Exam questions technical aspects Flashcards
2018
1ai)
Describe the process of injection moulding, including the key components
and steps as well as examples of typical applications.
- Plastic granules being loaded into a hopper
- The screw within a heated barrel forcing the polymer towards the nozzle.
- The clamping of the mould cavity and the mould.
- The injection of the molten polymer (details about runners and shot)
- The cooling of the mould
- The ejection of the component (including the potential use of ejection pins for example)
- Many people also included a comment about the final removal of the sprue and recycling of waste back into the process, which were excellent additional points.
Include points on
- the input materials and clamping, injection, cooling and ejection.
Detail was required in terms of
- the importance of pressure, runners and shot size
Any appropriate examples was acceptable if they were clearly showing this is a production process for use with high volume production because of the high tooling cost and capital investment.
Typical applications noted were:
- dashboards in cars, covers in consumer electronics and household products such as many plastic lids for fast moving consumer goods, such as shampoo bottles, etc.
2018
1aii)
Describe any two quality issues or defects commonly observed in products made by injection moulding. In each case, include a note on the possible underlying causes of the defect.
- Flow lines - These are lines or streaks, normally a darker shade than the surrounding plastic. This is due to the flow path and cooling during injection into the mould. The flow changes direction and speed when flowing around features and especially sharp corners. Solidification occurs at different speeds across the cavity when the injection speed is too low.
- Knit lines/Weld lines: This appears as a discoloured line, where molten plastics meet as they flow from different parts of the mould. The flow fronts do not bond correctly, most often due to partial solidification.
- Sink marks: Depressions on one side of a component due to the thicker section or a large feature on the other side. These thicker areas shrink upon cooling to give the depression. The cooling time needs to be sufficient to allow cooling in the mould.
- Warping: A deformation or bending where there is uneven shrinkage across the component. This is usually due to uneven cooling across the material. Different cooling rates or rapid cooling leads to internal stresses.
- Flash: If the clamp force is not sufficient, the mould/die are not precisely manufactured, the mould/die are worn or corroded or if the injection pressure is too high, there will be a leak of the polymer around the join leading to flashing.
2018
1aiii)
Describe three characterisation techniques you would use to study the PEEK. Include in your description a brief note about how each technique works, the properties it can define and the results you may expect to find in this case.
- This is a semi-crystalline polymer and so we should examine the level of crystallinity, and that this will have an effect on mechanical properties. In addition, because molecular weight also has an effect on modulus, the molecular weight distribution should be compared with previous batches. It would be good to identify if there are any contaminants present leading to a change in mechanical behaviour.
- Differential scanning calorimetry (DSC). The amount of energy needed to increase the temperature of a sample is measured. This detects phase transitions because of the quantity of energy needed to change temperature. The glass transition temperature can also be observed. Also, the percentage crystallinity can be defined.
- Gel permeation chromatography is a separation technique. The columns contained insoluble beads with a rigid pore structure. The pores can exclude very large molecules, allow partial permeation of medium sized polymers and allow total permeation of smaller molecules. The larger molecules therefore don’t have a long residence time in the column and flow through. This means the polymers are separated with the largest coming out first and smallest last. The full molecular weight distribution can be defined and compared with previous results to see if this is influencing the mechanical behaviour.
- A range of spectroscopy techniques can be discussed, including UV/Vis, FTIR or Raman. FTIR is often used to examine potential contamination.
- However, a good initial examination of contamination is with thermogravimetric analysis (TGA). This thermal technique measures the rate of change in mass as a function of temperature. This can identify changes in the oxidative stability and the composition. This is a highly sensitive technique and any contamination would be immediately highlighted. This technique is often used to identify the percentage of filler in a polymer sample, which also effects the mechanical properties.
- It is expected that the crystallinity may be lower than expected, the molecular weight may be lower than expected and there may be contamination in the batch
It was very important to include in the answer the expected results “in this case”, described in the question. This seemed to differentiate those who had memorised the technique, and those that could hypothesis about the likely results based on the problems seen in the example polymer.
2018
1bi)
Describe in detail what is meant by Primary Industries and Secondary Industries with relation to the chemical process industry. Include examples and
also typical characteristics of each industry type in your description.
- Primary industries convert raw materials into a primary form.
- Secondary industries convert primary products into final products
The majority of the marks were allocated to the detailed description requested in the question, by noting and explaining characteristics and including examples.
- Primary industries include base chemicals, petrochemicals & derivatives (formed by cracking, distillation), basic inorganics (sulphuric acid, sodium hydroxide) and fine chemicals.
- Secondary industries include speciality chemicals (paints, inks, dyes, crop protection) and consumer chemicals (detergents, soaps, toiletries).
Characteristics
- PRIMARY
- Plants tend to be large & integrated, capital intensive and the products are generally commodities.
- Large efficient plants dominate, and the innovation rate is necessarily low.
- The supply chains are often vertically integrated, and the volume and mix are stable and/or predictable.
- SECONDARY
- High velocity supply chains, with rapid product and process innovation.
- The mix and volume are usually volatile.
- Both automation and people skills are required in manufacturing.
Excellent answers can distinguish on a range of factors including competition, innovation, markets, plant and supply chain complexity.
2018
1bii)
Explain why the pharmaceutical industry is considering moving away from using only batch processing for some products. Describe in your answer an alternative approach being explored by the pharmaceutical industry and any advantages it offers.
Batch is very versatile but extremely slow and not very precise.
- There is approximately a 2- year timeframe from the start to the end of the process development (primary manufacturing part only).
- This approach requires capital intensive investment very early in product development to allow the running of clinical studies. However, this same process needs to be able to ramp up to full production. There is therefore a very high cost associated with failure.
- The batch approach is also not very agile to deploy around the world and leads to centralised manufacturing, whereas local production and distributed manufacturing may be important for future cost reduction.
- In batch manufacturing, it is difficult to reconfigure or change the design and this again adds to the cost of the products.
