Improvement of FDM 3D Printer
Diplomová práce
Studijní program: N2301 – Mechanical Engineering
Studijní obor: 2302T010 – Machines and Equipment Design Autor práce: Vignesh Mohan Kumar
Vedoucí práce: Ing. Petr Keller, Ph.D.
Improvement of FDM 3D Printer
Master thesis
Study programme: N2301 – Mechanical Engineering
Study branch: 2302T010 – Machines and Equipment Design
Author: Vignesh Mohan Kumar
Supervisor: Ing. Petr Keller, Ph.D.
Acknowledgement
I would like to thank the following people who was instrumental in making this project a reality. I am grateful for the precious time they had dedicated to motivate and guide me towards successful completion of this project.
ING. PETR KELLER, Ph.D. – Deputy Head of Department, Department of
manufacturing systems and automation, for his expert guidance, enormous patience, constant encouragement and inspiration to complete this challenging project.
ING. PETR ZELENÝ, Ph. D. – Head of Department, Department of manufacturing systems and automation, for his encouragement, support and guidance.
Abstract
This thesis deals with designing a compact head for 3D printing using Fused Deposition Modelling (FDM), which is registered by Stratasys. This technology is based on extrusion process, which is very popular and same as RepRap community.
The main aim is to design a print head with available basic components for printing two different materials. The printing head should control the extrusion process for each material separately. It also has the possibilities to switch nozzles with various diameters. The entire structure of the head should be compact in size and light in weight for easy installation for the 3D printer.
Key words:
FDM, 3D printing, dual head, design, RepRap
Abstrakt
Tato práce se zabývá návrhem kompaktní hlavy pro 3D tisk pomocí technologie Fused Deposition Modeling (FDM), která je registrována firmou Stratasys. Tato technologie je založena na procesu vytlačování termoplastů a je velmi populární v komunitě RepRap. Hlavním cílem je navrhnout tiskovou hlavu s dostupnými základními komponentami pro tisk dvou různých materiálů. Tisková hlava umožňuje řídit proces vytlačování pro každý materiál zvlášť. Je také možnost měnit trysky různých průměrů.
Celá konstrukce hlavy má kompaktní rozměry a hmotnost, pro snadnou instalaci do 3D tiskárny.
Klíčováslova:
FDM, 3D tisk, dvojitáhlava, design, RepRap
Table of Contents
1 Introduction ... 13
1.1 3D Printing ... 14
1.1.1 Stereolithography (SLA) ... 14
1.1.2 Digital Light Processing (DLS) ... 14
1.1.3 Selective Laser Sintering (SLS) ... 15
1.1.4 Selective Laser Melting (SLM) ... 16
1.1.5 Electronic Beam Melting (EBM) ... 17
1.1.6 Fused Filament Fabrication (FFF)... 17
1.2 Types of 3D printer ... 18
1.2.1 Cartesian ... 19
1.2.2 Delta ... 19
1.2.3 Core XY ... 20
1.2.4 Polar ... 20
1.2.5 SCARA ... 21
2 Literature Review ... 22
2.1 Additive Manufacturing Data Formats ... 22
2.1.1 STL Format ... 22
2.2 RepRap ... 23
2.3 Pre-processing ... 23
2.3.1 Slicing and G-code ... 24
2.4 Post-Processing ... 24
2.5 Stratasys Fused Deposition Modelling ... 24
2.5.1 Company ... 24
2.5.4 Principle ... 25
2.5.5 Strengths and Weaknesses ... 25
2.5.6 Applications ... 26
2.6 MANAGEMENT 3D PRINTER ... 26
2.6.1 Control board ... 26
3 Available solutions of extrusion head ... 29
3.1 Types of extruders ... 29
3.1.1 Geared extruders ... 29
3.1.2 Direct drive extruder ... 30
3.1.3 Bowden extruders... 30
3.2 Dual extrusion head... 31
3.2.1 Extruder duplication ... 32
3.2.2 Two independent nozzles in one cooler ... 33
3.2.3 One nozzle for two filaments ... 33
3.2.4 Manual Deployment during Printing ... 34
4 Materials & Methods ... 36
4.1 Extrusion head ... 36
4.2 Feed mechanism ... 36
4.3 Stepper Motor ... 37
4.4 Servo drive ... 38
4.5 Heat break ... 39
4.6 Cooler ... 39
4.7 Heating block ... 40
4.8 Thermistor ... 41
4.9 Nozzle ... 42
4.10 Limit switches ... 42
5 Current state of 3D printer ... 44
5.1 Problems in the current state of 3D printer ... 46
5.2 Resolving the problems in existing solution ... 47
5.2.1 Change in Design of Extrusion head ... 47
5.2.2 Holes in the design ... 48
5.2.3 Fixing connectors to the extruder head ... 49
5.2.4 Fixing Thermistor at the bottom of the extrusion head ... 50
5.3 Connecting Components to Control board ... 51
5.4 Comparison of First and Second Prototype... 52
5.5 Practical Realization of Printing ... 55
6 Conclusion ... 56
7 References ... 57
List of Figures
Figure 1. Principle of SLA[3] ... 14
Figure 2. Principle of DLP[3] ... 15
Figure 3. Principle of SLS[3] ... 16
Figure 4. Principle of SLM[3] ... 16
Figure 5. Principle of EBM[3] ... 17
Figure 6. Principle of FFF[5] ... 18
Figure 7. Cartesian head[6] ... 19
Figure 8. Delta[6] ... 20
Figure 9. Core XY[8] ... 20
Figure 10. Polar[9] ... 21
Figure 11. SCARA[9] ... 21
Figure 12. A sample STL file[10] ... 22
Figure 13. Arduino MEGA 2560 and RAMPS 1.4[12] ... 27
Figure 14. Sanguinololu[14] ... 28
Figure 15. Geared extruder[15, 16] ... 29
