J. Manuf. Mater. Process., Volume 2, Issue 1 (March 2018) – 20 articles

During the process of grind-hardening, the dissipated heat from the process is utilized for a surface layer hardening of machined components made of steel. A martensitic phase transformation occurs within the affected subsurface regions and compressive residual stresses are induced. However, the layout of a grind-hardening process for given hardness results (material modification) is very difficult. Thus, a series of extensive experimental tests is required. To reduce this experimental effort, the newly developed concept of Process Signatures is used to describe the material modifications based on the thermal load appearing during the grind-hardening process. Based on an analytical calculation of the temperature fields during the grind-hardening process (surface- and external-cylindrical-grind-hardening), the internal thermal load was characterized by the maximum contact zone temperature and the maximum temperature gradient at the surface and was correlated with the process quantities (heat flux to the workpiece and the contact time). Metallographic investigations were used to analyze the surface hardening depth and the hardness change at the surface, which were correlated with the quantities describing the internal material loads. The results show that the surface hardening depth was mainly governed by the maximum contact zone temperature and the maximum temperature gradient at the surface, whereas the hardness change at the surface was influenced additionally by the quenching time. Full article

In a production of filigree and complex geometries, different NC-controlled processes such as laser cutting, EDM milling, and micromachining require a constant feed rate to ensure high-quality manufacturing results. Due to the technically limited acceleration ability of the machine tool axes, the nominal feed cannot always be achieved. This in particular is the case when the machine tool has to perform a significant change of direction in corners. In this paper, the impact of too low feed rates on the process of precise micromilling of a hardened high-speed steel AISI (M3:2) 63 ± 1 HRC) is discussed. An unattained feed rate leads to a ploughing dominated process with a high burr formation resulting in a huge potential loss of micromilling processes. Furthermore, a simulation approach is presented which allows the prediction of the actually achieved feed rate. The developed machine model provides a reliable method to identify critical areas in the entire NC program. Full article

The metal 3-D printing market is currently dominated by high-end applications, which make it inaccessible for small and medium enterprises, fab labs, and individual makers who are interested in the ability to prototype and additively manufacture final products in metal. Recent progress led to low-cost open-source metal 3-D printers using a gas metal arc welding (GMAW)-based print head. This reduced the cost of metal 3-D printers into the range of desktop prosumer polymer 3-D printers. Consequent research established good material properties of metal 3-D printed parts with readily-available weld filler wire, reusable substrates, thermal and stress properties, toolpath planning, bead-width control, mechanical properties, and support for overhangs. These previous works showed that GMAW-based metal 3-D printing has a good adhesion between layers and is not porous inside the printed parts, but they did not proceed far enough to demonstrate applications. In this study, the utility of the GMAW approach to 3-D printing is investigated using a low-cost open-source metal 3-D printer and a converted Computer Numerical Control router machine to make useful parts over a range of applications including: fixing an existing part by adding a 3-D metal feature, creating a product using the substrate as part of the component, 3-D printing in high resolution of useful objects, near net objects, and making an integrated product using a combination of steel and polymer 3-D printing. The results show that GMAW-based 3-D printing is capable of distributed manufacturing of useful products for a wide variety of applications for sustainable development. Full article

Probes for CNC machine tools, as every measurement device, have accuracy limited by random errors and by systematic errors. Random errors of these probes are described by a parameter called unidirectional repeatability. Manufacturers of probes for CNC machine tools usually specify only this parameter, while parameters describing systematic errors of the probes, such as pre-travel variation or triggering radius variation, are used rarely. Systematic errors of the probes, linked to the differences in pre-travel values for different measurement directions, can be corrected or compensated, but it is not a widely used procedure. In this paper, the share of systematic errors and random errors in total error of exemplary probes are determined. In the case of simple, kinematic probes, systematic errors are much greater than random errors, so compensation would significantly reduce the probing error. Moreover, it shows that in the case of kinematic probes commonly specified unidirectional repeatability is significantly better than 2D performance. However, in the case of more precise strain-gauge probe systematic errors are of the same order as random errors, which means that errors correction or compensation, in this case, would not yield any significant benefits. Full article

