Machining Technologies Flashcards
What is the definition of Manufacturing?
The full cycle of activities from research and development, through design, production, logistics and services, to end life management, within an economic and social context
Short: The transformation of raw materials into finished products
What are four basic manufacturing processes?
Primary shaping
Secondary shaping
Joining&assembly
Surface treating
What are some example of primary shaping?
Casting
Molding
PM methods
What are some examples of secondary shaping?
Forming
Machining
What are some examples for joining & assembly?
Welding
Adhesives
Fasteners
What are some examples for surface treating?
Heat treatment
Surface treatment
What are some examples of conventional machining?
TURNING and related operations
DRILLING and related operations
MILLING
Grinding and other abrasive processes
What are some examples of non-conventional machining processes?
Electrochemical machining
Thermal energy processes
Chemical machining
What are the advantages and disadvantages for machining?
\+ Variety of materials used \+ Variety of parts can be made \+ Specific dimension easier to cut - Wasteful of material - Time consuming
What are the inputs of machining?
Machine tools
Cutting tools
Workpiece
What are the outputs of machining?
Productivity/economy Product accuracy Surface texture Surface integrity Environmental impacts
What is turning?
Single point cutting tool removes materials from a rotating workpiece form a cylindrical shape
What is drilling?
Used to create a round hole using rotating drill bit, usually with two cutting edges
What is milling?
Rotating multiple-cutting-edge tool is moved across work to cut a plane or straight surface
What are the following symbols used for: v φ α t0 tc
v=cutting speed φ=Shear angle α=Rake angle t0=undeformed chip thickness tc=chip thickness
What is the equation for undeformed chips?
t0=Ls*sin(φ)
What is the equation for chip thickness?
tc=Ls*cos(φ-a)
What is the shear angle equation?
tanφ=(rcos(a))/(1-rsin(a))
What is the thickness ratio?
r=t0/tc
What is the equation for shear strain?
𝛾=AB/OC=AO/OC+OB/OC
𝛾= cot(φ)+tan(φ-a)
What is the difference between actual chip formation and undeformed chip?
Firstly, Shear deformation does not occur along a plane but in the shear zone
Secondly, there is a second shear zone after the chip has been formed.
Thirdly, the formation of the chip is depend on the material and cutting conditions
What are the four actual chip formations?
Continuous
Built-up edges
Serrated or segmented
Discontinuous
What is continuous chip formation?
Usually formed with ductile materials that are machined at high cutting speeds, small feeds and depths
+Good surface finish
-Can become tangled around the tool holder
What is continuous chips with built-up edges?
A built-up edge (BUE) consists of layers of material from a ductile workpiece that gradually are deposited on the tool tip.
- Major factor to adversely affect surface finish
+ A thin stable BUE usually is regarded as desirable because it reduces tool wear by protecting its rake face
What are the serrated chips?
- Semi-continuous chips
- Normally occurs in metals with low thermal conductivity and strength that decreases sharply with temperature (titanium)
What is brittle chipping formations?
When relatively brittle materials are machined at low cutting speeds, the chips often form into separated segments
- Generate irregular surfaces texture on the machine surface
- Forces vary which means machine is not stiff which causes vibration and “chatter”
What are the Power P and Material Removal Rate (MRR)?
Power = shear force*Volume MRR = V*t0*w
What is the specific cutting energy equation?
U= P/MRR=FcV/Vt0w=Tct0*w0
What is cutting temperature?
Majority of cutting energy is converted to heat (98%)
Which causes temperatures to be very high at the tool-chip
What percentage of heat dissipation Q is on each of the tools?
Qchip=80%
Qtool=10%
Qwp=10%
What are some of the factors that affect tool temperature?
1) Cutting conditions
2) Thermal conductivity of the tool and workpiece
3) Cutting fluids
What are some of THE CONDITION that effect the tools wear and failure?
A) High localised stresses at the tip
B) High temperatures, especially along rake face
C) Sliding of the chip along the rake face
D) Sliding of the tool along the newly cut workpiece surface
What affects the RATE at which tools wear?
Material Tool geometry Process parameters Cutting fluids Characteristics of machine
What is the cutting energy percentage shear zone, chip sliding on tool and tool sliding?
shear zone - 75%
Chip sliding on tool 20%
Tool sliding on work 5%
What are some requirements for cutting tools materials?
High strength and toughness
High hardness and hot-hardness
High wear resistance
Others: Thermal conductiveity low cost, low coefficient of friction, chemically stable
What are high-speed steels used for? HSS
- Excellent toughness and cutting ability
- Older and less rigid machine tools
- Complex and single-piece tools (e.g drills and reamers and cutters)
- Workpiece involving interrupted cuts due to its excellent toughness
What are carbide tools?
- High hardness over wide range of temperatures
- High elastic modulus
- High thermal conductivity
- Low thermal expansion
- Versatile and cost-effective
- Higher speeds than HSS
- Two major categories tungsten carbide and titanium carbide
What is Tungsten Carbide used for?
For cutting steels, cast irons and abrasive nonferrous materials and largely have replaced HSS tools
What is Titanium Carbide used for?
Suitable for machining hard materials an for cutting at speeds higher than those appropriate for tungsten carbide
What are carbide inserts?
To compensate for the brittle and expensive nature of carbide a small insert for a larger tipped tool is added
What are some of the properties fo coated tools?
Lower friction
Higher adhesion
Higher resistance to wear and cracking
Higher hot hardness and impact resistance
What are some of the characteristics of ceramic cutting tools?
- Very high abrasion resistance and hot hardness
- Chemically they are the most stable
- Lack toughness and use may result in premature failure
- Effective for high-speed and uninterrupted cutting operations
What are some of the characteristics for Cubic Boron Nitride?
- 2nd hardest material next to diamond
- Does react with nickel or iron
- Used for finishing very hard steel
- EXPENSIVE
What are some fo the characteristics of diamond?
- Hardest material is known to man, 3-4 times more than carbide
- Brittle
- Very expensive
What are the main functions of cutting fluids?
Main:
Coolant
Lubricant
Other:
Reduce wear, reduce cutting power, better finish, prevents corrosion, reduces thermal distortion
What are the Three Main Types of cutting fluids?
1) Oils
2) Emulsions
3) Synthetics
What are the methods of cutting fluid delivery methods?
Flood cooling
Mist cooling technique
High-pressure cooling
Minimum quantity lubrication
