Metal Mold Research Articles

Comparative evaluation of sorption and solubility of Amalgomer CR and Cention N restorative material- An in vitro study

Introduction: The potential of direct restorative dental materials to resist masticatory force, without getting damaged and to remain unaffected after getting exposed to various media (chemical stability) in the mouth for a considerable period of time are important for their good clinical performance. Amalgomer CR is a ceramic reinforced posterior GIC having compressive, flexural and tensile strength close to that of amalgam. Cention N is a new material based on “alkasite” technology which is a subgroup of the composite resin. It is a novel bulk fill direct posterior restorative material. Every restorative material should meet the required ideal physical properties standards, among which water sorption and solubility are two important properties that influences the clinical durability of a restorative material. Chemical agents found in soft drinks and other beverages like coffee and tea can be exposed to restorative materials, continuously or intermittently. The modern dietary habit of frequent consumption of low pH carbonated drinks can alter the oral environment to an acidic range. Keeping all the above discussed factors in mind, this, in-vitro study was conducted to compare and evaluate the sorption and solubility of Cention N and Amalgomer CR in four direct solutions; Sprite, Pepsi, Coca Cola and artificial saliva. Aim: The aim and objective of this in-vitro study was to evaluate the sorption and solubility of Cention N and Amalgomer CR in four direct solutions; Sprite, Pepsi, Coca Cola and artificial saliva. Materials and methods: The materials that was used for this study are Cention N and Amalgomer CR. A total of forty samples of restorative material were prepared using a metallic mould and divided into two groups of twenty samples each (n=20); Group I: Cention N and Group II: Amalgomer CR. The weight before immersion in the test media (m1) was measured using digital analytical scale. Each group was subdivided into four subgroups (n=5) based on the test media they were immersed in; Subgroup 1: artificial saliva, Subgroup 2: Coco Cola, Subgroup 3: Pepsi, Subgroup 4: Sprite. Five specimens each of the test material were kept immersed in the test media for seven days. The weight of the samples after immersion (m2) in the test media after seven days and the final dry weight of the samples (m3) were measured. Sorption and solubility of Cention N and Amalgomer CR cement were calculated using ISO guidelines. Data was analyzed statistically using appropriate statistical tools. Results: In our study, both Amalgomer CR & Cention N showed values for sorption and solubility well under the values of ISO recommendations, however, Amalgomer CR had significantly more sorption and solubility when compared to Cention N. Among the test solutions used Sprite and Pepsi had the most degrading effect on Cention N and Amalgomer CR. Conclusion: The composition of material along with their setting / curing method and low pH carbonated drinks can influence the properties of direct esthetic restorative materials. In this present study, Cention N was marginally better when compared to Amalgomer CR.

Technology Forgiveness: Why emerging technologies differ in their resilience to institutional instability

Long-term public support may encourage the diffusion of emerging technologies by coordinating the generation of knowledge and providing patient funding, but unexpected policy changes may hinder private investment and even lead to situations of technology lockout. Leveraging archival data; insights from 45 interviews across academia, industry, and government; and 75 hours of participant observations, we develop insights about why institutional instability in Portugal affected the adoption of Polymer Additive Manufacturing (PAM) and Metal Additive Manufacturing (MAM) differently. In both cases, Portugal invested in the technology relatively early. While PAM has been widely adopted, including increasingly in high-tech applications, MAM adoption has been modest despite MAM's potential to greatly improve the performance and competitiveness of metal molds. From the comparison between PAM and MAM, we generate theory about technological and contextual factors that affect ‘technological forgiveness’, defined as the resilience of a new technology's adoption to institutional instability.