- One approach being examined is substituting a number of the batch steps with a continuous process. The approach requires the design of a modular continuous manufacturing plant.
- This building-block approach allows reconfiguration, agility to deploy, agility to re-use in other processes if the product fails,
- the benefit of the precision and higher levels of automation achieved in continuous manufacturing and the ability to build closer to the point of distribution rather than have large centralised manufacturing sites.
- Each module is a unit operation and these savings will be realised even by replacing a sequence of a few of the batch steps.
It may be noted that pharmaceutical companies are risk averse about moving the entire process to continuous manufacturing because of the challenge of controlling crystallisation and the significant knowledge currently in place that surrounds batch processing in this field.
2018
2ai)
Describe two manufacturing systems for additive manufacturing of bulk metal parts. In each case, include in your description example applications and
why additive manufacturing is chosen over conventional production processes.
Detail about the operating parameters, capabilities and also a schematic where it helped to show a detailed understanding.
Almost every powder-bed based AM system uses a powder deposition method consisting of a coating mechanism to spread a powder layer onto a substrate plate and a powder reservoir.
- Usually the layers have a thickness of 20 to 100 μm.
- Once the powder layer is distributed, a 2D slice is melted using an energy beam applied to the powder bed.
- The melting process is repeated slice by slice, layer by layer, until the last layer is melted, and the parts are complete. Then it is removed from the powder bed and post processed according to requirements.
Laser metal sintering
- The energy source is normally one high-power laser, but state-of-the-art systems can use two or more lasers with different power under inert gas atmosphere.
- Direct process powder-bed systems are known as laser melting processes and are commercially available under different trade names such as Selective Laser Melting (SLM), Laser Curing and Direct Metal Laser Sintering (DMLS).
- Laser based AM allows you to address a broader range of components with up to 150 cm3/hour deposition rate, significantly improves productivity
- Intelligent gas flow ensures the efficient removal of process emissions and extends filter life
- Integrated sieving and powder recirculation
Electron Beam Melting
Uses an electron beam under full vacuum.
- The electron beam gun generates a high energy beam (up to 3.000W)
- Extremely fast beam translation with no moving parts
- High beam power -> high melt rate (up to 200 cm3/h) and productivity
- Vacuum process -> eliminates impurities and yields excellent material properties
- High process temperature (650 oC for titanium) -> low residual stress and no need for heat treatment
- Example using e-beam is the production of turbine blades in TiAl
2018
2aii)
Discuss the challenges in applying metal additive manufacturing to high volume manufacturing. Include in your discussion any potential innovations that could overcome the challenges noted.
Challenges:
- Build speed:
- Using multiple lasers
- Build quality
- Better process monitoring technologies
- Many systems operate at low power (< 1kW) due to the technical difficulties of using multi-kilowatt single point laser scanning technology and the associated melt dynamics that cause melt flow instabilities at high scanning rates, particularly with multi-kilowatt lasers.
- There is a strong correlation between build rate and laser power.
- It is clear that current systems whilst capable, are not meeting the expectations of industry for higher build speed. However, increasing build rates cannot be delivered by simply increasing the power of single point scanning systems since there are a number of problems associated with high speed melt production such key hole effects, melt pool instabilities, and residual vaporisation.
- Those systems that do provide higher build rates, such as the SLM solutions 500, employ higher powers through multiple scanning heads, with 4 heads being employed in the case of the SLM 500. The consequence of employing multiple is scanning complexity and cost. An order of magnitude increase in build rate requires an order of magnitude increase in power since, notwithstanding the time penalty of powder deposition, power is the direct driver of build rate for any AM system.
Considering the position of the current state-of-the-art AM technology, increasing build rates by two orders of magnitude from 4 cm3 hr-1 to 400 cm3 hr-1 would require a stepwise power increase from 100 W to 10, 000 W. Applying the price-power relationship of Figure.2 would project a system price of $14,000,000. This cost is clearly untenable. Whilst cost reduction could be applied in future systems, the likelihood of current technology delivering x100 increase in build rates is extremely low.
There are two fundamental issues in the AM industry.
- Firstly, all current metal-based AM systems are based on technology concepts that are around 16 years old and have experienced incremental advances in this time (moderate power increases or multiple scanning systems).
- Secondly, the growing expectations of AM technologies by future users, i.e. build rates, cost, and quality, are currently in excess of the AM suppliers’ ability to deliver using current platform concepts.
There were a range of innovations discussed in lectures regarding reduction in cost, increase in throughput through laser arrays and increasing laser power, these and other valid suggestions were accepted.
2018
2bi)
Discuss similarities and differences between semiconductor manufacturing production methods and those of conventional additive manufacturing.
- Semiconductor fabrication, like AM technologies, apply material in layers. AM technologies have in some respect borrowed their techniques from semiconductor fabrication.
- Whilst the number of layers in semiconductor processes are relatively few, the number of steps per device is very high (several hundred). Since these involved the deposition of base materials such as resists (curing steps), alignment of masks (a significant overhead cost), photo exposure, planarization (removal steps), metallisation (for interconnects), oxidation and the process repeated for interconnects, and insulating layers.
- The process is much more complicated than AM techniques, although the parallel production methods, and high resolutions (nm) makes the process very efficient. On the other hand, AM techniques invariably use a single material, with lower resolution (um), and many more layers (1000s rather than 10s of layers).
The bigger parts that are produced in AM and therefore built far more slowly.
- We have many types of AM production technologies, although most are not useful for high volume manufacturing. The biggest issue is that most additive fabrication techniques are serial so larger areas take more time.
- Currently, mask-based lithography is the norm. Researchers are investigating, e-beam, maskless, and nanoimprint lithography. In all of these techniques, printing is done vertically on horizontally placed semiconductor wafers.
- Contemporary AM is for components with sizes ranging from mm (or submicron) to a metre or so.
- Processes for semiconductor manufacturing deliver resolutions in the nm range, 15-45nm, with EUV techniques offering 7.5nm resolution.
