These dictate how "flat" a sheet or plate must be and how "straight" a long member (like an H-beam) must remain after welding, ensuring the component does not twist or bow unacceptably. Importance of EN ISO 13920-BF in Fabrication
The chosen class for shape and position . It governs characteristics like straightness, flatness, and parallelism across the welded framework. The positional classes range from E (Fine) through H (Very Coarse), leaving Class F as the standard "medium" benchmark. Class B: Dimensional Tolerances (Linear & Angular)
Instead of hand-calculating specific limits for every component, engineers cite this framework on engineering drawings to instantly enforce specific tolerances. 1. General Tolerances for Linear Dimensions (Class B)
The standard covers the following aspects: en iso 13920-bf
When working with EN ISO 13920-BF, keep the following rules in mind:
Example: A 2,500 mm long beam should not bow more than 3 mm over its entire length.
: ±20 minutes of a degree (approx. ±6 mm per meter). These dictate how "flat" a sheet or plate
| Wrong usage | Correction | |-------------|-------------| | "EN ISO 13920-BF" as tolerance class | Use C/D/E/F only. BF is weld prep code. | | Assuming BF means both tolerance and prep | Split into two references: ISO 13920 for tolerances + ISO 9692-1 for BF | | Using Class B | Not defined – switch to Class C if fine needed |
Class B specifies the following typical tolerances based on the length ( ) of the part: plus or minus 1.0 plus or minus 1.0 plus or minus 3.0 plus or minus 6.0 (Tolerances continue to scale for larger structures) Shape and Position (Class F)
Refers to the Intermediate tolerance class for straightness, flatness, and parallelism. It represents a standard, reliable quality level in fabrication. The positional classes range from E (Fine) through
Class F dictates the allowable deviations for . It specifically caps errors in straightness, flatness, and parallelism. Geometrical classes span from E (tightest) to H (loosest). Class F strikes a balance, offering standard structural alignment ideal for frames that interface with secondary components. Technical Tolerance Values Under Class BF
Class B does not account for accumulated shrinkage. If you weld a 10-meter truss, expect 5–10 mm of overall shrinkage. The tolerance of ±8 mm may still be violated if you do not pre-set angles or use back-step welding techniques.
EN ISO 13920 is a European standard titled, "Welding — General tolerances for welded constructions — Dimensions for lengths and angles — Shape and position" . It is the European adoption of the international standard ISO 13920:2023, having been approved by CEN (European Committee for Standardization) without any modification. This standard is a critical tool in the manufacturing and engineering industries, as it specifies general tolerances for all welded structures, including weldments, welding assemblies, and other fabricated constructions.
Specifying on a contract or purchase order is not just a suggestion—it is a contractual obligation.