Manufacturing Engineering

what is metal casting

pouring molten metal into mould and allowing it to solidify

what effects the cool zone

mould temperature, size of cool zone

what factors affect the solidification of metals

the type of metal, the thermal properties of the metal and the mould, the geometric relationship between volume and the surface area of the casting, and the shape of the mould

what is supercooling

the temperature just before solidifying that goes lower then increases once again

what are dentrites

tree like structures which are formed when metals cool due to strengths in certain directions of the liquid

What happens to strength, ductility, microporosity, and tendency to crack when grain size decreases

Strength increases, ductility decreases, microporosity decreases, tendency to crack decreases. These are due to smaller spacing between the grains

what is chvorinov’s rule

how would you solve a chvorinov question

assume unit volume of 1 to find side lengths and in turn surface area. keep in mine that sometimes a surface might not be counted due to contact with the liquid aat another location

what is shrinkage

dimensional changes and sometimes warping and cracking.

1. liquid shrinkage (contraction of molten metal)

2. solidification shrinkage (contraction of metal during phase change)

   1. solid shrinkage (contraction of solid due to temperature drops)

what is the linear solid contaction equation

ΔL = Lα ΔT where α is the coefficient of linear expansion

what is a riser used for in metal casting

provides extra material to counteract the effects of shrinking, designed so that it is the last area that solidifies

how do we find the time it takes to fill a certain volume

use bernoulli’s to find the velocity of the liquid as height would be given then use mass flow rate equation to solve for time

what is aspiration in metals

unintentional entry of air into molten metal due to low pressure from high-velocity metal flow or low-pressure zones

how do you solve aspiration problems

use bernoullis to assume that pressures are equal then find velocities assuming the one with a large cross sectional area is 0

what is fluidity

the capability of molten metal to fill mould cavities

what characteristics reduce fluidity

high viscosity, high surface tension, lots of inclusions, pattern (high freezing range), low superheat, slow rate of pouring, heat transfer rate

what types of mould-related defects are there and what do they look like

what are hot tears

crack like—caused by uneven cooling and inner tensile stresses

how do we prevent hot tears from happening

use chills to make local hot spots colder, alter cast design, refine grains, change casting temperature

what is porosity and how do we prevent it

empty space or “holes,” supply adequate liquid, steep temperature gradients, subject it to hot isostatic pressing

what are the different methods for inspecting castings

liquid penetrant, radiography, simulation

how does liquid penetrant work

fluids applied to the surface of the part and allowed to penetrate, then found using developing agents

how does radiography work

x-ray inspection to determine cracks and porosity, typically projected onto a paper or film

what are the different types of castings and what are their advantages

sand (almost any metal, no limit to size, but coarse finish), investment (good surface finish and intricate shapes) die (good accuracy and production rate

what types of sand moulds are there

green sand: mixture of sand, clay, water. Cold-box mould: various organic and inorganic binders. No-bake mould: synthetic liquid resin mixed with sand

what are the major features in sand moulds

what are patterns

moulds the sand into the shape of the casting and can be made of various materials

what are cores

used for castings with internal cavities and passages such as those found in an automitve engine block or valve body. essentially makes holes

what are the steps of investment casting

what is permanent mould casting

the moulds are stuck together and heated (made of metal) to facilitate metal flow and avoid sticking

what is the difference between cold and hot chamber mould casting

in cold chamber liquid is directly added while in hot chamber processes there is a pot and furnance that directly heats liquid and is then inserted

why should corners be avoided in design

uniform cross section is better and prevents certain deformations

why should wall sections be uniform

to avoide or minimize shrinkage cavities

also helped by having rounded corners rather than sharp

how do ribs and fillets improve bosses

they add structural support by connecting the walls to the base

why do we have draft angles in casting

to prevent damage when removing

what is the parting line

which is more expensive type of casting

in short term scenarios, sand is cheaper due to high equipment cost of die casting but eventually there is a break-even point

what is powder metallurgy

components are made from metal powders

what advantages do metal casting and powder metallurgy have

metal casting: good for large simple shapes, not very precise

powder metallurgy: reduced waste, good microstructure control, ability to have specific porosity

what are the powder metallurgy steps

what is sintering

heat treatment that turns the powder into one sample T_sint=0.8TM

what is metal forming

process of re-distributing raw metal into a different shape under applied forces, usually bars, billets, ingots, or sheets

what is steady vs non-steady state

if “two pictures” were taken between point 1 and 2, if there is any difference then that is a non-steady state

what is open die forging

part is compressed between two flat surfaces or plates, such as blacksmith anvil and hammer

what is closed die forging

like open die but defined by a shape from a punch and die

what is flash

leftover metal pushed through, important as it forces material to fill the cavity but has to be trimmed away later

