Chapter 6 part 2 Final Exam Flashcards
CWhat are the three possible failures associated with tool life
fracture failure
temperature failure
gradual wear
What is fracture failure
This mode of failure occurs when the cutting FORCE at the tool point becomes excessive, causing it to fail suddenly due to BRITTLE FRACTURE.
What is temperature failure
This failure occurs when the cutting TEMPERATURE is too HIGH for the tool material, causing the material at the TOOL POINT to SOFTEN, which leads to plastic deformation and LOSS of the SHARP EDGE.
What is gradual failure
Gradual wearing of the cutting edge causes LOSS of TOOL SHAPE, reduction in cutting efficiency, and acceleration of wearing as the tool becomes heavily worn, and finally tool failure in a manner similar to a temperature failure.
Which form of tool failure is preferred
gradual failure because it leads to the longest possible lifespan of the tool
What is a crater wear
cavity in the rake face of the tool that forms and grows from the chip sliding against the surface. High temperatures and stresses cause this
What is flank wear
occurs on flank and results from rubbing between the work surface and the flank face adjacent to cutting edge. Characterized by plastic deformation
What is tool life
length of time a cutting tool can be used
Describe the visual graph and relation between tool flank wear (FW) and time of cutting
The initial stage of cutting is the break-in period, where rapid initial wear takes place.
Then, it is followed by a uniform wear rate in what is known as the steady-state wear region.
Until the Failure region, where an accelerating wear rate results in a final failure
What are the effects of cutting speed on tool life
higher cutting speeds shorten tool life
What are the three important properties that a tool requires? and which mode of tool failure does each correspond to
Toughness - Fracture Failure
Hot Hardness - Temperature failure
Wear resistance - gradual wear
What is toughness
To avoid fracture failure, toughness is the capacity of a material to absorb energy without failing
What is hot hardness
To avoid temperature failure, hot hardness is the ability of a material to retain hardness at high temperatures
What is wear resistance
To avoid gradual wear, wear resistance is directly tied to hardness, surface finish of tool, and application of cutting fluids
What are premature failures
Temperature and fracture failures because the tool was not used for its entire possible lifespan
What is a cutting fluid
Any liquid or gas applied directly to the machining operation to improve cutting performance
What main problems do cutting fluids address
Heat generation at shear and friction zones
and
Friction at tool-chip and tool-work interfaces
What other benefits do cutting fluids bring
- Wash away chips from grinding and milling
- Reduce the temperature of work part for easier handling
- Improve dimensional stability of work part
What are the cutting fluid classifications and describe the specifications of each classification
- Coolants - designed to reduce the effects of heat in machining
- Lubricants - designed to reduce tool-chip and tool-work friction
What is the base of coolants
Water
Where are coolants most effective and generally best used
At high cutting speeds where heat generation and high temperatures are problems. most effective on TOOL MATERIALS susceptible to TEMPERATURE FAILURES
What is the base of lubricants
Oil
Where are lubricants most effective
At lower cutting speeds. also reduces temperature but not as greatly
What is dry machining
no cutting fluid is used
