Part 2 of this 8 part series reveals the results of the Plastic Part Design workflow
Plastic Part Design tests the ability to import surface data from Alias, stitch the skins into a solid body, design the shell the part with a specified wall thickness, part using surfacing and plastic features, import new surfaces and update the model, and perform an injection molding simulation on the part.
Autodesk provided us with data files specifying the solid model, IGES and WIRE data files of the surfaces, and three movies depicting the workflow for surface import, engineering design, and simulation and validation.
What’s Important in Plastic Part Design
- Rapid design, ready for manufacturing
- Working with surfaces from industrial design software
- Ability to directly create mold ready parts, typically for injection molding
- •Evaluating the moldability of the part
Inventor was able to import the Alias wire file natively without issue. SolidWorks was unable to import the Alias wire file. Users must first translate Alias data to an IGES file, which is susceptible to translation errors, albeit not in this case.
Here is how Autodesk used Inventor to perform the surface import workflow:
Here is how TechniCom’s engineer used SolidWorks to perform the surface import workflow:
Building the Model
Creating a solid model from imported surfaces and being able to shell the resulting solid are typically the most error-prone steps in the process. Inventor was able to stitch and shell the part with zero errors. The shell was created in one step by defining the variable in the shell dialog box. SolidWorks was also able to stitch and shell the part with zero errors. Shell creation involved several steps to create and define the variable.
Plastic parts are typically designed using a set of standard features such as ribs, bosses, grilles, snap-fits, and lips to name just a few. The MCAD software should assist the user in efficiently modeling these features. Inventor used its plastic features toolset to add the two different types of bosses, a lip feature, and ribs. SolidWorks used plastic features for a majority of the features, although the recessed bosses required for this test first needed to be built manually and then added from the library of custom user features.
Here is how Inventor was used to build the model:
Here is how SolidWorks was used to build the model:
Simulate and Validate the Part Design
Plastic parts must be checked for potential quality defects prior to committing to the cost of designing and building the mold.
In the simulation to evaluate the manufactured quality of the product as-designed, Inventor simulated the injection molding process and uncovered high amounts of shear stress due to the part being too thin. If left uncorrected, this issue would lead to material degradation and molding defects or field failure. Inventor’s built-in mold analysis software also provided more extensive capabilities in terms of material selection and multiple gate analysis.
There are no built-in simulation capabilities within SolidWorks for evaluating the manufactured quality of the product as designed. However, we were able to use a third partner add-in module called SimpoeXpress. This has limited function, but allows for some material selection and a single gate. SolidWorks was able to simulate the molding process but the only result the user received was the filling pattern, which provided limited value. It was unable to identify any quality defects and the user was misled into thinking the design was acceptable. More comprehensive simulation packages are available at a cost of more than $5000.
After modifying the 3D CAD model, we reran the simulation to validate the design change. After making the recommended change to the part, Inventor automatically updated the model in the simulation environment; all that was required was to re-run the analysis. SolidWorks automatically updated the geometry but the analysis had to be setup from scratch, including processing parameters, gate location, and material selection.
Importing the IGES files and creating the plastic part was comparable for both products. While SolidWorks was able to import IGES curves from industrial design software, Inventor was able to directly read Alias (a leading industrial design software package) surface data, an advantage. Both products had excellent capabilities for building specialized plastic features such as the mounting boss and the lip and groove on the connecting halves of the model.
Inventor’s built-in analysis software powered by Moldflow provides impressive analysis capabilities, and is well integrated into part design. To perform these same tests with SolidWorks, on the other hand, required a no-charge third party product that was able to perform only a limited analysis of the part. The limited function mold analysis software that was free does not provide the engineer enough insight to be confident that parts can be manufactured at all or at acceptable quality. More complex mold analysis software with advanced analysis capabilities (which was not used) is available to SolidWorks users at considerable extra cost.