Varied Infill Options for CAD models brought into GrabCAD Print software for 3D Printing. (Image courtesy PADT)

GrabCAD Print Software, Part Two: Simplify Set-ups, Save Time, and Do Cool Stuff You Hadn’t Even Considered

(Edited 3 August 2020 to reflect GrabCAD Print V1.44)

You haven’t really lived in the world of 3D printing until you’ve had a part fail spectacularly due to open faces, self-intersecting faces or inverted normals. Your part ends up looking more like modern art than technical part. Or perhaps the design you have in mind has great geometry but you wish that some parts could have regions that are dense and strong while other regions would work with minimal infill.

In Part One of this blog post about GrabCAD Print software, we covered the basics of setting up and printing a part; now we’ll look at several of the advanced features that save you set-up time and result in better parts.

Behind the Scenes Repairs

Stratasys GrabCAD Print software, available as a free download, is crafted for users setting up solid models for 3D printing on Stratasys FDM and PolyJet printers. Once you’ve started using it, you’ll find one of its many useful advanced features is the automated STL file-repair option.

Imported STL file, with GrabCAD Print ready to automatically repair errors. PADT image.

Most people still create solid models in CAD software then convert the file to the industry-standard STL format before opening it in a given 3D printer’s own set-up software. Every CAD package works a little differently to generate an STL file, and once in a while the geometry just doesn’t get perfectly meshed. Triangles may overlap, triangles may end up very long and very skinny, or the vector that signals “point in” or “point out” can get reversed.

Traditionally, the 3D printer set-up program reacts to these situations by doing one of two things: it prints exactly what you tell it to print (producing weird holes and shifted layers) or it simply refuses to print at all. Both situations are due to tiny errors in the conversion of a solid CAD model to a tessellated surface.

GrabCAD Print, however, gives your file a once-over and immediately flags sections of the model in need of repair. You can see a color-coded representation of all the problem areas, choose to view just some or all, and then click on Automatic Repair. No hand-editing, no counting layers and identifying sections where the problems reside – just a click of the virtual button and all the problem regions are identified, repaired and ready for the next processing steps.

CAD vs. STL: Do So Much More with CAD

GrabCAD Print also uniquely allows users to bring in their models in the original CAD file-format (from SolidWorks, Autodesk, PTC, Siemens, etc.) or neutral formats, with no need to first convert it to STL. For FDM users, this means GrabCAD recognizes actual CAD bodies, faces, and features, letting you make build-modifications directly in the print set-up stage that previously would have required layer-by-layer slice editing, or couldn’t have been done at all.

For example, with a little planning ahead, you can bring in a multi-body CAD model (i.e., an assembly), assemble and group the parts, then direct GrabCAD to apply different parameters to each body. This way you can reinforce some areas at full density then change the infill pattern, layout, and density in other regions where full strength is unnecessary.

Here’s an example of a SolidWorks model intended for printing with a solid lower base but lighter weight (saving material) in the upper sections. It’s a holder for Post-It® notes, comprising three individual parts – lower base, upper base and upper slot – combined and saved as an assembly.

Sample multi-body part ready to bring into GrabCAD Advanced FDM. Image PADT.

Sample multi-body part ready to bring into GrabCAD Advanced FDM. Image PADT.

Here was my workflow:

1 – I brought the SolidWorks assembly into GrabCAD, assembled and grouped all the bodies, selected an F370 Stratasys FDM printer, chose Print Settings of acrylonitrile butadiene styrene (ABS) and 0.010 inches layer height, and oriented the part.

2 -To ensure strength in the lower base, I selected just that section (you can do this either in the model tree or on the part itself) and opened the Model Settings menu at the right. Under Body, I chose Solid Infill.

3 – Next I selected the upper base, chose Hexagram, and changed the Infill Density to 60%.

4 – Lastly, I selected the upper slot section, chose Sparse, and changed the Infill Density to 35%.

