In actual production, the rotary file does not crack after welding, but stress cracking occurs after tooth cutting, but relevant literature reports are few. This paper uses Cu-Ag-based multi-interlayer flux to weld cemented carbide/steel rotary files, analyzes the stress state of the rotary files after welding and the causes of cracking after tooth cutting. Starting from the principle, the process is optimized, and more economical and convenient measures to reduce welding and tooth cutting cracking are proposed.

(a)Original sample after induction welding; (b) Enlarged view of the polished rotary file after welding; (c) Sample after tooth cutting and surface finishing.

Fig.1 ?Macroscopic morphology of rotary file samples after welding, polishing, and tooth-cutting processes

Research Direction

Although the thermal conductivity of tungsten carbide is more than twice that of alloy steel, there is a significant difference in the coefficient of thermal expansion between alloy steel and cemented carbide. For example, the linear expansion coefficient of commonly used YG-grade cemented carbide is approximately 5×10??–7×10??/K, while that of commonly used 45 steel is approximately 11×10??–14×10??/K.

Zhang J et al. studied and found that during the cooling process of induction welding, steel shrinks faster, forming tensile stress in the steel shank of the rotary file and compressive stress in the cemented carbide end. Meanwhile, the distribution of residual stress in the above two parts does not change with the decrease in temperature, and the residual stress value reaches the maximum at room temperature. Amelzadeh M et al. found that the residual stress distribution on the welding surface after induction welding is uneven, and the residual stress near the boundary of the welding surface is higher than that inside the weld.

Bang H S et al. further confirmed that the distribution of brazing residual stress has directionality, which can be specifically divided into two directions: parallel to the welding surface and perpendicular to the welding surface. Among them, the peak value of longitudinal residual stress at the welding site is the highest, even reaching the yield strength of the material. The welding failure of cemented carbide/brazing layer/alloy steel mainly occurs near the boundary between cemented carbide and brazing filler metal.

In order to reduce the residual thermal stress in brazed joints, many researchers at home and abroad have carried out a large number of studies, which can be mainly divided into three aspects: pretreatment before welding, treatment during the welding process, and post-weld treatment, to alleviate the residual thermal stress of brazed joints.

(a)Macroscopic photo of the interface; (b) Schematic diagram of residual stress area testing.

Fig.2? ?Macroscopic image of tooth-cutting-induced cracking at the interface and schematic diagram of residual stress zone testing in post-weld rotary files

Research Methods

This paper uses XRD tester, infrared thermometer, metallographic microscope, scanning electron microscope and other equipment to test the micro morphology and residual stress distribution of the welding interface of cemented carbide rotary files, and analyzes the tooth cutting cracking problem of welded parts after induction welding. The results show that the Cu-Ag-based brazing multi-layer structure can release the residual thermal stress at the cemented carbide end near the weld, but the cemented carbide end far away from the weld maintains a high residual stress value, and the rotary file forms a high residual stress gradient along the direction perpendicular to the welding surface. At the same time, the fast heating and cooling rates and short holding time will also cause a large thermal stress gradient from the outside to the inside of the welding surface of the rotary file. When the tooth cutting process introduces processing stress, which destroys the stress balance state of the cemented carbide surface, the compressive stress value on the surface of the cemented carbide near the weld will rapidly increase, easily leading to crack generation. Optimizing the welding temperature, welding time, preheating of welded parts and cooling pressure treatment can all improve the residual stress of the rotary file along the welding surface and vertical direction to a certain extent, optimize the stress gradient distribution, and further reduce the cracking phenomenon of the sample during tooth cutting after welding.

Means for Strengthening Welding Performance of Rotary Files

Enhancement of Brazed Joint Strength by Periodic Grooves

Zhang Y et al. achieved the transformation of tensile stress to compressive stress at the interface by carving micron-scale periodic grooves on the ceramic surface, inhibiting crack propagation and enhancing joint bonding strength. Compared with the joint strength of untreated ceramics (24 MPa), the post-welding strength of grooved ceramics reached 66 MPa, increasing by 275%. In addition, the design of special brazing layer structures can also optimize the residual thermal stress in brazed joints. Directly using high-strength brazing filler metal to fill the welding surface is extremely likely to cause stress cracking in the brittle cemented carbide end of the rotary file. Composite solders such as copper-based, silver-based, or nickel-based materials with low yield points, easy deformation, and the ability to reduce shear stress are suitable brazing materials for cemented carbide rotary files. However, pure copper flux has problems such as high melting point and poor performance, while silver-based flux has a high cost. The Cu-Ag-based composite interlayer structure combines the plasticity and low melting point of silver-based solders with the low cost and good compatibility with other metals of copper-based solders, effectively reducing residual stress at the welding site. Such interlayers are mainly composed of an external soft porous metal fiber mesh buffer layer and a middle rigid interlayer. The soft buffer layer can alleviate residual stress through yielding, plastic deformation, and creep, while the internal rigid interlayer transfers the concentrated area of residual thermal stress from the weld side of the cemented carbide to the interlayer, effectively preventing the generation of initial cracks in the cemented carbide. Shirzadi A A et al. used Ag-Cu-based multi-layer brazing for alumina/stainless steel materials, and the bonding strength of the welded parts reached 33 MPa, which can withstand more than 60 cycles of thermal shock in air at 200–600°C.

(a)Thermal imaging diagram；(b) Schematic diagram of thermal diffusion

Fig.3 Thermal image of rotary files 2 seconds after welding during cooling and demolding and schematic of heat diffusion at the welding surface

Controlling Temperature to Optimize Brazed Joint Stress

Process control during brazing can also optimize the residual stress of joints to a certain extent. Kar A et al. studied the effects of different welding temperatures on Ag-Cu-Ti-based flux brazing of alumina and stainless steel. During the temperature rise from 900°C to 1100°C, alumina and the brazing layer underwent different diffusion reactions, resulting in significant differences in the composition and structure of the brazing layer. The phase types, micro morphology, and element arrangement in the brazing layer all affect the joint strength and residual stress distribution.

In addition to the brazing layer structure and welding process control, post-weld treatment is also the key to reducing welding cracking of rotary files. Various post-weld heat treatment measures, including cryogenic treatment, tempering, low-temperature and high-temperature pressurization, can reduce the residual stress value of alloy welding components to a certain extent.

Mishra S et al. adopted thermal cycling treatment after welding (200–500°C for 5–10 cycles, followed by cooling to room temperature), and the results showed that post-weld thermal cycling can reduce residual thermal stress caused by the difference in the coefficient of thermal expansion. It was also found that the lower the residual thermal stress value at the joint, the better the relief effect. After cryogenic and tempering treatments on YG8 cemented carbide/A3 steel welded parts, Lu Hangang found that the maximum compressive stress of the cemented carbide was 304 MPa, which was 40% lower than the maximum stress value of conventional welding. Cui Chen et al. found that after cryogenic treatment, the surface residual stress of austenitic stainless steel matrix/ferrite welded parts decreased by 36.8% and 16.3% in the X and Y directions, respectively, while ageing treatment reduced the surface residual stress by 61.2% and 58.8% in the X and Y directions, respectively.

Fig.4? Interface morphology of large-sized (D＞30mm) rotary files fabricated via induction welding

Fig.5? DSC-TG curves of Ag-Cu-based filler metal

Conclusione

Induction heating is characterized by short heating time, high temperature, and convenient operation, making it one of the main methods for large-scale industrial and automated welding of rotary files. However, excessively high heating temperature or too short heating time can easily cause high residual stress gradients in the rotary file along the welding surface and the direction perpendicular to the welding surface. Although these high residual stresses do not generate cracks immediately after welding, they often lead to cracking during the tooth cutting process of the rotary file. Based on DSC-TG analysis, combined with thermal imaging, metallographic, and electron microscopy analyses of the macro-micro structure of materials, appropriate welding temperature, moderate welding time, preheating of components (to increase the initial welding temperature of larger-sized rotary files), and cooling pressure treatment can all improve the residual stress gradient distribution of the rotary file in the directions of the welding surface and perpendicular to the welding surface to a certain extent, thereby reducing the occurrence of welding cracking in rotary files.