what is rolling

metal elongates plastically as it passes through rolls, exit speed is faster than entry speed, needs frictions to operate

what are backing rolls used for

large diameter rolls used to reduce rolling pressure and reduce deflection

what is extrusion

ram pushing into material with die to create shape

what is deep drawing

plate (called blank) held in place while punch (similar to ram) makes shape

what are the regions of the stress-strain curve

what is the equation for true strain

ln[L₁/L₀]

how do you convert from enginerring strain to true strain

e = ln(1+ε)

what is the bulge test

pressure to one side to clamped circular sheet to make dome and achieves true strains twice that of tensile, good measure of formability

what is the compression test

similar to tension but goes the other way, provides stress-strain data to be used for rolling, forging, and extrusion

what is flow stress

stress at which further plastic deformation occurs

what is the difference between forward and reverse extrusion

why do we need a die clearance angle

to reduce friction and damage to the extruded figure

what is a billet used for

to create hollow spaces during an extrusion

what is the equation for extrusion ratio

what is the reduction equation

what is the punch pressure equation

where Y bar is the average yield/flow stress and r is the reduction

what is johnson’s equation

a and b should be given within the question

what is piping

extrusion defect where metal forms oxide at the surface of the billet, can be avoided using small diameter punch to remove as skull

what is fir tree cracking

defect formed by fast extrusion rates and low melting point materials which results in this form of cracking

how to rear cavities form in extrusions

middle part of material is moving faster than the edges due to the die, non-uniform velocity makes cavity become wider and deeper as the extrusion proceeds, fixed by using a concave punch

which way does metal flow during a deep draw

radially towards the center of the material

why cant we do a drawing process at once

necking occurs at the walls thus multiple steps must be introduced to minimize this

what is the draw ratio equation

what is the draw ratio equal to

what is a common defect during deep drawing

the formation of ears, usually four, at the rim of the part, cause by material anisotropy, wrinkling, and tearing

how do we prevent wrinkling

use a blank holder with a lot of force, reduce lubrication

how does tearing occur

local tensile stress approaches UTS of metal, small punch corner radius, small die corner radius. reduced by increasing lubrication. fundamental limit is drawability

what is the drawability equation of an object

what is the reduction equation based on drawability

which equation would you use to solve for the number of draws needed to not exceed drawability

what is an ideal welded joint

indistinguishable from the parent material, joint similar property to parent material

what is arc welding

power is supplied to make arc between electrode and workpiece, through electrical breakdown of gas, electrode can be consumable or not, either AC or DC power supply, inert gas or flux needed

what are the different types of metal arc welding

shielded metal arc welding -

flux-cored arc welding -

submerged arc welding -

gas tungsten arc welding -

gas-metal arc welding -

what is shielded metal arc welding

manual, hand-held, consumable electrode, flux coating on electrode, all welding positions

what is flux-cored arc welding

automatic process, hand-held, filler wire fed continuously, flux granules embedded in wire, all positions

what is submerged arc welding

mechanised, filler wire fed continuously, flux granules, multiple at once, one position

what are the advantages and disadvantages of flux-base processes

good for out-of-position welding, wide range of compositions.

but, risk of flux inclusions and flux attracts moisture which contributes to cracking

what is gas tungsten arc welding

inert gas, tungsten arc torch, needs filler metal added seperately, distorions caused by heat

what are the advantages and disadvantages of gas-tungsten arc welding

control over heat source and metal, readily automated no flux, high quality

but slow and high skill needed

what is gas-metal arc welding

automatic, hand-held, inert gas shield, all positions

what are the advantages and disadvantages of gas-metal arc welding

self correcting arc length, automated, good quality

prone to spatter

what does the gas-metal arc welding process look like?S

what is electron beam welding

focused beam of electrons, high vacuum to avoid scatter, no need for filler metal but can be added, deep penetration

what are the advantages and disadvantages of electron beam welding

deep and narrow welds, less heat distortion

needs to be inside vacuum, hard to weld dissimilar materials

what is laser welding

high power density, narrow welds, no need for vacuum, penetration is less than for electron welding

what is friction welding

one piece rotates, the other is stationary, no melting occurs so solid state, avoids degradatino of material

what is power density

welding power per unit area (W/u_²)`

which of the welding types has the highest power density

name the different regions of electric arc as heat source

what are the physical aspects of gas tungsten arc welding

how do you increase the percentage of arc energy transferred to piece

increase conducitivity of piece, increase travel speed

how do you prevent oxides in magnesium and aluminium alloys from forming in welding

use AC current to avoid tungsten degradation and use rounded tip

how does droplet detachment look like in gas metal arc welding

how does spatter occur

short circuits leading to violent vaporisation, which then lead to cracks through rapid cooling