Abstract:
In the design of load bearing members for use in work machines, it is oftentimes beneficial to minimize the weight of such structures which, in turn, may allow for increased payloads and decreased cycle times of the work machine. A load bearing arrangement for use with a work machine of the type having a platform is provided. The load bearing arrangement comprises a plurality of pieces connectable to form a member structured and arranged for pivotable attachment to the platform. A weldment connects at least two of the pieces where at least one weldment is simulated for effects of heat on at least one of the pieces subject to the weldment.

Description:
TECHNICAL FIELD  
       [0001]     This invention relates to a load bearing member arrangement and method and, more specifically, to such a load bearing member and method thereof in which weld simulation, material preparation, and structural changes to the load bearing members all contribute in producing a load bearing member of reduces weight while not sacrificing the strength of such members.  
       BACKGROUND  
       [0002]     Load bearing members such as booms, sticks, crane booms and so forth typically must support loads which may produce a resultant load acting transversely across the member. Improvements in manufacturing processes such as the welding process allow for an improvement in the ability of the member to withstand such loads. It has been shown that fatigue strength, particularly at weld locations, is the limiting design factor when designing these types of structures. It is generally accepted that welding induces high tensile residual stresses in the local weldment region resulting in the presence on a microscopic level of small sharp discontinuities along the weld toe. These discontinuities, in turn, act as crack propagators, especially when the load bearing member is subjected to cyclic loading conditions. These improvements in the manufacturing processes, in turn, allow for use of thinner materials in creating these members resulting in possibly increased payloads and improved cycle times due to the decrease in weight of such structures.  
       SUMMARY OF THE INVENTION  
       [0003]     In accordance with an embodiment of the present invention, a load bearing arrangement for use with a work machine of the type having a platform is provided. The load bearing arrangement comprises at least one member structured and arranged for coupling to the platform; the member having an end comprising a material having a first yield strength; an aperture formed in the end and having an aperture wall; at least one support member contained within the opening adjacent to at least a portion of the aperture wall; and the support member having a second yield strength greater than said first yield strength.  
         [0004]     In accordance with yet another aspect of the present invention, a load bearing arrangement for use with a work machine of the type having a platform is provided. The load bearing arrangement comprises a plurality of pieces connectable to form a member structured and arranged for pivotable attachment to the platform; a weldment connecting at least two of the pieces; and at least one weldment being simulated for effects of heat on at least one of the pieces subject to the weldment.  
         [0005]     In accordance with even yet another aspect of the present invention, a method of manufacturing a load bearing member, comprising a plurality of pieces, for use with a work machine, is provided. The method comprises the steps of forming the pieces; connecting at least two of the pieces by a weldment; and determining the effects of heat caused by the weldment on at least one of said pieces subject to said weldment. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  is a side elevation view of an exemplary work machine embodying the principles of the present invention;  
         [0007]      FIG. 2  is an isometric view of a member comprising a boom embodying the principals of the present invention;  
         [0008]      FIG. 3  is a cross-sectional view taken on line  3 - 3  of  FIG. 2 ;  
         [0009]      FIG. 4  is a cross-sectional view taken on line  4 - 4  of  FIG. 2 ;  
         [0010]      FIG. 5  is a partial top view of the boom shown in  FIG. 2 ;  
         [0011]      FIG. 6  is an isometric view of a member comprising a stick embodying the principals of the present invention;  
         [0012]      FIG. 7  is a cross-section view taken on line  7 - 7  of  FIG. 2 ;  
         [0013]      FIG. 8  is a cross-sectional view taken on line  8 - 8  of  FIG. 6 ;  
         [0014]      FIG. 9  is a weld formed in accordance with a method of the present invention;  
         [0015]      FIG. 10  is a block diagram illustrating an embodiment of an integrated welding simulation model; and  
         [0016]      FIG. 11  is a block diagram illustrating an embodiment of a constitutive welding simulation model. 
