Design for 3D Printed Injection Mold Tools 101: Tips, Tricks, and Best Practices
Injection Molding Gets a Face Lift
Written by: Ben MacDonald, Senior Applications Engineer
What do the cap on your water bottle, strap on your smartwatch, and frame of your sunglasses all have in common? If they are all made out of plastic then they were all injection molded. Injection molding is a manufacturing process that has been around for over a century. In that time, the process and technology have made tremendous advancements. Similarly, mold design techniques and solutions have needed to evolve to match the technology and market needs. In the early days collapsible cores, conformal cooling, and advanced CAD softwares were beyond anyone’s wildest dreams. Today these are all standard tools in a mold designers toolbox, however, the only way these tools are useful to a mold designer is for them to gain the knowledge on how to use them. Even a simple tool, like a hammer, is just a paper weight to an individual who doesn’t know how to swing it.
At Fortify we believe 3D printed mold tooling is the next big advancement in injection molding. While printed mold tooling certainly isn’t something new to the industry, it has not been widely adopted. Anecdotally, we hear all too often that someone tried out printed mold tools years ago and they just didn’t work. And historically, 3D printed tools were not made from the right materials and/or printed on the right hardware to hold up in a mold press. Fortify dove deep into the application to understand exactly what inputs are needed to be successful. While standard inputs like material properties and printer quality are a major focus, less obvious inputs like the mold design itself has turned out to be a key contributor to successful or unsuccessful molding outcomes. One very basic principle that has guided us is that printed molds are fundamentally different from traditional steel molds. Steel molds are made out of metal while printed molds are made from a photopolymer. As a result, in order to be successful with a polymer based mold, different design strategies must be implemented.
Designing 3D Printed Injection Mold Tools Training
Over the next five weeks Fortify will be “pulling back the curtain” to showcase exactly how we go about designing mold tools, accompanied by tips and tricks that we have picked up along the way. Every week on Tuesdaystarting on Feb 15, 2022Fortify will be releasing a video module highlighting five discrete design steps to design 3D printed injection mold tools. These video modules will educate mold designers on the differences between designing polymer and steel molds. They will also give any individual who has CAD experience some of the basic tools needed to start designing their own molds. The five modules will include:
Module 1: Part Selection
Module 2: Setting up a Design Template
Module 3: The Basics of Mold Design
Module 4: Advanced Mold Design Techniques
Module 5: Finishing a Mold
MODULE 1: Part Selection
In our first module we dive into part selection. Part selection is critical for setting yourself up to succeed as not all parts are great candidates for printed mold tooling. A good first step with part selection is to identify if a given part fits within your physical capabilities. If a part is “unmoldable” it doesn’t matter what tools and techniques you implement during the design phase, you will be unsuccessful. If a part is too big for your frame or it requires a larger shot size than your machine is capable of, again you will be unsuccessful.
Once you have identified if the part is within your capabilities a great next step is to visualize what a mold for this part might look like. Ask yourself the following:
What are some potential parting lines?
What ejection strategies can I implement?
Where are my potential gate locations?
How will I ensure that this mold is properly vented?
These questions will help you put a plan together for designing the mold and if you can’t answer any of these questions, that is a sign that this particular part is not a good fit.
For parts that pass the test, there is still more work to be done before you begin the design. Typically a part must go through some DFM (Design for Manufactuability) work to prep for the mold design. DFM work includes: adding draft to undrafted or underdrafted surfaces, breaking sharp corners with radii or chamfers, and in rare cases redesigning certain areas of parts for robustness. Along with this DFM work it is good practice to make note of “higher risk” features on the part. These part features include through holes, ribs, and thin wall areas just to name a few. Nothing needs to be done with these areas during the DFM phase but later on in the process we will revisit them.
Lastly, a scaling factor needs to be applied to the part itself. This scaling factor is used to combat plastic shrinkage and it is a material-dependent value. That means that now you will need to know exactly what material you are going to use make your part. Once you have gone through all of this, you are ready to start designing your mold!
Follow us on LinkedIn where we will launch Modules 2 – 5 weekly.
MODULE 2: Setting up a Design Template
In our second module we cover setting up a design template. Although setting up a template doesn’t seem like the most exciting topic for mold design, it truly is the most powerful step of the process. Having a good template (master model) in place can save a designer multiple HOURS of design time on each mold. Not to mention the peace of mind that comes with knowing that all features are properly oriented and aligned. This master model is something that needs to be built once for each frame that you have in house. After that it becomes an evergreen tool for any future mold designs. At Fortify we have four separate templates for each of the four configurations that our frame has – I can confidently say that they have saved us over 100 hours of design time in the last year alone!
