Potential of Laser Engineered

Materials and Manufacturing Processes ,24:750–753,2009Copyright ©Taylor &Francis Group,LLCISSN:1042-6914print/1532-2475onlineDOI:10.1080/10426910902809776Potential of Laser EngineeredNet Shaping (LENS)TechnologyI.Palˇc iˇc 1,M.Balažic 2,felner 3,and B.Buchmeister 11Laboratory for Production and Operations Management,Faculty of Mechanical Engineering,University of Maribor,Maribor,Slovenia2Laboratory of Cutting,Faculty of Mechanical Engineering,University of Ljubljana,Ljubljana,Slovenia3EMO Tool-Shop,Celje,SloveniaThis article has a twofold purpose.The first part deals with introduction of innovative high technology laser engineered net shaping (LENS)that offers a breakthrough in manufacturing,maintaining,and repairing products.It also presents many possibilities for the use of LENS technology,especially in the tool-making industry and for medical purposes.The second part presents a comparison of a product manufactured by conventional technologies and the same product manufactured by LENS technology.The product is a titanium alloy medical implant.Keywords Hardness;Laser;Layer manufacturing;LENS technology;Medical implant;Medicine;Microstructure;Nail;Rapid manufacturing;Rapid prototyping;Rapid tooling;Titanium;Titanium alloy;Tool;Tool-making.1.IntroductionAt least two conditions have to be fulfilled to manufacture a product with a high added value.We need a sophisticated technology that offers possibilities to manufacture the most demanding products from different materials,and we need business ideas to apply the technology in areas that contribute the most to ser engineered net shaping (LENS)is one of these sophisticated technologies,and it has many advantages in comparison with conventional technologies and many areas for application.This article will,therefore,focus on description of the LENS technology and its applications in different areas,especially in tool-making industry and for medical purposes.2.LENS technologyLayer manufacturing techniques,also called rapid prototyping techniques ,have about 20years of history.These techniques directly fabricate,layer by layer,physical models from 3-D solid models produced in computer-aided design (CAD)[1].Layer manufacturing technology is the key technology of the rapid prototyping system,and it allows the fabrication of three-dimensional parts layer by layer.Selective laser sintering (SLS),LENS,3D welding,microcasting,3D cladding,and shape deposition manufacturing (SDM)are some important processes for the RP system [2,3].One of the most promising is LENS technology that is used to fabricate fully dense metal parts directly from CAD solid models.LENS is a laser fabrication technique developed at Sandia National Laboratory forReceived February 15,2008;Accepted August 15,2008Address correspondence to Assistant Professor Dr.I.Pal ˇc i ˇc ,Facultyof Mechanical Engineering,University of Maribor,Smetanova ulica 17,Maribor 2000,Slovenia;E-mail:iztok.palcic@uni-mb.si producing components that are difficult or impossible to process through conventional metal forming techniques.The process is similar to traditional laser-initiated rapid prototyping technologies such as stereolithography and selective laser sintering in that layer additive techniques are used to fabricate physical parts directly from CAD data.By using the coordinated delivery of metal particles into a focused laser beam,a part is generated.The laser beam creates a molten pool of metal on a substrate into which powder is injected.Concurrently,the substrate on which the deposition is occurring is moved under the beam/powder interaction zone to fabricate the desired cross-sectional geometry.Consecutive layers are additively deposited,thereby producing a three-dimensional part [4–6].This process exhibits enormous potential to revolutionize the way in which metal parts,such as complex prototypes,tooling,and small-lot production parts,are produced.The result is a complex,fully dense,near-net-shape part (Fig.1).LENS has many potential applications,including rapid prototyping,rapid tooling,and dissimilar metal joining.Samples have been successfully manufactured from a variety of materials including steels,stainless steels (SS),nickel-based alloys,refractory metals,tool steel alloys,titanium,and intermetallic compounds.Fabrication of bi-material joints as well as functionally graded materials through the use of LENS has also been ser processing has the benefit of concentrating much energy in the spot,but the drawback is its high cost [7,8].LENS is a technology that is gaining in importance and is in early stages of commercialization.Its strength lies in the ability to fabricate fully-dense metal parts with good metallurgical properties at reasonable speeds.Much research is still being done in the boratories.There are only three installations of LENS in Europe:U.K.,France,and Slovenia—a consortium of companies and R &D institutions within the Toolmakers cluster of Slovenia.750POTENTIAL OF LENS TECHNOLOGY751Figure1.—LENS technology in action.The main advantages of LENS technology are:1)Fabrication of complex products,novel shapes,hollowstructures,and material gradients that are not otherwise feasible;2)Efficient approach that reduces production costs andshortens time-to-market for high-value components; 3)Excellent material properties,possibility to combinedifferent materials,significantly reduced material waste;4)Low heat input—low distortion and heat-affected zone.Since mechanical properties are dependent upon the microstructure of the material,which in turn is a function of the thermal history of solidification,an understanding of the thermal behavior of the fabricated part during the LENS process is of special interest.Unlike other laser processing techniques,LENS uses low power lasers which produce a very small heat-affected zone;5)Direct manufacturing from CAD to part,computer-supported process with closed loop for precision deposition control.3.Where and how can LENS technology be used? In this part we would like to present the use of LENS technology for tool-making and medical purposes and present its advantages over conventional processing technologies such as turning,milling,and drilling.The tool-making industry produces highly-complex tools needed for manufacturing of products in automotive,aerospace,and other industries.One of the most promising applications for LENS is the manufacturing of plastic injection tools and die cast tooling.LENS enables building complex shapes. One of the biggest problems with tools is the building of cooling channels that follow the contour of the mold and cavity.Cooling is extremely important because it can reduce part cycle time by increasing the removal of heat from the mold.That