Numerical Simulation of Temperature Field for Laser Rapid Prototyping
The temperature field model for laser rapid prototyping is established by the mathematical treatment of laser power input. Temperature fields with different process conditions are numerical simulated, and the temperature is Gaussian distribution as the intensity distribution on laser beam cross-section. Temperature fields for laser rapid prototyping ware measured by thermal imager in real time. The simulation results agree with the experimental measurement. Experiments show that the temperature field model can be used for computer analysis and optimizing of laser rapid prototyping processing.
CAD/CAE/CAM integration for increasing the accuracy of mask rapid prototyping system
Stereolithography is a rapid prototyping (RP) process that uses photopolymers as the raw materials from which the prototypes are built. The photo-polymeric RP system uses lasers or other light sources to expose selectively the surface of the liquid resin. The absorption of energy causes photo-polymerization that changes the liquid resin into a solid, expanding the cured volume expanding but shrinking simultaneously. The volume shrinkage and curl distortion of the resin during photo-polymerization are the main reasons for the poor accuracy of the built prototype, especially when the part is hollow, in which case the bending is greater because of the bending stress and cannot be compensated for. Normally, a designer builds a support in this stage to limit the further bending and deformation of the prototype. However, after the support has been removed from the built prototype, the geometric profile is easily damaged and deformed, so time is wasted. This study initially uses dynamic finite element simulation code to simulate photo-polymerization, to determine the distortion of the outer profile of the part and thus reduce the deformation. Then, a reverse distortion correction is applied to the outer profile of the part. A new reverse compensation CAD model is produced and loaded into a RP machine for practical prototype processing, to increase the accuracy of the process. Finally, the ''H-4'' diagnostic part is used as an example to verify the experimental results. The results of the simulation and experiment on the final after compensation were accurate.
High-frequency hearing thresholds: effects of age, occupational ultrasound and noise exposure
AbstractPurpose
It has been suggested that high-frequency audiometry (HFA) could represent a useful preventive measure in exposed workers. The aim was to investigate the effects of age, ultrasound and noise on high-frequency hearing thresholds.MethodsWe tested 24 industrial ultrasound-exposed subjects, 113 industrial noise-exposed subjects and 148 non-exposed subjects. Each subject was tested with both conventional-frequency (0.125–8 kHz) and high-frequency (9–18 kHz) audiometry.ResultsThe hearing threshold at high frequency deteriorated as a function of age, especially in subjects more than 30 years old. The ultrasound-exposed subjects had significantly higher hearing thresholds than the non-exposed ones at the high frequencies, being greatest from 10 to 14 kHz. This hearing loss was already significantly evident in subjects with exposure <5 years and increased with years of exposure and advancing age. The noise exposure group had significantly higher hearing thresholds than the non-exposed group at the conventional frequencies 4 and 6 kHz and at the high frequency of 14 kHz. After stratification for age, there was a significant difference between the two groups at 9–10 and 14–15 kHz only for those under 30 years of age.ConclusionMultivariate analysis indicated that age was the primary predictor, and noise and ultrasound exposure the secondary predictors of hearing thresholds in the high-frequency range. The results suggest that HFA could be useful in the early diagnosis of noise-induced hearing loss in younger groups of workers (under 30 years of age).
