CRAZY MECH



RAGHU ENGINEERING COLLEGEPermanently Affiliated to JNTUK, Approved by AICTEAccredited by NBARanked AAA by Careers 360Ranked A Grade by AP State Knowledge MissionRanked 63rd among Top 100 Private Engineering Colleges in Indiaby Higher Education Review Magazine.Ranked 92nd among top private Engineering colleges in Indiaby the Week MagazineRanked 14th among 33 promising Engineering Colleges in India by GHRDDEPARTMENT OF MECHANICAL ENGINEERINGIVB.Tech 1st Semester Additive Manufacturing UNIT-IVRAPID TOOLING: Introduction to rapid tooling (RT), conventional tooling Vs RT, Need for RT. Rapid tooling classification: indirect rapid tooling methods: spray metal deposition, RTV epoxy tools, Ceramic tools, investment casting, spin casting, die casting, sand casting, 3D Keltool process. Direct rapid tooling: direct AIM, LOM Tools, DTM Rapid Tool Process, EOS Direct Tool Process and Direct Metal Tooling using 3DP.Day – 35What is rapid tooling?Ans:It is a technique that uses rapid prototyping techniques directly or indirectly to make molding tools for manufacturing processes.It is combination of both rapid prototyping and conventional tooling processes.What is the need of rapid tooling?Ans:The conventional tooling methods used to manufacture quality tools for the manufacturing processes but the tooling processes were very costly and time taking.Because of the long tooling time and heavy cost the lead time of the products used to be very high. Again, if there is any minute change in design of the product the whole set of tooling has to be replaced with a new one expending time, cost and effort.Therefore, there was a need of some tooling technique that would faster the process and this is when conventional tooling techniques were combined with rapid prototyping techniques and bringing rapid tooling into pare rapid tooling and conventional tooling.Ans:Table SEQ Table \* ARABIC 1Conventional toolingRapid toolingTooling time is moreTooling time much shorter (one-fifth of conventional tooling time)Much higher tooling costTooling cost is less (< 5% as compared to conventional tooling)Difficult to incorporate any changes in design.Flexible to any design changes.More tool lifeTool life is lessTighter tolerances can be achieved in conventional tooling.Tolerances are wider than for conventional tools.What are different types of rapid tooling techniques?Ans:Depending on either RP is directly used or indirectly used, there can be two types of tooling process.Indirect toolingIn this process, first a pattern of the object is prepared by some RP technique, from this pattern again a mold is prepared.Some indirect rapid tooling methods are: spray metal deposition, RTV epoxy tools, Ceramic tools, investment casting, spin casting, die casting, sand casting, and 3D Keltool process.Direct toolingIf directly mold of the object is manufactured using the Rapid Prototyping techniques, eliminating the in between step of preparing pattern. Then it is called direct rapid tooling.Some direct tooling processes are: direct AIM, LOM Tools, DTM Rapid ToolProcess, EOS Direct Tool Process and Direct Metal Tooling using 3DPAgain depending on the application of tooling, it can be Soft tooling It can be used for casting single part or for small batch production.The mold material can be plastic, silicone rubber, epoxy resin or some low melting metal alloys.Hard toolingPatterns are fabricated by machining either tool steel or aluminum and the mold is used mostly for metallic parts.These are used for mass production.Figure SEQ Figure \* ARABIC 1 Classification of Rapid tooling processWrite down the difference between hard tooling and soft tooling.Ans:Table SEQ Table \* ARABIC 2Soft ToolingHard ToolingIt can be used to intake multiple wax or plastic parts Patterns are fabricated by machining either tool steel or aluminum and used mostly for metallic partsHigher tooling costLow tooling costTool life is moreTool life is lessLower per piece manufacturing costHigher per piece production costHigh repeatabilityLow repeatabilityLonger lead timeShort lead timeLess curing timeMore curing timeGood for mass productionGood for low volume productionImportant questions:Explain the need of rapid pare direct and indirect pare soft tooling and hard tooling.Day – 36(Indirect soft tooling)Explain the spray metal deposition process.Ans:It is an indirect soft tooling process.By spraying molten metal on a RP model, it is possible to create very quickly an injection mold that can be used to create a limited number of prototype parts. The metal spraying process is operated manually, with a handheld gun or is robotically controlled.An electric arc is introduced