2018
2bii)
Describe two examples of emerging technologies that have the resolution of current semiconductor lithography processes and process characteristics of conventional additive manufacturing techniques.
- Nanoscribe: This process employs two photon photolytic techniques and high resolution positioning. The laser beam itself has a computer-controlled beam guidance system that translates a 3D CAD model directly into 3D structures of almost any complexity at any scale. Essentially it can fabricate microstructures as small as 500 nm, including those with complex geometries and support structures, at extremely high resolutions (100nm with reports of new materials reaching 45nm). The 3D printing technology that Nanoscribe developed has allowed sub-micron parts to be fabricated with geometries and internal structures that would be completely impossible to create using standard micro-scale manufacturing techniques.
Nano3Dsense
- 3D Nanoprinting can be employed in a conventional Scanning Electron Microscope that is adapted to employ e-beam deposition of materials from the gas phase. A highly focused electron beam with a diameter of a few nm is employed as an ultra-small “pen” for the layer-by-layer production process of structures. Very small dimensions as low as 10nm are achievable, on almost all material surfaces or geometrical shapes. The system operation is shown in the figure. Its application is focused on the maskless fabrication of chemical, and motion sensors, without the need to employ conventional lithographic techniques
Fountain pen nanolithography (FPN).
- FPN is a printing method, which, utilises a reservoir filled with nanoparticulate ink. These ink solutions can undergo nanochemical changes during the lithography process, resulting in the desired functional lines and structures. Line width control from 15 nm to over 1000 nm have been demonstrated. Line produced showed micrometer lengths, consistency of line dimensions, precise placement, and conductivity. Similar to the reservoir in fountain pens, the nanopipette reservoir enables numerous lines to be printed without refilling. This technology could be expanded to the production of conductors and actuators, correction of flat panel displays, and mask repair applications.
2018
3
A mobile phone manufacturer currently assembles two models of phones on a manual production line. One particular operation involves the fastening of all components to the inside of the front phone cover using self-tapping torque screws. The production manager has been asked to investigate the use of a robotic fastening cell to replace the current manual operation.
(a) Discuss the pros and cons of different robot types that could be used within the fastening cell. Rank the suitability of each of the robot types discussed.
- SCARA
PROS
- Ideal robot type for inserting screws into holes. Stiff in the Z Axis but compliant in X,Y.
- Due to its stiffness in the Z axis it can apply significant loads in the Z axis. This is essential when inserting self-tapping screws.
- Best repeatability of the different robot types on the market, making it ideal for the placement of small screws in an electronic assembly.
- Some of the fastest robots on the market, allowing it to easily service operations from the two lines and a screw feeder.
CONS
- Limited working volume, but easy to visualise for a 2D space
- Working volume is cylindrical in nature, complex to utilise.
- Payloads can be limited if full operating speeds are required.
2. Cartesian
PROS
- The Cartesian style of robot can carry out fastening type operations.
- Cartesian robots are made up from linear axis and can provide large working volumes
- Cartesian robots can support significant payloads, suitable for the operation of an electric screwdriver
- Cartesian robots have good repeatability, making them suitable for electronic assembly operations
CONS
- It has limited compliance in the X,Y plane.
- Cartesian robots tend to be the slowest of the different robot types. It may not be possible to meet the takt time required in servicing the two phone lines.
3. Anthropomorphic
PROS
- Very flexible robot, capable of working in a number of planes. (Not required in this application)
- Can be re-tasked or have its role extended to other tasks easily.
CONS
- Stiffness in the Z axis is limited. This is due to limited torque available in the wrist axis.
- Complex working volume that is spherical in nature.
- The anthropomorphic is one of the slowest robots.
- The repeatability of the anthropomorphic robot is mid-range and may need to be examined closely for applications in electronic assembly.
Delta
PROS
- The Delta robot has good repeatability required for electronic assembly.
CONS
- The working volume of the work space is limited in the Z Axis. Challenging to accommodate screwdriver operations.
- Payloads on the Delta robot is limited and not suitable for screwdriver operations.
- The Delta robot doesn’t have the appropriate stiffness in the Z Axis to support fastening type operations.
2018
3b)
(i) An end-effector is to be designed to facilitate the operation of the electric screwdriver when mounted onto the robot. Specify the type of actuators and sensors that would be required to perform fastening operations. Indicate how the sensors you select can be used to identify common error conditions.
Actuators:
- linear guide rail: to allow the screwdriver to move up and down during the fastening operation independently of the robots motion.Pneumatic piston / Control valve
- Pneumatic piston / Control valve: to allow the screwdriver to be lifted prior to a fastening operation and to ensure a positive pressure is applied to the screw during the self-tapping process.
- Vacuum port / Control valve: to control the vacuum pick-up capability on the screwdriver.
Sensors:
- Screwdriver in the up/down location (Inductive – Proximity) Best, (Optical – Diffused Sensor) Possible but needs to cleaned
- The sensor will be used to inform the control logic of the robot controller when the screwdriver is in the up position.
- Vacuum sensor attached to vacuum pickup port. (Diaphragm style with threshold control) Best (Diaphragm style with switch control) Possible
- The sensor will be used to inform the control logic of the robot controller that a screw has been picked up and is correctly engaged on the torque screw driver.
- Screwdriver torque contactor (Internal)
- The torque contactor will be used to inform the control logic of the robot controller that a screw has reached the required torque for a correctly fastened screw.
Error conditions
- Stripped screw on thread:
- Torque sensor (No) & Screwdriver down (Yes)
- Cross threaded screw
- Torque sensor (Yes) & Screwdriver down (No)
- Incorrect screw pick-up and/or bit engagement
- Slow speed engaged & Vacuum sensor (No)
- Correctly fastened screw
- Torque sensor (Yes) & Screwdriver down (YES)
2018
3b)
(ii) Draw a flowchart that depicts the logic required to control the operation of the robot, end effector and screwdriver when performing all actions required to fasten a screw. Include on the flowchart the logic associated with any error conditions that should be considered.
