Demonstration of an Effective Design Validation Tool for 3D Printed Injection Molds (3DPIM)
Injection
molding, the process of injecting plastic material into a mold cavity
where it cools and hardens to the configuration of the cavity, is one of
the world’s most popular manufacturing processes. It is best used to
mass produce highly accurate, and often complex, end-user parts.
To
obtain a comprehensive and accurate assessment of a part’s functional
performance or to run the safety tests on electrical or mechanical
components, injection molded parts must be produced using the actual
materials and injection molding process of the final production part.
Therefore, 3D printed injection molds (3DPIM) are increasingly adopted
to create prototype parts to detect issues in the part’s form, fit,
function and validations(/certificates) if needed.
These molds are
far less expensive than their steel (hard) counterparts with shorter
lead time, sometimes up to 90%, but dedicated analysis tools for 3DPIM
are not yet available. Therefore, Stratasys and Moldex3D joined together
to perfect 3DPIM solutions with upfront simulation predictions. Using
both solutions, one can develop the production tool much more
efficiently with better results. Furthermore, customers can increase the
longevity of the printed tool, improve the design and understand the
process better.
WHAT STRATASYS CAN DO
3DPIM
are able to create a prototype for a fraction of the cost and a matter
of days compared to the weeks-long lead time associated with traditional
tooling processes. For example, the price to create a small,
straight-pull mold ranges from $2,500 to $15,000 with delivery usually
taking 10 days to four weeks. This is an investment that most companies
find difficult to justify for a few dozen test parts. 3DPIM have the
capability to produce five to 100 parts in the same thermoplastic as
production parts. They can be constructed in one or two days for a
fraction of the cost of soft metal or steel tooling. Currently, 3DPIM
are mostly used with thermoplastics injected up to 300 °C, with some
limitation on part geometries and size relative to traditional metal
tools. However, they show great benefit to customers where this method
can be applied.
“Moldex3D is a powerful tool to help evaluate
the moldability of 3D printed injection molds. Combining Stratasys with
Moldex3D, customers have an enhanced solution for validating and testing
the parts and molds for successful production.”
Benefits of Using 3DPIM:
- Average time savings of 50% - 90% for lead development
- Average cost savings of 50% - 70%
- Functional evaluation with production plastics
- Efficiency gains and automated tool-making with few steps
- Early validation on part performance, mold design and thermoplastic selection
The
printed mold needs to bear the resin being injected at high temperature
and high pressure. Moreover, high shear stress exists and can ruin the
mold when ejecting the part. The amount of successful shots depends on
the injected material (flowability, viscosity and melting temperature)
and the mold geometry. To optimize the performance of a particular mold
geometry, it recommended for users to follow the Stratasys design
guidelines (TAG – Technical Application Guide [1]). This document
information will help 3DPIM users to:
- Evaluate the mold with a printed replacement
- Revise the printed mold design such as the gate locations or number of gates
- Use metal inserts for critical features
WHAT MOLDEX3D CAN DO
Moldex3D
is a process CAE (Computer Aided Engineering) simulator that evaluates
the effect of material properties, process conditions and part/mold
design on the process dynamics and part quality. The mold filling,
packing, cooling and post-molding warpage analysis provide valuable
information in the design phase as well as in the trouble-shooting of
the existing process/ design. Moldex3D also predicts the process
characteristics during the injection molding cycle and shrinkage
behavior of the molded part according to the selected material and
process conditions. It helps to quickly evaluate, verify, and further
optimize the design parameters.
Fig. 1 - True 3D numerical simulation technology.
Moldex3D
simulates the entire injection molding process using true 3D solvers,
thus, there is no need to manually simplify geometry models for the
simulation. For 3DPIM users the “Moldex3D Professional Package” or
“Moldex3D Advanced
Package” is the most suitable package for 3DPIM defect prediction and design optimization (Fig. 2).
Fig. 2 - The simulation process of Moldex3D.
Moldex3D
can generate full 3D solid mesh with enough boundary layers intuitively
to guarantee prediction accuracy. After solid mesh generation, users
can easily define process conditions and follow the basic operation
procedures to perform the analysis. According to the analysis results,
part/mold dimensions and layout can be optimized considering the
rheological, thermal, and mechanical properties.
USING MOLDEX3D TO DETECT POTENTIAL 3DPIM DEFECTS
The
product in this showcase is a test part designed by Stratasys® to test
several common design features that appear in injection molded parts
while using a printed mold (i.e 3DPIM process). Past experience
indicates feature cracking is a critical issue which has to be avoided
to ensure product quality and prototype mold life requirements.
Stratasys applied Moldex3D to predict potential flow-induced defects and
cracking. This showcase demonstrated the value of early defect
diagnosis for improving 3DPIM performance (Fig. 3).
Fig. 3 - The 3DPIM with towers
Challenges
- The towers are heated and softened due to low thermal resistance, and tend to break during injection or ejection (Fig. 4).
- The mold surface temperature of the specific area is significantly higher after part ejection.
Fig. 4 - The towers tend to break off after 2 to 6 shots.
Solutions
The molding condition data are provided as follows:
| Part | ABS Terluran GP-35 |
| material | | |
| | | |
| 3DPIM material | Digital ABS | |
| | | |
| CUSTOMIZED 3DPIM MATERIAL PROPERTIES |
| | | |
| Maximum machine | 80 MPa | Packing pressure: |
| pressure | | 20 MPa |
| | |
| | | |
| Filling time | 2.4 seconds | Cooling time: |
| | | 70 seconds |
| | | |
| Packing time | 2.5 seconds | Mold-open time: |
| | | 100 seconds |
| | | |
| VP switch | 98% | |
| | | |
Moldex3D
Designer BLM (boundary layer mesh) and MCM (multiple component molding)
analysis technologies are utilized to observe the flow behavior and
deformation of 3DPIM. In this case, the 3DPIM of core and cavity molds
are set as two “inserts” of a plastic mold in Moldex3D analysis (Fig.
5). We then can apply Moldex3D Core Shift analysis to predict the insert
deflection and stress results caused by non-uniform pressure
distribution during the filling stage (Fig. 6).
Results
The
comparison of simulated melt front and a short shot sample from real
molding at 1.24sec (Fig. 7) demonstrates the feasibility of using
Moldex3D to evaluate flow behavior inside a 3DPIM. The tower roots are
under higher von Mises stress by the unbalanced flow fronts around the
towers, implying greater stress subjection which may easily lead to
fracture. We can clearly observe the towers broke off at the same
locations in real molding (Fig. 8).
Comparison of the simulated
mold temperature distribution and thermal image from the real molding
further validates the accuracy of Moldex3D thermal analysis. The red
area indicates elevated 3DPIM surface temperature
