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Identifying And Describing The Deformation Process Engineering Essay

In the extrusion process a billet (usually rounded) is enforced through a die, in a behavior comparable to squeezing toothpaste from a tube. Almost any solid or hollow cross-section may be produced by extrusion, which can create essentially semi finished parts like shown above. The reason for this is because the die geometry remains the same throughout the operation, extruded products have a constant cross-section.

Depending on the ductility of the substance, extrusion may be carried out at room or at elevated temperature the reason or this is because a chamber is involved, each billet is extruded independently, and therefore extrusion is a batch or semi continuous process.

Extruded products can be cut into preferred lengths, which then become separate parts such as brackets, gears and coat hangers and shown above in the diagram. Frequently extruded materials are aluminum copper, steel magnesium and lead.

2: The diagram that is shown below uses forging moulding:

Forging is the shaping of metal using restricted compressive forces. Cold forging is done at room temperature or near room temperature. Hot forging is done at a high temperature, which makes metal easier to form and less likely to fracture. Warm forging is done at intermediate temperature between room temperature and hot forging temperatures. Forged parts can range in weight from less than a kilogram to 170 metric tons. Forged parts usually require further processing to achieve a finished part. Typical forged products are shown above in the diagram. There are:

Bolts

Rivets

Connecting rods

Shafts for turbines

Hand tools and

Structural components for machinery.

3:The diagram that is shown below uses hot rolling.

A slab or billet is passed or deformed among a set of work rolls and the temperature of the metal is usually above its recrystallization temperature, as opposite to cold rolling, which takes place under this temperature. Hot rolling permits large deformations of the metal to be achieved with a low number of rolling cycles. As the rolling process breaks up the grains, they recrystallize maintaining an equiaxed formation and preventing the metal from hardening. Hot rolled material characteristically does not need annealing and the high temperature will prevent residual stress from accumulating in the material ensuing better dimensional stability than cold worked materials.

Task2: Write a report on your presentation (150 words). Presentation should be attached with the report.

My presentation was on hot rolling. It was a great experience as it taught me how to stand in front of audience and present some work. It was challenging; the reason for this is because I had to make the class understand what hot rolling is and what it is used for. I had to talk about several things for example the temperatures that take place during hot rolling process. I had several diagram, videos to help me get the topic across to the audience. The presentation was quite useful; the reason or this is because some of the class students didn’t know what hot rolling was. In general the time that was taken during the presentation wasn’t wasted as several students understood the topic in dept. the presentation also helped me in several different ways for example it boosted my confidence to face the audience and it also improved my communication skills.

(P5): Identify and describe the deformation processes used to manufacture a polymer based component.

Task1: Explain brief the following processes with advantages and disadvantages.

(1):Vacuum forming: is a simplified version of thermoforming, whereby a sheet of plastic is heated to a forming temperature, extended onto or into a single-surface mold, and detained against the mold by applying vacuum among the mold surface and the sheet. The vacuum forming process can be used to make most manufactured goods packaging, speaker casings and even car dashboards.

Advantages

Disadvantages

Vacuum forming uses low pressures so only relatively low cost equipment / components are required.

Low pressures mean that moulds can be made of inexpensive materials and in a short time.

Prototypes, small and medium quantity runs become cost-effective.

Material allocation is tricky to manage.

Cannot manufacture as many parts.

Extremely comprehensive parts are difficult to achieve.

The vacuum forming process starts with a flat plastic sheet and there may be a need for a second process to trim the moulded end product. This means more expense to obtain additional equipment.

Advantages

Disadvantages

excellent when managing polymers which are heat sensitive, as it causes thermal degradation

Can combine polymers that contain high amounts of hard additives that don't get blended or fluxed.

Easy to utilize.

To run the process is expensive to perform.

The process doesn’t meet the measurement. (2): Calendaring: Process of smoothing and compressing a material (notably paper) during production by passing a single continuous sheet through a number of pairs of heated rolls. The rolls in combination are called calendars. Calendar rolls are constructed of steel with a hardened surface, or steel covered with fibres.

