Travis Schneider
Laser-cut hypotubes (LCHTs) enable minimally invasive procedures across arrange of medical applications. However, producing them in high volumes presents significant challenges– largely due to the precision required in their manufacture. Precision automation technologies that minimize LCHT manufacturing risks are reshaping the industry for better efficiency and patient outcomes.
What is a Laser-Cut Hypotube?
The human body consists of myriad tube-like passageways, including the vasculature or blood vessels that manage blood movement. These and other biological tubing systems are an avenue for delivering medical therapies and devices to specifc body parts. The production of medical products from hypodermic tubing (also known as hypotube) is central to implementing such therapies and devices.
LCHTs must be cut to precise dimensions and from specifc materials to ensure safe and effective fuid delivery, drug administration, blood sampling or device delivery. Medical hypodermic tubing is commonly made from small diameter stainless steel, nitinol or other metal alloys. These metals deliver mechanical performance characteristics, including torque transmission and push-ability, that are often key to a device's performance. Their durability and biocompatibility make hypodermic tubing ideal for use in both disposable, single-use applications as well as reusable medical devices. This is important because LCHTs are now a crucial component in the medical industry, providing the backbone for various medical products, including needles, cannulas and catheters. Figure 1 summarizes some of these end uses as well as the most common materials used in hypotubes.
Figure 1. Hypotubes, which are often made with small-diameter stainless steel or nitinol, are used in a variety of applications including device delivery systems and minimally invasive,neurovascular and vascular procedures.
Laser-cut hypotubes (LCHTs) represent a cutting-edge advancement in medical device manufacturing, enabling minimally invasive procedures with a combination of precision device engineering and innovative material manufacturing. These intricate tubes are meticulously crafted using high-precision motion control and lasers that cut tiny features (in some cases, down to single-digit micrometers) to achieve the right product performance. LCHTs are used in a wide range of medical applications, from cardiovascular and neurovascular interventions to endoscopy and urology. They are even used with some surgical robots.
By enabling smaller incisions, better manuverability and improved patient outcomes, LCHTs hold the promise of more efficient and less invasive treatment options for patients worldwide. While these products hold great potential, manufacturing them – especially in high volumes – presents significant challenges.
Laser-Cut Hypotube Manufacturing Workfow
To fully understand LCHT manufacturing risks, it's important to know the steps in a typical manufacturing process. While different products may have different workfows, a product generally goes through some or all of the following eight steps:
- Welding or drawing of the tube
- Laser cutting
- Deburring
- Heat treating and shape setting
- Oxide removal and electropolishing
- Inspection
- Sterilization
- Packaging
Figure 2 provides an overview of those steps.
Figure 2. Eight steps commonly taken in LCHT manufacturing include welding or drawing the tube, laser cutting, deburring, heat treating, electropolishing, inspection, sterilization and packaging.
Step 1:
Welding or drawing of the tube
LCHT manufacturing begins by turning raw material into a tube with specifc outer and inner diameters. This is usually achieved through mechanical methods such as drawing or welding.
Step 2: Laser cutting
Once the tube is formed to the specifed diameter, it undergoes precision laser cutting. This is often accomplished through the use of specialized automated machines that present the tube to a laser source, selectively removing material to create the desired features.
Step 3: Deburring
Cutting the tube may generate sharp edges or burrs along the cuts. This residual recast material (also known as dross) is typically removed through a deburring process. Additionally, some cut portions that should have fallen away – often called windows or islands – may remain attached to the tube and need to be removed. Deburring operations are conducted using mechanical means (e.g. brush or barrel polishing), water jetting and/or a chemical process that dissolves burrs with an acidic bath (e.g. phosphoric acid, sulfuric or fuorine-based baths).
Step 4: Heat treating and shape setting
After deburring, the part may undergo heat treatment to achieve the desired fnal mechanical properties. For medical products, particularly those made of nitinol, this process involves heating the part to a precise temperature to "set" the desired shape (also known as shape setting). This process ensures the product can expand and conform to vessel walls once deployed in the body.