The diagram below depicts a possible flow chart for this problem. The key items required to be evident in the flowchart are
- Set the initial conditions of the screw driver (Up Position and Stop)
- Move robot to a screw pick up location.
- Pick up Screw (Sensor checks required) maybe from an external screw feeder.
- Slow speed driver rotation, ensure screw engages on torque bit. (Sensor checks required)
- Move robot to screw fastening location 1.
- Fasten screw (Sensor checks required) a) Fastened, b) Stripped Thread & c) Cross Threaded 7. Repeat operation via (step 2) Question only asks for one screw!
- Good answers could show loop for multiple screws.
2018
4
Polymer food packaging waste is being targeted for reduction in the UK, with discussion of a range of measures that could be put in place. End-of-life plastic is seen as problematic partly because some of it enters the environment as uncontrolled waste, but there is also concern about some of the intended end-of-life routes and processes.
(a) What are the main end-of-life processes that can be used for polymers? Briefly assess their eco-impact.
Mechanical recycling:
- shred, sort, clean thermoplastics. In factory waste streams can produce recycled polymer that can be re-used for high grade applications. Post consumer polymer waste streams more often results in downcycling (contamination).
- Reduces amount of virgin polymer required to make products (e.g. closed loop recycling of milk bottles)
- Significant eco impact reduction if processing is not too energy intensive. Generall eco impact is low consumer recycling.
Other mechanical recycling
- Used as a filler or combined with other materials e.g. playground surfacing
- Limited benefit
Chemical feedstock or recycling
- Polymer is broken down into its constituent molecules
- Energy intensive, but robust to contaminants
- High energy use therefore high cost, generally only beneficial for specialist polymers
Biodegradation
- Composting generically. Aerobic degradation resulting in products that are beneficial to soil.
- Suitable only for a small number of polymers. Capability of commercial composting is unclear.
- Unclear eco benefits. Idea is good but problematic to implement.
Burning
- Thermal recycling with energy recovery
- Energy from waste plants or cement making
- Beneficial when using well controlled processes, but if uncontrolled can pollute dangerously.
Landfill
- Polymer included in waste stream that is placed under anaerobic conditions
- Space is limited, polymer is a useful resource so there may be missed opportunities
- Polymer is mainly inert so eco-impact is small. Uncontrolled landfill thought to be main contributor to ocean waste.
2018
4
(b) What are the difficulties associated with recycling of polymer food packaging?
- Recycling polymer to high-grade material is technically difficult because the polymer cannot be purified, so mechanical recycling relies on being able to sort and clean polymer waste to produce high purity material as the input to the recycling process.
- Difficulties increased by additives in polymers, use of coloured polymers, and use of mixed (often multi-layer) polymers to improve functionality (e.g. multi-layer polymer film). Costs are increased.
- Handling of polymer films is difficult.
- Economic benefits are at best marginal: oil prices are low so virgin polymers are relatively inexpensive and there’s no margin to accommodate costs of collection, sorting, cleaning and processing.
- Recycled polymers command only low prices unless they are from very well-controlled waste streams: the quality has to be consistently high to get close to virgin polymer prices.
- Public perceptions of plastics as ‘cheap’ and post-consumer polymer as ‘just rubbish’ can de-emphasise importance of recycling.
2018
4
(c) How can the global environmental impact of food packaging be assessed? Your answer should include discussion of system boundaries and the balance of factors that should be considered for food packaging. Based on your assessment, what measures should be considered for reducing food packaging waste whilst not compromising its global environmental impact?
Food packaging is (amongst other functions) designed to reduce food waste, primarily by
- (i) reducing damage whilst in the supply chain and
- (ii) increasing shelf life by providing mechanical or protective chemical environment (e.g. vacuum or inert atmosphere).
- Any discussion of its global environmental impact should note that packaging impact is small compared with food production (typically well below 10%), so assessment should therefore include some acknowledgement of the impact of food production.
- System boundaries might properly encompass food production, packaging production, transport, storage, end-of-life processing.
Environmental impact can be assessed using an LCA (full analysis of product function, system boundaries, inventory; gives impact assessment typically in 9 categories).
- Provides full data, but quality dependent on the assumptions made. The very considerable environmental cost of food production will often completely dominate the environmental cost of packaging:
- simplistic solutions to reducing food packaging waste tend to ignore this, so environmental impact is actually increased.
Eco-aware measures for reducing food packaging waste might include:
- reduction of non-functional packaging (already covered by existing legislation but difficult to enforce);
- reducing packaging volume (films instead of trays - negative impact on recyclability);
- making it easier for people to dispose of polymer waste to waste streams that can be recycled (uniform and clear national guidance across domestic and commercial waste disposal operatives);
- increase national capability for recycling by providing subsidies to recycling companies.
- More radical proposals look at reducing the range of polymers used for packaging, and this would require national/international agreement, such as using only a small number of uncoloured plastics.
2018
4
d) Biodegradable polymers are sometimes promoted as a ‘green’ packaging solution. To what extent is this justified?
- Traditional polymers have essentially infinite degradation times in landfill or in ambient environments (including marine);
- the expectation is that biodegradable polymers should disappear in a finite time. Biodegradable polymers will degrade in aerobic conditions (though not in anaerobic conditions such as landfill), but generally require higher temperatures than available in domestic composting, and higher than for some commercial processes.
- Biopolymers (polymers produced from renewable bio-based resources) are not necessarily biodegradable;
- some fossil-fuel based polymers are biodegradable.
- The aim is to use for packaging, biodegradable polymers that degrade at a comparable rate to food allow food-contaminated packaging to be processed with waste food.
- This is a low environmental impact route, but the product is not of very high value so financial considerations can be important.
- Identifying appropriate polymers during pre-processing is technically challenging (needs to be done e.g. by sorting on a conveyer belt in a MRF), and inclusion of non- degradable polymer in compost reduces value still further.
