INDIAN INSTITUTE OF TECHNOLOGY MADRAS (IIT MADRAS), an Indian autonomous body set up by the government of India under an act of Parliament, having its office at The Dean, Intellectual Property Management Cell, Centre for Industrial Consultancy & Sponsored Research (ICSR) , Indian Institute of Technology Madras, IIT P.O., Chennai 600 036. INDIA

The following specification describes the nature of this invention and the manner in which it is to be performed.

FIELD OF THE INVENTION

[001] The present invention generally relates to the field of CNC (computer numerical control) foam cutting and more particularly, an innovative method of fabricating complex 3D shapes using a simple 2-axis CNC system. The present application is based on, and claims priority from an Indian Application Number 201841012066 filed on 30 ^th March, 2018, and an Indian Application Number 201841040992 filed on 30th October, 2018, the disclosure of which is hereby incorporated by reference herein.

BACKGROUND OF THE INVENTION

[002] It is essential to fabricate complex foam shapes in CNC. But traditionally 3D fabrication needs complex 4- axis CNC machines. Such systems are expensive, requires accurate calibrations and complex to use.

[003] Layered Object Manufacturing (LOM) is a common method used to manufacture complex 3D shapes. But LOM in 2D machines produce staircase effects. To overcome staircase effects, linear approximation is typically used. However, producing tapered layers, requires a complex 4- axis wire cutting system. In spite of the 4- axis system, the tapers are still a linear approximation and original curvature is not possible. Obtaining the desired curvature is possible only if layer thickness is dropped very low. But this increases manufacturing time and cost. Hence there is a need to develop an intelligent low cost, simple fabrication system for 3D shape fabrication . OBJECTS OF THE INVENTION

[004] The primary object of the invention is to provide a method of manufacturing complex 3D shapes in a simple 2- axis system.

[005] It is another object of the invention to provide a method of fabricating 3D shapes using 2 axis CNC system, using LOM (Layered Object Manufacturing) method where the individual layers are fabricated by beam bending method.

[006] It is yet another object of the invention to provide a method of manufacturing OLOM (Offset Layers Object Manufacturing) objects using beam bending method in 2- axis CNC wire cutting machine.

SUMMARY OF THE INVENTION

[007] To meet the objects of the invention and to overcome the problems of the prior art, it is disclosed herein a method of 3d shape fabrication in 2-axis CNC machine comprising steps of: setting the dimensions of a beam; cutting the beam of material using a straight wire in a 2-axis CNC (computer numerical control) wire cutting machine; rotating the beam in an angle such that the slits are cut along the beam to form a layer of a complicated 3D shape and combining of multiple such layers fabricate a complicated 3D shape.

[008] It is disclosed here, a method of manufacturing OLOM (OFFSET LAYERS object manufacturing) objects using beam bending method in 2-axis CNC wire cutting machine comprising steps of: setting the dimensions of a beam; cutting the beam of material using a straight wire in a 2-axis CNC (computer numerical control) wire cutting machine; rotating the beam in an angle such that the slits are cut along the beam to form a layer of a complicated 3D shape; and stacking such layers to fabricate a desired 3D shape.

BRIEF DESCRIPTION OF THE DRAWINGS

These invention methods are illustrated in the accompanying drawings, throughout which like reference letters indicate corresponding parts in the various figures. The embodiments herein will be better understood from the following description with reference to the drawings, in which:

[009] FIG. 1 is the schematic representation of the exemplary 3D model (example 1) to be fabricated.

[0010] FIG. 2 shows the staircase style LOM method for example 1.

[0011] FIG. 3 shows the Linear approximated LOM method using 4-axis wire cutting machines for example 1.

[0012] FIG 4 is the schematic representation of the desired ideal curved layer transitions for example 1.

[0013] FIG 5 is the schematic representation of a typical curved layer LOM for example 1.

[0014] FIG 6 is the schematic representation of a straight beam profile cut by 2-axis wire cutting machine for producing one of the layer for example 1.

[0015] FIG 7 shows a sample revolved 3D object (example 2) that can be manufactured by OLOM method.

[0016] FIG 8 shows a sample OLOM offset profile example of a given shape .

[0017] FIG 9 shows a sample complex OLOM 3D object (example 3) that can be manufactured by OLOM method.

