This column was published in the
November/December 2005 prototyping selection supplement. For more great articles,
visit the "Time-Compression Technologies'"
Web site at

Protoyping Process Selection
Advisor's Note

Todd Grimm

to Time-Compression Technologiesí service provider supplement. In the following pages, you will find the tools for selecting suitable prototyping methods for both plastic and metal components. This prototyping selection guide is the first of its kind. Nowhere else will you find a decision making tool that covers additive (rapid prototyping), subtractive, and formative methods. We hope that you find this guide useful in process selection for your future prototyping needs.

Selecting the right prototyping process can be difficult, but it is critical to the success of your product development programs. Picking a solution requires experience, information, and understanding of a broad set of processes, techniques, and technologies. This is a skill that few possess, especially when expanding the scope to include all additive, subtractive, and formative methods. While some individuals can look at a design and quickly identify the best options, most of us don't have this ability. Often, the selection is based on familiarity and past experience. However, this is not the most effective way to select a process that delivers a suitable prototype in the time allowed and within budget constraints.

This selection guide is designed to help the novice or moderately informed individual navigate the wide range of prototyping options, Yet, even the well informed will find valuable information within this tool. Having participated in the world of product development for more than 20 years, I thought that I knew the advantages and limitations of all of the methods. How wrong I was. In researching the technologies to provide you a clear navigational aid, I learned new things about many of the processes.

Our goal is to offer you a tool that helps you to select a prototyping process-a tool that you can reference for each prototype that you need for your future projects. However, we also have loftier goals: first, to help you learn the methodology and the questions that are fundamental to the selection process; second, to give you an understanding of the differences and constraints of the prototyping methods; and third, combined with hands-on experience in selecting a technology and using the resulting prototypes, we hope that this tool will help you to become skilled at process selection without the aid of the decision making guide.

About the Selection Guide

Before using this tool, there are a few points to consider.

The decision making guide is designed for those seeking prototyping services. While this may mean subcontracting prototype development to a service bureau or job shop, it also applies to the selection of in-house technologies. The decision making guide is not intended as a selection tool for processes that your organization is evaluating for purchase or implementation. When selecting a technology or process for implementation, there are numerous parameters that will affect the final decision, and these are not reflected in this guide.

The information contained in the guide is a generalization for a given method. There are always exceptions, but those that have unique capability are not reflected in the guide. The information used to aid you in selecting a process is based on generally accepted parameters.

Cost is always a factor in making a buying decision, but it is not rep resented in the decision making tool. Due to the wide variance in price for a given process, it is not reasonable to present this factor in the decision making guide. Some vendors offer prototypes cheaply with acceptable output quality, and others use premium pricing when their deliverable is much better than their competitors. So, you will need to gather pricing information from the suppliers and weigh each option with respect to the project cost.

The decision making chart is intentionally liberal so that borderline processes are not excluded. The goal is to provide you with as many alternatives as possible, not to direct you to a sole process. By providing multiple alternatives, you have the opportunity to investigate the value of each to make your final decision.

Using the Guide

To arrive at an appropriate solution, you must have a clearly defined set of needs, and these needs must be listed by each prototype part. Even if all prototypes are in the same assembly, the specific requirements, with the exception of time, will vary from part to part. So, begin by defining the prototype's application and the quantity of parts that are needed. Then, specify the elements of quality, which may include items such as material properties , dimensional accuracy, and surface finish. The key to the selection guide is to have a clear understanding of what you expect from a prototype part.

When defining the requirements, beware of the trap of being overly conservative. It is easy to specify that you need all of the characteristics of a production part, but this level of demand will severely limit your options and will increase both time and cost. In genera l , your requirements should be looser when early in the design phase and tighter as you near the final phases of the product development process.

To understand the importance of properly specifying the requirements for the prototype, try using the decision guide in both a liberal and conservative manner. In doing so, you will see how a single variable can limit your process options. Since this is true, it is recommended that the decision guide be used in an iterative fashion. By adjusting the demands on a single variable, you will find that your process options shrink (if tight specifications) and swell (if loose specifications). As the guide will show you, if you want production materials, tolerances, and surfaces finishers, you will likely find that the production method is your only option.

With reasonable expectations, the selection guide will present you with prototyping alternatives that are likely to satisfy your needs. Note, however, that the guide is not designed to offer a final recommendation. Instead, it is a tool that leads you in the right direction. Due to the sheer number of variables in the decision making process, it is impossible to offer a single, best solution in a straightforward, easy to use tool.

While it is recommended that the decision tool be used for individual parts, it can be advantageous to consider the results of the individual parts collectively. In some technologies there are price and time advantages when different parts are constructed in a single o p e ration. Of course, the additive, rapid prototyping technologies enjoy this advantage, but it may also be available for the subtractive or formative processes.

Finally, consider that the best option may be a hybrid approach. Although the decision making tools present the technologies as stand-alone solutions, blending of methods is often the most effective approach to getting the job done. Hybrid operations are common in the manufacturing realm. For example, investment castings are often milled in areas where "as-cast" tolerances are not acceptable. To use the tool for hybrid methods, ease the parameters in areas that can be addressed with a secondary process.

Final Selection

After completing the decision making process with the use of the guide, consider the qualitative factors that may influence your final decision. For example, consider the value of your time and the extent of your workload. If two options are presented, you should consider the time and effort that will be demanded of you. If two processes can be completed in one week, but one will take a day of your time to coordinate, while the other will take only moments, the right choice would be the one that gets you the prototypes you need while letting you get back to pressing matters.

Another qualitative factor is your familiarity with a process. If the stakes are high, and there is little margin for error, trying a new process may be ill-advised. Save new methods for the time when trial-and-error can be accommodated.

The decision making process is involved and somewhat challenging when there is a gap in process information. Time- Compression Technologies hopes that you find the decision making guide to be a valuable tool for selecting prototyping methods in your day-to-day work. We also hope that it becomes a tool that increases your awareness of the wide variety of methods that are available.


For more information, please contact Todd Grimm, Grimm and Associates, Inc. (Edgewood, KY) at (859) 331-5340 or email at, or email at


Contact information:
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T. A. Grimm & Associates, Inc.
3028 Beth Court, Edgewood, Kentucky 41017
Phone: (859) 331-5340      Fax: (859) 514-9721


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