While many metal 3D printing methods have established a niche in their respective applications – for example, powder bed fusion for medical implants or binder jet for MIM components – tooling has long been a target for various approaches. This white paper serves as a guide to understanding the major metal 3D printing technologies and their role in printing injection mold tooling.
Note, this document is a general guide to 3D printing for mold tooling but the exact benefits, limitations, and specs. can vary based on specific printer and the actual application.
Plastic 3D printing technologies have long been used for prototyping, jigs, and fixtures. Plastic printing technologies offer incredibly fast lead times, often just hours, and low costs. But when it comes to tooling, they wear quickly and have poor thermal properties, resulting in short tool life and long cooling rates in molding.
Vat polymerization has long been the go-to method for producing prototype injection mold tooling. Vat polymerization uses light to cure a UV-curable resin, building up the part layer by layer. The two most common methods of vat polymerization are SLA and DLP. SLA uses a single UV light source (point) to scan the print bed. DLP uses a projector UV light source to expose the whole print bed simultaneously.
SLA and DLP feature incredible feature detail and smooth surface finishes, allowing for their printed tools to be used with little to no post-processing. When an end-use polymer is needed for a prototype, these vat polymerization methods are often the go-to method for producing a mold that can inject anywhere from 1 – 1,000 parts, depending on the molded material.
In recent years, advances in SLA and DLP material have allowed for longer tool lives, mostly resulting from fillers such as ceramics and chopped fibers being added to the printed resin.
Formlabs, Carbon, EnvisionTEC, Fortify, 3D Systems, Nexa3D
In powder bed fusion systems, printing occurs in a heated chamber filled with an inert gas at or under near-vacuum to create a clean, inert environment. A layer of metal powder is spread across the build plate via a roller or blade, and thermal energy (typically a laser or electron beam) traces the cross-section of the part, fusing the metal powder and forming each layer of the part. The process repeats until the full part is formed.
Parts printed via powder bed fusion typically require extensive post-process machining to meet accuracy and surface finish requirements. With nearly limitless geometric freedom and the ability to process materials like titanium and superalloys, this printing method has been very successful in aerospace and medical implant applications.
In the binder jetting process, a thin layer of metal powder is deposited on a build plate with a roller. Next, an inkjet print head moves over the powder and selectively sprays binder to define a layer of the part geometry. The process repeats until green parts (metal powder held together with binder) have been fully formed within the powder bed. The entire build box is then crosslinked in an oven to increase the binder strength, allowing for handling the green parts. Users can then remove parts from the build box by manually sifting through the powder, extracting each part, and brushing away any unbound powder. Once depowdering is complete, parts are placed in a sintering furnace where the binder is removed, and the parts shrink 15 to 20 percent as they densify.
The binder jetting process can produce rough parts that require post-process machining and other finishing work to meet the accuracy and surface finish requirements of tooling. This printing method has had success in producing low- to mid-volume small complex parts, as the properties are very similar to metal injection molding (MIM).
In material extrusion systems, filaments are made of metal powder mixed with a binder and encapsulated in wax. The filament is heated and extruded through a nozzle and selectively deposited onto a build plate, printing a green part one layer at a time. Each layer is printed on top of the previous one, with the binder holding each layer together. Printed parts are removed from the printer and undergo a solvent debinding step (bath) to remove much of the binder and wax, producing a brown part with just enough binder left to hold the metal powder together. Next, parts are sintered in a high-temperature furnace, removing any remaining binders and causing parts to shrink by 15 to 20 percent as they densify.
This process produces rough parts that require extensive post-processing to meet most tooling applications’ accuracy and surface finish requirements. Their relatively low cost and ease of use have made material extrusion systems popular for universities, design labs, and those just getting started with metal 3D printing.
In the hybrid powder bed fusion process, powder bed fusion technology is combined with a subtractive CNC mill. A layer of metal powder is applied to the build plate via a roller or blade, and thermal energy (typically a laser or electron beam) traces the cross-section of the part, fusing the metal powder and forming each layer of the part. After printing the layer, CNC cutting tools machine the part to improve surface finish and tolerances. This process can also be used to add material to an existing part, making it a popular manufacturing choice for repair.
The parts that emerged from the Hybrid Powder Bed Fusion process have CNC tolerance and surface finish and look identical to machined parts.
This hybrid process combines metal directed energy deposition (DED) with subtractive CNC machining. DED feeds metal powder or wire into a focused energy source, typically a laser. It melts the material and deposits it layer by layer to build a three-dimensional structure. DED can be used to make very rough parts quickly. Hybrid DED combines subtractive CNC with the DED process. Unlike the Hybrid Powder-Bed Fusion process, Hybrid DED typically waits until the entire part has been printed (deposited) before machining.
The parts that emerged from the Hybrid DED process have CNC tolerance and surface finish and look identical to machined parts. This hybrid method is commonly used for repair, as you can build onto an existing part.
Mantle’s TrueShape process is a metal 3D printing approach designed specifically for printing tooling. A hybrid process that combines material extrusion with subtractive machining, TrueShape uses a paste containing metal particles mixed with binder and solvent. This paste can flow without being heated, allowing it to be extruded to build a part layer-by-layer. After each layer is printed, the part is heated and dried to remove the solvent, resulting in a part with a very high green body density (densely packed metal powder). Every layer of the print is machined to refine the surface finish and tolerances and to add features that couldn’t be directly printed. After printing and machining, the part is placed in Mantle’s high-temperature furnace for sintering. Since the part has a high green body density and very little binder (the solvent is removed during the drying process), the part shrinks less than 9%, dramatically improving the final part dimensions.
Tools printed with the Mantle TrueShape process require minimal finishing before molding, often just fitting into the mold base and finishing of ejector pins.
Until recently, metal 3D printing has been used in a relatively small percentage of tools. However, as printing technologies evolve, additive manufacturing can be adopted more broadly to reduce cycle time, lead time, and cost for prototype and production tools. Additive manufacturing is becoming a viable resource in a mold maker’s toolbox, just like CNC machining and EDM burning have been.
