Ultrafast laser processing unlocks next-gen medical device manufacturing

Since their introduction to medical manufacturing, lasers have become a stalwart of device OEMs’ manufacturing methods. They are commonly used in applications for additive and subtractive (e.g. drilling, cutting and ablation) manufacturing, material joining, marking and surface treatment. Laser-based manufacturing techniques have enabled step changes in manufacturing’s efficiency, precision, quality and process control.

Many device OEMs now look to ultrafast laser technology as the next horizon for their manufacturing needs. Why is this?

To answer that question, it is important to understand what defines an ultrafast laser. In general terms, there are two primary operating modes for lasers: continuous wave (CW) and pulsed.

As their name implies, continuous wave lasers operate with a constant output. Pulsed lasers intermittently output laser energy at a constant interval known as the pulse width or pulse duration (see Figure 1 for a visual reference of these operating modes). Ultrafast lasers represent a segment of pulsed laser technology where the laser pulse duration is mere femtoseconds (10-15), an extremely short time period.

Because of this extremely short pulse duration, ultrafast lasers can deliver higher peak power to the part than CW or other pulsed lasers. This enables key differentiating laser process capabilities and, in turn, new manufacturing methods. The following subsections outline the advantages that ultrafast lasers bring to medical device manufacturers.
Athermal laser processing
CW and pulsed lasers can cut or machine materials, but ultrafast lasers do this in a powerful and unique way. Ultrafast lasers’ high peak power capability allows the material to be vaporized from a solid to a plasma with little or no heat transfer from the pulse to the surrounding material. This is commonly referred to as athermal laser processing, or cold ablation.

Athermal laser processing is highly advantageous for medical device manufacturing because it enables the processing of thin or thermally sensitive materials such as polymers and specialty alloys — including nitinol — without introducing a heat affected zone (HAZ) around the processed area. HAZ is a common consequence of laser processing that can lead to part distortion or even premature mechanical failure.

This ability to process parts without altering the material properties that are critical to product performance is a key advantage of ultrafast lasers when compared to CW or longer pulse duration lasers.

Minimized part post-processing
Because the part is heated during traditional laser cutting with a CW or pulsed laser with longer pulse widths, several post-processing steps are often required to improve part quality. For instance, parts typically require deburring to remove dross or sharp edges and electropolishing to remove oxide layers and improve surface finish. Figure 2 shows the imperfections present in a laser cut part before deburring and electropolishing operations.
These steps require additional equipment and processes — plus the accompanying control plans and time — that affect part throughput and cost. These additional steps may be avoided when material removal is done through a refined ultrafast process, improving part processing time and lowering cost.

Ultrafast lasers can also eliminate steps related to part coating. Because they can manipulate a material’s microstructure to generate hydrophobic or hydrophilic surface finishes, ultrafast laser processes can texture a surface directly. In this case, no additional steps would be needed to apply a coating.

By simply changing process parameters and adding some cycle time to the laser processing step, an ultrafast laser can reduce or eliminate post-processing steps needed to deliver a finished part. In these applications, special attention is paid to the controls and laser delivery system because it is critical to maintain the optimum laser spot over non-planar surfaces.

Unique laser welding advantages
An ultrafast laser also enables unique joining methods that have implications for novel medical device designs. By using different laser process controls and techniques (e.g. adjustable burst firing modes) it is possible to join dissimilar materials such as ceramics and metals or extremely fine metal foils.

However, these processes have a much smaller process control window, and the motion of the laser along the surface plays a significant role in achieving high-quality weld joints. Improper control of the laser’s position when triggering or the laser’s pulse control along that path can create inconsistencies in weld strength and reliability.

Getting started
From eliminating secondary processes to enabling new cutting or joining techniques, ultrafast laser technology has the potential to make significant improvements in medical device manufacturing. Despite the higher capital investment tied to ultrafast technology, the potential for cost savings is notable.

Because these advantages require significant refinement of the laser process to optimize the right parameters, it’s essential to have a suite of tools at your disposal that allow for proper experiment design.

Thorough verification and validation testing strategies should be used to trace the part performance criteria to known laser processing parameters. Most modern motion controllers provide direct control of the laser and motion control parameters, allowing manufacturers to quickly and easily iterate to find their optimum process.

When evaluating control solutions, it is key to work with suppliers who understand this interdependency and will help to align these technologies to best achieve your manufacturing objectives. Medical Design & Outsourcing