?Introduction to Cited Articles

This paper is another contribution to the study of the structure-property relationship in cemented carbides by the research team, following their previous works:

1. Regulation of interfacial phase stability in cemented carbides (Acta Mater. 2018, 149, 164?178,https://doi.org/10.1016/j.actamat.2018.02.018)

2.New methods and principles for enhancing the distribution of characteristic grain boundaries in cemented carbides(Acta Mater. 2019, 175, 171?181, https://doi.org/10.1016/j.actamat.2019.06.015)

3.Accurate analysis of residual thermal stress (RTS) in cemented carbides and its mechanism affecting material mechanical behavior (Acta Mater. 2021, 221, 117428, https://doi.org/10.1016/j.actamat.2021.117428)

Article link: https://doi.org/10.1016/j.actamat.2024.119649

About the Research

Research Background of WC grain morphology

For cemented carbides, a typical composite material, the influence of WC grain morphology on the mechanical behavior of the material, especially representative mechanical properties such as strength and toughness, remains unclear. Furthermore, cemented carbides prepared by powder metallurgy inevitably contain high-magnitude and complexly distributed residual thermal stress (RTS), and its accurate quantitative description is a common challenge in the field of cermet composites. Moreover, when working tools manufactured from cemented carbides are in use, the interaction between as-prepared RTS and external loads inevitably affects the material’s mechanical behavior and service performance. Therefore, studying the coupling effect of WC grain morphology and as-prepared RTS on the stress-strain response during material loading is of great significance for comprehensively understanding the mechanical behavior, failure mechanism, and performance enhancement approaches of cemented carbides in practical applications.

Research Methods

In this study, a method for constructing finite element models of real microstructures and phase distributions in cermet composites was proposed. Combining finite element simulation with quantitative analyses such as transmission electron microscopy (TEM) observation and X-ray diffraction (XRD) experiments, the influence of WC grain morphology on RTS characteristics and the mechanical behavior and properties of materials under external loads was analyzed. This provides important scientific evidence for optimizing microstructural stress-strain distribution through regulating grain morphology to achieve strengthening and toughening of cermet composites.

Fig. 1 Microstructural characteristics and finite element models of WC-10wt.%Co cemented carbides with different WC grain morphologies: (a) SEM image of E-WC-Co; (b) SEM image of P-WC-Co; (c) Schematic diagram of equivalent elliptical area method; (d) Probability distribution of WC grain geometric shape factors

Through the design of preparation methods and regulation of process parameters, WC-10wt.%Co cemented carbides with equiaxed and plate-like WC grain structures were successfully prepared, respectively. Based on EBSD experiments, a method for constructing finite element models was developed to reproduce the real microstructure, morphological and mechanical characteristics of cemented carbides, which can reflect the local stress field, strain field and properties of actual materials.

Research Findings

The researchers found that the compressive RTS level is higher in the WC region near the acute dihedral angle of WC/Co. In contrast, the RTS in WC near the WC/Co phase boundary away from the vertex of the acute dihedral angle mainly exhibits tensile stress. Furthermore, a higher geometric shape factor leads to more narrow WC connections in the cemented carbides with plate-like WC grain structures, where the WC regions have highly concentrated compressive RTS.

Fig. 2 RTS distribution in WC-10wt.%Co cemented carbides with different WC grain morphologies: (a) Transverse RTS distribution nephogram of WC grains in E-WC-Co; (b) Axial RTS distribution nephogram of WC grains in E-WC-Co; (c) Transverse RTS distribution nephogram of WC grains in P-WC-Co; (d) Axial RTS distribution nephogram of WC grains in P-WC-Co; (e) Transverse RTS distribution nephogram of Co phase in E-WC-Co;

(e) Transverse RTS distribution nephogram of Co phase in E-WC-Co; (f) Axial RTS distribution nephogram of Co phase in E-WC-Co; (g) Transverse RTS distribution nephogram of Co phase in P-WC-Co; (h) Axial RTS distribution nephogram of Co phase in P-WC-Co

It was found that the average RTS of WC grains presents an asymmetric dumbbell-shaped distribution with respect to the WC geometric shape factor. When the WC grain geometric shape factor is between 3 and 5, the average RTS distribution range of WC grains is narrow, and the average RTS of WC grains is in a compressive stress state. In addition, both finite element simulation and X-ray diffraction experimental results show that the WC grain morphology has little effect on the phase-averaged RTS of cemented carbides.

Fig. 3 The variation law of the average residual thermal stress (RTS) of WC grains with the WC geometric shape factor.

Fig. 4 Experimental determination of RTS in WC phase of cemented carbides with different WC grain morphologies: E-WC-Co

The compressive and tensile properties of cemented carbides exhibit significant asymmetry. The presence of RTS improves the compressive strength of both E-WC-Co and P-WC-Co. Compared with E-WC-Co, P-WC-Co has a relatively lower compressive yield strength but shows larger strain after yielding without obvious hardening. The presence of RTS reduces the tensile yield strength of E-WC-Co, while having little effect on the tensile strength of P-WC-Co.

Fig. 5 Strain responses of WC-10wt.%Co cemented carbides with different WC grain morphologies and initial stress states during compression and tension: (a) Compressive stress-strain curve of E-WC-Co; (b) Compressive stress-strain curve of P-WC-Co.

?

Conclusions

The study shows that the compressive deformation of cemented carbides can be divided into three stages: the elastic stage, the elastoplastic stage, and the plastic stage.

1.In the initial elastic stage of loading, the hard ceramic phase WC and the ductile metal phase Co undergo independent elastic deformation.

2.In the elastoplastic stage, plastic deformation occurs preferentially in the metal phase Co, while the ceramic phase WC remains in an elastic deformation state.

3.In the plastic stage, due to the much larger plastic strain in the metal phase Co than in the ceramic phase WC, strain gradients and strain localization are likely to occur in the Co region near the WC/Co phase boundary. These strain gradients and localization increase with the applied load, leading to an increase in dislocation density and strain hardening.

They cut materials with high precision. Be it metal, non-metal, or non-ferrous materials, they can transform them easily into the shapes you desire. But laser cutting is not limited to a single type. Instead, you can see varieties suitable for different materials and applications.

The question is, which suits your business or industry? We are here to answer your question with a guide to the different types of laser cutting ideal for your tasks.?

What are the Different Kinds of Laser Cutting?

With so many types of laser cutting, it can be difficult to identify the right one for your task. Each laser cutting method is suitable for different materials and applications. Understanding how each method works will give you deeper insight and help you choose the right one for your needs.

Fiber Laser Cutting

You might have noticed engraved serial numbers or logos in cars. Have you ever wondered how it is done precisely? The pro behind the job is fiber laser cutting. Not only just those serial numbers, but also from cutting engine components in automobiles, marking turbine blades in aeroplanes, customizing electronics, etching circuit boards, to creating jewelry, and more, fiber laser cutting has always played a major role.

How does it work? It uses optical fibers and generates a highly concentrated laser beam that works with computer numerical control (CNC). The laser beam is directed at a material to slice through it with high accuracy to convert it into desired shapes.?

You can either cut metallic or non-metallic materials like stainless steel, copper, aluminum, titanium, mild steel, and various alloys using these fiber lasers.

Pros?

• Help complete high-volume production within a short time?
• Create extremely precise and accurate cuts using a macchina per il taglio laser in fibra
• Consumes a low amount of energy while providing high-quality outcomes
• Adapts to cutting different types of materials and handles any projects
• Produces no waste material and significantly reduces expenses

Cons

• In rare cases, poor ventilation can cause fumes, potentially harming the operator while causing damage
• Complexity requires more training than any other type.