between two metallic wires, which melt the wires into tiny metal pressed air blows out the droplets in small layers of approximately 0.5 mm of metal and deposits it on a substrate.The following figure explains the arc spray concept.Figure SEQ Figure \* ARABIC 2 Metal Arc spray techniqueThe process:A master pattern produced by using any Rapid prototyping process.This is mounted onto a base and bolster, which are then layered with a release agent.A coating of metal particles using the arc spray is then applied to the master pattern to produce the female form cavity of the desired tool (refer figure 3).Figure SEQ Figure \* ARABIC 3 Spray metal deposition process – metal deposition on RP patternDepending on the type of tooling application, a reinforcement backing is selected and applied to the metallic shell. Types of backing materials include filled epoxy resins, low-melting point metal alloys and ceramics. Cooling channels are also inserted in the backing to increase the thermal conductivity of the backing.The whole assembly is turned up and the base plate is removed (refer figure 4).Figure SEQ Figure \* ARABIC 4 Spray metal deposition process – backing the moldThe other half of the RP pattern is now kept on the top of it and all the above said processes are repeated to prepare the other half of the mold.Now the molds are separated out and pattern removed.The mold is now ready for production.This method of producing soft tooling is cost and lead-time saving.Figure SEQ Figure \* ARABIC 5 Spray metal deposition process – preparing the second half of spray moldImportant questions:Explain the spray metal deposition tooling technique with neat sketch.Day – 37Explain the Room Temperature Vulcanization (RTV) tooling process.Ans:It is also an indirect soft tooling process.It is mostly used for making flexible rubber molds to be directly used or to be used for making Urethane or RTV rubber patterns for making epoxy and ceramics tools.Vulcanization is a chemical process for converting natural rubber or related polymers into more durable materials by the addition of sulfur or other equivalent curatives or accelerators.The Process:First an RP pattern is manufactured that replicates the final product.Next the pattern is fixed into a holding cell or box and coated with a special release agent (a wax based cerosal or a petroleum jelly mixture) to prevent it from sticking to the silicone.Runner and sprue are attached to it.Liquid silicone RTV is mixed in vacuum chamber and this de-aerated RTV is poured into the box.It is allowed to cure in low temperature.As RTV curing is an exothermic process, it is allowed to cool back to room temperature (12-24 hours).The mold is then extracted and cut along the parting line with a knife or scalpel.Figure SEQ Figure \* ARABIC 6 RTV silicone rubber moldingNow the mold is ready for use. For some applications, this RTV mold is used directly but for some cases like epoxy molds, ceramic molds the RTV rubber mold is used to prepare another RTV silicone or Urethane pattern.The reason for not using the RP pattern directly for preparing these epoxy molds is the RP pattern can’t bear the temperature generated due to curing of epoxy. The curing of epoxy is an exothermic process and it will harm the RP pattern.Urethane Pattern preparation process:The Urethane resin and catalyst are mixed in a vacuum chamber.This mixture is then poured in the RTV mold and allowed to cure.The cast urethane part is collected and further baked in an oven.Finally the rapid tooled pattern is ready.This rapid tooled pattern can be further used for different mold making purposes.Figure SEQ Figure \* ARABIC 7 From RTV mold Urethane pattern preparationFigure SEQ Figure \* ARABIC 8 RTV moldingExplain the process for preparing epoxy tools.Ans:This process is used for manufacturing prototype parts or for limited runs of production parts. So, this too is a soft tooling process.Epoxy tools are used as molds for prototype plastic injection, molds for castings, compression molds and reaction injection moldsThe epoxy tools should be prepared from RP pattern like the previous indirect processes but curing of epoxy is exothermic and it can harm RP pattern hence from the RP pattern another RTV silicone rubber pattern is prepared and the epoxy tools are prepared using this RTV silicone pattern.The process:The fabrication of the mold begins with the construction of a RP model.A RTV silicone rubber mold is prepared against the RP model following the RTV tooling technique and against the silicone rubber mold RTV silicone model is prepared.Then simple frame around the parting line of the silicone rubber model is built.Sprue gates and