3D Printed Inserts and Mold Cavities That Can Be Used for
Producing Wax PatternsJacob Lehman, CMfgE
Associate Professor
Pittsburg State University
Fall 2019
Introduction – Using 3D Printing in the Foundry
Current Uses for 3D Printed tooling at the PSU foundry-
• Printed patterns for sand castings– Quick way to produce tooling for student projects without the need for machining a pattern or match plate
• Printed patterns for investment castings• Printed patterns used to make Silicon-Rubber molds that may be filled with
wax• Investment/Lost PLA – Printed patterns are assembled onto sprue, coated,
then “burned out” during the shell firing
• What about printing dies/tooling that can be reused for producing wax patterns?
Project Scope - Summer 2019
• Utilize inexpensive 3D printing technology – widely available, easy to use, and reasonably reliable
• Explore the possibility of using of 3D printed inserts in existing wax injection dies
• Explore the possibility of using of printed mold cavities for injection dies as an alternative to machined dies
• Demonstrate a Proof of Concept – Printed inserts and die cavities for wax injection tooling
Printer – Equipment Used for this Project
• Ender-3 3D Printer
• Single Nozzle, FDM printer
• Print Bed: 8.7” x 8.7” x 9.8" (220x220x250mm)
• PLA Filament
• Purchased online ~$200
Printed Tooling Inserts
Results
• Attempted to used same process parameters (temperatures, shot time, die closed time, etc.)
• Parts cooled slower on side with PLA insert
• Frequent defects
• Stuck/Difficult to eject parts due to “rough” printed surface finishes
Common defects
Summary of Printed Inserts
• Produced lower quality parts than the machined inserts
• Printing did not save a significant amount of time vs. machining the simple aluminum inserts
• Slower cooling rates for the printed PLA inserts
• Less detail/resolution due to the layer thickness/nozzle size
• May work for prototype tooling with very simple geometries
• Further research to try methods of smoothing the insert surfaces
Printed Die Cavities
• Produce a very simple “Test” cavity
• Rectangular cavity that is 2 1/2” by 1 1/8” and is 3/8” deep
• 5 degrees of draft added for easy part removal
Printed Test Cavity in Aluminum Base
• Machined a simple “Universal” mold base to hold the printed cavity insert
• Able to withstand the camping force of the wax press without crushing the printed cavity
• A through hole (under the insert) allows for removal of the printed cavity
First Trial Run – Setup wax press
Summary of first Printed Cavity
• Part worked well – Very simple Geometry with plenty of draft angle
• Somewhat slow cooling time – insert tended to insulate / retain heat
• Reasonably fine detail – reproduced the printed surface finish with the layer/tool marks
• Considerably faster/easier than machining the cavity from Aluminum
Small Production Run w/ Printed CavitiesDouble 6 Domino Set
• A single cavity with 28 interchangeable domino inserts
Printing the Domino Cavity and Insert
• Used PLA filament
• Used a 0.2mm layer thickness
• Print time = approx. 4 hrs.
Installing the Printed Cavity – Compressed Air Removal
Mold base with different domino inserts
First Wax Domino from Printed cavity
Additional Cavities
• The PLA required longer cycle times due to slower cooling rates
• Additional cavities were printed to speed up cycle times
• 2 cavities were cooling while one was being injected
Wax Dominos
First production Run
Economics – Cost breakdown
• Ender-3 3D Printer – purchase price (online, included shipping) = $193.49
• PLA build material - $21.49 per 1 kg spool of filament
• Breakdown for the Domino Project:• Each cavity used approximately 52 grams of PLA build material, thus a material cost
of $1.12 per cavity. Since there were 3 cavities produced, a total of $3.36 for the build material for the prints.
• Each domino insert used approximately 6.2 grams of PLA build material, thus a material cost of $0.14 per insert. Since there were 28 inserts needed to produce a full set, a total build material cost of $3.92 for the printed inserts.
• Total expenditures - $193.49 (printer) + $3.36 (PLA for cavities) + $3.92 (PLA for inserts) = $200.77
* Not included – Labor, Aluminum Mold Base (reclaimed), Wax/Injection Press
Conclusion
• Proof of Concept – Possible to produce inexpensive printed wax tooling for simple geometries
• May not be ideal for large scale commercial production parts, but may be useful for small production runs or prototype tooling
• Educational potential - allows students to experiment with die designs without large costs or significant die manufacturing time
• Future research into • accuracy/sizing of the parts• methods for “smoothing” the printed surfaces• other printing technologies/materials• a more detailed economic analysis and comparison for a production part
Questions?
Jacob Lehman, CMfgEAssociate Professor
Pittsburg State University
1701 S. Broadway
Pittsburg, KS 66762