RP Brings 3D Printing to the Design Office

By Terry Wohlers

Published in Vol. 15, No. 8, August 1996 issue of Computer-Aided Engineering
Copyright 1996 by Terry T. Wohlers

It's hard not to get excited about the impact that rapid prototyping (RP) is having on manufacturing and tooling. This excitement is heightened even more, thanks to the introduction of a new generation of RP machine technology that some are referring to as "3D printing."

This class of machine is targeted at the design engineer for concept modeling and early design review. The equipment builds a physical model--think of it as a rough draft--that helps designers more quickly iterate and advance the design before going to more expensive prototyping options. These office-friendly machines--offered by RP vendors including 3D Systems Inc., BPM Technology, and Stratasys Inc.--sit next to CAD workstations, office copiers, and fax machines.

While a typical RP part usually costs a few hundred to more than a thousand dollars and takes days to a week or longer to produce and finish, 3D printed parts generally cost under $50 and take less than a day or two to build. While the life of an RP part is often days or weeks, the life of a 3D printed part may be only minutes or hours.

3D printers work from geometry generated by CAD solid modeling software. The machines are designed for speed and ease of use, so users are not given the range of software "build" parameters nor a choice of materials that are available for higher-end RP systems. However, most designers are willing to sacrifice flexibility for such significant time and cost savings.

Why 3D Printing?

As a communications tool, "good visuals" such as engineering drawings and shaded renderings help sell ideas. However, visuals that you can touch and study, such as 3D printed parts, are the most compelling. When a physical model is a part of a presentation, the proposal has a much better chance of coming out on top.

Andersen Corp., Bayport, MN, makers of the popular line of wood windows and patio doors, believes that having models available at presentations can have dramatic effects. "A rendering of a solid model communicates information 10 times more easily than engineering drawings," explains Jim Wyman, an engineer at the company. "The availability of a physical model increases this understanding by an additional 10-fold," he adds.

3D printing also helps to reduce the number of costly engineering change orders. The cost of an engineering change increases roughly by an order of magnitude as the design progresses from one significant development phase to the next.

Lockheed Martin Tactical Aircraft Systems, Fort Worth, TX, believes that because engineering can impact the cost of a product exponentially at the design phase, it is increasingly important to provide as much design information as early as possible. Art Kock, design manager at Laserform, an Auburn Hills, MI-based RP Service Bureau, concurs: "The more you can iterate early, the less you have to do it later when it's much more expensive."

To help continuously enhance designs, Andersen Corp. produces as many design iterations as time allows. On one project, using 3D printing, engineers were able to iterate the design as many as 15 times in a three-week period. This approach helped them catch mistakes that they otherwise would have missed.

For example, they caught a misalignment problem that initially wasn't evident in the CAD model, even though it was a very simple part. If they had produced new tooling and gone to production, not knowing that the part was flawed, they would have been faced with the decision of going to market with a substandard design or delaying the introduction of the product by several weeks. This model alone nearly paid for the cost of the 3D printing system.

Leveraging CAD

Many managers and users of CAD solid modeling do not know that they are not taking full advantage of their investment in CAD. It is not unusual for the cost of CAD hardware, software, network administration, maintenance agreements, technical support, training, and good people to add up to hundreds of thousands, sometimes millions, of dollars. Even after all of the training and years of improving and optimizing an approach to solid modeling, companies can wring out much more capability, productivity, and throughput.

One of the main purposes of CAD solid modeling is to create an exact replica--a digital mockup--of the proposed design, all within the CAD system. This has proven to work well, but not as good as it should. Short Brothers, makers of the Lear 45 executive jet, believes that solid modeling is not necessarily faster than alternative design methods, but it offers significant benefits in downstream activities.

One of those benefits is RP, yet companies often must wait a week or longer to receive back an RP model of their design. This time lag, coupled with the cost of the model, means that designers must intentionally delay the production of the first physical model until the design has been refined. The product development team would like to get the first model sooner, but time and cost prohibit it.

3D printing moves the first physical modeling cycle earlier in the design process. Rather than sending the CAD model data to a centralized site for processing, it occurs within the engineering office. The time and cost of producing 3D printed models are minimal (see What Does a 3D Printed Part Cost?), so designers can produce them routinely to help them understand and communicate how the design, and proposed changes to it, will affect the outcome of the new product.

Experienced managers and users of solid modeling view 3D printing as an extension of the CAD solid modeling concept. If they truly understand and believe in the benefits of CAD modeling, it's easy for them to understand the benefits of 3D printing.

David Tait, president of Laserform, believes that 3D printing enhances the creative ability of designers. "It permits them to experiment with new ideas and print them in 3D space," he explains. "Furthermore, designers are under intense pressure to turn around new designs quickly, so this technology is a perfect fit."

Robert Delisle, a project leader at Pratt & Whitney, Hartford, CT, expects that 3D printing will help designers catch and fix more errors. "This may mean that they spend more time refining the design near the beginning of the design process, but it will reduce the overall development time and improve product quality," he says.

Design Challenges

Designing complex parts and assemblies using CAD can be a difficult and time-consuming task. As complexity increases, so does the difficulty in checking the correctness of the geometric data. Problems occur with misaligned holes, interferences, structural ribs in the wrong place, and improper mating of parts. Interferences occur with cables, wire harnesses, hoses, and tubing as well as with other mechanical and electrical subassemblies.

Printing the design in 3D space allows the designer to verify the correctness of the CAD database. Identifying just one interference can pay for the purchase of 3D printing. Verifying the CAD database is especially important prior to creating tool paths for CNC machining of metal parts.

