In order to see billions of lights yearsinto space with the greatest clarity yet

possible,machining of glass mirrorelements down to the nano-level isrequired,and a UK project aims to deliverthe necessary machinery and processesthat will better existing approaches.

The glass in question is that of the2000-odd hexagonal segments that makeup the primary mirror of the EuropeanSouthern Observatory’s (ESO – see box,page 13) so-called OWL telescope(below). OWL is the acronym for,currently,“OverWhelmingly Large”,but islikely to become “Observatory at WorldLevel”. It has a predicted resolution 40 times better than the Hubble SpaceTelescope and a sensitivity that isseveral thousand

times greater.With OWL it is anticipated that the

very first stars formed in the universe willbe visible,while it would do the work of aflotilla of fly-by space probes forundertakings closer to home. CurrentlyOWL is reckoned to be able to start todeliver scientific data by 2012,andbecome fully operational in 2015.

The manufacture of the telescope’sreflector at economic cost is at the heartof its feasibility.A budget for the wholetelescope of just under e1 billion hasbeen set.The UK-based manufacturingapproach is competing with analternative,more traditional approachcurrently envisaged for OWL.

MIRROR, MIRRORSegment size for the primary andsecondary mirrors is limited to a size of2.3 m flat-to-flat due to a requirement forcost-effective transport in standardcontainers. Exact dimensions are stillsubject to a thorough trade-off; the mostlikely range estimated to be 1.5 to 1.8 m,flat-to-flat.

The currentlyfavouredmanufacturing optionis grinding,followed by

MACHINING FOR THE FINAL FRONTIER

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Polished UK performanceThe UK is aiming for a world lead in production techniques for glass optics.Targeting a major European

space project, the technology will have wider application. Andrew Allcock reports

parallel polishing then ion-beam figuring.This last stage involves the accurateremoval of surface material by a beam ofhigh-energy ions. It removes atoms withno smoothing action and can negativelyimpact micro-roughness. It is the lattertwo processes where most time is spent.The OWL website says that three to fourplanetary machines running round theclock – for maximum output but also formaximum machine stability – andcomplemented by one or two ion-beamfiguring facilities would allow a totalproduction time of about six years at acompetitive cost.This process wasapplied to an 11 m telescope – Hobby-Eberly.

But Cranfield University’s director ofmanufacturing technology,ProfessorDavid Stephenson,suggests that theworld’s entire production capabilitywould be required to produce just onehexagonal element a day – six to eightyears’work.

The UK approach involves thedevelopment of both novel machinesand processes. Managed by UniversityCollege London (UCL) and CranfieldUniversity – both members of thePrecision Engineering Network (PEN –see box,right),it also involves figuringtechnology developer Rapt Industries,Livermore,California and UK polishing

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COVER STORY

Precision Engineering Network

The Network (www.ukpen.co.org) is the brainchild ofProfessor Paul Shore, holder of the McKeown Chairof Ultra-Precision Technologies at CranfieldUniversity. He returned there in April 2002 having heldsenior R&D positions with the SKF Group, developingprecision mass production technologies.

Prior to this Professor Shore was responsible forprocess development at Cranfield’s Unit for PrecisionEngineering (CUPE, now Cranfield Precision),developing ultra-precision processes such adiamond turning and grinding, and hard turning.

His Scandinavian experience showed the powerof collaborative academic research, avoiding theduplication of both effort and resources, although research competition stillexisted. The situation is not like that in the UK, he says. “For precision engineeringresearch, we need advanced machine tools and these are expensive. So it’sunrealistic to expect all universities to have modern machines.” Followingestablishment of the Cranfield Innovative Manufacturing Research Centre: “Itseemed sensible to create a precision-engineering network so that the IMRCcould form good links with other universities.”

This idea originated in March last year, five universities were contacted andthe inaugural Network meeting held in July 2003. The Network played animportant part in bringing partners in the OpTIC project together. “I won’t say thatthe Network is the reason that the project happened, but...it was one of thefacilitation methods that brought people together....we probably wouldn’t haveapproached it in this way – one single, co-ordinated program.”

