Welded Robot Subassembly RFQ: BOM, Datums and Inspection

A welded robot subassembly is rarely just “several parts welded together.” A released module may combine laser-cut plates, formed brackets, tube, machined interfaces, inserted hardware, purchased items and finished surfaces. The finished unit must fit the next assembly stage while preserving the datums used by motors, rails, sensors, covers or calibration tooling.

Quoting that scope from a top-level model and a short email creates avoidable uncertainty. The supplier has to decide which file controls, which parts are included, where welding is permitted, which surfaces are machined after welding and what evidence should accompany shipment. Those decisions belong in the OEM’s released package.

This guide explains how to prepare an RFQ for a welded robot subassembly. It focuses on BOM completeness, assembly drawings, fixture datums, post-weld machining and inspection deliverables rather than on the design of a single welded bracket.

Define the delivered assembly state

Start by describing exactly what arrives at the OEM. Is the deliverable a bare weldment, a machined weldment, a coated frame with inserted hardware or a kitted mechanical subassembly? Are covers, hinges, labels, isolators or purchased brackets installed or packed separately?

The top-level drawing should identify the delivery state and link it to the controlled BOM. If multiple states are needed for prototype and production, assign separate part numbers or unambiguous configuration rules. A supplier should not infer the assembly level from model visibility or file names.

Also identify what is explicitly outside the fabrication scope. Cables, drives, bearings, sensors, lubrication, electrical assembly and functional commissioning may be installed elsewhere. Clear exclusions allow the supplier to plan fixtures, masking, packaging and final inspection around the actual mechanical deliverable.

Release a BOM that can drive purchasing and traceability

A useful BOM is more than a list of model names. Each line should identify a controlled item, quantity per assembly, revision and source responsibility. Make-versus-buy status should be explicit. For purchased items, provide the approved manufacturer reference or an OEM-controlled specification and substitution process.

BOM field	Question it resolves	Risk when omitted
Part number and revision	Which definition controls?	Mixed or obsolete components
Quantity per assembly	How many are installed or packed?	Incomplete kits
Make or buy status	Who sources the item?	Duplicate or missing purchasing scope
Material and finish reference	Which released requirement applies?	Conflicting notes between levels
Installation state	Welded, bolted, inserted or supplied loose?	Incorrect process and packaging
Approved source or specification	Is substitution allowed?	Unreviewed interface changes
Traceability requirement	What record must follow the item?	Missing purchase-order evidence

If hardware is welded, pressed or inserted, show its installation direction and location in the assembly definition. Do not make the shop reconstruct the intended stack from a generic BOM description.

Make the assembly drawing authoritative

The assembly drawing should show the relationships that the component drawings cannot. Identify weld locations and extents using the OEM’s applicable drawing convention. Define prohibited weld zones, accessible sealing surfaces, removable items and any sequence-dependent features.

Avoid duplicate dimensions that conflict between the part and assembly levels. A component drawing can control a hole within one plate, while the assembly drawing controls that hole’s relationship to the weldment datum system. State which requirement governs if model-based definition is used alongside drawings.

The package should also identify gaps, flushness or profile conditions that affect fit. If a joint includes intentional adjustment for fixture setting, show the adjustment range and the final acceptance characteristic instead of expecting the welder to center it by eye.

Build the fixture around functional datums

A welding fixture should reproduce the interfaces that matter downstream. The OEM should mark functional datums on the released assembly drawing and explain any installation state that affects them. The fabricator can then propose fixture locators and clamps that preserve those relationships while allowing realistic weld access.

Good locators constrain the assembly without hiding variation. Excessive clamping can force parts into an apparently correct shape that springs out after release. Poorly placed clamps can block the weld, distort thin flanges or make repeat loading dependent on operator judgment.

