Mold Shape Research Articles

Orbital shape in intentional skull deformations and adult sagittal craniosynostoses.

Intentional cranial deformations are the result of external mechanical forces exerted on the skull vault that modify the morphology of various craniofacial structures such as the skull base, the orbits and the zygoma. In this controlled study, we investigated the 3D shape of the orbital inner mould and the orbital volume in various types of intentional deformations and in adult non-operated scaphocephaly - the most common type of craniosynostosis - using dedicated morphometric methods. CT scans were performed on 32 adult skulls with intentional deformations, 21 adult skull with scaphocephaly and 17 non-deformed adult skulls from the collections of the Muséum national d'Histoire naturelle in Paris, France. The intentional deformations group included six skulls with Toulouse deformations, eight skulls with circumferential deformations and 18 skulls with antero-posterior deformations. Mean shape models were generated based on a semi-automatic segmentation technique. Orbits were then aligned and compared qualitatively and quantitatively using colour-coded distance maps and by computing the mean absolute distance, the Hausdorff distance, and the Dice similarity coefficient. Orbital symmetry was assessed after mirroring, superimposition and Dice similarity coefficient computation. We showed that orbital shapes were significantly and symmetrically modified in intentional deformations and scaphocephaly compared with non-deformed control skulls. Antero-posterior and circumferential deformations demonstrated a similar and severe orbital deformation pattern resulting in significant smaller orbital volumes. Scaphocephaly and Toulouse deformations had similar deformation patterns but had no effect on orbital volumes. This study showed that intentional deformations and scaphocephaly significantly interact with orbital growth. Our approach was nevertheless not sufficient to identify specific modifications caused by the different types of skull deformations or by scaphocephaly.

Influence of supercritical debinding and processing parameters on final properties of injection-moulded Inconel 718

In the metal injection-moulding process, the thermoplastic polymer binder plays an essential role as it provides fluidity to the high-loaded feedstock and strength to maintain the moulded shape. The purpose of this study is to develop an environmentally friendly feedstock loaded with a super-alloy Inconel 718 powder. Different binder formulations based on polyethylene glycol (PEG), for its water solubility, and bio-sourced polymers were investigated. Poly(lactic acid)/(polyhydroxybutyrate-valerate) was investigated as a bio-sourced polymer because its miscibility with the PEG. The results are compared to a standard formulation using polypropylene and PEG developed by our research group. A micro powder of Inconel 718 (nickel-based super-alloy) was chosen to elaborate the feedstock. The chemical and rheological behaviour of the feedstock during the mixing, injection, and debinding processes were investigated, with tight control of each process. The comparative impacts of the two different debinding processes and optimum sintering parameters were investigated: one by water and one by CO2 in supercritical state. The supercritical debinding caused no damage to the components for all types of feedstock and decreased the time to remove the PEG from 48 h to 4 h. Finally, the density, microstructure, and hardness of the different samples after final heat treatment were compared. The microstructure was clearly optimized, as the γ″ phases were promoted inside the grains. The results show that the well-adapted binder and debinding process produces an Inconel 718 component with high mechanical properties (Vickers hardness of 341 ± 19 HV). Moreover, this approach can be used with other formulations, powders, and binder systems.

Controlled cooling of an aluminum alloy casting based on 3D printed rib reinforced shell mold

3D printing technology has been used for sand molding and core printing, but they simply substitute the traditional molding and core making method without changing the shape or size of the sand mold (core) and their dense structure. In this study, a new type of hollow mold based on 3D printing is presented. The new type of mold is a rib reinforced thickness-varying shell mold. This mold design can realize the controlled cooling of castings, i.e., different cooling rates at different areas, and improve the temperature uniformity of a casting after its solidification. Therefore, the performance of castings can be improved and their residual stress and deformation can be reduced. This kind of new mold was applied to a stress frame of A356 aluminum alloy. The 3D printed rib reinforced thickness-varying shell mold was compared with the traditional dense mold, and the castings obtained by these two kinds of molds were also compared. The experimental results showed that the rib reinforced shell mold increased the cooling rate of the casting by 30%, tensile strength by 17%, yield strength by 11%, elongation by 67%, and decreased its deformation by 43%, while sand consumption was greatly reduced by 90%.

