Lecture 5: Machining Flashcards
Machining is
is the removal of the material or modification of
surfaces without changing the structure of the material.
Machining is done:
- Without changing the structure of the material since it does not heat up.
- By producing chips for removing material using
various tools.
Machining
has 5 characteristics:
b. Allows us to make complex shape
c. Tool doesn’t have information about product geometry
d. Good dimensional accuracy – depends on the knowledge of the tool operator which translates from the tool to
the material
e. Good surface finish
f. Advantage – we use generic tools, not special machines ➔ we don’t have to order machines, dies ➔ no long
initial period
3 Properties
i. cutting
* Rake angle – α
* Clearance angle
ii. shearing
* Shearing angle – Φ
iii. Depth - t0
iv. Important: Rake angle (α) + Tool angle (β) + Relief angle (γ) = 90°
Rake angle =
Angle of the cutting tool relative to the work. It
is mentioned with a
Relief / clearance angle =
Angle between the horizontal
surface and the cutting tool. It is mentioned with y
Tool angle =
the angle of the tip of the tool, which is β
Shearing angle =
The angle made by the shear plane with the direction of tool travel. It is
mentioned with ф
What determines (4) the name of a machining process?
- If the workpiece rotates: turning, cutting off, or hole making.
- If the workpiece slides: scraping.
- If the tool rotates: slab milling or end milling.
- If the tool slides: scraping or broaching
What are the key operating factors in machining processes? 6
Depth: Tool penetration into the workpiece.
Speed: Rotation of the workpiece.
Feed: Rate of material removal along the length of the workpiece.
Tool angle: Adjustment affecting cutting forces.
Type of chips produced.
Tool wear, a significant concern in machining.
How are fluids used in machining? 5 ways
Cooling.
Reducing friction and wear.
Flushing away chips.
Protecting against corrosion.
Types include oils, emulsions, semi-synthetics, and synthetics.
describe each type of fluid:oils, emulsions, semi-synthetics, and synthetics.
Oils: For low temperatures and low working speed, oils can be used. High speed will result in a big risk of burning the oil.
- Emulsions: Used for high speed and high temperatures. This is a mix of water and oil
- Semi-synthetics: Most of the time little oil in water.
How does temperature affect machining?
Most heat is removed by the chip, keeping the workpiece relatively cool.
Elevated temperatures can cause tool wear and affect product geometry.
Synthetics: Chemicals and additives in water
What factors influence cutting forces in machining?
Workpiece material strength.
Rake angle of the tool.
Feed rate.
Depth of cut.
Name 6 important characteristics of cutting tools.
Hot hardness.
Toughness and impact strength.
Thermal shock resistance.
Wear resistance.
Chemical stability and inertness.
ISO classification.
different tools have different cutting speeds. The 7 materials in
order of speed are:
Tool steel, High speed steels, Hard metal, Coated
Carbides, Ceramics, Cubic Boron Nitride, Diamond.
Dependent on the tool
characteristics, the life time of the tool will be changed:
- The constant (C) increases with decreasing depth of cut.
- The constant (C) increases with a decrease in feed.
- The constant (C) is affected by all factors around the machine
What does “turning” refer to in machining?
Turning involves a rotating workpiece and a stationary tool.
The resulting product is rotationally symmetrical.
What are some characteristics of turning?
Product geometry: Rotational symmetrical(straight, conical, curved/grooved).
Materials: All kinds.
Advantage: Use of generic tools.no lead
time
Disadvantage: Low production rate.
How is chip control managed in turning?
Chip breakers are used to prevent large, damaging chips from forming during the continuous cutting process.
What types of products can be made using turning?
Housing bases.
Inner bearing races.
Tube reducers.
Screw threads.
Surface finish
i. Explicit factors:
ii. Noise factors:
– feed rate (f), tool geometry (R)
– build up edge, vibrations
What 2 types of tools are used in turning?
Inserts: Various shapes, with sharper tools producing better finishes.
Guided lathe: Large machines, often computer-controlled.
What are 3 requirements for turning?
Machine size should accommodate product dimensions.
Tool should meet speed and cost requirements.
Product geometry is typically rotational symmetrical.
What is boring in the context of machining?
Boring enlarges holes with minimal force, often using large machines with rotating tables.
What are some common machining operations in turning?
Facing: Working on the front side of a rotating product.
Straight turning: Reducing the diameter of the product.
give 2 reasons why are simulations often used in turning?
To optimize logistics and speed.
To ensure that tools can reach every part of the product.
What distinguishes boring from turning?
Boring enlarges internal diameters, while turning cuts external diameters.
What is drilling?
Drilling involves making screw threads inside a hole.
What 2 factors determine the shape of the hole in drilling?
Tool geometry immediately determines the shape.
Maximum hole depth is related to the tool diameter
What is torque in drilling?
Torque refers to the rotational force between the drill string and the formation.
What is feed force in drilling?
Feed force is the force that pushes the tool against the material.
Tool wear – determined by
the remaining useful length of
the drill after sharpening
when making holes in a thin sheet of metal
the metal has to be stabilized, else it will start spinning
around the drill in the air
Chip angle – varies
over the diameter of the drill ➔ positive (outside diameter) and negative (near the core)
chip angles
What is milling?
Milling involves a rotating tool moving with respect to the workpiece.
What are the parameters involved in milling?
Rotational speed, feed, depth of cut.
What are the two strategies in milling?
Conventional milling (up milling).
Climb milling (down milling).
What is grinding?
Grinding uses a disc with many undefined cutting edges.
What factors affect grinding temperature?
Heat drain, high temperatures, and cooling methods.
What is electrical-discharge machining (EDM)?
EDM involves using electrical discharge to melt or evaporate material under a dielectric fluid.
What is electro-chemical machining (ECM)?
ECM shapes workpieces using electrolysis in a saline electrolyte.
What is electrolyte in ECM?
Electrolyte is a salty saline fluid that conducts electricity.
