Electron Beam and Laser Beam Materials Processing in Japan
Actual application Paton MHI(MELC0)
Hitachi Hitachi Osaka Univ 0 Kawasaki Steel (JEOL)
Production Steigerwald
I I I 1970 1975 1380 1 Year
Electron Beam and Laser Beam Materials Processing in Japan
Japan has become a world leader in high-power EB welding, and may soon challenge American technology in high-power COz laser beam processing
lapanese scientists have been interested in high energy- Many people believe that these processes will have a major density materials processing for many years. These process- impact on manufacturing methods in the future. es, consisting primarily of electron beam and laser tech- In 1970, Osaka University developed the world's most niques, are capable of producing heat intensities of 106 powerfulelectron beam welding machine, with a capacity of W/crn2 on the surface of a malerial. SIN 11 1w.11in~rnsili~", 1,111 1111) kW (¥rt Fi&. 1). Tln, was 1.itt.r lolk~weit liy UK- prukicà vdpwi/ati
WELDING IOURNAL 1 19 Total powers (beam powers number) kW 1-j 100 200 300 400 500 600 Industries 1 1 a I Number of Machines r?zz?z., 10 20 311 11 0 50 60 ... -- ...... - .---- Automotive I -I-.
I Electronics
Heavy industry I ...... -...* I Job shop
Research 1. - - -.
Fig. 2-Electron beam Wingmachines in fapan (from Ref. 1) facturing Complex with a High Power Laser" as one of commercial machines, as compared with 950 in the U. S. By approximately twelve large-scale national projects. To most 1984, the number in japan grew to 240, with 120 NEC units, Americans, the most famous of these Japanese large-scale 50 Mitsubishi Electric units, 40 Osaka Transformer units and national projects is the fifth generation computer project, 30 Sciaky-Hitachi units. Most of these are low-power (less but the inclusion of laser materials processing as another of than 30 kW); however, Japan currently has more very- these dozen projects illustrates the relative importance that high-power units than any other country. It is estimated that the Japanese attach to this technology. there are approximately 17 units above 60 kW, though all Today, it is dear that the Japanese lead the world in but two or three of these units are for research and are not high-power electron beam manufacturing-technology. Their for production. laser research effort is still a number of years behind the There is still significant growth in low-power electron effort in the United States, but it is growing more rapidly than beam units in japan. NEC sells approximately two units per in the U. S. It is likely that Japanese laser materials processing month. Less than 50% of the units are in the automotive technology will be equal to that of the U. S. within five years. industry (see Fig. 2), compared with 75% of all U. S. electron This report describes the current state of both electron beam machines being used in automotive applications. Since beam and laser materials processing technologies in Japan. the Japanese automotive industry is roughly equal in size to that in the United States, it would appear that continued Electron Beam Materials Processing growth of low-power machines will continue. This may not be true with high-power machii, which have not proven In the United States, electron beamtechnology began to be as useful as was envisioned several years ago. This some 20 to 30 years ago, and was driven by aerospace report discusses the difficulties encountered with high- applications. Since Japan did not have an active aerospace power electron beam processing and the attempted solu- industry at that time, electron beam processing was not tions which have been studied in Japan. developed in lapan until 15 years later. In 1969, Nippon Electric Company (NEC) licensed low-power electron beam units from Hamilton Standard, and in 1976 the Osaka High-Power Electron Beams Transformer Company licensed high power electron beam Early studies showed that electron beam welding technology from The Welding Institute, of Great Britain. It becomes less expensive than submerged arc or narrow-gap was not until 1979 that Mitsubishi Electric began marketing welding for metal thicknesses greater than 50 mm (2 in.) electron beam machines that were both designed and built (Refs. 1, 3). At 100-mm (4-in.) thickness, electron beam may in Japan. In 1981, it was estimated that Japan had 170 be only 50% to 75% of the cost of alternate processes, as
20 1 JULY 1986 Material : Steel. -. . -
Narrow gap GMAW -. /
