notes on moulding

uni/mmme/1029_materials_and_manufacturing/manufacturing.md

@@ -0,0 +1,373 @@
+---
+author: Alvie Rahman
+date: \today
+title: MMME1029 // Manufacturing
+tags: [ uni, nottingham, mechanical, engineering, mmme1029, manufacturing ]
+---
+
+# Cost Modelling
+
+Key issues in selection:
+
+- Component function, including materials and shape, form, and assembly
+- Manufacturing process may greatly affect material properties, such as yield strength
+- Similarly, the material will likely decide the manufacturing process
+- Cost of a material and manufacture
+
+The main requirement for a product to be viable is 
+
+$$cost < price < value$$
+
+Cost modelling equation:
+
+$$C = \frac{mC_m}{1-f} + \frac{C_t}{n} + \frac{1}{\dot n} \left[ \dot C_{oh} + \frac{C_c}{L\cdot t_{wo}} \right]$$
+
+# Shaping Processes
+
+## Casting
+
+- Can be used for large size range
+- Molten metal poured into solid mould to give shape
+- Heat removed leads to shrinkage
+- We need to be able to melt the metal and handlethe molten metal
+- Mould degradation by the liquid metal needs to be considered
+- Heat flowing from the molten metal into the mould causes a drop in temperature so solidification
+  starts from outside inwards
+- Rate of solidification depends on rate of heat flow into mould
+
+### Types of Mould
+
+- Expendable mould (sand, plaster, ceramic)
+
+  - The mould is used once, being broken to release the casting
+  - Can have multiple use or single use pattern (investment and lost foam casting
+
+- Multiple mold casting
+
+  - Die casting (pressure die casting)
+  - Permanent mould casting (gravity die casting)
+
+#### Sand Casting
+
+![](./images/vimscrot-2022-02-21T16:36:48,640821636+00:00.png)
+
+- Wide range of metals can be cast
+- Almost no limit to size and shape of casting
+- Poorer tolerances than other proces, rough surface texture
+- Slow
+- Economic for a low number of castings
+- Applications include cylinder blocks and large pipe fittings
+
+#### Investment Casting
+
+- A high cost process
+- Used mostly for complex shapes, such as sculptures, jewellery, and gas turbine blades
+- Can be used for a wide range of metals
+- Very high precision and surface finish
+
+1. Make a master die
+2. Make wax pattern by casting wax into master die
+3. Coat wax pattern with investment material 
+
+   1. First with a slurry of water and fine ceramic to capture fine details
+   2. Then coat with stucco, which is a thicker coating for strength
+
+4. Heat mould to melt wax out, bake and preheat mould
+5. Pour in molten metal
+6. Wait for solidification, break mould when done
+
+#### Permanent Mould Casting (Gravity Die Casting)
+
+- Mould cavity is machined into mating metal blocks
+- Molten material poured into mould
+- Mould material is cast iron, steel, bronze, graphite
+- Mould must disassebmble without locking
+- Mould is expensive but can be reused (typically around 25k times)
+- Mould life is reduce by casting high meling point metals
+- Good surface finish and dimensional accuracy
+- Cooling is rapid therefore high production rates
+- Example use is a piston
+
+#### Die Casting (High Pressure Die Casting)
+
+- Dies must be able to withstand high pressure
+- 0.1 mm slits at parting lines provide escape for air
+- Dies are made of expensive tool steels
+- High volume production is necessary to justify costs
+- Generally limited to low viscosity, low melting point, non ferrous metals like Al, Zn, Mg, and Pb
+- Good surface finish
+- Precision castings with thickness between 0.75 mm and 12 mm
+
+### Design of Castings
+
+- Distribute castings evently around parting planes
+- Need to be able to get patterns out of moulds and casting out of moulds where applicable
+- No re-entrants (complex multi-part moulds may be able to avoid this restriction)
+- Draft angle between surfaces
+
+    - Need to be able to get solid patternout of mould in sand casting
+    - Need to be able to get solid casting out of mould in die casting
+
+- Allow for shrinkage --- dimensions of casting mould/pattern needs to be made so that part is
+  desired size after shrinkage
+- Avoid rapid change in section or direction:
+
+  ![](./images/vimscrot-2022-02-21T17:12:20,117329889+00:00.png)
+
+### Solifidification of Metals
+
+- How well the liquid fills detail depends on viscosity of liquid
+- During freezing, latent heat of fusion is removed
+- During freezing, material is a solid/liquid mixture
+- There is a significant (~7 %v) shrinkage during solidification
+- Heat flows down steepest thermal gradient so usually there is an actively cooled section
+- Thin sections freeze faster than thick sections
+
+### Castability
+
+- Low melting point
+- Low viscosity and surface tension
+- Low solidification contraction
+- Low thermal capacity and high conductibity
+- Low solubility
+- Not contaminated by air
