There are thousands of cam-driven multi-spindles out in the field producing millions of parts 24 hours a day. And while there may always be a place for these machines when high volumes of relatively loose-tolerance parts are required, the tide is turning. CNC multi-spindles have emerged as a viable alternative now. This was not always the case. A few multi-spindle manufacturers jumped on the CNC technology bandwagon in the 1980s to offer users the option of cam or CNC when the acronym JIT was the fresh buzzword of the day. In practicality, however, CNC multis back then were simply too slow compared to their cam cousins, and it was difficult to justify the expense.
Today, however, there are several issues confronting precision machine shops that are driving them to look again at applying CNC multi-spindle technology because in many applications it offers the most practical, economical machining solution. The converging trends are the workpieces, JIT production flow, labor skills and new CNC multi-spindle technology. Let's touch briefly on each:
We Love Our Cell Phones And Palm Computers
As the makers of high-tech gadgets heed our cries to "keep making 'em smaller!" product designers are reducing the size, weight and number of parts that go into these devices. Further, they are integrating more functions into each part. Producing these types of parts on a cam machine would be out of the question. The very nature of cam-operated multis, with their myriad mechanical variables that can adversely affect part quality, crosses them off the list.
You Want It . . . When? LOL!
Not only are shops faced with an increase of small, tight tolerance, complex workpieces to produce, their customers are demanding shorter lead times than before, which also translates into smaller lots. Since it is common for cam multis to take 8 to 12 hours or more to set up properly, that time frame doesn't cut it in today's JIT production flow environment. Adding to that time frame is manufacturing the cams and special form tools that are required to machine parts on a cam-type model.
Cams—That Stands For Computer Aided Manufacturing Software, Right?
Labor skills are another key issue facing shops today. As mentioned above, it can take an entire shift to produce the cams for one multi-spindle, and that's by a highly skilled and experienced craftsperson. Today's technical school graduates know about computer G-codes and macros, CAD/CAM software, and perhaps even the basics of configuring entire factory network systems. "How to Cut Cams" is generally not even an elective course. Progressive shops are preparing themselves for the day when all of those beloved craftspeople have retired.
CNC multi-spindles match the skill sets of our younger generation and mature employees willing to learn advanced technology.
New CNC Multi-spindles Banish The Barriers Of The Past
Addressing workpiece, production and labor force trends, some manufacturers of multi-spindles have refined their CNC models to answer user needs for simplicity, flexibility, reliability, justifiable cost and advanced CNC technology. Tornos Technologies (Brookfield, Connecticut) and other multi-spindle manufacturers have also addressed the need for speed. In Tornos' case, dedicated software and a parallel operating system effectively blend a system of "virtual" cams with the CNC program and servomotors. The key areas of recent machine improvement are as follows.
- Utilization of preset and insert tooling, rather than form tooling, permit faster setups and lower tool costs.
- Higher accuracies, offset capability and barrel compensation eliminate mechanical "feel" adjustments.
- Automatic bar loading requires less operator intervention.
- Off-line programming results in less prove-out time on the machine.
- Cam elimination saves an entire shift of setup time and improves accuracy and versatility.
- CNC control permits users to change and optimize speeds and feeds quickly.
- Better machine enclosures, often integrating chiller units and mist filters, improve shop environments.
- Epoxy resin bases minimize thermal distortion and improve accuracy.
- Incorporation of Hirth coupling for barrel locating promotes higher accuracy and rigidity.
Justifying The Investment
Now for the most important consideration to shops—cost. Most financial gurus firmly believe that the only true measure of a machine's profitability to a company is based on the cost per part and the number of parts run. Ultimately the production of the parts is what's going to pay the tab, driven by the cost per part. That being the case, the least important part of the formula is the cost of the equipment. (See Sidebar.)
Following this example, there appears to be little risk to grow a business in this manner, yet many people still cringe at that big dollar figure investment in a multi-spindle. However, most who take the leap are realizing the cost-per-part savings that can accrue over time, that is, if their businesses lend themselves to harness multi-spindle advantages in the first place.
Is Your Shop Suited To Capture The Multi Advantages?
The timing may be right for your shop to explore applying CNC multi-spindles in your process. Tornos sees basically three categories of buyers:
Traditional cam multi-spindle users. They are generally faced with the problems associated with older cam machines—inflexibility, lack of accuracy, high tool costs and long setup times—that conflict with today's business climate. These "traditional screw machine shops" are realizing that to remain competitive they must respond quickly to changing conditions. Flexibility is the watchword of the day. Also, embracing computer technology and offering cleaner working environments is making it easier to attract and keep talented employees.
CNC single spindle users. Many companies that own single spindle CNCs are moving into multi-spindles when their volumes rise. Instead of purchasing several singles, the users may buy only one multi. The "fear factor" of learning to program a multi is drastically reduced once they have experience on the singles. Programming a 19- or 23-axis machine is no longer frightening, since it's similar to programming a three-axis lathe—just repeating it six or eight times. The advantage of fewer machines taking up less floor space is also a plus to these shops.
- OEMs. This group generally has families of parts to produce in-house, and to be efficient as possible, works to JIT parameters. As such, their lot quantities may be quite small, for example 500 pieces. Since these customers know exactly what their production requirements will be, they can do PPAP—Pre-Production Application Planning—in which they can stage production to run several different part numbers out of the same material, thus minimizing the changeover time from part to part. Multis are the perfect choice in these cases. Also, since the parts are typically families of similar components, even the tooling requires minimal changes from part to part. Who would've ever thought that small lots could be produced economically, and profitably, on a multi!
To sum up, in a recent study Tornos conducted for a customer comparing CNCs vs. cam multi-spindles, it analyzed over 50 part numbers. Considering the annual quantity, plus figuring in setup and changeover time, it took about the same number of CNC machines as it did cam versions to produce these parts. Even in that "tie" scenario, the CNCs won the vote as the better choice because the total cumulative changeover time was less. That translated into less "hands-on" labor time, which reduced the cost per part significantly enough to sway the customer to CNC.
What about you?