Good Dimensional Accuracy Research Articles

Preparation of Polypropylene Powder by Dissolution-Precipitation Method for Selective Laser Sintering

Polypropylene (PP) powder with spherical morphology and suitable particle size for selective laser sintering (SLS) was successfully produced by dissolution-precipitation method. The influence of preparation condition on properties of PP powder was investigated. The experimental results show that the optimal preparation conditions are as follows: dissolution temperature being about 166°C, pressure being about 0.7MPa, and the solid-to-solvent ratio being about 0.067g/ml. The prepared PP powder displayed a narrow size distribution with the mean size of about 42.7μm and the apparent density of powder about 0.40 g/cm3. The specimens produced by laser sintering of the PP powder showed smooth appearance and good dimensional accuracy. The tensile strength and impact strength of the sintered parts were 27.9MPa and 6.3KJ/m2, respectively, which are basically equal to the properties of the injection molded parts.

Improvement on Selective Laser Sintering and Post-Processing of Polystyrene.

Amorphous polymers are heavily utilized materials in selective laser sintering (SLS) due to their good dimensional accuracy. However, sintered parts of amorphous polymers cannot be used as functional parts owing to their poor forming performance, including their low relative densities and tensile strength. Therefore, post-processing methods are employed to enhance the mechanical properties of amorphous polymers SLS parts without damaging their relatively high dimensional accuracy. In this study, the forming process of selective laser sintering (SLS) and post-processing on polystyrene (PS) was investigated. The orthogonal experiment was designed to obtain the optimal combination of process parameters. The effect of a single process parameter and the laser volumetric energy density (LVED) on dimension accuracy and warpage of the sintered parts were also discussed. In addition, a three-dimensional (3D) thermal model was developed to analyze the temperature fields of single-layer SLS parts and PS powder sintering mechanism. Then, infiltrating with epoxy resin was employed to enhance the mechanical properties of the PS parts. Good resin-infiltrated formulation was obtained based on the mechanical property tests and fractured surface analysis. This research provides guidance for SLS process and post-processing technology in polymers.

Characterisation and Comparison of Process Chains for Producing Automotive Structural Parts from 7xxx Aluminium Sheets

Due to their high specific strength, EN AW-7xxx aluminium alloys are promising materials for reducing the weight of automotive structural parts. However, their formability at room temperature is poor due to pronounced natural ageing. Therefore, we investigated hot stamping and W-temper forming for EN AW-7075 and a modified variant of EN AW-7021. For hot stamping of the modified EN AW-7021, a low-temperature stabilisation heat treatment (pre-aging at 80 °C for 1 h) was incorporated into the process chain design to inhibit natural ageing after forming. The process chains were compared with respect to dimensional accuracy, mechanical properties, microstructure, precipitation status (assessed by differential scanning calorimetry) and crashworthiness. It was found that hot stamping is suitable to form failure-free parts with good dimensional accuracy for both alloys while W-temper forming suffers from springback. Within a time-span of 21 days after forming, hardness values of hot stamped and stabilised parts did not increase significantly. Compared to non-stabilised parts, stabilised parts also showed significantly improved folding behaviour in quasi-static compression testing and absorbed approximately 15% more energy.

Sensitivity Analysis of Tool Wear in Drilling of Titanium Aluminides

In the aerospace industry, a large number of holes need to be drilled to mechanically connect the components of aircraft engines. The working conditions for such components demand a good response of their mechanical properties at high temperatures. The new gamma TiAl are in the transition between the 2nd and 3rd generation, and several applications are proposed for that sector. Thus, NASA is proposing the use of the alloys in the Revolutionary Turbine Accelerator/Turbine-Based Combined Cycle (RTA/TBCC) Program for the next-generation launch vehicle, with gamma TiAl as a potential compressor and structural material. However, the information and datasets available regarding cutting performance in titanium aluminides are relatively scarce. So, a considerable part of the current research efforts in this field is dedicated to process optimization of cutting parameters and tool geometries. The present work is framed in the study of wear when machining holes in these difficult-to-cut alloys. In particular, the work presents the results from drilling tests on three types of gamma TiAl alloys, extruded MoCuSi, ingot MoCuSi, and TNB type, to define an optimal set of cutting parameters. Maintaining uniform, gradual wear is key to avoiding tool breakage and enabling good hole dimensional accuracy. So, this paper proposes a model based on ANOVA analysis to identify the relationships between cutting conditions and resulting wear and estimate tool life. The best cutting parameters were found at vc = 10–15 m/min and fn = 0.025 mm/rev.

