Creating optimal surfaces on metal components is REM’s business focus.  A component’s surface can impact a wide range of performance characteristics including contact fatigue, lubricant performance, bending fatigue, air/fluid flow, coating/plating adhesion, cleanliness, and many more.  However, the surface of a component is not always a primary focus during the design stage, and surface finish may be completely overlooked or simply given an Ra callout based on legacy practices without further consideration for end-use component requirements.

A metal component’s surface can be comprised of multiple layers of material that can help or hinder final component performance.  These layers may have different material properties.  The outermost layer or layers will determine the component’s texture (the combination of its roughness, waviness, and any directionality/lay to the surface features).  All three of these characteristics are produced by the forming mechanisms used to generate the component.

In a machined component (especially precision ground components, but also milled, honed, and rough ground components), roughness and waviness will be largely combined and viewed simply as roughness due to the expected low degrees of waviness generated by the machine tool—note that some machining operations may generate more significant levels of waviness thereby requiring more singular consideration when evaluating the surface.  Machined surfaces will almost always have an isotropic or periodic surface textures due to the directional nature of the forming process.  The cutting tool will create a series a parallel “rows” or “peaks and valleys” in the direction of the tool path—sometimes referred to as “machining marks” or “grinding lines”.  Additionally, the outermost layers of a machined surface will likely consist of a distressed material/metal resulting from the aggressive nature of the metal cutting process where the metal itself will experience high temperatures and forces resulting in plastic deformation as well as physical and thermal stress impartation.  Ultimately, this outer layer may not be optimal for its end-use application.

For an additively manufactured (AM) component made by powder-bed fusion (PBF), roughness and waviness should be considered separately due to the much higher level of waviness that is inherent to the building process and the impact that this waviness has on the roughness values of the component.  Unlike a machined surface, PBF surfaces are granular in nature, displaying multiple “tiers” of roughness that may nor may not have strong directionality depending on building parameters.  Additionally, AM components commonly display varying degrees of near-surface voids or porosity as a result of the building process.  Surface finishing operations may expose this porosity, which may in turn impact the surface finish achievable or the material removal requirements.

Much like the outer surface layer of machined components, the surface and near-surface characteristics of AM surfaces may not be suitable for use without additional post-processing (surface finishing) operations).  Similarly, shot-peened and cast surfaces often benefit from surface polishing to remove unfavorable surface textures.

Roughness and Ra are terms that are often considered interchangeable by the engineering and manufacturing communities.  In reality, roughness and more broadly surface texture are far more complex concepts whereby a singular Ra call-out has to the potential to inadequately define the necessary surface quality of a component to meet required operating performance.  When considering component performance requirements, a broader and more detailed understanding of surface quality should be considered.

REM’s process technologies produce isotropic surfaces that lack the directionally of machined surfaces.

For machined components, REM’s technologies are commonly used to produce isotropic superfinished surfaces which are characterized by very low roughness values and exceptionally high bearing ratios due to their greater levels of flatness as compared to machined surfaces (far exceeding “super-ground” and honed surfaces).  For AM components, REM’s processes can progressively eliminate loose/partially sintered or melted particles, eliminate granular roughness, and reduce or eliminate surface waviness depending on component requirements, ultimately progressing to a full isotropic superfinish.  REM’s processes can produce near-mirror levels of polish while maintaining a mechanically advantageous micro-texture (avoiding any issues or concerns with a surface being detrimentally, too smooth), or can produce generally texture-less surfaces if such a surface finish is required. However, the surfaces that REM generates do not have to be ultra-smooth, as REM’s processes are also highly efficient, providing cycle time advantages or process maintenance simplifications as compared to many traditional, abrasive processes.  Targeted roughness ranges can be achieved for applications with certain levels of optimal roughness exist.

While REM is commonly known for creating bright and shiny surfaces—and certainly many of the components polished in REM’s isotropic superfinishing technology will display a mirror-like, shiny appearance—the most important deliverables from REM’s polishing technologies are typically manufacturing and engineering benefits.  REM’s isotropic superfinishing technologies surpass essentially all other polishing processes in terms of the combination of benefits and capabilities that they possess including: minimized geometric alteration, uniformity of material removal, ability to finish recessed and none line-of-sight component surfaces, surface roughness reduction, and surface texture optimization, and a wide range of improved surface/material properties including wear, fatigue, corrosion resistance, and many others.

Whether your application requires a beautiful aesthetic finish, component performance improvements, controlled material removal, or any other of the range of benefits that REM’s technologies are known to impart, REM has the solution to metal component surface finishing needs.  Contact us today to start a project.