Rapid Tooling For Technology For Injection Moulding

speedy beasting For Technology For Injection Moulding fast pricking describes the subroutine where a Rapid Prototyping (RP) model is apply as a see ensample to establish a play cursorily. The Rapid Prototyping model may also be go ford directly as a brute. The two halves of a woodpecker be referred to as the core and cavity.Rapid Tooling (RT) first evolved in the proto(prenominal) 90s with the introduction of RTV silic bingle peckerwooding from SLA original patterns, the mid 90s saw the introduction of investment casting tooling, direct purpose tooling, sand casting and metal SLS tooling. By the late 90s die casting and laminate tooling were introduced.4The difference amid Rapid Tooling and conventional tooling isA time reduction of up to 1/5th is do when employ Rapid Tooling.Rapid Tooling disregard embody less than 5% of the conventional tooling cost.Conventional tools generally occupy a longer life cycle.Larger tolerances for Rapid Tooling than for convention al tooling.1The two types of RT regularity available be Direct and Indirect tooling. Direct tooling is a soft tooling method which uses an RP model directly as a tool for retching whereas indirect tooling is where the RP model is used as a master pattern to execute a mould or die.Reasons for Rapid ToolingWi supple the last 25 years mart trends energize channelised greatly, the product life span of m whatsoever products such as active phones has been rock-bottom drastically with updated models organism released as often as every 3 to 4 months. The variation and complexness of products available has dramatically increased with manufacturers under increased pressure to reduce the time to market for these products. Taking all of this into count it is clear to see that uses need to be prep atomic number 18d cheaper and prontoer, therefore enhancing the need for manufacturers to adopt RT methods.4Two of the to the graduate(prenominal)est degree important things that toolmake rs need to consider atomic number 18 if and when to adopt RT methods. RT has m all gains over conventional tooling methodsSpeed The volume of RT techniques offer an increase in speed comp atomic number 18d to conventional tooling methods. A tool with ribs and bosses may sustain ten-fold operations i.e. CNC programming, CNC milling and EDM however with RT the same tool may be done in one swift operation.2Cost effective for complex tooling With RT methods it is executable to ready complex geometries which would not hard-fought to nonplus by conventional methods.Automation Automation of many of the RT wait ones means tooling whoremonger be build 24 hours a day without any human interaction. This mends productivity, and more tools are produced without the increased amount of manpower it would take to produce the same number conventionally.Human error Human error can be significantly reduced by adopting RT methods and building a tool directly from the master pattern. Convent ional methods may mother incorrect CNC programming or misinterpretation of heel/technical drawings.2Design possibilities It is possible to integrate conformal cool down heads into complex tooling inserts when use RT methods. Tool design is not limited to designing tools which can be conventionally machined.2 cypher Rapid Tooling Vs Conventional shows the typical time savings which can be made by employing RT techniques oppose to conventional machining techniques.Rapid injection molding vs. conventional injection molding icon Rapid Tooling Vs Conventional Tooling3Direct ToolingDirect AIM ToolsDirect AIM (ACES Injection Moulding) is the process whereby tools are urinated directly on an SLA machine. The tools are initially designed apply frankfurter software and the process involves creating a part by SLA which is basically a shell on the underside. The purpose of the shell is to leave a cavity so that each half of the mould can be fill up with a accompaniment actual such as an epoxy rosin, metal or ceramic. By backfilling the mould a thermic conduit is provided for the heat exchange process and it is also possible to add any chilling carry to the mould at this stage.4The develop of the moulds is finished to improve the type of the surface. Using this method it is possible to create up to snow parts with an accuracy of 0.15 0.3mm. usual employment for this type of tool would be for smaller parts, in general prototype injection moulding tools, get-go volume wax injection tooling and low volume foundry patterns.5AdvantagesA relatively fast process a mould can be designed and create within a 2 week period.Cheap process for small tools, such as mobile phone and mp3 player casing. Building large parts on an SLA machine is not cheap.DisadvantagesA dog model of the tool is required as this has to be saved as an stl file in entrap for the SLA machine to build the 3D tool.Low durability the complexity