Production Process

Stainless Steel Sheet Metal Fabrication Services

Our Stainless Steel Manufacturing Process outlines the key stages from melting and refining to forming and finishing, producing cold and hot rolled stainless steel coil to spec.

Walmay provides stainless steel sheet metal fabrication as part of supply rather than as a separate service, which means the material arrives at your dock already at final size, shape and finish. We cut, slit, level, bend, stamp, weld, polish, passivate and heat treat in our own facility in Wuxi, in 201, 304, 304L, 316, 316L, 321, 410, 420, 430, 904L and 2205 duplex, from 0.2 mm foil-gauge coil to 150 mm plate. Cutting holds plus or minus 0.5 mm on length as standard and plus or minus 0.05 mm on laser-cut precision work, and every part is traceable to the heat number on its mill certificate.

Our Fabrication Operations

Operation	Capability	Tolerance
Cutting	Shear to 12 mm, plasma to 60 mm, laser to 25 mm, waterjet to 150 mm	plus or minus 0.05 to 0.5 mm by process
Slitting	Coil slit from 20 mm width, single or multi-strand	plus or minus 0.2 mm on width
Levelling	Roller and tension levelling to 3.0 mm thick	0.1 mm per square metre
Bending	Press brake to 6 m length, 12 mm in 304	plus or minus 0.5 degrees on angle
Stamping	Blanking, piercing, forming and deep drawing	plus or minus 0.1 mm on feature position
Welding	TIG, MIG, spot and seam welding of assemblies	Visual and dye penetrant to specification
Polishing	180, 320, 400 grit, satin, hairline, No.8 mirror	Roughness to 0.2 micrometres Ra
Surface treatment	Pickling, passivation, electropolishing, bead blasting	Passivation to ASTM A967
Heat treatment	Solution anneal, stress relief, H900 to H1150 on 630	Hardness verified per batch
Edge finishing	Deburring, radiusing, bevelling to 30 degrees	Burr-free to touch
Inspection	Dimensional, hardness, ultrasonic, dye penetrant, salt spray	Reported per batch
Packaging	PVC film, interleaved paper, crating, moisture barrier	Sea-freight rated

Choosing the Cutting Process

The four cutting routes are not interchangeable. Each trades edge quality against thickness and cost.

Process	Thickness	Edge quality	Heat affected zone	Best for
Shearing	To 12 mm	Slight burr, square	None	Straight cuts, rectangular blanks, lowest cost
Laser	To 25 mm	Clean, narrow kerf	Small	Profiles, holes, tight tolerance, no tooling
Plasma	To 60 mm	Rougher, slight bevel	Moderate	Heavy plate where edges will be machined or welded
Waterjet	To 150 mm	Clean, no heat	None	Thick plate, hardened grades, no metallurgical change

Waterjet is the choice where the specification prohibits any heat input, for instance on 2205 duplex where excessive heat can upset the austenite to ferrite balance, or on plate that must not be sensitised at the edge. Laser is the default for anything with holes, slots or a profile. For plain rectangular blanks, shearing is faster and cheaper than either.

Design for Fabrication

Most cost overruns on a fabricated stainless part trace back to the drawing rather than the shop. These are the rules our engineers apply when reviewing a job, using t for material thickness.

Feature	Recommended minimum	Why
Inside bend radius	1.0 t for annealed austenitic	Below this the outer fibre cracks, especially across the rolling direction
Flange length	4 t plus the bend radius	Shorter flanges cannot be gripped by the tooling
Hole diameter	1.2 t	Smaller holes deform and wear punches quickly
Hole to edge	2 t	Closer and the edge bulges when punched
Hole to bend	2.5 t plus the radius	Closer and the hole distorts into an oval
Slot width	1.5 t	Narrower slots break punches
Notch depth	Not more than 5 times the width	Deeper notches tear at the root

Two properties of stainless make it behave differently from mild steel on a press brake. It work hardens rapidly, so the same tooling produces more springback, typically 2 to 4 degrees more than mild steel at a 90 degree bend, which has to be over-bent to compensate. And its K-factor sits around 0.44 rather than 0.33, so a flat pattern developed for mild steel will come out short. Bending across the rolling direction rather than along it also improves the achievable radius noticeably.

Send us a STEP or DXF file with the material, thickness, finish and the critical dimensions marked, and we will confirm the flat pattern and the achievable tolerance before tooling.

