[Jolyn P.K. Key]

Researchers at the University of North Carolina at Chapel Hill were working on an atomic force microscopy project and needed to machine a magnetic pole structure with a thickness of 100μm to 150μm from Hiperco 50 sheet, an iron-cobalt-vanadium soft magnetic alloy that exhibits high magnetic saturation. They tried several cutting methods with limited success, but were pleased to discover that waterjetting was the best solution to their challenge. While a conventional waterjet could not cut the part, new microwaterjet technology could.


Micro Waterjet cut this comb prototype for a UNC-Chapel Hill medical microscopy project showing a three-peak pattern. Photo courtesy Jolyn P.K. Key.

3-D goal

The goal of the project is to extend atomic force microscopy (AFM) to work in 3-D, according to Leandra Vicci, director of the applied engineering laboratory in the Department of Computer Science, and her collaborators at the Nano Sciences Research Group and Department of Physics and Astronomy at UNC-Chapel Hill. With AFM technology, piezoelectric actuators move a probe at the end of a cantilever to trace the 2-D topography of a sample. However, it cannot probe inside a living cell, for example, or under the sides of 3-D objects, an issue Vicci’s team was determined to overcome by removing the cantilever and replacing it with a new, more functional design.


An oblique view of a test cut of a 6-mil Hiperco50 sheet, showing the dimensionally critical magnetic tip and gap to an opposite magnetic flat. Photo courtesy Lamar Maier.

The researchers developed a 3-D force micro-scope (3DFM) using electromagnets to pull on tiny, free-floating magnetic probe beads under a microscope. As the collaborators progressed from AFM to 3DFM, the project began to take shape.

UNC-Chapel Hill’s current technology is a single 3DFM that can be stepped sequentially over a set of wells that can receive samples to be analyzed from an automated pipette system. The researchers’ current goal is to make a densely packed, 12-microscope system capable of analyzing 96 samples in eight steps using a robotic system compatible with industry-standard, 96-well microchannel plates. This reduces the time required to analyze forces in a large number of medical applications, ranging from blood-clot progression and drug discovery programs, to measuring the mechanical properties of metastasized cancer cells.

Massive analysis

“The bottom line is having the ability to provide rapid, massive analysis that was not previously possible,” Vicci said.

Currently, biologists and medical professionals can only indirectly determine the viscosity of fluids in which cells might be living. They can observe if there are free particles, measure frequencies and infer mechanical forces, but are unable to make direct-force measurements with existing microscopes.

“We asked ourselves what would happen if we could have a free-floating bead that didn’t have the troublesome cantilever on it,” Vicci said. “This new technology applies controlled 3-D forces in the range of piconewtons to nanonewtons by electromagnets on free-floating magnetic probes from hundreds of nanometers to a few microns in diameter.” She explained that 3-D mechanical reactions are measured by optical techniques with demonstrated displacement resolutions below 5nm. This level of performance requires the fabrication of highly precise magnetic pole structures called “pole plates” that were successfully produced by Micro Waterjet LLC, Huntersville, N.C.

New technology

A startup contract manufacturing facility, Micro Waterjet uses proprietary technology to provide high-precision cutting capabilities that lend themselves well to the micromachining of combustible and noncombustible 2-D parts and prototypes. The abrasive waterjet micro machining (AWJMM) process developed by Micro Waterjet has positioning accuracy of ±3µm; cutting accuracy of ±0.01mm, depending on material and thickness; kerf width of 0.3mm; surface quality equivalent to N7 (1.6µm Ra); and a maximum workpiece size of 1,000mm×600mm.


A tip geometry providing more active high-force regions which occur nearest to the sharp tips was fabricated in a 4×4 well prototype. Photo courtesy Lamar Maier.

According to Daniel Leuthardt, development applications engineer at Micro Waterjet, the first prototype made for the UNC-Chapel Hill project was just a single copy of the actual part. After meeting the part requirements, Vicci requested the machining of a test part from the Hiperco 50 sheet with 16 identical features in a 4×4 pattern. The production part will have 96 identical features in a square, 8×12 pattern.


An enlarged frontal view shows the required vertical wall profile and lack of visible recast, or heat-affected zone, layers. Photo courtesy Lamar Maier.

“The project required a tight gap that was right at a kerf diameter of 300 microns—one that conventional waterjetting couldn’t meet,” Leuthardt said. “We produced a two-part piece as a result of the gap required. The inside section is precisely centered to the outside workpiece with a tab. The tab is required to line up the workpieces between the slide material during the lamination process to the [microscope] slide and is removed after the materials are bonded.”

The second prototype utilized a new design, consisting of three- and four-peak patterns found at the end of the comb prototype. The challenge was to produce a very small gap between the peaks. The team finessed the size of the jet and parameters even further to cut a multipeak pattern.

Vicci was looking to hold tight tolerances on a number of features, but primarily the smallest point at the tip of the part where the microscope’s objective lens focuses. Photochemical etching produced ragged walls. Laser seemed like a viable option but had heat-affected zone issues.

“The vertical walls at first looked good with laser, but there were two major problems,” Vicci said. “First, there was heat recrystallization that changed and degraded the critical metallurgical properties where the point is sharp. Second, a glassy slag byproduct ended up in places where we couldn’t successfully or reliably remove it. The slag is a metal oxide that can become magnetized and can’t be shut off as required.”

With the help of Micro Waterjet, the application is now under way. The company has prototyped a small but critical part for the device, which may be ready for commercialization in about a year. Development continues on the optics, getting video cameras packed close together and working on the software that will locate and analyze the magnetic bead reactions.

“As a startup, this was a great opportunity for us to be a part of ground-breaking technology,” Leuthardt said. “It helped open doors to more medical and research opportunities.” µ

About the author: Jolyn P.K. Key is marketing and communications manager for Micro Waterjet LLC, Huntersville, N.C. Telephone: (704) 948-1279. E-mail: jkey@microwaterjet.com. Web: www.microwaterjet.com.