Ocena własności obrabiarek na podstawie dokładności obróbki przedmiotów próbnych

• Autorzy: Skoczyński W.

Warianty tytułu

EN

Evaluation of machine tool properties based on machining accuracy of test pieces

• Języki publikacji: PL

Abstrakty

PL

Opracowano metodę kompleksowej oceny własności układów konstrukcyjnych obrabiarek i ich walorów eksploatacyjnych na podstawie badania dokładności obróbki przedmiotów próbnych i z uwzględnieniem stawianych maszynie zadań technologicznych. Metoda ta zakłada takie obciążanie obrabiarki, jakie występuje podczas realizacji stabilnego procesu obróbki wykańczającej. Dokładność obróbki jest oceniana przez pomiar i analizę odchyłek wymiarów próbnych przedmiotów obrabianych. Wprowadzono wskaźniki oceny, które uwzględniają związek między ocenianymi własnościami układu konstrukcyjnego a dokładnością obróbki przedmiotu próbnego. Umożliwiają one dokonanie zarówno całościowej oceny wpływu własności obrabiarki na uzyskaną klasę dokładności wymiarowo-kształtowej tego przedmiotu i jakość jego powierzchni, jak i ocen cząstkowych wpływu własności statycznych, dynamicznych i geometrycznych tej obrabiarki lub procesu skrawania na wspomnianą klasę. Wskaźniki te wiążą w czytelny sposób własności obrabiarki z efektami obróbki w postaci odchyłek wymiarów, odchyłek kształtu i chropowatości powierzchni obrobionego przedmiotu. Są one wyrażane ilościowo i odpowiadają wartościom liczbowym klas dokładności wymiarów ISO. Ich postać zależy od ogólnego celu oceny własności obrabiarek, gdyż zdefiniowane są w odniesieniu do badań prototypu i do badań odbiorczych. Wprowadzone wskaźniki i kryteria oceny własności i walorów eksploatacyjnych obrabiarek nadają się do włączenia do komputerowo wspartych procedur projektowania i optymalizacji układów konstrukcyjnych obrabiarek. Opracowana metoda oceny jest spójna z tymi procedurami, ponieważ umożliwia wykorzystanie wspólnych danych wejściowych i takich samych reprezentatywnych stanów konfiguracji struktury i stanów obciążeń układu konstrukcyjnego.