runners are then added to it.The exposed surface of the model is coated with a release agent and epoxy is poured over the model. Aluminium powder is usually added to the epoxy resin.Copper hose cooling lines can also be placed at this stage to increase the thermal conductivity of the mold. Once the epoxy has cured, the assembly is inverted and the parting line block is removed, leaving the pattern embedded in the side of the tool just cast. Another frame is constructed and epoxy poured to form the other side of the tool. When the second side of the tool is cured, the two halves of the tool are separated and the pattern is removed.Explain the process flow for preparing ceramic tools.Ans:Instead of epoxy, any ceramics can also be cast around a master to produce a tool cavity.Ceramic tools can be employed in plastics processing, metal forming and metal casting.Ceramics are sand based and can be poured over a master pattern to create a mold.The binder system can vary depending upon the applications.The ceramics and binder are mixed under vacuum conditions and system is vibrated to improve packing of the material around the pattern.In making ceramic tools, the amount of water used has to be controlled to avoid excessive shrinkage as the material sets.Recently, attention has been focused on non-shrinking ceramics. These calcium silicate-based castable (CBC) ceramics were initially developed for applications where metal spraying was not suitable.Important questions:Explain the RTV tooling technique with neat sketch.How the epoxy tools are prepared? Explain.Explain the ceramic tooling process.NOTE: The answer to question 3 should be same as that of Question 2 i.e epoxy tooling procedure only replace of epoxy with ceramics.Day – 38Explain the tooling procedure for different types of casting process.Ans:Investment casting:Investment castingis one of the most important molding processes for casting metals.This is used to cast complex and accurate parts. Wax patterns are employed to define the part shape and then are melted away. It is also possible for patterns to be produced from foam, paper, polycarbonate and other RP materials that can be easily melted or vaporized.Two forms of this process are known, Shell investment castingSolid flask investment castingThe Process:First of all a RP pattern is prepared.The pattern is dipped in slurry ceramic compounds to form a relatively strong coating, or investment shell, over it. This is repeated until the shell builds up thickness and strength. The shell is then used for casting, with the pattern being melted away or burned out of the shell, resulting in a ceramic cavity. Molten metal can then be poured into the mold to form the object. The shell is then cracked open to release the desired object in the mold. The investment casting process is ideal for casting miniature parts with thin sections and complex featuresFigure SEQ Figure \* ARABIC 9 Investment casting tools (a) RP pattern being dipped in slurry (b) Repeated dipping process (c) melting of pattern from the mold (d) investment casting of parts Spin casting:This process consists of injecting a material through a central sprue into a mold that is rotated at high speed. Spin casting molds for metal parts are made of heat-vulcanized silicone.The heat that is given out during the fabrication of such molds is too high for most RP patterns. For this reason, the fabrication of a metal part using spin casting consists of several steps. Process steps:First of all a RP master is prepared.A RTV rubber mold is made from the RP master. From this mold, a tin-based metal alloy part is cast and is used as a model for the fabrication of a heat-vulcanized silicone mold. This final mold can produce spin-cast zinc alloy parts that have similar physical strength properties to both die cast Aluminium parts and die cast zinc alloy (Zamak) parts.Sand casting:The sand casting process is often employed for the production of relatively large metal parts with low requirements for surface quality. RP techniques can be utilized to create master patterns for fabricating sand molds. These molds are produced by placing RP patterns in a sand box which is then filled and packed with sand to form the mold cavity. When employing RP techniques, it is easy to build patterns that include compensation for the shrinkage of the castings as well as additional machining stock for the areas requiring machining after casting. The other benefits of employing RP techniques are significantlyreduced lead-times and increased pattern accuracy.Figure SEQ Figure \* ARABIC 10.Sand casting processDie casting:Die casting is a metal casting process that is characterized