Introduction
Injection Molding is the most common manufacturing process for the mass production of identical parts. Over the past few years, the development and innovations of 3d printers and 3d printable materials has expanded to benefit the injection molding industry far beyond prototyping and testing designs. This article talks about the pros and cons of using additive manufacturing for creating low-run injection molds, the types of low run molds being used with 3d printing, and gives recommendations on 3D printing mold materials when producing 3D printed injection molds.
Understanding Injection Molding
In injection molding, a die or mold is manufactured (traditionally out of metal) and is inserted into an injection mold machine. This mold is then injected with hot liquid material at a rapid pace, producing thousands to millions of parts. The high initial setup cost associated with injection molding is a major limiting factor to this manufacturing method if not manufacturing extremely high volumes, but allows for a low per unit price. Typical prices range from $10,000 to $100,000 for tooling to be made for injection molding.
Why 3D Printed Low-Run Injection Molds?
In order to determine which type of mold is right for your project, it is important to know how many parts the mold will be making. For multiple thousands up to millions of parts, aluminum or steel molds would be required due to the amount of repeated injections. If you are looking to achieve a small volume of parts 1-200, 3d printed low-run molds will save you lots of time and money.
Benefits of these 3d printed molds:
Faster Turnaround Times (7-14 days vs 5+ weeks)
Low Volume Production
Mold designs with potential changes or iterations
Parts that are relatively small (less than 150 microns)
Types of 3D Printed Molds?
Aluminum Frame Mold Inserts: This is a common method within 3d printing. The mold is 3d printed and inserted into an aluminum frame to help it withstand the pressure and temperature wear from use in the injection molding machine.
Stand Alone 3D Printed Molds: These 3d printed molds do not use a the aluminum support frame. This allows for strategically placed breath holes to be integrated into the mold, but is more susceptible to warping or wear and tear with use.
Castable Molds: This process uses a part printed in a meltable material, such as wax, that will be inserted into a tight packed box of material that when it gets heated up, the material in the box hardens and the wax material melts out, creating a negative mold.
Mold Applications:
Plastics
Gels
Silicon
Ceramics
3D Printed Injection Mold Material Properties
The two most crucial material properties for 3d printed low run injection molds are high temperature deflection and high strength/stiffness.
Existing Materials & Properties
Formlabs High Temp resin*
Heat deflection temperature: 289 ℃ @ 0.45 MPa
Flexural modulus: 3.3 GPa
Highest Resolution / Layer Height: 25 - 50 microns
Impact strength (Notched IZOD): 14 J/m
Minimum detail size: 0.2 mm
Stratasys Digital ABS**
Heat deflection temperature: 92 - 95 ℃ @ 0.45 MPa
Flexural modulus: 1.7 - 2.2 GPa
Highest Resolution / Layer Height: 16 - 30 microns
Impact strength (Notched IZOD): 65 - 80 J/m
Minimum detail size: 0.2 mm
Polymaker PolyCast***
Decomposition Temperature: 260 ℃
Bending Strength: 60.2 +- 1.6 Mpa
Charpy Impact Strength: 9.6 +- 0.9 kJ/m2
Minimum detail size: ~150 microns
*Sourced from Formlabs
**Sourced from Stratasys
***Sourced from Polymaker