Revision Bill's stuff Flashcards
(63 cards)
What are the positive consequences of CNC?
Positive consequences of CNC
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Automatic tool changing on machining centres and lathes
- More productive time in machining cycle
- Fully enclosed machines
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Automatic workpiece loading/unloading
- Allowing unmanned production
- Bar feeder, Gantry robot, Pallet changing
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In cycle measurement of tools and workpieces
- Program offsets to compensate for tool wear
- Mechanical error calibration and compensation
- Ability to control multiple axes
What are the processing drivers in today’s environment
Processing drivers in today’s environment
Operational Cost
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Labour
- Automated workpiece handling
- Fabrications being replaced by “machine from solid”
- More accurate machining to aid downstream assembly
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Asset utilisation
- Raw material stock and WIP – reducing batch sizes
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Shorter product life cycles, quicker product info, shorter lead times
- Flexible machines
- CAD/CAM, machining simulation
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Energy efficiency
- Weight reduction
- Fewer but more complex parts
- Weight reduction
What are the major independent variables in the cutting process?
Major independent variables in the cutting process:
- Tool material and coatings: if not ductile material makes machining hard
- Tool shape, surface finish and sharpness
- Workpiece material and condition
- Cutting speed, feed, and depth of cut
- Cutting fluids
- Characteristics of the machining tool
- Work holding and fixturing
What are the major dependent variables in the cutting process
Major dependent variables in the cutting process:
- Type of chip produced
- Force and energy dissipated during cutting
- Temperature rise in the workpiece, the tool and the chip
- Tool wear and failure
- Surface finish and surface integrity of the workpiece
What are large shear strains associated with?
Large shear strains are associated with low shear angles or low or negative rake angles
What are the basic types of chip produced in metal cutting?
Basic types of chips produced in metal cutting and their micrographs
a) Continuous chip with narrow, straight primary shear zone
b) Secondary shear zone at tool chip interface
c) Continuous chip with build-up edge
d) Segmented or non-homogeneous chip
e) Discontinuous chip

What are the main points about continuous chips?
Continuous chips
- Formed with ductile materials machined at high cutting speeds and high rake angles
- Deformation takes place along a narrow shear zone called the primary shear zone
- Continuous chips may develop a secondary shear zone due to friction at the tool-chip interface

What are the main points about BUE and how to reduce them?
Build up Edge chips
- Consists of layers of material from the workpiece that are deposited on the tool tip
- As it grows, BUE becomes unstable and breaks apart
- BUE can be reduced by:
- Increasing the cutting speeds
- Decrease the depth of cut
- Increase the rake angle
- Use a sharp tool
- Use an effective cutting fluid
- Use cutting tool with low chemical affinity for workpiece
What are the main points about serrated chips?
Serrated chips
- Also called segmented or non-homogeneous chips
- They are semi continuous chips with large zones of low shear strain and small zones of high shear strain
- Chips have a sawtooth-like appearance
What are the main points about discontinuous chips?
Discontinuous chips
- Consists of segments that are attached firmly or loosely to each other
- Form under following conditions:
- Brittle workpiece material
- Materials with hard inclusions and impurities
- Very low or very high cutting speeds
- Large depths of cut
- Low rake angles
- Lack of an effective cutting fluid
- Low stiffness of the machine tool

How do chip breakers work?
Chip breakers:
- Chip breakers decrease the radius of curvature of the chip
- Grooves on the rake face of cutting tools, act as chip breakers
- Most cutting tools now are inserts with built in chip breaker features

What are the different power equations?

What are the different ways of measuring cutting forces?
Measuring cutting forces and power
- Cutting forces can be measured using:
- A force transducer
- A dynamometer or
- A load cell mounted on the cutting tool holder
- Cutting force can be calculated from the power consumption during cutting
- The specific energy in cutting can be used to calculate cutting forces

What are the three main sources of heat when cutting?
Cutting temperature
- In cutting, nearly all of the energy dissipated in plastic deformation is converted into heat that in turn raises the temperature in the cutting zone.
- Three main sources of heat when cutting:
- Plastic deformation by shearing in the primary shear zone (Q1)
- Plastic deformation by shearing and friction on the cutting face (Q2)
- Friction between chip and tool on the tool flank (Q3)

What are the different ways heat is dissipated?
Heat is mostly dissipated by,
- The discarded chip carries away about 60-80% of the total heat
- The workpiece acts as a heat sink drawing away 10%
- Cutting tool draws away 10%
- Any reduction of cutting temp will require substantial reduction in either the cutting speed or feed. However, cutting time and production rate decreases, coolants required.

Why do we want to avoid high cutting temperatures?
Why do we want to avoid high cutting temperatures?
- Affects the wear of the cutting tool. Cutting temperature is the primary factor affecting tool wear
- Can induce thermal damage to machined surface
- Causes dimensional errors in the machined surface
What are the different types of feeds in milling?
There are three types of feeds in milling
- Feed per tooth (fz): basic parameter equivalent to the feed in turning
- Feed per revolution (fr): determines the amount of material cut per one full revolution of the milling cutter
- Feed per minute (fm): calculated taking into account the rotational speed N and number of cutter’s teeth z

What are the different machining processes?
What are the different machining processes?
- Turning
- Boring
- Drilling
- Milling
- Planing
- Shaping
- Broaching
- Sawing
Explain cemented carbides and the effect of cobalt content on properties
Cemented carbides
- Co matrix with WC/TiC grains
- Effect of cobalt content. Hardness is directly related to compressive strength and hence, inversely to wear.

What is the different wear patterns of high speed steel uncoated and Ti N coated cutting tool?

What are the different types of tool wear?
What are the different types of tool wear?
- General wear
- Flank wear
- Crater wear
- Chipped cutting edge
- Flank wear and built up edge

Draw the different types of tool wear

Draw taylors tool life equation

What are the factors that affect tool wear?
Factors that feed into tool wear
- Contact stresses
- Due to cutting tool shape
- Cutting conditions
- Cutting temperature
- Depends on fluids
- Cutting conditions
- Cutting tool shape
- Tool material
- Work material


















