High velocity comes to die machining

Manufacturing Engineering, Jul 1998 by Barthelson, Carl

A new technology lets diemakers generate parts faster than ever before, not a minute too soon

The smallest job shop faces the same pressures as the largest automotive or aerospace supplier: less time to quote, less time to manufacture and deliver, and tighter tolerances. Even Wall Street now admits you can't make good parts faster with yesterday's machines. "The only way US manufacturers can survive," Sanford Weill, chairman of the Travelers Group, told the Chicago Tribune recently, "is to stay the low-cost producer. That means continuing to invest."

For five years, US manufacturers have done just that, in the biggest buying spree since 1966. US buyers now account for almost 20% of all machine sales worldwide. An International Special Tooling and Machining Association (Frankfurt, Germany) comparison of capital investments by die and mold shops around the world, however, shows the US in fifteenth place, lagging far behind countries like Ireland and Korea.

In 2000 and after, OEMs like Ford will continue to take out cost by taking out parts. When they cut total platforms from 32 to 16, they will need only half as many dies, and half as many subcontract die shops. Die and mold shops that depend on machines they bought in the mid'80s will not be the winners in this scenario.

ISTMA also surveyed the amount of subcontracting of die and mold work around the world. Eleven countries, again including Korea and Ireland, ranked ahead of US die and mold shops. On another measure, labor costs, Korea's were lowest. Korea was also first-place finisher in average hours worked annually2836, compared with 2136 for the group of US die and mold shops.

Given these numbers, die and moldmakers need to ask themselves a tough question. When choosing among shops in industrialized countries, will the Big Three pick the suppliers they've always picked, or will they go for those with lower labor costs, higher investment in new equipment, excess capacity, and 30% more work hours a year? That loud rustling sound is their buyers going through international telephone directories.

Posted Speeds

In 1990, die shops supplying the Big Three could complete die machining for next year's model in 24 months. Most of those dies would operate in single-action stamping presses. Today these shops must produce their dies in less than 12 months; Tier II suppliers can face a delivery window under 9 months. At the turn of the century, that window will narrow to about 6 months. At the same time, dies have become bigger, heavier, and more complex, thanks to larger double-acting transfer presses. Today a die can measure 5500 X 3000 mm and weigh up to 65,000 kg.

CNC die mills in the early '80s ran at 5 m/min feed rates. Today, machines finish at double that rate. Most die shops, in reality, still cut at speeds much less than 4 m/min. Some will admit that because of lack of spindle speed or CNC processing limitations like data processing or corner overtravel, feed rates really never go above 2 m/min.

In the next few years, Big Three automakers will take out cost by taking out parts, cutting platforms, numbers of dies, and suppliers. Speed will be the survival strategy of choice. How can a die or mold shop speed up? It can retrofit its three-axis die mills with PC-based open architecture controls to crunch surface data faster, but a new control won't raise feed rates above 5 m/min. It can add capacity by buying inexpensive commodity machines, but in five or seven years, when they wear out, the shop will have to replace them. Another option is to invest today in a technology for tomorrow, like high-velocity machining.

What's the difference between high speed and high velocity? High speed means higher spindle speed than conventional machines. High velocity means spindle speed of at least 10,000 rpm as well as a speedup in other areas. Average feed rates will be at least 10 m/min, while intermittent feed rates go up to 30 m/min. Rapid traverse rates will be 40 m/min. Accelerationdeceleration will be at least 0.3 g. Spindle power will be high (at least 15 kW), as will torque and spindle utilization (to eliminate noncutting time). High accuracy, as measured by a VDI bidirectional standard, and high reliability, defined as at least 6000 hrs/yr machine availability, round out the high-velocity requirements.

Pioneering High Velocity High-velocity machining began with threeaxis modules on transfer lines eight years ago. Four years ago aerospace manufacturers adopted it for large-part machining. Now it's moving to automotive die machining. Before the end of 1998, average 3-D contouring feed rates will reach over 12 m/min on automotive dies. Rapid traverse rates will reach 40 m/min, feed rates will reach 30 m/min, and acceleration-deceleration rates will near 1.0 g.

In 1993, a leading Japanese automaker pulled ahead of the pack with five-axis contouring feed rates of 6 m/min and spindle speeds of 6000 rpm, then added 20,000 rpm. Now it plans to leapfrog the competition again, making dies three times faster than current technology. Dies will be machined faster, and trim steels and details will be assembled into the dies quicker and will fit better. Inner panels will not require handwork or polishing, while outer panels will take no more than two days. Tryout will be faster, and production panels will be manufactured sooner.