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Bond, seal and beautify 3D printed parts.
Create models that exceed the size of your 3D printer’s build envelope, or combine 3D printed parts with other components through bonding and gluing. However, gluing 3D printed parts can be a tricky post-processing method. There are several different methods used to bond or glue parts together using Adhesive (epoxy), solvent, hot air welding, ultrasonic spot welding, and fasteners.
The primary considerations when selecting a bonding method are the strength of the bonded joint and the compatibility with each FDM material. For strength data, Stratasys conducted lab testing at the University of Texas El Paso to measure tensile strength. Other criteria — including time, cost, operation difficulty, part configuration and general performance — were also considered. Accuracy of bonded parts, however, is dependent on many factors. For example, adhesive characteristics, such as viscosity, will influence accuracy. The skill of the technician, style of joint and type of fixture will have even greater impact.
To assist in selecting the bonding approach most suitable for your needs, the following is a brief evaluation of the common methods for joining parts made in varying FDM materials.
Epoxies will differ in cure durations, material properties and bond strengths. But in general, they are easy to use. They offer very good mechanical strength, and typically exhibit good temperature resistance and chemical resistance. These adhesives offer the advantage of working times of 20 to 70 minutes, so minor adjustments can be made after mating the sections. However, the tradeoff is long curing times. When cured at room temperature, parts cannot be handled for many hours, and curing cycles will last from one to five days. If heat–cured, the cycle can be significantly accelerated.
The tensile strength of super-glued FDM parts is higher than that of epoxy adhesives. However, its resistance to high temperatures, chemicals and solvents is poor. Therefore, bonding with super glue may diminish the performance of an FDM parts. So, it is recommended for concept models and form and fit prototypes rather than functional prototypes or manufactured parts.
This method produces bonds that are stronger that those of many adhesives. Like super glue, the process is simple, and the bond sets in seconds. Another similarity is that it can be applied to hard-to-reach areas since the solvent will wick into a seam or fracture.
An advantage over super glue and epoxy is that after evaporation the bonded part will contain only FDM material. Although the bond sets in seconds, parts should be allowed to cure for at least eight hours. Also note that if the part is subjected to temperatures exceeding 176 F (80 C), surface blistering may occur. Solvent welding is not suitable for bonding PPSF or ULTEM 9085. These FDM materials are chemically resistant, so there is little reaction to solvents.
Parts can be put into service as soon as they are cool to the touch. Since the bonding material is a small piece of FDM plastic, the cost is negligible. Another advantage of using the FDM material as the bonding medium is that there is material continuity. The bond has the same properties and characteristics as the part. For best results, hot air welding should not be used on thin-walled sections. Also, the process requires some skill, so the results will depend on the experience and technique of the technician.
Compared to other bonding methods, there are few, if any, disadvantages to ultrasonic welding beyond the need to purchase the welding tool. Welded areas are stronger than the surrounding material, yet, the tensile strength is not as great as that of hot air welded or unbonded parts. The ultrasonic welder’s horn and horn tips are often interchangeable. A variety of horns and welding tips are available, which will determine the thickness of material that can be welded, the diameter of weld, as well as the type of weld created.
Since no material is introduced into the joint, there is little change to the accuracy of the part or its properties. This makes ultrasonic welding ideal for medical applications that must consider the quality of the part as well as its suitability of human tissue contact.
When higher strength is needed, ultrasonic welding may be used in combination with other methods. Tack weld individual pieces to fix their position and then apply adhesives, solvents or other bonding agents. This approach is especially useful for bulky or awkward assemblies. Ultrasonic welding is fast and very inexpensive. Once the welding operation is complete, the part can be immediately put into service. And since there are no consumables required, the only expense is that for direct labor.
Although this approach is a joining method, not bonding, it can be an effective alternative. There are a large number of mechanical fastening approaches and hardware options that can be used when joining FDM parts. One unique approach to mechanically join sections is to insert fastening hardware in the FDM part during its build process. When it emerges from the Fortus machine, the fasteners are integrated within the part.
For large models, the design can be separated into several parts for 3D printing, using a software cutting tool to ensure that the parts can be connected accurately. Parts can be attached using instant glue, or glue that requires an activator can be used to control bonding time and allow for repositioning.
The Magics software cutting tool provides an easy and intuitive way to glue together multiple parts while achieving these goals. The Magics software cutting tool has several options available. The following procedure is recommended when using this software tool:
1. Orient the part in view that coincides with the natural coordination system of the part (that is, front view, back view, left view, etc.). In this manner, you can get a clear perspective of where you draw the cutting line in relation to the part.
2. Draw the cutting line. It is recommended that you start with a point outside the part body and end with a point on the other side of the part body, thus creating a straight line across the part.
3. It is possible to choose between a triangle (most suitable to glued parts), square (most suitable to molds), jigsaw, or user–defined cut. You can also control the size and offset of the cutting type.
4. Make sure that you add a clearance between the cut parts. This leaves enough space for the glue and ensures that the final part maintains the designed dimensional properties. Note that the clearance value varies depending on the type of glue used and the recommended default value is 0.1mm. Two separate STL files are created when the cutting operation is complete, and they can be printed freely on the tray.
Post-processing parts for gluing
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