A thermoplastic and injection molding material guide are for engineers who want to make the best possible material choice for a given application based on the examination of loads, stresses, strains and environmental conditions. Every item should be designed, and materials picked correctly if life safety, reliability, or effectiveness are at stake. You can see why an engineer might be hesitant to propose a particular material for someone else’s component if you read this article and see the various aspects involved and how environment and application impact material selection.
Material selection may be a risky business. Material characteristics and internal structure are not well understood at the primary level, which is a significant problem. Second, it is common practice to overlook the need to outline an application’s requirements thoroughly. Even after overcoming the first two challenges, finding precise data on a material’s properties remains challenging. Before seeking injection molding services, you should consider the following:
Standard material data sheet
There is a lot of information on the standard material data sheet based on performance at room temperature. Furthermore, the performance characteristics are connected with catastrophic occurrences not deemed acceptable outcomes for designed plastic items. Materials are often measured in their yield strength and break length elongation; however, yield and break aren’t what plastic components should do when put under strain. Finding the right content for your application necessitates combining data from several sources that are only partially comprehensive.
- Understanding the short-use temperature capacity
Short-term usage temperature is one of the most critical parameters on a product datasheet when going through injection molding. DTUL, or heat deflection temperature, is the standard term for this temperature. The Vicat softening temperature is another relevant metric. The Vicat number is often more significant than the DTUL value because the Vicat point is closer to the polymer’s actual melting or softening point.
Yield and tensile strength
It is essential to consider “creep resistance” if the material is subjected to steady tension; fatigue resistance is more important when the load is intermittent. A material’s long-term behavior under load is difficult to predict because of the intricate interaction between stress, time, and temperature. Again, the data sheet may be able to offer an upper limit in this instance. The yield strength of a pliable material and the tension at the break of a brittle material serve as top limits. A catastrophic failure occurs when any of these two values is exceeded. If the material is subjected to stresses and strains that exceed these limits, it will be rendered unusable in the near term. The next step is to investigate the long-term impacts of temperature changes after using this primary filter.
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Understanding the relationship between stress and temperature
Multiple data points are needed to predict long-term performance at increased temperatures accurately. Thermal and mechanical characteristics of the material determine how much stress may be applied to a given material at a given temperature or for a given amount of time. According to correlations between short-term and long-term performance, thermoplastics’ long-term working stress levels are generally between 20–40 percent of the short-term strength at yield or break. This range is dominated by unfilled materials, with highly filled compounds being at the other extreme of the spectrum.
When the temperature of the application environment approaches the DTUL values, the sustainable working stress may only be 3–5 percent of the value specified on the datasheet. These values are reduced by safety considerations specific to the product. At various temperatures, several data sheets include tensile strength and modulus values. These statistics, if accessible, may reduce a great deal of uncertainty.
Modulus
Almost every data sheet has information about modulus. Modulus of elasticity, tensile modulus, or flexural modulus are the most common measurements. The modulus is a measure of stiffness since it links stress to strain. The stress-strain curve’s linear section is often used to compute modulus. At low pressures, you lose linearity.
- Strain rate and yield stress modulus
Strain rate influences several material characteristics. The modulus and yield stress are both affected by the rate at which the material is loaded. Modulus and yield stress rise with increasing strain rates. Datasheet characteristics might seem to change from one supplier to the next because of this lack of harmonization in strain rates utilized by different manufacturers of the same material.
Understand the different types of injection molding and know that all materials have their unique features. It is critical to consider each material category’s general defining characteristics. Even though there are over 85,000 varieties of plastics, it is possible to fine-tune a material’s qualities via additives and fillers if you think it is lacking.