Machined channel quality and tool life using cermet micro-mill in micro-milling aluminum alloy

Based on the superiority of self-developed cermet micro-mill over commercial cemented tungsten micro-mill in our previous work, the cutting characteristics, machined channel quality, and tool wear were investigated in this work, aiming at the evaluation of tool performance of this cermet micro-mill during micro-milling aluminum alloy 2024. Burrs and dimensional accuracy of machined channels, tool wear, and chip morphology were analyzed at various cutting parameters. The machining and forming mechanism related with cermet micro-mill were thoroughly discussed. It indicated that the cutting conditions can be optimized to enhance the performance of cermet micro-mills. The optimum cutting parameter can produce not only the good quality and high dimensional accuracy of channel with few small burrs but also the tool wear to a small degree ever after micro-milling of 10–20 min. The cermet micro-mill also exhibited the good capacity to break the chip. The good performance of cermet micro-mill was attributed to its good chemical stability and high hardness, especially the gained sharper tool tips and edges, and their better stability.

3D printing of NdFeB bonded magnets with SrFe12O19 addition

Rectangular, square, ring and horseshoe-shaped NdFeB bonded magnets with SrFe12O19 addition have been prepared by additive manufacturing, also known as 3D printing. The prepared NdFeB slurries with ferrite addition were deposited to form shaped parts using a 3D printer. Highly loaded pseudo-plastic printing slurries were employed to print bonded magnets with 98% of theoretical density. In the printed magnets with 20 wt.% strontium ferrite (SrFe12O19), good dimensional accuracy and surface quality were obtained with a relatively low surface roughness of ∼6 μm. In addition, good coalescence without obvious defects or pores was observed, and the ultimate tensile strength was 12 MPa. The magnetic properties of the hybrid magnets decreased with the increase of SrFe12O19 content due to a lower volume fraction of the NdFeB powder and lower magnetic performance of the SrFe12O19 powder. Nevertheless, the coercivity temperature coefficient β increased from −0.4%/°C to −0.2%/°C with the SrFe12O19 content increase to 20 wt.%, indicating better thermal stability of hybrid magnets. The proposed method of fabricating NdFeB bonded magnets significantly reduces the manufacturing cost of complex-shaped magnets, enables efficient utilization of rear earth elements and broadens elevated operating temperature applications.

Preparation and Characterization of Poly(butylene succinate)/Polylactide Blends for Fused Deposition Modeling 3D Printing.

To obtain a new type of biodegradable material with high toughness and strength used for fused deposition modeling (FDM) printing, a series of poly(butylene succinate) (PBS)-based polymer materials was prepared via blending with polylactide (PLA). The rheological, thermal, and mechanical properties as well as FDM printing performances of the blends, such as distortion, cross section, and the interlayer bond strength, were characterized. The results show that with increasing PLA content, the blends possess higher melt viscosity, larger tensile strength, and modulus, which are more suitable for FDM printing. Especially, when the content of PLA is more than 40%, distortion due to residual stress caused by volume shrinkage disappears during the printing process and thus products with good dimensional accuracy and pearl-like gloss are obtained. The results demonstrate that the blend compositions with moderate viscosity, low degree of crystallinity, and high modulus are more suitable for FDM printing. Compared with the low elongation upon breaking of commercially FDM-printed material, the PBS/PLA blend materials exhibit a typical ductile behavior with elongation of 90–300%. Therefore, besides biodegradability, the PBS/PLA blends present excellent mechanical properties and suitability as materials for FDM printing. In addition, our study is expected to provide methods for valuating the suitability of whether a thermoplastic polymer material is suitable for FDM printing or not.

