Welded frames for agricultural and construction machinery are load-carrying structures of cut plate and section steel, welded to a stated quality level and machined after welding at the pin bores, bearing seats and mounting faces. A drawing for one names the weld quality level (ISO 5817), the fabricator's quality requirements (ISO 3834), the tolerance class for as-welded dimensions (ISO 13920) and the fits for the machined bores (ISO 286).
What are welded frames for agricultural and construction machinery?
They are the structural parts a machine is built around: chassis and subframes, booms and arms, linkage parts, brackets, lugs and mounts. A frame is cut, fitted up, welded, possibly stress-relieved, machined and coated before it ships. The parts that carry the machine's functions, such as pin bores and mounting faces, are machined last because the welded structure moves during welding.
These machines work under changing loads, and the weld requirements follow from that. ISO 5817:2023 considers several types of load, among them static, thermal, corrosion and pressure load, and gives additional guidance on fatigue loads in its Annex B. Which welds are highly loaded is the designer's call; the supplier needs it as a quality level on the drawing. The process itself is described on our page on welded assemblies.
Which parts of the machine are welded and which are machined?
A frame order can also include brackets, pins, bushings and hydraulic blocks, and each needs different entries on the drawing.
Table 1. Part types in a machine frame job, process route and what the drawing must state
| Part type | Process route | The drawing must state | Standard basis |
|---|---|---|---|
| Frame, chassis, subframe | Cutting, fit-up, welding, optional stress relief, machining of mounting faces and bores | Weld quality level, ISO 3834 part, tolerance class for as-welded dimensions, which faces are machined after welding | ISO 5817; ISO 3834; ISO 13920 |
| Boom, arm, linkage | As above, with weld preparation and joint design set by the designer | Quality level per weld; any fatigue requirement from the machine builder's calculation | ISO 5817 (Annex B, fatigue) |
| Brackets, lugs, mounts | Cut from plate, welded to the frame or machined as loose parts | General tolerance class, weld level where welded on | ISO 13920; ISO 2768-1 |
| Pins and bushings | Turned, ground, heat-treated as drawn; bushings pressed into the bore | Fit class, hardness if specified, bore after pressing in | ISO 286-1 |
| Hydraulic blocks, cylinder bosses | Block milled and drilled; bosses welded into the frame | Cleanliness and pressure test, see the hydraulic block article | Drawing and machine builder's specification |
Source: ISO 5817:2023; ISO 3834-1:2021; ISO 13920:2023; ISO 286-1:2010. The split by part type is our recommendation, not a requirement of these standards.
For the hydraulic blocks in the last row, see hydraulic manifolds and valve blocks.
Which weld requirements belong on the drawing?
Four references cover the weld, the workshop and the dimensions. Statuses are as of 2026-10-30.
- Weld quality level, ISO 5817:2023. Levels B, C and D for imperfections in fusion-welded joints in steel, nickel, titanium and their alloys, from 0.5 mm material thickness. B corresponds to the highest requirement on the finished weld. The 2023 edition replaced ISO 5817:2014.
- Fabricator requirements, ISO 3834. Three levels: part 2 comprehensive, part 3 standard, part 4 elementary. Part 1 (2021) gives the criteria for choosing among them, applies in workshops and at field installation sites, and does not specify a total quality management system. ISO 3834-2:2021 was confirmed on 2026-09-22.
- As-welded dimensions, ISO 13920:2023. General tolerances for lengths and angles, shape and position of welded structures, in four classes chosen by function. The 2023 edition replaced ISO 13920:1996, so write the year.
- Qualification. Welding procedures are qualified to ISO 15614-1, whose 2017 edition (amended 2019) is current; a revision reached FDIS registration on 2026-10-21. Welders are qualified to ISO 9606-1:2012, confirmed in 2023, with a replacement in draft.
A procedure qualification covers a range of qualification, not every joint a workshop welds. The buyer can ask which qualified procedure covers which weld on the drawing. For the full explanation of levels and certificates, see weld quality levels, ISO 3834 and EN 1090.
Does high-strength steel change the welding?
It can, because structural steels such as S355J2 (EN 10025-2) and thermomechanically rolled high-yield grades such as S700MC (EN 10149-2) are not welded identically. For S700MC the designation reflects a minimum yield strength of 700 MPa (SSAB product page). The grade and thickness belong on the drawing, because the qualified procedure holds only for the range tested, and a change of grade or thickness after quotation can mean a new procedure test. Ask for the material certificate with the order, type 3.1 where the drawing calls for it.
How do you machine pin bores and bushing seats on a welded frame?
Bores that must line up across two lugs are machined after welding, in one setup where the part allows it, because the frame distorts during welding. Stress relief before machining, if the drawing asks for it, is stated on the drawing too.
The tolerance is the reason general tolerances do not apply here. For a 40 mm pin bore, a fit of H7 allows 0 to +25 µm, since IT7 for nominal sizes over 30 up to 50 mm is 25 µm (ISO 286-1:2010). ISO 2768-m would allow ±0.3 mm for the same size (ISO 2768-1:1989, Table 1), a zone 0.6 mm wide and 24 times that of H7. ISO 286 fits and IT grades lists the values for other sizes.
For a bushing, say which dimension is final: the outside diameter before pressing, or the bore after pressing in. The two are not the same, because the press fit closes the bore.
Which coatings suit welded frames and what must the drawing say?
A coating is chosen for the environment and the process route, and the drawing records the choice. Machined bores and faces are either masked or finished after coating; state which.