Step 5: Oxide removal and electropolishing
After heat treating and shape setting, products often undergo an oxide removal process. This step, crucial for medical products, eliminates the thin oxide layer formed during manufacturing using chemical etching, electrochemical polishing or mechanical methods. This process improves the device’s biocompatibility, corrosion resistance and overall performance. Additionally, electropolishing removes cosmetic defects and enhances the surface fnish.
Step 6: Inspection
LCHTs then undergo a thorough inspection of features to ensure they will conform with device design requirements. Microscopes that leverage different measurement technologies and are coupled to automated workholding are used to capture measurements. Given the tube’s length and typically small diameters (i.e. less than 1 mm), this can be quite challenging.
Step 7: Sterilization
Once a LCHT passes inspection, it is sterilized to eliminate surface microbes. This minimizes potential infection risk to the patient and is conducted with chemical processing, X-rays or traditional autoclaving.
Step 8: Packaging
After sterilization, the product is packaged to protect it from contamination or physical damage when in transit.
Key Manufacturing Risks
Many of the steps outlined above incorporate automation, and two – laser cutting and inspection – require particularly high precision. Laser cutting, which is often used to machine features as small as single digit micrometers in width, ensures optimal part reproducibility. Inspection is critical for confrming manufactured parts meet production requirements for verifcation and validation. In both steps, manufacturers need to consider the following precision-related risks:
- Inadequate machine precision
- Part movement
- Processing parameters
- Inadequate metrology and measurement automation
- Traceability and part data management
Risk 1: Inadequate Machine Precision
Since LCHT features are often measured in micrometers, the machine manufacturing them must deliver precision. With multiple axes moving concurrently to achieve the necessary motion – as shown in Figure 3 – the machine’s accuracy, stiffness and structural layout are critical to mitigating risk.
Figure 3. In this simplifed representation of a 4-axis, high-precision tube cutting machine, axes X and are responsible for LCHT manipulation and presentation to the laser head. The Z-axis maintains the precise focus required in cutting fne features. The Y-axis enables machining features off the tube’s centerline axis. For a more detailed description of tube cutting machines, watch this webinar.
Achieving the required precision performance is essential. One way to ensure cut accuracy is through error correction, which characterizes stage errors using metrology measurements. Generally, this approach focuses on on- and off-axis errors:
- On-axis errors: Differences between the commanded and actual position in the direction of travel
- Off-axis errors: Errors in the other five degrees of freedom
These errors can be measured at micrometer to nanometer levels for linear stages and microradians to fractions of a microradian for rotational stages. Figure 4 shows the difference in these types of errors with representative stages.
Figure 4. Linear and rotary precision stages produce on-axis and off-axis errors. These errors need to be corrected to achieve the most precise motion. For more information on stage error and error correction, read this whitepaper.
Laser interferometry is a common metrology technique used to measure stage performance and identify errors. Error data gathered with laser interferometry is typically stored in arrays or tables, with correction values applied to compensate for microscopic errors, as shown in Figure 5.
Figure 5. A laser interferometry setup (left) measures a linear stage. The table (right) is an example calibration table.
The data is fed to motion controllers to make software-based adjustments that compensate for hardware inaccuracies. This approach is particularly relevant for on-axis errors but is also useful for off-axis errors, which can be managed through sound machine design practices or advanced error mapping techniques.
External factors such as temperature variations and floor vibrations can affect machine performance, too. Temperature variations may cause thermal growth or contraction, infuencing system performance. Temperature sensors embedded within the stages can help compensate for this, but maintaining a stable thermal environment is ideal. Floor vibrations from nearby machinery, forklifts or trafc also threaten machine performance if not properly isolated. Passive vibration isolation can be achieved through engineered rubber pads or air isolation systems, as shown in Figure 6.
Figure 6. A machine base with air isolation integrated at its corners (blue highlights) tomitigate the effects of external disturbances.
The machine’s structural design may also have some effect on the manufactured parts’ performance. For example, stiff, closed structural loops composed of high elastic modulus materials are preferred because they help to support and constrain the energy motion might inject into the assembly.
Less favorable designs make use of cantilevered, Cartesian confgurations that are mounted to less stiff materials. These open structural loops allow for greater vibration of the laser cutting head in relation to the part.
