In English. Summaries in Estonian

Proceedings of the Estonian Academy of Sciences.



Volume 10 No. 4 December 2004




Preface; 235

Jüri Papstel †

A comparative analysis of global search procedures; 236–250

Alexander Janushevskis, Teodor Akinfiev, Janis Auzins and

Alexander Boyko

Abstract. This paper presents a brief overview and a comparison of global optimization methods and their software. By solving a set of recognized test problems, the reliability of obtaining the global extremums is compared. It is shown that the Edaopt algorithm, developed formerly by the authors, is more efficient than modern genetic algorithms. In most cases the Edaopt algorithm takes also noticeably less computation time.

Key words: optimization, stochastic global search, genetic algorithms.

A 3D turning system to reduce geometry errors of flexible rotors; 251–260

Thomas Widmaier, Petri Kuosmanen, Janne Haikio and

Pekka Väänänen

Abstract. Increased running speed and reduction of accepted vibration levels in paper machines have set new demands for the roundness and cylindricity of paper machine rolls. The diameter variation is mainly caused by the slideway straight­ness error of the machine tool. The rotational er­rors during the machining process come about because of the changing dis­tance between the roll axis and the tool and are copied to the roundness error in the roll. A 3D turning system, including a measuring device, was developed to compensate systematic roll geometry errors. The non-circular turning method was applied to a supercalender roll. The 3D turning reduced the average roundness error in the test roll by 62 %, the diameter variation in the axial direction was reduced by 83 % and the 3D geometry error by 78 %.

Key words: roll, roundness, measuring, non-circular turn­ing.

Modelling and optimal design of the incremental forming process; 261–269

Meelis Pohlak, Rein Küttner and Jüri Majak

Abstract. Recently, a new sheet metal forming technique, incremental forming, has been introduced. It is based on the use of a universal spherical tool, which is moved along the CNC controlled tool path. For optimal design of the incremental forming process, application of non-linear mathematical programming is suggested. To estimate the limitations and main parameters of the process, a complex model for process design has been developed. Incremental forming processes are investigated using experiments and finite element analysis.

Key words: incremental sheet metal forming, finite element analysis, optimal design, non-linear programming.

Advanced dynamic models for evaluation of accuracy of machining on lathes; 270–280

Gennady Aryassov, Tauno Otto and Svetlana Gromova

Abstract: This paper describes the influence of lathe vibrations on the accuracy and roughness of machined parts. The calculation schemes involve systems with one and two degrees of freedom, representing vibrations of the blank as a rigid body, hinged in the spindle and elastically supported in the tailstock of the lathe. Experimental measurements were performed on lathes of type 1K62 at different cutting speeds, feeds and depths of cut. The analysis of roughness measurement data confirmed the accuracy of the proposed calculation model. Surface roughness parameters of the blank satisfactorily agreed with the corresponding data of the theoretical investigation. To study the influence of gyroscopic forces on the surface roughness, the calculation model with two degrees of freedom was used. The results of experimental and theoretical investigations coincided satisfactorily.

Key words: lathe, vibration, calculation model, natural frequency, surface roughness.

Linear stability analysis of shear-flexible thin-walled beams; 281–289

Domagoj Lanc, Goran Turkalj and Josip Brniã

Abstract. This paper presents finite element based numerical stability analysis of thin-walled beam structures. Using the linearized virtual work principle with the assumption of large displacements, large rotations but small strains, a finite element equation is derived. Effects of cross-sectional shear deformations are also taken into account. To include large rotation effects, non-linear displace­ment field of the cross-section is used. A new two-node shear-flexible finite element with seven degrees of freedom per node is developed. Complete exact 14×14 elastic and geometric stiffness matrices are evaluated. An original computer program THINWALL-SHEAR is developed. Obtained results are compared with analytical and numerical results of other authors.

Key words: thin-walled beam, large displacements, large rotations, shear deformations.

Torque distribution control unit in automotive propulsion systems; 290–299

Jüri Resev and Lembit Roosimölder

Abstract. The paper considers energy flow modelling in automotive propulsion systems to provide basic data for the selection of the parameters of the differential, bearing in mind its impact on the vehicle lateral dynamics. The characteristics and operational conditions of the limited-slip differen­tial gear train are found. A virtual differential (algorithm of energy flow) has been created.

Key words: planetary gear train, limited slip, torque transmission, energy loss, modelling.

Design of sandwich support structures; 300–307

Martin Eerme, Mart Enok, Lembit Roosimölder and Rein Küttner

Abstract. In modern engineering industry the weight reduction of support structures of machines is important. One possibility to reach that is to use sandwich structures. Mechanical properties of sand­wich structures are characterized by higher strength/weight and stiffness/weight ratios than those of stiffened steel plate structures. This paper studies the possibility of replacing welded structures by sand­wich ones using topology optimization. In the conceptual phase, topological optimization has been performed that allowed to find a structurally sound initial model for further design and para­metri­cal optimization. Topological and parametrical optimization has been performed using a commercial FEM software system. This method is flexible by designing products with different con­figura­tions that is important by shortening the time to market new products. Welded steel structures, consisting of walls and ribs, are considered. Strength properties, depending on the ribs’ configuration and on the length of welds, have been examined. Technology of manufacturing sandwich frames are described. As an example, the design and reduction of mass of a brush-cutting machine has been investigated.

Key words: metal structures, optimization, FEM.

Performance of hard alloys in abrasive-erosive and sliding wear conditions; 308–314

Jakob Kübarsepp, Heinrich Klaasen and Vello Vainola

Abstract. The wear behaviour of some carbide composites differing in composition and structure (WC hardmetals, TiC and Cr3C2 cermets), has been investigated in abrasive-erosive and sliding wear conditions. Comparative trials in the same conditions with tool steels, complemented by SEM studies, have been performed. It has been shown that in abrasive-erosive as well as in sliding wear conditions the performance of a hard alloy (carbide composite, tool steel) is controlled primarily by its carbide phase (its properties and amount in the alloy).

Key words: abrasive-erosive wear, sliding wear, cemented carbides, tool steels.

Recycled hardmetal-based powders for thermal spray; 315–325

Valdek Mikli, Priit Kulu, Riho Tarbe, Priidu Peetsalu and

Sergei Zimakov

Abstract. The paper focuses on low-cost tungsten carbide based spray powders with particle size of 15–50 mm, produced from recycled hardmetal. Their properties are comparable with commercially produced (Tafa Inc., Sulzer Metco Inc., etc.) powders. Different methods of WC-Co hardmetal powder preparation (plating, milling and mixing) were used to produce spray powders. The composition and structure of recycled hardmetal-based spray powders, produced by the disintegrator, attritor and ball milling, were investigated. Powders were chemically and mechanically plated with Co or agglomerated, using different plating techniques and heat treat­ment. Chemical composition of powder particles was studied by energy-dispersive X-ray micro­analysis and element distribution inside powder particles was investigated on particle cross-sections with the X-ray mapping technology. Best results were obtained using monomodal initial WC-Co and Co powders with the mixing, agglomeration, sintering and crushing techniques.

Key words: recycling, disintegration, milling and mixing, agglomeration and sintering, double-cemented hardmetal powder, particle composition.

Contents of volume 10; 326–328