Metal Mold Surface Research Articles

Investigation of metal concentration distribution and corresponding health exposure assessment of fabricated metal product manufacturers

The fabricated metal product industries were identified as producers of variable and heterogeneous pollution. Workers in these manufacturing facilities are exposed to multiple pollutants present at variable concentrations. Specific known adverse health effects include bladder cancer associated with metalworking fluid exposure and lung cancer associated with electroplating processes. To reduce the incidence of these adverse effects, the main challenge is to identify the most hazardous pollutants within this complex exposure environment and evaluate the corresponding health potentials. In this study, exposure indices were formulated to assess multiple metal exposures with the ultimate goal of providing relevant information for exposure reduction and control measures. Fifteen plants, including metal mold manufacturing, metal casting, and surface treatment plants, were investigated in terms of total concentration, summation of corresponding ratio to threshold limit value (STLVr), hazard index (HI), and incremental cancer risk. The results revealed that emissions of aluminum, iron, and manganese were primarily found in the metal mold manufacturing/casting plants, while emissions of chromium, nickel, and zinc were found in surface treatment plants. STLVr and HI were more useful than the total concentration for identifying hazardous metals, which were chromium and nickel, and could specify the facilities that were in need of control measures. As for cancer risk, the metal mold manufacturing/casting plants had lower risk than the surface treatment plants, and the contributing metals for these two plant types were cobalt and chromium, respectively. This study established a useful procedure to evaluate health hazards and cancer risk. The resulting information is useful for prioritizing mitigation control of multiple metal exposures.

Theoretical Prediction of Crack Formation in Axisymmetric Multilayer Shell Molds

On the basis of the numerical method, the study has developed a general scheme for solving the problems on stress-strain state of axially symmetric shell molds. The study has developed a mathematical model for the process of casting melting metal into shell molds and hardening of castings. The results of the solution of the problem have showed that stresses of σ22 have the highest values, the stresses of σ11 have order of magnitude smaller values, and the stresses of σ33 vary over time and space like stresses of σ22, but they are 5-10% less in absolute values. The calculations show that the metal hardening in a shell mold starts in 31 seconds, and meanwhile, tensile stresses occur on the metal-mold surface and, therefore, metal tends to depart from the shell mold surface.

Improvement in Surface Characteristics by EDM with Chromium Powder Mixed Fluid

Surface finishing technology by EDM has recently progressed, and very small surface roughness can be readily obtained by controlling the electrical discharge conditions, or by using metal powder mixed working fluids. In addition, it was reported that EDMed surface using metal powder mixed fluids sometimes has high surface functions, such as high hardness, high corrosion resistance and so on. Therefore, the high functional EDM finished surface is well expected to be applied as a final metal mold surface. In this study, formation of chromium containing layer on the EDMed surface was tried by using chromium powder mixed fluid. Furthermore, the EDMed surface characteristics with chromium powder mixed fluid were experimentally evaluated.

Study on Surface Characteristics of EDMed Surface with Nickel Powder Mixed Fluid

EDM finishing technology has progressed recently, and very small surface roughness can be obtained by controlling the electrical discharge conditions. Also, EDM using powder mixed fluids can improve the surface characteristics. Therefore, the EDM finished surface is highly expected to be applied as a final metal mold surface. In that case, the characteristics of EDMed surface influence the molding performance and the life of metal molds. As a new surface finishing method by EDM, the characteristics of EDMed surface using a nickel powder mixed fluid was experimentally discussed in this study, since nickel coatings have been widely applied to improve the corrosion resistance and the mold releasability of metal molds. Experimental analysis clarified that the resolidified layer containing nickel content could be formed on the surface by EDM in nickel powder mixed fluid. Also, the water repellency and the releasability of molded resin from the EDM finished surface could be improved.

