You don’t have to look too hard to find a Swiss-style CNC automatic lathe to productively machine precision parts for medical devices. Parts are typically 12–20″ (305–508-mm) long, with length-to-diameter ratios of 12–15×, and machined from bar from 10 to 32-mm diameter. Outlier sizes down to 3 mm and up to 38 mm and even larger are available for specialized applications. Swiss-machined parts of these types require support with a guide bushing along their entire machining length to allow removal of a large amount of material in a single pass.
But there are some new innovations in the marketplace that are worth a fresh look, such as advanced Swiss machine technology with a fully programmable B axis, which provides the user with capability to machine complex shapes and drill angles and mill profiles. New developments in CNC automatic lathes aren’t limited to the Swiss-type, however. CNC automatic lathes that are convertible from Swiss to fixed headstock machines (often with changeover time as fast as 15 minutes) have been introduced by leading machine builders. These machines allow machining short parts close to the headstock and save material cost by reducing the remnant of expensive ground bar that is left by Swiss machines.
When Honor Med Maskiner Corp. (Elgin, IL) was looking for a new machine to replace the company’s older equipment, it chose the Tsugami B0326-II. “We wanted a machine that was extremely versatile and could hold tight tolerances,” said Patricia Hirsch, owner. “The three most important factors that made us choose a Tsugami were the capabilities of the machine, price and support. The modular live rotary tool units, live tooling speed and the option to run without a guide bushing are just a few of the reasons why Tsugami was the best option for us,” said Hirsch.
The Tsugami B0326-II Swiss-type machine can be quickly and easily converted from a direct-drive guide bushing bar-fed operation to nonguide operation when fitted with the chucker kit option, making it well-suited for short or prismatic part machining. “The chucker option is increasingly popular for relatively short parts like hardware, fasteners, electrical connectors, and even medical parts like spinal hooks and short instruments,” said Ron Gainer, Tsugami Rem Sales (Windsor, CT).
“The sweet spot in the Swiss machining market volume is the 20-mm machine, especially for medical applications where the heaviest volume is,” said Gainer. “We have a new 32-mm Swiss-type machine, the SS327-5AX model with full B axis that is convertible and can be run as a chucker. The 32-mm machine has great appeal for job shops because of the variety of work it can handle. Shops don’t want to be limited and it gives them good Swiss capability.”
For single setup solutions for complex parts, Tsugami has introduced the SS20M-5AX 20-mm multifunction machine. It features vertical machining capabilities, five-axis simultaneous control, and continuous B-axis movement. The Tsugami SS20M-5AX combines the versatility of a CNC automatic lathe with the functionality of a vertical machining center. It is capable of producing highly complex parts up to 20 mm in diameter and is equipped with a 24-tool automatic toolchanger and vertical tool spindle that performs multi-angle operation on main or subspindle workpieces.
“There is no question that in the Swiss market, the machine side is driving the programming side,” said Gary Hargreaves, vice president, business development, Mastercam/CNC Software Inc. (Tolland, CT). “In the past, the majority of these machines were programmed manually because they were very high volume, running for months at a time, and the user had a lot of time to get the next part programmed. What has changed is that due to CAD/CAM and the ability to program much faster, smaller shops are picking these machines to do much smaller quantities, sometimes as little as a thousand parts and they need faster turnaround,” said Hargreaves.
“A lot of people are using these B-axis equipped machines for basically 3+2 type of work where positioning is in three axes and pocket or drilling operations are performed. Even if they are just the drilling and pocketing, they don’t have to set up additional tools, making the machine that much more efficient,” said Hargreaves. “The next step is machining complex shapes and surfaces. We’re seeing an evolution where customers are moving from using it as a programmable fixed axis to actually starting to change the design and look of some of their parts so they have much more complex shapes that require simultaneous motion and CAD/CAM systems to program and machine. Fortunately for us we had a great suite of toolpaths that we were using in the traditional five-axis market that we were able to plug into our Swiss product,” said Hargreaves.
“Our new M4 Series of machines is available in 16, 20 and 32-mm versions,” said John Antignani, executive vice president, Marubeni Citizen Cincom Inc. (Allendale, NJ). “They have three machining sections: a slide on the main spindle; a turret that can work either on the main spindle or the back spindle; and a Y-axis slide which is predominantly for the back spindle. All the machines come with or without B-axis capability, with B-axis capability on both front and back spindles of our machines.”
Typical applications for angular B-axis machining include dental parts, instruments for arthroscopic surgery, trauma devices like bone screws with angular features and medical applications that require angular drilled holes. “The newest thing in the medical industry is double-lead bone screws that require higher pitch angles, so we developed a plus or minus 25° helix angle thread whirling unit for our machines. Thread whirling units are available on all our machines series including the L, M, and A series,” said Antignani.
“The L series is our most popular machine series. Last year, we introduced the Type 10 machine which has a back spindle Y axis. You can use the Y axis on the front and the back. So we didn’t apply the Y axis to the toolpost, we applied the Y axis to the actual subspindle, allowing the Y axis to be used on the front or the back and producing more simultaneous machining. Also the L20 Type 12, which was introduced at the last EMO show, is a B-axis capable machine, very similar to the B axis that we offer on the M series machine,” said Antignani.