At this point you are probably thinking “These templates sound great, what goes into them?” Good question! Watch the full video to find out all the components that go into creating a template. Some key examples include: Mold Block Sizes
Ejector Pin Locations
Mold block sizes are an essential component to this template. Without them there would be no template. These sizes are best defined with a sketch on the center plane to capture the width and height of the mold block and then two planes to capture the depth of each mold block. These three dimensions (width, height, and depth) should directly correlate to the pocket size on the target mold frame.
Runner misalignment between the frame and printed mold block can seriously impair (or even prevent) a mold’s ability to produce quality parts. By including the runner location in the master model guess work is eliminated and repeatable success is ensured.
Predefined ejector pin locations in the template is significant for expediting the part placement step (stay tuned for the next video!). With all potential ejector pin locations defined on a template, the mold designer has a distinct guide for placing the part on the mold. The designer is able to orient a part to “cover” certain ejector locations so that a solid ejection plan is in place before the mold design has even started.
Specifying mounting locations in a template is key to time savings. These mounting holes get added into every single mold that you might design and nothing about them changes from mold to mold. By adding these mounting holes into the master model you are able to completely eliminate the process of designing these holes leading to some pretty impressive time savings.
While these are some of the more powerful components of a template, everything mentioned in the video will lead to major time savings (and less headaches!) during the mold design process. With a quality template in place a designer is able to really focus on the best part of mold design, creating new molds!
Be sure to follow us on LinkedIn to find all these modules and tune in next week for Module 3, “The Basics of Mold Design”
MODULE 3: The Basics of Mold Design
The Basics of Mold Design are really … quite basic! In this module you will learn how to design something that looks like and functions like a Fortify 3D printed mold but it won’t include all of the advanced techniques that we implement to get the most out of our tools. After today’s module you will be able to:
Choose a mold block size
Determine part position and orientation
Create a core and cavity
Design a basic runner system and gate
These four items are the foundation of a functional mold tool. Just like a strong foundation leads to a sturdy house, getting these four items right leads to a robust mold tool.
Choosing the right mold block size can be likened to a minor balancing act. A block that is too small can lead to suboptimal part orientation and potentially premature mold failure. A block that is too large will lead to unnecessary material costs and longer print times. Clearly it is better to err on the side of caution by using a slightly larger block than necessary. At a minimum this block should allow you to place a part in its optimal orientation, enable a robust ejection strategy, and leave 10+ mm of space between the part geometry and the outer walls of the mold block. Depending on which of your predefined mold block sizes meets those requirements, the corresponding template will be your starting point for mold design.
With your mold block size defined, the next step is to place your part within the bounding box created by your mold block. Because we already asked ourselves to think about potential parting lines for this part in Module 1, we already have our target parting line in mind. If not, two general rules of thumb are to choose the parting line that leads to the least amount of hand loaded inserts and to choose the parting line that leads to the most robust ejection strategy (more to come in Module 4). With our parting line determined we just move the part around on the parting line plane to both cover the necessary ejector pins and maintain our 10mm wall thickness.
Creating the core and cavity blocks for a mold set requires both additive and subtractive CAD processes. Typically the cavity creation will be subtractive and the core creation will be additive, but there is a lot of overlap for the two. Any recessed features in a mold block are created by merging the part with the mold block and all standing features are created by copying the negative of the part geometry. With the core and cavity created the last step is to add in a runner system and gate. This step is fairly straightforward as it is just connecting the predefined runner start location to the target gate location. This target gate location should be a flat face of the part somewhere on the parting line.
With a basic mold design in place you are now able to start molding parts. With that being said, I know you all want to get the very most out of your molds. Make sure to tune in next week for Module 4, “Advanced Mold Design Techniques” and be sure to follow us on LinkedIn to find all these modules and more!
MODULE 4: Advanced Mold Design Techniques
The fourth module will cover Advanced Mold Design Techniques. This module is where we leverage Fortify’s deep applications knowledge. We dive into the unique design tools that Fortify uses to attack the most complex parts that we have come across. Some of these tools enable us to replace highly complex and expensive steel components, further emphasizing the value add of printed mold tools. We also start to think about our process engineer and what will make his or her life easier? While we can’t fully answer that question in one sitting, we will tackle the first half of that answer today.
So, what are Fortify’s most advanced mold design techniques anyways? The answer to that is simple: inserts and ejection. Take a look:
Fortify uses inserts for almost everything – and for good reason.
