How to Qualify a Robotics Sheet Metal Supplier: OEM Guide

Sheet metal fabrication for robotics is not mainly a question of whether a supplier owns a laser cutter and press brake. A robot frame is a mechanical reference system. Drive modules, sensors, payloads, batteries, controllers and covers all depend on relationships that must remain stable after forming, welding, machining and finishing.

The purchasing goal is therefore not to find the tightest general tolerance or the lowest piece price. It is to find a fabrication process that protects the interfaces affecting robot function, produces useful evidence at first article and remains controllable as the platform changes.

Define the fabrication scope before comparing quotes

Two suppliers can quote the same CAD package while assuming very different responsibilities. One may price loose laser-cut and bent parts. Another may include a welded chassis, post-weld machining, inserted hardware, finish, final inspection and a line-side kit. Those are not comparable offers.

Start the RFQ with an explicit supply boundary:

• Cut and formed sheet-metal parts.
• Tube, plate or extrusion subassemblies.
• Welding and any required weld finishing.
• Post-weld machining of local interfaces.
• Rivet nuts, studs, PEM-style hardware and purchased fasteners.
• Powder coating, anodizing, passivation or other finish.
• Mechanical assembly, fit checking and kitting.
• Inspection reports, material records and packaging.

Also identify components supplied only for fit verification, such as a wheel module, battery dummy, sensor bracket or top-module gauge. If the fabricator is expected to install electrical equipment, define that assembly scope separately rather than hiding it inside “complete chassis.”

Translate robot function into CTQs

A productive drawing review begins with critical-to-quality features, not with a debate over decimal places. Ask what happens if each interface moves, twists or receives too much coating.

Robot interface	Fabrication risk	Useful control
Drive and caster mounts	Uneven wheel loading, tracking error, tire wear	Common datums, mounting-plane checks and cross-chassis position
Sensor and docking mounts	Lost adjustment range or repeatability	Local machined or controlled formed datums, position and angle verification
Payload deck	Poor module fit or structural load transfer	Flatness where functional, hole-pattern position and loaded deflection criteria
Battery bay	Difficult insertion, connector strain or retention mismatch	Envelope gauge, rail alignment, positive stops and service-path trial
Covers and guards	Gaps, interference and slow service	Gap/flush targets, hardware checks and representative assembly

The correct CTQ list is usually short. A blanket tight profile tolerance over a large welded chassis increases inspection and correction work without necessarily improving the machine. The OEM should own the functional requirement; the fabricator should explain how the manufacturing process will preserve it.

Select an architecture the process can repeat

Robotics frames commonly combine formed sheet, plate, tube and machined inserts. Each has a useful role.

Formed sheet can create trays, covers, torsion boxes and self-locating features with relatively few parts. Tube or plate handles concentrated drive and payload loads. Machined pads establish precise local interfaces without forcing machining-level accuracy onto the whole weldment. A hybrid structure is often more practical than insisting on one process everywhere.

Material choice should follow load paths and production needs. Carbon steel offers stiffness, robust welded construction and familiar coating routes. Aluminum can reduce moving mass, but section depth, joint design and distortion control become more important. Stainless steel may suit corrosive or cleaning environments, with added forming and finishing considerations. Grade substitutions should never be made silently: sheet condition, temper, weldability and coating compatibility affect the result.

Make the prototype representative of production

A machined one-off block can prove packaging, but it does not prove a formed-and-welded production process. If the launch risk is bend accumulation, weld shrinkage or coating build, the first article must use representative material, bend tooling, joining sequence, hardware and finish.

A useful prototype plan separates learning stages:

1. Packaging mock-up: checks component envelopes, cable routes and service access.
2. Fabrication prototype: exposes bend, fixture, welding and machining risks.
3. Production-intent first article: uses the planned tooling, finish and inspection method.
4. Pilot lot: tests repeatability, kitting, takt assumptions and revision control.

Define the evidence required at each gate. Otherwise a visually convincing sample can be approved while the production process remains untested.

Review the weld fixture and free-state condition

Welding changes geometry through local heating and shrinkage. A credible fixture locates functional datums, supports a balanced tack sequence and lets the chassis be removed without forcing it into shape. More clamps do not automatically create better control.

