Research Projects

Additive manufacturing (3D Printing) opens up new capacity for tuning geometry and in some cases material properties that were not available to researchers previously. These capabilities change traditional considerations for design of products, systems, supply chains, and even business models. While there have been some notable successes, much of what has been done with additive manufacturing largely replicates parts made by traditional processes. New design methods and tools are needed to better utilize the capabilities of additive manufacturing.

Traditional methods of manufacturing utilize validated tooling and control of key process parameters to assure consistent product outcome. They often rely on statistical sampling to assure process control at minimal cost. However, additive manufacturing (AM) requires new approaches. On the one hand, the number of process variables increases because the properties and geometry are formed point by point. This increases the potential failure conditions by order of magnitudes. At the same time, production quantity is much too small to apply statistical process control at the part level. Thus, new methods are required.

One promising approach is in controlling the process parameters through the process in order to verify the quality at each point. However, this requires both new sensing modalities to track all the properties of interest efficiently and methods that can efficiently analyze the terabytes of data that can be generated.

One of the ways that we are addressing this challenge is through the study of new methods for active thermal probing to gather data about the printed parts during the printing process in order to assure that all elements are within spec or to even adjust process parameters in real time to improve process consistency.

Thermal image high intensity projection of a BYU logo shows how spatially controlled heating can be achieved.

One of the earliest methods of additive manufacturing (3d Printing) was laser sintering (LS). In LS, a laser is scanned over the surface of a semicrystalline polymer powder preheated close to its melting point. As the laser scans over the material, it heats the powder and fuses the particles together to form the geometry. The parts have excellent accuracy and strength comparable to injection molded components. However, there is a relatively limited range of materials that are used with the method, and material toughness remains well-below what is achieved with traditional manufacturing methods.

A possible culprit in these issues is the very fast heating time that is used. In order to economically produce parts while maintaining the ability to create fine features, the laser must be focused to a fine spot that is scanned very rapidly over the surface. This creates large temperature gradients that could locally degrade the material and limited time for complete densification. We are exploring the impact of these constraints by using a projected image to cure large areas (cm^2) simultaneously. We have demonstrated dramatic improvements in ductility (elongation at break) while maintaining comparable strength to traditional LS parts while using the same raw material.

Ongoing efforts are considering the mechanisms for these improvements and exploring how these benefits might be extended to other material systems.

Sponsor: National Science Foundation

LAPS processing increases both ductility and strength of Nylon 12 (PA 12) materials compared to commercial processes.

Several additive manufacturing (AM) processes rely on inkjet printing as a key component. In particular, two (binder jetting, high speed sintering/multijet fusion), require that the droplets be printed into a powder bed. The details of these interactions can make a significant difference in the quality of the resulting surfaces as seen in the images to the right.

These small droplets (Ø < 50 microns) impact even smaller powder particles at speeds of up to 10 m/s. The kinetic energy is often comparable to the wetting energy resulting in significant particle rearrangement on impact. The dynamics of this process play a key role in the accuracy of the geometric shape produced and can be a source of either beneficial particle realignment or void formation.

A high speed video provides some insight into the complex dynamics of these processes. In the video, a single nozzle is moving over the powderbed and printing droplets to form a line filmed at 2000 frames per second. Watch in slow motion as droplets splash, powder flies, and droplets merge into larger balls.

Existing work provides an incomplete picture of these interactions and is largely based on relatively low kinetic energy conditions in which droplets are substantially larger than the powder particles. A better understanding of these processes will enable better development of new materials and binders/inks for higher performance materials.

Electrowetting is a phenomenon in which a droplet shape is altered in the presence of an electric field. When utilized with a thin dielectric layer, electrical current is eliminated and a highly efficient actuation system can be created by controlling the field across the droplet. Traditionally this is done with a series of electrodes of the same approximate size as the droplet allowing for programmable droplet motion required in lab-on-a-chip systems for DNA sequencing or medical diagnostics.

We have developed a variety of actuation methods that allow for higher speed and/or higher accuracy motion. These include continuous electrowetting across distances much larger than the droplet utilizing a single electrode pair and sub-electrode stepping motion that allows for high accuracy open-loop position control.

In one illustration of a possible applications, the technique was used to move a metallized plate to tune a resonator frequency. This could be extended to other electrical devices to allow for high efficiency and high power RF electronics in a compact package.

Sponsor: National Science Foundation

Most corrosion-preventing coatings such as paints serve as a barrier to the ion transport that drives metallic corrosion. However, there are some cases in which a controlled corrosion rate is desired and/or coatings may be undesirable. For example, magnesium is of interest for temporary implants such as anchors in orthopedic surgery. It is biodegradable, nontoxic and has favorable mechanical properties for bone interface. However, it typically degrades too quickly in an aqueous environment. Alloying elements and coatings can help, but many raise toxicity concerns. We are exploring an alternative method of impeding the corrosion reaction.

We are creating surface textures in the magnesium similar to super hydrophobic surfaces. When immersed in a saline solution, the corrosion process generates hydrogen gas. This gas is trapped by the surface texture and dramatically slows the corrosion rate. The surface texture parameters may be used to control the time profile of the degradation alone or in combination with other corrosion control methodologies in order to achieve clinically required degradation rates.

Sponsor: National Science Foundation

Wetting is key to a wide variety of industrial processes. Examples include soldering, painting, adhesive, food processing, cleaning, and corrosion. It is critical to understand how common processing conditions impact the wetting phenomena in order to improve performance of these products or add new functionality. It has previously been demonstrated the droplet wetting states can be changed by exciting droplet vibration modes. However, the excitation frequency must be tuned for each droplet volume making this an impractical method for most applications. We are studying the use of high frequency (>10 kHz) excitations as an alternative approach.

We have shown previously unreported spreading effects due to the high frequency vibration. Droplet diameters increase linearly in proportion to the vibration acceleration of the surface across a wide range of viscosities. This may provide the means for careful modulation of wetting of droplets on a surface.

Ongoing studies are considering how this could impact wetting on textured substrates.

Sponsor: National Science Foundation