Composite StructuresMS_DT Pracitcum Research Proposal University of Michigan Winter 2013 Jeremy Luebker
This proposal lays out the trajectory of research based around the fabrication of light-weight structures formulated from a composite of plastic and fabric. The work proposes to build upon the current vein of research in extruded plastics to create a viable method of construction utilizing this method of fabrication.
There have been several project in recent years at various academic institutions such as SCI-Arc, MIT, and the University of Michigan that have sought to explore the possibilities and properties of CNC extruded martials. This research builds on the ideas inherent to 3D printing technologies and seeks to both scale up and explore a variety of material possibilities such as plastics and concrete. Most of these projects have been facilitated through a process of attaching either a repurposed industrial plastic extruder or a custom designed extruder to a multi-axis robotic arm.
The projects can be divided in to two categories: first expanding 3D printing technologies, and second, exploring the properties of extrusion. The first category of projects deals with the direct translation of digital three-dimensional forms into physical manifestations. The second deals with the affect of processes extrusion and attempting to push the extents of the physical properties of the material. None of these projects, however, work with this technique and material as an actual building material.
Fabric tests and selection
During the fall semester of 2012 at the University of Michigan, in collaboration with Jake Newsum, experiments with this material and technique were begun. This method encompasses several crucial elements. This project entails printing extruded plastic on fabric to create lightweight structural panels.
The first element of this technique is reliant on the fabric selection. A variety of fabrics were tested including an assortment of natural materials and synthetic. The finding was that the plastic didn’t bond with the fabric. Synthetic fabrics had better success on some of the selections. It was found that on polyesters tend to fuse with the Copolymer Polypropylene used in the extrusion. Other fabrics such as rip-stop didn’t fuse at all. The conclusion is that fabrics of similar plastic composition as plastic fuses the best.
Plastic Printing Techniques
As with all the extrusion projects, the process relies heavily on two elements: the first is temperature and something that has been termed “smash”, or vertical offset. The temperature dictates the strength of the fusion with the fabric; it was found that the greater the temperature the greater the bond. However, an excessive temperature could also cause too much penetration with the fabric, resulting in bonding with the substrate material and ultimately in some undesirable bonding and staining. The ideal temperature range was determined to be between 180 and 210 degrees Fahrenheit.
The second element, the vertical offset, determines the structural rigidity as well as cohesiveness of fabric accumulation. Two techniques were discovered, is to print above fabric, the second is the print with a determined offset less than the height of the printed plastic in successive layers, inducing “smash”. The ideal offset was found to be about 1/32 of an inch. This technique, although the more structural of the two, causes a limited amount of distortion due to drag and pinching of the fabric.
The structure of the panels is determined based on size of the panels. This in turn determines the techniques necessary. Smaller panels, roughly 12 by 12 inches can be made structural with a single line profile of plastic. However it was found that smashing plastic provides better shear resistance. A second technique developed was filleting the corners, this proved to be more successful than printing diagonals across the panels. The most successful structural solution, however, was a combination of these techniques. A single layer of smashed plastic directly on the fabric provided shear resistance while a layer of plastic with a larger offset directly on top of this provided a structural cross section. Adding a fillet to this allowed for panels of significant strength. One structural test of a 6 inch by 6 inch box, earlier in the process tested at over fifty times its own weight.
The difficulty this technique was discovered in assembling the panels in to folded geometric prisms. The method has resolution issues resulting in warping and infidelity of panel assembly. Connection tests focused primarily on attaching contained geometric volumes into an aggregated assembly. Attachment methods utilized consisted primarily of internal sowing and a pull-string method, which would ideally allow for minimal expression of the connections. However, further testing will be required to both improved the fidelity of the printing process as well as alternate connection methods.
One of the more significant discoveries during this process was the behavioral qualities of the plastic fabric fusion. By altering and varying the tool paths to result in open geometries rather than profile lines, it was discovered that the assemblies behaved more as a composite. The fabric provided flexibility and tensile restraint while the plastic provided rigidity and stiffness. Depending on the tool path arrangement, most of these composites took on spring like characteristics.
Light Weight Structures
The success of this project is in the ability to create structural components without the use of fixtures or precut fabric patterns.
This semester the work is proposed to be continued and a variety of methods to build upon the calibration of last semester. While developing methods to improve the techniques and fidelity of the current methods, further exploration of the possibilities of this technique will be explored.
While the previous semester’s panels were limited to flat, two dimensional prints, this semester, explorations into three dimensional panels will be conducted. Two potential methods are apparent: the first is pressing the printing the plastic on loose fabric stretched on a frame, using the pressure of the extruder nozzle. The second is to stretch the fabric over a three dimensional forms.
Another opportunity that is quickly apparent is the incorporation of robotics. Taking advantage of the open fabric surfaces at the center of the panels to create apertures is the first of these opportunities and the second is taking advantage of the light weight qualities of the panels to create dynamic surfaces.
The alternate and or parallel priority is to further the explorations of the properties of the composite. This will encompass most of the same issues as the development of the panels. But will also include calibration of the dynamic qualities.
Measure of Deformation and Simulation
The calibration of these qualities will require the cataloging of the taxonomy of the spring qualities associated with differentiating tool paths. Once this is accomplished these properties could then potentially be simulated allowing for incorporation into further design opportunities.
Secondary Material Interfacing and Self-Structuring Solutions
Both of these opportunities require further exploration of structural solutions. The first is to develop methods of interfacing with other materials such as wood or metal structural systems. The second solution is to continue to explorations of self-structuring methods utilizing plastic and fabric.
All of these explorations require further exploration in improvement of the fidelity of the printed tool paths. One of the first steps is to explore improved methods of securing the fabric to reduce the drag. The use of magnets has potential. The second avenue of improvement is to explore increased control of the plastic extrusion. One of the first apparent solutions is to experiment with alternate nozzle systems for the extruder. Decreasing the diameter of the nozzle and experimenting with forming the hot plastic as it is extruded will be the first of the explorations.
Final Demonstration Project
The culmination of this experimentation would be presented as situational design situated on a yet to be selected site. The sited project will take on the form of a self-structuring system possibly forming an enclosure or pavilion.
PDF VERSION DOWNLOAD: jluebker_proposal
Plastic netting: composite