Thesis--Ph. D., University of Hong Kong, 1977.

Abstract This thesis work is about finding out which coating should be used for which hardened tool steel and this was done by testing different coated cutting tools in different kinds of tool steels. The thesis work is performed at Uddeholms AB together with Uddeholms AB in the department of R&D at machinability cooperating with eifeler-Vacotec GmbH. The thesis work is going on from the end of January to the start of June and is a part of the education as mechanical engineer at Karlstad University and includes a total of 22,5 hp. The objective after finished thesis work is to be able to leave a recommendation to Uddeholms AB which coating is most suitable for each tool steel. To be able to leave that recommendation cutting tests are performed in four different hardened steel grades from Uddeholms AB combined with seven different coatings from eifeler-Vacotec GmbH. Steel grades tested are NIMAX®, DIEVAR®, VANADIS® 10 and ORVAR® SUPREME and coatings tested are CROSAL®, EXXTRAL® and SISTRAL® in different compounds. ORVAR® SUPREME gave such a long cutting tool-life that it was left for further investigation due to time limits that the thesis work had. In the other three tool steels it was possible to get a recommendation out of the four coatings tested in each tool steel. The coating that is recommended for each tool steel is only based on the cutting tool lasting the longest in each tool steel. That is not how a recommendation usually is formed, however for this thesis work there is no time for checking all the aspects that is vital for a proper recommendation. In order to get a proper recommendation, further more aspects that are checked are for example: Different cutting parameters (cutting speed, feed, etc.) Different geometries on the cutting tool Smoothness of the cutting tool and the coating In table 1 there is a compilation of which coating that was recommended for which tool steel. Table 1. This is a compilation of which coating that was recommended for which tool steel. NIMAX®               CROSAL® V1 DIEVAR®             SISTRAL® Ultrafine VANADIS® 10    SISTRAL® S

Thesis (Ph.D.) -- McMaster University, 1998. / Includes bibliographical references (leaves 187-195). Also available via World Wide Web.

Thesis (M. Phil.)--University of Hong Kong, 2008. / Also available in print.

Thesis (M.S.)--Oregon Graduate Institute of Science and Technology, 1989.

Thesis (Ph. D.)--Ohio State University, 2004. / Title from first page of PDF file. Document formatted into pages; contains xxii, 185 p.; also includes graphics (some col.). Includes bibliographical references (p. 178-185).

Sheet metal forming processes are mechanical processes, designed to make products from metal sheet without material removal. These processes are applied extensively by the manufacturing industry to produce commodities such as heat exchangers or panels for automotive applications. They are suitable for production in large volumes. A typical problem in forming operations is accumulation of local sheet material adherents onto the tool surface, which may deteriorate the subsequent products. This tool failure mechanism is named galling. The aim of this work is to explain the mechanisms behind galling and establish factors how it can be reduced. The focus of this work is on the influence of tool material for minimum risk of galling. Experimental tool steels alloyed with nitrogen were designed and manufactured for systematic tribological evaluation. Reference tool materials were conventional cold forming tool steels and coated tool steels. The sheet material was austenitic stainless steel AISI 304, which is sensitive for galling. A variety of lubricants ranging from low to high viscous lubricants were used in the evaluation. The properties of the tool materials were characterized analytically and their tribological evaluation included industrial field tests and several laboratory-scale tests. The testing verified that nitrogen alloying has a very positive effect for improving galling resistance of tool steels. Tool lives comparable to the coated tool steels were achieved even with low viscous lubricants without poisonous additives. The hypothesis used for the explanation of the positive effect of nitrogen alloying is based on the critical local contact temperature at which the lubrication deteriorates. Therefore, the contact mechanism at the tool-sheet interface and the local energy formation were studied systematically. Theoretical considerations complemented with FEA analysis showed that a small size of hard particles with a high volume fraction gives low local contact loads, which leads to low frictional heating. Also, an even spacing between the hard particles and their frictional properties are of importance. Nitrogen alloyed tool steels have these properties in the form of small carbonitrides. The finding of this work can be applied to a wide range of applications that involve sliding metal contacts under severe tribological loading.

published_or_final_version / Industrial Engineering / Doctoral / Doctor of Philosophy

Thesis (M.S.)--University of Missouri--Rolla, 2007. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed November 29, 2007) Includes bibliographical references.

