Abstract:
A method for manufacturing a component including a bi-metallic sheet includes performing a manufacturing process that heats the bi-metallic sheet and physically constraining the bi-metallic sheet from deformation during the cooling of the bi-metallic sheet. Optionally, the method additionally includes physically constraining the bi-metallic sheet from deformation during the manufacturing process that heats the bi-metallic sheet. A constraining apparatus is also disclosed and includes a first constraining component having a first thermally conductive contact surface adapted to abut a first surface of a metal sheet, a second constraining component having a second contact surface adapted to abut a second surface of the metal sheet, and an engaging device operative to fix the first constraining component and the second constraining component in position relative to one another. The metal sheet is constrained between the first contact surface and the second contact surface during heating and/or cooling.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of priority to co-pending U.S. Provisional Patent Application Ser. No. 61/320,006, filed Apr. 1, 2010 by the same inventors and entitled “System And Method For Preventing Warpage Of Metal Components During Manufacturing Processes,” which is incorporated by reference herein in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates generally to the manufacturing of enclosures (e.g., housings, battery covers, etc.) for electronic devices, and more particularly to the manufacturing of metal enclosures for 3C (computers, communications, consumer electronics) devices. Even more particularly, the present invention relates to preventing a bimetallic enclosure from experiencing warp deformation when heated by a manufacturing process, for example an NMT (Nano Mold Technology) process. 
         [0004]    2. Description of the Background Art 
         [0005]    Currently, the demand for 3C products is becoming increasingly more dependent on aesthetics. As a result, more and more eye-catching effects and differentiating characteristics are being incorporated into the enclosure design of such products. For example, metal housings are the current trend in the 3C market. 
         [0006]    Applicants have discovered that there are advantages to forming metal housings from bimetallic metal. One example of bimetallic material is sheet metal that is formed by cold rolling two sheets of different metals together to form a single two-ply sheet. As used herein, the term bimetallic is considered to also include materials having more than two layers formed of two or more different metals. 
         [0007]    Although advantages exist, there are some problems that must be addressed in order to increase product yield. For example, bimetallic sheet metal is prone to warp when subjected to significant temperature changes, because the two metals have a different coefficients of thermal expansion (CTEs). As a result, bimetallic components are particularly vulnerable during manufacturing processes in which the shell is exposed to heating. For example, bimetallic shells can experience serious warp deformation after being released from an NMT mold and allowed to cool at room temperature. 
         [0008]    What is needed, therefore, is a means for preventing warpage of bimetallic components during manufacturing. What is also needed is a means for preventing warpage of bimetallic components subjected to manufacturing processes involving heat. What is also needed is a means for preventing warpage of bimetallic components that are involved in molding processes. What is also needed is a means for improving the product quality and yield of manufacturing processes involving bimetallic components. 
       SUMMARY 
       [0009]    The present invention overcomes problems that occur when bimetallic parts are exposed to temperature fluctuations, by providing system and method for constraining parts as they are cooled. A first solution utilizes a cooling fixture to constrain the molded product once it has been released from the mold. The part or assembly is placed in the fixture while still warm and allowed to cool in the fixture fully constrained. A second solution uses a rapid heating and cooling method (RHCM) to rapidly heat and cool the product in the mold. Because the product has been heated and cooled under the full constraint of the mold, the deformation will be dramatically reduced. 
         [0010]    The process time of the second solution is substantially less than the process time of the first solution. However, both solutions use similar principles and provide significant improvements in quality and yield as compared to the prior art. Both solutions provide physical constraint during the heating up and/or cooling down process to prevent the free deformation of the bi-metallic product. This allows the stress distribution to reach a new balanced state under physical constraint. Although full constraint provides exceptional results, the amount of constraint required may vary depending on the specific details of a particular application. 
         [0011]    An example method for manufacturing a component including a bi-metallic sheet is disclosed. The bi-metallic sheet includes a first layer of a first metal and a second layer of a second metal. The second metal is different than the first metal and has a different coefficient of thermal expansion. The method includes performing a manufacturing process that results in the heating of the bi-metallic sheet, cooling the bi-metallic sheet, and physically constraining the bi-metallic sheet from deformation during the step of cooling the bi-metallic sheet. Optionally, the method additionally includes physically constraining the bi-metallic sheet from deformation during the manufacturing process that results in the heating of the bi-metallic sheet. 
