Summary of Visit to the Polish National Centre for Nuclear Research (Narodowe Centrum Badań Jądrowych = NCBJ) from 13th to 14th December 2011

Participant Institute Function Email
Marcin Wojciechowski NCBJ project coordinator
Marek Marczenko NCBJ machining coordinator
Grzegorz Brzezinski NCBJ metrology
Jan Litwiniuk CPL director CPL
Frank Gerigk CERN project coordinator
Rolf Wegner CERN project coordinator
Dominique Pugnat CERN metrology

Metrology at NCBJ:

  • One of the goals of the visit was to discuss and coordinate metrology procedures and standards used at NCBJ and CERN so that metrology reports will be coherent.
  • It had been foreseen to measure the 5 parts of the short module (2 end discs of module N, 1 ring of module G produced by milling only, 1 ring of module G finished by turning and 1 standard disc of module G) 1 week before the visit. However, only 1 end disc and the standard disc were available for a metrology check during the visit. Both parts were still missing final machining of the inner nose and beam-pipe region.
  • Dominique Pugnat (CERN) and Grzegorz Brzezinski (NCBJ) were nevertheless able to discuss the metrology procedures and standards. According to D. Pugnat, the metrology laboratory at NCBJ is well equipped and managed. The measurement precision is compatible with the tolerances required.
  • A detailed report of the measurements performed has been prepared by D. Pugnat:
  • A final metrology report of the 2 available discs is being prepared by NCBJ and sent to CERN.
  • As discussed during the last visit, the windows of the lab have been exchanged, shades and an air conditioning system have been installed in the metrology laboratory.

Preliminary evaluation of milling/boring rings:

  • Another goal of the visit was to evaluate the surface quality and precision that can be achieved by milling/boring the inner and outer surface of rings and discs where tight tolerances of up to ▒5 Ám and a surface roughness of Ra ≤ 0.8 Ám are required.
  • The rings were not available for analysis. The outside of the discs gave a good impression. However, measurements were not possible as the corresponding area was too small to place the sensor of the roughness measurement device (Mitutoyo SJ201).

Production status and outlook:

  • Rings: Due to a delay of qualifying the EB welding in Juelich, the 2 rings of the short module were welded end of October. They are now final machined at NCBJ (turning) and CPL (milling).
  • No problem in machining standard/central and end discs was expected due to the experience in machining 2 complete buncher cavities for Linac4. The challenge of tight tolerances, however, was underestimated. Machining of discs will take longer than expected.
  • As described above, 1 end disc and 1 standard disc are nearly finished. Some dimensions are out of tolerance. A list with non-conformities is in Annex I.
  • The standard disc was inspected by CERN and cannot be used for the construction of a cavity because of: i) non-parallelism of the two faces, ii) severe marks on various surfaces. This piece will be used as a test piece for further machining tests (see Action List).
  • The error in diameter on the final disc shall be compensated by adapting the diameter of the ring (module N) that connects to this end disc. It has been understood why a wrong diameter was machined and the procedure will be corrected.
  • An additional qualification step was discussed to be introduced to advance the series production while waiting for the short module: Rough machining step 1 (+2 mm) and step 2 (+1 mm) of discs for the PIMS series will be qualified with the metrology reports of the 2 available discs (end disc and standard disc). In order not to loose time, the metrology reports shall be sent to CERN latest 16th December so that a qualification can be given before the end-of-year closure (22nd December to 4th January).
  • Metrology reports of the 2 rings (before EB welding, after EB welding and after final machining), vacuum and X-Ray test reports will be sent to CERN end of December.
  • The 5 parts of the short module are expected to be finished end of January. If they are measured to be conform to specifications, they will be shipped to CERN and qualified in February.
  • Brazing of the waveguide ring: The brazing procedure for horizontal brazing will be sent to CERN in December. It will be discussed at CERN in January and comments will be given. Mid January, the nickel plating of stainless steel waveguide flanges will be finished and a horizontal brazing test on a test copper piece will be performed beginning of February.

