A welding quote requires more than individual part files or a general view of the structure. The manufacturer must understand how the components are positioned, where the welds are located, which dimensions are controlled after welding and what defines an acceptable finished assembly.

Incomplete documentation creates room for different interpretations. It may be unclear whether a joint is welded all around, which welds carry load, whether the assembly sequence may be changed and which characteristics must be inspected after the structure has cooled.

The drawing should not replace the manufacturer’s welding procedure, but it must define the functional requirements clearly: assembly content, materials, geometry, welded joints, datums, allowable variation, finishing, coating and acceptance criteria.

The documentation must show not only what is joined, but also the condition and geometry the assembly must retain after welding, cooling, straightening, machining and final inspection.

Which documents are needed for a welded assembly quote?

The most useful input is a coordinated document set in which item numbers, materials and revisions are consistent across all files.

• Assembly drawing. Shows component relationships, overall dimensions, datums, item numbers and welded joints.
• Individual part drawings. Required for laser cutting, turning, milling, drilling or other preparation before welding.
• Bill of materials. Lists item numbers, descriptions, materials, thicknesses, quantities and standard components.
• 3D model or STEP assembly. Helps review spatial geometry, weld access and the possible assembly sequence.
• Technical requirements. Define finished-assembly tolerances, straightening, grinding, coating, inspection and operating conditions.

Item numbers in the assembly drawing should correspond to the bill of materials and individual drawings. Mirrored parts, alternative versions and document revisions must be identified clearly.

If the documentation contains only a general arrangement without part dimensions, weld requirements or acceptance criteria, the manufacturing route cannot be defined reliably. The task may require development of the assembly drawing and manufacturing documentation.

Material, dimensional, tolerance and revision requirements for individual items are covered in the guide explaining what to include in a part drawing before requesting a quote.

How to define welded joints without ambiguity

The drawing should define the location, side, size and extent of every functionally important weld. A note saying only “weld” or an arrow without parameters is not enough for consistent interpretation.

Depending on the assembly, the documentation may specify:

• joint configuration and weld type, such as butt, fillet, tee, lap or another arrangement;
• the side of the joint to be welded;
• fillet-weld size, such as leg length z or throat thickness a, according to the selected notation system;
• continuous, intermittent or spot execution;
• weld length and pitch for intermittent welds;
• all-around welding or welding from both sides;
• edge preparation, root gap and other design-defined parameters;
• full penetration, leak-tightness or appearance requirements where functionally necessary.

Use one consistent symbolic system. The general notes should identify the applicable standard, such as ISO 2553, and the drawing should not mix different arrow-side and other-side conventions.

The size and layout of load-carrying welds should not be left for the welder to determine by judgement alone. When they are missing and affect strength or safety, separate approval or an engineering review is required. The manufacturer may propose the production method but should not change the structural intent without agreed requirements.

A larger continuous weld is not automatically better. Unnecessary weld volume increases heat input, labour and distortion risk. The related service page covers welding from drawings and technical requirements.

Which dimensions must be controlled after welding?

Welding creates local heating, followed by contraction during cooling. The geometry of the individual components before assembly and the dimensions of the completed weldment are therefore different levels of control.

The assembly drawing should identify the characteristics inspected after welding:

• overall frame, housing or support dimensions;
• distances between mounting holes and centre lines;
• diagonals and frame squareness;
• flatness of mounting and support surfaces;
• perpendicularity of uprights and parallelism of guide features;
• alignment of bushes, supports or bores;
• bracket positions relative to the primary datum.

Tight tolerances should not be applied to every non-functional dimension. Functional characteristics should be separated from reference dimensions; otherwise, more complex fixturing, additional straightening or post-weld machining may be required without improving assembly performance.

Tolerances may be specified individually or, where appropriate, through an agreed general tolerance class for welded constructions, such as ISO 13920. A general class does not replace individual tolerances for critical fits and interfaces.

If a face must be milled or aligned holes must be bored after welding, that operation should be included before the blanks are produced. The related article explains when laser cutting and welding must be followed by secondary machining.

1. Select the primary datum of the completed assembly.
2. Identify dimensions controlling installation and mechanism operation.
3. State which characteristics are inspected after welding.
4. Include machining allowance on surfaces finished later.
5. Define whether straightening is permitted when it affects the result.

Welded assembly drawing checklist

Review the main information groups before submitting the documentation for quotation.

What to define for assembly, grinding and inspection

The assembly drawing should show not only the final arrangement but also whether the structure can be assembled in a workable sequence. A component installed too early must not block access to a weld, fastener or inspection datum.

Clarify:

• whether a dedicated fixture is required or universal stops are sufficient;
• which components are installed first;
• which elements are removable, adjustable or permanently welded;
• whether bushes, fasteners, bearing supports, threaded inserts and other hardware are included;
• which welds remain visible and which must be ground;
• whether grinding is local, flush or decorative;
• which coating is applied and which surfaces must be protected.

Grinding every weld flush is not an automatic part of welding. It adds labour, may alter the joint profile and should be specified only where installation, safety, hygiene or appearance requires it.

The inspection scope must also be agreed. A standard commercial assembly may require visual and dimensional inspection against the drawing. Quality levels, nondestructive examination, leak testing or load testing should be specified separately only where the application requires them.

When the order includes component preparation, hardware installation, mechanical assembly and interaction checks, it becomes a broader mechanical assembly service. The approved characteristics of the completed structure are also linked to manufacturing quality control.

Final review before requesting a welded assembly quote

1. Item numbers in the assembly drawing correspond to the bill of materials.
2. Material, thickness or required stock is defined for each component.
3. One consistent weld-symbol system is used.
4. The location, side, size and extent of functional welds are unambiguous.
5. The main datums and critical dimensions of the completed structure are shown.
6. It is clear which characteristics are inspected after welding.
7. Straightening, post-weld machining, grinding and coating are specified where required.
8. All welds are accessible in the intended assembly sequence.
9. Quantity, repeat demand and possible fixture requirements are stated.
10. Special quality, appearance, leak-tightness or inspection requirements are defined.
11. The documentation uses the current approved revision.

An initial discussion can begin with an available drawing, STEP model, sketch or photographs. Before manufacturing, however, the requirements controlling strength, geometry, assembly and acceptance of the completed weldment must be agreed unambiguously.

The clearer the separation between individual part requirements, welded joints, assembly and secondary processing, the more accurately the manufacturer can define the route and quote the actual scope of work.