Title of Invention

INTEGRATIVE SOLID-FORM BASED PROTOTYPE FABRICATION METHOD

Abstract

A new rapid prototyping method is proposed to reduce cost as well as high build-up time involved "in fabrication of prototypes. Easily machinable plastics (HDPE) and metals are machined conventionally (as solid preforms) for a wide range of dimension and different cross-sections and are stored in a storage cell, monitored by a data library (computer controlled). The solid model, drafted in CAD is converted into STL format not into slices (layer by layer), but into a composite-like consisting of preformed solids and resin- based adhesives. The adhesives will bind the solids preforms, which are placed layer by layer, according to the profile drafted in CAD. An experimental illustration has been done for a prototype model.

Full Text

Integrative Solid-form based Prototype Fabrication Method. Broad Technical field of the invention; The present invention relates to a new method of fabrication and modelling of prototypes that could be either scaled-down models for design evaluation or actual size models used as patterns in casting, tooling, etc. Specific Nature of the Invention: Rapid Prototyping is an integral part of product development cycle. The basic applications of rapid prototyping are: • Model-design evaluation. Ex: Testing of scaled-down prototype model of air-foils (in wind tunnels) because fabrication of the actual profile to required dimensions is very difficult and time-consuming. Moreover, the design processes are iterative in nature. • Fabrication of master patterns in moulding and castings. Patterns of complex profiles are fabricated by Rapid prototyping and used in mould preparation. • Functional prototypes. Ex: A new link mechanism can be fabricated to study its dynamics. Rapid Prototyping thereby reduces costly design errors in the earlier phase of the product, development. Also, they are finding its application in bio-medical engineering for fabrication of surgical implants. The basic steps of rapid prototyping are: ? Drafting the model in CAD (Computer Aided Drawing) to dimensions ? The CAD file is converted into STL (Stereolithography) format in which the entire volume is segmented into layers of about 0.005-0.006 inch. ? This STL file is the input to the computer aided fabrication machine which develops the model by forming the layers one after the other to generate the complete model. ? The technique involved in the layer-formation varies according to the methodology employed. In Fused Deposition Modelling (FDM), thermoplastics, wax, resins are deposited in layers on a fixed platform by a die and its movement is controlled by the computer in the co-ordinate axis according to the STL file data. In Stereolithography, a vat containing photo-curable resin is stored. A laser source is used to solidify the resin and the movement of the laser and the vat is controlled by the computer. In Laminated Object Manufacturing (LOM), laminated sheets of required profile are stacked to fabricate the model according to the STL data. In Selective Laser Sintering (SLS), ceramic, metal powders are applied in layers and a laser source is used to sinter the powders to required profile. In Ballistic Particle Printing, a stream of plastic, wax, ceramic is ejected through a small orifice at a surface by using ink-jet mechanism. These are the methods that are employed in fabrication of prototypes by Rapid Prototyping. Advantages of Rapid Prototyping are the higher accuracy that could be achieved in fabrication of models irrespective of the complexity of the profile involved, reduction in development time. The scope of rapid prototyping has been restricted owing to the high operational cost involved mainly because of the cost of resins used (particularly photo-curable resin) and laser source. Also, the build-up time for the model increases with larger size of the model. These limitations thereby reduce the size of the prototype that could be economically fabricated. Statement of the Invention: The proposed method of fabrication involves integration of conventional machining and fabrication of prototypes by layer-wise deposition. The required model is drafted as CAD file and when converted into STL format they are generated as composite-like matrix consisting of solid preforms and binder mixture. This reduces the operational cost and build-up time significantly. This is because most of the volume is occupied by solids which are cheaper and the time is reduced because the volume that has to be deposited by the machine is tremendously reduced. Because of the re-enforcement of the solid with resin matrix the strength is also largely increased. Prior Art: There are several methods available now to fabricate prototypes. Rapid prototyping enables design analysis at the tooling phase of the product development and thereby reduces costly design errors before the actual shop floor-manufacturing. They are also employed to fabricate complex patterns in Rapid tooling and are finding its application even in fabrication of surgical implants. The prototypes are also used as effective instructional and marketing tool. In US Patent 6030199 (Tseng, 2000), a method of depositing pressurized molten materials in layers using containers has been described. The improved method of using nozzles for depositing pressurized molten material has been described in US Patent 6372178 (Tseng, 2002). In US Patent 6838035 (Ederer, et al. 2005), the method of depositing droplets of liquid building material to produce structural body has been discussed. In International Patent WO 2005/07519 Al, the method and apparatus for depositing successive layer of different thermofusible liquid has been discussed. US Patent 499143 (Hull, et al. 1999) describes Stereolithographic process of producing prototypes by a step-wise laminate build-up of the fluid medium. US Patent 5011635 (Murphy, et al. 1991) describe Stereolithographic method employing membrane separate phases of liquid organic phase and fluid phase. In US Patent 5059021 (Spence, et al. 1991), drift correction in production of models by Stereolithography has been described. Application of Photoformed precursor sheet in Stereolithography has been discussed in US Patent 5094935 (Vassiliou, et al. 1992). In US Patent 5174931 (Almquist, et al. 1992), method and apparatus for producing prototypes using a sweeping-smoothing member for uniform coating in each layer has been described. In US Patent 5545367 (Bae, et al. 1996), operation conditions like pressure, temperature, sequential polymerization of precursor fluid and combinations of these has been discussed. In US Patent 5578227 (Rabinovich, 1996), the laser source has been replaced by Electron beam source and their characteristics has been studied. In US Patent 6231802 (Mu, et al,2001), method of production involving Inverse Tomographic Construction without requiring conversion of CAD draft to slices has been described. US Patent 6251557 (Lapin, et al. 2001) gives the composition of the photocurable resin used in Stereolithography. In UK Patent GB 2297516 A (Steven Butterworth, 1996), Laminated Object Manufacturing method has been discussed where layers of stacked up sheets are cured to produce the model. In US Patent 5730817 (Feygin, et al. 1998), Laminated Object Manufacturing method by employing bonding tool or fuser tool to cure heat sensitive adhesive layers has been described. US Patent 5637175 (Feygin, et al. 1997) has described employing individually shaped contoured sheets used in Laminated Object Manufacturing. US Patent 5876550 (Feygin, et al. 1999) has also given a modification in the shapes of the individual contoured laminations used in Laminated Object Manufacturing. US Patent 6153034 (Lipsker, 2000) has described an apparatus with the adhesive dispenser possessing six degrees of freedom. In US Patent 5053090 (Beamen, et al. 1991), Selective Laser Sintering has been discussed where layers of powders are selectively sintered to produce the required model. US Patent 6767499 (Hory, et al. 2004) describes superimposed digitized section of the solid which are produced by sintering selective section of the powder. In International Patent WO 99/59800, gas atmosphere has been employed during selective layer-wise sintering of powders. Three dimensional printing method used to produce prototypes has been discussed in: US Patent 6402403 (Speakman, 2002), UK Patent GB 2412349 (Michael Nitz, et al. 2005), US Patent 6989115 (Russell, et al. 2006). Thus, as seen above, none of the above referred patents address ‘The method of using solid preforms and binders to fabricate the prototype models” and hence do not relate to the scope and field of our invention. The following patent could be considered related to the same field of application to that of our invention, but differ in their focus and methodology employed as discussed hereunder. Closest Prior Art: International Patent-DEIO 112629, Yang Dong Yol and et al. 2001-KR(Korea) has described a prototype manufacturing method where material sheets coated with adhesive are cut using heated linear cutter and stacked to produce the required model. Limitations of Prior Art: Problems faced in the present methods include high operational cost particularly in fabricating prototypes of larger volume. The cost of the photo-curable resin and the high build-up time involved has tremendous impact on the cost, since the entire volume is fabricated layer by layer and greater laser power consumption is required(in Laminated Object Manufacturing, Stereolithography and Selective Laser Sintering). Objective of invention: The objective is to reduce the high operational cost and build-up time by effectively integrating conventional machining of solids and computer-aided fabrication of required prototypes. Description of the invention; Easily Machinable plastics (HDPE), metals are machined conventionally (as solid preforms) and stored in a storage cell, monitored by a data library (computer controlled). The preforms can be machined for a wide range of dimension and different cross-sections. The solid model, drafted in CAD is converted into STL format as a composite-like consisting of preformed solids and resin-based adhesives. The adhesives will bind the solids, which are placed according to the profile drafted in CAD. Curing of the resin takes place and required coating is done for surface finish and accuracy. The main advantage in this method is the reduction of cost and time required for the prototype fabrication. Costly laser source and photo-curable resins has been eliminated, unlike other methods. Moreover, down-time if any can be used to machine the solids by conventional machining which has a relatively lower operation cost. Brief Description of the drawings: Fig-01 in Sheet-01 shows the sequence of the integrative fabrication method. Fig-02 in Sheet -02 shows the set-up of the apparatus used in the fabrication method. Fig-03, Fig-04, Fig-05 in Sheet-03 shows the application of the method in fabricating a prototype model. Fig-06, Fig-07 in Sheet-04 shows the application of the method in fabricating a Business-card holder. Fig-08, Fig-09, Fig-10 in Sheet-05 shows the photographs of the Business-card holder done experimentally by employing this method. Detailed description of the invention: Referring to Fig-01, (001) Solid preforms of HDPE (High Density Poly- Ethylene) and metals are machined conventionally. FIDPE has been preferred because of its low cost and ease of machining. Metal preforms are used where higher strength of the prototypes is required. The machined preforms (001) are stored in a storage cell (002) and their dimensional data are stored in a Data library (003). The preforms are machined for a wide range of dimensions and for different cross-sections like square, triangle, rectangle, trapezoid, etc. They can also be machined for custom profile depending upon the prototype to be fabricated. Referring to Fig-01 in Sheet-01, the prototype to be fabricated is drafted as a CAD file to required dimensions (004). They are converted into STL file format not as slices of volume as done in present Rapid Prototyping methods, but as a composite-like consisting of solid preforms and binders used to bind the solids (005). The best-fit preforms are selected by the system automatically, according to the profile drafted in CAD. The selection can also be customized. This method has been explained with a prototype model shown in Sheet-03. Fig-05 shows the model to be fabricated. Referring to the sequence of the method shown in Fig-01, the solids (001) that could be used to fabricate the model (006) is machined to required dimension as shown in Fig-03. The STL file to be generated for this model is shown in Fig-04. Referring to Fig-02, the solid preforms (02) are placed from bottom-to-top order in sequence by a computer-aided positioning machine. Simultaneously, the epoxy-based binder- (03), consisting of Resin and Hardener in proportion) is deposited by the computer-aided depositing machine (01) on a fixed platform (04). Prior shrinkage property of the binder mixture used is studied for providing corresponding allowance in the CAD draft. Segmental volume of the model which is too small to accommodate a solid can be formed by depositing only the resin by cutting off the hardener supply and by reducing the additives in the resin to have a slightly higher viscosity. Corresponding allowance must be provided in the CAD draft for surface coating to achieve the required dimensional accuracy and smoother finish. The advantages of this method are: • Time taken to fabricate larger prototypes is tremendously reduced. • Cheaper materials like High Density Polyethylene (HDPE) reduce the overall cost of manufacturing. • Strength of the model is increased as the model is similar to re-enforced plastic or metal part. • The wear in RP machine is reduced as only minimal deposition is done by the depositor. • Fabrication of too complex parts can also be achieved by fabricating individual parts and using them as solid preforms for the final product. Experimental model: To illustrate this method, a Business-card holder model has been taken up as an example to be fabricated by this integrative method shown in Fig-06. The dimensions of the model is 5.5”*4”*2.5”. Referring to Fig-07, the arrangement of the solids is shown with allowances provided for surface finish by coating and the translucent layer shown is the binder matrix to be deposited. Fig-08 shows the solid preforms of various cross-sections and dimensions that are shaped conventionally by CNC machines. The CAD model is provided corresponding allowance for the shrinkage of the binder and finishing, by surface coating. In the binder used in the experiment, 0.01% shrinkage has been observed. The epoxy binder used was 1:1 (by volume) mixture of resin (PEA-186) and hardener (PH-654). The following are the typical properties of epoxyresin and hardener: Epoxyresin: Type - Unmodified viscous epoxyresin Grade -PEA186 Appearance - Pale yellow liquid Viscosity - 12000-14000cps @ 25*C Specific gravity - 1.15-1.22 @25*C Epoxy equivalent-220-240 Hardener: Type -Aliphatic amine Grade -PH654 Pot life -3hrs@25*C Mix ratio -100:80 (parts by weight) The integrative process of binding machined preforms by layer-wise deposition of binders is done and curing takes place. The time for curing was observed to be three hours at room temperature. The bonded solid model is given surface coating to get the dimensional accuracy and surface finish as in Fig-10. The entire fabrication took 5 hours to complete, (1 hour for machining, 3.5 hours for deposition and curing, 0.5 hours for surface coating) which is significantly lesser than time taken by most other RP methods. Based on the experimental observation, the following tabular column has been conceived to study the cost and time advantages for different proportions of resin and solid preforms. A constant model profile has been selected for the study. Cost A= Cost of the solid material + Machining cost including labour cost, Tool wear, etc. Cost B=Cost of the resin + Operation cost of the computer aided depositing Machine Total Cost= Cost A + Cost B Time A^Time taken for machining the preforms to required dimensions Time B= Time taken for deposition of the