By Terry Wohlers
Published in Vol. 12, No. 9, September 1993 issue of Computer-Aided Engineering
Copyright 1995 by Terry T. Wohlers
Interested in rapid prototyping (RP) systems, but can't justify the $50,000 to $550,000 purchase price? No problem. Consider one of many service bureaus that specialize in producing models and prototype parts using RP systems such as stereolithography.
In a few short years, about 80 of them have popped up around the world. The majority of them, about 50, are located in the U.S. Their services range from making a single RP part to producing quantities of 50 or more copies using conventional prototype tooling techniques.
Usually, the first step in using an RP service bureau is to obtain a quote for the job. You'll need to describe the geometry, dimensions, and tolerances of the part(s) you want to have built as well as the intended application of the part(s). This will enable the company to recommend the most appropriate materials and processes to use. While you may think you know the best materials or processes, service bureau operators can recommend ones that best fit the performance requirements of the part(s). They are experts, so it's important to listen to their opinions.
Most service bureaus will accept nearly anything you give them, but you will pay extra if what you send them requires additional work. For example, if you send them drawings, they will need to create a 3D CAD model from the drawings before they can begin to produce the RP part. This task can cost as much or even more than producing the part itself.
One job performed at Laserform, an RP service bureau in Auburn Hills, MI, required 120 hours of CAD work before staff could begin to produce the physical part. According to David Tait, co-founder and managing partner of Laserform, the cost of the data conversion and CAD modeling exceeded the cost of producing the RP part by two to three times. The CAD data came to them from General Motors as a CGS (GM's corporate CAD) model, which contained a combination of wireframe and surface entities. As a side note, when Laserform converted it into a Catia solid, the file size grew from 2.5 megabytes to 7.2 megabytes.
Sending an STL file to the service bureau is usually the best and least expensive option. This file format is the industry de facto standard for linking CAD systems to RP systems. Nearly all CAD systems used for mechanical design can output an STL file. The steps and time to create an STL file are similar to creating an IGES or DXF file. Frost Prioleau, president of Plynetics Corp., a service bureau in San Leandro, CA, says that more than 50% of the jobs submitted to his company are now STL files. Four years ago, less than 20% of the jobs were submitted in STL format. This change is due mainly to an increased awareness of the STL file format and the fact that a translator comes as a standard or optional feature of many CAD programs.
Service bureaus will also accept IGES and DXF files. However, the bureau will need to import the file into its CAD system and then output an STL file. While this task is straightforward, the work in between can be very timely and expensive for the customer.
For example, RP systems require a fully closed, water-tight surface, so a skilled CAD technician must review the imported data. If the model contains missing surfaces, the work will require the creation of additional surfaces. This can take hours or even days. Also, the work may introduce unwanted changes that would result in an unsatisfactory part. If the file contains 2D geometry only, plan to pay nearly as much as if you had handed the service bureau a set of drawings. Adding surfaces to a wireframe model can be time-consuming. Creating an STL file from a solid model is the best.
Some customers of service bureaus will want to send a binary CAD file, the default file type created by their CAD system. The service bureau can accept the file only if it has the same CAD software as you-or a binary translator that enables the file to be converted into its CAD system. In most cases, there's no reason to send a CAD file when you can just as easily send an STL file. What's more, the STL file enables the bureau to send the file directly to the RP machine for part production, and it eliminates the chance of the bureau inadvertently introducing unwanted changes in the CAD file.
The cost of having a bureau make a single part can range from a few hundred to several thousand dollars. Cost depends entirely on the amount of preprocessing time, build time, and postprocessing time.
Preprocessing usually refers to the steps leading to the STL file creation, which include data conversion and CAD work. Build time is the time it takes to make the part on the RP system. Large, massive parts typically take longer than small ones. Height of the part is the most critical factor since all RP systems build parts in thin layers. Tall parts require more layers than short parts. Often, service bureaus will lay the part on its side to minimize the height of the build.
Postprocessing time refers to the work required after the part has been removed from the RP system. In the case of stereolithography, the part must be postcured in a flood of ultraviolet light. After the resin has been fully cured, a skilled technician will bench the part, requiring hand work such as sanding to produce a smooth surface finish. Sintered parts often require sand/bead blasting to remove the unsintered powder. Also, sintered polycarbonate parts may require hand sanding and an impregnation of epoxy resin to improve strength and surface finish. The amount of postprocessing work usually depends on how you plan to use the part. If you plan to use it as a master for molded tooling, surface finish is critical.
