Abstract:
In some embodiments, reconfigurable tooling is provided having an array of actuator columns affixed to a support base. A programmable controller is configured to position the actuator columns. The reconfigurable tooling has a tooling surface which includes a variable stiffness surface capable of controllable states of stiffness, the variable stiffness surface being capable of being deformed by the actuator columns in a soften state, and rigid in a stiff state. In some embodiments, the variable stiffness surface is configurable multiple times.

Description:
BACKGROUND 
     A composite structure is fabricated on tooling. Generally, the tooling is made as one piece. Thus, the tooling, form, or mold, is fabricated, and then the composite structure is fabricated on top of the tooling. Tooling is typically one sided, but could be two sided. 
     Typically, to form a composite structure, the composite material is placed on the tooling, and then pressure/vacuum is applied to hold the composite material during curing of the composite material, i.e. epoxy, thermoset composite, thermoplastic composite etc. Thus, to make a composite structure, the tooling is fabricated first, and then the composite structure. This process can be costly, especially for prototyping where one or two parts is made. What is needed is reconfigurable tooling, that can be easily and precisely configured and reconfigured to suit a particular need. 
     In one prior approach, reconfigurable modular tooling is proposed in U.S. Pat. No. 5,851,563 by Hoffman, herein incorporated by reference. A bed of pins is supported by a housing. Each pin is connected to a screw drive that allows the height of the entire array to be adjusted by a single motor that rasters across the unit. The work surface is defined by an array of “spring” heads which are mounted on ball joints and provide some degree of flexibility. A solid surface may be laid across these pins. In another approach, reconfigurable tooling is proposed for forming honeycomb cores in U.S. Pat. No. 6,209,380, by Papazian et al., herein incorporated by reference. In this approach, an array of rectangular cross section pins define a three dimensional work surface. The heads of the pins can be made of various types of spring loaded devises. This approach exhibits a degree pixelation of a surface, and thus is used for forming honeycomb cores, rather than the composite panels themselves. 
     What is needed is reconfigurable tooling that can provide a high stiffness continuous tool surface and still provide a large envelope of potential tool shapes. A continuous tool surface provides a high quality part exterior surface and also allows vacuum processing tools to be used reducing need for additional finish machining and lowering fabrication costs. Moreover, what is needed is a way to better tailor the surface shape of reconfigurable tooling than is possible with conventional tooling. Furthermore, what is needed is a way to control the local stiffness of a reconfigurable tooling surface. 
     SUMMARY 
     In some embodiments, reconfigurable tooling is provided having an array of actuator columns affixed to a support base. A programmable controller is configured to position the actuator columns. The reconfigurable tooling has a tooling surface which includes a variable stiffness surface capable of controllable states of stiffness, the variable stiffness surface being capable of being deformed by the actuator columns in a soften state and rigid in a stiff state. In some embodiments, the variable stiffness surface is configurable multiple times. 
     In some embodiments, reconfigurable tooling is provided having an array of actuator columns affixed to a support base. A means to control actuation of the actuator columns is provided. In some embodiments, the reconfigurable tooling has a tooling surface, which includes a variable stiffness surface capable of being deformed in response to the actuator columns. Furthermore, the variable stiffness surface may include controllable stiffness regions, with actuator columns coupled to the controllable stiffness regions. 
     In some implementations, a method is provided for forming tooling which includes configuring a variable stiffness surface and stiffening the variable stiffness surface. Further, the method includes unstiffening the variable stiffness surface and reconfiguring the tooling surface after unstiffening the variable stiffness surface. 
     Additional embodiments and implementations are disclosed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features and advantages of the present invention will be better understood with regard to the following description, appended claims, and accompanying drawings where: 
         FIG. 1  shows a simplified schematic of one embodiment of a reconfigurable tooling system including a control flow diagram. 
         FIG. 2  shows a side view of one potential design for an actuation column. 
