Resin Mold Research Articles

Towards bone replacement materials from calcium phosphates via rapid prototyping and ceramic gelcasting

Biomimetic porous scaffolds made of calcium phosphate mineral are promising structures to develop bone replacement materials. In order to fabricate scaffolds with a strut size of 450 μm, we used a stereolithographic technique which selectively polymerises photosensitive liquid resin by visible light to produce casting moulds for ceramic gelcasting. These moulds were filled with a water based thermosetting ceramic slurry which solidifies inside the mould. After burning the resin mould and sintering, hydroxylapatite structures with designed, fully interconnected macroporosity were obtained. The preosteoblastic cell line MC3T3-E1, derived from mouse calvariae, was used to test for biocompatibility in cell culture experiments. The cells were seeded on the scaffolds immersed in the culture medium and cultured for 2 weeks. Thereafter the cells on the scaffold were fixed and investigated by histological methods. The osteoblast-like cells were found to cover the whole external and internal surface of the scaffold, they were embedded in collagenous extracellular matrix. The cells had in particular the tendency to fill any crack or opening and to generally smooth the exposed surfaces.

Simple technique of securing intraoral skin grafts

Small defects following intraoral resection are often resurfaced by skin grafts. Skin grafting has the advantage of ease of harvest with minimal additional operating time and post-operative hospital stay, an acceptable functional cosmetic result, and the ability to survive post-operative radiation 1. In addition to adequate vascularity of the recipient area, the most important aspect for graft survival is immobilization and adherence of the graft to the defect. However, in the oral cavity due to the uneven wound bed and constant mobility of the cheek, the graft is not completely immobilized. In addition, the salivary secretions tend to accumulate beneath the graft, separating the graft from the bed. Graft-failure can be prevented by immobilizing the graft and closing up any potential dead space that might lead to separation 2. A variety of methods have been described for immobilization and bolstering the graft to the wound. Many types of stents have been used varying from the simple cotton balls, resin molds, and foam pads, to complex stents like metal, plastic, and dental liner 34. The traditional tie over bolster technique described by Schramm and Myers involves fixation of the skin graft to the raw area, followed by placement of non-absorbable silk sutures from the adjacent mucosa, which are then tied over the bolster 1. However, the placement of this tie over sutures requires adjacent normal mucosa for anchorage, which may not be sufficient especially in the gingivo-buccal sulcus. Although external fixation of the stents to the cheek has been described, this results in ugly scarring of the cheek 2. We describe a simple technique of fixation of the skin graft in the oral cavity, which avoids the placement of additional tie over sutures and in our opinion results in better anchorage.

Resin Infusion Between Double Flexible Tooling: Evaluation of Process Parameters

Manufacturers of lean weight vehicular structures are discovering the advantages of utilizing the high strength to weight ratios found in composite materials. However, traditional closed mold techniques require a long cycle time and relatively expensive tooling. This paper reports on a new technique called Resin Infusion between Double Flexible Tooling (RIDFT). In this innovative process, the resin infusion and resin-fiber wetting are finished between two flexible tools in a two dimensional flat shape and then the entire wetted reinforcement and flexible tooling is formed into a specified part shape by using a vacuum. This process avoids complex resin flow and mold filling issues and saves mold preparation and fiber stacking time. Using a RIDFT prototype, several components were produced. A larger industrial RIDFT machine was constructed to establish its viability for large component manufacture. An evaluation of production parameters, including infusion pressure, resin temperature, number of fiber layers and hardener content, ascertained their effect on mechanical properties and infusion times for the manufactured parts. The interaction between the hardener and fiber layers were found to directly affect tensile strength. The interaction between hardener and infusion pressure was also shown to affect tensile strength.