Ask the supplier to show or describe:

• Which surfaces and holes establish the fixture datums.
• Loading order, hard stops and replaceable locators.
• Tack sequence and intermediate checks.
• Weld sequence, access and heat management.
• Whether critical pads are machined before or after welding.
• How the frame is measured after release.

The last point matters. A chassis can appear perfect while clamped and move when released. Inspection should reproduce the drawing’s specified support or free-state condition. If restraint is necessary during measurement, define where it acts and why.

Specify an inspection plan that predicts assembly

Inspection should answer whether the chassis will accept its modules, not simply produce a long list of easy dimensions. Different feature groups justify different methods.

Inspection need	Possible method	Buyer question
Repeated wheel or payload pattern	Hard gauge or checking fixture	Does the gauge reference the same datums as assembly?
Large-frame positional relationships	CMM or articulated measurement arm	Is the supported condition defined and repeatable?
Local mounting plane	Surface plate, indicator or local scan	Is flatness required locally or across the full frame?
Battery and cover integration	Representative fit check	Are the checked modules production-representative?
Coated threads and masked contacts	Visual, thread and continuity checks	Is verification performed after final finish?

Agree which dimensions receive measured results, which receive attribute checks and what sampling applies after first article. Also define how nonconforming results are reviewed. A supplier should not “straighten to fit” a frame without a controlled method and a record.

For tolerance language, our GD&T basics for sheet metal provides a useful starting point.

Treat finish, grounding and assembly as one process

Coating can close holes, change slide fits, reduce gasket compression and insulate intended ground paths. The drawing package should identify masked machined pads, threads, electrical bonding locations and cosmetic zones. It should also state whether threads are chased after finish and when inserted hardware is installed.

Avoid broad notes such as “powder coat black” when function depends on pretreatment, coating system, texture, color, masking or edge coverage. At the same time, do not specify a finish by habit. The actual environment, cleaning method, corrosion exposure and appearance requirement should drive the choice.

Hardware deserves similar control. Mixed insert lengths or an old bracket revision can stop an OEM line even when the frame itself is correct. Include an approved hardware list, installation direction, torque ownership and retention checks where relevant.

Audit revision control, kitting and packout

Robot platforms change quickly. A sensor moves, a battery vendor changes or a top module receives a new interface. The affected CNC programs, bend setups, fixtures, inspection templates, work instructions and inventory must all follow the released revision.

During supplier qualification, trace one representative change through that chain. Ask how obsolete parts are segregated and how first-article records are tied to a drawing revision. This is more revealing than asking only whether the company has “document control.”

Packaging should prevent frame twist, coating damage and contact between precision interfaces. Define whether covers ship mounted or separately protected, how hardware is grouped and what identity is needed at kit level. A lower fabrication price can be a false economy if the OEM must sort, clean and rework every shipment.

Use safety standards at the correct boundary

The public summary for ISO 3691-4

identifies safety requirements and verification for driverless industrial trucks and their systems, including AGVs and AMRs. That does not turn an empty fabricated frame into a compliant vehicle. Motion safety, stability, controls, sensing, braking, operating environment and final system validation remain program-level responsibilities.

NIST’s mobile robotics research and standard test methods are also useful context when an OEM builds a validation plan. Use system-level test objectives to identify mechanical interfaces that must remain stable, then place those CTQs on the fabrication drawing and inspection plan.

Robotics fabrication RFQ checklist

Before requesting a production quote, include:

• Controlled 3D models and 2D drawings with revision.
• Functional datums and a short CTQ list.
• Payload, drive, sensor and battery interface data.
• Material, joining, finish and masking requirements.
• Prototype, first-article and pilot-lot expectations.
• Inspection methods, records and sampling.
• Purchased hardware and fit-check component list.
• Annual demand, order cadence and platform variants.
• Kitting, identity, packaging and delivery scope.
• Mandatory supplier credentials stated explicitly.

The best quotation is not the one with the fewest questions. It is the one that exposes assumptions before tooling, inventory and launch timing make them expensive.

DRAmetal supports build-to-print robotics sheet metal parts and robotics frame and chassis fabrication. For focused decisions, use the AMR chassis supplier RFQ checklist and compare aluminum with steel for AGV/AMR chassis, or send the controlled package and volume assumptions for a DFM and quotation review.