         FIG. 3  shows a conceptual illustration of a top view of an embodiments of the variable stiffness surface. 
         FIG. 4  shows a cut away side view of a composite processing system for resin infusion type processing. 
     
    
    
     DESCRIPTION 
       FIG. 1  shows a simplified schematic of one embodiment of a reconfigurable tooling system  100  including a control flow diagram. Some embodiments may include of several portions, which work together to provide the desired operation. They may include the mechanical, material and/or system model, and system controller units. The mechanical portion  110  of the system  100  is shown in  FIG. 1  and may include several parts. 
     One part is a variable stiffness surface  115 , which provides the form of the tooling surface  115   s . Another is a array of actuator columns  113  which introduce z-axis displacements to the surface. This actuator column array  113  may be either regular or irregular depending on the needs of the tool. A potential embodiment for the actuator columns of the array  113  are described further below. The columns of the array  113  are affixed to a base support  111 , which provides a ground for the forces generated on the columns of the array  113  during deformation. The base support  111  may itself be may deformed (not shown), either by mechanical linkages or using variable stiffness supports, so that a greater variety of shapes may be accommodates from a single tool. This may be useful, for example, to allow a tool to change from planar shapes to cylindrical shapes. 
     Various embodiments can provide two important advantages. First, because the tooling surface  115   s  is formed with a variable stiffness surface  115 , it can provide a high stiffness continuous tool surface and still provide a large envelope of potential tool shapes. A continuous tool surface provides a high quality part exterior surface and also allows vacuum processing tools to be used. Second, local control of the stiffness of sub-regions of the surface can better tailor the surface shape than is possible with a fixed stiffness surface. Furthermore, a continuous surface allows a degree of spline interpolation between actuation points that reduces the number of necessary actuators to achieve a particular fidelity of surface shape. These advantages can improve the functionality of this reconfigurable tooling so that it can be more widely used. 
     A controller portion  120  of the reconfigurable tooling system  100  may have of several components. These may include a computer controller  122  for the system  100 , which provides overall user control. An input  123  to the computer controller  122  provides a means to input desired shapes (CAD, FEA, etc.) into the system  100 . Sensor feedback  124 , from sensors at the actuator columns  123  and/or an optional global surface deformation analysis instrument  117 , such as a digital image correlation system, or a laser tracker system is provided. A surface model  126  predicts shape contours for given boundary conditions and prevents failure due to overstretching or overstressing of the system  100 . A controller algorithm  127  can determine the best choice of actuation and stiffness changes to the system  100  to reach the desired shape output on the variable stiffness surface  115 . 
     The controller algorithm  127  may be obtained by many different approaches, for example, a learning based genetic algorithm may be used. This controller portion  120  enables the system  100  to provide unique functionality as compared to open-loop manual tuning of the structure. This will increase the accuracy of the tooling surface  115   s , and reduce the numbers of actuators and control points required to reach the desired shape. 
     In some embodiments, the surface shape input  123  and the sensor feedback  124  may be provided to a microcontroller device (not shown), or a processor based system, such as a computer. The surface model  126  may be input into, or computed by, the computer, which may be programmed with the controller algorithm  127 . Typically, this would include the use of memory, or other storage devices (not shown). Thus, the controller portion  120  may be implemented in software and/or hardware, or the columns may be manually manipulated (not shown), or by a combination thereof, to provide a means to control the position of the actuator columns. 
       FIG. 2  shows a side view of one potential design for an actuation column  200 . The actuation column  200  are provided in an array  113  (shown in  FIG. 1 ), to define the forces applied to the surface. In the embodiment of  FIG. 2 , the actuator arm  226  is attached to the variable stiffness surface  215  by a ball joint pivot  224 . Z-axis (vertical) actuator so need a ball joint to allow lateral force as surface tilts or stretches. The column is relatively stiff, the pivot point allows a rotation but will transmit lateral loads. The pivot point will allow two axis movement. 
