Abstract:
Disclosed is an additive manufacturing device that facilitates the manufacturing of relatively large 3D objects at a short time. The device uses radiation-curable resin and radiation curing system. Layer shaping members are disclosed to provide both for shorter manufacturing time of an object, minimizing waste of resin and reduction of weight. Curing radiation sources are also designed to minimizing waste of resin and manufacturing time.

Description:
TECHNOLOGY FIELD 
       [0001]    The apparatus and method are related to the field of additive manufacturing and particularly to additive manufacturing devices utilizing radiation-curable resins. 
       BACKGROUND 
       [0002]    In some additive manufacturing (AM) devices a container is provided with a radiation-curable resin (RCR) in the container. The flat bottom of the container is typically made of a transparent material that allows the resin curing radiation to be transmitted through the bottom and interact with a radiation-curable resin layer adjacent to the bottom of the container. The transmitted through the bottom curing radiation interacts/cures a thin, adjacent to the bottom, layer of resin, typically 10-100 um thick. Once a layer of resin is cured the entire manufactured 3D object is lifted, typically 10-100 um above the bottom of the container, allowing to cure another layer of radiation-curable resin forming the object. This way the object is built a layer after a layer until the entire object is produced above the bottom of the container. 
         [0003]    Additive manufacturing (AM) devices where a layer of radiation-curable resin is deposited on the top of an earlier deposited layer are also known and described for example, in U.S. Pat. Nos. 6,586,494, 6,966,960, 7,291,002, and 8,509,933 and European patent EP2654412. Typically, the thickness of the cured or solidified material layer is about 10-60 micron. This is because the radiation-curable resin absorbs a large part of the curing radiation and makes it almost impossible to solidify thicker layers of radiation-curable resin. 
         [0004]    Such additive manufacturing devices are typically intended to manufacture objects with relatively small size and high dimensional accuracy. Manufacture of such objects results in a relatively long time of production. For example, production of a small 50×50×50 mm object would typically take more than an hour. Manufacture of larger size objects would naturally take more time making the method not suitable and cost effective for additive manufacture of large size objects, for example, of 1000×1000 mm or even 5000×5000 mm. 
       GLOSSARY 
       [0005]    “Radiation-curable resin”—as used in the current disclosure means any liquid or gel material that is in a liquid state or flow able state and becomes solid on interaction with radiation or heat. 
         [0006]    “3D pattern”—as used in the current disclosure means a generally non-flat surface on which a relief such as a 1D pattern, 2D pattern or 3D pattern is produced. The patterns could be of similar or different size in direction of each of three axes (X, Y, and Z). The 3D pattern could be a periodic pattern and the period of the pattern could be equal or different in direction of each of three axes (X, Y, and Z). 
         [0007]    “Direction”—as used in the current disclosure in the context of pattern of a surface means direction of x or direction of y or the direction of z in the Cartesian coordinate system. 
         [0008]    “Transparent”—as used in the current disclosure means “at least partially transparent” to the radiation used to cure the resin. 
         [0009]    DLP is a digital micro-mirror device originally developed in 1987 by Dr. Larry Hornbeck of Texas Instruments. The DLP imaging device is currently used by most available on the market video projectors. 
       BRIEF SUMMARY 
       [0010]    An apparatus for additive manufacturing of 3D objects includes a container configured to contain a radiation-curable resin and a radiation source configured to provide the curing radiation to cure at least a portion of the radiation-curable resin into a solid layer. The container includes a bottom with a surface that is in contact with the radiation-curable resin. The particular surface bears a 3D pattern and the cured (solidified) or solid layer of the radiation curable resin is a replica of the 3D pattern of the bottom surface, which is in contact with the radiation-curable resin. 
