Maroš Martinkovič

Analysis of Strain in Cutting Zone with FEM and Stereological Metallographic Evaluation

Finite element modelling (FEM) of machining is a widely applied way to get information about the phenomena occurring during the cutting process. This paper discusses experimental work and FEM analysis to investigate the mechanism of CK45 (1.0503) carbon steel chip formation during orthogonal turning process. Local strain in cutting zone is estimated by measurement of deformation of metallographic cut using stereological evaluation of the gain boundary orientation. Estimated local strain in cutting zone was compared to deformation analysis for orthogonal cutting was made, based on simulation results in numerical modelling software DEFORM 2D. Stress, temperature, tool wear is also discussed in the last part of this paper.

Estimation of Local Plastic Deformation in Cutting Zone during Turning

Local plastic deformation in cutting zone during turning is affected by technological conditions of the processes. Therefore it is needful to know detail structure changes of plastic deformed material during machining. It is localised, asymmetric deformation which operates at very large strains and exceptionally high strain rates. Three areas of intensive local plastic deformation in cutting zone were observed: the primary area of plastic deformation in shear plane, the secondary area of plastic deformation caused by friction of chip to tool face and the tertiary area of plastic deformation caused by friction of tool to machined surface. Local strain in these three areas was estimated by measurement of deformation of grains on metallographic cut. The effect of grains boundaries self-orientation caused by grains deformation was evaluated using stereology. But the orientation is not the same as deformation and so a correlation between the grain deformation and grain orientation was used. The turning piece was made of CK45 (1.0503) carbon steel. The specimen of cutting zone was obtained by using internal stress method.

Shear Strength of Joints Fabricated by Solders with High Indium Content

Feasibility of pure indium and solders containing high amount of indium as 70In30Sn to wet the different types of metallic and ceramic materials at application of power ultrasound was studied. The shear strength of soldered joints fabricated on metallic (Cu, Ni, Al, Ti, AISI 316 steel) and ceramic substrates was assessed. The shear strength of In solders on Al2O3 and SiC ceramic materials varied from 3.5 to 7 MPa. The shear strength on metallic materials attained from 12.5 to 71 MPa. Joint fracture in most cases occurred in the solder and was of ductile character. Failure took place by shear mechanism.

Determination of the Coefficient of Friction Under Cold Tube Drawing Using FEM Simulation and Drawing Force Measurement

Abstract The purpose of this article is to describe the methodology to define coefficient of friction between a tool and a forming material during tube cold draw technology process. In this regard, an experimental drawing process was done by using the tensile testing machine. The tensile testing machine was modified by additional equipment that allows drawing the tube. During the drawing, the force was recorded. Subsequently, the finite element simulation of cold draw forming was used to generate load-stroke curves with different friction coefficient. The friction coefficient was estimated by comparing the load stroke and the force recorded curves.

Estimation of Fibre Orientation in Injection Moulding Plastics Parts

Fibre orientation in short fibre reinforced thermoplastics depends on injection moulding parameters. There are a lot of different parameters that must be established and controlled to achieve proper injection moulding of a plastic part. These parameters fall within four major areas: pressure, temperature, time, and distance. The aim of this article is estimation of fibre orientation in injection moulding plastics parts and comparison of these results with numerical simulated ones. Stereological metallography was used for estimation of experimental orientation of fibres. The orientation of simple fibre may be defined by the two angles θ and Φ. In a Short Fibre Reinforced Thermoplastic (SFRT) component there are frequently millions of fibres, therefore each individual fibre orientation specifying is very impractical. The fibres orientation in space can be described by the probability distribution function (PDF), Ψ(θ, Φ). Numerical modelling of fibre orientation was realised using MOLDEX3D software. Moldex3D is the CAE product for the plastics injection moulding industry. This software allows to view results of fibre orientation as an orientation of the X direction, Y direction, Z direction, the total orientation and orientation at surface. These first three orientations are relevant for the establishment of second-order orientation tensor. They belong to tensor ́s values a11, a22 and a33. Utilization of stereological metallography for short fibre orientation in plastic matrix is very similar to its utilization for estimation of grain boundaries orientation in polycrystalline alloys cased by plastic deformation. In the case of short glass fibres reinforced thermoplastics it’s structure consist of thermoplastic matrix and reinforcing fibres, which has some preferred orientation in most of cases – the structure is anisotropy. The way of scalar measurement of structure anisotropy is determination of degree of orientation. The anisotropic microstructure is decomposed into isotropic, planar or linear oriented components using stereology methods.