Welding Stainless Steel

Grade family	Preferred process	Filler	Watch for
304 / 304L	TIG or MIG	ER308L	Distortion from high thermal expansion, sensitisation above 6 mm in standard carbon grades
316 / 316L	TIG or MIG	ER316L	Same as 304, plus preserving molybdenum in the weld pool
321	TIG	ER347	Stabilised grade, keep heat input low
2205 duplex	TIG or MIG	ER2209	Ferrite balance, so control heat input and interpass temperature
904L	TIG	ER385 or nickel alloy	Hot cracking, so low heat input and no weaving
430 / 409L	TIG	ER430 or ER309L	Grain coarsening in the heat affected zone, limited ductility
410 / 420	TIG with preheat	ER410	Preheat and post-weld temper required to avoid cracking

Low-carbon L grades exist specifically so that welded sections above about 6 mm do not need a post-weld solution anneal. Specifying 304 instead of 304L on a welded pressure part is one of the most common and most expensive specification errors we see. Every weld we produce is followed by pickling and passivation, because the heat tint left along a weld is depleted in chromium and will be the first place the part corrodes.

Surface Finishing and Passivation

Treatment	What it does	When to specify
Mechanical polishing	Produces 180 to 400 grit, satin, hairline or mirror	Visible architectural and food equipment surfaces
Pickling	Acid removal of scale and heat tint	After welding, hot forming or heat treatment
Passivation	Restores the chromium oxide film, to ASTM A967	All fabricated parts, mandatory for food and pharmaceutical duty
Electropolishing	Levels the surface at a microscopic scale, to 0.2 micrometres Ra	Sanitary process equipment, high-purity systems
Bead blasting	Uniform low-gloss matte texture	Anti-glare facades, non-directional finishes

Fabrication is where corrosion resistance is most often lost. Cutting, grinding and welding all leave free iron and heat tint on the surface, and a part that leaves the shop unpassivated can develop rust spots within weeks even in 316L. That is why passivation is part of our standard route rather than an option, and why we keep stainless tooling and stainless workshop areas separate from carbon steel.

Grade Selection for Fabricated Parts

If the part	Specify	Instead of
Is welded and over 6 mm	304L or 316L	304 or 316
Is deep drawn	304 in 2D finish	430, which will tear
Is machined in volume and never welded	303	304, which triples cycle time
Sees chlorides or seawater	316L, or 2205 duplex above 200 ppm	304
Must carry high stress	2205 duplex or 630	Thicker 304
Runs above 900 C	310S or 321	304, which scales
Is indoor, visible and cost-driven	201 or 430 with a No.4 finish	316L

Material for every one of these grades is drawn from our own stock; see the sheet and plate range, along with coil and strip, pipe and tube and rod and bar. The comparison guides on 304 versus 316, 430 versus 304 and 201 versus 304 work through the trade-offs.

What Drives Fabrication Cost

Quotations for the same drawing vary widely between shops because the cost is spread across five items that buyers rarely see broken out.

Material. Usually 40 to 70 percent of the part cost, and it moves with the nickel, chromium and molybdenum alloy surcharge rather than sitting on a list. Grade choice matters more than any other decision: 430 contains no nickel, 316L contains both nickel and molybdenum.
Nesting efficiency. How much of the sheet ends up in your parts rather than in the skeleton. Adjusting a part outline by a few millimetres often lifts yield by a step and takes real cost out.
Setup and tooling. Laser cutting needs no tooling, so it is cheaper at low volume. Stamping needs a die, so it is far cheaper per piece once the volume justifies it. The crossover is usually in the low thousands of pieces.
Secondary operations. Bending, welding, polishing and passivation are labour, and a mirror finish or an electropolished surface can cost more than the material underneath it.
Tolerance. Moving from plus or minus 0.5 mm to plus or minus 0.05 mm changes the process, the fixturing and the inspection regime. Specify the tight tolerance only on the features that need it.

The practical lever is to send the drawing early. We routinely find a bend radius, a hole position or a nesting change that reduces cost without altering function.