     
    
     DETAILED DESCRIPTION  
       [0017]     With reference now to the Figures, shown in  FIG. 1  is an exemplary work machine  100  incorporating the teachings of the present invention. The work machine  100  comprises a platform  101  onto which is mounted a plurality of load bearing members  105  embodied herein by a first member or boom  106  and a second member or stick  107 . The boom  106  is pivotally connected to the platform  101  and moveable relative thereto by a first movement means embodied herein by a pair of first hydraulic actuators  110  which may comprise an extensible and retractable hydraulic cylinders. Likewise, the first end  111  of the stick  107  is pivotally coupled to the boom  106  via a suitable connector such as a pin  112  and is moveable relative to the boom  106  by a second movement means embodied herein by a second hydraulic actuator  114  which also may comprise an extensible and retractable hydraulic cylinder. It is to be understood that the work machine  100  shown herein is embodied by a barge unloader, however such a showing is exemplary only and it is contemplated that the teachings of the present invention may have wide applicability for work machines used to support loads such as, for example, backhoe loaders, excavators and so forth.  
         [0018]     Attached adjacent the second end  115  of stick  107 , also by use of a suitable connector such as a pin  118 , is an attachment  119  for use in grasping and holding a load of material which may comprise debris, dirt, rock, goods or other material tapes. The attachment  119  shown herein is embodied herein by a clamshell bucket although it is contemplated that such a showing is for purposes of illustration and not limitation and that other attachment types may also be used without deviating from the spirit of the present invention. The attachment  119  may also include a third hydraulic actuator (not shown) for use in activating the attachment  119 .  
         [0019]     With reference now to  FIGS. 2 , the boom  106  is shown incorporating the teachings of the present invention. The boom  106  comprises a pair of spaced apart side plates  200 , each forming a respective first side  200   a  and a second side  200   b , with each attached preferably by a robotic welding process to a top plate  201  and a bottom plate  202 . The boom  106  includes a first end  205  comprising a pair of ears  206  wherein each ear  206  includes an aperture  209  for receipt of a pin (not shown) or other suitable device for pivotally coupling the boom  106  to the platform  101 . The boom  106  also includes a second end  210  also having a pair of ears  213  each having an aperture  214  for receipt of pin  118 . An attachment structure  217  extends from each side plate  200  and is used to couple the first hydraulic actuators  110  to the boom  106 . Coupling assembly  218  extend from the bottom plate  202  and are used to pivotably support the second hydraulic actuator  114  in a well known manner.  
         [0020]     Also shown in hidden detail in  FIG. 2  is a reinforcing structure  221  used to reinforce each of the side plates  200  against failure. Although the specific details of the reinforcing structure  221  will be explained in greater detail as this disclosure progresses, suffice to say for now the use of the reinforcing structures  221  of the present invention allows for the use of thinner side plates  200  while preventing buckling of the side plates  200  when load placed on the boom  106  reaches or exceeds a given amount. The top plate  201  may be provided with a plurality of mounting structures  222  used to secure the various hydraulic conduits (not shown) supplying hydraulic fluid to the first and second hydraulic actuators  110 , 114  as well as the attachment  119 . The details of the mounting structures  222  will be described further with reference to  FIG. 5 .  11  With reference to  FIGS. 3-5 , various structural features of the boom  106  will now be discussed. Shown in cross-sectional detail in  FIG. 3  is the attachment structure  217  which is used to secure each first hydraulic actuator  110  to the boom  106 . The attachment structure  217  is shown comprising two substantially hollow cylindrical members  301  and  302  which may be coupled together in coaxial alignment, but it is to be understood that a single such member may be utilized without deviating from the spirit of the present invention. As shown, the combined length of the attachment structure  217  is sufficient to extend the transverse length of the boom  106  with each distal end  305  of each member  301 , 302  extending beyond each side plate  200  for a user-selected distance. Placed within each respective member  301 , 302  adjacent each distal end  305  is a substantially cylindrical support member  306  which is attached to each respective member  301 , 302  by a suitable method such as laser welding. Although the details of the support member  306  will be discussed in greater detail as this disclosure progresses, suffice to say for now each support member  306  is sized to receive a respective bearing  307  each of which, in turn, supports a pin (not shown) used to secure the first hydraulic actuators  110  to the boom  106 .  
