This paper details frequency response function (FRF) measurement and simulation for a dynamic oscillator with a sliding (Coulomb) friction contact. The oscillator is approximated physically using the friction measuring machine (FMM), a parallelogram leaf-type flexure with a sliding friction contact. The flexure-based FMM provides linear motion between a polytetrafluouroethylene pin and (lubricated) polished steel counterface. Both the input force and response velocity are measured by impact testing to determine the FRF. Numerical simulations are completed to identify the best-fit friction coefficient for three input force levels (450 N, 1000 N, and 1450 N). It is shown that: 1) the FRF magnitude increases linearly with impulse (i.e., the area under the time domain force profile); and 2) a single friction coefficient (0.113) is sufficient to describe the dynamic response for the three force levels.

Handbook of Manufacturing, pp. 569-607 (2019) No AccessChapter 11: Manufacturing Quality Assessment and ControlLaine Mears, John Ziegert, John T. Roth and Beshoy MorkosLaine MearsClemson University, Mechanical Engineering Department, Clemson, SC 29634-0921, USA, John ZiegertUniversity of North Carolina in Charlotte, Mechanical Engineering Department, Charlotte, NC 28223-0001, USA, John T. RothPennsylvania State University—Erie, Mechanical Engineering, Erie, PA 16563, USA and Beshoy MorkosFlorida Institute of Technology, Mechanical Engineering Department, Melbourne, FL 32901, USAhttps://doi.org/10.1142/9789813271029_0011Cited by:0 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail Abstract: The following sections are included: Manufacturing Quality Quality Characteristics Quality Assessment Quality Control Methods Quality Control Strategy Selection Quality Improvement Conclusion References and Suggested Reading FiguresReferencesRelatedDetails Handbook of ManufacturingMetrics History PDF download

An in-situ Inverse Projected-Fringe system for on-machine inspection of axisymmetric parts is developed. Parts considered for this study are specular with RMS surface roughness > 1 mu m and have large slopes with radii of about 50 mm. The in-situ system is developed based on the previously reported Inverse Projected-Fringe technique in order to determine the on-machine measurement repeatability and reproducibility for industrial applications. In order to measure the whole part, a stereo arrangement and a new data fusion technique are used to increase the field of view of the system. A measurement trace with the highest Signal to Noise Ratio (SNR) is selected to achieve the best accuracy. The repeatability and reproducibility tests of the system are reported. It is shown the in-situ Inverse Projected-Fringe system is capable of measuring the form deviation from a master-part with repeatability and reproducibility of +/- 1 to +/- 7 mu m, equivalent to a dynamic range of one part in 25,000 to one part in 3,600, respectively for the areas with higher SNR to lower SNR. Simultaneously, the RMS surface roughness has been measured with an accuracy of +/- 1.2 mu m or better.

An inverse projected-fringe technique based on simulating the system of a projector-partcamera is proposed for an on-machine inspection of axisymmetric parts. The parts considered for this study are relatively large, have high specular surfaces and have sharp slopes. A computer simulation-based method and the CAD model of the part was used to produce the inverse fringes as well as to find an appropriate trace passing through the symmetrical axis of the part that offers the best signal to noise ratio (SNR). This technique measures the deviation from a master-part and provides an accuracy of better than 10 microns for the part with a radial dimension of about 10 cm. It is shown that the proposed technique improves the SNR and the repeatability of the system compared to the standard fringe projection technique, in particular for the areas with a steep slope.

This paper describes a new approach for parameterizing friction models. Velocity measurements of a spring-mass-damper oscillator with a friction contact are used to determine the Coulomb friction coefficient for the friction-based energy dissipation. The energy-based friction force is then calculated and compared to the friction force determined from the product of the friction coefficient and normal force. The friction measuring machine, or FMM, is used to enable transient, linear sliding motion between friction contact pairs under constant normal force loading and a laser vibrometer is used to measure the corresponding time dependent velocity. Tests results are presented for a pin on oscillating flat contact with three different initial displacements. The measured velocity is used together with the FMM structural dynamics to determine the Coulomb friction coefficient and estimate the corresponding friction force during motion.

When fringe projection profilometry is used for measuring texture on rough surfaces, the measurement resolution is subject to the spatial frequency response of the instrument. The instrument transfer function (ITF) is a good metric to quantify this property. A valid ITF analysis requires the system to be linear. In this paper, we investigate the validity of using ITF to characterize the spatial resolution of a fringe projection system. Approximate linearity is shown through a mathematical analysis and simulation. We also demonstrate a practical method for measuring ITF using a stepped surface. The measured ITF is compared with an ITF prediction, which is simulated with a theoretical model.

