3D printed molds for injection molding are becoming increasingly popular in the manufacturing industry. They are a great addition to the injection molding portfolio and offer a competitive alternative to traditional injection molding materials.
In this article we will see what a 3D printed injection mold is and its types, advantages and limitations. In the end, we also provide some useful tips and tricks for mold designers and engineers. Let's start!
What is an injection mold?
Injection molds are probably the most important component in injection molding systems. The mold is a multi-piece assembly with an internal cavity that is an exact replica of the final product geometry.
An injection system pumps the molten raw material into this cavity, where it cools and takes its final shape. An injection mechanism, also located in the mold, ejects the finished part. Injection mold is mainly used to shape the part and eject it.
A high-quality injection mold must have numerous properties. It must have good thermal stability to minimize thermal expansion, high strength to withstand clamping pressures and good wear resistance to ensure long service life.
3D printing mold vs. aluminum mold
Traditionally, aluminum is the standard material for producing small and medium volume injection molds. However, 3D printed molds for injection molding are quickly gaining traction due to numerous benefits such as cost savings and design flexibility.
The main difference between a 3D printed mold and an aluminum mold is the manufacturing method. The main manufacturing process for aluminum molds is CNC machining. 3D printed shapes, on the other hand, are obviously produced using the 3D printing process.
This may seem like an insignificant difference, but it is actually quite significant and deserves a discussion about 3D printing molds versus aluminum molds.
But first, let's look at the two main types of 3D printed injection molds.
Reinforced shape with metal structure
This type of injection mold uses aluminum mold elements and 3D printed molds. The basic internal structure, including cavity and channels, is manufactured by 3D printing. This 3D print is then fitted into an aluminum frame for better stability and durability.
Reinforced aluminum frame allows for higher mold pressures and extends mold life. Engineers can also easily replace 3D printed mold components if design changes or wear occur.
Standalone forms
The freestanding molds are manufactured entirely by 3D printing. As 3D printing rapidly becomes more robust, freestanding 3D printing molds are becoming increasingly popular in the injection molding industry.
A big advantage of standalone molds is that they give engineers additional design flexibility for features like injection ports, gates, etc.
Advantages of 3D printed injection molds
3D printed molds for injection molding offer numerous advantages over their metal counterparts. We will highlight some of the main benefits of using a 3D printed mold.
Cost benefit
It's no secret that cost management is an important part of efficient manufacturing. A 3D printed mold is significantly cheaper than metal molds.
CNC machine tools are often expensive and require extensive maintenance. 3D printers, on the other hand, are cheaper and easier to maintain machines. The cost of raw materials for 3D printing is also lower than that of injection molded metals.
Labor costs also differ between the two methods. CNC machines are complex devices and require a qualified machinist to operate them. While 3D printers are no picnic, they are still more accessible to a wider group of technicians.
Time saving
Another important aspect of high productivity in manufacturing is time management. A big advantage of using a 3D printed mold instead of an aluminum mold is the significant time savings in mold manufacturing.
CNC machining is a time-consuming process. Sometimes it takes up to a week to completely produce a complex injection mold. The 3D printing process is much faster and involves fewer steps than machining. The average time to produce a mold is just a few hours, giving 3D printed molds a clear advantage.
Design flexibility
3D printing is known for its rapid prototyping capabilities. It's fast, cheap, and allows engineers to test different design iterations.
The same logic also applies to 3D printing molds for injection molding. Mold designers can quickly correct errors or weaknesses in the mold design. Furthermore, it is also very convenient to incorporate product improvements into the production line – all that is required is a simple reprint.
This type of design freedom is not accessible with CNC machining, as even a single production puts a huge strain on the budget.
Suitable for injection molding in small quantities
3D printed molds are suitable for small batch production. As we will discuss shortly, although they possess remarkable mechanical properties, they tend to wear out more quickly over time than their metallic counterparts.
This makes them ideal for production runs that produce small to medium quantities. In these configurations, investing in an expensive metal mold is inefficient because the mold is underutilized at the end of production.
Additionally, low-volume production involves, on average, more product development and testing. The design may change mid-production if an update is needed or a bug is found. In this scenario, a 3D printed mold is ideal as the upgrade is cost-effective and saves time.
Limitations of 3D Printed Injection Molds
Advantages and disadvantages go hand in hand. Therefore, this discussion would be incomplete if we ignore the disadvantages of an injection mold for 3D printing.
Low structural integrity
3D printing is evolving very quickly, but in some aspects it still lags behind traditional manufacturing methods such as CNC machining. It has several inherent quality issues, such as porosity and lack of bonding, which reduce the structural integrity of 3D printed molds for injection molding.
