Plastic Injection Mold Design

Continuing on with part 3 of our blog series dedicated to showing the differences between Autodesk Inventor Professional 2011 and SolidWorks Premium 2011 for digital prototyping workflows, we examine the ability to design and validate molds, starting with a pre-designed part.

We show below, using videos from both systems,three major design aspects of mold design:  the ability to use a 3D model of a plastic part to create the core and cavity of the mold, designing and engineering the multiple components and systems of the mold, and validating the design to ensure it can manufacture high-quality plastic parts.

Autodesk provided us with a model of the handle to be molded, detailed specifications for the mold, and three videos of Inventor performing the desired tests showing the workflow for splitting core and cavity, engineering of the mold, and a simulation and validation of the mold.

The key differences you will see demonstrated below

Autodesk Inventor provides standard libraries of mold bases and components along with automated tools for splitting the core and cavity and for designing the runners, gates, and cooling and ejection systems. The inclusion of Autodesk Moldflow simulation software directly in the design workflow allows designs to be validated and improved upon until they will optimally manufacture products of the highest quality.

SolidWorks includes dedicated functionality for splitting the core and cavity, but that is where the mold design capabilities end. With no automated design tools and no libraries of components, the design of injection molds is entirely manual and inefficient. Without any built-in plastics simulation capabilities, mold designers must purchase third party software, such as Autodesk Moldflow, often at significant cost, to validate and optimize their designs to ensure quality.

What’s Important in Plastic Injection Mold Design

• Balance of speed in designing the mold while ensuring high quality.
• Accurate design of mold components including runners for injecting the plastic materials, cooling of the mold, and ejecting the finished part.
• Iteration of the mold design with simulation to arrive at an optimal design.

Observations

Splitting the Core and Cavity

The desired result was to generate parting surfaces and complete the core and cavity operations.

Inventor used a mixture of automated and manual patching and runoff surface creation tools. Surfaces for simple holes and profiles were created automatically which increases productivity. Complex patching and runoffs were created using Inventor’s surfacing tools.

SolidWorks also assisted the user in splitting the core and cavity with automated and manual tools for defining the parting line and creating patching and runoff surfaces.

The two systems are comparable in capability. SolidWorks required a few more menu picks and interactions, but both came up with an acceptable mold core and cavity. SolidWorks generated an odd triangular shape in the area to be removed, but it was temporary and did not affect the final part.

See the video of Autodesk’s engineer using Autodesk Inventor to perform the core and cavity workflow using Inventor: 

See how our engineer used SolidWorks to perform the core and cavity operation:

Engineering the Mold

The tasks completed included: designing the runners, adding a submarine gate, inserting a properly sized mold base, inserting a sprue bushing, designing cooling channels, attaching pipe fittings for cooling channels, and adding ejector pins as specified.

Inventor completed this task using a built-in workflow for designing injection molds that includes libraries of mold bases and standard components as well as automated design tools for runners, gates, cooling channels, slides, lifters, and ejectors.

 

SolidWorks had no built-in functionality for designing injection molds. All standard components needed to be searched for and brought in from external content centers or supplier websites, a time-consuming process. All modeling was done manually as there are no automated design tools for the various systems of the mold. This made mold design in SolidWorks a tedious and labor-intensive process with low user productivity. SolidWorks was able to build the geometry required for the moldbase design, but it was a laborious process.

See the video of the Autodesk engineer performing the mold design:

See TechniCom’s engineer performing the mold design using SolidWorks:

Validating the Mold Design

To validate the mold design for manufacturability we needed to first determine the optimal molding conditions for the entire system as designed. Next, we performed a filling analysis to determine if the mold, as designed, could completely fill the cavity at acceptable quality. Then, we assessed the location of air traps and weld lines. Lastly, we performed a shrinkage analysis so exact figures could be input for core and cavity sizing rather than manually inputting generic percentages.

Inventor includes Autodesk Moldflow simulation built-in to the mold design workflow, which was used to simulate the filling phase of multi-cavity molds and their respective runner systems to validate manufacturability. A shrinkage analysis was also used to ensure cavities were sized based on the specific design, rather than relying on generic shrinkage factors from the material supplier.

Inventor validates the mold design.

Users could use Autodesk Moldflow stand-alone software that would have the capabilities required, at extra cost. Our analysis did not include examining extra cost third party products. We only compared Inventor Professional to SolidWorks Premium. Therefore we do not have a video of SolidWorks performing the mold validation.

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The next blog in this series (Part 4) will examine designing and analyzing a clevis pin in a hydraulic clamping assembly. Stay tuned or sign up to be notified of my blog updates.

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