of the tool and thermoplastic substantia l used to build the tool all doctor its life cycle. Moulds produced this way can create as small as 10 parts.Moulds typically degrade gradually with each part that is moulded on it. optical maser shape ToolingTooling inserts made by sintering are initially designed using CAD software and because produced by using DMLS (Direct alloy Laser Sintering) or SLS (Selective Laser Sintering) methods.SLS Rapid SteelRapid trade name pulverize is used to directly build a tool cavity using laser sintering the powder consists of a stainless steel particles coated in a polymer binder. The parts which are produced are called green parts which are then(prenominal) found into a furnace. The furnace removes the polymer binder and infiltrates bronze into the mould to create a dense 60 (steel)/40 (bronze) part. The tooling inserts are then finished and fitted to a bolster.AdvantagesA relatively fast process which lead produce a strong metal tool.Conformal Cooling channels can be built into the tool.Possible to create complex geometries.DisadvantagesFinishing and polishing is required.Poor accuracy.Equipment cost is high. surface limitations, max 200 x 200 x 100mmCopper Polyamide ToolingA Copper and polyamide powder is sintered to form the tool. Only the polyamide particles in the powder are actually sintered. The advantage to this process is the tool strength and heat transfer compared with other methods. Copper provides the tool with these characteristics, delivering the tool to be used at high pressure and temperature.6This method is suitable for several hundred mouldings.5DMLS (Direct Metal Laser Sintering)Using a laser sintering machine, metal in the form of powder is sintered to produce a tooling insert. The two available materials are Bronze and Steel based, the bronze based material offers a higher(prenominal) definition of features than the steel based one.6Laminated ToolingLaminated tooling is very similar to the LOM (Layer Object Manufacturing) process as slic es of a CAD model are replicated by layers of cut sheet metal. The steel laminations are laser cut or cut with a water jet.Tooling inserts are initially designed using CAD software the CAD model must represent the cavity of the tool in order to produce the mould. The slices of the cavity are cut in sheet metal which has a burden someness of 1mm and then bonded, clamped or brazed together. The use of a thick laminate results in a poor surface finish so the tool must be finish machined.3Typical application for this type of tool would be large complex tools and aerospace tooling.2AdvantagesEfficient use of material due to layers being cut to the exact size required.Conformal Cooling channels can be built into the tool easily if required.Standard steel sheet is used, making the process relatively quick and cheap.Good for large tools up to 2000 x 1000 x 500mmDesign of parts can be easily changed by replacing a laminate layer as long as it has not been bonded.DisadvantagesTools grant t o be finish machined to remove the step like features to obtain accuracy.The joints between each lamination provide the tool with a weak link.Part complexity is open upon layer thickness.Indirect ToolingRigid Cast rosin ToolingThis process manufactures a tooling insert using atomic number 13 filled epoxy resin as the tool material. A master RP model is initially manufactured and the part is set up on a split roue. The resin is then cast onto the model which is within a bolster. The resin is then odd to cure, a release coat is applied to the mould, the exclude-off material aloof and the process is repeated for the other half of the mould. When both halves of the mould wear cured, the shut off material is removed and a bolster and ouster pins are added.2,4Typical application for this type of tool would be a small coat tool, low volume RIM (Resin Injection Moulding) tools or low volume press tools. Accuracy of the tool is dependent upon each step within the process so shrink age and deformation must be interpreted into account when reviewing the overall accuracy.AdvantagesQuick to produce, 2-3 days.Cost is typically 40% less than with conventional tooling.7Quick determine on tools is possible.DisadvantagesFlash can occur resulting in more effort required to trim mouldings. trying and slow to mouldFragile and easy to break.Rep arguments are not long lasting.Distortion is possible with larger tools due to exothermic processes.Cast Metal ToolingSand CastingA master pattern is position in Green sand to create a mould, the pattern is removed and the cavity of the mould is filled with resolve metal. The metal is left to cool and the sand mould is broken away to leave a finished casting.Investment CastingA master pattern is created from wax or a material which can be melted. The wax pattern is then dipped in slurry consisting of plaster of Paris, binder and silicon dioxide