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Quality and Standards

Standard	Applied to
ISO 9001	Quality management system
EN 10204 3.1	Mill test certificate with heat traceability
ASTM A967	Passivation of stainless parts
ASTM A240 / A312 / A276	Incoming material specification for flat, pipe and bar
ISO 2768	General dimensional tolerances where not otherwise stated
ASME BPE	Sanitary surface finish requirements on request

Every batch carries dimensional inspection, and hardness, ultrasonic, dye penetrant and salt-spray testing are added where the product warrants it. Salt-spray performance on our coastal-service material exceeds 1,500 hours. Third-party inspection by SGS, BV or TUV can be arranged before loading.

Industries We Fabricate For

Pharmaceutical and food production and kitchen workspaces, where passivation and surface roughness are audited
Chemical production workshops and wastewater treatment
Architectural facades and interior spaces, where levelling and finish consistency across panels decide the result
Machinery manufacturing workshops and hardware processing facilities
Medical device manufacturing and hospital hygiene zones
Automotive and rail transit equipment workshops

More background on the company and its supply chain is on our stainless steel manufacturing page, and the wider catalogue under stainless steel products.

How to Get a Quotation

Send a STEP, DXF or PDF drawing with the grade, thickness, finish, quantity, tolerance requirements and destination port through contact us. We return a quotation with the flat pattern confirmed, the achievable tolerance stated, and any design change we would recommend before tooling.

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FAQs

Can stainless steel be sheet metal?

Yes. Sheet metal simply means flat-rolled material thin enough to be cut, bent and formed, and stainless is supplied in exactly that form from 0.2 mm up to about 4.75 mm, above which it is called plate. Stainless sheet metal is worked with the same processes as mild steel sheet, with allowances for higher springback, faster work hardening and roughly 50 percent more press tonnage.

How much does stainless steel fabrication cost?

There is no rate per kilogram that holds across jobs, because material typically accounts for 40 to 70 percent of the total and the rest depends on nesting efficiency, setup and tooling, secondary operations such as polishing and passivation, and the tolerance you specify. A laser-cut and folded 304 bracket and an electropolished 316L sanitary enclosure of the same weight can differ by an order of magnitude. Send the drawing, grade, finish, tolerance and quantity and we will break the quotation down.

How much does stainless steel sheet metal cost?

Material is priced per tonne against the current nickel, chromium and molybdenum alloy surcharge, then adjusted for grade, thickness, width and finish. Ferritic 430 sits well below 304 because it contains no nickel, and 316L sits above 304 because of its molybdenum. Because those inputs reset frequently, quotations carry a validity window; our price commentary tracks the underlying moves.

Is 304 or 316 stainless steel stronger?

Their strength is almost the same, with a typical yield around 205 MPa and tensile strength between 485 and 620 MPa for both in the annealed condition. What separates them is corrosion resistance: the 2 to 3 percent molybdenum in 316 markedly improves performance in chlorides, seawater and reducing acids. If you actually need higher strength rather than better corrosion resistance, 2205 duplex roughly doubles the yield strength of either.

What tolerance can you hold?

Plus or minus 0.5 mm on sheared and plasma-cut length as standard, plus or minus 0.05 mm on laser-cut precision work, plus or minus 0.5 degrees on press brake angles, plus or minus 0.1 mm on stamped feature positions, and 0.1 mm per square metre on levelled flatness. Tighter requirements on specific features can usually be met, but they change the process and should be marked on the drawing rather than applied globally.

Do you passivate parts after fabrication?

Yes, as standard. Cutting, grinding and welding leave free iron and chromium-depleted heat tint on the surface, and an unpassivated part can rust within weeks even in 316L. We pickle and then passivate to ASTM A967, and electropolish where a sanitary surface roughness is specified.

What is the minimum quantity for a fabricated part?

There is no fixed piece minimum for laser-cut and folded work, since no tooling is involved; the practical constraint is the material minimum, typically 1 tonne from stock. Stamped parts need a die, so they carry a volume threshold that we confirm against the part geometry when we quote.

Which grade should I use for a welded fabrication?

Use a low-carbon L grade, 304L or 316L, for any welded section above about 6 mm that will not be solution annealed afterwards. Standard 304 and 316 can precipitate chromium carbides at the grain boundaries in the heat affected zone, which leaves the weld line vulnerable to intergranular corrosion. For duplex, use 2205 with ER2209 filler and control the heat input to preserve the phase balance.

Can you fabricate parts and supply the raw material together?

Yes, and it is the normal way we work. Because we hold the stock, cut it and finish it ourselves, a single order can combine finished parts with plain sheet, pipe or bar, consolidated into one container against one certificate set.

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