ARTICLE FOCUS:

• MIS procedures
• Advantages of metal tubes and instruments
• Design and manufacturing steps for metal MIS innovations

When it comes to minimally invasive surgery (MIS) there are many advantages. Patients prefer MIS because it is less painful and usually involves a speedier recovery. Doctors favor it because it minimizes bleeding, scarring and chances for infection. Hospitals like these procedures because they can increase their day-surgery practices. And insurance companies support them for all of the above reasons, which generally result in lower costs.

The MIS procedure usually starts with a tube, either plastic or metal piercing the abdominal wall. It is through these ports that all subsequent devices pass. Typical devices used in these procedures are a light fixture, camera, and instruments to conduct the particular procedure. Metal is often the material of choice for the tubes that are often used in the trocar for placing ports in the body as well as the structural support for many of the instruments. The reason for the costlier material choice (when compared with plastics) is metal’s strength relative to its cross-sectional area. Stainless steel (300 series) is a commonly used alloy used for MIS applications, due to its stain, corrosion, and rust-resistant properties.

Unlike fine hypotubes such as those used for penetrating a vein or artery, the diameter of metal tubing for minimally invasive surgery devices is usually larger, typically ⅛ to ¾ inches in diameter. The compromise is between the need to minimize the size of the port in the body while allowing room for the instruments to pass through. This is where metal tubing comes into play. Tubing processed to very exact tolerances provides a "skin and skeleton" for the instrument, allowing it to pass through the ports while providing a maximum amount of space for the internal working components. In some cases, the tube is also an integral part of the working components. It is critical to process metal tubing to meet the stringent medical quality level that complies with the orthopedic and medical device requirements contained in ISO 13485.

Another key to success is the ability to design tubes for manufacturability. Obtaining good surface finishes, tight dimensional tolerances, and going from a prototype to an economically producible volume that may number into the tens of thousands is challenging. In fact, designing for manufacturability (DFM) can be like playing chess. The tube fabricators have to think three or four moves ahead in process development to provide economical, quick-to-market product delivery to customers. Of course that means getting involved in the early stages of design, where prototypes play an important role in the process.

Step by step process
The key steps involved in precision tubing for medical devices include the following:

• Print evaluation fosters communication and idea sharing. The first step in the process is print evaluation, which includes communication with the design engineer, open discussions on what the application is for, how to achieve the goals, and recommendations for any changes. The design engineer may have only a concept, or may have gone as far as finalized prints. At this beginning stage, the tube fabricator conducts a dialog to discuss what is on the drawing as well as possible solutions or alternate ways to get to the end product.
• Internal discussion and quotation process refines the design. After evaluating the print and incorporating feedback from the print evaluation stage, there is an open discussion with the customer that should include all facets of the manufacturing, including engineering, purchasing, production, and quality. These conversations usually center on methods and techniques to form and shape components at the lowest possible cost, while preserving process capability.
• Prototyping the design – manufacturability is the goal. If a picture is worth a thousand words, then a prototype part is worth a million. Prototyping and short runs are important in the design process. A good prototype gives the design engineer something in their hands to touch and feel, allowing them to really get a handle on the concept. Manufacturing a part that is close to the concept under discussion gives the engineer a good idea of what a part looks like and how it will work in the device. If the drawing has any weaknesses, developing a prototype gives the team an opportunity to discuss the situation with their engineers and perhaps improve the design.

The key here is that the person making the initial prototype part is simultaneously thinking about the manufacturing process necessary for making hundreds of thousands of the part.

Two examples involving our company include using the DFM process as part of the development of a unique forming machine to construct a fabricated tube, which is used to pierce the skin and serve as a porthole into the body cavity for a variety of laparoscopic procedures. The solution provided a cost structure to support the new design, keeping the cost of goods sold to a minimum. Without the improvement, the part would have been too costly to manufacture.

The second example involves a surgical device for a leading dental device manufacturer. The project included a series of prototypes for a specialized tube for an instrument in which clearance and spacing between components is critical. Prototypes created to hold the center revealed performance characteristics that were an issue. That is, the device resonated, creating too much noise. The OEM experimented with different ways to hold the inner tubes apart in order to generate less noise. Having accomplished that, the OEM is poised to begin manufacturing the device.

These prototyping and precision tubing efforts, combined with precision machining of complex parts are providing MIS device manufacturers with better leadtimes and lower manufacturing and assembly costs, thus ensuring a bright future for MIS innovations.