Improvement of surface characteristics for long life of metal molds by large-area EB irradiation

This paper describes the applicability of large-area EB irradiation method to a new surface modification for metal molds. The previous papers clarified that the surface roughness on wide area uniformly decreased to less than 1μm Rz in a few minutes by the large-area EB irradiation. Therefore, the large-area EB irradiation method has high practicability as an efficient surface finishing process for metal molds, and then the EB irradiation equipment has already been introduced into the market for practical use. In this method called EB polishing, the surface material melts and a very thin resolidified layer is formed on the surface. In this paper, the surface structure of EB polished metal mold steel SKD11 was first observed by TEM, and also component analysis was carried out by EDX. Then it was found out that the crystal grain size became small and chromium carbide is uniformly rearranged in the layer. Next, using heat conduction analysis model considering the electron penetration on the surface, the temperature distribution was calculated. The results showed that the surface temperature rapidly raised over its melting point until the end of EB irradiation, and cooled down rapidly. As the important practical surface characteristics for long life of metal mold, resistance to corrosion, water repellency, and the releasability of molded resin from metal mold surface were evaluated. The corrosion resistance and the water repellency could be improved by EB polishing, since the surface structure changes and Cr content distributed uniformly on the surface. Also, the releasability of molded resin from the surface became better.

Fundamental study on releasability of molded rubber from mold tool surface

In compression or injection molding of rubber products, small pieces of residual rubber often remain on the metal mold surface after releasing the product. This is caused by excessive localized adhesion to the mold surface. Therefore, cleaning of metal mold surface must be often performed, which results in longer molding cycle time, and the lifetime of metal mold is often reduced. In this study, the separation forces between molded rubber and metal mold surfaces are measured with a tensile tester to evaluate the releasability of molded rubber from the metal mold surface. Mold surfaces treated by various surface coatings and surface modification methods including EB polishing were tested and compared. Experimental results show that the separation force between molded rubber and metal mold surfaces depends on the true contact area between them and the chemical composition of the metal mold surface. The separation force decreases with a decrease in contact area. The chromium content at the metal mold surface significantly reduces the separation force. EB polishing is one of the most effective surface treatments for metal molds since the real contact area can be decreased while also decreasing the surface roughness of the tool surface in a short time. Electron beam melting is also shown to be an effective method of distributing chromium uniformly on the metal mold surface.

S134012 ニッケル粉末混入放電加工面の表面特性に関する研究([S134]先進特殊加工技術)

Recently, EDM finishing technology has remarkably progressed, and very small surface roughness can be readily obtained by controlling the electrical discharge conditions. Also, EDM using powder mixed working fluids can improve the surface characteristics, such as wear resistance and corrosion resistance. Therefore, the EDM finished surface is well expected to be applied as a final metal mold surface in the near future. In that case, the surface characteristics of EDMed surface would influence the molding performance and the life of metal mold. As a new surface functionalization of EDMed surface, the surface characteristics of EDMed surface using a nickel powder mixed fluid is experimentally discussed in this study, since nickel coating has been widely applied to improve the corrosion resistance and the mold releasability of metal mold surface. Experimental analysis clarified that the resolidified layer containing nickel content could be formed on the surface by EDM in nickel powder mixed fluid. Also, the water repellency and the releasability of molded resin from the EDMed surface could be improved.

Curing and Consolidation of Advanced Thermoset Composite Laminate Parts by Pressing Between a Heated Mold and Customized Rubber-Faced Mold

