3.1 Printing Results
The printed elements EX1 and EX2 can be seen in Fig. 1. No difficulties were encountered during printing.
Element ED1 was printed seeking the most unfavorable situation, and its collapsed form can be observed in Fig. 2. To achieve this, the layer interval was kept at zero so that the material did not develop internal structure. Additionally, a situation in which the material needed to be less consistent was simulated, aiming to further reduce the stability of the element.
Element ED2 was printed three times to evaluate the failures of a stable and complete element. The first attempt, presented Fig. 3, was interrupted on the third layer as the element quickly deformed and collapsed. Adjustments were made to enable the complete printing of the element, including an increase in the layer interval, consistency, and a reduction in printing speed. Thus, two additional complete prints were made, which can be viewed in Figs. 4 and 5.
The main failure events were documented based on the printed elements with images and videos recorded during the printing. These events were then grouped, with their possible causes, consequences, and solutions identified and analyzed in depth in the process of building the Fault Tree Analysis. The identified groups were:
- Discontinuities in the filament which can be seen on Figures 6 and 7;
-
Variations in the section, which can be in the dimensions of the filament between layers of an element, as seen on Fig. 8, or in one layer, as seen on Fig. 9;
-
Material buildup that can be visualized on Fig. 10;
-
System clogging;
-
Buildability failures that can be caused by excessive deformation of lower layers (Fig. 11), geometric non-conformity (Fig. 12), or deformation due to height (Fig. 13);
-
Insufficient adhesion between layers.
It should be noted that during the printing process, there were moments of machine-related failures or errors, such as sudden stop of printing due to code and software errors or poor contact in the machine or pump circuits. In these cases, it was necessary to simply restart the system or check the connection points of the printing machine or control panel. As these were only machinery or software initialization problems, these situations were included in the failure tree as secondary events, not requiring a more in-depth approach. For the mentioned cases, photographic records cannot be made, and a simple check of the systems, which must be performed before each print, is shown to be the solution to the problem. Such situations will not be further investigated and will be included in the failure tree as secondary events since they do not originate from complex causes requiring evaluation and study and do not generate significant consequences.
3.1 Fault Tree Analysis
The first step to build the fault tree consists of determining the top event, physical limitations of the system, components, interactions, specifications, and failure modes. The system in this paper is defined as the printing process using a 3D printing machine, which can be divided into five subsystems: the material system, the control system, the machine system itself, the pumping system, and the extruder system. A schematic representation of the printing process and subsystems can be seen in Fig. 14.
The considered subsystems can then be divided into their components or, in some cases, stages. In addition, knowing the components allows decomposing each subsystem into a schematic representation. The complete decomposed system can be assembled, as presented in Fig. 15.
It is then necessary to categorize failures according to the components affected by them and determine to which class such failure belongs. Regarding the classes, failures were divided into top event, basic, secondary, and intermediate events. The top event is chosen as the occurrence that covers the largest number of possible failures, which is the disposal of the specimen. The intermediate events are the result of interactions guided by logical gates between other events. The basic events are the lowest level in the fault tree, not caused by any other event and independent of other basic events. Finally, secondary events are those that cannot be developed either due to lack of information or not having a specific cause.
Regarding the affected components, failures were associated with software, machine, pump, extruder, code, material, and printed element. Furthermore, in case the failure is caused by interference from elements not related to the subsystems, it was associated with an external component. The "material" component was subdivided into general component, mixture, ratio, and storage. The "code" component was subdivided into general, geometry, parameters, and origin. Finally, the "machine" component was subdivided into parts and cables. The other components did not present subdivisions.
The complete fault tree has 224 elements, which is too large to be presented and can be found in Felfili (2023), therefore Table 6, which was used to build the fault tree, will serve as an visual representation of the events, possible consequences, their connections, associated components and type of event considered.