The fixture review should answer:

• Which features locate the first component?
• Which degrees of freedom does each locator constrain?
• Where can part variation accumulate?
• Can every required weld be reached in the released sequence?
• Is the completed weldment removable without damage or forced deflection?
• Which fixture features require calibration or wear checks?
• How will an approved engineering change be reflected in the fixture revision?

Plan post-weld machining before welding begins

Machined rail pads, bearing seats, motor mounts and precision hole patterns often need to be finished after welding. Their machining plan should not be added after the first weldment has already distorted.

Define machining stock where appropriate, accessible clamping regions and the datums used to locate the weldment. The drawing should distinguish surfaces that remain as-fabricated from surfaces finished after welding. It should also identify coating masks and thread protection for machined interfaces.

The fabricator should review whether tools can reach each feature and whether the weldment can be supported without bending during machining. If a setup datum is not a functional datum, document how the finished coordinate system is transferred and verified.

Choose inspection evidence from assembly risk

An inspection report should demonstrate that the subassembly will fit and function mechanically at the next OEM station. It should not become a long list of easy dimensions while ignoring the relationship between motor, rail and sensor interfaces.

Classify characteristics by consequence. A critical datum relationship may need coordinate evidence or a functional gauge. A repeated tab width may be controlled by the cutting process and verified according to an approved sampling plan. Appearance and finish need their own acceptance references.

Agree in advance whether the inspection state is free, supported or restrained. Identify the measurement equipment or functional surrogate required for complex interfaces. If a mating component is used, control its identity and revision so later reports remain comparable.

Useful deliverables may include:

• Ballooned first-article report tied to the released revision.
• Defined setup and restraint photographs.
• Critical datum and interface results.
• Material, hardware and finish records requested by the purchase order.
• Weld inspection records for the specified scope.
• Gauge or fixture identification and calibration status where applicable.
• Approved deviation and reinspection records.
• Final configuration and serial or lot identification if specified.

Prevent finish and packout from undoing the work

Welded assemblies can be damaged after dimensional acceptance. Coating can build on locating pads or fill threads. Aggressive blasting can alter thin edges. Poor handling can load a projecting sensor bracket or allow two machined interfaces to strike one another.

Release finish masks, grounding points, cosmetic classes and thread-protection requirements. Define whether removable hardware is installed before finishing, after finishing or shipped as a controlled kit. Packaging should support the weldment at suitable structural points and protect precision interfaces from contact and contamination.

Destination and handling method belong in the RFQ because they influence packout design. The OEM should approve any reusable rack, lifting point or preservation method that interfaces with its facility or equipment.

Use a complete RFQ and validation checklist

Before sending a robotic welded assembly for quotation, check that the package includes:

• Released top-level drawing, 3D model and complete BOM.
• Current drawings or specifications for every make item.
• Approved source information for purchased items.
• Defined delivered state and explicit exclusions.
• Weld definition, prohibited zones and finish requirements.
• Functional datums, CTQs and inspection state.
• Post-weld machining definition and machining stock where required.
• Hardware insertion, masking and thread-protection notes.
• First-article, production-inspection and document requirements.
• Quantity, revision mix, packaging, destination and desired schedule for review.
• Formal process for questions, substitutions, deviations and engineering changes.

Related customer project: Modular Robot Assembly: One Shared Datum Plate. Related resources: robotics sheet metal quality-plan article.

Keep engineering ownership explicit

DRAmetal manufactures the mechanical scope defined by released customer drawings, models, BOMs and approved inspection requirements. We can review manufacturability, fixture concepts, machining access and evidence formats. We do not define robot application loads, motion control, electrical architecture, safeguarding, certification or final system acceptance. The OEM, system integrator and appropriately qualified electrical and safety personnel retain responsibility for application design, standards, certification decisions and final validation.

Review the robotic welded OEM assemblies capability, our welding service scope and the wider robotics manufacturing hub. When the assembly drawing, BOM, datum scheme and inspection deliverables are ready, send the released package to DRAmetal for a project-specific mechanical fabrication review.