Application of Computer Simulation in Automatic Glass Producing

František Novotný, Ivo Matoušek, Marcel Horák, Vlastimil Hotař, Department of Glass Producing Machines and Robotics, Technical University

of Liberec, the Czech Republic

Introduction The article presents a summary about the scope and methodology of the use

of C-technology applications used for the solution of technical problems in the Department of Glass Producing Machines and Robotics, Technical University of Liberec. The attention is focused on three fundamental directions of numerical simulation used for the solution of technical problems in glass industry, as follows: numerical simulation of glass forming processes based on FEM, application of computer modeling in a sphere of robotic manipulation, principles of fractal geometry.

Possibilities of virtual simulations use for effective problem solving are shown on concrete examples from production practice. Numerical outputs are presented in the form of temperature and strain (strain rate) field process during individual stages of glass forming cycle. The approach to the optimization of glass forming with a view to glass forming tools optimization is outlined too. Special attention is paid to the problem of virtual simulation of two-step forming of domestic glass producing by press and blow process. The applied approach is effective way for the identification of potential technological problems and their subsequent optimization especially in the production of nonstandard products with extreme technological requirements.

Computer modeling possibilities of dynamical forces are presented below. Results of numerical solutions are used by solving complicated handling tasks in the sphere of a robotics manipulation and contact tasks for a design of special grippers. The paper describes records of research in the field of modeling of an automatic dynamic handling with thin glass sheets. Methodology of the computer modeling is focused to the problems of simulation of gripping head system, gripping elements and object of handling (glass sheet). Material properties, a design of contact bodies and character of contact surfaces are respected and the real courses of handling cycle are described by specific initial and boundary conditions. Concrete results are summarized to the database system for an optimalization of a computer design of vacuum gripping heads.

Finally, principles of fractal geometry and examples of application possibilities are shown for the objective specification of defects in glass products, for evaluation of data set captures in the form of time series and for a glass production control. A new principle of a corrugation test objectification for the evaluation of glass sheet quality with a possibility of its full automation is significant results.

About department of Glass Producing Machines and Robotics

The Department has participated in a basic and applied research, provided teaching specialized in „Glass and Ceramic Producing Machine“ as well as teaching basic studies at the Technical University of Liberec. It has taken an active part in cooperation with the leading companies of the glass industries in the Czech

Republic, and also had contacts with other important home and foreign partners in this sphere.

Since its foundation in 1963, the Department has taken an active part in research and development for the glass industry, controlled centrally in that time, cooperated intensely both with research institutes such as SVÚS Hradec Králové, VÚSU Teplice and with companies such as Sklostroj Turnov, SU Teplice, Crystalex, Jablonecká bižuterie focusing its applied research on physico-technological experiments, on diamond tools application and on glass producing machine designs.

During the transition to the market economy, connections with research institutes and indipendent join-stock companies were severed. Within the second half of the 1990s the Department succeeded in making a cooperation with leading glass companies: GLAVERBEL CZECH Teplice, PRECIOSA Jablonec nad Nisou, SKLO BOHEMIA Světlá nad Sázavou, CRYSTALEX Nový Bor, KAVALIER Sázava etc. Also the cooperation with the Department of Glass and Ceramics at the Institute of Chemical Technology Prague is important.

C-technology applications – basic and applied research

The Department has participated in a basic and applied research. The research can be divided into fields as follows:

Numerical simulation of glass melt forming processes (pressing, press-and-blow process) and subsequent handling of products on the hot end of production lines. Operational and model measurements of machine forming of glass melt.

Design of handling devices and industrial robots, optimization of handling flows, design and optimization of effectors and peripheries for the handling of glass.

Design of machines and devices for the glass industry, and optimization of the forming process, glass moulds and plungers.

Interpretation of data obtained during experiments as well as from the industrial practice using statistic tools and fractal geometry. The numerical simulation is concentrated especially on the glass forming

process, distribution of temperature fields, and handling with products. The Department has obtained excellent results in these spheres. The numerical simulations are based on the data obtained by primarily temperature and temperature field measurements made during manufacture. The Department has at its disposal a broad spectrum of instruments and devices for temperature measurements (thermocouples, pyrometers, thermovision cameras).

Results of the computer modelling are applied on the optimization of the process and tool design, and - in the case of the computer simulation of handling processes - on the optimization of the contact tasks and dynamic behaviour of the system. The design and optimization of handling flows, effectors, and peripheries including numerical simulations and verification using functional prototypes.

The evaluations of data obtained from the practice and experiments are carried out using own as well as commercial software tools. Statistics and relatively new tools of so-called fractal geometry are used. Surface pictures, time series, material and light boundaries and such like can be described.

Main activities are part of 5 basic projects: Optimization of glass melt forming processes Robotized handling of glass products Evaluation of experimental data from industrial practice using fractal geometry

and statistic tools Study of glass rheological characteristics Gravity glass forming process modelling

Synergic interconnections of the mathematical modelling with physical experiments for the verification of results in mentioned spheres of the glass forming, for the optimization of forming tools, for the optimization in the sphere of dynamic robotic handling, and in the effective descriptions of production data having chaotic properties.

The projects are financed by grant funds of the Ministry of Education and Science, the Ministry of Industry and Commerce and by several industrial clients.

More information of the cooperation with the industry as well as of grants solved can be found on the Department website: www.ksr.tul.cz.