+
+## Deformation
+
+When a metal is plastically deformed, dislocations move and multiply.
+
+Annealed aluminium may have a dislocatio density of around 200 m per mm$^3$.
+This is a very low amount.
+A heavily cold worked piece may have a density of up to 270 km per mm$^3$.
+
+As dislocation density increases, the dislocations impede the motion of other dislocations.
+This means that to continue plastically deforming, more stress has to be applied.
+
+The stress goes down towards the end of the graph due to the material necking, meaning the
+material gets thinner.
+This means that the engineering stress is lower as the true area is lower.
+The true stress, however, is going up:
+
+![](./images/vimscrot-2022-02-28T20:01:59,453437307+00:00.png)
+
+### Effect of Prior Deformation (*Work Hardening*)
+
+![](./images/vimscrot-2022-02-28T20:02:42,050513187+00:00.png)
+
+See
+[here](materials.html#work-hardening-and-cold-working)
+for more information
+
+### Effect of Temperature (Diffusion)
+
+In an alloy, atoms tend to migrate from regions of high concentration to low concentration.
+This is diffusion.
+
+More information on diffusion [here](materials.html#diffusion).
+
+### Annealing
+
+Annealing is a process by which a component is heated to reduce work hardening.
+
+![](./images/vimscrot-2022-02-28T20:32:47,838820599+00:00.png)
+
+These are diffusional processes and only occur at higher temperatures.
+
+When the temperature of a material, $T > 0.55T_m$, it is said to be hot.
+A material being worked on hot has its deformations eliminated as fast as they are created.
+
+A material is said to be cold when $T < 0.35T_m$.
+
+# Powder Processes
+
+Poweders can plowflow if forces between them are low
+
+With small amounts of binder, they can form "*plastic*" materials like clay.
+
+A *slurry* can be formed with a liquid carrier (where there is enough liquid to separate particles).
+In a slurry, often you want to reduce liquid content but avoid the particles touching or attracting
+each other.
+Adding a *deflocculant*[^d_deflocculant] results in the formation of a stable *slip*.
+
+Making the powders is often quite expensive when you have a controlled size distribution.
+
+## Clay and Ceramics
+
+Clay is an abundant raw material but it needs to be milled and screen for a controlled size
+distribution.
+When mixed with water it forms a *plastic* material.
+
+Structural clay products include bricks, tiles, and pipes.
+Other proucts include whitewares such as porcelain, pottery, and tableware.
+
+Ways to form the clay include pressing, isostatic pressing, extrusion, and machining.
+
+Engineering ceramics (e.g. silicon carbide, alumina) are shaped with small amounts of binder ---
+commonly pressed or isostatically pressed.
+
+## Slip Casting
+
+1. Pour slip into a mould (e.g. plaster of Paris)
+2. The mould is extremely water absorbing. This results in the remaining part developing some
+   structural integrity.
+3. Remove the mould and place in the oven to reduce water content.
+4. Fire to harden
+5. Add glaze and fire again.
+
+Drying leads to shrinkage and potential cracking.
+It also gives strength and allows for handling and maybe machining.
+
+![](./images/vimscrot-2022-02-28T22:03:43,392791602+00:00.png)
+
+## Sintering of Metals and Ceramics
+
+![](./images/vimscrot-2022-02-28T22:17:23,587537954+00:00.png)
+
+Atoms diffuse to points of contact, creating bridges and reducing the pore size.
+Diffusion is driven by a desire to reduce the surface area as surfaces are regions of high energy.
+
+## Powdering Metallurgy
+
+- Competitive with processes like casting, forging, machining
+- Used when the melting point is too high, a chemical reaction occurs at melting point, the part is
+  too hard to machine, or a very large quantity (on the order of 100 000) of the part is needed
+- Nearly 70% of parts produced is by powder metallurgy
+- Good dimensional accuracy
+- Controlloable porosity
+- Size range from balls in ball point pens to parts weighing 50 kg
+
+Basic steps of powder metallurgy:
+
+1. Powder production (commonly atomization) --- this is often a costly process and you must minimize
+   oxidation of the metal
+2. Blending/mixing --- add binders to keep the particles together and lubricants to reduce damage to
+   dies and aid consolidation
+3. Powder consolidation
+
+   - Shaping in a die
+   - 100-900 MPa of pressure applied
+   - Fast process as no heat needs to be removed
+
+4. Sintering at $0.7T_m$ to $0.9T_m$
+
+Shaping equipment has no requirement to be able to withstand high temperatures and the sintering
+equipment does not have the need for complex designs.
+This separates problems, making them easier to design.
+
+The pressing equipment is costly but the time spent pressing is quite small, allowing for greater
+throughput.
