Improvement In Dimensional Accuracy Research Articles

An Experiment-Based Variable Compensation Method to Improve the Geometric Accuracy of Sub-mm Features Fabricated by Stereolithography (SLA)

In this paper, we present an experimental procedure to enhance the dimensional accuracy of fabrication via stereolithography (SLA) of features at the sub-mm scale. Deviations in sub-mm hemispherical cavity diameters were detected and measured on customized samples by confocal microscopy. The characterization and experimental observations of samples allowed the identification of inaccuracy sources, mainly due to the laser beam scanning strategy and the incomplete removal of uncured liquid resin in post-processing (i.e., IPA washing). As a technology baseline, the measured dimensional errors on cavity diameters were up to −46%. A compensation method was defined and implemented, resulting in relevant improvements in dimensional accuracy. However, measurements on sub-mm cavities having different sizes revealed that a constant compensation parameter (i.e., C = 85, 96, 120 μm) is not fully effective at the sub-mm scale, where average errors remain at −24%, −18.8%, and −16% for compensations equal to 85, 96 and 120 μm, respectively. A further experimental campaign allowed the identification of an effective nonlinear compensation law where the compensation parameter depends on the sub-mm feature size C = f(D). Results show a sharp improvement in dimensional accuracy on sub-mm cavity fabrication, with errors consistently below +8.2%. The proposed method can be extended for the fabrication of any sub-mm features without restrictions on the specific technology implementation.

Improving the Three-Dimensional Printability of Potato Starch Loaded onto Food Ink.

This study focuses on improving the 3D printability of pea protein with the help of food inks designed for jet-type 3D printers. Initially, the food ink base was formulated using nanocellulose-alginate with a gradient of native potato starch and its 3D printability was evaluated. The 3D-printed structures using only candidates for the food ink base formulated with or without potato starch exhibited dimensional accuracy exceeding 95% on both the X and Y axes. However, the accuracy of stacking on the Z-axis was significantly affected by the ink composition. Food ink with 1% potato starch closely matched the CAD design, with an accuracy of approximately 99% on the Z-axis. Potato starch enhanced the stacking of 3D-printed structures by improving the electrostatic repulsion, viscoelasticity, and thixotropic behavior of the food ink base. The 3D printability of pea protein was evaluated using the selected food ink base, showing a 46% improvement in dimensional accuracy on the Z-axis compared to the control group printed with a food ink base lacking potato starch. These findings suggest that starch can serve as an additive support for high-resolution 3D jet-type printing of food ink material.

Software compensation to improve the Stereolithography fabrication of porous features and porous surface texturing at micro-scale

Nano and micro-porous structures exhibit intriguing properties for a wide variety of applications, spanning from the biomedical to sensing. However, their fabrication is a challenge in terms of dimensional accuracy, which affects devices' performance and sensitivity. In this paper, we present a route to enhance the dimensional accuracy of fabrication via Stereolithography (SLA) of porous features at the micro-scale. Using a custom benchmark part, deviations in feature dimensions (micro-pores diameters and depths) were measured by confocal microscopy. Sample characterization and experimental observations allowed the identification of inaccuracy sources (i.e., laser spot size and its compensation on path generation), and a compensation method of the nominal laser spot diameter (85|um) was defined. Implementing such a method results in relevant improvements in dimensional accuracy: 9.8% and 11.3% on full-open pores diameter and depth, respectively. Partially open pores accuracy improvements were 15.8% on diameters and 1.5% on depths. Since machine optical equipment can result in deviations in the actual laser spot diameter from the nominal value, the actual laser beam spot diameter was estimated by printing a test part and adopting this information to adjust a calibration procedure. The measurements revealed that the actual laser beam spot size is 93±8um. The proposed method can be extended for the fabrication of any micro-porous structures.

