New Trends in Welding in the Aeronautic Industry Patricio F. Mendez (MIT/Exponent) Thomas W. Eagar (MIT) 1

Welding for Aeronautics is Growing!

Outline Fundamentals Case studies Research at MIT Analysis of trends Physics Economics Case studies LBW EBW FSW Research at MIT Analysis of trends

Ordering of welding processes The intensity of the heat source determines most properties of the welding process. 10 2 4 5 6 7 3 Air / fuel gas flame Electroslag , oxyacetylene thermite Friction Arc welding Resistance welding Oxygen cutting Plasma Arc Welding Electron beam Laser beam W/cm practical range for welding d/w efficiency HAZ size interaction max speed cost - % cm s cm/s $ .2 1 1-10 10-100 0.1 99 .01-.1 -4 - 10 -3 1000 0.1-1 Penetration increases dramatically--> higher efficiency and higher welding speeds Interaction time of 0.3 sec= minimum human operator can do.

Characteristics of aeronautical industry low unit production high unit cost extreme reliability severe operating conditions

Joining processes in aeronautics Bird’s eye view Laser beam welding Electron beam welding Friction stir welding

Laser beam welding Concentrated heat source Can be done in open atmosphere Uses: A318, A380

Electron Beam Welding Concentrated heat source Must be done in vacuum Uses: F22, Titanium

Friction Stir Welding Solid-state process No need for shielding gas Uses: Eclipse, Space Shuttle

Concentrated heat makes stronger welds Electron beam and laser beam make stronger welds than arc welding 2219 alloy Ironically, the strongest alloys are also the less weldable. This is because they obtain their strength from microstructure and heat treatment, and welding destroys those two.

Concentrated heat causes less distortion Electron beam welding and laser beam welding melt much less than other processes much less distortion less metallurgical defects Electron beam GTAW

Solid state processes have no solidification defects No cast structure, fine grain Friction Stir Welding Can weld 7XXX stronger than 2XXX Diffusion Welding Can weld Ti, not Al

Velocity, weight, money 1 10 100 1000 10000 100000 Velocity [km/h] Savings per pound lighter [$/lb] car $2/lb airliner $200/lb military jets $2,000/lb rockets $20,000/lb

The pursuit for weight reduction 10-15 tons lighter! $5 million in fuel savings over lifetime

Weight reduction in small planes Beechcraft Baron 58 1395 kg Eclipse 500 1225 kg Range increased 4% Savings ~ $7000/lb

Weight reduction in space 2219 Al2195 Al-Li 1% Li 7500 lb weight savings Essential to to get to the ISS $75 million savings per launch

Weight reduction in engines Compressors, fans machined titanium, composites, friction welded Hot sections friction welded inconel

Welding equipment is expensive The cost of the equipment is proportional to the intensity of the heat source Friction stir FSW incredibly expensive, that’s the reason it’s in aerospace

Welding expenditures per unit Total welding expenditures Units produced in a year Welding expenditures per unit $2.5 billion 30 million ~$100 $200 million 2,500 ~$100,000 $50 million 100 ~$500,000

Proportion of welding expenditures

Labor costs are highest in aero industry

Welding expenditures are smallest for aerospace

Implications of welding economics Welders in aeronautics are highly qualified Proportion of welding expenses are small Large window of opportunity for process development employment Cost efficiency likely to increase with scale Laser and friction stir welding cheaper than riveting

Case Studies

Laser Beam Welding: A318/A380 Riveting consumes 40% of man hours on structure LBW cuts time by half (8 m/min!) Less expensive (fewer mfg steps) Less corrosion (no holes, crevices) Lighter (no sealing) Stronger than rivets Same fatigue life

New Structures Skin sheet unaffected Welding on both sides simultaneously

Electron Beam Welding: F-22 Aft fuselage 90 m of EBW, 76 cast parts)

Friction Stir Welding: Eclipse 500 65% of riveted joints=30,000 rivets eliminated Welded: Cabin, aft fuselage, wings, and engine mounts Riveted: Tail, longitudinal fuselage joints, skins thinner than 0.040”

Friction Stir Welding: Eclipse 500 Welds three times stronger Equal fatigue strength Better corrosion properties Riveting: 6 in/min FSW: 20-40 in/min $50,000-$100,000 savings per plane Less factory space

Friction Stir Welding: Space Shuttle GTAW VPPA FSW: solves purging problems stronger

Friction Stir Welding: Boeing Boeing made $15 million investment in FSW Delta rockets (1st flight: Delta II on 8/99)

Friction Stir Welding: A380 FSW faster, stronger, better fatigue, less corrosion Incompatible with Glare

Research at MIT: modeling New modeling technique: OMS Order of Magnitude Scaling Can reduce number of experiments Can give approximate solutions to equations Can generalize numerical or experimental results

Research at MIT Ceramic to metal joining TLP, patterned interfaces

Research at MIT EBSFF (3D bodies without mold)

Startup: Semi-Solid Technologies Fast manufacturing: SSM-SFF Semi-solid die-casting Semi-solid welding

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Conclusions (2002) Rivets are being replaced by welding at a fast pace Welding is expanding its role in airplanes From fuselage parts, to wings Use of welding will influence materials selection Favors metals over composites Development of high-strength Al alloys

Conclusions (2002) FSW is the focus of much attention If Eclipse 500 is successful: FSW will increase role in airplanes Boeing might use FSW rocket experience to airplanes Airbus might revive FSW plans For rockets FSW replacing fusion processes VPPA losing appeal EB welding losing appeal (Russia) For jet engines FSW not ready yet for Ti and superalloys Linear friction welding used for military apps.