         [0011]    A 3D object manufactured by the apparatus is a stack of 3D layers and not a stack of flat layers as it is manufactured by existing apparatuses. The dimensions of the three-dimensional layers exceed 8 to 20 times the thickness of the flat layers. The time required to manufacture a 3D object is generally proportional to the number of cured radiation curable resin layers of which the 3D object is made. Accordingly, the manufacturing time by the described apparatus is 8 to 20 times shorter, making feasible additive manufacture of large 3D objects. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The apparatus and method will be better understood in reference to the following Figures: 
           [0013]      FIG. 1  is a simplified illustration of an example of an additive manufacturing apparatus using bottom radiation to cure radiation-curable resin; 
           [0014]      FIG. 2  is a schematic illustration of a cross section of a bottom of the container containing radiation-curable resin according to an example; 
           [0015]      FIGS. 3A, 3B, 4A, 4B, and 5  are examples that illustrate different 3D patterns produced on bottom surface of the container containing radiation-curable resin; 
           [0016]      FIGS. 6A and 6B  are schematic illustrations of a 3D object manufacturing process according to an example; 
           [0017]      FIGS. 7A through 7D  illustrate examples of different shifts between neighbor layers of a 3D object; 
           [0018]      FIGS. 8A and 8B  are schematic illustrations of a manufactured 3D object according to an example; 
           [0019]      FIG. 9  is a schematic illustration of a post-processing low cost radiation curable or heat curable material solidifying station; 
           [0020]      FIGS. 10A through 10C  are schematic illustrations of an example of a 3D object that includes volumes with different properties and different 3D structures; and 
           [0021]      FIG. 11  is a schematic illustration of an example of a container with bottom surface including different 3D structures. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    The maximal thickness of a radiation curable resin that could be cured by the curing radiation is limited by the absorption of the curing radiation in the radiation-curable resin. This limits the rate at which the 3D object layers could be added and cured or solidified. The possible 3D object material addition rate also limits the size of the objects that could be produced at an acceptable cost and time. The current document discloses an apparatus and a method of employing an apparatus that facilitates faster manufacturing of 3D objects. 
         [0023]    Reference is made now to  FIG. 1  which is a simplified illustration of an example of additive manufacturing apparatus using bottom radiation to cure radiation-curable resin. Apparatus  100  includes a container  102  shown in a cross section. Container  102  includes at least a bottom  104  (the structure of the bottom will be described later) that could be made of a material transparent to curing radiation. Container  102  is configured to contain radiation-curable resin  106 . Container  102  rests on support  110 . In some examples, support  110  could be configured to move in at least two directions, typically, these would be the directions of coordinate axis X and Y. In some examples, support  110  could be configured to move in three directions, typically, these would be the directions of coordinate axis X, Y, and Z. Existing motion providing mechanisms or actuators could be employed to facilitate movement of support  110  in one, two or three directions. 
         [0024]    Typically, also not necessary, the radiation source  114  could be placed under container  102  performing what is termed as down-up additive 3D object manufacture. The curing radiation source  114  could be a matrix of LEDs, a Xenon Lamp, a mercury vapor lamp, a solid state laser, a gas laser, or other source of curing radiation. Curing radiation source  114  could be made similar in size or equal to bottom  104  of container  102 . When the size of radiation source  114  is smaller than the size of bottom  104  of container  102 , radiation source  114  could be configured to move in two directions as shown by arrows  126 , such that the curing radiation emitted by curing radiation source  114  could reach every point at the bottom  104  of container  102 . Existing motion providing mechanisms or actuators could be employed to facilitate movement of curing radiation source  114  in both X and Y directions. 
         [0025]    In some examples, a DLP® light switch, commercially available from Texas Instruments, Inc., Dallas, Tex. 75243 USA, could be used to selectively transmit curing radiation to cure only certain areas of object  108  to be manufactured. The DLP light switch could be coupled with Xenon or a mercury vapor lamp or other source of curing radiation. In another example, a scanning laser beam could be used to selectively transmit curing radiation to cure only certain areas of object  108  to be manufactured. 
         [0026]    Apparatus  100  also includes a base  118  configured to adhere to one of the surfaces of object  108 . Base  118  is connected to a rod  122 , which schematically represents a mechanism such as a screw with a nut or a rack and pinion mechanism configured to displace base  118  with adhered to it object  108  in the direction of arrow  128 , which typically would be the Z axis direction. 
         [0027]    Apparatus  100  could include different auxiliary units. For example, unit  130  could be configured to constantly or periodically replenish radiation curable resin consumed in process of object  108  manufacturing. Unit  134  could be configured to drain remaining in container  102  after completion of object  108  manufacturing, radiation curable resin. 
