Product category:
Rotary and linear transfer machines
News Release from: Mike Page - editor's feature articles | Subject: Rotary transfer machines
Edited by the Manufacturingtalk Editorial
Team on 14 December 2007
Take another look at rotary transfer
machines
Rotary transfer machines were originally conceived with short cycle times and long, high volume production runs, but today, they offer flexibility, writes Mike Page.
At one time, companies bought rotary transfer (dial) machines to perform a variety of machining operations on a component in one clamping Depending on the job complexity, cycle times could be as little as a few seconds or up to 20s or more
Quite often the rotary transfer machine was dedicated to one job.
When the job's life expired, the machine was junked.
The factory specified another rotary transfer (RT) machine for the next new job.
It took a long while to set the machines up, so, apart from worn tool replacements, the machines ran and ran.
If a user considered changing tooling, cams and fixtures to run a different job, changeover could be two or three shifts.
In other words, a job changeover could take the same time as doing a complete changeover on a 1950s-built cam-driven, multi-spindle automatic lathe.
* CNC brings changes - CNC machining centres and CNC mill-turn centres, coupled with 'just in time' thinking, removed work from the RTs in subcontractor's shops, though the RT continued where it was directly linked to other operations, such as assembly.
It was in the early 1980s that Alfing Kessler Sondermaschinen (AKS) of Aalen-Wasseralfingen and Witzig und Frank (now MAG Witzig und Frank) of Offenburg (both companies in Germany) developed modular 2-axis, and later, 3-axis CNC machining modules.
The companies also designed modular fixturing systems that speeded up job changeovers on RTs, at first, on 'like' members of component families.
Moving on with the machining modules, automatic tool changers (ATC) arrived, so literally, a RT could become a form of multi- machining centre, having a number of 'machining centres' around the horizontal or vertical indexing table.
These developments brought a lot of flexibility into the RT concept.
CNC modular machining heads developed further into twin-spindle units, later with independent machining spindles, as well as four-spindle and even six-spindle units.
Other companies developed flexible CNC RTs, such as the Giuliani Division of IGNI and Buffoli Transfer in Brescia in Italy, IMAS Transfer, Italy, Eubama in Rottweil and Ketterer in Bad Duerrheim in Germany.
Not all the RTs are horizontal indexing table types.
There had been some attempts to do short shaft turning and grinding on RTs.
For example, some builders did it by transferring the component from the milling/drilling fixtures into a turning unit at the side of the RT's indexing table, and back again.
It worked well, but reclamping led to accumulated error, if not contained.
Giuliani and Eubama had the idea of literally using the rotary table as the machining units' carrier and running bar stock from a bar magazine to it.
Not a multi-spindle lathe, but carrying the pre-worked and parted-off billet in a central carrier served by five or more work units.
Giuliani describes its machine as a sliding headstock system, which takes bar up to, say, 36mm diameter.
The machine can bring up to 26 high frequency machine spindles and additional tool carriages into play to work on one or two jobs simultaneously.
Giuliani also has developed its TRM vertical axis machines; essentially a suspended RT served by, typically eight machining modules and a load/unload position.
Two TRMs, robotically fed and linked onto following assembly operations, machine three, two-part families of diesel engine rocker arms at a subcontractor in Sweden.
Sinteco, like Giuliani, is a member of the Italian Bucci Group and supplied the automation links to the TRMs.
The subcontractor said complete changeover takes 3h.
As well as horizontal RTs with up to 16 machining stations, Eubama builds a vertical RT machine, which has a vertical axis indexing ring with up to six stations.
The CNC machining modules include one with a swivelling collet chuck that allows five sides machining for the company's S20 horizontal RT machine.
Eubama can offer CNC multi-axis machining units including circular milling and continuous path milling.
MAG Witzig und Frank has developed its LSA System with a horizontal indexing axis and four to six machining stations.
In total, some 10 machining units - including two to a station - can be grouped around the indexing table, The company has developed machining turret heads that can adapt to changing workpiece shapes - such as in machining varieties of plumbing equipment.
Most of the above companies say that users can begin with a basic machine type and add on machining modules as the work variety and complexity increases.
Also, two or more RTs can be readily linked, say with robots, to form a line.
Advantages are summarised as follows.
* RTs offer an accuracy advantage that a component is never 'let go' or transferred from one fixture to another during a machining cycle.
So accumulative error is limited.
* RTs offer very short cycle times and continuous production when wanted.
Also, job changeover times have been considerably shortened.
What mainly determines changeover time is program change, tool change, machining heads change and fixture/probing system change.
Depending on the complexity of job changeover, changeover down times are now 15min to 3h - and not a shift or more as it was before the advent of CNC.
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