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Influence of the contact pressure in the deep drawing processes is a very actual research topic in the metal forming technology. Within this research the tribological model of the strip sliding in the flat die was developed. The original experimental computerized apparatus for testing of the strip sliding in the variable contact pressure conditions was developed, as well. The complex, multi-factor experiment was performed by application of the Al thin sheet, with the contact elements of various roughnesses, with different lubricants application and with the variable contact pressure. Besides the description of the developed apparatus, the theoretical way for determination of the pressure dependences was also presented. Based on the theoretical changes of pressure, set in advance, the real influence of the contact pressure was obtained, for each of the given conditions. That makes possible to determine the influence of the tribological factors on the actual pressure. The obtained real contact pressure has verified the reliability of the experimental apparatus, namely the degree of the theoretical pressure dependences deviation from the real ones.

The spot welded thin steel sheets specimens are experimentally and numerically examined in this paper. The two specimens are joined using Resistance Spot Welding (RSW) method. The spot-welded joints consist of three zones with different material properties. Change of material properties during the welding process is caused by mechanical and thermal loading. The mechanical properties of thin steel sheets are determined by several tension tests. The specimens are cut in three different directions regarding a rolling direction of the basic material plate. Shear resistance of the spot welded joints is experimentally examined on the universal testing machine by displacement-controlled tensile loading tests. The numerical analysis is performed by large-strain plasticity theory implemented into a Finite Element Method based software. Comparison of the Finite Element (FE) modeling and experimental results verifies the proposed stress integration algorithm and modeling technique as powerful tools for prediction of the spot-welded joint behavior.

Kovački alati su dijelovi, koji rade na povišenim temperaturama, dok su istodobno izloženi promjenljivim opterećenjima, koja mogu biti tlačna - čak i udarna i smična. Utjecaj tehnologije navarivanja je vrlo jak, pošto se variranjem njegovih parametara direktno utječe na izlazne karakteristike navarenih slojeva. Kriterij za procjenu tog utjecaja bio je utemeljen na rezultatima obavljenih triboloških ispitivanja. Praćeni tribološki parametri bili su faktor trenja, širina traga (brazgotine) habanja kao i površina habanja navarenih slojeva, uz uporabu dva tipa maziva. Tehnologija navarivanja je podrazumijevala selekciju procesa zavarivanja, dodatnih materijala, temperature predgrijavanja i ostalih parametara procesa navarivanja. Utjecaj predložene tehnologije navarivanja je određivan praćenjem tvrdoće, mikrostrukture i otpornosti na habanje izvedenih spojeva, nakon navarivanja i nakon otpuštanja. Cilj ovog rada bio je uspostavljanje korelacija izabrane tehnologije navarivanja, dodatnih materijala i primijenjene toplinske obrade s mehaničkim i tribološkim karakteristikama izvedenih navarenih slojeva., The forging dies are parts, which are operating at elevated temperatures, while simultaneously subjected to variable loads that can be compressive - even impact and shear. Impact of the hard facing technology is very strong since varying of the hard facing parameters directly affects the output characteristics of the hard faced layers. The criterion for estimating that impact was based on results of performed tribological investigations. The tribological parameters that were monitored were the friction coefficient, the wear scar/trace width and the wear area of the hard faced layers, with the two different types of lubricants. Hard facing technology implied selection of the welding process, filler metals, preheating temperatures and other parameters of the hard facing process. The influence of the proposed hard facing technology was determined by monitoring hardness, microstructure and wear resistance of the executed joints after the hard facing and after tempering. The objective of this work was to establish the correlation between the selected hard facing technology, filler metals and applied heat treatment on mechanical and tribological characteristics of the executed hard faced layers.

