Pint-sized precision: Medical Manufacturing

If you enjoy the growl of heavy milling cuts, the machine-gun sound of chips striking glass and the heady odor of superheated cutting fluid, a compact machining center might not be the right machine for you. Like I used to, you scoff at phone booth-sized machining centers, with their tiny toolholders and tables not much larger than a 6″ machinist vise. If so, you’re not looking at the big picture.

Compact machining centers are … well, compact. But they save valuable floor space, are fast and agile, and are able to turn corners on a dime. Axis and spindle acceleration rates are often 1 G or higher, and with tool changes of a few seconds or less, compact machining centers get in and out of the cut quickly. Also, with the light radial DOCs and high feed rates commonly employed today, compact machining centers can often remove more material per minute than larger, heavy-duty machines.

FANUC’s latest RoboDrill, left, sports a new, user-friendly control interface, faster tool changes and a number
of high-speed machining functions. The Haas Super MiniMill, right, is the largest of the company’s compact
machining centers and is equipped with a 40-taper spindle. A special, no-frills version is available specifically
for educational organizations. Images courtesy of FANUC America and Haas Automation.

Call Me Robo

Many in the industry know compact machining centers as drill-tap centers. One of the first machines marketed as such was the RoboDrill, introduced by FANUC in 1972. The early versions of these and other models were equipped with light-duty spindles that limited their ability to handle the side loads common when milling, making them suitable for little more than holemaking. Still, they were quick, boasting rapid-traverse and spindle speeds far faster than their clunky 40-taper cousins.

Drill-tap machines were among the first to come standard with synchronous thread cutting, aka rigid tapping, eliminating the need for floating holders and reversible tapping heads. Because of this, they became popular in the automotive industry for secondary drilling and tapping operations in magnesium and aluminum casting houses and similar high-volume applications.

Since then, the metal-removal performance of drill-tap machines has continued to improve, as has their popularity.

Sergio Tondato, director of sales at FANUC America Corp., Rochester Hills, Mich., said the RoboDrill is used across the entire machining spectrum, with the aerospace, medical and automotive industries taking center stage. “The RoboDrill is an excellent machining solution for any part that fits in a 24″×16″×16″ cube.”

FANUC controls engineer Charles “Cal” Faunt said the α-DiB series RoboDrill was introduced at IMTS 2016 and sports a number of features that make it well-suited to job shop work and other types of general-purpose machining.

The control interface has been redesigned, with three main areas corresponding to functions planning, machining and process improvement, he said. “We have 20 percent faster chip-to-chip times than previous-generation RoboDrills and 1,000-psi through-the-spindle coolant. There’s also a function called HRV 3plus (high-response vector control), which provides better surface finishes and accuracy during high-speed machining. As an example, we can achieve circular interpolation accuracy of 3.1µm at 8,000 mm/min. when machining mild steel.”

Heavy-Hitting Horizontals

Another indication that so-called drill-tap machines are no longer limited to holemaking is their use in 5-axis work. FANUC and others noted increased sales to “major medical manufacturers” for machining titanium implants and similarly challenging parts.

Most compact machining centers can be equipped with 4- and 5-axis capability, making them suitable
for complex machining tasks. Image courtesy of Kitamura Machinery of USA.

One such offering is from Kitamura Machinery of USA Inc., Wheeling, Ill. Slawomir “Sal” Swierczek, the machine builder’s sales applications engineer, said the Mycenter-HX250iG offers high-feed machining functions, tool life management and axial load sensing that adjusts machining parameters on the fly—features required for the multiple-axis profiling common to medical work.

The Mycenter-HX250iG is a horizontal machining center, a platform that few would place in the “compact-machine” category. Despite this, it’s small for a machine with a 40-tool magazine (field-retrofittable to 102 tools) and an integrated pallet changer that measures just 111″×116″ (2,832mm × 2,948mm). It comes standard with a 15-hp, 15,000-rpm, BT 30 spindle; a 30,000-rpm, HSK E40 spindle is available.

Admittedly, the 30-taper and smaller toolholders commonly used with compact machining centers can’t handle the same radial loads as 40-taper toolholders. Swierczek said heavy cuts in steel on many small machines using indexable endmills can overload drive motors, as can face-mills much larger than 2″ (50.8mm) or so. Nor is drilling 1″-dia. (25.4mm) holes advisable, for example, or tapping ¾-16 threads. Either operation might stall the spindle.

According to Swierczek, the HX250iG is indeed capable of heavy cuts in stainless, titanium and other difficult-to-cut materials, but leveraging a compact machining center’s ability to take multiple light cuts at high feed rates is often a more-effective approach than heavy cuts at lower feed rates.