Epitaxial Lift-Off of GaAs/AlGaAs Films with Vertical Cavity Surface Emitting Lasers for High-Density Packaging of OptoElectronic Interconnections

We have developed a method for epitaxial lift-off of GaAs/AlGaAs films with vertical cavity surface emitting lasers (VCSELs) that enables device characteristics to be evaluated before and after epitaxial lift-off. The method is also utilized in combination with a technique that fabricates a deep hole in GaAs substrate to enable light emission at a wavelength of 850 nm. Thermal resistances of the 10-µm-thick VCSELs analyzed by emission peak wavelength shift are estimated at 0.89–0.90 K/mW for devices buried in resin mold and 0.76–0.86 K/mW for devices without resin mold, respectively. These values are 20–40% larger than that of VCSELs before epitaxial lift-off. The emission peak shifts of these thin-film devices do not exceed 2 nm, indicating that the method is applicable to optoelectronic interconnections requiring high-density packaging.

Mesolevel analysis of the transition region formation and evolution during the liquid composite molding process

Liquid Composite Molding is a composite manufacturing process in which fiber preforms consisting of stitched, woven or braided bundles of fibers, known as fiber tows, are stacked in a closed mold and polymeric resin is injected to impregnate all the empty spaces between the fibers. An important step is to ensure wetting and saturation of all the fiber tows and regions in between them. Mesolevel analysis refers to study at the order of a fiber tow. Numerical simulations at the mesolevel are conducted by incorporating the governing equations for free boundary flows around and inside a fiber tow into a set of subroutines. The simulation can track the advancement of the resin front promoted by both hydrodynamic pressure gradient and capillary action. Efficiency and appropriateness of several stabilization techniques is explored. Numerical results are in good agreement with reported experimental studies. The results clearly show that wicking flow plays an important role at the mesolevel and cannot be omitted.

Flexural properties of denture base polymers reinforced with a glass cloth–urethane polymer composite

Objectives. A newly designed light-cured reinforcement made from urethanemethacrylate oligomer and woven glass cloth has orthotropic anisotropy. This is produced for incorporation into the outermost position under the greatest tension in denture base resins. In this study, the flexural properties of self-, heat-, and light-curing reinforced resins were determined. Methods. The silanized glass cloth was soaked in urethanemethacrylate oligomer containing camphorquinone and 2-(dimethylamino)ethylmethacrylate. It was sandwiched between two pieces of polyethylene film and pressed to form a reinforcement sheet 0.3 mm in thickness, which was light-cured and prepared using four different surface conditions: with or without the polyethylene film and with or without a bonding agent. The reinforcement sheet was fixed in a fluorocarbon resin mold 3 mm in thickness, which was filled with self-, heat-, or light-curing resin and cured. The cured laminated plate was cut for flexural testing (40×7×3 mm 3). A three-point flexural test was carried out at a crosshead speed of 2 mm/min and a span length of 30 mm. In this study, the glass fiber content was measured at percentages by weight because it was not possible to determine accurately the volume of the various polymers. Results. The baseline flexural strengths of the self-, heat-, and light-curing resins were 76.2, 68.6, and 55.6 MPa, respectively, and these values were increased to 271.7, 216.4, and 266.5 MPa by the reinforcement sheet. The baseline flexural moduli of self-, heat-, and light-curing resins were 2.0, 2.4, and 2.1 GPa, respectively. These values were increased to 7.2, 5.1, and 6.6 GPa by the reinforcement sheet. SEM photographs revealed good impregnation of the glass fiber within the polymer matrix. Significance. The differences in the flexural strengths and flexural moduli of the control and reinforced specimens were significant ( p<0.01).

The effect of a translucent post on resin composite depth of cure

Objective. To evaluate the effect of a light-transmitting post on the depth of cure of a resin composite. Methods. Acetate resin molds were filled with resin composite in which a light-transmitting post was inserted into the center and photopolymerized to the manufacturer's recommendations. Identical molds without a light-transmitting post were photopolymerized in a similar matter and served as a control. Molds were sectioned on a water-cooled, diamond saw at prescribed distances and the depth of cure was determined using a Knoop Hardness bottom-to-top ratio criterion. Data within each group were analyzed using 2-way (depth-by-distance) repeated measure ANOVA. Between-group contrasts (post versus no post) were accessed by a 3-way (2 within-subjects and 1 between-subjects) ANOVA with critical p=0.05. Results. The presence of the post did increase ( p<0.001) Knoop Hardness values in simulated apical regions as compared to a control. However, there was no difference in the depth of cure between the groups (3-way analysis p=0.2) and also when evaluated using an 80% bottom-to-top Knoop Hardness ratio. Significance. The results suggest that these posts may have a limited utility when judged against a Knoop Hardness ratio criterion.

