April 16, 2012 No.1526
Tokyo, April 16, 2012 - Mitsubishi Heavy Industries, Ltd. (MHI) has completed the development and begun full-scale marketing of a double column machining center - dubbed the "LH250" - capable of high-precision machining of workpieces up to 2 meters in length. The new unit not only offers significantly enhanced vibration absorption capability in the machine structure and greater rigidity in the high-speed main spindle, it also incorporates MHI's unique main spindle lubrication cooling technology and suppresses self-heating of the machine normally caused by long hours of continuous operation, which take a toll on machining precision. Through these innovations, the LH250 has achieved machining with 5 micrometer (µm, 0.001 millimeter) level precision, the highest level in the same size machine category. MHI targets broad use of the machine at machining shops that handle difficult-to-cut plate materials such as aircraft parts, and dies and molds.
The LH250 was developed applying the concept behind the company's micro milling machine - the "µV1" (micro V1) - to large-size workpiece machining. MHI has been marketing the µV1 since 2006 for direct milling of high-precision dies and molds and machining of electrodes and precision parts. The LH250 has a 2,500 millimeter (mm) long and 1,000 mm wide table with loading capacity up to 3,000 kilogram (kg).
In the LH250, MHI employed a special sliding surface structure that has significant vibration absorption capability. The new machine also employs an inner spindle and external housing cooling system for the main spindle head which has been proved in application to precision milling machines, plus a special jet lubrication system for bearings that is highly reliable and superior in cooling efficiency. Together these devices suppress thermal displacement caused by high-speed operation of the spindle, realize high rigidity in spindle rotation by optimizing the bearing preload throughout the low- to high-speed rotation range, and provide stable machining accuracy even through long hours of operation.
For the main spindle head, the HSK-A63* is adopted. By employing the wide-range type motor capable of producing large torque through the entire spindle speed range from 200 through 20,000 revolutions per minute (rpm), the LH250 can cope with a variety of machining conditions for diverse workpiece materials. By adding extra axis table as an optional equipment, the machine becomes capable of 4- and 5-axis machining. For machining of workpieces of extraordinary height, a 250 mm higher column model is also available. For convenience in carry-in and installation at the enduser's site, the length of the machine is kept to 3,300 mm.
MHI's machine tools are widely used at company factories and at partner companies for various machining needs, a situation that enables MHI to incorporate the detailed requirements of machining shops into new product development. The company developed the LH250 in full consideration of opinions voiced by its workshops involved in various business fields, including aerospace, power generation systems, and mass- and medium-lot manufacturing products. The new machine also integrates elemental technologies accumulated from MHI's operations in large-size double column machining centers and small-size high-precision milling machines.
MHI will introduce the LH250 at Intermold 2012 (Die and Mold Asia 2012), to take place at Intex Osaka from April 18 through 21. With the addition of the new machine, MHI intends to gain momentum in expanding its customer base by steadily probing market demand for precision milling machines able to accommodate long and medium-size workpieces – a niche that has been difficult to fill with earlier machines.
Major Specifications of "LH250" Double Column Machining Center
Spindle head specification: HSK-A63*
Spindle rotation speed: 200 – 20,000 revolutions per minutes (rpm)
Spindle motor output (rated): 22 / 18.5 kW (30 minutes / continuous)
Maximum spindle torque: 124 Nm (newton-meter), continuous
Stroke (X-axis / Y-axis / Z-axis): 2,500 mm / 1,000 mm / 600 mm
Rapid traverse rate (X-, Y- and Z-Axis): 12,000 mm/min
Machine size (width x depth x height): 7,380 mm x 3,593 mm x 3,300 mm
Machine weight: 20,000 kg
* Note: HSK is an ISO (International Organization for Standardization) standard cutting tool holding method, employed at the spindle head, referred to as "hollow-taper shank tooling." In HSK-A63, the cutting tool is held to the spindle at the coupling by two surfaces – the tapered and flange portions – which enables high-accuracy machining suppressing run-out of the cutting tool. A63 is the code for a hollow taper shank as defined by ISO. "A" indicates a shank type mainly used for the milling spindle of a machining center, and "63" indicates the diameter range of applicable tools.
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