Table 2. Coating options for welded frames and what to specify
| Coating | The drawing must state | Standard basis |
|---|---|---|
| Liquid paint system (primer and topcoat) | System, film thickness, colour, masked areas | ISO 12944 for steel structures, or the machine builder's own specification |
| Powder coating | Thickness, colour, masked areas, pre-treatment | Machine builder's specification |
| Cataphoretic e-coat | Thickness, whether a topcoat follows, masked areas | Machine builder's specification |
| Hot-dip galvanizing | Zinc coating requirements, vent and drain openings in hollow sections, distortion allowance | ISO 1461:2022 |
Source: ISO 1461:2022; ISO 12944-1:2017. The columns are our recommendation for the order; no standard prescribes this table.
ISO 12944 is written for steel structures, not machines, and ISO 12944-1:2017 is flagged for revision, so the drawing should say which parts apply or name the machine builder's specification. Salt spray hours are a number from that specification: ISO 9227:2022 covers apparatus and procedure, does not set exposure periods or how results are read, and is not a means of predicting long-term corrosion resistance. Plating and anodizing for the smaller machined parts are a separate topic.
What stays with the machine builder?
The design, the load case and the conformity of the finished machine. Machinery placed on the EU market before 20 January 2027 must comply with Directive 2006/42/EC; from 20 January 2027 Regulation (EU) 2023/1230 applies on a mandatory basis (European Commission, status as of 2026-10-30). A parts supplier contributes records that match the drawing revision: material certificates, weld documentation and measurement reports.
Protective structures sit in the same category. ISO 3471:2008 specifies performance requirements for metallic roll-over protective structures on earth-moving machines of 700 kg and above; ISO 3449:2005 specifies laboratory tests for falling-object protective structures on ride-on earth-moving machines. A cab frame welded by a supplier is made to the builder's drawing, and a change of material, weld or geometry goes back to the builder.
On the commercial side, industrial goods covered by the EU–Türkiye customs union move at zero customs duty when accompanied by an A.TR movement certificate (European Commission, Access2Markets, page version 2026-10-14), and road freight from Bursa to central Europe typically takes 5 to 10 days. The article on machined and welded parts for machine builders describes how a one-off or small batch runs through our network.
Frequently asked questions
- What is a welded frame for agricultural and construction machinery?
- A load-carrying structure of cut plate and section steel, welded to a stated quality level and machined after welding at the pin bores, bearing seats and mounting faces. Chassis, subframes, booms, arms and brackets are typical examples.
- Which weld quality level should the drawing state?
- ISO 5817:2023 offers levels B, C and D, with B the highest requirement on the finished weld. The designer chooses the level per weld from the load case; a weld without a stated level has no agreed acceptance limit.
- Is ISO 3834 mandatory for a frame supplier?
- ISO 3834 applies to a supplier when the order or drawing calls it up. Part 1 gives the criteria for choosing among part 2 (comprehensive), part 3 (standard) and part 4 (elementary).
- Why are pin bores machined after welding?
- Welding distorts the structure, so bores that must align across two lugs can only be held to an ISO 286 fit if they are machined once the frame is welded. A general tolerance such as ISO 2768-m is far too wide for them.
- Does a salt spray test hour count prove a coating lasts?
- No. ISO 9227:2022 describes the test apparatus and procedure, leaves exposure periods and the interpretation of results to the product specification, and states that the test does not predict long-term corrosion resistance.
- Are welded frames from Türkiye duty-free in the EU?
- Industrial goods covered by the EU–Türkiye customs union move at zero customs duty when accompanied by an A.TR movement certificate, according to the European Commission. Import VAT and customs formalities still apply.
Sources
- ISO 5817:2023, Fusion-welded joints in steel, nickel, titanium and their alloys, quality levels for imperfections (ISO catalogue)
- ISO 3834-1:2021, Quality requirements for fusion welding of metallic materials, Part 1: criteria for selecting the level (ISO catalogue)
- ISO 3834-2:2021, Part 2: comprehensive quality requirements, confirmed 2026-09-22 (ISO catalogue)
- ISO 13920:2023, General tolerances for welded constructions (ISO catalogue)
- ISO 15614-1, Welding procedure test, Part 1, draft revision at FDIS stage 2026-10-21 (ISO catalogue)
- ISO 9606-1:2012, Qualification testing of welders, Part 1: steels (ISO catalogue)
- ISO 286-1:2010, ISO code system for tolerances on linear sizes (ISO catalogue)
- IT grades by nominal size range, ISO 286-1 values (table reproduced on Wikipedia)
- ISO 2768-1:1989, General tolerances, Part 1 (ISO catalogue)
- SSAB Strenx Section 700MC, product page naming EN 10149-2 and 700 MPa minimum yield strength
- ISO 1461:2022, Hot dip galvanized coatings on fabricated iron and steel articles (ISO catalogue)
- ISO 9227:2022, Corrosion tests in artificial atmospheres, salt spray tests (ISO catalogue)
- ISO 12944-1:2017, Corrosion protection of steel structures by protective paint systems, Part 1 (ISO catalogue)
- ISO 3471:2008, Earth-moving machinery, roll-over protective structures (ISO catalogue)
- ISO 3449:2005, Earth-moving machinery, falling-object protective structures (ISO catalogue)
- Machinery Regulation (EU) 2023/1230, application from 20 January 2027 (European Commission, DG GROW)
- EU–Türkiye Customs Union (European Commission, Access2Markets, page version 2026-10-14)
Questions on a drawing? sales@ertas.engineering