Thickness (mm) Fs. 3-Esthted costs of vahwelding methods (from Ref. 1) shown in Fg. 3. ~ft&the energy crisis of 1973, there were of the rest of the world combined. Unfortunately, the large many projections for future pressure vessels of 100- to market for heavy-wall pressure vessels has failed to materi- 300-fnm (3.9- to 11.8-in.)wall thickness; hence, MTT1 began a ake; however, even if it had, it is unlikely that electron beam major development program for high-power electron beam welding would be applied extensively today. Japanese welding in 1976. Most of the research costs were borne by research has identified a number of significant problems with the steel companies and the heavy manufacturing compa- this process. nies. Since there are approximately 15 high-power electron The major problems encountered in electron beam weld- beam research machines in Japan lliat hiive been in opera- ing heavy section sleek include: tion an average of five years, each with a cost of $ I- to 1) Lack of long-term beam stability. $2-million and operational costs of 1500,000 to $1-million 2) Repair methods for defects. per year, one can estimate that $SO-million to 1100-million 3) Nonuniform penetration. has been spent on this research. Allhough similar research 4) High price of equipment. has been performed in the United Kingdom, France, the 5) Low ulilizalion faitor. Soviet Union and the United States,the lapanese effort in 6) Extreme cleanliness requirements for steel. high-power electron beam research is probably equal to that 7) joint tracking. beams. Currently, the most promising solution is use of a vpry-rapid-r~fnv~rypower supply that restores full twam vfillagr in onf millisecond or less. Such a power supply was base metal developed by the Paton Institute in Kiev (Ref. 4). and Hitachi and Osaka Transformer are explonng.the use of this new technology with the Soviet researchers. Rpfwr Mr*lhfnhfor fJffprlv afifl Nmmiffirm Penplratic. Currently, tlirre isno simple solution for repair of wclfls in plate greater than 50 mm (2 in.) in thickness. A number of studies have attempted remelting with the beam, but the starting and stopping regions are partial-joint-penetration regions wh-K-h often produce additional porositydue to instabilities of the molten metal in the beam hole. No economical repair method has been found. The problem of nonuniform penetration in partial-joint- penetration welds has been solved.in the laboratory by Professor Y. Arata, of Osaka University, who showed that dual electron beams can give uniform results; however, this method makes the process more complex and increases the cost of the equipment. The usual solution is twonly produce full-penetration welds. In addition, most welds are made in the horizontal position, as the beam hole is more stable and up to 50% deeper penetration can be achieved. The problem of welding positional capability is one that is not generally discussed, but it should be considered when designing siructures for high-power electron beam weld- ing. Prof.Arata, who developed the dual-beam technology. k 2 4 6 8 10 12 14 16 18 20 24 Director of the Center for Ultra-High Energy Heat Sources at Heat input kJ/cm2 Osaka University and is a very influential engineer in lapan. In 1 , , I June1985, he was the only engineer to receive the annual 1 5 10 20 40 japan Science Prize from the national government for his Cooling time from 800.C to SOO'ClseC) work on high energy-density heat sources. An interesting history of his work and the progress of electron beam and F*. 4-Relation bet ween heat input and Charpy impact value (from laser science in lapan can be found in a recent volume Ret. 1) aultiored by Prof. Arata. (Ref. 32). In complete-joint-penetration welds, Hilachi, Ltd., has developed a method of controlling the back bead geometry 8) Poor fracture toughness in many steels. by using the electron flux emitted from the underside of the 9) Nondeitmctive testing. weld (Ref. 5). Although this has only been applied to 15-kW 10) Weld end crater defects. machines, it may also be useful for more powerful equip- 11) Need for large vacuum chamber or local vacuum ment. system. There has been considerable research on the formation of 12) Narrow range of processing variables for thick porosity and desirable weld bead shapes (Refs. 6-9). Many plate. weld flaws can be controlled by restricting the processing Due to their large investment in heavy-section electron conditions, but, as will be shown later, the restrictions can beam welding, the Japanesecontinue to study each of these become very severe as the plate thickness increases. Since technical problems; however, one finds that research activity many of the flaws are caused by convection within the beam is decreasing rapidly. Many research machines in Japan hole, methods of controlfing convection by using non- appear to be used very infrequently today. Progress in Gaussian beam energy profiles are being tesled. The Nation- solving these problems to date can be summarized as al Research Institute for Metals in Tokyo has found that a follows: "top hat" beam energy profile creates a more violent beam Long-Term Beam Stability. Although, in many cases, the hole. but a nearly stagnant solidifying weld pool. It is hoped electron beam process can produce welds of high quality that such changes in the process will make flaw