Technology for Plastic Mold Tooling - Direct Metal Deposition

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This whitepaper highlights the benefits of DMD(Direct Metal Deposition) technology in mold cycle time reduction. It presents a comparative analysis conducted for cycle time performance of a mold consisting of a conventionally machined tool steel insert to a mold fitted with a Chromium Copper insert with a coating of tool steel deposited by the DMD process.

Transcript of Technology for Plastic Mold Tooling - Direct Metal Deposition

  • 1. Technology for Plastic Mold Tooling -Direct Metal Dep sition

2. AbstractAbbreviationsTable of ContentsPlastic Injection Mold ToolingMoldflow AnalysisDirect Metal Deposition (DMD)Evaluation of DMD Technology for Mold ProductivityComparative Analysis Steel Mold vs. Copper Mold coated withH13 Steel by DMDConclusionReferencesAuthor Info3345689101111 2014, HCL Technologies. Reproduction Prohibited. This document is protected under Copyright by the Author, all rights reserved. 3. AbstractTechnology for Plastic Mold Tooling - Direct Metal Deposition | 3The development of various plastic materials and manufacturing processes in the last century has stirred arevolution in product development. The majority of plastic components are made through injection moldingand extrusion processes. One of the key aspects of the injection molding industry is the design and manufac-tureof the molds. Conventional mold making consists of extensive machining and assembly operations. But,prior to mold design, the part model can be analyzed with Finite Element Analysis (FEA) software such asMoldflow. The analysis results are utilized to check the molten plastic feeding and part cooling systems,pprreeddiicctt the process parameters and trouble shoot for molding defects. An exciting new technology in toolmanufacturing today is the Direct Metal Deposition (DMD) process, marketed by DM3D Technology LLC, pre-viouslyknown as Precision Optical Manufacturing (POM), Michigan. The DMD process utilizes a high powerlaser to construct or repair a metal part, by spraying the metal powder over a molten metal pool, thuscreating a dense, high quality part. DMD can be used to deposit a layer of tool steel over a high conductivitymetal such as Chromium Copper in the mold insert. This approach can enhance the transfer of heat from themold and effectively reduce molding cycle time.Until recently, the benefits of DMD technology in mold cycle time reduction had not been evaluated. Thispaper presents a comparative analysis conducted for cycle time performance of a mold consisting of a con-ventionallymachined tool steel insert to a mold fitted with a Chromium Copper insert with a coating of toolsteel deposited by the DMD process.AbbreviationsSl.No12345678910Acronyms Full FormDMDPOMCADCAMCAEEDMDDMMEEHASCOMPAMPIDirect Metal DepositionPrecision Optical ManufacturingComputer Aided DesignComputer Aided ManufacturingComputer Aided EngineeringElectro Discharge MachiningDDeettrrooiitt MMoolldd EEnnggiinneeeerriinnggHasenclever GmbH + Co KGMoldflow Plastic AdvisorMoldflow Plastic Insight 2014, HCL Technologies. Reproduction Prohibited. This document is protected under Copyright by the Author, all rights reserved. 4. Plastic Injection Mold ToolingTechnology for Plastic Mold Tooling - Direct Metal Deposition | 4Injection molding is a process in which plastic is melted and forced into a mold in a molding machine, andcooled to form a part. An injection mold is an assembly of steel plates consisting of mainly two halves withimpressions or cavities of the part to be molded. The mold has two halves representing the inside surfaceknown as the core and the outside surface called the cavity. Figure 1 shows a mold for a five sided thin wallContainer Box part in a closed and open position. The part impressions are usually machined on high qualitytools steel inserts and assembled in a mold base made of carbon steel such as mild steel.Figure 1: Injection Mold in closed and open positionOther components in the mold base include the guiding elements such as guide pillars and bushes, fasteners,support columns, a register ring for locating the mold in the molding machine, coolant connectors, and theplastic feed system. The feed system consists of a sprue bush, a series of machined channels called runnersand a narrow section called the gate through which the molten plastic enters the cavity. Some molds havehot runner systems for improving material efficiency and part quality. The ejection system includes ejectorpins, pillars and bushes for movement and return pins to push back the pins after the part is ejected. Varioustypes of mold cooling systems include drilled holes, baffles and bubblers in core aanndd ccaavviittyy iinnsseerrttss..Molding machines essentially consist of an injection unit with a barrel and heater bands for melting theplastic material, platens for clamping the molds, toggle and hydraulic mechanisms for mold opening andclosing, and a control unit as shown in Figure 2. These machines are classified generally by their clampingtonnage such as 30 tons, 2000 tons, etc. Some of the generally used plastic materials are Polypropylene (PP),Nylon, Polycarbonate (PC), Poly Vinyl Chloride (PVC), Acrylonitrile Butadiene Styrene (ABS), Polystyrene (PS),Acrylic, and Polyethylene (PE), either in plain form or mixed with filler materials such as glass or talc, mixed inaa ratio of 10%-30%. Material properties that are important for mold design and the molding process includetypes of material (amorphous or crystalline), melting temperature (high or low) and shrinkage (high or low). 