Application of the Multicomponent Method of Assessment o f Student ’ s Progress in Physics

The multicomponent method of assessing the progress in physics of students from the Technical University of Gabrovo is discussed in the paper. It is shown that tests papers as a modern form of examining students can successfully be combined with other traditional forms of examination. In that way the teacher can get important feedback on how students understand lectures and laboratory teaching material during the semester and to adjust their work so that they can in time adapt to the necessary level. Thus, students are actively involved in the learning process, which improves the results they show at the final exam. These conclusions are based on the results of the last decade, ever since the method was introduced

METHOD FOR PRELIMINARY ESTIMATION OF THE CRITICAL POWER DENSITY IN LASER TECHNOLOGICAL PROCESSES

For a number of new laser technology processes, it is essential to plan an experimental plan for primary experimental engineering activities in terms of quality. The assessment of the critical power density to reach the melting or evaporation temperature of the surface with a suitable theoretical model is an important stage in the development of a particular manufacturing technology. With the help of numerical experiments, this report provides a method for pre-examining the influence of wavelength on the laser technological process. The calculations are performed with a specialized program, running MATLAB. A series of temperature fields were obtained at a change in power density and wavelength at laser impact for concrete types of structural steel. The temperature dependence of the optical and thermo-physical characteristics of the material is also reporded. The analysis is made for laser technology complexes working with lasers emitting in the ultraviolet, visible, near and distant infrared areas. For these wavelengths the critical power density of melting and evaporation is determined

INVESTIGATION OF THE INFLUENCE OF THE NUMBER OF REPETITIONS ON THE PROCESS OF LASER MARKING OF HS6-5-2-5 STEEL

Today, methods for marking parts and components in industrial production are constantly improving, and they must meet several basic criteria for active traceability by consumers. The parameter that is of paramount importance for the quality of the marking is related to the contrast of the marked sign or QR code. To achieve optimal contrast, a number of technological factors and the functional relationships between them must be taken into account.The report examines the role of the number of repetitions on contrast in raster marking of HS6-5-2-5 tool steel products. The dependences of the number of repetitions on the speed and frequency are also taken into account - the main factors in the process of laser ablation. Graphs of the depth of the marking are drawn depending on the number of repetitions and the linear density of the pulses. The experiments were made with a fiber laser. By the performed analyses the working intervals of processing between the studied factors are deduced, allowing to achieve the desired optimal result.

CONTACTLESS MEASURING OF TEMPERATURE WITH DIFFERENTIAL PHOTO RECEIVER

A method for contactless temperature measurement has been created with two photo receivers with different spectral sensitivity. An algorithm for processing the signals from both receivers of a single-chip microprocessor system has been developed. An optical system for the LWIR diapason of the spectrum is proposed

INFLUENCE OF THE OVERLAP COEFFICIENT ON THE CONTRAST IN LASER MARKING OF C110W STEEL

The laser marking process by melting samples of C110W carbon tool steel was studied. The experiments were performed with a fiber laser and a CuBr laser. A field of squares is marked in a raster method for different values of the overlap coefficient and power density. The contrast of the marking is determined on each marked square. From the obtained experimental data, graphs of the dependence of the contrast on the overlap coefficient for three power densities were drawn. The obtained results for the two lasers are compared and the influence of the wavelength is indirectly analysed. The working intervals of the overlap coefficient for the studied power densities for the two lasers at which the optimal contrast in the processing zone is obtained are determined

DETERMINATION OF WORKING INTERVALS OF POWER DENSITY FOR LASER MARKING OF 50ChN STEEL

Studies relate to two basic methods of steel marking − by melting and by evaporation. Based on theoretical considerations, preliminary intervals of power density for laser marking of 50 ChN steel are determined. Experiments are carried out with fiber laser, operating in the near infrared area. Graphics on the dependence of contrast of marking from the power density of laser radiation for two methods of marking were developed. Working intervals of the power density for marking by melting and by evaporation for visual perception of marking and using the readers were defined.Studies relate to two basic methods of steel marking − by melting and by evaporation. Based on theoretical considerations, preliminary intervals of power density for laser marking of 50 ChN steel are determined. Experiments are carried out with fiber laser, operating in the near infrared area. Graphics on the dependence of contrast of marking from the power density of laser radiation for two methods of marking were developed. Working intervals of the power density for marking by melting and by evaporation for visual perception of marking and using the readers were defined

