Many areas of workpieces machining, for example in precision engineering with its applications in the watch industry, in the automotive sector or in medical technology, require the use of especially precise machining centers because the high quality standard allows only slight tolerances. Now SW (Schwäbische Werkzeugmaschinen GmbH) has developed a two-spindle machining center for 4 and 5-axis machining with a spindle distance and X-axis working range of 200 mm to allow for typical multiple clamping applications. The BA 222, which features a monoblock construction, box-in-open-box machining unit and a double swivel carrier for loading and unloading in parallel to machining time, rounds off the SW series for ball screw drive machining centers with a spindle distance of 700, 600, 400 or 300 mm. Additions have also been made to the series of machining centers with linear motor technology: The BA W02-22, currently the smallest model, is specially oriented for high-precision machining with free-form surfaces of 5-axis workpieces made of non-magnetic materials. Featuring an expanded spindle distance of 250 mm, it achieves top TCO results with direct drive technology.

“The BA 222 and BA W02-22 product family was designed for machining workpieces, primarily in the area of precision engineering,” explains Wolfgang Armleder, Director of Development at SW. “The recently developed BA 222 is a two-spindle machining center 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 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 center are equipped with ball screw drives, the rotary axes with torque drives”.

Monoblock construction and box-in-open-box design

A special system feature of the BA 222 is its monoblock construction, which minimizes deflection and ensures optimum flow of force between the machining unit and the workpiece carrier. “The monoblock as the bearing machine bed forms the basis for stability and dynamics. At the same time it is an integral part of the crane hook machine consisting of the machine itself and the complete power supply,” Armleder continues. To allow for high acceleration rates of 4 m² for the machining unit, the monoblock is designed as a composite structure made of steel with a solid mineral case core that ensures high damping capacity with excellent temperature stability.

The three-axis unit itself was also designed to allow for high damping for heavy-duty machining operations. Because of this, the block spindle boxes of the unit’s Z slide and X slide are made of spheroidal graphite cast iron (EN-GJS-400-15). To keep the moving masses low, the slide is also designed as a welded steel structure. In addition, the machining unit was designed with a “box-in-open-box” concept specially developed by SW for very small and low-weight machining units which require free and convenient access from the back and top for service and maintenance tasks. The entire rear end of the machining unit is inserted into the monoblock and the machine area with the freely accessible components is protected against swarf ejected from the working area by a combination of steel and textile covers.

Chip-to-chip time of 2 seconds

Another system feature of the BA 222 is the gantry drive of the Y-axis: “We connected two physically separated feed drives Y1 and Y2, each consisting of a linear motor, a direct absolute distance measuring system and a drive controller, coupled electronically on the control side,” explains Armleder. “This guarantees optimum positioning accuracy, even with eccentric loading.” An overall positioning tolerance (Tp) of less than 0.006 mm can be guaranteed. A Kv factor of eight and a jerk of 600 m/s³ make the BA 222 especially suitable for machining precise contours. To reduce the thermal stress of the Y feed motors, the weight of the vertical axis is compensated for nearly 100%, which leads to a significant boost in energy efficiency. With a spindle distance of 200 mm, the 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. The chip-to-chip time for a tool change is just 2 seconds.

The BA 222 can be loaded in parallel to machining time by means of a double swivel carrier with integrated rotary axes, thereby reducing auxiliary process times. “During machining the double swivel carrier is hydraulically locked in a Hirth coupling and the rotary axes are fixed in place with safety clamping,” explains Armleder. “The geometry of the rotary axes makes it possible to load the machine at a favorable height and also to have a very good view of the machining process.” Directly driven planetary modules can be integrated if necessary, thereby allowing for 5-axis machining. Machining of workpieces in a suspended position, together with the horizontal arrangement of the working spindle, guarantees swarf will fall freely.

Technologies to boost energy efficiency

As just one example of further increasing the energy efficiency for machining with the BA 222, three-phase synchronous machines with servo controllers are used for all feed and spindle drives. Operation with the drive group and the possibility of recovering braking energy make it possible to achieve maximum energy efficiency standards. Due to the hydraulic weight compensation of the vertical axis, no compressed air is consumed. The machining center also has an IO link which allows for example for dynamic changes to sensor/actuator parameters through the user interface.

The tool magazine is separated from the working area and protected from swarf and spray water. It is fitted through the open working area door with 2 x 20, 2 x 40 or 2 x 60 slots. Tool management is performed directly from the main control panel. “This central and ergonomically favorable position saves the operator from walking all the way around the machine,” explains Armleder.

Comprehensive life services

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 centers, supporting the customer through the entire lifecycle of the system: “For example the life startUp service includes setup and installation, support in the startup phase, commissioning of automation and clamping fixtures, and machine moves as well as production monitoring, thereby ensuring a smooth and speedy start of production,” explains Armleder. “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 analyzing faults – plus a spare parts and repair service as well as regular software and hardware updates round off the service portfolio.