3D Model-to-Router Slashes Prototyping Time

A wide range of engineering OEMs, subcontractors and engineering design firms are discovering that machining 3-D models on a router can slash prototyping leadtime and expenses. The traditional approach of producing prototypes with hand tools or manual machine tools requires large amounts of time from highly skilled employees and makes it difficult or impossible to achieve high accuracy levels.

Using CNC machine tools or SLA as an alternative reduces the need for skilled labor and leadtime, but requires a minimum $100,000 capital investment to produce medium- or large-sized parts. On the other hand, CNC routers - designed specifically for machining plastics and other lighter materials - can produce large prototypes at high levels of accuracy without requiring skilled labor. Yet, an accurate and durable CNC router can be purchased for as little as $20,000, putting CNC prototyping within the reach of virtually any company.

Anderson Design Associates (Plainville, CT) - a general-purpose industrial design house - has taken advantage of this approach. Preparing prototype models for client review is a critical part of the product development process at Anderson Design. Until recently, this was done by hand using urethane foam. The company had no way of generating models from its Pro/Engineer CAD data unless it went to an outside service. When the decision was made to bring this capability in-house, company officials investigated a variety of options.

Considering SLA

Anderson Design first considered SLA, but determined that it had several draw-backs:

1. It was not suitable for all parts. Aesthetically critical parts with complex surfaces, for example, couldn't be produced with SLA since this technology makes tiny steps or facets in a curved surface.

2. The least expensive SLA system cost about $100,000.

3. That system had only a 12-inch by 12-inch by 10-inch high working area. Many of Anderson Design's projects would require parts made in sections and bonded together. This is a time-intensive and costly option.

4. Because operating expenses are high, SLA models cost nearly twice as much to produce as foam models.

5. The firm also considered a traditional CNC machine. These machines start at $50,000 - not including the CNC programming software. To get a model with a large-enough working area, Anderson Design would have had to buy one of the larger machines costing at least twice that.

A Different Direction

Then a chance encounter in an industrial directory led the company in a different direction. The ad described a new breed of gantry CNC routers that interfaced with CAD systems, had a large cutting area and a low price. Anderson Design ended up purchasing that machine from Techno-Isel (New Hyde Park, NY). The price was less than $19,000 and had a working area of 24 inches by 36 inches with a Z-axis height of six inches, which was large enough for most of the firm's projects. Plus, it could handle all of the materials that Anderson Design needed to cut.

After purchasing the Techno machine and related equipment such as clamps, vacuum systems, cutting tools and software, the total cost of bringing automated model production in-house was approximately $40,000. Within three days of installing the Techno system, Anderson Design was billing clients for work completed on it.

The programming software provided with the machine includes IGES, DXF and CADL converters so that geometry can be uploaded from many CAD systems including Anderson Design's Pro/Engineer.

Although the Techno machine was de-signed for production routing and drilling on a wide variety of materials including wood, plastic, MDF, solid surfacing materials and nonferrous metals, so far Anderson Design has used it mostly for cutting models out of seven-pound or 15-pound density polyurethane foam, or #35 or #65 Ren Shape. Typically, four-inch thick sheets of four-foot by eight-foot foam are used, although a few polycarbonate parts also have been made.

The Techno machine's 0.0002-inch resolution and repeatability, and 0.003-inch absolute accuracy ensure that the foam models are faithful representations of the designs created on the computer. This is critical in an industrial design application since the models must give the client an accurate likeness of the eventual end product. In approximately 300 hours of operation, Anderson has had no problems with the Techno machine. This is partly due to the strength and rigidity of the table, which is constructed from extruded aluminum profiles that provide easy clamping capability. The machine also has four ground and hardened steel shafts and eight re-circulating bearings in each axis.

Combining SLA With a CNC Router In another application, combining SLA with a CNC router makes it possible for ARRK Creative Network Corporation (San Diego, CA) to produce injection molding prototypes of a much higher quality than can be produced on SLA alone.

SLA is an outstanding method of producing geometrically complex proto-types. The problem is that it's not capable of producing fine details with the crispness associated with CNC machining. As a result, prototypes produced by this method are often rejected for styling reasons. CNC routers can dramatically improve the quality of prototypes produced with SLA. Modifications to the SLA model can be made by machining the SLA material itself or machining small pieces of ABS, which can then be bonded into the original model. These can be small logos or icons as well as any overall modifications to the parts including the addition of ribs, bosses, through-holes, etc.

This technique also can be used to make modifications to SLA parts in much less time than would be required to produce a new part. In one case, ARRK made an SLA part from a PRO/Engineer file. When the customer checked the fit of the prototype, they decided to make several modifications and needed the prototype returned the next day. This didn't leave enough time to produce another SLA part.

Therefore, ARRK bonded additional material onto the prototype and machined it on the router to the new specifications. The cost was only 15 percent of what it would have cost to produce a new SLA prototype.

