Gantry-Loader Chucker Outproduces Barfeeder, Makes Better Parts

Presented with an opportunity to capture a contract from Caterpillar for small, precise, cylindrical parts, engineers at a mid-sized job shop assumed they would do the job with tried-and-true barfeeding technology. But special requirements forced them to compare barfeeding with Amada Wasino's gang-tooled, gantry-loaded G-7s. In the end, the G-7s proved to be better for this classical barfeeding application, in terms of accuracy, efficiency and total cost per part. The workpiece had a 1.8110" O.D. and a 0.8661" I.D. Optimum surface speed would require 4-5,000 RPM. The bar-fed approach required a 30-35 hp machine to spin a 12 foot x 2 inch bar, considering the necessary 3-inch through-hole spindle size and available configurations of such machines. Such high-horsepower, high-torque drives generally limit maximum spindle RPM to 3,000. In comparison, the G7, with 7.5 hp and an optional 6,000 RPM spindle, machined the workpiece at optimum surface speeds and with a much shorter machining time and total cycle time.

The special requirement that forced the company to look at the G-7s in the first place was Caterpillar's demand for 100% inspection and close tolerances. The workpiece required 0.0012" TIR on the bore, maintained to a level of 2 Cpk. Vibration caused by the whipping of a 12 foot bar made this tolerance virtually impossible to hold with barfeeding. The gang-tooled G-7s handled it easily. Even so, the inspection was to be conducted offline, which meant that the finished parts had to be oriented for loading into an automated inspection system. Amada Wasino's gantry loaders are ideal for such applications; in this case, they would unload parts – chip-free and oriented -- onto a multi-machine conveyor. A bar-fed machine would require a separate offloading system to feed the conveyor.

Once they opened their thinking to consider gantry loading, the engineers at this jobbing firm realized they'd gain these advantages by using gantry-loaded G-7s:

• Fewer machines would be required. Turning at faster speeds, only five of the smaller chuckers would be needed to do the job of seven bar-fed machines.
• The layout would be more compact. Not only were fewer machines needed, but they wouldn't have long barfeeders extended beyond the lathes' headstocks.
• The automation would handle both ends of the operation, loading and unloading, without add-on workhandling.
• The parts would be more accurate. Freedom from bar whip is part of the reason, and the inherent accuracy of the G-7's cross-slide gang tooling is another.
• Separate barfeed units (at $35,000 each, in this case) weren't required. Gantry loaders are standard, built-in items on the G-7.
• When the time comes to change parts, the G-7 can be re-tasked to machine a wider variety of parts sizes and configurations.

Barfeeding is well-developed and well-proven, but so is gantry loading. Amada Wasino has well over 1,000 gantry-loaded machines in the field, some of which have been working steadily for a decade or more. When a turning job has to be automated and put to work quickly, conventional thinking tends toward barfeeding first. But, as this jobber learned, gantry loading can vastly outperform barfeeding both in finished parts cost and quality.