RAPID PROTOTYPING

INTRODUCTION:-

RAPID PROTOTYPING IS A PROCESS FOR CREATING A REALISTIC MODEL OF A PRODUCT’S USER INTERFACE. A RAPID PROTOTYPED USER INTERFACE IS EASY TO CHANGE AND GETS CUSTOMERS INVOLVED EARLY IN THE DESIGN OF THE PRODUCT. THIS REPORT SUGGESTS THAT SUCCESSFUL RAPID PROTOTYPING IS DONE QUICKLY AND ITERATIVELY BY DOMAIN EXPERTS. IT SUGGESTS STEPS FOR THE RAPID PROTOTYPING PROCESS AND DESCRIBES ADVANTAGES AND DISADVANTAGES OF RAPID PROTOTYPING. TO PROTOTYPE SUCCESSFULLY, THE REPORT RECOMMENDS THAT YOU PICK A RAPID PROTOTYPING TOOL THAT MEETS YOUR NEEDS, FORM A SMALL PROTOTYPING TEAM, GET LOTS OF CUSTOMER FEEDBACK, AND ITERATE UNTIL CUSTOMERS ARE DELIGHTED WITH YOUR USER INTERFACE.

RAPID PROTOTYPING INVOLVES CREATING A REALISTIC MODEL OF A PRODUCT’S USER INTERFACE TO GET PROSPECTIVE CUSTOMERS INVOLVED EARLY IN THE DESIGN OF THE PRODUCT. USING RAPID PROTOTYPING, YOU MODEL THE LOOK AND FEEL OF THE USER INTERFACE WITHOUT INVESTING THE TIME AND LABOR REQUIRED WRITING ACTUAL CODE. THEN YOU SHOW THE PROTOTYPE TO PROSPECTIVE CUSTOMERS, REVISE THE PROTOTYPE TO ADDRESS THEIR COMMENTS, AND KEEP REPEATING THESE TWO STEPS. YOUR GOAL IS TO PRODUCE A COMPLETE, AGREED-UPON DESIGN OF THE PRODUCT’S USER INTERFACE BEFORE WRITING A SINGLE LINE OF ACTUAL CODE. WHEN WALKTHROUGHS AND USABILITY TESTS SHOW YOU THAT CUSTOMERS ARE DELIGHTED WITH YOUR PROTOTYPE USER INTERFACE, THEN PROGRAMMERS CAN MODEL IT WHEN THEY CODE THE ACTUAL PRODUCT.

ELEMENTS OF SUCCESSFUL RAPID PROTOTYPING

SUCCESSFUL RAPID PROTOTYPING IS PERFORMED:

• QUICKLY – THE FIRST PASS MUST BE DONE QUICKLY, AND SUBSEQUENT IMPROVEMENTS SHOULD BE INCORPORATED IMMEDIATELY. WHILE THE PROTOTYPE NEEDS TO GIVE CUSTOMERS A REALISTIC FEEL FOR THE PRODUCT, IT DOES NOT NEED TO INCLUDE SPECIAL GRAPHICS OR COMPUTATIONAL ALGORITHMS THAT REQUIRE A LOT OF TIME AND EFFORT TO CREATE.
• ITERATIVELY – THE PROTOTYPED USER INTERFACE IS REVIEWED, COMMENTED UPON, IMPROVED, AND REVIEWED AGAIN IN A REPEATING CYCLE. NO ONE CREATES A PERFECT DESIGN THE FIRST TIME. THIS ITERATIVE CYCLE ALLOWS YOU TO GRADUALLY IMPROVE THE USER INTERFACE. THESE CYCLES CAN BE COMPLETED MORE QUICKLY IF THE PROTOTYPE IS EASILY CHANGED.
• USING DOMAIN EXPERTS – IDEALLY, THE PROTOTYPE SHOULD BE BUILT BY A DOMAIN EXPERT. DOMAIN EXPERTS ARE FAMILIAR WITH THE USER – HIS OR HER JOB, EXPECTATIONS, REQUIREMENTS, JARGON, AND PRIORITIES. THESE PEOPLE MAY HAVE DONE THE USER’S JOB IN THE PAST. DOMAIN EXPERTS CAN DO THE BEST JOB OF INCORPORATING USER REQUIREMENTS INTO THE PROTOTYPE. IF YOUR PROTOTYPING TOOL IS TOO DIFFICULT FOR THE DOMAIN EXPERT TO USE, MAKE SURE THAT THE DOMAIN EXPERT WORKS CLOSELY WITH THE PROGRAMMER.

TRADITIONAL DEVELOPMENT PROCESS VERSUS RAPID PROTOTYPING PROCESS

THE TRADITIONAL PROCESS USED TO DEVELOP A PRODUCT FOLLOWS THE GENERAL STEPS SHOWN IN FIGURE 1. DURING STEP 1, “ANALYZE PROPOSED SYSTEM,” MARKETING AND PLANNING IDENTIFY A CUSTOMER NEED AND DETERMINE WHETHER THE COMPANY CAN DEVELOP A PRODUCT THAT WILL PROFITABLY MEET THAT NEED. IN STEP 2, “SPECIFY REQUIREMENTS,” MARKETING AND PLANNING DRAFT GENERAL REQUIREMENTS FOR THE PROPOSED PRODUCT. IN STEP 3, “DESIGN SYSTEM,” DEVELOPMENT WRITES DETAILED SPECIFICATIONS FOR THE PROPOSED PRODUCT. IN STEP 4, “DEVELOP SYSTEM,” DEVELOPMENT CREATES THE PRODUCT. IN STEP 5, “RELEASE PRODUCT,” THE COMPANY RELEASES THE PRODUCT.

THERE ARE TWO OBVIOUS DIFFERENCES BETWEEN THE TRADITIONAL PRODUCT DEVELOPMENT PROCESS AND THE RAPID PROTOTYPING PROCESS SHOWN IN FIGURE 1. THESE DIFFERENCES ARE CUSTOMER INVOLVEMENT AND ITERATIVE DESIGN. CUSTOMERS ARE INVOLVED ONLY INDIRECTLY AT THE BEGINNING OF THE TRADITIONAL PROCESS, WHEN MARKETING AND PLANNING SPECIFY REQUIREMENTS. IN RAPID PROTOTYPING, CUSTOMERS ARE INVOLVED DIRECTLY THROUGHOUT THE DEVELOPMENT PROCESS. ALSO, THE TRADITIONAL PROCESS GOES FROM REQUIREMENTS, TO DESIGN, TO DEVELOPMENT IN A FIXED SERIES OF STEPS. IN RAPID PROTOTYPING, THE PROCESS IS ITERATIVE. THIS MAKES IT EASIER TO CHANGE OR ADD REQUIREMENTS THAT WILL MAKE THE PRODUCT MORE POPULAR WITH CUSTOMERS.

PARTS MADE BY RAPID PROTOTYPING SYSTEMS MAY BE USED DIRECTLY IN MANY FINAL APPLICATIONS TODAY. THIS REFLECTS GREAT STRIDES IN MATERIALS AND MACHINERY THAT HAVE BEEN SPURRED BY INSISTENT MARKET FORCES OVER MANY YEARS. ADDITIVELY-FABRICATED PARTS MAY WELL OFFER A DIRECT SOLUTION TO APPLICATION PROBLEMS HAVING MATERIAL REQUIREMENTS RANGING FROM PLASTICS OR CERAMICS, TO STEEL OR TITANIUM. ADDITIVE FABRICATION IS MAKING ITS GREATEST HEADWAY IN MANUFACTURING APPLICATIONS THAT TAKE ADVANTAGE OF ITS UNIQUE BENEFITS. IT HAS BECOME AN ACCEPTED SOLUTION FOR FABRICATING GEOMETRICALLY-COMPLEX, LOW-VOLUME OR CUSTOMIZED PARTS. RP IS ALSO RECOGNIZED AS A MEANS TO PRODUCE PARTS AND TOOLS IN FORMS AND COMBINATIONS NOT OTHERWISE POSSIBLE, SUCH AS IN THE USE OF GRADIENT OR MULTIPLE MATERIALS. WHILE MANY APPLICATIONS ARE STILL IN THE DEVELOPMENT STAGE THEIR POTENTIAL RANGE IS VAST, EXTENDING FROM THE MICROSCOPIC SCALE OF NANO-DEVICES AND INTEGRATED CIRCUITS TO THE CONSTRUCTION OF ENTIRE BUILDINGS, BOAT HULLS AND THE LIKE. IN SOME CASES ADDITIVE FABRICATION'S NOMINAL LIABILITIES ARE BEING TURNED INTO ADVANTAGES. FOR EXAMPLE, THE CAPABILITY OF SOME RP TECHNOLOGIES TO CREATE POROUS PARTS IS BEING FOUND USEFUL IN FABRICATING COMPLEX FILTERS, GAS STORAGE DEVICES AND SIMILAR PRODUCTS. DESCRIPTIONS OF MANY OF THE RP TECHNOLOGIES AVAILABLE FOR RAPID MANUFACTURING ARE PROVIDED IN THE SECTIONS UNDER COMMERCIALLY-AVAILABLE PROCESSES. ALSO SEE THE ACCOMPANYING TECHNOLOGY COMPARISON TABLES. SEE THE RAPID MANUFACTURING SECTION FOR AN EXTENSIVE EXPLORATION OF THE ENORMOUS POTENTIAL OF THIS APPLICATION OF ADDITIVE FABRICATION. DIRECT FABRICATION OF PLASTIC PARTS PLASTIC PARTS ARE MOST OFTEN DIRECTLY FABRICATED FOR END USE USING SELECTIVE LASER SINTERING (SLS), FUSED DEPOSITION MODELING (FDM) OR STEREOLITHOGRAPHY. OTHER TECHNOLOGIES ARE ALSO USED, BUT THESE ARE THE MAIN ONES THAT ARE OF COMMERCIAL IMPORTANCE AT PRESENT. THE CHOICE OF A TECHNOLOGY IS MOST GREATLY INFLUENCED BY THE END-USE MATERIAL REQUIREMENTS. THE DEVELOPMENT OF PHOTOPOLYMERS FOR USE IN STEREOLITHOGRAPHY AND SIMILAR LIGHT-BASED TECHNOLOGIES HAS LED TO MATERIALS THAT EXHIBIT A WIDE RANGE OF PROPERTIES. MATERIALS ARE AVAILABLE THAT MIMIC THE MECHANICAL PROPERTIES OF POLYPROPYLENE AND OTHER PLASTICS, EXHIBIT FLEXIBILITY FOR SNAP-FITS AND HAVE OPTICAL PROPERTIES SUCH AS HIGH TRANSPARENCY. EFFORTS ARE ONGOING TO DEVELOP SPECIALIZED PHOTOPOLYMERS TO WIDEN THEIR APPLICATIONS. MATERIALS WITH PROPERTIES SUCH AS LOW SHRINKAGE, RUBBER-LIKE FLEXIBILITY AND THERMAL CONDUCTIVITY, OR TO ADDRESS SPECIALIZED APPLICATIONS SUCH AS THE CONSTRUCTION OF SCAFFOLDS FOR TISSUE ENGINEERING ARE EITHER IN DEVELOPMENT OR HAVE ALREADY BEEN INTRODUCED. WHILE TODAY'S MATERIALS CAN SOLVE MANY PROBLEMS AND THE FUTURE LOOKS VERY PROMISING, PHOTOPOLYMERS ARE ANALOGS OF ENGINEERING PLASTICS. THEY MAY NOT POSSESS ALL OF THE PROPERTIES REQUIRED FOR A PARTICULAR APPLICATION, AND IN SOME CASES THEIR PROPERTIES MAY NOT BE STABLE OVER TIME. BOTH SELECTIVE LASER SINTERING AND FUSED DEPOSITION MODELING CAN PRODUCE PARTS IN FINAL ENGINEERING POLYMERS. THEY MAY OFFER SOLUTIONS WHEN PHOTOPOLYMER-BASED TECHNOLOGIES CANNOT. SLS CAN BE USED TO FABRICATE PARTS IN SEVERAL TYPES OF ENGINEERING PLASTICS, INCLUDING GLASS-FILLED NYLON. FDM CAN FABRICATE PARTS IN ABS, POLYPHENYLSULFONE, POLYCARBONATE, POLYESTER AND A FEW OTHER MATERIALS. THESE TECHNOLOGIES MAY OFFER PARTS WITH ADDITIONAL STRENGTH OR OTHER PROPERTIES NOT CURRENTLY AVAILABLE FROM PHOTOPOLYMERS. ONE THING TO NOTE IS THAT THE PROPERTIES WILL NOT BE QUITE THE SAME AS A PART FABRICATED IN AN INJECTION MOLDING PROCESS OF THE SAME MATERIAL, HOWEVER. HOW THE ADDITIVE FABRICATION MACHINERY BUILDS THE PART INFLUENCES THOSE PROPERTIES TO A CONSIDERABLE EXTENT. DIRECT FABRICATION OF METAL PARTS METAL PARTS ARE MOST OFTEN DIRECTLY FABRICATED WITH SELECTIVE LASER SINTERING OR LASER POWDER FORMING PROCESSES. HERE AGAIN, OTHER TECHNOLOGIES CAN BE AND ARE USED, BUT THESE ARE THE MOST COMMERCIALLY IMPORTANT ONES AT THE MOMENT. SLS CAN BE USED TO FABRICATE STEEL, STAINLESS STEEL AND BRONZE PARTS. POROSITY IS ELIMINATED BY SECONDARY METAL INFILTRATION. PARTS USUALLY NEED FINAL MACHINING AND THEIR PROPERTIES WILL NOT BE QUITE THE SAME AS PARTS FORMED ENTIRELY OF THE INTRINSIC MATERIAL. LASER POWDER FORMING PROCESSES CAN PRODUCE PARTS IN STEELS, TITANIUM AND OTHER METALS AT FULL DENSITY. HOWEVER, THIS DESIRABLE CHARACTERISTIC MAY HAVE TO BE TRADED-OFF AGAINST SOMEWHAT HIGHER FINISH MACHINING REQUIREMENTS COMPARED TO SLS. DIRECT FABRICATION OF METAL PARTS IS FINDING ITS GREATEST APPLICATION IN HIGH VALUE-ADDED APPLICATIONS SUCH AS AEROSPACE AND MEDICINE.

