Rapid Prototyping Systems: Buy Now... Next Year... or Never?

Terry Wohlers
Published in Proceedings of the Third International Conference on Rapid Prototyping, June 1992, Dayton, Ohio
Copyright 1992 by Wohlers Associates


Should you buy a rapid prototyping (RP) system now, wait a year, or postpone a purchase indefinitely? Waiting may mean lost opportunity, but buying prematurely can mean something worse. Industry consultant Terry Wohlers sorts through the issues and helps you decide. He comments on the obstacles to increased popularity of RP, offers advice to buyers, developers and entrepreneurs, and provides a glimpse of the future.


If you are a decision maker, or influence decisions, the following information will help you when considering the purchase of an RP system. It offers basic recommendations and guidelines you should weigh as you compare the strengths and weaknesses of RP technologies. Additionally, it discusses the importance of CAD, the most practical means of creating files for processing on RP systems. Finally, it discusses other important technologies and management strategies, such as 3D digitizers and concurrent engineering, that compliment RP and enhance product design, prototyping and manufacturing.

My Advice to Buyers

Rapid prototyping systems permit you to make parts faster, and usually at a lower cost, than using conventional methods. Because you can turn out parts quicker, be careful not to create parts unnecessarily. Avoid adding a step to the process only because it is convenient to do so. Often, a soft (computer) prototype will suffice. A soft prototype is a model that exists only in the CAD system. The CAD model represents the same geometric data as a physical (hard prototype) model, but you can not hold it or transport it as easily. Solid models are rich with information, such as mass properties. They allow you to create sectional views so you can examine the interior of the part. Also, solid models permit you to color and shade the model to more closely resemble the appearance of the finished part.

Be careful you do not view rapid prototyping as an isolated function. Instead, view it as an integral, but optional, part of the design and manufacturing process. It may be helpful to think of an RP system as an output device, such as a printer or plotter. Often, you must produce a hardcopy of the design, but sometimes you can do as well without.

Solid Modeling

Before you consider an RP system, check your present design process. If you are not using a CAD system with solid modeling capabilities, consider one first. Install and use solid modeling before you install an RP system. You may discover that a CAD system with solid modeling satisfies your design and modeling needs. If you find you need an RP system, solid modeling will be in place before encountering the challenges of installing and using an RP system.

Most companies now have at least one AutoCAD station. Large companies, such as Boeing, have hundreds. AutoCAD's solid modeling option, called the Advanced Modeling Extension (AME), now lets you produce an STL file -- the file type required by most RP systems. This means that literally tens of thousands of AutoCAD users have a simple link to RP systems. AutoCAD AME does not offer solid modeling features comparable to products like Pro/Engineer and SDRC's I-DEAS. However, you can create basic parts with it, and reserve the complex parts and assemblies for more expensive and robust configurations.

The lack of 3D CAD modeling, particularly solid modeling, is one the most serious obstacles to increased growth of rapid prototyping. Information gathered at last year's Second International Conference on Rapid Prototyping shows that stereolithography users agree. The requirement of 3D CAD will be a significant impediment to rapid prototyping growth. The RP industry may, in fact, grow only as fast as the solid modeling industry grows. Fortunately, RP is encouraging sales of solid modeling systems, because 3D CAD is a prerequisite to rapid prototyping. Likewise, solid modeling applications are encouraging the purchase of RP systems. For this reason, AutoCAD AME and other popular packages will have a positive impact on the RP industry. As these low-cost solid modelers improve, the industry is likely to experience a noticeable rise in RP sales and service bureau work.

You may be reluctant to move to 3D because of technical and organizational problems. Talk to those who have successfully implemented it. Learn from their mistakes and listen to them carefully. After you have decided to work in 3D, select a small project, one without a tight deadline, or one with no deadline at all. Pick one that does not contain complex surfaces. If you have CAD now, you probably have 3D capabilities, since most CAD software packages offer 3D as a standard part of the product. However, be careful not to invest time with software that offers limited, or substandard, 3D modeling features. It may be more economical to consider a new solid modeler, even though it would require an investment in new software and hardware.