ワイヤ流れに及ぼす封止用樹脂内フィラ粒度分布の影響

Plastic package has mainly been used in current IC package, and transfer mold is the mainstream of the molding technology. When high viscous mold resin flow into mold cavity during filling stage, bonded Au wire connected between chip and lead frame usually deform. This deformation is called ‘wire sweep’. Excessive wire sweep may cause defects such as electric short at semiconductor chip and wire. This paper describes effect of filler profiles involved mold resin on wire sweep.

Heuristic algorithm for determining optimal gate and vent locations for RTM process design

In the resin transfer molding (RTM) process, locations of gates and vents are important design parameters that have a great impact on the resin flow pattern and mold filling time. The resin flow pattern is crucial to the quality and properties of the final product. A good resin flow pattern can cover all dry areas in the mold with liquid resin; whereas, a poor flow pattern will lead to some dry spots, which directly result in defects. In this paper, a single gate, multiple vents location problem for 2-D RTM process design is formulated as an optimization model. A process performance index is introduced as the objective function to evaluate the flow pattern in a 2-D RTM process. The authors introduce the concept of general distance between any two locations within the mold. To avoid forming dry spots during the process, all potential vents are determined once a gate is given. A two-phase optimization method, called a graph-based two-phase heuristic (GTPH), is used to find the appropriate locations of the gate and associated vents. The results are compared with those from other methods such as genetic algorithms.

熱硬化性樹脂の信頼性解析(J01-3 熱変形と衝撃,J01 エレクトロニクス実装における熱制御および信頼性評価)

熱硬化性樹脂の信頼性解析(J01-3 熱変形と衝撃,J01 エレクトロニクス実装における熱制御および信頼性評価)

On-Line Characterization of Bulk Permeability and Race-Tracking During the Filling Stage in Resin Transfer Molding Process

Resin Transfer Molding (RTM) is widely used to manufacture polymer composite materials. In this process, the fiber preform is placed in a closed mold and thermoset resin is injected to saturate the preform. After the resin cures the mold is opened and the net shape composite part is obtained. With RTM, one is capable of making complex and high quality composite parts with short cycle times. However, by introducing more complexity into the part, one also introduces higher probability of disturbances, such as race-tracking of resin during impregnation along preform edges. This can lead to incomplete saturation of fiber preform forming flaws such as dry spots in the composite part. The strength and existence of race-tracking is a function of the fabric type, perform manufacturing method, and their placement in the mold. It can vary from one part to the next in the same production run and usually it is not repeatable. The characterization of race-tracking and preform permeability is a key input for simulation tools that optimize the gates and vents locations and for designing advanced sensing and flow control strategies. This paper describes a method to estimate the strength and location of race-tracking and characterize the preform bulk permeability during the resin impregnation stage of RTM. The approach can be described in two steps. The first step generates simulations off line that map the overall range of potential disturbances likely to occur during the injection. The second step uses sensors placed in the mold, which allow one to identify the simulation within the database that resembles the experiment in terms of the filling behavior during the filling stage on the manufacturing platform. In the final step, this information is used to estimate race-tracking strength and location as well as the bulk permeability. Both experimental and numerical case studies show the reliability and accuracy of this method. It could be utilized for a broad range of applications such as active flow control, vent location optimization, and process monitoring of mold filling processes.

Improvement and enlarging of the CFRP flywheel with superconducting magnetic bearings

Superconducting flywheel usually adopts carbon fiber resin mold plastic (CFRP) material that has the basic characteristics such as higher strength and lighter weight. Stabilized rotation of flywheel requires lower unbalance individually about flywheel and supporting disc. And supporting disc is needed to steadily follow the expansion of the inside diameter on the flywheel by centrifugal force and keep the concentricity of the flywheel and its own rotating axis. We developed the flywheel rotor, which was composed of CFRP flywheel, and partially spherical supporting disc made of high strength aluminum. They were combined with expanse fitting each other and most precisely machined to realize the extremely precise axial symmetric shape and enable to be supported and driven at the point near the center of gravity. We manufactured and confirmed that the flywheel rotor rotated up to peripheral speed of 628 m/s quietly without permanent set.