One of the most obvious advantages of using a service bureau is the low risk. Someone else bears the cost of buying and maintaining the RP system, not you. Investing in an RP system can add up to more than a quarter million dollars. The most expensive setup will approach $750,000 by the time you add in the hidden costs. The least expensive option is around $60,000. In addition, you'll have to employ trained technicians to operate the equipment and bench the parts. Organization and control of the jobs that are submitted to the RP operation also require management resources. When using a service bureau, you can ignore these issues.
So why would you ever consider buying an RP system when you can use a service bureau? The same reason you own CAD systems rather than contracting your design and drafting work.
When the operation is in-house, you have more control, and turn-around can be shorter. Also, many projects are sensitive, making it riskier to send them outside the company. Of course, service bureaus sign nondisclosure agreements all the time, but managers are sometimes more comfortable keeping secrets inside the company.
Also, if your in-house RP facility is efficient and well-managed, you can produce parts at a lower cost than having them built by a service bureau. If your company has plenty of jobs to keep the RP machine busy most of the time, lower part cost and savings in turn-around time can justify an RP system purchase. If the machine is operating only a few hours a day, you may be better off using a service bureau.
Customers of service bureaus often want more than one copy of a part. Most RP systems enable you to create more than one part at a time, and most RP system users take advantage of this capability. However, building multiple copies of the same part geometry with the RP system is not necessarily a good approach. It can be faster and less expensive to produce copies of a part using a secondary tooling process.
Typically, a service bureau will use the RP system to produce the original model-the most difficult and historically time-consuming part of the process-and use it as the master (pattern) for creating tooling. The RP part is the link between CAD and secondary tooling.
According to Laserform's Tait, 80-90% of the stereolithography parts the company builds are used for secondary tooling. "The tooling," he says, "allows us to produce parts in materials that offer mechanical properties that are superior to RP parts. This permits us to produce parts for fit and functional testing." Better material properties, coupled with the time and cost savings, are the driving factors toward using secondary tooling processes.
Service bureaus are taking advantage of traditional model making and prototype tooling to meet customer demand. The techniques include RTV silicon rubber tooling for 2-50 pieces and aluminum-filled epoxy or spray metal tooling for 50-1,000 pieces. Using these processes, service bureaus can produce parts in urethane, ABS, poly-carbonate, polypropylene, polystyrene, and polyethylene. Some service bureaus produce metal parts using plaster and sand casting processes. Presently, RP systems, such as stereolithography, produce parts in acrylate and epoxy-based materials only. DTM's Sinterstation can produce sintered parts in polycarbonate, nylon, and investment casting wax.
"When we began our business four years ago, I didn't realize how important traditional model-making was to our business," says Prioleau. "Blending new techniques with the old ones is critical." When Prioleau started Plynetics in 1989, the company offered very little in the way of conventional processes. Now, Prioleau runs a traditional model shop with 9 full-time people out of 17 total employees. Having the capacity to offer a variety of solutions is what Prioleau feels makes his company special. He's been successful at bringing together modernized tools-stereolithography, selective laser sintering, and CNC-with traditional techniques-model-making, molding, and casting-that have been around for decades.
Laser Prototypes of Denville, NJ, has taken a different approach. It agrees that secondary processes are important but has not brought these capabilities in-house. Instead, it subcontracts the necessary work with other companies that have the tools and expertise. According to Bill Coleman, founder and co-owner of Laser Prototypes, the company stays focused on creating good parts using two SLA-250 stereolithography systems but arranges to have someone else do the secondary tooling and multiple part production.
Coleman has spent the last several years building a network of organizations that can deliver whatever his customers need. The customer doesn't usually care who does the work as long as it's done correctly, on time, and at a reasonable price. Laser Prototypes operates Aries' Conceptstation, SDRC's I-DEAS, and Autodesk's AutoCAD. In addition, most of the 10 sales representatives, who work directly with the customer, have CAD modeling capabilities. If Laser Prototypes receives a CAD file it cannot read, the file is sent to a company that translates the file into a readable format. Presently, Coleman says that about 75-80% of the files his company receives are in STL form.
Rather than going after the entire market, many service bureaus have specialized and targeted specific markets. Laserform, for instance, has carved a niche in the production of rubber seals, the kind that you see around the doors and windows of an automobile. The complexity of the seal geometry makes it ideal for RP processes.
Typically, RP pays off the most when building complex parts, so the more complex, the better. It's often more practical to produce less complex shapes using tools found in most machine shops, such as mills and lathes. The really tough jobs go to companies that have RP capabilities, such as Laserform.
Laserform has experienced rapid growth, expanding from two employees in 1989 to 13 full-time employees. In addition to its SLA-250 RP system, it operates IBM's Catia, SDRC's I-DEAS, Aries' Conceptstation, and Cubital's new Data Front End (DFE) software to view and repair STL files. "Expertise in the use of this software is as important as the expertise required to run the RP system," claims Tait. "The parts that come off the system are only as good as the data you feed into it," he adds.
Mack Industries, also in the Detroit area, concentrates on delivering high-quality metal castings from complex tooling. Mack is the only company that owns and operates two Helisys Laminated Object Manufacturing (LOM) machines. It runs them 24 hrs a day, seven days a week. The company has ordered a third machine.
Merlin Warner, vice president of sales and marketing at Mack, says that traditional pattern-makers are very comfortable with LOM parts because of their wood-like properties. LOM parts resemble wood because they are created from thin sheets of paper.
The company employs 15 pattern makers, with many spending much of their day benching parts as they come off the LOM systems. The company uses the parts as patterns for tooling, which in turn are used for castings of automobile parts such an intake and exhaust manifolds. The company has created 250-300 LOM parts since it installed the first LOM machine 11Ú2 yrs ago. Many of the parts are large compared to the average size of an RP part.
Presently, Mack is using LOM to produce 60-70% of its patterns. The company expects this to increase to about 80% over the next year, after it receives the third machine. Eventually, it plans to produce nearly all of them using LOM, but Warner believes there will always be a need to do a small percentage the old way.
Who else has gotten into the RP service business? Large corporations, including Baxter Healthcare, Hughes Aircraft, and DuPont, now offer RP part-building services. Baxter's Advanced Engineering Design Center (AEDC), for example, operates Ster-eoLithography and Solider equipment from 3D Systems and Cubital, respectively. Services include not only rapid prototyping but also conventional molding and casting techniques, 3D laser scanning, engineering analysis, and production tooling. Because AEDC functions as an integral part of Baxter Healthcare Corporation's product development arm, the Baxter RP service bureau has an unusual number of resources at its fingertips.
RP system manufacturers, including 3D Systems, DTM, Helisys, and Stratasys, also offer outside services, similar to that of a service bureau. DTM offers two: one in Cleveland and one at its headquarters in Austin. The company has opened its own service bureau in Germany and plans to establish a network of franchise service bureaus in Europe. Cubital doesn't offer a service in the U.S., but Stature Machining Technologies, a service bureau in Detroit, owns two Cubital Solider systems. Protogenic, a service bureau in Boulder, CO, also owns a Solider system.
Terry Wohlers is Chairman of the Rapid Prototyping Association of SME and President of Wohlers Associates, Fort Collins, CO, a consulting firm.
Copyright 1995 by Terry T. Wohlers
Baxter Healthcare Corp., Round Lake, IL, 708/270-4056, Fax: 708/270-4077
DTM Corp., Austin, TX, 512/339-2922, Fax: 512/339-0634
Du Pont Company, New Castle, DE, 302/328-5635, Fax: 302/328-5693
Helisys Inc., Torrance, CA, 310/782-1949, Fax: 310/782-8280
Hughes Aircraft Company, El Segundo, CA, 310/616-3415, Fax: 310/616-0262
Laserform Inc., Auburn Hills, MI, 313/373-4400, Fax: 313/373-4403
Laser Prototypes Inc., Denville, NJ, 201/361-7666, Fax: 201/361-9677
Mack Industries, Troy, MI, 313/588-1742, Fax: 313/588-2452
Plynetics Corp., San Leandro, CA, 510/613-8300, Fax: 510/632-6682
Protogenic Inc., Boulder, CO, 303/442-4604, Fax: 303/442-1368
Stature Machining Technologies Inc., Warren, MI, 313/758-7333, Fax: 313/758-7337
Stratasys Inc., Eden Prairie, MN, 612/937-3000, Fax: 612/937-0070
Tri-Tech Precision Inc., Anaheim, CA, 714/970-1363, Fax: 714/970-1902
3D Systems Inc., Valencia, CA, 805/295-5600, Fax: 805/295-0249