Suitability of natural rocks as materials for cutting tools

Abstract

This study presents an investigation of the usability and suitability of natural rocks as cutting tool materials. Therefore, indexable inserts are manufactured from eight different rocks and two mono minerals in this study and are used for turning of an aluminium alloy. Besides that, a characterization of the rock properties is performed. The wear of the rock tools and the surface roughness of the workpiece generated by the tools are used to evaluate their operational behaviour. Subsequently, the rock properties and the corresponding operational behaviour are used to assess the suitability of the rocks as cutting tool material. The results show that rock inserts can be used as cutting material for the turning of an aluminium alloy showing a width of wear marks between 83 and 1665 µm at the flank face after a cutting length of 500 m depending on the rock used. Furthermore, it is shown that rock tools are able to achieve surface roughness values which are comparable to those obtainable by using a conventional cemented carbide insert. The study shows that natural rocks can generally be used as alternative cutting material for the turning of aluminium. In addition a possible way for a systematic investigation and assessment of the suitability of natural rocks as cutting tool materials is presented, the relevance of the rock properties for the operational behaviour of the rock inserts is described and relevant future research topics concerning the use of rocks as cutting tool material are identified. Article highlights Demonstrating the possibility to use natural rocks as alternative environmentally friendly cutting tool material. Evaluation of operational behaviour and wear mechanisms of rock tools in turning aluminium. Identification of rock properties relevant for the operational behaviour of rock inserts.

Turning Copper and Aluminum Alloys with Natural Rocks as Cutting Tools

“…The results show an arithmetic average roughness Ra between 0.85 and 1.19 µm and a mean roughness depth of Rz between 8.28 and 15.4 µm at the flank face of the rock inserts. Rocks with a higher critical bending strength tend to show a lower roughness at the flank face, as described in [ 6 ]. However, other factors, such as cracks in the microstructure and the interlocking of mineral grains, can also influence the roughness of the inserts after grinding [ 6 ], which is an explanation for the higher roughness values of Alta-quartzite in comparison to quartz, despite the higher critical bending strength of Alta quartzite.…”

“…The raw rocks were cut into samples with dimensions of 18 × 18 × 5.5 mm. To account for the influence of the existing mica textures in the quartzites on the material properties and operating behavior, as described in [ 6 ], the perpendicular orientation of the mica textures to the loading direction was ensured during the three-point bending tests and cutting tests. Afterward, the targeted sample thickness of 4.76 mm was acquired with a grinding process performed on a Blohm Profimat MC 407 (Blohm, Hamburg, Germany) grinding machine with a diamond grinding tool (D46, C100) with a metallic bond.…”

“…The hardness H and the critical bending strength σ c of the rock samples were used for the characterization of their mechanical properties. The critical bending strength can be used as a measure of load-bearing capacity and structural cohesion for solids with multiple phases, as has already been shown in [ 6 , 16 ]. The mentioned properties of the rocks used in this paper have already been investigated and discussed for different temperature levels in [ 17 ].…”

“…At the same time, this would provide the industry with the opportunity to advance the transition to a more sustainable economy, which is particularly important in the context of climate change. The machining of comparatively soft materials, such as aluminum and copper alloys or plastics, has already been identified as the first potential area of application in which natural rocks could be used as alternative, and environmentally friendly, cutting tool materials [ 6 , 7 ]. However, their operational behaviors, such as their process forces, tool wear and their interactions, have not been investigated so far.…”

“…Bending strength and texture orientation were defined as the main selection criteria for their usage as a cutting tool. The possibility of grinding indexable inserts from rocks and using them in turning operations was also demonstrated [ 6 , 7 ]. The present study extends these investigations to include the influence of tool and rock properties after grinding on the process forces during machining.…”