Figure 16. Direct drive extruder[17] ... 30
Figure 17. Bowden extruder[18] ... 31
Figure 18. Extruder duplication[19] ... 32
Figure 19. Two independent nozzles in one cooler ... 33
Figure 20. One nozzle for two filaments[19] ... 34
Figure 21. LCD display for replacing filament[20] ... 35
Figure 22. Principle of the printing head[21, 22] ... 36
Figure 23. Feed mechanism ... 37
Figure 24. Stepper motor ... 38
Figure 25. Servo drive ... 38
Figure 26. Heat break[12] ... 39
Figure 27. Cooler ... 40
Figure 28. Heating block[12] ... 41
Figure 29. Thermistor ... 41
Figure 30. Nozzle[12] ... 42
Figure 31. Scheme of existing temperature[23] ... 44
Figure 32. Stepper motor details[23] ... 45
Figure 33. Control board ... 46
Figure 34. Previous design with 7mm[23] ... 47
Figure 35. New design with 3mm ... 47
Figure 36. Contact between nozzle and brush... 48
Figure 37. Design holes for wiring ... 49
Figure 38. Fixing connecting board to extrusion head ... 50
Figure 39. Fixing Thermal fuse ... 51
Figure 40. Connecting plate ... 52
Figure 41. Comparison of previous design to the new one ... 53
Figure 42. Previous Prototype of wiring arrangement ... 54
Figure 43. New Prototype of wiring arrangement... 54
List of Abbreviation
3D Three dimensional
ABS Acrylonitrile butadiene styrene
ASCII American Standard Code for Information Interchange CAD Computer Aided Design
FDM Fused Deposition Modelling FFF Fused Filament Fabrication LCD Liquid Crystal Display
NTC Negative Temperature Coefficient PLA Polylactic acid (polylactic acid) PTC Positive Temperature Coefficient PTFE Polytetrafluoroethylene (Teflon) PVA Polyvinyl alcohol
RAMBo RepRap Arduino compatible Mother Board RAMPS RepRap Arduino Mega Polo Shield
RepRap Replicating Rapid Prototype SD Secure Digital
STL Standard Triangulation Language USB Universal Serial Bus
1 Introduction
The next industrial revolution is all about personal fabrication, and it is happening now. 3D printing is poised to unlock the potential in every person to create, innovate and fabricate. It is already transforming manufacturing and soon it will change the world.
3D printing has taken by the storm design companies all over the world. It allows designers to visualize the object in 3D. It is a prototyping process in which a real object is created from a 3D model. Since the raw material is added layer by layer to form the final object, 3D printing is also called as addictive manufacturing or desktop fabrication[1].
One of the most widespread 3D printing methods is addictive FDM technology. It began to appear in the eighties of the last century. But in recent years it has been given new impulse in the global interest of RepRap community developers[1].
Fused Layer Modelling (FLM) is one of the most widespread additive technologies, which is also named as Fused Deposition Modelling (FDM) by the stratasys company.
Its initially traced in 1980’s, however it recently got a new impulse in the form of worldwide interest of RepRap community developers[2].
The goal of the article is to replace the non-functional printing head with the functional and compactable printing head. The designed printing head allows two different materials in the form of thermoplastic wire with a diameter of 1.75mm. The whole solution should be as compact as possible, and both nozzles should be as close to each other as much as possible to avoid unnecessary reduction in the printing area. The design should be light in weight as much as possible to ensure good movement for the head during printing.
1.1 3D Printing
3D printing is an additive manufacturing process that creates a physical object from a digital design. There are different 3D printing technologies and materials in which you can print. All the technologies are based on the same principle which states that a digital model is turned into a solid three-dimensional physical object by adding material layer by layer. There are different types of technologies stated below.
1.1.1 Stereolithography (SLA)
Stereolithography (SLA), widely used for visualizing design concepts, SLA enables user to construct complex, three-dimensional models one layer at a time. During operation, an ultraviolet laser, driven by successive slices of the CAD model, systematically, solidifies the photopolymer resin. SLA accommodates a wide range of photopolymer materials to approximate the characteristics of thermoplastic like polypropylene, polyethylene, nylon and ABS.[3]
Figure 1. Principle of SLA[3]
1.1.2 Digital Light Processing (DLS)
Digital light processing is relevant to stereolithography and it is another 3D printing process. Digital micro mirrors laid out on a semiconductor chip. This type is used in
cell phones, projector and 3D printing. Liquid plastic resin is used as the material, which is placed in the transparent resin container. The resin gets harden quickly when affected by large amount of light[3]. The speed of the printer is high and impressive.