Figure 7 provides an example of a closed-loop structural design with a very stiff granite bridge.
Figure 7. An example of closed structural loop (red dashed lines) and rigid machine base. To learn more about optimizing your machine’s design watch this webinar.
Risk 2: Part Movement
Unintended part movement is the enemy of precision manufacturing. Machining very long LCHTs involves regripping the tube, and this can introduce such movement.
Regripping is achieved by securing a clamp on the tube near the laser head, then releasing the pneumatically actuated collet that is integrated into the rotary stage. Once released, the linear stage then retracts the rotary stage in order to regrip the tube before continuing with the laser cutting. Each of these parts is shown in Figure 8.
Figure 8. In this image of a linear and rotary stage advancing a LCHT, allparts involved in the regripping step are visible.
Even when the tube is clamped for stability, regripping can cause translation along its length. While small (typically around 10-20 micrometers), this movement can still affect machining of the part’s smallest features. Using a dead-length style collet (e.g. Levin, Type C, or Type D) mitigates this movement. Unlike ER style collets, which accommodate a wider range of part diameters due to their collapsible range and therefore require fewer collets, dead-length collet design ensures there is no axial motion of the tube during regripping. This difference is visible in Figure 9.
Figure 9. During regripping, an ER style collet (left) offers lessstability than a dead-length collet (right).
Another unintended movement is defection. The part may defect under its own weight because it’s not fully supported or as a result of rapid rotation. Figure 10 illustrates this potential scenario, whereby a small tube is extended from the collet in a rotary stage.
Figure 10. This Aerotech LaserTurn5 has a small tube extending from the collet.
In order to mitigate this risk, bushing systems can support the part while it's being processed, as shown in Figure 11.
Figure 11. Laser cutting system with part extended through bushing.
Special attention must be paid to the ft and friction between the part and the bushing to avoid excess drag on the tube, especially when it's being rotated.
Risk 3: Processing Parameters
To achieve desired part tolerances and feature sizes, the laser’s fring, or interaction with the material, must be highly controlled. Laser fring often happens in the time domain. However, as the motion control system changes velocity, this time-domain fring approach can become less controlled and yield inconsistent laser power delivery to the part.
One solution is coupling the laser output with the motion controller to deliver laser power in the spatial domain. This process, called Position Synchronized Output (PSO), brings user experience and output benefts to the laser process engineer.
With PSO, all laser and motion axis commands are developed and issued from a common environment. This frees the laser process engineer to focus on refning the process and not waste time troubleshooting disparate control systems. It also enables improved part quality because laser pulses are delivered consistently along the part’s surface regardless of its rotational or linear velocity. Higher throughput is another beneft since the motion velocity and acceleration can be optimized for only contouring performance, eliminating any constraints related to laser power consistency. The difference between time domain and spatial domain laser power delivery is shown in Figure 12.
Figure 12. Spatial domain laser pulsing is more controlled than time domain pulsing anddelivers consistent results.
Just as with laser spot placement, accurately capturing surface data with high-resolution measurement sensors depends heavily on unifed control. Similar position-based triggering via PSO is ideal for LCHT measurement as it delivers the same values to the inspection process. Triggering from the same interface improves throughput during part inspection without sacrificing data quality. Figure 13 shows an example LCHT measurement.
Figure 13. An image of the measured section of a LCHT (top), example measurement data(center) and statistical summary of results (bottom).
Risk 4: Inadequate Metrology and Measurement Automation
LCHTs’ small diameters and feature geometries often pose metrology challenges during inspection. Figure 14 provides context for these challenges, showing the scale of the measurements being taken over a span of LCHT.
Figure 14. An image of an inspection system measuring a 0.6 mm diameter LCHT.
Due to their cylindrical shape, LCHTs are more challenging to measure than fat surfaces. Because the measurement system's depth-of-feld is limited, it often has difculty measuring a tube’s full radius. For applications demanding high measurement resolution, a 3D system is typically needed to capture an LCHT’s entire surface. Closely integrating precision stages with the metrology sensor delivers a full 3D dataset that captures an LCHT’s complete top surface in focus. Figure 15 compares LCHT images taken with 3D and 2D systems.