CO2 Laser Cutting

CO2 laser cutting, also known as carbon dioxide laser, is a popular laser cutting type. This is not similar to other types because it generates and directs in a way that’s completely different from the others.

It uses both electricity and a gas mixture of carbon dioxide and generates high-intensity infrared light. With many lenses and mirrors, it directs and focuses on the material, changing it into desired shapes.

Although it can be used for either metal or non-metal surfaces, it is best for cutting non-metallic materials like wood, leather, fabric, paper, plastic, rubber, and more.?

Pros?

• Cuts with high precision and offers intricate features
• Works at high production speed to cut thinner materials
• Offers high overall efficiency and typically consumes less power.
• Minimizes waste cleanup that’s in the form of dust.

Cons

• May emit harmful fumes when cutting highly reflective materials
• May find it hard to cut materials that are above a certain thickness
• Creates a heat-affected zone with high heat input that may alter nearby material properties

Direct Diode Laser Cutting

This is also known as a laser diode. It transforms electrical energy into coherent light energy, with a focused and monochromatic beam of light. This compact device uses semiconductor materials to generate laser light. It relies on it as an active medium and so known as energy efficient and cost-effective.

They cut non-metallic materials like plywood, MDF sheets, Bamboo, Oak, laser board, and more. Moreover, this is best for personal use, more than for complex work.

Pros

• Compact and more cost-effective than fiber and CO2 lasers
• Available in a wide range of wavelengths to cut many suitable materials

Cons

• Not suitable for all applications due to the rectangular beam spot size
• Poor absorption rates can pose complications during medical applications.

Nd: YAG/Nd: YVO Laser Cutting

Nd:YAG is Neodymium-doped Yttrium Aluminum Garnet, and Nd:YVO is Neodymium-doped Yttrium Orthovanadate. The Nd:YAG, a synthetic crystal, produces a laser beam with a wavelength of 1.06 micrometers, approximately.? And Nd:YVO works similarly but uses a slightly different crystal composition.

It has high cutting power and can be used for a wide range of applications. It can be used to work on metals (coated and non-coated) as well as non-metallic materials like plastics. They are better at handling reflective materials.

Pros

• Operates continuously throughout the process
• Cuts a wide range of materials, including powder-coated materials
• Cuts even through thick materials

Cons

• Costly purchasing and setting up
• Relies on pump diodes that are expensive to replace
• Less serviceable than other types of laser cutters

Conclusione

People use laser cutting to cut materials easily in precise shapes and designs. But which one suits you is more important to consider. These lasers can be of many types; among them, you need to consider a few things before purchasing. There are a few factors, like precision, quality, thickness, speed, and cost, to analyze so that you can make your decision on purchasing the right type.?

Selection Criteria for Cutting-in Methods

In the actual machining process, selecting an appropriate cutting-in method for end mills requires comprehensive consideration of multiple factors. First, the characteristics of the workpiece material, such as hardness and toughness, are crucial. For materials with low hardness, vertical cutting-in can be appropriately considered; for materials with high hardness and great toughness, gentle cutting-in methods such as oblique cutting-in or spiral cutting-in should be prioritized.

Pre-drilling

Pre-drilling a hole in the workpiece (5 – 10% larger than the diameter of the end mill) is the safest way to insert the milling cutter. This method can prevent premature wear of the tool. Chip evacuation is smoother, thus reducing the risk of chip accumulation and tool breakage. This method is usually employed when machining materials prone to built-up edges, ensuring consistent machinability.

Vertical Cutting-in

Vertical cutting-in is the most basic and common cutting-in method for end mills. This method refers to the end mill directly cutting in perpendicular to the workpiece surface. It is simple to operate and convenient for programming, and is widely used in rough machining with low requirements for machining accuracy and low material hardness. For example, when performing preliminary contour machining on aluminum workpieces, vertical cutting-in can quickly remove a large amount of material. However, vertical cutting-in also has obvious disadvantages. Since the cutting edge of the end mill is subjected to a large impact load at the moment of vertical cutting-in, it is prone to aggravate tool wear and even cause edge chipping. In addition, the large cutting force generated during vertical cutting-in may cause vibration of the workpiece, affecting the quality of the machined surface. Therefore, vertical cutting-in is not suitable for machining materials with high hardness or in cases where high requirements are placed on machining accuracy and surface quality.

Oblique Cutting-in

Oblique cutting-in is a relatively gentle cutting-in method. The end mill cuts into the workpiece along an oblique line at a certain inclination angle (typically between 3° and 15°). Compared with vertical cutting-in, this cutting-in method can effectively reduce the impact at the moment of tool cutting-in, lower the peak value of cutting force, and reduce tool wear. Meanwhile, oblique cutting-in can make the cutting process more stable, which is conducive to improving the quality of the machined surface.

Recommended Angles: For hard/ferromagnetic materials: 1°-3°

For plastic/non-ferromagnetic materials: 3°-10°

When machining high-hardness materials such as cast iron, the oblique cutting-in method demonstrates obvious advantages. By gradually cutting into the workpiece, the cutting edge of the end mill comes into contact with the material step by step, avoiding the severe impact of vertical cutting-in and extending the service life of the tool. In mold machining, for some complex cavities, oblique cutting-in is also commonly used in the roughing stage to improve machining efficiency and tool durability.

?Spiral Cutting-in

Spiral cutting-in is a more advanced and efficient cutting-in method. When the end mill cuts into the workpiece, it gradually penetrates along a spiral trajectory, similar to the drilling principle of a drill bit. The advantages of spiral cutting-in are remarkable: it enables the tool to maintain a continuous cutting state during the cutting-in process, with uniform distribution of cutting force, which greatly reduces the impact and vibration on the tool.

Spiral cutting-in is widely used in machining high-hardness alloy materials such as titanium alloys and nickel-based alloys. Due to the poor cutting performance of these materials, traditional cutting-in methods easily cause rapid tool wear and damage. In contrast, spiral cutting-in can effectively reduce the cutting temperature, minimize friction between the tool and the workpiece, and thus improve machining efficiency and quality.

Programming Note: When using this method, the programmed diameter should be 110-120% larger than the diameter of the cutting insert. Additionally, spiral feed has advantages in achieving precise surface finish, making it the preferred choice for high-precision and high-surface-quality machining in industries like aerospace and medical device manufacturing.

Arc Cutting-in

Arc cutting-in is a method where the end mill cuts into the workpiece along an arc trajectory. This cutting-in approach is mainly used for machining contours or surfaces with special requirements, enabling the tool to maintain a stable cutting state during both cutting-in and cutting-out. It reduces tool engagement marks on the machined surface and improves surface finish. When machining complex curved parts such as cams and blades, the arc cutting-in method can precisely control the tool’s movement trajectory to ensure machining accuracy. Additionally, during contour milling, arc cutting-in avoids over-cutting or under-cutting caused by sudden changes in cutting force at corners, making the machined contour smoother and more accurate.

Rolling Cut

Rolling entry into the cut ensures that the tool can fully penetrate and naturally achieve an appropriate chip thickness. In this case, the feed rate should be reduced by 50%. Rolling tool engagement is particularly advantageous in slotting and contour machining, where maintaining consistent chip thickness is crucial for surface finish and dimensional accuracy. Machinists often use this method in high-speed cutting operations to maximize material removal rate while minimizing tool wear and heat generation.

Second, machining accuracy and surface quality requirements are also important reference factors. If high requirements are placed on the surface finish and accuracy of the machined part, vertical cutting-in should be avoided, and methods ensuring stable cutting such as arc cutting-in or spiral cutting-in should be chosen. Additionally, factors such as the performance of machining equipment, the type and size of tools, and machining costs need to be incorporated into the consideration.