formation and low distortion with good economy, its application to less likely. large structures requires stable beam output for several High-Price and Low-Utilization Factor of Equipment. hours. Early electron guns were susceptible to arc discharges High-power electron beam equipment is very expensive, three to four times per hour. The Welding Institute devel- primarily because of the cost of the vacuum chamber, but, in oped a magnetic ion trap which decreases the amount of addition, there is a low-utilization factor of about 10%. This metal vapor entering the gun and reduces arc discharges to low-use factor is due partly to the time required for vacuum one or two per hour; however, this is still unacceptable, as chamber evacuation, partly to the precise setup and fixturing many applications require one- to two-hour welding times. required by the narrow welds produced, and partly to the Each discharge produces a defect that is so expensive to extremely high production rate of the process. The high repair that the advantage of the process is lost. Many beam energy density permits rapid welding, which gives the lapanese researchers consider this to be one of the most process some of its economy. Nonetheless, the processing serious problems for application of high-power electron time is so short that it requires a very large amount of product to keep such a machine busy. Since very large a solution for the problem of low HAZ fracture toughness in structures are often made inlow volume or even as many of the steels of interest. one-of-a-kind pans, the setup and fixturing times for most Nondestructive Testing (NOT). There is considerable dis- heavy section electron beam welded parts are usually much agreement among the fapanese as to whether adequate greater than the actual welding times. NDT techniques exist for deep, narrow electron beam Steel Cleanliness Requirements. In order toavoid porosity, welds. Ultimately, it is a question of what size flaw one can it has been found that the oxygen content of the steel must ' tolerate. In low-performance parts, large flaws are accept- be less than 60 ppm and the nitrogen must be less than-100 . able,but in most pressure vessels, the allowable flaw size is ppm. This generally requires vacuum degassing of the steel. relatively small. It is generally agreed that ultrasonic testing is In addition, phosphorus and sulfur levels must be closely best for these heavy-section electron beamwelds, but the controlled to prevent hot cracking (Ref. 10). For austenitic sensitivity of this method is limited. Some researchers list stainless steels, the total phosphorus plus sulfur must be less better NOT methods as a major area of future research and than 450 ppm (Ref. 11). one which will be necessary to achieve full regulatory code Cold cracking of most electron beam welded steels-is approval. There is currently a special committee established greatly reduced when the carbon content is less than 0.24%. by MlTl to determine code requirements for heavy-section Unfortunately, this means that many pressure-vessel steels electron beam welding. require significant preheating. In addition, the heating times Weld Crater Uel'ecls. For many welds, the starting and for the greater thicknesses can become very long, thus stopping position can be located on expandable run-off tabs; reducing the economy of the process. however, for circumferential welds on pressure vessels, it is These compositional requirements are sometimes very necessary to complete the weld within the useful part. As severe and increase the cost of the process. In many cases, the beam power is decreased, the complete-joint-penetra- only Japanesesteelmakers have the facilities or the techno+ tion beam hole becomes a partial-joint-penetration hole, and ogy to produce large plates of -the required composition. porosity usually forms. For plate of less than 80-mm (3.1-in.) There is also considerable research by the larger lapanese thickness, circular beam oscillation of several kHz reduces steelmakers to develop lower carbon but equal strength crater porosity. For 100-mm (3.9-in.) thick plates, 5- to pressure-vessel steels (Ref. 12). Such lower-carbon steels will 10-mm (0.2- to 0.4-in.) oscillation in the weld travel direction be required for large-scale use of electron beam welding of . at 1000 to 2000 Hz is most effective for reducing porosity pressure vessels. (Ref. 17). Seam Tracking. The very narrow weld bead of electron Vacuum Requirements. Although there was some beam welds is very susceptible to incomplete-fusion defects, research on out-of-vacuum electron beam welding in the due to small errors in joint tracking. One of the earliest United States and in Japan about 15 years ago, very- problems was beam deflection due to residual magnetic deep-penetration welding must be performed in a vacuum. fields. This problem is often eliminated by using a steel tube This usually