Thomas Mueller of Prototype Express claims the cost of preparing a CAD file for their SLA-250 spans from about one-third to two times the cost of producing the RP part itself. Their CAD modeling work ranges from adding support structures to a finished solid model to converting paper drawings to a solid format. Prototype Express is an RP service bureau located in Arlington Heights, Illinois.

Your work may involve the conversion of a 3D wireframe to a solid model. Al DeWitt of Laserform claims his company spent 130 hours on a project involving the conversion of a wireframe to a solid model. Laserform is an RP service bureau located in Auburn Hills, Michigan. The 2 megabyte wireframe model grew to 7 megabytes in size and required lots of computer horsepower.

Reverse Engineering

One of the obstacles to applying 3D CAD is the job of creating the original part geometry. The problem is greater when a part contains odd shapes, such as sculptured surfaces. Human anatomy, for instance, is very difficult to create from scratch. Three-dimensional digitizers and scanners permit you to capture the surface topology of a shape and store it as an ASCII list of x/y/z coordinates. CAD systems enable you to read the file, build splines and create surfaces. Using basic CAD editing tools, you can modify the part and create the STL file.

Consider reverse engineering tools, such as 3D digitizers and coordinate measuring machines (CMMs), as a companion to your RP system. In addition to reverse engineering, companies use these measuring devices for part inspection and quality control, copying clay, foam and wood models, developing prostheses and implants, and duplicating old patterns and tooling.


Once your organization begins to experience success with the RP system, the word will get out and demand will increase. This could create a backlog. According to Lavern Schmidt of Chrysler's Jeep & Truck Engineering, backlogs have varied from a low of a couple of jobs to a high of 38 jobs. Prepare for it. Jet travel is faster than alternate forms of travel only when you have a seat on the plane. Chrysler says it like this: Rapid prototyping is only rapid if it's your part being built. If you're waiting in the queue, it's tortoise prototyping. Average build (machine) time at Chrysler is 18 hours per part. This does not include CAD modeling time, file slicing, merging of files, removal of support structures, post curing, and part cleaning and finishing.

At the risk of sounding pessimistic, it is possible your RP installation collects dust. This is unlikely, but you may experience spans of idle time. The reasons may not be technical but rather organizational in nature. If this lack of work volume becomes frequent, you may have bought a system prematurely. Using one of the many excellent service bureaus would have been better. As you work with service bureaus, record your activity. Use this documentation when you propose the purchase an RP system.

Concurrent Engineering

Concurrent engineering, also called simultaneous engineering and cross functional teams, is a strategy of bringing people together early in the design of a product. The individuals, who come from several functional areas in the organization, provide input when design changes are inexpensive. Representatives from engineering, manufacturing, materials management, quality assurance, marketing, and so on, develop the product as a team. Everyone is on the same page from the start, and they perform their tasks in parallel.

Contrast this with traditional manufacturing. The design moves sequentially through the organization. Suppose marketing spots a subtle flaw in the design after the company has made a $60,000 steel tool. The company must either spend more money on the tool and delay manufacturing several more weeks, or go to market with a second-rate product.

Rapid prototyping can have a positive impact on the practice of concurrent engineering. Making a prototype part available for feedback early in the design cycle can decrease the chances of expensive retooling. Product features and overall quality also usually improve.

Additional Tips

Budget $85,000 to $490,000 for a rapid prototyping system. Budget 30-90 percent of this amount for other costs. For stereolithography systems, examples include a post cure oven, cleaning tools, such as an ultrasonic cleaner, and protective equipment. Since certain resins are toxic, your organization may require expensive facility changes, such as the addition of wall partitions, ceilings and proper ventilation.

Also consider CAD system upgrades, training and hidden costs. For example, consider the time it takes to properly prepare the CAD model and create support structures. You may find that it is better to build the part upside down or laying on its side. If the walls of the part are too thin, you may need to make them thicker. If the part is too large for the build chamber, you may need to break it into two or more parts, build them separately and glue the parts together at the end.

