8 December 2015

On Point!

Development in industrial metal forming and welding processes sent the price of hollow, stainless steel, hypodermic needles plunging during the middle of the last century. This meant that doctors and hospital staff could afford to use needles once and throw them away instead of having to sterilise and reuse the same one time and again. Indeed, this advance in hygiene probably saved almost as many lives as the medication the needles are used to inject.

A billion needles
While no official statistics are available, it is safe to assume that more than a billion hypodermic needles are thrown away daily on a global scale. This turns the small price of needle into hefty sum.

“Medical technology is expensive, even for what appears to be a cheap product and we are working to reduce the costs,” explains Ralf Egerer, Director of Machine and Cryogenic Systems at Nexans in Germany. “Our aim is to halve the price of hypodermic needles in the near future.”

Egerer intends to achieve this goal using NanoWema, a machine set up at Nexans in Hannover, which rolls extremely narrow stainless steel strips into ultrathin tubes and then welds them with a TRUMPF laser beam.

Nexans is primarily a cable manufacturer with over 25,000 employees and deemed to be one of the cable giants, providing the deep-sea cables and industrial wiring and telecommunications lines that connect our world. With its NanoWema concept, Nexans is applying its core business expertise to a new market.

“It’s not such a great leap from cables to hypodermic needles,” Egerer continues. “To shield the wire bundles inside deep-sea cables against the effects of water pressure, we wrap them in thin-walled sheaths made of copper or aluminium. So, we are used to producing long, thin metal tubes. With NanoWema, we’ve managed to refine the process so we can make even narrower, finer tubing.”

The tubes he refers to are 1.8mm in diameter with walls 0.5mm thick. This kind of tubing is usually manufactured using TIG welding processes.

Lessons learned from cable production
Egerer explains: “TIG systems have technical limitations in terms of the amount of steel that can be processed and the wall thickness that can be achieved. TIG-welded tubes are usually twice the diameter of tubing that has been joined with a laser and have walls that are three times as thick.”

As a result intensive reworking is required after the TIG welding process to make the walls thinner and reduce the diameter. This involves pulling the thin tubing over a mandrel and forcing it through a narrower ring. The stainless steel hardens, becoming more dense and brittle.

But the steel has to remain malleable for subsequent finishing processes so the metal has to be relaxed again. To do this, the kilometre length of tubing is pulled through a red hot oven and heated throughout.

“Five reductions and three annealing steps are the norm for tubes produced conventionally, which involves a tremendous amount of energy and labour,” Egerer adds. “With a TRUMPF TruDiode diode laser, however, we can make tubes that are already close to the required dimensions, saving our customers the expense involved in subsequent processing and the large amount of space the finishing process requires.”

A welding seam five kilometres long
The NanoWema process starts with the machine unwinding a thin, five kilometre strip of metal from the spool and applying a lubricant to it. In a series of steps, the machine shapes the metal into a perfectly round, open tube using forming rollers. At the end of the shaping process, the outside edges of the strip are brought together to lie in parallel, side by side.

So fine is the gap between the edges that the TRUMPF TruDiode laser has to be incredibly precise, focusing its beam to an accuracy of 0.2mm. Instead of tracking the seam with the laser, Nexans developed a system for mechanically fixing the gap in place so that it is forced to pass exactly through the beam’s focal point.

The machine then pulls the tube-shaped metal strip through a narrow ring called a closing die. A small fin sticking out inside the ring rests in the gap, acting as a guide that keeps the seam centred as it passes along the line.

The TRUMPF laser can now weld the five-kilometre long seam from above in one go, without once having to adjust its focus. As soon as the tubing has been welded, the NanoWema system immediately winds it onto the spool and after four hours the laser gets a short break.

“We turn the laser on, pull kilometres of tubing beneath it and then switch it off again. It’s that simple,” Egerer says.

Of course, it isn’t as simple as that! The success of the operation is born out of Nexans’ long standing experience and it certainly provides the company with significant competitive advantage.

The TRUMPF laser can continuously weld kilometres of tubing at rates of up to 20 metres per minute which is twice the speed of a TIG welder. Also there is no dirt build-up on the material which has to be removed later. Welding lubricated tubing with TIG technology causes impurities due to the encrusted grease that forms on the welding wire. With laser, the grease simply burns off.

“Laser technology has become much cheaper in the last ten years. We’re able to get significantly more kilowatts of power out of every Euro we spend, with far greater efficiency,” Egerer concludes. “So taking all these factors into account, using the TRUMPF diode laser and the NanoWema process lets us produce ultra-thin tubing with unit costs that are half of the current market rate.”

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