Effect of resin properties and processing parameters on crash energy absorbing composite structures made by RTM

The effects of resin properties and resin processing parameters on the crush behaviour of thermoset composite tubes manufactured using resin transfer moulding are considered. The aims were to quantify the performance of tubes produced over a broad spectrum of conditions and to correlate this performance to the properties of the material. The effects of the mould temperature, post-cure time and resin composition were investigated for random and engineered reinforcement fabrics. Relationships between Young's moduli and ultimate stresses of the material in tension and compression were established from plaques moulded under similar conditions. Random reinforcement fabrics gave higher specific energy absorption (SEA) levels than engineered fabrics, but were more sensitive to processing conditions. Epoxy absorbed more energy than vinyl ester. Vinyl ester absorbed more than polyester, and additions of vinyl ester resin to unsaturated polyester gave a linear increase in SEA. The ultimate compressive strength of the composite proved the best indicator of performance for the selected materials and processing conditions.

Measurement of Melt Temperature Distribution along the Cavity Thickness Direction by Using Integrated Thermocouple Sensor

Following the previous study, the resin temperature distribution through the thickness of a cavity was directly measured using an integrated thermocouple sensor. The following conditions were controlled in this study: (1) resin temperature and mold temperature, (2) surface roughness conditions and (3) cavity thickness.The conclusions of this present study are the following:(1) When the (incoming) resin temperature was raised at a fixed mold temperature, no peak was observed in the temperature distribution. However, when the mold temperature was appropriately adjusted at constant (incoming) resin temperature, a peak in the temperature distribution could develop. This peak was relatively insensitive to changes in the mold temperature.(2) Adjustment of the cavity surface properties from a satin surface finish to a mirror finish did not change the location of the temperature peak, but did alter the temperature distribution in the region between the temperature peak and the cavity wall.(3) When the cavity thickness was changed, the temperature peak was found to occur at the same distance from the cavity wall. It was also confirmed that the temperature distribution was relatively flat from the peak to the cavity wall.(4) The conclusions from the previous studies and the above results clarify that the following five factors cause the temperature peak phenomenon: (1) the crystallization temperature “Tc” or viscosity properties near the glass transition point “Tg”, (2) latent heat, (3) thermal conductivity, (4) resin temperature and (5) cavity thickness.

High Throughput Measurements of Polymer Fluids for Formulations*

ABSTRACTRapid prototyping of microfluidic handling devices has gained popularity due to the ability to quickly test and modify new design features several times in one day. At the NIST Combinatorial Methods Center (NCMC), we have modified common microfluidic fabrication techniques to extend their use to organic fluids. Ultraviolet (UV) curable adhesives were used to create molded resins with increased solvent resistance. This has allowed the preparation of new types of combinatorial libraries and development of new measurement methods to complement the small sample sizes of these libraries. Most importantly, it can be used to tie together multiple stages of the formulation process, from the synthesis of polymers to the measurement of complex-fluid properties, in small and inexpensive platforms. Our first demonstrations of this technology are in the areas of emulsions and polymer blends. Measurement techniques include light and x-ray scattering and rheology. Milli-fluidic handling and measurements will increase the dimensions of parameter space that are available to accurate and systematic study of polymer solutions. These capabilities will also enable the generation of new information in the field of polymer formulations, which is presently dominated by empirical knowledge.

