Model-based design techniques can help you break out “of the box” to explore creative ways to design and manufacture hardware.

Rapid prototyping technology has advanced to offer 3D printing of CAD models where you choose the material, surface finish, accuracy, color, and size. These improvements increase your options when determining how to manufacture engineering models for marketing, form and fit checks, testing, and even to use as final products. If environment conditions are favorable and overall dimensions are less than 10 x 15 x 8 inches, it is feasible to use 3D printed parts as final production components or as the entire system, a capability now known as Digital Manufacturing.

3D printing can give you a direct path from design to manufacturing, enabling you to realize the ROI on existing CAD tools and reduce your overall design cycle time and costs. 

For Walter Holemans, President of Planetary Systems Corporation and the creator of the Lightband Separation System (a lightweight, low shock, low cost, reliable spacecraft separation device), the use of model-based design techniques helps him break out of the box to innovate design concepts that take him to the next level of hardware design. His latest project is developing a robotic boat prototype, which led to the exploration of creative ways to design and manufacture hardware.

While investigating the requirements of the robotic boat, Holemans found he was constrained by the need for lightweight and easy to manufacture components. The realization steered him towards rapid-prototype 3D printers to produce his boat components as final products. He not only uses the 3D printer to test out his concepts, but also will use the actual 3D printed components to create his robotic boat.

In developing the boat concept, he saw that the greatest challenge would be the rudder with its complex curved surfaces. Standard manufacturing techniques would require the rudder section to be machined on a 6-axis CNC machine using a ball end mill. It would produce a wavy surface finish and increase the drag on the rudder, violating function requirements.

His next course of action was to create the rudder using a mold. The mold could be manufactured through a 3D printer. However, once he moved down this path, he discovered that a final product from the 3D printer would meet the design objectives. This creative thinking spawned his all-in-one flex rudder design.

The rudder design takes advantage of 3D printing capabilities. Instead of designing complex load paths of rotating components, such as shafts, bearings, springs and hard-stops, Holemans modeled the articulating rudder components directly into the design. One such component was a flexure to attenuate the rudder motion and an all-in-one rotating joint. There is no assembly of the moving parts; once it is printed from the 3D printer, he installs an actuator and the unit is completely assembled. It is fast, it is cheap, and better yet, it provides quick direct hands-on experience without requiring costly manufacturing and assembly time. This approach to design drastically speeds up the design iteration process. You can view a video of the rudder under test at the Design World website: www.designworldonline.com. Search by article title.

He evaluated the design through FEM, made appropriate modifications directly in the CAD model and sent it to 3D printing. Within one week from design and analysis completion, his rudder was ready for test and evaluation.

Holemans, accustomed to using model based design techniques where the CAD models are the design database and contain all features, was well prepared to evolve his manufacturing techniques to use digital manufacturing as his final product.

His plan is to use the same design approach for the entire boat design. The final boat size is 8 ft long x 4.5 ft wide, so the boat will be printed in sections. Because the models are directly transferred, drawings are eliminated. If he were using a traditional process of creating a drawing in order to provide it to a supplier, then it would have taken about 40 hours to produce the drawings alone, not to mention the time the manufacturer would spend re-converting the 2D data into their machine tool to create a 3D part.

In developing the robotic boat concept, the greatest challenge was the rudder with its complex curved surfaces. Machining would result in a wavy surface finish that would increase drag on the rudder. Walter Holemans decided to use a 3D printer, but he discovered that a final product from it would meet the design objectives. This realization spawned his all-in-one flex rudder design.

For the rudder, instead of designing complex load paths of rotating components, such as shafts, bearings, springs and hard-stops, Holemans modeled the articulating rudder components directly into the design. There is no assembly of moving parts. Once the design is printed from the 3D printer, he installs an actuator and the unit is completely assembled.

The direct transfer lends itself to increased accuracy and prevents human error when transferring and interpreting drawings. In fact, no drawing interpretation is required.

Boat Rudder digitally manufactured by Redeye on Demand (www.redeyeondemand.com) using FDM process with ABS M30 material.

In order to successfully implement model-based design, full features and tolerances are required in the 3D CAD model, thus increasing the time an engineer spends on the model. However, looking at the time spent compared to a traditional drawing design cycle process, it is clear that model based design saves significant effort because it eliminates unnecessary data duplication. Remember, the data are there; they are just in the model. Verification of part dimensions and tolerances can be done through direct query of a 3D model or by using a Limited Dimension Drawing with verification dimensions. By eliminating design cycle steps, such as creating drawings, Holemans realized a 59% reduction in design cycle time and a 67% reduction in hardware delivery schedules.

Changing the way we think of the design-to-manufacture process, saves time in making part and assembly drawings, saves costs in machining or molding complex surface geometry and saves time in final assembly.

A direct path from design to manufacturing is exactly what model-based design advocates, driving home the point of realizing the ROI on existing CAD tools and reducing your overall design cycle time and costs.

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How to use model based design for production level designs

Planetary Systems Corporation has instituted Limited Dimension Drawings (LDD), which accompany 3D CAD files. These drawings exclude geometry data, already well documented in the CAD file, and include specifications for tolerance, material and inspection. Both the CAD file and drawing are shipped to the machine shop where the CAD files are directly imported into the CNC programming interface.

“We were motivated to create an LDD standard when a recent job required tight production deadlines,” said Walter Holemans, President of Planetary Systems Corp. “We have since seen the benefits.”

Holemans estimates they are saving 5% in labor costs by embracing LDD. In addition, there is a savings and reduced transfer errors when the machine shop is not forced to interpret a drawing from scratch.

MPF

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