Producing Box-Like Components

Besides their use in finishing SLA components, the Techno routers also provide a unique method of producing box-like prototypes such as bezels for electronic systems. Bezels are normally produced on a CNC machining center from a solid block of material. This is a very time-consuming process on an expensive machine that typically requires a high degree of operator attention. Machining parts from a solid block also is expensive from a material standpoint.

The original model of the housing is exploded into six separate walls. On a router, these walls are produced from sheet material and bonded together to form a cube. Material cost is typically reduced by 50 percent and machining time is cut by about 33 percent. Finally, the hourly cost of the CNC router is typically half the cost of the machining center. As a result, the cost of producing the prototype is cut by about 50 percent without any reduction in quality.

Producing bezels piece by piece also provides the opportunity to enhance the finish of the prototype. ARRK recently produced a business telephone bezel using this approach. Making the bezel prototype in pieces made it possible to polish the top panel so it was transparent and produce a second panel that fits underneath it containing the buttons. This second panel was silk-screened, adding a level of realism to the prototype that would have been impossible to achieve with a solid block.

Foam Packaging Models

A CNC router allows Foam Fabricators (Scottsdale, AZ) - a coast-to-coast network of 14 facilities providing shape-molded foam products, packaging and components - to produce the typical order of 20 sample models in two days compared to the five days needed to cut the foam pieces by hand.

When a customer comes to Foam Fabricators with a new product that needs to be packaged, the first step is to work with one of the company's engineers to determine the appropriate material and develop a rough design of the foam part. The Foam Fabricators engineer specifies the material, size and performance characteristics for the product and uses the SolidWorks (Concord, MA) - a developer of 3-D mechanical solutions - CAD system to create a 3-D model of the initial concept. At this point, most customers request between 20 and 30 samples for drop testing. Some customers have this testing done by Foam Fabricators while others prefer to take the samples and do the testing in-house.

Previously, samples were produced by hand. An engineering assistant used a band saw, drill press or hot wire to cut the foam, working from the specifications on the SolidWorks CAD drawing. This was a time-consuming process. A typical order for 20 samples took one person about one week to make. When a customer wanted an unusually large number of samples, the work was spread out over numerous people, including engineers.

Problems With the Manual Approach

There was an additional drawback to producing samples by hand. Some of the shapes that customers needed were not possible to produce this way. For example, a jet ski manufacturer asked Foam Fabricators to make a bow flotation unit - a piece of foam that fits in the bow of a four-man jet ski to provide buoyancy. This part had a lot of complex geometry and it was impossible to shape it by hand. The company was not able to make the sample, so they were unable to take the job. A third drawback was that the handmade models were not accurate since the process of cutting them required some interpolation between surfaces. This was acceptable to some customers, but others wanted greater accuracy.

One of Foam Fabricators' larger customers, who typically requests a large number of samples for its extensive testing program, asked the company to consider using a CNC machine to cut the foam samples. As the company looked into this, it discovered two options: heavy and expensive machining centers primarily designed for metalworking and low-end routers that didn't provide the needed table area and accuracy.

Then Foam Fabricators found the Techno Model 160 Production CNC router from Techno Isel, which met all of its requirements. The technical specifications of the Techno machine selected include a working area for the router of 59 inches by 50 inches and Z-axis height of 12 inches, a vacuum hold-down table, a five horsepower Columbo spindle and a raised gantry for large-part clearance.

New Prototyping Process

Now when a customer comes to Foam Fabricators with a request for a new product, the engineer creates the Solid-Works model, as he/she did in the past. But instead of creating a drawing, he/she exports the solid model directly into the Techno system's CAM program.

Originally designed for metalworking, this CAM program also is well suited for foam because of its ability to generate the most complex contours with little programming effort. In the CAM program, the engineer gives the command and the software creates the toolpaths for cutting the sample. The only additional input required is information such as feedrates and cutting speeds. Total programming time - from when the SolidWorks model is imported into the CAM program until the system is ready to cut foam - ranges from 30 minutes to two hours depending on the complexity of the part.

After a piece of foam stock is fastened to the Techno machine, the operator hits the "start" button and the sample is then carved automatically. The machine does not require any supervision, except to remove the finished piece and attach a new foam block to repeat the process. With this machine, a typical order for 20 samples is completed in two days. Large sample orders no longer require the production assistance of engineers. The machine is simply kept supplied with stock and run until the order is finished.

Having the CNC machine has paid off for all of these companies in a number of ways including faster turnaround on samples, more accurate samples, better satisfied customers and the ability to take on more complex jobs.

"Making samples on a Techno CNC router is becoming the norm in our industry," explains Nathan Musgrove, an applications engineer at Foam Fabricators' Jefferson, GA, regional design and test center. "With the Techno machine, we found a cost-effective way to meet this requirement."

For more information contact Techno-Isel (New Hyde Park, NY) at (516) 328-3970, or via its website at www.techno-isel.com.