Print for metal casting
Summary and final tips
One of the most important decisions when 3D Printing is the orientation you print the model in. Considerations must be made to minimize required support material, ensure a reliable print with the best surface quality and maximize strength.
There are cases where these considerations may contradict each other so sometimes compromises must be made. Let’s look at how to optimize printing for each of these considerations.
First Layer / Adhesion
The first layer of a 3D print is the single most important layer your printer will print. If your print is poorly stuck to the bed; the print is susceptible to moving, wobbling and even warping. All of these can in severe cases result in print failure.
Aside from ensuring our bed is leveled and using the right printing surface and settings for the desired material; it is important to orientate your print so the first layer is large enough to secure the print to the bed.
- Firstly we look for large flat surfaces on the model which will provide a stable first layer.
- When printing files with no distinguishable flat surface you can either modify the file (cutting) to create a flat base or alternatively you can print with supports and a raft which will hold the print in place.
- If the print is tall and the first layer is fine or covers a very small area, we recommend printing with a raft or brim to improve adhesion to the bed.
In the case of part 1, the first layer is made up of many small extrusions which are later built upon and connect to each other. The corner of the model is built from one singular point which would be unstable and likely fall over before connecting to the rest of the print. There are no better orientations for this model so to ensure success, we would print Part A with a raft or brim for improved stability.
In the case of part 2, the sides of the gear are flat surfaces so printing this gear on its side will provide a nice first layer to print upon. This orientation requires no support material, achieves the best surface finish and will result in the best mechanical performance; considerations we will discuss next.
For many applications achieving the best surface finish is critical to minimize post-processing and manual clean up. Firstly we must understand which geometries / shapes print best in each orientation.
Minimising layer lines with orientation.
Each time the printer extrudes a layer, visible micro-stepping known as layer lines are created in the Z axis (height). While this stepping can be minimized with finer layer heights or even removed with post processing, we can minimize the effects of this stepping by optimizing the orientation of our model.
This stepping at each new layer is only visible in the z-axis so while the 3D printer can’t replicate a perfectly smooth curve or diagonal line in the Z-axis, it can print this same curve or line with near perfection in the X and Y axis.
Gravity and overhangs.
In addition, the horizontal top and the vertical surfaces of a print will typically print with better quality than the underside where overhangs require supports or bridging. This is because not only must overhangs / bridges be printed with the right flow rate as top layers, they must also cool and solidify before gravity causes them to sag.
The surface quality of undersides can be improved with a cooling fan (material specific), lower printing temperatures or dense / soluble supports however it is equally important to optimize the orientation with the presentation of our part in mind.
Example of scarring that can occur on the undersides of certain geometry.
BONUS TIP: Cutting a file to avoid overhangs.
Sometimes a file can be printed in multiple pieces to improve the surface quality of the entire printed part. Cutting an stl file into 3 pieces allowed us to avoid supports when printing this life sized human head. Printing the head in 1 section would have required supports under the chin and nose which would scar the part . This method ensured a professional quality on all sides of the part without requiring excessive post processing.
Minimize Support Material
Support structures or support material is an essential element of the printing process, expanding the shapes and geometries we can 3D print. Support structures act as scaffolding to support overhangs and details which would otherwise fall due to gravity. Supports are most prominently used to support ledges and overhang angles less than 45°. These supports are removed after printing however can leave scars on the surface and support removal can be difficult with some materials.
By understanding why supports are used we can orientate and even design our models to minimize and even eliminate the need for support materials.
Picture: Polymaker PolySupport™ attached to a bunny printed in red PLA.
Supports aren't always required.
Not all overhangs will require support material; in fact the printer can bridge between two supported points. In the following example, if we two walls at an angle above 45°, the printer can now bridge the entire overhang, removing the need for supports. There is of course a limit to how far a printer can reliably bridge, so supports may still be required when printing long unsupported overhangs.
In this example we have a part which was specifically designed for 3D Printing. There are no ledges and all angles are above 45° so printing this part upright in orientation B is ideal. In orientation B there will only be supports in the drill holes but realistically these are optional. Other orientations (A and C) require unnecessary support material or affect the surface finish with no benefit to performance, reliability or aethsetics.
This part has two flat surfaces so the part could be safely orientated in one of two ways. Orientation A is the most ideal orientation in regards to minimizing support material and also achieves the best surface finish. Layer height is less important in this orientation as most curves and angles will be printed in the X and Y axis.
The surface of the underside being supported in orientation A won't be as smooth as other surfaces, so in a case where the appearance of this side was crucial, orientation B could be used.
