Indirect Additive Manufacturing: Pros & Cons

Investment casting - lost wax casting

The surface of this gold ring has a perfect cast without imperfections. This gold cast of a ring was made with the lost wax casting process. In this case, traditional wax was replaced by our castable 3D resin: 3Dresyn Perfect Cast HPP Yellow which was used for printing rings with a low cost monochrome LCD printer.

Direct vs indirect Additive Manufacturing AM

Modern 3D printing technology is instrumental in providing on-demand solutions for various needs, ranging from personal protection, medical, transportation, industrial, etc. In addition, advanced software and hardware allow for versatile and quick designs. Depending on your goals, manufacturing can be divided into direct and indirect additive manufacturing, with its pros and cons and specific advantages. In this section we will focus on indirect additive manufacturing, its types, how it works, and opportunities for this method.

Indirect Additive Manufacturing Processes

Compared to direct additive manufacturing in which materials are printed directly without the need of molds, indirect additive manufacturing is a multi step process that involves printing the molds first, followed by injection or casting of waxes, resins, plastics, ceramics, or metals in the molds.

Resin and Injection Casting

Resin Injection at high temperature - solid thermoplastics such as polyamide are injected hot (eg 290ºC) at a certain pressure in molds printed by SLA, DLP, LCD, and Inkjet printers.
Ceramic Injection Molding (CIM) - ceramic feedstock containing binders are injected hot at a certain pressure in molds printed by SLA, DLP, LCD, and Inkjet printers.
Metal Injection Molding (MIM) - metal feedstock containing binders are injected hot at a certain pressure in molds printed by SLA, DLP, LCD, and Inkjet printers.

Metal Casting by Lost Wax and 3D resins

This process allows for accurate recreation of parts with precise tolerances. Lost wax casting or investment casting uses a wax pattern to create a sacrificial wax model. The sacrificial wax model is dipped into a gypsum or ceramic slurry to create a hardened shell or investment of the model. The inner wax is then melted off in an oven then molten metal is poured inside the shell or investment. Once hardened, the outer shell is cracked open, and the hardened product is cut and cleaned. Nowadays, 3D printed castable resins can also be used as alternatives to castable waxes for creating sacrificial models.

Pros and Cons of Indirect Additive Manufacturing

Pros:

Faster and more cost-effective for medium and long runs (high number of produced units)
Low costs for printing the 3D resin molds, especially with the correct type of SLA, DLP, and LCD printers.
Ideal for making tough biocompatible plastic products such as polyamide materials
Ideal for cost effective manufacturing ceramics and metals by combining the best of 3D printing and CIM & MIM technologies.
Each “3D resin” does not need to be tuned/adjusted to each printer: only durable or sacrificial 3D resins for printing molds are tuned once in the printer.
Ceramics & metals by indirect additive manufacturing have significant benefits vs. direct manufacturing
- Faster debinding and sintering times.
- Affordable printers below a thousand Euro can be used for printing the molds.
- Better ceramic and metal properties: higher isotropy, density, lower porosity, etc.
Lost wax casting has very few limitations on the type and kinds of metal that can be used. This allows manufacturers to have a wide selection in designing parts and makes the process adaptable to any industry.
Most of the materials that are used in the lost wax casting process are saved and reused, which eliminates waste.
Parts made from lost wax casting are lightweight, flexible, and have fine details. This allows for greater flexibility in engineering designs.

Cons:

Compared to direct additive manufacturing, indirect additive manufacturing is a multi-step process.
Indirect manufacturing can be more expensive for short runs (low number of produced units).
The whole process is slower for basic plastic modeling/prototyping.

Existing Opportunities for Indirect Additive Manufacturing

A wide variety of parts, components, and products can be made using indirect additive manufacturing methods like lost wax processing, injection of resin, CIM, MIM, PIM, of plastic, ceramic, metal, and exotic sintering powders, etc. The accuracy and precision of the process make it ideal for producing small and intricate parts with close tolerances. Indirect additive manufacturing is used in highly technical industries like aerospace, medical, automotive, robotics, jewelry and security.

3D resin	Process	Product	Properties	Benefits	Limitations
Castable 3D resins	Direct investment Casting DC	Metal cast objects	Typical properties of Cast Metals	Cost effective direct investment casting of metal objects	Most castable competitor's 3D resins suffer from imperfections of fine detail finishes
Non Castable 3D resins	Indirect investment casting IC	Metal cast objects	Typical properties of Cast metals	Less cost effective indirect investment casting production of metal objects with very high resolution	Slower process since there are several time consuming production steps
Durable injection molding 3D resins	Direct plastic, and sintering ceramic, metal, polymer (such as polyimide), and exotic powder feedstock injection in 3D printed durable injection molds	Plastics, ceramics, metals, polymers, and exotic materials	Properties of plastics, ceramics, metals, polymers, and exotic materials	Cost effective production of durable injection molds for simple shaped plastic, ceramic, metal, polymer, and exotic material injection	Not suitable for complex intertwined shapes
Easy breakable sacrificial 3D resins	Direct plastic injection in 3D printed easy breakable sacrificial molds	Soft plastic, rubber or silicone objects	Properties of soft plastics, rubbers, and silicones	Cost effective production of easy breakable sacrificial molds* for complex shaped soft plastic, rubber and silicone injection molding	Not needed for simple 3d printed shapes, mold is lost during production
Sacrificial 3D resins	Direct plastic, and sintering ceramic, metal, polymer (such as polyimide), and exotic powder feedstock injection in 3D printed sacrificial injection molds	Plastics, ceramics, metals, polymers, and exotic materials	Properties of plastics, ceramics, metals, polymers, and exotic materials	Cost effective production of sacrificial injection molds for complex shaped plastic, ceramic, metal, polymer, and exotic material injection	Not needed for simple 3D printed shapes, mold is lost during production

The Lost Wax or Investment Casting Process

Castable 3D printed resins are becoming a more important technology with the amount of advantages they bring, especially in manufacturing new and high-quality products for our day to use.