Installing a Rapid Prototyping System

The Economic and Organizational Issues

Terry T. Wohlers

Copyright 1991 by Wohlers Associates


Considering the purchase of a rapid prototyping system? If so, this paper will assist you in determining your costs and staffing needs. Use it as a check list when studying such factors as training, site preparation, equipment, and maintenance. Don't underestimate the role of the CAD system as you begin to plan your modernized fabrication operation.

Keep an eye on future developments as you consider one of seven systems commercially available today. Several developers are working on new processes that are likely to rival the techniques used in today's systems. These new processes may prove to be far simpler and less expensive to purchase and maintain. However, you may not be able to afford to wait years before taking advantage of rapid prototyping technology.

Staffing Needs

Your people are the single most important factor. They can make the difference between a successful operation and disaster. Certain rapid prototyping vendors, and even the press, have been accused of saying "the systems are as simple as pushing a button." Not so. It can take an organization one week to more than a month to get up and running. A Florida-based company is not yet making parts after several months with a system. A Minneapolis company has sold their system.

Meanwhile, companies such as Chrysler's Jeep and Truck Engineering Division and Texas Instruments, have purchased additional systems based on positive experiences with their first rapid prototyping system. In most cases, it comes down to the individuals responsible for making it happen.

Rapid prototyping requires a great deal of practice and experimentation before good parts are made. For example, here's a summary of what is involved when using 3D Systems' SLA-250 system.

A solid or fully-closed surface model of a part is created with a 3D CAD system. A support structure is created and attached to the bottom of the CAD model. The support structure, which is later removed after the part is built, attaches the part to the elevator platform, and supports the part as it is built. The support structure is critical for parts which contain overhanging features. The best location and shape of the support is not always obvious, especially at first.

When the CAD model is complete, the CAD file is converted into an STL file format. The STL format is an interface specification given to CAD software vendors by 3D Systems. Approximately 40 CAD software products are capable of creating an STL file. Nearly all suppliers of rapid prototyping systems, including 3D Systems, Cubital, Quadrax, Stratasys, Light Sculpting, DTM, DuPont, and Helisys, accept (or require) STL files.

The STL file of the model is then sliced, from bottom to top, by the SLA slice computer. Thin cross sections are created with special slicing software called Slice. With Slice, the user can adjust the slice thickness between 0.0015 inch and 0.030 inch. Thin slices create a smoother and more accurate surface, but require more time to process, both at the slice computer and during the SLA building process.

The sliced data accurately defines the shape of the model and is stored in SLI files created by Slice. The SLI files are then merged using special merge software which, in turn, creates additional files. These files are then read by the control computer which runs additional software that controls the movement of the laser and elevator mechanism. Users of the SLA-250 admit that more than 30 input variables exist, and tweaking these variables are key to making good parts. This is why experimentation with the SLA is so important. New designs may require more than one attempt before making an acceptable part.

The processing time varies widely depending on the specified layer thickness and the size of the part. On average, a small part will process about one inch of thickness per hour. One hour of continuous processing on the SLA-250 will cure four cubic inches.

After the part is removed from the SLA, excess material is removed. The most popular method employs ultrasonic cleaning that reaches into small crevices and openings. SLA users also use an alcohol bath to wash off the uncured polymer, as well as a method known as wicking. It involves the use of any kind of blotting material that will soak up excess polymer.

The part is then post-cured using the Post Curing Apparatus (PCA), a chamber in which an intense long wave UV flood of light solidifies the uncured resin contained throughout the part. Natural sunlight will also cure the part. After approximately 20-30 minutes, depending upon its thickness, the part is removed from the PCA. The support structure is cut from the part, and if necessary, the part is sand-blasted, hand-finished, and coated to provide a desirable surface finish.

Plan to dedicate at least one person per machine just for part finishing. Most tools used to trim, smooth, and polish parts are readily available at hardware stores. The cost of all finishing equipment, generally, will not exceed $1,000.

