The EMPF has been utilizing Computer Aided Modeling and Computer AidedManufacturing (CAM) in its product design system. Computer Aided Modeling has many benefits in bringing new products to market such as lowering product development costs and reducing time to market for a concept. Computer Aided Manufacturing is the generic term for designing a product from concept to prototype using 3-dimensional or “solid” models. Some of the more common programs to perform this type of design work are SolidWorks, E-Drawings, and AutoCAD. Almost all of the CAM software available has the ability to create 3-D models of each part in an assembly, and then place the parts together using the proposed “mating” surfaces. CAM software will check for interference between parts in an assembly and allow the real time editing of the part from the assembly if necessary. There are many computer design tools for printed circuits as well. Most of these enable the designer to layout a circuit, define integrated circuit parameters (package and pinouts), and then go directly to the printed circuit board (PCB) layout and check that all circuits are completed according to design rules. Cadence and PADS are common tools in the circuit design and PCB layout arena.
Benefits
Product development costs can be reduced in pre-production design verification. The creation of engineering samples and the coordination of the various engineering disciplines can help verify all phases of the product before committing to costly tooling costs. This reduces the time and costs associated with rework due to unforeseen interferences. The designers can check assembly tolerances and perform stack up analyses of the final assemblies using solid models of the individual components (Figure 3-1). These models are frequently available from the component manufacturer in multiple 3-D formats in order to encourage the use of their components in new designs. Design engineers can also use these models to perform stress and thermal analyses by including actual material properties of the components.
3-D CAM software can also be used to make prototype components using a process called stereo lithography. Stereo lithography works by utilizing a laser to solidify a liquid polymer on the surface. A platform moves the hardened polymer down about a tenth of a millimeter and the laser hardens the next layer. This process is repeated until a full three dimensional model of the part has “printed.” There are many stereo lithography companies that can import a 3-D CAM file and print a full size polymer model of the component. The quick turn ability of this process allows a functional prototype to be in the hands of the design team within a day of laying out a part. The speed and low cost of the stereo lithography process can allow the developers to mock up an assembly and check form and fit before cutting metal or making expensive molds. Minor changes can be implemented even before pre-production runs are started.
The EMPF design team has used Computer Aided Modeling to layout the components and set the overall dimension requirements of PCBs of a recent project. The considerations and process that was followed are described here.
Project Design Constraints
This project modeled some commercial off-the-shelf (COTS) components in detail using our three dimensional modeling software. Some 3-D models were available from the manufacturer; some were created from 2-D drawings, and when there were no drawings or models available, the EMPF created models by measuring the actual components.
Custom components that were needed to interface with or house the COTS parts were then designed. Using the overall size requirements for the system, the preferred form factor for each subsystem, and the size and material constraints of the COTS components, the layout of the custom assembly components could be completed (Figure 3-2).
Computer aided modeling even came into play when designing PCBs. Using the solid models to define the spacing of user interface components, PC board outlines, keep out areas, and mounting locations were defined and documented. The board physical dimensions were forwarded to the EMPF layout engineers along with the circuit schematics and bill of material for each board. Using this method, even the PCB layouts were completed with a significant cost and time savings over the three to four turns usually required.
Originally, the boxes that housed the systems were to be made from steel. Weight restrictions that were later imposed on the project required the material to be changed to aluminum. The computer models were then changed to reflect the material change. After changing the three dimensional model of the assemblies, a simulated stress analysis was done to find any stress points that may cause premature failure (Figure 3-3). The weak points that were found were redesigned and strengthened, and the stress analysis was run again (Figure 3-4). Once the components were found to be strong enough, drawings were created from the models and the parts were fabricated in aluminum.
As the project developed, customer added requirements were quickly evaluated by the EMPF and changes which impacted other components were found using the modeling software’s interference detection feature. Some times a clearance hole was needed or electronic components were moved on the board. Other times it meant finding a place to mount a hardware part that did not interfere with the current layout of a printed circuit board. The PCB layout software used in the EMPF project allowed quick modification of the circuit boards and verification of the interconnections between electrical components.
Conclusion
The use of Computer Aided Manufacturing requires the synchronization of the many different engineering disciplines that go into a preliminary design of a new product. Each member of the team must be aware of the constraints of their section of the design, whether imposed by the customer requirements or by another’s discipline. The EMPF team was in constant contact with each other throughout the design phase to ensure that any changes from one group did not adversely impact others.
For more information regarding Computer Aided Modeling at the EMPF, please contact Ken Friedman at 610.362.1200, extension 279 or via email at kfriedman@aciusa.org.
