3D printing speeds design cycle

Model-making has long been an element of the design process. But the time and expense of traditional model-making techniques have always limited their use. Recently, new rapid-prototyping technologies were introduced, expanding the use of models. And now, a particular method of rapid prototyping called "3D printing" has further expanded the use of model-making as an integral component of the design process by producing models dramatically faster at a substantially lower cost.

Traditional model-making techniques . Traditional, low-end methods of generating models involve interpretation of a 2D drawing by a skilled model-maker. These methods include:

Hand-forming of clay

Wood carving

Wire-cutting of foam

Manual or CNC machining of various materials such as artificial wood, foam, or plastic

Although these approaches can be up to twice as expensive and take twice as long as producing a 3D printed part, they have the advantage of not demanding a 3D CAD file because the model-maker can simply interpret a sketch scrawled on a napkin. Ultimately, however, this attribute turns into a disadvantage because the designs are then subject to interpretation and to potential errors of the model-maker-the physical model does not necessarily represent the CAD data and so may not represent the actual design that will be produced.

High-end rapid prototyping . Rapid prototyping (RP) refers to any additive method-where a part is built up, instead of carved down-of fabricating a part directly from a CAD file. This has the benefit of forming a part that is inherently true to the CAD design. High-end RP has been used for over ten years and has been adopted by many companies for the later stages of the design cycle. However, the equipment costs $100,000-$800,000. Also, extensive training and expertise is required, the processes are labor-intensive, and the materials and ongoing maintenance are expensive.

3D printing . 3D printing is a less-expensive method of RP that is often faster. The essence of 3D printing is that it gives the designer better access to models, which provides the freedom to make many more of them. This accessibility comes from its high speed, low cost, and ease of use.

Speed is the most important criterion in the early stages of the design cycle because the design process cannot stop to wait. A model that requires more than a few hours to be produced becomes obsolete before it is complete. The total cost per model made by 3D printing is low enough-a few dollars for a hand-held part-that the designer is not inhibited from making thirty iterative design models on a given project.

These models are as disposable as paper printouts, and can be printed inside the office, so engineers are not reliant on third-parties to make their parts.

When to use 3D printing. 3D printing can be used from the first moment the 3D CAD file is complete. Since each iteration of the design can result in a new 3D-printed model, design proofing becomes more simple and convenient. As a means of communication, 3D-printed models can provide a common medium of exchange between designers, engineers, marketers, customers, managers, or manufacturing personnel. Models are also valuable for appearance review, and evaluation of form and fit.

The method is most useful for visualizing parts with complex geometries. Ergonomic testing is elevated to a higher standard; ergonomics can be incredibly misleading on the computer screen, and are instantly verified with a 3D model. Testing of form, assembly fit, and even air flow is possible with these physical models. Finally, models can be used for early-stage functional prototypes or for secondary processes such as casting and molding. The result is improved communication, fewer mistakes, and better design.

When not to use 3D printing. 3D printing will not closely replicate the end material properties of the end product. If your end product is metal or requires snap-fit, it may be best to pursue one of the other forms of RP or CNC.

Choosing a 3D printing technology. Many companies provide 3D printing services, including 3D Systems (Valencia, CA), Stratasys (Eden Prairie, MN), and Z Corporation (Burlington, MA), so your first choice is whether to use a service bureau or to buy your own equipment.

When using a service bureau, turnaround time will depend more on current machine capacity than the inherent speed of each technology. When purchasing the equipment, it is helpful to run a timed benchmark of a representative file of one of your own product designs using the different technologies.

The best way to evaluate ease of use is to talk with users of the technology, and request references from vendors. If the process you are investigating requires support structures, make sure you test the process of removing the support structures before you make a purchase decision.

When evaluating part quality, consider properties such as: part strength, accuracy, resolution, and surface finish. Make sure you have your own design prototyped on the various technologies, as the different technologies have varying abilities to replicate complex geometric features, thin walls, or parts of large or small proportions. If you plan to handle the parts in meetings or send them through the mail, some rough handling or a drop test might be a good idea. In addition, consider not simply the quality of the part as it is removed from the 3D printer, but also the ability to further finish the part for improved part quality. It may be useful, for example, to be able to simulate an injection-molded plastic part for obtaining feedback on new product introductions at critical trade shows.

Secondary processing refers to the use of 3D printed models for subsequent use as patterns for investment casting, sand casting, RTV molding, and similar processes. While clearly outside the scope of the concept of quick draft modeling, some technologies are well suited for these applications.

The cost of 3D printing
The total cost per model is easy to calculate using the initial investment, utilization forecasts, materials and labor. These assumptions can vary, depending on factors such as part complexity, part quality desired, and-for CNC-materials used (e.g., Ren, yellow foam, ABS).

Converting to an STL file

. In order to utilize RP, the design must be exported from the 3D CAD system into the STL file format. STL is the de facto standard file format for all rapid prototyping equipment and approximates the surface of the solid model by covering it with a multitude of small triangles. A good method to keep down the file size is to save the file as binary STL and use the minimum number of triangles you require for acceptable accuracy.

Bringing 3D printing to your organization. When the CAD file of your next design project is complete, export the STL file and e-mail it to a colleague with a 3D printer, to a service bureau, or to a vendor of 3D printers. Then bring the 3D-printed part to your design review meetings, and see how it changes the process compared to paper or CAD plans. Keep in mind that the most significant advantages of 3D printing are its speed and low cost, features that will be lost in using a third party vendor. Quotations from service bureaus will vary with the particular 3D printing equipment used, the part complexity and any finishing requirements.

Effect on the design cycle . 3D printing brings a variety of changes to the design cycle. Design verification and error detection is possible by the designers themselves, but also enhances their communication with others.

Overall, there can be more iterations of a design, more experimentation of alternate design possibilities, and less of a push to fix on a concept early on. Designers' arguments over alternate concepts can be easier to resolve because the model will provide the answer.

By providing almost instantaneous feedback on each proposed design change, 3D printing allows the designer to make more iterations of a design at a faster rate. By improving communication between engineering groups and feedback from the marketing department and potential customers, 3D printing leads to better product design. It is cheaper than any other method for obtaining a physical model that can ultimately lead to early detection of potentially costly flaws in the design for manufacturing.

Marina Hatsopoulos is CEO and a founder of Z Corp., which makes the Z402TM 3D Printer. She can be reached at [email protected] or via the company's web site at www.zcorp.com .