Coupling additive manufacturing (AM) with interlayer peening introduces bulk anisotropic properties within a build across several centimeters. Current methods to map high resolution anisotropy and heterogeneity are either destructive or have a limited penetration depth using a non-destructive method. An alternative pseudonondestructive method to map high resolution anisotropy and heterogeneity is through energy consumption during milling. Previous research has shown energy consumption during milling correlates with surface integrity. Since surface milling of additively manufactured parts is often required for post-processing to improve dimensional accuracy, an opportunity is available to use surface milling as an alternative method to measure mechanical properties and build quality. The variation of energy consumption during the machining of additive parts, as well as hybrid AM parts, is poorly understood. In this study, the use of net cutting specific energy was proposed as a suitable metric for measuring mechanical properties after interlayer ultrasonic peening of 316 stainless steel. Energy consumption was mapped throughout half of a cuboidal build volume. Results indicated the variation of net cutting specific energy increased further away from the surface and was higher for hybrid AM compared to as-printed and wrought. The average lateral and layer variation of the net cutting specific energy for printed samples was 81% higher than the control, which indicated a significantly higher degree of heterogeneity. Further, it was found that energy consumption was an effective process signature exhibiting strong correlations with microhardness. Anisotropy based on residual strains were measured using net cutting specific energy and validated by hole drilling. The proposed technique contributes to filling part of the measure gap in hybrid additive manufacturing and capitalizes on the pre-existing need for machining of AM parts to achieve both goals of surface finish and quality assessment in one milling operation.

Acoustic emission (AE) sensing techniques have been found to be practical for both conventional and nontraditional manufacturing processes because of high reliability, low cost and easy installation. Traditional AE techniques include the use of the root mean square (RMS) voltage, zero crossing rate, rise time, pulse width, Kurtosis and frequency analysis of the signal. Limitations have been reported when using these methods for on-line control. Potential limiting factors include the proper selection of the integration time constant for RMS measurement, and the need for high speed, data intensive calculations. This paper reports on the use of a new AE technique which monitors specific high and low frequency components of the AE signal. The advantages of this technique are demonstrated for two nontraditional machining methods: abrasive flow machining (AFM) and abrasive electrodischarge grinding (AEDG).

Stereolithography, which was the first commercially available Rapid Prototyping (RP) technique, currently represents a major portion of the worldwide RP market share. Parts manufactured with the stereolithography apparatus (SLA) are presently used for design verification, medical modeling and rapid tooling applications. Dimensional accuracy of the prototype is very important for design and form/fit applications. Tooling applications, such as patterns for investment casting, also require good surface finish. Stereolithography provides three different build styles and many part and recoat parameters which can be optimized for these various applications. This paper presents the results of an investigation into the effects of build styles (ACES, WEAVE and Quick CAST) and build parameters (Z level wait, pre-dip delay, dip velocity and acceleration, sweep period and workpiece geometry angle) on the performance measures of dimensional accuracy, surface roughness and build time. All of the prototypes were built on an SLA-250 which used the SL-5170 photopolymer resin. Statistical analysis of the results of the fractional factorial design showed that ACES produced the highest degree of dimensional accuracy while QuickCast was the least accurate build style. On a horizontal surface, ACES produced the best surface roughness and WEAVE produced the least desirable surface roughness. However, on an inclined surface, QuickCast produced the best surface roughness and ACES produced the least desirable surface roughness. The QuickCast workpieces were produced in the shortest time and ACES workpieces took the longest time. In addition to the statistical analysis, surface profiles of the prototypes were studied with Data Dependent Systems (DDS), a stochastic modeling and analysis methodology. DDS analysis of the surface profiles found that layer thickness was the major component of the profile on inclined planes and hatch and fill spacing were the major components on horizontal planes.

Deburring and surface finishing methods represent a critical and expensive segment of the overall manufacturing process. A relatively new non-traditional process called Abrasive-Flow Machining (AFM) is being used to deburr, polish, radius, remove recast layers, or produce compressive residual stresses in a wide range of applications. Material is removed from the workpiece by the flowing of an abrasive-laden viscoelastic compound across the surface to be machined. There currently exists a lack of pertinent data which industry can use in selecting AFM for finishing workpiece surfaces generated by conventional and non-traditional machining processes.This paper presents the results of an investigation of the effects of AFM on surfaces produced by turning, milling, grinding, and wire electrical-discharge machining. The machining characteristics studied included material removal and surface finish improvement. The statistical analysis found that the type of machining process affected both metal removal and surface finish results. The initial surface condition significantly affected the amount of metal removal and was very close to meeting the significance requirement for surface finish improvement. In particular, all of the Wire EDM surfaces were improved greatly by AFM. Media viscosity significantly affected only surface improvement, while extrusion pressure did not have a significant effect in this experiment.Scanning Electron Microscopy (SEM) was used to study the surface characteristics of the workpieces. The photographs showed that AFM smoothed out the effects of the machining processes, leaving a more uniform surface. Data Dependent Systems (DDS), a stochastic modeling and analysis technique, was used to study the surface-roughness profiles before and after AFM. Overall, many similarities were found between grinding and abrasive-flow machining. This suggests that AFM is a very capable finishing process, and that its area of application should be expanded.

Finishing operations in the metal working industry represent a critical and expensive phase of the overall production process. A new process called Abrasive Flow Machining (AFM) promises to provide the accuracy, efficiency, economy, and the possibility of effective automation needed by the manufacturing community. The AFM process is still in its infancy in many respects. The process mechanism, parametric relationships, surface integrity, process control issues have not been effectively addressed.This paper presents preliminary results of an investigation into some aspects of the AFM process performance, surface characterization, and process modeling. The effect of process input parameters (such as media viscosity, extrusion pressure, and number of cycles) on the process performance parameters (metal removal rate and surface finish) are discussed. A stochastic modeling and analysis technique called Data Dependent Systems (DDS) has been used to study AFM generated surface. The Green's function of the AFM surface profile models provides a "characteristic shape" that is the superimposition of two exponentials. The analysis of autocovariance of the surface profile data also indicates the presence of two real roots. The pseudo-frequencies associated with these two real roots have been linked to the path of the abrasive grains and to the cutting edges of the grain. Furthermore, expressions have been proposed for estimating the abrasive grain wear and the number of grains actively involved in cutting with a view towards developing indicators of media batch life. A brief introduction to the AFM process and related research is also included in this paper.

The main goals of wire electrical discharge machine (WEDM) manufacturers and users are to achieve a better stability and high productivity of the process, i.e., higher machining rate with desired accuracy and minimum surface damage. The complex and random nature of the erosion process in WEDM requires the application of deterministic as well as stochastic techniques. This paper presents the results of current investigations into the characteristics of WEDM generated surfaces. Surface roughness profiles were studied with a stochastic modeling and analysis methodology to better understand the process mechanism. Scanning electron microscopic (SEM) examination highlighted important features of WED machined surfaces. Additionally, energy dispersive spectrometry (EDS) revealed noticeable amounts of wire electrode material deposited on the workpiece surface.