by forcing molten metal under high pressure into a mold cavity. The die casting method is especially suited for applications where large quantities of small- to medium-sized parts are needed with good detail, fine surface quality and dimensional consistency. Most die castings are made from non-ferrous metals, specifically zinc and aluminum. The level of versatility offered by die casting has placed it among the highest volume products made in the metalworking industry.The process starts with a RP pattern using any of the RP technique. (SLA is mostly preferred)Form the RP pattern ceramic tooling is prepared.Against this ceramic tooling, the castings of required metal are prepared.Important Questions:Explain the tooling methodology for different casting processes.Day – 39Explain the 3D keltoolprocess.Ans: The 3D Keltool process is an indirect hard tooling method.This process is based on a metalsintering process introduced in 1976. The 3DKeltool process converts RP master patterns intoproduction tool inserts with very good definition and surface finish.There are two possible ways of this process. Same generation – It uses a negative shape of the final part i.e the core and cavity to generate the mold cavity.Reverse generation – It uses a pattern i.e positive shape of the final part i.e the pattern of the part is used to generate the mold cavity.Same generation:This process starts with a RP model of core and cavity inserts. The shape of the core and cavity is reverse or negative shape of the final part. Hence called negative model.From this negative model, a positive RTV silicone rubber mold is produced by the RTV silicone rubber tooling process (refer 2nd image in figure 11).This rubber mold is now filled with a mixtureof powdered steel, tungsten carbide and polymerbinder with particle sizes of around 5 mm toproduce ‘green’ parts (powdered metal heldtogether by the polymer binder) duplicating thecore and cavity (refer 3rd image in figure 11).These green parts are then fired in a furnace to remove theplastic binder and sintering the metal particlestogether (refer 4th image in figure 11)..Now the sintering process causes some vacant space in the part (70 per cent dense inserts). So, infiltrating the sintered parts with copper in a second furnace cycle is done to fill the 30 per cent void space.Finally, finishing of the core and cavity is done.Figure SEQ Figure \* ARABIC 11 3D Keltool processReverse generation:This process starts with a RP pattern that resembles the final part rather than core and cavity is preparedi.e the positive shape of the final part.Against this RP pattern a RTV silicone mold is prepared by the RTV tooling method i.ethe negative shape of the final part (refer 2nd& 3rd image in figure 12).Then a positive silicone model is prepared from the RTV mold.This silicone mold is now kept in a box and that box is filled with a mixture of powdered steel, tungsten carbide and some polymer binder to produce ‘green’ parts duplicating negative shaped pattern (refer 4th image in figure 12).These green parts are then fired in a furnace to remove the plastic binder and sintering the metal particles together.Now the sintering process causes some vacant space in the part so infiltrating the sintered parts (70 per cent dense inserts) with copper in a second furnace cycle is done to fill the 30 per cent void space.Finishing of the core and cavity is now done.Figure SEQ Figure \* ARABIC 12 Same generation and Reverse generation in 3D Keltool processNote: Even though the reverse generation takes extra two steps, it is preferred over the other. The reason is the RP pattern needs to be finished before using it and finishing a negative pattern (as used in same generation)is more difficult and time taking than a positive one (as used in reverse generation) and hence increases the lead time of the tooling process. Important questions:Explain the 3D Keltool process.Day – 40What is the need of direct rapid tooling techniques?Ans:Indirect methods for tool production as described in the previous section necessitate a minimum of one intermediate replication process. This might result in a loss of accuracy and could increase the time for building the tool. To overcome some of the drawbacks of indirect methods, some RP apparatus manufacturers have proposed new rapid tooling methods that allow injection moulding and die-casting inserts to be built directly from three-dimensional CAD models.What are the different categories of Direct Rapid Tooling?Ans:According to their application, direct RT processes can be divided into two main groups.Firm tooling or Bridge tooling or soft tooling:The first group includes less expensive