AFTER YOU SELECT A TOOL AND FORM A TEAM, YOU CAN BEGIN THE RAPID PROTOTYPING PROCESS. FIGURE 1 SHOWS SUGGESTED STEPS FOR DEVELOPING A PRODUCT WITH THE RAPID PROTOTYPING PROCESS.

• ANALYZE PROPOSED SYSTEM – FIRST, MARKETING AND PLANNING IDENTIFY A CUSTOMER NEED AND DETERMINE WHETHER THE COMPANY CAN DEVELOP A PRODUCT THAT WILL PROFITABLY MEET THE NEED.
• IDENTIFY INITIAL CUSTOMER REQUIREMENTS – MARKETING AND PLANNING IDENTIFY GENERAL REQUIREMENTS FOR THE PRODUCT.
• IDENTIFY OBJECTS AND ACTIONS – NEXT, YOUR PROTOTYPING TEAM IDENTIFIES SPECIFIC OBJECTS (NOUNS) AND ACTIONS (VERBS) TO BE USED IN THE PRODUCT. FOR EXAMPLE, THE PRODUCT COULD HAVE “MEMO” AS AN OBJECT AND “PRINT” AS AN ACTION. SPECIFYING OBJECTS AND ACTIONS HELP YOU DESIGN YOUR SCREENS TO BE COMPLIANT WITH THE OBJECT-ACTION SYNTAX IN IBM’S COMMON USER ACCESS GUIDELINES. TO PERFORM THIS STEP, YOUR TEAM REFINES THE INITIAL, GENERAL REQUIREMENTS INTO SPECIFIC OBJECTS AND ACTIONS. YOUR TEAM CAN ALSO ADD OTHER OBJECTS AND ACTIONS THAT ARE NEEDED.
• PUT TOGETHER RELATED OBJECTS AND ACTIONS – AFTER THE TEAM HAS IDENTIFIED MOST OF THE APPLICATION OBJECTS AND ACTIONS, THE NEXT STEP IS TO ORGANIZE THE OBJECTS AND ACTIONS IN A LOGICAL, EASY-TO-UNDERSTAND WAY. BASED ON THEIR KNOWLEDGE OF THE CUSTOMER, YOUR TEAM MEMBERS CAN GROUP RELATED OBJECTS ON PANELS AND RELATED ACTIONS ON ACTION BAR PULL-DOWNS. ONE HELPFUL WAY TO DO THIS GROUPING IS TO MIMIC A CONCEPT WITH WHICH CUSTOMERS ARE ALREADY FAMILIAR. FOR EXAMPLE, IBM’S OFFICEVISION PRODUCT ORGANIZES OBJECTS AND ACTIONS BY USING IN-BASKETS, OUT-BASKETS, A TELEPHONE, AND OTHER CONCEPTS FAMILIAR TO OFFICE WORKERS.
• PROTOTYPE PANELS – IN THIS STEP, YOUR PROTOTYPING TEAM WORKS TOGETHER TO PROTOTYPE A PORTION OF THE PROPOSED APPLICATION USER INTERFACE. IDEAS ARE DISCUSSED, PROTOTYPED, COMMENTED ON, IMPROVED, AND PROTOTYPED AGAIN IN QUICK, INFORMAL STEPS.
• GET FEEDBACK – ONCE YOUR PROTOTYPING TEAM IS REASONABLY SATISFIED WITH THE PROTOTYPE, SHOW IT TO OTHER DOMAIN EXPERTS, INFORMATION DEVELOPERS, MARKETERS, PLANNERS, USABILITY REPRESENTATIVES OR ANYONE ELSE WHO HAS KNOWLEDGE AND INTEREST IN THE PRODUCT. EVENTUALLY, YOU CAN SHOW THE PROTOTYPE SCREENS TO CURRENT OR FUTURE CUSTOMERS. YOU CAN DO THIS THROUGH INFORMAL WALKTHROUGHS OR MORE FORMAL USABILITY TESTS. THIS FEEDBACK WILL GENERATE ADDITIONAL REQUIREMENTS THAT WERE NOT IDENTIFIED IN THE INITIAL REQUIREMENTS.
• IMPROVE PROTOTYPE – USE THE FEEDBACK TO IMPROVE THE PROTOTYPE. THE FEEDBACK MAY TRIGGER NEW IDEAS AMONG THE PROTOTYPING TEAM. MAKE THOSE CHANGES THAT ARE BEST FOR THE CUSTOMER AND THAT CAN REASONABLY BE DONE.
• ITERATE – REPEAT THE “PROTOTYPE-FEEDBACK-IMPROVE PROTOTYPE” CYCLE AS QUICKLY AND AS FREQUENTLY AS YOU CAN. KEEP ITERATING UNTIL CUSTOMERS ARE DELIGHTED WITH YOUR PROTOTYPE USER INTERFACE. THE CUSTOMERS’ EVALUATIONS CAN BE MEASURED WITH QUESTIONNAIRES. TO MOST CUSTOMERS, THE USER INTERFACE IS THE PRODUCT. IF CUSTOMERS ARE DELIGHTED WITH YOUR PROTOTYPE USER INTERFACE, THEY ARE LIKELY TO BE DELIGHTED WITH THE PRODUCT. WHEN CUSTOMERS ARE DELIGHTED WITH ONE PORTION OF THE PROPOSED APPLICATION USER INTERFACE, GO ON TO ANOTHER PORTION.
• CONVERT PROTOTYPE CODE TO ACTUAL CODE – THE NEXT STEP IS TO ASK PRODUCT PROGRAMMERS TO CODE THE PROTOTYPE USER INTERFACE. DURING THIS STEP, THEY BUILD THE ACTUAL PRODUCT. THE PROTOTYPE SERVES AS THE PRODUCT FUNCTIONAL SPECIFICATION.
• GET FEEDBACK – SINCE THE ACTUAL CODE INCLUDES ELEMENTS OF THE USER INTERFACE THAT YOU DID NOT PROTOTYPE, GET FEEDBACK AGAIN. USE INFORMAL CUSTOMER WALKTHROUGHS AND FORMAL USABILITY TESTS TO GET THIS FEEDBACK.
• IMPROVE ACTUAL CODE – BASED ON THE CUSTOMER FEEDBACK, THE PROGRAMMERS REFINE THE CODE TO MAKE THE PRODUCT EASIER TO LEARN AND USE.
• ITERATE – REPEAT THE “ACTUAL CODE-FEEDBACK-IMPROVE ACTUAL CODE” CYCLE AS QUICKLY AND AS FREQUENTLY AS YOU CAN. REMEMBER, GOOD SOFTWARE IS EASY TO USE AND HARD TO DESIGN.
• RELEASE THE PRODUCT – FINALLY, WHEN CUSTOMERS ARE DELIGHTED WITH THE ACTUAL USER INTERFACE, RELEASE THE PRODUCT.

COMPARED TO THE TRADITIONAL PROCESS OF PRODUCT DEVELOPMENT, RAPID PROTOTYPING PRODUCES REALISTIC SCREENS EARLIER IN THE DESIGN PROCESS, PUTS MORE EMPHASIS ON THE CUSTOMER THROUGHOUT THE DEVELOPMENT PROCESS, AND ALLOWS DESIGNERS TO MAKE CHANGES MORE QUICKLY AND EASILY.

ADVANTAGES OF RAPID PROTOTYPING

RAPID PROTOTYPING HAS MANY ADVANTAGES OVER THE TRADITIONAL PROCESS USED TO DEVELOP A PRODUCT, INCLUDING THOSE DESCRIBE BELOW.

