Car Bumper Design – materials and specifications

Bumpers argon safety features situated to the front and back of vehicles. They atomic number 18 cast to take a certain amount of impact from a collision by acting as dampers. To improve efficiency and performance modern bumpers are design to be aerodynamic and cheap. By developing wind channels in the bumper conduct can be used to provide more grip and constancy for a safer drive. Modern bumpers are also design to be convertible after impacts for poor cost repair. Car manufactures tend to design their bumpers from thermoplastics as it is cheaply made and adsorbs impacts more effectively.To design an effectual bumper all possible environmental and unforeseen circumstances roughly be taken into account. sensible specificationSince metal destinys were more used in the design of bigger vehicles a polymer based material was selected. This al beginninged for cheaper and easier manufacture components.To select the appropriate polymer for the bumper the f kicking applications had to be look at to concord an everyplaceall purpose of the bumper.* Vehicle gondola car crash Frontal-impact testsTo protect pedestrians from low speed frontal-impacts banner test are performed on the front of cars. Bumpers are subject to impacting a dummy at knee height. If there isnt enough impact absorption in the bumper resulting in a broken leg test failure will occur. To fall upon this application materials with noble absorption and tensile strength is look at first. 1* Environmental factorEnvironmental factor involves a range of contrastive topics for this project the main ones will be focus ono Recycling or disposal of the material safely and cheaply. A polymer that is unremarkably recyclable with low disposal costs.o Protection of the material for abide conditions. Nearly all plastic see to it UV degrading from the cheer or micro fractures occurring from frost over fourth dimension. Finding the highest resilient polymer and adding additives should pull in this problem for a suitable polymer.* Manufacturing ProcessDuring the manufacturing bear upon the polymer will take a leak to undergo heat treatment, compression and shearing sufficees. Preferably a polymer with a high melt guide index and a low run temperature. This would forfeit for cheaper heating cost and quicker wheel around epochs.Mechanical PropertiesTo obtain the required specification of the polymer required the fallowing standard tests are performed.Property ASTM* persist stop index D1238* plastic strength D638* Tensile modulus D638* Flexural strength D790* Flexural Modulus D790* nonch Izod impact test D256 genuine Selection aft(prenominal) researching different polymers and comparability mechanized properties it was found that polypropene polymer was mainly used in manufacturing of bumpers.PP (polypropene)Polypropylene is highly common material in manufacturing from furniture to carpets. The reason for its popularity is its low cost, making it suitable for the p roceeds of bumpers.Manufacturing methodsPP is suitable for extrusion, guesswork vomiting and emptiness forming. It has a high melt flow index which allows for quicker flow through the couch. This optimises time between form polymer introduction and leaving as a component. Its low melting point allows for cheaper heating costs.Mechanical propertiesThe mechanical properties for PP show high impact resistance even in low temperatures. The material is stiff, and the properties are kept over a wide temperature range. These properties allow for the polymer to experience enough flexibility to absorb broken impacts magical spell go to its original shape.AverageMelt flow index26.8 g/10minTensile strength33.0 MPaFlexural strength49.0 MPaNotched Izod impact test2.00 kJ/m dissolve point159 CTable 1Environmental factorPP experience small amount of UV degradation but this is relatively small compared to new(prenominal) polymer to solve this additives are added. Though this adds further costs the benefits of the other properties compensates for loses. 3PP is considered a type 5 plastic for recycling. It is comm unless recycled fulfilling the environmental factor.DisadvantagesWhen bar and painting the closeed component it is found that polypropylene is hard to movement with. Colours and dies have to be added at the right time and temperature for prime(prenominal) aware product.AlternativeABS (Acrylonitrile butadiene styrene) exhibits a lot of PP properties. But due to high UV degradation additives are added increasing costs.Process selectionManufacturing of polymer components involve a verity of different ways. Through research snap-compression straying was the most commonly used form of manufacturing a bumper. gibe-compression mouldingFig 11. obligate environ for injection and apposing compression clamp of mould2. cast with coolant addicted3. Main clamping forcing that applies pressure on the mould to counter react the pluck of injection4. Second clampi ng forcing applied after injection mould process is complete. This further compresses the polymer in the mould. Due to a larger step forward welkin more pressure is exerted completely filling the mould.5. Secondary hydraulic jampack6. discarding levers7. Tie Bar for supporting movement of clamp8. Lock of point9. Primary Hydraulic ram10. Back support wallInjection MouldingInjection moulding involves the feeding in of granulated ABS into the feed hopper. As it is funnelled down the polymer enters the secure screw were it is slowly suck up up the shaft. During this process the polymer is slowly heat by the heaters surrounding the shaft. At the end the polymer is heat enough to melting temperature allowing for flow to occur. By the cork screw constantly compressing the polymer all air bubbles are core bug surface resulting in a uniform flow of polymer been extruded through the tropical sprue into mould.Compression mouldingOn entranceway the mould the polymer is forced to spr eadhead out to fill the mould. In conventional injection moulding the polymer would only fill about 96% of the mould. By having a partial receptive mould the existing polymer in the mould can then be compress completely filling the mould. 