The COVID-19 pandemic has brought into clear focus the need for safe, sterile surgical devices. Accordingly, healthcare providers are increasingly turning to single-use or disposable products. Disposable surgical products inherently reduce risk of infection related to cleaning and sterilization since they are presterilized and individually packaged. Such devices are often viewed as safer alternatives to reusable devices, as the latter can still lead to infection in some cases. Many in the medical device industry will recall news stories relating to field recalls of some reusable surgical devices that had complex designs and intricate parts that were challenging to clean thoroughly. As the healthcare industry increasingly moves toward an outcomes-based model, solutions such as disposable products that can drive better outcomes for patients help meet the needs of hospitals to provide value-based healthcare. In light of all of this, it is perhaps not surprising that the use of disposable surgical instruments continues to gain favor.

Rolled Tube Technology can reduce both component and subassembly costs of single-use handheld endoscopic surgical devices such as scissors, graspers, dissectors, and tissue-holding forceps. (Credit: MICRO)

Stainless steel tubing is a primary support feature of single-use handheld surgical devices. Medical device OEMs and contract manufacturers have a number of options to choose from for producing these tubes efficiently and cost-effectively, ranging from manual production to fully automated systems. Depending on the device being produced — along with factors such as volume and features needed — drawn, or stamped and rolled, tubing can be used to manufacture metal tubes quite effectively.

Several criteria must be factored in during the design stage before determining which technique to use, including the size of the components, tolerance, thickness of the tubes, and whether the device will require the tube to move or remain static. Design engineers should be aware that these factors play a critical role in the type of process that can be used to produce a given tube. For instance, wall thickness may well dictate which process is selected. Generally speaking, most single-use medical tubing tends to be thin-walled, typically 0.010-in. thick, and can be produced in a variety of manners. By contrast, a thicker wall of 0.030 or 0.040 in. usually requires a machining process to accommodate tube features such as grooves and slots.

Drawn Tubing Approach

Stainless steel tubing can be drawn in a range of profiles. Stock tube is extruded through a die to achieve a particular cross section. Drawn tubing is typically used when tightly controlled dimensions such as straightness or strict diameter consistency are needed for critical functions throughout the entire length of the metal tube shaft. Drawn tubing is also a good choice for more robust end features such as flanging and flaring, expansions or reduction features, or end sharpening. In addition, drawn tubing is usually better suited when additional processes are needed; for example, for piercing and slotting, precision sharpening, electropolishing, and laser welding and for projects that require secondary assembly.

‘Rolled’ Tubing Method

One cost-effective way to produce high-volume thin-walled stainless steel tubing is through a progressive stamping process which actually “rolls” the tube into its final form. This innovative method allows a tube to be stamped out of flat stock, resulting in a finished tube with complex features. Features such as holes, slots, and windows can be punched into raw flat stock during the initial stage of the stamping process.

This process helps reduce production time and component expenses, along with costly and time-consuming secondary operations. It is now possible to stamp and roll a finished tube using a power press in just a few seconds, as opposed to drawing raw tubing, cleaning it, cutting it to the desired length, and processing secondary features. This method is best reserved for higher volume parts — generally quantities greater than 300,000 pieces. MICRO’S patented, Rolled Tube Technology, for example, can reduce both component and subassembly costs of single-use handheld endoscopic surgical devices such as scissors, graspers, dissectors, and tissue-holding forceps.

Automation

Drawn tubing is usually better suited when additional processes are needed such as piercing and slotting, whereas rolled tubing is best reserved for higher volume parts. (Credit: MICRO)

Fully integrated systems allow full-length drawn metal tubing to be used with automated work cells, a process that can combine operations, shortening setup and cycle times that can reduce costs. Rather than precutting tubing, integrated systems allow the 10-ft tubing to be fed into a machine in one automated process, increasing productivity and decreasing cost and waste. In addition, quality is improved because there is less movement of a part and fewer variables that can impact quality.

