Forming techniques for stainless steel (1) bending

Introduction

Stainless steel can be formed in the same way and using the same type of equipment as for most other steels. Some differences in technique apply and these are explained below. The information in this article is specifically directed towards austenitic stainless steels, the most frequently used family of stainless steels.

Austenitic stainless steels exhibit strong work hardening characteristics which affect many of the forming techniques. Machinery power levels need to be increased (or existing capability levels down-rated) compared with carbon steels. A higher rigidity of tools and machinery is necessary for working stainless steel.

All fabrication processes should be carried out in a clean, and if possible, a dedicated environment.

Bending flat material and bars

Flat sheet/plate and bar products can be bent using the press brake or bending machine. The work should be executed as quickly as possible due to work hardening characteristics of stainless steels, and a degree of over bending is necessary to counteract the springback of the bend. Inside radii of bends sharper than a figure equal to the material thickness under consideration should not be attempted.

Tube bending

Numerous architectural and process applications of tubular pipework and bends exist. In the bending of tube, guidelines can be set down, but first hand experience has to be gained to achieve regular reliable results.

Tubes can be bent satisfactorily using Rotary Bending machines, where one end of the (straight) tube is clamped and the machine former rotates to pull the tube to the designed radius. Alternatively, bending in a hydraulic press will push a radiused head on to the tube to force the tube into roller dies.

In considering either in-house or sub-contract tube bending, the quantity involved will have a significant bearing, as will the complexity of the final shapes.

Centre-line bend radii of 2 x tube diameter are generally considered to be a minimum for stainless steel materials.

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