5 – With all three sections defined, I clicked on Slice Preview, sliced the model and used the slider bar on the left to step through each section’s toolpath. For the screenshots, I turned off showing Support Material; the yellow bits indicate where seams start (another parameter that can be edited).

Here is each section highlighted, with screenshots of the parameter choices and how the part infill looks when sliced:

Upper base set up in GrabCAD to print as Hexagram pattern, 60% infill; sliced toolpath shown at right. Image PADT.
Upper slot section set up in GrabCAD to print as Sparse pattern, 35% infill; sliced toolpath shown at right. Image PADT.

So that you can really see the differences, I printed the part four times, stopping as the infill got partway through each section, then letting the final part print to completion. Here are the three partial sections, plus my final part:

Lower base (solid), upper base (hexagram) and first part of upper slot (sparse), done as partial prints. Image PADT.
Completed note-holder set up in GrabCAD Print, Advanced FDM mode, weighted toward the bottom but light-weighted internally. Image PADT.
Completed note-holder set up in GrabCAD Print using advanced infill features, weighted toward the bottom but light-weighted internally. Image PADT.

Automated Hole Sizing Simplifies Adding Inserts

But like the old advertisements say, “But wait – there’s more!” Do you use heat-set inserts a lot to create secure connections between 3D printed parts and metal hardware? Planning ahead for the right hole size, especially if you have different design groups involved and fasteners may not yet be decided, this is the feature for you.

Sample part set up for easy insert additions, using Advanced FDM in GrabCAD Print. Image PADT.

Sample part set up for easy insert additions, using advanced, automated hole-resizing features in GrabCAD Print. Image PADT.

In your CAD part model, draw a hole that is centered where you know the insert will go, give it a nominal diameter and use Cut/Extrude so that the hole is at least the depth of your longest candidate insert. Save the file in regular CAD format, not STL. Next bring your part into GrabCAD Print and go to Model Settings in the right-hand menu.

This time, click on Face (not Body) and Select the inner cylindrical wall of your hole. Several options will become active, including Apply Insert. When you check that box, a new drop-down will appear, giving you the choice of adding a heat-set insert, a helicoil insert or creating a custom size. Below that you select either Inch or Metric, and for either, the appropriate list of standard insert sizes appears.

Automatic hole-resizing in GrabCAD Print, for a specific, standard heat-set insert. Image PADT.

Choose the insert you want, click Update in the upper middle of the GrabCAD screen, and you’ll see the hole-size immediately changed (larger or smaller as needed). The new diameter will match the required oversized dimensions for the correct (melted into place) part-fit. You can even do this in a sidewall! (For tips on putting inserts into FDM parts, particularly with a soldering iron, see Adding Inserts to 3D Printed Parts: Hardware Tips.)

Note that this way, you can print the overall part with a sparse infill, yet reinforce the area around the insert to create just the right mass to make a solid connection. The Sliced view will show the extra contours added around each hole.

Sliced view showing insert holes with reinforced walls, done in GrabCAD Print. Image PADT.
Manufacturing notes automatically created in GrabCAD Print when insert holes are resized. Image PADT.

To document the selected choices for whoever will be doing the insert assembly, GrabCAD also generates a numbered, manufacturing-footnote that lists each insert’s size; this information can be exported as a PDF file that includes a separate close-up image of each insert’s location.

GrabCAD Print keeps adding very useful functions. Download it for free and try it out with template versions of the various Stratasys 3D printers, then email or call us to learn more.

PADT Inc. is a globally recognized provider of Numerical Simulation, Product Development and 3D Printing products and services. For more information on Stratasys printers and materials, contact us at info@padtinc.com.

Adding Inserts to 3D Printed Parts: Hardware Tips plus One-Click Design in GrabCAD Print Advanced FDM

Heat-set, ultrasonic, helicoil: metal inserts are exceedingly useful when you want to add threads to a plastic part, preparing it for a strong screwed-in connection. Whether you heat up the insert and push it down into the pre-made hole (purposely melting the plastic as you do so) or tap a hole to allow a helicoil to dig into its side, you create a better grip for whatever hardware you eventually install. Inserts are especially useful for parts that will be assembled and disassembled multiple times.