Enhancing Dimensional Accuracy in Budget-Friendly 3D Printing through Solid Model Geometry Tuning and Its Use in Rapid Casting

Achieving precise dimensional accuracy and improving surface quality are the primary research and development objectives in the engineering and industrial applications of 3D printing (3DP) technologies. This experimental study investigates the pivotal role of solid model geometry tuning in enhancing the dimensional accuracy of affordable 3D printing technologies, with a specific focus on economical engineering applications. This experiment utilises low-cost Material Extrusion/Fused Filament Fabrication (FFF) and Stereolithography (SLA)/Digital Light Processing (DLP) 3D-printed patterns for the meticulous measurement of errors in the X, Y, and Z directions. These errors are then used to refine subsequent solid models, resulting in a marked improvement in dimensional accuracy (i.e., 0.15%, 0.33%, and 2.16% in the X, Y, and Z directions, respectively) in the final DLP 3D-printed parts. The study also derives and experimentally validates a novel and simple mathematical model for tuning the solid model based on the calculated linear directional errors (ei, ej, and ek). The developed mathematical model offers a versatile approach for achieving superior dimensional accuracy in other 3D printing processes. Medium-sized (4 to 10 cm) wax-made DLP- and PLA-made patterns are used to test the ceramic mould-building capacity for rapid casting (RC), where the FFF-based 3D-printed (hollow inside) pattern favours successful RC. This work comprehensively addresses the critical challenges encountered in low-cost DLP and FFF processes and their scopes in engineering applications. It provides novel suggestions and answers to improve the effectiveness, quality, and accuracy of the FFF 3D printing process for future applications in RC.

Dimensional accuracy enhancement of machined-hole through UAECDM-process under the magnetic-field-assistance

ABSTRACT Electrochemical discharge machining (ECDM) is a micro-machining hybrid technique that utilizes electrical discharge and electrochemical machining principles. However, the issue of insufficient electrolyte in the hydrodynamic region hinders the continuation of the machining action. Although ultrasonic tool vibrations have been used to overcome this problem to some extent, the excessive mechanical energy produced by high-amplitude tool vibration may lead to surface crack formations. As a result, the present work employs two flushing improvement methods, namely the ultrasonic vibrations and magnetic filed assistances, in the ECDM process. A comparative study has been performed to identify the effect of the magnetic field on discharge quality. The material removal rate and depth of penetration were increased by 11% and 24%, respectively, and the observed reduction in hole overcut and taper angle was around 35% and 50%, respectively. Optical microscope images quantified improvement in dimensional accuracy and decreased HAZ area.

Comparison between continuous and modulated wave laser emission modes for the selective laser melting of Ti-6Al-4V: Dimensional accuracy, microstructure and mechanical behaviour

This study investigated the difference between the properties of Ti-6Al-4 V alloy parts printed using continuous wave (CW) and modulated wave (MW) laser emission modes, with equivalent input energy densities. Laser powers in this powder bed fusion process, were systematically altered to evaluate the effect of different input energies on the as-built parts. Printed alloy parts were obtained across five equivalent laser energy densities, in the range of 31–51 J/mm3, investigated using the two laser emission modes. The impact of changes in laser emission mode and energy density was examined based on printed part dimensions, microstructure, porosity, hardness and tensile properties. It was demonstrated that microstructural refinement occurs as a function of melt pool size, which was associated with the penetration depth of the laser energy. The microstructure of samples produced using CW laser emission mode were characterised by thinner laths and narrower prior β grains. Tensile testing according to ASTM E8M, obtained at the different energy levels, demonstrated that over the energy density range investigated there was up to a 17.4% increase in yield strength (YS) and a 2.5% increase in Ultimate Tensile Strength (UTS) for the CW printed samples, when compared with those obtained using the MW laser wave emission mode. Comparatively, MW laser emission mode resulted in thicker laths with slightly wider prior β grains, which exhibited an elongation at break of 13.6% during tensile testing at high energy densities. The influence of the laser emission mode on dimensional accuracy was also investigated. Sample printed using the MW laser emission mode showed up to a 50% improvement in dimensional accuracy when compared with that obtained for CW wave laser emission mode.