         [0012]    In an example method, the step of performing a manufacturing process that results in the heating of the bi-metallic sheet includes performing a molding process. The example molding process includes molding a structure directly on a surface of the bi-metallic sheet, for example as in an NMT process. In this example method, the step of constraining the bi-metallic sheet from deformation during the manufacturing process that results in the heating of the bi-metallic sheet includes constraining the bi-metallic sheet with the mold used in the manufacturing process. In addition, the step of constraining the bi-metallic sheet from deformation during the step of cooling the bi-metallic sheet includes constraining the bi-metallic sheet with the mold and actively cooling the mold. As an example, actively cooling the mold includes circulating a thermal regulating fluid in contact with the mold. 
         [0013]    In an alternate example method, the step of constraining the bi-metallic sheet from deformation during the step of cooling the bi-metallic sheet includes removing the bi-metallic sheet from the mold, placing the bi-metallic sheet in a separate constraining device, and allowing the bi-metallic sheet to cool while in the separate constraining apparatus. Optionally, the step of allowing the bi-metallic sheet to cool while in the constraining device includes actively cooling the constraining apparatus by, for example, circulating a thermal regulating fluid in contact with the constraining apparatus. 
         [0014]    A constraining apparatus for constraining an item including a metal sheet is also disclosed. An example embodiment includes a first constraining component having a first thermally conductive contact surface adapted to abut a first surface of the metal sheet and a second constraining component having a second contact surface adapted to abut a second surface of the metal sheet. The second surface of the metal sheet is on an opposite side of the metal sheet as the first surface of the metal sheet. The example embodiment further includes an engaging device operative to fix the first constraining component and the second constraining component in position relative to one another, whereby the metal sheet is constrained between the first contact surface and the second contact surface. A thermal reservoir is coupled to accept heat energy from the metal sheet via the first thermally conductive contact surface of the first component. Optionally, the second contact surface of the second constraining component can be thermally conductive, and the thermal reservoir can be coupled to accept heat energy from the metal sheet via the second contact surface of the second constraining component. 
         [0015]    Various means for constraining the metal sheet during a manufacturing process wherein the metal sheet is heated and cooled are disclosed. 
         [0016]    In an example embodiment, the first constraining component is made of a thermally conductive material and, at least a portion of the thermal reservoir includes the thermal mass of the first constraining component. In addition, the first constraining component is made of metal, and the thermal reservoir includes an amount of metal having a thermal mass at least ten times larger than the thermal mass of the metal sheet. Optionally, the thermal reservoir includes a solid thermally conductive portion and a fluid passage thermally coupled to the solid thermally conductive portion. 
         [0017]    The engaging device includes at least one clamp fixed to bias the first contact surface and the second contact surface against opposite sides of the metal sheet. The disclosed example embodiment includes a plurality of clamps disposed to apply substantially equal pressure over a majority of at least one of the first contact surface or the second contact surface. Also, in the example embodiment, one of the first contact surface and the second contact surface include a concave portion, and the other of the first contact surface and the second contact surface include a convex portion. 
         [0018]    In an alternate example embodiment, the first constraining component and the second constraining component are parts of a mold, for example an injection mold. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The present invention is described with reference to the following drawings, wherein like reference numbers denote substantially similar elements: 
           [0020]      FIG. 1  shows a perspective view of an electronic device with a housing formed from bimetallic sheet material; 
           [0021]      FIG. 2  is a perspective view of a component of the housing of  FIG. 1  having molded structures formed thereon; 
           [0022]      FIG. 3  shows a first surface area of the component of  FIG. 2  that is held under constraint by a cooling fixture while the component is cooled; 
           [0023]      FIG. 4  shows an opposite surface area of the component of  FIG. 2  that is held under constraint by a cooling fixture while the component is cooled; 
           [0024]      FIG. 5  is a representational diagram of the constraining forces applied to the component of  FIG. 2  during heating and/or cooling of the component; 
           [0025]      FIG. 6  is a perspective view of a base portion of cooling fixture; 
           [0026]      FIG. 7  is a perspective view of the base portion of the cooling fixture of  FIG. 6  with the component of  FIG. 2  seated therein; 
           [0027]      FIG. 8  is a perspective view of the cooling fixture of  FIG. 7  with a removable top portion of the cooling fixture engaged with the base portion, clamping the component of  FIG. 2  there between; 
           [0028]      FIG. 9  is a side cross sectional view of the cooling fixture of  FIG. 8  with the component of  FIG. 2  clamped therein; 
           [0029]      FIG. 10  is a flow chart summarizing an example method for reducing warpage of a bimetallic part during a manufacturing process according to one embodiment of the present invention; 
           [0030]      FIG. 11  shows a heating and cooling cycle for an injection mold according to a second embodiment of the present invention; and 
           [0031]      FIG. 12  is a flow chart summarizing an example method for reducing warpage of a bimetallic part according to a second embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    The present invention overcomes problems that occur when bimetallic parts are exposed to temperature fluctuations, by providing system and method for constraining parts as they are heated and/or cooled. Such heating and cooling of parts is common during a wide variety of manufacturing processes. Aspects of the invention are described with reference to a particular process, wherein plastic structural features are molded onto a bimetallic laptop display housing using an NMT process. However, it should be understood that the present invention can be used to prevent warpage of all types of parts in conjunction with other manufacturing processes (other than NMT) that cause susceptible parts to be heated and cooled. In addition, certain specific details (e.g., mold materials and temperatures) not necessary for an understanding of the present invention are omitted, so as not to unnecessarily complicate the explanation of the invention. 
