Defects In Final Product Research Articles

Study of PET Spectral Absorbance in Designing Infrared Heating Control of Vacuum Forming Machine

Heating process is the first step in vacuum forming that transforms the plastic sheet from its glassy state to rubbery state, pliable enough to be formed to mold’s shape. Infrared ceramic heaters with zoning control are commonly used in thermoforming industry, in which temperature distribution and its consistency throughout processing time become very important in determining the thickness and properties of manufactured parts. Compared to other thermoplastics, Polyethylene Terephthalate (PET) with its crystallization characteristics is known to have narrower process window. Slight uneven temperature distribution and overheating will degrade PET as well as cause visible defects in final product. In order to obtain proper parameter setting of infrared ceramic heater in PET vacuum forming, a numerical approach that considers PET spectral absorbance was deployed and two methods to control temperature were compared. The experiment resulted in a reliable temperature distribution by means of voltage potentiometer control for pre-heating and implanted thermocouple inside ceramic emitter for main heating in PET vacuum forming machine.

Support Vector Representation Machine for superalloy investment casting optimization

• Original and innovative application of Machine Learning techniques to investment casting industry. • Key performance indicators to simultaneously increase quality and reduce defects in final products (i.e. turbine blades). • Innovative solutions of Support Vector Representation Machine technique to define set-points of Key performance indicators. Machine learning techniques have been widely applied to production processes with the aim of improving product quality, supporting decision-making, or implementing process diagnostics. These techniques proved particularly useful in the investment casting manufacturing industry, where huge variety of heterogeneous data, related to different production processes, can be gathered and recorded but where traditional models fail due to the complexity of the production process. In this study, we apply Support Vector Representation Machine to production data from a manufacturing plant producing turbine blades through investment casting. We obtain an instance ranking that may be used to infer proper values of process parameter set-points.

Structural characterization and detecting processes of defects in leaded brass alloy used for gas valves production

The structure of leaded brass alloy used for gas valves production is studied. Some scientific knowledge and facts about this subject are introduced. The melting and casting of leaded brass billets, hot extrusion with cold drawing of rods and hot forging of gas valves are performed. Some changes in production parameters are performed and 30% of pure materials added to improve the final products and minimize the defects. The structure of alloy is studied using optical and SEM/EDS devices for inspections. Radiographic and ultrasonic tests are used to detect the cracks and other defects in final products. The results indicated that the structures, phase distribution and the quality of leaded brass alloys differ slightly during casting, extrusion and hot forging processes. Also, most of samples consist of α and β phases with lead particles distributed on the grain boundaries or inside these phases. Very small crack is appeared in one sample of the forged gas valve, while the other valves are free. Improving the production parameters and also using of pure materials in charge elements are contributed by result improvement. SEM/EDS investigation results confirm the microstructure results of optical microscope for sample element distribution.

Effect of UV Radiation by Projectors on 3D Printing

Polymers that solidify under light radiation are commonly used in digital light processing (DLP) 3D printing. A wide range of photopolymers use photoinitiators that react to radiation in range of ultraviolet (UV) wavelength. In the present study we provided measurement of radiant fluence in the UV wavelength range from 280 nm to 400 nm for two data projectors and compared effect of radiation on quality of 3D printing. One projector is commonly used DLP projector with high energy lamp. Second one is an industrial projector, in which RGB light emitting diodes (LEDs) are replaced by UV LEDs with wattage at the level of 3.6 % of the first one. Achieved data confirmed uneven distribution of radiant energy on illuminated area. These results validate, that undesired heating light causes internal stress inside built models that causes defects in final products.

Microbulging extrusion of aluminum alloy to fabricate micro/meso features for heat pipes

Aluminum microextrusion is an efficient technology to fabricate profiles with micro/meso features at low cost. However, die failure is often observed during the process of high extrusion ratio due to excessive stress concentration, which is caused by irrational design. This study aims at extruding a certain aluminum alloy profile with the symmetrical micro/meso features of twin wing and double hole based on microbulging extrusion process. 3D FE simulations illustrated that the bulging angle had a major impact on velocity and temperature distribution of the extrudate, as well as internal stress distribution and elastic deformation of the dies. A series of detachable mandrels with various bulging angles were designed and fabricated. By experiments and simulations, velocity distribution was obtained, which indicated that the bulging angle was beneficial to the balance of metal flow. An appropriate bulging angle could achieve better material flow uniformity with a lower standard deviation of velocity (SDV), which contributed significantly to the success of extrusion. However, an overlarge bulging angle would increase the deformation of mandrel core and raise the temperature of extrudate, which led to the local defects in final products.