Surface Roughness Improvement by Sliding Friction Burnishing of Parts Produced by Selective Laser Melting of Ti6Al4V Titanium Alloy

Selective laser melting is a frequently used, powder bed fusion additive manufacturing technology for producing metallic parts. However, appropriate surface quality cannot be achieved, so post-processing is often necessary. Subsequent machining of surfaces serves multiple objectives such as improvement of dimensional accuracy, changing surface roughness and modification of the residual stress state for higher surface hardness. Beyond its several advantageous properties, Ti6Al4V material has, as its weaknesses, low tribological behavior and wear resistance. Sliding friction burnishing is a conventional chipless and coolant-free environmentally conscious technology for surface modification that is appropriate for simultaneously decreasing surface roughness and increasing surface hardness. Until now, there has been a research gap regarding the diamond burnishing of selective laser melted Ti6Al4V parts. In this study, we investigated how the surface roughness of selective laser melted parts can be modified via sliding friction burnishing. 2D and 3D characteristics of surface roughness were measured by a chromatic roughness measuring device. Indices of surface roughness improvement were defined and studied as a function of selective laser melting parameters. Optimal manufacturing parameters of laser power—P = 280 W and scanning speed u = 1200 mm/s—for effective surface improvement via burnishing are proposed.

In-process adaptive dimension correction strategy for laser aided additive manufacturing using laser line scanning

Additive manufacturing (AM) technologies have seen rapid growth in the past decade. Achieving high-quality consistency and accuracy remains a challenge in the fabrication of large-format metallic parts using the directed energy deposition AM processes. An efficient dimension correction strategy is required to prevent build failure during the AM process. In this paper, a laser line scanning sensor was integrated into a robot-based laser aided additive manufacturing (LAAM) system to realise the on-machine measurement of the part geometry. With this system, an in-process adaptive dimension correction strategy was proposed. The dimensional deviations in the intermediate layers could be corrected immediately after they were detected during the LAAM process, thus avoiding excessive dimensional deviation leading to build failure. A tool-path generation process for dimension correction was proposed which did not rely on traditional time-consuming CAD reconstruction. Only 3D point cloud was used directly, enabling the quick response of the LAAM system in restoring the dimensional accuracy. The deviated surface could be automatically filled up, and the subsequent deposition processes were resumed after each cycle of the dimension correction. To facilitate the proposed dimension correction strategy, a Robot Operating System (ROS)-based software platform was developed. Experimental comparisons between the part built with and without correction were conducted. The results demonstrated a significant improvement in dimensional accuracy when the correction strategy was applied.

The effect of build direction and geometric optimization in laser powder bed fusion of Inconel 718 structures with internal channels

A laser powder bed fusion (LPBF) strategy was developed for manufacturing small channels with high dimensional accuracy in Inconel 718 structures. Particular attention was paid to surface characteristics such as equivalent diameter and shape factor. The inherent surface quality of external surfaces was optimized by a systematic variation of the LPBF contour parameters as well as the channel cross-section. The mean arithmetic roughness Sa was analysed for upskin, vertical and downskin surfaces with respect to the build platform. Simultaneously, the effect of the build direction on the quality of internal free-shaped surfaces was investigated on channels with diameters from 500 to 1000 µm and build orientations from the horizontal (0°) to vertical (90°). A significant improvement in dimensional accuracy was achieved by using an optimized droplet-shaped cross-section that is scaled as a function with the build inclination. An angular analysis of the surface roughness in different regions of the channels confirms that this modified cross-section reduces the fraction of channel regions that show a particularly high surface roughness due to inward melting. In combination with an optimized contour processing strategy, the modified channel resulted in the best properties for inclinations below 45°. The shape factor increased from 0.4 to almost 0.9, i.e., close to the ideally round shape.

On-Line Compensation for Micromilling of High-Aspect-Ratio Straight Thin Walls.

