- ASC Proceedings of the 40th Annual Conference
- Brigham Young University - Provo, Utah
- April 8 - 10, 2004
|
|
|
Rapid Prototyping and its Current and Future Uses in the Construction Industry
The Rapid Prototyping (RP) process made its first appearance in 1987, with the introduction of the StereoLithography Apparatus-One (SLA-1) developed by Charles Hull. This machine was able to use three-dimensional CAD data and automatically build parts or models from an ultraviolet sensitive liquid plastic. The process initially found several uses in the manufacturing industry for building prototypes quickly that could be used for form, fit and limited functional testing, thus reducing the time-to-market cycle. Today, the RP process is finding uses in the construction industry. These uses include prototyping construction related products, architectural modeling, aids for construction scheduling, and in the future, building full-scale functional structures. The RP process will continue to be increasingly utilized in the construction industry as more construction professionals become familiar with the RP process. Especially in the areas of new product development, architectural modeling, scheduling and eventually fully automated construction where an RP machine can build an entire structure.
Key Words: Computer Aided Design, Contour Crafting, Fused Deposition Modeling, Helisys, Laminated Object Manufacturing, Stratasys, StereoLithography Apparatus-One.
Introduction
This paper is intended as an introduction to Rapid Prototyping (RP) and its current and future applications in construction. Rapid prototyping is a technology that had its beginnings in 1987 with the introduction of the first RP machine the StereoLithography Apparatus-One (SLA-1) (Jacobs, 1992). Since its inception the RP process has found many applications in the manufacturing industry, but few applications in the construction industry. This now is changing as the RP technology is becoming more affordable, available and familiar to college educators, construction and architectural/engineering professionals. This article is written to provide a brief background on the RP process, necessary computer aided design (CAD) data required for RP and uses of RP in construction.
Charles Hull, is the person given credit for experimenting and bringing to production the first commercial RP machine in 1987. His concept was to use three-dimensional (3-D) CAD data and a RP machine to produce an object automatically. He accomplished this by first creating a 3-D, CAD drawing of the object to be produced. This data was exported to the RP machine’s computer as a .stl file. This file format has become the industry standard and is an available option on most 3-D software packages. Second, the RP machine’s software sliced the object into thin layers and generated the necessary tool paths the machine needed to build the part. Third, the machine built the part by lowering a build platform into a vat of ultraviolet (UV) sensitive printing ink. Fourth, an X, Y-axis scanning mirror directed a UV laser beam into the plastic, curing the exposed liquid. This process would continue until the product was completed. Hull named this process StereoLithography, or three-dimensional printing. Today, StereoLithography is one of the most popular of the RP processes (Wohlers, 2002). It is more refined then the first machine and uses better suited UV liquid plastics designed specifically for the RP process. Today, other manufactures, using other processes and materials have entered the market. However, all RP processes have two things in common. First, they all depend on 3-D, CAD data to build their models and second, the models are built in thin layers.
Necessary CAD Data
All RP processes require three-dimensional CAD data obtained from a true solid modeling program. True 3-D modelers create solids that contain information not only about the building surfaces and edges, but also the volume of the structure. When investing time or money into producing a solid model of the project, it is important to guarantee that this volume data will be maintained in the software’s database, without which the model will not be able to be used for fabricating RP models. For example, older wire frame and surface modeling software will not provide the necessary data to build an RP model.
After the solid model is complete, the data is exported to the RP machine in a StereoLithography (.stl) or other acceptable file format. Many commercial solid modelers now offer a variety of export options (export file formats) and more students and professionals are being exposed to data exchange techniques making data transfer relatively easy. However, it must be noted that not all programs export functions are created equal. For example, some .stl exports do an inadequate job, leaving a database that is incomplete and a faceted model that is full of holes (unconnected facets). It will save time and money if the program’s export function is verified and the program contains a guarantee that an adequate .stl will be created that can be used to build a RP model.
Texas State University has two different RP machines that were obtained through two separate National Science Foundation (NSF) grants. The first machine is a Helisys (now Cubic Technology) model 1015, Laminated Object Manufacturing (LOM) machine. This machine creates its models using the layer subtractive process, a carbon dioxide infrared laser and heat sensitive adhesive backed paper. The process begins by adhering a new layer of paper to the previous layer, using a heated roller. Then the laser is used to first cut the profile of the part and second, cut the unused paper into tiles, which are removed later. This process continues until the part is built. The Helisys machine is best used to build larger parts with relatively gross features.
Both Colorado State and Texas State University have a Stratasys, Fused Deposition Modeling (FDM) machines (Illustration 1). This machine uses two small extrusion nozzles, usually having diameters between .012-.016 of an inch. One nozzle is used to extrude ABS plastic or casting wax to build the part or model. The other nozzle is used to extrude the support material necessary to provide a base for the ABS plastic or wax and to support overhanging features as the part is being built. After the model is built, the support material is either mechanically removed or dissolved in a water bath. This is a layer additive process and is usually slower then the Helisys layer subtractive process. This is because new material is added to the part in about .010 inch layers that are about .020 of an inch wide. The FDM process is better used to build smaller more detailed parts or models.