enables more rapid cooling of the part,which can be ejected sooner.More rapid cooling of selected areas of the mold can reduce part distortion and improve accuracy.LENS technology enables building these cooling channels in a variety of extremely sophisticated shapes.LENS is a highly targeted metal deposition technology that produces a veryfine weld bead,exposing the component to far less heat than conventional methods.The resulting “heat-affected zone”with LENS is smaller and more controlled so that the repair process does not damage the underlying part.And,since a LENS deposit is muchfiner and more precise than welding techniques,far lessfinishing work is required.The superior material properties with LENS extend component life,reducing life cycle costs. Microscopy studies show the LENS parts to be fully dense with no compositional degradation.Mechanical testing reveals outstanding as-fabricated mechanical properties. The process also improves designflexibility by allowing novel geometries,structures,and material gradients. Tools are often subject to wear in specific areas. Since LENS is a highly targeted solution that can precisely add material to worn or damaged areas with minimal heat effect it enables repairing of the most sensitive thin-walled components.The LENS system integrates well with conventional processes to create unique hybrid manufacturing solutions.For instance,LENS can be used to enhance an existing component by adding layers of wear-resistant material or other surface treatments.LENS technology also found its place in medicine. With its fast turnaround times and the design freedom it affords,LENS is an emerging solution for medical device manufacturing,including the development,prototyping, and production of specialty surgical instruments and prosthetic implants,such as hip,knee,and spinal prosthetics. These products,built with LENS technology,have much better characteristics,e.g.,thicker material structure,less corrosiveness,less porosity which leads to much smaller possibility of bacterial infection.Medical implants have to be extremelyflexible tofit in a specific patient.It is also important that the weight of these implants is as small as possible while still ensuring proper material characteristics. This is the reason that thin-walled parts are desired.It is extremely hard(if not impossible)to produce thin-walled implants with conventional technologies;therefore,LENS technology is a much better solution.4.Experiment with medical T i-implantThe last part of the article represents an example of a modern medical implant.Generally,medical implant products have to satisfy strict requirements regarding materials,machining technologies and their functionality. They are regulated and classified in order to ensure safety and effectiveness in the patient.A favorite biomaterial used for biomedical applications is titanium alloy Ti6Al4V due to its combination of the most desirable characteristics including immunity to corrosion,biocompatibility,shear strength, density,and osteointegration.The excellent chemical and corrosion resistance of titanium is to a large extent due to the chemical stability of its solid oxide surface layer to a depth of10nm.Ti6Al4V is,therefore,one of the most widely used titanium alloy in industrial applications[9,10].For thefixation of the radius bone head(caput radii) fractures in the elbow joint a special Intramedullary(IM)752I.PAL ˇCIˇC ETAL.Figure 2.—(a)Improved conventional IM nail with sieve-like head;(b)Preliminary design of IM nail with attendance instruments.nail had been developed.The nail prototypes were manufactured with conventional and LENS technology.Material used for machining of the IM nail is titanium alloy Ti6Al4V in classical form (bars)for conventional processing technologies and in powder form (45 m grain size)for LENS technology.With conventional machining technologies (turning and drilling)we get a full nail form with two lines of fixation screw holes on the head of the nail and two stabilizing screw holes in the lower part of the nail [Fig.2(a)].For this design attendance instruments had to be developed [Fig.2(b)].Due to incapability of fulfilling predicted biofunctionality requirements,the conventional preliminary design had to be changed and improved.The sievelike nail head form had been developed,and cadaver biofunctionality test results fulfilled required demands.The nail produced with LENS technology is hollow,thin-walled,and with two stabilizing screw holes in the lower part.Fixation of the fragments of the caput radii is done with drilling screw holes during the surgical operation to the head of the nail coincidentally in the best possible way to gain primary stabilization of the fracture.This is possible because of the thin walls of the nail (1mm)and specially developed drilling tools [Figs.3(a)and(b)].Figure 3.—(a)Cross-section of LENS prototype IM nail;(b)LENS IM nailbefore and after final finishingprocess.Figure 4.—Hardness of LENS and conventional IM Ti nail trough cross-section.Conventional IM nail prototypes had been produced and tested in the Laboratory of Cutting (LABOD)at the Faculty of Mechanical Engineering,University of Ljubljana.LENS IM nails had been produced in EMO tool-shop and tested in LABOD.IM nail prototypes produced with both technologies (conventional and LENS technology)were tested with computer simulations (Finite Element Analysis or FEM)which have shown both designs will withstand predicted forces acting on the nail in the bone.For adequate material properties comparison,a full IM nail with LENS technology had been built.Hardness in HV of both prototypes of IM nail through cross-section is presented in Fig.4.As seen in Figs.5(a)and (b)the size of crystal grain is more regular and the order structure is better at IM nail produced with LENS technology.From this,we can assume better mechanical properties of material produced with LENS technology.This was also proved with tests regarding hardness and biofunctionality of the IM nail.Further tests based on microstructure research will be done and presented in the future.5.ConclusionThe IM nail produced with LENS technology has more advantages for practical usage than a conventional titanium IM nail.It is lighter due to its hollow structure,easier to insert,and the operation procedure is less complicatedPOTENTIAL OF LENS TECHNOLOGY753Figure5.—(a)Microstructure of conventional Ti6Al4V;(b)Microstructure of LENS Ti6Al4V.with no complex attendance instruments needed.The LENS IM nail has better mechanical properties than conventional titanium IM nail.The surface of the LENS IM nail could stay rough which consequently improves its stabilization in the 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