Another Network benefit is that a single request for funding for sharedequipment was successfully made by Bristol and Cranfield universities togetherand not singly, as would have happened previously. Other collaborative proposalsinclude Leeds’ machine tool modelling theory allied to Cranfield’s appliedproduction research. Another has been put forward by Birmingham, Manchesterand Cranfield, this time with a hybrid machining techniques focus. Indeed, one ofthe Network’s overall focuses is expected to be machine tool technology.

The Network’s target is “hard manufacturing technology”, and it is not just atalking shop about current research, but a forum to suggest what the UK shouldbe researching and developing – Professor Shore’s suggestion is next-generationmagnetic bearings for machine systems and associated control technology.

Industrial members of PEN include: helical screw machine maker Holroyd(owners of Jones & Shipman); grinding machine specialist Landis-Lund; CMMmaker LK; the Manufacturing Technologies Association (MTA); NewallMeasurement Systems; Taylor Hobson; Thales Optics; and Rolls-Royce.

Core academic partners include: Interdisciplinary Research Centre inMaterials Processing, University of Birmingham; Dept of Manufacturing Systems,Cranfield University; Centre for Precision Technologies, University ofHuddersfield; Inst. of Grinding Technology, University of Bristol; Dept. MechanicalEngineering, Liverpool John Moores University; and Optical Sciences Laboratory,University College London.

New members are welcomed, says Professor Shore. The next meeting will beheld at the OpTIC Technium (see box, next page) in September.

machine maker Zeeko,Coalville,Leics– Zeeko is a UCL spin-out company,infact. Precision machine tool developerand optic grinding specialist CranfieldPrecision is also central to the project,which is to be centred at the OpTICTechnium,Wales (see box,right).

The project aim is to producemachines and processes that can makeultra-precision surfaces at an accuracy 10times better than now and at a rate 10 to100 times faster than currently possible. Inhard numbers this means accuracy to 1part in 108,or nano-level precision –representing ultra-precision at anunrivalled level and polishing andfiguring in hours not days.

An additional project aim is to enablethe ‘deterministic fabrication’of complexmirror forms.This freedom of shapeselection would also allow the otherstrong European extra large telescopeconcept candidate,the Swedish EURO 50design,to be realised (pictured above –www.astro.lu.se/~torben/euro50).

Processes to be developed by theproject group include fixed abrasive

grinding,with which Cranfield Precisionis well acquainted.A machine basedaround Cranfield University’s Tetraformmachine (www.cranfield.ac.uk/sims),able to accommodate parts 1 m across,will be built.The Tetraform is a spaceframe-type structure in which forces onlytravel in closed loops.The resultingdesign gives very high static and dynamicstiffness,supporting ultra-precisiongrinding at very high speeds. Followingthis grinding stage comes polishing.

Zeeko (www.zeeko.co.uk) haspioneered the development of so-called‘Precessions’polishing with the OpticalScience Laboratory at University CollegeLondon. Dr David Walker is technicaldirector of Zeeko and also directs theUCL laboratory,holding a Royal Society

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COVER STORY

OpTIC Technium

Launched last September, OpTICTechnium (Opto-electronicsTechnology and Incubation Centre)is the brainchild of the Welsh Opto-electronics Forum, the supportorganisation for opto-electronics inWales. This development willcreate a high-quality environmentof 7,700 m2 dedicated to the needsof opto-electronics and enablingtechnologies. It will be located inan existing cluster of opto-electronic companies around StAsaph in North Wales and in closeproximity to the University ofWales, Bangor. It is one of four UKoptic clusters(photonicsclusters.com).

The facility at the centre of theconcept will offer three services: ❏ An Incubator Centre of 24 unitswith a basic serviced incubator of52 m2 which can be extended to 100or 150 m2 for new or relocatingbusinesses from universities andindustry within the UK andinternationally; ❏ Larger companies or jointprojects between universities andindustry researchers will belocated at the Technology Centrewhere innovative new productsand processes in near-marketopto-electronics can be developed.This area will boast state-of-the-artclean room facilities;❏ A Business Support Unit will giveadvice and assistance to start-upcompanies in the early stages oftheir development, includingsources of funding.

Planning for expansion isalready under consideration. OpTICTechnium will occupy just over 5acres of a 14 acre site; theremaining land is dedicated to ascience park where companiesleaving incubation after two tothree years can set up business.

