Lasersko reparaturno zavarivanje alata s različitim oblicima impulsa

Repair welding of cold-work tool steels with conventional methods is very difficult due to cracking during remelting or cladding and is generally performed with preheating. As an alternative, repair welding with laser technology has recently been used. This paper presents the influence of different pulse shapes on welding of such tools with the pulsed Nd:YAG laser. Repair welding tests were carried out on AISI D2 tool steel, quenched and tempered to hardness of 56 HRc, followed by microstructural analysis and investigation of defects with scanning electron microscopy. Test results suggest that it is possible to obtain sound welds without preheating, with the right selection of welding parameters and appropriate pulse shape.Reparaturno zavarivanje alatnih čelika za rad na hladno konvencionalnim metodama je vrlo teško zbog pukotina nastalih tokom pretaljivanja i navarivanja i općenito vrši se uz predgrijavanje. U posljednje vrijeme se kao alternativna metoda koristi reparaturno zavarivanje upotrebom laserske tehnologije. Ovaj rad predstavlja utjecaj različitih oblika impulsa na zavarivanje alatnih čelika s pulsnim laserom Nd:YAG. Reparaturno zavarivanje testirano je na alatnom čeliku AISI D2, termički obrađenim na tvrdoću 56 HRc, poslije čega je provedena analiza mikrostrukture i traženje defekata skeniranjem elektronskim mikroskopom. Rezultati testiranja sugeriraju da je moguće izvesti dobre zavare bez predgrijavanja pravilnim izborom parametara zavarivanja i odgovarajućeg oblika impulsa

Laser grooving of surface cracks on hot work tool steel

The paper presents the analysis of laser grooving of 1.2343 tool steel hardened to 46 HRC. The effect of laser power and grooving speed on groove shape (i.e. depth and width), the material removal rate and the purity of produced groove as a measure of groove quality was investigated and analyzed using response surface methodology. Optimal parameters of laser grooving were found, which enables pure grooves suitable for laser welding

Procjena mikrostrukture alatnog čelika za hladni rad nakon pretaljivanja pulsirajućim laserom

The aim of this study is the investigation of micro-structural behaviour of a Mat. No. 1.2379 (EN-X160CrMoV121; AISI D2) cold work tool steel after remelting with a precise pulsed Nd:YAG laser. The investigated steel is one of the most hard to weld tool steels, due to large amount of alloying elements. The analysis was done on single spots remelted with specific laser pulse shape and parameters, assuring crack-less solidification. Re-solidifi ed areas were investigated with microscopy, hardness measurements, X-ray spectroscopy and diffraction method. Laser treatment causes rapid solidification leading into a formation of a fine dendritic microstructures containing high amount of retained austenite causing a significant decrease of hardness.Namjena ove studije je ispitivanje ponašanja mikro strukture alatnoga čelika za rad na hladno Mat. No.1.2379 (ENX160CrMoV121; AISI D2) po pretaljivanju s preciznim pulsiranim Nd:YAG laserom. Zbog velike količine legirnih elemenata istraživani materijal spada u grupu vrlo teško zavarljivih alatnih čelika. Analiza je provedena na pojedinim pretaljenim točkama korištenjem specifi čnog oblika i parametara laserskog impulsa koji osiguravaju skrućivanje bez pukotina. Pretaljena područja su ispitivana mikroskopom, mjerenjem mikro tvrdoće, rendgenskom spektroskopijom i defrakcijskom metodom. Tretman laserom uzrokvao je brzo skrućivanje koja dovodi do formiranja fi ne dendritičke strukture s velikim udjelom zaostalog austenita što uzrokuje bitno smanjivanje tvrdoće

Pukotine na kalupima (alatima) za tlačno lijevanje uslijed toplinskog umora

Die-casting dies are exposed to high thermal and mechanical loads. Thermal fatigue cracking of dies due to thermal cycling may importantly shorten the life-time of the die. Cracks degrade the surface quality of dies and consequently the surface of castings. In this study, thermal fatigue cracking of dies was analyzed during the process of die casting aluminium alloys. During the process cracks were observed and measured and their location and size were determined. Thermal and mechanical loads cause high local stresses and consequently surface cracks. First cracks occur as early as after 2000 cycles and propagate progressively with cycles.Kalupi (alati) za lijevanje pod tlakom su izloženi velikim toplinskim i mehaničkim opterećenjima. Pukotine uslijed toplinskog umora su zbog izmjene toplinskih ciklusa važan ograničavajući mehanizam životnoga vijeka kalupa. Pukotine smanjuju (degradiraju) kvalitetu površine kalupa i posljedično površinu odljevka. U ovom radu su analizirane pukotine nastale na kalupu zbog toplinskog umora tokom tlačnog lijevanja aluminija. Tokom procesa su promatranjem i mjerenjem utvrđene lokacije i veličine nastalih pukotina na kalupu. Toplinska i mehanička opterećenja uzrokuju velika lokalna naprezanja i posljedično pukotine na površini kalupa. Prva pukotina pojavljuje se već nakon 2000 ciklusa i progresivno se širi povećanjem broja ciklusa

Termo-mehaničke pukotine uslijed toplinskog umora na novom i lasersko zavarenom alatu za tlačno lijevanje