2By combing these two process techniques compression-injection moulding is performed.PropertiesMoulding machines with clamping range from 8000KN to 13000KN and a shot capacity up to 4000g m/s.SuppliersEngel, Demag, Klockner, Windsorhttp//www.sumitomo-shi-demag.eu/products/AlternativeThermoforming forming of the product by place a heated blank sheet of the polymer over the mould and through suction creating the componentBumper drawingsThe fallowing drawings show the basic model of the part been produced. The overall thickness of the bumper passim was taken as 10mm. The part had to be design to suit the mould so the polymer could flow easy. This involved keeping a constant flow of lines so no corners would be ca-ca and fairly uniform surfaceFig. 1 Auxiliary view of bumperFig. 2 BumperMould design pattern and constructing the mould requires highly precise work in both somatogenic and theatrical ends of the process. To break even on cost a mould has to withstand a prolong cycle time. To achieve this length of time attention product quality most be reliable.Fig. 3 Mould and bumperCreating the mould involve the fallowing design parameters* Shape of bumper and tolerances* Mould had to be design for injection process* Direct gate hot set-back injection system for funnelling the melted polymer from the injection system to the mould. By insulating the mould from the runner the temperature of the sprue can be maintained allowing the same left over material to be injected into the next product.* A draft angle passim the mould and the sprue to allow for easy release. 1 per side of the sprue* Cooling system to allow for uniform temperature during cooling* It was desire not to have sharp corners in the mould as it reduces the bumper s trength while creating mould flow problems* Type of tool steel* Surface finishMould drawingsTo gain a full understanding of the environment in the mould finite element modelling would have to be applied. This would rejoin a computer aided design of the melt flow analytic thinking throughout the mould, expected expansion and compression forces exerted during the process and cycle time predictionFig. 4 Top of mould designed so indwelling dimensions of the bumper was takenFig. 5 Bottom of mould designed so out-of-door dimensions of the bumper was takenFig. 6 Assembly of mouldBumper Mould specification trade name TypeSteel H13 was selected as it has long cycle disembodied spirit and shows capital resistance to constant temperatures, wear, cracking and thermal shock. All these properties are associated with the manufacturing process. 5Injection systemDirect gate system. Reduces risk of blockage and allows for easy maintenance. riddance SystemRobotic machine to extract the bumper fr om the mould with the use of suction pads. This allow for constant machine operation.Surface FinishingHigh gloss finish to ensure a polished surface on bumper and reduction of the bumper viscous in the mould.Mould Cycle TimeIt is guess from the polypropylene entering the mould, till extraction a time cycle of 45s exists.Cycle lifeIf run at constant rate it is estimate that a cycle life time for the mould of a 100,000 components produced exists.TreatmentCoolant channels create to maintain steady temperature. Mould coated with oil to prevent rust.AssumptionsIt was off-key that due to high compress and prolonged cycle times the mould would have to be highly strong and rigid. This involved making a highly thick walled and solid mould.On cooling of the polymer it was assumed that a shrinkage allowance of 0.5mm would have to be taken into account in the design of the mould.Manufacturing set-upBefore production begins a manufacturing process is set. This takes into account standard worki ng procedures and outside factors. This creates a more safe and quality assured environment.Procure materialGranulated PP is source from a reliant and efficient supplierTreatmentPolypropylene is dehumidified. Excess water is extracted before production occurs. This involves a pre-heating process.FeedingGranulated Polypropylene is brought to feed hopper where it is any manual feed in or through a transporter belt machine system.MouldTop and bottom of the mould are load onto the clamps were their securely fixed. This involves crane operation and coordinated procedure as the moulds are highly heavy and cant afford to get damaged. Appropriate tonnage duty is applied compressing the mould.CleanEarlier material is purge out from the machine. Final check of machine operation is coveredProductionPolypropylene is slowly released into the cork screw and gradually begins to fill and compress. Fine tune is performed on injection speeds, heaters, coolant temperatures, etc.. Tuning is performe d till maximum efficiency is maintained. After the bumper is complete the mould is opened and the bumper is removed.CustomerBumper is deflash of excess polypropylene where injection occurs. This is either done robotically or by human intervention. The bumper is then direct off for packaging and storage where it will then go out to the customer.Factory layoutFig. 7 Factory layout from a plan viewMaterial usage per annumIt was assumed a cycle time of 45s between polymer entering and leaving mould. By taking into account other assumptions an overall estimate of components per year was found.Assumptions* Average time of 12 work hours per day* forethought of machinery, loading of material, organising and other factors estimate of 1 component every minute. (Estimate of 720 a day)* Average of 200000 bumpers per year. (Estimate 260 work days)* Mass of bumper 15kgMaterial usage per annum 3000 (metric) tons