Additive printing technology is increasingly establishing itself in the textile and apparel industry. The fast-moving fashion industry has also recognized the advantages of three-dimensional (3D) printing technology for itself. Textile knee bandages and tight-fitting garments or components with additively printed protective elements are current application examples. The development of additively manufactured protective elements to reduce abrasion and wear of textile surfaces in stressed areas is the aim of this study. Abrasion protection structures with shock absorption properties were designed for high-stress areas (knee, elbow and/or shoulder areas) and additively manufactured on the textile [1,2,3]. In the area of combining textile materials with additive manufacturing, however, development activities are limited either to the production of composite components (short or continuous fibre reinforcement) or to the printing of textile surfaces in the planar direction. In principle, the application of additively manufactured elements to flat textiles is possible and versatile in terms of the products to be manufactured, enabling new functional garments [4,5]. Textiles and stiff additively printed elements are nowadays produced in one planar direction and only then joined together by suitable fabrication (cutting) or by reshaping (stretching) of the fabric.
However, the textile sector faces challenges in high-quality manufacturing when using additive printing technology. The adhesion between the textile and the thermoplastic polymer (filament) to be applied in the fused filament fabrication (FFF) printing process is one of the most decisive factors. The additive printing process must be adjusted accordingly between the printing technology and the textile. The influencing parameters for sufficient adhesion between the element to be printed and the textile are many and varied, with adhesion being influenced by the filament type, viscosity of the molten filament,
The additive manufacturing process is based on a basically identical sequence of operations. A component is built up layer by layer, starting with the first, lowest layer. The component geometry is created by adding material. This makes it possible to manufacture highly complex geometries in a cost- and time-efficient manner, since the component shape is not dependent on the tool shape, as is the case, for example, with casting or lathe technologies [12]. Furthermore, additive manufacturing offers a high degree of design freedom. Although colloquially referred to as 3D printing, it is more of a 2.5D print, as a 3D structure is generated by stacking 2D layers [13].
Printing on pre-formed, non-planar materials is possible using a special 3D printing technology. The technology of non-planar printing allows direct application on curved objects. This would eliminate additional fabrication steps and save costs.
A non-planar print path is a print path that can be curved in several axes in space. As non-planar 3D printing increases design freedom in additive manufacturing, this technology is useful for the majority of industries. One way to print curved components is to use a curved print bed, such as the one used in this study. A curved print bed allows printing on pre-curved surfaces, thus new geometries are possible and especially in combination with textiles new functional textiles are possible. These combinations make it possible, for example, to manufacture garments for personal protection with partial reinforcements on flexible substrates or to produce highly customizable support structures for the medical sector (orthoses) [14,15].
In summary, a high research effort is being made on additive 3D printing technologies and the redesign of new functional textiles. However, additive built on textiles has always been reduced to 2D in-plane application. Additive printing on curved contours with pre-tensioned textiles to produce customized structures (e.g. protectors, orthotics, abrasion protection) is so far a new method of manufacturing in this field. The application of curved elements to tensioned textiles is a new manufacturing field and therefore existing norms and testing standards are not or only partially applicable.
For this reason, this study deals with the non-planar printing process on textile surfaces. For implementation, an FFF printer is modified. By means of a controlled cylindrical print bed, constant curved elements can be printed. The conversion is explained in more detail in the first part of the study. The cylindrical print bed allows a textile to be stretched in order to carry out non-planar printing on it. For planar printing on textile surfaces, there are few experience reports and investigations available, but not for non-planar printing on textiles. Therefore, the adhesion between non-planar printed elements and textile is investigated. In the course of the investigation, it becomes clear that the adhesion on non-planar textiles cannot be applied by means of existing standards, such as DIN EN 28510-1, 53530 and 8510-2. A new test method for the adhesion of non-planar printed elements to textiles has to be developed and will be presented.
An Original Prusa i3 MK3S FFF printer was used for the study. The printer and slicer is an open-source system. Structurally, the individual components such as the circuit board, stepper motors for
First, the diameter of the cylindrical print bed must be defined. The diameter of the cylindrical print bed depends on the original print bed dimensions. According to the manufacturer, the print build space size is 250 mm × 210 mm × 210 mm (
The diameter gives the curvature
In the Prusa printer’s conventional planar print bed, three individual NEMA (National Electrical Manufacturers Association) stepper motors are used to drive all three axes (
For a defined cylindrical diameter
The cylindrical print bed with a
Figure 1
Schematic drawing of the cylindrical print bed.

