Application of Nylon – 12 in plastic industry Essay

Nylon-12 has a large number of applications in the fields of plastic industry including the preparation of films and also in the automotive industry to prepare oil- and gasoline-resistant tubes. Other applications include odor-free films in food industry, in the electrical field due to low water content, in the textile industry and also in making well-fitting swimwear due to its good dimensional stability. Even though SLS is the preferred RP process due to the strength of the parts produced and the high possibility of performing functions, a number of factors need to be kept in mind to obtain good quality parts. The main areas of concern are usually the material quality and the surface quality.
It is very important to keep in mind the shape and size of the material powder used in the SLS process. It is generally recommended to make use of spherical shaped powder for better re-sults as they are distributed on the bed by a roller or blade system and hence will not be com-pacted again [SAW2014, Pg.1]. Determination of bulk and tap density is a good indication of the powder density and also the flowability with the help of the "Hausner ratio" (HR).
HR < 1.25 means free flowing powder behaviour and a HR > 1.4 means fluidization problems (cohesive properties). Here the loose bulk density _bulk indicates the density of the particles when the powder is just poured onto the bed and allowed to settle by itself while the tap bulk density _tap is the density of the powder when they are closely packed together by tapping or in this case the roller. [BOJY2005, Pg. 55]. It is very common nowadays to use potato shaped powder produced by Precipitation. Cryogenic milled powders show reduced flowability hence leading to reduced powder density and thus poor properties of the SLS part. Another factor that has to be taken into consideration is Particle size distribution (PSD). Here the optimum size of the powder preferred is between 20mum and 80mum. When the PSD of small particles is very high then it leads to adhesion of the powder leading to reduction in free flowing powder behavior and prevention of SLS processing. [SAW2014, Pg.4]
One of the common effects encountered during any RP technique is stairstepping. As it is a layer-wise manufacturing technique, there is always the need to find the optimum thickness of each layer sintered else leading to surface roughness of the part. If the thickness of each layer is more, then there is high risk of stairstepping effect and when the thickness of each layer is too less, then the manufacturing process time would be very high. The optimum layer thickness for PA12 is 150mum [VeWe2004, Pg. 231]. It is important to find the optimum building direction of the part and the material to avoid stairstepping effect. There are other factors also that affect the surface quality like focus diameter and part size. It is important to be aware of the restrictions involved in the SLS process.