3D gel-printing of Sr ferrite parts

3D gel-printing (3DGP) opens new possibilities to process complex-shaped Sr ferrite parts for magnetic applications. In this study, a novel 3DGP process based on the hydroxyethyl methacrylate gelation system was employed to prepare complex-shaped Sr ferrite samples. To obtain highly loaded pseudo-plastic slurries, the Sr ferrite powder was modified by 1 wt% silane coupling agent and 2.5 vol% polymer Silok7050S was introduced into the ceramic slurry as a dispersant. In the printed samples, good dimensional accuracy and surface quality were achieved with a relatively low surface roughness of 5 µm. After sintering, the Sr ferrite ceramics exhibited good surface quality and the surface roughness was 3.2 µm. A homogeneous microstructure was observed. The bending strength for the sintered samples with the relative density of 97% was 83 MPa. In addition, the corresponding coercivity, remanence, and maximum magnetic energy product values were 271.2 kA/m, 0.383 T, and 26.34 kJ/m3, respectively.

Sensing and control in glass additive manufacturing

There has been tremendous interest in the Additive Manufacturing (AM) of polymers, metals, and ceramics leading to a wealth of research and development of these processes. By contrast, there has been little attention paid to AM processes for glass. This paper presents a custom-made glass additive machine. A CO2 laser is used to generate a molten pool of glass into which glass filaments are fed. A motion system is used to trace a layer, after which the build platform is lowered to fabricate the next layer. Two of the unique issues that must be addressed in the AM of glass are 1) various mechanisms can cause the formation of bubbles that deteriorate part optical and mechanical properties and 2) significant processing forces can move the melt pool away from its desired location. In this paper a melt pool temperature controller is designed to regulate the melt pool temperature at a constant value and a path and trajectory generation algorithm is constructed to maintain a constant glass filament feed direction relative to the scan velocity. The experimental results demonstrate that the melt pool temperature controller is able to avoid bubble formation over a wide range of build speeds and that the path planned directional-control is able to maintain good dimensional accuracy throughout closed contours. The capabilities of the AM for glass machine are demonstrated on a thin-walled, multi-layer star pattern and a spring in which the material is printed in freespace without the need for support structures.

Effects of Vegetable Oil Based Cutting Fluid in Machining Kevlar Composite Material

Composite laminates are the first priority for many applications such as aerospace and aircraft structural components due to their superior properties. Composites offer a number of distinct advantages over more conventional engineering materials such as aluminium, steel etc. These benefits include higher specific strengths and stiffness’s, superior corrosion resistance as well as improved fatigue properties. However, the benefits of its application are limited by the difficulty of machining due to its poor thermal conductivity. Excess cutting temperature affects the dimensional accuracy of the drilled hole and deteriorates its surface finish. As a result, acquiring a good surface finish and dimensional accuracy greatly dependent upon the control of the cutting parameters and appropriate use of cutting environments. The objective of the article is to evaluate the performance of vegetable oil-based cutting fluid on machining Kevlar composite. Furthermore, machining responses are compared with dry and wet cutting conditions to have appropriate machining environment. Drilled holes were evaluated based on surface roughness and dimensional accuracy. Apart from machining parameters, tool wear and chips formations also have been observed on given different machining conditions. Experimental investigation revealed that Vegetable based cutting fluid is better for surface roughness where machining accuracy deteriorate. Furthermore, tool wear and chips formation also improved significantly on vegetable based cutting fluid.

Early progress on additive manufacturing of nuclear fuel materials

Additive manufacturing of thorium dioxide has been investigated using a commercially available stereolithography-based 3D printer and photopolymer resin. Three-dimensional thorium dioxide objects have been printed with good dimensional accuracy. High-density thorium dioxide parts (>90% theoretical density) were achieved by sintering the 3D-printed parts. Despite significant shrinkage, the overall shape of the objects was maintained during sintering with slight distortion. Additive manufacturing is seen to have potential application for advanced nuclear fuel concepts with complex geometries.

Investigations for mechanical properties and biocompatibility of SS-316L implant prepared as rapid investment casting for batch production

In this work, a detailed procedure for the development of biomedical implant (SS-316L) by combining fused deposition modeling (FDM), chemical vapor smoothing (CVS), silicon molding (SM) and investment casting (IC) for batch production has been outlined. In spite of being biocompatible and bioactive within the body, the implant must possess good surface quality and dimensional accuracy along with sufficient hardness in order to reduce the wear inside the body. So in this research work, investigations have been made on the surface finish, dimensional accuracy and hardness of the implants by varying two controllable factors of the IC process (drying time of primary coating and mould thickness). The tolerance grades for the selected dimension of the casted implants were within the allowable range as defined in UNI EN 20286-I (1995) standard of ISO. The process capability indices (Cp and Cpk) values greater than 1.33 for the surface hardness and radial dimension indicated that the proposed process is statistically controlled. Further, in order to evaluate the biocompatibility, an in vitro study was conducted to ensure the attachment of mouse embryonic fibroblasts cells (NIH-3T3) to the casted samples. The results of invitro study indicated that samples were capable of supporting cell adhesion and cell proliferation and hence can be used for tissue engineering.

