7  and  8   , in the washing machine  1000  according to this embodiment, the drum back  200  may be formed as a one-piece body by changing a shape of a base sheet  201  having a plate shape. Here, the base sheet  201  refers to a material before being processed into the drum back  200 , and may have an entirely flat plate shape. 
     In particular, the base sheet  201  may be made of a stainless (STS) material such that when the base sheet  201  is pressed, the shape of the base sheet  201  can be changed, and at the same time, the base sheet  201  has a certain degree of rigidity after going through a molding process. 
     When the drum back  200  is manufactured, if any one of the protruding portion or the recessed portion is separately molded and the molded portion is then joined to the drum back  200 , the manufacturing process may be relatively complex, and the joined portion may be vulnerable to cracking or creasing. 
     Accordingly, considering workability and structural rigidity of the drum back  200 , it may be preferable to form the drum back  200  as a one-piece body from a single plate member. 
     Accordingly, in the washing machine  1000  according to this embodiment, since the drum back  200  is formed as a one-piece body by changing the shape of the plate-shaped base sheet  201 , there is no separately joined portion in the drum back  200 , and thus a portion vulnerable to structural deformation may be minimized. 
     Here, the drum back  200  may be formed by pressing the base sheet  201  through a mold  203 . That is, when the plate-shaped base sheet  201  is pressed by the mold  203 , the base sheet  201  may be protruded or recessed corresponding to a shape of the mold  203 , and thus the shape of the base sheet  201  may be changed. 
     For example, as illustrated in  FIGS.  7  and  8   , a groove and a protrusion may be respectively formed at areas of the mold  203  that correspond to the protruding portion and the recessed portion of the drum back  200 , and the shape of the base sheet  201  may be changed by pressing the base sheet  201  through the mold  203 . 
     That is, in the washing machine  1000  according to this embodiment of the present disclosure, as the drum back  200  is formed by pressing the base sheet  201  through the mold  203 , a large quantity of drum backs  200  may be molded in the same size. 
     Meanwhile, when the drum back  200  is manufactured through the mold  203 , the second surface  213  may be a portion that is supported by the mold  203  and thus most vulnerable to creasing. Accordingly, it may be preferable to form the reinforcement portion  230  in the second surface  213 . 
     Furthermore, the drum back  200  may be formed by simultaneously pressing both surfaces of the base sheet  201 . That is, two molds  203 , which have protruding portions and recessed portions, may be positioned on both surfaces of the base sheet  201 , and then the molds  203  may be pressed against each other with the base sheet  201  therebetween so as to come into close contact with the both surfaces of the base sheet  201 . By doing so, the drum back  200  may be formed. 
     If a primary processing is performed for only one surface of the drum back  200 , and then a secondary processing is performed for the other surface of the drum back  200 , unpredictable defects such as deformation or stress concentration may occur at a portion of the drum back  200  that went through the primary processing when the secondary processing is performed. 
     In the washing machine  1000  according to this embodiment of the present disclosure, since the drum back  200  is formed by simultaneously pressing the both surfaces of the base sheet  201 , the molding process may be relatively simple, and defects that can be caused by a multi-stage compression molding process may be minimized. 
       FIG.  9    is a flowchart illustrating a manufacturing method of a washing machine according to an embodiment of the present disclosure. 
     The manufacturing method of a washing machine according to an embodiment of the present disclosure will now be described below with reference to  FIG.  9   . Here, the manufacturing method of a washing machine according to this embodiment may be described based on the main features of the washing machine  1000  described in detail above. Therefore, the description of the manufacturing method of a washing machine will be made together with reference to  FIGS.  1  to  8   . 
     Firstly, a base sheet  201  having a plate shape is prepared (S 100 ). Here, the base sheet  201  may be formed as a one-piece body without any separately joined portion. 
     Next, the drum back  200  is manufactured by changing the shape of the base sheet  201  (S 200 ). Here, the base sheet  201  may be processed in such a shape that a portion thereof protrudes and another portion is recessed, to be formed in the shape of the drum back  200 . 
     Thereafter, the manufactured drum back  200  is coupled to a drum  100  and a spider  300  (S 300 ). That is, the drum back  200  may be coupled to the drum  100  so as to cover a back surface portion of the drum  100 , and the drum  100  and the spider  300  may be coupled to each other through the drum back  200 . 
     Here, S 200  may include: a step of forming a coupling portion  210  to protrude in a front direction of the drum  100  at a portion of the drum back  200  to which the spider  300  is coupled so as to correspond to a shape of the spider  300  (S 210 ); a step of forming a first forming portion  220  to be recessed in a back direction of the drum  100  at a portion of the drum back  200  to which the spider  300  is not coupled (S 220 ); and a step of forming a reinforcement portion  230  which additionally protrudes in the front direction of the drum  100  at a portion of the coupling portion  210  that is adjacent to the first forming portion  220  (S 230 ), and S 200  may further include a step of forming a second forming portion  400  to be recessed in the back direction of the drum  100  at a portion of a first surface  211  of the coupling portion  210 . 
     Accordingly, appropriate reinforcement may be made for defects that can occur in the process of manufacturing the drum back  200  of the washing machine  1000  having a relatively large size. In addition to the reinforcement against defects, the drum back  200  may be manufactured in a shape capable of securing a relatively large capacity of the drum  100 . In addition, a certain level of washing performance may be secured for the drum  100  coupled to a relatively large-sized drum back  200 . 
     Meanwhile, the main elements and features of the manufacturing method of a washing machine according to an embodiment of the present disclosure are the same as or similar to those of the washing machine  1000  according to the embodiments of the present disclosure described above. Therefore, detailed description of overlapping contents is omitted. 
     While specific embodiments of the present disclosure are described and illustrated above, it would be obvious to those skilled in the art that various modifications and variations thereto can be made within the spirit and scope of the present disclosure. Accordingly, such modifications or variations are not to be regarded as a departure from the spirit or scope of the present disclosure, and it is intended that the present disclosure cover the modifications and variations of the present disclosure provided they come within the scope of the appended claims and their equivalents.