New Product Development: RP can be used to prototype new products for use in the construction industry. These prototypes can be used for form, fit and often limited functional testing. The RP process can save considerable time in reducing the time-to-market cycle over traditional prototyping methods. This is important to a manufacturer, since most products have a technological lifespan of five to seven years (Steward, 1991).
This statement implies that if it takes too long to develop a product, its usable sales life may be shortened as newer, more technologically advanced products replace it in the market or the product may be obsolete before the development phase is completed. RP can greatly shorten a products development time by creating a physical model, or prototype, of the 3-D CAD drawing in a matter of hours or days versus weeks or months to create a traditional prototype. This allows the model to be subjected to form, fit and limited functional testing much sooner than conventional methods would allow. Illustration two shows an underground conduit spreader, which was designed for a local plastic injection company. The spreader will properly position the conduit in the ground prior to the pipe being encased in concrete. The first prototype was built using the Helisys machine in about six hours. However, the prototype’s conduit holes were too small, so it was redesigned and within 24 hours a working prototype model was available. In another example, a nozzle for a high-end water fountain company, was built on the Stratasys RP machine out of ABS plastic and actually tested using low-pressure water at the company’s test facility (Illustration 3). It was redesigned because the water pattern was not uniform. After making the necessary corrections, a production model was made in investment casting wax by changing the extrusion head on the Stratasys machine from ABS to wax. The wax part was then investment cast at a local investment casting company in stainless steel. Total time duration, from original design to production part was six weeks.
Architectural Modeling: Construction students at Texas State University have made several architectural models using RP in their advanced architectural drafting class that they wished to study in further detail. Illustration 4 shows a detailed front door façade that can be shown to the customer for evaluation. These models help tremendously when the client has little skill in interpreting a two-dimensional drawing. Also, the model is useful in explaining the detail necessary to construct the architectural features to craft people. In the article, Planning with Pixels, Not Pencils (Read, 2003) many architecture
schools are experimenting with using 3-D, CAD software instead of tradition T-squares and triangles to create their drawings. One instructor found that the RP technology “gets this stuff off the screen and into the hand” (Read, 2003, pg. 2). It also forces students to concentrate on assemblies that might seem abstract to students on the computer screen. This is good news for the construction industry, which often has to deal with lack of technical detail in plans. Also, these 3-D architectural models can be used by construction professional in discussing the best way to build and to schedule complex projects. This practice is common in complex projects such as electrical generating plant construction. Often complex models are created by hand using crafts people. These models show the detailed location of piping and other features of the plant and are used in scheduling and in determining the implications of any changes to the original plans. RP can reduce the time needed to create these models along with reduce the time needed for generating updated models.
Automated Construction: The construction industry has been slow to adopt automation when compared to the manufacturing industry. However, things may be changing, as a professor at the University of Southern California has developed a process using RP technology that is capable of building full size structures. The process is called Contour Crafting or CC. This process uses a robot, installed at the building site, an extrusion nozzle and two trowels. The nozzle extrudes thin layers of various materials such as concrete, adobe or plastics to build the outside and the inside of the structure’s walls, including window and door openings and utility conduit openings. The trowels are used to smooth the surfaces so no further preparation is necessary prior to painting. The cavity between the RP formed walls can then be filled with various materials such as concrete. Also, a modular system is being developed that would allow a structure to be
reinforced with steel, or ducts can be provided for post-tensioning cables. The shape of a structure is only limited by the CAD data and it is estimated that construction costs can be reduced by fifty percent. (Khoshnevis, 2002)
Conclusions
Rapid Prototyping is a relatively new technology that has found many uses in manufacturing and is just beginning to be used in the construction industry. The technology can certainly be used to bring construction related products to market sooner by shortening the time needed to build a prototype. Architectural colleges along with professional architects are beginning to use the technology to develop models of the structures they design. These models will help both the architects and the constructors to see the construction project as a whole along with being able to concentrate on specific features of the structure. The model may prove to be very helpful in scheduling as various scenarios can be played out to determine the most efficient method to build and/or schedule a structure. Finally, RP may revolutionize the way structures are built by providing large-scale RP machines that are capable of building a structure onsite, from CAD data. The future of RP in construction is beginning to emerge, and may revolutionize the industry as more construction professionals become aware of it potential.
References
Jacobs, P.F. (1992). Rapid prototyping and manufacturing: fundamentals of stereolithography. Society of Manufacturing Engineers, Dearborn, MI.
Khoshnevis, B. (2002). Automated construction using contour crafting-applications on earth and beyond. Paper presentation at the 19th International Symposium on Automation and Robotics in Construction (ISARC)
Read, R. (2003). Planning with pixels, not pencils. Chronicale of Higher Education, http://chronicle.com/prm/weekly/v50/i12/12a02901.htm.
Steward, T. (June 3, 1991). Brainpower. Fortune, vol. 123 no. 11, p. 44-60.
Wohlers, T (2002). Wohlers report 2002. Wohlers Associates, Inc., Fort Collins, CO.
Illustration 1, Stratasys FDM RP Machine
Illustration 2, Conduit Spreader
Illustration 3, Water Fountain Nozzle
Prototypes
Illustration 4, Architectural Model
