M. Alkan Donmez

An Additive Manufacturing Test Artifact

A test artifact, intended for standardization, is proposed for the purpose of evaluating the performance of additive manufacturing (AM) systems. A thorough analysis of previously proposed AM test artifacts as well as experience with machining test artifacts have inspired the design of the proposed test artifact. This new artifact is designed to provide a characterization of the capabilities and limitations of an AM system, as well as to allow system improvement by linking specific errors measured in the test artifact to specific sources in the AM system. The proposed test artifact has been built in multiple materials using multiple AM technologies. The results of several of the builds are discussed, demonstrating how the measurement results can be used to characterize and improve a specific AM system.

A review on measurement science needs for real-time control of additive manufacturing metal powder bed fusion processes

Additive manufacturing technologies are increasingly used in the development of new products. However, variations in part quality in terms of material properties, dimensional tolerances, surface roughness and defects limit its broader acceptance. Process control today based on heuristics and experimental data yields limited improvement in part quality. In an effort to identify the needed measurement science for real-time closed-loop control of additive manufacturing (AM) processes, this paper presents a literature review on the current AM control schemes, process measurements and modelling and simulation methods as it applies to the powder bed fusion process, though results from other processes are reviewed where applicable. We present our research findings to identify the correlations between process parameters, process signatures and product quality. We also present research recommendations on the key control issues to serve as a technical basis for standards development in this area. Complimentary details to this paper with summary tables, range of values, preliminary correlations and correlation figures can be accessed from a National Institute of Standards and Technology Report (http://nvlpubs.nist.gov/nistpubs/ir/2015/NIST.IR.8036.pdf). This paper is developed based on the report.

Diagnostics for geometric performance of machine tool linear axes

Machine tools degrade during operations, yet knowledge of degradation is elusive; accurately detecting degradation of linear axes is typically a manual and time-consuming process. Manufacturers need automated and efficient methods to diagnose the condition of their machine tool linear axes with minimal disruptions to production. A method was developed to use data from an inertial measurement unit (IMU) for identification of changes in the translational and angular errors due to axis degradation. A linear axis testbed, established for the purpose of verification and validation, revealed that the IMU-based method was capable of measuring geometric errors with acceptable test uncertainty ratios.

Integrated inspection system for improved machine performance

An integrated inspection system for improving the accuracy of CNC machine tools is proposed. The system described in this paper emphasizes the integration of the on-machine inspection and analysis techniques with the information coming from post-process and on- machine inspection to improve machine performance automatically. Algorithms are derived for analyzing the post-process and on-machine inspection data to identify residual systematic errors and relate them to the machine performance. Various data analysis algorithms and techniques are compared. A feature comparison approach is developed to relate the dimensional and form errors of a manufactured workpiece to the systematic machine tool errors. Inverse kinematics technique and statistical methods are used to identify and characterize the contribution of each geometric error component. A self tuning algorithm is also proposed to fine tune the geometric-thermal model.

Real-time compensation for tool form errors in turning using computer vision

Deviations from the circular shape of the cutting edge of a single-point turning tool cause form errors in the workpiece during contour cutting. One can compensate for these tool-form errors by determining the size of the effective deviation at a particular instant during cutting and then adjusting the position of the cutting tool accordingly. An algorithm for the compensation of tool-nose-radius errors in real time has been developed and implemented on a CNC turning center. A previously developed computer-vision-based tool- inspection system is used to determine the size of the deviations. 1 Information from this system is fed to the error compensation computer which modifies the tool path in real time. Workpieces were cut utilizing the compensation system and were inspected on a coordinate measuring machine. Significant improvements in workpiece form were obtained. 1.

Repeatability Analysis on the Tool Point Dynamics for Investigation on Uncertainty in Milling Stability

Stability analysis is needed to maximize milling performance while avoiding chatter. However, such an analysis is time-consuming, requiring the use of sophisticated instrumentation, and has significant level of uncertainty, which impedes the widespread use by industry. A main source of uncertainty is believed to be the changes in dynamics of the tool-holder-spindle system during the milling operation. This study investigates the variation in the tool point dynamics reflecting the dynamics of the tool-holder-spindle system and associated machining stability. The investigation focuses on the effects of the conditions generated by typical milling operations, such as tool changes and spindle warm up. The results of analyses demonstrate the necessity of continuous updates of the tool point dynamics during milling process by in-situ measurements to minimize uncertainty in evaluation of machining stability.© 2007 ASME

SEM sentinel-SEM performance measurement system

This paper describes the design and implementation of a system for monitoring the performance of several major subsystems of a critical dimension measurement scanning electron microscope (CD-SEM). Experiments were performed for tests involving diagnosis of the vacuum system and column stability by monitoring of the following subsystems and associated functional parameters. These include: 1) Vacuum system with pressure as a function of time being recorded for the electron-optical column (gun chamber), the specimen chamber, and the sample-loading unit. 2) The action of several components of the wafer handling system can be timed. 3) The electron gun emission currents and other signals to monitor the characteristics of the condenser and objective lenses may be used to correlate with image quality. 4) Image sharpness, electron beam current, signal-to-noise ratio, etc. can be evaluated.

Impacts of Automation on Precision

Automation has significant impacts on the economy and the development and use of technology. In this chapter, the impacts of automation on precision, which also directly influences science, technology, and the economy, are discussed. As automation enables improved precision, precision also improves automation.