resin + Time taken for curing of that amount of resin Time C= Time taken for coating The effect of strength of the various proportions could be further analyzed, in order to select the required proportion according to the application. The complexity of the model profile decides the epoxy binder proportion that has to be used. Other factors include resin properties and the strength required (according to the application). Moreover, solid proportion could be higher for simpler profiles than that of a very complex profile in which accommodation of the solid in the profile and placement of the solid while fabrication is difficult. Preferred and Optional Features: To decrease the curing time of the binders, photo curing can even be done in few seconds by exposing certain compatible binders to mercury vapour lamp at 200W per inch. Rate of curing could be controlled by adding ketones, which enhances the flexibility of the method for different thickness of the model. If an angular cross section for aparticular angle (eg: groove angle) is unavailable, straight edged surfaces like rectangle can be tilted and placed for the corresponding angle. Modifiers like amine-based surfactant can be used to increase the flexural strength of the prototype. Chemical additives can be added to vary the viscosity of the binder as required. Surgical implants can also be fabricated by giving appropriate non-toxic titanium based coating. We Claim: 1. A method of fabricating prototype model characterized by: Starting with the first layer of solid preforms employed as the base layer of the model to be fabricated; Depositing the epoxy resin and hardener mixture onto the said first layer; Placing the subsequent layer(s) of preforms on / above / near / surrounding the said first layer to form the next layer of the model; Depositing the epoxy resin and hardener mixture onto the said subsequent layer(s); Repeating the aforesaid process until the above steps yield the prototype being modeled is completely built up as needed; Coating the said model entirely with paint to get surface finish and dimensional accuracy. 2. A method of fabricating a prototype model as claimed in claim 1 wherein: Placing the first layer of solid preforms that are actually the base layer according to the 3D solid model drafted by the software; Depositing the epoxy resin and hardener mixture over the placed layer; Placing the second layer of solid preforms that are actually the next layer to the base layer according to the drafted 3D solid model; Depositing of the epoxy resin and hardener mixture over the placed layer; Repeating this placing and depositing until the 3D solid model as drafted in the software is obtained; Curing of the entire prototype model that is fabricated; Surface coating of the entire model that is fabricated 3. A method of fabricating the prototype model as claimed in claim 1 wherein said solid preforms are manufactured by machining the existing solids to different shapes conventionally to close dimensional tolerances. 4. A method of fabricating prototype model as claimed in claim 1 wherein said solid preforms are made of machinable solids like High Density Polyethylene (HDPE), metals. 5. A method of fabricating prototype model as claimed in claims 1, 2&3 wherein volume dimensions and surface texture details of the solid preforms to be manufactured are stored in a computer controlled storage cell and in a data library. 6. A method of fabricating prototype model as claimed in claims 1 through 4 wherein said solid preforms that are to be placed layer-wise are from the data library that best fits the profile of the 3D solid model drafted. 7. A method of fabricating prototype model as claimed in claims 1 through 6 wherein said the selection logic of solid preforms can be customized. 8. The method of claim 1 wherein said depositing die moves in x-y-z directions by means of a mechanism wherein said mechanism is controlled by the software program. 9. The method of claim 1 wherein said the deposition of this resin and hardener mixture should be mixed in proportion. 10. The method of claim 1 wherein said curing of the fabricated model is done at pre-defined temperature or at higher temperatures according to the requirement. 11. A method of fabricating prototype model claimed in claims 1 through 6, wherein said curing of the fabricated model can also be done by adding curing agents like polyamines, acrylic acids, styrene that are available. 12. A method of fabricating prototype model claimed in claims 1 through 6 wherein deposition of said epoxyresin could be added with amine based modifiers wherein said modifiers enhance flexural strength of the prototype model. 13. The method of claim 2 wherein said coating is accomplished using jet spray coating. 14. A method of fabricating prototype model as claimed in claims 1 through 13, wherein the said methodology of building up of the prototype model as above is employed for any other application that needs similar volume deposition and modular build-up technique.

Documents:

0474-che-2006 abstract duplicate.pdf

0474-che-2006 claims duplicate.pdf

0474-che-2006 description(complete)duplicate.pdf

0474-che-2006 drawings duplicate.pdf

474-che-2006-abstract.pdf

474-che-2006-claims.pdf

474-che-2006-correspondnece-others.pdf

474-che-2006-correspondnece-po.pdf

474-che-2006-description(complete).pdf

474-che-2006-drawings.pdf

474-che-2006-form 1.pdf

474-che-2006-form 9.pdf