Combining composite and metal 3D printing, or hybrid printing, you can create complex designs, pinpoint material usage based on property requirements and lower the weight in final parts. It basically means lower cost per part with optimized properties. Check out this case on how I designed and printed a pair of innovative pliers using both composite and metal 3D printing.
What is hybrid 3D printing
There are two main material categories of 3D printing – plastic and metal. The two material families both have pros and cons. For example, plastic is cheaper and easier to print with than metal. But on the other hand, metal is stronger and more durable than plastic. What if we could get the best of both worlds?
Well, in fact, you can. This is achievable by combining parts printed in a plastic printer and parts printed in a metal printer. The technique is called hybrid design. To give you a better understanding of hybrid design, we have created an example part – a pair of hybrid pliers. These have a plastic grip and a metal jaw.
Firstly, we need a Markforged composite printer, which can print fibre reinforced nylon with continuous fibre inlay for extra strength. Secondly, we need to print with Markforged’s Metal X system, which can print metals such as Stainless, Inconel, Copper etc. These printers even share slicer software, so it is more or less the same procedure if you define a part in composite or steel material, making combining the materials a breeze.
In this example with a set of 3D printed pliers I will go through the different steps of designing and printing such a hybrid geometry.
Designed with SOLIDWORKS
You need to start thinking about how the parts are going to be produced early in the design process. This is so that the geometry can be optimized for a specific production method, for 3D printing/additive we call this Design for Additive Manufacturing (or short DfAM).
For example were the handles and jaws designed as separate components to be able to print them using varied materials.
They were also designed so that they could be connected to each other by using “dovetail joints”.
The plan was to incorporate the metal section (head) inside the handle. This is possible by defining a pause mid-print on the Markforged Composite machines. Both components were therefore designed flush at the bottom so that a pause could be done mid print, and the jaw inserted into the handle.
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Simulation to check the strength
Doing a structural analysis of the CAD model to check the strength before the geometry is created can save you a lot of time when it comes to prototyping. Therefore, an FEA study was done in SOLIDWORKS Simulation to check how the pliers would act when exposed to a force of 200N (20kg).
The jaws where to be printed in stainless steel, so for material Stainless steel where added.
The handles were to be printed in Onyx which is a blend of 80% Nylon PA6 and 20% chopped carbon fiber. Since the part will be printed with infill (not solid as the FEA model is) pure PA6 were defined as material.
The study was done in SOLIDWORKS Simulation Premium using a non-linear study (to consider any change in structural stiffness when the force was applied). Also, jaws were fixed to simulate that they were “biting” on a sheet (image below).
A load of a total 200N was applied to the top/bottom surface of the handles.
After running the analysis, I could see that maximum stress in the handles where around 40MPa (in the transition area between metal and plastic), this is way below the yield strength of PA6 which is 100MPa, so it should not be any problems. The “jaws” were not showing any stress at all, which means that these jaw components could be optimized by removing material, we will get back to that later.
For connecting the plier jaws to each other, a Barell nut was designed.
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Printing the hybrid pliers
First, the jaws where to be printed on the Metal X system. Since I earlier had concluded that the jaws in stainless steel were more than strong enough, I decided to optimize them.
For this I used an option in Eiger (which is the slicer software used by Markforged (both for composite and metal)) called Exposed Infill. This feature generates parts without any roof or floor layers leaving the infill exposed and by this reducing the weight and print-time.
The parts are printed on a raft (as can be seen in the picture below) to increase stability and uniform shrinking during the sintering process.
The picture below showing the jaws in “Green state” right out of the printer before wash and sintering.
Then the handles were printed. Even though Onyx is quite strong with chopped carbon fibre, additional continues carbon fibre was added to the walls to improve the strength even more. Can be seen visualized in blue in the picture. You can also see that the parts were not printed solid, but with triangular infill. This was done to save weight, material, and print time.
A pause was defined on the last layer of the hollow section so that the jaws could be inserted before the printer continued.
The metal part was inserted during the pause mid print.
Print was continued, and the metal part incorporated in the handle.
The two parts were then connected to each other using the 3D printed barrel nut.
And the 3D printed hybrid pliers were finished.
The image below shows the difference in weight between an “ordinary” plier = 227 g and a hybrid 3D printed plier = 69 g.
So, to sum this up. By using the hybrid design method, I was able to use 3D printing to produce the parts opening for the possibility for complex design without any extra cost. I was also able to select the use of different materials based on the sections of the pliers (higher strength and durability in the jaw section) while using a cheaper and faster to print composite material in the handle areas. I was also able to reduce the weight of the pliers compared to traditional ones due to open infill structure for the plier heads and lightweight composite material in the handles.
By being able to combine different materials and production methods (this can of course also be done with CNC machined metal parts), we are opening up many doors when it comes to product development. I bet you also have some examples on your workplace where this hybrid method would be suitable.