One of the key goals when 3D printing any functional part is to ensure the part will meet all performance expectations. In addition to designing the part correctly and choosing the right material / settings, sometimes a specific printing orientation is also required.
The reason for this is the layer lines in the 3D print. These layer lines act as weak points, so less force is required along the layer lines to create layer separation and finally fracturing. This is very similar to how the wood grain in a piece of timber behaves.
Source: Polymaker PolyMax PC TDS (Testing method ASTM D638 (ISO 527, GB/T 1040))
By understanding that features printed along the Z axis can be considerably weaker than in the X and Y axis, we can orientate our prints to improve the mechanical performance of our part and prevent fracturing / layer separation.
In this example, the part is a simple design which can be printed without support material in most orientations.
When printed in orientation A it will be easy to snap off both walls as forces in the x axis are applied along the layer lines. Ideally this shape would be printed in orientation B where each layer acts against the forces, reinforcing themselves.
In this example we have a 3D printed bolt designed for a fully functioning car jack. The key to this design is printing the bolt with enough strength to withstand the weight of a car.
In orientation A the bolt will print with suitable bed adhesion, and sharp high quality threads. When printed in this orientation the downward force will be applied across the layer lines. It is unlikely the bolt will handle the required weight and will snap between the layers.
In orientation B a raft will be required to improve bed adhesion and underside of the bolt will require support material. In this orientation the layer lines are now positioned horizontally against the downward force. While orientation B will require filing or sanding to improve the thread, this will be the best orientation for mechanical strength.
For this controller handle accessory, a smooth surface on the handles is equally important for aesthetics and comfort. There is a connection slot which the manufacturer’s controller slides into, so a reasonably smooth surface in this slot is also ideal for easy assembly and to avoid scuffing or scratching the original controller.
In orientation A the top surfaces of the controller will print with decent quality however support material will be required on both the underside of the handles and the connection slot. The surface on the underside of these handles will be quite rough without post-processing. Due to how each layer is printed in this orientation, the thin rails of the connector slot will be at risk of snapping off should the user slide the controller onto the handles with unnecessary force.
In orientation B the controller is printed upright; minimizing support material on the handles and printing with more smooth vertical surfaces. There will be visual stepping on the tip of the handles however this won’t be felt by the users and can be solved with variable and finer layer heights. There will be supports in the connector slot to remove, however the the connection slot will be more durable than orientation A due to the new position of the layers.
In orientation C the controller is printed on its side, the top and underside surfaces of the controller will be reasonably smooth however the right side of both handles will be quite rough. The connector slot requires no support material and due to the orientation of each layer, the connector slot will be more durable than both orientation A and B.
We would print this part in orientation B, as the controller handles will require a balanced combination of durability with comfort. Removing support from the connection slot will be quite simple and is large enough for us to lightly file the rails.
Print for metal casting
In this example we have a complex part which will be 3D printed and burnt away cleanly for investment metal casting (also known as lost-wax casting). The two cylindrical tabs in the design will become part of the ‘wax tree’ which is important for channeling the molten metal into the ceramic mold. These tabs will be manually removed from the metal casted part.
A smooth and high quality surface finish is critical to ensure a casting result which will be suitable for industry use. The filament designed for this casting method; PolyCast™, can be easily post-processed with a companion product (the Polysher™). The Polysher™ removes the layer lines and smooths the layer stepping in the z-axis so we don’t need to worry about orientating our model to avoid layer stepping on curves and angles. A clean and smooth surface on the undersides on the model will still be important as the Polysher™ can't easily smooth out the rough scarring left after support material removal.
In orientation A, the first layer while thin is still large enough to ensure a stable and reliable print. With this orientation, the part is printed upright, with support material primarily attached to two overhangs and the two cylindrical tabs.
In orientation B the cylindrical tabs will provide a flat surface and excellent first layer for the 3D print. While the amount of support material is similar in both orientations, more support material will be required on the back of the part with no support material required for the cylindrical tabs.
While this part will be post-processed in the Polysher™ before the casting process, we will need to compromise print quality regardless of the orientation we choose. Luckily in orientation A the rough surfaces and support material will be mainly situated on the undersides of the two cylindrical tabs. As these tabs are removed from the part after casting, the print quality of these tabs isn't critical and won't affect the casting result. Orientation A will be ideal and result in an excellent 3D print for investment casting.
Often times there will be one or many orientations which are all suitable however there will be cases where the most obvious orientation may not fit within your 3D printers defined build volume or suit your needs. In these cases compromising certain aspects of the print may be required or perhaps even redesigning or editing the file to better suit the printing process.
With these tips and tricks in mind and by understanding each constraint, we can prioritize the most important aspects of our print through taking advantage of orientation.