3D printing provides a significant advantage by enabling users to quickly produce prototype mold and die inserts and short-run manufacturing of complex designs. However, years of testing reveal that specialized, porous mold steels can compete with today’s metal 3D printed steels, yielding a more consistent, stronger product with improved venting performance. Ultimately, the best manufacturing method depends on the specific application, the required tool longevity and the production volume.

Here are five key findings when it comes to these materials and mold and die venting:

1. Size, Number and Placement of Pores in Venting Inserts
3D printed parts usually have larger and fewer pores or slots. This design is essential for preserving structural strength and preventing part failure. However, these larger pores can lead to issues such as a poor surface finish, premature clogging and difficulties with part ejection like sticking.

Pressed porous mold steel can be produced in large blocks with uniform porosity, approximately 25% and an average pore diameter of just 7 microns. These pores are evenly distributed throughout the material, enabling consistent venting across the entire insert. For example, a 4″ “×” 4″ molding surface has roughly one square inch of surface venting. This network of interconnected pores plays a crucial role in achieving high part quality and ensuring reliable release.

2. Surface Finish
3D printed parts often exhibit a rough surface finish, resembling that of sand castings, due to the layer-by-layer fabrication process. Therefore, they usually require significant post-machining to achieve the surface quality necessary for mold and die applications.

3. Quality
Residual stress buildup is a common issue in the 3D printing laser sintering process. The technique of sintering powder layer by layer can result in significant warping and cracking of mold or die components. In some instances, cracks may develop later during heating and cooling cycles or even during the ejection of parts in plastic injection molding or die casting. Also, stray powder particles can become lodged in engineered holes or slots, resulting in sintering that blocks clear gas passages.

Challenges with dimensional accuracy and part distortion remain despite advancements in surface roughness. As a result, parts produced through 3D printing often need to be built larger than required, followed by CNC machining to achieve precise final dimensions.

While technologies like Direct Metal Laser Sintering (DMLS) have made progress in thin-layer build-up, significant issues still need to be addressed. In contrast, pressed porous steel offers a stable structure with uniformly distributed porosity, enabling trapped gases to escape effectively. This greatly reduces common molding problems, such as scorching, short shots and incomplete fills.

4. Mechanical Properties
Anisotropy, the property of being directionally dependent, is a key characteristic of 3D printing. On the other hand, isotropic materials such as forged steel or traditional mold and die steels exhibit uniform properties in all directions, which contributes to their strength and reliability.

Unlike traditional mold steels, which are either rolled or high-tonnage pressed to enhance their mechanical properties, 3D printing processes construct parts layer by layer. This method of layer-by-layer construction is similar to casting and does not achieve the same level of densification that typically improves strength and toughness.

Also, the layer-by-layer process can trap air and gas bubbles between layers, leading to voids that may appear as cracks or surface imperfections after machining. So, experts in 3D printed tool design often recommend using larger radii to reduce stress concentrations.

We also advise caution when determining the placement of ejector pins and suggest incorporating greater draft angles compared to conventional mold steels. These precautions help compensate for reduced toughness and reduce the risk of the mold insert cracking during injection or flexing during part ejection.

5. Repairability
Pressed porous steel can be laser welded, providing a reliable method for repair while 3D printed molds and inserts are more challenging to repair using conventional welding techniques due to their unique microstructure and porosity. The most common methods for repairing 3D printed parts involve using silver solder or brazing rods, but these repairs often lack durability.

Due to this limitation, molders are frequently advised to invest in a backup printed insert. While this incurs an additional cost, it serves as a practical precaution in case the original insert cracks or gets damaged during molding or maintenance.

Traditional mold steels can be repaired using standard welding or laser welding techniques, using filler rods made from the same material to ensure a strong and durable restoration.