2014, HCL Technologies. Reproduction Prohibited. This document is protected under Copyright by the Author, all rights reserved. 5. Technology for Plastic Mold Tooling - Direct Metal Deposition | 5Figure 2. Mitsubishi 120mj Molding Machine at the University of LouisvilleUndoubtedly, mold design and manufacture is the most critical aspect in the molding industry. Mold designand product design are highly interactive activities. The complexity in part geometry along with functional andappearance requirements throws up many challenges to mold designers and tool makers. The primary goalis to develop a part which can be tooled and molded at an optimum cost. It is estimated that industries in theU.S. spend around $12 billion (POM, 2001) every year on injection mold tooling. Conventional mold makingmethods involve activities like machining, heat treatment, surface finishing and assembly operations, involv-ingexpensive machinery and labor.WWiitthh the advent of CAD/CAM/CAE software, mold design and documentation time has been drasticallyreduced. Many of the popular 3-dimensional softwares offer Mold Design packages.These packages have thedata available for mold base standards such as DME, HASCO, Futuba and Stark. Prior to the design of themold, the part can be analyzed with FEA packages in order to determine the feed system, cooling network andprocess parameters. Different molding defects can be diagnosed and the mold design can be optimized. Themost popular analysis software for plastic molded parts is Autodesk Simulation Moldflow, from AutodeskCCoorrppoorraattiioonn.. This software was previously known as Moldflow from Moldflow Corporation, USA until May2008.Moldflow AnalysisThe Moldflow package has a number of modules for analyzing various aspects of a plastic part, mold, and themolding process. It has a database for more than 500 grades of materials of all the major plastic manufactur-ers.Analysis can be performed with MPA (Moldflow Plastic Advisor), which is a simple package for designersat the early stages of part or mold design. CAD models can be directly brought into MPA without the mesh andcan be analyzed to check confidence of fill, gate locations, identify the position of knit (weld) lines, air traps,and to check the alternative part designs. However, more detailed flow and advanced analyses can be per-ffoorrmmeeddonly with MPI (Moldflow Plastic Insight), which needs a meshed, mid-surface model of the part. CADmodels in the IGES (Initial Graphics Exchange System) or other suitable forms can be brought in to MPI. MPIhas a mid-surface and meshing generator to create the finite element model. The modeler in MPI also can beused to create surfaces, mesh, feed systems, cooling and mold models. 2014, HCL Technologies. Reproduction Prohibited. This document is protected under Copyright by the Author, all rights reserved. 6. Technology for Plastic Mold Tooling - Direct Metal Deposition | 6Some of the general modules of Moldflow are MF/FLOW, MF/COOL, and MF/WARP. MF/FLOW performs aMulti-Laminate Filling Analysis, which uses finite difference algorithms with logic that molten plastic fills in thecavity layer by layer. Results of MF/Flow are referred to for conducting further analyses such as cooling andwarpage. Boundary conditions for the flow analysis include an Injection location node in the meshed model.The meshed model for a Container Box part with sprue feed system is shown in Figure 3.The fill time simula-tionfor this part is shown in Figure 4.Figure 3. Mid-surface mesh model of container box Figure 4. Plastic fill time simulationFill Time (sec)After being filled with molten plastic, the cavity needs to be packed to compensate for the volumetric shrink-age,which can be as high as 30% of the part volume. The packing of the mold cavity can be analyzed throughMulti-Laminate Packing Analysis. If volumetric shrinkage is too high, sink marks may appear at thickersections of the part like ribs and bosses. Variations in shrinkage can also lead to the warpage, which is charac-terizedby bends and bows in the molded part. MF/COOL is a type of heat transfer analysis to analyze the tem-peraturedistribution in the mold with cooling channels. Outputs of this analysis can be used to determine theeffectiveness of the cooling line location, size of the mold, and performance of inserts made of high conduc-tivemetals such as Beryllium Copper with respect to the cycle time. The challenge in using high conductiveBeryllium Copper or Chromium Copper is that these metals are comparatively soft and have low wear resis-tanceduring the molds life. Therefore, they need to be covered with a layer of high strength tool steel to actas contact surface in the mold core or cavity inserts. One of the latest technologies for depositing tool steelover high conductive metals is Direct Metal Deposition (DMD).Direct Metal Depos