Step count
Step width
The components (holder, cylindrical print bed, pinion) were also printed with the Prusa printer on the conventional planar printing plate. The components should have high strength with low flexibility and also have minimal shrinkage. For this reason, polylactic acid (PLA; NatureWorks LLC) was chosen as the printing filament [17]. For the fabrication of the cylindrical print bed as well as for the fabrication of the test specimens, PLA was distributed by Prusa Research a.s. The other printing parameters are listed in Table 1.
Printing parameters for the production of the cylindrical printing bed and its components
Printing parameters | |
---|---|
Extruder temperature (°C) | 200 |
Print bed temperature (°C) | 60 |
Layer height (mm) | 0.15 |
Infill (%) | 10 |
Nozzle diameter (mm) | 0.4 |
The printed parts were assembled accordingly and the axis of the cylindrical print bed was equipped with bearings. For better fixation, magnets were installed in the holders of the construction and could thus be precisely aligned and prevented slipping during the printing process. A constant and repeatable placement of the construction was achieved by markings on the planar print bed. By using a designed holding device for the planar print bed and thus for the cylindrical print bed, it was always possible to ensure the same positioning. The nozzle was thus always at the vertex of the cylindrical print bed. The movement of the planar stepper motor, responsible for the
Figure 2
Realized modification to the cylindrical print bed.

A common method for testing the adhesion between 3D printed elements is a so-called peel test. There are various peel tests for measuring adhesion, such as the standards DIN EN 28510-1, 53530 and 8510-2. Depending on the standard, the test differs in its scope of application and its execution [18,19,20]. A test standard for printed additive elements on textiles does not yet exist. Therefore, testing can only be carried out on the basis of the standards. DIN EN ISO 8510-2 was used for the investigation in these studies [21]. The standard is used for a 180° peel test. For this purpose, a bar-like structure of a certain width and height is printed on the textile surface. The printed PLA specimens on textile in this study have dimensions of 120 mm × 50 mm × 2 mm (
Figure 3
Schematic drawing of the 180° peel test according to DIN 8510-2.

To test printed and curved elements, a clamp had to be rotated 90° so that a peel test could be performed without the parts getting in each other’s way.
Figure 4 shows a simplified schematic of the test setup, in more detail the action range of the peel test for non-planar specimens. It must be ensured that the distance
Figure 4
Schematic layout of the equipment for measuring the adhesion between textile and imprinted elements.

For the peel test (according to DIN 8510-2) of the planar printed specimens, the holder frame is dismantled and clamp 2 (E) is mounted on the actual holder (G) of the tensile testing machine. The planar printed specimen is now fixed with clamp 2 (E), the textile is fixed in clamp 1 (B) and the textile is pulled off upwards, analogously as schematically shown in Figure 3. Figure 5 shows the setup and testing in the laboratory.
Figure 5
Realized measuring equipment for measuring the adhesion of non-planar pressure elements on textile.

A cotton fabric (twill weave, sanforized, with a 185 g/m2 fibre area weight) was selected as the textile printing substrate. The choice of fabric was based on previous tests and literature research, which showed that PLA prints well on textile surfaces [22], as well as the combination cotton–PLA proves to be a good combination [23].
For the peel test, three different sample types with three samples each are prepared. A PLA was also used to print on textile: Specimen type 1: planar manufactured specimens – specimen identification P Specimen type 2: non-planar specimens on the constructed cylindrical print bed – specimen identification NP Specimen type 3: non-planar manufactured specimens on the constructed cylindrical print bed with an additional shift of the nozzle by 10 mm in the
Figure 6 shows the schematic diagram of the nozzle placement of sample types 2 and 3.
Figure 6
Left: schematic representation of the nozzle arrangement of sample type 2 (NP). Right: schematic representation of the nozzle arrangement with a shift – sample type 3 (NPV).