+Additionally, the furnace can operate continuously and is simple and cost effective.
+
+![](./images/vimscrot-2022-02-28T22:50:45,735174146+00:00.png)
+
+### Green Density
+
+The *green density* is a fraction of the true density.
+A low green density will result in high shrinkage on sintering.
+
+## Moulding
+
+Moulding is a shaping process used for viscous materials (typically polymers and glasses).
+Here the material can hold a shape unsupported but not for very long or under even small stresses.
+
+In order to mould a material we must raise the temperature above the glass transition temperature,
+$T_g$.
+At this temperature, the C-C bond in the chapolymer chain are able to easily rotate around each
+other.
+
+Large side chains or molecules on the main chain make it harder to rotate these bonds, making
+$T_g$ higher.
+Polar groups (e.g. chloride, cynaide, and hydroxide) have also hinder bond rotation.
+
+More information about polymers
+[here](https://notes.alv.cx/notes/uni/mmme/1029_materials_and_manufacturing/materials.html#polymers-1).
+
+## Extrusion
+
+Extrusion produced parts of constant cross section, like pipes and rods.
+The process is used primarily with thermoplastics and 60% of polymers are prepared by extrusion.
+
+![](./images/vimscrot-2022-03-01T18:28:42,810593415+00:00.png)
+
+## Blow Moulding
+
+Blow moulding is a rapid process with low labour costs.
+It produces hollow components that do not require a constant thickness, such as
+bottles, petrol tanks, and drums.
+Common materials to blow mould are HDPE, LDPE, PP, PET, and PVC.
+
+There are three common types of blow moulding:
+
+- Extrusion blow moulding
+- Injetion blow moulding
+- Stretch-blow processes
+
+However, they involve the following stages:
+
+1. A tubular preform, called a *parison* (a word I haven't been able to remember since GCSE) is
+   produced by either extrusion of injection moulding
+2. The *parison* is transferred into a cooled split-mould
+3. The *parison* is sealed and inflated to take up the shape of the mould
+4. The moulding is let to cool and solifidies under pressure
+5. The mould is opened and moulding is ejected
+
+![](./images/vimscrot-2022-03-01T18:30:18,545745201+00:00.png)
+
+## Injection Moulding
+
+1. Powder or pellets of polymer heated to liquid state (low viscosity)
+2. Under pressure, the liquid polymer is forced into a mould through a *sprue*, a small opening
+3. The pressurized material is held in the mould until it solidifies
+4. The mould is opened and the part is removed by ejector pins
+Selection was cancelled by keystroke or right-click.
+
+![](./images/vimscrot-2022-03-01T21:30:56,215686378+00:00.png)
+
+Theromoplastics are most common in injection moulding.
+A very high level of detail is attainable through this process and it produced little waste.
+
+Similar to [Die Casting](#die-casting-high-pressure-die-casting), you must consider corners (avoid
+sharp ones), draft angles (so you can get the part out), and section thickness (using ribs instead
+is preferable).
+
+Due to the high capital cost, injection moulding is only economical at high production volumes.
+
+### Co-Injection Moulding
+
+There is *sequential moulding* (one after the other) and *co-injection moulding* (together).
+
+These processes reduce assembly costs by integrating the parts and can use low grade recycled
+material for the inside of a component.
+It also allows for a part have to have multiple colours.
+
+This process requires special attention to be payed to shrinking/cooling.
+
+## Rotational Moulding
+
+Rotational moulding involves coating the insides of a heated mould with a thermoplastic.
+It is a low pressure alternative to blow moulding for making hollow components and is used
+for large components such as storage tanks, boat hulls, kayaks, and cones.
+
+## Moulding for Thermosetting Polymers
+
+There are two types:
+
+a. Compression moulding
+b. Transfer moulding
+
+![](./images/vimscrot-2022-03-01T22:15:05,965638775+00:00.png)
+
+### Compression Moulding
+
+For thermoplastics, the mould is cooled before removoal so the part will not lose its shape.
+Thermosets, however, may be ejected while they are hot so long as curing is complete.
+
+The process is slow but the material only moves a short distance and has lower mould pressures.
+It also does minimal damage to reinforcing fibres in composites and it is possible to make large
+parts.
+
+More manual labour is required and has longer cycle times than injection moulding.
+
+# Glossary
+
+[^d_deflocculant]: a substance which, when added to scattered particles in suspension, causes a reduction in apparent viscosity. Deflocculants are substances which prevent flocculation by increasing zeta potential and therefore the repulsive forces between particles. (<https://digitalfire.com/article/deflocculants%3A+a+detailed+overview>)