     The variable stiffness surface  215  may be adhesively fixed to the actuation column  200  in order to reduce the stress concentration near the connection. In some embodiments, a detachable load spreader  222  is connected to the ball joint  224 . Connection to variable stiffness surface detachable so can release surface if want to use for multiple surfaces. Detachable at load spreader contact surface, may have adhesive or velcro or other release mechanism between load spreader and surface, or between load spreader  222  and actuator arm  226 . This connection may also be made using through bolting and/or pin supports (not shown), or other detachable connection. 
     A motor or hydraulic actuator  228  is attached to the actuation arm  226 , which provides the necessary level of z direction actuation to the variable stiffness surface  215 . The actuator  228  should be capable of repeatable displacement output and force requisite with that necessary to deform the variable stiffness surface  215 . The actuator  228  itself may be mechanical (for example a screw drive), electromagnetic, hydraulic, ultrasonic piezoelectric, or other similar technology. The actuator  228  may be selected based on the desired force level and displacement accuracy. Combinations of various types of actuators in series may be used to provide both large extensions and high precision. 
     In one embodiment, the variable stiffness surface  115  (shown in  FIG. 1 ), may be a composite structure of shape memory polymer in combination with steel or aluminum platelet/segment reinforcement as disclosed in U.S. patent application Ser. No. 11/193,148, filed Jul. 29, 2005, by McKnight et al., entitled VARIABLE STIFFNESS STRUCTURE, herein incorporated by reference. In one embodiment, the variable stiffness surface  115  has the property of being stiff and strong below a transition temperature, and then once raised above a threshold transition temperature, reduces stiffness and increases the malleability. Deformations accrued in the high temperature state, can be elastically recovered while in the high temperature state, or can be “set” or be quasi-permanent by cooling below a transition temperature. If heated above the transformation temperature without constraint, the variable stiffness surface  115  recovers the deformation and return to the original home state. 
     In embodiments where thermally activated shape memory polymer is used, certain considerations must be taken into account. First, the transition temperature of the shape memory polymer material of the variable stiffness surface  115  must be above the processing temperature of the workpiece. Currently, shape memory polymers with many chemistries have been formulated and the transition temperature can be varied between room temperature and 160 C. Higher temperature formulations may be conceived in the future which will allow higher temperature resins to be more easily processed using a reconfigurable tooling surface. 
     A second condition resulting from the use of the variable stiffness surface  115 , are considerations of the resistance of the tooling surface to deformations when being used as a tool, which could lead to inaccuracies in the tool shape. In general, a thicker variable stiffness surface  115  will provide a more rigid support for composite manufacturing operations. Thicker surfaces  115 , however, will require that larger strains be accommodated in the surface  115  during the course of deforming from one shape to another. In general, the variable stiffness surface  115  must be selected for a particular range of operation to provide the required stiffness and/or recoverable strain values. This must be considered as part of the whole system design, but, in some embodiments, it is expect that practical surfaces may be produced with thicknesses ranging from about 0.5 mm to about 20 mm. The stiffness of the variable stiffness surface  115  may be between very rigid plastic and aluminum. This will provide sufficient stiffness to tolerate vacuum pressure applied to the mold to assist in maximizing volume fraction in wet lay up and resin transfer molding approaches. Depending on the design of the system, hydrostatic pressure such as that achieved in an autoclave can be used to further consolidate the composite parts. 
     In some embodiments, to exact a change in stiffness, the variable stiffness surface  115  must be heated above its transition temperature. This may be performed using a variety of methods. The first is environment heating where the surface is subject to still or moving air which has been previously heated using heating coils. Another possible approach is the incorporation of integrated resistive heating elements within the variable stiffness surface  115 . These must be able to accommodate deformation, or not at least not detrimentally interfere with the deformation of the variable stiffness surface. Embedded heaters offer one of the fastest method of heating the material. Other potential approaches include microwave heating through small dielectric particles incorporated into the shape memory polymer material. Applying microwaves to these materials will induce volumetric heating that is also potentially provides large rates of temperature increase. Another method to heat the surface is place heating blankets on top of surface. Another is to used heated air guns to indirectly hear the surface. Many other methods are possible. 
