December 12, 2006
The stainless steel stampings Viking Range produces often require complex draws and piercing, as well as sharp corners and creases—with flawless exterior finishes. Viking has moved from outsourcing its stampings to using press brakes to investing in hydraulic presses of increasing capacity and sophistication—all in an effort to gain greater control over the design, quality, and availability of stamped parts.
Viking Range Corp., Greenwood, Miss., was the first appliance-maker to popularize commercial-grade stainless steel appliances for residential kitchens with the introduction of its original range in 1987.
According to the appliance-maker, it has some of the highest standards for metal forming precision and aesthetics in any industry. It's no surprise that Viking has equally high standards when it comes to specifying metal forming equipment. According to Billy Peacock, plant manager—dishwasher, Viking Range Corp., the company has always faced a wide range (no pun intended) of metal forming challenges.
Viking product production has increased tremendously over the years, but it still produces a small number of stamped parts compared with other appliance-makers. The stampings the manufacturer produces often require complex draws and piercing, as well as sharp corners and creases—with flawless exterior finishes. Also, an unusually large proportion of Viking's stamped parts are stainless steel, including its signature exterior panels. On some products, half the parts formed are a stainless alloy. Stainless is notoriously difficult to form, and as a result, Viking had an unacceptably high scrap rate because of flaws or offal formation.
Viking's product line has expanded to include nearly every kind of kitchen appliance, from toasters to refrigerators to ventilation systems. As a result, Viking's approach to metal forming has evolved. It has moved from outsourcing its stampings to using press brakes to investing in hydraulic presses of increasing capacity and sophistication—all in an effort to gain greater control over the design, quality, and availability of stamped parts.
Over the years Viking purchased hydraulic presses from a variety of manufacturers, including a 200-ton press from Standard Industrial Corp. in 1990 that's still in use. However, its two latest hydraulic presses were purchased from AP&T. "We needed the best combination of capabilities, precision, and dependability," Peacock said.
As Viking Range's reputation and product line rapidly grew in the '90s, the company occasionally relied on subcontractors to produce products that couldn't be made in-house. One of these was the Viking dishwasher line, which was produced by Asko Cylinda, a Swedish manufacturer. Impressed with the quality of the dishwashers coming from Asko, Viking management traveled to Vara, Sweden, to tour the plant and evaluate its production capabilities.
In 1997 Asko updated its hydraulic press line in its Vara plant to an AP&T automated press system. The resulting installation handles complex production matrixes that use 776 different press tools. At Vara, it's not unusual to run 19 different tool sets over a three-day period.
After the trip, Viking executives chose an AP&T ZM 500-ton hydraulic press for one of their Greenwood plants. "The new press was going to be used for both blanking and drawing a range of parts, so it had to be flexible," Peacock said. To be flexible, the press, which was installed in September 2001, needed a wide coil window, a secondary hydraulic system, and a two-level press control system.
Many of the challenges that make stainless difficult to work with—hardness, tearing and cracking, springback, and easily marred surfaces—are further amplified by complex forming and high aesthetic standards required of Viking stampings (see Figure 1). "The press has consistently produced the most challenging stainless parts with low scrap rates," Peacock said.
The hydraulic press also addressed another chronic problem endemic to stainless steel stamping: short die life. In the past some dies lasted as briefly as 100 cycles before they needed sharpening. The same dies are now working for years without sharpening; one die has been in use for three years and has yet to require service. "Of course, good die design contributes a lot to performance like that," Peacock said. "There have been a few minor issues from time to time, as with all equipment, but they all have been easily resolved."
As demand for the Viking dishwasher line grew, it became obvious it needed its own dedicated production facility. In 2005 planning began for constructing the new facility, as did the search for a new 600-ton hydraulic press to handle the stamping duties.
Although experience with its existing AP&T press had been encouraging, Viking management wanted to be certain they found the best press for the application. As a result, the search initially included both mechanical and hydraulic presses. "We had three major selection criteria: reliability and precision, cost, and machine height. One of the competitors fell out early in the running because its machine was too tall for the new facility," Peacock said. "In the end, we decided to purchase another ZM-5000 hydraulic press."
The new AP&T press has fewer features than the one Viking purchased in 2001. Because this new unit will be producing a narrower range of parts exclusively for the dishwasher line, it doesn't require the operational flexibility the current press needs. Accordingly, the machine was specified with a narrower coil window, a single hydraulic unit, and a single level of control.
However, several features were considered essential for the new machine. "We needed motorized damping spindles to cushion impacts and minimize die wear and reduce operating noise to keep the building from shaking," Peacock said. This second hydraulic press also is equipped with an automatic hydraulic tool clamping system, as well as a tool monitoring interface system that links mounted dies directly to the press's control system.
The hydraulic press will be at the heart of the new Viking dishwasher production facility. The press already is in Greenwood, and it is being tweaked in a leased pilot plant facility while the new building is finished. Plant completion is scheduled for February 2007, and according to Peacock, the press will be one of the first pieces of equipment to be installed and have up and running.
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