SW - BA 321: High-technology and economics in complete harmony

11/25/2007 - Oliver Hagenlocher

The combination of design elements from machining center and rotary index machine in the new BA 321 promises to be a success, as it offers a great many advantages. The concept was developed in answer to market demands for a machine that produces large quantities of workpieces with an emphasis on three-axis machining economically and with precision. An essential element of the SW BA 321 Machining Center is the workpiece carrier, a rotary axis in the form of a horizontal beam. This beam swivels around its longitudinal axis with a precision of ±5”. It is supported on both sides in generously dimensioned receptors in the monobloc machine base. Short positioning times are achieved by a torque motor that gives the rotary axis a maximum speed of 50 rpm. The four clamping stations on the workpiece carrier, each measuring 180 x 850 mm, accommodate two or four workholding fixtures each. Each station also features up to seven distributor ports for the hydraulics and pneumatics needed to clamp the workpieces. This provides great flexibility for the multiple clamping of workpieces.

A moderate investment for high-productivity three- and four-axis machining
The layout of the horizontal workpiece carrier, in conjunction with special, well sealing, automatic partition doors at the front of the machining area, makes it possible, during the machining cycle, to unload, load and clamp workpieces on each of the four 90° positions. The workpiece carrier arrangement allows the two main spindles to machine the workpieces on each of the three clamping stations within the machining area, whilst the operator loads and unloads workpieces from the fourth station in the loading station. With the partition doors open, machining can also take place with the workpiece carrier positioned at any desired angle. Compared to other SW machining centers equipped with double swivel trunnion and two integral rotary axes, the new concept offers the user a low-cost, high quality alternative for the economic, three- and four-axis machining of mass-produced steel, cast iron and light alloy components. Such workpieces include calipers, master cylinders and ABS control units, as well as hydraulic and pneumatic components. 

Tried and tested technology integrated
The cost benefits of the new BA 321 go hand in hand with the reliable, high value technology for which SW is well known. The economical solution the BA 321 machining center represents has its basis on well-proven design elements and components. The SW-patented monobloc machine base provides for optimal force distribution and, consequently, the highest possible degree of rigidity and stability. The design also allows for a compact machine construction. The remaining machine assemblies are all integrated into the monobloc, making this a “hook-up-and-install” machine. At the same time, all drive components can be accessed quickly and easily from the rear of the machine. The two synchronous motor spindles with their power rating of 32 kW, a torque of 72 Nm and HSK 63 tool receptor, make a substantial contribution to the high productivity rating of the machining center. These spindles reach their top speed of 10,000 rpm in as little as 0.7 seconds. SW also offers spindles with a maximum speed of 17,500 rpm for the machining of light alloys. The distance between spindles on the BA 321 is 300 mm. The sturdy headstock, in which the two spindles are mounted from the rear against a fixed stop, utilises the tried and tested box-in-box principle to move in a vertical composite construction with the gantry. The gantry drive guarantees a high degree of precision, even under off-centre load. Travel in X is 300 mm, in Y 500 mm and in Z 375 mm. Ball screws with oil-lubricated motion guides allow axis speeds of up to 70 m/min in Y- and Z-direction and up to 60 m/min in X-direction, at accelerations of 10 m/s² in X- and Z-axis and 8 m/s² in Y-axis. The chain magazine for 2x20 (optionally 2x32) tools is located above the machining area. For the pick-up tool change the two spindles travel upwards 250 mm into the magazine area, which is partitioned off from the machining area by sliding doors. With a chip-to-chip time of less than 3 seconds this layout protects the tools well against chips. Arrangement of the tool magazine in the smallest possible space immediately above the machining area is also of benefit to the machine operator. The magazine is loaded through a door located next to the side-mounted control terminal. There is no need for an additional terminal to handle control of the tool magazine. The completely enclosed machining area, lined with coated sheet steel, allows even large amounts of chips to fall unhindered into the chip conveyor below.

Service of the highest standard
For the first time, an alternative to the well proven Siemens S840D Powerline control system has been made available: the IndraMotion MTX CNC control from Bosch Rexroth. It is particularly convincing in its programming and operator friendliness. To make it easier for manufacturing enterprises to get to grips with this innovative control system, SW and Bosch Rexroth AG will, during start-up, offer extensive technological support and training. To minimise possible downtimes and the expense of service and repair call-outs, the company will offer the familiar SW online services for both control systems. Experts will be available by phone and also offer – dependent on the measures to be taken – personal advice and assistance in word and deed. Short-term machine reinstatement after a malfunction is aided by the excellent accessibility from the back and by standardised plug-and-socket connections between the various component assemblies.

New chances for local mass production
The SW machining center has proven its viability most emphatically in the batch production of a variety of components for the automotive industry and its sub-contractors. This has been helped by the outstanding quality and the optimal combination of high productivity and flexibility. The special characteristics of the SW machine include stability and reliability. The basic concept of the existing machining centers from SW includes two fourth axes. For the many manufacturing companies that primarily need to machine with three axes only, this means avoidable expense. It is for these users in particular that the BA 321 Horizontal Two-Spindle Machining Center has been developed. With this compact and highly productive machine SW opens up new opportunities for these enterprises. The BA 321 allows them to economically integrate their technologically less demanding three- and four-axis 2.½D machining into otherwise cost-intensive areas of production.  And thus the Swabian machine tool manufacturer once more confirms his strong position in the area of mass production of components for the automotive industry and its sub-suppliers.