uni/mmme/1029_materials_and_manufacturing/materials.md

@@ -318,6 +318,19 @@ They are made of long carbon-carbon chains.
 
 ![](./images/vimscrot-2021-11-01T11:13:39,370133338+00:00.png)
 
+## Industrially Important Polymers
+
+The worldwide production of polymers in 2019 was $368\times10^6$ tonnes and the majority is from
+just 5 polymers:
+
+- Polyethylene (PE) --- wire insulation, flexible tubing, squeezy bottles
+- Polypropyene (PP) --- carpet fibres, ropes, liquid containers, pipes, chairs in Shoreham Academy
+- Polyvinyl chloride (PVC) --- bottles, hoses, pipes, valves, wire insulation, toys
+- Polystyrene (PS) --- packaging foam, egg cartons, lighting panels
+- Polyethylene terephthalate (PET) --- carbonated drinks bottles
+
+All of these materials are low cost.
+
 ## Thermoplastics
 
 The simplest polymer is poly(ethene):
@@ -1140,7 +1153,74 @@ You can apply the Arrhenius equation for all thermally activated diffusion:
 
 $$D = D_0 \exp{\left( - \frac{Q}{RT} \right)}$$
 
-where $Q$ is the activation energy and $R$ is the ideal gas constant (8.31 J k$^{-1}$ mol$^{-1}$).
+where $D$ is the diffusion coefficient, $D_0$ is the frequency factor, $Q$ is the activation energy,
+$R$ is the ideal gas constant (8.31 J k$^{-1}$ mol$^{-1}$).
+
+You can find the diffusion distance, $x$, with the following equation:
+
+$$x ~ \sqrt{Dt}$$
+
+![](./images/vimscrot-2022-02-28T20:31:12,395307966+00:00.png)
+
+
+# Materials in Sustainable Transport
+
+- Concerns over use of fossil fuels, climate change
+- Const of energy
+- Energy use in making and moving vehicles
+- Rising energy prices mean cost of fuel is comparable to cost of car
+- 1/4 of energy used in UK is to transport goods and people
+- Legislation and voluntary targets set by EU to improve fuel efficiency
+- In 2015 average CO2 emmisions as 130 g / km
+- Engine powerhas gone up significantly from 2001 to 2018 (~30%) yet engine displracement has gone
+  down ~10% and CO2 emissions down ~18% while weight has gone up ~10%
+
+## Is the car emissions reduction target significant?
+
+Overall CO2 emissions in 2016 is 466 Megatonnes.
+
+Does a reduction from 130 g / km to 95 g / km (a 35 g/km reduction) make a significant difference?
+
+There are 33 million registered cars in the uk.
+
+If they average around 8000 miles each (~13000 km) per year that's a ~15 Megatonne reduction,
+or about 3% of the annual C02 emmissions, a significant reduction.
+
+## Materials in Cars
+
+- Most of the energy used by cars is during driving (71%)
+- This means the mass of the vehicle has a great effect on its emmissions across a lifetime
+- The body, suspension, drivetrain, and interior all contribute roughly a quarter to the mass of the
+  car
+- However, the mass of cars are increasing
+
+### Material Substitution
+
+- The material will likely have performance requirements:
+
+  - It may need to be a physical size
+  - It may need to operate at certain temperatures
+  - It may need to bear a certain load
+
+- The component mustalso be designed for convenient manufacturing, assembly, servicing, disposal,
+  remanufacturing and/or disassembly
+
+#### Case Study --- 2012 Honda Accord
+
+- Body --- opted to stay with steel --- aluminium intense and multi-material approaches were both
+  rejected due to higher costs and limitations in manufacturing and assembly.
+  Recyclability was also noted as an issue due to different grades of aluminium needing to be
+  separated at end of life.
+- Doors and bonnets --- move to aluminium from steel --- more costly but the mass savings made this
+  option worth it
+- Wiring --- aluminium to copper --- lower mass for same conductivity, copper is more expensive
+  (I think)
+- Seats --- steel to composites or magnesium structural components --- very high weight savings
+
+## Choosing a Material
+
+
+
 
 # Glossary