Erosion characteristics of water droplet machining Mitchell, Benjamin R.; Korkolis, Yannis P.; Kinsey, Brad L.
Journal of materials processing technology,
June 2024, 2024-06-00, Letnik:
327
Journal Article
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Water Droplet Machining (WDM) is a new manufacturing process, which uses a series of high-velocity, pure-water droplets to impact and erode solid workpieces, for the purpose of through-cutting, ...milling and surface profiling. The process is conducted within a vacuum environment to suppress aerodynamic drag and atomization of the waterjet and droplet train. This preserves droplet momentum and allows for a more efficient transfer of energy between the water and workpiece, than in standard atmospheric pressure. As a new manufacturing technique, parameter-specific details and characteristics of this process are absent from the scientific literature. Therefore, this study aims to elucidate the capabilities of WDM, and uncover its erosion characteristics. Experiments are performed using a custom-fabricated machine, where a range of waterjet-types (and droplet trains) are produced. The experiments are performed on two industrial-relevant metals: stainless steel SS 316 L and aluminum AA 6022-T4. The target shape is a partial-cut through the material, i.e., a trench. A parametric study investigates the effects of stand-off distance, orifice diameter, and feed-rate on the trench shape, material-removal-rate, and reveals the conditions which render WDM an effective machining process. It was found that, for orifice diameters of 100 μm, an effective stand-off distance is between 457 and 686 mm; below that, no material removal is observed. In this configuration, accurate through-cuts are produced and can be used for manufacturing purposes. For large orifice diameters, e.g., 250 μm, an atomized spray is produced, which features a comparatively large material removal rate, and can be used for surface profiling and milling.
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•A new pure waterjet cutting technology is proposed, which utilizes a series of droplet impacts for material removal.•The workpiece and waterjet are immersed in a vacuum environment to suppress aerodynamic drag and droplet atomization.•Parameter-specific details of the process are provided, which facilitate high material removal rates.•The technique can be used for precise through-cutting or for rough milling and surface profiling.
The use of abrasive waterjets (AWJ) to machine metal surfaces is prevalent through-out industry. AWJ requires the purchase and disposal of costly abrasive particles which increases manufacturing ...costs and environmental-footprint. This motivates the exploration for low-cost, eco-friendly alternatives. A novel method which utilizes a stream of high-speed water droplets (WD) travelling through a sub-atmospheric pressure environment to remove material without using abrasive grit is presented. In this paper, the efficacy of this new process is investigated and compared to AWJ and pure water jet (WJ) (i.e., without abrasive particles) by measuring the material removal rates (MRR) of each process on a hard-to-machine steel, DP 1180, for equivalent water-flow conditions. Trench profiles are created by traversing each of the jets across a metal sample, from which the MRR and trench profiles are obtained. The MRR results reveal that WD is significantly faster than WJ, but is subordinate compared to AWJ for MRR efficiency. This identifies a trade-off between manufacturing cost and time.
As components with proportional feature and tooling sizes are miniaturized, strain gradients through the cross-section increase. This causes strain gradient hardening as the density of geometrically ...necessary dislocations increases. This will lead to higher required forces in the process than expected. In this paper, an analytical model to predict the dislocation density increases, and thus strain gradient hardening, during microbending is presented. These results match previous research in terms of the feature size where modest and significant strain gradient hardening was observed.
There continues to be a desire to incorporate advanced high strength steels (AHSS) into automotive and other applications in order to reduce the overall weight of the final product. However, these ...materials exhibit limited ductility prior to fracture and require high forming forces. One means to address these concerns, at least in a laboratory setting, is by subjecting the material to continuous-bending-under-tension (CBT). In this procedure, a set of three rollers reciprocate over the gauge length of the specimen while the material is continuously pulled in tension. The adjustable parameters during CBT testing are the roller depth, the crosshead velocity (which applies the continuous, tensile force to the specimen), and the carriage speed for the reciprocating rollers (which is typically set to the highest value possible while maintaining a safe process). The formability improvements obtained through CBT processing are decreased applied force and increased elongation to fracture. The latter is achieved by assuring that during the CBT process the entire gauge length elongates to the maximum possible value before fracture occurs. Past research has shown that the concentrated deformation in the fracture location of a tensile specimen is similar to the deformation over the entire gauge length of a CBT processed specimen. In this paper, a parameter space study of the DP 1180 AHSS is conducted in order to determine the optimal roller depth and crosshead velocity to achieve the maximum formability improvements for this material. The results demonstrate a promising means to improve displacement (approximately four times over that in simple tension) prior to fracture for this AHSS when subjected to CBT processing.
Miniaturization of systems and devices continues unabated, which in turn requires the production of microscale components. Similar to the macroscale process, microextrusion provides a means to ...fabricate metallic micropins having characteristic dimensions on the order of 1 mm or less with a lower-cost, high-throughput process. In this paper, the effect of the specimen size and grain size on deformation during microextrusion is investigated. Microhardness, microstructure, and X-ray texture analyses show that when the grain size becomes comparable to the specimen feature size, together with miniaturization, penetration of the shear deformation occurs. As a result, the coarse-grained structure has higher hardness than the fine-grained structure, especially in the central regions of the cross-section for the two smallest size extrusion cases investigated, which have Ø0.76/0.57 mm and Ø1.5/1.0 mm dimensions before and after extrusion, respectively. For the largest size extrusion case investigated, Ø2.0/1.33 mm pins, the coarse-grained structure has a lower hardness than the fine-grained one, which is typical for macroscale processes and consistent with the Hall–Petch relationship.
► Microextrusion was performed on specimens with different specimen and grain sizes. ► Deformation was characterized by microhardness, X-ray, and microstructure analyses. ► Miniaturization resulted in higher hardness values especially in the inner regions. ► The penetration of shear deformation was observed for coarse-grained structures.
Double-sided incremental forming (DSIF) is a die-less sheet metal forming process capable of fabricating complex parts. The flexibility of DSIF can be used for in-situ mechanical properties ...alteration, e.g., by controlling deformation-induced martensite transformation of austenitic stainless steels. In this paper, SS304L is deformed using DSIF at three different cooling conditions and two different tool paths to affect the martensite transformation. Additionally, finite element analyses were used to understand the effect of tool paths on springback and plastic strain. Implementing a reforming tool path at the lowest achievable temperature resulted in a martensite volume fraction as high as 95%.
Modelling of metal forming processes is an essential task of production engineering. Due to the latest technological developments, a huge variety of models is already available and extending ...continuously. Thus, it is important to find a suitable model. This paper gives an overview on the common classification and characterization of modelling and models in metal forming, as well as introduces a model selection procedure. Based on this classification, various relevant process limits for metal forming are investigated regarding existing models. The conclusion of the paper shows open topics as well as upcoming challenges in modelling process limits in metal forming.
Crystallographic texture in metals influences material properties, e.g., r-value. In this work, a moderately strong texture is obtained in AA5182-O through continuous-bending-under-tension processing ...followed by a recovery heat treatment from the initial weak cube texture. EBSD scans confirm that the texture is retained after heat treating. The processed material exhibits increased strength and reduced planar anisotropy, providing benefits to subsequent forming operations, compared to the as-received material. Crystal plasticity simulations confirm the texture change during deformation and predict the flow stress response. Such simulations can be used for stress superposition process design to intentionally manipulate material properties.
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