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LASER and LASER based manufacturingOn February 23, 2011, the Materials Processing group of theCSIR’s National Laser Centre (NLC) held an open day toillustrate what laser technology can do for South Africanmanufacturers and to showcase the group’s achievements in the10 short years since its inception. Far from being research-bound,Materials Processing is one of the most industrially active groupsin the CSIR, not only in terms of application development, but alsooffering a component processing service to make best use of its laserinvestments. Peter Middleton reports.When I was a child, lasers were all about futuristic weapons of virtualdestruction. At university, they were straight-line measuring toolsand, in my current travels, laser-cutting seems to have mushroomedinto the preferred solution for precision cutting of flat plate – a hightechflame cutter. Perhaps we get used to the technology bar beingcontinually raised, but I can’t help feeling a little disappointed thatthe technology has not developed towards those exciting expectationsimplanted in my childhood.But lasers remain an exciting technology and the NLC MaterialsProcessing group’s open day, although as far away from a child’sfantasies as you can imagine, did not disappoint.On arrival I was immediately drawn to the Unit’s 5,0kW CO 2laser,which although on-show was being used for a production run of aBMW undercarriage component. The niche of this particular laseris its 3D capability. It is in routine use for small production runs for:3D edge-trimming and final hole cutting of pre-pressed parts. Thebig advantage of machining a 3D-pressing is that perfect consistencycan be achieved every time. I was drawn to ask about the jigginginvolved to achieve this level of precision. Specialised softwareavailable at the NLC provides a jig design and manufacturingcapability. Jig designs for the laser cutting bed are generated togive best access to the cutting paths required. The jigs are thenmanufactured by the laser, which profiles sets of flat interlockingplates that arefitted together to give a 3D support structure for the part.The laser even engraves an assembly-part number on everypiece so that it can be easily slotted together once cut.I watched pressing after pressing being loaded into the laser andidentical finished parts being unloaded – and the only anxiety beingexpressed was whether the ordered nitrogen would arrive in time.The NLC, along with its Materials Processing group, was set upjust 10 years ago, to support South African industry in implementinglaser technology and today, “… this unit is the most interactive withindustry,” says Ndumiso Cingo, the CSIR NLC manager, in a shortintroduction to the day’s proceedings. The aim of the open day?“To show what Laser Technology has to offer, particularly for themanufacturing sector of South African Industry.”An overview of the NLC’s activities follows, presented by Isabelvan Rooyen, the competency area manager for the MaterialsProcessing group. “The NLC’s turnover is R50-million, of which30% is funded through internal CSIR grants and 70% is raisedthrough contract research proposals and services,” she tells us.It has three competence areas: the Laser Physics and Technologygroup; the Laser Materials Processing group, hosts of the day; andthe Higher Education Institute, which was set up to make lasersmore accessible to university students.According to van Rooyen, the Laser Materials Processing group’sambition is to “research and develop laser based manufacturingtechniques for different materials; to develop and maintain localtechnological expertise; to promote industrial competitiveness; andscarce skills development. We support local industry as a centre ofexcellence for laser-based manufacturing.”Van Rooyen talks of a push strategy linking basic and appliedresearch. By creating awareness of laser-based manufacturingtechnology and through developing relationships withpotential laser users, specific application opportunitiesand manufacturing techniques can be identified.The need for highly precise fit-up prior to welding canbe overcome by changing the joint design.32
The potential of these can be established via feasibility studiesand manufacturing solutions. “And we also provide specialisedproduction services,” she adds. “We use our laser equipment toprocess real components for industry.”But the pure research side is also important: “It is not helpful simplyto maintain the knowledge base,we must further our knowledge.We must keep in touch withnew developments so that wecan provide an upfront serviceto introduce new technology,”she suggests, “and through allof these processes, youngstersare being developed who haveup-to-date laser knowledge andexperience that can be directlyused in future careers.”Moving onto creatingawareness of what lasertechnology has to offer, VanRooyen introduces Charl Smal,one of two International Weldingengineers on the group’s staff.From a material’s processingpoint of view, the key advantageof using a laser is that its lightsource can be focused – andthe better the focus the betterthe processing: “Energy densityis the name of the game,” saysSmal.For welding, a laser comesinto its own because the energycan be so concentrated that acylindrical fusion zone can becreated to melt right through thethickness of the joint. “10kWcan be concentrated on 1mm 2 .In fact, the focus is so sharp,typically within a 50µ radius, that we have fit-up gap problems. Onplates less than 3,0mm thick, the maximum allowable gap is 10% ofthe plate thickness, ie. 300µ on 3,0mm plate. On thicker plate, thisreduces to 5%, so when butt-welding on 30mm material, the jointsshould be aligned to within 1,5mm,” he warns. This problem can beovercome to a great extent, by changing the joint design, by using amachined overlapping joint arrangement, for example, and then laserwelding through both thicknesses.The key benefit of high heat intensity, says Smal, is low distortion.He shows us a graph of the deformation resulting from differentwelding processes. The best (lowest distortion levels) are achievedby using electron beam welding, but laser-welding is not significantlyfar behind. MIG and submerged arc welding, in contrast, producein the order of 10 times moredistortion and often have to bere-machined after welding torestore dimensional accuracy.“As a ball park figure, a laseruses about 10% of the energythat an arc welding process willuse, ie, the heat input is reducedby a factor of 9,” explains Smal.Another key advantage oflasers, linked directly to theirdeep-penetration ability, is theopportunity to complete a fullpenetration weld with access toonly one side of the joint. Also,close proximity to the joint is notrequired, which makes for moreflexible automation and reducedclash risks. The smaller fusionand heat affected zones alsomean that much less material ismicrostucturally changed by thewelding process.The disadvantages? The costof the capital equipment andincreased preparation coststo achieve the joint precisionrequired. But Small believesthat the high productivity gainsof using a laser – welding speedsof 10-12m/min are possible –along with better consistencyand weld quality, often make theinvestment worthwhile.Maritha Theron is the next laser specialist to present. Herexpertise is on laser transformation hardening, a technique usedto obtain a hard and wear resistant surface layer, typically in theorder of 0,5-1,5mm thick, by transforming the microstructure of acarbon steel to martensite. The principle is simple, you use a laser toirradiate the surface for short periods of time, and depending on thewavelength of the laser used, the absorptivity of the metal surface,and the travel speed of the laser beam, heat transfer takes placeMarch 2011 33
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