In general, a 3D printed mold has lower strength, hardness and wear resistance (hence the need for aluminum reinforcements). They tend to fail at the extreme temperatures and pressures that are sometimes required to produce high-quality injection molded products.
For this reason, in some cases, 3D printed molds are not a suitable replacement for cast/forged aluminum molds.
Surface wear
3D printed molds for injection molding are not as wear-resistant as metal molds. Its surface quality deteriorates more quickly than aluminum under the high temperatures and pressures of injection molding. This is also transferred to the surface of the product.
Furthermore, 3D mold printing is a layer-by-layer manufacturing process. For this reason, 3D printed injection molds have a wavy surface pattern (also known as a ladder effect), which increases the surface roughness of injection molded parts.
A common solution is to use surface finishing methods such as sanding, grinding or chemical treatment to improve the mold surface quality. However, it is challenging to perform these operations on a small shape with complex geometry, which is often the case with 3D printed shapes.
Long production cycle
Cooling time accounts for a large portion of the injection molding production cycle. Because metals generally have higher thermal conductivity than the plastic materials used for 3D printed molds, it takes longer for the molten raw material to solidify in a 3D printed mold than in an aluminum mold.
For this reason, we advise moldmakers to calculate the expected cooling time for their injection mold designs before deciding on a manufacturing process.
Shrinkage and deformation
Shrinkage and warping are two common 3D printing defects that affect the quality of a 3D printed injection mold. Plastics are very sensitive to heat and tend to warp (deform) during injection molding.
As the mold itself deforms, the shape of its cavity changes, affecting the final dimensions of the part.
In most cases, mold designers can mitigate this problem by creating appropriate shrinkage tolerances in their molds. However, for 3D printed shapes, these tolerances are difficult to predict due to the non-uniform behavior of 3D printed structures.
Tips and Tricks for 3D Printed Injection Molds
We hope the above information about 3D printed injection molds for injection molding has increased your knowledge on this topic.
In this section, we will give you some useful tips and tricks from our design experts that will help you improve your mold design skills.
Improve thermal conductivity with composite materials
High thermal conductivity improves cooling time during injection molding. Various additives that improve conductivity are available on the market, such as graphene, boron nitride, metallic fillers (copper powder, aluminum flakes), etc.
Surface coating
A major disadvantage of 3D printing molds is their low wear resistance. Suitable surface coatings such as metal or ceramic are very helpful in improving the surface properties of 3D printed injection molds.
Avoid supporting structures on critical interior surfaces
Most 3D printing processes use support structures to support the part during the printing process. They leave marks on the piece after the finisher removes them. Make sure that none of these supports are on the surfaces that form the mold cavity, as their traces will also be visible on the part.
Reduce layer thickness and print speed for better surface finish
The surface finish of a 3D printed mold depends on the layer thickness and printing speed parameters of the 3D printer. Keep these settings low for a finer 3D printing surface finish.
Draft angles are slightly higher than aluminum molds
Due to different material properties, 3D printed structures require larger tilt angles in the mold. Experts recommend planning an average tilt angle of 3° for the vertical surfaces of the injection mold.
Ventilation is essential
Air pockets often form in mold cavities, which affects surface quality. To avoid this problem, it is recommended to have shallow ventilation openings just below the surface of the cavities.
3D printing methods and materials for making molds
In this final section, we briefly introduce some 3D printing techniques and materials suitable for 3D printing shapes.
Common 3D printing processes
- Stereolithography (SLA)
- Fused Deposition Modeling (FDM)
- Blasting of materials
- Selective laser sintering (SLS)
Common 3D printing materials
- ABS (acrylonitrile butadiene styrene)
- PETG (polyethylene terephthalate)
- PP (polypropylene)
- nylon
- Thermoplastic elastomers (TPE)
University Degree
This concludes our discussion on the interesting topic of 3D printed molds for injection molding. 3D printed molds are a new alternative to aluminum molds, offering advantages such as cost and time savings as well as design flexibility and are ideal for low volume production.
Their disadvantages include lower structural integrity and wear resistance compared to metal molds, but special solutions exist to eliminate these problems.
Common questions
How expensive are 3D printed molds compared to metal molds?
3D printing molds are relatively cheap compared to metal molds. Typically, a 3D printed mold costs less than $200. A metal mold easily costs more than $5,000. For small batch production, 3D printed molds are a clear choice.
Which common 3D printing is best for injection molds?
If we only compare FDM, SLS and SLA, we recommend using SLA to make injection molds. SLA products are robust, smooth and precise. FDM molds have release problems and are not as smooth as SLA molds. Similar issues are commonly reported with SLS products.
How to improve the cooling time of a 3D printed injection mold?
3D printed molds do not cool as quickly as metal molds due to their low thermal conductivity. A good tip is to use compressed air to increase convection heat transfer or use replaceable batteries.