         [0033]      FIG. 1  shows an electronic device  100  that includes a metal housing  102 . By way of example, electronic device  100  is a lap-top computer. However, it should be understood that the present invention is not limited to housings for lap-top computers. Rather, the present invention can be used in conjunction with any manufacturing process and/or part that is susceptible to warping. 
         [0034]    Housing  102  includes a top shell  104  and a bottom shell  106  hinged in a clam shell relationship. Top shell  104  houses a computer display and speakers (not visible in  FIG. 1 ), and bottom shell  106  houses a keyboard  108 , a user input device  110 , a computer board (not visible), and any other hardware components (not visible) that are desirable in lap-top computer  100 . 
         [0035]      FIG. 2  is a perspective view of a top shell  104 , which includes a plurality of molded mounting features  204  (e.g., screw bosses). Shell  104  includes an interior surface  206  and an opposite exterior surface  208 . In addition, shell  104  is constructed from bimetallic metal (e.g., CLAD metal) having two distinct metal layers  210  and  212  bonded together by some suitable means (e.g., cold-rolling, metal deposition, etc.). Each of layers  210  and  212  is formed from a different type of metal such that surface  206  is formed of a first type of metal and surface  208  is formed of a second type of metal. The first type of metal (e.g., aluminum alloy) facilitates the bonding between shell  104  and mounting features  204 , while the second type of metal (e.g., titanium, stainless steel, etc.) provides strength and rigidity to shell  104 . 
         [0036]    Although the present invention can be used with any type of sheet metal material, bimetallic sheet material is used as an example, because bimetallic sheet material is particularly susceptible to warping. In addition, bimetallic sheet material provides important advantages, both functional (e.g., as described in the previous paragraph) and aesthetic, in many applications. As used herein, the term “bimetallic sheet material” includes sheet material including two or more layers of different metal compositions. 
         [0037]    Mounting features  204  facilitate the mounting of top shell  104  to, for example, the frame of the display (not shown) and/or bottom shell  106 . Mounting features  204  are, for example, formed from plastic that is insert-molded directly on surface  106 . A direct plastic-to-metal bond between the insert molded plastic mounting features  204  and surface  206  is achieved using NMT. Insert molding is just one example of manufacturing processes that can cause metal sheet material included in manufactured parts to be heated and cooled and can, therefore, result in the undesirable warping of the metal sheet material. The present invention can be used to facilitate many other such manufacturing processes that heat and cool the metal sheet material of parts. 
         [0038]      FIGS. 3 ,  4 , and  5  illustrate the areas of shell  104  that are simultaneously held under constraint by a cooling fixture when shell  104  is cooled.  FIG. 3  is a front plan view of shell  104 . The shaded area  302  shows the area of interior surface  206  that is held under constraint by a cooling fixture. 
         [0039]      FIG. 4  shows a rear plan view of exterior surface  208  of shell  104 . The shaded area  402  shows the area of exterior surface  208  that is also held under constraint by a cooling fixture. In this particular embodiment, area  402  covers the entire, or at least the majority, of exterior surface  208  of shell  104 . 
         [0040]      FIG. 5  shows a representational cross-sectional view of shell  104 . The dashed lines  502  and  504  represent the application of constraining forces applied to areas  206  and  208 , respectively, by surfaces of a cooling fixture. The constraining forces on shell  104  are applied by surfaces of the cooling fixture in the direction shown. For clarity, dashed lines  204  are shown above surface  106  and dashed lines  206  are shown below surface  108 . However, it should be understood that the forces represented by dashed lines  502  and  504  would be applied by directly abutting surfaces  206  and  208 , respectively, with similarly contoured surfaces of the cooling fixture. 