[0018] Fig 10(a) and Fig 10(b) shows the method of slitting and bending a beam along a curve, respectively. [0019] FIG. 11a illustrate an isometric view of an example model with stair case effect, in FIG. llb-llc its orthographic views with nomenclature of layers and curve profiles ;

[0020] FIG. 12 is a flow diagram illustrating a method for fabricating a 3D shape using a layer sheet cladding procedure, according to the embodiment as disclosed herein;

[0021] FIG. 13a-FIG. 13c illustrate an isometric and front views of an example reference standard model for sheet cladding with stacked layers for support, FIG. 13b shows the cladding sheet and core support structure for cladding. FIG. 13c shows the final outcome from the sheet cladding method, according to an embodiment as disclosed herein;

[0022] FIG. 14a-FIG. 14d shows an example object to illustrate the cladding procedure. FIG 14a is the support core structure build with 2 axis machine using the sliced profiles. FIG. 14b and 14c, shows the front and top view of the sheet cladding between layer 1 and 2. FIG. 14d is the unwrapped development sheet for cladding according to an embodiment as disclosed herein;

[0023] FIG. 15 is a flow diagram illustrating method of a layer sheet cladding procedure, according to the embodiment as disclosed herein;

[0024] FIG. 16a-FIG. 16f illustrate a complicated example with complicated profile, according to an embodiment as disclosed herein;

[0025] FIG. 17 illustrates an unwrapped 2D development surface with including TABs to physically hold the sheet to the support structure layers, according to an embodiment as disclosed herein; and

[0026] FIG. 18 is example prototypes made with the cladding process, according to an embodiment as disclosed herein. DETAILED DESCRIPTION OF THE INVENTION

[0027] The embodiments herein describe an intelligent CNC cutting system and method of fabricating complex 3D shapes. Referring now to the drawings, and more particularly to Figures 1 through 9, where similar reference characters denote corresponding features consistently throughout the figures, there are shown 10 embodiments .

[0028] FIG 2 shows traditional way of fabricating 3D shapes using 2 axis CNC machines. This produces staircase effect and hence undesirable. Fig.3 shows Linear approximated taper LOM using 4-axis wire cutting machine. Fig.4 shows the Ideal curvilinear LOM surface that needs to be manufactured. In FIG 5. 301, 302,303 are the individual layers; 304, 305, 306 are the cross-section shapes of each layer, and 307, 308, 309 are the transition curves from one layer to next. Fig.6 shows a beam of material cut using a straight wire in a 2-axis CNC wire cutting machine. Let 311, 312 be the nominal radius at each layer. The shape of Fig.6 has base dimension 401, height 402 and curve 403. Curve 403 is same as the curve 307 shown in fig.5. 402 is the layer thickness of bottom most layer (313) and Base width 401 >= (311-312) . Now the beam is turned by 90 degrees and slits are cut along the beam as shown in FIG 10, such that the beam can be bent along the desired shape. In this case, it is bent along the curve shape obtained by interpolating 304 and 305.

[0029] In the instant method, to make a particular required model, process starts with a CAD model; this can be modelled in any shape or in any software. Then, the model is sliced at different locations in any angle based on the geometrical complexity to ease further steps while manufacturing. Sliced individual layers of 3D model is taken to get the side profile of each slice, this side profile will be taken to give need geometry to a long beam by cutting in hotwire CNC machine . Similarly, for each layer we have to cut the profiled beam by taking the side profile from the CAD model. After getting beam, we keep it with a proper angle (i.e. by rotating or tilting the beam such a way that 'cutting wire' can be align with the bending axis or bending profile) . Then, a cutting tool path is given to the CNC machine to cut the beam. This cutting tool path call it as 'slitting' which is generated from special software. This software takes the profile along which beam need to be bent and cutting parameters as input and gives a tool path to cut the work piece (Beam) . The tool path can be same or different for the individual layers. For each layer tool path is generated and then profiled beam is cut to bend for getting final layers. Bent layers are stick with any glue or adhesive to hold it in shape manually outside the machine. The individual stuck beam layers are further stacked and glued to get the final object.

[0030] This procedure may be applied to any design.

Especially, a special category of objects called 'Offset Layer Objects', which are modelled by extruding the offset profiles can be manufactured. The method of building this type of objects is named as OFFSET LAYERS OBJECT MANUFACTURING (OLOM) ' . The main aim of using multiple layers is to build the complicated models and to give the strength to the structure. This total method can be automated from the design stage to the stacking stage. The material that can be worked are EPS (Expanded Poly Styrene) or XPS (Extruded Poly Styrene) materials but this process can also be employed for other foam materials. We can adopt this technique to make both positive parts as well as negative part of a model.

[0031] The method of slitting and bending a beam along a curve is called as "Beam Bending method". The sample slits and bends are shown in Fig. 10. Thus, by combination of straight cutting in 2D wire cutting, followed by Beam Bending slit cuts, layers of any complicated shape can be fabricated. By combing such layers several types of complex 3D shapes can be fabricated in a 2-axis wire cut machine. One type of such object is 3D revolved shapes obtained by rotating a given shape about a given axis. FIG 7 shows some sample revolved shape objects.