methods with shorter lead-times that are appropriate for tool validation before changes become costly. Direct RT methods that satisfy these requirements are called methods for firm tooling or soft tooling. Sometimes these are also known as ‘bridge tooling’ as these processes are believed tofill the gap between soft and hard tooling. As these tools are capable of short prototype runs of approximately 50 to 100 parts using the same material and manufacturing process as for final production parts. Some direct soft tooling examples are: Direct AIM, LOM tools with polymer sheets, DTM tools with copper PA.Hard tooling:The second group includes RT methods that allow inserts for pre-production and production tools to bebuilt. RP apparatus manufacturers market these methodsas ‘hard tooling’ solutions. Currently availablesolutions for ‘hard tooling’ are based on the fabricationof sintered metal (steel, iron and copper) powder insertsinfiltrated with copper or bronze (DTM RapidTool) process, EOSINT metal from EOS, three-dimensionalprinting of metal parts from Soligen.e.g. LOM Rapid tools (Laserform), EOS direct tooling, metal tools with 3D printing. Explain the direct AIM process.Ans:It is a direct soft tooling method.Direct AIM is direct AECSInjection Moulds where AECS refers to Accurate Clear Epoxy Solid.Stereolithography is used to produce epoxy inserts for injection mould tools for thermoplastic parts As the temperature resistance of curable epoxy resins available at present is up to 200°c and thermoplastics are injected at temperature as high as 300°c. Accordingly specific rules apply to the production of this type of projection tools.Using a 3D CAD package, the injection mold is drawn. Runners, gates, ejector pins and clearance holes are added and mold is shelled to a recommended thickness of 1.27mm. The mold is then built using accurate clear epoxy solid style on a Stereo lithography machine. The supports are subsequently removed and the mold is polished in the direction of draw to facilitate part release. To impart strength the back of the insertsis filled with a mixture made up 30 per cent byvolume of aluminium granulate and 70 per cent of epoxy resin.To remove the maximum amount of heat from the tool and reducethe injection molding cycle time, copper watercooling lines are added.The cooling of the mold is completedby blowing air on the mold faces as they separateafter the injection molding operation. Advantages:It is suitable for molding up to 100 parts.Disadvantages:Number of parts that can be obtained using this process is dependent on the shape and size of the molded part as well as skills of good operator who can sense when to stop between cycles to allow more cooling.Process is slightly more difficult than indirect methods because finishing must be done on internal shapes of the mold.Also draft angles of order up to one and the application of the release agent in each injection cycle are required to ensure proper part injection.A Direct AIM mold is not durable like aluminum filled epoxy mold.Injection cycle time is long.Day – 41Explain the LOM tool process.Ans:This is another method that is quite promising for RT applications. The process applies metal laminated sheets with the Laminated ObjectManufacturing (LOM) method.The sheets can be made of steel or anyother material which can be cut by the appropriate means, for exampleby CO2 laser, water jet, or milling, based on the LOM principle.The CAD 3D data provides the sliced 2D information for cutting thesheets layer by layer. However, instead of bonding each layer as it iscut, the layers are all assembled after cutting and either bolted orbonded together.Some new materials based on epoxy or ceramic capable of withstanding harsh operating conditions have also been developed.Polymer sheets: These sheets consist of glass and ceramic fibres in a B-staged epoxy matrix. Parts made with this material require post curing at 175oc for one hour. Once fully cured they have good compressive properties and heat deflection temperature of 290oc.Ceramic sheets: Two ceramic materials have been developed for LOM, a sinterable AIN ceramic and a silicon infiltrableSiC ceramic. Both materials are mixed with 55% by volume of polymeric binder.The ceramic process is less advanced and requires more software and hardware modifications to the LOM machine.Explain the DTM tool process.Ans:It is a technology invented by the DTM Corporation to produce metal molds for plastic injection molding directly from the SLS Sinterstation.The molds are capable of being used in conventionalinjection molding machines to mold the final product with thefunctional material.The CAD data is