         [0028]    Computer  138  governs operation of apparatus  100  and all of apparatus  100  units or modules. Computer  138  could be configured to control: container support  110  movements in each of the mentioned above directions; movement of base  118  and rod  122 ; operation of curing radiation sources  114  and their movement; operation of the DLP® light switch or of the scanning laser beam; activate radiation curable resin replenishment and drainage. Computer  138  could be configured to displace support  110  on a desired distance along each of the three coordinate axes. 
         [0029]    Computer  138  could also be configured to receive object  108  design data from a Computer Aided Design (CAD) system  142  and adapt the design data to a particular manufacturing process. Typically, CAD system  142  would not be a part or a component of additive manufacturing apparatus  100 , although computer  138  of apparatus  100  could run suitable CAD software to facilitate object  108  preview and other operations that could assist apparatus  100  operation. 
         [0030]      FIG. 2  is a schematic illustration of a cross section of the bottom of the container according to an example. The known apparatuses or systems for additive manufacture of 3D objects typically, in what is termed as down-up additive manufacture, have a transparent bottom with flat surfaces and each cured layer is also flat. In the present apparatus  100  bottom  104  of container  102  includes a surface  200  that bears a 3D pattern  208  and the cured (solidified) or solid layer  204  of the radiation curable resin is a replica of the 3D pattern  208  of bottom surface  200 , which is in contact with the radiation-curable resin  106 . 
         [0031]    The 3D pattern that surface  200  bears, could be a periodic pattern or a non-periodic pattern. It could be a periodic pattern in at least one direction or two directions or all three directions. The period of the 3D pattern that surface  200  bears, could be the same in all of the three directions or different in at least one direction. A variety of 3D patterns such as for example, patterns  208 ,  408 ,  508  and others, could be produced on surface  200 .  FIGS. 3A, 3B, 4A, 4B and 5  illustrate different 3D patterns formed on surface  200  of bottom  104 , which in course of 3D object  108  manufacture are in contact with the radiation-curable resin  106 . In one example the 3D pattern could be a non-periodic pattern. 
         [0032]      FIG. 5  also illustrates some of the parameters of a 3D pattern produced on surface  200  of bottom  104  of container  102  according to an example. Letter “P” denotes the length or a period of one cycle of the pattern  508  produced on surface  200  of bottom  104  of container  102  and the amplitude of the 3D pattern is denoted as “h”. The term spatial frequency will also be used in reference to the 3D pattern of surface  200  and it means spatial frequency F of 1/P. Such terms in reference to the surface  200  of bottom  104  of the container will be used for different types of bottom surfaces  200  patterns  208  and the specific usage would be understood from the context in reference to the particular bottom surface discussed. The amplitude of the 3D pattern could vary between 50 micron to 900 micron and more typically between 100 micron and 250 micron and the spatial frequency could vary between 1 to 50 periods per centimeter. 
         [0033]    The 3D patterns of surface  200  could for example, be manufactured by molding container  102  bottom  104  using a mold with the desired pattern. The mold material and manufacturing process would depend on the material used for container bottom  104 . Common known glass molding techniques could be used for molding of different patterns on surface  200  of bottom  104  of the container. Other than glass, transparent for curing radiation materials also could be used for bottom  104  of container  102  manufacturing. 
         [0034]    Curing radiation transmitted through the 3D structure could be partially reflected at the boundary with the radiation-curable resin. Proper selection of the ratio of the refractive indices of the materials used for bottom  104  and the refractive indices of the radiation-curable resin  106  could facilitate effective radiation-curable resin  106  curing process. In some examples, container  102  bottom  104  could have a 3D pattern on surface  200  and another 3D pattern or a diffractive or holographic pattern facilitating effective curing radiation penetration of the curing radiation into the radiation-curable resin. 
