Versatility of CNC in Today's Prototyping Industry
CNC machining systems can be used in many facets of prototyping; they create works of art in extremely rapid timeframes, while maintaining the integrity and aesthetic intentions of the design.
The process of CNC (computer numerical control) machining as an instrument in the rapid prototyping (RP) "tool box" has been rapidly emerging over the past 10 to 15 years. Advances in CAD/CAM and machining technologies coupled with human talent have led to an explosion in the use of CNC machining in every aspect of the prototyping industry. These advancements enable more versatility than previously used within the framework of typical repetitive production machining.
The benefits of CNC machining in developing solutions in the RP environment are nearly unlimited. Along with engineering prototypes, CNC machining lends itself to the creation of conceptual foam models, fully decorated marketing models, prototype injection mold tooling and a host of support within. Of course, finding the correct combination of human talent, software and machine equipment is of utmost importance in capitalizing on the many uses that CNC has to offer in the prototyping world. From professional observation, at one time, 25 to 30 percent of the technology used to produce models involved CNC machining. Currently, that figure is closer to 75 percent. CNC machining plays a huge, vital role.
Models
Early concept study models constructed from foam or tooling board are
typically simplified models where wall thickness and presentation
quality finishing is not typically important. They are used to give
very quick feedback on the overall form of the product. This allows the
designer the option of going back and reworking the database to get a
form that is more to their liking. Traditionally, the task of creating
a concept model was dependant on the manual and artistic skills of a
model builder. It takes time to build templates and remove stock with
manual machinery and by hand. With today's CNC machining systems,
shaping time has drastically decreased, and the increase in accuracy
allows for very quick feedback on the design aesthetics. This is
especially true with the ever-increasing, complex organic shapes that
can be created with today's powerful design software.
Presentation quality and database verification models, which are used in advertising photography, marketing studies and industrial design reviews, can also benefit greatly utilizing CNC machining capabilities. External geometry, surface strategies and graphics need to "appear" like the actual consumer product. Paint and faux finishes sometimes have limitations. In most cases, the best way to achieve the desired aesthetic is to use the actual material, specifically when trying to duplicate a clear or metal component. Most graphics and patterns within the part can be machined very cleanly. This relates to minimal, if any, handwork.
Prototypes
CNC machining systems can be used to create prototypes strictly for
engineering review, in real world materials, for functional testing and
analysis. By machining the stock away from a billet or block of
material, similar to the process of carving, but by using a much more
complex and expensive jack knife, the machinist creates a final part in
any of a wide variety of possible materials. Some of the more common
materials are ABS, acrylic polycarbonate, nylon, acetel, aluminum and
stainless steel. Raw material manufacturers are continuing to provide
materials in a wide variety of sizes in many production materials,
which will allow for a wider selection of stock available to the
designer or engineer.
Prototype injection mold tooling has rapidly emerged for short term run parts in production resins. In this case, the CNC machining system can be used to create complete steel or aluminum stand-alone tooling or inserts for one of the many injection molded frame systems that are readily available. These molds can be used for prototype purposes only or they can be used to serve as bridge tooling until the actual production tools are complete.
The creation of molds for vacuum formed prototypes is another commonly used application. This is where the CNC machining system can be used to create a female or male form with the entire draw-by and details required for pulling the formed parts. The prototyped parts help evaluate the design, packaging requirements and possible issues relating to a high quantity production run.
CNC machining can also be used as support for other facets of prototyping. For instance, in the urethane casting process, fixtures for complex parts can be created directly from CAD data to improve lay up time and parting line crispness when making a silicone mold. Custom cores can also be machined to improve features that RTV silicone would otherwise prove difficult to cast accurately. Secondary machining can be performed on the urethane castings themselves in order to improve the precision that a silicone mold might not warrant. Modifying SLA, SLS and FDM prototypes due to design changes as well as sharpening details, especially recessed graphics, can also be an advantage.
Of course, the most vital link between the finished prototypes and the machining technology is the capability of the technology user. It takes a special mindset to be proficient in the use of CNC machining systems. First of all, the machinist needs to have excellent communications skills in working with the model and mold builders. Details including surface strategies, graphics, methods and materials are very important to discuss and understand up front. Also, having the ability to envision the end product and understand the aesthetics of the design is critical. And, the programmer needs a good working knowledge of the CAM software and machine capabilities. Although the process of programming machined parts is time intensive, which many consider to be the biggest drawback, the advances in the CAM software with associative tool paths are making that less of an issue.
A Viable Solution
Continuous improvements in the industry are going to make the CNC
method of prototyping and tooling a valid choice for the foreseeable
future. Customers will continue to demand higher quality prototypes in
an efficient, accurate and cost effective manner. CNC machining systems
in the hands of a talented programmer/machinist/model building can be
used in many facets of prototyping, creating works of art in extremely
rapid timeframes, while maintaining the integrity and aesthetic
intentions of the design. CNC machining is a viable prototype solution.