Production experience:

  • The tight tolerances require a long machining time. Final machining of discs for example consumes about 60% of the entire machining time (4 machining steps in total, cutting advance about 1 mm/min). Care is needed for precise positioning of discs and rings for machining the 2 sides in several steps. 5 to 6 days are typically needed to complete a disc. 2 milling machines and 1 boring machine are available at CPL; 2 machines are available at NCBJ.
  • The Kaiser tool for milling/boring discs (outside) and rings (inside and outside) showed good results (confirmed by metrology: the ellipticity of the ring diameter is below the required 10 Ám).
  • Machining of cooling channels caused no particular problem. A carbon drill is used at CPL and a stainless steel drill at NCBJ. Long swarfs are developing during boring and need to be broken after 10 mm of drilling. Care needs to be taken when joining 2 channels under a small angle.
  • Temperature during machining was stabilised between 19 and 20░C at CPL.

Discussions and decisions taken during the visit:

  • Pinholes and reference surfaces for metrology will be machined into discs after the final machining of the discs (better surface quality, positioning more difficult).
  • The required machining direction of waveguide flanges for placing helicoflex« joints has been discussed in detail.
  • Equipment Codes will be milled into each waveguide ring according to:
PIMS module B <= part identifier => PXACPMB001-OS000001
PIMS module C <= part identifier => PXACPMC001-OS000001
PIMS module D <= part identifier => PXACPMD001-OS000001
PIMS module E <= part identifier => PXACPME001-OS000001
PIMS module F <= part identifier => PXACPMF001-OS000001
PIMS module G <= part identifier => PXACPMG001-OS000001
PIMS module H <= part identifier => PXACPMH001-OS000001
PIMS module I <= part identifier => PXACPMI001-OS000001
PIMS module J <= part identifier => PXACPMJ001-OS000001
PIMS module K <= part identifier => PXACPMK001-OS000001
PIMS module L <= part identifier => PXACPML001-OS000001
PIMS module M <= part identifier => PXACPMM001-OS000001
PIMS module N <= part identifier => PXACPMN001-OS000001

  • The following 2 modifications have been accepted by NCBJ: machining an additional groove in end discs for vacuum tests and machining additional pinholes for alignment arms in standard discs.
  • Transport boxes for 6 modules will be prepared by NCBJ. It is intended to use ~ 3 boxes for stocking (NCBJ and CERN) and ~ 3 for transportation in circulation between NCBJ and CERN.
  • The remaining raw copper for discs will be shipped to NCBJ. Marek Marczenko will inform Rolf Wegner 1 month in advance.

Production schedule:

  • Difficulties in production need to be identified and solved. A meeting at CERN will be arranged to transfer the experience gained in machining discs for the 1st PIMS module (clamping, avoiding deformations during milling).
  • When the parts of the short module are sent to CERN, Marek Marczenko will prepare an updated production schedule which takes into account the machining experience made so far, and the option of introducing additional shifts at CPL (up to 3) and NCBJ (up to 2), aiming to complete the PIMS series production in 2012.

Issues to be discussed at CERN:

  • Relaxation of tolerances: Tolerances will be reviewed and relaxed were possible (beam dynamic, RF, assembly and alignment requirements).


  • An action list is attached at the end of this document

We would like to thank our Polish colleagues for the good visit and the extraordinary hospitality!

Rolf Wegner, 21. December 2011

Action list:

