Grinding Fluid Selection Guide for Cemented Carbide Tools

Since the beginning of the 21st century, the global manufacturing sector has intensified its focus on precision, efficiency, and automation. This evolution demands cutting tools that offer superior performance: higher strength and toughness, extended service life, and enhanced reliability under extreme conditions including high temperatures, wear, oxidation, and impact. Consequently, the development of advanced tool designs, manufacturing processes, and specialized metalworking fluids has become critical to meeting these modern industrial challenges.

1. Cemented Carbide Tools: Characteristics and Grinding Challenges 

Cemented carbide, known for its exceptional hardness and wear resistance, presents significant challenges during the grinding process, especially for tools with substantial grinding allowances. The key material properties that complicate grinding are:

• High Hardness: Requires the application of considerable grinding pressure.

• Low Thermal Conductivity: Makes the material susceptible to heat buildup, necessitating effective heat management to prevent thermal damage.

• High Brittleness: Increases the risk of micro-cracks and chipping during machining.

Therefore, successful grinding of cemented carbide tools hinges on a combination of factors: a self-sharpening grinding wheel, optimized grinding parameters, and a grinding fluid with superior cooling capabilities.

A critical concern is controlling the grinding temperature. Exceeding approximately 600°C can lead to surface oxidation, discoloration, and various forms of grinding burn. In severe cases, this thermal stress can induce micro-cracks in the carbide substrate. These cracks are often preceded by visible oxide tints—such as blue, purple, brown, or yellow—on the ground surface.

2. Strategic Selection of Grinding Fluids and Oils for Carbide Tools

For tool manufacturers, the selection of the appropriate grinding fluid is as crucial as the choice of equipment and abrasives. The right fluid directly impacts tool quality, surface integrity, and process efficiency.

(1) Key Criteria for Selecting a Grinding Fluid

Given the high hardness and brittleness of cemented carbide, and the extreme temperatures (reaching up to 1000°C) generated during grinding, the selected fluid must perform multiple functions. It's important to note that only about 15% of the generated heat is carried away by the chips and 8% by the workpiece, placing a heavy cooling burden on the fluid.

An ideal grinding fluid for cemented carbide tool manufacturing should possess the following characteristics:

a. Enhanced Lubricity and Extreme Pressure (EP) Performance: Reduces friction at the grinding interface, minimizing heat generation and wheel wear.

b. Superior Cooling Capacity: Efficiently dissipates heat from the grinding zone to prevent thermal damage to the tool.

c. Effective Cleaning and Anti-foaming Properties: Ensures the fluid can flush away abrasive debris and worn grit without foaming, even under high-flow, high-speed conditions, maintaining consistent cooling and cleaning.

d. Cobalt Leaching Inhibition: Specifically formulated to prevent the corrosive leaching of cobalt from the carbide binder, which can weaken the tool structure.

(2) Key Criteria for Selecting a Grinding Oil

In contrast to water-based fluids, the primary function of a grinding oil is not cooling but lubrication. By significantly reducing friction, it minimizes heat generation at its source.

The requirements for a high-performance grinding oil in carbide tool manufacturing include:

• High-Flash-Point, Low-Evaporation Base Oils: The use of hydrocracked or synthetic base oils is preferred. These offer lower volatility, reducing oil mist and consumption, and contributing to a cleaner, safer workshop environment, even at optimal viscosities.

• Optimal Viscosity: A carefully selected viscosity ensures excellent flushing capability to remove swarf while allowing for rapid settling of fine particles in the system.

• Advanced, Non-Corrosive Additive Packages: The formulation should avoid aggressive sulfur and chlorine-based EP additives that could corrode non-ferrous components of the machine tool. Modern additive technology provides the necessary lubricity without this risk.