- In addition, biodegradable polymers which get into the traditional polymer mechanical recycling waste stream can cause contamination.
The environmental impact of biopolymer production is controversial and depends on system boundaries: by some metrics, biopolymers have higher impact than fossil fuel based polymers. Production is generally more expensive so remains small-scale and will never have the capacity to supply global demand In summary: biodegradable polymers are at best only a very partial solution
2018
5
a)
Describe six supply chain risk mitigation strategies. Explain possible unintended consequences of supply chain risk mitigation, using examples.
Supply Chain Risk Mitigations:
- Increase capacity
- Build centralised capacity for unpredictable demand
- Build decentralised capacity for managing supply chain disruptions due to natural disasters
- Acquire redundant supplier
- Favour more redundant supply for high volume products, less redundancy for low volume product
- Centralise redundancy for low volume products in a few flexible suppliers
- Increase responsiveness
- Favour cost over responsiveness for commodity products
- Favour responsiveness over cost for short life products
- Increase inventory
- Decentralise inventory for predictable, low value products
- Centralise inventory for unpredictable, high value products
- Increase flexibility
- Favour cost over flexibility for predictable, low volume products
- Favour flexibility for low volume, unpredictable products
- Centralise flexibility in a few locations if it is expensive
- Increase capability
- Prefer capability over cost for high value, high risk products
- Favour cost over capability for low value, commodity products
- Centralise high capability in flexible source if possible
Unintended consequences of supply chain mitigations
- Adding capacity increases cost of operation. High capacity cannot be sustained in the long run if there is perfect competition
- Increasing inventory increases cost of operation.
- Having redundant suppliers increases cost of operation.
2018
5
b) Compare and contrast the traditional and the configurational approach to supply chain risk management.
Traditional approach of supply chain risk management:
- Identifying Supply chain risk characteristics
- Identifying risks linked to supply chain characteristics
- Evaluate risks
- Choose relevant risk mitigations
- Evaluate impact of chosen mitigation
- Plan mitigations
- Monitor risks and risks mitigation
Configuration approach of supply chain
- Mapping Supply chain : Including network structure, process flow, value and product characteristics
- Understanding event: characteristics and database
- Identifying risks: overlaying event data on SC map and identification of vulnerability led risk
- Mitigations: Change in network structure, alternative process flow, value adjustment and product redesign
2017
1a) (i)
Define what is meant by the term biopolymers. Include specific examples of
two different biopolymers in your answer. For each biopolymer, give two examples of typical applications, explaining why the biopolymer is particularly suited to that application.
- Using renewable feedstocks to make polymers.
- Other definitions in use, including polymers which biodegrade
- Also polymers that are used to interface with the human body and are biocompatible.
Examples:
- Starch-based biopolymers
- Applications include as a substitute material for expanded polystyrene packing. This has the right density and mechanical properties while having the advantage of being biodegradable also.
- Films for tunnels or coverings over rows of plants/crops for conserving water. Mechanical properties and biodegradability again were noted by candidates.
- Can be used as an additional component blended into other, non-bio polymers, to improve biodegradation. Up to a certain inclusion level, the properties were excellent but then there is a tradeoff between improving degradation at the expense of the mechanical properties.
- Can be used as a substitute for polyethylene and polypropylene, with some food packaging being applications that lead to better biodegradation and ease of disposal of food products.
- Polylactic acid (PLA)
- Applications in bottles, some fabrics, plastic cutlery and other food packaging. The mechanical properties, similar to polystyrene are important and also the ability to replace polyethylene and polypropylene, especially in terms of mechanical properties and optical properties (good clarity).
- The biopolymer is resistant to oils and greases so again is very useful for products in contact with foodstuffs. In addition the biodegradation reduces the challenges of disposal as food and polymer can degrade.
- Polyhydroxyalkanoates (PHA)
- Applications in cutlery, plastic food containers, a range of consumer products (razors, toothbrushes, shampoo bottles).
- PHA is often chosen because of its strength or rigidity for these applications.
- It can also be sent to composting or anaerobic digestion for degradation, which can simplify disposal.
- Applications could be noted where a replacement is needed for PVC, PE or PP.
2017
1aii)
Why is there an interest in moving from standard petroleum-based polymers
to biopolymers? What barriers may hold back such a move?
Drivers,
- unsustainability of fossil fuel based feedstock.
- The environmental issues with synthetic polymers should also be noted and there are a number of point, such as:
- The accumulation of waste in its bulk form in oceans and lakes as a result of poorly managed waste disposal.
- Poor disposal management has led to plasticisers leaching into the environment along with other additives. Examples include phthalates (plasticiser) and PBBs which add flame retardancy properties required in many applications.
- There have been reports of knock-on effects of these leaching materials in terms of changing reproductivity of sea life and also, once in the food chain, this can lead to health issues in human consumers. Examples were noted, such as the recent news item on plastic particulates making its way into the food chain.
- There is a general drive to improve the waste disposal of polymers and enable biodegradability in a wider range of products, which is feasible with biopolymers.
- There is a benefit to moving to industrial symbiosis activities and the raw materials of biopolymers can be sourced this way.
- There is now also consumer pressure for the use of renewable materials and more environmentally responsible material choices.
- In addition, while bio-based polymers have been available for some time, recent research is bringing down costs and making them more attractive for applications.
Barriers
- It is believed that this will need intensive farming and specifically large scale monocultures to be feasible, which can lead to significant issues, such as the exhaustion of nutrients from soils and the large scale use of herbicides/insecticides and other agrochemicals.
- There is significant competition for the use of land for food or biopolymer (and biofuel) material growth. This was pointed out as a real challenge, considering the significant demands on increasing food production with a growing population globally.
- Another barrier is the use of fossil fuel based energy sources in the rest of the production process for agricultural sources.
- The cost, while reducing due to R&D efforts, is still significantly higher than synthetic polymers.