Table 5
Failure
|
Consequence
|
Component
|
Event Type
|
Material buildup at filament points
|
Inadequate aesthetics
|
Printed Element
|
Intermediate
|
Stresses buildup
|
Total or partial collapse
|
Printed Element
|
Intermediate
|
Inadequate nozzle lifting height
|
Layers with different cross sections
|
Code - Parameters
|
Basic
|
Inconsistent nozzle lifting height
|
Layers with different cross sections
|
Code - Parameters
|
Basic
|
Low water-to-cement ratio
|
Very consistent material
|
Material - Mix
|
Basic
|
Layers with different cross sections
|
Inadequate aesthetics
|
Printed Element
|
Intermediate
|
Instability
|
Total or partial collapse
|
Specimen disposal
|
Printed Element
|
Intermediate
|
Very sharp curves
|
Accumulation of material at filament points
|
Code - Geometry
|
Basic
|
Filament discontinuities
|
Deformation due to height (buckling)
|
Instability
|
Printed Element
|
Intermediate
|
Excessive deformation of lower layers
|
Inadequate aesthetics
|
Printed Element
|
Intermediate
|
Instability
|
Specimen disposal
|
-
|
Printed Element
|
Top
|
Layers detachment
|
Specimen disposal
|
Printed Element
|
Intermediate
|
Filament discontinuities
|
Decrease in contact area
|
Printed Element
|
Intermediate
|
Inadequate aesthetics
|
Instability
|
Insufficient hose diameter
|
System clogging
|
Pump - Hose
|
Basic
|
Difference between layer states
|
Cold joints
|
Printed Element
|
Intermediate
|
Decrease in contact area
|
Poor layer adhesion
|
Printed Element
|
Intermediate
|
Very slender element
|
Deformation due to height (buckling)
|
Printed Element
|
Basic
|
System clogging
|
Print interruption
|
Pump
|
Intermediate
|
Inadequate aesthetics
|
Specimen disposal
|
Printed Element
|
Intermediate
|
Inadequate geometry
|
Deformation due to height (buckling)
|
Code - Geometry
|
Basic
|
Internal structuring of stored material
|
Material consistency variation
|
Material - Storage
|
Intermediate
|
Failure
|
Consequence
|
Component
|
Event Type
|
Internal structuring does not occur in necessary time
|
Insufficient initial material strength
|
Material
|
Intermediate
|
Force or impact against the element
|
Layers detachment
|
External
|
Basic
|
Total or partial collapse
|
Poorly distributed particle size
|
Very consistent material
|
Material - Mix
|
Basic
|
Inconsistencies between batches
|
Layers with different cross sections
|
Material - Mixing
|
Basic
|
Instability
|
Total or partial collapse
|
Printed Element
|
Intermediate
|
Print interruption
|
Specimen disposal
|
External
|
Intermediate
|
Inadequate layer interval
|
Internal structuring does not occur in necessary time
|
Code - Parameters
|
Basic
|
Dry layer surface
|
Cold joints
|
Poor layer adhesion
|
Printed Element
|
Intermediate
|
Poor layer adhesion
|
Accumulation of stresses
|
Printed Element
|
Intermediate
|
Layers detachment
|
Deformation due to height (buckling)
|
Material with very slow setting time
|
Internal structuring does not occur in necessary time
|
Material - Mix
|
Basic
|
Limitation of machine movements
|
Layers misalignment
|
Machine - Parts
|
Basic
|
Poor contact in circuits
|
Print interruption
|
Machine - Cables
|
Secondary
|
Material with very fast setting time
|
Dry layer surface
|
Material - Mix
|
Basic
|
Internal structuring of stored material
|
Material at rest for too long
|
Internal structuring of stored material
|
Material - Storage
|
Basic
|
Very consistent material
|
Filament discontinuities
|
Material - Mix
|
Intermediate
|
System clogging
|
Very inconsistent material
|
Deformation due to height (buckling)
|
Material - Mix
|
Basic
|
Insufficient initial material strength
|
Poor material mixing
|
Material segregation
|
Material - Mixing
|
Basic
|
Layers misalignment
|
Inadequate aesthetics
|
Printed Element
|
Intermediate
|
Instability
|
No shape retention after deposition
|
Filament dimension variation
|
Material - Mix
|
Intermediate
|
Inconsistent origin
|
Layers misalignment
|
Code - Origin
|
Intermediate
|
Excessive weight of subsequent layers
|