Here at PADT, Inc., we thought we’d research the different installation approaches and demonstrate several ways to use inserts in FDM 3D-printed parts (be sure to check out the short video further on). Our awesome intern-turned-employee Austin Suder had already designed and printed some LED light boxes for off-roading with his truck, so we used his parts for our tests and demos. (Stay tuned – we’ll soon be featuring a whole variety of Austin’s automotive upgrades in an upcoming PADT post.)

For a classically milled plastic part, you plan ahead by drilling a slightly undersized hole that is enlarged as the heated insert is pushed into place. For a 3D printed part (let’s say ABS), you plan ahead in a similar way, using the hole dimensions given on any insert data-sheet. However, to get the best anchor against torque-out and pull-out, holes in 3D printed FDM parts need multiple material contours around them. You don’t want to melt through a thin wall into the infill region, and you don’t want weird bulges on the exterior if the hole is close to an edge.

An LED light box for off-road automotive lighting.
An LED light box for off-road automotive lighting, showing sections ready for M3 heat-set inserts. Sample side part printed in white for clarity. (Images courtesy PADT)
An LED light box for off-road automotive lighting, showing sections ready for M3 heat-set inserts. Sample side part printed in white for clarity. (Images courtesy PADT)

Heat-Set versus Ultrasonic Inserts

We’ll talk about defining those beefed-up contours in a moment. First, let’s describe the difference in installing heat-set (also called heat-staked) versus ultrasonic inserts, and talk about the pros and cons of their use. Inserts can also be dropped into slightly oversized holes if you pause the printer, add the part, and continue to print over them with enough material to just trap them in place. (Note: Helical inserts require tapping and then an installation tool, and do not give quite the strength of the former two types.)

Both types of inserts may come as small as #0-80 and M2.5×0.45 up to 3/8-16 and M8x1.25 (inches and metric, respectively), depending on whether you choose tapered or straight-sided versions. Material choice typically is aluminum, brass or stainless steel, in order to provide high thermal conductivity with strength.

Close-up of M3 size metric heat-set inserts to show relative size, ready for installation. (Image courtesy PADT)
Close-up of M3 size metric heat-set inserts to show relative size, ready for installation. (Image courtesy PADT)

A heat-stake machine looks like a small drill-press with a soldering-iron tip, and does ensure a perfectly vertical motion. However, the easiest insertion tool is a handheld soldering iron fitted with a flat-end heat-set tip that matches the inner diameter of the insert. Heat-set tips cost less than $20, and their benefit (compared to using just the default soldering iron tip) is that the flat head is easier to retract after the insert is completely in position. You can add package prints for that refer short run package prints.

(Left) Using a standard chisel-tip on a soldering iron to install a heat-set insert can make it difficult to get the insert in straight. (Right) Using a specialized heat-set tip gives a good vertical installation. Tips are sold to match each insert type and size (Image courtesy PADT)
(Upper) Using a standard chisel-tip on a soldering iron to install a heat-set insert can make it difficult to get the insert in straight. (Lower) Using a specialized heat-set tip gives a good vertical installation. Tips are sold to match each insert type and size. (Image courtesy PADT)                                                

A useful guide from Stratasys, “Inserting Hardware Post-Build,” suggests pre-heating the soldering iron or heat-staking press to a temperature that is approximately 170% of the glass transition temperature (Tg) of the FDM material, or work with a variable-power iron set for about 40 watts. Stratasys material data sheets list Tg values for each material.

Step-by-step Installation

To install a heat-set insert, set the metal insert on the 3D-printed part surface, centered on the hole. Tapered inserts are self-seating and make it easier to ensure the insert goes in straight, but even the straight-wall designs have a slightly smaller lead-in section to assist with alignment.