fed into the Sinterstationwhich bonds polymeric binder coated metal beads together using theSelective Laser Sintering (SLS) process. Next, debinding takes placeand the green part is cured and infiltrated with copper to make it solid.The furnace cycle is about 40 hours with the finished part havingsimilar properties equivalent to aluminum. The finished mold can be easily machined.Shrinkage is reported to be no more than 2%, which iscompensated for in the software.The latest materials developedfor the RapidTool process of producing metal partsby SLS are LaserForm and copper Polyamide(PA).Each of these materials requires different processing techniques as given below:LaserForm:This is a powder made of 420 stainless-steel-based particles, coated with athermoplastic binder. These undergo sintering, debindingand then infiltration with bronze to produce final Laser-Form inserts are 60 per cent stainless steel and 40 per cent bronze fully dense parts, which can be finished by any technique, including surfacegrinding, milling, drilling, wire erosion, EDM, polishing and surface plating.Copper PA:This is a metal–plastic composite designed for short-run tooling applications involving several hundred parts (100–400 parts) from common plastics. After the SLS process no furnace cycle is needed. Only subsequent finishing operations like sealing of the insert surfaces with epoxy, finishing them with sandpaper and finally backing up the shell inserts with a metal alloyis necessary before integration of the inserts in the tool base. The molds are capable of being used in the conventional injection molding machines to mold the final product with the functional material.Explain the EOS direct tool process.Ans:The Direct Metal Laser Sintering (DMLS) technology was developed by EOS.The process uses a very high-powered laser to sinter metalpowders directly. The powders available for use by this technology arethe bronze-based and steel-based materials. Thesemetal powders are selectively sintered in a specially developed machine. The sintered parts are porous and usually must undergo infiltration with an epoxy resin in order to increase their strength. Bronze is used forapplications where strength requirements are not crucial. Upon sinteringof the bronze powder, an organic resin, such as epoxy, is used toinfiltrate the part. For steel powders, the process is capable ofproducing direct steel parts of up to 95% density so that furtherinfiltration is not required. After infiltration, further polishing of the part surfaces is possible to achieve the quality required for injection molding inserts.The Direct-Tool process is mainly utilized for rapidly producing complex inserts, the surfaces of which cannot be machined directly. The process is a viable alternative for prototype and pre-production tooling applications, requiring the manufacture of up to a few thousand parts in common engineering plastics.Explain the direct metal tooling using 3DP.Ans:This RT process uses 3Dimensional Printing techniques to build tooling inserts in a range of materials including stainless steel, tungsten and tungsten carbide fortooling of plastic injection molding parts, lost foam patterns andvacuum forming. This technology uses an electrostatic ink jet printhead to eject liquid binders onto the powder, selectively hardeningslices of an object a layer at a time. The process allows the fabrication of parts with overhangs, undercuts and internal volumes as long as there is an escape route for the unused loose powder. The production of metal parts includes the following steps:A fresh coat of metal powder isspread on top and the print head deposits a binder liquid to the powder.Building starts by combining powder and binderThe process repeats until the part is completedSintering the printed parts is done in a furnace to increase their strengthInfiltration of the sintered parts with a low melting point alloy to produce fully dense partsTooling produced by this technology for use in injection molding have reported withstanding pressures up to 30 000 psi (200 MPa) and surviving 100 000 shots of glass-filled nylon.The 3DP process can be easily adapted for production of parts in a variety of material systems, e.g. metallic/ceramic compositions with novel material properties.Home work:Rapid tooling videos study and JNTUK questions1. Explain the process of RTV epoxy tooling. Write advantages, dis-advantages and applications of it.2. Explain about ceramic tooling process.3. Classify direct rapid tooling method. 4. What are the steps involved in production of inserts using 3D Keltool process. ................
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