This paper reports on the manufacturing features and difficulties experienced for the preliminary mass production of the main mechanical components of the dipole cold mass. The production of about 600 km of superconducting coil copper wedges, 5'000 coil layer jump spacers and boxes, 12'500'000 austenitic steel collars and 5'800'000 low-carbon yoke laminations is spread over 4 European countries and involves 6 manufactory firms. The general technical requirements for the manufacturing process as well as the imposed production checks and quality controls are reviewed. An overview of the preliminary results is presented with an outlook towards the analysis and statistical which are in a process to be implemented for the follow-up of the mass production

Fessia, P

Lanza, C

Perini, D

Verbeeck, T

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1256 IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 12, NO. 1, MARCH 2002First Experience in the Mass Production ofComponents for the LHC DipolesP. Fessia, C. Lanza, D. Perini, and T. VerbeeckAbstract—This paper reports on the manufacturing featuresand difficulties experienced for the preliminary mass production ofthe main mechanical components of the dipole cold mass. The pro-duction of about 600 km of superconducting coil copper wedges,5000 coil layer jump spacers and boxes, 12 500 000 austenitic steelcollars and 5 800 000 low-carbon yoke laminations is spread over 4European countries and involves 6 manufactory firms.The general technical requirements for the manufacturingprocess as well as the imposed production checks and qualitycontrols are reviewed. An overview of the preliminary resultsis presented with an outlook toward the analysis and statisticalwhich are in a process to be implemented for the follow-up of themass production.Index Terms—S.C. Dipole components.I. INTRODUCTIONTHE MASS production of the main mechanical compo-nents for the 1248 LHC main dipoles involves 4 differentEuropean countries and consist in about 600 km of supercon-ducting coil copper wedges, 5 000 coil layer jump spacers andboxes, 12 500 000 austenitic steel collars and 6 000 000 low-carbon yoke laminations.The production technologies of these components are verydifferent spanning from cold-drawn copper profile to precisemachining of glass fiber charged epoxy resin to fine-blanking ofmetal coils or sheets. Nevertheless the quality control and pro-duction follow-up is very similar and most of our efforts con-centrated to find standard manufacturing process controls andprocedures.The geometry of these components is critical for the correctassembly of the cold masses and contributes to attain the re-quired stringent tolerances in field quality. In particular, for theprecise positioning of the cables in the superconducting coilsthe copper wedges are critical. The correct position of the coillayers and blocks will be maintained by the collars that surroundand compress the coils. The yoke laminations will contribute tothe accuracy of the mechanical assembly and to the fine-tuningof the magnetic length.II. QUALITY CONTROLTo follow a mass production it is necessary to analyze a hugeamount of data concerning the process. All these data are con-tained in the so-called “Traceability files.” ISO 9000 definesManuscript received September 24, 2001.The authors are with the Main Magnet and superconductor Group, LHCdivision, CERN, 1221 Geneva 23, Switzerland (e-mail: {Paolo.Fessia;Cristiano.Lanza; Diego.Perini; Theodore.Verbeeck}@cern.ch).Publisher Item Identifier S 1051-8223(02)04173-8.traceability as: the ability to trace the history, application or lo-cation of an entity by means of recorded identifications.Two useful tools to organize and manage the necessary dataare the workflow and the ABS (Assembly Breakdown Struc-ture) [1], [6]. The workflow shows all the phases of a productionprocess and in which position, during the process, the data arecollected in a “traveler” (Fig. 1). The ABS shows the history ofan entity passing trough different processes.The results of the measurements are usually recorded on stan-dard EXCEL® spreadsheets before being automatically loadedin a centralized ORACLE® database structure designed with aWeb interface application.The follow-up of the production must be based on a powerfulstatistical analysis program. Not often this kind of analysis isavailable in all the manufacturing firms and it imposes there-fore the data to be analyzed off-line resulting in delays in thecorrective reaction time over the production process. The usedapproach rely mostly on graphical analysis of the data:• a graphical representation of the measurements as a func-tion of time to monitor the trend and eventually to detectdrifts or shifts of the recorded data;• a histogram with the frequencies of the measurements toverify the distribution of the data.III. COPPER WEDGESGeneralThe series production of the copper wedges consists of asupply of about 600 km of superconducting coil copper wedgeswith four different profiles. One dipole cold mass contains ap-proximately 114 meters of copper wedges for each profile.As mentioned in the introduction, the quality of the magneticfield is given by the accurate position of the cables in the super-conducting coils. The correct position of the cables is achievedby inserting the insulated copper wedges during the winding ofthe coils to separate different blocks of cable.To obtain the desired field quality, very tight geometrical tol-erances are imposed: a few hundredths of millimeter for criticaldimensions. The cold-drawn copper wedges are shaped at roomtemperature from round