[0032] Another type of 3D object, whose layers are obtained by OFFSETTING of the previous layer can be fabricated by the instant method. (Constant Distance Offset) method. For example, layer 305 is obtained by offsetting 304. i.e.: 305 == OFFSET1 (304). Similarly, 306 == OFFSET2

(305) etc. OFFSET1 can be different from OFFSET2. Offset can be in positive or negative direction. Layer height can be independently varied. Curve 307 connecting 304 to 305 can be of any fixed shape, concave or convex or straight or any combination of such shapes. Such 3D shapes obtained by this Layer offset rule are called "OFFSET LAYERS object manufacturing" (OLOM) .

[0033] Referring to FIG 8, 601 is an ellipse. 602 is an interior curve. When 602 is obtained by scaling, 603 is small and 604 is large. When 602 is obtained by OFFSET, 603 and 604 are equal. This invention deals with layers obtained by this OFFSET process. Fig 9 shows some sample OLOM objects. Individual layers of the OLOM objects are obtained by the same beam bending and slitting method. However, the slit angles are precisely calculated to match the curvature of the given shape at any point. Thus, a straight profile cut in straight wire 2-axis wire cut machine can be bent along any curve/shape.

[0034] For manufacturing non-OLOM objects, the layers can be approximated to the nearest offset layer shape and fabricated with excess material and the excess material can be later shaved off. It is possible to alter dimensions 401 and 402 shown, after 90 degrees turn, resulting in more complex shapes manufacturing. Also, 401 and 402 need not be straight and perpendicular to each other, but can be of any shape and angle also, as feasible in a straight wire 2-axis cutting. Thus, several types of library of OLOM objects can be constructed, where subsequent layer is offset of the previous layer, but following variations are allowed; a) variable Z distance between layers; b) Any curve shape joining the 2 layers; and c) Offset up or down or constant etc.

[0035] Given any random shape, it is suggested to slice layers corresponding to the offset curves (Z values along the offset curve in XY plane) . This is an alternate way of slicing 3D objects, which are traditionally sliced along constant Z planes, i.e.: XY curve at any given Z. Variable layer height slicing can also be easily achieved by this method. Considerable material saving is achieved in this method, as hollow 3D shapes can be fabricated.

[0036] For example: A sphere can be manufactured in a single layer by beam bending method. But splitting into multiple layers has several advantages a) Resultant structure is relatively stronger, as materials connectivity is available at every layer, b) Can make large sized 3D shapes from even thin sheet of raw material .

[0037] The descriptions above explained the method of 3D shape fabrication using OLOM, Beam bending etc. methods.

[0038] In another embodiment of the invention, it is possible to fabricate 3D shapes by a combination of core LOM layers and wrapping/cladding of the layers by SHEET material, whose shape is intelligently calculated by the proposed software, to achieve a clean wrinkle free wrapped surface, exactly matching the original desired 3D surface. The following description explain this CLADDING method in more detail.

[0039] Fiber and resin can be applied on the clad surface to fabricate the surface in harder materials like FRP, carbon Fiber etc. Concrete or POP etc. materials can also be applied to convert the CLAD surface into harder materials .

[0040] The given 3D shape is sliced into Individual layers Lll, L12, L13 etc. as shown in Fig 13 & 14. The individual layers are fabricated in 2-axis CNC machine and stair case LOM is assembled.

[0041] The transition surface SI between Cl to C2 is manufactured on a flat sheet of paper, and clad on to the staircase LOM using pins, glue etc., achieving a full 3D shape. The cladding material can be any sheet material: Paper, plastic, foam board, flute board etc.

[0042] The 3D surface S21 is mapped to a flat surface D21 by using triangulation and unfolding methods. The flat surface D21 is easily manufactured on a 2 or 3 axis CNC and clad around Cl, C2 curves to achieve the exact S21 surface. In similar manner surfaces S22, S23 etc. are manufactured in sheet material and core curves Cl C2, C3 etc. are manufactured in foam or other light weight core materials and the Entire 3D surface shape is achieved.

[0043] An automatic software system is proposed in this invention, in which a given full 3D surface S is sliced in to layers Lll, L12, L13. The software outputs the cross-section shape of each layer as curves Cl, C2, C3 etc. The software also outputs the unfolded/flattened surface curves D21, D22, D23 etc. corresponding to the transition surfaces S21, S22, S23 etc. By using these outputs, the entire 3D surface can be accurately fabricated in a 2 or 3 axis CNC machine easily.

[0044] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.