     One method of improving the surface control precision is to subdivide the heating elements into subregions such that the stiffness across the area of the surface can be individually tailored. An example of this is discussed in detail in the U.S. patent application Ser. No. 11/347,505, filed Feb. 3, 2006, by McKnight et al., entitled ACTUATION CONCEPTS FOR VARIABLE STIFFNESS MATERIALS, herein incorporated by reference, which discusses techniques for control of heating, or stiffness along various zones to tailor shape. This allows the variable stiffness surface to achieve a large number of shape outputs in response to discrete actuation inputs. 
       FIG. 3  shows a conceptual illustration of a top view of an embodiments of the variable stiffness surface  315 . A grid of variable stiffness control regions  315   r , and an array of attachment points  322  for the actuation members (not shown). This grid shows a total of 5×9, or 45 actuator attachment points  322 . The number of actuation points will help determine the accuracy of the surface. One chief discriminator of some embodiments over previous inventions is the ability to spline fit between actuation points, thus increasing significantly the precision of surface control. 
     The surface  315  can be subdivided into control regions  315   r  for which the stiffness can be individually controlled. The control regions  315   r  can provide higher and lower stiffness regions within the variable stiffness surface  315  during deformation of the variable stiffness surface  315 . For example, the heating of the individual control regions  315   r  can be different, some made hot and some cold to control stiffness in the different regions  315   r.    
     By taking advantage of non-uniform stiffness capability of the surface  315 , further control of deformation can be achieved in the surface when you apply a particular actuation combination. The control algorithm may be used to control the stiffness of the regions  315   r  in combination with control of the actuators (not shown in  FIG. 3 ). This allows greater precision and control with same set of actuators. 
     In  FIG. 3 , the variable stiffness surface  315  is shown subdivided in discrete control regions  315   r  in a grid fashion. The layout of this grid of control regions  315   r  is variable and may be regular or irregular depending on the particular application. For certain applications, the entire surface may be controlled as a single stiffness region and solely actuation is used to control the deformation of the surface rather than combinations of actuation and regional stiffness control. The actuators (not shown in  FIG. 3 ) may be attached to this grid of control regions  315   r  in a number of ways. For example, the attachment points  322  may be at the vertices of the control regions  315   r , as shown in  FIG. 3 , in the center (not shown) of the control region  315   r , or some combination or variation this. 
     Referring to  FIG. 1 , because the deformations may be held with zero power in some embodiments, the tools need not be attached to the base  111  once shape forming is complete. Thus, in embodiments where the variable stiffness surface  115  is removable, it is possible to create several tooling surfaces  115   s  for use at the same time, with a single actuation base  111  unit. At the end of a production run, the tooling surfaces  115   s  could be reset to begin another project. 
       FIG. 4  shows a cut away side view of a composite processing system  400  for resin infusion type processing. A resin infusion layer  440  is supplied to the composite workpiece  450  via a resin infusion port  420 . A vacuum enclosure  460 , such as a vacuum bag, encloses the composite workpiece  450 , which may be a composite reinforcement perform, over the variable stiffness tooling surface  415 . This type of process may be easily employed with solid surface reconfigurable tooling as described in this discussion. Many other techniques may benefit from this type of tooling. These include vacuum assisted resin transfer molding, wet lay-up, spray forming with chopped fiber, and the like. This invention is suitable for use with thermoplastic matrix composite materials as long as the thermoplastic matrix flow temperature is below the glass transition temperature of the variable stiffness materials. 
     The example embodiments herein are not intended to be limiting, various configurations and combinations of features are possible. Having described this invention in connection with a number of embodiments, modification will now certainly suggest itself to those skilled in the art. As such, the invention is not limited to the disclosed embodiments, except as required by the appended claims.