Figure 15. A 2D scan of a LCHT with only the top of the tube in focus (left), and a 3D scan with the full tube in focus (right). Note how the 3D image provides more of the part being measured in focus.
Data produced by a 3D system gives process engineers a deeper understanding of the LCHT’s features. For instance, 3D information can provide greater detail about the edge of a tapered cut as well as the taper profle, as depicted in Figure 16.
Figure 16. An image of 3D sensor data providing detail of the edge of a tapered cut as well as the taper profle.
With 3D metrology, other defects or anomalies are also more easily identifed. For example, Figure 17 shows 2D and 3D views of a scanned portion of a surface anomaly.
Figure 17. An image of 2D sensor data presenting a small anomaly on a LCHT (left), andcorresponding anomaly presented with a 3D sensor (right).
The 2D view indicates the anomaly is present and gives some indication of surface. The 3D view, however, provides much more information about the anomaly’s size and shape.
Outside of inspection technologies, other sensors are often integrated into LCHT cutting machines to enhance the manufacturing process and mitigate potential manufacturing risks. A popular example, driven by the U.S. FDA’s increasing pressure to support universal device identifcation (UDI), is the integration of computer vision systems to directly read in part-specifc coding. These sensors are increasingly vital in establishing traceability throughout the LCHT manufacturing process. By integrating these sensors into modern motion controllers, as shown in Figure 18, part-specifc details can be exchanged with manufacturing execution systems (MES) in real time.
Figure 18. A computer vision sensor with illumination ring is integratedinto a LCHT cutting machine for the detection of UDI data.
Coaxial vision is another example of a real-time sensor being integrated to motion control equipment to examine the cutting process or help with job setup.
Sensors can also improve the machine’s automation, minimizing operator time during setup. For example, a non-contact sensor can find the tube’s top apex (also called top dead center or TDC). Typically, this process involves manual operator intervention with jigs and fixtures to determine the TDC’s location. A sensor, however, can automatically detect the TDC without operator intervention. Figure 19 shows an example of a TDC sensor.
Figure 19. A top dead center (TDC) sensor scans a section of tube todetermine its centerline.
Risk 5: Traceability and Part Data Management
Data management related to cutting or measuring parts also presents risks.
Controlling this process is critical, as it ensures product efcacy and safety.
Quality engineers use several methods to analyze manufacturing metrics, including statistical process controls (SPC), Cpk studies (process capability analysis) and Gage R&R (repeatability and reproducibility). These rely heavily on large data set aggregation, enabling quality or process engineers to make informed decisions about their manufacturing process. Given the resolution at which LCHT cutting or measurement equipment operates, an abundance of data is available for exploitation.
Historically, the communication exchange between motion controllers and information technology (IT) infrastructure was either computationally too expensive or too slow. Modern day motion controllers, however, enable high-speed data visualization and output, as shown in Figure 20.
Figure 20. Modern motion control equipment allows for high-speed data capture and output to MES data repositories.
When a supporting IT infrastructure is in place, machine parameters of interest can be output to manufacturing execution system (MES) data repositories for many purposes.
Final Thoughts
LCHT’s medical applications are nothing short of a modern marvel. In many ways, we are still scratching the surface for potential medical uses. While the proliferation of this technology is exciting, it relies heavily on the manufacturing technologies that enable its use. Given the stringent precision requirements for both cutting and inspecting these parts, special attention must be paid to their manufacturing systems.
Medical device manufacturers encounter numerous risks while producing these products, but fortunately technologies exist to help mitigate – if not resolve – those challenges. When evaluating motion control solutions, it’s important to collaborate with suppliers who grasp this interdependency and will assist in aligning these technologies to effectively meet manufacturing objectives.
Travis Schneider is Aerotech’s business development manager for advanced manufacturing market segments, including electronics manufacturing, laser processing, medical technology, data storage and precision manufacturing. He has 14+ years of experience in precision automation and robotics, holding roles in applications engineering, feld sales, product management and business development. Travis earned his bachelor's degree in mechanical engineering from the Milwaukee School of Engineering. His expertise and passion for innovation make him an invaluable resource for partners seeking to push boundaries in precision automation for advanced manufacturing.