An approach for hydrophobic fixed abrasive pad based on layer-by-layer method

Fixed abrasive polishing pad plays an important role in planarization of the surface of integrated circuit and semiconductor substrate. This paper reports a systematic approach for fabricating the pad using polyurethane, metal mold and layer-by-layer curing without binders. The pad surface with uniformly and orderly arranged convexities is undamaged during the fabrication process. Because of using prepolymer with hydrophobic groups, self-conditioning, stable polishing process and no water swelling are observed during the polishing process. The experimental results show the material removal rate is 72.972 nm/min and the polished surface roughness is 0.007 μm for SiC wafer. It builds a basis for high efficient preparation technology on hydrophobic fixed abrasive pad.

Biomimetic Soft Polymer Microstructures and Piezoresistive Graphene MEMS Sensors Using Sacrificial Metal 3D Printing.

Recent advances in 3D printing technology have enabled unprecedented design freedom across an ever-expanding portfolio of materials. However, direct 3D printing of soft polymeric materials such as polydimethylsiloxane (PDMS) is challenging, especially for structural complexities such as high-aspect ratio (>20) structures, 3D microfluidic channels (∼150 μm diameter), and biomimetic microstructures. This work presents a novel processing method entailing 3D printing of a thin-walled sacrificial metallic mold, soft polymer casting, and acidic etching of the mold. The proposed workflow enables the facile fabrication of various complex, bioinspired PDMS structures (e.g., 3D double helical microfluidic channels embedded inside high-aspect ratio pillars) that are difficult or impossible to fabricate using currently available techniques. The microfluidic channels are further infused with conductive graphene nanoplatelet ink to realize two flexible piezoresistive microelectromechanical (MEMS) sensors (a bioinspired flow/tactile sensor and a dome-like force sensor) with embedded sensing elements. The MEMS force sensor is integrated into a Philips 9000 series electric shaver to demonstrate its application in “smart” consumer products in the future. Aided by current trends in industrialization and miniaturization in metal 3D printing, the proposed workflow shows promise as a low-temperature, scalable, and cleanroom-free technique of fabricating complex, soft polymeric, biomimetic structures, and embedded MEMS sensors.

Effect of stirrer geometry and stirrer position on tensile strength of aluminium matrix composites (AMCs) cast in sand mold and metal mold

The present study deliberates effect of stirrer geometry (SG) and stirrer position (SP) on tensile strength of AMCs developed using sand as well as metal molds. The reinforcement-matrix interface influence on tensile strength was also studied using XRD and SEM. It was observed that average tensile strengths of specimens casted in metal mold are 9.8% higher than the sand mold. The highest tensile strength was obtained at 45° SG and 40 mm SP for both mold conditions due to low intensity peaks of Al4C3 compound and absence of de-cohesion at the reinforcement-matrix interface.

Manufacture of polyurethane foam parts for automotive industry using FDM 3D printed molds

Metal molds have traditionally been used in the manufacture of polyurethane foam parts. This type of molds presents several disadvantages: have a high cost; need a long time for their manufacture; involve the use of release agents during the demolding operation. As an alternative, the use of molds manufactured by fused deposition modeling is proposed. These 3D printed molds have a poor surface finish, which complicates the demolding operation. To overcome this handicap, materials that can be chemically polished have been studied: acrylonitrile butadiene styrene and high impact polystyrene. Acrylonitrile butadiene styrene can be polished by exposure to acetone vapors and high impact polystyrene by immersion in limonene. This post-processing operation allows to reduce the surface roughness of the 3D printed mold. To simulate the industrial use of the mold, seven molding-demolding cycles have been performed. To measure the ease of demolding of each material, a pull-off test has been used. The results indicate that high impact polystyrene has less affinity with polyurethane foam than acrylonitrile butadiene styrene. In addition, although release agent is used in cycle 1, with high impact polystyrene specimens, it is not necessary to use it in cycles 2, 3 and 4; this means a saving of release agent. Furthermore, the chemical polishing of high impact polystyrene by immersion in limonene has several advantages: it is performed in a short time; it allows to obtain an excellent finish regardless of the initial surface roughness; it is done using a biodegradable solvent of organic origin. To experimentally demonstrate the viability of the proposed solution, a mold for the back of a car seat has been printed in high impact polystyrene via fused deposition modeling and chemically polished by immersion in limonene (1min); the geometrical deviations generated were less than 1mm.