The paper presents the analysis of thermo-mechanical fatigue cracking of die casting die during industrial use. An innovative, production friendly approach to monitor the surface crack dimensions was introduced, which is based on measuring defect-fin on the casting part. A new four moulds die casting die was monitored 40 000 cycles in order to complete the production series. The production was stopped three times for laser repair welding of cracks since the defect-fins were not acceptable. The defect-fin heights were measured every 1 000 cycles on the castings before and after repair welding of die surface cracks. The in-service die life can be prolonged with laser repair welding for several times, even thought that in-service die life for a particular repair varies.U radu je prikazana analiza termo-mehaničkih pucanja kalupa za tlačno lijevanje tijekom industrijske upotrebe. Inovativni pristup praćenja dimenzija pukotina je uveden, koji temelji na mjerenju defekata na odljevku. Četiri nova kalupa za tlačni lijev su promatrana 40 000 ciklusa tj. jednu proizvodnu seriju. Proizvodnja je zaustavljena tri puta zbog laserskog zavarivanje pukotina na kalupu, jer su defekti na odljevku bili neprihvatljivi. Visina defekta mjerena je svakih 1 000 ciklusa na lijevanim dijelovima prije i nakon popravka pukotina laserskim zavarivanjem. Životna doba kalupa za tlačno lijevenje može se produžiti s laserskim zavarivanjem više puta, iako produženje životne dobe kalupa zavisi od kvalitete laserskog zavarivanja

Problemi kod reparaturnog zavarivanja alatnog čelika sa duplex zaštitom

The present paper addresses problems in laser welding of die-cast tools used for aluminum pressure die-castings and plastic moulds. To extend life cycle of tools various surface improvements are used. These surface improvements significantly reduce weldability of the material. This paper presents development of defects in repair welding of duplex-treated tool steel. The procedure is aimed at reduction of defects by the newly developed repair laser welding techniques. Effects of different repair welding process parameters and techniques are considered. A microstructural analysis is conducted to detect defect formation and reveal the best laser welding method for duplex-treated tools.U radu su istraženi problemi kod laserskog zavarivanja alata za lijevanje u industriji tlačnog lijeva aluminija ili plastike. Za produženje života alata primjenjena su različita poboljšanja površine. Ovakva poboljšanja značajno smanjaju sposobnost materijala za zavarivanje. U radu se opisuje razvoj grešaka kod reparaturog zavarivanja alatnog čelika sa dupleks zaštitom. Nametnuta procedura nastoji smanjiti greške sa novom zavarivnom tehnikom. Proučeni su I efekti različitih parametra procesa i tehnika zavarivanja. Mikrostrukturnim istraživanjima nastoju se naći greške za odabir najboljeg postupka za lasersko zavarivanje alata za dupleks zaštitom

Procjena utjecaja operativnih parametara Nd:YAG pulsnog lasera na metalurška svojstva različitih alatnih čelika pomoću DOE softvera

To ensure the reliability of repair welded tool surfaces, clad quality should be improved. The relationships between metallurgical characteristics of cladding and laser input welding parameters were studied using the design of experiments software. The influence of laser power, welding speed, focal point position and diameter of welding wire on the weld-bead geometry (i.e. penetration, cladding zone width and heat-affected-zone width), microstructural homogeneity, dilution and bond strength was investigated on commonly used tool steels 1,2083, 1,2312 and 1,2343, using DOE software.Poboljšanje kvalitete navarenog sloja nužno je za osiguranje pouzdanosti površina alata, obrađenih postupkom reparaturnog navarivanja. Odnos između metalurških osobina navarenog sloja i ulaznih parametara laserskog zavarivanja istražen je pomoću softvera Design of experiments. Utjecaj snage lasera, brzine zavarivanja, položaja žarišta i promjera žice za zavarivanje na geometriju navara (t.j. na penetraciju, širinu navara i širinu zone utjecaja topline), mikrostrukturna homogenost, miješanje i snaga spoja istraženi su na uobičajenim alatnim čelicima 1,2083, 1,2312 i 1,2343 pomoću softvera DOE

Thermomechanical modelling of laser surface glazing for H13 tool steel

A two-dimensional thermomechanical finite element (FE) model of laser surface glazing (LSG) has been developed for H13 tool steel. The direct coupling technique of ANSYS 17.2 (APDL) has been utilised to solve the transient thermomechanical process. A H13 tool steel cylindrical cross-section has been modelled for laser power 200 W and 300 W at constant 0.2 mm beam width and 0.15 ms residence time. The model can predict temperature distribution, stress–strain increments in elastic and plastic region with time and space. The crack formation tendency also can be assumed by analysing the von Mises stress in the heat-concentrated zone. Isotropic and kinematic hardening models have been applied separately to predict the after-yield phenomena. At 200 W laser power, the peak surface temperature achieved is 1520 K which is below the melting point (1727 K) of H13 tool steel. For laser power 300 W, the peak surface temperature is 2523 K. Tensile residual stresses on surface have been found after cooling, which are in agreement with literature. Isotropic model shows higher residual stress that increases with laser power. Conversely, kinematic model gives lower residual stress which decreases with laser power. Therefore, both plasticity models could work in LSG for H13 tool steel