Developing Metamodels for Fast and Accurate Prediction of the Draping of Physical Surfaces

In this paper, the use of methods from the meta- or surrogate modeling literature, for building models predicting the draping of physical surfaces, is examined. An example application concerning modeling of the behavior of a variable shape mold is treated. Four different methods are considered for this problem. The proposed methods are difference methods assembled from the methods kriging and proper orthogonal decomposition (POD) together with a spline-based underlying model (UM) and a novel patchwise modeling scheme. The four models, namely kriging and POD with kriging of the coefficients in global and local variants, are compared in terms of accuracy and numerical efficiency on data sets of different sizes for the treated application. It is shown that the POD-based methods are vastly superior to models based on kriging alone, and that the use of a difference model structure is advantageous. It is demonstrated that patchwise modeling schemes, where the complete surface behavior is modeled by a collection of locally defined smaller models, can provide a good compromise between achieving good model accuracy and scalability of the models to large systems.

Experimental and numerical studies on compaction of carbon fiber composite joint with variable cross‐section using thermal expansion process

For hollow composite with complex shape, thermal expansion process is usually used to ensure uniform compaction pressure and excellent processing quality. This study focused on compaction of carbon fiber/epoxy matrix composite joint with variable cross‐section using thermal expansion process. Three kinds of silicone rubber core molds were adopted and experiments were performed to study the effect of elastomer core mold on resin pressure distribution inside prepreg stack during process and processing quality of composite joint. Moreover, based on numerical analysis, thermal expansion behaviors of different core molds and compaction pressure on prepreg stack were studied. The results indicate that material properties and geometric structure of core mold significantly influence thermal expansion behavior of core mold and compaction pressure distribution on prepreg stack. Due to irregular shape of core mold, thermal expansion of core mold at the regions with different cross‐sections is obviously uneven. And core mold with large coefficient of thermal expansion and small compressive modulus is more likely to fill process gap and achieve uniform compaction pressure distribution on prepreg stack. Therefore, controlling thermal expansion behavior of core mold to improve processing quality of composite involves reasonable material properties of core mold and adjusting process gap at different cross‐sections of composite. POLYM. COMPOS., 40:E1057–E1074, 2019. © 2018 Society of Plastics Engineers

Design and Analysis of Hot Core Box Mold for New Energy Vehicle Motor Shell

To achieve rapid batch production with high-quality stability for the integral molding process of sand cores in low-pressure casting for the water-cooled aluminum alloy shell of new energy vehicle motors many process parameters were measured. The forming process and die structure of a circumferential sand core were analyzed. In addition, the electric heating power of each core box mold was accurately calculated using thermodynamic calculations. These details, combined with the three-dimensional shape of the core mold, the layout of the electric heating rod and the hole position for temperature measuring as well as the entire cylindrical waterway of a hot core box mold and the core way were designed to realize accurate control of the box temperature by adjusting the curing temperature and time parameters. Thus, improving the sand core curing quality and production efficiency, which will meet the casting specifications for mass production of the water-cooled motor shell.

Mould design for manufacturing of isogrid structures in composite material

In the transport industry, fuel consumption and emissions can be reduced introducing very light parts. An optimal solution to these problems consists in the construction of isogrid structures made of composite materials, whose manufacturing process is a critical step, since it can induce some damages that cause the rejection of the produced part. The forming technology, the necessary equipment and the process parameters must be carefully chosen, since they strongly affect the part quality. The mould shape has to be carefully designed since the part presents a complex geometry, due to the presence of ribs, that could present a bad compaction.The aim of this work is to introduce and verify through structural tests a design methodology for the manufacturing of isogrid structures made of composite materials. In particular, the mould groove geometry was defined in order to obtain the right compaction degree. Then, different experimental tests were carried out to determine the quality of the produced structures.

Biopolymer-Based Composite Materials Prepared Using Ionic Liquids.

