Doosan’s two-spindle VMC to double capacity
Doosan Machine Tools has introduced the DMP 500/2SP to its line of vertical machining centres. Equipped with 2 spindles and 2 automatic toolchangers (ATCs), this model is designed for production job shops and high-volume parts manufacturers. Compared to single-spindle machining centres, the system doubles productivity by machining 2 parts simultaneously, reducing work loading, unloading and idle time. For reduced set-up time, the right spindle features a W-axis adjustment of 20 mm (0.8”), allowing quick compensation for any variability in fixture heights between spindles.
Direct-drive, 12,000-rpm spindles with 87 foot-pounds of torque are standard, and 8,000-rpm spindles with 211 foot-pounds of
torque are optional. The load capacity is 1,763 lbs, and the table size is 47” * 20.5”, easily accommodating a variety of workpieces and fixtures. With the 20.5” Y-axis stroke, it offers a machining space well-suited for a range of parts. Dual 24-tool capacity magazines are standard, and 30- and 40-tool magazines are optional. The dual ATCs boast of 1.7 sec. tool-change time, keeping the tools in the cut longer.
The two-spindle VMC has just 1 table and one set of axes. Its work is thus machining in stereo—the machine makes 2 identical parts at once. A single cycle, programmed just as it would be for a standard VMC, executes the same tool path simultaneously on 2 workpieces. However, one addition is a single W axis. The new axis inclusion is part of the reason why a twospindle machine does not have to be challenging to use.
Doosan’s very first user of the two-spindle machine was a high-volume manufacturer fitting this description. Doosan designed the two-spindle DMP machine with this user in mind after the company came to the builder with its problem. The production demand this plant faced for a new set of parts, would have required 66 VMCs—too many for the maximum potential space the plant had available. Instead, the manufacturer asked for a machine with 2 spindles. Doosan’s development of this solution enabled the company to buy only 33 machines instead. (It has since installed more of them for other part numbers).
Rotary tables can be effective with this machine type, but a rotary table with 2 rotary axes introduces further X-Y variation to a set-up that is more complex than that of a typical machining centre. For the parts produced on the 33 machines in the initial installation, angled holes are added to the parts using a dual-axis rotary table on a singlespindle VMC.
Another important factor to consider is, when the machine door opens, the operator has to be right there to unload the 2 finished pieces and loading 2 new pieces. The initial high-volume user of this machine happens to excel at this; the company has a disciplined team of operators to attend to the two-spindle machines. To make it possible to realise the value of the machine with somewhat less discipline, the next version of the machine will likely feature a pallet changer to enable pairs of parts to be loaded and unloaded outside the work zone while the twospindle cycle is under way.