A Soft Tooling Process Chain for Injection Molding of a 3D Component with Micro Pillars

A protocol for fabricating injection molding inserts for complex geometry with micro features on surfaces employing Additive Manufacturing (AM) is presented.

Transcript

This method can help address key questions in the manufacturing field, such as how to reduce machining time and cost for pilot production. The main advantage of this technique is that microfeatures can be achieved on surfaces of complex parts thanks to additive manufacturing. Demonstrative of the additive manufacturing part will be Dr.David Bue Pedersen, who is a senior researcher and Federico, who is a PhD student, Michael, who is a technician, will do the injection molding parts.

First, use computer-aided design software to design the insert. Here are depictions of the movable side and the injection side of a mold to produce the ring with four tines. The tines are at an angle of 60 degrees.

The manufacturing tolerance is 1/20th of a millimeter. Next, prepare the resin for photopolymerization. Mix its components thoroughly in a mixing device for 30 minutes.

For fabrication, choose a photopolymerization machine. Inspect the build stage and make sure the machine is properly set up for the fabrication step. Import the design and run the build at the highest vertical machine resolution.

After fabrication, take the printed inserts to clean them. Place them in isopropanol in an ultrasonic bath for three minutes, three times. After the solvent evaporates at room temperature, place the inserts in a room temperature desiccator.

Recover the inserts and cure them twice with UV flashlights. When done, remove the inserts. This is an example of the inserts at this point.

To assess them, use a laser scanning digital microscope. Measure the diameter and depth of four holes close to gate on the insert of movable side and on the injection side. In addition, perform measurements on four holes far from the gate.

These microscope images provide examples of the movable side insert and the injection side insert at this stage. The SEM picture illustrate the surface quality. Work with a conventional injection molding machine.

Ensure the microinjection module is installed. Then, work with the inserts and mold plates. Then, load the hopper with polyethylene granules.

At the controls, set the machine parameters and allow cooling time for the part to be de-molded. Heat the screw during the first to the fifth session. When the melt temperature is 175 degrees Celsius, start accurate injection molding.

Once the cavity is filled, maintain a packing pressure of 300 bar for five seconds. Next, open the mold. Allow the ejection pin to push the part out.

This is an example of the part molded with this protocol. One hundred cycles were executed. To assess the molded pieces, return to the laser scanning digital microscope.

Pillars are obtained on the surface. Measure the diameter and height of the pillars on the tracked lines on two areas at different distances from the gate. This is a scanning electron micrograph image of the insert surface fabricated by additive manufacturing.

For comparison, here is an SEM image of the polyethylene part produced by injection molding. The nominal dimensions of the holes on the insert are 200 micrometers in diameter and 200 micrometers in depth. This is a comparison of the pillar height divided by the depth of the hole, referred to as the pillar height replication degree.

The batches are in groups of 10 in the order produced in the run of 100 produced parts. The values are from one randomly chosen sample from each group. Different colored bars refer to different positions on the insert.

Here is an analogous plot for the pillar diameter replication degree. The pillar diameter divided by the hole diameter. These plots demonstrate the process was stable at each position over the course of 100 cycles.

The dimension of the holes on the parts were unchanged after injection molding, which supports the conclusion. This technique paved the way for researchers in the manufacturing and polymer processing to explore the soft tooling process. It makes possible the creation of microfeatures on free form surfaces on the new production platform that meets industrial demands.

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Journal (Engineering)

Journal (Engineering)

A Soft Tooling Process Chain for Injection Molding of a 3D Component with Micro Pillars

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