Biopolymer-based composite materials have many potential applications in biomedical, pharmaceutical, environmental, biocatalytic, and bioelectronic fields, owing to their inherent biocompatibility and biodegradability. When used as solvents, ionic liquids can be used to fabricate biopolymers such as polysaccharides and proteins into various forms, including molded shapes, films, fibers, and beads. This article summarizes the processes for preparing biopolymer-based composite materials using ionic liquids. The processes include biopolymer dissolution using ionic liquids, regeneration of the biopolymer by an anti-solvent, formation of shapes, and drying of the regenerated biopolymer. In particular, the preparation and applications of biopolymer blend-based composite materials containing two or more biopolymers are addressed.

Passive control of wrinkles in woven fabric preforms using a geometrical modification of blank holders

Textile preforms have become materials of choice in numerous modern industries, partly due to their superior conformability onto complex 3D mould shapes. Maximum formability of this category of composite reinforcements, however, is still limited by defects such as wrinkling, which remains a challenging issue for composite designers during optimization of thermo-stamping operations. The aim of this article is to gain a deeper understanding of the effect of blank holding boundary condition on the extent of wrinkling as well as other local defects such as tow slippage and yarn jamming, and thereby to introduce a passive defect mitigation approach via geometrical modification of the blanks. To verify the applicability of the approach, a series of hemisphere forming experiments under unmodified and modified forming boundary conditions have been performed and compared on both single and multiple ply lay-ups, using a comingled polypropylene/E-glass thermoplastic plain weave.

Effect of Sodium Hydroxide and Mould Shape in Geopolymer Fabrication Made With Synthesised Local Clay for Water Filtration

The preparation and testing of geopolymer ceramic membranes for water separation is presented. Geopolymers are typically used in refractories and as precursors to ceramic formation, allowing the production of ceramic-like materials with low temperature processes. A new geopolymer material was synthesized using local clay from Sabah, Malaysia and its filtration performance was compared to a commercial clay fabrication. The synthesized formulation of geopolymer ceramic paste was made by mixing local metakaolin clay as a source of aluminosilicate with alkaline solution, and then curing in a sealed environment. The amorphous paste was crushed and moulded prior to firing at an elevated temperature up to 700C. The feasibility of this laboratory-fabricated geopolymer for water filtration applications was studied by evaluating its performance at different thicknesses and mould shapes of fabricated membrane using 8 to 16 Molar natrium hydroxide (NaOH) as the alkali activator in the synthesis of the geopolymer. The result found that increased molarity of sodium hydroxide results higher compressive strength and affect filtration rate. Improved filtration performance (subject to the shape and width of the geopolymer membrane) was found by analysis and separation rates of 47% for blue dye colour and 88% for turbidity were achieved when operated without pressure or pump.

Experimental Validation of Surrogate Models for Predicting the Draping of Physical Interpolating Surfaces

This paper concerns the experimental validation of two surrogate models through a benchmark study involving two different variable shape mould prototype systems. The surrogate models in question are different methods based on kriging and proper orthogonal decomposition (POD), which were developed in previous work. Measurement data used in the benchmark study are obtained using digital image correlation (DIC). For determining the variable shape mould configurations used for the training, and test sets used in the study, sampling is carried out using a novel constrained nested orthogonal-maximin Latin hypercube approach. This sampling method allows for generating a space filling and high-quality sample plan that respects mechanical constraints of the variable shape mould systems. Through the benchmark study, it is found that mechanical freeplay in the modeled system is severely detrimental to the performance of the studied surrogate models. By comparing surrogate model performance for the two variable shape mould systems, and through a numerical study involving simple finite element models, the underlying cause of this effect is explained. It is concluded that for a variable shape mould prototype system with a small degree of mechanical freeplay, the benchmarked surrogate models perform very well.

Fabrication of ordered submicrometer-scale convex lens array via nanoimprint lithography using an anodized aluminum mold

The fabrication of submicrometer-scale ordered convex lens array was demonstrated through nanoimprint lithography using an aluminum dimple array mold fabricated by etidronic acid anodizing and selective oxide dissolution. Highly-pure aluminum plates were anodized in a 0.2M etidronic acid solution at 260V for the formation of ordered porous alumina. The anodized specimens were immersed in a 0.2M CrO3/0.51M H3PO4 solution to dissolve the porous alumina, and an ordered dimple array measuring approximately 670nm in dimple diameter was obtained on the aluminum surface. Phosphonic acid-based self-assembled monolayers (SAMs) were coated on the aluminum dimple array as a release agent for nanoimprint lithography. The shape of the aluminum dimple array mold was transferred to a UV curable photopolymer by nanoimprint lithography. An ordered convex lens array, which corresponded to the negative shape of the dimple array, was successfully obtained by the removal of curable polymer. However, the polymer surface was contaminated with phosphonate molecules due to the multilayered phosphonate films being formed on the aluminum mold. This contamination can be avoided by ultrasonication of the aluminum mold before nanoimprint lithography.