         [0035]    One of the problems associated with the existing 3D objects manufacturing equipment is related to the completeness and filling time of the liquid layer of radiation-curable resin  106  ( FIG. 1 ) that fills-in a gap  142  between the earlier manufactured and solidified radiation-curable resin layer  204  ( FIG. 2 ). In existing 3D printing equipment, gap  142  is to be filled by the liquid radiation-curable resin  106  ( FIGS. 1 and 2 ) is 25 to 50 micron and surface tension forces impede fast and complete filling of the gap. Frequently, to facilitate the empty volumes filling, vibrations are applied to container  102  or object  108 . 3D patterns produced on surface  200  of bottom  102  of apparatus  100  could vary between 50 micron to 1000 micron and more typically between 100 micron and 250 micron. Such gaps are sufficient to avoid negative effects that could be caused by the surface tension forces and facilitate fast filling of gap  142  between the earlier manufactured and solidified radiation-curable resin layer  204  and bottom surface  102 . 
         [0036]      FIG. 6A  is a schematic illustration of a 3D object down-up manufacturing process according to an example. 3D object  108  that is being manufactured is adhered to base  118 , that is connected to rod  122 , which could be a screw with a nut or a rack and pinion mechanism configured to displace base  118  with adhered to it object  108  in the direction of the Z axis. 
         [0037]    3D object  108  is shown at a phase of adding a new, to be cured material  106  layer  204 - 5  between the earlier produced object&#39;s  108  layers ( 204 - 1  through  204 - 4 ) and surface  200  of bottom  104  bearing the 3D pattern. Each of the cured resin layers  204 - 1  through  204 - 4  are a replica of surface  200  3D pattern. The 3D pattern parameters, for example, the amplitude of the 3D pattern could define the distance between the current  204 - 5  and earlier produced object  108  layers  204 - 4 . For example, if the amplitude of the 3D pattern produced on surface  200  of bottom  104  is 250 micron, the amplitude of cured radiation curable resin layer  204  would also be 250 micron. Assuming that the 3D object is a cuboid with 100×100×100 mm, only 400 cured resin layers would be required to produce such a cuboid. 
         [0038]    The time required to manufacture a 3D object is generally proportional to the number of cured radiation curable resin layers  204  of which the 3D object is made. It is known that conventional 3D object additive manufacturing methods, practically do not support curing or solidification of curable resin layers thicker than 20-25 micron. Assuming that the cured layer produced by conventional additive manufacturing methods would be 25 micron thick, manufacturing of cuboid  108  would require deposition and curing or solidification of 4000 layers. This means that manufacturing cuboid  108  by the present method would be 10 (ten) times faster than manufacturing of the same cuboid  108  by conventional additive manufacturing methods. It also means that the weight of cuboid  108  would be a fraction of the weight of a similar cuboid manufactured by conventional additive manufacturing methods. This weight advantage and material savings are particularly important for additive manufacture of large 3D objects. 
         [0039]    Curing radiation source  114  ( FIG. 1 ), for example, a DLP® with a lamp or a scanning laser beam could be configured to project a 2D curing radiation pattern focused within curable resin layer  204  to cure or solidify the next 3D object (cuboid) layer. In cases where the radiation source cannot irradiate the entire cross section of bottom  104  or cannot provide proper radiation dose for curing curable layer  204  or a part of it, radiation source  114  could be, as explained above, translated in X-Y plan, although in some examples translation in direction of Z axis/plan or even angular translation could be implemented ( FIG. 1 ) to facilitate delivery of a proper radiation dose for curing or solidifying radiation curable resin layer  204  for objects with cross section larger than the dimensions of the radiation source  114 . 
         [0040]    Following curing or solidification of a current layer  204 - 5  of liquid volume of radiation curable resin  106 , object base  118 , to which object  108  is adhered, moves 250 micron in the direction of arrow  128  to provide for the manufacture of the next layer  204 . The process continues until the manufacture of 3D object  108  is accomplished. 
