According to the World Health Organization, healthcare-associated infections (HAIs) are the most frequent adverse event in care delivery worldwide. COVID-19 has prompted hospitals and clinics to increase protections against infection on top of the stringent sterilization and disinfection protocols already in place. Complicating this ongoing effort are the wide range of surface materials to be cleaned, more-frequent disinfection, and the use of harsh chemicals, which may be incompatible with traditional plastics.

Acrylonitrile-butadiene-styrene (ABS) and polycarbonate (PC) resins were traditionally used for medical device housings and enclosures. Chemical resistance became an issue, and components made with these materials started to fail from environmental stress cracking (ESC). So, manufacturers began replacing ABS and PC with blends of PC and ABS or polybutylene terephthalate (PBT).

PC/ABS and PC/PBT blends are currently the standard amorphous and semi-crystalline materials, respectively, for device housings and enclosures. However, these incumbents can fall short in chemical resistance, especially considering additional measures to prevent COVID-19 transmission.

In addition to chemical resistance, device enclosure and housing polymers need high-impact properties to withstand being dropped or to resist external applied forces. Repeated application of disinfectants can degrade impact strength throughout time, so these properties are tightly connected. Other important material requirements include dimensional stability, custom colorability, and flame retardance for powered devices.

Although high-end, polysulfone (PSU) and polyphenylsulfone (PPSU) offer good chemical and impact resistance, they may be over-engineered for enclosures that do not require sterilization.

Advanced PC copolymers may be the material solution that checks all the boxes. As a potential replacement for conventional resins and blends, PC copolymers can balance mechanical performance (impact, flow) with chemical resistance performance to mitigate crack propagation. Availability of advanced PC copolymers avoids the need to over-engineer these types of applications, providing an alternative, cost- effective solution.

When designing a medical device, OEMs must clearly understand compatibility between candidate polymers and new chemical agents, such as disinfectants, in the context of application requirements. The ESC test can screen polymer material candidates, but there is no current industry standard for chemical compatibility testing. Test methods aimed at simulating end-use conditions can aid in evaluating the effects of commonly used healthcare disinfectants on polymer properties such as impact resistance, toughness, tensile strength, and color stability.

Environmental stress cracking

One of the most common causes of premature failure in plastic parts used in healthcare devices and equipment such as ICU monitors, imaging equipment, infusion pumps, and hospital bed components is ESC.

To prevent HAI spread, hospitals and clinics are thoroughly cleaning and disinfecting medical equipment and high-touch surfaces with disinfectants based on quaternary ammonium, hydrogen peroxide, bleach, and other chemicals.

These measures heighten the risk of ESC, which can lead to poor aesthetics, costly repairs or recalls, downtime of a critical piece of equipment, and a negative patient experience.

Stress cracking depends on more than just the compatibility between a chemical and the resin. The elements that drive ESC are stress (internal in-mold stress and externally applied stress) and chemical exposure (a function of exposure concentration, duration, temperature). When a plastic part under mechanical stress is exposed to aggressive chemicals that penetrate the molecular structure of the resin, polymer chains break down and the material becomes more brittle. Given time, the part can develop a web of thin cracks around the points of stress, called crazing. As these small cracks propagate, the part can develop fractures and fail, particularly if there is an external impact collision or torsional force such as inserting a screw head into a threaded insert.

Other factors contributing to chemical compatibility are stresses introduced by the design, the processing method, and the way the part is used. However, the first step in preventing ESC is choosing the right material for the application.

 

Compatibility testing

To evaluate and compare compatibility with typical healthcare cleaning agents for industry-standard PC blends and advanced PC copolymers, SABIC conducted ESC testing using an aggressive method based on ASTM D543: Standard Practices for Evaluating the Resistance of Plastics to Chemical Reagents. This test continually exposes test bars of the material to strain and a specific chemical agent for three-to-seven days. With no established industry standard, this exposure range was selected to push the material to its test limits.

The test bars are kept saturated with the chemical agent (wrapped in disinfectant wipes) and are bent to a specific strain level (1% in this case) in a test fixture. Constant strain is maintained throughout the test period.

This test method is one of the most stringent protocols and serves as a highly accelerated version of normal exposure to disinfectant wipes in a healthcare setting.

