How to Source Weldments
Weldment RFQ checklist: material specs, weld symbols, welding code, distortion limits, post-weld machining, stress relief, NDT and finish.
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A weldment is cut parts fitted and welded into a frame, base, bracket or structure, and often machined afterwards. What it costs depends less on the steel than on the hours: fit-up, the number and size of welds, grinding, straightening, and whatever machining and testing follow. What it risks is distortion, because every weld pulls the part as it cools.
A good weldment RFQ carries real weld symbols on the drawing, names the welding code and acceptance criteria, and says which features are machined after welding. It states whether the part is stress relieved, how welds are inspected, and how the part is finished. Without a code and an inspection level, one shop quotes a shop-floor frame and another quotes a code-inspected structure, and neither quote is wrong.
RFQ checklist
14 things to settle on the drawing or in the request before you ask for weldment quotes. Print it and tick it off against the print, or copy it into the RFQ.
Material and cut parts
Material grade and form by spec for every part: plate, sheet, tube and structural shapes (for example A36 plate, A500 Grade B tube, 304L sheet)
Tube and structural specs differ from plate, and low-carbon L grades of stainless resist corrosion next to the weld. The shop buys to the spec, not to the picture.
Cutting method allowed (laser, plasma, saw, waterjet) and weld joint preparation: bevels, lands and root gaps
Plasma leaves a hardened, slightly beveled edge that may need grinding before welding. Groove welds need their preps cut to the joint design.
Welds and code
Weld symbols on every joint per AWS A2.4 or ISO 2553: type, size, length and pitch, all-around, contour and finish
A note saying "weld all joints" leaves size, length and passes to the welder. Symbols make weld time countable, and weld time is what the shop is pricing.
Welding code: AWS D1.1 (structural steel), D1.2 (aluminum), D1.3 (sheet steel), D1.6 (stainless), D17.1 (aerospace), ISO 3834 or EN 1090, or ASME Section IX for pressure work
The code sets procedure and welder qualification and the inspection criteria. Code work costs more because the paperwork is real.
Procedure (WPS) and welder qualification records, and whether you want copies
Most code shops have procedures on file. A new procedure qualification means test coupons and lab testing, with their own lead time.
Acceptance and cosmetic requirements: visual to the code, and whether welds are ground, blended or left as welded
Grinding and blending can double the labor on a visible frame. If welds may stay as welded, say so.
Filler metal, where it differs from the code default (for example 4043 versus 5356 on aluminum, or low-hydrogen electrodes)
Strength, crack sensitivity, color match after anodizing and service temperature all depend on filler choice.
Distortion and machining
Which dimensions hold as welded and which are machined after welding, with machining stock shown
Welded frames typically hold about ±1.5 mm (±1/16") on overall dimensions. Bores, pads and flatness within tenths of a millimeter need machining after welding, on a machine big enough for the whole weldment.
Flatness and squareness requirements on mounting faces and frame diagonals
Shops meet them with fixtures, weld sequence and straightening; the tighter the requirement, the more fixture and time.
Stress relief before machining: thermal cycle or vibratory, with a certificate
Machining a weldment that was not stress relieved releases stress and moves the machined features, sometimes overnight. Thermal stress relief needs a furnace large enough for the part.
Inspection, finish and delivery
Nondestructive testing: method (visual, magnetic particle, penetrant, ultrasonic, radiographic), extent, and acceptance standard
NDT is priced per joint and per method and is often done by an outside lab. Unless the extent is stated, shops assume visual only.
Inspection reports: dimensional report, and weld inspection signed by a Certified Welding Inspector if required
A CWI report costs inspector time; a dimensional report on a large frame may need a portable arm or laser tracker.
Finish: blast grade and paint system with film thickness, powder coat, or hot-dip galvanizing (with vent and drain holes)
Closed sections going into a galvanizing bath need vent and drain holes or they can burst. Paint systems need a surface prep grade, such as a commercial blast (SSPC-SP6).
Lifting points, shipping configuration and quantity, including repeat volume
A welding fixture pays for itself over a few dozen parts, robotic welding over hundreds of repeats. Big weldments need lifting lugs and a shipping plan.
What to send with the RFQ
- A drawing with weld symbols on every joint, the welding code, the material list and the finish.
- A STEP model of the assembly, and of each cut part if you have them.
- A cut list or bill of materials with material specs and sizes.
- Machining drawings or notes for post-weld features, with datums.
- The load or service, if you want the shop to question weld sizes.
- Quantity per release and annual usage.
Lead times
| Prototype or first parts | 2-4 weeks for a small steel weldment from stock material; add 1-2 weeks for post-weld machining and 1-2 weeks for galvanizing or paint. |
|---|---|
| Production or repeat orders | 4-10 weeks depending on size, code, NDT and finish; plate and shapes in less common grades can add weeks. |
Typical of U.S. job shops, from order or approved drawing to shipment; confirm with the shop for your part.
What drives the cost
- Weld volume: fillet weld metal grows with the square of the leg size, so an oversized weld is expensive.
- Fit-up and fixturing for each unique weldment.
- Grinding and cosmetic finishing of welds.
- Post-weld machining on a large machine, and the stress relief before it.
- Code work: procedure qualification, welder certification, CWI inspection and NDT.
- Material: stainless and aluminum cost more to buy and weld than carbon steel, and need separate tools to avoid contamination.
- Finish: galvanizing, multi-coat paint systems and masking of machined faces.
Common mistakes
- Missing weld symbols, or "weld all around" on every joint.
- Machining tolerances such as ±0.1 mm on as-welded frame dimensions.
- Machined features on the drawing with no note that they are machined after welding.
- No vent and drain holes in closed tube that will be galvanized.
- Oversized fillet welds "to be safe", which add cost and distortion.
- No code or acceptance criteria, then rejecting welds on appearance.
Questions to ask the shop
- Which codes do you weld to, and do you have qualified procedures for this material and thickness?
- Do you have a Certified Welding Inspector on staff?
- Can you machine the weldment after welding, and what is your largest machine?
- How do you control distortion: fixtures, weld sequence, straightening?
- Do you stress relieve in-house, and how big is the furnace?
- Who does the finish, and how are machined faces protected?
Typical processes
Typical materials
Charts and calculators
Frequently asked questions
- Which welding code should my weldment use?
- For structural carbon and low-alloy steel, AWS D1.1; aluminum, D1.2; sheet steel up to about 4.8 mm (3/16"), D1.3; structural stainless, D1.6. Pressure equipment qualifies procedures and welders to ASME Section IX. In Europe, EN 1090 or ISO 3834. If none applies, name one anyway: it gives you and the shop a shared acceptance standard.
- Do I need stress relief before machining a weldment?
- If machined features must hold position, flatness or bore alignment, usually yes. Welding locks in residual stress, and machining lets it move. Thermal stress relief, commonly around 595-650 °C (1100-1200 °F) for carbon steel, is the dependable method; vibratory stress relief is used where a furnace is impractical, and its effect is more debated.
- MIG or TIG welding for a weldment?
- MIG (GMAW) is faster and suits most steel frames and structures. TIG (GTAW) is slower and gives cleaner, more controlled welds on thin stainless, aluminum and cosmetic joints. Unless the application or code requires one, specify the weld and the acceptance criteria and let the shop pick the process.
Build the RFQ: attach the print and this checklist
Attach the drawing (PDF) and the model (STEP), and put your answers to the checklist in the description. A Noramark sourcing specialist matches the request with U.S. shops that make weldments and contacts you within 1 business day.