Figure 7 shows the three printed specimen types. Planar printed specimens (P) are identified as P1 to P3, non-planar printed specimens (NP) as NP1 to NP3 and non-planar offset printed specimens (NPV) as NPV1 to NPV3.
Figure 7
Printed samples on textile – planar sample (P), non-planar sample (NP) and non-planar sample with shift (NPV).

For printing on textile, the
Print parameters for the preparation of the specimens
Print parameters | |
---|---|
Extruder temperature (°C) | 220 |
Print bed temperature (°C) | Not possible |
Layer height (mm) | 0.15 |
Nozzle diameter (mm) | 0.4 |
Print speed (mm/s) | 50 |
Sample dimensions (mm) | |
in | 120 |
in | 50 |
in | 2 |
Infill | No |
When the three different printed sample types are visually examined, it is noticeable that there are qualitative differences on the top layer. The samples with the shift (NPV) show an uneven surface compared to the other samples. As can be seen in Figure 7, the non-planar print with shift (NPV) has an uneven and partially roughened surface. The uneven surface can be explained by the fact that the nozzle has a different distance to the cylindrical print bed. Towards the vertex, the distance is smaller than that towards the opposite side. Figure 8 shows the different nozzle distance to the cylindrical print bed of the nozzle. If the nozzle is shifted and the angle to the cylindrical print bed is not adjusted, a critical point is created. The different distance to the print bed causes printing problems, as shown above in figure 7 NPV. It should be mentioned again that the distance between the cylindrical print bed and the nozzle was kept the same. For the NPV samples, the nozzle was shifted downwards by 1 mm. For optimisation, the angle of the nozzle would have to be adjusted and it would have to be perpendicular to the cylindrical print bed to avoid the critical point and achieve optimised print results.
Figure 8
Possible critical point causing an inaccurate printing surface.

Figure 9 shows another irregularity that occurs during non-planar printing. The print object shown was printed in different gradations (gradation 1 with 10 mm to gradation 4 with 40 mm). As the print height increases, it is noticeable that the individual lanes no longer bond sufficiently to each other. At 40 mm (gradation 4), the print webs are no longer connected to each other, gaps appear between the filament layers. As a result, the printed object loses stability. This fact occurs with increasing print height and thus increasing radius to the cylindrical print.
Figure 9
Test print object with different gradations (1 – 10 mm, 2 – 20 mm, 3 – 30 mm, and 4 – 40 mm) with visible print lanes that are not connected at gradation 4.

Figure 10 shows the change in step width as the layer height to be printed increases for different cylindrical print set radii.
Figure 10
Step size for different cylindrical pressure beds with increasing layer height.

Step width for the number of layers to be printed is given by:
The layer height (
In Figure 10, we can observe that the appearance shown in Figure 9 is less for smaller radii than for larger radii. As the number of layers (
In the printed non-planar test prints (NP and NPV seen in Figure 7), the separating layers occurred but was hardly visible due to the low number of layers, in that case 13 printed layers. Therefore, it can be assumed that this has no influence on the adhesion to the textile, since it is mainly the first layer that adheres to the textile.
The 180° peel test and the method introduced were evaluated according to the DIN 8510-2 standard. Chapter 8 of the standard specifies that the average peel forces must be determined in Newtons. At least a peel length of 100 mm must be evaluated, with the first 25 mm being discarded. In the study, the starting point of the evaluation was set to be 25 mm after the first peak, and then 125 mm of precipitation length was evaluated. Figures 12 and 13 show the entire measured range.
Figure 11 shows the force characteristics during the developed non-planar peel test. It should be noted that the measured forces change during the non-planar peel test due to the angular change of
Figure 11
Schematic illustration of the force curves during non-planar measurement.

Looking at Figure 12 of the non-planar measurement (NP), it can be noted that all three measurements are very similar in their course and all measurements are very close to each other. It can be assumed that these results are well reproducible. If, on the other hand, the non-planar measurement is considered with a shift of the nozzle, the courses of the three measurements are very different. Also the forces vary very much – steep increases and decreases. In the NPV force measurements, it can be stated that the adhesion is very different within a sample, but also in different measurements. A process reliability is not given, whereas it is possible to speak of process reliability with the NP.
Figure 12
Peel test results of all three sample types – over the whole recorded peel test.