         [0041]    For the simplicity of explanation the 3D pattern produced in surface  200  of bottom  104  and illustrated in  FIG. 5  is a periodic pattern in one direction. 3D object  108  is manufactured as a stack of 3D layers  204 . Layers  204  are shown to be in registration with each other. Apparatus  100  produces 3D object  108  as a three dimensional periodic structure with hollow volumes  604  ( FIG. 6 ) located in free spaces according to the period or periods of 3D pattern produced on surface  200  of bottom  104 . In some examples, it could be desired to reduce the size and period of hollow volumes  604 . Computer  138  ( FIG. 1 ) could be configured to displace support  110  on a desired distance along each of the three coordinate axes. Support  110  ( FIG. 1 ) could be displaced on a distance equal to the period of the 3D pattern produced on surface  200  of bottom  104  or on a fraction of the 3D pattern period. The fraction of the 3D pattern period could be equal to 0.1, 0.2, 0.32, 04, 0.5, 0.6, 0.65, 0.7, and 0.8 or any other fraction of the 3D pattern period as illustrated in  FIG. 7 . In some examples, the shift could be larger than the 3D pattern period. 
         [0042]      FIG. 6B  is a schematic illustration of a 3D object up-down manufacturing process according to an example. 3D object  620  that being manufactured is adhered to a support  624  placed into a tank  628  filled in with radiation curable polymer  632 . Support  624  is configured to move as shown by arrow  636 . Surface  640  of base  644  bears a 3D pattern similar to pattern produced in surface  200  of bottom  104  ( FIGS. 2-5 ). Surface  640  is in contact with radiation curable polymer  632 . A curing radiation source  648  such as for example, a DLP with a lamp or a scanning laser beam could be configured to project a 2D curing radiation pattern focused within curable resin layer  652  being in contact with surface  640  to cure or solidify the radiation curable resin layer being in contact with the 3D pattern made in surface  640 . 
         [0043]    3D object  620  is shown at a phase of adding a new, to be cured material layer  652  between the earlier produced object&#39;s  620  layers ( 652 - 1  through  652 - 3 ) and surface  640  bearing the 3D pattern. Each of the cured resin layers  652 - 1  through  652 - 3  are a replica of surface  640  3D pattern. The parameters of the 3D pattern could be similar to parameters of the 3D pattern produced in surface  200  of bottom  104 . 
         [0044]      FIG. 7A  illustrates a shift  704  between two neighbor layers  708  similar to layers  204  equal to a quarter of the 3D pattern period “P”.  FIG. 7B  illustrates a shift  712  between two neighbor layers  708  equal to about one tenth of the 3D pattern period “P”. 
         [0045]    Depending on the 3D pattern, curing of some segments, for example, segments including sharp bends of the surface could result in non-uniform cured layer thickness. In some examples the 3D pattern could be composed of surfaces with smooth curves ( FIG. 7C ). Shifts between the odd and even layers  720  could improve uniformity of the cured pattern and also reduce jaggedness of the external edges of a 3D object to be manufactured. Intentional, small shifts between the odd and even layers could also be introduced in manufacture of objects with curved external surfaces  730  ( FIG. 7D ). 
         [0046]    Support  110  displacement could be intentional or as a result of an error in support displacement. Support  110  displacement errors are possible and also depending on the type of 3D pattern produced in the surface  200  of container  102  bottom  104  they are not affecting object  108  manufacture. 
         [0047]    Typically, apparatus  100  also includes some mechanisms or arrangements configured to completely separate manufactured 3D object  108  from radiation curable resin  106  and tank  102 . Any suitable mechanism could be used for the purpose of removing manufactured object  108  from apparatus  100 . 
         [0048]      FIG. 8A  is a schematic illustration of a manufactured 3D object according to an example. 3D object  108  is manufactured as a stack of solidified 3D layers  204 . A desired outer surface quality of the 3D object could be manufactured by selecting proper amplitude “h” of the 3D pattern of tank  102  bottom surface  200  ( FIG. 5 ) and support  110  ( FIG. 1 ) displacement value. In some examples, it could be desired to produce a completely solid 3D object, for example such as object  800  external borders of which are shown by broken lines  804 . This could be achieved, as illustrated in  FIG. 8B  by employing a 3D pattern including extensions supporting formation of walls  830  manufactured from the same radiation-curable resin. 3D object  800  manufactured with walls  830  could be filled in with a low cost radiation curable or heat curable material  834 , which would occupy hollow volumes  604 . Material  834  could be solidified by curing radiation or heat. 