involves a large vacuum chamber, but the as a flux shield (Ref. 13). This process is patented by Hamilton Japanese have also performed considerable work on local Standard, and works very well for most steels; however, vacuum apparatus that conforms to the surface of the part when dissimilar metals are welded, the thermal electromag- to be welikd (Refs. 18-20). Kawasaki Heavy Industries is netic force (emf) can cause internal beam deflection. Hitachi perhaps the most advanced developer of local vacuum finds that thermal emf's above 5.8 mV at 800° (1472°F electron beam equipment. The company hopes to commer- cause unsolved difficulties in internal beam deflection (Ref. cialize some local vacuum systems within the next five years, 7). although no definite plans have been made. Some fapanese A new method of joint-tracking control is in-process researchers consider the lightweight 300-mm (11.8-in.) long, ultrasonic monitoring of the weld joint; however, due to 100-kW electron gun, developed by Paton Institute in Kiev, thermal limitations and part geometry, this process may not as a major advance, which will aid in development of local be universally applicable (Ref. 14). vacuum equipment. Hitachi shipbuilding 15 hoping to use this Low Fracture Toughness of Steels. Although the electron compact gun with a local vacuum system within five beam welding process has relatively low-weld-heat input as years. compared with many other processes, there are still some The two largest commercial users of highpower electron problems of excessive grain coarsening in many heavy- beam welding in japan are Hitachi, Ltd., and Mitsubishi section steels (Refs. 15, 16). Even though very narrow welds Heavy Industries (MHI). As seen in Figs. 5 and 6, these may be produced in the laboratory, in production the weld companies also have the largest vacuum chambers. Howev- depth-to-width ratio generally should not exceed a factor of er, it is interesting to note that MHI's electron gun is only 45 ten, in order to achieve a stable beam hole without many kW. While this can weld up to 100 mm thickness in principle, flaws. This means that a 50-mm (2-in.) thick plate has a5-mm it is considerably smaller insize than many of the research (0.2-in.) wide fusion zone and a heat-affectedzone (HAZ) of machines, which may' indicate that the Japanese have approximately equal width. Such an HA2 can have very poor experienced many problems in the IWkW da% welding fracture toughness, as shown in Fig. 4. In this case, the heat machines and with thickness in excess of 100 mm. input of 9 kVm2(which is heat input per unit length of weld Narrow Range of Acceptable Processing Conditions. per unit length of plate thickness) corresponds roughly to Although the Japanese have demonstrated electron beam 50-mm-thick plate. If one compares this with Fig. 3, it can be wrhling of 2tX)-nim (7.9in.) thic-k sleds (and they fldiin that seen that heavy-section electron bedin welding is only processes fur .tiHkinin (I'l.ti-in.) thick material will be devel- economical above 50-mm plate thickness, but that the oped soon), as the thickness increases, one of the difficulties fracture toughness is only adequate below 50-mm thickness! is a reduced range of acceptable welding variables. Figure 7 It is believed that this fracture-toughness problem is one of shows that the iiliowable welding speed and heat input for the major reasons why heavy-section elcdron beam weld- austeiiitic stainlei.-?steels is very ncirrow when the thickness ing research is declining in Japan. Many of the processing equals or exceeds HO mm (3.1 in.). MHI has used electron. problems have been or can be solved, but no one has found beam welding for production of 50- to 60-mm (2.0- to
WELDING JOURNAL123 1 I I .~ ,. Fig. 5- Change of volume of 1970 1975 ' 1980 . ~' ' l! vacuum chamber (from Ref. 1) ... Year
m. 6 - The world's ~areest elearon beam weldng chamber (courtesy of Mitsubishf Heavy Indusfnes)
I 24 DULY 1986 SUS 304 Horizontal position ......
Accelerating voltage 60kV :: ; ? : .. . - -,
Heat input 16 kJ/cm2 . Heat' input: .. / 8 JUfzmL- . . I I I Thickness:ZOmm .-. .. - -. -. .- - - Work distance=320mm? Focal length=220mm / / t I / / . ....-
@#'Thickness:5~mm / / 5 - / /. / / Â ; representative condition . ,
~-/Thicknes:8Omm F.L.=670mmW.D.=470mm 11
I I 8 I 1 . Fig. 7 -Sidable a speed - 200 400 600 800 1000 and ki &ur lor various Ilikknmsin, 01 mlfnii~ sIdInk-ss slwlpLile llrom Welding speed (mrnlrnin) Ref. ?I)