Selection Between Climb Milling and Conventional Milling

Principles of Climb Milling and Conventional Milling

Climb milling?refers to the scenario where the rotation direction of the milling cutter is the same as the feed direction of the workpiece, and the cutting thickness gradually decreases from maximum to zero. During climb milling, the cutting edge first contacts the machined surface of the workpiece, then cuts into the material, and the chip thickness continues to decrease as cutting proceeds.

Conventional milling?is when the rotation direction of the milling cutter is opposite to the feed direction of the workpiece, and the cutting thickness gradually increases from zero. During conventional milling, the cutting edge slides on the workpiece surface for a certain distance before cutting into the material, with the chip thickness increasing from thin to thick.

Advantages and Disadvantages of Climb Milling and Conventional Milling

Advantages of climb milling

The cutting process is relatively stable, and tool wear is relatively small. Since the chip thickness decreases from large to small, the cutting edge is subjected to less impact during cutting. Meanwhile, the vertical component of the cutting force always presses against the worktable, helping to reduce workpiece vibration and improve the surface quality of the machined part, especially suitable for finishing. However, climb milling has high requirements for machine tools: the feed mechanism of the machine tool must have a function to eliminate clearance; otherwise, under the action of cutting force, the worktable may move abruptly, affecting machining accuracy or even damaging the tool.

Advantages of conventional milling

It has lower requirements for machine tools and does not require special clearance elimination devices. During conventional milling, the horizontal component of the cutting force is opposite to the feed direction, which can effectively prevent abrupt movement of the worktable. However, during conventional milling, the cutting edge needs to slide on the workpiece surface first, which aggravates tool wear and generates more cutting heat. The surface quality of the machined part is inferior to that of climb milling, so it is generally used for rough machining or when the machine tool rigidity is insufficient.

Key Points for Selecting Climb Milling or Conventional Milling

Selecting between climb milling and conventional milling requires comprehensive consideration of factors such as workpiece material, machining accuracy requirements, and machine tool performance. For materials with low hardness and good plasticity such as aluminum and copper, as well as for finishing with high surface quality requirements, climb milling is often the better choice; for steels with high hardness, or when the machine tool rigidity is poor and there is no clearance elimination device, conventional milling is more appropriate. Additionally, when machining castings with hard skins, conventional milling can avoid the cutting edge directly contacting the hard skin and accelerating wear.

Riepilogo

There are various cutting-in methods for fresas, each with its unique characteristics and application scenarios. Mechanical machining practitioners need to deeply understand the principles, advantages, and disadvantages of various cutting-in methods, as well as climb milling and conventional milling. According to actual machining needs, they should comprehensively consider multiple factors to reasonably select the cutting-in method and milling method for end mills, so as to achieve efficient and precise machining and improve product quality and production efficiency. With the continuous development of machining technology, the cutting-in methods and milling methods for end mills will also continue to innovate and optimize, bringing more possibilities to the mechanical machining industry.

Article Source

Kareem, S. J., Wurood Asaad, M., & Al-Ethari, H. ?Enhancement of tribological properties of carbide cutting tools by ceramic coating deposition.?Heat Treatment and Surface Engineering,(2024).?6(1). https://doi.org/10.1080/25787616.2024.2331865

Astratto

Coating by sol–gel deposition to modify the tribological properties of K10 carbide cutting insert was performed. The study examines the thermal and tribological characteristics of uncoated cutting inserts and the cutting inserts coated with TiO₂/8YSZ and TiO₂/15YSZ layers respectively. The TiO₂/8YSZ and TiO₂/15YSZ coatings had a hardness of 1151.6 and 1678.9 HV, respectively, and the TiO₂/8YSZ and TiO₂/15YSZ coated inserts had scratch hardness of 2.73 and 22.98 GPa respectively. Among the uncoated and coated inserts, the TiO₂/15YSZ coated inserts had the lowest coefficient of friction and rate of wear. The TiO₂/8YSZ coated insert had a lower thermal conductivity when compared to TiO₂/15YSZ coated insert and uncoated carbide cutting insert (10.3 vs. 14.1, and 41.8 W/m.K). The thermal expansion coefficients of the 8YSZ layers, 15YSZ layers, and carbide cutting tool were 3.66*10^?6, 3.546*10^?6 and 14*10^?6 K^?1, respectively. The reasons for the enhancement of the tribological properties of the carbide cutting tools by the ceramic coatings are discussed.

Key Findings

Research Team: The team from the Department of Materials Engineering, University of Babylon, Iraq

Technical Approach: The research team deposited TiO?/yttria-stabilized zirconia (YSZ) multilayer ceramic coatings on K10 tungsten carbide inserts via the sol-gel method, systematically analyzing the effects of 8% and 15% yttrium contents (8YSZ vs. 15YSZ) on performance.

Key Data Highlights (with partial data from Figure 10)

Hardness and Scratch Resistance

Microhardness: The 15YSZ-coated insert achieved 1,679 HV (uncoated insert: only 866 HV), a nearly 2-fold increase!

Scratch Hardness: The 15YSZ coating reached 22.98 GPa, significantly enhancing interfacial bonding strength.

Friction and Wear Resistance of Tested Tools

Friction Coefficient: The 15YSZ coating showed a coefficient of only 0.17, a 76% reduction compared to the uncoated insert (0.71) (Figure 12).The key data from the experiments are remarkable. In terms of hardness and scratch resistance, microhardness tests show that the 15YSZ-coated insert achieves an impressive 1,679 HV—nearly double the 866 HV of the uncoated insert. This means the coated insert can more effectively withstand high-intensity cutting, reducing tool wear. Scratch hardness tests further confirm the coating’s excellence: the 15YSZ coating’s 22.98 GPa value directly reflects a significant enhancement in interfacial bonding between the coating and substrate, akin to armoring the tool with a robust, well-adhered layer.

In the realm of friction and wear resistance, the experimental data are equally striking. The friction coefficient test chart (Figure 12) clearly shows that the 15YSZ coating has a coefficient of only 0.17—76% lower than the uncoated insert’s 0.71. This dramatic reduction enables smoother tool operation during cutting, minimizing energy loss from friction. Even more impressive, wear rate tests (Figure 14) reveal that the 15YSZ coating has a wear rate as low as 0.24×10?3 g/m—85% lower than the uncoated insert—significantly extending tool service life.

Figure 10. The micro hardness of uncoated insert and different coatings, and the images of indents produced on the surface of uncoated inserts and different coatings.

Figure 12. Coefficient of friction versus time of uncoated insert and the inserts coated by TiO2/8YSZ and TiO2/15YSZ coatings respectively.

Figure 14. Wear rate of the uncoated and coated inserts.

Technical Breakthrough

Low-Temperature Process Advantages

The sol-gel method completes coating deposition at a low temperature of 700°C, avoiding thermal damage to the substrate caused by traditional high-temperature processes while achieving high purity and uniformity (Figure 4).

Yttrium Content Regulation Mechanism

Grain Refinement: Increasing yttrium content from 8% to 15% inhibits grain growth and refines the coating structure (XRD shows stable cubic phase, Figure 3).

Performance Balance: High yttrium content enhances hardness and wear resistance but requires trade-offs with thermal conductivity (15YSZ has slightly higher thermal conductivity than 8YSZ).

In terms of thermal performance optimization, the 8YSZ coating exhibits unique advantages. With a thermal conductivity of only 10.3 W/m·K, it effectively blocks heat conduction generated during cutting, preventing tool performance degradation due to overheating. Meanwhile, the YSZ coating (3.5–3.6×10?? K?1) has a smaller difference in thermal expansion coefficient from the tungsten carbide substrate (14×10?? K?1), a feature that significantly reduces the risk of coating spalling caused by thermal stress and further enhances tool stability and reliability.