Multi-material structures (MMSs) are attractive due to their unique advantages in achieving tailored properties at different locations in a single part. Producing such structures by additive manufacturing has been gaining more and more attention because of the beneficial characteristics of additive manufacturing processes such as its ability in building complex geometries, shortening producing chains, and most importantly, easily integrating with multi-material feeding systems. This PhD thesis investigates the potential of MMSs fabricated by directed energy deposition (DED) using tool steel and copper alloy. Specifically, AISI H13 hot work tool steel is deposited on copper-beryllium alloy (CuBe) substrate using three deposition strategies: directly depositing H13 on CuBe (H13/CuBe), SS316L buffer (H13/SS316L/CuBe), and commercially pure nickel buffer (H13/Ni/CuBe), aiming to minimize cracking issues. The morphology of single-track, single-layer, and multi-layer specimens is analyzed. The microstructure of deposited specimens is also investigated, along with its mechanical and thermal properties, such as microhardness, wear resistance, load-bearing capability (LBC), and thermal conductivity. The results show that directly depositing H13 on CuBe cannot avoid cracking in the H13 layers while preheating the CuBe substrate at 150℃ and 250℃ reduces the cracking tendency but damages the strength of the CuBe substrate due to over-aging while introducing difficulty to manage processing procedure. Using SS316L buffer can suppress the crack extension in H13 cladding due to a barrier mechanism, i.e., its ability to reduce the Cu penetration into H13 layers. However, SS316L itself is prone to cracking when directly deposited on the CuBe substrate as a buffer layer. Through analysis of cracking morphology, parameter effects, and element distribution, it was possible to identify solidification cracking as the primary cracking mechanism in all specimens. Two metallurgical factors, solidification temperature range and amount of terminal liquid, were found to dominate the cracking tendency. The introduction of Cu into steel can significantly extend the solidification temperature range, thereby increasing the susceptibility to cracking. However, as the Cu composition continuously increases, the cracking susceptibility decreases due to the backfilling of the terminal liquid into cracks resulting in a healing effect. The solidification paths of the Fe-Cu binary system were calculated as a function of Cu composition. Using this data, a map was generated reporting the solidification temperature range and terminal liquid amount as a function of Cu composition for the Fe-Cu binary system. Even if only to a first approximation (the effect of alloying elements in both, steel and CuBe alloy), this map can be used as a tool to estimate the cracking susceptibility of steel/copper alloy MMSs deposited by DED. The experimental results are in good agreement with thermodynamic calculations. Based on this analysis, a pure nickel buffer strategy was selected and proved to be effective in minimizing the cracking issue in H13 due to the narrow solidification temperature range of Ni-Cu and Ni-Fe binary systems induced the high solubility of Ni in Fe and Cu. By employing this strategy, crack-free specimens were produced. The high hardness of the H13 single-layer cladding, with an average value of 740 HV, provided a significant improvement in wear resistance compared to the CuBe (400 HV). However, in multi-layer specimens, a gradual decrease in microhardness of H13 cladding from the outer to the inner layers was observed due to the mixing of remelted soft buffer materials into H13 and the in-situ tempering effect in the previous deposited H13 layers. The above result, further confirms that the load-bearing capability (LBC) cannot be infinitely improved by adding more H13 layers. In general, in the low loading range (From 5 to 10 kN), the LBC of MMS specimens was higher than the CuBe due to the higher hardness of outer H13 layers. However, it became lower in the high loading range due to the presence of soft sublayer materials such as softened martensite, soft buffer layers (H316L = 260 HV or HNi = 130 HV), and the heat-affected zones in the CuBe substrate. The thermal conductivity of MMS specimens first drops rapidly to half of the original value as the cladding thickness ratio (tcladding/tCuBe) increases from 0 to around 20%. After that, the decrease becomes slower, with a further reduction of around 37% in thermal conductivity as the cladding thickness ratio increases from 20% up to 50%. Therefore, a tradeoff between mechanical and thermal properties must be considered looking for the application of these cladding systems. A proper cladding thickness ratio of around 20% is recommended to achieve reasonably high strength while still maintaining thermal conductivity at an acceptable level. Overall, these findings have important implications for the selection of appropriate materials and processing parameters to optimize the mechanical and thermal properties of tool steel/copper alloy MMSs deposited by DED.