         [0041]      FIGS. 6 ,  7 , and  8  show a cooling fixture  600  in various stages of use.  FIG. 6  shows a base portion  602  of cooling fixture  600 . Base portion  602  includes a thermal reservoir  604  and defines a recessed receiving surface  606  that is contoured to match surface  208  of shell  104 . In this particular embodiment, surface  606  is generally flat in the center with concave peripheral border. The concave border is complementary to the convex edge of shell  104  and an optional convex surface of an upper portion of constraining apparatus  602  (not shown). Receiving surface  606  is thermally conductive and facilitates the flow of heat energy between shell  104  and thermal reservoir  604 . 
         [0042]    Thermal reservoir  604  includes a relatively large thermal mass (e.g., at least ten times greater) as compared to shell  104 . In this particular embodiment, thermal reservoir  604  and surface  606  are formed from a block of thermally conductive metal, for example steel or aluminum. Thermal reservoir  604  includes conduits  608  that facilitate the circulation of a thermal regulating fluid through thermal reservoir  604 . The circulated thermal regulating fluid facilitates the active heating and/or cooling of thermal reservoir  604  and, therefore, shell  104 . 
         [0043]    Base portion  602  is coupled to a plurality of engaging devices  610 . In this example embodiment, engaging devices  610  are clamps that fix a removable portion of cooling fixture  600  (described below with reference to  FIG. 8 ). Each of clamps  610  is fixed to base portion  602  of cooling fixture  600  via respective base portions  612 . A plurality of edge constraining blocks  614  are also positioned adjacent the edge of receiving surface  606 . Edge constraining blocks  614  restrain the edges of shell  104  during the cooling of shell  104 . Each of base potions  612  and edge constraining blocks  614  include an inclined alignment surface  616  that, together, guide an upper portion of cooling fixture  600  into position, as will be described below. 
         [0044]      FIG. 7  shows base portion  602  of cooling fixture  600  with shell  104  disposed therein, with inner surface  206  of shell  104  facing upward. The outer surface  208  (not visible in  FIG. 7 ) of shell  104  rests on surface  606  (obscured from view by shell  104 ) of base portion  602 . Edge restraining blocks  614  overhang the edge of shell  104  and abut both a top surface of base portion  602  and surface  206  of shell  104 . 
         [0045]      FIG. 8  shows cooling fixture  600  with an upper portion  802  disposed over shell  104  (not visible) and engaged with base portion  602 . Upper portion  802  includes a pair of handles  804 , which facilitate the insertion and removal of upper portion  802  Although not visible in the view of  FIG. 8 , the bottom of upper portion  802  includes a surface contoured to match the interior surface  206  of shell  104 . Clamps  610  bias upper portion  802  toward base portion  602 , constraining shell  104  there between. In addition, clamps  610  are arranged to maintain even pressure on shell  104  So constrained, shell  104  is held in an unwarped condition until shell  104  cools and the layers of shell  104  return to an unstressed stable state. 
         [0046]      FIG. 9  is a side cross sectional view of cooling fixture  600  with shell  104  clamped therein. As shown in  FIG. 9 , upper portion  802  of cooling fixture  600  includes a top portion  902 , an intermediate portion  904 , and a contact portion  906 . Top portion is fixed to intermediate portion  904  by a plurality of fasteners  908  (e.g., machine screws) and to contact portion  906  by one or more fasteners  910  (e.g., machine screws). Intermediate portion  904  includes a positioning surface  912  and defines a cavity  914 . Positioning surface  912  contacts the upper surface of base portion  602  to ensure that excess pressure is not exerted on shell  104 , which could result in the deformation of shell  104 . Cavity  914  provides clearance for molded mounting features  204 . Contact portion  906  abuts shell  104  in area  206  (shown in  FIG. 3 ). 
         [0047]    While constrained in cooling fixture  600 , heat flows from shell  104 , through thermally conductive surface  606  and into thermal reservoir  604 . In this example embodiment, thermal reservoir  604  can be actively heated and/or cooled by circulating a thermal regulating fluid through conduits  608 . However, thermal reservoir  604  can also be passive. For example, thermal reservoir  604  can be simply a thermally conductive object (e.g., a metal block) having a relatively large thermal mass with respect to shell  104  and/or sufficient surface area to dissipate heat into the ambient atmosphere. 