Laser replacement costs range from $12,500 to $25,000. Expect 4000 to 6000 hours of operation per laser. System maintenance agreements cost from $10,000 to more than $70,000 annually. Liquid resin prices range from about $250 to more than $800 per gallon. Set aside more than $20,000 for the cost of filling the SLA-500's 67-gallon vat at $300 per gallon. One spool of Stratasys filament (equal to about 0.5 gallon) is $350.

Experiment before you buy. Use one or more of the 35 RP service bureaus spread throughout the U.S. Your people are key. When you begin to explore the options, identify someone to champion the research, installation and management of the system. During the first few months of using the RP system, it may take several tries to build good parts. Part accuracy depends largely upon user experience. Note also that the RP part will be only as good as the CAD model. At times, it is more practical to make parts using conventional tools and processes rather than consuming the resources of an RP system. NC milling machines, for example, offer a much wider selection of materials.


Keep an eye on developments not yet commercially available. You may discover a unique RP technology that has the potential of accelerating your company's efforts. Consider funding the development of the technology, or consider a research and development partnership. It could lead to a win-win situation. More than 30 R & D efforts are underway at universities, government labs and corporations around the world.

Today, most RP suppliers are selling into a general market for general-purpose use. A typical RP user uses the system for concept modeling and design verification, fit and function testing, presentations to potential customers, requests for bids, and patterns for molded tooling and investment casting. Big paybacks come from applying RP in as many areas as possible. Also, be creative and explore new ways of applying the technology.

In the future, this will change. Systems will be available for specific market niches and used in very specialized areas. For example, you will see machines that produce parts in nothing but investment casting wax. The machine will sell to companies with foundries that use the familiar lost wax casting process. Texas Instruments happens to be working on such a system. By the end of the year, you will be able to buy a system that produces expendable ceramic shells (molds) complete with cores, directly with an RP device. This will end the need for wax patterns and tooling for cast metal parts. Massachusetts Institute of Technology has pioneered this technology; Soligen, Inc. will bring it to market by the end of this year. Soligen is a startup company located in Northridge, California.

Systems will get faster. Speed enhancements will come from improvements in slicing and control software and using more powerful computers for data processing. Improved resin applicators and lower viscosity resins will contribute too. The availability of materials for use with RP systems will expand to include ABS-like plastics. Carnegie Mellon University, DTM, Helisys and Incre are working on systems that produce metal parts.

Increased speed, coupled with production-quality materials, will enable companies to produce final manufactured parts. Already, a few companies have made production parts with RP systems, where volume and material requirements are not high. As it becomes widespread, the industry may choose to call this rapid manufacturing (RM) technology. Continued miniaturization of system components and computers will make it possible to build small, light weight RM systems. BPM Technology, Helisys, Stratasys and Texas Instruments have publicly expressed interest in selling scaled-down machines. Not until these machines become available will we have genuine desktop manufacturing.


So, should you buy now, next year or never? As with most engineering and manufacturing automation decisions, it depends. If you are an organization that can see an immediate return on investment, and if you have the proper endorsement from top level individuals within your company, you may be ready for a system. You must have staff in place that are committed to making it work. If you are just beginning to explore the technology and have not gained the support from the necessary individuals within your organization, a purchase is likely to extend into 1993.

Are there organizations that should never buy an RP system? Yes, if the price/performance ratio of RP systems were to stay the same. However, the technology and prices will continue to improve to the point where nearly every organization, no matter how big or small, will be able to justify a purchase. Before the 90s come to a close, you will be able to buy some form of RP technology for the price you would now pay for a medium-priced pen plotter. By the mid-90s, systems will be available for under $40,000 and it will sit on your desktop -- if your desk has sturdy legs. However, hundreds of organizations will not wait because the competitive advantage of owning a system before then will be intense.