INVESTIGATING THE INFLUENCE OF THE NUMBER OF REPETITIONS AND VOLUMETRIC ENERGY DENSITY ON LASER MARKING OF PRODUCTS

The basic factors affecting the laser marking of products – volumetric density of the absorbed energy and the number of repetitions, were studied. Experiments were conducted of marking the samples of stainless steel with fiber laser. The dependence of the contrast of marking from the power density for different number of repetitions, and also the volumetric density of the absorbed energy from speed was obtained and the experimental results analyzed.The basic factors affecting the laser marking of products – volumetric density of the absorbed energy and the number of repetitions, were studied. Experiments were conducted of marking the samples of stainless steel with fiber laser. The dependence of the contrast of marking from the power density for different number of repetitions, and also the volumetric density of the absorbed energy from speed was obtained and the experimental results analyzed.

STUDY OF THE INFLUENCE OF DEFOCUSED LASER MARKING PROCESS BY MELTING ON SAMPLES OF STEEL

The studies relate to the process of laser marking by melting on the samples of structural steel. The zone of Raleigh for fiber laser was determined. The theoretical dependences of the diameter of the working spot from defocusing and diameter of the radiation falling on the lens were received. Experiments were realized with 50G structural steel. The dependence of contrast of marking from defocusing for two power densities was determined. Working intervals were determined for studied magnitudes for visual perception of the marking.The studies relate to the process of laser marking by melting on the samples of structural steel. The zone of Raleigh for fiber laser was determined. The theoretical dependences of the diameter of the working spot from defocusing and diameter of the radiation falling on the lens were received. Experiments were realized with 50G structural steel. The dependence of contrast of marking from defocusing for two power densities was determined. Working intervals were determined for studied magnitudes for visual perception of the marking

Concept and development of an autonomous wearable micro-fluidic platform for real time pH sweat analysis

In this work the development of an autonomous, robust and wearable micro-fluidic platform capable of performing on-line analysis of pH in sweat is discussed. Through the means of an optical detection system based on a surface mount light emitting diode (SMD LED) and a light photo sensor as a detector, a wearable system was achieved in which real-time monitoring of sweat pH was performed during 55 minutes of cycling activity. We have shown how through systems engineering, integrating miniaturised electrical components, and by improving the micro-fluidic chip characteristics, the wearability, reliability and performance of the micro-fluidic platform was significantly improved

INFLUENCE OF BASIC PARAMETERS OF THE LASER MARKING PROCESS ON STAINLESS STEEL SAMPLES

The role of basic quantities influencing the process of laser raster marking of AISI 304 stainless steel products using a fiber laser was investigated. Some dependencies were found when changing the contrast of the marking when changing the parameters in wide intervals. As the raster step increases, a non-linear decrease in contrast occurs as the rate of contrast decrease. Regarding the influence of the speed on the contrast, it was found that as the speed increases, the contrast of the marking decreases non-linearly, and as the step increases, the speed of the contrast decrease also increases. Above 20 kHz, the frequency has relatively little influence on the contrast, as with increasing frequency the contrast slowly increases and the dependence is almost linear. The effective energy is strongly influenced by the contrast. At effective energy values below 18 kJ/cm2 the contrast of the marking is insufficient for visual perception of a good quality marking, but in the interval from 6 kJ/cm2 to 46 kJ/cm2 the contrast increases very quickly. At values of the effective energy above 100 kJ/cm2, the contrast of the marking hardly changes. The obtained results can be used by the operators of laser systems to evaluate the working ranges and quickly determine the boundary areas of the optimal technological parameters when obtaining a good contrast in the laser marking of stainless steels with a fiber laser