Due to their high ductility, high durability, and excellent corrosion resistance, stainless steels are attractive materials for a variety of applications. However, high work hardening, low thermal conductivity, and high built-up edge (BUE) formation make these materials difficult to machine. Rapid tool wear and high cutting forces are the common problems encountered while machining these materials. In the present work, the application of Taguchi optimization methodology has been used to optimize the cutting parameters of the drilling process for machining two stainless steels: austenitic AISI 304 and duplex AISI 2205 under dry conditions. The machining parameters which were chosen to be evaluated in this study are the tool material, cutting speed, and feed rate, while, the response factors to be measured are the tool life (T), cutting force (F_c), and specific cutting energy (k_s). Additionally, empirical models were created for predicting the T, F_c and k_s using linear regression analysis. The results of this study show that AISI 2205 stainless steel has a shorter tool life, a higher cutting force, and a higher specific cutting energy than AISI 304 stainless steel. In addition, the Taguchi method determined that A₃B₁C₁ and A₃B₃C₁ (A₃ = TiN-coated twist drill, B₁ = 13 m/min, B₃ = 34 m/min, C₁ = 0.12 mm/rev) are the optimized combination of levels for the best tool life and the lowest cutting force, respectively. Meanwhile, the optimized combination of levels for all three control factors from the analysis, which provides the lowest specific cutting energy, was found to be A₃B₁C₃ (A₃ = TiN-coated twist drill, B₁ = 13 m/min, C₃ = 0.32 mm/rev) for both stainless steels. Full article

This paper discusses the impact of different machining parameters on structuring quality in a diamond turning process for the machining of diffractive optical elements (DOEs). Special attention is paid to the impact of the material on the geometric structuring quality. First, the machining process for DOEs is described. The structuring process is based on a face turning process combined with a nano Fast Tool Servo (nFTS), which varies the depth of cuts within a range of up to 1 μm at a maximum frequency of 5 kHz. The diamond tools being used exhibit customized rectangular tool geometry with a tool width of 10–20 μm. To determine the material impact and the influence of several machining parameters, different structures have been machined, and their geometric and topographic quality has been analyzed. Full article

Monitoring of the relative deviation between commanded and actual tool tip position, which limits the volumetric performance of the machine tool, enables the use of contemporary methods of compensation to reduce tolerance mismatch and the uncertainties of on-machine measurements. The development of a primarily optical sensor setup capable of being integrated into the machine structure without limiting its operating range is presented. The use of a frequency-modulating interferometer and photosensitive arrays in combination with a Gaussian laser beam allows for fast and automated online measurements of the axes’ motion errors and thermal conditions with comparable accuracy, lower cost, and smaller dimensions as compared to state-of-the-art optical measuring instruments for offline machine tool calibration. The development is tested through simulation of the sensor setup based on raytracing and Monte-Carlo techniques. Full article

Lightweight design is gaining in importance throughout the engineering sector, and with it, workpieces are becoming increasingly complex. Particularly, thin-walled parts require highly accurate and efficient machining strategies. Such low-rigidity structures usually undergo significant deformations during peripheral milling operations, thus suffering surface errors and a violation of tolerance specifications. This article introduces a general approach to mitigating surface errors during the peripheral milling of thin-walled aluminum workpieces. It incorporates an analytical approach to predicting surface-error characteristics based on geometrical quantities and process parameters, which is presented in detail. Milling experiments, including geometrical measurements of the samples, have been performed to verify the approach. The approach allows for a pre-selection of parameter sets that result in surface errors that can be compensated with minimal effort. Additionally, the introduced model offers a simple criterion to assess potential error mitigation by applying the respective tool-path adjustments. In doing so, the amount of costly numerical simulations or experiments is significantly reduced. Full article

One of the most essential components of the fused deposition modeling (FDM) additive manufacturing (AM) process is the build plate, the surface upon which the part is constructed. These are typically made from aluminum or glass, but there are clear disadvantages to both and restrictions on which materials can be processed on them successfully. This study examined the suitability of heated aluminum-polycarbonate (AL-PC) composite print beds for FDM, looking particularly at the mechanical properties, thermal behavior, deformation behavior, bonding strength with deposited material, printing quality, and range of material usability. Theoretical examination and physical experiments were performed for each of these areas; the results were compared to similar experiments done using heated aluminum and aluminum-glass print beds. Ten distinct materials (ABS, PLA, PET, HIPS, PC, TPU, PVA, nylon, metal PLA, and carbon-fiber PLA) were tested for printing performance. The use of a heated AL-PC print bed was found to be a practical option for most of the materials, particularly ABS and TPU, which are often challenging to process using traditional print bed types. Generally, the results were found to be equivalent to or superior to tempered glass and superior to standard aluminum build plates in terms of printing capability. Full article