Single-point metal turning processes can create chip nests that are hazards to both parts and machine tools. This is mitigated by a process called Modulated Tool Path (MTP) machining, which superimposes an oscillation in the tool tip feed direction in order to break these chips and provide an adequate surface finish. MTP machining is highly sensitive to the amplitude and frequency of this oscillation, both of which can often be diminished by standard machine tool controllers. These controllers are also unresponsive to iteration-varying disturbances such as temperature fluctuations, which can cause positional and velocity-related inaccuracies. This paper presents a library based variant of Iterative Learning Control (ILC) called Disturbance and Performance-Weighted ILC (DPW-ILC), which is designed to improve the accuracy of machine tool trajectories that are highly oscillatory in nature, as well as provide robustness to varying, but measurable disturbances. DPW-ILC has been shown in simulation to provide a tremendous accuracy benefit over standard ILC techniques, specifically in the presence of two separate types of temperature-based disturbances.

The objective of this paper was to conduct a study of the multi-level multi-variable design space in titanium machining through high performance computing (HPC) simulations that was otherwise too vast to be explored by physical experiments alone. For tool wear-based performance metrics, this resulted in a validated set of machining parameters for achieving profitable material removal rates (MRR) (optimized cost of processing and tooling) across multiple operational configurations, alloys, tool geometries, and process conditions. The approach was to include all machining-related variables and their distributions available within the software as inputs to finite-element models (FEM) of the machining process. The time intensiveness of conducting such large numbers of lengthy simulations was handled by wrapping Third Wave Systems AdvantEdge FEM machining simulation software with Dassault Systemes iSight to automate the building of experimental designs and their parallel execution on a HPC cluster. Results were analyzed using SimaFore software to identify key characteristics through bivariate analyses. A subset of simulations was validated through physical experiments, and these were in turn used to augment physically untested regions in the design space. Based on this, an MRR-based cost model for orthogonal turning was derived to drive optimal machining setups. This study showed the feasibility of integrating and automating a HPC loop involving the generation of suitable design of experiments (DOE), creating simulation jobs, deploying/executing it on a HPC cluster, and scripting outputs in a useful format. Besides highlighting the challenges in reading/transferring data across different software and in handling/compiling large amounts of data, this study also shed light on the need for benchmarking processor–operating system–software combinations for computational efficiency.

When fringe projection profilometry is used for measuring rough/textured surfaces, the fidelity of the measurement is subject to the spatial frequency response. The instrument transfer function (ITF) is one appealing approach to characterize this property. The foundation of ITF analysis is based on the linear theory; only linear systems are appropriate for ITF analysis. A fringe projection system is intrinsically nonlinear, but it can be approximated as a linear system when certain conditions are met. Here we investigate the linear conditions of a custom fringe projection system designed for an additive manufacturing application. The applicability of ITF is discussed through mathematical analysis and simulations.

INTRODUCTION Existing force-based methods for parametrizing friction models are limited by large uncertainties (approximately parts in 102 [1]). This paper provides experimental results for a new method that uses velocity measured during free vibration to quantify the energy dissipation in friction contacts. The final goal is a friction measurement method that provides reduced uncertainty, particularly for low friction and low velocity applications.

This paper describes an experimental machining platform that provides metrology during tube turning (orthogonal cutting) for force, global temperature, feed motion, tool wear, and chip formation during continuous feed and modulated tool path, or MTP, turning. MTP is a technique which produces discontinuous chips by superimposing tool oscillations in the tool feed direction on the nominal feed rate to repeatedly interrupt the cutting process. AISI 1026 cold-drawn steel machining experiments are performed and data is presented for: 1) feed motion and modeling; 2) force measurement and modeling; 3) temperature measurement; and 4) chip formation for constant and MTP tool paths. Shear-localized chip formation that begins and ends during a single MTP chip is demonstrated.

INTRODUCTION One of the biggest challenges for metal additive manufacturing is the inability to control surface quality. An approach to solve this problem is to use in-situ metrology systems. Fast data acquisition and a relatively long working distance make fringe projection a viable solution for in-situ metrology of layered metal additive manufacturing process [1], [2]. Surfaces created by metal additive processes, particularly the laser powder bed fusion (LPBF) process, are rough, porous and textured. The roughness and texture are the results of laser scanning and are related to the process parameters such as laser power, scan velocity, and hatch distance (laser step over). The combination of the parameters creates a unique surface texture with rich spatial frequency content. Figure 1 shows such a texture with a fused square on a layer of Inconel-625 metal powder. The laser scan path is along the vertical axis with a step over of 90 μm. The laser power is 290 W, and the scan speed is 110 mm/s. The fused surface is measured in situ by a fringe projection system. The measured topography shows clear periodic structures near the bottom edge along the x-axis (Figure 1 (d)). Fourier analysis of the measured profile shows a strong peak at the spatial frequency corresponding to twice the hatch distance, suggesting a merge of two scans due to the closeness (time-wise) of the two scan paths.

INTRODUCTION Experimental methods are commonly used to identify friction behavior, particularly for manufacturing processes [1-22]. The majority of these friction measurements are made on tribometers, which apply a normal force to a pin that is pressed against a rotating or translating surface. The normal and friction forces are measured and the friction coefficient is calculated. However, misalignment between the force transducer axes and the motion and the applied direction of the normal force are critical factors in establishing the accuracy of the derived coefficients of friction [23]. Current methods used to measure friction behavior and parameterize complex friction models can suffer from high uncertainty, especially for low friction interfaces. Relative uncertainties on the order of two to four parts in 102 of the measured value are typical for low friction interfaces [23]. In contrast, displacement can be measured by laser interferometry with relative uncertainties on the order of a few parts in 107, four to five orders of magnitude better. The research described in this paper will evaluate a fundamentally new method for measuring friction and parameterizing friction models with lower uncertainty than conventional methods. The innovation is the use of high-accuracy displacement and velocity measurements during dynamic motions to characterize the energy dissipation.

