|
|
| High-performance milling with a parallel kinematic system | | Milling on the ceiling | The Sud-Ouest Système company in France that specializes in processing machines for the aviation industry has developed a very innovative three-axis high speed processing center with "overhead" architecture. The control and linear drives are supplied by Siemens.
Mecanic Vallée, a region at the foot of the Massif Central in France, home to many mechanical engineering companies, calls itself. Small, highly innovative "high-tech" outfits have moved in next door to such well-known companies as Ratier-Figeac, Robert Bosch and Forest Liné. These also include the Sud-Ouest Système company which specializes in processing machines for the aerospace industry. The 35-man company with its headquarters in Figeac has now presented the prototype of an innovative three-axis high-speed processing center which turns the milling principle "upside down". The name of the machine - "Skymill" - is apt: The workpiece is located in a parallel kinematic holder "on the ceiling" and moves in the Z and X axes. The machining spindle only moves in the Y axis. A combination of linear drives in the workpiece holder and the spindle feed in this machine enables an extremely dynamic and efficient processing.
The designer and inventor of the concept is André Greffioz, an expert for mechatronic analysis and structural calculations in high-performance machine tools, whose company ELPS (Etude, Logiciel, Procédés spéciaux) has also registered the patent for the Skymill. His company did the simulations which provided the information about the expected dynamic behavior of the machine during high-speed processing. The prototype was then developed and built in less than a year.
Impressive performance data
The machine is designed consistently for highly productive high-speed cutting-processing - primarily of lightweight metal parts for the aerospace industry.
The high frequency spindle which travels on the Y axis underneath the workpiece holder has a rated power of 20 kilowatts, 2400 revolutions per minute and a torque of 21 Newtonmeters. The high powered motor spindle has a ceramic mount and uses the so-called minimum volume cooling for the HSC milling in which the smallest amounts of cooling lubricant are atomized as a mist on the tool blade and produce a "dry chipping". A curtain of compressed air shields the spindle from falling chippings. All three axes are driven with water-cooled linear motors 1FN3 from Siemens and reach an acceleration of 15m/s2. The linear axes are controlled by a Siemens Sinumerik 840D.
The cubic workpiece with the maximum dimensions of 600 x 500 millimeters and a permissible weight of 100 kilograms is fixed to the workpiece holder. The travel distances are 570 millimeters in the X axis, 500 millimeters in the Y axis and 250 millimeters in the Z axis.
The machine is fitted with a double pallet changer for maximum processing efficiency. Whilst one workpiece is being processed the next one can already be clamped completely. In the automatic workpiece change the workpiece then tips over into the "upside down" position within 15 seconds. The automatic tool changer with a tool magazine with 24 slots also speeds things up with a chip-to-chip time of 5 seconds.
Due to the processing direction from bottom to top and the funnel-like shape of the processing space, the chips collect automatically on the floor of the machine. The cutting volume of 1200cm3 per minute is disposed of by a chip conveyor.
Vibration-free structure
Guides, linear motors and measuring instrument are arranged so that they protrude as little as possible over the center of gravity of the machine. This guarantees the maximum possible stability and dynamic necessary for the high-speed processing of precision parts. The robust and extremely rigid welded construction of the machine housing also contributes to the freedom from vibration. Sud-Ouest Système quotes the range of accuracy of the machine as five micrometers.
The machine is presently being tested intensively under real production conditions. "We foresee a market of about ten machines a year for this type of high-performance processing center", Jean-Luc Baleydier, General Director of Sud-Ouest Système concludes. |  |
|
|
|
