Albright offers 3D printed LSR (Liquid Silicone Rubber) casting, RTV casting, and printed thermoplastic components. Albright has developed a process for casting using commercial grade LSR and color dispersions using a rapid turnaround in-house printed mold. Our 3D printing provides another way to test functionality, reduce iteration and trial cost, and decrease lead time. This is a unique solution for customers trying to develop and prove a concept before investing in tooling.
Benefits of our 3D printed cast parts:
- Molded part made of production grade materials with full material properties.
- Quickturnaround for 2-10 parts.
- Mold complex shapes.
- Mold with undercuts.
- Test first stage overmolding.
Our capability continues to expand with this technology. Using this process, we have successfully supported an increasing number of customer projects. These parts have been used as initial prototypes for testing and verifying size, shape, and some functionality. Our LSR cast parts have been used for demonstrations at product launches and trade shows with investors, users, and other stakeholders.
Molding and Cast Material Options
- Molding with commercial grades of LSR between 10 and 80 Shore A durometer. These silicone materials typically offer you significantly better elongation and tear strength compared to RTV silicones. LSRs typically allow for higher durometers. The greatest value is the scalability of the material since most silicone injection machines are configured for LSR. This is recommended as a starting point for most applications if possible.
- RTV (Room Temperature Vulcanizing) silicone. These materials have the advantage of very low cure temperature, which may be an advantage to silicone overmolding of sensitive materials. RTV silicones typically have lower physical properties as compared to LSR. These materials often have very high tear propagation so a small rip or nick can cause a total failure. RTV materials are not easily scaled into an injection process due to the short pot life and very low viscosity.
- Color matching can be done against industry standards as well as specific color samples. This is possible regardless of which silicone material you choose.
Cast Complexity versus Cost Advantage
Molding parts starting at approximately 1mm (0.037in) and up to 75mm (2.953in) in size is possible. Smaller features may be possible, but this is evaluated on a case by case review. The crayfish sample below demonstrates some of the detail that can be achieved with this process.
Undercuts may be created in a number of ways but one common example is as lip within a gasket as shown in the figure below. Due to the high elongation of many silicones, the part may be removed without collapsing the core. This is an advantage for silicone compared to many TPE and TPU materials, which may have relatively low elongation before failure occurs. The amount of undercut is a function of the elongation, which tends to decrease with increasing durometer. The hot (first out of the press) tear strength and elongation are lower than the final tear strength and elongation once cooled but this property is a good starting point. A 30-50 durometer with 10-20% of stretch to free the undercut has a high probability of being feasible compared to 50% or more in a 60-80 durometer material, which likely exceeds the stretching ability without damaging the core or part during part removal from the mold. Typically, this is part of our normal review during our quoting process.
An additional savings may be possible on some projects when a mold can be printed as a top and bottom only. 3D printing allows the creation of undercuts. Undercuts that have small angles of less than 30 degrees may not require support material during printing. This can allow for faster prints and ultimately lower cost. An example of this is shown below for a part that has a groove around the outside edge and a hole through the center. The Mold Side B can be printed as one part instead of two. This same principle has allowed the addition of letters or marks of sufficient size on printed molds without a significant cost addition. We review undercuts and find solutions on a case by case basis.
Limitations and Expectations
The cast process is an excellent starting point for many projects that ultimately transition into an aluminum or steel prototyping or production tool. The purpose of this process is to provide a relatively close representation of the final part. A second stage prototype may be required to refine the design, or this may provide enough feedback to transition to a production tool in some cases.
The cast tool process has a limitation of approximately 4-10 parts per print depending on part geometry, material interactions, and parting line complexity.
The surface finish is limited to the resolution of the printer so gentle curves and some smooth surfaces tend to see patterning of the print layers at between 0.05mm (0.002 inches) to 0.25mm (0.010 inches).
This resolution ties into the dimensional accuracy, which is limited in a 3D printed cast mold. The accuracy is driven by both the printing accuracy as well as shrinkage due to thermal expansion of the silicone and mold. We design our molds to account for as much of the mold and material thermal expansion and pressure effects as well as mold deflection as possible. RMA (Rubber Manufacturers Association) A4 tolerances tend to be the limit of this process. The flash is trimmed so this tends to be range between 0.25-0.50mm (0.010-0.020 inches) for many products. Much tighter tolerances and flash reduction is achieved by upgrading to aluminum or steel molds.
Printed parts and printed molds are currently limited to a maximum size of approximately 25mm (1 in) x 100mm (4 in) x 152mm (6 in). Our compression, injection, and transfer processes using machined prototyping and production molds are not limited by our printer footprint. We have built a significant knowledgebase working on and solving silicone product challenges. We carefully review each part on a case by case and provide feedback to assist in reducing lead time and improving molding performance and cost of your products.
The duckbill valve shown below was designed with a 1mm (0.039 inch) wall thickness across the entire profile. We cast a 50-durometer short term implantable-grade commercial LSR. The surface finish is limited to matte with some patterning, but it allowed for preliminary design testing to be performed.
The part below was cast in a 70 durometer LSR with a black color. The part was used by the product engineers for functional testing before investing in production tooling. The lead time and cost savings was approximately 65-75% and helped avoid a second iteration of hard tooling, saving the team’s valuable resources in the development of this product.
Substrates and Jigs
Nylon may be reinforced with carbon fiber, Kevlar, or glass. The same undercut capability discussed before is true.
In many parts, a support material can be printed into the open space and can allow for significant undercuts, as shown with the part below.
We can print a wide range of relatively detailed substrates and cores to support overmolding and assembly for our customers.
We are actively printing jigs for slitting, punching, adhesion, and assembly. These help us rapidly support our customers’ projects and at a lower cost.
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