Miroslav Plančak

Experimental Tooling for Contact Stress Measurement in Bulk Metal Forming Processes

Experimental Tooling for Contact Stress Measurement in Bulk Metal Forming Processes Knowledge of contact stresses in metal forming operations is essential not only for optimal die design, but also for theoretical and numerical analysis of the metal forming processes. Determination of contact stresses can be performed theoretically and experimentally. This paper presents a tool construction with built-in pin-load cells for experimental determination of contact stresses and friction coefficient at upsetting of prismatic specimen with cylindrical dies. This construction allows measurement of contact stresses in any point of the contact surface of specimen, due to adjustable location of pin-load cells. The adjustments are performed by turning cylindrical dies around its own axis in combination with the change of axial position of the specimen. Experimental determination of contact stresses in upsetting of Ck35 prismatic specimens using cylindrical tools was performed at the Laboratory for technology of plasticity, FTN Novi Sad. Alati Za Eksperimentalno Određivanje Kontaktnih Napona u Procesima Zapreminskog Plastičnog Deformisanja Određivanje relevantnih parametara procesa po fazama obrade plastičnim deformisanjem bazirano je na detaljnoj analizi napona i deformacija. Metode određivanja napona i deformacija dele se na teorijske, eksperimentalne i numeričke. U ovom radu prikazana je metoda eksperimentalnog određivanja kontaktnih napona pomoću merne čivije u procesu sabijanja prizmatičnog pripremka cilindričnim alatima. U radu je prikazana detaljna konstrukcija alata sa ugrađenim mernim čivijama za određivanje kontaktnih napona i koeficijenta trenja pri sabijanju cilindričnim alatima. Ovakva izvedba alata omogućuje merenje kontaktnih napona u bilo kojoj tački kontaktne površine, zbog mogućnosti promene početnog položaja merne čivije rotiranjem cilindričnih pritiskivača u kombinaciji sa aksijalnom promenom položaja pripremka. Eksperimentalna ispitivanja kontaktnih napona u procesu sabijanja prizmatičnog pripremka od Č1431 su izvedena su u Laboratoriji za tehnologije plastičnog deformisanja na Fakultetu tehničkih nauka u Novom Sadu. Provera tačnosti prikazane metode izvršena je na osnovu dijagrama deformacione sile određene direktnim merenjem tokom sabijanja i integracijom eksperimentalno određenih kontaktnih napona. Metoda merne čivije omogućuje precizno određivanje kontaktnih napona u procesima plastičnog deformisanja, uz uslov da postoji mogućnost ugradnje mernih elemenata u radne elemente alata.

Material formability at cold upsetting of cylinder by different plates as a base for metal forming technology design

Upsetting of cylinder by flat dies is one of the elementary bulk metal forming operation. But, upsetting of cylinder can also be performed by the dies different than flat, which influences the stress-strain state and material formability. This paper describes the formability analysis at cold upsetting of cylinder and hollow cylinder by different plates (flat plates, hollow plates and hollow plates whit concentric channels). The aim of this investigation is determination of influences of die and workpiece geometry on stress-strain state and material formability. The obtained results are integrated in formability limit diagram, which represents relationship between limit strain (ϕe1) and stress indicator (s). Experimental investigations have been performed on steel specimens C4146 (EN: 100Cr6). The determined diagram is a base for metal forming technology design, as it enables to predict damages of material structure during plastic deformation.

Different Possibilities of Process Analysis in Cold Extrusion

Cold extrusion is a technology which offers a number of advantages when compared to other manufacturing technologies. High mechanical properties of extruded component, short production time as well as significant cost effectiveness which can be achieved by implementation of this technology are the main characteristics of cold extrusion process. In order to design the complete extrusion process in optimal way it is crucial to know the main process parameters such as load, die pressure, stress and strain distribution within deformation zone etc. There is a number of methods for the analysis of cold extrusion processes. Current paper gives the insight into the possibilities of process analysis in three different cases of cold extrusion. Radial extrusion of gear like elements has been analyzed theoretically (Upper Bound method), numerically by FE simulation and experimentally. Die stressing has been measured by special device (pin load cell) in the process of forward extrusion. Third analyzed process was backward extrusion with profiled punch. In this process loading characteristics as well as some of the mechanical properties of extruded component were obtained experimentally.

Numerical Simulation of Combined Forward-Backward Extrusion

The paper analyses the process of simulation forward-backward extrusion. In metal forming industries, many products have to be formed in large numbers and with highly accurate dimensions. To save energy and material it is necessary to understand the behavior of material and to know the intermediate shapes of the formed parts and the mutual effects between tool and formed party during the forming process. These are normally based on numerical methods which take into account all physical conditions of the deformed material during the process. For this purpose, the finite element method has been developed in the past in different ways. The paper highlights the finite element simulation as a very useful technique in studying, where there is a generally close correlation in the load results obtained with finite elements method and those obtained experimentally.

Modeling Approach for Determination of Backward Extrusion Strain Energy on AlCu5PbBi

In the paper, firstly on the basis of different theoretical methods and by means of different strain determining criteria the analytic modeling of backward extrusion process was done. Analyzed analytical models are derived directly from the mathematical description of the backward extrusion physical phenomena and their mathematical description has been presented. Afterwards, numerical modeling of strain energy by means of ABAQUS 6.4.1. software [1] was done. Also, stochastic modeling, founded on the statistic processing of experimental data according to the mathematical theory of experimental design, has been examined. For establishing of process strain energy, the second order stochastic model has been introduced. Analytic, numerical and stochastic research and experiments were performed according to central composite design (type CCC). As industrial case, the material AlCu5Pb Bi was chosen. The power law which describes material compression properties is obtained as 334.33 . = ⋅ϕ 0.192 f k The extrusion strain energy is dependent on the change in section size, friction coefficient, and material properties. Because of that, these parameters were varied variables at the all points of CCC design. The diameter of workpiece used in this design was set predetermined as industrial case, but both coefficient of friction and wall thickness of workpiece has been varied according to experimental design. The best results in modeling were derived by means of stochastic modeling, and the best strain energy model in the form 2 2 W = -1111.82 − 88.7 ⋅μ − 3200 ⋅μ + 625 ⋅μ ⋅ s + 816.43 ⋅ s − 42.25 ⋅ s has been obtained.