More and more manufacturers are requiring their precision machined parts suppliers to enter into just-in-time (JIT) relationships in which smaller order quantities are supplied at more frequent intervals. That trend would suggest reduced use of rotary transfer machines, which can produce completely machined parts in very fast cycle times but are usually associated with lengthy setup times and long-running, high-volume jobs. However, Italian machine tool manufacturer Buffoli Transfer S.p.A. has introduced the Trans-Bar 55+, a CNC rotary transfer machine that adds flexibility and fast setup capability to the productivity for which such machines are noted. This makes it more suited for today’s JIT production needs.
The new model is a 12-station transfer machine with an indexing table (turret) that rotates on a horizontal rather than a vertical axis. A Hirth coupling ensures indexing accuracy and repeatability. Turret rotation can be controlled (forward, backward and in-between stations) to allow for maximum accessibility to tools and workpieces, reducing setup and down times.
Non-rotating bar is fed from the machine’s integral automatic bundle bar loader/feeder into the first of the 12 working stations, where the slug is cut to the appropriate length by a circular saw. The slug is secured in a self-centering chuck or collet on the turret, and the turret indexes to present the part to each machining station in turn. The basic version of the machine is equipped with ten machining spindles, but up to 27 spindles can be installed on the right, left, top and bottom, machining the part from every direction in as many as 40 separate operations.
One version of the machine accepts two bars for simultaneous machining. The bars can have the same profile, doubling the output for a particular part, or different profiles, enabling two different jobs to be processed simultaneously.
The machine can also be equipped with one- or three-axis CNC machining units and attachments that increase its flexibility. For example, a CNC profiling head, which rotates about the stationary slug, permits such operations as facing, turning, recessing, contouring, grooving and single-point threading—all with low-cost standard inserts. “Typically, rotary transfer machines use fixed-diameter turning heads that simply move to turn the part and then retract,” explains Dean Bentzien, president of TPS International (Sussex, Wisconsin), U.S. distributor for Buffoli transfer machines. “However, the user can program our CNC profiling head to generate anything from complex OD contours to single-point threading. The profiling head can be reprogrammed to provide simple change-over between part profiles and can be moved from one station to another as required by the job.
“We also offer an indexing milling attachment that uses straddle milling cutters to generate hexes, squares, octagons and other shapes at a single station,” Mr. Bentzien continues. “We can also do slot milling with the same attachment.
“Our three-spindle turret head is still another attachment that accepts up to three tools so that we can, for example, center drill, drill and tap the part at one station if cycle time considerations permit,” he adds. “On a conventional rotary transfer machine, you typically perform one operation per station so you quickly use up all of your stations and are forced to do some machining operations on secondary machines. By contrast, we have a better chance of completing challenging parts in one setup.”
The attachments can be moved from station to station as required and installed in a left, right or radial position. As many as seven contouring and multi-process attachments can be installed in the machine at one time (two left, two right and three radially). The attachments have been described as the most important feature of the machine: They provide the level of flexibility that the user needs to support JIT manufacturing. According to TPS International, setups for completely different parts typically run from 30 to 90 minutes, and the user can usually go from one part in a family of parts to another without any downtime for setup changes.
The machine’s CNC control also helps incorporate a diagnostics program that helps plant personnel identify and fix problems fast to keep downtime to a minimum. The program not only provides an alarm, but it also displays a digital image on the screen identifying the problem. The software provides some 2,000 error messages that identify the problem and the fix needed to get the machine up and running again.