The process of deep drawing is influenced by many factors. During the forming process, only two of those factors can be controlled. They are blank holding force and drawbead height. Realisation of such control requires relatively complex computerized apparatus. For this experimental research, electro-hydraulic sheet-metal strip sliding device has been constructed. Basic capacity of realized device is obtaining contact pressure and drawbead height as functions of time or stripe displacement. Additional features consist of the ability to measure drawing force, contact pressure, drawbead displacement etc. Presented in the paper are the results of influencing of increasing and decreasing drawbead height functions in combination with increasing-decreasing function of contact pressure. Stripe material is aluminium alloy AlMg4,5Mn0,7 sheet metal. Contact condition are additionally influenced by application of mineral oil or completely dry tool and stripe surfaces. Drawbead geometry, with rounding radii of 2 and 5 mm, is also varied. The accomplished results indicate that simultaneous effects of variable drawbead height, variable contact pressure, tool geometry and appropriate friction conditions can influence the plastic flow process in line with desired change of forming force., Na proces dubokog vučenja utječe više faktora. Tijekom trajanja procesa oblikovanja moguće je upravljati samo s dva faktora. To su sila držanja i visina zateznog (vlačnog) rebra. Ostvarivanje takvog upravljanja zahtjeva relativno složenu kompjutoriziranu aparaturu. Za ovo pokusno istraživanje razvijen je elektro-hidraulički uređaj za klizanje traka od lima s kompjutorskim upravljanjem. Njegova osnovna karakteristika je ostvarivanje kontaktnog tlaka i visine zateznog rebra, kao funkcijskih ovisnosti o vremenu, odnosno hodu trake. Pored toga, moguće je mjeriti vučnu silu, silu pritiska, pomak rebra itd. U radu su izloženi rezultati ispitivanja utjecaja opadajuće i rastuće ovisnosti visine rebra u kombinaciji s rastuće-opadajućom funkcijom kontaktnog tlaka. Materijal trake je legura aluminija AlMg4,5Mn0,7 debljine 0,9 mm. Na kontaktne uvjete se dopunski utječe s dva tipa trenja. U prvom slučaju površine su suhe, a u drugom se primjenjuje podmazivanje odgovarajućim mineralnim uljem. Geometrija rebra se mijenja preko polumjera zaobljenja 2 i 5 mm. Ostvareni rezultati pokusa pokazuju istodobno djelovanje promjenljive visine rebra, promjenljivog kontaktnog tlaka, geometrije rebra i odgovarajućih uvjeta trenja, mogu utjecati na proces plastičnog tečenja u skladu sa željenom promjenom sile oblikovanja.

This paper outlines the bases of the friction welding process, especially when it comes to friction welding of different materials. This was illustrated on an example of friction welding of aluminum and copper, which is often applied in electrical engineering. The analysis of influential parameters was conducted based on the data obtained by an experiment, since the data on this topic are very seldom in the available literature., Ovaj članak daje osnove procesa zavarivanja trenjem, naročito kada je u pitanju zavarivanje trenjem različitih materijala. To je ilustrirano na primjeru zavarivanja trenjem aluminija i bakra, koji se često primjenjuje u elektrotehnici. Analiza utjecajnih parametara provedena je na temelju podataka dobivenih eksperimentom jer su podaci o ovoj temi vrlo rijetko u dostupnoj literaturi.

This paper outlines the basic principles of welding by friction of high-speed cutting steel and tempered steel from the viewpoint of metallurgic processes that are going on in the material. The bases of welding by friction of different materials are outlined in a theoretical way. The experimental part of the paper also relates to friction welding of samples made of different metals: high-speed cutting steel (HS 6-5-2-5) on one hand and the tempered steel (C60) on the other., Ovaj rad daje osnovne principe zavarivanja trenjem brzoreznog čelika i kaljenog čelika s motrišta metalurškog procesa koji se odvija u materijalu. Osnove zavarivanja trenjem različitih materijala navedene su teorijski. Eksperimentalni dio rada odnosi se na zavarivanje trenjem uzoraka izrađenih od različitih metala: brzoreznog čelika (HS 6-5-2-5) s jedne i kaljenog čelika (C60) s druge strane.

In this paper the problems related to the maintenance of large forging mallets of pneumatic hammers including hard facing of cracked or worn working surfaces are considered. Actually, the choice of optimum technology for the reparation of hard facing of the broken forging press frame and cracked mallet of the forging pneumatic hammer are taken into consideration., U ovom radu se razmatra problematika održavanja velikih batova kovačkih pneumatskih čekića, uključujući tu i navarivanje napuklih i pohabanih radnih površina. Konkretno, ovdje je riječ o izboru optimalne tehnologije reparaturnog zavarivanja napuklog bata. Pored tehno-ekonomske analize, u radu se navodi i energetska analiza, kao dodatni kriteriji za ocjenu primijenjene tehnologije.