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Discussion on importance of tungsten carbide – cobalt (WC-Co) cemented carbide and its critical characterization for wear mechanisms based on mining applications

Nahak S., Dewangan S., Chattopadhyaya S., Krolczyk G., Hloch S.

Archives of Mining Sciences

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2018

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Vol. 63, no. 1

229--246

EN

Cemented carbide (CC) is an important material for the mining tools. During mining applications, the service life of the CC gets highly reduced due to complex conditions offered by mines. In various applications, such as, rock drilling and coal cutting, the tools show different type of wear behaviour. Wear assessment has been an important area of research for a long time. In order to develop improved mechanical properties in the tools, it is necessary to know the characteristics and cause of wear mechanisms. For analyzing wear mechanisms in the CC, researchers have adopted mainly three different conditions. They are: rock drilling, coal cutting, and laboratory wear test methods. In the present work, an attempt has been made to review and summarize all those wear mechanisms found in the CC. The causes and effects of each mechanism are also explained comprehensively. In addition, various properties of recently developed cemented carbide have also been discussed.

PL

Węglik spiekany (CC) jest znanym od dawna lecz wciąż powszechnie używanym twardym stopem metalu. Korzystne właściwości węglika spiekanego sprawiają, że jest niezwykle pożądanym materiałem z którego wykonywane są narzędzia górnicze. W trakcie prowadzenia wierceń w skałach i urabiania skał, narzędzia pracują w bardzo złożonych warunkach i różnorodnych zastosowaniach, stąd też wykazują różne oznaki zużycia zmęczeniowego. Ponieważ zużycie materiału skraca okres eksploatacji narzędzi, wielu badaczy podjęło się badań nad tym zagadnieniem. Kwestia oceny zużycia zmęczeniowego narzędzi wykonanych z węglika spiekanego badana jest od dłuższego czasu. Niezbędne jest poznanie charakterystyki procesu zużycia zmęczeniowego i jego przyczyn tak by można wyodrębnić do badania narzędzia nadające się do dłuższej eksploatacji, tym samym poprawiając opłacalność produkcji. Badano rozmaite mechanizmy zużycia zmęczeniowego węglików spiekanych związane z użytkowaniem narzędzi w wiertnictwie oraz urabianiu skał, opracowano także laboratoryjne metody jego badania. W artykule tym podjęto próbę zebrania i usystematyzowania wszystkich mechanizmów zużycia zmęczeniowego, jakiemu podlegają narzędzia wykonane z węglików spiekanych. Przyczyny i skutki każdego z procesów rozpatrywano w ujęciu całościowym. Ponadto, omówiono właściwości niedawno opracowanych węglików spiekanych.

2

Optimization of CNC face milling process of Al-6061-T6 aluminum alloy

Jarosz K., Löschner P., Niesłony P., Krolczyk G.

Journal of Machine Engineering

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2017

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Vol. 17, No. 1

69--77

EN

In modern machining industry, the use of computer software is an integral element in the design of technological processes. This work aims to present possibilities for optimization of milling operations with the use of commercial software designed especially for that use. A face milling operation of an aluminium flange was chosen for this study. Several different optimization strategies were described and their results shown, analysed and discussed. The effect of variable radial depth of cut on cutting force values in milling processes was reflected upon. Additionally, further research involving comparison of experiment results with simulation was proposed. It was proven that correct optimization strategy can reduce machining time for the analysed face milling operation about 37% without exceeding imposed process parameter constraints.

3

Microstructural study of failure phenomena in WC 94%-Co 6% hard metal alloy tips of radial picks

Nahak S., Chattopadhyaya S., Dewangan S., Hloch S., Krolczyk G., Legutko S.

