• Journal of the Korean Society for Precision Engineering
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• v.14 no.4
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• pp.30-37
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• 1997

This thesis is concerned with the study on the characteristics of the tool failure occuring at the beginning of cutting in finish machining of hardened steels such as carbon tool steel and alloy tool steel by a ceramic tool (Al$_{2}$O$_{3}$+TiC) with nose radius. In the machining of hardened carbon steel STC3, the wear mechanism on the flank face of the ceramic tool is abrasion wear. The mode of tool failure is developed into catastropic fracture with flaking. It is thought that the fracture caused by FeO and TiO$_{2}$ results from the oxidation of Fe in the workpice and TiC in the ceramic tool and the deposit of Fe formed on the surface of the ceramic tool. In the machining of hardened alloy steel STD11, the wear mechanism on the flank face of the ceramic tool is that abrasion and adhesion wear exist simultaneously. The mode of tool failure at the beginning of cutting features is DOC notch wear. It is thought that the DOC notch wear caused by FeO and TiO$_{2}$results from the oxidation of Fe and TiC in the workpiece and ceramic tool, respectively.

• Tribology and Lubricants
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• v.9 no.1
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• pp.38-44
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• 1993

The present study was undertaken to investigate the dry wear characteristics of die steel STD 11 for cold molding. The wear test was experimentally carried out under different conditions using a wear device, which was made in laboratory, and in which annular surfaces of wear testing specimens wear rubbed in dry sliding condition with varying the sliding speed, contact pressure, and sliding distance. The wear loss by variation of sliding speed was much in 0.3 m/sec and less in higher speed range above its sliding speed according to formation of the boundary lubrication film. The critical sliding speed with maximum value of the specific wear rate switched over to lower speed side according. as contact pressure increased. The critical sliding distance was increased with decrease in oxidation reaction velocity. The depth below subsurface showing maximum hardness (Hv) came out at the position, $60 \mu m$, of the maximum shear stress due to strain hardening.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.927-931
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• 1997

In process of the finish face milling of the hardended STD11 steel(H /sab r/ c50,55) by CBN tool, the optimum tool shape is suggested,which can minimize the tool fracture and by chipping by impact. The obtained results are as follows. (1) The optimal chamfer angel was about 25 .deg. , and the suitable chamfer width was 0.2mm. (2) The nose radius of tool was most excellent at 1.2mm in the viewpoint of tool wear and surface roughness. (3) Wear speed was effected by sintering method of CBN tool B.U.E

• Journal of Advanced Marine Engineering and Technology
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• v.22 no.6
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• pp.809-815
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• 1998

This study has been performed to investigate MRR(metal removal rate) surface roughness with various pulse-on duration using the copper and graphite electrode according to the electrode size on the heat treated STD 11 which is extensively used for metallic molding steel in the EDM. The results obtained are as follow ;a)MRR increases a lot when pulse-on duration is 100 $\mu{s}$ or less but MRR has little difference with pulse-on duration of 100 $\mu{s}$ or more b) According to the increase of Pulse-on duration the large the electrode size the more MRR c) Safe discharge is needed to make maximum of MRR and the metallic organization must be complicated for discharge induction. d) Actual machining time is longer than theoretical machining time at the short pulse-on duration because of skin effect of current. e) Graphite electrode needs the larger electric discharge energy than copper electrode to remove remained chips completely.

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.5
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• pp.671-677
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• 1999

This study has been performed to investigate REW(relative electrode wear) in condition of vari-ous pulse-on duration using the copper and graphite electrode with change of the electrode size on the heat treated STD11 which is extensively used for metallic molding steel with the EDM. The results obtained are as follows; a) Graphite has much benefits than copper electrode when rapid machining is done without electrode wear, b) Neative REW result from the electrode that is very liable attach to decomposition carbide c)Increasing of machining time cause to increase wear length of the copper electrode and decrease wear length of the graphite electorde d)The more pulse-on duration copper electrode has the less REW. e) The edge portion of the electorde wears remarkably at the beginning of machining,.

