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.
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.
How Does CAM Software Work?
So now that we’ve understood what a Swiss-type lathe is, let’s understand how a typical CAM system works. While CAM typically refers to Computer-Aided Manufacturing, in this case we lathes to be the norm has begun to flip rather dramatically. As a result, manual will really be discussing Computer-Aided Machining. All CAM systems more or less work on the same principle and follow a similar work flow, which is: geometry is presented to the CAM system, either by importing it from a CAD system or drawing it in the CAM system. Once the geometry is present, certain motions are applied to the geometry by selecting desired cutting tools in concert with certain machining strategies, or patterns the tool follows to remove material from a work piece. Once the user is satisfied with the motion of his tools (called toolpaths) across a raw material to produce a finished part of the desired shape as visually displayed on the PC by the CAM system, he generates a CNC program.
A CNC program (also known as G-code) is an alphanumeric character set that commands a computer numerically controlled machine to make tool movements to form a completed part. Converting the geometric and process data in the CAM system into a G-code program is known as post processing as the binary information in the CAM is flushed through a template that formats the data calculated by the CAM system into a format a CNC machine can understand.
Historically, CAM systems have been very much the domain of milling applications because milling parts are generally geometrically complex and thus impractical to program manually as doing so could take hours if not days of complex mathematics. Turning programs, because they involve much simpler geometric motions, have typically had less call for the assistance of CAM software.
What’s Wrong with Programming Medical Devices Manually?
The problem with programming medical devices manually on Swiss-type lathes is that the process can be highly error prone. Programming manually not only can introduce human error, but can also be agonizingly slow. Another major drawback to programming manually is that that the programmer really has no visual check of his work until he makes the first part on the machine. The problem here is that Swiss-type lathes are very expensive machines with a high opportunity cost of capital, so every moment spent not producing parts represents lost time and money. Additionally, mistakes can cost more than just wasted time as they can result in costly machine crashes which can be both expensive to repair and very dangerous to the machine operator.
Why Did Applying CAM Software to Swiss-Type Lathes Take the Industry So Long?
The challenge in applying CAM for Swiss is that a Swiss lathe allows for both turning as well as many different kinds of milling operations in a variety of coordinate systems. Additionally, because of the ability to perform the simultaneous machining described above, synchronization of multiple NC programs for single part must also be handled. These complications present a real challenge for traditional CAM systems, conceived only to consider the motion of one tool across a work piece.
One software system applies a totally unique and patented approach to automating the programming of Swisstype lathes, directly addressing the issue of programmed turned and milled features in a single setup, while also taking account for synchronized machining operations. In fact, there are two US patents on this approach to programming Swiss-type lathes. The first technology, illustrated in Figure 1, automates the programming of numerous types of milling operations in the context of turning. This “divide and conquer” approach lets the user break down a part into its most basic operations. The second patented technology, called visual synchronization, and illustrated in Figure 2, automates the programming of simultaneous machining operations. By applying a completely novel approach to CAM programming of Swisstype lathes, this software system has become a medical device industry standard for the programming of Swisstype lathes. The world’s 10 largest medical device manufacturers have chosen it for the programming of their Swisstype lathes, as have many leading medical device sub-contractors.
What’s the Benefit of Programming Swiss-Type Lathes with CAM Software?
Programming medical devices on Swiss-type lathes has a number of benefits. Using CAM allows for a better organization of the manufacturing process, faster programming, and fewer errors. Additionally, using CAM lets the user better visualize machining before sending the CNC program to the machine. As shown in Figure 3, the software can allow the user to see both the finished machined part as well as a full machine simulation before sending the CNC program to the shop floor. As the saying goes, seeing is believing. And that’s something that can happen too late when programming medical devices manually on Swiss-type lathes.
This article was written by Hanan Fishman, President, PartMaker Inc., a Division of Autodesk’s Delcam Unit, Fort Washington, PA. For more information, Click Here .