Excessive deformation of lower layers
|
Printed Element
|
Basic
|
Pump problems
|
Accumulation of material at filament points
|
Pump
|
Secondary
|
System clogging
|
Material flow variation
|
Change in element or machine position
|
Inconsistent origin
|
External
|
Basic
|
Code problems
|
Material flow variation
|
Code
|
Basic
|
Inconsistent origin
|
Extruder system problems
|
Material flow variation
|
Extrusion
|
Basic
|
Software problems
|
Print interruption
|
Software
|
Secondary
|
Excessive material production with poor planning
|
Internal structuring of stored material
|
Material - Mixing
|
Basic
|
Insufficient initial material strength
|
Excessive deformation of lower layers
|
Material - Mix
|
Intermediate
|
No shape retention after deposition
|
Dry layer surface
|
Cold joints
|
Printed Element
|
Intermediate
|
Inadequate or not respected open time
|
Internal structuring of stored material
|
Code - Parameters
|
Basic
|
Material flow variation
|
Filament dimension variation
|
Code - Parameters
|
Intermediate
|
Material consistency variation
|
Layers with different cross sections
|
Material - Mix
|
Intermediate
|
Very consistent material
|
Material flow variation
|
Difference between layer states
|
Material segregation
|
System clogging
|
Material
|
Intermediate
|
Paste separation within the system
|
Material segregation
|
Material
|
Basic
|
Filament dimension variation
|
Decrease in contact area
|
Printed Element
|
Intermediate
|
Inadequate aesthetics
|
Instability
|
Inconsistent nozzle speed and extrusion rate
|
Filament discontinuities
|
Code - Parameters
|
Basic
|
Filament dimension variation
|
The analysis was done through the observation of the constructed fault tree and the data obtained from it. The number of times each failure appeared in the fault tree can be observed in the table.
Table 6
No. of appearances per failure event
Failure Event
|
No. of Appearances
|
Failure Event
|
No. of Appearances
|
Material buildup at filament points
|
1
|
Limitation of machine movements
|
2
|
Stresses buildup
|
1
|
Poor layer adhesion
|
3
|
Inadequate nozzle lifting height
|
2
|
Poor contact in circuits
|
1
|
Inconsistent nozzle lifting height
|
2
|
Material with very slow setting time
|
6
|
Low water-to-cement ratio
|
5
|
Material with very fast setting time
|
15
|
Layers with different cross sections
|
2
|
Material at rest for too long
|
13
|
Failure Event
|
No. of Appearances
|
Failure Event
|
No. of Appearances
|
Total or partial collapse
|
1
|
Very consistent material
|
5
|
Very sharp curves
|
5
|
Very inconsistent material
|
7
|
Deformation due to height (buckling)
|
1
|
Poor material mixing
|
1
|
Excessive deformation of lower layers
|
2
|
Change in element or machine position
|
2
|
Specimen disposal
|
1
|
Layers misalignment
|
2
|
Layers detachment
|
1
|
No shape retention after deposition
|
4
|
Filament discontinuities
|
4
|
Inconsistent origin
|
2
|
Insufficient hose diameter
|
1
|
Excessive weight of subsequent layers
|
2
|
Difference between layer states
|
2
|
Pump problems
|
6
|
Decrease in contact area
|
2
|
Code problems
|
6
|
Very slender element
|
1
|
Extruder system problems
|
4
|
System clogging
|
1
|
Software problems
|
1
|
Inadequate aesthetics
|
1
|
Excessive material production with poor planning
|
13
|
Internal structuring of stored material
|
13
|
Insufficient initial material strength
|
6
|
Internal structuring does not occur in necessary time
|
6
|
Material segregation
|
1
|
Force or impact against the element
|
2
|
Paste separation within the system
|
1
|
Inadequate geometry
|
1
|
Dry layer surface
|
2
|
Poorly distributed particle size
|
5
|
Inadequate or not respected open time
|
13
|
Inconsistencies between batches
|
2
|
Material flow variation
|
4
|
Instability
|
1
|
Material consistency variation
|
13
|
Print interruption
|
1
|
Filament dimension variation
|
4
|
Inadequate layer interval
|
8
|
Inconsistent nozzle speed and extrusion rate
|
8
|
Cold joints
|
2
|
Total
|
224
|