         [0021]     As should be appreciated by those or ordinary skill in such art, each of the side plates  200  may be attached to each respective member  301 , 302  by a welding process preferably comprising a robotic welding process which may be optimized based on the teaching to be described herein with respect to  FIGS. 9-11 . When prepared in such a manner the need to provide a conventional attachment structure comprising a heavier casting to compensate for the traditionally weaker weldment is eliminated. To further secure each member  301 , 302 , reinforcement plates  310  may be attached to each member  301 , 302  by a welding process or other suitable attachment method.  
         [0022]     With respect to  FIG. 4 , shown is an arrangement for coupling the different pieces of the boom  106  in which the pieces may comprise plates of different thicknesses. For exemplary purposes, shown is the side plate  200  comprising two adjacent plates denoted plate  400  having a centerline  401  and plate  404  having a centerline  405 . As shown, plates  400  and  404  are attached by a welding or like process such that the centerlines  401 , 405  are substantially co-linear. By attaching adjacent plates  400  and  404  in such manner, a more uniform distribution of stress flow may be obtained which, in turn, may allow for thinner plates  400  and  404 .  
         [0023]     Shown in  FIG. 5  is a top view of mounting structures  222 . Each mounting structure  222  is preferably integrally formed with the top plate  201 . As also should be appreciated, forming the mounting structures  222  as a part of the top plate  201  eliminates the need to weld such attachment structures to the top plate  201  which, in turn, eliminates tensile residual stresses in the local weldment region which may require the need to utilize thicker plate materials. Each mounting structure may be provided with apertures  500  each sized to receive a suitable fastener (not shown) for use in securing the hydraulic conduits to the top plate  201  by use of a bracket (not shown) or other suitable attachment device.  
         [0024]     With reference now to  FIG. 6 , the stick  107  is shown also incorporating the teachings of the present invention. The stick  107  also comprises a pair of spaced apart side plates  600  each attached, also preferably by a robotic welding process, to a top plate  601  and a bottom plate  602 . The stick  107  includes the first end  111  sized to fit between the ears  213  of the second end  210  of the boom  106 . The first end  111  further includes an aperture  606  for receipt of pin  112  thereby providing for the aforementioned pivotal attachment to the boom  106 . The second end  115  of the stick  107  also includes an aperture  607  sized to receive pin  118 . Coupling assembly  609  extend from the bottom plate  602  and is used to pivotably support the second hydraulic actuator  114  in a well known manner.  
         [0025]     Also shown in hidden detail in  FIG. 6  are a plurality of reinforcing structures each denoted by the reference numeral  610  which are used to reinforce each of the side plates  600  against buckling at pre-determined buckling prone areas. Although the specific details of the reinforcing structures  610  will also be explained in greater detail as this disclosure progresses, suffice to say for now the use of the reinforcing structures  610  of the present invention also allows for the use of thinner side plates  600  on the stick  107  while preventing buckling of the side plates  600  at pre-determined buckling prone areas when loads placed on the stick  107  reach or exceed a given amount. It should be appreciated by those of ordinary skill in such art, that the number of reinforcing structures  221 , 610  to be used is a matter of design selection and need not constitute any more than is necessary to achieve the needed performance, and by limiting the number of reinforcing structures  221 , 610  used the weight of the boom  106  and the stick  107  may be minimized. The top plate  601  may also be provided with mounting structures  611  which are used to secure the various hydraulic conduits (not shown) supplying hydraulic fluid to the first and second hydraulic actuators  110 , 114  as well as the attachment  119 . The details of the mounting structures  611  are substantially similar to those of mounting structures  222  described above and so will not be described any further herein.  
