The Critical Raw Materials in Cutting Tools for Machining Applications: A Review

Abstract

A variety of cutting tool materials are used for the contact mode mechanical machining of components under extreme conditions of stress, temperature and/or corrosion, including operations such as drilling, milling turning and so on. These demanding conditions impose a seriously high strain rate (an order of magnitude higher than forming), and this limits the useful life of cutting tools, especially single-point cutting tools. Tungsten carbide is the most popularly used cutting tool material, and unfortunately its main ingredients of W and Co are at high risk in terms of material supply and are listed among critical raw materials (CRMs) for EU, for which sustainable use should be addressed. This paper highlights the evolution and the trend of use of CRMs) in cutting tools for mechanical machining through a timely review. The focus of this review and its motivation was driven by the four following themes: (i) the discussion of newly emerging hybrid machining processes offering performance enhancements and longevity in terms of tool life (laser and cryogenic incorporation); (ii) the development and synthesis of new CRM substitutes to minimise the use of tungsten; (iii) the improvement of the recycling of worn tools; and (iv) the accelerated use of modelling and simulation to design long-lasting tools in the Industry-4.0 framework, circular economy and cyber secure manufacturing. It may be noted that the scope of this paper is not to represent a completely exhaustive document concerning cutting tools for mechanical processing, but to raise awareness and pave the way for innovative thinking on the use of critical materials in mechanical processing tools with the aim of developing smart, timely control strategies and mitigation measures to suppress the use of CRMs.

Keywords: critical raw materials; cutting tools; modelling and simulation; new machining methods; new materials.

Figure 1

Cutting tool global market distribution by cutting technology (a) and by workpiece material (b) as presented by Dedalus Consulting. Data taken from [7].

Figure 2

Critical raw materials list for 2011–2017 overlaid on the periodic table of the elements [5,6].

Figure 3

(a) Composition of the smart cutting tool, (b) assembly of the tool, (c) cross-section view of the tool, as taken from [10].

Figure 4

Important advancements made in machining technology. (a) Thermal-assisted machining [46]; (b) cryogenic machining [47]; (c) schematic diagram to illustrate the mechanism of vibration-assisted machining [48].

Figure 5

(a): Schematic diagram indicating the differences between the mode of deformation during conventional machining and surface defect machining (SDM) observed through an FEA (Finite Element Analysis) simulation of hard steel and MD (Molecular Dinamics) simulation of silicon carbide, respectively; (b) effect of providing nanogrooves on the tool [78]. (a) Surface defect machining. (b) Providing nanogrooves on the tool.

Figure 6

World market of cemented carbide cutting tools. Data from Dedalus Consulting, taken from [7].

Figure 7

Comparison of enhancement factors of coated tools over uncoated tools (based on their lifetime). Analysed data are taken from selected published works [94,95,96,97,98]. The results strongly depend on operational conditions, such as the cutting method and speed, the workpiece material, and the thickness of the protective coating.

Figure 8

Criteria required for the success of the protective coatings of cutting tools.

Figure 9

Scanning electron microscope (SEM) micrographs of the rake and flank face after the dry milling test for an AlCu_2.5Si₁₈ alloy [109].

Figure 10

Properties of transition metal nitrides, carbides and borides [117].

Figure 11

Tribological characteristics of TiN and nanocomposite nc-TiN/SiN_1.3 films as a function of the H³/E² ratio: (a) wear coefficient; (b) erosion rate [132].

Figure 12

Toughening and strengthening mechanisms in multilayer coatings (taken from [158]).

Figure 13

Cross-section SEM image of the surface of a graded cemented carbide material obtained in [201].

Figure 14

Tool inserts made of ceramics.

Figure 15

(a) Microstructure of the samples for a diamond composite with 5 wt.% TiB₂ and (b) an insert with a diamond cutting edge.

Figure 16

The methodology of criticality, showing the importance of substitution in the vertical axis (see [259]).

Figure 17

(a) Materials project thrusts. (b) In silico prototyping and iterative design steps of materials [292].

Figure 18

Search results for W–C–Co in two state-of-the-art computational data repositories. (a) In NOMAD [266]. (b) In the Materials Project [275].

Figure 18

Search results for W–C–Co in two state-of-the-art computational data repositories. (a) In NOMAD [266]. (b) In the Materials Project [275].

Figure 19

(a) Flowchart of a genetic algorithm as USPEX [309]. (b) Ashby plot of predicted new W-B phases (red points) compared to known superhard materials (blue points) [308].

Figure 19

(a) Flowchart of a genetic algorithm as USPEX [309]. (b) Ashby plot of predicted new W-B phases (red points) compared to known superhard materials (blue points) [308].

Figure 20

GAP-RSS (Gaussian approximation potential-based random structure searching) scheme and protocol [314].