In order to improve the machining quality and reduce the dimensional errors of micro high-aspect-ratio straight thin walls, the on-line cutting parameter compensation device has been introduced and corresponding micromilling processes have been investigated. Layered milling strategies for the micromilling of thin walls have been modeled and simulated for thin walls with different thicknesses based on the finite element method. The radial cutting parameters compensation method is adopted to compensate the thin wall deformation by raising the radial cutting parameters since the thin wall deformation make the actual radial cutting parameters smaller than nominal ones. The experimental results show that the dimensional errors of the thin wall have been significantly reduced after the radial cutting parameter compensation. The average relative dimensional error is reduced from 6.9% to 2.0%. Moreover, the fabricated thin walls keep good shape formation. The reduction of the thin wall dimensional error shows that the simulation results are reliable, which has important guiding significance for the improvement of thin wall machining quality, especially the improvement of dimensional accuracy. The experimental results show that the developed device and the machining strategy can effectively improve the micromilling quality of thin walls.

Improvement of dimensional accuracy and surface quality of microlens arrays by a profile cutting method

Single-point diamond cutting is an efficient method to fabricate microlens arrays (MLAs). However, machining MLAs at the microscale with high dimensional accuracy and a smooth surface finish is a difficult task. In this study, a method of profile cutting is proposed to machine MLAs on electroless nickel–phosphorus (Ni–P) plating. To improve the dimensional accuracy of MLAs, a precision tool setting method is introduced, via which the precision of MLA sag can be controlled to within 20 nm. In addition, the formation mechanism of corrugation defects is studied via a finite element (FE) simulation of the wedge nano-cutting process and a cutting experiment of concentric ring grooves. By optimizing the tool settings and the machining parameters, high-quality MLAs with apertures of Φ100 μm can be created.

Comparisons of Process Capability in Cold Chamber Die Casting of Aluminium Alloy

The purpose of the present investigations is to study and compare the effect of processing parameters on process capability of cold chamber die casting of Al alloy. The study presented in this paper is based on a previously published macro model (based on Taguchi design). Castings prepared at proposed parametric settings have been studied and compared using X chart, R chart and process capability histogram (for functional validation of the parts). The study suggested significant improvement in dimensional accuracy and process capability (expressed in terms of sigma ‘σ’ limit) at proposed parametric settings.

COLD CHAMBER DIE CASTING OF ALUMINIUM ALLOY: A CASE STUDY

In the present work cold chamber die casting solution of Al alloy has been investigated as a case study of industrial component (crankcase). The study presented in this paper is based upon Taguchi based model on dimensional accuracy in cold chamber die casting. The castings prepared at proposed parametric settings have been studied for functional validation of the parts, as per statistical control point of view. The result of study highlights significant improvement in dimensional accuracy (as regards to statistical process control isconcerned) at proposed parametric settings of cold chamber die casting process.

Investigations for Statistically Controlled Hot Chamber Die Casting Solution of Aluminium Alloys

The purpose of the present investigations is to study the effect of processing parameters on statistically controlled hot chamber die casting solution for Al alloy. The study presented in this paper is based on a macro model (based on Taguchi design). Castings prepared at proposed parametric settings (as per macro model) have been investigated for functional validation of the parts. The study suggested significant improvement in dimensional accuracy (ΔD) at proposed parametric settings and the process was found to be under statistical control.

Assessing the challenges and issues in entry-level additive manufacturing machine

Entry-Level Additive Manufacturing (ELAM) machines are made far less sophisticated compared to premium Additive Manufacturing (AM) machines for the sake of affordability. Often, machine resolution is also compromised, which may raise a question mark on quality. It is essential to gain a working knowledge of quality issues, considering the present rate of penetration of 3D printers in manufacturing. The objective of this paper is to examine geometric limitations and challenges of entry-level AM machines when fabricating complex objects. A systemic literature review providing an overview of additive manufacturing technology, the definition of ELAM, followed by a discussion on challenges in ELAM and improvement in dimensional accuracy to help the end users understand their machine well are presented in the paper. Ten experiments were performed on ELAM using acrylonitrile butadiene styrene polymer to illustrate and classify the developed defects. Most of the parts produced from ELAM machine suffer from quality issues such as geometrical and dimensional inaccuracy, warpage, oozing and surface imperfection, nesting, non-formation and deposition. This investigation displays a more realistic picture of ELAMs by identifying important restrictions and limitations which otherwise are hardly available to the end users or the manufacturers. The findings will help ELAM manufacturers to innovate their machine and make it better for professional use.

