On-line pH value measurement of solution on the removing support material process
Introduction
New market realities need faster product development due to global competition. To effectively shorten new product development time, rapid prototyping (RP) was developed [1]. RP is a manufacturing technology that fabricates three-dimensional (3D) physical models using the layer by layer building process that stacks and bonds thin layers in one direction. Prototyping is an essential part of the product development and manufacturing cycle required for accessing the form of a design before conventional steel tooling is made. In comparison with the numerically controlled manufacturing technology, RP technology can rapidly manufacture physical models with complex shapes without geometric restriction under more comfortable working environments. Fused deposition modeling (FDM) is one method among a few capable of developing rapid prototyping parts from a thermoplastic material such as polycarbonate, acrylonitrile butadiene styrene (ABS), investment casting wax and medical grade ABS [2]. FDM is one of the most promising RP techniques in terms of dimensional accuracy, machining speed and cost-effectiveness [3]. This system is viewed as a desktop prototyping facility in an office because the materials it uses are non-toxic and non-smelly. Physical models made by this system have a high stability because they are not hygroscopic. A commercial FDM machine uses a computer numeric controlled extruder-head which squeezes a fine filament of melted thermoplastic through a modeler nozzle. The controller activates the modeler nozzle to deposit heated plastic layer-by-layer to build the desired 3D physical models. In general, FDM machine possesses a second nozzle for fabricating the structures to support any overhanging section of the prototype. In recent years, some issues about FDM technology have been intensively studied by many researchers all over the world. These issues include surface modification of fused deposition modeled parts [4], enhancing the surface finish of fused deposition modeled parts [5], [6], [7], development of new materials for FDM system [8], development of a mobile FDM system [9], fabrication of scaffolds using FDM system [10], fabrication of fiber Bragg grating using FDM system [11] and improving dimensional accuracy of fused deposition modeled parts [12]. For practical application, support material of the fused deposition molded parts should be removed when the physical model is further employed. Thus, removing the support materials from fused deposition modeled parts fabricated using FDM system efficiently is a very critical process because the product life cycle is shorter than before. The major process parameters influencing the removal efficiency of support material were investigated in previous study [13], showing the pH value of the solution is a major factor affecting the efficiency of removing support material from the fused deposition modeled parts. Thus, on-line measuring the pH value of solution and compensating the pH value changed are critical to the efficiency of removing support materials during removing process. Although the pH value of solution can be determined by traditional methods including litmus paper and pH meter, the main drawbacks include time consuming, human error, unacceptable precision, solution pollution and long-term stability. This study is to develop an optical measurement system to on-line pH value measurement of solution during the removing support material process. Linear regression equation was investigated for predicting the pH value of solution. The relative error of the linear regression equation was discussed. The time saving in removing the support material from RP parts was also investigated and discussed.
Section snippets
Experiment
Fig. 1 shows the schematic illustration of the experimental setup for on-line pH value measurement of solvent during removing support material from fused deposition modeling parts. This optical measurement system is composed of a He–Ne probe laser (λ = 632.8 nm, 0.8 mW, NT 61-337, JSD Uniphase, Inc.), a spectrometer (SV2100L, K-Mac, Inc.), an ultrasonic cleaner (1002, LEO, Inc.) and a circulation pump (M101, San Xing, Inc.) [14]. Six different pH values of solution (pH 10.5, pH 11.68, pH 11.5, pH
Results and discussion
It is a well-known fact that optical measurement method has the main advantage of reliability [15], [16]. Fig. 6 shows the variation in transmitted total power of probe laser before optical measurement. As can be seen, a warm-up time of at least 30 min for probe laser is required [17]. After warm-up of the probe laser, standard deviation of the transmitted total power is obviously reduced to 0.0032 mW.
To obtain the linear regression equation for predicting the pH value of solution using the
Conclusions
From the point of view of the green manufacturing, removing support material from the fused deposition molded parts efficiently is an important issue. In this paper, an on-line optical measuring system for measuring the pH value of solution during removing support material from fused deposition molded parts has been implemented. The main advantages of this system include simplicity in experimental setup, fast measurement speed, high measurement accuracy, without solution pollution, long-term
Acknowledgement
The authors gratefully acknowledge the financial support of the National Science Council of Taiwan under contracts nos. NSC101-2221-E-131-007 and NSC 101-2815-C-131-001-E.
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