Process improvements such as these can help achieve the goals of lean manufacturing by increasing use of automation, improving manufacturing efficiency, and reducing costs by eliminating waste. Automated processes ensure a high degree of accuracy, precision, and uniformity, and production is more economical without sacrificing on part quality.

CNC Machining

For thicker-walled tubing, a computer numerical controlled (CNC) machine is typically required. A CNC machine takes a raw material — in this case, metal — and cuts, grinds, drills, turns, mills, and shapes it into parts that meet exact specifications, using a computer program to control the operation of machine tools such as lathes and mills. When cutting metal, CNC machines generate massive amounts of heat. Consider that these machines are made almost entirely of metal. The latest CNC machines are equipped to collect data in real time as they run, and to control for factors such as thermal growth.

To visualize this, think back to when you were young and couldn’t remove the metal cap from the ketchup bottle because it was too tight. We may remember our parents running it under hot water in the sink. Miraculously, the cap came off after that. The science behind this home remedy is that metal expands at a different rate than the glass when heated. The heated cap ultimately became larger than it was in its cold state, naturally releasing its grip on the bottle. Therefore, imagine the expansion occurring with hundreds of metal parts bolted and welded together, six feet high and eight feet wide. In this situation, a part produced in a CNC machine when cold will be substantially different from a part made when the CNC reaches operating temperature, unless the machine self-adjusts to account for this.

Laser Cutting

Newer CNC lathes with integrated laser cutting equipment can also be used for fabricated tube production. In the past, two machines were needed for turning and laser cutting. Transfers from one machine to another increases the risk of misaligned features versus a single setup. This combination of capabilities allow laser cutting and machining in one setup, with registration capability within 0.0005 in. A Citizen L200 CNC machining center combined with a Swiss style 7 axis CNC lathe and an integrated 400 W laser cutter is particularly well suited for fabricated tube production and various metal tubing projects.

With this integration, laser-cut slots and holes can be achieved while simultaneously machining different outside diameters, reducing setup time, secondary processes, and handling costs. The equipment uses long-length drawn metal tubing with automatic feeding, cutoff, and part ejection. Automated work cells can cut features and holes into tubing while in-line inspection using a two-camera vision system ensures quality. These machines also use algorithms to adjust themselves in a timely fashion to maintain accuracy. The process can easily accommodate when there is a design change needed. All that is required is a programming change versus a more expensive tool change. These work cells can help to reduce set-up time, the need for secondary processes, and some associated assembly costs, thereby lowering overall manufacturing costs.

Wire EDM

Wire electro discharge machining (EDM) is another process that can be used for cutting tube features. These machines use a taught wire carrying high voltage to remove metal. Wire EDMs work differently than milling and can be used to create unique features such as window shapes, which are not always suitable with a laser cutter. The process also works well when the angle of the cut in the tube wall needs to mate with other components. EDM requires a slower production process, but for creative fixtures on multiple stacked parts, it can streamline production very effectively and cost-efficiently.

MICRO’s tube fabrication center combined with its laser cutting technology, automated work cells, and dedicated tube mill, enables the company to meet customers’ requirements for manual, semi-automated, or fully automated products. The company is able to reduce tubing costs on high-volume, disposable instruments while adhering to strict quality standards, resulting in products that meet all functional, visual, and dimensional requirements.

This article was written by Steve Santoro, Executive VP of MICRO, Somerset, NJ. MICRO is a full-service contract manufacturer of precision medical devices, injection and insert molding, metal injection molding, fabricated tube assemblies, subassemblies, and complete devices. With over 75 years of manufacturing excellence, the company offers product development and design assistance capabilities and excels in prototyping and validation to full-scale production, with a mission “to help customers save lives.” For more information, visit here .


Medical Design Briefs Magazine

This article first appeared in the April, 2021 issue of Medical Design Briefs Magazine.

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