Curing and consolidating thermoset composite laminates and sandwich structures typically involves vacuum bagging an uncured and formed layup over a thin-walled mold, placing it in an autoclave, and subjecting the entire unit to temperature, vacuum, and pressure cycles as prescribed by the manufacturer. Autoclaving is generally considered the major bottleneck in manufacturing advanced composite parts because of high capital and consumable costs, energy usage, waste generated, and process scalability. A new curing and consolidation process called “thermal press curing” is presented and demonstrated as an alternative to autoclaving. The process involves compressing a composite laminate between a special mold set––a heated metal mold and a matching rubber-covered mold made of an insulative material––designed to provide uniform temperature and pressure over the metal mold surface, that is, mimic the process conditions provided by an autoclave. The thermal press curing process is demonstrated for the first time using a mold set for a simple two-dimensional axisymmetric shape. An aluminum curing mold with embedded electric resistance cartridge heaters is heuristically designed to provide uniform temperature in operation across the mold surface within 1°C of the target value (177°C). With the mold set compressing an eight-ply carbon/epoxy composite workpiece and well insulated on all sides, the power draw is at least one to two orders of magnitude less than a comparable autoclaving operation. The potential to significantly improve pressure uniformity from the compressed rubber mask is shown by changing the mask shape. Even without an optimized rubber layer shape and thickness, the eight-ply composite part was successfully cured. Finally, a plan for future work is described.

Fabrication of Hierarchically Micro- and Nano-structured Mold Surfaces Using Laser Ablation for Mass Production of Superhydrophobic Surfaces

Many studies have examined the formation of surfaces with mixed patterns of micro- and nano-sized lotus leaves that have hydrophobic properties. In this study, micro- and nano-shapes such as lotus leaves were fabricated on a metal mold surface using laser ablation and ripple formation. A microstructure on the mold surface was replicated onto poly(dimethylsiloxane) (PDMS) using the polymer casting method to manufacture low-cost hydrophobic surfaces. A PDMS surface with micro- and nano-structures that were the inverse image of a lotus leaf showed hydrophobic characteristics (water contact angle: 157°). From these results, we deduced that portions of the microstructures were wet and that air gaps existed between the microstructures and the water drops. In this paper we suggest the possibility of the mass production of hydrophobic plastic surfaces and the development of a methodology for the hydrophobic texturing of various polymer surfaces, using the polymer casting method with laser-processed molds.

S1304-2-2 成型ゴムと金型表面の離型性に及ぼすEBポリッシングの効果([S1304-2]微細放電加工およびその他の加工法)

S1304-2-2 成型ゴムと金型表面の離型性に及ぼすEBポリッシングの効果([S1304-2]微細放電加工およびその他の加工法)

Adhesion Effects between a Molten Polymer and a Stamper in a Transcription Process for Fine Patterns

To clarify the adhesion effects on the transcription of fine patterns to the surface of a thermoplastic polymer, the numerical simulation of the filling and transcription behavior in Melt Transcription Molding Process was carried out using a numerical model based on the adhesion between a molten polymer and a metal stamper with microstructure. The microstructure was completely transcribed at the initial stamper temperature 180℃. Up to this temperature, the rim height of transcribed hemispherical projection increased but the center height decreased, when the mold temperature was raised. The transcribed shapes simulated theoretically at the initial stamper temperature 170, 175 and 180℃ were closely duplicated with experimental ones which were reported in our previous study. Immediately after the release of compression force, the internal stress of the polymer filled near the contact interface changed from compression to tensile stress. From these results, it was confirmed that the adhesion force between the polymer filled in the microstructure and the metal mold surface keeps the transcribed shapes of the microstructure stable against the elastic recovery force. Furthermore, it was suggested that the adhesion effects play a critical role in successful operations of the coating, compression and demolding stages in Melt Transcription Molding Process.

Filling and Transcription Behavior of Molten Polymer Coating on Microstructures in Melt-Transcription-Molding Process

To clarify the fabrication mechanism of molten polymer coating on microstructures such as optical display parts and bio-tip in Melt-Transcription-Molding (MTM) process, the transcription experiments between a metal stamper engraved with microstructures and a molten polymer (PC: polycarbonate and COC: cyclo-olefin copolymer) were carried out under various molding conditions (mold temperature, polymer temperature, polymer pressure and coating speed) and transcript results were evaluated from the dimensional aspect. In this study the complete transcription of the microstructures was obtained at mold temperature of 170°C for COC and 175°C for PC, respectively. However, the rim height of the microstructure was increased and its center depth was decreased, when lower mold temperatures were applied. From these experimental results, it was suggested that the adhesion force between a molten polymer filled with the microstructure and the metal mold surface plays an important role in fixing the transcript shape of the microstructure against the elastic recovery force and/or shrinkage by cooling. Furthermore, a model to explain the filling and transcription behavior of molten polymers was proposed from viscoelastic properties of each polymer, and it was confirmed that predicted microstructure geometries deduced with the model are well fitted with the transcript results which were experimentally obtained under various mold temperatures.