         [0048]    Because shell  104  is thin, upper portion  802  can be thermally conductive or thermally insulating. Indeed, depending on the particular application, either embodiment can provide advantages. For example, in an actively cooled embodiment, a thermally insulating upper portion will direct most of the heat from shell  104  into thermal reservoir  604 , where it can be carried away by the thermal regulating fluid in conduits  608 . However, in a passively cooled constraining apparatus, it might be desirable to maximize the heat dissipation to the ambient atmosphere. In that case, it would be an advantage if upper portion  802  is thermally conductive. 
         [0049]    After being cooled to a stable temperature, shell  104  can be removed from cooling fixture  600  without warping. Shell  104  is removed by releasing clamps  610  and lifting upper portion  802  from cooling fixture  600  by handles  804 . Then, shell  104  can be removed from base portion  602  by any suitable means. 
         [0050]      FIG. 10  is a flow chart summarizing one method  1000  for reducing warpage during the manufacture of a part including metal sheet material. In a first step  1002 , manufacturing equipment (e.g., a mold) is provided. Then, in a second step  1004 , a cooling fixture is provided. Next, in a third step  1006 , a part including metal sheet material (e.g., bimetallic sheet material) is provided. Then, the part is subjected to a manufacturing process. For example, in a fourth step  1008 , the part is positioned in a mold. Then, in a fifth step  1010 , the mold is heated. Next, in a sixth step  1012 , melt material is injected into the mold. Then, in a seventh step  1014 , the mold is opened, and the part is removed. Next, in an eighth step  1016 , the part is placed in a cooling fixture. Then, in a ninth step  1018 , the part is cooled to a stable temperature under physical constraint. Finally, in a tenth step  1020 , the part is removed from the fixture, and the method ends. 
         [0051]      FIG. 11  shows a heating and cooling cycle for an injection mold according to a second embodiment of the present invention. In this embodiment, a manufacturing process that causes heating of a sheet metal component (e.g., bimetallic shell  104 ) is adapted to physically constrain the component during cooling of the component to a stable state. For example, the advantages of the invention can be obtained by adopting a rapid heating and cooling (RHCM) process for NMT molding on the bimetallic shell  104 . In this process, at time t 0  the metal part  1102  will be loaded into the mold  1104  when the mold is at a lower temperature. This helps to prevent the metal part from initially warping since there will be no contact with a pre heated mold cavity. As shown in  FIG. 11 , heat is being applied to mold  1104  at t 0 , but mold  1104  is still at a lower temperature from the previous cycle. Mold  1104  will begin to heat up and get to the desired temperature after it has been fully closed. Then, at time t 1 , the injection of melt into mold  1104  begins. The mold remains at the desired high temperature until the melt is fully injected into the mold  1104 . Then, at time t 2 , cooling of the mold begins. At time t 3 , the metal part  1102  remains physically constrained in closed mold  1104 , until part  1102  is cooled down to a desired stable temperature. Then, at time t 4 , mold  1104  is opened, part  1102  is removed, and heating of mold  1104  begins in preparation for the next mold cycle. 
         [0052]    This alternate embodiment of the invention is a specific example of a broader aspect of the present invention. In particular, this alternate embodiment demonstrates that different types of manufacturing equipment for certain processes that result in the heating of parts can be modified to embody and utilize a cooling fixture according to the present invention. Thus, a separate cooling fixture is unnecessary in these instances. 
         [0053]      FIG. 12  is a flow chart summarizing an alternate example method  1200  for reducing warpage in a part incorporating metal sheet material (e.g., bimetallic sheet material) during a manufacturing process that results in the heating of the sheet material. In a first step  1202 , manufacturing equipment embodying a cooling fixture (e.g., a modified mold) is provided and, in a second step  1204 , a part including metal sheet material is provided. Then, in a third step  1206 , the part is placed and constrained in the mold. Next, in a fourth step  1208 , the mold is rapidly heated. Then, in a fifth step  1210 , melt is injected into the mold to form molded features on the constrained part. Next, in a sixth step  1212 , the part is cooled while being constrained in the mold. Finally, in a seventh step  1214 , the cooled part is removed from the mold. 
         [0054]    The description of particular embodiments of the present invention is now complete. Many of the described features may be substituted, altered or omitted without departing from the scope of the invention. For example, the cooling fixture of the present invention can be incorporated into manufacturing equipment/process (e.g., soldering, welding, cutting, etc.) other than molding processes. In addition, the present invention can be used with other types of parts and/or manufacturing processes that may be susceptible to warping problems. These and other deviations from the particular embodiments shown will be apparent to those skilled in the art, particularly in view of the foregoing disclosure.