An Investigation of Bimodal Cellular Distributions via Supercritical Fluid Assisted (SCF) Foam Injection Molding

The Corporate Average Fuel Economy (CAFÉ) standards for 2025 are set to introduce a fleet-wide average of 54.5 MPG for cars and thereby, prevent emissions of 6 billion metric tons of CO2 [1]. This has propelled the automotive industry to renew their focus on lightweighting cars, particularly through the use of crude oil-based structural foams. While these foams offer a unique combination of ultra-lightweighting with adequate strength, they are practically non-renewable, non-biodegradable and contribute to the growing anthropogenic carbon footprint. An alternative paradigm to such foams is the use of biosourced polymers as they offer immense advantages due to their renewable, sustainable and biodegradable nature. Currently, polylactic acid (PLA) remains the most abundant commercially consumed biopolymer, but it suffers from two major drawbacks: its inherent brittle nature and poor melt processability. Blending PLA with an inherently toughened counterpart provides an effective mechanism to overcome both these drawbacks [2]. Additionally, foaming of PLA-based blends can provide a replacement for synthetic structural foams. However, processing of such blended foams is inhibited by challenges associated with structural foam molding with regard to controlling foam microstructure – specifically, cell size and cell density. Additionally, controlled processing of bimodal cell structure has remained elusive with currently used molding parameters and chemical blowing agents. Bimodal cellular distributions are preferred for their superior properties – enhanced toughness and compressive strength, weight reduction, and insulating properties –compared to their unimodal counterparts. This study investigates the effect of material properties and processing parameters on unique cellular distributions of polylactic acid (PLA), polybutylene succinate adipate (PBSA) and their blends processed via supercritical fluid-assisted injection molding. Cell morphology, size and density were determined via scanning electron microscopy, while their influence on mechanical properties was studied using tensile testing. Thermal stability of the blends was studied via differential scanning calorimetry and thermo-gravimetric analyzer. Effect of melt rheology and viscoelastic behavior was studied in an effort to explain the bimodal cellular structure obtained

Thermoplastics Foams: An Automotive Perspective

The automotive industry has witnessed a massive shift in terms of materials used, ranging from being a metallic heavyweight in the 1950s to employing a hybrid sandwich of multiple material systems. This apparent shift can be attributed to achieving improvements in performance, safety and fuel efficiency, along with responding to the various environmental regulations imposed by different governments. The recent advocacy of Corporate Average Fuel Economy (CAFE) standard of 54.5 MPG by 2025 by the US Environmental Protection Agency (EPA) to reduce greenhouse gas (GHG) emissions [1] has spurred the sector at large towards the use of lightweight materials

COMPOSITES 4.0: ENABLING THE MODERNIZATION OF LEGACY MANUFACTURING ASSETS IN SOUTH CAROLINA

Composites 4.0 is the implementation of Industry 4.0 concepts to plastics and composites manufacturing with the goal to overcome the complexities associated with these materials. Due to very complex process-structure-property relationships associated with plastics and composites, a wide range of process parameters need to be tracked and monitored. Furthermore, these parameters are often affected by the tool and machinery, human intervention and variability and should thus, be monitored by integrating intelligence and connectivity in manufacturing systems. Retrofitting legacy manufacturing systems with modern sensing and control systems is emerging as one of the more cost-effective approaches as it circumvents the substantial investments needed to replace legacy equipment with modern systems to enhance productivity. The goal of the following study is to contribute to these retrofitting efforts by identifying the current state-of-the-art and implementation level of Composites 4.0 capabilities in the plastics and composites manufacturing industry. The study was conducted in two phases, first, a detailed review of the current state-of-the-art for Industry 4.0 in the manufacturing domain was conducted to understand the level of integration possible. It also helped gain insights into formulating the right questions for the composites manufacturing industry in South Carolina. Second, a survey of the plastics and composites manufacturing industries was performed based on these questions, which helps identify the needs of the industry and the gap in the implementation of Composites 4.0. The study focuses on the three leading composite manufacturing industries: injection molding, extrusion, and 3D printing of thermoset and thermoplastic materials. Through the survey, it was possible to identify focus areas and desired functionalities being targeted by the industries surveyed and concentrate research efforts to develop targeted solutions. After analyzing the survey responses, it was found that updating old protocols using manufacturer support and customized integration of cost-effective solutions like retrofit kits, edge gateways, and smart sensors were identified as best-suited solutions to modernize the equipment. Composites 4.0 is already being implemented for Preventive Maintenance (PM), Manufacturing Execution System (MES), and Enterprise Resource Planning (ERP) to some extent, and the focus is on process optimization and equipment downtime reduction. The inferences drawn from this study are being used to develop highly targeted, supplier-agnostic solutions to modernize legacy manufacturing assets