High Efficiency Surface Finishing of Metal Mold by Large-area Electron Beam Irradiation (3rd Report)

A new finishing process for metal molds by large-area electron beam irradiation (EB polishing) was proposed and the fundamental effects of EB irradiation conditions on surface finishing, the surface modification effect and others were investigated in the previous report. As a result, the surface roughness on the whole surface within 60mm in diameter could be reduced from 6μmRz to less than 1μmRz in just a few minutes under a proper condition, and the surface roughness could be well improved even if the surface tilting angle is close to 90 degrees. In addition, the corrosion resistance of metal mold surface could be improved. However, small craters sometimes were generated on the EB irradiated surface, which might deteriorate the quality of products. In this study, the relationship between crater generation and workpiece material was examined. Experimental results made it clear that the generation of crater and its disappearance were repeated on the surface with EB irradiation, and the generation of crater greatly depends on the nonmetallic additives in base material, particularly on MnS. Moreover, the impurity of workpiece material also has a significant influence on the crater generation.

A new polishing method of metal mold with large-area electron beam irradiation

A new polishing method by large-area electron beam (EB) irradiation is proposed in this study. In the large-area EB irradiation equipment used here, an EB with high energy density is irradiated without focusing the beam. An EB irradiation in a few microseconds with a maximum diameter of 60 mm can be used for melting metal surface instantly. The experimental results made it clear that the surface roughness decreases from 6 μmRz to less than 1 μmRz in a just few minutes under a proper machining condition. The corrosion resistance of metal mold surface also could be greatly improved by large-area EB irradiation. Furthermore it is clarified that even the surface roughness of tilting surface close to 90° could be well improved. Therefore, large-area EB irradiation method has a high possibility to become a high-efficiency polishing method of metal mold.

High-efficiency finishing process for metal mold by large-area electron beam irradiation

Abstract A new finishing process for metal molds by large-area electron beam (EB) irradiation is proposed in this study. In the large-area EB irradiation equipment used here, an EB with high-energy density is irradiated without focusing the beam, and so the EB with a maximum diameter of 60 mm can be used for melting or evaporating metal surface instantly. Experimental results show that the surface roughness decreases from 6 μmRz to less than 1 μmRz in just a few minutes under proper machining conditions. The corrosion resistance of metal mold surface also could be greatly improved by large-area EB irradiation. Furthermore, the surface roughness of tilting surface close to 90° could be well improved. Therefore, large-area EB irradiation method has a possibility to become a high-efficiency finishing process for metal molds.

A New Surface Modification Method of Metal Mold by Large-area Electron Beam Irradiation(Electrical machining)

We have already proposed a new surface finishing process for metal molds by large-area electron beam (EB) irradiation in the previous report, and the effects of EB irradiation conditions on surface smoothing characteristics were investigated. As a result, the surface roughness could be reduced to less than 1μmRz in just a few minutes under a proper condition. Furthermore, the surface roughness of tilting surface close to 90 degree also could be well improved, which indicated that in the case of small simple shaped mold consisting of relatively small tilting surfaces, the smoothing of the whole surface is possible without moving and tilting the mold. In this paper, the surface characteristics of the EB irradiated surface were discussed by TEM observation, XRD analysis, and corrosion test. The surface structure changed by large-area EB irradiation, and consequently, the corrosion resistance of metal mold surface could be improved well.