Effect of tin addition on corrosion resistance and microstructure of Cu-based shape memory alloy

Abstract This research investigates the effect of tin addition on corrosion resistance and micro structure of Cu-Al-Ni shape memory alloy with addition three different percentages of Tin (0.3, 1 &3)wt% to the base alloy. These alloys were prepared by casting and pouring in the metallic mold under argon atmosphere, then the prepared ingots were homogenized and machined by wire cutting into a small samples for corrosion test. X-ray diffraction inspection and scanning electron microscope were used for microstructural observations. Corrosion tests were carried out in sea water (3.5 wt% NaCl solution) at three different temperatures (25, 40 and 60) °C. The results showed that the corrosion resistance increased with addition percentage of tin metal and with rising temperature, It was observed that the 3% tin addition gave the best results in corrosion rate with rising temperature upto 60 °C and also in microstructure the same percentage gave a fine grain size Then the 0.3% Tin Addition and Finally the 1% Tin Addition.

Novel and simple technique for interfacial shear strength of liquid-solid compound casting specimen

A novel testing technique for the interfacial shear strength of the liquid-solid compound casting specimen was designed. Two different bimetallic materials specimens were fabricated and subsequent cut for interfacial shear testing. To ensure the easy cutting and testing of bimetallic specimen, two kinds of bearing materials were cast into metallic mold contain two different ferrous solid substrates. Direct tinning process using a mixture of tin powder and flux was applied on the solid substrates before pouring the liquid metal. In current novel testing technique, a minimum cutting and machining processing on the bimetal casting specimen were applied to minimize the internal stresses resulted from multi steps of cutting and machining processes that used in other interfacial shear strength testing techniques. Other previously used shear strength testing technique for bimetal materials was used for a comparison with the current technique. The present shear test technique offers simple and convenient approach for preparing and testing the bimetallic specimens.

Pre-heating by defocusation of the CO2-Laser polishing beam: an experimental report from the lab-floor -INVITED

The laser beam polishing for glass and plastics is a purely thermal process and melts the ground or lapped structures to a depth of limited extent. This results in a smoothing of the surface, whereby the 1st - 4th order shape deviations can be corrected very well and transparent surfaces are created. The process is excellently suited for quartz glasses and other optical glasses with a low coefficient of expansion α. Furthermore, thermoplastics or metallic molds for injection molding and precision molding applications can also be polished with the laser beam. On the other hand, special measures are required for glasses with a high α, e.g. preheating of the component. For the investigations, a defocused laser beam was used for the defined preheating of glasses with high linear expansion coefficients. After reaching the material-specific preheating temperature, the laser beam was focused and the polishing process started. A defined cooling process follows again with a defocused beam. In this way, a ground biconvex lens made of boron crown glass was successfully polished. The laser-polished surfaces have an RMS value of 1- 3 nm. The polishing process can be used very flexibly. Likewise, very differently shaped optical components can be polished. The newly developed polishing regime is transferable to other optical glasses with high linear expansion coefficients.

Application of Niyama criterion for predicting of shrinkage porosity of shaped castings

Method for determining of the critical value of the Niyama criterion based on computational experiment is developed. It is found that the critical value of the Niyama criterion depends on the alloy cooling conditions and therefore is applicable only to the given technological process. The critical values of the Niyama criterion for casting s made of ML10 and 14Kh17N2L alloys obtained in permanent metal moulds and in moulds of coldhardening mixtures are determined. The obtained results are confirmed on shaped casting.

Extended-pour and conventional alginates: effect of storage time on dimensional accuracy and maintenance of details.