Role of the CAD System

Many rapid prototyping users will confess they underestimated the significance of the CAD system. The problem is most evident in companies new to both rapid prototyping and CAD. The challenge is most evident when they discover the amount of expertise required to create 3D CAD models. Solid modeling software, as well as mature software capable of surface modeling, is very compute intensive and usually requires an expensive workstation with lots of MIPS, MFLOPS, system memory, and disk storage. Budget between $25,000 - $40,000 for one CAD system, complete with software and hardware. Allow for several days of training and learning, combined with weeks of hands-on practice.

If individuals in your organization are already familiar with CAD, particularly 3D modeling, one of the biggest hurdles of rapid prototyping is behind you. Unfortunately, 3D modeling is not used by most organizations -- even those organizations that have it -- so additional emphasis may need to be placed on producing geometrically correct and water-tight models.

The CAD software must be capable of generating an STL file. CAD vendors offering an STL output capability in their software include Aries, Autodesk (available from Enigmatic Associates of Costa Mesa, CA), Cadkey, IBM, Computervision, Hewlett-Packard, Schroff Development, Control Automation, Intergraph, Parametric Technology, Prime, SDRC, Schlumberger, and Matra Datavision.

Equipment Costs

Today, rapid prototyping systems (excluding the CAD system) range in cost from $95,000 to just under $500,000. Some of the more progressive developers are considering the introduction of systems for under $50,000 in the future, but no formal announcements have been made to date.

The primary differences between 3D Systems' three SLA models are maximum part size, speed and cost. The SLA-190 is priced at $95,000, compared to $187,000 for the SLA-250, and $385,000 for the SLA-500. Budget an additional $10,000 for 3D Systems' Post Curing Apparatus (PCA) and $1,000 - $2,000 for an off-the-shelf ultrasonic cleaner. While both of these components are optional, you will need to consider some means for post curing and removing the excess resin prior to the post cure.

Quadrax Laser Technologies (Portsmouth, RI) has priced their Laser Modeling System, called the Mark 1000, at $195,000. This price includes the Laser Modeling System, Light Curing Oven for final curing of parts, software interfaces, 15 gallons of resin, supervision of installation by a Quadrax engineer, and two weeks of training at the Quadrax facility in Rhode Island.

Meanwhile, Helisys, Inc. of Torrance, CA (formally Hydronetics), is selling beta units for $75,000 and $110,000. Cubital America Inc. of Warren, Michigan, has priced their huge Solider 5600 Solid Ground Curing system at $490,000. Light Sculpting (Milwaukee, WI) offers systems for $99,600, $129,700, and $159,500. The optional mask photoplotter for use with Light Sculpting's systems is $25,000. Their post curing apparatus is $10,000.

The Stratasys, Inc. (Minneapolis, MN) Fused Deposition Modeling system, called the 3D-Modeler, is priced at $178,000. The system consists of the main 3D-Modeler unit, StrataSlice slicing software, and a Silicon Graphics Personal Iris workstation. You can purchase the system without the workstation and Camax system software for $130,000. In early 1992, DTM Corporation (Austin, TX) expects to introduce their SLS Model 125 in the $300,000 - $400,000 range.

Technology from Perception Systems, Inc. (Easley, SC), called Ballistic Particle Manufacturing (BPM), is not yet available. However, the company hopes to introduce a system in 1992 for under $50,000. Small systems designed for applications with less restrictive tolerances may cost as low as $15,000. The ceramic-based ink jet process being developed at the Massachusetts Institute of Technology is still two or so years away from commercialization, so pricing is not yet available.

Maintenance Costs

System maintenance varies greatly from system to system. First, you should consider whether or not a local service person is available to service the system. Most companies now launching systems will not have a local service organization in place. Those systems without a laser, generally, will cost less to maintain. For instance, 3D Systems charges $36,000 per year for their SLA-250 maintenance agreement. This includes full replacement of the laser. Without laser replacement, the maintenance cost drops to $16,000 per year. The replacement price of an SLA-250 laser is $9,200. The SLA-500 laser is priced at $25,000.

Most of the other system developers are presently formulating and fine-tuning their maintenance agreements. For example, Scott Crump, president of Stratasys, does not yet know the amount of maintenance required for his 3D-Modeler system. He says he will know more after beta testing is complete, which is currently underway at five sites. The 3D-Modeler comes with a one-year warranty, and is engineered to stay operational for five years, according to Crump. The system does not use a laser, so replacement of this expensive component is not a concern.