The technological breakthrough of this study is of milestone significance. First, the sol-gel method can complete coating deposition at a low temperature of 700°C. Compared with traditional high-temperature processes, this low-temperature process successfully avoids thermal damage to the substrate. As clearly shown in the FESEM images (Figure 4), the coating prepared by the sol-gel method features high purity and uniformity, with a dense and homogeneous structure, laying a solid foundation for improving tool performance. Second, the research on the yttrium content regulation mechanism has also achieved important results. As the yttrium content increases from 8% to 15%, the XRD pattern (Figure 3) shows that the cubic phase remains stable, and grain growth is effectively inhibited, achieving refinement of the coating structure. However, the research team also points out that although high yttrium content can improve hardness and wear resistance, it needs to be balanced with thermal conductivity, as reflected in the slightly higher thermal conductivity of 15YSZ than that of 8YSZ.

Figure 4. FESEM image of a multilayer coating (YSZ) on carbide insert: (a) 8YSZ 100000 Mag., (b) 8YSZ 25000 Mag.

Figure 3. XRD Pattern of (a) carbide cutting tool, (b) 8YSZcoating

Industrial Application Prospects

In terms of industrial application prospects, the research findings offer broad market space and significant economic value. In high-wear scenarios such as automotive manufacturing and mining drilling, experimental data show that the service life of coated tools is increased by over 50%. This means enterprises can reduce tool replacement frequency and downtime, thus significantly improving production efficiency. Meanwhile, the 85% reduction in wear rate directly translates to substantial machining cost savings, effectively controlling both tool procurement and maintenance costs. Additionally, the low friction coefficient reduces energy consumption during tool operation, aligning with the global trend of green manufacturing and yielding non-negligible environmental benefits. The research conducted by the team from the Department of Materials Engineering, University of Babylon, Iraq, not only paves a new path for tungsten carbide tool coating technology but also demonstrates the immense potential of sol-gel processes in high-temperature industrial components. Looking ahead, with further optimization of yttrium content and multi-layer structure design, the performance of tungsten carbide tools is expected to achieve new breakthroughs, bringing more surprises and transformations to the industrial processing field.

Conclusione

This study not only provides a novel solution for tungsten carbide tool coating technology but also reveals the huge potential of sol-gel processes in high-temperature industrial components. In the future, optimizing yttrium content and multi-layer structure design may further break through performance limits!

This article focuses on introducing suitable powder raw materials for ultrafine-grained cemented carbides. Our next two weeklies will delve into the topics of grain growth inhibitors and sintering processes.

Quality Requirements for Powder Grains

The primary prerequisite for preparing ultrafine-grained or nanocrystalline cemented carbides is the production of ultrafine/nano WC powder or WC-Co composite powder, which has become a current research focus. According to relevant literature, ultrafine/nano powder raw materials must meet stringent criteria, including uniform average grain size with a narrow distribution, high purity, and reasonable carbon and oxygen content. Additionally, factors such as particle morphology, crystallographic perfection, and subgrain size directly influence the performance of ultrafine-grained cemented carbides.

Achievements in Powder Production

In 1989, Rutgers University in the United States took the lead in successfully developing nanostructured cemented carbides. Subsequently, Nanodyne Company developed nanostructured WC-Co cemented carbide composite powder with a particle size of 40 nm based on this foundation. Renowned companies in Japan, Switzerland, Germany, and other countries have also successively developed nanostructured cemented carbides. Among them, Switzerland’s Sandvik Company’s T002 ultrafine-grained cemented carbide has the finest grains, reaching 200 nm. Domestically, Zigong 746 Factory and Zhuzhou 601 Factory have both developed their own nanostructured cemented carbides, with grain sizes less than 500 nm, hardness of 93 HRA, and strength of 4000 MPa.

Technological Development in Ultrafine-Grained Cemented Carbide Powder Production

In summary, the preparation technologies for ultrafine/nano-grained cemented carbide powders at home and abroad mainly include the following aspects:

(1) Oxide Reduction-Carbonization Technology

This method involves granulating a mixture of WO and carbon black, followed by low-temperature carbonization reduction under N?and H?atmospheres to produce ultrafine WC with a grain size of 0.5 μm. This technology was jointly developed by Tokyo Tungsten and Sumitomo Electric in Japan. Its characteristics include rapid and continuous production of ultrafine and uniform WC powder, with the finest WC powder achieving a BET grain size of 0.11-0.13 nm. However, its drawback is that during the carbonization reduction process, H? reacts chemically with carbon black, making it difficult to control the carbon content in the product. The U.S. company EMO introduced the Rapid Carbonthermal Reduction (RCR) technology from Dow Chemical, operating at temperatures of 1500-2000°C. This technology is characterized by low cost and mass production capabilities, yielding WC powders with grain sizes of 0.2 μm, 0.4 μm, and 0.8 μm.

Domestically, significant progress has also been made in this technology. Wuhan University of Technology has improved the oxide reduction-carbonization process by employing vacuum or inert gas atmospheres, thereby avoiding the adverse effects of H? on the reduction products and successfully producing ultrafine WC-Co composite powders with grain sizes ranging from 0.1 to 0.3 μm.

Advantages:

Enables rapid and continuous production, with the finest grain size reaching 0.11-0.13 μm (BET method).

Low cost and suitable for large-scale production (e.g., EMO’s mass production of 0.2-0.8 μm WC powders).

Svantaggi:

H? reaction with carbon black makes carbon content control challenging.

Although vacuum/inert gas atmospheres mitigate this issue, they increase process complexity.

(2) Low-Temperature Reduction-Carbonization Technology

This method involves reducing blue or purple tungsten oxide with hydrogen gas at low temperatures to produce tungsten powder, which is subsequently carbonized into ultrafine WC powder. This technique is widely adopted in China, with notable users including Xiamen Golden Egret Special Alloy Co., Ltd., Zhuzhou Cemented Carbide Group, and Zigong Cemented Carbide Plant.

Advantages:

Simple process and extensive domestic application (e.g., Xiamen Golden Egret, Zhuzhou Cemented Carbide Group).

Low equipment requirements.

Svantaggi:

Insufficient precision in carbon content control, necessitating inhibitor optimization.

Potential limitations in grain size distribution uniformity.

(3) Thermochemical Synthesis Technology (Spray Drying)

Thermochemical synthesis, or spray drying, comprises three main steps: (a) preparing cobalt solutions from ammonium metatungstate and cobalt chloride or ethylenediamine tungstate, followed by homogeneous mixing; (b) spray-drying the mixture to obtain ultrafine and uniform cobalt-cobalt salt composite powders; and (c) reducing and carbonizing the powders in a fluidized bed reactor to produce nano WC-Co composite powders. Characteristics: The nano WC-Co composite powders retain the morphology of the precursors, with grain sizes controllable by adjusting reaction temperature, holding time, and carbonization gas activation. They exhibit high specific surface area and enable alloy densification at relatively low temperatures. Disadvantages: The process is complex, and carbon content control is inaccurate, though controllability can be improved by effectively blending carbonization atmospheres as carbon sources.

Advantages:

Controllable grain size (via temperature, time, and carbonization atmosphere adjustments).

High specific surface area and excellent low-temperature densification performance.

Svantaggi:

Complex process and challenging carbon content control.

Requires carbonization atmosphere regulation for stability.

(4) In-Situ Carburization Technology

In-situ carburization involves directly reducing precursors to single-phase nano WC-Co composite powders using hydrogen gas without external carbon sources (e.g., CO/CO?). This is achieved by dissolving tungstic acid and cobalt salt in a polyacrylonitrile solution, followed by low-temperature drying and reduction in a 90% Ar-10% H? mixed gas atmosphere at 800-900°C, yielding WC-Co powders with grain sizes of 50-80 nm. This method was first reported by Y.T. Zhou of the University of Texas in 1994. Key Innovation: Replacing CO/CO? mixtures with polyacrylonitrile as the in-situ carbon source, enabling direct hydrogen reduction of precursors to single-phase nano WC-Co composites. Process parameters such as reduction temperature, atmosphere, and trace cobalt acetate catalyst additives significantly influence the final nano composite powder quality. Disadvantages: Insufficient reduction due to shortened diffusion times results in residual undecomposed polymers or free carbon, adversely affecting product performance.

