Accuracy Of Machined Features Research Articles

Inverse methods to gradient etch three-dimensional features with prescribed topographies using abrasive jet micro-machining: Part II—Verification with micro-machining experiments

Cross sectional shape and centerline waviness along the length of a micro-channel can affect different characteristics of microfluidic flow, including heat transfer, pressure distribution and dissipation, and separation of flow. Current existing technologies that allow such micro-machining have many limitations. The accompanying paper presented inverse techniques that can be used to predict the required non-uniform velocity to gradient etch, using abrasive jet micro-machining (AJM), micro-channels and pockets with a wide variety of prescribed textures and cross-sectional shapes. Methods to predict the final three-dimensional (3D) profiles of such features were also presented. In this paper, the velocity functions predicted using the inverse methods were used to machine micro-channels with prescribed centerline depths that varied linearly, parabolically and sinusoidally, pockets with prescribed textures in two directions, and micro-channels with prescribed W-shaped cross sections. Two different erosive efficacy sources were used, one resulting from an adjustable shadow mask and one using a maskless technique. The inverse and 3D shape prediction techniques were verified by comparing the measured feature topographies with those that were initially prescribed. The effect of process parameters such as source shape and the machined feature size on the accuracy of machined features and predictions of the models were also discussed. Overall, the inverse techniques were found to be very effective for predicting the process parameters required to machine a wide variety of desired micro-channel and pocket topographies.

Tool deflection and geometrical error compensation by tool path modification

Accuracy of CNC machined components is affected by a combination of error sources such as tool deflection, geometrical deviations of moving axis and thermal distortions of machine tool structures. Some of these errors can be decreased by controlling the machining process and environmental parameters. However other errors like tool deflection and geometrical errors that have a big portion of total error need more sophisticated solutions. Conventional error reduction methods are considered as low efficiency and human dependent methods. Most of recently developed solutions cannot fulfill workshop needs and are limited to research papers. In the present study, machining code modification strategy has been considered as an applicable and effective solution to enhance precise machined components. Appropriate tool deflection estimation model as well as geometrical error analyzing methods have been selected and complementary algorithms for compensation of these errors have been developed. Metal cutting process has been modeled in a 3D simulation environment and implemented in force/deflection calculations. A software has been developed to generate compensated tool path NC program by tracing the initial tool path and compensating deflection/geometry deviations. The new procedure developed in the present work has been validated by machining Spline contours. The results show that using the new method, accuracy of machined features can be improved by about 8–10 times in a single pass.

Global workpiece positioning system (GWPS) Part 2: Development of an ultrasonics-based system

Abstract Datum establishment uncertainty is a major source of error affecting the geometric accuracy of machined features. In part one of this two-part paper, a novel concept, the Global Workpiece Positioning System (GWPS), was presented for datum establishment in a multiple-setup machining operation, where a laser triangulation based prototype was implemented and its concept feasibility validated. However, the approach based on a laser triangulation probe has several limitations. These include sensitivity to the optical quality and orientation of the artifacts, a short stand-off, and the necessity to operate in a scanning mode while held in the spindle of the machine tool. Ideally, it would be preferred if the sensors were fixed and outside of the workspace of the machine tool. This would eliminate the time required for a probe scanning cycle and potentially minimize the effect of machine tool positioning uncertainty on the locating accuracy of the GWPS. A solution to this problem lies in the development of a GWPS that is analogous to the current satellite-based Global Positioning System (GPS). In such a system, a set of receiver and transmitter pairs would operate in a manner similar to the satellite transmitters and ground-based receivers of the GPS, and a universal system to locate the workpiece in the work zone of the machine tool would be accomplished. To explore the potential of this approach, an ultrasonics-based GWPS was examined where, as an initial step, the laser triangulation probe was replaced with an ultrasonic receiver and a series of ultrasonic transmitters was affixed to the workpiece. This approach was found to permit a wider and longer detectable range of the artifacts (ultrasonic transmitters). Thus, the workpiece and artifacts can be deployed more freely. A 2D machining experiment demonstrates that the workpiece can be positioned by the ultrasonic GWPS without the use of physical contacts. An average positioning error of 0.185 mm (0.007 in.) was obtained in five test runs. Although the positioning accuracy is insufficient for machining applications, the ultrasonic GWPS may be applicable to less demanding situations where greater artifact sensor flexibility is needed. Furthermore, the use of time-of-flight ranging best embodies the general concept of GWPS. If advancements in electromagnetic GPS technology continue to occur at the current pace, it is anticipated that an electromagnetic time-of-flight GWPS will achieve the accuracy needed for machining applications in the future.