ABSTRACTObjective: This study aimed to evaluate the dimensional stability and maintenance of details of conventional and high stability alginates up to 5-day storage. Methods: Two types of alginates were selected (n=10) for this study, conventional (Hydrogum) and high stability alginates (Hydrogum 5), which were produced with the aid of a cylindrical metal block and a ring-shaped metal mold (Specifications 18, 19, and 25, ANSI/ADA). Ten images were obtained from the molds for the dimensional stability test, which were taken immediately after their production and at each different storage periods (15 min, 24 h, 48 h, 72 h, 96 h, and 120 h) by a digital camera. The specimens were kept hermetically sealed in plastic bags (23°C) and then used to obtain 140 (n=70) dental stone models, used in the detail reproduction test, in which the angular accuracy of three grooves (20 µm, 50 µm, and 75 µm) was observed at each period. The details reproduction accuracy was classified using a predetermined score classification. Measurements of dimensional changes were made in the Corel DRAW X6 program. The data were submitted to the Student’s t-test (α?#8197;= 0.05). Results: A statistically significant difference concerning the size of the matrix was observed after 24h for both alginates, and a statistically significant negative linear dimensional change (contraction) was verified after 24 h of storage (1.52% for the high stability alginate, and 1.32% for the conventional alginate). The high stability alginate kept the full details for 72 hours, while the conventional alginate, for 24 h. Both alginates reproduced the 75 µm groove at all storage periods. Conclusion: Impressions made with both alginates presented satisfactory clinical results when the alginates were immediately poured.

Технологія одержання тонкостінних виливків з високоміцного чавуну в облицьованих кокілях з використанням внутрішньоформового модифікування розплаву

Технологія одержання тонкостінних виливків з високоміцного чавуну в облицьованих кокілях з використанням внутрішньоформового модифікування розплаву

Comparative evaluation of shear bond strength of acrylic teeth with heat polymerized acrylic resins using different surface treatments and curing cycles – An in vitro study

Purpose: This study evaluated the bond strength of acrylic resin denture teeth to heat cure denture base resin processed under different curing cycles and after various surface treatments on the bonding surface area of acrylic denture teeth.Materials and Methods: A two-piece metal mold of 35 mm length and 12 mm diameter was fabricated to standardize the attachment of teeth at 45°. Ninety such wax cylinders were obtained and were randomly divided and coded into three groups of 30 samples each: Group “A” – the “Control” group, Group “B” – the “MMM” group, and Group “C” – the “Acetone” group with Subgroup 1 – processing with short curing cycle and Subgroup 2 – processing with long curing cycle in each group. These 90 wax cylinder specimens were then flasked, dewaxed as per the standard protocol and surface treatment of teeth, and curing was done. The samples were tested in a universal testing machine.Results: ANOVA analysis inferred that there was a statistically significant difference between the mean bond strength values among the groups.Conclusion: Analysis of mean bond strength values reveals that the mean bond strength values of acetone were significantly higher (P < 0.05) when compared to the other groups.

Comparative evaluation of the effectiveness of denture cleansers on surface hardness of permanent silicone denture liners – An In vitro study

Aim:This study aimed to determine the effect of three commercially available denture cleansers on surface hardness of two different silicone denture liners at various time intervals.Materials and Methods:A total of 120 cylindrical specimens of permanent silicone-based soft liners were prepared from a custom made metal mold with dimensions of 15 mm × 10 mm, of which 60 specimens were fabricated using Voco™ and the remaining 60 specimens with Molossil™ permanent denture liners. All specimens were divided into four major groups based on cleansing treatments, comprising 30 specimens each. And then, all cleansers dissolved in 250 mL water as recommended by the manufacturer. Specimens of the first group were cleansed daily by rinsing with water and second group with Periogard™ denture cleansing solution and third group with Secure™ denture cleansing solution and the fourth group with Polident™ denture cleansing solution. Specimens of all groups were tested on 1st week, 1st month, and 6th month time interval using a Shore A Durometer. Three readings were noted for each sample and the mean of those readings was taken.Results:Surface hardness of all the samples was significantly higher after a period of 6 months irrespective of the cleansing treatment. Statistically significant changes were observed between Polident™, Secure™, and Periogard™ denture cleanser groups over control with time. Minor changes were observed in surface hardness of Voco™ denture liners as compared to Molossil™ soft liners for all groups, as time progressed.Conclusion:Voco™ soft denture lining material can be performed significantly better than Mollosil™ soft denture lining material in all cleansing treatments and Polident™ denture cleanser has the least effect on surface hardness of soft liners than Periogard™ and Secure™ denture cleansing agents.