         [0026]     With reference to the cross-sectional shown in  FIG. 7 , the location and configuration of the reinforcing structures  221 , 610  will now be discussed. For purposes of brevity the following discussion will be limited to the reinforcing structure  221  for the boom  106 , however it is to be understood that the disclosure herein is equally applicable to the reinforcing structures  610  used for the stick  107 . As shown, at least one reinforcing structure  221  is attached to an inner surfaces  700  of the side plates  200  by a suitable attachment method preferably a laser welding method. As should be appreciated by those of ordinary skill in such art, it has been found that the use of laser welding to attach the reinforcing structure  221  to the side plates  200  reduces the heat effected zone surrounding the weld area, thereby allowing for thinner side plates  200  then would otherwise be required for different welding-type attachment methods. It is to be understood that the attachment location of each reinforcing structure  221  is exemplary only and it is contemplated that other attachment locations for the reinforcing structures  221  may be had such as, for example, the outer surface  701  of each of the side plates  200 .  
         [0027]     As shown, each reinforcing structure  221  comprises a substantially straight member having a base portion  704  and a rib portion  705  extending from the base portion  704 . The reinforcing structure  221  may comprise a metallic or other rigid material and has a length which is user-selected based on the failure analysis performed by using a suitably selected failure analysis package such as Nastran (TM). Furthermore, it is also contemplated that other geometry&#39;s for the reinforcing structure  221  may also be used with deviating from the spirit of the present invention such as, for example, a cylindrical or flat configuration.  
         [0028]     Shown in cross-section in  FIG. 8  are the details of the first end  111  of stick  107 . A pair of substantially cylindrical support members  801  are received within the aperture  606  are used to house a corresponding pair of bearings  802  which, in turn, support pin  112 . Each of the support members  801  are sized to lie adjacent to the aperture wall  803  and each are preferably laser welded to the surrounding stick material denoted  805 . In addition, and the material comprising each support member  801  is preferably chosen to have a yield strength exceeding that of the surrounding stick material  805 . In selecting a material for the support members  801  having a higher yield strength then the surrounding stick material  805 , the support members  801  can absorb the radial stresses produced by pressure fitting the bearings  802  into the respective support members  801  which allows for less stick material  805  surrounding the aperture  606  then otherwise would be required. By providing for less stick material  805  at the first end  111 , the effective moment arm between the stick  107  and the boom  106  may be decreased resulting in a decreased stress level produced in the stick  107  for the same relative loading condition. As should be apparent to those of ordinary skill in such art, support members exhibiting similar properties can be provided in the remaining stick aperture  607 , the boom apertures  209  and  214 , as well as the support members  306  used with the attachment structure  217 .  
         [0029]     Shown in  FIG. 9  is a diagrammatical representation of the weldment  900  created to secure two plates together both denoted as  901 . The weld geometry of the weldment  900  includes a weld toe  904 , a weld profile  905  and a penetration  908 . In the manufacture of the load bearing members  105  described herein, it is advantageous to control the resultant residual stresses at the location of the weldment. For example, the stress diagram denoted  910  illustrates the resultant residual stress located under the weld toe  904  with “+” indicating a compressive residual stress, and “−” indicating a tensile residual stress. At the weld toe  904  it is desirable to achieve a compressive residual stress without the need for any post weld treatment of the weldment  900 . To control the resultant residual stress at the location of the weldment  900 , the weld simulation tools to be discussed immediately hereinafter may be utilized. The results of the simulation may then be used to control the weld process which preferably comprises a robotic welding process. To control the fit-up of the plates  901  as well as the penetration  908 , it is preferred that the plates are formed from a precision cutting operation such as laser cutting.  
         [0030]     Referring to  FIG. 10 , a block diagram illustrating a preferred embodiment of a set of integrated models  1000  for performing a simulation analysis of a welding process is shown. The integrated models  1000  work together to determine stresses and distortions of a material which is welded in the welding process. The stresses and distortions have an adverse effect on the strengths and characteristics of the material. Therefore, it is desired to model the stresses and distortions and use the information from the models to determine methods which may minimize the adverse effects of welding.  
         [0031]     In the preferred embodiment, an interconnection tool  1014 , such as a graphical user interface (GUI), interconnects the models into an integrated network of working models to determine stresses and distortions of the material.  
