Nonwoven mats from hemp and polypropylene fibers in various proportions are produced and hot pressed to make composite material. The effect of hemp fiber content and anisotropy in the nonwoven mats resulting from the carding technology are examined on the basis of the three-point bending, tensile, and impact properties of the resultant composite materials. Because of the hydrophilic nature and poor dimensional stability of cellulosic fibers due to swelling, the effect of water sorption on mechanical performances is also investigated. Optimal mechanical properties are achieved in composites made from 40 to 50% of hemp fiber by weight. As expected, better mechanical properties are found in the specimens cut from the composite sheets parallel to the direction of carding. A strong decrease in three-point bending properties is noticed after immersing the composite samples in distilled water for 19 days, while the impact strength increased. Double carding of raw materials results in a decreased anisotropy in the composite material.

Rapid prototyping (RP) is a widely used process in the industry to shorten development time.Another advantage of this technology is the ability to create conformal cooling systems, thus not only cooling time and cycle time can be shortened, but also shrinkage, thus warpage can be decreased. The main disadvantage of Rapid prototyping materials is their low thermal conductivity, which strongly influences cooling properties and warpage.The research based on a special developed injection mold for novel rapid prototyping based mold inserts with cooling systems. A method has been introduced to determine the most important thermal parameters for injection molding simulations using rapid tools. Those parameters, which can be measured such as the specific heat and thermal conductivity of the mold materials, are directly implemented into the software. The heat transfer coefficient between the polymer melt and the rapid tool insert surface cannot be measured in a reasonable way, thus simulation software was used to determine that based on indirect calculation 2 derived from real measurements. In the paper, the method was proved with Fused Deposition Modeling (FDM) and Polyjet mold inserts.

Abstract:The most time-consuming phase of the injection molding cycle is cooling. Cooling efficiency can be enhanced with the application of conformal cooling systems or high thermal conductivity copper molds. The conformal cooling channels are placed along the geometry of the injection-molded product, and thus they can extract more heat and heat removal is more uniform than in the case of conventional cooling systems. In the case of copper mold inserts, cooling channels are made by drilling and heat removal is facilitated by the high thermal conductivity coefficient of copper, which is several times that of steel. Designing optimal cooling systems is a complex process; a proper design requires injection molding simulations, but the accuracy of calculations depends on how precise the input parameters and boundary conditions are. In this study, three cooling circuit designs and three mold materials (Ampcoloy 940, 1.2311 (P20) steel, and MS1 steel) were used and compared using numerical methods. The effect of different mold designs and materials on cooling efficiency were examined using calculated and measured results. The simulation model was adjusted to the measurement results by considering the joint gap between the mold inserts.

Summary: Nonwoven mats from hemp and polypropylene fibres in various proportions were produced and hot pressed to make composite material. The effect of hemp fibre content and anisotropy in nonwoven mats resulting from the carding technology were examined on the basis of the three‐point bending, tensile and impact properties of the resultant composite materials. Because of the hydrophilic nature and poor dimensional stability of cellulosic fibres due to swelling, the effect of water sorption on mechanical performances was also investigated. Optimal mechanical properties were achieved in composites made from 40–50% of hemp fibre by weight. As it was expected, better mechanical properties were found in the specimens cut from the composite sheets parallel to the direction of carding. A strong decrease in three point bending properties was noticed after immersing the composite samples in distilled water for 19 days, while the impact strength increased. Double carding of raw materials resulted in a decreased anisotropy in composite material.

No abstract