It is essential for a staircase manufacturer to achieve perfect surfaces. And that can mean only one thing: perfect sanding! To best achieve this process, Wiehl, the staircase manufacturing company, purchased an eleven-metre long "dmc system bt" with top/bottom groups wide belt sander, that cut the cycle time by 60% and resulted in a unique quality.
Wooden staircase experts for over 75 years and now in their third generation. Wiehl, is a company based in Bingen in Upper Swabia, just a few kilometres from Sigmaringen, and is at the heart of this "Made in Germany" story of excellence. Over the decades, the production centre covering over 5,000 m2 has seen the creation of more than 70 thousand staircases, all of them produced with the utmost precision and modern technologies.
And it is here that we will gain access to the "secrets of success" behind the Wiehl creations. Inside the plant, we instantly spot an SCM "dmc system bt" wide belt sander, in front of which stands a trolley with roughly cut, unfinished pieces of wood. These will be used to create the stringers.
Before the stringers are machined on a NC machining centre, the Head carpenter, Thomas Vogel sands their surfaces on this exclusive SCM technological solution. The glued unfinished pieces of wood, initially rectangular, have already been shaped by his colleagues using a band saw. Thomas Vogel stands in front of the sanding machine's touch screen, keys in a nominal thickness of 56 mm and selects the "Oak stringers" program. At this stage, he can see all the machine's working units on the screen in a 3D graph and, with a few simple taps on the screen, can turn each unit on and off as well as select the relative cutting speed. And that's not all: the graph also provides additional information by showing which abrasive belts are worn and need replacing.
The first part of the machine sands the top side of the piece and has a steel calibrating roller, a rubber-coated sanding roller, a crossbelt sanding unit, a planetary unit for multidirectional sanding and lastly a superfinishing pad unit. On the second part of the machine, specifically designed to sand the underside of the piece, we find a calibrating roller, a soft rubber-covered roller and a sanding pad unit.
Right at the start of work on the order, Vogel's colleagues strove to ensure the side most visible on the staircase was facing upwards so it could be sanded at the end with the superfinishing pad unit. The work program used for the unfinished pieces requires 60 grit belts for calibrating rollers, 120 grit for rubber-coated rollers and 180 grit for pad units. Using the machine's doors, fitted with transparent panels, Thomas Vogel observes the units and makes sure that the right belts are being used.
The stringer that is almost six metres long and weighs over 70 kg is lifted by a vacuum lifter that rests one end on the sander infeed roller unit and the other on a roller table. Vogel then turns off the lifting unit's suction device and inserts the stringer into the sanding machine; at which point, he can pick up the next stringer. Behind the machine, an operator stacks the sanded stringers. The machine removes 1 mm of material from each side at a feed speed of 6 m/min. The end result is a perfectly sanded surface on both sides.
With 50 employees, Wiehl produces around 2,000 wooden staircases per year, especially for manufacturers of pre-fabricated houses. Most of the production is done on NC machines that route the edges of the stringers, handrails, treads and landings. The treads are then profiled, together with the stringers and handrails.
Specific copying feelers ensure that the radius of the edges proceeds tangentially to the adjacent surfaces. In order to achieve maximum precision, Wiehl's experts calibrate the pieces before they reach the NC machining centre.
In 2019, when the time had come to replace a wide belt sanding machine purchased twenty years earlier, the CEO Jörg Wiehl opted for this SCM "dmc system bt" with top/bottom groups wide belt sander. Jörg Wiehl aimed to achieve even better quality for his machining work with this investment.
The aim was to increase ergonomics and efficiency. In addition, the machine would simplify the passage to water-borne paints. As is well known, water causes swelling and the wood fibres rise; a more precise, finer sanding contains this phenomenon. Lastly, the machine needed to have a wire brush unit for rustication of the surfaces. The need for a more ergonomic technological solution is satisfied not only by the vacuum lifters, but above all by the working units for sanding the bottom side of the piece on the SCM "dmc system bt" wide belt sander. Indeed, the latter avoids the need to rotate the panel and it going through the machine a second time. Furthermore, while the previous sanding machine was fitted with only three traditional units, this new solution also has a planetary unit and a superfinishing unit with electronic sectional pad and lamellar belt. The latter prevents excessive strain on the abrasive belt and subsequent overheating of the surface being machined. The planetary unit, in turn, simultaneously sands or brushes in every direction. This ensures an excellent surface treatment on painted surfaces and an even, well-defined structuring.
"We regard the sanding machine as essential - says Jörg Wiehl -. Each piece goes through twice, once to sand the raw material upstream of the CNC and once for an intermediate sanding of painted surfaces. Thanks to this SCM sander, the machine operator and assistant no longer need to bend down, lift or tilt heavy pieces and no longer need to return them to the machine infeed to go through again. In addition, the cycle time has been reduced by 60% and the surface quality has improved, and even the painting stage can be done more efficiently. My employees particularly appreciate the intuitive machine control and technological reliability offered by this solution".
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