液中懸濁粒子の凝集挙動

Coagulation of particles in the fluid is often observed in nature and it is a multiphase phenomenon utilized in various processes. Coagulation phenomenon is also observed in molten metal system in the same as water and air system. Until now, coagulation of particles such as oxide inclusions, have been focused on because large inclusions raise harmful defects in final products. Therefore, many researches have been performed in the both side of theory and experiment. In this paper, kinetics of coagulation behaviors is summarized for information to analyze the growth rate of aggregates, particle size distribution and so on. In addition, recent researches and issues for coagulation mechanism are introduced briefly in the view point of multiphase phenomenon.

가압-진공 하이브리드 주입 성형에 의한 알루미나의 성형에 미치는 다단 가압의 영향

Conventional cold isostatic pressing, slip casting, and filter pressing are not completely suitable for fabricating large plates because of disadvantages such as the high cost of equipment and formation of density gradient. These problems could be avoided by employing pressure-vacuum hybrid slip casting (PVHSC). In the PVHSC, the consolidation occurs not only by the compression of the slip in casting room, but also by vacuum sucking of the dispersion medium around the mold. We prepared the alumina bodies by the PVHSC in a static- or stepwise-pressure manner for loading up to 0.5 ㎫ using an aqueous slip. The green bodies were dried at 30℃ with 40 ~ 80% relative humidity. Under static pressure, casting induced a density gradient in the formed body, resulting in cracking and distortion after the firing. However, the stepwise pressure loading resulted in green bodies with homogeneous density, and the minimization of the appearance of those defects in final products. Desirable drying results were obtained from the cast bodies dried with 80% RH environment humidity. When sintered at 1650℃ for 4 h, the alumina plate made by stepwise-pressure casting reached full density (＞ 99.7% relative density).

Ti 첨가 18%Cr 스테인리스 용강의 Al 탈산 및 Ca 처리시 개재물 변화거동

Titanium is added to ferritic stainless steels in the range of 0.2-0.3 wt% to improve corrosion resistance and mechanical properties. However, titanium is very reactive with oxygen in liquid steel, and it can cause an unstable Ti yield. Therefore, titanium is generally added after the aluminum deoxidation process in the ladle. However, the inclusions formed by Al-Ti deoxidation can cause nozzle clogging and various defects in final products. Calcium injection can be carried out to resolve these problems. In this study, two different deoxidation patterns of Al→Ti and Al→Ti→Ca additions were carried out in Fe-18%Cr ferritic stainless steel melt at 1873 K. The melt composition and the inclusion morphology changes during the deoxidation process were investigated. With Al→Ti addition, the Al{sub 2}O{sub 3} inclusions changed to dual phase Al{sub 2}O{sub 3}-TiO{sub X} inclusions with time by the reaction with Ti in the melt. The morphology of the inclusions in the melt finally changed to a polygonal type indicating that the inclusions were solid phase. The size and number of inclusions in the melt did not change with time after Ti addition. With of Al→Ti→Ca addition, Ca reacted with Al{sub 2}O{sub 3}-TiO{sub X} inclusions to form liquid CaOAl{sub 2}O{sub 3} inclusions embedded with solid CaTiO{sub 3} particles. The morphology of the inclusions in the melt were observed to be spherical and polygonal. The size of inclusions in the melt increased and the number of inclusions decreased by the coalescence of liquid inclusions.

Simulation and Physical Modeling of Forging Sequence of Bj Type Outer Race

The outer race of a constant velocity (CV) joint is an important automotive component that is difficult to be forged because its shape is very complicated and the required precision is high. Since traditional cold forging methods are not always capable of producing complexly shaped parts, such parts are often made by processes, which require intense machining operations at relatively high costs. Thus near net shape forging is an attractive option for producing of outer race. Actual problems in final ironing sequence are prevention of ductile fracture and surface defects in final product and true formation of internal ball grooves of the workpiece. In this study Cockroft&Latham failure criterion was applied to final ironing sequence. Finally physical modeling is down using lead. In order to investigate the flow of the billet material during forging, the experimentally obtained section profile of internal grooves as measured by a CMM is compared with simulation based profile.