repeatedly to create a surface on it. The mould is then change up in an oven leav ing the wax to melt away. The consummate mould can then be filled with a molten metal to create the part.Rubber Plaster CastingA master RP pattern is created and shut off, silicone polymer is cast in the shape of the tool. Liquid plaster slurry is poured around the silicone, once cured the silicone is removed. Molten metal is then poured into the plaster mould.8AdvantagesSolid metal tools are produced.Conformal cooling is possible.One master can allow multiple tools.Steel tools can be made but with increased difficulty.DisadvantagesTools may need to be finish machined and polished.Difficult to hold tolerances.http//www.crptechnology.com/sito/images/stories/ElementiFissiHome/rapid-casting.jpgFigure Investment Casting, RP model on left.9Metal Spray ToolingThis method is used to produce soft tooling inserts. A master pattern is produced and shut-off a thin shell of 1-2mm of zinc is sprayed over the pattern, this shell is then removed and backed up with an epoxy resin or ceramic to m ake the mould more rigid. This is then repeated for the other half of the tool. The surface of the metal shell is usually polished and even sealed.Electric Arc SprayingIn this process two conductive metal wires are melted by means of an electric arc. The metal melts, and the molten material is atomised by a sport and propelled on to the surface of the pattern. The molten particles on the pattern rapidly wholeify to form the metal coating of the shell.10High Velocity Oxygen FuelMetal powder particles are injected into a high velocity jet. The jet is formed by oxygen and fuel combusting and warmth and accelerating the molten metal towards the surface of the pattern. Metal coatings produced this way are strong and very dense allowing a thicker coating to be applied to the pattern compared to electric arc nebulizer.11AdvantagesHigh quality surface finish.comparatively quick.Fine detail such as graining can be achieved.Conformal cooling is possible.Large ordered series tools can be produced.DisadvantagesLine of sight limitations impossible to spray undercuts or narrow slots.Surface is porous so may need to be sealed to reduce percolation.Any repairs and modifications are very difficult to undertake.Special equipment and operating environment is required.Figure H.V.O.F process12Electroformed Nickel ToolingNickel Shell ToolingThis method involves a nickel surface being created on an RP model. A master RP pattern is produced and shut-off, the part is then put in an electroplating bath to form a nickel shell on the surface. Once plated, the part is removed from the bath the nickel shell is removed and backed up with a caloricly conductive ceramic material. Cooling channels, typically made from copper can be built into the mould at this time.13Typical application for this type of tool would be large production vacuum forming tools and composite forming tooling for the aerospace industry.AdvantagesDetail from the master model is picked up almost perfectly.Nickel provides a smooth surface which is dense and hard.Low thermal stress compared to metal spray techniques.DisadvantagesSlow process which can take up to 6 weeks to produce a 6mm shell.Line of sight limitationsNickel Vapour Deposition (NVD)This method converts Nickel Carbonyl gas (NiCO4) into a solid Nickel shell. A master pattern is created from aluminium or steel, and placed into a special chamber which heats the pattern up to 110-180oC. Nickel Carbonyl gas is passed over the pattern, and nickel is deposited onto the pattern to create a metal shell. The pattern is then removed from the chamber the shell is backed up and removed from the pattern. This process is then repeated for the other half of the mould.AdvantagesExtremely fast, 0.25mm/hr (20 times instantaneous than electroforming).14A more uniform wall thickness than electroforming.8No stemma of sight limitations.Conformal heating and cooling is possible.DisadvantagesA dangerous process which can be explosive.The master patte rn must be heated evenly.Indirect Sintered Tooling3D Keltool ProcessKeltool is the name apt(p) to the powder metal sintering process which involves the infiltration of a fused metal part with copper alloy.15An RTV mould is created from an SLA master pattern. When the pattern is de-moulded, slurry consisting of A6 tool steel and tungsten carbide is poured into the RTV mould. Once cured this mould is infiltrated with copper and sintered to cure the mould and increase its strength. The completed tool can be machined and has a hardness similar to A6 tool steel.9Using this process it is possible to create a tooling insert, from master pattern to the finished product in under two weeks. Tool life expectancy can be anything between 100,000 to 10,000,000 shots dependent upon material being moulded.9Typical application for this type of tool would be small