2.4-in.) thick austenitic stainless steels; hence, the process is unique advantages; nonetheless, Us use is limited particularly viable, but it becomes less so at greater tliicknesses. with regard to pressure vessel steels and in thicknesses greater than 100 mm (3.9 in.). It is currently the process of first choice for 60-mm thick austenitic stainless steel pressure vessels and will be the primary choice for a deep-diving In summary, the use of low-power electron beam welding titanium submersible of similar thickness. It is used in produc- has expanded steadily in japan. It .is best suited for small, tion of large gears, large diesel engine piston heads, turbine high-volume pans, such as automotive components, or very stators, nuclear waste containers, heat exchanger shells, specialized, high-value parts, such as those produced in the fusion reactor vessels, large diameter piping, steam genera- aerospace industry. Most of this low-power beam technolo- tor cases, and large diameter metal electrodes (Ref. 3). gy has been licensed or borrowed from the United States, The heaviest plate produclion experience is 160 mm (6.3, France or West Germany. in.) on high-Mn austenitic steels (Ref. 22). Thelapanese retain Japan leads the world in development of high-power great hope for thick-plate welding with the electron beam electron beam welding procedures,.althwgh the Soviet process, as evidenced by Table I.This table lists'23 heavy- Union apparently leads in ifwelupment IJIvquipnienl. Hie section prwkit 15, four of which are currently welded by Japanese research has shown that electron beam welding elearon beam. 11 is envisioned that up to 16 of these produces the best properties in carbon steel of less than products are future candidates for this process; however, as 50-mm (2-in.) thickness. The process works well in austenitic has already been discussed, there are many problems in stainless sleds of up to BO-mm (3.1-in.) thickness and in a WELDING JOURNAL 125 LNG Carrier, Equalor CMA Welding. High-Current EBW for Parts ISO At Alloy 5083 CTA Wdding of Spherical Tank Construction - EBW (Partial GTA is Ship 6000 m Deep 70 6Ak'-4V-Ti EBW (Partial CTA is used.) 1ihmpromnr~... .-. .. . - dl Research Vehicle, . . Spherical 50 - lUNWo EBW (Partial CTA Is used.) ERW (Partial GTA Is Pressure Vessel . .. used.) Siihmerged Arc 150 HT60, HT70 EBW Sea Construction Column Weld'me GMA Wehtin~ A50B Suhmeigrd Arc Pressure Wrou~hl Narrow-Cap CMA Wekhn,?, Narrow-Cap, Vessel St-I, A533 Welding CMA Welding Steel Plate PWR Core Ausienittc Narrnw-Gap GTA Welding. EBw Internal ~tainless EW Nuclear Plant Core Aimenil~ Narrow-Gap CMA Inlemal Slamles< Narrow* ~TAWelfing EBw Nudrar fusion Nontna~nrlif - E11W Reador Itaw Ilicli-Mn Steel kitmerged Arc Automatic Wer 150 SB49 Welding. Narrow-Cap Narrow-Cap GMA ($MA) Welding Welding, EBW Thermal-Power Sulwnfrgptl Arc Aulomatfc Plant Main Steam Pii 70 2 'A Cr- 1Mo Welding, Narrow-Cap Narrow-Cap GMA GMA Welding Welding. EBW Mono-Block Submerged Arc Narrow-Gap Welding 250 2 Cr-1Mo Pressure Veswf 'A Wckling (EBW) Chemical Plant coilayer Cr-Mo + Slitimcrgpri Arc 200 Welding, Narmw-Cap Narrow-Gap Welding Pressure Vessel HT60 - IiT7O GMA Welding Coal Liquef-tion Vessel 3~400 (2Mcr-lMn) - arrow-~iip Welding Plant (EBW) Penstock Sibmrged Arc Wekiii, Narrow-Cap GMA Spherical 200 HT-80 CMA Welding, SMAW Welding. EBW Bifurcation sled ~onslructionPier ofTruss Sulnin~gedArc Welding. Narrow-Cap GMA -.. .- 150 Bridge HT-80 CMA Welding. SMAW WeMing. EBW Sulmerg~dArc Narrow-Gap GMA Turbine Casing 200 G-Mo Welding, Narrow-Cap CMA Weldmg WeMing Steam Turbine Turbine Rotor 300 Ni-Cr-Mo - CTA Welding. EBW Turbine Parts GTA Weldmg, GMA 100 12% Cr Nozzle Ring Welding, EBW EBW . COÃSemiautomatic Runner' . . sew Welding, Ektroslag Narrow-Cap Welding SC46 . Weldme SMAW CO? Semiautomatic SM50 Water ~il Speed Ring Weldmg, Electroslag Narrow-Gap Welding 70 9441 . Weldmg, SMAW CO? Semiautomatic Narrow-Gap Welding Casing 50 5% Wekling. SMAW kon-Making Ekctro'liag Ekctrosia~ Ron Stand 350 Machine ' Welding Welding KSFl.0 Nanow-Gap GMA DidEngine Gank Shaft 250 Suhmaged Arc Welding Welding, EBW Cr-Mo Steel researchers cite the need for more weldable steels, for commercial units to 5 kW and research units of 10 to 20 kW. better filler metal addition methods, tor better NOT tech- Malsushila, whose largest commercial unit is 1200 W, is the niques, lor more flexible processing conditions, for code largest seller oi CO; lasers, with three to four units sold per acceptance, and for more stable welding equipment as the month. With several foreign manuiacturers also included, it primary reasons for llie currently liiiiiled iiie of Ihis Itt linol~ appears tlut the totdl nunilwr of liiglrpower CO, lasers in ogy. There are no obvious answers to these difiiculties in Japan may be increasing by more than '100 per year. sight, and the overall research effort is rapidly declining. Toshiba began YAG laser sales in 1972 and CO; laser sales However, if advances are made in three or four of these in 1982. Ishikawajirna-tiarima Heavy Industries (IHl) devel- problem areas, heavy-section electron beam welding labri- oped its own 1-kW CO; laser in 1978, but the company cation could develop rapidly in Japan. In the meantime, it is a does not sell it commercially. In 1977, when MITI initiated a useful process with several