(3): Stiffened mouldings. Processes that have properties that are extra improved than standard procedure and this makes a stronger substance. Stiffened moulding produces three dimensional sector of polymerized liquid.

Advantages

Disadvantages

Material becomes stronger

Cheap to run

reduces deformation

misuse of materials

time consuming

Acquires expert staff.

Task 2: Explain in details the polymers and types of polymers.

Thermoplastic: Thermoplastic polymers are normally produced in one step and then made into products in a

Subsequent process. They become soft and formable when heated. The polymer melt can be formed or shaped when in this softened state. When cooled significantly below their softening point they again become rigid and usable as a formed article. This type of polymer can be readily recycled because each time it is reheated it can again be reshaped or formed into a new article.

Polycarbonate: are a particular group of thermoplastic polymers. They are effortlessly worked, moulded, and thermoformed; as such, these plastics are extremely generally used in the current chemical industry. Their attractive features such as

temperature resistance,

impact resistance and ocular properties)

Place them between commodity plastics and engineering plastics. Polycarbonates do not have a unique plastic identification code 

Acrylic: are groups of thermoplastic or thermosetting plastic which are derived from

acrylic acid,

Methacrylic acid or related compounds.

Polymethyl acrylate is an acrylic resin which is used in a shape of lacquer.

Another acrylic resin is

Polymethyl methacrylate which is used to make solid plastics.

Polyvinyl chloride: is a thermoplastic polymer. It is a vinyl polymer constructed of repeating vinyl (ethenyls) having one of their hydrogens replaced with a chloride group.

ABS: is a general thermoplastic used to create:

lights,

rigid,

molded products such as pipes, golf club heads (used for its goodshock absorbance),

automotive body parts,

wheel covers,

protective head gear, and

Toys.

It is a copolymer made by polymerizing styrene and acrylonitrile in the presence of polybutadiene. 

Thermoplastic sheet: The formed sheets can be formed of a thermoplastic material, such as flat sheets of reinforced thermoplastic, which can be lightweight, strong, and perform well in flammability, smoke, and toxicity tests. The apparatus includes a heater for heating the sheet to a processing temperature and a structure for configuring the sheet to a desired shape using one or more rollers, shapers.

Task3: Explain in details use of additives in deformation process for polymers:

Plasticisers: Plasticisers are a rather special type of additive. Without plasticisers for example, PVC would have been too brittle and fragile to be able to conquer the huge market it has taken over today; without plasticisers most injection molding compounds would be entirely unsuitable for that purpose, and without plasticisers, some blends of rubber simply could not be produced. Not only do plasticisers make plastics extensible, plastic, elastic and flexible at low temperatures, in many cases it is only possible to process polymer products on a commercial basis by incorporating a plasticiser. 

Antistants: since plastics are electrical insulators, they tend to hold any charge which builds up on then accidently. During processing this can cause annoying clinging and even dangerous sparking. During use it can accumulation of dust, to reduce such static build up, antistatic agents are often added. Most common types are amines, quaternary ammonium compounds and polyoxyethylene.

Lubricant: may be added to polymers to reduce friction during their subsequent processing into useful products and to prevent parts from sticking to molds. Typical lubricants are linseed oil, mineral oil and waxes. Lubricants are also important in preventing thin polymer films from sticking to each other.

Heat stabilisers: To prevent decomposition of the polymer during processing. Processing usually results in temperatures well above 180 degrees Celsius, this without the addition of heat stabilisers would result in the plastic material literally falling apart.

(P8): Identify and explain the health and safety issues that relate to each of the primary forming process considered:

Direct extrusion: When dealing with extrusion processes it is always important to wear safety equipment, such as overalls, gloves and eye protection. This is because in the extrusion process, this is because there are common injuries that can be caused during the process for example:

Fatalities

Amputations

Avulsions

Fractures

Burns

Cuts and bruises

Sprains and strains

Electric shock

It is very important that hands and unguarded areas of one’s body is as far as possible from the hot objects to make sure no burns are obtained. Also when the material is pressed through the die, it is important to stay away from the process; so that no loose pieces of clothing or other materials are pushed through the die other than the work piece. It is also important to Recognize the hazards in the job you are doing, understand the requirements for guarding machines, Implement guarding solutions. It is also important to know where the emergency button is and also what it controls and when to use it. It is also important to understand all the warnings and hazards sign.