• SAVES TIME AND MONEY – RAPID PROTOTYPING ENCOURAGES CREATING A DETAILED DESIGN AT THE BEGINNING OF A PRODUCT’S DEVELOPMENT. THIS EARLY DESIGN WORK CAN LEAD TO A MORE USABLE PRODUCT IN A SHORTER PERIOD OF TIME. IN FACT, ONE STUDY (1) FOUND THAT DEVELOPMENT TEAMS THAT PROTOTYPED PRODUCED SYSTEMS THAT WERE EASIER TO LEARN THAN DEVELOPMENT TEAMS THAT DID NOT PROTOTYPE. TEAMS THAT PROTOTYPED GOT THESE RESULTS USING 45% LESS EFFORT AND 40% LESS CODE. A COMPLEX SYSTEM CAN BE PROTOTYPED SUCCESSFULLY FOR LESS THAN 10% OF THE TOTAL SOFTWARE DEVELOPMENT COST (2).
• PROMOTES CONSISTENCY IN USER INTERFACE DESIGN – SINCE RAPID PROTOTYPING PRODUCES SCREENS THAT ARE EASY FOR YOUR TEAM TO REVIEW AND COPY, YOU CAN ESTABLISH SCREEN DESIGN CONVENTIONS. THE CONVENTIONS ALLOW THE TEAM TO PRODUCE SCREENS THAT ARE CONSISTENT, THEREBY REDUCING THE AMOUNT OF CODE THAT HAS TO BE REWRITTEN DURING PROTOTYPING AND CODING.
• ALLOWS EARLY CUSTOMER INVOLVEMENT – RAPID PROTOTYPING ALLOWS CUSTOMERS TO SEE AND USE REALISTIC SCREENS EARLY IN PRODUCT DESIGN, WHEN CHANGES CAN BE MADE QUICKLY AND CHEAPLY. YOU CAN CONDUCT WALKTHROUGHS AND USABILITY TESTS WITH THE PROTOTYPE, THEN USE THIS CUSTOMER FEEDBACK IN REVISING THE PROTOTYPE TO BETTER MATCH CUSTOMER REQUIREMENTS AND PREFERENCES. A STUDY (3) FOUND THAT USERS OF A PROTOTYPED SYSTEM EVALUATED IT MORE FAVORABLY AND WERE MORE SATISFIED WITH IT THAN USERS OF THE SAME SYSTEM DEVELOPED IN THE TRADITIONAL WAY.
• CHANGES PERCEIVED OWNERSHIP TO CUSTOMERS – AS CUSTOMERS SEE THEIR DESIGN SUGGESTIONS INCORPORATED QUICKLY INTO THE PROTOTYPE, THEY COME TO THINK OF IT AS “THEIR” PRODUCT. CUSTOMERS CAN BEGIN TO BELIEVE THAT THEY ARE DESIGNING A PRODUCT TO MEET THEIR UNIQUE NEEDS, WITH IBM SIMPLY FACILITATING THE PROCESS. CUSTOMERS TAKE PRIDE IN THE PROTOTYPE AND TRY TO MAKE IS AS USEFUL AS POSSIBLE. THIS PRIDE OF OWNERSHIP RESULTS IN A PRODUCT THAT CLOSELY MATCHES CUSTOMER NEEDS.
• SHOWS PROGRESS TO MANAGEMENT IN A CONCRETE WAY – SEEING IS BELIEVING. INSTEAD OF TELLING MANAGEMENT HOW MANY KSLOCS (THOUSAND SOFTWARE LINES OF CODE) YOU’VE FINISHED, MANAGEMENT CAN SEE YOUR PROGRESS AS YOU BUILD AND REFINE THE PROTOTYPE. THIS VISIBLE PROCESS BUILDS YOUR CREDIBILITY AND PROVIDES A DIRECT, EASY-TO-UNDERSTAND WAY TO DEMONSTRATE PROGRESS.
• ALLOWS MARKETERS AND PLANNERS TO ENSURE THAT CUSTOMER NEEDS ARE MET – BY REVIEWING YOUR PROTOTYPE, THESE TEAM MEMBERS CAN GET AN EARLY UNDERSTANDING OF THE PRODUCT’S FUNCTIONS AND USER INTERFACE AND CAN SUGGEST IMPROVEMENTS THAT MEET CUSTOMER NEEDS.
• ALLOWS DOMAIN EXPERTS, INFORMATION DEVELOPERS, AND USABILITY REPRESENTATIVES TO GET INVOLVED EARLIER – RAPID PROTOTYPING ALLOWS DOMAIN EXPERTS, INFORMATION DEVELOPERS, AND USABILITY REPRESENTATIVES TO BECOME AN INTEGRAL PART OF THE DESIGN TEAM. INSTEAD OF WAITING FOR THE CODE TO BE FINISHED, THEY CAN WORK SIDE-BY-SIDE WITH DEVELOPMENT TO PRODUCE A USER INTERFACE (SCREENS, SCREEN FLOW, HELP, AND DOCUMENTATION) THAT IS SIMPLE, CONSISTENT, AND EASY-TO-USE.
• REDUCES THE TIME REQUIRED TO CREATE A PRODUCT FUNCTIONAL SPECIFICATION – INSTEAD OF WRITING A LONG AND DETAILED SPECIFICATION THAT DESCRIBES THE PROPOSED SCREENS AND NAVIGATION OF YOUR PRODUCT, SHOW THE SCREENS AND NAVIGATION BY USING THE PROTOTYPE AS THE PRODUCT FUNCTIONAL SPECIFICATION. USING THE PROTOTYPE WILL SAVE YOU SIGNIFICANT DOCUMENTATION TIME AND WILL BE A MUCH EASIER WAY FOR PEOPLE TO UNDERSTAND YOUR PROPOSED PRODUCT.

DISADVANTAGES OF RAPID PROTOTYPING

RAPID PROTOTYPING ALSO POSES SOME SPECIAL CHALLENGES THAT ARE USUALLY WORTH OVERCOMING. SOME OF THE DISADVANTAGES OF RAPID PROTOTYPING ARE DESCRIBED BELOW.

• HAS POOR TOOLS – RAPID PROTOTYPING IS JUST NOW BECOMING A STANDARD STEP IN THE DESIGN OF COMPLEX SYSTEMS. AT THE SAME TIME, USER INTERFACES ARE BECOMING INCREASINGLY DIFFICULT TO PROGRAM (E.G., IBM’S PRESENTATION MANAGER-BASED ADVANCED COMMON USER ACCESS). ALTHOUGH RAPID PROTOTYPING TOOLS ARE MOST NEEDED FOR THESE NEW USER INTERFACES, THE VERY FACT THAT THEY ARE NEW AND DIFFICULT TO PROGRAM MEANS THAT THE USER INTERFACES ARE EVOLVING FASTER THAN THE TOOLS TO HELP BUILD THEM. SIMPLY PUT, RAPID PROTOTYPING TOOLS HAVE NOT BEEN ABLE TO KEEP UP WITH THE USER INTERFACES. AS A RESULT, WE OFTEN END UP WITH A TOOL THAT CAN REPRODUCE THE FUNCTION THAT WE WANT (E.G., DRAGGING AN ICON) BUT IS VERY DIFFICULT TO USE.
  
  TO REDUCE THE RISK OF USING A POOR PROTOTYPING TOOL, CAREFULLY EVALUATE A VARIETY OF CANDIDATE TOOLS AND SELECT THE ONE THAT BEST MEETS YOUR NEEDS. YOUR NEEDS CAN INCLUDE SPECIFIC FUNCTIONS, OPERATING SYSTEMS, PROGRAMMING LANGUAGES, AND EASE OF USE. IF NO TOOL MEETS YOUR NEEDS, CONSIDER COMPROMISING ON YOUR NEEDS TO MORE CLOSELY MATCH THE AVAILABLE PROTOTYPING TOOLS. IT IS MORE IMPORTANT TO BE ABLE TO CHANGE YOUR PROTOTYPE QUICKLY AND EASILY THAN IT IS TO SIMULATE EVERY FEATURE OF THE PROPOSED PRODUCT.
• SOMETIMES ENCOURAGES PROTOTYPING BY PROGRAMMERS RATHER THAN DOMAIN EXPERTS – SINCE CURRENT RAPID PROTOTYPING TOOLS ARE DIFFICULT TO USE, PROGRAMMERS OFTEN END UP BEING THE PEOPLE WHO OPERATE THEM. THIS CAN BE A DISADVANTAGE SINCE THOSE MOST FAMILIAR WITH THE CUSTOMER – DOMAIN EXPERTS, INFORMATION DEVELOPERS, MARKETERS, PLANNERS, AND USABILITY REPRESENTATIVES – SHOULD PROTOTYPE THE USER INTERFACE. YOU CAN REDUCE THIS POTENTIAL PROBLEM BY HAVING YOUR PROTOTYPING TEAM WORK TOGETHER CLOSELY. THE TEAM MEMBERS WHO ARE MOST FAMILIAR WITH THE CUSTOMERS CAN HELP THE PROGRAMMER BY ADDING VALUE, SUCH AS BY USING TERMS WITH WHICH THE CUSTOMER IS FAMILIAR AND BY PRIORITIZING THE ACTIONS WHICH APPEAR IN A PULL-DOWN MENU.
• USUALLY DOES NOT PRODUCE REUSABLE CODE – PROTOTYPING TOOLS CAN BE LUMPED INTO TWO GROUPS. TOOLS IN THE FIRST GROUP LET YOU PROTOTYPE USER INTERFACES QUICKLY, BUT DON’T PRODUCE REUSABLE CODE. TOOLS IN THE SECOND GROUP LET YOU PRODUCE REUSABLE CODE, BUT CREATE PROTOTYPE USER INTERFACES THAT ARE DIFFICULT TO REVISE. THE TWO KINDS OF TOOLS ARE USEFUL FOR DIFFERENT, MUTUALLY EXCLUSIVE PURPOSES. YOU ARE MOST LIKELY TO BENEFIT FROM THE TOOLS THAT LET YOU PROTOTYPE QUICKLY. THESE TOOLS ARE MORE LIKELY TO REFLECT CUSTOMER REQUIREMENTS, PRIORITIES, AND PREFERENCES. THE SACRIFICE OF REUSABLE CODE FOR CUSTOMER SATISFACTION IS GENERALLY WORTHWHILE.
• SLOWS DEVELOPMENT PROCESS IF PUT UNDER FORMAL CONFIGURATION CONTROL – PROTOTYPING IS A VERY DYNAMIC, INFORMAL PROCESS. YOU WANT TO ENCOURAGE PEOPLE TO GIVE YOU AS MUCH FEEDBACK AS POSSIBLE. AN OFFHAND COMMENT CAN HELP YOU TO MAKE YOUR PRODUCT EVEN BETTER. ONE SURE WAY TO KEEP PEOPLE FROM GIVING YOU FEEDBACK IS TO REQUIRE THEM TO WRITE DESIGN CHANGE REQUESTS FOR EACH SUGGESTION. INSTEAD, ASK PEOPLE FOR THEIR VERBAL SUGGESTIONS AND WRITE THEM DOWN. THEN ALLOW YOUR PROTOTYPING TEAM TO DISCUSS THE SUGGESTIONS. WHEN THE TEAM HAS TROUBLE DECIDING BETWEEN TWO MUTUALLY EXCLUSIVE SUGGESTIONS, PROTOTYPE BOTH OF THEM AND SHOW THEM TO PROSPECTIVE CUSTOMERS. LET CUSTOMERS DECIDE WHICH OPTION IS BETTER.
• LACKS AN OBVIOUS STOPPING POINT – A DEDICATED PROTOTYPING TEAM ALWAYS FEELS THAT THEIR PROTOTYPE CAN BE IMPROVED A LITTLE MORE. ENCOURAGE THIS PRIDE, BUT KEEP IN MIND THAT YOU WANT TO BUILD AND SELL A REAL PRODUCT. YOU AN ALWAYS IMPOSE AN ARTIFICIAL STOPPING POINT BASED ON SCHEDULE OR COST. A BETTER STOPPING POINT MIGHT BE CUSTOMER DELIGHT. DON’T SATISFY CUSTOMERS. DELIGHT THEM. DELIGHTED CUSTOMERS TELL OTHER CUSTOMERS ABOUT YOUR PRODUCT AND ARE MORE LIKELY TO BUY OTHER PRODUCTS FROM YOUR COMPANY. TO ATTAIN CUSTOMER DELIGHT, IMPROVE YOUR PROTOTYPE QUICKLY AND ITERATIVELY UNTIL WALKTHROUGHS AND USABILITY TESTS SHOW THAT PROSPECTIVE CUSTOMERS ARE DELIGHTED WITH IT.