- There are significant end-of-life complexities. Not all biopolymers can be handled the same way, with some requiring anaerobic digestion rather than home or industrial composting.
- Also, the incorporation of biopolymers into blends with synthetic polymers an lead to challenges in identifying a useful recycling route. While the synthetic polymer may be replaced, there is often still a need for the fillers and additives noted for their environmental impact.
2017
1aiii)
What are the challenges when attempting to carry out and analyse Life Cycle Assessments of biopolymers?
- While LCA is standardised framework, users can interpret differently within this framework, which then makes comparing across studies and final interpretation extremely difficult.
- The LCA should cover the entire life-cycle: extraction of raw materials to disposal but this is not always the case.
- So firstly, there is this flexibility in terms of scope, and secondly within this scope there are areas that are not defined in a standard way.
- For example, soil carbon/nitrogen dynamics, emissions from composting, the local manufacturing environment and maintenance of equipment can all be interpreted differently.
- In addition, there are very location-specific challenges that can be noted in the answer.
- Farming practices and their resource requirements will be very different depending on location due to climate.
- Energy production and its environmental impact is linked to the country, energy source and regulations.
- There will also be an impact from the distances across which materials need to be transported and the disposal routes available.
- Some answers gave details on the challenge of identifying appropriate categories of impact and ensuring that metrics across these categories can be compared. Allocation approaches were also noted to be different across different studies.
2017
2 (a)
(i) Describe the key advantages to manufacturing by additive techniques. Include three example applications of additive manufacturing and explain why additive manufacturing is a good choice for each of these examples
- Additive manufacturing (AM) is expected to be advantageous due to the ability to reduce waste involved with manufacturing. Subtractive manufacturing naturally produces waste in a process, whereas additive uses close to the required material.
- There is the potential to distribute manufacturing, reducing the need for transport of final products. This compresses the supply chain considerably.
- AM also leads to compression of time required for product development, both due to the speed of setting up manufacturing processes but also the ability to trial innovations quickly.
- There are advantages for designers and manufacturing engineers because it extends capabilities to more complex, geometric shapes and features that were previously not feasible (e.g. nested structures).
- AM is also advantageous because some techniques are low cost and so accessible to a very broad array of industries and also students, hobbyists and entrepreneurs.
- While there are significant material limitations, the range of materials and final material properties have been rapidly increasing, allowing end-use parts to be produced in a wide variety of polymers, metals and ceramics.
There are a very broad range of example applications from which to choose.
The applications most often referred to fell under
- prototyping applications, with the rapid turnaround time and great flexibility of fabrication being noted;
- or tooling applications, with the importance of flexibility in jig, die or mould design noted;
- or the direct final part production for spares and repairs applications, with the
- fine art and jewellery applications noted because of the low demand on rapid fabrication but great advantage of rapidly producing new designs.
- Aerospace and automotive applications were also noted under this category, but only for applications where there is no need for high throughput manufacturing.
- The 3D printed fuel nozzle was an example discussed in the lectures.
- Some also mentioned the fabrication of custom-made medical devices because of the ability to tune for a patient’s needs.
2017
2aii)
There are a wide range of techniques for additive manufacturing. Briefly describe any two different additive manufacturing technologies and highlight any significant benefits or constraints in each technique.
- Powder bed fusion, vat photopolymerisation, directed energy deposition, material extrusion, material jetting, binder jetting and sheet lamination were among the main approaches covered.
For example, when discussing powder bed fusion,
- The material that the final product will be made from is initially in powder form and present in two powder beds.
- Software is used to use a CAD drawing of the 3D object and reproduce it as a series of 2D layers, starting at the base and working up to the top of the shape.
- A laser is raster scanned over one powder bed to fuse the powder together to represent that first 2D layer.
- A fine layer of the powder is transferred from the other bed to then just cover the fused layer and the next 2D slice is then patterned with the laser.
- Each slice fuses the particles both in the 2D layer but also with the particles underneath.
- This final, fused 3D object is removed from the powder bed, cleaned of the remaining loose powder, and may undergo additional post-processing.
The benefit is that this approach is very flexible and has been shown to work with metals, some polymers and even ceramics. Also, this approach can make very complex parts because the powder that is not fused can act as a support material adding structure to otherwise hollow shapes.
- The constraints include the very slow speed, of this approach,
- the limit of resolution due to both the influence of the heat affected zone and the particle sizes.
- Also, this approach does not yet give final structures that are identical to fabrication with standard techniques, due to the different crystallography and porosity.
A second approach may be VAT photopolymerisation.
- In this case, there is a VAT of fluid polymer and initiator, that drives crosslinking when exposed to focused UV radiation from a laser.
- Again a 3D image is converted to a series of 2D slices.
- The first slice is patterned onto the surface of the VAT, this polymer cross-links and so hardens.
- A layer of fluid polymer is then spread over the top and the patterning process is repeated.
- There is a shelf within the VAT that is steadily lowered with each layer to allow a final 3D object to be produced.
- This needs to be carefully cleaned upon removal from the VAT.
This has great benefits because of its high resolution and very good final product finish.
- It is also a relatively quick process.
- It is constrained by the very limited range of materials that can be used (photocurable polymers),
- and the poor biocompatibility of these materials.
- Also, it can’t create very complex 3D structures as the fluid that is not cured can’t act as a support (for overhanging structures etc.).
2017
2b
iii) Describe three different micro-manufacturing processes you may choose if you need to manufacture only a small number of micro-gears. Include details about suitable materials, advantages over other methods, or process constraints.
- The basic process for photoelectroforming
- (1) the suitability for thin metal components,
- (2) the application of photosensitive polymer to the surface of a flat underlying material,
- (3) the use of a mask to let through UV light that will modify the polymer so it can be easily removed (or hardened, depending on the polymer).
- (4) The polymer that is now “washable” is removed through developing and washing steps.