copper profile beams which are forcedthrough a precise die. The wedges are delivered in 3.6 m longpieces.Acceptance Criteria for the Production ProcessesThe cross-section dimensions of the copper wedges are mea-sured with a spherical probe using a three-dimensional com-puter-controlled scanner. The dimensions have to be checked1051-8223/02$17.00 © 2002 IEEEFESSIA et al.: FIRST EXPERIENCE IN THE MASS PRODUCTION COMPONENTS FOR THE LHC DIPOLES 1257Fig. 1. Example of a workflow for the collar production.in at least three sections evenly spaced along the same copperwedge.At the beginning of the series production, the geometricalchecks were carried out three times per batch (for a profile, abatch is the quantity necessary to assemble ten dipoles): the first,the middle and the last copper wedge of the batch. From batchnumber 11 onward, for each profile, only the middle copperwedge produced in a batch will be checked.AnalysisIn order to monitor the production and according to thequality control requirements presented in the introduction,the collected data for the copper wedges are representedgraphically as shown in Fig. 2.In this case, a shift is clearly visible in the mean of the pro-duction; although all the values remain well inside the intervalof specification, the origin of the behavior and the implicationson the coil assembly performance may easily be investigated.The small shift which can be seen is mainly due to a new man-ufacturing lot after a production stop of about 2 months.IV. LAYER JUMP SPACERS AND BOXESGeneralThe electrical connection between the inner layer coil andthe outer layer coil in the LHC dipoles is called layer jumpFig. 2. Measurement trend of a batch series of the type 1 copper wedge (USL:upper specification limit; LSL: lower specification limit).and splice. The layer jump and splice is a complex 3-D re-gion housed in special collars. Tapered plastic elements, calledlayer-jump spacers, are placed in contact with the coils. The “S”shaped inner layer cable, going in radial direction to the outerlayer, is kept in position by the so called layer-jump box. For thecomplete LHC dipole production, we need 10 000 layer-jumpspacers of two different profiles and 5000 layer-jump boxes. Asthese elements are in contact with the coils, it is essential thattheir tolerances be comparable to those given for the coil geom-etry: 20 m.1258 IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 12, NO. 1, MARCH 2002Fig. 3. Results of measurements on two different dimensions for layer jumpspacer production.The layer-jump spacers are machined from glass-fibercharged epoxy tubes. The support tooling during cutting hasbeen carefully studied. Experimentally, it was shown that theforce exerted by the cutter during the machining was sufficientto bend the piece if not properly kept and hence to producepieces outside the tolerances.The layer jump box is molded in ULTEM® 2300 (30% glass-fiber charged ULTEM®). Then the “S”-shaped groove is ma-chined.Acceptance Criteria for the Production ProcessesAll the parts are checked for their geometry. The dimensionshave to be validated for at least three sections along each piece.For the measurements, special jigs were manufactured. Thepiece is fixed onto the jig and checked with transducer touchgauges in pre-defined locations. The zero is made using cali-brated steel pieces. The use of dedicated jigs allows the precisemeasurement of each piece and only a few seconds are neces-sary to measure one section.AnalysisAlthough the delivered layer jump spacers are all within tol-erances, the analysis outline shows two Gaussian distributionsoverlapped with the most frequent values close to the upper andlower acceptance levels (Fig. 3). This may be explained by thehigh rejection rate of the produced parts and, in particular, to thetight tolerances to be achieved which are nearly at the limit ofthe state of the art for machined charged plastics.In order to increase the acceptance and the production rates,the manufacturer has now started to implement some changesin the tooling design and to optimize the production.V. COLLARS AND YOKE LAMINATIONSGeneralThe production of high-strength austenitic-steel collars [2]and low-carbon steel half-yoke laminations and inserts [3]involves the supply of respectively 12 500 000 and 6 000 000pieces. A dual sourcing policy for both supplies was applied soas to cope with eventual delivery or manufacturing difficulties.In total three fine-blanking manufacturers located in Europeare involved in these supplies.High precision and tight tolerances are required for criticaldimensions (typically 0.02 mm) and are obtained with a pre-cision fine-blanking process.ToolsFor the collars, there are a total of six different configurationsto be manufactured. For the standard yoke laminations, one typeonly is required while four different types are necessary for thecold mass yoke extremities. Considering the large number ofelements to be made and the tight tolerances involved, a mod-ular structure of the blanking tool allowing easy re-sharpeningand corrective actions on critical parts was requested. One con-tractor favored a single tool for the two collar types while theother made two standard separated tools. After the fine-blankingprocess, the pieces must be carefully deburred, cleaned and, forthe low-carbon yoke laminations, protected against oxidation.An average of three to four tool corrections were necessary be-fore tolerances could be attained. Many more corrections wereneeded for both collar types made with a single tool.Acceptance Criteria for the Production ProcessesThe tool acceptance