3. Analysis of Mechanical Properties of Injection-Molded Plastics
Injection molding is a versatile process for producing plastic parts with high dimensional accuracy and large quantities. The injection molded plastic material has a variety of mechanical properties that must be evaluated to ensure that the end product satisfies the design requirements. This article describes the mechanical properties both before and after injection molding.
A. Tensile Strength
Tensile strength refers to the maximum stress a material can withstand when pulled apart axially along its length. It is a measure of the material’s ultimate strength in a tension test. Compare to other properties, like impact strength and hardness, tensile strength is an important mechanical property of plastic materials. Generally, the higher the tensile strength of a material is, the higher its resistance to stretching, pulling and other forms of stress.
B. Impact Strength
Impact strength is a measure of a material’s ability to absorb energy when it is subjected to an impact force. The impact strength of an injection molded plastic is affected by factors such as compound formulations and injection molding process conditions. Impact strength of a material can also be affected by its hardness and threshold temperature. Higher impact strength generally results in a better performance in applications such as automotive components and other products that require impact resistant materials.
C. Flexural Modulus
Flexural modulus of a material is a measure of stiffness under flexing, bending or buckling. It is an important parameter for engineering applications, such as structural components and support frames for machinery. The flexural modulus of injection molded plastics is affected by a variety of factors, including, but not limited to, resin type, wall thickness, part geometry and molded features, cycle time, and cooling rates. The flexural modulus of injection molded plastics varies significantly among different resin types, with higher modulus values generally producing materials that are more rigid and better-suited to applications that require greater stiffness.
D. Hardness
Hardness is a measure of a material’s resistance to plastic deformation, usually through indentation. The hardness of an injection molded plastic is affected by a wide variety of factors, including but not limited to mold geometry, wall thickness, cycle time, and cooling rates. A material’s hardness can be increased with higher mold temperatures, longer cooling times, and greater pressure during injection molding. Harder materials generally have better wear resistance, higher strength and stiffness, and greater stability in heat, cold, and humidity.
E. Summary
Injection molded plastics offer unique mechanical properties that must be evaluated in order to ensure that the end product is suitable for its intended use. Tensile strength and impact strength are important parameters for many applications, while flexural modulus is useful for assessing the stiffness of materials. Hardness is a useful parameter for measuring a material’s overall resistance to plastic deformation. Each of these properties must be evaluated in order to determine the optimal formulation for a particular application.