- (5), the underlying material (which must be conductive), enables electrodeposition of a metal.
- This means when all of the remaining polymer is removed (resist stripping), and the underlying material, there is a replica of the pattern in the electrodeposited structure.
- This can be carried out in repeated stages with etching and forming allowing the fabrication of complex 3D structures. Rather than UV, X-ray lithography can be used to get a higher resolution pattern and make higher aspect ratio products.
In terms of advantages, very high feature precision is achieved. The technique can be used to make very thin structures. Also, this is an industrially scalable process, already used in industry. There is however a limitation as to the materials that can be deposited to a high quality using this technique, with nickel being the most used. Also, it is extremely expensive to move to using X-rays and so the particular design needs to be carefully considered.
- End-milling
- It is important to note that this is a scaled-down version of a well understood and commonly used fabrication technique.
- In this case, the workpiece is kept stationary, commercially available micro-scale end-mills are used (down to 10 microns in diameter).
- The cutting speeds are increased significantly compared to end-milling (around 1 m/s relative speed of workpiece and cutting edge), this could be approximately 200,000 rpm.
- The system does not use flood cooling but instead relies on spray cooling or gas cooling.
- The tool life is greatly affected by the cutting speed, with a linear decrease noted (differing slopes depending on materials).
The advantages include the high precision on a very wide range of materials along with the fact that it is a well understood technique. There are constraints because it is difficult to detect tool breakage during use of such small end-mills. The depth of cut is limited because the radius of the tool is very small and leads to the tool appearing blunt. When milling metals and the grain sizes are on the same order of magnitude as the end-mill, materials are no longer homogeneous and this can lead to issues in terms of surface finish and dimensional tolerance. Also, another constraint is that this is a very slow fabrication technique.
2017
3b)
The project manager has proposed a draft project plan as shown in Fig.1. The plan shows production loads within the factory and some of the key activities that need to be undertaken by the different parties involved in the automation project.
(i) Consider both the project and supplier information provided and critique the draft project plan shown in Fig.1. Identify the weaknesses in the plan and discuss how they could be addressed.
No system testing shown on the plan
- Incorporate a system test phase at the end of the project (Integration and testing should take around 40% of the total project period). Some unit testing activities could be undertaken by suppliers, helping to reduce the testing time.
No provision is provided to address solution concerns about the Injection moulding supplier.
- A prototyping activity should be included. This could commence as soon as the specification work has been completed. Design work could not be completed until the end of the prototype activity.
The final system build at the valve manufacturer will impact on the peak production period in June.
- The final system build has to be split into two activities.
- Activity 1) Line modifications taking place before the June peak.
- Activity 2) New system build during the summer shutdown.
It is unlikely that the system design work at the valve manufacturer can be completed prior to design work at the injection moulding supplier.
- Design work at both the Injection moulding company and the valve manufacturer have to be extended to accommodate prototyping work.
Equipment from the material handling supplier will not arrive prior to the summer shutdown.
- Tasks undertaken by the material handling supplier need to be carried out earlier.
No overlap is shown for tasks being carried out by either of the suppliers. Not realistic in a project plan.
- Introduce overlap of tasks to help handover of activities. It’s unusual to have a snap change between one process and another.
2017
3bii)
Produce a revised project plan to ensure that the project is successfully implemented during the summer shutdown and ensure that peak production periods are protected. Include in your plan measures to address key risks in the successful execution of the plan.
- The tasks being undertaken by the Injection moulding supplier are currently on the critical path.
- The task being undertaken by the Injection moulding supplier have the highest risk. These tasks need to be pulled forward with additional solution investigation tasks added (Prototyping).
- Until the Injection moulding supplier has a working solution the design phase of the other project suppliers should not be completed (This is to accommodate late changes).
Final system build has to be split into two activities to ensure that it can be carried out during non- peak production periods.
The proposed time plan provides extra time for the Injection moulding supplier to develop a solution but moves the material handling tasks on to the critical path. Note the material handling build process has to commence before the project design phase is finished. This risk is balanced by the fact that the solution being requested is fairly standard and readily available.
2017
4c)
Using the data given in Table 1 test whether solely basing a movie on a book has a statistically significant impact on the movie’s gross earnings (use a 95% confidence level). State your assumptions. Use the following formula for standard error:
Standard error of the difference is 7.13.
Students can then do either one of the following.
Check the upper and lower bounds of within 95% confidence:
Upper confidence interval: 33.09
Lower confidence interval: 5.14
Since zero is not in this interval, reject the hypothesis that the true means are the same. Thus, earnings of a movie based on a book and not based on a book are not the same.
Alternatively candidates can calculate the distance of the test statistic, 19.1, from 0: t-stat = (19.1-0)/7.13 st.errors = 2.68 st.errors
Greater than 1.96 so reject H0. Thus being based on a book has a significant impact on earnings.
2017
5b)
Factories making the same product can show large variation in operational efficiencies. Outline the factors which may influence variations in resource efficiency. Suggest ways in which resource efficiencies may be improved. Use specific examples, from module presentations or from your own experience, to illustrate your answer.
Improvement hierarchy:
-
Prevention
- eliminate unnecessary equipment/processes
- switch off equipment when not in use
- e.g. use gravity feeds, standby mode
-
Waste reduction
- good maintenance and repair
- sort/treat waste to optimise its value
- optimise layout
- e.g. fix leaks, insulate, separate waste, keep equipment clean
-
Resource use reduction
- optimise production schedule and start up
- match supply and demand
- e.g. lower compressed air pressure, use highest temp for cold storage
-
Reuse of waste as a resource
- look for compatible waste demand
- understand reuse opportunities
- e.g. reuse cutting fluid, recover waste heat and water
-
Substitution
- replace resource (renewable and non toxic)
- change way function is achieved
- e.g. replace cutting tools, install optimum motors, replace obsolete tech
2017
6 (a)
Describe using examples, the terms vulnerability, risk and resilience in the context of supply chains.
