According to CECIMO (1), Sustainable Manufacturing is when engineers use or create processes that are economical for the environment whilst not producing any hazards that can affect the surrounding environment as well as the employees/employers. Manufacturing is a process that affects the environment as we use raw materials such as metals that have an impact as we use a lot of energy to produce and use these materials. The processes for the raw material can produce emissions that affect the environment and introduce the problem that there is only a finite amount of material that can be used and will eventually all be used up. Another problem is that producing other materials such as polymers involves linking hydrocarbons which end up putting harmful emissions into the atmosphere therefore continuing to produce polymers could have potential harmful impacts on the environment in time to come. Overall engineers are currently trying to figure out methods on processes that are capable of being sustainable so that way we don’t harm the environment or use up all of our raw materials.
Standards have now even put in place such as British Standard 8887-220:2010 (Design for Manufacture, Assembly, Disassembly, and End of Life Processing (MADE)) that are designed to show how to be most efficient during the full process of design to manufacture whilst being sustainable. This is capable of ensuring engineers can produce a product whilst being able to remain cautious of the environmental hazards that could potentially occur.
Throughout this report, I will use case studies to analyse the effect of sustainable manufacture including its advantages /limitations and produce an evaluation of a full life cycle of the entire process with the use of appropriate standards such as BS 8887-220:2010 (which was previously mentioned), ASTM E2987/E2987M – 16 (Standard Terminology for Sustainable Manufacturing), and ASTM E2986 – 15 (Standard Guide for Evaluation Aspects of Sustainability of Manufacturing Processes). Furthermore I need to identify the key factors of the case studies and justify why they are appropriate, thus making me able to make a conclusion on what are the key factors that define sustainable manufacture. Finally I will talk about possible future methods that could potentially change how we create new products, as well as how they run efficiently.
Case Study 1
Sustainable Manufacturing of Gears
The Problems
Gears are important to mechanical engineering due to a majority of mechanical systems having to use gears meaning that they are mass-produced all the time for new products or maintenance. (2) Machining (Milling, shaping), forming (stamping, extrusion), and additive processes (die casting, powder metallurgy) are used to create gears. They can even be heat treated (hardened, annealed, tempering) in order to improve the properties of the material that the gear is made from in order to ensure that it is less likely to wear out. All of these processes will require energy, especially if gears are being mass-produced at such a high rate. Obstacles occur during the process of constructing the gears, one example is when metal is being cut for the gears, the excess metal and cooling agent become difficult to handle and dispose of. The metal would be difficult to recycle as it requires a lot of energy to reform it but the cooling agent is more dangerous to the environment as it could potentially contaminate the ground. Another example is that pumping the cooling agent on the metal whilst it’s being machined does consume more power than other systems meaning energy could be easily wasted. The finishing processes such as heat treatment, powder metallurgy, and trimming does consume lots of energy as well due to there being maintenance performed on it regularly making it more challenging to recycle, the situation is that gears have to made to a good standard therefore lots of finishing processes must be used in order to achieve this quality therefore showing that large amounts of energy is used up to produce gears of a high quality. Furthermore if these processes are being used constantly, the tool bits are going to be worn out quickly therefore more has to be produced in order to replace it or it has to be taken to maintenance that would then repair it, both of these methods use up a lot of energy as well.
Solutions
One strategy that was implemented was to use an environmentally friendly cooling agent that couldn’t potentially endanger the environment, make it less likely for workers to injure themselves on wet excess metal, and overall would mean less waste disposal due to the fact that it would also be used to a minimum to ensure that coolant wouldn’t be used negating the need for more coolant/ energy to be produced.
The second scheme was to use advanced manufacturing processes for the gears, the process used was called gear rolling, and this process was flat rolling the gear at a cold temperature (the temperature is when the metal is below its recrystallization temperature), that move in opposite directions and then rolling dies make the teeth using compressive forces. This would consequently increase its compressive strength thus allowing for finishing processes such as heat treatment to not be used allowing for energy to be saved, the process is more sustainable due to it removing the need for forming and additive processes to be used, another factor is that tool bits are used less frequently meaning they do not need to be repaired/ replaced as frequently. This process gives the added benefit of improved performance meaning that they are less likely to wear once produced therefore this reduces the amount of gears needed to be made as they last longer in machines because they will not need to be maintained as regularly.
