Wear mechanisms and surface engineering of forming tools

Abstract

The manufacturing of parts is faced with ever-increasing demands for higher strength (hardness) and toughness of the work material, as well as higher productivity and environmental concerns. At the same time, the quality requirements are high and will continue to grow in the future. This leads to restrictions in terms of the type and use of lubricants and especially to increased requirements relating to the wear and fatigue resistance of tools. The main focus on improving the wear resistance and tribological properties of forming tools has mainly been on developing tool steels with an improved fracture toughness and then modifying the lubricants for better retention and permeability at the tool/work-piece contact area. Nevertheless, the wear resistance of forming tools can also be successfully improved by surface-engineering techniques. In recent years, hard coatings in particular have shown enormous potential for improving the tribological properties of contact surfaces. This paper reviews the wear mechanisms encountered in forming processes, as well as various surface-engineering techniques designed to improve the wear resistance and the anti-sticking properties of forming tools. The possible benefits and restrictions of different surface-engineering techniques are presented for the example of sheet-metal forming, fine blanking and forging. Keywords: surface engineering, forming, hard coatings, topography, friction, wear Preoblikovalna industrija se spopada z nenehno nara{~ajo~imi zahtevami po vi{ji trdnosti (trdoti) in`ilavosti preoblikovanih materialov, kakor tudi ve~ji produktivnosti in skrbi za okolje. Isto~asno se pove~ujejo zahteve po kvaliteti izdelkov, kjer predvsem kvaliteta povr{ine postaja vedno bolj pomembna. To pomeni omejitve pri uporabi maziv ter seveda ve~je zahteve po obrabni odpornosti in vzdr`ljivosti preoblikovalnih orodij. Do nedavnega je izbolj{evanje obrabne obstojnosti in tribolo{kih lastnosti preoblikovalnih orodij temeljilo predvsem na razvoju bolj`ilavih in~istej{ih orodnih jekel ter modifikaciji maziv z bolj{imi mazalnimi lastnostmi. V zadnjih letih pa tudi na podro~ju preoblikovalnih orodij tehnike in`eniringa povr{in, {e posebej nanos trdih za{~itnih prevlek, omogo~ajo nadaljnje izbolj{anje tribolo{kih lastnosti kontaktnih povr{in. V prispevku so tako predstavljeni obrabni mehanizmi, ki so jim izpostavljena preoblikovalna orodja, kakor tudi razli~ne tehnike in`eniringa povr{ine, namenjene izbolj{anju obrabne obstojnosti in tornih lastnosti preoblikovalnih orodij. Problemi in prednosti uporabe in`eniringa povr{ine so poudarjene na primeru hladnega preoblikovanja plo~evine, {tancanja in kovanja.

Investigation studies involving wear-resistant ALD/PVD hybrid coatings on sintered tool substrates

“…The coating of ceramic materials in PVD processes, including also tool ceramics, is difficult due to dielectric properties, since the inability of the substrate polarization during the coating process makes it difficult to obtain coatings with a good adherence to ceramic substrates. 2,[7][8][9][10][11] The fabrication technology of stratified coatings of the type "adhesive layer/PVD layer" using the multistage surface machining is one of the most modern methods to modify the properties of the surface layer and it consists, in a successive application, of two (or more) technologies of surface engineering. In terms of material effects, we obtain multilayer systems whereof one part is made up of an appropriately selected adhesive layer fabricated on the surface of the substrate, which protects the "proper" PVD layer against a loss of internal cohesion and an insufficient adhesion to the substrate.…”

Performance of Fe-based hardfacings on hot forging die: experimental, numerical and industrial studies

“…The harsh working conditions can cause premature failures of hot working dies [1]. Statistically, 70 % of forging dies are discarded and not used as a part of production due to the fact they lose dimensions, as a result of abrasive wear and plastic deformation, 25 % -as a result of fatigue cracks and only 5 % -for other reasons (disregarding the technology guidelines, construction defects, material defects or thermal and thermochemical treatment defects) [2,3].…”

Characteristics of the thermal fatigue resistance for 3.1C, 0.8Si, 0.9Mn, 1.7Cr, 4.5Ni and 0.3Mo ICDP cast iron roll at 600 °C

“…The occurrence of different damage, i.e., cracks, fracture, plastic deformation and wear, are a consequence of the different magnitudes of the mentioned loads as well as their different mutual ratios, materials properties, etc. [1][2][3][4][5][6][7] Thus, in the case of cyclical subjection to high temperatures, i.e., the heating of rolls (also above 600°C) and their water cooling, these conditions lead to the occurrence of cracking on the die's surface, which appears in the shape of a crack network that consequently results in spalling of the die material that further leads to a deterioration of the surface finish of the workpiece. In hot-working rolls the thermal stresses are usually comparable or even larger than the mechanical stresses.…”

“…In hot-working rolls the thermal stresses are usually comparable or even larger than the mechanical stresses. [3][4][5][6][7][8][9][10] To increase the die's service time it is important and also the common task for both die designers as well as for producers of die steels, to shift the occurrence of cracks to later times and to decrease their growth rate. Hot working rolls are usually alloyed with Cr, V, Mo, W, and after solidification process they are heat treated accordingly.…”

“…), thermal, microstructural properties as well as oxidation resistance should be engineered. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] Several research works related to thermal fatigue resistance of die materials (i.e. steels, cast irons) were carried out where reasons for initiation and growth of cracks at hot working dies (forging, die casting) [17][18][19][20][21][22][23][24][25][26][27][28][29][30] and hot working rolls [3][4][5][6]9,[31][32][33][34] were investigated using various laboratory tests.…”