Advantages:

Highly innovative, achieving grain sizes of 50-80 nm.

Simplifies the process by eliminating traditional carbon sources (e.g., CO/CO?).

Svantaggi:

Incomplete reduction leads to residual polymer or free carbon, impacting performance.

High sensitivity to temperature, atmosphere, and catalysts (e.g., cobalt acetate).

(5) Plasma Technology

Plasma technology utilizes a plasma-generated heat source maintained at 4000-5000°C to decompose, react, and synthesize raw materials (W, WC, or WO?) and carbon sources (CH?), yielding products with grain sizes as fine as 5-20 nm. The primary heat sources include direct current (DC) plasma, high-frequency plasma, or a combination of both. Disadvantages: Plasma sustainability is poor, making it difficult to ensure complete evaporation and reaction of the raw materials.

Advantages:

Produces extremely fine grain sizes (5-20 nm), suitable for ultra-high-end applications.

Rapid reaction rates.

Svantaggi:

Poor plasma stability leads to incomplete raw material evaporation and reactions.

High equipment costs and energy consumption.

(6) Sol-Gel Technology

The sol-gel process involves the hydrolysis and polycondensation of hydrolyzable metal compounds in a solvent, followed by gelation, drying, and reduction to produce nanostructured powders. This low-temperature process relies on hydrolysis and polymerization reactions, resulting in high-purity powders with narrow grain size distributions, high chemical activity, and homogeneous multi-component mixtures. For instance, scientists like Srikanth Rahunathan have utilized sol-gel technology to develop nano W-Co, W-Mo, and W-Cu composite powders. Characteristics: The sol-gel method offers precise chemical controllability, simple operation, and low cost for producing nanostructured composite powders with uniform structures. Disadvantages: The process is complex and challenging to scale for mass production.

Advantages:

High purity, narrow grain size distribution, and controllable chemical activity.

Suitable for multi-component composite powders (e.g., W-Co, W-Mo).

Svantaggi:

Complex preparation process and difficulty in large-scale production.

Higher costs and longer production cycles.

(7) Mechanical Cemente Carbide Alloying Technology

Mechanical alloying involves blending elemental powders in specific ratios and milling them under inert gas protection in a high-energy ball mill. Mechanical energy from milling induces repeated deformation, cold welding, and fracturing of the powders, resulting in a dispersion of ultrafine particles and solid-state alloying. Advantages: The process is technically simple, requires minimal equipment, and is easy to operate. Disadvantages: Alloying may introduce impurities, and internal stresses/agglomeration within the powders due to compressive/shear forces can negatively impact compressibility and sintering behavior.

Advantages:

Simple technology, inexpensive equipment, and ease of operation.

Svantaggi:

Risk of impurity introduction during alloying.

Significant internal stresses and severe agglomeration in powders, affecting compaction and sintering properties.

Domestically, the Institute of Physics, Chinese Academy of Sciences, successfully produced nano WC powder with a grain size of 7.2 nm using mechanical alloying in 1944. Similarly, Professor Wu Xijun of Zhejiang University synthesized nano single-phase W?C powder with an average grain size of 6.0 nm using the same method.

Advantages:

Simple equipment and easy operation.

Capable of producing extremely fine grain sizes (e.g., 7.2 nm WC powder).

Svantaggi:

High risk of impurity introduction.

Significant internal stress in powders and severe agglomeration, adversely affecting compaction and sintering properties.

Riepilogo

For the production of ultrafine-grained cemented carbide powders:

1.Oxide reduction-carbonization and low-temperature reduction-carbonization technologies are suitable for large-scale production due to their low cost and mature processes. Plasma and sol-gel technologies can produce nano-scale powders but require addressing stability and cost challenges.

2.In-situ carburization introduces polymer-based carbon sources as an innovative approach to carbon content control, though optimization of reduction completeness is needed.

3.Institutions such as Wuhan University of Technology and the Institute of Physics, Chinese Academy of Sciences, have achieved notable advancements in improving conventional processes (e.g., vacuum carbonization, mechanical alloying). However, high-end powders (e.g., sub-50 nm grades) still rely on imports.

In high-temperature, high-wear industrial processing scenarios, the lifespan and performance of tungsten carbide (WC-Co) inserts directly determine production costs and efficiency. While traditional coating technologies (such as CVD/PVD) can enhance performance, their high-temperature processes often lead to a reduction in substrate hardness. How can we achieve low-temperature, high-efficiency coatings while maintaining high hardness, low friction, and thermal shock resistance? A recent study published in Heat Treatment and Surface Engineering (HTSE) provides an innovative solution!

Intro of the paper

Source

Kareem, S. J., Wurood Asaad, M., & Al-Ethari, H. ?Enhancement of tribological properties of carbide cutting inserts by ceramic coating deposition. Heat Treatment and Surface Engineering,(2024).?6(1).
https://doi.org/10.1080/25787616.2024.2331865

Abstract?from the paper

Coating by sol–gel deposition to modify the tribological properties of K10 carbide cutting tool was performed. The study examines the thermal and tribological characteristics of uncoated cutting inserts and the cutting inserts coated with TiO₂/8YSZ and TiO₂/15YSZ layers respectively. The TiO₂/8YSZ and TiO₂/15YSZ coatings had a hardness of 1151.6 and 1678.9 HV, respectively, and the TiO₂/8YSZ and TiO₂/15YSZ coated inserts had scratch hardness of 2.73 and 22.98 GPa respectively. Among the uncoated and coated tools, the TiO₂/15YSZ coated inserts had the lowest coefficient of friction and rate of wear. The TiO₂/8YSZ coated insert had a lower thermal conductivity when compared to TiO₂/15YSZ coated insert and uncoated carbide cutting insert (10.3 vs. 14.1, and 41.8 W/m.K). The thermal expansion coefficients of the 8YSZ layers, 15YSZ layers, and carbide cutting insert were 3.66*10^?6, 3.546*10^?6?and 14*10^?6?K^?1, respectively. The reasons for the enhancement of the tribological properties of the carbide cutting inserts by the ceramic coatings are discussed.

Research Team

Materials Engineering Department, University of Babylon, Iraq

Technical Approach

Deposited TiO?/Yttria-Stabilized Zirconia (YSZ) multilayer ceramic coatings on K10 tungsten carbide (WC) inserts via sol-gel method, systematically analyzing the effects of 8% vs. 15% yttria content (8YSZ vs. 15YSZ) on performance.

Key Data Highlights (Partial data from Figure 1):

1.Hardness & Scratch Resistance

Microhardness:

15YSZ-coated insert: 1679 HV (vs. 866 HV for uncoated tool) → ~2× improvement

Scratch hardness: 15YSZ coating reached 22.98 GPa, indicating significantly enhanced interfacial adhesion.

2.Friction & Wear Performance

Coefficient of friction (CoF):

15YSZ coating: 0.17 (vs. 0.71 for uncoated tool) → 76% reduction! (See Figure 2)

Figure 1. The micro hardness of uncoated tool and different coatings, and the images of indents produced on the surface of uncoated inserts and different coatings.

Figure 2. Coefficient of friction versus time of uncoated insert and the tools coated by TiO2/8YSZ and TiO2/15YSZ coatings respectively.

Figure 3. Wear rate of the uncoated and coated inserts.