A machining method that was introduced to reduce the amount of energy used to pump coolant as well as using multiple machining methods, that process is Wire Electric Discharge Machining and the process is done by using a wire that feeds through the gears and cuts the material so accurately that it makes processes such as milling and extrusion unneeded due to it being so precise. Instead of coolant being pumped into the system, deionised water is used as a dielectric to protect the metal from being damaged overall being an efficient process that is very economical. Since it is a process that can be reused easily, the process can make the gears on a mass scale whilst giving it a nice surface finish which helps reduce the overall amount of methods required to give the gears the quality required for it to be sold.
Finally, the hob tool that is used in dry hobbing (the process that is responsible for gear cutting and creating the teeth) undergoes surface treatment in the form of coating in order to extend its use. The hob tool is coated in a Titanium doped Aluminium-Chromium-Nitrate coating. This improves the tool tremendously as it will not wear out easily making it last a long time before being replaced. Despite being more expensive, the hob tool (5) performs better as it can be recoated if it begins to wear making it cheaper than replacing the tool itself. The tool then becomes more reliable to use as the coating can cut material at a low rpm making it efficient as other hob tools that does not undergo this treatment will break quicker. Hob tools that are coated are sustainable because although it takes energy to coat it, more energy and material is used to produce new hob tools.
Case Study 2
Sustainable Methods for Injection Moulding
The Problem
(5) Injection moulding is a very common process that is done to help produce polymers such as ABS (Acrylonitrile-Butadiene-Styrene); this process involves granular plastic being fed into a hopper where it travels down the barrel by it being pushed by the screw also heating the plastic causing it to melt and fit into the mould where it cools and forms a new shape, it is then ejected from the mould. (3) Injection Moulding is used widely throughout many industries as it can be used for thermoplastics and thermosetting plastics. However it will require finishing processes to improve the overall quality of the product as shrinkage or warp marks are capable of ruining the surface of the material. This means that more energy is produced for these finishing processes. The process uses energy heat up the barrel and melts the granular plastic therefore showing that the process can be improved to be more sustainable. (6) During the moulding process, different polymers have different melting points meaning that the shrinkage is different for materials and increase the likelihood of warpage. This means that if products are being ruined as they cannot use product that have low quality, they may have to be thrown away wasting material/energy or remoulded which again uses up energy. Finally if the injection pressure is not right for the material to mould, it will mean that production will have to be delayed in order to achieve the pressure needed, making it a waste in energy as well as time.
Solutions
Selecting certain materials is important because when they warp, they warp towards the gate therefore selecting materials with similar properties (melting points) help prevent any possible warpages that could occur.The barrel does not have to be heated to different temperatures meaning that energy does not have to be wasted by having to heat polymers that have a high melting point, another reason energy is conserved is that warpages are less likely to occur as there is less change is the crystalline structure making it difficult to change its shape from the mould. Therefore meaning fewer products need to be thrown away/reused saving energy and fewer materials are wasted. By choosing specific materials with similar properties you are capable of using materials that require a smaller injection pressure thus requiring less energy to reach that pressure. Being able to remove warpages makes some finishing processes for polymers unneeded as material does not have to be removed and surfaces will be within tolerance of its specified dimensions.
(7) The use of lean manufacturing tools helps improve the injection moulding process by reducing the total amount of wastage produced by the injection moulding process by identifying possible defects and then using lean manufacturing techniques to fix the defects, an example of this is using the Kanban Pull System which works by taking all the orders from clients and customers and controlling the amount by ensuring that there aren’t too many customers that have been taken on causing an increase in the production line leading to more emissions being produced and a higher energy demand.