MOST COMMERCIALLY AVAILABLE RAPID PROTOTYPING MACHINES USE ONE OF SIX TECHNIQUES. AT PRESENT, TRADE RESTRICTIONS SEVERELY LIMIT THE IMPORT/EXPORT OF RAPID PROTOTYPING MACHINES, SO THIS GUIDE ONLY COVERS SYSTEMS AVAILABLE IN THE U.S.

STEREOLITHOGRAPHY

PATENTED IN 1986, STEREOLITHOGRAPHY STARTED THE RAPID PROTOTYPING REVOLUTION. THE STEREOLITHOGRAPHY PROCESS IS THE MOST WIDELY USED OF ALL RAPID PROTOTYPING PROCESSES IN THE YEAR 2004.

THE TECHNIQUE BUILDS THREE-DIMENSIONAL MODELS FROM LIQUID PHOTOSENSITIVE POLYMERS THAT SOLIDIFY WHEN EXPOSED TO ULTRAVIOLET LIGHT. AS SHOWN IN THE FIGURE BELOW, THE MODEL IS BUILT UPON A PLATFORM SITUATED JUST BELOW THE SURFACE IN A VAT OF LIQUID EPOXY OR ACRYLATE RESIN. A LOW-POWER HIGHLY FOCUSED UV LASER TRACES OUT THE FIRST LAYER, SOLIDIFYING THE MODEL’S CROSS SECTION WHILE LEAVING EXCESS AREAS LIQUID.

FIGURE 1: SCHEMATIC DIAGRAM OF STEREOLITHOGRAPHY.

NEXT, AN ELEVATOR INCREMENTALLY LOWERS THE PLATFORM INTO THE LIQUID POLYMER. A SWEEPER RE-COATS THE SOLIDIFIED LAYER WITH LIQUID, AND THE LASER TRACES THE SECOND LAYER ATOP THE FIRST. THIS PROCESS IS REPEATED UNTIL THE PROTOTYPE IS COMPLETE. AFTERWARDS, THE SOLID PART IS REMOVED FROM THE VAT AND RINSED CLEAN OF EXCESS LIQUID. SUPPORTS ARE BROKEN OFF AND THE MODEL IS THEN PLACED IN AN ULTRAVIOLET OVEN FOR COMPLETE CURING.

STEREOLITHOGRAPHY APPARATUS (SLA) MACHINES HAVE BEEN MADE SINCE 1988 BY 3D SYSTEMS OF VALENCIA, CA. TO THIS DAY, 3D SYSTEMS IS THE INDUSTRY LEADER, SELLING MORE RP MACHINES THAN ANY OTHER COMPANY. BECAUSE IT WAS THE FIRST TECHNIQUE, STEREOLITHOGRAPHY IS REGARDED AS A BENCHMARK BY WHICH OTHER TECHNOLOGIES ARE JUDGED. EARLY STEREOLITHOGRAPHY PROTOTYPES WERE FAIRLY BRITTLE AND PRONE TO CURING-INDUCED WARPAGE AND DISTORTION, BUT RECENT MODIFICATIONS HAVE LARGELY CORRECTED THESE PROBLEMS.

LAMINATED OBJECT MANUFACTURING

IN THIS TECHNIQUE, DEVELOPED BY HELISYS OF TORRANCE, CA, LAYERS OF ADHESIVE-COATED SHEET MATERIAL ARE BONDED TOGETHER TO FORM A PROTOTYPE. THE ORIGINAL MATERIAL CONSISTS OF PAPER LAMINATED WITH HEAT-ACTIVATED GLUE AND ROLLED UP ON SPOOLS. AS SHOWN IN THE FIGURE BELOW, A FEEDER/COLLECTOR MECHANISM ADVANCES THE SHEET OVER THE BUILD PLATFORM, WHERE A BASE HAS BEEN CONSTRUCTED FROM PAPER AND DOUBLE-SIDED FOAM TAPE. NEXT, A HEATED ROLLER APPLIES PRESSURE TO BOND THE PAPER TO THE BASE. A FOCUSED LASER CUTS THE OUTLINE OF THE FIRST LAYER INTO THE PAPER AND THEN CROSS-HATCHES THE EXCESS AREA (THE NEGATIVE SPACE IN THE PROTOTYPE). CROSS-HATCHING BREAKS UP THE EXTRA MATERIAL, MAKING IT EASIER TO REMOVE DURING POST-PROCESSING. DURING THE BUILD, THE EXCESS MATERIAL PROVIDES EXCELLENT SUPPORT FOR OVERHANGS AND THIN-WALLED SECTIONS. AFTER THE FIRST LAYER IS CUT, THE PLATFORM LOWERS OUT OF THE WAY AND FRESH MATERIAL IS ADVANCED. THE PLATFORM RISES TO SLIGHTLY BELOW THE PREVIOUS HEIGHT, THE ROLLER BONDS THE SECOND LAYER TO THE FIRST, AND THE LASER CUTS THE SECOND LAYER. THIS PROCESS IS REPEATED AS NEEDED TO BUILD THE PART, WHICH WILL HAVE A WOOD-LIKE TEXTURE. BECAUSE THE MODELS ARE MADE OF PAPER, THEY MUST BE SEALED AND FINISHED WITH PAINT OR VARNISH TO PREVENT MOISTURE DAMAGE.

HELISYS DEVELOPED SEVERAL NEW SHEET MATERIALS, INCLUDING PLASTIC, WATER-REPELLENT PAPER, AND CERAMIC AND METAL POWDER TAPES. THE POWDER TAPES PRODUCE A "GREEN" PART THAT MUST BE SINTERED FOR MAXIMUM STRENGTH. AS OF 2001, HELISYS IS NO LONGER IN BUSINESS.

SELECTIVE LASER SINTERING

DEVELOPED BY CARL DECKARD FOR HIS MASTER’S THESIS AT THE UNIVERSITY OF TEXAS, SELECTIVE LASER SINTERING WAS PATENTED IN 1989. THE TECHNIQUE, SHOWN IN FIGURE 3, USES A LASER BEAM TO SELECTIVELY FUSE POWDERED MATERIALS, SUCH AS NYLON, ELASTOMER, AND METAL, INTO A SOLID OBJECT. PARTS ARE BUILT UPON A PLATFORM WHICH SITS JUST BELOW THE SURFACE IN A BIN OF THE HEAT-FUSABLE POWDER. A LASER TRACES THE PATTERN OF THE FIRST LAYER, SINTERING IT TOGETHER. THE PLATFORM IS LOWERED BY THE HEIGHT OF THE NEXT LAYER AND POWDER IS REAPPLIED. THIS PROCESS CONTINUES UNTIL THE PART IS COMPLETE. EXCESS POWDER IN EACH LAYER HELPS TO SUPPORT THE PART DURING THE BUILD. SLS MACHINES ARE PRODUCED BY DTM OF AUSTIN, TX.

FUSED DEPOSITION MODELING

IN THIS TECHNIQUE, FILAMENTS OF HEATED THERMOPLASTIC ARE EXTRUDED FROM A TIP THAT MOVES IN THE X-Y PLANE. LIKE A BAKER DECORATING A CAKE, THE CONTROLLED EXTRUSION HEAD DEPOSITS VERY THIN BEADS OF MATERIAL ONTO THE BUILD PLATFORM TO FORM THE FIRST LAYER. THE PLATFORM IS MAINTAINED AT A LOWER TEMPERATURE, SO THAT THE THERMOPLASTIC QUICKLY HARDENS. AFTER THE PLATFORM LOWERS, THE EXTRUSION HEAD DEPOSITS A SECOND LAYER UPON THE FIRST. SUPPORTS ARE BUILT ALONG THE WAY, FASTENED TO THE PART EITHER WITH A SECOND, WEAKER MATERIAL OR WITH A PERFORATED JUNCTION.

STRATASYS, OF EDEN PRAIRIE, MN MAKES A VARIETY OF FDM MACHINES RANGING FROM FAST CONCEPT MODELERS TO SLOWER, HIGH-PRECISION MACHINES. MATERIALS INCLUDE ABS (STANDARD AND MEDICAL GRADE), ELASTOMER (96 DUROMETER), POLYCARBONATE, POLYPHENOLSULFONE, AND INVESTMENT CASTING WAX.

SOLID GROUND CURING

DEVELOPED BY CUBITAL, SOLID GROUND CURING (SGC) IS SOMEWHAT SIMILAR TO STEREOLITHOGRAPHY (SLA) IN THAT BOTH USE ULTRAVIOLET LIGHT TO SELECTIVELY HARDEN PHOTOSENSITIVE POLYMERS. UNLIKE SLA, SGC CURES AN ENTIRE LAYER AT A TIME. FIGURE 5 DEPICTS SOLID GROUND CURING, WHICH IS ALSO KNOWN AS THE SOLIDER PROCESS. FIRST, PHOTOSENSITIVE RESIN IS SPRAYED ON THE BUILD PLATFORM. NEXT, THE MACHINE DEVELOPS A PHOTOMASK (LIKE A STENCIL) OF THE LAYER TO BE BUILT. THIS PHOTOMASK IS PRINTED ON A GLASS PLATE ABOVE THE BUILD PLATFORM USING AN ELECTROSTATIC PROCESS SIMILAR TO THAT FOUND IN PHOTOCOPIERS. THE MASK IS THEN EXPOSED TO UV LIGHT, WHICH ONLY PASSES THROUGH THE TRANSPARENT PORTIONS OF THE MASK TO SELECTIVELY HARDEN THE SHAPE OF THE CURRENT LAYER.

AFTER THE LAYER IS CURED, THE MACHINE VACUUMS UP THE EXCESS LIQUID RESIN AND SPRAYS WAX IN ITS PLACE TO SUPPORT THE MODEL DURING THE BUILD. THE TOP SURFACE IS MILLED FLAT, AND THEN THE PROCESS REPEATS TO BUILD THE NEXT LAYER. WHEN THE PART IS COMPLETE, IT MUST BE DE-WAXED BY IMMERSING IT IN A SOLVENT BATH. SGC MACHINES ARE DISTRIBUTED IN THE U.S. BY CUBITAL AMERICA INC. OF TROY, MI. THE MACHINES ARE QUITE BIG AND CAN PRODUCE LARGE MODELS.

