Bench profilometers (roughness and profile)

Bench profilometers for roughness and profile are laboratory metrology stations dedicated to the combined measurement of surface roughness and macroscopic geometric profile (form, waviness) of mechanical components. Compared with portable roughness testers they offer superior metrological performance in terms of accuracy, repeatability and advanced analysis capability, the possibility of motorized measurements over long traverses, and integration with CAD systems for comparison with nominal drawings. They are the reference instrument for precision inspection of molds, aerospace components and high-end engine parts, and for the qualification of machining processes.

Configurations

Bench profilometers consist of: a high-flatness granite reference base, a motorized guide arm (typical traverse 50-200 mm) with a high-resolution encoder, a contact stylus with a diamond tip and a vertical position transducer (inductive or LVDT, with resolution down to 0.1 nm on the most advanced models), a workpiece positioning system (cross slide, rotary table) and a dedicated PC with advanced analysis software. There are combined models that integrate roughness measurement (standardized cut-offs) and profile measurement (form and waviness) in the same instrument.

Measuring capability

Typical performance is: vertical resolution 0.1 nm to 10 nm, vertical accuracy ±1-5 nm, vertical traverse 1-5 mm, horizontal traverse 50-200 mm and horizontal accuracy of the order of a few µm. The parameters that can be calculated are all those provided for by ISO 4287 (2D) and ISO 25178 (3D areal, with raster scanning). Advanced functions include multi-cut-off filtering, analysis of the Abbott-Firestone curve, calculation of the functional parameters Rpk/Rk/Rvk, periodicity measurement and evaluation of special profiles (racks, gears, threads).

Geometric profile measurement

As well as roughness, profilometers allow the measurement of macroscopic geometric profile: distances, angles, radii, radius compensation, comparison with nominal CAD, and calculation of straightness, parallelism and perpendicularity over the measured traverses. On the most advanced models, combining roughness, profile and waviness measurement in a single scan allows a surface to be fully characterized with one set-up. Motorization allows long profiles to be recorded without operator intervention.

Applications

Bench profilometers are used in high-end quality laboratories: aerospace (turbine blades, rotor shafts, structural components), automotive (cams, injector seats, valve seats, piston rings, crankshafts), optics (lenses, mirrors, mounts), micromechanics (miniature bearings, MEMS) and medical (joint prostheses, osteosynthesis screws, surgical instruments). They are also used in the research and development of new machining processes (grinding, lapping, burnishing, electropolish finishing) and in the characterization of functional coatings.

Standards and calibration

The reference standards are ISO 4287, ISO 4288, ISO 12179, ISO 16610 and ISO 25178 (3D areal parameters). For profile measurement, ISO 12781 (flatness) and ISO 12780 (straightness) also apply. Periodic calibration uses ISO 17025 certified specimens: roughness shims, sinusoidal profiles, spheres of known radius for verifying the stylus, and high-precision gauge blocks for verifying length. The measuring room must be temperature-controlled (typically 20 °C ±0.5 °C) for the best metrological performance.

Selection criteria

Choosing the right profilometer involves considering the vertical and horizontal range needed, the resolution required (optically finished surfaces call for sub-nanometer resolution), the capability for combined roughness and profile measurement, the drive (manual, CNC), the analysis software (2D versus 3D functions) and integration with the company’s LIMS and CAD systems. Laboratories dedicated to a single product should look towards specialized models; for multi-application laboratories, modular models are preferable.