Silicon nanotubes (SiNTs) have been researched as a promising anode material to replace graphite in next-generation lithium ion batteries. Chemical etching synthesis of SiNTs is a simple, controllable and scalable process for SiNT fabrication, but the environmental emissions are of grave concern. In this paper, the process emissions from chemical etching synthesis of SiNTs as anode for lithium ion batteries is studied through experimental techniques, considering the categories of aqueous wastes, gaseous emissions, aqueous nano-particle emissions, and gaseous aerosol emissions. The synthesized SiNTs are measured at 10 μm length and 1–2.2 μm diameter, and can maintain a specific capacity of over 800 mAh/g after 100 cycles in battery testing. In aqueous waste, the chemical compositions of all elements participating in the chemical etching are experimentally determined, with AgNO₃ and Co(NO₃)₂ identified as the major pollutants. The only gaseous emission generated from the chemical etching synthesis process is H₂, with 0.0088 ± 0.0002 mol H₂ generated to produce 1.0 mg SiNTs. The aqueous nanoparticle sizes are found to be between 250 nm and 1540 nm. A large number of aerosol nanoparticle emissions of up to 2.96 × 10⁷ particles/cm³ are detected through in situ experimental measurement. Full article

Transparent, brittle materials, like glass, are used in various applications due to their advantages of mechanical and optical properties. However, their hard and brittle nature causes significant challenges to researchers when they design and test a new machining process. In order to optimize this time-consuming process, discrete element method (DEM) is applied to simulate the cutting process of soda-lime glass in this study. The first step is to create a synthetic material that behaves like soda-lime glass. Then, the macroproperties are calibrated by adjusting the microparameters of the DEM model to match the mechanical properties of the real soda-lime glass. Finally, orthogonal machining simulations are conducted and model validation are conducted by comparing the predicted cutting forces with those from the orthogonal cutting experiments. Full article

The question, how certain surface layer properties (for example, hardness or roughness) can be specifically influenced in different manufacturing processes, is of great economic interest. A prerequisite for the investigation of the formation of surface layer properties is the metrological assessment of the material stresses during processing. Up to now, no commercial in-process measuring system exists, which is able to determine material stresses in the form of mechanical strains in high-dynamic manufacturing processes with sufficient accuracy. A detailed analysis of the resolution limits shows that speckle photography enables deformation measurements with a resolution in the single-digit nanometer range. Thus, speckle photography basically offers the potential to measure material stresses during processing. Using the example of single-tooth milling, the applicability of speckle photography for in-process stress measurements is demonstrated. Even in such highly dynamic manufacturing processes with cutting speeds up to 10 m/s, the absolute measurement uncertainty of the strain is less than 0.05%. This is more than one order of magnitude lower than the occurring maximal strain. Therefore, speckle photography is suitable for characterizing the dynamic stresses and the material deformations in manufacturing processes. Full article

In this study, a precision motion stage, whose design utilizes a single shaft supported from the bottom by an air bearing and voice coil actuators in complementary double configuration, is evaluated for its dynamic properties, motion accuracy, and potential machining force response, through modal testing, laser interferometric metrology, and spectral analysis, respectively. Modal testing is carried out using two independent methods, which are both based on impact hammer testing. Results are compared with each other and with the predicted natural frequencies based on design calculations. Laser interferometry has been used with varying optics to measure the geometric errors of motion. Laser interferometry results are merged with measured servo errors, estimated thermal errors, and the predicted dynamic response to machining forces, to compile the error budget. Overall accuracy of the stage is calculated as peak-to-valley 5.7 μm with a 2.3 μm non-repeatable part. The accuracy measured is in line with design calculations which incorporated the accuracy grade of the encoder scale and the dimensional tolerances of structural components. The source of the non-repeatable errors remains mostly equivocal, as they fall in the range of random errors of measurement in laser interferometry like alterations of the laser wavelength due to air turbulence. Full article

Machining grooves and ridges (peaks) into the surface of wooden deckboards reduces undesirable checking that develops when “profiled” boards are exposed to the weather. We aim to develop improved profiles for amabilis fir decking to reduce its susceptibility to checking, and also to examine whether profiling influences distortion (cupping) of deckboards. We systematically varied radii of grooves and peaks, and the heights and widths of peaks in profiled deckboards, exposed them to the weather, and measured checking and cupping of boards. Profiling significantly reduced the numbers and sizes of checks in amabilis fir deckboards, but increased cupping. Profiles with narrow grooves and tall peaks were generally better at restricting checking than profiles with wide grooves and shorter peaks. Our results suggest that one of the profiles we tested would be better at restricting checking than profiles used previously to manufacture profiled decking from amabilis fir. We conclude that the surface checking of profiled amabilis fir decking can be significantly reduced by altering the geometry of surface profiles. In principal, the same approach could be used with other softwood species that have potential to capture a share of the large and important market for wood decking. Full article

