How to audit a heavy fabrication shop

Most supplier problems are visible before the PO is signed, in the answers to questions nobody asks. A shop that cannot state its furnace dimensions from memory does not own a furnace. A shop whose WPS takes three days to produce does not use it. The information is there; the audit is just the discipline of asking.

This is the sequence we run before a shop enters the network, condensed to what actually predicts performance. The audit sits in the middle of our guide to machine frame fabrication sourcing, after the RFQ and before the supply agreement.

Before the visit: what the paperwork tells you

Ask for six documents up front. What comes back, and how fast, is itself the first result.

1. Equipment list with travels, capacities and ages — cutting, welding, stress relief, machining, cranes.
2. Welding certifications — ISO 3834 level, and a sample WPS with its supporting PQR for a joint resembling yours.
3. Welder qualification records, current, covering the process, position and thickness range your part needs.
4. Two or three reference projects with photographs, sizes, weights and markets served.
5. A recent inspection report from a comparable part, redacted as needed.
6. Quality certifications — ISO 9001, and whatever else applies.

A shop with a functioning system returns these within a day or two. A shop that takes two weeks and sends a marketing PDF has told you something important for free. Which standards actually matter for your part is covered in which welding standard to put on a machine frame drawing.

The fifteen questions

Ask these directly, and notice which ones produce a number and which produce a story.

Capacity and equipment

1. What is the largest part you have built, by size and weight, in the last twelve months?
2. What are the travels on your largest machining centre, and its table load rating?
3. What is the internal envelope of your stress relief furnace — and is it yours or subcontracted?
4. What crane capacity serves each bay, and what is the maximum single lift?
5. What plate thickness can you cut, and by what process?

Process control

6. Do you produce a written weld sequence for large frames, and can I see one?
7. What preheat does your WPS call for on 40 mm Q345?
8. Where in your routing does stress relief sit relative to rough and finish machining?
9. What machining allowance do you leave before stress relief?
10. Is the machining bay temperature-controlled, and to what range?

Quality

11. Who performs NDT — your people or a third party — and to what qualification level?
12. Can I see a furnace chart from a recent job?
13. What is your measurement capability on a four-metre part, and what is the calibration status?
14. Show me a recent non-conformance report and how it was closed.
15. What proportion of your output is export, and to which markets?

Question 14 is the most revealing on the list. A shop that produces an NCR file with real entries, real root-cause analysis and real corrective actions has a functioning quality system. A shop that says it has never had a non-conformance is either not recording them or not looking.

Question 3 catches the most common misrepresentation in this industry. Furnace capacity is expensive and a great many shops subcontract it while quoting as though they do not. Subcontracting is entirely fine — it is undisclosed subcontracting that creates schedule risk, because you have inherited a supplier you did not choose. The thermal cycle requirements are in stress relieving welded machine bases.

The walk-around

If you can visit, twenty minutes on the floor tells you more than the documents.

Look at parts in process, not the showroom. Ask to see a frame mid-fabrication. Are the fit-up gaps consistent? Is there a fixture, or is the assembly being held with whatever was to hand? Are the tack welds placed or scattered?

Look at the floor. A heavy-fab shop is not clean, but it should be organised. Offcuts stacked and labelled rather than piled. Plate stock with heat numbers still legible. Consumables stored dry and in a rod oven, not in an open box in humid air — that one detail predicts hydrogen cracking risk better than most certificates.

Look at the welders working. Are they using the parameters on a WPS taped to the bay, or from memory? Is there a welding coordinator visible on the floor?

Look at the inspection area. Is there one? Is the equipment calibrated with current labels? Is anyone using it while you are there?

Look at the machining bay. How is a large part supported? Is it blocked properly, or sitting on two stands and a jack? Is the bay enclosed?

Ask to meet the engineer who will handle your drawings, not the salesperson. If that person does not exist, your drawings will be interpreted by whoever is free.

Red flags

• Cannot state furnace or machine dimensions without checking
• WPS produced slowly, or produced for the audit rather than in use
• No written weld sequence for large frames
• NDT performed exclusively in house, with no third-party option offered
• No NCR records
• Welding consumables stored in ambient humidity
• Quotes returned within hours with no questions about the drawing
• Reference projects that are all domestic when you need export
• Reluctance to let you see work in process

That last-but-one matters. A shop that returns a price on a complex frame by lunchtime and asks nothing has not read the drawing. The shops worth using come back with three sharp questions about your datum scheme — which is a sign they are reading it, as a drawing checklist for welded machine bases explains.

Green flags

• Answers with numbers, immediately
• Volunteers what they cannot do, and names who they would subcontract it to
• Asks about your machining allowance, datums and tolerance intent before quoting
• Shows a fixture built for a previous customer’s repeat part
• Has an IWE or IWT, or names the welding coordinator
• Proposes a hold-point schedule without being asked
• Has export documentation experience in your destination market

The second one is the strongest single predictor. A shop that says “we do not have a furnace that size, we use X in the next province, here is their capability” is a shop being straight with you about a subcontract that was going to happen either way.

Trial order

Do not put a flagship frame into a new shop. A trial job sized so both sides can walk away — a simpler weldment, or one frame from a batch — surfaces communication problems, documentation gaps and schedule realism at a cost you can absorb.

Run the full hold-point sequence on the trial even though the part is simple. What you are testing is the process, not the part; the structure is in first article inspection on large weldments. The terms to settle before the first order are in the machine frame supply agreement checklist.

If you would rather not run this yourself

Running this audit properly means a factory visit, a translator in most cases, and enough welding and machining background to know when an answer is evasive. Many machine builders do not have a spare week or a person with that mix.

That is the service on offer here: the shortlisting, the audit and the hold-point oversight are done before your drawing reaches a shop floor. Send a drawing and the feasibility note and shortlist come back within 24 business hours — and the capability envelope sets out what the network covers.

See also: answering EcoVadis and LkSG questionnaires as a frame fabricator.