         [0032]     The interconnection tool  1014  is preferably computer-based and may be configured to operate autonomously, through manual intervention, or some combination of the two modes. For example, the interconnection tool  1014  may coordinate the modeling functions while displaying the status and results to a human, who may override the system or input additional information at any desired time.  
         [0033]     A geometry modeler  1002  determines the geometry model for the materials to be welded. Preferably, the geometry modeler  1002  simplifies the geometry by removing unnecessary features of the materials from the model. Examples of such features include, but are not limited to, chamfers, holes, slight irregularities, and the like.  
         [0034]     The geometry model data is then delivered to a meshing tool  1004 . The meshing tool  1004  is used to generate a finite element analysis mesh, preferably by defining coordinates for elements and nodes which constitute the mesh. Finite element analysis techniques which use mesh coordinates are well known in the art and will not be described further.  
         [0035]     A thermal analysis model  1006  is used to perform a thermal analysis of the materials during the welding process. In the preferred embodiment, the thermal analysis model  1006  includes at least two models. An analytical solution model  1008  provides a rapid analytical solution of the thermal process, i.e., welding process, for a global solution of distortions caused by the welding process. A finite element analysis model  1010  provides local detailed analysis of residual stress from the welding process.  
         [0036]     In the preferred embodiment, the analytical solution model  1008  determines solutions of point heat sources, the point heat sources being obtained from heat input based on welding processes and reflected heat sources determined from adiabatic boundary conditions of the material. The total analytical solution is determined from superposition of all the point heat sources. The principle of obtaining reflected heat sources from adiabatic boundary conditions is well known in the art and will not be discussed further. The analytical solution model  1008  provides a rapid solution for the complete welding process. However, the solution is not highly detailed. Therefore, the analytical solution model  1008  is typically used when a fast, global solution is desired, and a high degree of detail is not needed.  
         [0037]     The finite element analysis model  1010  employs numerical computations of conditions at each of the desired node and element coordinates of the finite element analysis mesh. The finite element analysis model tends to be computationally lengthy and intensive. Therefore, the finite element analysis model  1010  is generally used only when a detailed analysis of a specific portion of the model is desired.  
         [0038]     The information from the thermal analysis model  1006  is compiled into a thermal history and delivered to a structural analysis model  1012 . In addition, the finite element mesh provided by the meshing tool  1004  is delivered to the structural analysis model  1012 . The interconnection is automatically established in the interconnection tool  1014 . In the preferred embodiment, the thermal history is delivered from the thermal analysis model  1006  to the structural analysis model  1012  by way of an interface module  1016 . Preferably, the interface module  1016  is automated from the interconnection tool  1014  and is adapted to seamlessly connect the thermal solution from the analytical solution model  1008 , the finite element analysis model.  1010 , or both, to the structural analysis model  1012 .  
         [0039]     The structural analysis model  1012  provides further analysis of the materials during the welding process. Typically, the behavior of the material during welding is analyzed and modeled. Examples of features analyzed include, but are not limited to, melting and remelting of the material, phase transformation of the material, cyclic effects of multiple weld passes, and the like. The stresses and distortions of the material are determined by the structural analysis model. Preferably, the determined stresses and distortions may be further analyzed and subsequently used to modify the welding process to reduce the adverse effects of the extreme heat associated with welding.  
         [0040]     Referring to  FIG. 11 , a model  2000  of the weld process is shown, which is based on a constitutive model  2002 . Constitutive models, e.g., for welding process simulation, are well known in the art and have been used for many years. A constitutive model is a model based on a compilation of physical laws associated with the phenomenon desired to be modeled.  
         [0041]     A history annihilation model  2004  models melting/remelting of the material during the weld process. In addition, annealing of the material during cyclic melting/remelting of the material during multiple weld passes is modeled. As the material melts, the deformation history, i.e., the stresses and deformations, of the material is eliminated, and the material is restored to a virgin state. Therefore, for accurate modeling of the welding process, stresses and distortions must be reset in response to the occurrence of a melting/remelting condition.  