Possibilities of Stereological Analysis of Grain Boundary Orientation in Longitudinal Sections of Precision Cold Drawn Seamless Steel Tubes

Cold drawing of steel tubes refers to a forming operation where a precision steel tube is being formed in a die while reducing tube cross-section, altering the wall thickness and making the final tube much longer than the original hollow. The forming itself takes several drawing passes (a.k.a. draws) depending on the final tube dimension requested. The selection of relative reduction for a particular tube diameter plays an important role because an excessive reduction during drawing causes stresses that induce substantial plastic deformation, eventually leading to cracking. In this paper we evaluate the effect of selected reductions on the longitudinal grain boundary orientation in cold drawn tubes, taking tube sample measurements and making necessary calculations of grain boundary orientation in selected planes.

Production Technology for Precision Seamless Steel Tubes from the Perspective of Microhardness Changes

The production of precision seamless steel tubes in Železiarne Podbrezová is using hot rolled tubes with multiple cold drawing passes and intermediate annealing. It utilizes intensive plastic deformation during cold drawing, taking full advantage of the microstructural state from a physical point of view. In this paper, optimization of technological processes for cold drawn tubes made from ferritic-pearlitic steel has been elaborated. We use microstructural and substructural analysis, dislocation hardening theory and stress analysis. The subject of this article is the experiment with multiple drawing passes and intermediate annealing for production of precision steel tubes with dimensions of 31.8 x 2.6 mm. The drawing itself consists of 5 processes (also called „runs“) with 7 drawing passes in total. The results presented show strain hardening of the material after drawing along with relaxation mechanism during intermediate annealing. The possibility of utilizing the microhardness values on intensity assessment of these processes is investigated, too.

Analysis of Local Plastic Deformation of Machined Surface

Technological processes of machining lead to plastically deformation of workpieces. Therefore it is needful to know influence of machining to machined material. The area of plastically deformation caused by friction of tool to machined surface was analysed. Local strain in structure was estimated by measurement of deformation of grains on metallographic cut using stereology. Local plastic deformation in deformation zone around the surface of drilled holes, local plastic deformation in deformation zone near the surface of milled workpiece and local plastic deformation near the surface of turned workpiece were investigated. The working piece was bulk from carbon steel CK45 (1.0503). Local plastic deformation was observed in case of drilling and turning, in case of milling no deformation of surface was present.

Evaluation of Grain Deformation in Polycrystals

Method of local strain estimation based on evaluation of relative surface area of grain boundaries in deformed and undeformed state is used very often [. Unfortunately, this method requires information about the parameter of structure in case of zero value of initial deformation. Mentioned parameter is unknown in most cases. In addition, value of parameter of structure depends on grain size and it can change in volume of material.

Influence of Drill Wear to Local Plastic Deformation in the Wall of Drilling Hole

Final properties of plastic deformed parts of workpieces are affected by production technological processes. Therefore it is needful to know detailed structure changes of plastic deformed material caused by machining - grinding, drilling etc. Friction of tool to work surface caused one of three areas of plastic deformation in cutting zone. It has great influence to quality of work surface and local mechanical properties of surface layer of workpiece. Influence of drill wear to local plastic deformation in deformation zone around the surface of drilled holes was investigated. Two types of cutting tools were used: high speed steel drill IZAR HSSCO with diameter 6,0 mm surface hardened by boriding and the same one without boride layer. Standard cutting parameters were used. During the machining process, axial component of cutting force and torque were observed. The work piece was bulk from carbon steel Ck45 (1.0503). Wear of the tool was estimated as a wide of wear on tool flank. The local strain in analysed place of probes on their sections was obtained by stereological measurement of degree of grain boundaries orientation, which is proportional to grain boundaries deformation degree. Estimation of grain boundary orientation degree leads to determination of local plastic deformation in arbitrary place of workpiece. These results lead to detailed analysis of material structure changes caused by drilling from which local mechanical properties result.