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13 February 2017

Schwäbische Werkzeugmaschinen BA 222 two-spindle, 4- or 5-axis horizontal machining centre for precision machining

High precision, 2-spindle HMC - SW BA 222 Schwäbische Werkzeugmaschinen BA 222 two-spindle, 4- or 5-axis horizontal machining centre for precision machining
The SW (Schwäbische Werkzeugmaschinen GmbH) BA 222 two-spindle, 4- or 5-axis horizontal machining centre boasts positional tolerances (Tp) of less than 0.006 mm, in accordance with statistical method VDI/DGQ 3441 (non-statistical methods would deliver a lower figure).

The machine is intended for demanding applications in precision engineering, such as within the watch, automotive and medical parts sectors. A position loop gain (Kv) factor of eight and a jerk factor (rate of change of acceleration) of 600 m/s³ make the BA 222 especially suitable for machining precise contours, as close adherence to the programmed path at speed is achieved at such figures.

Working area per spindle is 200 by 350 by 300 mm (X, Y, Z), with the spindle distance and X-axis working range of 200 mm allowing for multiple clamping scenarios. All feed axes accelerate at up to 20 m/s² to a rapid traverse of 70 m/min. The HSK-A40 motor spindles reach a maximum speed of 25,000 rpm in the first configuration level within 0.7 seconds, while chip-to-chip time for a tool change is just two seconds. Up to 60 tools per spindle are available.

The BA 222 features a monobloc main frame construction, basically a cube that contains all forces. This forms the basis for stability and dynamics, while at the same time is an integral part of the ‘crane hook machine’ consisting of the machine itself and the complete power supply.

Within this monobloc, at the front is located a horizontally-indexing unit that holds two working platforms: one outside the working area ready for loading/unloading, while the other is inside the working area. Each platform has two integrated rotary work tables, with the platforms rotated about a horizontal axis (up-and-over/down-and-under action) into/out of the working area in just 2.25 seconds.

The rotary tables can carry objects 425 mm diameter by 630 mm high. In the 5-axis version, the platforms have controlled rotary axis movement in addition to the rotary tables’ motion. To work parts, a 3-axis, twin-spindle machining unit is also housed within the frame.

In addition to this development, which rounds off the SW series machining centres having spindle distances of 700, 600, 400 or 300 mm, additions have also been made to the complementary series of machining centres with linear motor technology, specifically, the BA W02-22 (the linear motor counterpart to the BA 222). Currently the smallest model, this is targeted at high precision machining of free-form surfaces of parts made of non-magnetic materials via 5-axis machining and now has an expanded spindle distance of 250 mm.

The BA W02-22 features linear motors

Says Wolfgang Armleder, director of development at SW: “The BA 222 and BA W02-22 product family was designed for machining workpieces, primarily in the area of precision engineering. The recently developed BA 222 is a two-spindle machining centre with horizontal arrangement of the working spindle, which is especially suitable for 4- and 5-axis micro-machining of nearly all materials.

“A spindle distance of 200 mm [BA 222] with a working range of the X-axis that also extends to 200 mm allows for typical multiple clamping processes of workpieces, especially in the 4-axis version. The linear axes of the machining centre are equipped with ballscrew drives, the rotary axes with torque drives.”

The BA 222’s monobloc, so-called box-in-open-box design sees the machine frame designed as a composite structure made of steel with a solid mineral case core. This ensures high damping capacity with excellent temperature stability. This approach also minimises deflection and ensures optimum flow of force between the machining unit and the workpiece carrier. The Z-axis and X-axis slide of the block spindle box of the 3-axis machining unit (inserted into the main frame) is composed of spheroidal graphite, while the Y-axis slide is designed as a welded steel structure. This combined construction approach delivers high damping and stiffness, plus low moving mass that allow high acceleration rates of 4 m² to be achieved.

Explaining construction details that underpin precision, Armleder adds: “We connected two physically separate feed drives Y1 and Y2 [machining unit vertical travel], each consisting of a ballscrew drive, a direct absolute distance measuring system and a drive controller, coupled electronically on the control side. This guarantees optimum positioning accuracy, even with eccentric loading.”

And to reduce the thermal stress of the Y-axis motors, the weight of the vertical axis is compensated for by almost 100%, which leads to a significant boost in energy efficiency, he offers.

Turning to ergonomic matters, the tool magazine is separated from the working area and protected from swarf and spray. It offers two by 20, two by 40 or two by 60 positions. Tool management is performed directly from the main control panel. “This central and ergonomically favourable position saves the operator from walking all the way around the machine,” Armleder says.

As regards maintenance and service, the box-in-open-box concept specially developed by SW for very small and low-weight machining units allows free and convenient access from the back and top for service and maintenance tasks.

Attention has been paid to energy efficiency, too. As an example, three-phase synchronous motors with servo-controllers are used for all feed and spindle drives. Operation as a drive group and recovery of braking energy make it possible to achieve maximum energy efficiency standards. And, due to the hydraulic weight compensation of the vertical axis, no compressed air is consumed. The machining centre also has an IO link that allows, for example, for dynamic changes to sensor/actuator parameters through the user interface.

And to be able to make optimum use of the BA 222 from the very beginning, SW offers extensive services for this model, as it does for all of the company's machining centres, supporting the customer through the entire lifecycle of the system: Says Armleder: “For example, the ‘life startUp service’ includes set-up and installation, support in the start-up phase, commissioning of automation and clamping fixtures and machine moves, as well as production monitoring, thereby ensuring a smooth and speedy start of production. ‘life academy’ is a comprehensive, broadly based range of training options with a generous practical component that customers are able to participate in worldwide.”

Remote access for recording and evaluating data – useful for boosting productivity and analysing faults – plus a spare parts and repair service, as well as regular software and hardware updates, round off the service portfolio.

Andrew Allcock

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Supporting Information

Related Websites
http://www.sw-machines.com/en/

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