The EURO 50 – a 50 m diameter

telescope – is an OWL alternative

Industry Fellowhip to stimulatetechnology transfer from the universityinto the company,and out of thecompany into astronomy and otherapplications. In conventional polishing,the mis-match between tool andworkpiece as the tool traverses theasphere’s varying local curvature tends tomake necessary the use of very smalltools.This results in tool edge-effects,surface defects and low removal-rates.

UNDER THE BONNETThe Precessions,or ‘Zeeko Classic’process,makes use of a spinninginflatable tool,coated with polishingmaterial such as impregnatedpolyurethane,and which is pressedagainst the surface.The inflated,so-called‘bonnet’,conforms to the local surface,mating over a much greater area thanwould a traditional polishing tool. Since2001,some seven machines have so farbeen built,applying 7-axis control via aFanuc 16i controller or its Boschequivalent. (see video atwww.zeeko.co.uk).

The company sub-contractsmanufacture of its smaller,200 mmworkpiece diameter Precessionsmachine to German optic fabricationmachine tool company LohOptikmaschinen,producing the larger,more specialised machines in-house.

Zeeko has exclusive rights to the useof this technology,and has recentlyadded fluid-jet polishing to its range,developed in collaboration with TNO-TPD Delft,Holland.

But the final piece of the jigsaw – finalpolishing and figuring – is based on the

Reactive Atom Plasma (RAP) method ofpolishing optical and semi-conductormaterials – a process being developedwith funding from the USA’s NationalInstitute of Standards and Technology’sAdvanced Technology Program.

The project,started in May 2003,finishes in May 2006 and a prototypesystem for etching and polishing opticaland semiconductor materials 10 to10,000 times faster than current methodssuch as ion-beam figuring,while causingsignificantly less sub-surface damage,isunder way.

The RAP method uses a chemicallyreactive jet of plasma gas to rapidly andprecisely shape optical andsemiconductor surfaces at the atomic,nano level. Surfaces can be polished bythe chemical action of the plasma,and asmaterial is removed chemically,there isno sub-surface damage.

RAP processing can achieve precise,complex shapes; in principle it also canbe used to deposit material,such ascoatings. If successfully developed,RAPprocessing could produce polished,defect-free optics in hours instead ofdays.And the technique could helpexpand the market for precision asphericoptics.The technology also has potentialapplications in semiconductor waferprocessing,particularly for advancedsilicon carbide wafers,which areextremely hard and unusually difficult topolish.

RAP will be incorporated intospecialist machine tool technology atCranfield Precision having similarcharacteristics to the OAGM 2500grinding machine built for Eastman

Kodak,USA (see image,page 8/9).Thismachine weighs 130 tonnes,has 9 axesand 2.5 nano-metre resolution.

The UK project centred at the OpTICTechnium has drawn funding of £3.526million under the UK Research CouncilsBasic Technologies Programme(www.basictechnologies.gov.uk). It willtake three years to develop the newmachines. In year four,they will beinstalled within the OpTIC Technium todemonstrate that the technology andprocesses can deliver a reliable industrialprocess at the target rate and precision.

SCIENCE SPIN-OFFThe developed facility will ultimatelyoffer low-volume componentmanufacture in support of the UK’sscience base,but its techniques areexpected to be exploited more widely,including turbine blade and medicalprosthetics applications.

Longer term,the project offerspotential for the OpTIC Technium to forma national large optics fabricationlaboratory,achieving internationalstanding over time.This will offer theopportunity for commercial exploitationthrough its developing network of clientcompanies,and the foundations forinternationally competitive advancedproduction facilities.

In addition,Cranfield Precision andZeeko’s places as world leaders ingrinding,polishing and final form figuringmachine technology will also bestrengthened – UK machine toolcompanies operating at the very limits oftechnology,machining at the atomic,nano level. M

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COVER STORY

European Southern Observatory

ESO, the European Southern Observatory, was created in 1962 to: “Establish andoperate an astronomical observatory in the southern hemisphere, equipped withpowerful instruments, with the aim of furthering and organising collaboration inastronomy”. ESO is supported by 10 countries: Belgium, Denmark, France,Germany, Italy, the Netherlands, Portugal, Sweden, Switzerland and UnitedKingdom. OWL telescope link www.eso.org/projects/owl.