tooling inserts.AdvantagesGood for complex mould geometry.Extremely fast process.Disadvantages size limitations 6 in all directions.Diff icult to machine detailed designs.Figure 3D Keltool parts16Tool ConsiderationsWhen designing a tool, a number of considerations must be taken into accountWall Thickness. slide Cores.Size and location of runners and ejector pins.Gate design.Size and number of cooling channels if required.Split line position.ShrinkageWall ThicknessIt is possible to create walls with various thicknesses. A wall with an uneven thickness can cause problems for the tool designer, as thicker walls cool much slower than thin walls therefore resulting in greater shrinkage at the thicker sections. A uniform wall thickness will minimise any defects caused by uneven cooling. Shrinkage will also occur at wall intersections (tees).17 slew CoresSliding cores allow undercuts to be made sometimes it may be possible to relocate the split line to reduce the number required. Sometimes it may be a case of re-designing a feature in order to reduce tooling costs. Any additional cores will just increase the overall cost a nd complexity of the tooling insert. Figure Redesigning a feature18 shows a hinge feature which has been redesigned to eliminate the requirement for the sliding core shown on the left.Figure Redesigning a feature18Ejection MethodsEjector pins are placed in the cavity or core of the mould and push the solidify moulding out of the mould. This is the most common method of ejection, the ejector pins are carried in an ejector plate which is in the mould. These pins should be positioned at points with good strength to head off any lasting damage to the part.5Other methods of ejection may use plates or some method of gas or air ejection to ease the part out of the moulding.Gate DesignA Gate is the opening in the mould where the resin will enter from. The design and placement of render is an extremely important factor to consider. Resin is injected into the mould at pressures of up to 20,000 psi. The immense pressure can cause gas to be forced into the liquid resin, which when cooled r esults in bubbles being formed in the solidified moulding. To eliminate this problem it may be necessary to add vents within the mould to allow air to be displaced as the resin is injected.19Gates should be positioned at the thicker areas of the part the thinner areas will drop off heat quicker causing the resin to cure forrader it reaches the thicker areas.Knit lines occur when the flow of resin is split by a core in the mould. Where the resin rejoins there may be a slight defect due to cooling and the two edges not full(a)y merging together to create a smooth blend. This will result in a visible line which may affect aesthetics or structure of the part. A more structured gate placement may improve the resin flow and eliminate any knit lines.17Conformal CoolingCooling channels for Moulds are traditionally drilled in a secondary machining operation. These cooling channels are only able to retrace straight lines, if a complex cooling channel is required, the mould is split into s egments and channels milled into each segment. The segments are then welded back together so the channels align producing a cooling channel which is not straight.20Conformal cooling channels follow the shape of the mould and allow temperature to be distributed uniformly in the moulded material. This method is only available when using RT methods to create a mould.Conformal cooling can save funds when thermal management is extremely difficult via traditional tooling methods. Recent studies have shown a 30-60% reduction in cycle times compared to conventional methods.21Figure Conventional Vs Conformal Cooling18 shows the same mould with traditional drilled channels on the left and conformal cooling channels on the right. The conformal cooling channels follow the curves of the mould closely.Figure Conventional Vs Conformal Cooling18Split LineThe split line is the line at which the two halves of the mould meet. In some cases the tooling may not be precise allowing the mould halves to open and close without any precision. The high pressure injection process will cause resin to creep into any gaps between the mould halves this material is referred to as flash.Strategic positioning of the split line is necessary to improve part quality and to facilitate with ejection.22 shows the same part but with the split line (red line) at diametric locations. On the image on the left, the walls of the part are in the bottom half and are slanting to allow the part to be ejected. This leaves the wall at the base being much thicker. If conventional methods of tooling are used, the doubtful narrow cut may have to be made wider to allow the machine tool full operation resulting in an even thicker wall.19On the image on the right the top half of the tool is the core which forms the walls. This