Fit the soldering-iron tip into the center of the insert, then push the insert down gently into place – you’ll feel the plastic around it starting to melt. Stop pushing when you see the insert has almost completely gone in, then pull back on the tip. Immediately place a flat aluminum plate on the insert/part area and push down until the insert is completely flush with the part surface. Alternatively, you can turn the part upside down and push the face against a table or flat plate – whatever is easiest given the part geometry.

Once you remove the soldering iron (heat source), the cooling, melted plastic reflows into the grooves, knurls and slots cut into the insert’s outer walls and solidifies. This connection is what forms the excellent grip between metal and plastic.

Finished part with insert flush to the part’s surface. (Image courtesy PADT)
Finished part with insert flush to the part’s surface. (Image courtesy PADT)

Ultrasonic installation also melts the plastic and ends up with the same result, but the process and equipment are quite different. The user (or an automated system) sets the insert in place then lowers an ultrasonic horn directly onto the metal’s surface. Ultrasonic vibrations create frictional heat, again melting the plastic, and the equipment pushes the insert down to a preset depth.

Both methods work, but unless you need the speed of automated assembly, heat-insertion is a simpler and less expensive approach. The equipment for ultrasonic insertion can be expensive, is very loud when operating, and can be harder to control. There’s also the chance that metal chips get generated and stuck in the part.

For more information comparing the two methods, see the in-depth Machine Design article, “Putting inserts in plastic parts: ultrasonic or heat?

Designing CAD Models for Inserts

The key to sizing holes to be insert-ready is to slightly undersize them. Insert datasheets provide diameter and depth information for all the standard sizes, with virtually identical values regardless of brand (one company might list a diameter as 5.2mm and another as 5.23mm but these are negligible differences for this purpose).

Two online resources are SI Inserts for Plastic and the McMaster-Carr insert webpages.

These online charts or diagrams give the minimum hole depth and diameter that must be designed into the CAD model. For tapered inserts, the mounting hole officially has its own taper, but the difference is so minimal that for most cases, a straight hole will grip the insert just fine, as shown in the figure below.

CAD part with straight-walled holes set up for adding M3 inserts (Image courtesy PADT)
Sample CAD part with straight-walled holes set up for adding M3 inserts (Image courtesy PADT)

In print set-up software such as Stratasys Insight, the recommendation is to create four to six contours around each hole that is designated for an insert. This is done by creating a Custom Group under the Toolpath heading, defining the number of contours, and selecting all the relevant holes. When you review the toolpath layer by layer you’ll see those contours show up.

One-Step Insert Set-Up in GrabCAD Advanced FDM Software

For parts printed on many Stratasys FDM printers – from the F170/270/370 Series up through the larger Fortus 380, 450 and 900 models – users can even more quickly prepare their parts for inserts using GrabCAD Print’s Advanced FDM features. Since GrabCAD Print’s set-up software works directly with CAD files, all the feature intelligence is retained, meaning the software recognizes bodies and faces, including the cylindrical sides of a hole.

As long as your part has a hole whose center is in the desired location, GrabCAD does something very cool. It lets you choose an insert from a drop-down menu then automatically resizes that hole to the correct dimensions and reinforces its perimeter with an optimized number of contours. No need to create custom groups, isolate model slices, rebuild tool paths or wonder if you added enough material.

Automated contour-creation around holes for heat-set inserts, created using Stratasys GrabCAD Print software. (Image courtesy PADT)
Automated contour-creation around holes for heat-set inserts, created using Stratasys GrabCAD Print software. (Image courtesy PADT)

Try GrabCAD Print for yourself – it greatly simplifies optimizing the contours and hole-sizing, and makes it easy to evaluate different insert sizes on-the-fly without having to edit the original CAD file.

To learn more about working with inserts in general, GrabCAD Print software and FDM printers and materials, contact the PADT Manufacturing group; get your questions answered, have some sample parts printed, and share your success tips.

PADT Inc. is a globally recognized provider of Numerical Simulation, Product Development and 3D Printing products and services. For more information on Insight, GrabCAD and Stratasys products, contact us at info@padtinc.com.