Обеспечение износостойкости и усталостной прочности поверхностей при электроэрозионной обработке

This paper represents the results generalization of theoretical investigations in the matter of an electro-erosion processing impact upon operating properties of die mold shaping parts. A basic problem is wear-resistance and fatigue strength support at the electro-erosion processing of the products of these types. The analysis carried out has shown that the processing modes and a coefficient after an electro-erosion processing influence fatigue strength. A wear-resistance index is defined both by processing modes, and physical-mechanical properties of blank material. To ensure product operating characteristics a physical situation of complex parts processing should be defined through the choice of optimum modes for electro-erosion processing.

Simulation of Blowtorch Reflow of Fused Silica Micro-Shell Resonators

Fabrication of high-precision micro-shell 3-D resonators is a challenging task. We report a non-isothermal model and finite-element simulation results for the prediction of geometries of fused silica micro-shell resonators fabricated with a blowtorch molding process. The model considers coupling between thermal and mechanical aspects of the reflowing process and heat transfer at the fused silica/mold interface, which dramatically controls the final shape of the resonator. The model is successfully applied to investigate the production details of 3-D hemi-ellipsoidal shells of revolutions with eccentricity, such as birdbath shell resonators. Comparisons of numerical results with experimental observations demonstrate that the model can predict an overall trend of thickness distribution. The numerical model can be used to optimize shell geometry and thickness by changing different fabrication parameters, such as surface heat flux, conductivity of the mold material, and initial temperature of the mold. The simulation technique also allows the mold shape and design to be optimized to fabricate different micro-shell geometries and dimensions. The model clarifies the blowtorch molding capabilities and limitations for fabrication of hollow 3-D shell resonators. [2016-0251]

Assessing the thermoformability of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/poly(acid lactic) blends compatibilized with diisocyanates

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is a renewable alternative to conventional barrier packaging polymers due to its thermoplastic properties, biodegradability and gas barrier performance but its potential industrial applications are limited by its high price and difficult processability. A thorough study concerning the thermoforming ability of PHBV, and blends with poly(lactic acid) (PLA) incorporating three different diisocyanates as compatibilizers (hexamethylene diisocyanate, poly(hexamethylene) diisocyanate and 1,4-phenylene diisocyanate) is herein presented after component melt blending. A straightforward universal qualitative method is proposed to assess the thermoformability, based on a visual inspection of a thermoformed specimen and the ability to reproduce the mold shape, and the thermoforming window of the material. The results reveal a significant improvement in the thermoforming capacity and a widening of the thermoforming windows as the correct amounts of diisocyanates are incorporated. The barrier properties and the biodisintegrability of the blends was also studied, confirming a predictable slight decrease of the barrier performance when PLA is added, but without negatively affecting the disintegrability under composting conditions with respect to pristine PHBV.

The Impact of the Thickness of the Ceramic Shell Mould on the (γ + γ′) Eutectic in the IN713C Superalloy Airfoil Blade Casting

AbstractIn the study the wall thickness of ceramic shell mould influence on (γ+γ′) eutectic in the IN713C nickel-based superalloy airfoil blade casting was described.Two castings formed as a blade from two wax pattern assemblies were analysed. In the experiment in one pattern the thick ceramic layer was obtained on pressure side and in another one on suction side of the airfoil blade. The microstructure of the cross-sections of the castings were observed on polished and etched metallographic specimens. The microstructure and phases chemical compositions of specimens was analyzed by using the scanning electron microscope Hitachi S-4200 equipped with EDS. It was established, that wall thickness of ceramic shell mould affect size, shape and volume fraction of (γ+γ′) eutectic islands in airfoil blade made from IN713C superalloy.The analysis was provided in accordance to the typical statistical methodology [1].