To demonstrate compatibility with a given chemical agent, a material must achieve >90% tensile stress at yield and 80%-to-139% tensile elongation at break, per ASTM D638: Standard Test Method for Tensile Properties of Plastics.

The testing described here was conducted to determine the susceptibility to chemical attack of PC copolymers vs. standard PC blends.

The materials tested were a PC/ABS blend, a PC/PBT blend, and four PC copolymers from SABIC’s new LNP ELCRES CRX family. Two of the ELCRES CRX grades are semi-crystalline copolymers and the other two are amorphous copolymers.

SABIC conducted this ESC study to assess compatibility between incumbent materials against widely used surface disinfectants. Test samples were exposed to 12 different healthcare disinfectant products, such as PDI Sani-Cloth wipes and Diversey Virex wipes.

Disinfectants used in these products include:

• Quaternary ammonium compounds. Cationic surfactants (positively charged surface-active agents) bind readily to the negatively charged surface of most microbes.
• Sodium hypochlorite (bleach). Bleach active ingredients can kill viruses, bacteria and fungi.
• Hydrogen peroxide. Not as strong as bleach, it does have disinfectant properties that effectively kill viruses and bacteria.
• Ethanol. Ethyl or isopropyl alcohol is an effective disinfectant when used at a high enough concentration.

The U.S. Environmental Protection Agency (EPA) has published a list of disinfectants that meet its criteria for use against SARS–CoV-2, the novel coronavirus that causes COVID-191. Several of these disinfectants are listed in Table 1. Data shown in the table is based on SABIC’s compatibility criteria scale.

Results: Broad chemical compatibility of PC copolymers

All four PC copolymers demonstrated broader compatibility with the selected disinfectant chemical products than the PC/ABS blend. Further, semi-crystalline PC copolymers surpassed the PC/PBT blend in compatibility with Sani-Cloth AF3 and Virex TB wipes, considered among the most aggressive products on the market. Specifically, the PC/PBT blend did not meet the compatibility criteria for elongation at break for these two disinfectants.

The new PC copolymers are based on unique building blocks tailored to the backbone of PC to lessen the negative effects of chemical attack and chemical degradation for reduced crack initiation and propagation.

Testing for resistance to external stress

In addition to the ESC test, SABIC conducted a high-speed puncture test on selected material samples before and after exposure to one of the disinfectant chemicals to reveal fracture patterns – either ductile or brittle fractures – as a gage of impact resistance and toughness.

Brittle fracture means that with prolonged exposure, the material tends to be more susceptible to ESC during application of an external force. Ductile fracture indicates a material with more toughness, i.e., more energy is needed to initiate a crack and there is less tendency for crack propagation.

For this test, we compared the PC/ABS blend to one of the amorphous PC copolymer materials. We tested each sample with the high-speed puncture tool before and after exposure to PDI Sani-Cloth AF3 wipes for three days. Face impact testing was completed using the INSTRON CEAST 9350 with a 0.50" hemispherical dart and 10.47kg sled weight. The test data determined differences in impact force and energy for the materials before and after chemical treatment of the molded parts.

Results: Ductile vs. brittle fracture

When exposed to Sani-Cloth AF3 wipes for three days and then subjected to the high-speed puncture test, the PC/ABS blend sample experienced brittle fracture.

In contrast, the amorphous PC copolymer sample exhibited ductile fracture using the same conditions, with higher force (N) and energy (J) associated to initiate a crack in the puncture test.

Figure 3 does not show any change between the unexposed sample and the chemically treated sample following the high-speed puncture impact test. However, there is a noticeable difference between the PC/ABS and the CRX1414 copolymer failure modes. The PC/ABS sample shows significantly more radial cracking and would be classified as a brittle failure, whereas the CRX1414 copolymer has minor radial cracking and would be classified as a ductile failure.

While ESC data and puncture test results are good screening tools, the performance and interpretation of end-use testing are important. Therefore, extensive testing of the finished part is strongly recommended.

 

Material selection sets the stage

Proper selection of plastics for medical device housings and enclosures will continue to be a focus to control HAIs and improve patient safety while reducing operating costs from premature failure of costly equipment. There is a need for advanced materials with improved chemical resistance that can extend the useful life of devices and equipment that get cleaned frequently.

Advanced PC copolymers can surpass traditional PC blends in chemical compatibility with harsh disinfectants and reduce crack propagation that can lead to failure.

