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Micro abrasive waterjet cutting head (here with 300 micron jet) with 5 axis manipulator allowing for taper angle compensation and cutting slanted surfaces up to a 15 degree angle.

Micro abrasive waterjet (MAW) machining has gained traction in the manufacturing of precision components. This cutting-edge method offers a non-thermal process capable of machining virtually any material while preserving their properties and producing fine surface finishes, reducing the need for extensive finishing processes. These qualitative and economic advantages present important opportunities for the manufacturing industry to meet the challenge of new advanced materials sensitive to distortion of their engineered material properties.

We believe that MAW machining systems can achieve significantly finer and more precise cuts compared to traditional waterjet technology.  With jet diameters as small as 0.008”, they can produce intricate features as fine as 0.004”. The new micro cutting technology shares the benefits of traditional waterjets in cutting virtually all materials without thermal influence avoiding recast layers or changes in material properties. It quickly pierces and cuts in one operation. The integration of these process benefits into a rigid machine tool design with a reliable mechanical linkage between tool and work material is an important prerequisite of precision of the high-end micro abrasive waterjet machine. In comparison, both the very precise motion path and the fixturing system differ from what we see in traditional waterjet machines, and this results in a capability to produce precision parts down to a tolerance of 0.0004”. This level of precision has earned it the nickname “Wireless EDM” due to its ability to deliver precision on par with wire electrical discharge machining (WEDM), but without the associated setup time and recast layers.

Rather than being viewed as a competitor to WEDM, MAW is better described as a complementary method. Workshops equipped with multiple WEDM machines seeking to expand their capabilities can benefit from the ease of use and rapid turnaround provided by MAW. Furthermore, MAW can cut non-conductive materials like carbon fiber reinforced polymers (CFRP), polymers, glass, and ceramics, opening new possibilities. We feel that MAW generally offers significantly higher cutting speed and ability to pierce and cut in the same setup, which eliminates the need of start holes.

The applications that benefit from this process are diverse, as micro abrasive waterjet machining can handle a wide variety of materials, including soft tissue, rubber and plastic polymers, advanced metal alloys, fiber-reinforced materials, powder materials, and ceramics. It can even cut combined materials, such as sandwiched or compound materials. The erosion process enables the cutting of all these materials without the need to adjust settings other than selecting cutting speed which is the primary factor in achieving the desired surface quality and tolerance requirements. This simplicity contributes to a relatively short learning curve for new users.

Left – Consumption of water and abrasive for 1 minute of cutting with an 200 micron abrasive waterjet.
Right – Vascular clip cut from NiTi-sheet demonstrating current capabilities of Finecut micro abrasive waterjet technology. 100 micron sections and +/- 10 micron tolerances.

Major Market Projection: NiTi Component Production

Finepart Sweden AB, a Swedish machine tool manufacturer at the forefront of this market, is specialized in the development and marketing of highly precise micro abrasive waterjets. Their FinecutTM machines have been available worldwide since 2009 and are widely used for various applications, particularly in cutting exotic materials. A notable recent trend has been the increased adoption of Finecut machines for NiTi applications, primarily cutting sheets ranging from 0.3 to 5 mm. These applications account for over 50% of machines sold in 2021 and 2022. While most machines cutting NiTi are utilized in medical and dental applications, the energy sector also benefits from this technology.

NiTi (an abbreviation for the alloy Nickel-Titanium), or Nitinol, is an advanced alloy renowned for its exceptional super elastic and shape memory properties, as well as its biocompatibility. These attributes allow it to be programmed to retain a specific shape or to serve as a reliable spring-back material for delicate structures. However, NiTi is challenging to machine using traditional methods. Laser cutting, for instance, compromises the mechanical properties and leaves a brittle recast layer with micro cracks near the cut. Wire electrical discharge machining faces similar thermal challenges. An alternative method employing femtosecond lasers operates with ultra-short pulses, creating instant removal by ablation without recast layers or heat-affected zones, thus eliminating the need for time-consuming post-processing. These machines are costly, and low average cutting power results in moderate cutting speeds. The advantages of MAW observed in NiTi also extend to other advanced materials, where surface integrity plays a crucial role in the application’s functionality. Recent applications include amorphous metals (liquid metal), Invar, titanium alloys, and super-alloys.

Applications of Micro Abrasive Waterjet

Figure 1 illustrates an advanced product, a vascular clip used in laparoscopic surgery, which exemplifies the capabilities of the Finecut process. This component, cut from 0.9 mm NiTi sheet, features toothed contact areas on each jaw with an interlocking latch mechanism to hold it in a closed state. The geometry includes thin spring sections measuring 100 µm in width, and the part maintains tolerances of +/- 10µm. Due to the narrow openings and radii approaching 100 mm, a 200-micron diameter jet (Finecut FAW200TM) was utilized. The process is swift, with each clip taking approximately 1 minute and 31 seconds to cut, resulting in a machine running cost of roughly 50 cents per piece, inclusive of power, consumables, and preventive maintenance.

In addition to advanced metal alloys, micro abrasive waterjets provide solutions for piezoelectric materials like Lead Zirconate Titanate (PZT). Fabricated through sintering methods, these materials possess a hard but brittle polycrystalline structure that makes conventional cutting methods challenging. Diamond saws or core drills have limitations on the achievable geometries, while lasers can induce spallation and microcracks due to thermal stresses. Micro abrasive waterjets excel in providing good surface finishes and cutting complex geometries. They can cut sintered materials with electrically isolated layers without smearing or melting the surface, preserving the integrity of the individual layers. Figure 2 showcases an example of a micro abrasive waterjet-cut surface of a 2.2 mm thick PZT component with included layers, cut at a speed of 55 mm/min.

Left – Flexure cut by a 200 μm diameter micro abrasive waterjet.
Right – Figure 2: A cut surface on a PZT component including layered materials. The micro sized removal process eliminates risk of electrical shortcut between layers.

Versatility and Productivity

The ability to cut nearly any material to high tolerances positions the micro abrasive waterjet process as an ideal choice for prototyping and a development enabler for new materials. The machines come with an intuitive operator interface and CADCAM that helps select cutting speeds and optimize the programming for MAW cutting. Advanced machining tasks can be facilitated through a range of available options, including 3, 4, or 5-axis manipulation for producing complex geometries, smart fixturing solutions utilizing simultaneous axes to manipulate parts, and on-board measuring devices, such as tactile probes or video-based systems capable of measuring to a few microns within the machine. These devices are often employed to verify part or fixture setup locations.

A typical feature of MAW is a kerf taper related to the cutting speed exhibiting a narrower cut width towards the bottom. In a 3-axis machine taper can in general be eliminated by reducing the cutting speed which allows more material removal towards the bottom of the cut. With a 5-axis machine the jet can simply be tilted to compensate for taper and a higher speed can be used, only limited by the surface quality requirement. In our studies we have found that for alloys this may reduce cycle time to less than 50%. These savings often justify the added investment within a year.

For certain applications, the material challenges associated with workpieces make waterjet the only viable or cost-effective means of production. Micro abrasive waterjets are being utilized in series production. MAW machines, operating in two shifts, for cutting NiTi components, are equipped with automated spent garnet removal systems and chillers to maintain a constant temperature. The advancements in production capabilities underscore that micro abrasive waterjets have evolved into a mature manufacturing technology that should be considered by design and manufacturing engineers.

Photos & Article Supplied – Dr. Christian Öjmertz, Finepart Sweden AB