Cutting Tools Flashcards
What are the key properties of cutting tools?
- Hardness
- Toughness
- Wear resistance
- Strength to resist bulk deformation
- Adequate thermal properties
- Correct geometry
What is the basic principle of hardness in cutting?
You need a tool material with a higher hardness than your workpiece material
What are the three modes of tool failure?
- Fracture failure
- Temperature failure
- Gradual wear
What is fracture failure?
When the forces on the tool exceed the tool’s strength, leating to brittle fracture.
What is temperature failure in cutting?
high temperatures leading to plastic deformation or premature wear
What is gradual wear in cutting?
Gradual wearing of the cutting tool
What is the most preferred mode of wear?
Gradual - both of the thers are premature, gradual allows for longest lifespan
Where are the two locations that gradual wear occurs on a tool?
Crater - top rake face
Flank - side of tool
What is abrasion?
Mechanical wear due to hard particles (primary cause of flank wear)
What does hot hardness value mean?
Can cutting tool material retain hardness at high temperatures
What is adhesion?
Workplace material adheres/fuses to the cutting tool, causing rupturing
What chemical reaction is a primary cause of wear?
Oxidation
What is the break-in period on a wear curve?
Represents rapid wearing of the tool, usually within first minute or two of use
What is the steady-state wear period in a wear curve?
A region of gradual linear wearing of the tool
What is the failure region on a wear curve?
The tool is so worn out that it can no longer cut efficiently.
What is the relationship between cutting speed and tool wear?
As cutting speed increases, tool wear will occur much faster, and tool life decreases
How do we know when a machine is failing?
- Machine makes strange noise
- An increase in power
- Change in the quality of chips
- Conducting a “fingernail test” to see if the cutting tool is usable
Generally, what happens to hardness as temperature increases?
Rapidly decreases
What types of materials are significantly harder at elevated temperatures?
Cemented carbides + ceramics
What material is used when high cutting speeds are NOT a priority?
plain carbon steel
What are common uses of plain carbon steel in manufacturing?
- Taps, dies, chisels, and cheap drills
- Custom tools
- Not used much in modern manufacturing, as it loses hardness around 300-650F
What are characteristics of tools such as taps, chisels, and dies?
- Go through large deformations when used
- Used at low speeds, heat generation not a concern
- Toughness of cutting tool material is main priority
What are the two basic types of high speed steel (HSS) used in cutting?
Tungsten (T grades,) and Molybdenum (M grades)
What are the benefits of using high speed steel?
- Capable of maintaining hardness at elevated temps. better than high carbon and low alloy steels
- Suited to applications involving complex tool shapes (drills, taps, milling, broaches.)
What are some other alloying ingredients for high speed steel?
Chromium + Vanadium, carbon, and cobalt
What are cemented carbides?
Class of hard tool material based on tungsten carbide (WC) using power metallurgy techniques w/ cobalt as the binder
What are the two basic types of cemented carbides?
Non-steel cutting grades, and steel cutting grades
What are some general properties of cemented carbides?
- High compressive strength + hardness + thermal conductivity + elastic modulus
- Good hot hardness + wear resistance
- Low to moderate tensile strength
- Toughness lower than HSS
What are cermets?
Combinations of TiC, TiN, and titanium carbonitride (TiCN) w/nickel or molybdenum as binders
What are the benefits of using cermets?
Higher speeds and lower feeds than steel-cutting cemented carbide grades, and better finish achieved.
What are some applications of cermets?
High speed finishing/semifinishing of steels, stainless steels, and cast irons
What are coated carbides?
Cemented carbide insert coated w/ 1 or more layers of TiC, TiN, and/or Al2O3 (or other hard metals)
How are the coating of coated carbides applied?
chemical vapor deposition or physical vapor deposition
What are some key applications where coated carbides are used?
cast irons and steels in turning and milling operations, best applied at high speeds where dynamic force + thermal shock are minimal
Why are coatings added to tool materials?
increase resistance to wear
What does a cutting tool wear curve represent?
The tool flank wear (FW) vs. cutting time (min)
What graph is used to monitor if a tool needs repair?
A cutting force vs. time graph
What is the shape of a cutting speed vs. tool life plot?
Natural log - log.
What is the Taylor Tool Life Equation?
Relates cutting speed, tool life, slope of graph, and C (intercept on the speed axis at 1minute tool life)
What are key applications of ceramics in cutting?
high speed turning of cast iron and steel, grinding.
Why is it not reccomeded to use ceramics for rough milling/heavy interrupted cuts?
low toughness
when are diamonds used in cutting?
high speed machining of nonferrous metals and abrasive nonmetals (figerglass, polymer, graphite, and wood.) NOT for steel cutting