unique qualities, but its use large-scale program including high-power laser develop- should be carefully considered in light 01 the vast Japanese ment, Hitachi led other researchers in COi laser technology. experience. The official position of the Japanese is that For this reason, Hitachi chose not to participate in the MITI electron beam welding of heavy sections is the welciing cooperative development program, but Toshiba and Mitsu- process of the future; but, unofficially, they admit that the bishi Electric did. Today, all three of these companies offer future may be farther removed than they had hoped a few commercial C02 lasers up to 5 kW. years ago Most of the lasers in current use are of relatively low power and are used for culling, drillingor welding of fine Laser Beam Materials Processing parts, as in the electronics industry. Work with n~ultikilowatt Idsers is generdlly limited to research laboratories, although Early development of lasers for materials processing in there are several significant production applications of these japan lagged considerably behind the United Stales. Howev- higher-power units. Since most of the laser materials pro- er. Japaneseinterest in this technology has advanced rapidly cessing in l~panis still in its t!drly st~gfi.the uevelolbinents ~IIlliu ~dslfive yvtir,. diid niiiy nnw lw ~~i~wiiigniure qt~it kly will IÈL~liit ii'>si:d in lour gruups: the uquipnient ni~ituldci~ir- thdn in llie United Stales. It is estimated tlut there dre nfdily ers, the universities, the sieel conipdnies, and the heavy 2000 YAG and 600 COi lasers in use in japan (Ref. 231, industry manufacturers. although many of these may be in the less-than-100-W class. Nippon Electric Company and Toshiba are the primary Laser Equipmen1 Manufacturers manufacturers of YAG Idsers, with MhJ-W maximum sizi">. Hitachi, Toshiba, Mitsubishi Electric, Osiika Transformer and Toshiba Corporation. Toshiba Corporation began devel- Matsushita are the mapr CO; laser manufacturers, with opment of lasers in the 1960's aidcompleted a 1.2 kW C02 WELDING fOUKNAL 127 -~--tmmme~as-flow lasers because of their better beam Table 24aier Development Goals of Mm Flexible characteristics; however, the commercial units up to 2.5 kW Mimilxlurini; Sysiem Naliinal R&D Project -... . - are transverse flow due to manufacturing economies. Hna- chi's 5-kW unit is axial flow, and it has outstanding beam Technolo@isfor control of high-power laser oscillators uniformity. Its 20-kW research machine may be the largest Development of triaxial orthogonal COi-gas laser axial flow CO? laser in the world. o wide for use with robot manioulators. which~ is-~ shown ~ in Re. welding, cutting and hardening. The YAC laser is used to 8. This articulated tubing armcan beused for input powers break machine chips during internal boring operations, using up to 1 kW with 85% transmission efficiency when 12 a fiber opticlight guide. The major objectives of laser mirrors are used. The transmission distance is 10 m (33 It), development during this national R&D program are listed in using tube segments up to 3 m (10 It) in length. Table 2. Hifachi, Ltd. Hitachi began development of hiiher-power CO; lasers in the early 1970's and had a considerable lead University-Based Laser Materials Processing over other Japanese firms when MITI began the national - - program in 1977. As a result, Hitachi did not participate in the The Welding Research Institute at Osaka University has a MITI project but continued its own parallel development. At 15-kW Avco COi laser, a smaller CO; laser. and a YAG unit this writing, the company had 30 laser development engi- manufacturedby Control Laser. The Department of Welding neers and 14 research engineers, producing $1.5-million Engineering has a 1.2-kW CO; laser. Most of the research is worth of 500-, 1000-, 2500-, and 5000-W lasers per year. rather fundamental, with studies of beam shape using acrylic Sales are small but growing. beam measurement techniques (Ref. 26). Methods of Hitachi has emphasized research on axial flow rather than removing underside dross during cutting of stainless steels :thematic diagram of the KML Welder Laser oscillator nd bead grinder ^^k Laaar beam fig. 9-Kawasaki Steel's sheet co3 laser beam welding unit . include cutting through a top plate of carbon steel or using laser for sheet welding of coils and began production in 1979 auxiliary gas jets (Ref. 27). Professor A. Matsunawa is with this system. Figure 9 shows this coil-welding production studying surface hardening of titanium by laser nitriding in a line. Currently, the company uses I-, 1.5-, and 5-kW CO; nitrogen atmosphere (Ref. 28), as well as fundamentals of lasers to weld high-carbon steels, high-silicon steels, and the laser beam interaction with the vaporized plume (Ref. stainless steels in thicknesses to 6 mm (0.24 in.) at high speed 29). He finds that the plume Is weakly ionized (less than 10%) (Ref. 30). One of the major reasons for this success is the and consists of ultrafine partides that aid in scattering the decision to use filler metal wire. Most other researchers light. Since the panicle size can be controlled by changing attempt to eliminate filler metal from laser beam welds in the ambient pressure, thii work may become part of a order to reduce costs. Kawasaki Steel has shown that this national study of production methods for ultrafine powders. requires tight butt joints, which are not sufficientlyuniform in Such powders may be of interest as catalysts or as powder practice (Ref. 31). By using a square butt joint with 0.1- to metallurgy/ceramic starting materials. 