Today, companies are creating an unprecedented number of plastic injection-molded parts that contain smooth-flowing, ergonomic shapes. Other ergonomic design considerations include ease of use, noise, vibration, balance, size, and weight. With the support of 3D printing, designers can more easily test new shapes and sizes very early in the design cycle.

In Sync with Suppliers

Delays often occur at the tooling phase when communication is weak between the designers and the tooling experts. Overly complex designs, walls that are too thin, and improper draft angles cause unnecessary delays. Companies can minimize these headaches by communicating more often and with greater accuracy. Models from 3D printing give the tooling department a chance to influence the design when changes are inexpensive. In a sense, it moves expensive tooling iterations into the design office--an approach that can save companies weeks of time.

Suppliers admit that they pad their quotes to cover misinterpretations of the design requirements. When it's time to send an official request for a quotation, the sender can enclose an inexpensive 3D printed model of the design. This helps to clarify any ambiguities in the engineering drawings and design specs.

From a supplier's point of view, Laserform's Tait also recognizes the opportunity of installing a 3D printing system at toolmakers' sites. He believes that it could be a catalyst that brings together designers and toolmakers.

"Contractors routinely include an additional expense of one-third to two-thirds to cover any misunderstandings," maintains Pratt & Whitney's Christopher O'Neill. Both Pratt & Whitney and Laserform have sent models with requests for quotes, but this practice can be expensive when producing these models with high-end RP equipment. The use of 3D printing reduces this cost considerably.

O'Neill believes that it makes sense to also locate 3D printing systems in the purchasing department so staff can more easily access models and forward them to those bidding on projects. "Companies that use printed renderings from 3D CAD models typically see quotes that are lower by 10%," says Peter Marks of Design Insight, Santa Cruz, CA. Suppliers quote even more accurately, potentially lowering quotes further, when a physical model is included with the request.

Justifying the Cost

"The task of justifying the cost of 3D printing at Andersen Corp. is easy," notes Merlyn Leslie, Sr., manager of CAE Technical Support at the company. "We compare the cost of producing in-house models," he says, "with those produced by other companies on a contractual basis. On average, we have found 3D printing to save us more than 90% of the cost of modeling."

Leslie continues, "In-house, a model may cost $50, but having it done by someone else can easily cost more than $1,000. Doing the work within our company also provides for faster turnaround, and proprietary designs stay inside the company."

In justifying the cost of 3D printing, Laserform considers the cost of a small part such as a machine knob. "If a company were to have it built by a service bureau (SB) using stereolithography technology, the part might cost about $250," explains Tait. "If the same SB were to build it using 3D printing," he adds, "it would probably cost around $95. If the company were to build it in-house, on its own 3D printing equipment, it would cost in the $25-$50 range. Also, turnaround would be much shorter."

Andersen Corp. has not yet encountered a part that it could not build with its 3D printing system, a Genisys machine from Stratasys. "When faced with the decision of buying four engineering workstations or two workstations and one 3D printing system," says Andersen's Wyman, "the two workstations and 3D printing combination would be the preferred choice.

"The company," he continues, "sees no boundaries for the use of 3D printed models and expects to use them company-wide. In the future, we envision each major project having a 3D printer dedicated to it."

Prototyping, with or without RP, is expensive. By modeling early and often, companies rely less on both conventional prototypes and RP parts. Essentially, much of this physical modeling can and should occur as it did before, but at the front end of the process.

"3D printing moves some of the prototyping to a point much earlier in the design cycle," according to Pratt & Whitney's Delisle. "It might be helpful," adds Laserform's Kock, "to build scaled models before producing a full-scale model on a larger and more expensive RP machine." This should help reduce the number of prototype iterations, which can be expensive, both in time and money.

How does Andersen Corp. see 3D printing impacting prototyping at the company? Jim Wyman sums it up in one word. "Huge!"

WHAT DOES A 3D PRINTED PART COST?

What's the cost of building a small part using the Genisys 3D printer from Stratasys? About $27. This estimate assumes that you are building Chrysler's speedometer adapter benchmark part which measures 2 2 2 2 3.25 in. Larger parts, of course, would take longer and cost more to build.

Based on a Genisys purchase price of $55,500, the machine depreciation is estimated at $3.09/hour, assuming that the machine runs 12 hours/day, 5 days/week, for 5 years, and has a salvage value of 10% of the machine purchase price at the end of the 5-year period.

The maintenance contract expense is estimated at $1.54/hour, based on $5,000/year maintenance contract. Staffing cost is an estimated $5.00 (10 minutes of time) based on an hourly rate of $30.00/hour. Material cost is estimated at $8.00. Total build time for the part is about 3 hours.

The total estimated cost to build the part, therefore, is $26.89. This does not include indirect overhead, a cost that can range from 10% to more than 300% of the direct costs associated with producing a part. Also, this estimate does not include any file conversion or repair work such as translating IGES files or fixing defective STL files.

Considering the value of a model, most large companies would view $27 (for a small model) as an insignificant expense, although this can vary from company to company. Pratt & Whitney agrees that it is insignificant, but some companies carefully consider the cost of paper and other consumables when producing prints of line drawings and renderings.

Terry Wohlers of Wohlers Associates, Fort Collins, CO, focuses on CAD/CAM, rapid prototyping, and reverse engineering developments, applications, and management strategies. 

Copyright 1996 by Terry T. Wohlers