This report describes the methods utilized in the fabrication of a collimator from 0.001 inch thick beryllium and tantalum foil. The laser welding process proved to be an acceptable method for joining the beryllium in a standing edge joint configuration

Anglin, C. D.

Lingenfelter, A. C.

UNT Digital Library

•9 UCIU^ 93032 PKEPXINT LASER WELDING OF A BERYLLIUM/TANTALUM COLLIMATOR A. C. Lingenfeltcr C. D. Anglin This paper was prepared for submittal to IMOG Joining Subgroup Meeting Los Alamos National Laboratory Los Alamos, MM April 2-4, 1965 Ape .; i 1 9 g 7 I IhfcbaMajriatafanyfrhrt tmtommmtA fat* «aa •f * t «K5W 7W •UTRMUTItN OF THIS MOMENT IS UWUMTEf MKXAIMC* •^pJtt^p]M£ f^^£ A^^gjj i telMttft^ A t g^^^^^^A^AHg^ fpM flpM M I H I f l N M . AA^BHBAJMJ^^^^ J U MMH b̂pft-M. M» <M»M Mt I«IWW)» MllMWI «WJM~ HgMt. MJM1MM MUM to Mf t f l M * • i m M i «jiMM» «T MMW« tXMMMl MMM M M« MMMM% MJM M MMM M M t « < M c l ^ l M » M M r i l l l « l l l W « r M f t W l M j M J l » C M l l l l l l ) M < l M * M I kMltoalMMiiiiiMMiMwwlMliM. «* LASER WELDING OF A BERYLLIUM/TANTALUM COLLIMATOR A. C. Lingenfelter, C. D. Anglin U C R L — 93032 DE87 008144 PURPOSE The purpose was to fabricate a collimator from 0.001 inch thick beryllium and tantalum foil. CONCLUSIONS 1. A collimator can be fabricated to meet the requirements of this application. 2. The laser welding process has proven to be an acceptable method for Joining the beryllium in a standing edge Joint configuration. 3. Because of the tedious fitup requirements, each collimator requires approximately four man hours to fabricate. The yield of acceptable units has been approxiiaately 60J. BACKGROUND Nuclear Test Engineering Division requested we fabricate a collimator from beryllium and tantalum foil. The part is shown schematically in Figure 1. The objective was to sandwich a piece of 0.001 inch thick tantalum foil between two pieces of 0.001 inch thick beryllium foil. The beryllium was to be fused along one edge. The gap between the fused beryllium and the tantalum was to be .001 ± 0.001 inches. We also fabricated a second part which had the same detail as the 3 inch unit shown but was 1.5 inches in length. Approximately forty parts have been fabricated to date. PROCEDURE AMD RESULTS Materials The beryllium foil was identified as high purity beryllium, 99.89 1F-1, ingot foil. The foil was 0.001 t 0.0001 inches. The tantalum was commercially pure and was 0.0012 inches thick. Pure beryllium wire 0.002 inches In diameter was also used. Weld Joint Preparation In order to achieve a precise fitup of the weld Joint, it was necessary to have clearly sheared edges. Shearing on available equipment resulted in 1 excessive rollover of the edge and inadequate precision on the width of the part. We devised a method of hand shearing the part illustrated in Figure 2. The foil width was cut about 0.040 inches oversize and claaped between two pieces of precision ground tool steel. A shin positioned about 0.020 inches of the oversize above the edge of the tool steel. A carbide tool was used to hand shear the excess flush to the tool steel surface using a scrapping action. The procedure was repeated along the opposite edge this tiae without a shim. This gave us foil pieces with a clean sheared edge with ainiaal rollover (0.0001 inches) and of the precise width needed. Weld Fixturing The copper weld fixture is shown in Figure 3. The surfaces were precision ground. A 0.001 inch flat bevel was honed along the edge. This acts to reflect the laser energy into the weld area. Our Initial procedure was to fitup the weld Joint; then, using tweezers, roll the beryllium over the tantalum so the beryllium foils foraed a tight fitting standing edge joint configuration. Because of the very Halted ductility of the beryllium foil, this procedure proved difficult. When we were able to achieve a reasonable fitup, the weld all too often showed unfused areas such as is illustrated in Figure 4. We were unable to successfully fabricate any of the 3 inch collimators using this approach. A second procedure was aore successful. P. R. Landon