results in walls with a uniform thickness. If conventional methods are used, tooling is made easier as larger sized cutting tools can be used.19http//www.protomold.com/designtips/2006/2006- 05_designtips/images/fig1.jpgFigure Split line at different locations.22ShrinkageThe absolute majority of tooling methods involve a change of phase. A material is transformed from a liquid to a solid or solid to a liquid and back to a solid. In each case, the phase change results in a decrease in volume therefore results in shrinkage.23All of the tooling processes involve some level of volumetric shrinkage therefore some sort of shrinkage compensation is usually given for each process. It is usually a case of measuring the linear shrinkage for a given material in a particular process and then applying a shrinkage compensation factor to any other part dimensions produced this way. A part is intentionally built oversized so that when shrinkage occurs, the part will be the correct size.20In principle this sounds great but in practice it is not so easy to achieve precise dimensions through shrinkage compensation.Case StudiesThermoplastic composite (GMT) forming tooling using thermal s praying Zinc.5The aim of this project was to find a way to reduce the time taken to produce tooling by evaluating a different method using thermally sprayed zinc, backed with ceramic.The GMT beautify pan assembly required 5 parts Main floor, 2 cross beams, battery disaster and lid.The master pattern was machined and thermal sprayed with a 2mm layer of zinc. The shell was then put in a steel bolster and copper cooling channels were added. The zinc shell was then backed with a chemically bonded ceramic. The die was then ready for moulding. Moulding trials took place with a 1000 tonne press.It took 8 weeks to produce using a metal spray tooling technique oppose to the 16 weeks it would of taken using traditional machined tools. The total cost was 80,000 a saving of 170,000.5Feasibility study of arc spray join onto a master RP model.24The model used for this project was a handheld phone. Overall dimensions of the model were 100 x 50 x 20mm. An ABS RP master was fabricated and put in to a bolster, and then arc sprayed to create a shell of 1.5mm thickness.Aluminium epoxy was used to back the shell this took 24 hours to cure. The process was then repeated for the other half of the mould. The surface of the shell was polished to improve surface finishing then it was ready for injection moulding.Tool training costITEMCOST ($)RP Master200 slog500Sand Blasting100MMA resin system500Arc metal spraying800Sprue bushing200Reinforcement block50PVA50Labour ($20/h)20 x 89hrs = 1780TOTAL = $4180Estimated cost of the tool was $4180, a traditional tooling shop quote was between $10,000 -$15,000 for the same tool. An approximate time and cost saving of 50% was achieved, the tool was also completed in less than 2 weeks.Kodak reduces tooling costs.20A project being run at Kodak needed 25 different plastic injection moulded geometries. By using rapid tooling as a method of bridge tooling they reduced lead times by up to 85% compared with CNC/EDM generated tools. By using a composit e aluminium filled epoxy they were able to create tooling inserts capable of moulding in excess of 1000 parts. in some case product development cycles were cut by a year. 20By employing RT methods, Kodak are typically saving about 25% in tooling cost compared with traditional methods. They are able to Test, iterate, retest and make multiple designs far more rapidly. Form, fit and function can be tested with true prototypes which have been injection moulded with the desired end use material.20ConclusionsRapid Tooling is a growing area which still has elbow room for improvement and development. In the future, reducing the cost of tooling will play an important role in enabling smaller runs of parts to be made as well as allowing more product customisation for ecological niche markets. Developments in Rapid Tooling will mean product development can be initiated closer to market entry time meaning manufacturers can gather more up to date market trends before the product is manufactu red.From the research conducted and case studies viewed it is clear to see that time and cost savings can be made and productivity increased when employing Rapid Tooling techniques. The production time of tooling inserts can be shortened by a near fully automatic procedure from start to finish.Rapid Tooling is not however cheap, cost of the RP machine and other machinery such as Arc welding equipment and resins has to be taken into account. The future development of SLA resins and further improvements in Rapid Prototyping machines will only aid in the development of Rapid Tooling.Rapid Tooling still has a lot to offer, this is just the beginning future improvements in CAD software will allow the whole process to become far more efficient.