The word “new” is often used to describe repackaged versions of processes that have been around for years and only provide incremental improvements. In contrast, a technique called Micro Machining Process (MMP) is truly innovative in that it entirely rethinks production and part finishing.

MMP is a new “superfinishing” technology that completely replaces several steps in finishing parts. It keeps geometries intact and replaces the hand polishing of parts such as orthopedic implants. And besides hard alloys, the process works on a wide range of materials including most types of coatings. The technology was developed in Europe and just became available in North America.

The words “micro” and “machining” may bring to mind a process that focuses on small parts, but in this case it refers to the extremely small tools the process uses and its capability to dramatically reduce surface roughness by removing tiny amounts (microns) of material.

Traditional surface finishing options are limited in their capability to handle complex geometries without altering the geometry itself. That’s because conventional techniques merely remove material from the surface in a relatively uncontrolled manner, relying on abrasives, lasers, electrical currents, harsh acids or bases, and low or high temperatures. Until now, polishing surfaces on complex geometries generally meant rounding sharp edges, obliterating fine details, and subtly altering the actual shape. Some traditional methods also make parts such as orthopedic implants susceptible to hydrogen embrittlement.

MMP takes a different approach. It first measures surface roughness with a profilometer, which displays results as waves or spikes on a graph (amplitude or size of surface irregularity versus position) that can be thought of as representing different so-called “frequency ranges.” MMP maps surfaces into four main frequency ranges:

• The highest frequency is termed “secondary micro roughness.” In these areas, surface roughness comes from the roughness of the cutting tool’s surface, which is transferred to the part during manufacturing.

• The next highest frequency range is called “primary micro roughness.” This roughness comes from the rotation of the cutting tool.

• The next frequency range is termed “waviness.” In this case, roughness results from built-in operating tolerances of the manufacturing machine itself.

• The lowest frequency range is considered the basic form — the pure shape the designer intends, without roughness.

After being mapped, parts to be processed are fixtured in MMP’s “vat,” where they are completely surrounded by thousands of tiny micro tools specifically selected for the job at hand. There are hundreds of different kinds of micro tools, each designed to work on a certain frequency range, material hardness, and various other attributes. The tools work using a proprietary form of physical-mechanical energy that produces a true nano-cutting action.

Our engineers select tools for jobs based on factors including what roughness levels must be targeted and whether the surfacefinish objective is based on technical performance or aesthetics.

After undergoing MMP, the part has the needed technical or aesthetic surface. (Note that the scale of this post-MMP image is nanometers versus the micrometer scale of the pre-MMP image.)	The readings show surface profiles in “frequencies” of a part undergoing MMP.

The tools surround the parts, so they work homogeneously across the part surfaces, “skating” along all the surfaces. The tools polish off roughness by removing material (typically 5 to 10μm) — but only where the roughness frequency matches the range the tools were designed for, not just the tops of the peaks like most traditional polishing processes. They first work on the highest frequency range and proceed down the frequency ranges. The tools are engineered to work only until they remove their particular frequency range and then “turn off.”

Because MMP does not contaminate surfaces, it suits critical applications such as polishing orthopedic implants. For other uses, MMP can leave specific mid-range roughnesses untouched to improve fluid-retention or promote lubrication while eliminating higher frequency components that create friction and micro abrasion. In addition, MMP suits high-volume production of parts, repeatedly creating the same surface finish on all of the parts. The technique basically lets designers tailor surfaces for particular applications.

Surface-finish parameters Modern profilometers can measure a variety of surface-texture parameters. These include: • Ra is the most widely used description of a surface. Leveling all the peaks and filling in all the valleys of a surface would produce a theoretical mean line. The arithmetic average of the deviations up and down from this line is Ra. • Rt is the distance from the highest peak to the deepest valley. • Rmax is based on the Rz DIN parameter, which divides the measured length into five equal lengths and then averages the Rt readings of each of the five lengths. Rmax is the distance of the highest peak to the deepest valley in any of the five sections.