Injection molding with 3D Printed Molds

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INJECTION MOLDING WITH 3D PRINTED MOLDS

WHEN DOES IT MAKE SENSE?

Early stages of product development when the design changes frequently or very low volume production need (i.e., 100 parts).

Requirements for precision, repeatability, better physical and thermal part properties.

To eliminate secondary operations commonly experienced in 3D printing. 

Potential parts:

• Eyeglass frame
• Shaft bushing
• Mask strap
• Shield clip
• Golf ball markers and tees
• Small miniature toys

PROS AND CONS

The 3D printed mold can make the product development process little bit faster and reduce the initial costs compared to 3D printing. Plus, it improves the product quality with functional prototypes.

However, you may still need to use CNC machining or hand sanding to prepare the 3D printed mold. The mold pairs need to align perfectly during the clamping stage. Due to surface imperfections, the secondary operations may be required. If you need holes smaller than 0.5mm on the mold that would also require a secondary operation. In small mold sizes (6" by 4.8"), there is not much cost difference between a 3D printed mold and a CNC machined aluminum mold

REQUIRED EQUIPMENT

SLA 3D Printer: 

SLA printers are a better choice compared to FDM. Smoother surface finish and higher precision. Chemically bonded, dense and isotropic. You can create surface finish texture-out of the SLA printing. The Form 3 from Formlab can be a good option to use.

Injection Molding Machine: 

To get good and consistent parts, the injection molding machine should have precise process control for the injection pressure, plastic temperature, and clamp force. The APSX-PIM injection machine provides the best value for injection molding with 3D printed molds. The precision and the pricing are hard to match. 

PROCESS STEPS

• Mold Design:  

Any CAD software is ok to use to design the 3D printed mold. There is a guideline available on our website. Follow these additional guidelines below:

Add 2-5 degrees draft angle, air vents (0.05mm) and use larger gates.

Design one side flat and other side carrying the design to eliminate the misalignment risk.

Have walls greater than 1-2mm and features larger than 0.5mm.

• 3D Printing:  

It is suggested using an SLA type 3D printer:

The material needs to withstand clamping, injection pressure, and high temperatures. There are available options in the market for the 3D printed material:

Formlab has Rigid 10K or High Melt. Asiga has FusionGray. Markforged has Onyx. 

Printing in 50-micron layer is a good approach.

Preparing the mold, including the "post-curing" process. Typically a CNC machining or hand sanding operation is required after the 3D printing. 

Larger the mold size, the more difficult it is to process for injection molding.

• Mold Installation:  

There are benefits to use a aluminum mold holder (MUD) along with the 3D printed molds:

It adds stability to the 3D printed mold.

It increases the life of the 3D printed mold by helping it to cool faster.

• Injection Molding:  

There are benefits to use a aluminum mold holder (MUD) along with the 3D printed molds:

It adds stability to the 3D printed mold.

It increases the life of the 3D printed mold by helping it to cool faster.

Guidlines below for some injected material and injection parameters: high melt flow rate is better - PP and TPE are the best

• Material | Temperature | Injection pressure | Cycle time | Mold life
• PP | 220C | 100BAR | 150sec 100cycles 
• HDPE | 225C | 150BAR | 120sec | 100cycles
• ABS | 220C | 95BAR | 160sec | 60cycles
• PC/ABS | 240C | 95BAR | 160sec | 60cycles
• Delrin (POM) | 180C | 150BAR | 120sec | 60cycles
• Nylon | 260C | 80BAR | 120sec | 50cycles

The mold life is a function of the part design, injection material, and molding parameters.

The part design includes the wall thickness and part volume. Thin walls and large part volume requires higher pressures and clamping. There may be cracks on the mold corners and detailed part features.

Injection material determines the flow rate and processing temperature. Lower flow rate and high processing temperatures increase the required temperature. The mold material becomes very brittle quickly. 

Molding parameters have pressures and temperatures. 

The need for a silicone release agent (Sprayon or Slide brands) for sticky materials such as TPU and Polycarbonate (PC) may damage the mold. 

• Air Cooling:  

Using an aluminum mold holder (MUD) increases the life of the 3D printed mold by helping it to cool faster. APSX-PIM offers one and uses a variable speed fan for cooling the mold.

• Part Ejection:  

Using a large draft angle (2-5 degrees) helps pull the part out of the mold at the end of the injection cycle. As an option, an ejector mechanism can be added to the mold for automatic injection molding cycle mode. Since the mold life is not too long, adding additional costs for the ejector pins may not make sense.