Advances in Science and Technology. Research Journal

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2017

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Vol. 11, no 1

36--47

EN

An excellent combination of hardness, strength, stiffness and high melting point has proved the WC-Co as an ideal material for tools that are used for metal cutting, coal mining, oil drilling, etc. The ongoing research in WC-Co is focussed on enhancing its wear resistant properties as much as possible. For the purpose, many attempts have been made to study the tribological behaviour of WC-Co for a long time. Researchers have used various grades of WC-Co in different working environments and accordingly they have characterized the wear phenomena involved there within. In this direction of research, the present paper makes an attempt to understand various wear behaviours in WC 94%-Co 6% hard metal alloy. WC-Co was used as a tip of the coal cutting tool named radial pick. Two radial picks have been taken for critical analysis through field emission scanning electron microscopy (FESEM) attached with energy dispersive X-ray spectroscopy (EDS). In this work, the failure behaviours in the tools have been divided into five categories: (1) Abrasion on individual grain; (2) Corrosion in carbide grains; (3) Fragmentation and removal of WC grains; (4) Pores in WC grains; and (5) Coal and rock embedding. The most possible reasons behind each failure phenomenon have been explained comprehensively with the help of high-resolution microscopic images. However, it is usually observed that, initially, the tool gets minor cracks due to sudden impact. These cracks provide a path to the rock and coal particles to get entrenched inside the microstructure of cemented carbide. Finally, the intermixed external elements degrade the binder content (i.e. cobalt) and the tool becomes useless.

4

Wear characteristics and defects analysis of friction stir welded joint of aluminium alloy 6061-T6

Kumar R., Chattopadhyaya S., Hloch S., Krolczyk G., Legutko S.

Eksploatacja i Niezawodność

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2016

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Vol. 18, no. 1

128--135

EN

This paper deals with the wear characteristics and defects developed during friction stir welding at different process parameter of aluminium alloy (AA) 6061-T6 having thickness 6 mm. Four welded samples are prepared with rotational speed 500 rpm, 710 rpm, 1000 rpm and with welding speed of 25 mm/min & 40 mm/min. Welded samples and base material are put in wear condition under grinding machine for 120 s. Material removal is measure by taking the difference of weight before and after wear. Different types of defects and fracture are observed on the wear surface. These defects and fractures are analysed under field emission scanning electron microscope (FESEM). It is concluded that material removal from welded sample is less compared to base metal, hence wear resistance increases after friction stir welding.

PL

Praca dotyczy charakterystyki zużycia i uszkodzeń podczas zgrzewania tarciowego z przemieszaniem stopu aluminium (AA) 6061T6 o grubości 6 mm dla zmiennych parametrów. Cztery zgrzewane próbki były wykonane z prędkością obrotową 500 obr/min, 710 obr/min, 1000 obr/min dla prędkości zgrzewania 25 mm/min i 40 mm/min. Zgrzewane próbki i materiał bazowy były poddawane zużywaniu za pomocą szlifierki w czasie 120 s. Ubytek materiału mierzono jako różnicę wagi przed i po zużywaniu. Różne rodzaje wad i pęknięć zaobserwowano na zużytej powierzchni. Wady i pęknięcia analizowano za pomocą mikroskopu polowego (FESEM). Stwierdzono, że ubytek materiału ze zgrzewanych próbek jest mniejszy w porównaniu z ubytkiem dotyczącym materiału bazowego. Zwiększa się więc odporność na zużycie po zgrzewaniu tarciowym z przemieszaniem.

5

Cryogenic machining, surface integrity and machining performance

Kopac J., Krolczyk G.

Archives of Materials Science and Engineering

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2015

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Vol. 71, nr 2

83--93

EN

Purpose: Of this paper is to present state-of-the-art on cryogenic machining and delivery principles of liquid nitrogen to the machining/cutting zone. Additionally, the influence of cooling/lubrication conditions on the surface integrity, generated during turning of Inconel 718, are analysed and presented. Design/methodology/approach: Of the paper are to present the design of the cryogenic machining system and how the liquefied nitrogen is delivered to the cutting zone. Additionally, the system is used to evaluate the effect on surface integrity of machined Inconel 718 workpiece. Methodologies used for the surface integrity evaluation are: electro-polishing, X-ray diffraction and micro indentation hardness measurements, with the approach to evaluate the extent of cryogenic influence on machined surface. Findings: The results show that the cryogenic machining process generates larger compressive residual stresses, and prevail at deeper levels beneath the machined surface, thus resulting in improved product quality and performance characteristics in terms of fatigue life and wear resistance. Research limitations/implications: The solutions of the delivery and the evaluation results have been all performed for the turning process, while there is still a challenge for the implementation of findings on the milling and drilling process kinematics. Practical implications: Work shows that cryogenic machining is capable of improving surface integrity and with this, as practical implication, having high potential for improving the sliding conditions, fatigue life of the final product, corrosion resistance, etc. Originality/value: Originality of the paper is shown by novel solutions (patents) on cryogenic machining system (delivery) and in machined surface modification capabilities with alternative cooling/lubrication fluid.