Case study: Automotive headlight lens
Over the past three decades, plastics have made steadily increasing progress in automotive applications and much of this success is due to ability to reduce weight and therefore overall production cost. However the aforementioned reasons are not the only ones since the versatility of the material have created a wide range of applications where the polymer family can be used. In particular, automobile manufactures have focused on lighting vehicle improvements as a way to improve vehicle safety as a great percentage of traffic accidents occur during poorly visibility conditions. The following paper summarizes the case of redesigning the lens of an automobile headlamp, which function is to protect the bulb and reflector and focuses the light where required. Objective
To contact a research and select appropriate material that meet specific requirements for manufacturing automotive headlight lenses. Requirements
Table 1 summarizes the formulation of the constraints that a material must meet in order to fulfill the requirements of the design. Applying these by using a combination of Limit and Graph stage in CES EduPack 2012 leads to logical results. Table 1. Translation of the redesigned automotive headlight lens case. Function
| Automotive night vision systems to protects bulb and reflector and focus light
| Transparent with optical quality
| Easily Injection-molded
| Very good resistance to fresh and salt water
| Very good resistance to UV light
| Good abrasion resistance
| Minimize cost
| Choice of material
The following figures illustrate the material selections resulting from the Limit stage (Fig.1a-d ) according to the required constraints; and Graph stage (Fig.2) by using Edu Level 2: Materials with Durability properties.
Fig.1a Optical property constraint
Fig.1b Processability property constraint
Fig.1c Aqueous durability property constraint
Fig.1d UV resistance property constraint
Fig.2 Graph stage: Price vs Hardness
Two material groups have resulting from the process namely glass and polymers presented in the following figure (Fig.3), ranked by price.
Fig.3 Ranking of resulting material in terms of cost
It can be clearly seen from Fig.2 that the cheapest and hardest material that meets all the constraints is Soda-lime glass, which was used in the past for headlight lenses. In the case that a polymer is selected Polymethyl methacrylate (PMMA) is suggested; used already in car tail lights and has approximately twice the price of Soda-lime glass (Fig.3). It should be note that Polycarbonate (PC), which is also widely used for manufacturing of headlight lances, is not included in the resulting selections due to the fact that the UV radiation resistance property is ranked as ‘‘Fair’’ in CES EduPack 2012 database. Discussion
Plastic optics offer several benefits over glass elements. In applications, where optics are involved, the possibility of hazardous breakage of glass is a safety issue that can be avoided by using a plastic element. Therefore the choice of material for the redesign of the automotive headlight lens is PMMA. Polymers are truly transparent only if they are completely amorphous, that is non-crystalline structure. The shape of PMMA molecules ensures such amorphous structure and its stability further provides good weathering resistance (CES EduPack 2012). PMMA is the hardest, clearest and most scratch resistance plastic. Its refractive index of 1.49 - 1.56 matches that of the most commonly used optical glass (Soda-lime glass 1.5 - 1.52). It has low shrinkage and is very resistant to UV degradation. Its main disadvantage however, is the high moisture absorption and low continuous service temperature ranging from 41.9 to 56.9 C0 compared to Soda-lime glass of 170-400 C0 (CES EduPack 2012, UK Optical Plastics Ltd). Glasses are...
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