3Wear Performance

15YSZ coating:

Wear rate: 0.24×10?3 g/m (85% reduction compared to uncoated tools, see Figure 3)

Thermal Performance Optimization

Thermal conductivity:

8YSZ coating: 10.3 W/m·K (effectively blocks cutting heat transfer)

Thermal expansion matching

YSZ coating (3.5-3.6×10?? K?1) vs. WC substrate (14×10?? K?1)

Minimal mismatch significantly reduces thermal stress-induced delamination risks

Technical Breakthroughs

1Low-Temperature Processing Advantage

2Sol-gel coating deposition achieved at 700°C (low-temperature)

3Avoids thermal damage to substrate caused by conventional high-temperature processes

4Achieves high purity and excellent uniformity (see Figure 4)

Content Optimization Mechanism

Grain refinement:

Increasing yttria content from 8% to 15% effectively inhibits grain growth and refines coating structure (XRD confirms stabilized cubic phase, see Figure 5)

Performance balance:

Higher yttria content (15YSZ) enhances hardness and wear resistance

Requires trade-off with slightly increased thermal conductivity compared to 8YSZ

Figure 4. FESEM image of a multilayer coating (YSZ) on carbide tool: (a) 8YSZ 100000 Mag., (b) 8YSZ 25000 Mag.,

Figure 5. XRD Pattern of (a) carbide cutting insert, (b) 8YSZcoating, (c) 15 YZS coating.

Industrial Application Prospects

Extended Insert Lifespan:

Experimental results demonstrate over 50% longer tool life for coated inserts, making them ideal for high-wear applications like automotive manufacturing and mining drilling.

Cost Reduction:

An 85% reduction in wear rate translates to fewer tool replacements, significantly lowering machining costs.

Environmental Benefits:

The low friction coefficient reduces energy consumption, aligning with green manufacturing trends.

Conclusione

This study not only provides an innovative solution for tungsten carbide tool coatings but also highlights the immense potential of sol-gel technology in high-temperature industrial components. Future optimization of yttria content and multilayer structure design could push performance boundaries even further!

Cemented carbides are widely used in demanding engineering applications where corrosion resistance is crucial for long-term performance. While extensive research has focused on conventional hard alloys, the corrosion behavior of materials with controlled matrix granule-to-network structure ratios remains poorly understood. This structural parameter significantly influences both mechanical properties and chemical stability, yet systematic studies comparing different configurations are notably absent from the literature.

Fig.1?FSEM morphology of matrix and granular cemented carbide

Comparative Investigation of Corrosion Mechanisms in Hard Alloys with Engineered Matrix Granule-to-Network Architectures

This study systematically examines how controlled variations in the granule-to-network ratio (20:80 to 80:20) influence the electrochemical degradation behavior of WC-Co cemented carbides. Using a combination of potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and advanced microstructural characterization, we establish quantitative correlations between three-dimensional phase connectivity and key corrosion parameters, including charge transfer resistance, corrosion current density (i_corr), and passive film stability. The research particularly focuses on elucidating how network continuity versus granular isolation affects: (1) anodic dissolution kinetics of the cobalt binder phase, (2) galvanic coupling effects between WC grains and metallic binder, and (3) penetration pathways for corrosive species in marine-grade NaCl environments. Our findings provide a microstructure design roadmap for developing next-generation hard alloys with optimized corrosion-wear synergy for extreme service conditions in offshore, mining, and chemical processing applications.

Corrosion Resistance: A Critical Factor in Cemented Carbide Applications

Cemented carbides are widely used in engineering practice, and their corrosion resistance has always been a critical factor affecting engineering reliability. In industrial applications, cemented carbides are susceptible to oxidation, chemical corrosion, and erosion. After exposure to corrosion, the alloy exhibits various degradation phenomena during service, leading to a sharp deterioration in surface properties and wear resistance, thereby shortening the operational lifespan of engineering components. Therefore, enhancing both physical properties and corrosion resistance is crucial for materials intended for complex working environments.

Fig.2?Mechanical properties of cellular cemented carbides with?different matrix granule ratios

(a)XW5；(b) XW6；(c) XW7；(d) XW8

Fig.3 SEM morphology of cellular cemented carbides with different matrix granule ratios

Grain Size Effects on Electrochemical Corrosion Behavior

ZHANG L et al. investigated the electrochemical corrosion behavior of WC-10Co cemented carbides with different WC grain sizes. Their results demonstrated a strong linear correlation between charge transfer resistance, corrosion current density, and WC grain in the solution. Similarly, KELLNER F J J et al. studied the corrosion behavior of cemented carbides with varying grain sizes using electrochemical methods. Their experimental findings revealed that smaller grain sizes enhance corrosion resistance, and the corrosion behavior is significantly influenced by the dissolved W and C content in the Co binder phase.

Fig.4 Potential polarization curve of cellular cemented carbides with different matrix granule ratios

Research Gap: Network-Structured Alloys in Corrosive Environments

While the corrosion behavior of conventional cemented carbides has been extensively studied, there is limited comprehensive research on network-structured alloys in corrosive environments. In this study, YG10-grade alloy was selected as the matrix material, and YG8-grade alloy as the granular material to fabricate network-structured alloys. The research focuses on examining the influence of matrix-to-granule volume ratio on the microstructure and corrosion performance of the network-structured alloy.

Fig.5 Nyquist curve of cellular cemented carbides with different matrix granule ratios

Fig.6 Bode curve of cellular cemented carbides with different matrix granule ratios

Fig.7 Equivalent circuit diagram used to fit EIS

(a)XW5；(b) XW6；(c) XW7；(d) XW

Fig.8 Corrosion topography of cellular cemented carbides with different matrix granule ratios

?

Conclusione

This study investigated the effects of the matrix-to-granule ratio on the microstructure and corrosion resistance of network-structured alloys in a 3.5% NaCl solution. The key findings are as follows:

1.Mechanical Properties

As the granule proportion increased, the Vickers hardness of the alloy first increased and then decreased, while the flexural strength gradually improved.

The optimal comprehensive mechanical properties were achieved at a matrix-to-granule ratio of 30:70.

2.Polarization Curve Analysis

Both the corrosion potential and corrosion current density initially decreased and then increased with higher granule proportions.

Increasing the granule ratio reduced both the corrosion tendency and corrosion rate of the network-structured alloy.

3.Electrochemical Impedance Spectroscopy (EIS) Results

A higher granule proportion enhanced the electrochemical impedance of the alloy.

At a matrix-to-granule ratio of 30:70, the fitted charge transfer resistance (R_t = 1,860 Ω·cm2) and constant phase element exponent (n = 0.8878) reached their maximum values, indicating minimal surface corrosion and the fewest corrosion pits.

Understanding Carburo di tungsteno’s Machinability

Tungsten carbide’s extreme hardness (1,300–1,900 HV) means traditional cutting tools like carbide or high-speed steel (HSS) quickly wear out or fail. Additionally, its brittleness makes it prone to chipping under mechanical stress, while its low thermal conductivity causes heat to concentrate at the cutting zone, accelerating tool degradation.

The material’s machinability also depends on its cobalt content. High-cobalt grades (10–20% Co) are tougher but slightly softer, making them more suitable for grinding and EDM. Low-cobalt grades (3–6% Co) are harder and more wear-resistant but require even more precise machining techniques to avoid cracking.

Optimal Machining Methods

Grinding: The Go-To Method for Precision Finishing

Grinding remains the most effective way to machine tungsten carbide, especially for achieving tight tolerances and fine surface finishes. Diamond grinding wheels are the preferred choice due to their superior hardness and wear resistance. For rough grinding, cubic boron nitride (CBN) wheels can be used, but they are less efficient than diamond for finishing operations.

Key parameters for successful grinding include:

Wheel speed: 15–25 m/s

Feed rate: 0.005–0.02 mm per pass

Coolant: Essential to prevent thermal cracking and extend wheel life

Electrical Discharge Machining (EDM): Ideal for Complex Geometries

When grinding isn’t feasible—such as when machining intricate internal features or deep cavities—EDM is the next best option. This non-contact process uses electrical sparks to erode the material, making it ideal for hard, conductive materials like tungsten carbide.