0.3-mm (0.004- to 0.012-in.) joint clearance and placing a Other studies of laser processing at Osaka University 0.9-mm (0.035-in.) diameter filler metal wire at the top of the include surface melting of plasma-sprayed ceramic coatings joint, the laser beam welding process is much more forgiving to reduce porosity and studies of high-power beam penetra- of material variations. A uniform beam can be produced tion in a vacuum. Recently, 4-crn (1.6-in.) penetration was consistently with low cycle fatigue lives that are up 10 10 achieved in steel at 12-kW power input. Similar studies with times better than conventional arc welded sheets. The a.2-kW C02laser at Nagoya Universily show that penetra- Kawasaki Steel laser beam welding unit does not provide lion increases by 30 to 50% in vacuum, as compared to much higher productivity welding, l)ut there is a significant atmospheric pressure. Nagoya and Osaka appear to be increase in qudltty, especially in the thinnest sections. Olten- among the few Japanese universilies with laser materials times, the rolled weld is of sufficient quality that it need not processing facilities. be removed after processing. This permits Kawasaki to ship very large coils to the Japanese automotive industry, which Laser Processing in the Steel Industry gives these end users an advantage in productivity. Several years ago, Nippon Steel pioneered a form of Kawasaki Steel is one of the leaders in applying laser very-high-power-density laser shock hardening for silicon technology in the steel mill. It began research in 1975 on a iron transformer sheet (Ref. 33). Laser pulses of 10" W/cm2 WELDING JOURNAL 129 produce rapid vaporization of the sheet surface. which surface roughness, whereas silicon nitride has a 100 pm produces an intense shock wave that, in turn. produces surface. Porous zirconia can be cut in 1-cm (0 4-in.) thick- dnlwations in the metal. This mechanically dist~uiwdarea nws~with 1.5-kW power. Hitachi Shipbuilding believes acts as a nucleus for grain rec~ystafliz.ititm(hiring ç.ul~'i~~ii~nlhat crx king rluriiig (uttmc i~tiu~ to rewliial stressf*s art- annealing. By controlling the nucleus for grain growth in this ,. ing on the surface roughness, which might explain why way, Nippon Steel has been able to produce finer-grained, zirconia, which has the smoothest surface, is the easiest to - highly oriented silicon steel with the lowest magnetic core cut. losses in the world. The process works without removal of. , MitsubishiHeavy hdus1ries. MHI has had a 3-kW Mitsubi- the magnesium-silicate coating on. the sheet. In fact.. this shi Electric CO; laser since 1981. Most of the company's coating may be more of an advantage than a disadvantage in research includes welding (where beam oscillation is used to that~ ~~~~- its insulatine nronerties also oermit high absorotivitv of orevent oorosilv), cutting and surface alloying. MHl has tried the laser energ;Thislaser-assisted re~~tahzationof silicon- to weld and cutsilicon nitride and alumina. The company's iron sheet has~ -.-.- been licensed .. ~~~ in the United States to Armco merience with alumina is the tame as Hitachi Shiobuilding's.- Steel. ~iliconnitride cuts well but does not weld. It is reported that Nipon Steel is also using CO; lasers for MHI has a German-built 100-W excimer laser, which the sheet coil welding similar to the work of Kawasaki Steel. It is. company believes to be the highest power excimer laser in also believed that Nippon Steel is using either a 5- or 10-kW the world. Researchers atMH1 are studying formation of laser for research at its Yawata Works. but such works is in ceramic powders with this unit. They also have developed a the formative stages and is proprietary at present. process for cutting of 8-mm (0.3-in.) thick ceramics using a Nippon Kokan K.K. purchased a 5-kW Toshiba laser for its 60-W YAG laser. research center in late 1984. Initial studies included butt joint Kawasaki Heavy Industries (KHI). KHI has participated in welding in b-rnm (0.24-in.) thick stainless steel, presumably to CO; laser processing studies at other institutes and, at this develop a coil-welding process, but future plans include writing, planned to install its own 5-kW