3-D INK-JET PRINTING

INK-JET PRINTING REFERS TO AN ENTIRE CLASS OF MACHINES THAT EMPLOY INK-JET TECHNOLOGY. THE FIRST WAS 3D PRINTING (3DP), DEVELOPED AT MIT AND LICENSED TO SOLIGEN CORPORATION, EXTRUDE HONE, AND OTHERS. THE ZCORP 3D PRINTER, PRODUCED BY Z CORPORATION OF BURLINGTON, MA (WWW.ZCORP.COM) IS AN EXAMPLE OF THIS TECHNOLOGY. AS SHOWN IN FIGURE 6A, PARTS ARE BUILT UPON A PLATFORM SITUATED IN A BIN FULL OF POWDER MATERIAL. AN INK-JET PRINTING HEAD SELECTIVELY DEPOSITS OR "PRINTS" A BINDER FLUID TO FUSE THE POWDER TOGETHER IN THE DESIRED AREAS. UNBOUND POWDER REMAINS TO SUPPORT THE PART. THE PLATFORM IS LOWERED, MORE POWDER ADDED AND LEVELED, AND THE PROCESS REPEATED. WHEN FINISHED, THE GREEN PART IS THEN REMOVED FROM THE UNBOUND POWDER, AND EXCESS UNBOUND POWDER IS BLOWN OFF. FINISHED PARTS CAN BE INFILTRATED WITH WAX, CA GLUE, OR OTHER SEALANTS TO IMPROVE DURABILITY AND SURFACE FINISH. TYPICAL LAYER THICKNESSES ARE ON THE ORDER OF 0.1 MM. THIS PROCESS IS VERY FAST, AND PRODUCES PARTS WITH A SLIGHTLY GRAINY SURFACE. ZCORP USES TWO DIFFERENT MATERIALS, A STARCH BASED POWDER (NOT AS STRONG, BUT CAN BE BURNED OUT, FOR INVESTMENT CASTING APPLICATIONS) AND A CERAMIC POWDER. MACHINES WITH 4 COLOR PRINTING CAPABILITIES ARE AVAILABLE.

3D SYSTEM VERSION OF THE INK-JET BASED SYSTEM IS CALLED THE THERMO-JET OR MULTI-JET PRINTER. IT USES A LINEAR ARRAY OF PRINT HEADS TO RAPIDLY PRODUCE THERMOPLASTIC MODELS (FIGURE 6D). IF THE PART IS NARROW ENOUGH, THE PRINT HEAD CAN DEPOSIT AN ENTIRE LAYER IN ONE PASS. OTHERWISE, THE HEAD MAKES SEVERAL PASSES.

SANDERS PROTOTYPE OF WILTON, NH USES A DIFFERENT INK-JET TECHNIQUE IN ITS MODEL MAKER LINE OF CONCEPT MODELERS. THE MACHINES USE TWO INK-JETS (SEE FIGURE 6C). ONE DISPENSES LOW-MELT THERMOPLASTIC TO MAKE THE MODEL, WHILE THE OTHER PRINTS WAX TO FORM SUPPORTS. AFTER EACH LAYER, A CUTTING TOOL MILLS THE TOP SURFACE TO UNIFORM HEIGHT. THIS YIELDS EXTREMELY GOOD ACCURACY, ALLOWING THE MACHINES TO BE USED IN THE JEWELRY INDUSTRY.

BALLISTIC PARTICLE MANUFACTURING, DEPICTED IN FIGURE 6B, WAS DEVELOPED BY BPM INC., WHICH HAS SINCE GONE OUT OF BUSINESS.

RAPID TOOLING

INTRODUCTION:-

WHILE THERE IS MUCH PROGRESS IN DIRECT PART FABRICATION, EVEN THE FASTEST RAPID PROTOTYPING SYSTEMS ARE FAR TOO SLOW AND LIMITED IN OTHER WAYS. THEY SIMPLY CAN'T PRODUCE PARTS IN A WIDE ENOUGH RANGE OF MATERIALS; AT A FAST ENOUGH RATE, TO MATCH THE ENORMOUS SPECTRUM OF REQUIREMENTS OF INDUSTRY. CONVENTIONAL PROCESSES SUCH AS MOLDING AND CASTING ARE STILL THE ONLY MEANS AVAILABLE TO DO THAT. HOWEVER, ADDITIVE FABRICATION IS OFTEN THE STARTING POINT FOR MAKING THESE MANUFACTURING PROCESSES FASTER, CHEAPER AND BETTER. INDEED, THE FABRICATION OF TOOLING IS ONE OF THE MOST IMPORTANT APPLICATIONS OF RAPID MANUFACTURING, AND PROVIDED MUCH OF THE EARLY IMPETUS FOR THE DEVELOPMENT OF THE FIELD.

RAPID PROTOTYPING IS USED IN TWO WAYS TO MAKE TOOLING: MOLDS OR OTHER TOOLS MAY BE DIRECTLY FABRICATED BY AN RP SYSTEM, OR RP-GENERATED PARTS CAN BE USED AS PATTERNS FOR FABRICATING A MOLD OR TOOL THROUGH SO-CALLED INDIRECT OR SECONDARY PROCESSES.

DIRECT FABRICATION PROCESSES

SPECIALIZED RAPID PROTOTYPING PROCESSES HAVE BEEN DEVELOPED TO MEET SPECIFIC APPLICATION AND MATERIAL REQUIREMENTS FOR MOLDING AND CASTING. THESE MAY BE FORMS OF BASIC RP PROCESSES, SUCH AS STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING, OR MAY BE UNIQUE RP METHODS DEVELOPED FOR A SPECIFIC APPLICATION. A LARGE NUMBER OF TECHNOLOGIES HAVE BEEN OR ARE BEING EXPLORED, BUT ONLY A RELATIVELY FEW ARE COMMERCIALLY IMPORTANT AT PRESENT.

INDIRECT OR SECONDARY PROCESSES

ALTHOUGH THE PROPERTIES OF RAPID PROTOTYPING MATERIALS CONTINUE TO IMPROVE AND EXPAND, THEIR COMPARATIVELY SMALL NUMBER AND A LIMITLESS ARRAY OF APPLICATIONS MEANS THAT THERE WILL ALWAYS BE A NEED TO TRANSFER PARTS FABRICATED IN A MATERIAL USED IN AN ADDITIVE FABRICATION PROCESS INTO YET ANOTHER MATERIAL. CONSEQUENTLY, NUMEROUS MATERIAL TRANSFER TECHNOLOGIES HAVE BEEN DEVELOPED. TYPICALLY A PART MADE BY THE RP SYSTEM IS USED AS A PATTERN OR MODEL IN THESE PROCESSES. AS IN THE CASE OF THE DIRECT FABRICATION PROCESSES DISCUSSED ABOVE, THERE ARE MANY SECONDARY PROCESSES IN VARIOUS STAGES OF DEVELOPMENT. HOWEVER, OF THE MORE THAN TWO DOZEN SUCH METHODS AVAILABLE OR UNDER INVESTIGATION, JUST A FEW ARE COMMON AND COMMERCIALLY IMPORTANT TODAY.

SILICONE RUBBER TOOLING:- THIS IS A STANDARD METHOD OF MAKING SMALL QUANTITIES OF POLYMER PARTS. ANY RAPID PROTOTYPING-GENERATED PART CAN BE USED AS A PATTERN TO MAKE SILICONE RUBBER TOOLING. THESE TOOLS CAN BE USED TO MOLD SMALL TO MEDIUM QUANTITIES OF PARTS IN A LARGE VARIETY OF URETHANE, EPOXY OR OTHER POLYMERS. SOME OF THESE POLYMERS HAVE PROPERTIES WHICH EMULATE PARTICULAR ENGINEERING THERMOPLASTICS, AND IT'S ALSO POSSIBLE TO FILL THEM FOR ADDED STRENGTH. THE METHOD DOESN'T PRODUCE A PART WHICH IS IDENTICAL TO AN INJECTION MOLDED PART, HOWEVER, BECAUSE THE CONDITIONS OF MANUFACTURE AREN'T THE SAME. INJECTION MOLDED PARTS MAY HAVE FUNCTIONALLY-IMPORTANT ANISOTROPIC MECHANICAL PROPERTIES THAT DEPEND ON HOW THE MATERIAL FLOWS IN THE MOLD AND COOLS, FOR EXAMPLE. NEVERTHELESS, SILICONE RUBBER TOOLING IS INEXPENSIVE, OFFERS GOOD ACCURACY AND FINISH, AND THE PARTS PRODUCED ARE OFTEN ADEQUATE FOR PROTOTYPES OR SMALL PRODUCTION RUNS. THE MATERIALS ARE OFTEN USED IN A NATURAL STATE, BUT PAINTING AND OTHER SECONDARY OPERATIONS CAN RESULT IN PARTS THAT ARE VERY ATTRACTIVE.

SILICONE TOOLS CAN TYPICALLY BE USED TO MOLD SEVERAL PARTS BEFORE IT BECOMES NECESSARY TO REPLACE THEM. THE NUMBER DEPENDS ON ACCURACY AND FINISH REQUIREMENTS AND THE SPECIFIC GEOMETRY OF THE ITEM PRODUCED. IT MAY BE POSSIBLE TO MAKE MANY DOZENS OF SIMPLE OR NON-CRITICAL PARTS FROM A SINGLE SILICONE RUBBER MOLD, BUT TEN TO TWENTY IS TYPICAL IF THE PARTS ARE MORE COMPLEX. WEAR OF THE MOLD OCCURS DUE TO THE EXOTHERMIC AND REACTIVE NATURE OF THE POLYMERS, AND BECAUSE OF THE NECESSITY TO MECHANICALLY DEFORM THE MOLD TO REMOVE THE PART. IT MAY OFTEN BE NECESSARY TO REPLACE THE RP-GENERATED PATTERN AS WELL, DEPENDING ON THE NUMBER OF MOLDS TO BE MADE AND SIMILAR ACCURACY AND GEOMETRIC CONSIDERATIONS.

THE PROCESS IS CARRIED OUT BY PLACING THE RP-GENERATED PATTERN IN A FRAME, USUALLY MADE OF WOOD. THE PATTERN ITSELF USUALLY MUST UNDERGO SECONDARY OPERATIONS TO BRING IT TO THE DESIRED STATE OF ACCURACY AND FINISH BEFORE IT CAN BE USED. SEE THE SECTION ON RP-GENERATED PATTERNS. SILICONE RUBBER ROOM TEMPERATURE VULCANIZING (RTV) MOLDING COMPOUND IS THEN POURED AROUND THE PATTERN. IT MAY BE NECESSARY TO APPLY A VACUUM TO THE ASSEMBLY TO PULL AIR BUBBLES OUT OF THE RUBBER AND INSURE FIDELITY TO THE PATTERN. ONCE THE RUBBER HAS SOLIDIFIED, THE PATTERN IS REMOVED AND THE MOLD IS READY TO BE USED.

SILICONE RUBBER TOOLING IS MOST OFTEN USED IN MANUAL CASTING PROCESSES, BUT IN RECENT YEARS MORE AUTOMATED TECHNOLOGIES HAVE APPEARED. SO-CALLED REACTION INJECTION MOLDING (RIM) SYSTEMS CAN PRODUCE SEVERAL PARTS PER HOUR FROM RUBBER MOLDS. MOLDS ALSO LAST LONGER BECAUSE OF THE LOWER EXPOSURE TIME TO CHEMICAL PROCESSES. A NUMBER OF OTHER VARIANTS OF THE PROCESS ARE ALSO AVAILABLE FROM PARTICULAR VENDORS, SUCH AS RUBBER PLASTER MOLDING. RPM ALLOWS THE TECHNIQUE TO BE EXTENDED TO OTHER MATERIALS, SUCH AS METALS.