Comparison of Different Finishing-Polishing Systems on Surface Roughness of Nanofilled Composite Resin

Aim: This in vitro study was conducted to evaluate the effectiveness of different finishing and polishingsystems on the surface roughness of nanofilled (Z350XT) composite resin.Materials and Methods: A total of 60 disc-shaped samples were prepared in composite resin usingstandardized cylindrical metal mold (10 mm in diameter and 2 mm thick). The specimens were randomlydivided into six groups (n= 10): Group 1- Mylar strip, Group 2- Sof-Lex polishing system, Group 3- SuperSnap polishing system, Group 4- OptiDisc polishing system, Group 5- Opti1Step polishing system andGroup 6- OneGloss polishing system. The average surface roughness (Ra) of each specimen was measuredthree times and the mean Ra values were determined using a surface profilometer.Results: According to the one-way analysis of variance, surface roughness was in the following order:Mylar strip < Super Snap polishing system < OptiDisc polishing system < Opti1Step polishing system <SofLex polishing system < OneGloss polishing system. This difference in surface roughness was statisticallysignificant (P < 0.05) in all the six experimental groups.Conclusion: Composite surface roughness depends on the composition, number of steps and flexibility ofthe finishing and polishing system used.

The Effect of Mechanical Vibration on Casting Properties of Grain Refined A356 Alloy

In this study, it was aimed to have the desired microstructure at low cost (fine and spherical) of aluminum alloys which have a wide usage in engineering materials and a wide variety of production methods. Al5Ti1B was added to the A356 aluminum alloy melted in a 700 °C resistive furnace with Ti content of 0.1, 0.2 and 0.3% by weight. Casting was performed on a 20, 10 and 5 mm cross-section metal mold placed on a vibration table producing a mechanical vibration of 50 Hz fixed frequency and 1.5 mm amplitude, vibration and non- vibration. Microstructural investigations on the cross-sections of the final casting products were carried out in two stages. In the first step, the distance between the secondary dendrite arms (SDAS) and the length of the secondary dendrite arms (SDAL) were measured on the images taken by optical microscope. In the second stage, EDS analysis was performed by SEM. Hardness measurements of the samples were made by Brinell method and the relationship between the microstructure and hardness values was tried to be revealed. SDAS and SADAL values decreased due to Ti content and section thickness. Accordingly, hardness tends to decrease as it progresses from thin section to thick section.

Manufacturing of Compound Parabolic Concentrator Devices Using an Ultra-fine Planing Method for Enhancing Efficiency of a Solar Cell

Various structural patterns are used to control light properties during propagation. In particular, when light is trapped and concentrated onto solar cells, they generate more electricity than without concentration. Since the sun moves continuously, a compound parabolic concentrator (CPC) can enhance the efficiency of solar cells by light-trapping and concentration because a CPC minimizes optical loss by reducing the reflection and the scattering on the surface of solar cells. However, CPC devices are generally expensive to manufacture and are too large in size to be used for applications requiring portability. Here, we developed a novel manufacturing process for a small CPC device and verified the enhanced efficiency of solar cells. Based on ultra-fine planing and injection molding, this process is an efficient method for mass production because it relies on replication. Two metal molds were precisely machined using an ultra-fine planing method with a diamond tool, and a CPC device was accurately manufactured by injection molding at low cost and within one minute. The variation of the specific cutting resistance during machining of the metal molds increased by four times, and the minimum uncut chip thickness decreased from 1.3 to 0.5 μm, which is called a size effect. The finished CPC device exhibited a surface roughness less than 40 nm and showed high optical efficiency in virtue of light-trapping. Finally, the efficiency of a solar cell with the CPC device was enhanced about 10%.