# Action Institute / Person Status Deadline / Result
1 Details on plugs for cooling channels for protection during cleaning CERN, R.Wegner done Plugs with O-rings are needed for protecting cooling channels : The whole opening including the threaded part must be completely, liquid-tight closed. No protection for other holes (pinholes and threaded holes) is needed. (Source: CERN workshop and Marina)
2 X-ray norm to apply for investigation of EB welding of copper, level B of ISO 13919-1 (stainless steel) or ISO 13919-2 (aluminium and alloys) CERN, R.Wegner done "Indeed we use the reference to the stainless steel part of the standard ISO 13919-1 which is better adapted and more restrictive than the one for Al (accepting higher porosity which is intrinsic to the behaviour of Al-alloys but not adapted to Cu)." (Stefano Sgobba)
3 Discussion with CERN workshop how to clamp discs on milling machine CERN, F.Gerigk, R.Wegner done Suggestions / recommendations:
1. The milling needs to be done in several steps, otherwise the copper parts will deform too much. At CERN with a combination of turning and milling operations, 4 steps were sufficient: +2mm, +1mm, +0.2mm, final => see report from Gilles.
2. Measurements of the pieces after each machining step on a flat measurement table (for example at 3 points) are required to compensate machining errors (temperature, machine characteristics). This can also be done at CPL.
3. Machining of the outer diameter of the standard and central discs: As Mr Litwiniuk suggested, a precisely machined stainless steel ring should be used as support for both disc types (supporting the outside diameter). For the fixation, we suggest to machine a 2nd ring made of aluminium that fixes the inside radius (radius 235-256mm) - as Marek already suggested. In this way, the disc does not deform when machining the upper-side outside radius. Aluminium is preferable here because it will not damage the inner surface of the rings.
4. For machining the nose part and coupling holes (maybe also tuning islands), a support closer to the nose is required - at the tuning islands or even closer to the nose.
Further suggestions:
* checking milling machines: machining the test disc on 1st machine, precise metrology; machining this disc a bit further on 2nd machine, precise metrology; comparison of planarity and surface quality
* clamping tools for standard and central discs might use the openings for the support feet
4 Cross checking: Do tools for alignment of discs and rings for EB welding act only on the precisely machined strips of discs and rings? CERN, R.Wegner done Yes (source: Thierry)
5 Detailed metrology reports on end disc and standard disc that have been sent to the metrology lab at NCBJ NCBJ done 30.12.2011
6 Prepare a list of non-conformities and missing information of the 2 discs measured CERN, D.Pugnat, R.Wegner done 24.01.2012
7 Depending on results of metrology reports above, give green light for rough machining of discs for series production to +2 or +1 mm CERN, F.Gerigk, D.Pugnat, R.Wegner done 10.01.2012
8 Send the machining procedure for standard/central discs and drawings of the new tooling for clamping to CERN NCBJ / CPL changed 03.02.2012, NCBJ has developed the tools and machining procedure in own responsibility. Machining tests are being performed.
9 Use already machined standard-disc, which was rejected by CERN for further machining tests: Machining with new tools and new procedure to achieve the required tolerances (planarity, roughness at the nose cone) at reduced dimensions (outside, inside radius) NCBJ / CPL done December 2011 => modified to February 2012
10 Finishing inner nose and beam-pipe region of test disc, sending metrology report to CERN. Difficulties might be met here. NCBJ / CPL done 02.02.2012. Problems and improvement seen. Test disc is re-machined for testing new tooling at NCBJ.
11 Before machining further discs (end/standard/central), machine the 2nd end disc (module N) and standard disc (modul G) for the short module to final dimensions+1mm everywhere but with final tolerances. This leaves a reserve for further adjustments of the production procedure, if needed. NCBJ / CPL pending January 2012.
CERN has been informed that end disc N_14 has already been party machined to final dimensions. Machining has been stopped to wait for new tooling.
12 Send metrology reports of the 2 rings of the short module 1. before EB welding of the ports, 2. after EB welding of the ports and 3. after final machining and reports on vacuum and X-ray tests of the 2 rings to CERN NCBJ partly done 05.01.2012 up to rough machining +1mm.
31.01.2012 final machining
X-ray test results pending
13 Can tight tolerances be relaxed? Discussion with CERN workshop, design office and RF designer. CERN, F.Gerigk, R.Wegner done January 2012
14 Can tolerances of pinholes and reference surfaces, used for alignment be relaxed? Discussion with CERN design office and alignment specialists. CERN, F.Gerigk, R.Wegner done January 2012
15 Transport of remaining raw copper parts to NCBJ M. Marczenko, R.Wegner pending CERN being informed 1 month in advance to prepare transport (space still needed at NCBJ).

-- RolfWegner - 09-Feb-2012

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