Sheet Metal Forming and Aerospace Welding
Aerospace sheet metal is formed with radii and tempers chosen to avoid cracking, and aerospace fusion welds are made and accepted to AWS D17.1, which sorts welds into Class A, B or C by the consequence of failure. Electron beam welds are often controlled by AMS 2681, or AMS 2680 when fatigue critical.
Forming: radius, temper and grain
The minimum bend radius depends on alloy, temper, thickness and grain direction, and it increases with thickness and with harder tempers. That is why one number does not fit all sheet. Practitioners publish charts as multiples of thickness, and the FAA advisory circular AC 43.13-1B carries a minimum bend radius chart widely used for aircraft sheet. Published data from different producers disagree, so take the minimum radius from the material spec or the supplier for the exact temper and gauge you are buying.
Three rules hold across sources:
- Bend across the grain where possible. Bending parallel to the rolling direction cracks sooner.
- Never bend tighter in a hard temper than the material allows in the annealed O condition.
- If a T3 or T6 part cannot be formed at the required radius, form it in the O or W condition and then heat treat and age to temper, which brings in the heat treat controls on the heat treatment page.
Alloy choice matters. 5052 forms and welds far more easily than 6061, which is why it is common on non structural brackets and enclosures, while 2024 and 7075 sheet usually needs O or W condition forming for tight bends. The aluminum alloys page compares them.
Flat patterns and drawing callouts
Flat pattern accuracy depends on the bend allowance the shop uses for its tooling, which is why many aerospace drawings dimension the formed part and let the fabricator develop the flat. If your drawing shows a flat, mark it reference unless the flat dimensions are truly controlled.
| Drawing item | Recommendation |
|---|---|
| Inside bend radius | Give a nominal radius and tolerance that the alloy and temper can achieve, not a sharp corner |
| Grain direction | Flag it on the drawing when bends are near the minimum radius |
| Relief at bend intersections | Show bend reliefs or corner holes to prevent tearing |
| Hole to bend distance | Keep holes far enough from the bend line that they do not distort |
| Flatness after forming | State it if it matters, and expect straightening operations |
| Edge finish | Call out burr limits and edge break, especially on laser or waterjet cut blanks |
Thin aluminum skins and panels often go to rubber pad forming, stretch forming or hydroforming rather than press brake. If your part has compound curvature, ask the source which method it intends, because tooling cost and lead time change a great deal.
AWS D17.1: the aerospace fusion welding spec
AWS D17.1/D17.1M is the specification for fusion welding for aerospace applications. The current fourth edition, 2024, covers welding of aluminum, nickel, iron, cobalt, magnesium and titanium based alloys by electric arc and high energy beam processes. Its scope includes design, procedure and welder qualification, fabrication, inspection and acceptance criteria for aerospace, support, non-flight and crewed spaceflight hardware, plus repair welding.
Welds are classified by consequence of failure:
| Class | Definition (from AWS) | Examples given |
|---|---|---|
| A | Failure would result in loss of, or completely compromise the integrity of, a critical system | Engine and turbine components, fuel rails, hydraulic systems |
| B | Failure would reduce the strength or effectiveness of a system | Ducting whose failure forces operational changes |
| C | No structural role or effect on performance | Cosmetic repairs, less critical ground support hardware |
Each class sets the amount of procedure qualification testing, documentation and inspection. Class A requirements cover B and C, so many shops qualify procedures and welders to Class A for flexibility. Acceptance tables give separate limits by class for porosity, undercut, cracks and other discontinuities. The D17 committee cautions that acceptance criteria tighter than the process can achieve lead to high reject rates, so pick the class from the failure analysis, not by habit.
On a drawing, a complete weld note names D17.1, the weld class and any additional inspection beyond the class minimum, for example radiograph 100 percent of Class A butt welds.
GTAW and electron beam welding
Gas tungsten arc welding (GTAW, or TIG) is the default for thin aerospace sheet and tube in stainless, nickel alloys, aluminum and titanium. Titanium needs full inert gas coverage of the weld and the hot heat affected zone on both sides, often using trailing shields or a chamber, because oxygen and nitrogen pickup embrittles the weld. Weld color is the shop floor indicator of shielding quality, and many procedures set acceptance by color. The titanium alloys page explains the metallurgy.
Electron beam welding (EBW) is done in vacuum and produces deep, narrow welds with low heat input, which is why it is used for nickel alloy and titanium rotating parts, pressure vessels and assemblies that must stay distortion free. AMS 2681 defines EB welding procedures and requirements in hard and soft vacuum, and points fatigue critical applications to AMS 2680, which adds minimum procedure parameters and internal discontinuity limits. Laser beam welding is also covered as a high energy beam process under D17.1.