Effects of tool electrode size on surface characteristics in micro-EDM

Micro-electrical discharge machining (micro-EDM) is one of the most effective and economical processing methods for micro-features with good dimensional accuracy and repeatability. During micro-EDM, the energy stored in stray capacitance is significant due to the low discharge energy. The stray capacitance changes as tool electrode size changes, thus affecting machining performances; this is the so-called scaling effect in micro-EDM. The effects of tool electrode size on surface characteristics tend to be ignored although it is significant. In this study, micro-EDM experiments were conducted using tool electrodes with different diameters. When machining with lower energy, the tool electrode size exerted significant influence on surface roughness and material migration—scaling effect was significant in low energy discharge. When machining in deionized water, this scaling effect was weakened due to larger discharge gap and ability to easily remove the melted material. The results presented here may provide a better understanding of micro-EDM scaling effect in aspect of surface topography, as well as a reference for building accurate machining performance prediction models of micro-EDM.

The role of powder layer thickness on the quality of SLM printed parts

Achieving good mechanical properties as well as the dimensional accuracy and the smooth surface quality of selective laser melting printed parts with minimal post treatments are essential in additive manufacturing. In the present study, Inconel 718 samples with different powder layer thickness (20, 30, 40 and 50μm) were additively fabricated using 3D Systems ProX-300 machine. The results reveal that the lower the layer thickness, the denser and good dimensional accuracy were achieved. Marginally higher mechanical properties and microhardness were also obtained at the lower thickness while the failure strain was still high. This can be explained through significant change in the microstructure due to different cooling rate and thermal cycles. In addition, the formation of ɤ′ and ɤ″ intermetallic phases, which were well distributed in the matrix and grain boundaries, during heating/cooling, gave rise in the strengths. Fractography shows the plastic deformation band due to work hardening and the crack initiation sites at sub-micro/micro pores, lack of fusion areas and the boundary of unmelted particles. The study would guide engineers balance their options between the production rate and the building parts’ quality.

3D-printed rib-enforced shell sand mold for aluminum castings

A rib-enforced shell mold for castings is proposed to replace the traditional dense mold. The 3D printing methods of sand mold make this new mold design a reality. The rib-enforced shell mold has been applied to cast a stress frame specimen of Al alloy A356. The effects of rib-enforced shell sand mold and traditional dense mold on the cooling of this casting have been investigated and compared. The results show that the cooling efficiency of the casting increases significantly by using rib-enforced shell mold, and approximately 40% cooling time is saved in natural condition and 35% further is saved in air blowing condition for the stress frame specimen before shakeout. This mold makes it possible to adjust the cooling condition of interested locations. It ensures fast and uniform cooling of the casting which can improve production efficiency and reduce deformation and residual stresses of the casting. Temperature distribution in the rib-enforced shell sand mold during the solidification was measured by an infrared imaging camera. The produced casting has good dimensional accuracy and surface quality. Meanwhile, nine-tenths of the sand is saved per mold.

Investigation of dimensional variation in parts manufactured by fused deposition modeling using Gauge Repeatability and Reproducibility

In the additive manufacturing (AM) market, the question is raised by industry and AM users on how reproducible and repeatable the fused deposition modeling (FDM) process is in providing good dimensional accuracy. This paper aims to investigate and evaluate the repeatability and reproducibility of the FDM process through a systematic approach to answer this frequently asked question. A case study based on the statistical gage repeatability and reproducibility (gage R&R) technique is proposed to investigate the dimensional variations in the printed parts of the FDM process. After running the simulation and analysis of the data, the FDM process capability is evaluated, which would help the industry for better understanding the performance of FDM technology.