• Transactions of Materials Processing
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• v.31 no.1
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• pp.11-16
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• 2022

In this paper, wear characteristics of PVD coatings were compared on the die surface for cold stamping of MART1470 steel sheet with the finite element analysis and the pin-on-disc wear test. Three types of PVD coatings (CrN, TiAlCrN, and MoS2TiCr(W)N) were considered for the tool surface made of STD11 material. The stamping process of an auto-body part was analyzed with the finite element method. Ranges of process variables for the wear test such as contact pressure, relative speed, and sliding distance were predicted from analysis results. In order to quantitatively analyze wear characteristics of each coating, the amount of wear was measured and compared according to process variables with the pin-on-disc wear test. The influence of each process variable was investigated and the wear characteristics of the three coating layers were quantitatively compared. It was confirmed that the wear characteristics of MoS₂TiCr(W)N coating were better than those of CrN and TiAlCrN. It was noted that the proposed prediction approach could predict and respond to the wear phenomenon occurring in the stamping process.

• Journal of the Korean Society for Heat Treatment
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• v.14 no.1
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• pp.8-16
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• 2001

The effects of gas composition, pressure, temperature and time on the case thickness, hardness and nitride formation in the surface of tool steels(STD11 and STD61) have been studied by micro-pulse plasma nitriding. External compound layer and internal diffusion layer and the diffusion layer were observed in the nitrided case of tool steels. The relative amounts and kind of phases formed in the nitrided case changed with the change of nitriding conditions. Generally, only nitride phases such as ${\gamma}(Fe_4N)$, ${\varepsilon}(Fe_{2-3}N)$, or $Cr_{1.75}V_{0.25}N_2$ phases were detected in the compound layer, while nitride and carbide phases such as ${\varepsilon}-nitride(Fe_{2-3}N)$, $(Cr,Fe)_{\gamma}C_3$ or $Fe_3C$ were detected in the diffusion layer by XRD analysis. The thickness of compound layer increased with the increase of nitrogen content in the gas composition. Maximum case depth was obtained at gas pressure of 200Pa.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.11 no.5
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• pp.88-93
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• 2012

This paper describes the machinability of the sintered carbide and tool-die steel(STD-11) by electric discharge drilling with various tubular electrodes which have multi-holes. Various types of electrode which have different diameters and materials are used with the application of continuous direct current and axial electrode feed. Inner part of electrodes are inserted with smaller tubes or Y-channel or bar. In ED-Drilling, the dielectric flushed down the interior of the rotating tube electrode, in order to remove machining debris from the hole. As result of experiments, the bigger the diameter of the electrode is, the lower the material removal rate is. Machinability of copper electrode is higher than that of brass. In machining of sintered carbide, to use oil is better than distilled water as dielectric.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.5
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• pp.53-59
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• 1997

This study has been performed to inmvestigate MRR(metal removal rate), REW(relative electrode wear), surface roughness, heat transumutation layer and microhardness distribution in cross-section of the machined surface with various pulse-on duration and peak pulse current, using the copper and graphite electrode on the heat treated STD11 which is extensively used for metallic molding steel with the EDM. The results obtained are as follows; a) There exists critical pulse-on duration(If Ip equals 5A, .tau. on is 50 .mu. s) which shows the the maximum MRR in accordance with peak oulse current and the MRR decreases when the pulse-on duration exceeds the critical pulse-on during because of the abnormal electric discharge. b) Safe discharge is needed to make maximum of MRR and the metalic organization must be complicated for discharge induction. c) Graphite has much more benefits than copper electrode when rapid machining is done without electrode wear. d) The most external surface has the highest microhardness because of car- burizing from heat analysis of the dielectric fluid and the lower layar of the white covered layer has lower microhar dness than base matal because of softening.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.12
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• pp.121-126
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• 1997

The use of CBN tool material has been greatly increased because of the superior metal cutting performance for the machining of hardened steel. This paper presents some experimental results on the ball endmiling of harened steels. Three different hardnesses of STD11 workpieces were machined using CBN ball endimills, and the machining characteristics including cutting forces tool wear, and surface roughness of machined surface were compared. It has been found that the CBN ball endmill works better in the machining of harder workpieces. The microscopic examination explains that this unusual phenomenon is caused by the difference of microstructure of each workpieces.