Upset forging: Upset forging mainly increases the width of the work piece by compressing its length. During the process is it important to be aware of all the hazards around you and also that the operator is aware of all the safety procedures as this process can cause several health and safety hazards. Upset forging is generally completed in particular high speed machines called crank presses; these machines can cause several injuries as you are dealing with high speed materials that are being operated.

If the speed of the crank press is too high, the work piece can be over pushed or turn out to be deformed; which will give increase to un-wanted products; in addition to that if the speed is to high the work piece can crack and fly into someone’s eyes and this can causes serious problem and that is why is it important to wear protective clothing during tasks including eye protection.

Upset forging can also be done in a vertical crank press or a hydraulic press. It is important that one stands in a safe position from the machine when the work piece is being compressed the reason for this is because fingers or loose clothing or items surrounding the hydraulic press might possibly get trapped causing serious danger.

Vacuum forming: When dealing with vacuum forming its means you’re dealing with high temperatures where there are serious hazards and you need to take extra care of yourself and people around by wearing safety equipment, such as overalls, gloves, mouth guard and eye protection. The reason for this is because when vacuum forming; you have to first heat treat the work piece to a certain temperature before it is vacuumed. When heating plastic, strong vapors will be released which can be inhaled; which can be harmful. Also it is important to wear gloves when managing the heated plastic which may come in contact with your skin, causing burns, leaving polymer remains left on your skin. Also when hardening the material, a combination of resin and fibres are added to the work piece. The combination of resin and fibres can be really risky if it comes in contact with someone’s skin, as it can become firm and can cause many skin problems.

(M2): Compare and contrast the different deformation processes used to manufacture products from metals and polymers:

Below I am going to compare the two different deformation processes hot rolling and cold rolling. I am always going to talk about the advantages of both processes.

The primary objectives of the flat rolling process are to reduce the cross-section of the incoming material while improving its properties and to obtain the desired section at the exit from the rolls. The process can be carried out hot, warm, or cold, depending on the application and the material involved. The rolled products are flat plates and sheets. Rolling of blooms, slabs, billets, and plates is usually done at temperatures above the recrystallization temperature (hot rolling). Sheet and strip often are rolled cold in order to maintain close thickness tolerances.

Basically flat rolling consists of passing metal between two rolls that revolve in opposite directions, the space between the rolls being somewhat less than the thickness of the entering metal. Because the rolls rotate with a surface velocity exceeding the speed of the incoming metal, friction along the contact interface acts to propel the metal forward. The metal is squeezed and elongated and usually changed in cross section. The amount of deformation that can be achieved in a single pass between a given pair of rolls depend on the friction conditions along the interface. If too much is demanded, the rolls will simply skid over stationery metal. Too little deformation per pass results in excessive cost.

Rolling involves high complexity of metal flow during the process. From this point of view, rolling can be divided into the following categories:

Uniform reduction in thickness with no change in width: Here, the deformation is in plane strain, that is, in the directions of rolling and sheet thickness. This type occurs in rolling of strip, sheet, or foil.

Uniform reduction in thickness with an increase in width: Here, the material is elongated in the rolling direction, is spread in the width direction, and is compressed uniformly in the thickness direction. This type occurs in the rolling of blooms, slabs, and thick plates.

Moderately non-uniform reduction in cross section: Here, the metal is elongated in the rolling direction, is spread in the width direction, and is reduced non-uniformly in the thickness direction.

Highly non-uniform reduction in cross section: Here, the reduction in the thickness direction is highly non-uniform. A portion of the rolled section is reduced in thickness while other portions may be extruded or increased in thickness. As a result, in the width direction metal flow may be toward the center.

Hot Rolling

The characteristic mark of hot rolling is not a crystallized structure, but the immediate incidence of dislocation spread and softening processes, with or without recrystallization during rolling. The leading mechanism depends on temperature and grain size. In general, the recrystallized structure becomes finer with lower deformation temperature and faster cooling rates and material of superior properties are obtained by controlling the finishing temperature.