Beyond choosing between these two types of materials, device makers and designers must decide whether an amorphous or a semi-crystalline grade is better suited to the application and use environment. In general, amorphous polymers surpass semi-crystalline polymers in ductility, toughness, and dimensional stability for parts with tight tolerances. Semi-crystalline polymers have better chemical resistance due to their inherent chemical structure – but at the expense of dimensional stability due to higher shrinkage and part warpage.

After material selection, other factors affecting ESC come into play. Part design and processing are important to maximize chemical compatibility. Pay close attention to good design principles for part geometry and gating to minimize weld lines and avoid sharp corners to reduce areas of stress concentration. Any initial stress points in the part design will become weak links for chemical attack. Thus, poor part design can negate good material selection.

Poor chemical resistance and weakness in a plastic part can also be attributed to molded-in stresses introduced during processing. Localized in-mold part stresses should be minimized during molding and secondary operations.

As illustrated in Figure 4, a combination of informed material choice, good design principles, and processing and secondary operations that minimize stress can help device makers improve the performance and durability of equipment exposed to today’s healthcare disinfectants.

SABIC
https://www.sabic.com

About the authors: Manish Nandi, Ph.D., is business development leader, healthcare and Nithin Raikar, is senior business manager, LNP copolymers at SABIC. They can be reached at productinquiries@sabic.com.

1 List N: Disinfectants for Coronavirus (COVID-19). EPA website. https://www.epa.gov/pesticide-registration/list-n-disinfectants-use-against-sars-cov-2

After nearly 40 years of serving medical and semiconductor customers, Connecticut-based Raym-Co was ready for the leap into state-of-the-art equipment. But, after spending heavily to upgrade from 30-year-old manual machines to about 60 pieces of CNC equipment, the results were underwhelming.

“We saw an increase in the ability to hold tolerances and a decrease in cycle time,” says Brandon Artibani, Raym-Co’s vice president. “But not as much as we had hoped.”

That’s when Jim Roberts, sales engineer at tool distributor Lindco Springfield, suggested the 37,000ft² job shop try Haimer shrink-fit tool holders. Roberts provided some sample tool holders to test in the new CNC machines and Raym-Co almost immediately noticed the difference in rigidity.

Mike O’Connor, regional sales manager at Haimer, then recommended the Haimer Power Clamp Economic Plus NG with adjustable coil and 15 tool holders to start.

Raym-Co machinists instantly noticed the difference between the shrink-fit holders and their old, low-quality tool holders. With the old equipment, cutting aluminum averaged 60ipm to 100ipm – with the new tool holders, cutting averaged 1,000ipm.

Artibani explains that, “Fifty percent of that increase was due to the new CNC machines; the other 50% was because of the shrink-fit system. Without the holders, we can’t do that.”

With Haimer tool holders, holding tolerances is effortless. Raym-Co now runs at ±0.005mm on location and hole size.

“A lot of that has to do with the fact that the holder runs so true that everything falls in right away,” Artibani says. 

Roughing to finishing

After investing in the Haimer shrink-fit system, Raym-Co initially planned to use it for roughing. Engineers were using only one Haimer Power Shrink Chuck for each roughing job, however, they soon started to run tighter tolerances and required more standard shrink-fit holders.

“We found that the tolerances were holding in place and tool life was significantly increased,” Artibani explains.

Shrink-fit holders are the fastest, most consistent method of cutting tool clamping. Cutting tool changeover takes 5 seconds to 10 seconds, and results are repeatable from operator to operator. This leads to consistent setup and translates to consistent part production and reliable tool life. On average, Raym-Co’s tool life increased 40% with some jobs achieving a 200% to 300% increase.

“Now it’s our main tool holder,” Artibani says. “From roughing to finishing, as long as it’s an endmill, it goes into shrink-fit.”

Eliminating runout checks

The Haimer Power Clamp Economic Plus NG can shrink solid carbide and HSS end mills from 3mm to 32mm diameters. Normally, it comes with one base holder, but the company purchased an additional base to have one tool holder heating while another one was cooling.

The high-performance coil, contact cooling, and additional base guarantee rapid, simultaneous shrinking and cooling. Heating a tool holder takes 10 seconds while cooling takes 30 seconds to 60 seconds. Raym-Co noticed that it took 10 extra seconds to use the shrink-fit system compared to inserting the tool into a collet chuck.