樹脂(ゴム)成形品断面における新形態観察法(&lt;特集&gt;みせる技術)

樹脂(ゴム)成形品断面における新形態観察法(&lt;特集&gt;みせる技術)

Rapid Moulding Using Epoxy Tooling Resin

Rapid prototyping (RP) is fast becoming a standard tool in today's product design and manufacturing environment. Significant benefits in terms of lead time and cost savings have been reported with the use of RP technology. However, these benefits can be derived only during the design and planning stages of a new product where RP parts are produced in small quantities for design evaluation, form fitting, and marketing analysis. The high cost of raw material stock used in current RP systems makes them economically unsuitable even for small-batch production during the product evaluation and manufacturing stages. Further to this, the difference between the mechanical and physical properties of RP and traditional manufacturing materials limits the functionality of RP end products. Rapid tooling (RT) technology has opened up new cost-effective solutions for small-batch production. In this paper, a technique using a rapid soft-tooling approach, namely, aluminium filled epoxy resin tooling for injection mould preparation is successfully explored. An aluminium filled epoxy resin mould is evaluated and the characteristics of the injection-moulded end products are presented.

Measurement of Adhesive Force Between Mold and Photocurable Resin in Imprint Technology

In order to reduce the strong adhesive force between the mold and photocurable resin in UV-curable imprint lithography, release coating materials of the quartz mold and easy to release photocurable resin were examined. Furthermore, measurement methods of release properties of the imprint mold and photocurable resin were established using a tensile testing machine. The surface-treated slide-glass (SG) did not adhere to the resins and the adhesive forces were markedly reduced. For the release coating materials, the adhesive force for KP-801M was smaller than that for Aquaphobe CF. In the case of the photocurable resins, the adhesive force for PAK01 was smaller than that for TSR820. According to the measurement result of durability, Aquaphobe CF showed good durability compared with KP-801M using PAK01 as a photocurable resin. The fracture energies were measured by the double cantilever beam method, and the resultant values were 3.64 N/m and 2.77 N/m, respectively, for no-treatment SG and the surface-treated SG with Aquaphobe CF using PAK01 photocurable resin. The rectangular patterns of 1 µm×2 µm were imprinted with good fidelity without ripping on the PAK01 resin using a surface-treated quartz mold with Aquaphobe CF under 0.2 MPa pressure and 10 J/cm2 UV dose.

Processing of ceramics and composites by rapid prototyping

Injection moulding is accepted as one of the most important methods for shaping complex ceramic cores, which are used to form intricate internal cooling passages of gas turbine blades. But the relatively long lead time and high costs involved in the fabrication of hard tooling render it uneconomical for new products development and low-volume production. In the study, a rapid prototyping process is developed to fabricate complex-shaped alumina-based ceramic core by combining stereolithography (SL) with gelcasting. SL is utilized to fabricate an integral sacrificial resin mold, and gelcasting is utilized to form a wet ceramic core green body through polymerization of aqueous ceramic slurry. The freeze-drying process is adopted to treat the wet green body surrounded by the resin mold, the drying shrinkage is decreased, and the generation of crack can be prevented. The sintering shrinkage of ceramic core is controlled by adding magnesium oxide power and developing a novel sintering process. After the resin mold is burnt out, the complex-shaped alumina-based ceramic core is obtained.

Optimization of filling process in RTM using a genetic algorithm and experimental design method

AbstractIn the resin transfer molding (RTM) process, preplaced fiber mat is set up in a mold and thermoset resin is injected into the mold. An important issue in RTM processing is minimizing the cycle time without sacrificing part quality or increasing the cost. In this study, a numerical simulation and optimization process for the filling stage was conducted in order to determine the optimum gate locations. The control volume finite element method (CVFEM), modeled as a 2‐dimensional flow, was used in this numerical analysis along with the coordinate transformation method to analyze a complex 3‐dimensional structure. Experiments were performed to monitor the flow front to validate the simulation results. The results of the numerical simulation corresponded with that of the experimental quite well for every single, simultaneous, and sequential injection procedure. The optimization analysis of the sequential injection procedure was performed to minimize fill time. The complex geometry of an automobile bumper core was chosen. A genetic algorithm was used to determine the optimum gate locations in the 3‐step sequential injection case. Taguchi's experimental design method was also used for determining the pressure contribution of each gate. These results could provide the information on the optimum gate locations and injection pressure in each injection step and predict the filling time and flow front.