KUHN recognised that its existing tube specification needed adjusting as it was receiving too many tubes that were too concave, too convex or outside acceptable tolerances.

Tata Steel and KUHN co-developed a new high strength cold formed hollow section specification unique to this application: Hybox TT (Tight Tolerances). This specification corresponds perfectly to the design of the gyrotedders and particularly the welding process of the hinges to the tubes.

Tata Steel’s specialist sector team modified the settings of its tubes mill, which ensured the tight specifications required could be met every time.

The collaboration between KUHN and Tata Steel has improved product quality such that KUHN’s tube rejection rate is now almost zero. The need for manual re-working has been eliminated, which has boosted output yield and overall production efficiency.

Concavity/Convexity

The dimensional and concavity/convexity tolerances, in particular, are very small. If the tube is too large or too convex, it does not fit into the space on the hinge. If it is too small or too concave, robot welding must be supplemented by a manual process, which incurs extra manufacturing time.

Tolerances on tube straightness are also very tight. If the section is not straight enough, the transmission axle will be put under unacceptable tension between each set of hinges.

Within KUHN’s gyrotedder range, tube wall thicknesses vary from small to large working widths. However, the same hinges are used in all the machines, so the tubes need to conform to the same specifications regardless of wall thickness.

Health and Safety

An additional consideration for KUHN is the health and safety of its employees. So it is vital that the ends of the tubes are free of burrs and sharp edges to avoid cuts during handling.

Surface Finish

The final challenge is cosmetic. Dents, scratches or rolling marks must be avoided so there is no need for heavy shot blasting or other finishing work before painting. In addition, the surface finish must be perfect, with a weld line that is extremely smooth and almost invisible. This is also a critical aspect of communicating KUHN’s premium brand positioning.

Historically, KUHN had written its own tube specifications. But it was increasingly apparent that these needed adjusting and refining because too many tubes were being rejected or reworked before use.