- The supply chain risk and resilience framework explains the concept of event, vulnerability, risk and resilience.
- At its centre is ‘event’ (such as climate change, war, new regulation or financial crisis), which might have significant impact on supply networks.
- Next is ‘vulnerability’, which is associated with structure of supply network and particularly its lack of flexibility.
- ‘Risk’ appears when key events and vulnerability interacts with each other, which leads to supply network failure.
- Next is ‘risk mitigation’, which is an action or set of actions taken by companies to minimise either impact or changes (probability) of risk.
- ‘Resilience’ is an ability to recover from network failure, which is achieved by continuously changing supply networks in response to risks by using risk mitigation approaches, such as adopting new processes and /or practices or by reconfiguration
2018
6aii)
Use a graphical approach to describe how the Simplex Method of solving a
linear programming problem can be used to determine the optimal number of each product to make. What is the corresponding maximum total profit?
in the graph represent the constraints.
The fundamental basis of the Simplex Method is based on the fact that the optimal solution (if it exists) is a corner point feasible (CPF) solution. If a CPF solution has no adjacent CPF solutions that are better (as measured by Z), then it must be an optimal solution. The CPF solutions in this problem are (0,0), (10,0), (0,11), and (4,9). This can be found either directly by observing the graph above, or by solving for the intersections of the lines forming the constraints.
The steps within the simplex method are:
- Initialisation: Choose (0,0) as the initial CPF solution to examine.
- Optimality test: Conclude that (0,0) is not an optimal solution (adjacent CPF solutions are better).
- Iteration: Move to a better adjacent CPF solution (0,11).
- Optimality test: Conclude that (0,11) is not an optimal solution (adjacent CPF solution is better).
- Iteration: Move to a better adjacent CPF solution (4,9).
- Optimality test: Conclude that (4,9) is an optimal solution (adjacent CPF solutions are not better).
- Hence, the optimal solution is to make 4 tables and 9 chairs, giving a total profit of £96.
2014
3a)
The main functions of packaging in the food and drink industry may be summarised under the headings of
- product handling,
- mechanical protection,
- barrier function,
- provision of information, and
- tamper-evidence.
Give examples of how these functions are achieved, and discuss their resulting environmental implications.
Product handling:
- Achieved by:
- Containers for loose goods and liquids; clustering of small items
- Example:
- Bottle, box, bag (liquids, powders). Tray, bag (meat, cheese, loose foods, other products)
- Environmental consequences
- Positive: Reduction in product wastage by damage etc.
- Negative: Packaging material required.
- Verdict: Unless excessive packaging used, expect small positive impact.
Mechanical protection
- Achieved by:
- Impact-resistant packaging for fragile items; surface protection for many items.
- Example:
- Egg box; blister pack; plastic film wrapping
- Environmental impact:
- Positive: Reduction in damage so less product wastage.
- Negative: More packaging material. Increased bulk reduces transportation packing efficiencies.
- Verdict: Generally large positive impact.
Barrier function
- Achieved by:
- Prevents contact between atmosphere/environment and product;
- selective passage of gases;
- protect from light;
- prevents odours escaping;
- enables inert gas atmosphere
- Examples:
- Plastic bag for foods. Multi-layer packaging for meat and cheese
- Environmental impact:
- Positive: Product life increased by orders of magnitude, so reducing wastage. But by enabling longer supply chains it promotes globalization of food production – with both positiveand negative environmental consequences
- Negative: Complex multi-layer films very difficult to recycle
- Verdict: Huge positive impact
Provision of evidence
- Achieved by: Writing and pictures on packaging
- Examples: Labels attached to product, or inkjet- printed onto packaging
- Environmental impact:
- Negative: Stuck-on labels may impair recyclability if appropriate materials not chosen.
- Verdict: Negligible impact
Tamper evidence:
- Achieved by: Sealed container
- Examples: Tamper-evident tabs; sealed lids
- Environmental impact: Positive: Some reduction in wastage.
Overall summary: Packaging is typically responsible for between 0.5 and 5% of the energy footprint of packaged foods: most of the impact comes from the food itself. So using a small amount of packaging to reduce the food wastage by (typically) at least 50% makes it environmentally very beneficial. The overall environmental consequence of whether packaging can be recycled at end-of-life is small. However, this is something which consumers focus on as a negative environmental influence of packaging.
2014
3b)
How may polymers be recycled at end-of-life?
Why is recycling of post-consumer polymer packaging generally regarded as problematic?
What are the environmental consequences (benefits and penalties) of the different end-of-life disposal options for polymer packaging?
Mechanical recycling: Sort, shred, clean, melt/reprocess (extrusion, pressing)
Chemical recycling: Polymers broken down into constituent monomers which can be used in refineries or in petrochemical production
Energy recovery: Burning
Polymers are difficult to recycle for technical reasons:
- Polymers cannot be purified, so quality of input waste stream is critical.
- Polymers need to be cleaned thoroughly, and then sorted very accurately into different polymer types – including segregating by colour.
- Polymer properties depend not only on ‘chemical formula’ but also on chain length and configuration, so polymer from different sources may have very different properties.
- Polymers contain a range of additives (e.g. to improve processing, surface modifiers etc) which may compromise quality of recycled material.
- Polymers tend to decompose on heating and can be degraded by processing.
But there are other reasons why polymer recycling is often not favoured:
Economic:
- Polymer quality often low, so recycling usually means downcycling: applications are limited, so re-sale value low
- Oil prices still comparatively low, so virgin polymer prices low (often not much more expensive than recycled polymer)
- The recycling business has slender profit margins: polymer collection and processing are expensive.
Social:
- Worries about safety of recycled polymers – e.g. dioxins, additives
Eco-impact: Most important factor is whether polymers can substitute for virgin polymers so potentially saving virgin polymer production. Improves as supercleaning technologies allow polymers to be recycled to food-grade applications (particularly PET, HDPE), and legislation is relaxed to permit this.