supplied soae 0.002 inch diameter beryllium wilfe which proved to be the key to successful fabrication of this part. The wire was placed between the two beryllium foils and in contact with the tantalum foil. This arrangement is Illustrated by Figure 5. With the wire in place, the fitup of the beryllium foil was less critical. Figure 6 shows a transverse cross-section of the welded Joint; Figure 7, the weld surface. This technique markedly laproved the yield of 3 inch parts froa 0% to approximately 60S. The problem of fish eyes or unwetted areas such as seen in Figure 4 remains the principle cause of rejections. Using our current techniques, it requires about four aan hours to produce a part. The laser welding parameters used are shown in Table I. There is nothing unusual about the welding parameters with the possible exception of the pulse width. We ordinarily used a pulse width of 5 - 7 ms for welding applications. Using our normal pulse width,, we had difficulty reducing the power input to a low enough level to avoid' burnback and excessive penetration. Using a short pulse width of 0.6 as proved an acceptable way of avoiding the burnback problem. Gas Tungsten Arc Welding was evaluated as an alternative welding method. We were unable to control the penetration and avoid the undesirable alloying of the tantalum into the berylliua. The weld also showed extensive cracking. 2 Working with beryllium requires extensive safety precautions to avoid inhaling particulate Batter. Our procedures were reviewed and approved by Hazards Control and were carefully adhered to during the processing of parts. DISCUSSIOH The lasers because of its capability of focusing controlled amounts of energy on a very saall area, is ideally suited for applications such as this. The keys to successfully producing the part were to carefully prepare the edges of the Material, properly fixture the weld joint, and attain a good tight consis­tent Joint fitup. In this case, the addition of the beryllium wire to the joint proved crucial to being able to repeatedly produce a satisfactory part. AUSPICES Work perforaed under the auspices of the U.S. Departaent of Energy by Lawrence Llveraore Mational Laboratory under Contract W-7405-ENG-18. Table I LASER WELDING PARAMETERS - Be/Ta COLLIMATOR Laser Processing - Raytneon SE330 MATERIAL Be/Ta - JOB NAME Foil Weldment THICKNESS .001" JOIKT TYPE Standing Lip w/.002" wire Insert SURFACE Sheared NETWORK (pulse width »8 .63 as APERTURE 1.5 — PULSE RATE 10 Hz P.F.N. 525 POWER J/W .085 J LASER MODE Clean PENETRATION Good ___:_ SPOT SIZE .007" METALLOGRAPHY NO. P.F.N. K.V. 1.30 RESERVE K.V. .62 LAMP POWER K.W. 1.0 FOCUS f V (3-980") L E H S #1B 100 ma GAS/PURGE Argon 30 CFH/.062 nozzle TRAVEL SPEED TRAVEL/MIN. 1.2 IPH Tack f 6 IPM TRAVEL/PULSE .002" '" TIME/REV. • POT SETTING CNC 100* - » . t . t * t * k * t • . • » • * • -•M*4ft T=E=n Figurt 1 Schaaatic Diagraa of the Ba/Ta C o l l i u t o r Figure 2 The foil to be sheared is positioned and claaped between two surface ground tool steel squares. The oarbide cutting tool is used as a scraper to produoe a good clean sheared edge free of rollover. Figure 3 The oopper fixture was surfaoe ground. Flat bevels .001 inches wide were ground along the edge to help focus the laser energy into the Joint. The bervlllua was positioned 0.003 inches above the copper surfaoe; the tantalus was flush with the surfaoe. Figure 4 Magnification 497X '"*'•,. Scanning electron •lcroaoope picture of an area of lack of wetting. This has been the aoet prevalent defect. Figure 5 Magnirioation 95X and 265X Soamlng electron microscope pictures of the 0.002 inch dlaaeter beryllluB wire fitted between the berylllua foil. V Figure 6 Magnification 200X Transverse eroes-section of tMld area Figure 7 Magnification 267X Seeaning electron •loroeoope picture of the weld surface. ^ bracking la evident. no 

Laser welding of a beryllium/tantalum collimator

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Laser welding of a beryllium/tantalum collimator

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