IN THE THICK OF IT

In most die and mold shops, one of the biggest single chunks of machining time goes to slab milling, so speeding that operation exerts a lot of positive leverage on profitability and competitiveness.

Just ask Riviera Tool Company (Grand Rapids, MI) a very progressive die and mold shop that runs 24/6 serving the automotive and truck-body market. Over the past year, the company has switched over to tangential milling for the rough and finish slabbing work, and raised throughput more than 40 percent. Tool life rose as well, while power consumption dropped.

Riviera does the slab milling with an assortment of Ingersoll tangential milling cutters ? 4 in, 6 in, 8 in, 12 in and the new 1 in diameter cutters, the smallest tangential milling cutter available.

SAVING 20 HOURS ON EVERY SHOE

"Every time I slab a die shoe now ? and we do several of them daily ? I save 20 hours," says Frank Upton, Riviera machine manager. "Tool life is up as well, and power consumption is down. The power meter that used to read 95 percent of machine capacity or higher now hovers nearer 80 percent. We gradually standardized on tangential milling for flat slabbing work a couple of years ago, and since then I know we've already saved more than $100,000 in machining time, and I'm sure the power reduction will also help our machines last years longer."

Riviera represents one of the first applications of the new 1 in S-MAX Micro tangential milling (TM) cutter, which brings the proven benefits of tangential milling to smaller work.

INSERTS LIE FLAT FOR STRONGER PRESENTATION

In tangential milling, the inserts are oriented differently. They lie flat around the cutter's pitch line rather than standing up radially, as in conventional cutters (Figure 1).

This tangential orientation presents the insert's strongest cross section to the main cutting force so that the inserts last longer. The result has always been much longer edge life.

The tangential milling concept was introduced back in the 1960s and expanded ever since. The main original role for the tangential milling process was to improve tool life on big jobs like hogging wide-area flats on large automotive castings and steel parts.

Now with freer cutting insert geometries and smaller cutter diameters, tangential milling is emerging as a solution for faster removal with lower cutting forces. The wider size range of cutters also makes it a good option on small slots and cavity work as well as large-area slabbing. The only ?must' is that the bottom of the cut be flat. "Todays' tangential milling may be a lot of good things to a lot more people, even on low hp machines," says Ingersoll product manager Scott Tilton, "but its Z-axis contouring capabilities are limited.

TEST SHOWS A BETTER WAY

Riviera's conversion to tangential milling began with a suggestion, and a test, in early 2006. Upton was looking for a way to speed up one of their bedrock operations and eliminate too-frequent tool failures, and asked Ingersoll's Chad Meyer for suggestions. Their main obstacle to faster milling with the old tool was tool rupture, not gradual wear.

"The inserts simply broke off, leaving a stump," said Upton. He was also concerned about and the high power consumption that could burn out a motor or stall the machines. "Sometimes the needle on the power meter pegged," he added.Riviera mills the dies dry on an Okuma MCRV 2 and a G&L bridge-type machine. Meyer suggested the S-MAX tangential milling cutter and proposed a test against Riviera's old conventional zero-rake face mills and other competitors. The trial was comprehensive, running over four weeks and including four other leading makes of face mill. All the other candidates had conventional radial insert orientations and a variety of lead angles: 30 deg, 45 deg and 90 deg.

All tests were run on identical cast iron material on the same Okuma and G&L machines, with the same operator. All began with the same starting conditions, and then Meyer and Upton pushed the removal rate to find a new optimum.

The starting point was Riviera's previous standard: 25 ipm feed, 0.150 in depth of cut (DOC). At the end of the test, the Ingersoll tangential cutter had optimized out at 40 ipm and 0.300 in DOC, and with 30 percent longer edge life and 10 to 15 percent less power consumption. That was three times faster than Riviera's previous norm for rough slabbing, and 40 percent faster than with any other cutter in the test.

STANDARDIZING, PUSHING THE LIMITS

Over the next few months, Upton trained his operators with the new tool and phased in additional sizes of the tangential milling cutter as the need arose and older tools wore out. Meyers assisted throughout. "We've worked with Chad for more than nine years, so our operators trust him as much as they would another Riviera colleague."

Today Riviera does virtually all rough and finish slabbing with 4 in, 6 in, 8 in or 12 in S-MAX face mills, depending on the size of the die, the width of the cut and the amount of material to be removed.

The 4 in and 1 in cutters have a 90 deg lead angle for milling square corners in pockets. They are just phasing in the new 1 in S-MAX Micro cutter to speed machining of up step-down pockets and trim line cutting as well as bottom and shoulder milling in cavities.

"It appears at least as fast in the small spots as the larger cutters are in the wide-area slabbing," says Upton. "It also cuts smoother because the tangential design fits more inserts into the pitch circle than is possible with conventional cutters."

And they've notched up the removal rate still further besides. Riviera's standard for rough slabbing cast iron die blocks now stands at 40 to 60 ipm and 0.400 in DOC. For finishing, it's now 108 ipm at 0.010 in to 0.015 in DOC. Their previous standard for finishing was 30 ipm at 0.010 in to 0.015 in DOC.

WIDENING ROLE FOR TANGENTIAL MILLING

"The Riviera application demonstrates how tangential milling has expanded its role," explains Tilton. "Originally the TM process was targeted as solution for improving insert life for heavy milling on high-power machines in transfer lines.

"On such synchronous lines, throughput at a single station is rarely an issue unless it is the slowest station. Today, the combination of tangential orientation and free-cutting insert geometries makes TM a solution of choice for smaller cuts, even on lower-power stand-alone machines and machining cells. As long as the bottom of the cut is flat, the TM process stands a good chance of speeding up most any milling operation."

Riviera Tool Company, 5460 Executive Parkway, Grand Rapids, MI 49512, Tel: 1+ 616.698.2100, Fax: 1+ 616.698.2470, rivsales@rivieratool.com, www.rivieratool.com