Machining Center saves energy with Hydraulic Power Packs

  • June 18, 2014
  • Case Study

June 18, 2014 - HAWE Hydraulics supplied leakage-free seated valves, two-way pressure reducing valves and a higher efficiency  radial piston pump to Schwaebische Werkzeugmaschinen, whichb was able to achieve energy savings of  73 percent on its BA 400 machining centers.   "One of the main ways to save energy with a machine tool is to control the creation of heat, so you don't  need to cool the tool down again," says Ullrich Breuner, sales manager with  Hawe Hydraulics , which worked  with Schwaebische Werkzeugmaschinen to increase the efficiency of its BA 400 machining centers.   "Working with Schwaebische Werkzeugmaschinen, we started  developing seated valves that are leakage  free, which is a very different function compared to spool valves."  Breuner says the compact hydraulic  power packs used to revamp the BA  400 help save energy in three ways.  The first, and most obvious way, is by  using the leak-free seated valves to  eliminate permanent leakage. A  second way is the use of two-way  pressure-reducing valves to control  the different pressures for different  functions required by the machine  tool while also limiting the leakage  rate. The third way involves use of a  radial piston pump, which is more  efficient than a gear pump.   "A major benefit in developing these  machines has been the realization  that if you reduce the leakage rate,  the application can use a smaller  pump," says Breuner. "If you don't  have the permanent leakage rate and  the need to re-fill, it's possible to use  a 10-liter rather than a 15-liter pump.  You are still able to achieve the same  clamping time but use a smaller  power unit because you have  eliminated the leakage. And by using  a submersible motor, it helps create a  compact system that limits the  amount of oil needed."   Radial Piston Pump Efficiency

The BA 400 series machining center is used for small to  medium-sized workpieces, as well as ferrous metal  machining. The machining center is available with two  or four spindles and provides torque up to 200 Nm. It  is designed for clamping blanks while workpieces are machined on the opposite worktable; it can also be  used for multiple workpiece clamping on a double swivel table with three linear axes and two rotary axes.  The workpiece handling is done via robots or linear gantries.  Before implementation of the Hawe solution, the machine was fitted with standard hydraulic controls, but  Schwaebische Werkzeugmaschinen was looking for a solution  that would yield substantially more energy  savings.   The Hawe system eliminates use of a gear pump to generate hydraulic energy and replaces it with a radial  piston pump, which offers a higher efficiency than gearpumps or vane pumps. The choice of the pump's  power pack (HK series) also comes with a submerged motor  for the drive.   One key advantage is that the  significantly smaller motor keeps the  overall dimensions of the power pack  compact; and it loses less power in  idle mode than a standard air-cooled  motor. Plus, at peak demand,  submerged motors generate up to  twice the rated output where a  standard motor would break down  due to thermal reasons. In a  submerged motor, after  approximately 30 min, the oil reaches a steady-state temperature, which is considered an ideal condition for  operating machining tools. And because the HK power pack is built into an extruded aluminum casing with  cooling gills, it allows unhindered heat transfer, as  the air flowing by can easily dissipate the low thermal  energy.   A key advantage of this design is its low oil volume which, depending on the size of the power pack, can be  kept between 0.8 to 4 gal. Lower oil demand brings down the costs of exchanging oil as well as the strain on  the environment. For the machining center, the power pack's selected size holds 4 gal of oil. Using its radial  piston pump, the power pack supplies pressurized oil for operating pressures of up to 10,000 psi (700 bar).   Breuner says those pressures are  unusual for machining tools because  the majority of applications operate at  pressures between 2,200-4,400 psi  (150-300 bar). But because Hawe  manufactures all of its pressurized  components from steel, such high  operating pressures are not  problematic because the components  can withstand these loads over long  periods. Seated valves made from  steel wear less than slide valves in  cast housings.  A cooling wheel mounted at the top of  the power pack cools both the oil and  motor, which means that an additional  external cooling unit is avoided by  using Hawe's modular construction kit  system. Due to the size of the motor, low oil volume and compact dimensions, the power pack can be built  into the machine and integrated into the machining center.  Machine Operation with the New Pump The machining center's working mode varies depending on the workpiece. Many applications work with a  mixture of different workpieces, so that both the machine and hydraulics supply must be able to handle  everything from continuous operation to machine set-up  time. At standstill, the Hawe system operates in  storage mode and saves additional energy which can be used in the machining center.   A smooth switching accumulator charge valve recharges the storage whenever the duty switch point is  reached. Because storage is charged when the machine is started, the machine control monitors this  operation constantly. Once the predefined pressure has been attained, the valve will switch itself into  depressor circulation. At the slightest pressure, oil is re-fed into the tank.   Hawe's modular system provides options for the input block, such as pressure and return filters or TÜV- certified valves. A variety of filters and valves can be combined with the BA block to achieve highly  customized specifications.  The BA 400 machining center comes with a combination of sub-plates and a seated valve block (NBVP 16),  which again increases the machine's efficiency. Because the  seated valves are pre-controlled, they work  with minimum switching capacity. The directional seated valve provides a maximum volume flow of 5.3  gal/min and maximum operating pressure of 5,800 psi (400 bar).  The use of directional seated valves saves considerable electric power during operation of the machining  center. A machine with 15 spool valves and/or 3-way pressure reducers accumulates a leakage of  approximately 0.4 gal/min at 2,200 psi (150 bar), and  the configuration requires an additional drive input of  375W compared to a solution with seated valves.  In a two-shift operation, each with eight hours per  day and 200 working days per year, this adds up to 1,200 kWh for each machine. Plus, the heat generated by the additional energy input also needs to be lowered,  which means that the power saved doubles once more.   "The hydraulic power pack system has been available for more than 10 years," says Breuner. "But, until  recently, few companies were thinking about energy savings. Now companies are thinking more about the  total lifecycle, not only the initial investment but also  ongoing operational costs. If you need 1,200 kilowatts  less per year to run the machine and there are 10 machines, the savings are significant." About HAW E Hydraulics North  America:  Sixteen years ago North America was introduced to HAWE Hydraulik through its American subsidiary  HAWE Hydraulics. Today, the partnership brings more than 60 years of German engineering and  experience to North American mobile and industrial markets. HAWE provides integrated services that  include design, manufacture, set-up, a distributor network, and local inventory. Based in Charlotte, NC,  HAWE Hydraulics is positioned to respond quickly to service needs, as well as provide prototypes in a timely  manner. Headquartered in Munich Germany, HAWE Hydraulik is an ISO 9001:2000 certified international  supplier with a strong focus on supporting rapidly developing niche markets 

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