For qualitative analysis, basic events were analyzed, which alone or accompanied by only one other basic event can directly lead to the occurrence of the top event, and the number of times these appear in the tree. It is possible to observe that the events that appeared most frequently in the minimum cut analysis were mainly those with a causal relation to the variation of material consistency, largely due to the selection of the mixture and printing parameters. Therefore, this failure and the events related to it should be a focus when developing the study plan.
In addition to the analysis of minimum cuts, it was considered necessary to perform a component-based analysis of the components that presented failures and the total sum of occurrences of events related to these components. This analysis was carried out by combining data from Table 5 3 and Table 5 4, resulting in Table 7.
Table 7
No. of appearances per failed component
Failed Component
|
No. of Appearances
|
Pump
|
8
|
Code
|
51
|
Printed Element
|
36
|
External
|
5
|
Extruder
|
4
|
Material
|
116
|
Machine
|
3
|
Software
|
1
|
This data can then be combined into a column chart, presented in Fig. 16, for a better understanding of the results. It is noted that most of the failures are concentrated in the Material, Code, and Printed Element components. The Printed Element component cannot be decomposed, but the Code and Material components can, according to the component classifications proposed.
Following the subdivision presented previously, the Material component is decomposed into general failure, mixture failure, trace failure, and storage failure. The number of occurrences of each is presented graphically in Fig. 17, indicating the percentages according to the total quantity of material failures.
It is evident, then, that the vast majority of failures associated with the material are due to the trace, making it necessary to prioritize this aspect and the properties related to developing study proposals.
Similarly, the Code component can be decomposed into general failure, geometry failure, parameter failure, and origin failure. The number of occurrences of each is presented as a graph was also created, which can be seen in Fig. 18, presenting the percentages according to the total quantity of code failures.
For events associated with the code, the vast majority are concentrated in the parameters, i.e., the selection of these, prior to printing, is being performed incorrectly. As incorrect parameters trigger various failures, it is important to define the study of these as a priority.
The component-based analysis confirms the conclusions drawn from the minimum cut analysis that the aspects of 3D printing related to the selection of trace and printing parameters are the major causes of failures and problems found, and therefore, should be improved first.
Taking into account the identified failures and the assessment of their importance, proposals for future studies are presented. These proposals are based on bibliographic research and data analysis and aim to expand knowledge and improve the 3D printing process of the Alya 130 at the University of Brasília. Such investigations are important to provide more effective solutions to the identified challenges and to improve the quality of the produced elements. The proposals are divided into initial, second, third, and fourth stages, as shown in Fig. 19.
The initial stages should be carried out first, providing a theoretical basis that will enable the advancement of the research. The studies that are part of the second stage serve as preparation for the third stage, which, although being the most critical and essential for the development of the process, can only be carried out after the completion of the previous stages. Finally, the studies included in the fourth stage are more in-depth and specific, being possible only after the definition of the best trace. A flowchart showing the proposals, their priority, and their sequencing is presented in Fig. 20.