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1. Development of a Contrived Tool Wear Method in Machining

   Grimm, Tyler; Potthoff, Nils; Kharat, Nilesh; Mears, Laine; Wiederkehr, Petra (November 2021, Proceedings of ASME International Mechanical Engineering Conference and Exposition)

   null (Ed.)

   Tool wear in machining is generally observed as early and late stage tool wear. During early stage tool wear, the tool is rapidly worn during a break-in period, followed by a stable region of tool wear. After machining more material, the tool reaches late stage tool wear. At this point, tool wear becomes unstable; tool failure occurs quickly or it may take some time. Therefore, late stage tool wear represents a bifurcation point, making it difficult to predict tool wear past this point. Tool wear is well known to be stochastically influenced. Due to this effect, it is difficult to perform studies on late stage tool wear since machining tools will be affected differently up to this point, introducing unknown variables. A novel method is presented in this research which utilized artificial wear to reach late stage tool wear. This method, termed contrived tool wear, may be capable of reducing the stochastic tool wear that occurs during early stage tool wear. As an initial investigation, machining tool inserts were worn by taking several passes over a grinding wheel with the tool rotating in reverse. Several parameters were tested in attempt to match the natural worn state as close as possible. Subsequent to artificial wear, the inserts were used to machine IN718. The presented method of contrived wear was found to be a good approach, but could not sufficiently replicate the tool wear typically produced in IN718 machining. Future work should aim at implementing a multi-axis approach to enable grinding at various angles to the rake face of the insert. 

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2. Evaluation of Contrived Wear Methodology in End Milling of Inconel 718

   https://doi.org/10.1115/1.4062603  

   Potthoff, Nils; Agarwal, Ankit; Wöste, Florian; Wiederkehr, Petra; Mears, Laine (October 2023, Journal of Manufacturing Science and Engineering)

   Abstract Tool wear plays a decisive role in achieving the required surface quality and dimensional accuracy during the machining of Inconel 718-based products. The highly stochastic phenomenon of tool wear, particularly in later stages, results in difficulty in predicting the failure point of the tool. The present research work aims to study this late-stage wear of the tool by generating consistent wear conditions and thereby decoupling the late-stage wear from the wear history. To do so, a multi-axis grinding operation is employed to create artificial tool wear that replicates the topology of natural wear occurring in the process. In order to evaluate the imitating ability of the proposed methodology, microscopic images in different wear states of naturally and contrived worn tools were analyzed. The methodology was validated by comparing the resulting process forces measured during end milling with the natural and contrived worn tool for different path strategies. Finally, a qualitative finite element (FE) analysis was conducted, and specific force coefficients for worn tool segments were determined through simulation. 

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3. Experimental and simulative analysis of an adapted methodology for decoupling tool wear in end milling

   https://doi.org/10.1016/j.mfglet.2022.07.050  

   Potthoff N; Agarwal A; Wöste F; Liß J; Mears L; Wiederkehr P (January 2023, Manufacturing letters)

   The machining of nickel-based superalloys such as Inconel 718 still poses a great challenge. The high strength and temperature resistance of these materials lead to poor machinability, resulting in high process forces and extensive tool wear. However, this wear is stochastic when reaching a certain point and is di cult to predict. To generate consistent wear conditions, the tool wear can be decoupled from the milling process by creating artificial wear using grinding. In this paper, a multi-axis approach for decoupling tool wear is presented and analyzed. Therefore, scanning electron microscope images of di erent wear states – worn and artificially worn – are analyzed. In addition, the occurring process forces of naturally and contrived worn inserts are compared in orthogonal cutting experiments as an analogy setup. Finally, a finite element analysis using a novel methodology for segmenting relevant cutting edge sections using digital microscope images provides qualitative insights on the influence of different wear conditions. 

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4. Analysis of burr formation in finish machining of nickel-based superalloy with worn tools using micro-scale in-situ techniques

   https://doi.org/10.1016/j.ijmachtools.2023.104030  

   Zannoun, Hamzah; Schoop, Julius (June 2023, International Journal of Machine Tools and Manufacture)

   The formation of burrs is among the most significant factors affecting quality and productivity in machining. Burrs are a negative byproduct of machining processes that are difficult to avoid because of a limited understanding of the complex burr formation mechanisms in relation to cutting conditions, including both process parameters and tool condition. Thus, the objective of this work was to characterize burr formation under finish machining conditions via a high-speed, high-resolution in-situ experimental method. Various parameters pertaining to burr geometry such as height, thickness, and initial negative shear angle were measured both during and after cutting. Results showed that varying the conditions of uncut chip thickness, tool-wear, and cutting speed all have a significant effect on burr formation, although certain burr metrics were found to be insensitive with respect to different process conditions because the difference was statistically insignificant. This study provides new insights into the relationships between the workpiece material’s microstructure, machining parameters, and tool condition on both crack formation and propagation/plasticity during burr formation. Using digital image correlation (DIC) and a physics-based process model not previously utilized for burr formation analysis, the displacement and corresponding flow stress were calculated at the exit burr root location. This novel semi-analytical approach revealed that the normalized stress at the exit burr root was approximately equal to the flow stress for a variety of different conditions, indicating the potential for model-based prediction of burr formation mechanics. Finally, this study investigates factors that influence fracture evolution during exit burr formation. It was found that negative exit burrs are a direct result of high strain rate and high uncut chip thickness, which was expected, but also a microstructural size effect and a tool-wear effect, neither of which have been previously reported. By harnessing ultra-high-speed imaging and advanced optical microscopy techniques, this manuscript deals with the fundamentals of burr formation, including new insights into material response at the grain-scale to the loads imposed with both sharp and worn tools. 

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5. Analyzing the evolution of tool wear area in trochoidal milling of Inconel 718 using image processing methodology

   https://doi.org/10.1016/j.mfglet.2022.08.002  

   Agarwal A; Potthoff N; Shah A; Mears L; Wiederkehr P (January 2023, Manufacturing Letters (special collection Proceedings of SME North American Manufacturing Research Conference))

   Nickel-based superalloys belong to a category of material employed for extreme conditions and exhibit high strength properties at elevated temperatures that result in poor machinability. Machining such di cult-to-cut materials like Inconel 718 leads to a high rate of tool wear, and therefore trochoidal milling toolpath is used to improve productivity and tool life. The current study analyzes the evolution of the flank wear area of the tool during trochoidal milling of Inconel 718 using an image processing methodology. It is attempted by performing experimental studies until tool failure occurs at several cutting conditions. The machining is performed through several iterations on an identical cutting path, and the number of iterations to failure is recorded. The microstructural image of a flank wear area is captured upon each iteration and processed using an image processing algorithm. It is realized that the evaluation of flank wear area can be an e ective parameter to analyze tool wear. Also, the image processing methodology works e ectively and can be extended during real-time machining. 

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