Get the Screws Turning Part 1 of 3

by Jeff Lendermon

ScrewExploring the technology of 3D printed injection molds

Welcome to a hands-on experiment of utilizing 3D printed core and cavity inserts in the injection molding process. Here are the tools I used for this project:

  • Design: SOLIDWORKS CAD Software
  • Finite Element Analysis: SOLIDWORKS Plastics
  • 3D Printing: Stratasys J750 3D Printer
  • Tabletop Injection Molding Press

I chose to use insert and two-shot molding to create a custom screwdriver with a rubber overmolded grip handle.

Designing the Screwdriver

I modeled the shaft, handle, and grip as separate parts.

The shaft was created using a simple revolve, an extruded boss for the flat tab and a cut sweep to form the Phillips style tip.

I used a revolve boss to form the basic shape and an extruded cut to square it off. Next, I added some fillets to create the overall shape of the screwdriver handle.

(Note: a revolve cut feature and an extruded boss feature with circular pattern form the internal structure that will be overmolded.)

The grip was created using the same workflow as the handle to get the basic overall shape. The interior will be designed with the cavity feature in the next step, so I left it as a solid.

Final Design Steps

I created an assembly with the three parts. I chose an assembly so that I could use the cavity feature to create areas where the handle fits the shaft,  and the grip fits the handle.

This creates a fit with no overlaps or gaps which is important when creating the simulation mesh. After creating the cavity features in the handle and grip, I saved the assembly as a part file thus creating the multibody part required for SOLIDWORKS Plastics flow simulation.

Now, I have a complete custom screwdriver design.

To make this design easier to mold, I leveraged SOLIDWORKS Plastics along the way.

Two-Shot Molding Simulation

The next step in the process was to verify the design for injection molding using SOLIDWORKS Plastics simulation software.

There are three required steps to run a flow simulation in SOLIDWORKS Plastics:

  • Mesh the model: During this step, I set the cavity and insert domains as well as improving and refining the mesh
  • Assign the material: Since this is a two-shot process, I had to set a material for each of the cavity domains. I chose a high-density polyethylene (HDPE) for the handle and a thermoplastic elastomer (TPE) for the soft grip material.
  • Assign the injection locations:  Each cavity domain has its own injection location using the material selected in the previous step.

After completing these steps, I was able to run a SOLIDWORKS Plastics flow simulation. The simulation allowed me to see the plastic flow through the handle and subsequently see the grip fill. The software indicated that my parts would mold with an injection pressure of  205 Psi for the handle and 1,290 Psi for the grip.

The pressure requirements got me thinking: How can I get a decent estimate of pressure produced with our hand-press injection molder?

This lead me astray and added another step in the process. Time for a SOLIDWORKS Simulation study. In part 2,  I will explain how I got an estimate of the force needed and the pressure created to meet the injection pressure requirements.

You can see more on setting up the two-shot molding process and insert molding in the recorded webinar on co-injection, gas assist, and valve gates found on the GoEngineer YouTube channel.

Check out part 2 and 3:

Part 2 of 3 – Injection Molds

Get the Screws Turning: Part 3 of 3 Exploring the technology of 3D printed injection molds

 

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