A precise characterization of material behavior is necessary to identify yield criteria or hardening laws for an accurate numerical design of sheet metal forming processes. Current models like Yld2000-2d or Hill’48 do not consider the plane strain state, though this condition is primary cause of failure in deep drawing. It is anticipated that an improved yield locus contour which considers the stress under plane strain conditions leads to better results in numerical simulations of a deep drawing process. Within this contribution, a new experimental setup to characterize both principal stress components under plane strain as additional input data for material modelling is presented. Therefore, hydraulic bulge tests are carried out with a novel elliptical die, which implements a plane strain condition. Moreover, the improvement of the material model is investigated exemplarily for the three sheet metal alloys DC06, DP600 and AA5182. The resulting material parameters are used to identify the yield locus for plane strain by varying the yield locus exponent of Yld2000-2d. The results prove that considering plane strain yield locus results in a better sheet thickness distribution in comparison to conventional modelling of the deep drawing process. Full article

Polymer optics are widely used in various applications, replacing traditional glass lenses. The ability to create free-form and micro-structured optics, as well as fast replication, gives them major advantages over traditional glass lenses. However, the fabrication of complex optical components requires full process control and understanding of influencing factors on the quality of the polymer optical parts. In this work, a curved diffractive optical element (DOE) is fabricated using injection compression molding. Different gate designs were evaluated and the movement of the compression stamper was optimized to obtain good filling behavior. The process stability was analyzed and improved by controlling the melt temperature precisely. Finally, the molding parameters were optimized, focusing on the mold temperature, melt temperature and compression force. Curved diffractive optical elements were replicated with feature sizes of 1.6 μm. The experiments showed that all aspects of the molding process have to be controlled perfectly to produce complex polymer optics. High mold temperatures and compression force are necessary to replicate micro-structured features. The work presents a broad investigation and description of the fabrication process and their influences. Full article

This paper describes an error separation method for a precision measurement of the run-out of a microdrill bit by using a measurement system consisting of a concentricity gauge and a laser scan micrometer (LSM). The proposed error separation method can achieve a sub-micrometric measurement accuracy of the run-out of the microdrill bit without the requirement of ultra-precision rotary drive devices. In the measurement, the spindle error motion of the concentricity gauge is firstly measured by using the LSM and a small-diameter artifact, instead of the conventionally used displacement probes and large-diameter artifact, in order to determine the fine position of the concentricity gauge when the spindle error motion is at its minimum. The microdrill bit is rotated at the fine position for the measurement of the run-out, so that the influence of the spindle error motion can thus be reduced, which could not be previously realized by commercial measurement systems. Experiments were carried out to verify the feasibility of the proposed error separation method for the measurement of the run-out of the microdrill bit. The measurement results and the measurement uncertainty confirmed that the proposed method is reliable for the run-out measurement with sub-micrometric accuracy. Full article

The concept of Zener–Hollomon (Z) based Forming Limit Surface (Z-FLS)—which has minor strain, major strain, and ln(Z) as its three axes—was initially proposed in a previous study. In the Z-FLS diagram, strain rate and temperature effects on the major limit strain are reflected by ln(Z). In the current study, the concept of Z-FLS is revisited to provide a practical approach to construct Z-FLS. A Z-FLS then is constructed for magnesium alloy AZ31B sheet material using available experimental forming limit curves. The constructed Z-FLS is used to identify fracture in a non-isothermal warm cup forming process, which was modeled as a coupled thermo-mechanical process. Based on the Z-FLS, the determined limiting draw ratio (LDR) matches well with the published experimental results. Full article

Titanium aluminide (TiAl) turbine blades produced by isothermal forging have recently been implemented in the low-pressure part of commercial aircraft jet engines. However, the slow speed of isothermal forging, costly molybdenum-based dies and the required protective forging atmosphere makes the process rather expensive. Currently, industrial forging is done by closed-die isothermal forging processes with stationary dies. Idle time occurs when single parts are inserted and extracted from the dies. As an interesting alternative for forging small parts, a new set-up is devised and explored in this work, i.e., batch processing. Using a die set which allow for off-line preassembly and preheating, multiple parts can be forged in one stroke. The design of the batch process was based on a new material model, which was implemented into a finite element system to identify the forging parameters. The setup of the press transport system for batch processing, as well as the results of the simulations and forging experiments are presented. A cost comparison between the new process and conventional forging with stationary dies concludes that for smaller parts such as compressor blades, batch processing offers advantages regarding productivity and cost. Full article