Branko Tadic

Locating and clamping of complex geometry workpieces with skewed holes in multiple-constraint conditions

Purpose – The purpose of this paper is to propose a general model for locating and clamping workpieces of complex geometry with two skewed holes under multiple constraints. Design/methodology/approach – Numerous constraints related to application of the proposed model are discussed as prerequisite to design of fixture solution. Based on theoretical model, a fixture was designed and successfully tested in experimental investigation. Experimental results were also verified using FEM simulations. Findings – This study showed that, opposed to conventional approach, novel solution results in significantly smaller fixture dimensions, while providing greater stability. Insertion of mandrels and supports element sub-assemblies into the workpiece holes significantly increases workpiece stiffness through an increased moment of inertia, while the internal support elements largely diminish the problem of thin wall deformation in the workpiece. Practical implications – The fixture designed in this case was actually us...

Multi-criteria decision-making and life cycle assessment model for optimal product selection: case study of knee support

Selection of the optimal product, where several products’ aspects are expressed through criteria, is a multi-criteria decision-making problem. Besides technical, exploitational, functional, structural, market and aesthetic criteria, nowadays, environmental criteria are inevitable aspects of a modern product. Environmental product properties can be successfully evaluated with a life cycle assessment. This paper proposes a multi-criteria decision-making model for optimal product assessment that uses environmental criteria obtained from a life cycle assessment. The proposed model presents a comprehensive approach that aims to overcome complex decision-making problems for optimal product selection, where special attention is given to the product’s environmental impact. Verification of the proposed multi-criteria decision-making and life cycle assessment model was performed on the case study of optimal knee support selection. By changing the criteria weights in multi-criteria decision-making, a sensitivity analysis was performed. The model output results show the product alternatives ranking that supports decision-making in optimal product selection.

Static Friction at High Contact Temperatures and Low Contact Pressure

The problem of measuring static friction at high temperatures and low contact pressures is theoretically analyzed, as well as the instruments for the accurate determination of the coefficient of static friction at high temperatures for contact pairs made of steel and bronze. The results of experimental investigation show that at low contact pressure and temperature above 120°C coefficient of static friction dramatically increases. This increase in the coefficient of friction can be of great practical value with regard to the load capacity of contacts where external forces are balanced with friction forces.

Investigation of ball burnishing processing on mechanical characteristics of wooden elements

Numerous research results indicate that the finishing processing of metal materials using ball burnishing has positive effects from the aspect of surface roughness decrease to the hardness increase in the surface layers of the processed materials. Little research has been devoted to this type of processing for nonmetal materials. This paper presents research results related to the influence of ball burnishing processing on the hardness increase of a wooden element. It was determined that the hardness can be increased up to three times for processing of wood using this technology, which is not the case for processing of metal materials.

Increasing Stiffness of Constructions through Application of Enhancing Elements

Presented in this work is a study on construction stiffness, based on examination of their neutral lines for various cross-section geometries and different force magnitudes. Investigations were conducted both through numerical simulations and experimentally. The results of numerical simulations indicate that stiffness enhancement reduces deflection in the range of 41-52 %, while the experimental tests showed the reduction of 42-54 %. Also reviewed is comparative analysis between the stiffness results obtained by numerical analyses and experiments, which showed high degree of their compliance. The deviations between the results offered by the two methods are 1-3 %, on average, while in the worst case, which occurs in just a couple of points, the deviation equals 10 %. This study revealed significant increase of element stiffness, which was obtained by employment of additional stiffness enhancing elements.

Vibroplatform modeling with allowance for tribological aspects

A vibroplatform model has been presented, which is used in industry for the separation and transportation of granular materials. An analysis of the results of theoretical and experimental studies of the coefficient of friction between the screen and sand granules has been carried out in real operating conditions of the vibroplatform.

Inteligentno projektiranje i optimizacija konstrukcija naprava za strojnu obradu

This work presents an integral system for machining fixture layout design and optimization. The optimization module of this system allows determination of optimal positions of locating and clamping elements, which provides required accuracy and surface quality, while at the same time guarantees design of collision-free fixtures. The design module performs selection of required fixture elements based on a set of predefined production rules. Adequate criteria for the selection of fixture elements are defined for locating, clamping, tool guiding, and tool adjustment elements, as well as for fixture body elements, connecting elements and add-on elements. The system uses geometry and feature workpiece characteristics, as well as the additional machining, and process planning information. It has been developed to accommodate machining processes of turning, drilling, milling, and grinding of rotational and prismatic workpieces. A segment of output results is also shown. Finally, conclusions are presented with directions for future investigation.