The Mark 1000 from Quadrax comes with a one-year system warranty (re: the laser, one year or 2000 hours, whichever comes first), and two service calls. An additional year of maintenance and warranty is priced at $16,000; the following year is $24,000. Light Sculpting's systems comes with a one-year parts and labor warranty. Set aside $10,000 for their optional annual maintenance agreement.

Resin Costs

Generally, the cost of the liquid polymer is $300 - $350 per gallon for the SLA and Quadrax system. The cost per part will vary depending upon its size. The material cost of a small part (that fits inside a six-inch cube) is usually under $25. DuPont's 2100 and 3100 resin materials, currently being beta tested, will sell for $550 per gallon.

A mile-long spool of wax or nylon filament for use with Stratasys' 3D-Modeler is currently priced at $350. One spool is equivalent to one gallon of polymer. Therefore, budget $8,750 - $10,500 for 25-30 spools per year.

Consider the initial cost of filling an SLA vat. The SLA-190, which has a vat size of 5.5 gallons, will cost $1,925, at $350 per gallon. The SLA-250's 7.8 gallon vat would cost $2,730 to fill. Budget $23,450 to fill the SLA-500's 67-gallon vat.

Site Preparation

You may need to make a few facility changes when installing certain rapid prototyping systems. For instance, most liquid resin-based systems, such as the SLA-250, requires proper ventilation. The facility must have the capacity to change the room air at least six times a minute. As for electrical needs, the SLA-250 only requires a 110-120V outlet and a 20A circuit. Also, set aside adequate space for the rapid prototyping unit, CAD system, UV oven, ultrasonic cleaning, finishing area, and storage of supplies, such as the polymer.

Experiment Before You Buy

A rapid prototyping system is not the answer for the development of all parts. For instance, it may be more practical to use conventional CNC milling, depending on the shape of the part and material requirements. If it is impossible for the cutter to reach small interior cavities and parts with complex internal geometry, a rapid prototyping system may be the answer.

Many of the companies developing rapid prototyping systems are also operating as a service bureau. This gives developers the opportunity to apply their systems to industrial needs and improve the design prior to full-scale system production. Also, they generate cash.

The service bureau approach gives potential buyers the opportunity to experiment before buying. Companies such as Quadrax, Cubital, Helisys, Stratasys, Light Sculpting, DTM, and DuPont will create parts for you on a contract basis. Approximately 40 independent SLA service bureaus are available in the U.S., Canada, Europe, and Japan. Send them engineering drawings, pictures, and CAD or STL files and they will send you a quote.

Return on Investment

Many companies with rapid prototyping systems say it is difficult to accurately measure their return on investment. Most, however, believe they made a worthy investment. The difficulty with measuring success is similar to quantifying the benefits of 3D CAD modeling. Part modeling on a CAD system introduces new capabilities, such as the automatic generation of mass properties, which is difficult to compare with old methods. Also, design is an iterative process which involves a wide mixture of ideas, what-if scenarios, and trial 'n error.

The same is true with rapid prototyping. Most companies believe the investment is paying off because they are able to do things that could not be done previously. For instance, companies can more easily send a part with a bid package, making the quote much more accurate. This is one of the primary benefits of rapid prototyping at Ford Motor Company. Additionally, concept models and models for design verification usually improve the design process, but the extent to which it improves varies widely from user to user and job to job. Client presentations are also enhanced greatly and companies genuinely believe this powerful visual aid attracts dollars. But they have no way to accurately quantify the return.

Companies, such as the Packard Electric Division of General Motors say their rapid prototyping system has reduced the time to produce prototypes for form, fit, and function applications. The division has built hundreds of parts to date with an average build time of just five hours per part. Ford Motor believes that rapid prototyping systems reduce their prototype development time by 75-95 percent. Medical companies and service bureaus also shorten the time required to produce masters for molded tooling and investment castings.

Copyright 1991 by Wohlers Associates