The production technology from bar has taken advantage
from the evolution and improving of the static bar process.
This brings advantages to productivity, flexibility,
tools life and machining quality.

Normally, for the production of mechanical parts starting from bar, the bar is clamped leaving the part to be machined projecting; then the internal and external surfaces are turned by rotating the whole bar and, at the end of the machining, the piece is cut.
Examining the working cycle of a multi-spindle lathe, one can wonder whether, for the production of pieces having a few ten of millimiters tolerances, there are no other solutions than rotating 6-8 very long bars, with consequent noise and vibration problems caused by the rotation.
Moreover, sometimes the bar rotating system is not able to produce completely finished pieces, being necessary to stop the bar rotation or to clamp again the piece with tooling (i.e.: pick-up) suitable for final machining or, in more complex cases, to transfer the pieces onto another machine which carries out the necessary final machining.

PRODUCTION FROM NON-ROTATING BAR
An alternative solution, represented by the bar transfer machine, consists in not rotating the bar, but in separating the necessary part for the piece production by means of a disk saw. The part so obtained is transferred, by a rotating turret, to successive working stations, where operating units equipped with rotating tools produce pieces completely finished in all directions.
In the transfer machine the cutting and feeding speed are set independent for each tool; in this way it is possible to optimise the cutting parameters and then the finishing degree, the cycle time and the tool life.
The following pictures show some piece examples, where the bar transfer machine has been particularly suitable for their production.
The figure 1 shows three pieces machined in two opposite directions that, using a bar transfer machine, can be worked without a new clamping, improving the machining alignment and concentricity.
The figure 2 shows applications where the machining in three different directions is required. This can be made by a bar transfer machine with one piece clamping only, avoiding the cumulative errors due to further clamping.
BUFFOLI TRANSFER, after having constructed and installed hundreds of machines in the world, has specialised in the design and construction of transfer machines fed by static bar , where rotating tools work pieces completely finished with all the operations required (transversal or out of centre milling, broaching, rolling, burring of cross drilling, seats or inserts driving, marking, etc.) in opposite (aligned or misaligned) and transversal (in any way arranged) directions, as shown in figure 3.
The bar bundles are loaded on the bar loader up to 3 tons; then the bars are automatically introduced into the machine and, if profiled (T, L, cross, etc.), are previously oriented without operator intervention.
Being the bars fed one immediately following the other, the time without production between the previous bar end and the next bar beginning is 3 seconds only.
Concerning the material saving, the bar end scrap is always lower than the length of the piece to be machined and, thanks to a thin blade sawing machine designed by Buffoli, the material scrap of the bar parting-off is reduced to 1.2 mm.
Since 1980, in order to double the productivity using a reduced space in the plant, BUFFOLI TRANSFER has installed several machines fed by two parallel bars in the world.
The first of these transfer machines, installed in U.S.A. about 12 years ago for the production of nuts and straight pipe fittings starting from hexagonal bar 42 A/F, has manufactured over 250 million of pieces, working three-shift for six days a week with a cycle time of 2 seconds and the production of 1 piece per second (see figure 4).
This machine is still in production and continues to satisfy the quality requirements of the customer that, confirming the validity of this technological choice, has decided to purchase tens of other similar machines.

THE RECENT EVOLUTION OF THE BAR TRANSFER MACHINE:
NC, MULTIPLE MONITOR POWER, SPC
The application of modern NC has allowed to develop flexible machines for the production of families of similar pieces with tooling change time reduced to 30 minutes. In some case, as for example the small shafts of figure 2 where the ends machining are identical with same diameter but different length, the introduction of NC has permitted to realize a sort of "just-in-time" without operator intervention, who can program directly, through the machine computer, a succession of batch sizes having different lengths without interrupting the machine production.
In the machining of easy materials like brass, some NC transfer machines continue to work during the third unattended shift, producing acceptable components with factory heating and lighting being required, as the thermal movement is very limited in comparison with the tolerance range.
In the machining of hard materials (like stainless steel, steel alloys, etc.), where the tool cost remarkably affects the finished product cost, Buffoli Transfer has developed its own multiple monitor power system that, in real time, detects the torque and thrust values for each tool and compare them to the ones acquired in self-learning during the correct working.
This system stops the machine, for the tool or insert replacement, when its wear reaches the economically more opportune condition, preventing an anomalous working or the tool breakage without manufacturing scrap pieces (Total Quality).
Actually the machine so equipped has a continuous self-supervision system (one hundred samplings per second) concerning its production efficiency condition. It has been proved that this device stops the machine when the tool wear degree (cutting edge rounding) is such as to allow to gather the worn tools (for instance once a month) in order to regrind them in economic batches.
Thanks to the high degree of electronics and information integration, the recent evolution of the Buffoli transfer machine permits to use the last stations for the measurement of critical dimensions by means of independent probes (after the washing station) in order to select the pieces according to the tolerance (figure 5). Moreover it is possible to utilise unskilled personnel that is guided through the computer menu for carrying out quickly the machine tooling operations, the tools maintenance and, finally, for optimising the working cycles in order to get better tool performances and higher working quality in shorter cycle time.

Figure 1
Samples of pieces machined in two opposite directions that, using a bar transfer machine, can be worked without a second clamping, improving the machining alignment and concentricity.

Figure 2
Rotating tools work pieces completely finished in 4-5-6 directions in the bar transfer machine.

Figure 3
In the transfer machines fed by static bar, the rotating tools work pieces completely finished with all the operations required.

Figure 4
One nut per second from hexagonal bar with a Buffoli double production transfer machine.

TWO PIECES PER CYCLE MACHINED IN THREE DIRECTIONS
Example of flexible rotary transfer machine for the production of a family of pieces machined in three directions (hexagon 30 mm - length 80 mm). The machine is constituted by a horizontal axis turret, on which 16 self-centring chucks are installed, and by 26 operating units arranged as follows:
Station 1 : two cutting units with disk blade having thickness of 1.2 mm.
Station 2 : two turning units + two drilling units.
Station 3 : two finishing units + 2 milling units.
Station 4 : two units equipped with recess front-heads for the realisation of external grooves.
Station 5 : four threading units with roll threaders.
Station 6 : two units for deep central drilling + two units for off-centre drilling.
Station 7 : two 90° radial drilling units + two lapping units.
Station 8 : two threading units with roll threaders + two manipulators for finished piece unloading.

The Buffoli bar transfer machine is available in two base sizes:
bar from 10 mm to 42 mm
bar from 30 mm to 70 mm
Inside the machine there are several coolant jets oriented towards the turret, the jaws and the tools for a plentiful washing in order to allow for unattended working and so avoiding swarf building up.

Figure 5
Example of steel piece obtained from profiled bar.
If very limited tolerances are required, the integration of SPC (Statistical Process Control) systems in the bar transfer machines allows the detection of linear, angular and position dimensions of the pieces manufactured and their successive processing on control cards.