“Complete milling on Swiss machines is something that is desirable for medical, defense or gun applications, as well as aerospace. The medical market is always looking for more of everything, more tools, more axes, and more capability,” said Bob Erickson, regional manager, Hanwha Machinery America (Franklin, WI). “That’s not unusual. The heart and soul of the market, about 80– 90% of market needs, are satisfied by the standard 7-axis machine, at least what we call 7-axis. We have a C axis standard on the main spindle and on the subspindle.”
Hanwha has introduced a large capacity eight-axis Swiss-type turning center, the XD38HII with Y2 axis. “We have taken our standard 7-axis machine and added a Y axis on the back working station, adding more tooling capabilities. The large capacity 8-axis XD38HII Swiss-type turning center has bar capacity up to 38 mm at the main and subspindle and features high rigidity and cutting accuracy.
“The other big buzz in the marketplace is the programmable B axis, which is driven more by aerospace and medical applications. The programmable B axis helps in any type of application where angular drilling, milling, three or four-axis simultaneous milling capability are desired. Our new H2 series platform has the Y2 as standard and the B axis optional,” said Erickson.
“We also have two different styles of machines that are 11-axis machines that are available to those who want to do some pinch milling, turning, pinch drilling, or tool up with a lot of tools for machining many different parts. In addition to our newer machines in the H2 series, we’re also introducing the XE 20 entry-level machine with limited live tooling to bridge the gap between the 7-axis and 11-axis machines,” said Erickson.
“In medical applications, Swiss machining is being called upon to meet quality requirements that are increasing because parts are getting smaller and the tolerances are getting tighter,” said Hans Koschig, technical sales, Index Corp. (Noblesville, IN). “Geometrical complexity of these parts is requiring a B axis. It’s very important that you are able to touch the part with the tool, because you need all three or four axes X,Y,Z and the B axis in the tool.”
Koschig said that one very simple example is an injection medical needle with a tight tolerance. The 12-mm long part with a wall thickness of less than 0.1 mm has to be drilled with a 0.5-mm diameter gundrill 24× D. “Any alignment error in the tool and you won’t be able to drill the part. For other medical applications like machining bone screws, thread whirling with the B axis brings the thread whirling head into the right pitch angle, something that had to be done manually in the past,” said Koschig.
Traub’s TNL 18 and 32 CNC automatic lathes are essentially the same machine in two sizes. “Both machines have B axis and on the top turret that can swivel 100°, which means we can achieve each point on the part. The additional Z axis and the ability to swivel the B axis in one position means the tip of the tool will move and be brought into the right position,” said Koschig. Traub TNL series CNC automatic lathes can be used as sliding headstock and fixed headstock versions. You can run each machine with and without guide bushings.
“The ZPS Swiss CNC 32 machine is designed to push the envelope of performance for high-end Swiss applications like machining difficult-to-machine parts and material for the medical, aerospace, and automotive sectors where other Swiss machines aren’t likely to be competitive,” said Olaf Tessarzyk, managing partner, ZPS America (Indianapolis, IN). One application that isn’t normally associated with Swiss machining is the ability to do gear hobbing, which the ZPS Swiss machine’s rigidity allows it to do.
The solidly built machine’s cast iron base weighs in at 11,000 lb (4989 kg). It has the ability to put up to four tools in the cut simultaneously and has 12 axes with 23 tool positions. Gang tool slides on the front of the machine allow pinch milling, pinch turning, which are time savers. They allow the machine to rough and finish while the part is pushed through the guide bushing. “At the same time, end working attachments from the front, driven or static, can work off-center and have three tools in the cut while working independently with the subspindle doing the backworking machining. Front and back sides of the part can be worked independently with a subspindle that has the same power as the main spindle,” said Tessarzyk.
ZPS America has its own software. “It’s not a post, and that’s important because on a post you have to go back and forth and never are able to emulate the machine program 100%. What we did was get a European manufacturer of a CAM post to build it into our machine control. As a result we can use our software on the computer as an exact machine replica and go back and forth without losing any data, like clearances, safety positions, tool crash avoidance and the like,” said Tessarzyk.
ZPS design for the Swiss 32 employs several features, specifically aimed at heavy-duty milling. ZPS uses a spindle disk brake for heavy mill cutting rather than using only a C-axis clamp that wouldn’t be likely to hold up under heavy C-axis milling. Also a programmable guide bushing isn’t slotted on the inside, it’s slotted only on the outside to prevent debris from contaminating the guide bushing. “The pneumatically actuated guide bushing is virtually maintenance free. Again, if you do heavy milling, you want to lock your spindle in position and lock the guide bushing so you can use it as a fixed headstock. The other advantage is that in the open position you can advance material and run standard stock that isn’t ground,” said Tessarzyk.
This article was first published in the May 2014 edition of Manufacturing Engineering magazine.
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