Influence of Rare Earth Additions to an Inconel 718 Alloy

AbstractThis work analyzes the effect of rare earth additions to an Inconel 718 superalloy; for this purpose, two 8 kg ingots of a commercial composition of Inconel 718 were made in a vacuum induction furnace. One of them (In718) with the base composition and the other one (In718RE) with an addition of 0.04wt% of mischmetal (rare earths alloy based on cerium and lanthanum). Both alloys were cast into metallic molds into the vacuum chamber and let to solidify. The alloys were then solubilized for two hours at 1155 °C to eliminate deleterious phases, rolled at 1100 °C to get a reduction of 50% in thickness, then aged for 16 hours at 720 °C and 620 °C by 8 hours each. A complete microstructural characterization was undertaken by optical and electronic (SEM and TEM) microscopy and X-ray diffraction. Mechanical characterization was done by hardness tests, tensile and Charpy impact tests. Results show a slight improvement of the tensile and hardness values for the alloy with rare earth additions. However, no notorious difference was observed during the impact tests, since both alloys show the same values. These mechanical results are discussed in terms of the obtained microstructure. Both alloys are mainly composed by γ, γ´, γ´´ and carbides. It was observed that primary carbides nucleate rare earth particles; therefore, higher number of carbides and of larger size (according to a size distribution) are observed in the alloy with rare earth additions. The presence of such carbides prevents the grain growth during the thermomechanical processing which in turn improve the mechanical properties.

Experimental investigation of hot tensile properties of Al-8Si-0.4 Mg alloy with varying Ni addition

An examination was carried out to decide the impact of Ni expansion and differing test temperature on the hot tensile properties of the cast Al-0.4 Mg-8Si alloy. The Al-0.4 Mg-8Si combination was softened in an electric furnace and Ni was added to the liquefy. The liquefy was cast in a metal mould. The cast samples were solutionised at 537 °C for 12 hrs and after that aged for 100 hrs. The hot tensile properties were resolved at 200, 250, 300 and 350 °C. The microstructure was observed utilizing an optical magnifying lens and the stages displayed in the microstructure were distinguished utilizing SEM, energy dispersive spectroscopy (EDS), XRD and TEM. The eutectic Si morphology was refined and a transitional stage Al3Ni was observed. Ultimate tensile strength (UTS) and yield strength (YS) expanded and %elongation (%El) expanded imperceptibly with expanding Ni expansion, though UTS and YS diminished and %El expanded insignificantly with expanding test temperature. It is reasoned that the Ni expansion altogether enhances the hot tensile properties of the base Al-8Si-0.4 Mg alloy and hot elasticity diminishes with expanding test temperature.

Simulation of lead Antimony Alloy Solidification and its Experimental Validation

The solidification of metals continues to be a phenomenon of great interest to physicists, metallurgists, casting engineers, and software developers. It is a non-linear transient phenomenon, posing a challenge in terms of modeling and analysis. During the solidification of a casting in a mould, the heat-transfer between the casting and the mould plays a vital role. This paper attempts to study heat flow within the casting, as well as from the casting to the mould, and finally obtains the temperature history of some points inside the casting. The most important instant of time is when the hottest region inside the casting is solidifying. ProCAST software has been used to obtain the temperature distribution in the casting process by performing Transient Thermal Analysis. In this research work, solidification of lead-2wt%antimony alloy has been carried out in the different sizes of metallic mold to predict the formation of shrinkage during solidification. Theoretical results have been validated experimentally for a particular case of lead-2wt%antimony alloy solidification. Results obtained by simulation software are compared with the experimental reading of temperature and found to be in good agreement. Voids appeared at the top and isolated area of castings for the defect-free direct method used in this study.