“We gain the time back because we don’t have to check the runout and play around with the tool trying to get it to run true every time,” Artibani explains.

Further investments

Artibani has convinced several machinists to invest in Haimer shrink-fit technology.

“The amount of time taken off every job and the ability to trust the Haimer equipment at the levels I can now, it’s worth every penny,” Artibani says.

In addition to shrink-fit, Raym-Co acquired a new balancing machine from Haimer in March 2020. However, due to COVID-19, the company has not been able to use it to its full potential.

“I can’t wait to see what kind of benefits this brings as well,” Antibani says.

Haimer
https://www.haimer-usa.com

Lindco Springfield
https://www.lindcospringfield.com

Raym-Co
https://www.raymco.com

Adopting modern communications and computer technology in industrial settings can be difficult, especially for the highly regulated medtech industry that uses many legacy, customized systems.

Medtech manufacturers aim to maximize supply chain profitability and build high-quality products, with many using lean manufacturing techniques.

However, these traditional methods take immense time and effort to reach maturity. Actions follow a reactive, stop-and-fix approach. Machines, tools, and products in modern manufacturing plants are much more sophisticated than they were when lean methods were launched and, as process flows become increasingly complex, this linear approach is no longer sufficient. Manufacturers using only traditional lean manufacturing methods have reached a barrier that requires a new way forward.

Industry 4.0 (I4.0 or the 4th industrial revolution) focuses on improving process efficiency to deliver high-quality products at lower cost. However, high product margins in the medtech industry reduce the motivation to change. For businesses that want to remain competitive, they can’t afford to ignore the benefits these new technologies offer.

Using digitalization to access and understand the right data presents a new opportunity for a step-change in quality, above what can be achieved through lean or Six Sigma.

Path to digitalization

Manufacturing is often regarded as a rigid, human-led operation with fixed process steps and a focus on local key performance indicators (KPIs), preventing a progressive vision for the entire value chain. In medtech, masses of information are still stored in paper and legacy systems, preventing a real-time, dynamic approach. Harnessing the benefits of I4.0 requires a roadmap, the roots to which lie in applying a digital mindset to existing manufacturing operating systems.

The move to Big Data, the Internet of Things (IoT), distributed intelligence, artificial intelligence (AI), and completely autonomous systems is costly and complex and requires careful, strategic planning. Many medtech companies have grown through acquisitions and inherited different systems.

The maturity level of different plants may vary significantly, with some still relying on paper processes. This makes it challenging to understand where to prioritize transformation.

“An IT approach may be to standardize systems, but in a manufacturing environment, it’s difficult to take things out because they are so embedded in processes. A different approach is required to modernize and digitize manufacturing,” says Paul Straeten, head of manufacturing IT at Medtronic. “We have done a lot of analysis of revenue, value, and cost across different sites to understand our priorities.”

With the right vision and strategy, the path to making I4.0 a reality isn’t as terrifying as it may first appear. I4.0 uses existing technology and connects information and systems to gain visibility and understanding of the complete value supply chain. The first step to this is data and having better information to predict markets and make better decisions.

Strategic development objectives must be defined. Where does the business want to be in three years and how does it get there? Key capabilities and commonalities between plants can be identified (it’s better to get 1% improvement across five plants than 3% in one). By understanding the level of maturity of existing products and systems across different plants and areas of cohesion, leaders can prioritize investments and create a sequence of what the journey to I4.0 will look like. They can then identify technology gaps, creating a plan for common architecture and standardization between plants.

Data to information

Machines, sensors, operators, and products, along with the wider supply chain and external related sources, generate data. However, few manufacturers use this to gain insights into operations and processes. Even analog signals from older equipment can be digitized to incorporate them into modern systems. If we can collect, collate, and contextualize all data that relate or influence manufacturing operations, we have the building blocks to move from reactive to predictive operation.

“Medtronic has grown significantly through acquisitions,” Straeten says. “The manufacturing sites have processes and systems implemented that are aligned with our quality management system. But how the data is stored and managed is a very diverse landscape, which adds enormous complexity. It’s one of our key challenges.”