EPOXY TOOLING:-

PLASTIC TOOLS CAN BE UP TO 50% CHEAPER THEN CONVENTIONAL TOOLING AND USUALLY TAKE 70% LESS TIME TO MANUFACTURE. SINCE THEY ARE MADE OF PLASTIC, THEY ARE LIGHT IN WEIGHT AND EASY TO HANDLE AND NEED NO SPECIAL STORAGE. BUILDING PLASTIC MATERIALS ARE USUALLY EPOXIES OR POLYURETHANE WHICH BOTH SET AT ROOM TEMPERATURE. OVEN TREATMENT IS NECESSARY ONLY WHEN HEAT RESISTANT TOOLS ARE TO BE MADE. PLASTIC TOOLS ARE EASY TO PATCH AND NOT BRITTLE. THEY BOND TO PRACTICALLY ANY MATERIAL WHEN INNER SUPPORT STRUCTURES FOR ADDITIONAL TOOL STIFFNESS IS REQUIRED. THEY ARE DURABLE AND WON'T RUST AND WON'T WARP. THEY PROVIDE QUICK, EASY AND INEXPENSIVE MODIFICATION FOR REPAIR OF VALUABLE TOOLS. BEFORE DISCUSSING THE STEPS INVOLVED IN BUILDING A PLASTIC TOOL, MODEL PREPARATION SHOULD BE TAKEN INTO ACCOUNT. MODELS REPRESENT THE BASIS ON WHICH THE TOOL WILL BE MADE ON.

MODEL PREPARATION WOOD .

1. ONCE THE WOODEN MODEL HAS BEEN SHAPED AND SURFACE SMOOTHENED.

2. SPRAY A LACQUER SEALER ON THE MODEL SURFACE AND LET IT DRY COMPLETELY.

3. IF THE LACQUERED MODEL HAS BEEN PREPARED LONG TIME AGO, CLEAN IT BY WIPING IT WITH A LINT-FREE CLOTH THAT WAS MOISTENED IN ALCOHOL.

4. APPLY ALL PURPOSE RELEASE AGENT AND RUB OUT THOROUGHLY WITH A LINT-FREE CLOTH.

5. SPRAY A COAT OF PVA PARTING AGENT AND LET DRY COMPLETELY.

6. APPLY AN ADDITIONAL ALL PURPOSE RELEASE AGENT COAT, WIPE OFF EXCESS LIGHTLY WITH LINT-FREE CLOTH AND POLISH.

.

PLASTER

1. A PLASTER MOLD MUST BE SEALED COMPLETELY TO ELIMINATE MOISTURE OR ANY CHEMICAL LEAK-THROUGH WHICH WOULD BREAK DOWN THE RELEASE AGENT. FOR THIS REASON

2. SPRAY A LACQUER OVER THE MODEL MAKING SURE NO SPOTS ARE LEFT UNSPRAYED.

3. APPLY TWO COATS OF ALL PURPOSE RELEASE AGENTS. EACH APPLICATION SHOULD BE WIPED OFF AND POLISHED WHILE IT IS STILL WET, UNTIL IT IS DRY AND SHINY.

PLASTIC

1. REMOVE ALL FOREIGN MATTER FROM SURFACE OF MODEL.

2. APPLY 3 SUCCESSIVE COATS OF ALL PURPOSE RELEASE AGENT, LIGHTLY POLISH AND BUFF WHILE STILL WET UNTIL DRY AND SHINY SURFACE IS ACHIEVED.

METAL

1. REMOVE ALL SURFACE DIRT OR WASH WITH SUITABLE SOLVENT.

2. APPLY 3 TO 4 COATS OF ALL PURPOSE RELEASE AGENT BY LIGHTLY POLISHING AND BUFFING EACH COAT WHILE IT IS STILL WET UNTIL DRY AND SHINY SURFACE IS ACHIEVED.

PLASTIC TOOLING MAY BE DIVIDED INTO 3 GENERAL CATEGORIES

1. LAMINATED TOOLS

LAMINATED TOOLS ARE MADE OF ALTERNATE LAYERS OF GLASS CLOTH AND LIQUID LAMINATING PLASTIC. AFTER LAMINATION IS COMPLETED, THE LIQUID PLASTIC SOLIDIFIES INTO STRONG, RIGID FORM. THE FINISHED PIECE HAS THE EXACT SIZE AND SHAPE OF THE SURFACE FROM WHICH IT WAS MOLDED. LAMINATED TOOLS ARE USUALLY REINFORCED WITH, OR BECAME A PART OF A FRAMEWORK. THIS FRAMEWORK CAN BE MADE OF PLASTIC MATERIALS, FABRICATED STEEL OR ALUMINUM. THE TYPE OF FRAMEWORK DEVELOPED DEPENDS ON THE END USE OF THE TOOL. THESE TOOLS ARE USED WHEREVER ACCURACY, STRENGTH AND WEIGHT ARE PRIME CONSIDERATIONS. THEY POSSESS THE BEST DIMENSIONAL STABILITY OF ANY PLASTIC TOOLS AND ARE WIDELY USED FOR SPOTTING, CHECKING AND INSPECTION FIXTURES, PLUS MANY OTHER APPLICATIONS.

BUILDING PROCEDURE

THE LAMINATED METHOD CONSISTS BASICALLY OF BUILDING UP ALTERNATE LAYERS OF GLASS CLOTH AND PLASTIC ON A FORM, PATTERN OR MODEL UNTIL THE DESIRED THICKNESS IS OBTAINED. EACH LAYER OF 0.013" THICK 10-OUNCE GLASS CLOTH, PLUS THE LAMINATING MATERIAL LAYS UP TO APPROXIMATELY 0.20" THICKNESS (I.E. 18 LAYERS = 0.360").

1. "BUILD-UPS" - FOR PARTING PLANES, RUN-OUT APRONS, DAMS OR RETAINING BOXES. BUILD-UPS ARE USED TO CONFINE THE PLASTIC LAY-UP TO A CERTAIN AREA. PATTERN MAKER'S SHEET WAX OF VARYING THICKNESS IS USED FOR COMPOUND CURVES WHILE THIN SHEETS (1 TO 2 LAYERS) OF GLASS CLOTH LAMINATE ARE USED FOR SHARP RADII. WOOD OR MASONITE SHOULD BE UTILIZED FOR STRAIGHT SIDES AND LARGE RADII. WHITE PINE BLOCKS CUT AND SHAPED TO THE CORRECT SIZE ALSO MAY BE USED.

2. THICKNESS WAX - PATTERN MAKER'S SHEET WAX IS USED TO SIMULATE THE MATERIAL THICKNESS IN OBTAINING EITHER THE INSIDE OR THE OUTSIDE MOLD LINE. IT IS ALSO USED FOR REVEALING CERTAIN AREAS IN CHECKING FIXTURES AND BUILD-UPS. IT CAN BE APPLIED BY PAINTING THE MODEL AND ONE SIDE OF THE SHEET WAX WITH SHELLAC. THE SHELLAC SHOULD BE TACKY BEFORE APPLYING THE WAX TO THE MODEL. SHEET WAX IS ALSO AVAILABLE WITH ADHESIVE ON ONE SIDE. THE WAX WILL ALSO ADHERE TO THE MODEL BY USING A THIN LAYER OF PETROLEUM JELLY, BUT EXTREME CARE SHOULD BE TAKEN TO INSURE A UNIFORM COAT TO ELIMINATE ANY IRREGULAR SURFACE.

3. APPLY PARTING AGENT TO SURFACE OF MODEL, DIKE BOARDS, ETC. ACCORDING TO INSTRUCTIONS UNDER MODEL PREPARATION.

4. APPLY DESIRED SURFACE COAT.

5. CUT SECTIONS OF FIBERGLASS (CLOTH, SCRIM, MAT, ETC.) IN READINESS TO FIT AS PATCH WORK OVER THE MODEL. THE SECTION SHOULD BE TAILORED TO FIT NEATLY INTO CORNERS AND OVER COMPLEX CONTOURS. WHERE THE MODEL IS FLAT OR HAS SIMPLE CURVATURES, THE FIBERGLASS IS NORMALLY CUT INTO SQUARES MEASURING 15 X 15 CM TO 25 X 25 CM (6" X 6" TO 10" X 10"). BY UTILIZING THE TIME SPAN BETWEEN THE SURFACE COAT AND LAMINATING OPERATION TO CUT THE NECESSARY CLOTH FOR THE INITIAL LAYERS OF THE TOOL AND TO BUILT UP SHARP CORNERS, ETC., NO LOST TIME IS INVOLVED AND THE OPERATOR IS IN "TOUCH" WITH THE NOW CRITICAL SURFACE THAT MUST BE CHEMICALLY JOINED WITH THE FIRST LAYER IF GLASS CLOTH.

6. USING A "GLASS PASTE" MIXTURE, FILL IN ALL SHARP CORNERS AND DETAILS. THIS REDUCES THE POSSIBILITY OF VOIDS OR BUBBLES DEVELOPING UNDER THE FIRST LAYER OF THE GLASS CLOTH.

7. PREPARE THE LAMINATING MIX ACCORDING TO THE APPROPRIATE MIXING INSTRUCTIONS.

8. USING THE LAMINATING MIX WET-OUT THE ALMOST TACK-FREE SURFACE. IF MATERIAL CAN BE DENTED, BUT DOES NOT STICK TO YOUR FINGER TIP, IT IS CONSIDERED "TACK-FREE".

9. LAY-UP THE FIRST LAYER OF FIBERGLASS SECTIONS. STIPPLE INTO POSITION BY BRUSH OR WOODEN SPATULA SO THAT THE EDGES BUTT, THE CLOTH IS COMPLETELY SATURATED WITH LAMINATING MIX AND ALL ENTRAPPED AIR WORKED OUT.

10. APPLY SECOND COAT OF LAMINATING MIX AND IMMEDIATELY LAY-UP A SECOND LAYER OF GLASS CLOTH SECTIONS. APPLY AS BEFORE, BUT ARRANGE SO THAT THE SECOND-LAYER SECTIONS COVER THE BUTTED JOINTS OF THE FIRST-LAYER SECTIONS. IT IS ESSENTIAL TO ENSURE THAT WHILE THE GLASS CLOTH IS COMPLETELY WETTED OUT, THERE IS NO EXCESS RESIN. ROLLING IS A SIMPLE, RAPID WAY TO ELIMINATE THE FLOATING OF GLASS CLOTH ON RESIN, BRING EXCESS RESIN TO THE SURFACE AND REMOVE ENTRAPPED AIR. STIPPLING LAMINATE WITH A SHORT, STIFF BRUSH WILL ALSO GIVE SATISFACTORY RESULTS. IDEALLY A LAMINATE SHOULD CONSIST OF 60% GLASS TO 40% RESIN BY WEIGHT. THIS IS AN APPROXIMATION AND IS DEPENDENT TO SOME EXTEND ON THE USE FILLED VERSUS UNFILLED SYSTEMS.

11. AFTER APPROXIMATELY TWO LAYERS ARE APPLIED AS DESCRIBED ABOVE, LARGER SECTIONS OF CLOTH (UP TO 1/3 OF THE ENTIRE SURFACE OF THE TOOL) MAY BE APPLIED DIAGONALLY ACROSS THE TOOL SURFACE. EACH SUCCEEDING LAYER SHOULD BE ROTATED TO AVOID ALIGNMENT OF THE CLOTH JOINTS. CONTINUE THE ABOVE PROCESS UNTIL THE DESIRED THICKNESS IS ATTAINED. DO NOT STRETCH THE CLOTH OR WARPING MAY RESULT WHEN THE TOOL CURES OR UNDERGOES TEMPERATURE CYCLING.