Wire EDM is particularly effective for cutting complex profiles, while sinker EDM is better suited for creating molds and dies. To optimize results:

Use graphite or copper electrodes for better wear resistance.

Maintain a well-filtered dielectric fluid to prevent arcing.

Apply high flushing pressure to remove debris and improve cutting speed.

Laser Machining: Precision Micro-Cutting and Drilling

For ultra-fine features, laser machining offers a high-precision alternative. Fiber lasers (1μm wavelength) are the most efficient, capable of cutting thin tungsten carbide sheets with minimal heat distortion. Picosecond lasers provide even finer control, reducing the heat-affected zone (HAZ) for critical applications.

However, laser cutting is slow for thicker sections (>5 mm) and may require multiple passes. Using an inert assist gas (such as nitrogen or argon) helps prevent oxidation and improves edge quality.

Conventional Machining: Limited but Possible in Certain Cases

While traditional milling or turning is generally impractical for sintered tungsten carbide, it can be used for green-state (unsintered) carbide before final heat treatment. Polycrystalline diamond (PCD) tools are the only viable option for such operations, but even then, cutting parameters must be carefully controlled:

Speed: 30–50 m/min

Feed: 0.02–0.1 mm/rev

Depth of cut: <0.5 mm to avoid excessive tool wear

Tool Selection and Process Optimization

Choosing the right tooling is critical for successful tungsten carbide machining. Diamond-coated tools outperform carbide in grinding and milling, while EDM requires high-quality electrodes to maintain precision. When using lasers, pulse duration and assist gas selection significantly influence cut quality.

To minimize common issues like cracking, tool wear, and poor surface finish:

For grinding: Use fine-grit diamond wheels (600+ grit) for mirror-like finishes and dress wheels frequently to maintain sharpness.

For EDM: Optimize spark frequency and dielectric flushing to prevent uneven erosion.

For laser cutting: Use pulsed mode to reduce heat buildup and improve edge quality.

Conclusion: Best Practices for Machining Tungsten Carbide

Successfully machining tungsten carbide requires a combination of the right techniques, tooling, and process parameters. Grinding and EDM are the most reliable methods, while laser cutting excels in precision applications. Conventional machining is only viable for pre-sintered carbide and must be approached with caution.

By following these guidelines—prioritizing coolant use, optimizing feed rates, and selecting appropriate tool materials—manufacturers can achieve high-quality results while extending tool life. For those working with tungsten carbide regularly, investing in advanced grinding or EDM equipment will yield the best long-term efficiency and cost savings.

For custom tungsten carbide components, consulting with a specialist can help determine the most effective machining strategy for your specific needs.

This article systematically introduces the principles of tool selection in turning operations, focusing on the selection methods for external turning inserts.Through practical examples of different turning types, it helps readers master key application techniques.

Basic Principles of Tool Selection

When selecting tools, clamping reliability and modular tool priority must be considered.During the turning process, ensuring secure clamping between the insert and tool holder is critical as it directly affects machining stability.

The type of tool holder selected is influenced by the lead angle (entering angle), shape, and size of the insert being used.Meanwhile, corresponding tool holder systems should be chosen based on different operation types.Additionally, deciding between negative or positive rake angle inserts is an important consideration.To facilitate replacement and adjustment, modular tool options should be prioritized.

Next, we will delve into the selection methods for external turning inserts. One of the four main application areas is longitudinal turning or face turning, which represents the most common type of turning operation.

Different Turning Types

Longitudinal Turning

In longitudinal turning or face turning, diamond-shaped C-type inserts paired with appropriate lead angles constitute the most commonly implemented solution.

In longitudinal turning or face turning, the diamond-shaped C-type (80°) insert is a commonly used option.

The tool holder’s lead angle is typically set at 95° and 93° (entering angles of -5° and -3°) to ensure optimal cutting performance.

In addition to C-type inserts, D-type (55°), W-type (80°), and T-type (60°) inserts can serve as alternatives to accommodate different requirements.

Contour Turning

Selecting appropriate lead angles to ensure machining versatility and accessibility is crucial in contour turning.

In contour turning processes, selecting an appropriate KAPR (entering angle) is crucial.

Typically, a 93° lead angle (corresponding to a -3° entering angle) is most commonly used as it achieves an internal contour angle of 22°-27°, ensuring machining versatility and accessibility.

D-type (55°) and V-type (35°) inserts serve as frequently used alternative options to meet different cutting requirements.

Face Turning

Tools require radial feed movement with proper lead angle selection to ensure cutting stability and machining quality.

In face turning, tools feed radially to complete workpiece machining.

This turning method demands appropriate insert and lead angle selection to guarantee process stability and output quality.

Common lead angles include 75° and 95°/91°, with corresponding entering angles of 15° and -5°/-1° respectively, fulfilling diverse cutting needs.

Additionally, C-type (80°) and S-type (90°) inserts are standard alternative choices.

Contour Groove Turning

Implementing round inserts for shallow grooving to enhance production efficiency represents a key methodology in contour groove turning.

An effective method for shallow grooving or groove widening operations.

Round Insert Performance

Round inserts demonstrate excellent performance in plunge turning, suitable for both radial and axial feed directions, significantly enhancing machining flexibility.

The 90° neutral holder design represents the most common round insert configuration, particularly favored in face turning applications.

Lead Angle & Contour Angle Effects

Large Lead Angle Advantages

Effectively directs cutting forces

Ideal for shoulder turning operations

Note: Potential machining quality impacts constitute a distinctive characteristic of large lead angle designs.

In face turning operations, the large lead angle (or small entering angle) design effectively directs cutting forces toward the chuck, enhancing machining stability.

This configuration is suitable for shoulder turning, expanding processing capabilities.

However, when machining superalloys and hard materials, groove wear may potentially affect machining quality.

Advantages of Small Lead Angle

Concentrated cutting forces adapt well to multiple working conditions

Note: The core advantage of small lead angle design lies in mitigating groove wear concerns

The small lead angle design (i.e., large entering angle) offers the following benefits in practical applications:

Concentrated cutting forces facilitate stable chuck control

Thinner chip thickness during machining helps improve productivity

Reduced groove wear extends tool life

Contour Angle Selection

Proper selection ensures machining strength and tool longevity. The influence on cutting force distribution is a key factor in contour angle selection.

During contour turning, cutting conditions vary with changes in cutting depth, chip thickness, and cutting speed.

To ensure both strength and cost-effectiveness in the cutting process, we must select the maximum tool nose angle suitable for the insert.

When choosing an appropriate contour angle, detailed analysis of the workpiece profile is essential to maintain proper clearance between the material and cutting edge.

At the same time, to ensure the safety and efficiency of the cutting process, a clearance angle of at least 2° should be maintained between the workpiece and the blade.

Cutting Force Influence

The cutting force needs to be balanced. A larger lead angle can reduce axial cutting force, thereby improving the stability of the cutting process.

During the copying turning process, axial and radial cutting forces are important factors to consider. It is necessary to monitor the variations in these cutting forces.

Adopting a strategy with a large lead angle (i.e., a small entering angle) can effectively reduce axial cutting force, thereby improving the stability and safety of the cutting process.

However, when using a small lead angle (i.e., a large entering angle), it was observed that the cutting force was distributed in both axial and radial directions, reducing the tendency for vibration.

Conclusione

Through systematic analysis in this study, the following key conclusions can be drawn: First, tool selection must comprehensively consider factors such as workpiece material, operation type, and cutting parameters. Second, proper selection of lead angle and profile angle is crucial for machining quality. Finally, understanding the distribution patterns of cutting forces helps optimize the machining process. In practical applications, engineers are advised to flexibly apply the tool selection principles and techniques introduced in this study based on specific working conditions to achieve efficient and precise turning operations. With the continuous advancement of machining technology, ongoing learning and mastery of the latest tool application knowledge will be key to maintaining a competitive edge.