Development of tungsten carbide based self lubricant cutting tool material: Preliminary investigation
Introduction
Self lubricating materials are being used in practice for load bearing applications including bearings and gears. However, utilization of solid lubricant materials in the manufacturing industries is not yet established due to the limited data and incomplete understanding. Very few research works were carried out for the development of self lubricating material for machining application [1], [2], [3], [4]. Deng et al. [1] developed an Al2O3/TiC ceramic cutting tool with a CaF2 solid lubricant and evaluated the performance of the developed cutting tool. Deng et al. [2] evaluated friction and wear characteristics of developed Al2O3/TiC/CaF2 composites under sliding friction. Investigation confirmed the reduction of friction and wear under sliding and machining. Deng et al. [3] developed a cutting tool by filling MoS2 powders in the microholes at the rake and flank surfaces of the cemented carbides. Cutting forces, tool wear and coefficient of friction were evaluated. Al2O3 and TiB2 powders were prepared via wet ball milling followed by hot pressing and sintering [4]. Machining was carried out and reduction of friction and wear was observed.
Hewitt and Kibble [5] utilized high energy ball milling and effects of milling time on the nanostructure of WC–Co composites are investigated. With increase in milling time, particle size reduces however; contamination also increases beyond particular milling hours. Iron contamination is the most common problem while milling tungsten carbide in a steel vial at very high milling speed [6]. Avettand et al. [7] investigated the milling characterization of tungsten carbide based materials and contamination after prolonged milling time was observed.
Upadhyaya and Bhaumik [8] sintered a WC–Co material and evaluated hardness and transverse rupture strength. Nickel was considered as a binder material; however cobalt exhibited a superior binding behavior. Sharifi et al. [9] developed and evaluated the mechanical properties of aluminum reinforced with boron carbide (5–15%). With the increase in boron carbide, hardness increases due to the presence of hard phase and reduction in particle size. Suzuki and Hayashi [10] studied the effect TiC (6–17%) in the tungsten carbide material. 6% TiC alloy exhibited a higher strength than that of 11 and 17%. Beyond this amount, TRS decreases due to the poor wettability. Deng et al. [11] studied the effect of solid lubricants, CaF2, MoS2 and BN (5–15%) contents on the flexural strength and hardness of Al2O3/TiC composites. The addition of solid lubricant decreases the hardness and flexural strength due to the formation of microcrack.
From the prior literature, it is observed that very few works have been reported on the development of solid lubricant cutting tool material. It is also observed that there is a need to understand milling, compaction and strength of the proposed solid lubricant cutting tool material. The main aim of the present work is to develop a tungsten carbide based solid lubricant material and to investigate the effect of ball milling time and the amount of solid lubricant material on the transverse rupture strength of the material.
Section snippets
Materials and processing
Tungsten carbide (WC) of 15–18 μm size with 99.8% purity (Rapicut carbides) is used as a basic cutting tool material due to its high hardness, good strength, and excellent wear resistance. Cobalt (Co) of 20–30 μm size with 99.5% purity (Loba Chemie) is used as a binder and 10 wt.% of Co is commonly used for the development of the WC based composite [5], [12], [13]. Among solid lubricants, calcium fluoride (CaF2) of 170–180 μm size with 98% purity (Loba Chemie) is considered for cutting tool
Morphology of milled powders and particle size analysis
Milled powders were observed under a scanning electron microscope (LEO, 1430vp) to study the morphology. Fig. 1(a–c) shows the morphology of as received WC, Co and CaF2 particles. It is observed that the particle size of the cobalt and calcium fluoride is bigger than that of tungsten carbide. Cobalt particle shape is nearly spherical which can improve the packing density. Fig. 2(a–c) shows the morphology of WC–10 wt.%Co–5 wt.%CaF2 powder after 20, 40 and 100 h of ball milling. Most particles
Summary and conclusions
The present study revealed the significant effect of milling time on the density and hardness of the developed solid lubricant cutting tool materials. The amount of solid lubricant in the cutting tool material affects the transverse rupture strength significantly. The following major conclusions were arrived from the present work:
- 1.
40 h of milling period was found to be most suitable for the chosen materials and milling condition to obtain superior density and hardness.
- 2.
Insufficient and excess
Acknowledgments
Authors wish to thank Aerospace Manufacturing and Value Engineering Panel of ARDB, India (DARO/08/1103/M/I) for funding this project. Authors also wish to thank Professor PS Robi, IIT Guwahati and Centre for Instrument Facility, IIT Guwahati for their kind assistance.
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