Optimization of Micro EDM Drilling Process Parameters for Titanium Alloy by Rotating Electrode

Present era demands better quality of micro holes and good dimensional accuracy with regards to drilled workpiece. Micro EDM drilling utilizes thermal effect rather than mechanical force to remove material, so it is suitable for machining hard materials and is free from burr formation. Main problem encountered in micro EDM drilling is removal of debris particles, hence to overcome this problem electrode rotation method is used. This paper presents the experimental study for optimization of micro EDM drilling of Titanium alloy (Ti6Al4V) by using copper tungsten (CuW) electrode. Planning of experiment was done using response surface methodology (RSM) based central composite design (CCD) for analyzing effect of process parameters like pulse on time, discharge voltage, capacitance and electrode rotation speed on responses such as material removal rate (MRR), side gap width and taper ratio. ANOVA was performed to find the influencing process parameters. For MRR discharge voltage, capacitance and electrode rotation speed are influencing parameters. While side gap width is influenced by pulse on time, capacitance and electrode rotation speed whereas taper ratio is influenced by pulse on time and capacitance. The optimised values of process parameters viz pulse on time, discharge voltage, capacitance and electrode rotation speed for MRR, side gap width and taper ratio with single objective and multi-objective optimization are reported for Hyper 15W machine.

“Performance Comparison of Sol-gel with White Alumina Abrasives for Grinding of Super Duplex Stainless Steel (SDSS)”

Super duplex stainless steel (SDSS) serves different applications in industry categories like oil and gas, offshore platforms, naval, nuclear, pharmaceutical, mining, etc. due to its high strength, resistance to pitting and stress corrosion cracking properties. The two-phase microstructure of SDSS along with the other alloying elements makes this a difficult-to-machine material. The above-mentioned applications require finished components with good dimensional accuracy and surface finish. Traditionally, grinding process is used as a final machining process to achieve the prescribed tolerance requirements. In the current industrial practice, the grinding wheel with fused white alumina grains is most widely used for finishing of ferrous components. In spite of its acceptance in industries, there is a need for an abrasive grain with extended redress life for grinding a wide variety of steel grades. To cater for this requirement, sol-gel alumina abrasive grains were introduced which has a prolonged redress life due to its high fracture toughness characteristics. In this paper, the performance of the sol-gel alumina grinding wheel is compared with the white alumina wheel for grinding of SDSS material. To compare the performances of both the grinding wheels, indices such as grinding force, specific grinding energy, surface roughness, grinding ratio, and grinding efficiency were calculated based on the experimental work. The results obtained indicate that grinding wheel with sol-gel alumina grains performed better than the fused white alumina grains.

Shrinkage Compensation Study for Performing Machining on Additive Manufactured Parts

The main issues of parts made by extrusion based additive manufacturing techniques is the poor surface finish and dimensional accuracy. The current study presents a hybrid additive subtractive technique in which part is manufactured in additive manner followed by the subtractive process to improve the finish and accuracy. During subtractive operation, shrinkage in the fabricated parts was the main issue which needs to be addressed for performing proper machining. Therefore, present paper aims to study the shrinkage in the fabricated parts so that hybrid toolpath can be modified by providing shrinkage compensation factor. In order to study shrinkage, nozzle temperature and raster angle were varied. The shrinkage was measured by comparing the CAD model and fabricated parts dimensions. Based on the obtained results, a shrinkage compensation factor was determined for each set of process parameters. Hybrid toolpath was modified by incorporating this factor and again experiments were performed. Experimental results indicates the good surface finish and dimensional accuracy in the fabricated parts which shows the effectiveness of approach.

Comparative experimental investigation and gap flow simulation in electrical discharge drilling using new electrode geometry

Abstract. This study presents experimental and numerical investigation on the effectiveness of electrode geometry on flushing and debris removal in Electrical Discharge Drilling (EDD) process. A new electrode geometry, namely side-cut electrode, was designed and manufactured based on circular electrode geometry. Several drilling operations were performed on stainless steel 304 using rotary tubular electrodes with circular and side-cut geometries. Drilling performance was characterized by Material Removal Rate (MRR), Electrode Wear Rate (EWR), and Tool Wear Ratio (TWR). Dimensional features and surface quality of drilled holes were evaluated based on Overcut (OC), Hole Depth (HD), and Surface Roughness (SR). Three-dimensional three-phase CFD models were built using ANSYS FLUENT software to simulate the flow field at interelectrode gap. Results revealed that the overall performance of side-cut electrode was superior due to improved erosion rates and flushing capabilities, resulting in production of deep holes with good dimensional accuracy and surface quality.