Current Research Projects

Optimization of the Fused Filament Fabrication (FFF) Printing Process

Fused Filament Fabrication (FFF) is the fastest growing and among the most common Additive Manufacturing technologies, often referred to as 3D printing or FDM™. While it is widely used by the open source community and for visual prototypes, the manufacturing of end use parts is still limited. Mainly because the resulting part properties are still inferior to the bulk polymer properties. Moreover, the resulting 3D components exhibit extensive anisotropy in their mechanical properties. Parts are much stronger in the bead direction than perpendicular to it.

As a first step important print parameters and their impact on the part density are analyzed. The study shows a vast effect of the density on the ultimate tensile strength. It was shown that this effect even surpasses the importance and effect of different bead orientation whenever mechanical resistant parts are needed. However increases a bead aligned with the load direction the tensile strength compared to a bead perpendicular to the load direction.

Furthermore, many of the numerous parameters involved with the FFF process itself are being investigated, such as the effect of build orientation to the strength of the final part or the effect of the temperature field on the adhesion between layers. Moreover will the ascertained strength effect of high solid parts compared to parts with lower solidity and different bead orientations. These results will then function as a benchmark for the design process of a 3D printed parts.

FLM print of Bucky

Researchers: Carsten Koch, Jianxing Chen, Luke van Hulle

Optimized 3D Air-Side Heat Transfer Surfaces with 500% Heat Transfer Enhancement

Collaboration between UW-Madison and Oakridge National Laboratories

The objective of the ARPA-E ARID program is to develop technologies that allow power plants to achieve high thermal-to-electric energy conversion efficiency with zero net water dissipation. The most direct method of achieving this goal is to improve the thermal efficiency of dry-cooled condensers by reducing the air-side thermal resistance without significantly increasing either the capital cost or the fan power required to operate these devices. This project will apply the additive manufacturing technique of Fused Filament Fabrication (FFF), best known under the trademark Fused Deposition Modeling (FDM®), to the development of air-cooled heat exchangers.

The designs of conventional air-side heat transfer surfaces are dictated as much by manufacturing constraints associated with conventional manufacturing techniques as they are by thermal-fluid performance. The project will develop a 3D heat exchanger geometry using FFF additive manufacturing techniques that would allow unprecedented design freedom for the optimization of the air-side heat transfer surfaces, leading to 500% enhancement in heat transfer coefficient. The projected cost of the proposed 3-dimensional heat exchanger is $17.64/kW with a COP of 200. The proposed technology is both transformative and innovative. It would shift the heat exchanger industry into a new paradigm, enable US industries to lead at the international level, and result in substantial new jobs growth.Read more here.

optAirHT

In order to produce competitive and effective plastic heat exchangers, the base polymer material should be strong at elevated temperatures, and the thermal conductivity of the matrix should be enhanced with fillers. Due to their high thermal conductivity and relative cost effectiveness, copper and carbon fibers are being investigated as fillers in a PA6 matrix. Compounding and mixing of high-volume-fraction fillers in the thermoplastic matrix is achieved with a co-rotating twin screw extruder. The resulting material can then be characterized with a number of methods, such as micro-computed tomography (micro-CT) to see the filler content, orientation and distribution, and laser flash analysis to measure the thermal diffusivity. Suitable materials will then be extruded into filament for use in the FFF printers. The orientation of the copper or carbon fibers, which enhances the thermal conductivity in the fiber direction, may be used selectively and advantageously in the FFF process.

Researchers: Tom Mulholland, Anja Falke

Additive Composite Manufacturing

The drive for higher performance, reduced cost and speed to market, in combination with the need for reduced resource consumption has accelerated the R&D efforts in the emerging industries of additive manufacturing and fiber reinforced composites manufacturing. While additive manufactured parts have the highest potential for waste reduction, significantly reduced development cycles and application of the right material at the right location, composites manufacturing has the highest potential to combine lightweight and high performance characteristics (e.g., strength, stiffness).

Both composites and additive manufacturing result in parts that consist of 2D layers stacked on top of each other. At the same time, the resulting 3D components exhibit extensive anisotropy of their properties. For example, the parts are much stronger in the fiber or filament direction than perpendicular to it. However, this apparent advantage (i.e., the ability to orient fibers preferentially and thus take advantage of its anisotropy) is often seen as a disadvantage due to limitations in current composite manufacturing. Recently, the introduction of Automated Fiber Placement (AFP) has enabled a load-path optimized design and manufacturing capability. However, this capability is restricted to a layer-wise composition that is often referred to as 2.5D. We are currently developing a 6-axis Additive Composites Printer that will allow for printing in any plane and direction, thus enabling unrestricted design freedom in all three dimensions.

Researchers: Thomas Pfeifer, Thomas Laduch, Luke van Hulle

Recycling of Plastic Packaging

Economical, Ecological and Technical Analysis of the Plastic Recycling Process

For the last 40 years the amount of plastic consumed has been growing steadily and thus the plastic waste of both industry and private households increased as well. Consequently, plastic waste handling is getting more and more important.

