Viewpoints: Make Money Making Precision Parts
American manufacturers of precision parts are being chased up the pole by global competition. Those still in business have found that the simple parts are being produced offshore, and that the remaining parts tend to be more complex and do not necessarily come with guaranteed long runs.
Adjustments to these realities are essential—and for some, painful. Part designs are increasingly complex, and may change frequently. To be profitable making such precision parts, shops must be able to drop them complete. They must be able to go from bar to part in one operation. Handling the part more than once introduces the possibility of error, and secondaries require operator attendance. If a shop can make parts in a single operation, it will do well. This approach reduces labor, and yields faster cycle times and better quality—one machine will make concentric diameters better than will two.
It's demonstrated every day that successful shops have developed machining strategies that permit high-precision, multiple operations in a single setup with rapid changeover and zero handling. Quick changeover part-to-part and untended complete machining cycles can make CNC multispindle machines a profitable answer for turning and milling workpieces—chucked material or from bar—from less than 1" (25.4 mm) to several inches in diam—in small, medium-to-high lot sizes (starting from 15,000 to sometimes 1 million and above).
These machines, equipped with six fully independent CNC spindles each capable of operating at up to 10,000 rpm, are already popular in European shops because of the full CNC capability and flexibility for production of precision parts in variable volumes with very short setup times. This design allows quick cycle times—starting around 2 sec, depending on the workpiece. In many family owned shops in Europe, you see ranks of CNC multispindles, not just one here and one there.
The medium-to-complex workpiece market in the US, which has until now been dominated by camcontrolled multispindle automatics and simple sliding and fixedheadstock automatics, can gain more profit, and much improved competitive ability on complex, high-value parts, by converting to full-CNC multis.
Combining the speed of a cam machine with the flexibility and front-open design of CNC technology, multispindles represent a very cost-effective alternative to cam-controlled multispindle automatics because of shorter changeover times and lower piece costs. Shops can set up a front-open multispindle CNC as quickly as they can a twin-spindle two-turret lathe. And the latest multispindle machines can pay for themselves with lot sizes as small as of 5000 parts with repeat orders.
Another benefit is that the fully CNC multi machines use off-the-shelf, presettable singlepoint tooling, so shops avoid the high cost of form tools. And the CNC control frees shops from the need to make time-consuming, inherently imprecise cam adjustments as well as long-term job planning due to long lead times for form tools.
For different lot sizes, there are different CNC answers.
There is often room to consider another machine configuration that fits between single-spindle CNC twin-turret machines and CNC multispindles. There is a large middle ground where it may not be obvious which machine to use. Although some shops changeover a multispindle CNC four to five times a week, the hourly rate for a multi for some parts—depending on their complexity—may prevent using that machine. Or it may be occupied with other jobs, while the cycle time on the single may make it unprofitable for certain volumes.
The decision to invest in any machine configuration depends largely on expected production, the operations necessary, and the quality level demanded. For most, the ability to machine a part complete in one setup is an unquestioned advantage, and is in many cases essential to achieve the required precision.
To drop parts complete in one operation, today's more advanced CNC machines are increasingly not only multitask-capable, but also able to put more than three tools on the part simultaneously. A new machine from our company, for example, can put four tools on the part at one time—either fixed or driven tools.
These advanced production lathes are what it will take for a shop to machine complex parts quickly to high levels of quality in just one setup. And that's the key to making money producing precision parts. By investing in the best multiaxis machinery available and building on your experience creating tight tolerance parts, your business can deliver manufacturing quality at costs comparable to those of offshore manufacturers.
This article was first published in the May 2007 edition of Manufacturing Engineering magazine.