unit in micl-1985. The machining of alumina and zirconia ceramics. Sumitomo has company is particularly interested in using the laser to shape had a 5-kW Mitsubishi laser for two years and is studying thick plate because the high heat intensity can produce welding of thin-wall pipe. high-temperature gradients and small heated zones. KHI has developed a YAG laser marking process for parts Laser Research hi the Heavy Equipment Industries in its shipyard. lhh YAG laser is better than COi lasers . because it only burns the paint and not the steel. They Ishikawajha-Harima Heavy Industries. IHI developed its project labor savings of seven times over the current EPM own 1-kW CO; laser in 1978; however, the company process, though it may take three years to actually imple- apparently has no plans for commercial development, per- ment the process in production. haps became of its close affiliation with Toshiba, which is . . already producing commercial CQ lasers. 1H1 is studying examer lasers and has marketed a tunable dye laser primarily Conclusions -. for use in laser-assisted chemical vapor deposition. Current research with the 1-kW CO; laser includes oxygen-assisted lapanese government and industry have actively promot- cutting of 4-mm (0.157-in.) thick steels and welding of mullite ed high-energy-beam materials processing for the past ten ceramic pipes. This ceramic welding works well but requires years. Although initiation of this research lagged similar Â¥7WeC (1290-F) preheat to prevent cracking. IHI has used a studies in the United States by a decade, the lapanese now 400-W YAG laser for drilling of jet engine casings.and.turbine lead the world in high-power electron beam welding and are blades since 1982. In the spring of 1985. the company rapidly approaching American technology in high-power installed a 5-kW Toshiba laser for welding titanium engine CO; laser processing. The intense investment in high-power parts. The laser replaced an electron beam welding process, electron beams does not seem to have produced the since it can weld interior joints of cylinders. It performs in the expected benefits: however, laser materials processing is atmosphere rather than vacuum, and the fatigue life of the much more flexible and can be applied to many more parts is increased due to less undercut with the laser than products than the electron beam. There are already a with the electron beam welding machine. number of product applications of laser materials processing Hitachi Shipbuilding Corporation. Although Hitachi Ship- in japan and, with the easier system of investment in capital .building does not have its own CO; laser, Hitachi has been equipment, it is likely that laser manufacturing may grow using equipment at Milsubishi Electric Company. Much of more rapidly in lapan than in the United States. Certainly, the research has involved cutting of alumina, silicon nitride, there is a strong increase in laser processing research in silicon carbide, and zirconia. All work was done with a japan, while the interest in such research in the United States Gaussian beam of up to 1.5 kW, which is the highest power appears stable or even declining. The very high energy Gaussian laser in lapan. Althoughalumina welds well with the densities possible with electron beam and laser processing laser, it cracks during cutting, even in thin sections. Siiicon- permit efficient manufacturing of high-volume parts. Since carbide cracks above 3-mm (0.118-in.) thickness, white high-volume manufacturing is one of the key elements of silicon nitride can be cut to 4-rnm (0.157-in.) thickness at 50 japan's business success, it is likely that they will continue to crn (19.7 in.) per minute. Zirconia cuts the best, with a 10 urn exploit both of these technologies wherever possible. 0 Acknowledgments pressure vessels. Welding in the World 22(1/2):2. 16. Kosuge, S., Kunisada, Y., Nakada. K., and Tanaka, 1. 1985. The author expresses his deep appreciationto the U. S. Effect of weld width on EB weld metal toughness of carbon steels. Office of Naval Research for the o~o~rtunitvto soend a vear . -~ Quarterly I.olbpan WeWing Society 3(2):55. in japan. He is also indebted to many lapan& scientists and 17. Kanatani. F.. Atsuta, T., Nagai, ti., Yasuda, K., and Koga, S. engineers who graciously gave of their lime and their frank 1984. Studv on crater treatment in electron beam weldi of thi~k opinions. Their support and friendship made the experience plate. &lerly I.olbpdn Welding 5ocety 213) 66 (in lapinese). A worthwhile. less complete report is available in UW Document IV-337-83. 18. Saio.. 5..~ Tanano. C.. Minam.. M.. Enami. K.. Uchkawa. T.. References Kun. 5. Feoruary 1983 Practical applicat&n of 61vacuum eleclron 1. Onoue, H., Shimoyama, T., Nakaiima. T.. and Shono, 5. An bedm welding technology. M~rwbihHeavy Indusfn^ Tecfvw.al industriial perspective of research nee WELDING JOURNAL 131