There are three ways of handling plastic waste: landfilling, incineration with energy recovery and recycling. In a recent study conducted at the PEC it was determined that from an economical point of view, incineration with energy recovery currently is the most profitable waste handling method with a profit of $8.19 per ton of plastic waste. Landfilling one ton of plastic amounts to a profit of -$23.10, recycling to -$9.76. The image below shows costs and revenues for the current plastic recycling process. However, from an environmental point of view, recycling of plastics is indispensable for todays and especially future society.

Recyc_Raphael

For this reason, different alternatives of improving the profitability of the plastic recycling process are being investigated, for example reduction of sorting steps during the plastic recycling process and blending of different recycled plastics, such as LDPE-PP or HDPE-PP.

Researcher: Raphael Kiesel



Investigation of the Blending of Recycled Plastic Waste

In recycling facilities, different materials are sorted. However, a big amount of the plastic waste has similar density and thus, cannot be separated. The combination of LDPE, HDPE and PP causes this problem in polymer waste streams. At the same time, these materials make up the majority of the plastics; LDPE-22.8%, HDPE- 17.2% and PP-22.9%; (EPA, Facts and Figures 2013). Without sorting, blends of different materials could be produced with higher profitability.

Therefore, the effect of processing parameters on the properties of recycled materials such as the rheological behavior, morphology and mechanical performance is studied in pure and blended polymers. In particular, the focus is on the rather immiscible blend of PP and LDPE, which is inseparable in the current municipal recycling stream. The study uses simple techniques available in industry, such as MFI measurements, incorporated with more scientific techniques such as rheometry, Differential Scanning Calorimetry, along with morphological studies conducted via microscopy techniques. This will lead to a scientifically-based design methodology for the recycling of polyolefin blends, starting with PP-LDPE, that will allow designers to select an appropriate blend to achieve the desired properties. The goal of the study is therefore to reuse plastic waste directly in a variety of tailored products.

In our recent study, blending of LDPE and PP results in partially compatible materials at small proportions of PP (£ 25wt%) without adding compatibilizer. Blends of recycled LDPE/recycled PP maintain good properties compared to the original components. By varying the blending ratios, the mechanical properties of recycled LDPE and the flowability of recycled PP can be improved.

The image below shows the effect of different proportions of LDPE and PP on the crystal growth rate. With higher LDPE content the crystallization of PP is slowed down and the speherulite size is reduced.

LDPPBlends

Researcher: Chuanchom Aumnate



Sort-by-Number Project

The aim of this project is to study the upgrading possibilities of blends of recycled materials and/or the maintenance of similar properties to those of virgin materials to eliminate the sorting process. Therefore, we evaluate the effect of processing parameters on the properties of recycled materials such as the rheological behavior and their miscibility as a function of different blend compositions.
Read more on the Sort by Number project



Reprocessing of PP - Thermal and Rheological Properties

To evaluate the processing and service life properties of recycled plastics, a better understanding of the effect of multiple reprocessing cycles is essential.

Polypropylene, a material widely used for packaging and containers, causes the biggest portion of plastic waste (22.8% in 2013). Therefore, it has a high potential for recycling and is used for this investigation. Mechanical recycling requires shredding, cleaning and re-melting of the material. During repeated reprocessing and especially re-melting, the material properties start to degrade. This can be caused by three mechanisms: thermal degradation, mechanical degradation and thermal oxidative degradation. The influence of these mechanisms will be separated to investigate the thermal and mechanical degradation of PP. Therefore, the melting and crystallization temperature of the reprocessed material as well as the crystallinity will be measured as a function of the reprocessing cycle. Furthermore, changes in viscosity and molecular weight will be determined after each cycle. Based on this data the impact of the different degradation mechanisms on specific properties will be evaluated. The image shows the change in MFI after multiple reprocessing cycles of manufacturing regrind in comparison to the virgin material.

MFI_extrusion

Researcher: Claudia Spicker



Past Research Projects

Investigation of Damage-Tolerant Composite Joints

The importance of lightweight materials such as fiber-reinforced composites is continuously increasing.The US composite materials market grew by 6.3 percent last year to reach $8.2 billion in value and the demand is expected to reach $12 billion by 2020. This is driven by the continuing growth in aerospace and automotive industry. Commonly used materials are carbon fiber reinforced plastics (CFRP) due to their excellent property set, e.g. high strength, high stiffness, low density, corrosion resistance, and long fatigue life. However, challenges occur in joining different CFRP parts because traditionally used mechanical fasteners such as bolts and rivets add weight and can interfere with the structure of the composites.

A new promising technology is the use of internal pin structures in the joints where the pins are oriented perpendicular to the fibers. In this project different designs of the pin structures are laser sintered with PA 12. The composite joints are then manufactured using Vacuum Assisted Resin Infusion (VARI) and later tested through single-lap shear tests. The goal of this project is to optimize the VARI process with the intrinsic pin structures and to evaluate the effect of the different pin designs on the strength of the joints.

Researcher: Lennart Krenckel