Both EBW and laser welds have narrow fusion zones, so joint fit up tolerances are tight. Design the joint for the process: square butt or self fixturing joints with controlled gaps.
Distortion and machining sequence
Every fusion weld shrinks as it cools. On precision assemblies the usual answer is to weld with stock left on critical features, stress relieve if the procedure calls for it, then finish machine to the drawing. If your drawing tolerances on a weldment assume no post weld machining, say so and expect the source to push back or price heavy fixturing.
Weld inspection
D17.1 requires inspection scaled to weld class. Visual inspection applies to every weld. Surface methods (penetrant on nonferrous, magnetic particle on ferromagnetic steels) and volumetric methods (radiography, sometimes ultrasonic) are added as the class and drawing require. Radiography practice is controlled by ASTM E1742, but weld acceptance comes from the D17.1 class tables or the drawing. See nondestructive testing.
Records an auditor will ask for: the welding procedure specification and its procedure qualification record, welder performance qualification records, the weld map tying each weld to a qualified welder and procedure, and NDT reports. Welding is a Nadcap commodity, and audits through the Performance Review Institute review these records. Post weld heat treatment, where required, needs the same pyrometry controls as any other heat treat.
Ground support equipment fabrication
A large share of aerospace welding is not flight hardware at all: stands, dollies, handling fixtures, slings and access platforms. D17.1 Class C covers some of this, but lifting and handling equipment usually carries its own design and proof load requirements from the program or the operating site. Structural steel GSE is frequently welded to structural welding codes rather than D17.1, so state which code applies. Large frames also raise machining and transport questions, covered on the large part machining page.
Get formed and welded parts quoted
If you have sheet metal parts, welded assemblies or GSE to build, send the drawings with the weld class and material callouts. We source from qualified fabricators and welders, flow down D17.1 class, procedure qualification and inspection requirements, check weld records and certs before shipment, and a person replies within one business day. We sign a mutual NDA before files. For export controlled drawings, read controlled programs. Back to the processes hub.
Questions
What is the minimum bend radius for 6061-T6?
It depends on thickness, grain direction and the producer data, and published charts disagree. Treat any single number with caution. The reliable approach is to take the minimum radius for your exact temper and gauge from the material specification or supplier, bend across the grain, and use the FAA AC 43.13-1B chart as a sanity check for aircraft sheet. If you need a tight radius, form in the O or W condition and heat treat after.
Which AWS D17.1 class should my weld be?
Pick it from the consequence of failure. Class A applies where failure would cause loss of, or completely compromise, a critical system. Class B applies where failure would reduce strength or effectiveness. Class C applies to welds with no structural or performance role. Over-classifying adds inspection cost and rejects without improving safety, and the D17 committee warns against criteria tighter than the process can meet.
Does D17.1 cover electron beam welding?
Yes. D17.1 covers fusion welding by electric arc and high energy beam processes, which includes electron beam and laser beam welding. Many drawings also reference AMS 2681 for electron beam welding practice, and AMS 2680 for fatigue critical electron beam welds, which adds minimum procedure parameters and internal discontinuity limits. Check which document your customer flows down.
How is titanium weld quality judged on the shop floor?
Primarily by shielding and weld color, backed by the inspection the weld class requires. Titanium picks up oxygen and nitrogen when hot, which embrittles the weld, so the weld and heat affected zone must stay under inert gas until cool. Procedures commonly set acceptable color limits. Dark or flaky discoloration indicates contamination and is normally rejectable regardless of how the weld looks otherwise.
What weld records should I expect with parts?
Expect a certificate of conformance referencing the weld specification and class, plus NDT reports where required. For flight hardware your quality clauses may also require the weld map, welder identification and the WPS and PQR numbers used. Ask for these up front, because recreating weld traceability after the fact is usually impossible. Nadcap welding audits review these same records.
Related
Sources
- AWS Welding Digest: how specifications keep aerospace vehicles up to standard
- ANSI Webstore: AWS D17.1/D17.1M:2024
- Inspenet: AWS D17.1 in aerospace engineering
- SAE: AMS 2681 electron beam welding
- SAE: AMS 2680 electron beam welding for fatigue critical applications
- FAA: AC 43.13-1B acceptable methods, techniques and practices
- The Fabricator: predicting an air formed inside bend radius
- Aircraft Spruce: aluminum alloy bend radius chart
- ASTM E1742/E1742M-23 radiographic examination
Ready to
source it?
A person replies within 1 business day. NDA first.
Request a quote