Laser-Etched Designs for Molding Hydrogel-Based Engineered Tissues.

Rapid prototyping and fabrication of elastomeric molds for sterile culture of engineered tissues allow for the development of tissue geometries that can be tailored to different in vitro applications and customized as implantable scaffolds for regenerative medicine. Commercially available molds offer minimal capabilities for adaptation to unique conditions or applications versus those for which they are specifically designed. Here we describe a replica molding method for the design and fabrication of poly(dimethylsiloxane) (PDMS) molds from laser-etched acrylic negative masters with ∼0.2 mm resolution. Examples of the variety of mold shapes, sizes, and patterns obtained from laser-etched designs are provided. We use the patterned PDMS molds for producing and culturing engineered cardiac tissues with cardiomyocytes derived from human-induced pluripotent stem cells. We demonstrate that tight control over tissue morphology and anisotropy results in modulation of cell alignment and tissue-level conduction properties, including the appearance and elimination of reentrant arrhythmias, or circular electrical activation patterns. Techniques for handling engineered cardiac tissues during implantation in vivo in a rat model of myocardial infarction have been developed and are presented herein to facilitate development and adoption of surgical techniques for use with hydrogel-based engineered tissues. In summary, the method presented herein for engineered tissue mold generation is straightforward and low cost, enabling rapid design iteration and adaptation to a variety of applications in tissue engineering. Furthermore, the burden of equipment and expertise is low, allowing the technique to be accessible to all.

Development and characterisation of a biosourced feedstock of superalloy in metal injection moulding process

ABSTRACTIn the metal injection moulding process the binder plays the most important role. It provides fluidity of the feedstock and strength to keep the moulded shape. The goal of this study is to develop an environmentally friendly feedstock of superalloy Inconel 718. For this different binders formulations based on polyethylene glycol and biosourced polymers were studied. Polylactic acid was investigated as biosourced polymer due to his miscibility with the PEG. The results are compared to a standard formulation using polypropylene. The chemical and rheological behaviour of the binder formulation during mixing, injection and debinding process were investigated. Moreover, a powder of superalloy Inconel 718 was chosen to produce a feedstock. The feedstock was characterised like the binders and the interactions between the powder and the binders was also studied. The results show the well adapted formulation of polymer binder to produce a superalloy Inconel 718 feedstock.This paper is part of a special issue on the Advances in Materials and Processing Technologies (AMPT) 2015 and has subsequently been revised and extended before publication in Powder Metallurgy.

Improvement in Quality and Yield of the Low Alloy Steel Ingot Casting Through Modified Mould Design

The internal quality and yield in 4 ton steel ingot of 40cmd8 grade was studied by comparing its solidification in a square cross-section mould with a slender rectangular cross-section mould, using FEM simulation. The model predicted various solidification aspects like fluid flow, thermal and solidification profiles, mushy zone, local solidification time, porosity and piping for both the molds. The convective flow of the molten metal during solidification showed higher velocity in square ingot than rectangular ingot under similar conditions due to lower surface area to volume ratio that affected the heat transfer in the rectangular ingot. Higher amount of air gap between the ingot and the mould was formed in rectangular ingots. Lower microsegregation as measured in terms of local solidification time was observed in rectangular ingot. Based on microstructure parameters such as thermal gradient and rate of solidification, it was found that the square ingot had more equiaxed zone than rectangular ingot. The rectangular ingot solidified at a faster rate and showed more propensity for core porosity than the square ingot. The ingot yield was improved by 3.6% through mould shape modification from square to rectangular. Model was validated to limited extent by carrying out a typical experiment with square mould.

Model supporting the use of pressure in the hot slumping of glass substrates for X-ray telescopes.

Thin glass foils are nowadays considered good substrates for lightweight focusing optics, especially for X-ray telescopes. The desired shape can be imparted to the foils by hot slumping, a process that replicates the shape of a slumping mould. During thermal slumping, when the glass and the mould come into contact, ripples in the glass surface appear spontaneously if the thermal expansions are mismatched. In our hot slumping setup, pressure is applied to ease the mould shape replication and to enhance the ripple relaxation. Starting from an existing model developed to explain the ripple formation in hot-slumped glass foils without pressure, we have developed a model that includes the pressure to support our experimental results.