Time To Think In One-Hit

Any self-respecting turning shop that thinks it is operating the latest in CNC lathes must feel itself constantly under siege from OEM and Tier 1 customers saying they can get parts machined cheaper in Eastern Europe, Malaysia or China. That is the growing problem in Europe, and I guess in the United States, Mexico would also be on the list.

The customers appear to be trying to camouflage the issue. They don’t want to say that the high precision spindles, the clutch housings or the water pump bodies can be machined cheaper overseas. A favorite among the European aerospace OEMs is to ask the already hard-pressed machine shops to ‘meet stringent cost-down targets.’ That fuel pump component costs ‘X’. Inside 1 year, it has to cost‘X-A’ where ‘A’ can often be an infinite variable. Such a variable will dodge and weave around according to how much the OEM thinks it can squeeze the long-faithful supplier.

To meet such pressures, the operational costs of the traditional two-axis CNC lathe—perhaps with a programmable C axis and backed up by traditional drilling machines, a machining center and a very able jigs and fixtures team—cannot be cut back any more.

Let us consider Kigass Aero Components in Gosport, U.K. Kigass thought it had the very latest in CNC lathes—that is, subspindles, heavy duty milling heads and so on. The company had been long used to using such advanced CNC lathes for back end machining in addition to front end in the same machine tool. Practically every turned part requires back-end machining. Indeed, the proportion of prismatic machining operations as part of a typical complete machining cycle is 20 to 30 percent. I know a lot of shops that would still operate machining centers for such a high prismatic machining content rather than try to get to grips with multi-axis ‘mill-turn’ programming.

Kigass was able to make full use of a new German-built Index G200 Compact with a Y-axis facility for performing prismatic machining off-center. The G200 offers 5.5 kW/6,000 rpm milling power available for 14 live tools located in two turrets. What impressed Kigass was the machine’s ability to slice 10 to 15 percent off cycle times and take another 15 percent off setup times.

Similarly, another U.K. aerospace parts manufacturer, Doughty Precision Engineering (DPE) has been adding to its advanced mill-turn capability to strengthen its ‘one-hit machining’ capabilities. DPE uses Nakamura Tome seven-axis CNC mill-turning centers to produce aerospace connector components—flanges, sockets, connectors and so on. The company supports the idea that such mill-turning centers, capable of simultaneously machining the back end of one part on one spindle while working the next one’s front end, minimize cycle times and allow as much milling as possible to be done. The components have up to 50 percent of cycle times devoted to prismatic machining.

Like Kigass, DPE had experienced a steady eroding of profit margins owing to aerospace OEMs’ constant demands for ‘cost-down’. Such demands encouraged DPE to select the twin-spindle and one-hit route in 1997, buying two Nakamura Tome WT-20s. The company has since doubled its Nakamura Tome mill-turn center inventory, the latest addition being a WT-250.

The Index G200 has 60 mm bar capacity and the WT-250, 65 mm bar. If you had not considered just what you can machine in ‘one-hit’ from 2 1/2-inch bar of high grade stainless—maybe because you thought that no CNC lathe would have the right milling power or rigidity to do such work—then it is time to look again. Looking at trends in the aerospace industry, it’s obvious that if your machine shop still depends on multi-machine scheduling, you may not be in the aerospace parts supplier business for much longer. The job will either go to Mexico or to the guy next door who just bought that twin-spindle CNC mill-turning center!