12. WHEN THE LAMINATING TOTALS A THICKNESS OF 4 TO 6 MM (3/16" TO ¼ ") ALLOW THE LAMINATE SKIN TO CURE UNTIL AT LEAST TACK-FREE.

13. DO NOT APPLY MORE THEN 12 LAYERS (6 MM -1/4") AT ANY ONE TIME SINCE THE EXOTHERMIC HEAT GENERATED BY THE PLASTIC MAY CAUSE EXCESSIVE SHRINKAGE OR WARPAGE OF THE FINISHED TOOL. IF EXCESSIVE HEAT IS NOTED AT ANY TIME, IT IS A GOOD RULE TO STOP UNTIL THE MATERIAL "SETS-UP" AND HAS COOLED OFF. IF SURFACE IS GLOSSY, IT SHOULD BE SANDED BEFORE NEXT LAYER IS APPLIED. TO ELIMINATE HAND SENDING, PUT DOWN A PEEL

14. PLY OR ALTERNATELY SPRINKLE DRY, FINE ALUMINUM GRANULES, OR SILICA SAND ON THE LAST LAYER OF LAMINATE WHILE IT IS STILL WET. THIS WILL RESULT IN A ROUGH SURFACE WHICH PROVIDES BETTER BONDING WHEN LAMINATING IS RESUMED.

15. IF A FRAMEWORK IS TO BE ADDED TO THE LAMINATED TOOL FACING, THIS SHOULD BE DONE IMMEDIATELY AFTER LAMINATING, BEFORE REMOVING THE PLASTIC TOOL FROM THE MODEL.

2. SURFACE CAST TOOLS

A SURFACE CAST TOOL USUALLY CONSISTS OF A METALLIC CORE, ROUGH CAST TO THE GENERAL SHAPE OF THE FINISHED TOOL. THIS CORE IS SUSPENDED OVER A MODEL OF THE WORKING SURFACE OF THE TOOL AND LIQUID PLASTIC IS THEN CAST INTO THE SPACE BETWEEN THE MODEL AND THE METALLIC CORE. EITHER EPOXY OF POLYURETHANE MAY BE USED. PRELIMINARY PREPARATIONS ARE MADE SO THAT THE PLASTIC CAST BONDS TENACIOUSLY TO THE METALLIC CORE, BUT WILL PART CLEANLY FROM THE MODEL. THE RESULTANT TOOL WILL HAVE EXACT SHAPE AND FINISH QUALITY OF THE MODE;. GENERALLY SPEAKING, SURFACE CASTS ARE MADE AGAINST A METAL SURFACE SUCH AS KIRKSITE, ALUMINUM OR STEEL. BULK CASTING MADE OF REN MATERIALS ARE USED AS CORES FOR SURFACE CAST TOOLS. THIS TYPE OF TOOL IS USED IN SOME INDUSTRIES FOR METAL FORMING DIES. IN THE FOUNDRY INDUSTRY, IT IS USED TO MAKE PATTERNS OF CORE BOXES. THE DIMENSIONAL STABILITY OF SURFACE CAST TOOLS IS SOMEWHAT LESS THEN THAT OF LAMINATED TOOLS.

BUILDING PROCEDURE

1. THE CORE MUST BE FIRST MADE, AND THIS IS USUALLY PRODUCED IN THE KIRKSITE OR ALUMINUM FOUNDRY. A ROUGH PATTERN IS MADE TO CAST THE METALLIC CORE. THE WORKING FACE, THAT IS, THE FACE ON WHICH THE PLASTIC SURFACE IS TO BE CAST, IS MADE APPROXIMATELY ½" SMALLER THAN THE FINISHED SURFACE TO ALLOW SPACE FOR THE SURFACE CASTING PLASTIC. THIS PATTERN IS THEN RAMMED INTO FOUNDRY SAND AND INTO THE KIRKSITE OR ALUMINUM CORE CAST. IF A PLASTIC CORE IS REQUIRED RATHER THEN THE KIRKSITE OR ALUMINUM, REFER TO THE MASS CASTING SECTION.

2. THE ALUMINUM OR KIRKSITE CORE CAN BE USED AS IT HAS BEEN COOLED TO ROOM TEMPERATURE. THE WORKING FACE IS USUALLY CLEANED BY SAND BLASTING. IF THE CORE IS NOT TO BE USED WITHIN 24 HOURS AFTER SAND BLASTING, PAINT THE SURFACE WITH A REN LIQUID PLASTIC TOOLING (LAMINATING OR CASTING TYPE) TO PREVENT OXIDATION OF THE SURFACE. WHEN READY TO BE USED, THE PAINTED SURFACE SHOULD BE SANDED WITH DENATURED ALCOHOL.

3. PREPARE THE SURFACE OF THE DIE MODEL OR PLASTER SPLASH IN THE SAME MANNER AS FOR LAMINATING.

4. DEPENDING UPON THE SURFACE CAST METHOD TO BE USED, SET UP THE CORE AND DIE MODEL FOR THE CASTING OPERATION. IT IS USUALLY ADVISABLE TO TRY TO CORE IN THE MOLD BEFORE THE RESIN IS ADDED, ESPECIALLY WHEN THE SQUASH METHOD IS BEING CONSIDERED. THIS SHOULD BE DONE BEFORE MIXING THE RAISIN AND HARDENER,

5. CHECK SET-UP TO SEE IF AIR COULD BE ENTRAPPED BY THE CASTING PLASTIC AS IT ENTERS THE MOLD. DRILL WENT HOLES THROUGH THE CORE IN THESE AREAS OR ELEVATE ONE END OF THE SET-UP TO ELIMINATE THE POSSIBILITY OF ANY AIR ENTRAPMENT. ALWAYS HAVE CORE ON TOP OF DIE MODEL SINCE THIS WILL KEEP ANY SMALL AIR BUBBLES AWAY FROM THE WORKING FACE OF THE TOOL.

6. MIX PLASTIC MATERIALS THOROUGHLY ACCORDING TO DIRECTIONS ON THE CAN. WHEN POURING INTO THE MOLD, ALLOW A STEADY STEAM OF MATERIAL TO FLOW UNTIL THE COMPLETE CAST IS FINISHED. DO NOT CHANGE POSITION OF POURING AS THIS MAY ENTRAP AIR.

7. AFTER PROPER CURING PERIOD, TOOL MAY BE REMOVED FROM THE MASTER.

8. FOR AN ALTERNATE METHOD OF CORE CONSTRUCTION MOLD SURFACES ARE LINED WITH A POLYETHYLENE SHEET. A LAYER OF MODELING CLAY (THE CLAY PROVIDES THE THICKNESS ALLOWANCE FOR THE SURFACE CASTING MIXTURE),1/2 TO 1 CM (3/16" TO 3/9) THICK IS APPLIED TO THE LINED MOLD AND DRAPED WITH A SECOND POLYETHYLENE SHEET, WHEN DRAPING THE SECOND SHEET IT IS NOT NECESSARY TO ELIMINATE SLIGHT CREASES: THESE GIVE THE CORE SURFACE IRREGULARITIES WHICH AID BONDING TO THE FACING MIXTURE. THE SAND OR WASHED GRAVEL-LOADED MIXTURE (EITHER LAMINATING OR SURFACE CASTING MIXTURE MAY BE USED) IS TRAWLED AND TAMPED INTO THE CLAY MOLD AND AROUND VENTS LOCATED WHERE AIR LOCKS ARE LIKELY TO OCCUR WHEN SURFACE CASTING MIXTURE IS APPLIED TO THE COMPLETE CORE. THE CORE MIXTURE IS CURED AT ROOM TEMPERATURE.

3. MASS CAST TOOLS

MASS CAST TOOLS ARE USUALLY MADE OF PLASTIC MATERIAL; HOWEVER, METAL INSERT ARE SOMETIMES BUILT INTO THE UNIT FIR ADDED STRENGTH AT CERTAIN STRESS POINTS. EITHER EPOXY OR POLYURETHANE MAY BE USED. MASS CASTING OF PLASTICS IS USUALLY USED WHERE A LARGE TOOL SURFACE IS INVOLVED, SUCH AS AN AIRCRAFT STRETCH BLOCK OR HAMERFORM. HERE A MATERIAL IS REQUIRED WHICH WILL PROVIDE GOOD PHYSICAL PROPERTIES, IS RELATIVELY INEXPENSIVE TO USE AND CAN BE CAST IN LARGE, THICK SECTIONS UP TO 60 CM (24") THICK. THE LATTER IS POSSIBLE IN PLASTICS TOOLING WITH THE AID OF SUITABLE HEAT ABSORBING FILLER MATERIALS. THE DIMENSIONAL STABILITY OF A MASS CAST TOOL IS LOWER THAT THAT OF A LAMINATED TOOL BUT IS STILL WELL WITHIN THE NORMAL TOLERANCES OF STRETCH FORMING OPERATIONS.

BUILDING PROCEDURE

MASS CASTING HAS THE OBVIOUS ADVANTAGE SPEED AND EASE OF APPLICATION. IT ALSO ELIMINATES THE COST OF PRODUCING AND PREPARING THE METAL CORES NEEDED TO SURFACE CASTING. MASS CASTING CAN BE POURED UP TO 4 IN THICK OR EVEN THICKER IF FILLERS ARE USED TO REDUCE THE BUILD UP EXOTHERMIC HEAT. THESE ADVANTAGES EMPHASIZE THE SAVINGS POTENTIAL OF MASS CASTING. THERE ARE ALSO SOME DISADVANTAGES, HOWEVER, AND THESE MUST BE CONSIDERED BEFORE THE SYSTEM IS CHOSEN TO BUILD A TOOL. ONE OF THESE DISADVANTAGES IS THE LOW STRENGTH PROPERTIES OF MOST MASS CASTING MATERIALS. EVEN THE ADDITION OF FILLERS SUCH AS SAND AND GRAVEL, ALUMINUM GRANULES OR GRAIN, GLASS BALLS, VOLCANIC ASH, PUMICE, CORK OR GROUND NUT SHELLS DO NOT APPRECIABLY INCREASE THE PHYSICAL PROPERTIES OF THIS TYPE OF CONSTRUCTION. ANOTHER POSSIBLE DISADVANTAGE IS THE HIGH SHRINKAGE ENCOUNTERED, PARTICULARLY IN HEAVIER CASTINGS. THIS IS DUE TO THE HEAT GENERATED WHEN THE CASTING IS CURED. IN THE PAST THIS SHRINKAGE HAS MADE IT ADVISABLE TO BUILT A LAMINATED SURFACE FIRST AND THEN BACK IT UP WITH A CASTING MATERIAL, OR CAST THE TOOL OVERSIZE AND REWORK THE SURFACE. RECENT DEVELOPMENTS IN PLASTICS HAVE GREATLY BOTH OF THESE OBJECTIONS. CURRENT CASTING SYSTEMS OFFER A CONSIDERABLE INCREASE IN PHYSICAL PROPERTIES WHILE PERMITTING CASTING FROM 2.5 CM TO 10 CM (1" TO 4") THICK, WITH OUT GENERATING EXCESSIVE HEAT WITH THE ACCOMPANYING HIGH SHRINKAGE. THE PREPARATION OF THE MOLD FOR MASS CASTING IS THE SAME AS THAT USED FOR SURFACE CASTING. FOLLOWING PREPARATION, THE REQUIRED AMOUNT OF IS POURED INTO THE CAVITY, ALLOWED TO CURE FOR THE NECESSARY LENGTH OF TIME AND THEN PULLED FROM THE MOLD.