If the planar measurement (P) (Figure 13) is taken into account, differences in the force measurement curves can also be seen here. These are not as uniform in their course as in the NP measurement. It is interesting to compare the two measurements of planar (P) and non-planar (NP), because it could be assumed that the adhesion of the NP pressures decreases due to the modification of the cylindrical print bed, orientation and gear drive, or the progression is irregular in the NP measurement, which is not the case. This shows that the cylindrical print bed allows uniform adhesion, as long as the nozzle is placed vertically on the textile.
Figure 13
Planar peel test results – over the whole recorded peel test.

Figure 14 shows the average maximum peel forces for all specimen types. The planar specimens were tested using the 180° peel test (Figure 3) and the non-planar specimens, as well as those with offsets, were tested using the method presented (Figure 4). As already mentioned, these are two different measuring methods and therefore cannot be compared with each other. Only, the non-planar measurement method and its results, by using the same print bed radius, can be compared. The planar test must be considered separately.
Figure 14
Maximum tensile force of all three specimen types – non-planar and offset specimens were tested according to the presented methodology and the planar specimens were tested according to the 180° peel test.

The maximum force in the 180° peel test for the planar specimens is 54.7 N (standard deviation of 1.7). For the non-planar specimens, the maximum force according to the method presented is 49.2 N (standard deviation of 2.1). The maximum force for the non-planar specimens with a shift is significantly lower. Here, it is only 28.7 N (standard deviation of 6.9). The non-planar samples with a shift (NPV) exhibit half as much adhesion between the textile and the imprint, compared to NP. The standard deviation is also very large for non-planar (NPV) printing.
At this point, it can be stated that if the nozzle is not printed vertically (apex) on the textile (on the planar base), there is a significant loss of adhesion. In addition, the print quality decreases significantly with an offset, as can be seen in Figure 7.
After analysing and discussing all experimental results, the following conclusions can be drawn: Additively applied elements can be printed not only on planar textiles but also on non-planar stretched textiles. Due to the constructed cylindrical print bed, it was possible to print non-planar textiles. The orientation of the nozzle is important and must always be set on the vertex. If there is a shift, the adhesion decreases significantly. With a shift of 10 mm of the nozzle to the vertex with constant When using multi-axis printers on textiles in the future, it is important to ensure that there is no shift from the apex and that the nozzle is perpendicular to the substrate. A new test device had to be developed for measuring adhesion, since curved printed textiles cannot be tested with the previous standards. However, this measurement method is only applicable and comparable for printing on the same radius of the cylindrical print bed. A possible future improvement is a video recording during the test and subsequent observation of the angle change. From this, the force changes during the measurement could also be analysed. The print quality of non-planar printing with an offset (NPV) is lower compared to planar or non-planar printing. This is due to the angle of the print nozzle to the print bed (Figure 8). This can be improved by aligning the nozzle vertically to the print bed, which was not possible with the current printer, due to the rigid axes. Due to the layered structure of print objects, it is noticeable that the lanes no longer connect sufficiently with each other. As a result, the printed object loses stability. This effect occurs with increasing print height and thus increasing radius of the cylindrical print object. However, this could be improved by adapting the G-code. The adaptation can ensure that the individual filament webs are still connected to each other as the radius increases. A heated print bed temperature has a positive effect on adhesion [22,24]. In this study, the print bed was not preheated, so it can be assumed that a heated print bed could improve adhesion. This should be taken into account in further development of the cylindrical print bed.
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Figure 13

Figure 14

Print parameters for the preparation of the specimens
Print parameters | |
---|---|
Extruder temperature (°C) | 220 |
Print bed temperature (°C) | Not possible |
Layer height (mm) | 0.15 |
Nozzle diameter (mm) | 0.4 |
Print speed (mm/s) | 50 |
Sample dimensions (mm) | |
in |
120 |
in |
50 |
in |
2 |
Infill | No |
Printing parameters for the production of the cylindrical printing bed and its components
Printing parameters | |
---|---|
Extruder temperature (°C) | 200 |
Print bed temperature (°C) | 60 |
Layer height (mm) | 0.15 |
Infill (%) | 10 |
Nozzle diameter (mm) | 0.4 |
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