Optimization of glass melt forming processes

A prediction of technological problems of the forming process in pre-production phase is already based on the comprehensive analysis of a virtual model describing the course of individual stages of the whole forming cycle (Fig. 1). An optimization of the course of the forming cycle focused on the production quality increasing, on higher efficiency of the forming course, and on the forming cycle stability increasing. Based on knowledge of the course of temperature and deformation fields in individual phases of the forming cycle, great emphasis is put on the optimization of forming tools design and cooling (pressing) as well as on the optimization of technological parameters (press-and-blow process). The output of the optimization cycle is a new type of glass mould coming from the concept of the controlled cooling being developed in our Department.

Main advantages and innovative aspects of the technology are an increase in the forming cycle efficiency with simultaneous improvement of qualitative indices, substantial reduction of the waste rate and minimization of the onset time of new products manufacture.

We can offer collaboration on solutions of production problems, the forming cycle optimization in the pre-production phase and an optimization of the forming tools design and cooling.

Based on the principle of the glass mould controlled cooling, an integral methodology for design optimization of forming tools was originated. The development in the sphere of temperature and deformation characteristics of rheological properties of the glass melt being formed as well as the development of optimization algorithms for the control of the forming cycle technological parameters are continued.

See more about this kind of the research in the paper: Matoušek, I. Computer modelling and optimisation of glass forming cycle (in these proceedings).

(a) (b) (c) Fig. 1 Numerical simulation of glass forming - temperature distribution in glass melt

during pressing Robotized handling of glass products

Handling processes in the glass industry must be solved putting emphasis on mechanical properties of the manipulated object – glass, when destructions of surfaces, changes in shapes of hot glass products or even their destruction can occur during the handling process. These ground problems can be solved comprehensively using a mathematical model (Fig. 2). Then the design solution of gripping heads including adjustments of handling device parameters can be optimized.

The innovative aspect is the use of the computer simulation allowing to solve comprehensively the handling of glass products assortment including the contact connections description. The main advantage is the effective use of results obtained for an optimal solution of gripping heads, furthermore a possibility to predict conflict states which can cause the handled object damage.

In the present time the verified model of the handling task with glass sheets is available taking account of specific mechanical properties of glass.

In this field of research we can offer to collaboration: Noncontact measurements of deformations by laser optical sensors;

Experimental data processing including the frequency analysis; Virtual model processing for the given system or problematic design part; Optimization of kinematics parameters (acceleration, speed) of handling

devices for minimum loading the object being handled taking acount of the gripping head design;

Solution of contact tasks in the handling processes as well as in industrial applications generally, namely from the standpoint of both static and dynamic stresses. See more about this kind of the research in the paper: Novotný, F.,

Horák, M. Robotic handling with flat glass (in these proceedings).

Fig. 2 Numerical simulation of handling process with glass products

Evaluation of experimental data from the industrial practice using the fractal geometry and statistic tools

Data obtained from production processes and experiments are often structured in a complex fashion. Their description can be carried out using typical as well as advanced tools of statistics. However, it turns out that a description using so-called fractal dimension is very suitable (Fig. 3). The description of „data complexity“ is possible – in the ideal case by means of one and only number which quantifies „complexity degree“. An appropriate combination of the results of statistics and fractal dimension allows to describe data better and obtain more information applicable to the description and check. Now the developed as well as commercial software tools make the description possible in the form of time series, digital (data) pictures and boundaries.

The main advantages of these developed software tools in combination with commercial programmes are their ability to describe complex data better and also universality of the developed methodology. It is relatively new and perspective application of the fractal geometry in the industry.

Now the developed methodology has verified using data from the production as well as improved. The software tools are reached the level of commercial programmes.

Data processing as well as a possible future application of the software tools in the industrial practice for off-line or on-line data evaluation can be offered.

See more about one part of the research in the paper: Hotař, V., Hotař, A. Surface Profile Evaluation Using Statistic Tools and Fractal Dimension (in these proceedings).

Fig. 3 Estimating of the fractal dimension using the box dimension

Study of glass rheological characteristics The research in the laboratories of the department is focused on section of

molten glass shaping – material with expressive rheological characteristics which change depending on warmness. Molten glass, from rheological point of view, is defined by many parameters not enough described for the commercial used types of glass. For the description of viscous-elastic behavior is needed the knowledge of material characteristic of molten glass which serve for to specification of mathematical model process of molten glass shaping and also for verification of outputs from computer modeling based on principle of finite element method. A

number of prestigious authors, in the world, are concerned with research of rheological parameters, but their work is only usable for formulation of solving theoretical resource.

Gravity glass forming process modelling

High demands on a shape accuracy and next particular requirements force producers of windscreens to deeper understanding of the gravity forming process. Glass forming in the windscreen production from physical point of view is a complicated thermomechanical process. The relation between heat transfer and viscous molten glass flow is the dominant criterion. A numerical simulation is the main way of more detailed study of gravity forming process. A number of prestigious authors are concerned with numerical simulation of this problem in the world. Experimental modeling appliance for gravity glass forming is applied for numerical results verification on our workplace.

Assoc. Prof. František Novotný, head of the Department of Glass Producing Machines and Robotics, Technical University of Liberec, Hálkova 6, 461 17 Liberec 1, the Czech Republic, e-mail: frantisek.novotny@tul.cz, www.ksr.tul.cz