EN

The aim of the study presented in the monograph is to work out a comprehensive method for evaluating properties of machine tools structures and their performance characteristics based on machining accuracy of test pieces and taking into account desired production tasks. There is still a great need for such methods as is clearly seen from a review of procedures used in testing of machine tools both in the laboratory and on the plant floor . It can be said that at the moment there are no truly workable methods for evaluating properties of the machine tool structure. "This is primarily due to the lack of suitable evaluation criteria and sound reference values as well as to insufficient knowledge concerning relationships between properties of machine tool and its basic operational functions. Assessment of machine tool parameters is now usually done based on indexes or reference parameters a priori adopted by a designer or a user. What is more, there are no manufacturer- or user-independent methods of evaluation that could account for the machine's range of application or the desired manufacturing tasks. The present approach to evaluation assumes actual operational loads and manufacturing performance of a machine tool as crucial factors of evaluation (Sect. 5.1). The presented comprehensive method assumes a machine tool to be loaded in the same manner as during a stable finishing process. Load conditions and the corresponding configurations of the working units depend on desired machining tasks. They result from dimensional analysis of a variety of workpieces that a machine is capable of dealing with. Machining accuracy is assessed by measuring and analyzing dimensional deviations of test pieces. Evaluation indexes were established (Sect. 5.2) that are able to account for relationships between properties of the machine tool structure and machining accuracy. A notion "properties of machine tool structure" was in this study confined to the deformability of this structure, which kind depends on the nature of operating loads. The effects of deformations expressed in geometrical and form deviations of machined workpiece were evaluated. The proposed indexes allow an investigator to arrive not only at a complete picture of the relation between this properties and ISO accuracy grade but also at estimates of particular effects of static, dynamic or geometrical properties of the machine or of cutting process conditions on this grade. These indexes can be made insensitive to specific conditions of a given cutting process (Sect. 6.8.4). A general procedure was formulated for determination of the indexes based on structural analysis and on desired machining tasks that gives some directions relative to the loads distribution in the working space (Sect. 5.3, 6.3 and 6.4), the selection of representative workpieces, tools, cutting parameters and instrumentation (Sect. 5.4 and 6.5). The manner the cutting tests are to be conducted and the dimensional deviations of a workpiece measured was determined in Sect. 5.5 and 6.6. The presented indexes explain clearly how the machine tool properties affect dimensional tolerances, form errors and finish quality of the workpiece (Sect. 5.2). The indexes are expressed as numbers of the continuous distribution of the ISO accuracy grade (see Fig. 5.2). They can be juxtaposed with clearly defined reference values in the form of ISO accuracy grades corresponding to particular machining operations. It is also possible to perform a partial evaluation using absolute values of a given type of permissible deviations and comparing the measured deviations with the reference values given in Tables 4.1, 4.2 and 4.4. The indexes enable design variants of a machine tool or various units of the same make to be compared. A particular form of the indexes is dependent upon the purpose of the machine tool evaluation since they are defined with respect to prototype and acceptance tests (Sect. 5.2). The global and local evaluation indexes recommended for prototype studies can be helpful in identifying malfunctions and performing design changes. The acceptance evaluation indexes enable the tests to be conducted in a short time and their values are close to the global index values. The indexes can be used in evaluating quality of the machine tool structure. The proposed method and the established indexes and criteria can be implemented in formal procedures of design and optimization of structural components of individual machines and flexible machining systems (Sect. 5.7). Experimental verification of the evaluation method was done on a medium-size universal lathe (Sect. 6.1). The tests proved the method to be capable of accounting for the effect of both the machine tool structure properties and the machining process conditions on dimensional-geometrical accuracy of the workpiece. The indexes were found to be sensitive to changes in the configuration of the machine tool structure (Sect. 6.8). The study allows the author to formulate the following conclusions: 1. The proposed method for evaluating structural properties of machine tools and their performance characteristics enables an investigator to prescribe clear quantitative evaluation indexes and express them similarly to ISO accuracy grades. A designer and a user can use such indexes to make an efficient evaluation concerning structural and functional qualities of a machine. 2. The comprehensive method can be used for analyzing the effect of both the machine structure properties and the cutting process conditions on workpiece machining accuracy due to its sensitivity to the structural parameters and process variables. 3. The method allows for actual working loads that are inferred from the desired machining tasks and for level of dimensional-geometrical accuracy of workpiece. Properties of a machine and its operational performance are evaluated based on indexes accounting for dimensional deviations, form deviations and roughness of machined surfaces. 4. The proposed indexes are universal in character. They can be used either in global evaluation of a machine tool, be it a prototype or a finished machine to be commissioned, or in partial evaluation of selected properties. The indexes can be referred to the ISO accuracy grade. The values of appropriate measured deviations can be compared with the absolute values of permissible deviations quoted in the monograph. 5. The proposed evaluation criteria and indexes can be integrated within computer aided procedures of design and optimization employed in the machine tool industry. The proposed method is cohesive with these procedures since it makes use of the same input data and it takes into account the same states of configuration and states of load of the structure both in design processes and in experimental study. 6. Workpiece databases are integral part of evaluation procedures since they can generate machining tasks that form the same input data for both design processes and tests done on prototypes and machines put in for acceptance. 7. Experimental verification performed on a universal lathe proved the method to be fully workable and can be considered its practical application when it comes to this class of machines. 8. Experience gained in the course of investigations will be helpful in working out manufacturer- and user-independent recommendations concerning the prototype tests. It can be also a theoretical basis for standardization of acceptance tests in the area of evaluation of test piece machining accuracy.

Słowa kluczowe

PL

obrabiarka; układ konstrukcyjny; ocena własności; kryteria i wskaźniki oceny

• Wydawca: Oficyna Wydawnicza Politechniki Wrocławskiej
• Czasopismo: Prace Naukowe Instytutu Technologii Maszyn i Automatyzacji Politechniki Wrocławskiej. Monografie
• Rocznik: 2001
• Tom: Vol. 81, nr 25
• Strony: 159--159
• Opis fizyczny: s., bibliogr.216 poz.

Twórcy

autor

Skoczyński W.

• Instytut Technologii Maszyn i Automatyzacji Politechniki Wrocławskiej, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław