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The manufacture of medical devices involves some of the most sophisticated machining processes found in industry today. From a machining perspective, the machine tools that make up the “back bone” of medical device machining are 5-axis Computer Numerical Control (CNC) Mills, Wire EDMs (Electrical Discharge Machining) and Swiss-type lathes. For years, computer aided manufacturing (CAM) software has been used to automate the programming of the first two of those machining operations: 5- axis CNC Mills and Wire EDMs. However, CNC Swiss have been slower to move CAM.

Fig. 1 – The software employs a patented divide and conquer programming approach to simplify the programming of multi-axis Swiss-type lathes.
Until relatively recently, much of the CNC Swiss machining applications in the medical device field were actually programmed manually. Even today, some portion of medical parts for CNC Swiss-type lathes are programmed manually, or “by hand” without the use of CAM software. The reason for the slow migration to CAM programming of the medical devices manufactured on Swiss-type lathes are myriad. These included the fact that CAM software development had historically been focused largely on the domain of CNC milling and not specifically geared toward Swiss-type lathes.

Arguably, this lack of CAM industry focus on the discipline of programming Swiss-type lathes could perhaps be viewed as a chicken and egg sort of dilemma. CNC Swiss-lathe programmers in the medical device field didn’t program Swiss-type lathes with CAM, so CAM developers didn’t develop efficient solutions for programming Swiss-type lathes. Since CAM developers didn’t develop efficient solutions for programming Swiss-type lathes, CNC Swiss-lathe programmers in the medical devices field chose not to use CAM to program medical devices. Of course, that was far from the only reason.

Other reasons given for proliferation of manual programming of medical devices made on Swisstype lathes included the fact that part geometries were not complicated and part lots sizes were high, thus, program development was not necessarily the major bottleneck in manufacturing.

In recent years, the traditional script of factors that caused manual programming of medical devices on Swiss-type programming of Swiss-type lathes is proving to be a major competitive disadvantage for medical device companies and adoption of CAM software for this application has become a must. This article will explore these changing paradigms in greater depth.

What Is a Swiss-Type Lathe Anyway? Why Are They So Popular in Medical Device Manufacturing?

Before we can explore the challenge of programming CNC Swiss-type lathes for medical device applications, let’s define what a Swiss-type lathe is. The first Swiss-type lathes do indeed date back to Switzerland, where they first used to make tiny parts for the Swiss watch industry. That tradition of craftsmanship went global, and today’s Swisstype lathes are made from manufacturers the world over. A Swiss-type lathe has similar characteristics to a traditional CNC lathe, a machine tool that fabricates rotationally symmetrical parts by moving a tool in two axes of motion across a two-dimensional form.

The signature difference between a Swiss-type lathe and standard lathe is a sliding stock, which is to say material is removed by the machine pushing the material into a tool rather than having the tool move across the material. As a result, a Swiss machine is able to produce small parts where the length of the part might be four times or more the diameter of the part.

The Swiss-type lathe is able to do so by always maintaining the cutting forces of the tool very near to the point where the part is being supported. On a traditional CNC lathe, such small parts would deflect or even break as the tool exerted cutting pressure on very small diameter material far away from where the material was actually being held. Generally, parts made on Swiss lathes will fit into a metal bar that is at most 1.25 inches in diameter, though in many cases the starting material is much smaller.

Swiss turning is as effective a manufacturing process for today’s implantable medical devices such as all manner of bone screws as it was for the tiny screws found in Swiss watches of years gone by.

However, what makes the Swiss lathes of today unique machine tools is not just the fact that they can make long, skinny parts with great accuracy. Today’s Swiss-type lathes have a variety of on-board milling functionality, making them truly “multi-tasking” machine tools capable of producing almost any small part that can fit into their tiny work envelope. As such they are able to fabricate a number of shapes all in one machine, from rotationally symmetrical forms (turning), to prismatic features (2½-axis milling) all the way through free-form sculpted features (3- and 5-axis milling). All of this of course makes them ideally suited to the manufacture of implantable medical devices, which are, by definition, very small parts.

Adding to the sophistication of today’s Swiss-type lathes is the fact that they are really two machines in one. They have two spindles opposing one another, each holding one end of a part. First, a part evolves through the sliding headstock, supported by a guide bushing. This first spindle is called the “main spindle.” After a number of operations are completed, the bar stock is cut-of while being held with a secondary spindle called a sub-spindle. Once the bar is cut off, the remaining unfinished part is brought to the back of the machine where work on the back of it can be completed. To make this more efficient, the work on the sub spindle can be done at the same time or “simultaneously” to the machining on the main spindle. If programmed cleverly enough, this simultaneous or synchronous machining can effectively reduce the time it takes to make a given part by 50 percent. Needless to say, such a production reduction could result in a huge potential cost savings for the part manufacturer.

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