Cutting Tool Materials SME
Introduction to Cutting Tools and Tool Materials
This section introduces cutting tools and tool materials used in precision metalworking, emphasizing the importance of selecting the right tools for efficient and quality machining processes.
Types of Cutting Tools
- Cutting tools are categorized into single-point cutting tools (e.g., lathe tools) and multi-point cutting tools (e.g., milling cutters, drills, reamers).
- Selection criteria for cutting tools include safety, efficiency, quality requirements, cost-effectiveness, and complexity.
- Common errors in tool selection include focusing on cost per tool rather than productivity and tool life maximization.
Factors Influencing Tool Selection
- Machinists need specific information about workpiece characteristics like shape, hardness, tensile strength, abrasiveness, chip formation behavior, workholding setup, and machine capacity.
- Changes in workpiece material properties or machining requirements necessitate adjustments in tool materials or geometry selected.
Characteristics of Cutting Tool Materials
- Ideal cutting tool materials should be harder than the workpiece, retain hardness at high temperatures, resist wear/shock/chemical reactions while being impact-resistant.
- Different tool materials offer trade-offs; newer materials aim to improve performance over traditional ones like high-speed steel.
Evolution of Cutting Tool Materials
- Advancements in cutting tool materials have progressed from high-speed steel to carbide to ceramics and other super hard materials for enhanced metal removal rates.
- High-speed steel was a significant advancement over carbon steel due to its faster cutting speeds and temperature resistance.
Utilization of Carbide Tools
- Carbide tools are widely used today due to their higher cutting speeds compared to high-speed steel and their ability to operate at higher temperatures.
Metal Cutting Tools and Grades
This section discusses the importance of carbide grades in metal cutting applications, highlighting factors to consider when selecting the appropriate grade for specific work materials.
Carbide Grades Selection
- Choosing the correct carbide grade can significantly impact tool life and cutting speed.
- Factors to consider when selecting a carbide grade include workpiece material hardness, workpiece condition, cut intensity, and machine rigidity.
- Carbide grades vary among manufacturers due to the lack of standardized specifications; suppliers recommend suitable grades based on applications.
- Carbide inserts are identified by a seven-character ANSI code representing shape, relief angle, tolerance class, clamping system type, insert size, thickness, and corner radius.
Coatings and Applications
Coated carbide tools offer enhanced performance in terms of tool life and cutting speeds compared to uncoated grades. Various coatings provide wear resistance and improved productivity.
Coated Carbides Advantages
- Coatings enhance wear resistance and hardness of carbide tools while maintaining fracture resistance.
- Common coating materials include titanium carbide, titanium nitride, aluminum oxide, and titanium carbonitride.
- Coating methods such as chemical vapor deposition (CVD) and physical vapor deposition (PVD) contribute to improved tool performance.
- Ceramic tools are harder than carbide but more brittle; they excel in high-speed machining of hard materials like cast iron and super alloys.
Ceramic Cutting Tools
Ceramic cutting tools offer superior hardness and heat resistance compared to carbide tools. Different types of ceramic materials cater to specific machining requirements based on toughness, thermal shock resistance, abrasion resistance, etc.
Types of Ceramic Tools
- Aluminum-based ceramics are ideal for high-speed finishing but lack toughness for rough turning or interrupted cuts.
- Silicon nitride-based ceramics provide greater toughness and thermal shock resistance suitable for high-speed roughing applications on various materials including super alloys.
- Whisker-reinforced ceramics combine silicon carbide whiskers with an aluminum oxide matrix for increased strength and thermal conductivity.
Turning and Boring Tool Materials Overview
This section discusses various tool materials used in turning and boring processes, including super hard materials like cubic boron nitride and polycrystalline diamond.
Super Hard Tool Materials
- Super hard tool materials like cubic boron nitride and polycrystalline diamond are tough enough to handle rough turning and milling applications on carbon steels, stainless steels, and some ductile irons.
Cubic Boron Nitride (CBN) Applications
- CBN, the second hardest material after diamond, provides long tool life when machining very hard, tough ferrous materials such as hardened steels, alloy steels, and hard-facing materials.
Polycrystalline Diamond (PCD) Characteristics
- PCD is over 50 times harder than common carbide and is composed of micro-sized diamond particles in a metallic binder. It is used for non-ferrous applications like cutting brass, glass-reinforced plastics, and hardwoods.
Tool Wear Types and Prevention Strategies
This section delves into the different types of tool wear during cutting operations and strategies to prevent premature tool failure.
Cutting Tool Life Cycle
- All cutting tools have a working life cycle that may involve single use or multiple resharpening. Perishable tools should not be run until they break to avoid scrap impacts, high costs, reduced productivity.
Types of Tool Wear
- Edge wear and flank wear are normal types of tool wear. Abrasive work materials can accelerate wear. Cratering behind the cutting edge is common in machining long-chipping steels.
Tool Failure Causes
- Chipping on a tool edge can lead to unpredictable failures but can be mitigated by using different edge preparations or lead angle changes. Built-up edges occur when workpiece material adheres to the insert's rake face.
Tool Deformation & Thermal Cracking
This section explores issues related to tool deformation due to high temperatures during cutting operations and thermal cracking caused by rapid heat-cool cycles.
Built-Up Edge & Deformation
- Built-up edges result from workpiece material welding onto the cutting edge causing deformation at high temperatures. Detection without a microscope is challenging; resistant grades or coatings are needed.
Thermal Cracking Prevention
- Thermal cracking occurs during rapid heat-cool cycles leading to notch formation on inserts. Proper edge preparation, increased lead angles help reduce notching risks caused by pressure welding of work material.
Heat Treatment of Super Hard Materials
The discussion focuses on the characteristics and applications of super hard materials like cubic boron nitride (CBN) and polycrystalline diamond (PCD) in cutting tools, highlighting their durability compared to carbides and the types of wear they experience.
Characteristics of Super Hard Materials
- Cubic boron nitride (CBN) is used for Ferris applications, while polycrystalline diamond (PCD) is utilized for non-Ferris applications.
- Both CBN and PCD are expensive but can outlast carbides by 10 to 100 times.
- Cutting tools have a finite performance life as they wear out or fail, known as perishable tools.
Types of Cutting Tool Wear
- Various types of cutting tool wear include edge wear, flank wear, cratering, top wear, chipping, edge deformation, and damage caused by material pulling away on a built-up edge.
- Thermal cracking and notching are two additional types of tool wear discussed.
Types of Tool Wear
This section delves into different types of tool wear experienced by cutting tools during operations.
Varieties of Tool Wear
- Tool wear includes thermal cracking and notching.