Being able to characterize the process signatures of powder bed based additive manufacturing process is key to improving the product quality. This paper demonstrates the implementation of a digital fringe projection technique to measure surface topography of the powder bed layers during the fabrication. We focus on developing the metrology tool and observing the types of information that can be extracted from such topographical data. The performance of the system is demonstrated with selected in situ measurements. Experimental results show this system is capable of measuring powder bed signatures including the powder layer flatness, surface texture, the average height drop of the fused regions, characteristic length scales on the surface, and splatter drop location and dimension.

Complex metal parts produced by additive manufacturing processes are often very difficult to dimensionally characterize by traditional contact and non-contact metrology systems. The most efficient and effective approach to measuring metal additively produced parts, particularly those produced in a laser powder bed fusion process, is to measure each layer of the part as it is sintered. In this layer-wise measurement approach, what are internal and obscured features in the final part are accessible to measurement while the part build is still in process. This paper describes the development of a metrology system which performs non-contact measurement of a nickel powder laser fusion system. The metrology system discussed herein uses a traditional machine vision linear approximation to measure the planar dimensions of each build layer, and a phase shifting fringe projection system to produce an area height profile of each layer. The independent measurements can be combined to produce a high density 3D point cloud of the final part, including all internal and obscured features. This project is ongoing, and results are incomplete.

In single-point metal turning and boring processes, a chip nest can often be created that is a hazard to part and operators alike. In order to mitigate this, a process called modulated tool path (MTP) machining was developed that superimposes a sinusoidal motion tangent to the feed direction onto the tool feed path to break chips. The sinusoidal motions are created under CNC control in the part program. In the current implementation, the sinusoidal motion is approximated as a series of short linear moves. Linear interpolation is currently used to create position and velocity commands to the axis servomotors at each control loop closure. Linear interpolation is a computationally heavy and dated method that is not well tailored to a sinusoidal trajectory. In this paper a new method called the sigmoidal interpolator is introduced that honors all physical constraints of a machining system while offering better tracking performance and lower accelerations than the linear interpolator, all while reducing the number of possible state transitions of the implemented software from approximately 17 to 4.

A post-processing algorithm for CNC machine NC code was developed for altering NC code based on measurements from a stand-alone coordinate metrology system that measures the orientation and offset of the part and machine coordinate systems (CS). With this post-processing algorithm, the ability to machine a monolithic part larger than the working area of a machine in multiple sections becomes possible. A series of test parts were machined with a Haas Vertical Milling Machine (VMM) and a Leica laser tracker as proof of concept and to determine the errors introduced into the machining process by adding the additional metrology system. Monte Carlo simulations confirm that adding the stand-alone metrology system increases the magnitude of errors to approximately the accuracy of the metrology system itself, about 50 micrometers. The initial set of test parts machined showed errors at a factor of 25 larger than expected. It was determined that a component used to determine the machine's spindle location was introducing significant error into the process. The component was replaced and new parts machined that showed a significant improvement but still with errors larger than expected. Machine squareness errors showed the importance of measuring CS features within the same plane. Finally, it was determined that the definition of the part CS is sensitive to how the part is fixtured to the machine. Sub-scale machining is a viable process for machining large components with a slight increase in feature location error.

The modulated tool path (MTP) chip breaking process has been modified to improve chip management capabilities and to prevent large chip nest accumulations commonly encountered in threading operations. The use of MTP to create segmented chips requires a different approach for threading operations than for normal MTP turning operations, although the fundamental principal is the same. The primary difference between MTP for threading and for straight turning is that the part surface that the tool repeatedly engages and disengages, during the modulation process, is the thread root rather than the cut face. The threading MTP part program developed in this paper is capable of machining a thread with the desired lead, depth, undercut angle, and taper angle while also producing segmented chips.

Two sub-pixel resolution approaches to measure in-plane displacements and in-plane rotation of a known target, through image processing, are described in this research. A dynamic known target is displayed on a pixel grid, which is attached to one end of the kinematic chain of an XYθ Z stage; the latter represents the experimental testbed. At the other end of the kinematic chain, a digital monochrome camera is fixed to the bottom of the stage and provides 3D position information used as the feedback signal to the vision-based control system in charge of the tool’s motion. The illuminated pixels on the display are captured in real time by the digital camera, and the stage motion control system attempts to keep the displayed image in the proper location with respect to the camera image plane. The result is a direct sensing multi-DOF position feedback system. The proposed camera-pixel grid sensing setup eliminates the reliance on the kinematic model and also avoids the need for traditional error compensation techniques, along with their associated cost and complexity. Positioning resolutions on the order of 1/100th of the pixel size on the display are achieved.