Hot rolling offers several advantages:

Flow stresses are low, therefore forces and power requirements are relatively low, and even very large work pieces can be deformed with equipment of reasonable size.

Ductility is high; therefore large deformations can be taken (in excess of 99% reduction).

Multifaceted part shapes can be generated.

Cold Rolling: Cold rolling, in the everyday sense, means rolling at room temperature, although the work of deformation can raise temperatures to 100-200°C. Cold rolling usually follows hot rolling. A material subjected to cold rolling strain hardness considerably. Dislocation density increases, and when a tension test is performed on this strain-hardened material, a higher stress will be needed to initiate and maintain plastic deformation; thus, the yield stress increases. However, the ductility of the material as expressed by total elongation and reduction of area drops because of the higher initial dislocation density. Similarly, strength coefficient rises and strain-hardening exponent drops. Crystals (grains) become elongated in the direction of major deformation.

Cold rolling has several advantages:

In the absence of cooling and corrosion, tighter tolerances and better surface finish can be obtained.

Thinner walls are possible.

The final properties of the work piece can be closely controlled and, if desired, the high strength obtained during cold rolling can be retained or, if high ductility is needed, grain size can be controlled before annealing.

Lubrication is, in general, easier.

Hot and cold Rolling Problems and Defects: The main problem during hot and cold rolling process is the calibration of rollers. This calibration faults may occur in case of used bearings and may affect the thickness of parts. A simple classification is as here below:

Lengthwise Occurring Defects

Change of rollers speed

Material temperature

Roller temperature

Inlet thickness

Material properties

Eccentric and conical rollers

Used bearings

Transversally Occurring Defects

Parallel position of rollers

Surface geometry of rollers

Conclusion:

Hot and cold rolling both have several different advantages and disadvantages for example Flow stresses are low, therefore forces and power requirements are relatively low, and even very large work pieces can be deformed with equipment of reasonable size. Even in cold rolling there are advantages such as: in the absence of cooling and corrosion, tighter tolerances and better surface finish can be obtained. I would say that hot rolling is better then cold rolling the reason for this is because due to the high temperatures in hot rolling it provides you with better accuracy then cold rolling and also it gives you your desirable design. Even though cold rolling is cheaper hot rolling is better as it provides accuracy.

(D1): Evaluate and suggest improvements to primary forming process used in the manufacture of a product.( note: the suggested improvements could relate any aspect of the moulding technique, deformation or shaping/assembly process being applied(e.g. type of method/technique, choice of material, component design, mould design) as relevant to the your choice of component).

Improvements in injection molding are essentially constrained by the physics which determine pressure, flow, and thermal dynamics. While incremental improvements can be made through process optimisation, more substantial gains are possible through new process concepts. New process designs enable critical boundary conditions to be controlled, with performance and productivity improvements beyond the theoretical limits of conventional injection molding. Nearly all injection molding processes can be continuously improved with respect to performance and/or cost.

Continuous improvement in molding technologies are providing molders with increases in productivity and reductions in materials and energy usage. With competition, the processes are commoditized and differentiated along a performance: cost curve in which nearly all producers maintain similar profit margins determined by market forces plus or minus some variation associated with the efficiency of their internal processes. As time progresses, however, the magnitude of potential improvements are reduced as the process performance approaches unknown but real constraints.

Development and initial adoption is slow, followed by rapid growth in which major gains in product quality and cost are realised. For instance, the reciprocating screw was the main method for plasticising in injection molding, and provided significant improvements in melt consistency, product quality, and cycle time reduction. PC-based control systems are similarly augmenting and/or replacing PLC-based control systems, thereby providing improvements in machine response and flexibility.

Eventually, however, these technologies become standardized and commoditized with small or incremental gains in the benefit to cost ratio. Breakthroughs in process, mold, material, and/or machine designs are required to relax the existing set of process constraints, and thereby enable higher levels of performance at lower costs. A stream of innovation has sustained the plastics industry by providing new process capabilities to design and manufacture more complex products at reasonable costs.