The path to autonomous manufacturing started many decades ago with computerization, so it becomes easier to see how this progression can continue to meet new objectives. Following computerization, plants progressed to tools that provided visibility of the shop floor, providing deeper insight into areas such as individual machine productivity. Today, as we make better use of this data, we are moving to a stage where information can be used to predict what will happen, enabling prepared responses to be formulated. Ultimately the aim is a completely self-adapting system that requires no human intervention. If we can get the right information from the data, AI algorithms and machine learning tools can use it for predictions and autonomous operations.

Once the right data are captured, we can gain insight and foster an appropriate response. When an event occurs, sensors detect what’s happening. It takes time to understand and analyze the data. It then takes more time to decide on a course of action and follow through. Every second lost in this flow of events costs money. I4.0 technology can shorten that sequence, providing much quicker insight into what the data mean.

New intelligent manufacturing execution systems (MES) are the backbone of autonomous systems. The software can add needed context for data and connect disparate data sources and systems. It integrates legacy equipment with new, distributed edge-processing devices and brings data together to give a complete picture of a smart, digital shop floor. It also provides a common interface and ensures business procedures and quality processes are not bypassed as the system becomes more automated. Paper records will become obsolete as all process information is gathered and stored in electronic device history records (eDHR). Data can be securely accessed from anywhere, and compliance becomes part of the manufacturing process instead of reactive procedure.

Summary

Technology has progressed enormously, but many medtech manufacturers still use outdated systems and manual processes. Increasingly sophisticated and complex products, combined with more stringent regulatory requirements, require us to embrace digitalization to remain competitive. Once a company understands where it is in the process and where it wants to be, it can start taking the necessary steps.

The path to I4.0 is progressive, using legacy systems and IT infrastructure already in place, but it’s a step change in manufacturing. A modern MES enables integration of old and new, bringing together disparate systems, information, and communication protocols into a single source of truth that provides a backbone for progression to greater autonomy and smart manufacturing.

Medtech companies must start making digitalization part of their DNA or they risk being left behind. I4.0 is a journey we have all been on since the dawn of computers. Evolution or revolution, extinction cannot be an option.

Critical Manufacturing
https://www.criticalmanufacturing.com

About the author: Chris Parsons, vice president of marketing for Critical Manufacturing can be reached at chrisparsons@criticalmanufacturing.com.

Shrink-fit tool holder

Additions to the AccuGrip shrink-fit tool holder line include AccuKool coolant port holes. The ports provide coolant through the body, and the precise exit angle puts coolant into the vortex of the rotating cutting tool. This vortex occurs around 1.5xD to 2.5xD from the tool holder face, vacuuming 100% of the coolant into the tool’s cutting edge for improved tool life, part finish, and part dimensional control.

Accutek Inc.
https://www.accutekusa.com

Round face grooving

The micrOscope line has added a range of solid carbide internal tools for boring, grooving, chamfering, and threading in bores as small as 0.5mm (0.020"). The micrOscope internal round face grooving tools, with positive chip former for greater chip control, provide 3x better tool life compared to competitors. Designed with reinforced structure, the tools support internal round face grooving applications.

Grooving width ranges from 1mm to 3mm (0.039" to 0.118"). These tools for small part machining can be used with pressure coolant-thru up to 100 bar (1,450psi).

The tools use VTX grade, a tough sub-micron substrate, with AlTiN PVD coating.

Vargus Ltd.
https://www.vargus.com

Swiss mill-turn machine

The Genturn-52CS Y2, 2" bar capacity, 8-axis Swiss mill-turn includes a sub-spindle and dual C- and Y-axes for complex work in one handling. Twenty tool stations service front-side work and an additional 13-backworking tool positions are standard. The 20 front-side tool positions six live cross tools, three live axial tools, six turning tool stations, and five ID tool stations in a quick-access gang configuration. The counter spindle’s 13 tool stations include four axial driven stations with four live tool holders. Nine ID stations are included, four from the dedicated sub-spindle tool block, and five shared from the backside of the main spindle tooling bridge.

The main and counter spindle feature accurate dead-length gripping and a high-performance C-axis with full contouring and 360,000 radial positions (0.001° resolution). C-axis operations facilitate engraving and milling highly complex part details. The 51mm (2") bar capacity spindle runs up to 6,000rpm and the rapid traverse rate is 1,181ipm.

Expand Machinery
https://www.expandmachinery.com