Taking Stock of Turning
New developments can make big differences in production.
Turning has evolved over the years to offer a technology choice for a vast majority of parts. It is not difficult to find horizontal CNC turning centers with dual spindles equipped with live tooling for simultaneous machining on different sections of the part, vertical turning centers for external and internal turning operations along the Z-axis and a plethora of multi-tasking models that essentially take a multi-axis milling machine and add C-axis turning (mill-turn) or a CNC turning center with a milling spindle (turn-mill).
Part complexity, volume, programming, and automation all take important roles in determining the appropriate technology choice. DMG MORI (us.dmgmori.com) has launched the second generation of its CTX gamma 3000 TC, sporting a turning length of 3,050 mm (120.1 inches) and a milling spindle with 120 percent more torque than the previous generation. Driving such technology is product diversity across a number of different applications, driving down lot sizes, the company says. At the same time, workpiece complexity continues to grow, making complete machining in a single setup worth economic consideration.
With a standard tool magazine of 36 tools (up to 120 optional) and an optional lower turret, complete five-axis machining can be performed on complex parts, or optional steady rests can be used in place of the second tool mount for complete machining of shaft products.
Of course, such high-tech machine tools exhibit the latest “Industry 4.0” control capabilities. Vibrations, forces and temperatures are continuously recorded during operation by numerous sensors and then collected, processed and saved in a special evaluation unit. Process parameters are visualized in DMG MORI’s CELOS control in the “Condition Analyser,” for real-time machine performance and status. The data collected are brought together and stored on the cloud, improving the forecast of potentially damaging events, for example on the spindle, based on empirically determined behavioral patterns. In short, the machine learns by doing.
Straightforward Cells and Process Planning
Naturally, not every turning assignment suggests a complete machining approach. Volume is everything in Anthony Glueckler’s world and his company, Glueckler Metal (gluecklermetal.com), Elmvale, Ontario, is among the leaders in high-volume automated turning projects. The scale of his alternator shaft turning cell is impressive: 10 Nakamura Tome WT-150 multi-axis CNC turning centers (available in the U.S. from Methods Machine Tools Inc., methodsmachine.com), 10 LNS Sprint automatic bar feeders, one Mitutoyo America Corporation Mach V coordinate measuring machine (CMM) with automatic part fixturing and transfer, integrated vision system and integrated scrap-removal. The cell has been fully loaded for 10 years running, he says.
People were paramount in building the turning cell with CNC equipment. He wanted to develop a process so friendly that people with limited skill sets could jump in and start contributing. “We put together an automation plan that would accommodate a semi-skilled workforce and durable equipment that would operate 24/7/365,” Glueckler says. GMI’s degree of success is the fact that they readily identify personnel with no previous CNC experience but are able to follow procedures well. “People become our best assets when they function within a team collaborative atmosphere, where everyone contributes to create and agree upon a process,” he adds.
The result has been a business plan that has withstood a tumultuous time in North American manufacturing and is exhibiting steady growth. “Maintaining zero defects and flexible cell options means we can continue investigating opportunities linked to our core competencies. More and more of our customers are in the same game we are, so we’ll see where industry takes us. With reshoring, industry is realizing it needs to rebuild trust that the supply chain is strong and secure. Products that went away are now coming home and worth guarding.”
Choosing the correct turning approach also means looking at all the options for better performance. CNC lathes from Okuma America Corporation (okuma.com) with a P200 control or higher have harmonic spindle-speed control settings that, when programmed, automatically adjust spindle speed to prevent vibration buildup before the onset of chatter. Harmonic spindle speed control has largely been manual, but with a few lines of NC code, parameters can be pre-set to control amplitude, interval time and pitch in rpm changes. Shaft parts out of alloyed steels or with high L/D ratios can be good candidates.
Internal turning can mean threading, and in this case, Okuma provides a variable that can override automated threading cycles to manually change rpm to maintain thread pitch. The reason is the same, to avoid any buildup of harmonics before chatter occurs.
In some instances, the utilization of high-pressure coolant systems can make a major difference in productivity. In a recent test, the use of a 1,000-psi coolant system on an Okuma LB3000 CNC turning center reduced cycle time from 24.01 minutes to 12.30 minutes. What’s more, it greatly aided in chip clearing compared to the low-pressure approach.
By John R. (Jay) DoubmanIn concept, not much has changed in double disc grinding since the invention of the machine in the 1890s.
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