Thermoforming process effects on structural performance of carbon fiber reinforced thermoplastic composite parts through a manufacturing to response pathway

Thermoforming process of thermoplastic-based continuous CFRP\u27s offer a major advantage in reducing cycle times for large-scale productions, but it can also have a significant impact on the structural performance of the parts by inducing undesirable effects. This necessitates the development of an optimal manufacturing process that minimizes the introduction of undesirable factors in the structure and thereby achieves the targeted mechanical performance. This can be done by first establishing a relationship between the manufacturing process and mechanical performance and successively optimizing it to achieve the desired targets. The current study focuses on the former part, where a manufacturing-to-response (MTR) pathway is established for a continuous fiber-reinforced thermoplastic composite hat structure. The MTR pathway incorporates the thermoforming process-induced effects while determining the mechanical performance and principally comprises of material characterization, finite element simulations, and experimental validation. The composite material system selected for this study is AS4/Nylon-6 (PA6) with a woven layup. At first, the thermoforming simulations are performed above the melt temperature of PA6 using an anisotropic hyperelastic material model, and the process-induced effects such as thickness variation, fiber orientations, and residual stresses are captured from the analysis. Residual stresses developed in the formed structure during quench cooling from the elevated temperature are predicted by the implementation of classical laminate theory (CLT). These results are then mapped onto a duplicate part meshed suitably for mechanical performance analysis. A quasi-static 3-point bend test and a dynamic impact test are carried out and the results are compared with experimental tests. Experimental results from thermoforming, bending and dynamic impact trials show good agreement with the simulation results for the hat structure under consideration. Further, the static and dynamic performance is evaluated for the thermoformed structure and the effects of the thermoforming process are compared numerically, for the cases with and without the inclusion of process effects

Design and Development of a Multi-material, Cost-competitive, Lightweight Mid-size Sports Utility Vehicle’s Body-in-White

Vehicle light-weighting has allowed automotive original equipment manufacturers (OEMs) to improve fuel efficiency, incorporate value-adding features without a weight penalty, and extract better performance. The typical body-in-white (BiW) accounts for up to 40% of the total vehicle mass, making it the focus of light-weighting efforts through a) conceptual redesign b) design optimization using state-of-the-art computer-aided engineering (CAE) tools, and c) use of advanced high strength steels (AHSS), aluminum, magnesium, and/or fiber-reinforced plastic (FRP) composites. However, most of these light-weighting efforts have been focused on luxury/sports vehicles, with a relatively high price range and an average production of 100,000 units/year or less. With increasing sports utility vehicle (SUV) sales in North America, focus has shifted to developing lightweight designs for this segment. Thus, the U.S. Department of Energy’s (DOE) Vehicle Technologies Office has initiated a multi-year research and development program to enable cost-effective light-weighting of a mid-size SUV. The proposed designs shall enable weight reduction of a minimum of 160 lb. (~72.7 kg), with a maximum allowable cost increase of $5 for every pound of weight reduced. The proposed designs shall enable vehicle production rates of 200,000 units/year and will be aimed at retaining the joining/assembly line employed by the OEM. A systems approach has been utilized to develop a multi-material, light-weight redesign of the SUV BiW that meets or exceeds the baseline structural performance. This study delves into the development of design targets for the proposed redesign at the system, sub-assembly, and component levels. Furthermore, results from topology optimization studies on a design volume were assessed to understand the load paths under various loading conditions. Several multi-material concept designs were proposed based on the insights provided by the topology optimization study. Novel multi-material joining methodologies have been incorporated to enable maximum retention of the OEM’s joining and assembly process without significantly increasing cost. This paper presents the systems approach, and results from design studies undertaken to meet the program challenges

Understanding Process-Structure-Property-Performance Relationships of Thermoplastic Olefins (TPO) Foams Through a Novel Manufacturing to Response Pathway