was granted after a pre-series of 100 col-lars and yoke laminations had shown that, for two successivesamples every ten produced, the geometrical dimensions mea-sured with a 3-D computer-controlled scanner were within tol-erances (type A checks). During the series production, two di-mensional check levels were imposed:• the low-frequency level, using a 3–D scanner on one pieceevery 2500 pieces produced• the on-production level, check every 500 pieces produced,using a laser beam scanning machine (type B checks).The rates of these checks will be decreased by a factor threeafter the first 90 dipoles have been assembled.The imposed check points are related to the most critical re-gions involved for the good functionality of the assembled parts.As an example, Fig. 4 is showing the location of the imposedcheck points for the yoke lamination production.Another checking method, based on a smart-fit technique, ismainly used during the initial phase of the tool optimization orto get a good image of the complete profile of a produced piece.Based on a precise CCD camera, the method is inspectingthe piece to be measured. A software program is performing abest fit with respect to fixed reference points and comparing theresults with the drawing file. Fig. 5 shows a result for a collarpiece, the boundaries for the tolerances are visualized and theregions outside the tolerances are identified and evaluated.FESSIA et al.: FIRST EXPERIENCE IN THE MASS PRODUCTION COMPONENTS FOR THE LHC DIPOLES 1259Fig. 4. Low-carbon yoke lamination with location of check points.Acceptance Criteria for the Production ProcessesThe criteria assessment was defined after statistical devia-tions measurements (e.g., Gauge R&R study [5]) had been maderepeatedly on a same collar and on consecutive collars. The cri-teria was set as follows: the batch (one batch is equivalent to thetotal number of fine-blanked pieces necessary for one dipole) isaccepted if the mean value recorded on the three level A checksare within the tolerances. When the inspection frequency willbe released to only one check per batch (after the production of90 cold masses), a floating mean of the current batch and thetwo previous ones will be considered.Implemented Analysis MeansFrom a Web application written in Java script, a data selec-tion facility combined with an interactive drawing allows a visu-alization of the measuring points to be analyzed. Based on thisconcept, a powerful statistical facility including standard param-eters is available (Fig. 6). Covering the selected samples, a sum-mary table for the maximum, minimum, average, and standarddeviation of the selected points are shown; a moving average fa-cility can also be displayed [4].For each batch produced, the drift of the recorded checkingpoints are closely followed-up and, as soon as required, preven-tive tool re-sharpening operations are programmed to recoverthe initial boundaries of the tolerances. Based on the present ex-perience, a tool re-sharpening is made after about 30 000 pressstrokes for both the collar and yoke lamination productions.Fig. 5. Smart-fit plot for a particular of a collar. The outs of tolerance werecorrected during the tool optimization.VI. CONCLUSIONSThe series production of different components used in thesuperconducting LHC dipoles has started. We have used thefirst year to settle and to clarify the production and quality con-trol techniques. As now the major problems for producing largescale pieces are practically solved, there remain some improve-ments to be implemented to increase the production rate andto reduce the larger spread in dimensions observed for certainpieces.Finally, it must be stressed that the mass production of four-teen different parts produced in four different countries by sixdifferent firms and using in most cases different techniques havebeen all monitored and analyzed with the same standard ap-proach.1260 IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 12, NO. 1, MARCH 2002Fig. 6. Example of a statistical web application (see text for detail).ACKNOWLEDGMENTThe authors would like to thank the staff of the six firms whoare supplying the parts described in this note. In particular, wewish to thank G. Malvestiti (Malvestiti, Italy), G. Biana (Elay,Spain), G. Vezzaro (O.M.A, Italy), F. Tosti and G. Franceschelli(Tosti, Italy), V. Iljanko, E. Oikarainen and I. Vuoristo (Out-okumpu, Finland); without their valuable expertise and collab-oration this work would not have been possible. Finally, theywould like to thank R. Perin, J. Vlogaert, and C. Wyss for theircontinuing encouragement throughout this large scale produc-tion project.REFERENCES[1] “LHC Quality Assurance Plan no. LHC-PM-QA-302.00,”, to be pub-lished.[2] C. Lanza and D. Perini, “Characteristics of the austenitic steels used inthe LHC main dipoles,” IEEE Trans. Appl. Superconductivity, submittedfor publication.[3] S. Babic, S. Comel, F. Beckers, F. Brixhe, G. Peiro, and T. Verbeeck,“Toward the production of 50 000 tonnes of low-carbon steel sheet forthe LHC superconducting dipole and quadrupole magnets,” IEEE Trans.Appl. Superconductivity, submitted for publication.[4] J. Beauquis and J. Miles, “Data analysis and geometry measurement re-sults for LHC dipole components,”, CERN/LHC-MMS Divisional Re-port, to be published.[5] “Measurement systems analysis (MSA) reference manual,” ChryslerCorporation, Ford Motor Company, General Motors Corporation.[6] P. Bonnal, “private communication,” unpublished.

First Experience in the Mass Production of Components for the LHC Dipoles

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