インパクト成形における寸法精度向上のためのスライドモーションの検討

インパクト成形における寸法精度向上のためのスライドモーションの検討

Dimensional accuracy of Electron Beam Melting (EBM) additive manufacture with regard to weight optimized truss structures

The Electron Beam (EBM) additive manufacturing process is well suited to fabricating complex structural designs in Ti–6Al–4V because of the design freedoms it offers combined with strong and consistent material properties. However it has been observed that complications may arise when manufacturing truss-like structures (such as those produced via structural topology optimization) in the form of undersized features on the finished part. The issue appears to affect truss members that are not aligned with the vertical build direction, with an apparent lack of material on the negative surfaces. This effect appears to worsen with a greater angle between the truss member and the build direction, even with the use of support structures. This investigation has characterized and measured the dimensional errors that result from this issue through 3D scanning techniques. Process modifications have then been made which result in significant improvements in dimensional accuracy. This investigation highlights the importance of heat management at features with negative surfaces to yield parts that are dimensionally accurate without introducing excessive internal melt defects in the form of voids and porosity.

Reduction of Residual Stress and Improvement of Dimensional Accuracy by Uphill Quenching for Al6061 Tube

The purpose of this study is to reduce the residual stress and machining distortion of an Al6061 tube by using uphill quenching. During uphill quenching, solid-solution heat-treated aluminum parts are usually immersed in LN2 at 77 K (−196 °C), followed by the rapid heating of the parts, to produce a new residual stress that is opposite in nature to the original. The uphill quenching method used in this study employed two types of heating methods: boiling water at 373 K (100 °C) and high-velocity steam at 448 K (175 °C). First, FE-simulation coupled with a CFD analysis was performed to predict the residual stress of the backward hot-extruded Al6061 tube with the following dimensions: O200 mm × h200 mm × t10 mm. Experiment of uphill quenching was also conducted to measure the residual stress using the boiling water and high-velocity steam uphill quenching methods. The predicted residual stresses were compared with the experimental results obtained via micro-indentation and saw-cutting tests, and a deviation of about 10.4 pct was found. In addition, the experimental results showed that uphill quenching could relieve up to 91 pct of the residual stress induced by water quenching. Finally, the dimensional accuracy of uphill quenched tubes was evaluated by measuring the roundness after the machining process, which showed that the uphill quenching method could improve the dimensional accuracy of an Al6061 tube by reducing the residual stress.

Experimental Investigations for Use of ABS Replicas in Investment Casting Applications

In the present research work effort has been made to study the use of acrylonitrile butadiene styrene (ABS) replicas in investment casting (IC) applications. The study starts with selection of the component for industrial application with an idea of improvement in dimensional accuracy (Δd) of the component. The input parameters are part orientation in fused deposition modeling (FDM), number of layers, layer combination and type of materials in IC. The study highlights the percentage contribution of different input parameters on Δd for ABS replicas in IC.

Improvement in dimensional accuracy of roll-die-formed clutch hub used in automotive transmission

Roll die forming is investigated as a new process for manufacturing a clutch hub; in this process a tooth shape is formed by a deep drawing process using a die set with rotational rolls. Some problems are still encountered during roll die forming, such as a proper process design that takes into consideration the forming limit of sheet material, the improvement in the wear resistance of the punch and the rotational roll, and the control of dimensional accuracy. Particularly, the dimensional accuracy of the final product is affected by the clearance between the punch and the roll. Therefore, the objective of this study is to determine the optimal clearance between the punch and the roll for improving the dimensional accuracy during the roll die forming for a clutch hub. FE-simulation and the design of experiment method are employed to determine the optimal clearance required to produce a final product with satisfactory dimensional specifications. An experiment is performed under the same process conditions as the FE-simulation with an optimal clearance to validate the results obtained in this study. The results of the FE-simulation are in good agreement with the experimental ones within a maximum error of 5.55[%].