In the evaluation of any molding system, it is important to consider the current state of performance compared to the theoretical feasibility. The “efficient frontier” is a term used to imply that one aspect of a design, process, or system cannot be improved without adversely affecting other important aspects. It is rarely possible to continually increase performance and continually decrease costs. Any such gains made from “continuous improvement” are typically achieved by reducing the inefficiency currently in a system.

Awareness of the concept of the efficient frontier can help the decision maker to improve their product by increasing performance or reducing costs. In practice, however, it is not possible to precisely know the boundaries of the efficient frontier and operate at a truly efficient point. This may seem surprising, but it is true for at least three reasons:

indefiniteness of specifications

behavioral uncertainty

relative valuation of multiple objectives.

The performance of conventional molding processes are governed by the physics of pressure, flow, and thermal dynamics, with significant trade-offs required in the design of the part geometry, molding process, and polymeric materials.

For instance, a thin-walled product may require very high injection pressures and a lower viscosity resin. High injection pressure drives the need for a high clamp tonnage, and may also result in reduced part properties and high scrap rates. Lower viscosity resins may also tend to reduce the structural properties of the thin walled, molded product. For these reasons, it is desirable to consider the development of new molding processes that decouple filling, packing, and cooling. Specifically, it is desirable to maintain the temperature of the mold surface above the glass transition temperature of the polymer during the filling.

Such isothermal mould filling would provide two benefits:

First, isothermal filling would prevent the cooling of the polymer melt and development of the solidified layer, thereby enabling longer fill times to be used and decreasing the injection pressure required to fill the mold.

Second, isothermal filling would allow for the equilibration of pressure throughout the cavity after mold filling. The packing stage could then proceed from a uniform state.

To avoid the development of non-uniform stress distribution in packing due to viscous melt flow from the gate to the freeze front, profiled thickness compression of the polymer in the mold cavity is suggested. This approach provides two substantial benefits:

First, shrinkage compensation is accomplished through reduction in the mold thickness. As a result, a uniform pressure is maintained throughout the cavity.

Second, the shrinkage compensation can be maintained longer than would normally be possible in conventional molding, which would result in lower shrinkage and improved aesthetic and structural part properties.

Cost is another thing that can be considered:

The areas of cost savings are:

Reduction in wall thickness

Reduction in cycle time

Reduction in clamp tonnage

Reduction in associated hourly rates

Example1:

For discussion purposes, consider the top cover of a laptop or rear housing of an LCD display shown in Figure 10. This part is approximately 300 mm by 200 mm, center gated with a wall thickness of 1.8 mm, which corresponds to a flow length: wall thickness ratio of 100:1. Molded of a high flow ABS/PC blend with an apparent viscosity of 300 PaSec, and a 1 sec injection time, this part requires an injection pressure of 166 MPa (24,200 psi) and clamp tonnage of 560 mTons. The melt and mold coolant temperature are 280C and 90C, respectively with a cycle time of 13.96 seconds.

The marginal cost of the molded product is driven by material and processing costs. Given a material cost of £2/kg, the material costs would be approximately £0.216 per part. Given an hourly rate of £95/hour for a 560 mTon machine, the processing cost per part is approximately £0.369.

Consider a reduction in wall thickness from 1.8 to 1.4 mm, which would result in a 22% material savings. Such a reduction would normally be impossible per conventional injection molding without adding gates or other major process changes.

Example2:

In injection molding the temperatures are very high and plastics are used. The reason I am considering this is because due to high temperatures it is possible for the plastics to get trapped to the injections moulding. To prevent this from taking place is to use coolant while the process is running

Conclusion:

Plastics injection molding is perceived by many as a mature technology. However, many performance constraints in plastics injection molding still exist that prevent the development and manufacture of higher performance products at lower cost. A primary issue is not whether these performance constraints can be overcome, but rather which performance constraints should be overcome. With respect to control of the melt temperature in plastics injection molding, this paper has provided analytical, experimental, and economic proof of feasibility. This analysis provides convincing argument that control of melt temperature should be overcome and beneficially utilized in many commercial applications.


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