More Like this

1. Physics-Informed Uncertainty Quantification in Modeling of Machining-Induced Residual Stress

   https://doi.org/10.1016/j.procir.2023.03.025  

   Hasan, Md Mehedi; Schoop, Julius (January 2023, Procedia CIRP)

   Machining processes involve various sources of uncertainty which lead to inaccurate interpretation of results in the surface integrity of machined products. This work presents a physics-informed, data-driven modeling framework for achieving comprehensive uncertainty quantification (UQ) of the impact of process and material variability on machining-induced residual stress (RS). Uncertainty due to the variation in bulk material properties and model input parameters in machining are considered. Preliminary results showed that variations in calibration parameters have a substantial effect on modeling RS, while the variation in material properties has a smaller effect. Further research directions for UQ in machining are also outlined. 

   more » « less
2. Increased ductility of Ti-6Al-4V by interlayer milling during directed energy deposition

   https://doi.org/10.1016/j.addma.2023.103818  

   Karunakaran, Rakeshkumar; Sotelo, Luz D; Maharaja, Hitarth; Nez, Calsey; Ramoni, Monsuru; Halliday, Scott; Mishra, Sushil; Karunakaran, KP; Turner, Joseph A; Sealy, Michael P (September 2023, Additive Manufacturing)

   Additive manufacturing (AM) often results in high strength but poor ductility in titanium alloys. Hybrid AM is a solution capable of improving both ductility and strength. In this study, hybrid AM of Ti-6Al-4 V was achieved by coupling directed energy deposition with interlayer machining. The microstructure, residual stress, and microhardness were examined to explain how interlayer machining caused a 63% improvement in ductility while retaining an equivalent strength to as-printed samples. Interlayer machining introduced recurrent interruptions in printing that allowed for slow cooling-induced coarsening of acicular α laths at the machined interfaces. The coarse α laths on the selectively machined layers increased dislocation motion under tensile loads and improved bulk ductility. The results highlighted in this publication demonstrate the feasibility of hybrid AM to enhance the toughness of titanium alloys. 

   more » « less
3. Intermethod comparison and evaluation of near surface residual stress in aluminum parts subject to various milling parameters

   https://doi.org/10.1007/978-3-030-30098-2  

   Chighizola, Christopher R.; D’Elia, Christopher R.; Hill, Michael R. (June 2019, Residual Stress, Thermomechanics & Infrared Imaging and Inverse Problems, Volume 6; Proceedings of the 2019 Annual Conference on Experimental and Applied Mechanics)

   Near surface residual stress (NSRS) induced by machining (e.g., milling) is known to drive distortion in machined aluminum, particularly in thin complex geometries with tight tolerance requirements where large distortion is undesirable. The understanding and characterization of NSRS in milled aluminum parts is important and should be included in the design and manufacturing process. There exist a variety of experimental tests characterizing these stresses. The objective of this paper is to assess the quality of three experimental methods for evaluating NSRS in prismatic aluminum parts subject to various milling parameters. The three methods are: hole-drilling, slotting, and x-ray diffraction, all of which include incremental material removal. The aluminum parts are cut from stress-relieved plate, AA7050-T7451. A combination of milling table and tool speeds are used to machine a flat surface in the parts. Measurements are made at specified locations and depths on each part. NSRS data from the hole drilling and slotting measurements were comparable; NSRS data from x-ray diffraction differed and was less repeatable. NSRS data for different milling parameters shows that the depth of NSRS increases with feed per tooth but is unaffected by different cutting speeds. 

   more » « less
4. Influence of clamping technique on the resulting surface roughness in diamond machining of CaF2

   Adam, B.; Riemer, O.; Rickens, K.; Lucca, D.A.; Tunesi, M. (June 2022, Proceedings of the 20th euspen International Conference and Exhibition)

   Single crystal calcium fluoride (CaF2) is widely used for transmissive optics in the ultraviolet and vacuum ultraviolet (UV and VUV) spectral regions because of its high optical transmission. Optical components made of CaF2 are usually manufactured by precision machining to generate high quality surfaces with low surface roughness. However, the influence of the clamping technique on the resulting surface roughness of diamond machined CaF2 has not been reported. In this research, two clamping techniques, vacuum clamping and gluing with wax, are used in off-axis diamond turning experiments with zero degree and negative rake angle diamond tools. Surface characterization by white light interferometry and atomic force microscopy show surfaces with low surface roughness. Furthermore, a significant influence of the clamping technique on the generated surface topography is observed. 

   more » « less
5. Intermethod Comparison and Evaluation of Measured Near Surface Residual Stress in Milled Aluminum

   https://doi.org/10.1007/s11340-021-00734-5  

   Chighizola, C. R.; D’Elia, C. R.; Weber, D.; Kirsch, B.; Aurich, J. C.; Linke, B. S.; Hill, M. R. (October 2021, Experimental Mechanics)

   Abstract Background While near surface residual stress (NSRS) from milling is a driver for distortion in aluminum parts there are few studies that directly compare available techniques for NSRS measurement. Objective We report application and assessment of four different techniques for evaluating residual stress versus depth in milled aluminum parts. Methods The four techniques are: hole-drilling, slotting, cos(α) x-ray diffraction (XRD), and sin 2 (ψ) XRD, all including incremental material removal to produce a stress versus depth profile. The milled aluminum parts are cut from stress-relieved plate, AA7050-T7451, with a range of table and tool speeds used to mill a large flat surface in several samples. NSRS measurements are made at specified locations on each sample. Results Resulting data show that NSRS from three techniques are in general agreement: hole-drilling, slotting, and sin 2 (ψ) XRD. At shallow depths (< 0.03 mm), sin 2 (ψ) XRD data have the best repeatability (< 15 MPa), but at larger depths (> 0.04 mm) hole-drilling and slotting have the best repeatability (< 10 MPa). NSRS data from cos(α) XRD differ from data provided by other techniques and the data are less repeatable. NSRS data for different milling parameters show that the depth of NSRS increases with feed per tooth and is unaffected by cutting speed. Conclusion Hole-drilling, slotting, and sin 2 (ψ) XRD provided comparable results when assessing milling-induced near surface residual stress in aluminum. Combining a simple distortion test, comprising removal of a 1 mm thick wafer at the milled surface, with a companion stress analysis showed that NSRS data from hole-drilling are most consistent with milling-induced distortion. 

   more » « less