         [0042]     A large deformation model  2006  is used to model thermal and mechanical strain increments of the material being welded. More specifically, the large deformation model  2006  models the distinguishing characteristics between plastic and elastic annealing strains during the welding process.  
         [0043]     A virtual elements detection model  2008  provides virtual elements for weld passes which have not actually occurred. In a multiple pass welding process, models must include all passes before any weld metal is actually deposited. For example, the stiffness of the material must be modeled as though all weld passes have been completed, even though welding has not begun. Typical welding model packages compensate for this by a process known as element birth and death. The finite elements of the weld metal must be deactivated until later in the modeling process. This method is very tedious and requires much time and computational power to perform, since the elements must be removed from the files and restored later. The virtual elements detection model  2008  overcomes this by assuming that the weld metal has been deposited at a minimal stiffness. As the subsequent weld passes are performed, the metal stiffness from each pass is modified to more closely reflect the actual stiffness created by the welding process. In the preferred embodiment, the virtual elements detection model  2008  is a three-dimensional model to provide modeling not only of the portion of the material being welded, but to also provide modeling of portions of the material to be welded as the overall weld process takes place.  
         [0044]     A strain hardening model  2010  models the yield strength which increases as a result of the thermal cycles associated with the multiple weld passes. Yield strength increases as the stresses and strains of welding move from a zero state to a yield state, i.e., from before heating the material to a point just prior to the material yielding to the application of the heat. The strain hardening model  2010  is adapted to perform a series of iterations to determine the increments of plastic strain of the material.  
         [0045]     A phase transformation model  2012  models changes in the microstructure of the material during the welding process. The changes in the microstructure of the material are a function of parameters such as the chemical composition of the material, conditions of the welding process, and the like. Changes in the material include, but are not limited to, volumetric changes during the phase transformation, transformation plasticity, and yield hysteresis due to phase differences in the heating and cooling processes.  
         [0046]     A temperature history database  2014  stores and provides a temperature history of the material during the welding process. Preferably, the temperature history database  2014  provides temperature history data to the constitutive model  2002  and the history annihilation model  2004 .  
         [0047]     A microstructure database  2016  stores and provides data of the microstructure of the material during the welding process. Preferably, the microstructure database  2016  provides microstructure data to the constitutive model  2002  and the phase transformation model  2012 . In addition, the microstructure database  2016  may receive microstructure data of the material from the phase transformation model  2012 .  
         [0048]     A material data database  2018  stores and provides data of the material, e.g., stresses and strains of the material, during the welding process. Preferably, the material data database provides data to the constitutive model  2002 , the strain hardening model  2010 , and the phase transformation model  2012 .  
       INDUSTRIAL APPLICABILITY  
       [0049]     In use and in operation, the present invention provides for weight savings in load bearing members  105  while maintaining the same payload capacity of the work machine  100 . As should be appreciated by those of ordinary skill in such art, controlling the amount of distortion and residual stresses at the weldment  900  provides for a weld having a greater fatigue life then otherwise would be possible. The present invention also utilizes an enhanced and more accurate model of the stresses and distortions which occur during a welding process, as compared to typical welding process models currently known. The characteristics of the materials being welded are modeled as temperatures approach levels which cause changes in the material properties. Examples of welding related material behaviors which are modeled include, but are not limited to, melting/remelting caused by multiple weld passes, material history annihilation caused by annealing, thermal cycling, i.e., alternate heating and cooling of the material, phase transformations, and the like. The results of the above modeling are incorporated into a constitutive weld model to provide a complete model of the effects of the weld process. This complete model may then be used to minimize adverse effects caused by welding.  
         [0050]     In addition, it should also be appreciated by those of ordinary skill in such art, the use of support members  306 , 801 , integral mounting structures  222 ,  611 , aligned centerlines  401 , 405 , reinforcing structure  221 ,  610  and the attachment structure  217  all as illustrated and described herein may contribute to a further weight savings in the weight of these structures.  
         [0051]     Other aspects, objects and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims.