New dressing technology improves processing of exotic materials

The Studer S41 with a WireDress dressing unit enables sintered metal bonds to be dressed in the grinding machine at full wheel speed. Photo courtesy of Studer.

Situation

Switzerland’s Fischer AG, a manufacturer of high-precision spindles, needed to increase productivity at its Herzogenbuchsee facility, while at the same time improving its ability to grind exotic materials such as titanium.

Alfred Mair, head of grinding technology at Fischer, faced a challenge because he found he could not solve the problem with a conventional grinding machine. Grinding specialist Studer suggested a new technology available on its S41 CNC universal cylindrical grinding machine.

Specifically designed for large workpieces, it has a length between centres of 1,000/1,600 mm and a centre height of 225/275 mm. It processes workpieces up to a maximum weight of 250 kg.

The key for Fischer, however, was the Studer’s WireDress® dressing system.

“We had high hopes that we could use metal-bonded grinding wheels for a measurable and reproducible highest quality, higher productivity, more universal machining options, as well as reduced tool costs,” said Mair.

Resolution

According to the manufacturer, not only does electro-erosive integrated dressing technology reduce downtime, it also enables sintered metal bonds to be dressed in the grinding machine at full wheel speed.

Studer configured the grinder with additional features to solve Fischer’s manufacturing challenges.

The machine received a special high-speed external grinding motor spindle in which the axial growth is particularly small. In addition, the spindle is tapered at the rear end, avoiding possible collision situations.

This is a specific benefit for face/shoulder grinding with the spindle at an angle.

The grinder was also built with a fully automatic workpiece magazine and handling system.

“[We see production that is] three to five times faster than with conventional technology, with absolute reproducibility, ground in a tolerance range of less than 1 μm,” said Mair.

But how does this dressing technology work?

“It is a well-known fact that metal-bonded grinding wheels are much more durable and dimensionally stable when machining difficult-to-machine materials and ultimately enable higher productivity,” explained Michael Klotz, project manager for development at Fritz Studer AG. “The problem with this is that metal bonds can only be dressed to a very limited extent using conventional methods in the grinding machine. In addition to this, there is a high dressing tool wear associated with a low cutting ability. This is neither an operator-friendly, nor a high-quality and process-consistent dressing method.”

That’s why, according to Klotz, the “best” bond, a metal bond, is rarely used.

With the WireDress system, dressing is done at full wheel speed. In contrast to conventional mechanical or external EDM dressing, this type of dressing occurs by a modified wire erosion in the grinding machine, where the grinding oil serves as a dielectric.

The dressing process is contactless and wear-free. The grit itself is not dressed, the metallic bond around the grit is removed. Depending on how deep the grit is embedded in the bond, it either falls out or remains with original sharpness in the bond.

The grinding wheel receives a high grain clearance for maximum cutting capability, lower grinding forces, and low burning risk.

Using a bond with a high dimensional stability, almost any profile can be precision-contoured in the μm range.

With this technology, the accurate processing of sophisticated and small geometries that was neither economical nor possible before, now becomes feasible, according to the manufacturer.

“If you have the right technology, the process is peanuts. In the past, you had to feel your way. Today everything is process-stable. This also has the advantage that you can calculate the costs more clearly,” said Mair.

Another advantage that should be of interest to engineers and design engineers in particular: not only can straight forms be dressed, but also very fine profiles, which was previously not possible with metal-bonded grinding wheels. This opens completely new design possibilities for engineers.