Precision in surgery is paramount. Surgeons rely on a variety of handheld instruments, and they increasingly want tools that can aid in accessing hard-to-reach areas in the body where tip and positional control need to be seamless.
Articulating instruments that offer greater bend, flex, and reach over rigid tools are being embraced by surgeons for laparoscopic, endoscopic, and arthroscopic minimally invasive procedures where incisions are small and challenging to navigate. Articulating instruments provide more natural dexterity and can help reduce shoulder, arm, and hand fatigue during surgery.
Manufacturing components for these handheld articulating instruments that offer multiple functionalities can be challenging if design planning is not well executed from the start. A host of factors must be considered before a design can be manufactured efficiently, yielding both a high return on investment and positive patient results.
Take Time with Design
Medical device designers often find themselves in pressured situations related to cost, time, and other factors and may dismiss manufacturing considerations early on during the design phase. It's essential to ensure that a product can be manufactured effectively as early as possible in the design phase, before product development is initiated. Failing to properly account for manufacturability can be detrimental, especially for devices that have more sophisticated features and require greater attention to detail, leading to significant cost inefficiencies and possible product failure. Once the manufacturing process has begun, going back to make design revisions can be counterproductive and costly, often resulting in development and production delays.
To prevent such pitfalls, all devices should undergo a process known as design for manufacturability (DFM). This process, which can be combined with lean manufacturing or Six Sigma, entails extensive design review that ensures every product design is optimized for production. DFM is critical because it enables potential problems to be identified early and addressed in a timely fashion during the design phase. It strives to minimize and simplify the number of steps required to manufacture the product. This approach can save time and money, and it can prevent wasted resources in the long run.
Asking the Correct Questions
Understanding the application and subsequently asking the correct questions is key to applying DFM to any component design. For articulating instrument components, for example, it is important to consider the number of times a tube must articulate, the degree of articulation, and the constraints on the design from interactions with the human anatomy.
These considerations will drive initial material selection, laser cut geometry, and the need for post processing to achieve the desired metallurgical properties. Once these questions are answered, DFM can be applied to refine the design to strike the balance between functional requirements of the instrument such as grasping and dissecting and manufacturing capabilities such as laser cutting, molding, or machining.
Selecting the Optimal Material
Material selection during the DFM process is something that the contract manufacturer can guide the OEM product designer through. Not all stainless steels, for example, are created equal, and the specifics of how the tubing is fabricated, shaped, and processed can have a great impact on the function of an articulated instrument.
Finite element analysis and simulation can be used to analyze stress concentrators and determine the fatigue and work hardening that the articulated elements will be exposed to, thus enabling the engineer to understand potential conditions and optimize the design. Understanding these factors and the requirements for assembly will determine the required grade and chemical composition of the material.
Refining the Cut Geometry
In laser cutting, the laser itself is only a means to melt the base material in a localized area. The actual material removal takes place from the high pressure assist gas being used to literally blow away the molten material. This high-pressure gas is also the means by which the shape that is cut is removed from the workpiece. This is where the design of the articulation geometry comes into play. Imagine the difference between cutting a square and cutting a barbell shape where there is a significant difference between the widest part of the cut and the smallest part of the cut.
The square is very likely to be easily flushed away with the high-pressure gas, but the barbell shape has the potential to lock in place. This “slug” could then be welded onto the part from the laser depositing molten material from another cut, or worse, it could cause a crash in the machine and lead to accelerated wear of the cutting nozzle. The other important consideration is the economics of the operation. Choosing a simpler geometry helps avoid costly rework and manual operations required to remove troublesome laser slag and difficult-to-remove material slugs.
Execution and Development
Along with component DFM, process execution is equally important to yielding a profitable and capable operation. Partnering with a contract manufacturer that implements DFM can make this significantly easier. Lessons learned are applied to important parameters in the cutting process such as optimal pierce locations, nozzle geometry, and cut paths. The cut path and how a particular cut is divided into individual segments can also have a great effect on the stability of the process. For example, there are techniques that can be employed to increase the likelihood of a slug being removed without greatly increasing the complexity of the process.
Many of these techniques, however, can potentially increase piece part price because they usually require additional cycle time to break a cut into smaller sections, therefore minimizing the impact of the cut geometry on the slug removal potential. This is why there is such an emphasis on DFM being considered as early as possible in the product design cycle for articulating instrument components. Because most articulating instruments have a large number of individual cuts for their overall length, even small changes in cut geometry to articulation windows will add significant cycle time. Understanding and accounting for this mitigation is essential to profitability.
Developing an efficient design is crucial to keeping costs manageable and return on investment high. This is especially true for components and devices that require sophisticated features and intricate designs such as articulating instruments. DFM helps to achieve the best possible cost to repeatably produce a functional product that will pass all necessary approvals to reach the marketplace.
This article was written by Steve Jacobsen, Process Development Engineering Manager at MICRO, Somerset, NJ. For more information, visit here.