SPRAY METAL TOOLING:-

THIS PROCESS APPLIES A ZINC/ALUMINUM ALLOY WITH AN ARC SPRAY TO A PATTERN OR MODEL. THE PATTERN OR MODEL CAN BE A STEREO LITHOGRAPHY PART OR A MODEL MADE FROM WOOD OR METAL. THE ALLOY IS SPRAYED OVER THE PATTERN TO A SHELL THICKNESS FROM .060-INCHES TO 0.125-INCHES AS REQUIRED. IT SOLIDIFIES INTO THE DESIRED SHAPE AND ADHERES TO THE PATTERN. THE SPRAYED METAL SHELL IS THEN REINFORCED WITH A HIGH-TREAT ALUMINUM-FILLED EPOXY RESIN. THE FINISHED MOLD CAN PRODUCE PARTS FROM VIRTUALLY ANY PRODUCTION MATERIAL, FROM POLYPROPYLENE TO GLASS-FILLED POLYCARBONATE.

PROCESS DESCRIPTION

MODEL PREPARATION IS THE FIRST AND ONE OF THE MOST IMPORTANT STEPS IN THIS PROCESS. DEPENDING ON THE FINISH OF THE MODEL, IT SHOULD BE SANDED SMOOTH BECAUSE ALL SURFACE IMPERFECTIONS BECOME APPARENT IN THE SPRAYED SHELL. TYPICALLY, THE MASTER, (SLA, LOM ETC....), MUST BE HAND FINISHED TO THE DESIRED QUALITY BEFORE THE MOLD IS MADE. IN MOST CASES A SILICONE MOLD AND URETHANE REPRODUCTION ARE MADE FOR THE TOOLING MASTER BECAUSE CHANCES ARE THIS MASTER WILL BE DESTROYED.

THE PARTING LINES ARE ESTABLISHED WITH CLAY OR PARTING BOARDS. SLIDES AND LOOSE PIECES CAN BE MADE IN A SIMILAR MANNER TO PROTOTYPE INJECTION MOLDS AND INSTALLED PRIOR TO SPRAYING THE SURFACE. AN ALUMINUM OR STEEL FRAME IS FABRICATED TO ABSORB THE PRESSURES OF MOLDING AND TO ALLOW THE COMPLETED MOLD TO BE INSTALLED IN THE MOLDING EQUIPMENT. THESE MATERIALS WILL ABSORB MOST OF THE COMPRESSION PRODUCED BY THE MACHINE.

AT THIS TIME THE METAL SURFACE IS SPRAYED ON. AFTER THE METAL SURFACE IS APPLIED, WATER LINES AND ANY ADDITIONAL SUPPORTS CAN BE ADDED. NEXT A HIGH STRENGTH ALUMINUM FILLED EPOXY IS POURED IN TO BACK FILL THE MOLD. THIS EPOXY IS SIMILAR TO THE MATERIAL USED FOR THE EPOXY MOLDS.

ANOTHER TECHNIQUE IS TO BACK FILL THE MOLD WITH A LOW MELT METAL ALLOY. THIS MATERIAL HAS EXCELLENT HEAT TRANSFER AND CAN SUSTAIN MORE COMPRESSION THAN THE EPOXY. THE SAME PROCESS IS APPLIED TO THE OTHER SIDE OF THE MOLD. THE MOLD IS POST CURED, SECONDARILY MACHINED AND PUT IN TO SERVICE. THESE MOLDS CAN ALSO BE PLATED TO INCREASE TOOLING STRENGTH.

THE RAPID PROTOTYPE MODEL IS AN IDEAL STARTING POINT TO PRODUCE SPRAY METAL TOOLING. THE LONGEVITY OF THE TOOL IS PROCESS DEPENDENT. LOW PRESSURE OPERATIONS SUCH AS CASTING, BLOW MOLDING OR RIM WILL YIELD MORE PARTS THAN THE HIGHER PRESSURE APPLICATIONS. TURNAROUND TIME FOR PRODUCING A SPRAYED TOOL FROM RAPID PROTOTYPE PATTERN IS BETWEEN TEN DAYS TO THREE WEEKS DEPENDING ON COMPLEXITY OF THE TOOL.

TYPES AND QUANTITIES OF PARTS MADE:

• POLYURETHANE 300 TO 20,000
• POLYUREA 300 TO 20,000
• EPOXY 100 TO 600
• INVESTMENT WAX PATTERNS 500 TO 10,000
• LOW MELT METAL ALLOYS 100 TO 1,500
• POLYURETHANE FOAM 2,000 TO 20,000
• SILICONE RUBBER 10,000+
• INJECTION MOLDING 10 TO 1,000
• RIM MOLDING 1,000 TO 15,000
• BLOW MOLDING 300 TO 500
• VACUUM FORMING 5,000 TO 100,000

INVESTMENT CASTINGS

NUMEROUS RP TECHNOLOGIES ARE APPROPRIATE FOR USE AS INVESTMENT CASTING PATTERNS. THESE MATERIAL DISPLACEMENT CASTING METHODS ARE AMONG THE FIRST INDUSTRIAL PROCESSES EVER DEVELOPED AND ARE THOUSANDS OF YEARS OLD. THE CASTINGS PRODUCED CAN BE EXQUISITELY DETAILED AND INTRICATE. BEESWAX WAS THE FIRST MATERIAL USED FOR PATTERNS, BUT THE PROCESS IS SO ADAPTABLE THAT BEES THEMSELVES HAVE BEEN USED AS PATTERNS TO PRODUCE STUNNINGLY DETAILED GOLD JEWELRY. MORE ENVIRONMENTALLY AND SOCIALLY CONSCIOUS JEWELRY IS A SIGNIFICANT APPLICATION OF RAPID PROTOTYPING-GENERATED CASTING PATTERNS EVEN TODAY. THERE ARE NUMEROUS APPLICATIONS IN INDUSTRY WHERE PARTS ARE PRODUCED IN A VARIETY OF METALS WITH CASTINGS WEIGHING UP TO SEVERAL HUNDRED POUNDS.

THESE PROCESSES TYPICALLY INVOLVE THICKLY COATING, OR INVESTING, A PATTERN WHICH IS MADE OF A MATERIAL THAT MELTS OR BURNS OUT EASILY WITH A MATERIAL SUCH AS CERAMIC, WHICH DOESN'T. THE PATTERN MAY BE EXTENDED TO PROVIDE A GATE INTO WHICH METAL IN A HOT, LIQUID STATE IS POURED. PASSAGEWAYS ARE ALSO PROVIDED TO ALLOW MELTED OR BURNED PATTERN MATERIAL AND AIR TO ESCAPE. THE INVESTED PATTERN IS THEN FIRED IN A FURNACE TO BURN OUT OR MELT THE PATTERN AND FUSE THE CERAMIC INTO A STRONG HOLLOW MOLD. MOLTEN METAL IS THEN POURED INTO THE CERAMIC MOLD. AFTER THE METAL COOLS AND HARDENS, THE MOLD IS BROKEN AWAY TO REVEAL THE FINAL OBJECT. EXTRA GATE MATERIAL IS CUT OFF AND USUALLY THE PART WILL REQUIRE SUBSTANTIAL FINISH MACHINING AND CLEAN-UP.

INDIRECT OR SECONDARY PROCESSES THAT UTILIZE RP-GENERATED PATTERNS

RP-GENERATED PATTERNS CAN BE OBTAINED FROM FUSED DEPOSITION MODELING (FDM) IN WAX, SELECTIVE LASER SINTERING (SLS) IN POLYSTYRENE OR OTHER PLASTICS, AND INKJET TECHNOLOGY IN WAX-LIKE PLASTICS. THESE MATERIALS MAY BE MELTED OR BURNED OUT OF THE INVESTMENT VERY CLEANLY. THE PATTERNS FROM THESE PROCESSES TEND TO BE SMALL TO MEDIUM IN SIZE, AND ESPECIALLY FOR INKJETS, OFFER THE HIGHEST RESOLUTION AND DETAIL.

STEREOLITHOGRAPHY IS ALSO USED TO PRODUCE PATTERNS FOR INVESTMENT CASTING, BUT THE PHOTOPOLYMER MATERIALS USED IN THAT PROCESS ARE MORE DIFFICULT TO BURN OUT THAN THE MATERIALS USED IN OTHERS MENTIONED ABOVE, AND ALSO HAVE A TENDENCY TO EXPAND AND CRACK THE MOLD. TO GET AROUND THESE PROBLEMS, 3D SYSTEMS HAS PRODUCED A SPECIAL BUILD STYLE FOR THIS APPLICATION, WITH THE TRADE NAME QUICKCAST^TM. THE RP-GENERATED PATTERN IS BUILT IN HOLLOW, THIN SECTIONS WHICH TEND TO CRUMPLE DURING BURN OUT RATHER THAN EXPAND AND ALSO RESULTS IN A SMALLER MASS OF PATTERN MATERIAL TO REMOVE. THE PROCESS HAS BEEN DEVELOPED OVER A NUMBER OF YEARS IN PARTNERSHIP WITH LARGE FOUNDRY COMPANIES AND CUSTOMERS.

LAMINATED OBJECT MANUFACTURING (LOM) HAS ALSO BEEN USED FOR INVESTMENT CASTING, ALTHOUGH A MORE TYPICAL APPLICATION IS FOR SAND CASTING. SEE BELOW. THE PAPER MATERIAL USED IN THE LOM PROCESS IS SAID TO SOMETIMES BE DIFFICULT TO REMOVE COMPLETELY FROM THE MOLD, ALTHOUGH THIS IS PROBABLY A STRONG FUNCTION OF THE PARTICULAR GEOMETRY BEING PRODUCED.

DIRECT FABRICATION OF INVESTMENT PATTERNS

SOLIGEN WAS A LICENSEE OF MIT'S 3D PRINTING PROCESS AND USED IT TO PRODUCE INVESTMENTS DIRECTLY WITHOUT PATTERNS AT ALL, BUT THE COMPANY CLOSED ITS DOORS IN 2006. ANOTHER MIT 3DP LICENSEE, Z CORP. INTRODUCED THE ZCAST^TM PROCESS IN 2002, WHICH IS VERY SIMILAR IN CONCEPT TO SOLIGEN'S TECHNOLOGY. THE PROCESS USES THE COMPANY'S PRINTERS WITH SPECIALIZED MATERIALS AND WAS DEVELOPED IN CONJUNCTION WITH GRIFFIN INDUSTRIES. THE METHOD CAN BE USED TO CAST LOW TEMPERATURE MATERIALS SUCH AS ALUMINUM, ZINC AND MAGNESIUM AT PRESENT. FINISHES ARE SIMILAR TO THOSE AVAILABLE FROM SAND CASTING AND PARTS CAN BE FINISH-MACHINED NORMALLY.