The global transportation industry is the second highest contributor to climate change. As a result, there has been a concerted effort to spearhead research in economical lightweighting technologies, as every 10 % reduction in weight will lead to to 6 – 8 % improvement in fuel efficiency. Additionally, the recent push for electrification and the emphasis on Corporate Average Fuel Economy (CAFE) standards have seen original equipment manufacturers (OEM’s) dive into lightweighting of materials to improve overall range and/or fuel-efficiency. Thermoplastic Olefins (TPOs) have in recent years carved out a niche in the automotive industry due to advantages such as increased impact resistance, lower production costs, short production times, and improving fuel efficiency on account of lower densities. TPO’s have been successfully used in interior and exterior automotive applications such as bumper fascia’s, trims, cladding, and wire insulation. Logically, the adoption of TPO foams either via conventional chemical agents or new physical blowing agents would be largely beneficial to the automotive sector given the need to drive down weight and increase efficiency. However, conventional TPO foams have not seen widespread adoption in the automotive industry. Generally, TPO foams can be manufactured via two different approaches, viz., using either chemical or physical foaming agents in existing manufacturing processes like injection molding. TPO foams produced via chemical foaming agents are the current standard due to their low upfront costs and good molded-in color appearance but come with challenges in the form of unpredictable foaming in different cross-sections, decreased thermal stability and residual foaming agent migration induced by weather changes leading to pitting in class A painted surfaces. Alternatively, physically foamed TPO’s are yet to be adopted by a majority of the industry primarily due to higher upfront costs, splay marks on the surface that would fail the molded in color appearance requirements of almost all OEM, and the lower solubility of supercritical N2 in TPO’s making it challenging to foam. Lastly the lack of a holistic modeling pathway that couples manufacturing, microstructure, and mechanical responses pose a major impediment as they cannot be incorporated into current automotive product development cycles. This study begins with developing a structure-property relationship for Super Critical Fluid (ScF) assisted IM TPO foams using a conventional IM tool to understand the current limitation of the process and tooling. Subsequently, a manufacturing-to-response pathway is developed to help simulate the process-structure-property relationship via the use of rheological, bubble growth, and FEA models via a mean filed homogenization approach. Furthermore, this work investigates the development of a proprietary tooling concept that can control pressure drop and cooling, both vital parameters in controlling cell nucleation and structure. Lastly, as a proof of concept, this work delves into the design and prototyping of an interior garnish part that serves as a demonstration of an industry-scaled TPO foamed product

Investigation of Thermal and Thermomechanical Properties of Biodegradable PLA/PBSA Composites Processed via Supercritical Fluid-Assisted Foam Injection Molding

Bio-based polymer foams have been gaining immense attention in recent years due to their positive contribution towards reducing the global carbon footprint, lightweighting, and enhancing sustainability. Currently, polylactic acid (PLA) remains the most abundant commercially consumed biopolymer, but suffers from major drawbacks such as slow crystallization rate and poor melt processability. However, blending of PLA with a secondary polymer would enhance the crystallization rate and the thermal properties based on their compatibility. This study investigates the physical and compatibilized blends of PLA/poly (butylene succinate-co-adipate) (PBSA) processed via supercritical fluid-assisted (ScF) injection molding technology using nitrogen (N2) as a facile physical blowing agent. Furthermore, this study aims at understanding the effect of blending and ScF foaming of PLA/PBSA on crystallinity, melting, and viscoelastic behavior. Results show that compatibilization, upon addition of triphenyl phosphite (TPP), led to an increase in molecular weight and a shift in melting temperature. Additionally, the glass transition temperature (Tg) obtained from the tanδ curve was observed to be in agreement with the Tg value predicted by the Gordon–Taylor equation, further confirming the compatibility of PLA and PBSA. The compatibilization of ScF-foamed PLA–PBSA was found to have an increased crystallinity and storage modulus compared to their physically foamed counterparts

The Power of Processing: Creating High Strength Foams from Epoxidized Pine Oil

The present work reports on the synthesis of foams from epoxidized pine oil (EPO) with polymethylhydrosiloxane (PMHS) used as a foaming agent. The effect of two different processing methods involving modifications of curing agent and foaming agent addition timings was also analyzed. Resultant foams were characterized via density, mechanical and thermal testing, and microstructure. Foams produced using a modified processing method displayed properties that deviate from the Ashby–Gibson models, resulting in superior compressive strengths over many synthetic and biobased epoxy foams, ranging from 6.1 to 11.3 MPa. The impact of the method on cellular microstructure was also significant, with 20- and 30-fold increase in cell density from the original processing method for the same levels of foaming agent in both the methods. Glass transition temperatures of the foams ranged from 61.8 to 97 °C, higher than those of many foams in their class

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