         [0049]    Alternatively, 3D object  108  could be manufactured as a stack of solidified 3D layers  204 . In some examples, it could be desired to produce a completely solid 3D object, for example such as object  800  ( FIG. 8A ) external borders of which are shown by broken lines  804 . This could be achieved by placing the earlier manufactured and separated from base  118  3D object  108  into a suitable size tank  900  ( FIG. 9 ), which could be made of opaque or transparent material. Typically, the size of tank  900  would match the external dimensions of manufactured object  108 . Tank  900  with placed into it manufactured object  108  could be filled in with a low cost radiation curable or heat curable material  906 , which would fill in hollow volumes  604 . Material  906  could be solidified by curing radiation or heat. One or more curing radiation sources  910  could be placed around object  108  to facilitate faster curing. Alternatively, tank  900  with object  108  could be placed into a furnace (not shown) and heated to a suitable temperature sufficient to cure or solidify the low cost radiation curable or heat curable material  906 . Such temperature could be between 60 degrees C. to 100 degrees Celsius. 
         [0050]    Radiation source  114  of apparatus  100  ( FIG. 1 ) configured to provide the curing radiation to cure at least a segment of the radiation-curable resin into a solid layer  204 . The same radiation sources combined with, for example DLP or a scanning laser beam, could be also configured to provide at least one void (opening; hole)  820  in the solid layer of cured resin  204 . Voids or holes  820  ( FIG. 8 ) are manufactured to support drainage of at least a part of the liquid low cost radiation curable or heat curable material  906  into hollow volumes  604  of 3D object  108  as well as support trapped air evacuation. Voids  820  could be small or large and one void could include a number of 3D structures. Large voids  820 , especially ones made in the inner volumes of the object could save expensive radiation-curable resin and reduce the weight of the 3D object. 
         [0051]    In one example, illustrated in  FIG. 9 , tank  900  with a low cost radiation curable or heat curable material  906  and manufactured object  108  could be implemented as a stand-alone or in-line material solidifying station  914  or simply a post-processing station. Tank  900  could be placed on a motorized support  918  configured to support tank  900  with the three dimensional object or structure  108 . Support  918  could support movement in two directions, for example X and Y. A low cost radiation curable or heat curable material  906  dispensing facility  930 , a number of radiation curing units  910  could be arranged around tank  900 . Computer  138  ( FIG. 1 ) could be configured to control the motorized support  914  and displace it in one or both X and Y directions, the dispensing facility configured to dispense the low cost radiation-curable or heat curable material across tank  900 , such as to fill with the radiation or heat curable material the hollow spaces  604  of the three dimensional object  108 ; and radiation or heat sources  910  configured to provide the curing radiation to cure the low cost radiation-curable resin into a solid body. 
         [0052]    Different 3D objects could require use of different curing materials and even different 3D pattern structures. This could be achieved by exchanging bottom  104  of container  102  on a bottom with a different 3D pattern. In some examples ( FIGS. 10A-10C ) the 3D object could include different 3D patterns.  FIG. 10A  illustrates a 3D object a volume  1004  of which is manufactured using a bottom with a first type of the 3D pattern and a volume  1008  of which is manufactured using a second type of the 3D pattern. This could be of help when the 3D object should include volumes with different structure, manufactured from different material or have different properties. The present system supports exchange of bottom  1012  ( FIG. 10B ) of a container on a bottom  1014  ( FIG. 10C ) with a different 3D pattern even in course of manufacture of the same 3D object. 
         [0053]    In one example illustrated in  FIG. 11 , container  1100  similar to container  100  could be made large enough to support production of different 3D structures on different segments of bottom  1102  surface. For example, each of segments  1108  through  1120  could include a different 3D pattern. Different volumes of a 3D object that require different structures could be manufactured simultaneously and later connected together in one 3D object. 
         [0054]    It will also be appreciated by persons skilled in the art that the present method and system are not limited to what has been particularly shown and described hereinabove. Rather, the scope of the method and system includes both combinations and sub-combinations of various features described hereinabove as well as modifications and variations thereof which would occur to a person skilled in the art upon reading the foregoing description and which are not in the prior art.