Do you have a high aspect ratio pin feature? Use an insert!
Do you have an intricate core feature? Use an insert!
Does this part have threads? Use an insert!
Do you need more venting? Use an insert!
I think we all get the point, inserts are very versatile. Beyond versatility, inserts are also functional. The three main inserts that we use on a daily basis are: fixed inserts, removable inserts, and floating inserts (the latter two are commonly referred to as handloads). Each of these inserts have distinct use cases to enable a variety of outcomes.
Fixed inserts are inserted through the back of a mold and as a result are fixed in place for the duration of a mold run. These inserts are particularly useful to de-risk challenging features and to enable greater venting in specific areas (more on that next week).
Removable inserts are inserted through the parting line face of a mold tool. They accomplish the same goals as fixed inserts but with the added benefit of a more creative ejection process. After a cycle is complete these inserts get ejected with the part and are subsequently removed by hand. These inserts are super beneficial when it comes to threads or any other features that can’t have a straight pull ejection.
Floating inserts are also inserted through the parting line face but for an entirely different purpose. These inserts are used to replace any feature that would require a side action component on a standard metal mold. The easiest example of this would be a through hole in a part. They also work well for any undercut features on the outside of a part.
Ejection is often initially overlooked in the design process, and can make or break a mold tool. If you can’t properly eject a part from a mold then that mold is useless. At Fortify we stress ejection throughout the full design process because if you wait until this point to think about ejection you will have to start your design all over again. At this point in the process we already know how we plan to eject the part. That could be with:
Standard ejector pins
Printed ejector plates
Whatever the ejection strategy is, it is very important to put yourself in the process engineer’s shoes for a moment. How will this design actually play out? This question can shed light on an area for improvement with the design or give confidence to the design.
As I hinted to earlier, we still have yet to really cover venting, something that we heavily leverage to expand our processing window. As always, be sure to follow us on LinkedIn to find all these modules and tune in next week to Module 5, “Finishing a Mold” to learn all about venting along with our specialized tips and tricks.
MODULE 5: Finishing a Mold
When you are under a lot of pressure, sometimes you just need to vent! I’m not talking about venting to your friend though, I’m talking about venting your mold block! Ventilation for a mold block is when you create areas for air to escape during the molding process. This idea is nothing new for the injection molding industry but at Fortify we take it to a whole new level with our 3d printed mold tools. Whenever we can add ventilation to a mold we do. This enables us to run with injection pressures that are incredibly low compared to industry standards. Take a look for more tips and tricks on finishing your mold:
I think my favorite tool that we use here at Fortify is the raised parting line. It is such a simple design tool but its capabilities are so powerful. All we do is recess the area that is greater than 5 mm away from the parting edge and our effective control over clamp tonnage is significantly increased. If you have a small press this lets you get the most out of your available clamping tonnage. Also, if you are molding a very low viscosity plastic this allows you to seal off the parting line that much more effectively.
Manual slides are basically just a more refined form of a floating insert. Technically they accomplish the same goal of a floating insert but visually they more closely resemble the production component. These come in handy when you want to validate that a slide component will work prior to ordering this slide component.
Finally we get to venting! Venting is something that we add in at the very end of our mold design. This is because we take into account our ejector pins and existing inserts when we determine where to add venting as those are both great opportunities for venting. Once we take those into account we look for deep recessed features throughout the mold. If there is anything greater than 10mm in depth we will add ventilation. We also think about where the end of fill might be (if you have mold simulation software, this is a great use for it) as this is another good location for venting. With all of this in mind we go to our tool box to select which tool is right for the location. These tools include:
Depending on what the geometry in the target area looks like we will choose one of those five tools to get the job done. Sometimes we use more than one.
Once venting is in place the very final step of any mold design is DFAM (Design for Additive Manufacturing). While this step is technically DFAM, we mainly focus on making a few slight adjustments for printability. These adjustments include adding in chamfers and radii to sharp corners around the edge of the mold block. At this point our mold is ready to print!
A little bonus to this full process is adding in texture. I wait until this point to bring up texture because this is the point in the design process when it would actually be added in; after the design is done. Doing any sort of texturing during the design process leads to significantly slower software speeds while designing. In order to avoid that, we wait until the design is complete.
With that our design modules are complete and you are now ready to start designing your own molds. Feel free to reference these modules as you go through the design process. Also, if you haven’t done so yet, be sure to follow us on LinkedIn as we continue to post more exciting content about Injection Molding!