12/16/2021 | Industries & applications

Stainless precision steel strip with outstanding welding and forming properties for the manufacture of medical cannulas

Cannulas, such as those needed for intravenous access, are mass-produced medical devices that are used billions of times a year. Their safe use, however, requires each and every one to be absolutely uniform and free of defects. As a result, this medical product’s multistage manufacturing process places high demands on the material, particularly in terms of its weldability and formability. Stainless precision steel strip from Waelzholz offers the perfect properties for this purpose.

“The production of fine medical cannulas from cold rolled steel strip requires several production steps with different requirements – the most crucial of which are forming and welding the material into tubes, as well as the subsequent drawing process, which reduces the cross-section by up to 80 percent,” explains Ralf Sauer, sales specialist for stainless precision steel strip at Waelzholz.

Our materials meet a wide range of requirements from customers in the medical technology sector:

Stainless steel material
Perfect weldability
Excellent formability
Flawless surfaces
Consistently high quality over numerous production batches

Precise weld seams thanks to flatness and exact cutting edges

In the first stage of production, the narrow steel strip supplied by Waelzholz is formed into tubes with a diameter of just a few millimeters and then welded shut. The precision of the weld seams plays a critical role in the subsequent processing steps and in the subsequent use of the cannulas. “When it comes to the process of welding the later cannulas, it’s extremely important that the strip is completely flat and that the cutting edges are uniform,” says Jan Ullosat, materials engineer at Waelzholz.

Waelzholz has optimized the cutting process using specially developed tools, particularly for materials whose efficient further processing requires highly uniform edges. This results in extremely precise cutting edges, meaning that it’s possible to almost completely avoid asymmetrical weld seams (see microscope images).

By optimizing the technically relevant material parameters, the stainless steel material for medical devices also offers clear financial advantages, often saving our customers time-consuming and cost-intensive preparatory processing steps.

Cross section of stainless precision steel strip with high-precision edges (microscope image 1)

Cross section of stainless precision steel strip with high-precision edges (microscope image 2)

Medical cannula with perfect weld seam thanks to stainless precision steel strip (microscope image 3)

A look through the microscope at the cross-section of stainless precision strip steel shows the high-precision edge finish with very low burr formation (image 1 and 2). The special feature here: The precision of the cutting edge remains constant over the entire strip length. This enables the production of fine cannulas with a perfect weld seam and flawless, smooth surfaces (image 3).

Uniform microstructure and high degree of purity for ideal drawing processes

To produce a fine cannula, the diameter of the tubes is reduced after welding by a drawing process in several passes from, for example, 6 to as little as 1.4 millimeters (from 0,236 to 0,055 in). “This considerable level of deformation requires a material with a uniform microstructure as well as a high degree of purity. Our nickel-alloyed stainless precision steel strip offers all of this for this special application,” explains materials engineer Ullosat. To ensure that the finished tubes have a uniform diameter, it’s also essential to maintain extremely tight width tolerances along the entire strip length. Moreover, the surface quality also plays a significant role in the production of high-quality cannulas. “Even the smallest scratches could lead to cracks during forming. That’s why we pay special attention to consistently flawless surfaces,” says Ullosat.

Sophisticated quality management system for reproducible properties of stainless material grades

“Waelzholz has a proven track record of manufacturing absolutely homogeneous strip across many production batches. This applies equally to our stainless steel materials’ flatness, cutting edges, and surfaces as well as to their microstructure and degree of purity. Thanks to its consistently high quality, customers from the medical technology sector have been relying on our stainless precision steel strip for over 10 years,” Sauer reports. In addition to medical cannulas, blood lancets and various spring applications for insulin pens, among other devices, are also manufactured using stainless precision steel strip from Waelzholz.

We achieve this high level of confidence in our products through sophisticated quality management with transparent traceability and thorough documentation, among other measures. “We’re excited about every new project with technically complex requirements and high standards when it comes to seamless quality management. This is because we can also score points with and delight our customers when it comes to these two aspects,” sums up Sauer.