When the first layer is finished, it will be moved up and the next layer is started to be worked on.
Figure 2. Principle of DLP[3]
1.1.3 Selective Laser Sintering (SLS)
Selective laser sintering (SLS) creates three-dimensional object from powdered materials, including plastics and metals for the wide latitude in material properties.
Heat from the carbon-di-oxide laser also driven by parts CAD data which fuses or sinters the powder layer by layer within a precisely controlled process chamber. SLS offers parts suitable for functional analysis and application[3].
Figure 3. Principle of SLS[3]
1.1.4 Selective Laser Melting (SLM)
Selective laser melting is a technique which also uses 3D CAD data as the source and forms 3D object by means of high power laser beam which fuses and melts the metallic powder together. Selective laser melting is one of the subcategory of selective laser sintering[3]. Similar, to other 3D printing methods, CAD file needs to be processed by the special software which reads .STL file. The final metal powder is evenly distributed onto a plate, in which the image is fused by high laser energy that is directed to powdered plate. Metals that can be used for SLM includes stainless steel, titanium, cobalt chrome and aluminium.
Figure 4. Principle of SLM[3]
1.1.5 Electronic Beam Melting (EBM)
Electronic beam melting is another type of additive manufacturing for metal parts. This process is also based on powder bed fusion technique. In SLM high power laser beam is used as the power source, whereas in EBM electron beam is used as the power source. The metal powder is used as the material for electronic beam melting, which melts the 3D part layer by layer, this process is controlled and conducted in the temperature up to 1000 degree Celsius[3].
Figure 5. Principle of EBM[3]
1.1.6 Fused Filament Fabrication (FFF)
Fused filament fabrication (FFF) is anadditive manufacturing technology commonly used for modelling, prototyping, and production applications. It is one of the techniques used for 3D printing. FFF works on an "additive" principle by laying down material in layers; a plastic filament or metal wire is unwound from a coil and supplies material to produce a part[4].
Figure 6. Principle of FFF[5]
In FFF process, the materials would be of high strength. It is cost-effective and waterproof. It can use ABS (Acrylonitrile Butadiene Styrene and PLA (Polylactic acid) material for its impact resistance and toughness. Though many other materials are available ranging in properties we even use those two materials for better impact strength and resistance.
FFF can print concept models, final end-use product and functional prototype. The good about this technology is to print all parts with high-performance and engineering grade thermoplastic, which is very beneficial for mechanical engineers and manufactures[4].
1.2 Types of 3D printer
FDM 3D printer takes place in many forms. FDM printer differs in mechanical arrangement and coordination systems. The most popular mechanical arrangements for FDM 3D printer.
• Cartesian
• Delta
• Core XY
• Polar
• SCARA (robot arm)
1.2.1 Cartesian
The first RepRap 3D printer is based on this arrangement Cartesian XY-head. In this arrangement, the extruder head moves along the X and Y axis and the bed over the Z axis. Z axis movement on these kinds of 3D printer is very precise and needs low acceleration. In order, to maintain the accuracy, the bed should be light in weight. The second RepRap 3D printer is based on the arrangement of Cartesian XZ-head. The arrangement differs from the previous one, why because the bed moves over Y axis and the extruder moves along X and Z axis. The main advantage of this arrangement is that the bed can hold a lot of weight[6].
Figure 7. Cartesian head[6]
1.2.2 Delta
Delta 3D printer works with the Cartesian plane. However, the setup is totally different when compare with other types. The extruder head is suspended by three arms in the triangular configuration. The bed of this type of print will be in circular shape. The advantage of this type of printer is that the moving parts are light in weight, which results in faster printing with great accuracy[7].
Figure 8. Delta[6]
1.2.3 Core XY
Core XY is also one of the Cartesian arrangements which is growing rapidly. The movement of XY depends on the combined effect of X and Y motors. Core XY is the parallel manipulator system gives more rapid acceleration than Cartesian XZ head.
Figure 9. Core XY[8]
1.2.4 Polar
This type of printer also has rotating print bed, also the extruder head can in all directions namely left, right, up and down. A polar 3D printer is energy efficient
because it only needs two stepper motor, whereas in the Cartesian type it requires one stepper motor for each axis, so totally four[7, 9].
Figure 10. Polar[9]
1.2.5 SCARA
Selective Compliant Assembly Robot Arm or Selective Compliant Articulated Robot Arm, which means the robot arm moves along the X-Y plane and uses the additional actuator to move along Z axis. It doesn’t need bearings and timing limits for the arrangement which is one of the advantage of SCARA[9].
2 Literature Review
2.1 Additive Manufacturing Data Formats 2.1.1 STL Format
It is the representation method used to describe the CAD geometry vary from one system to another. A standard interface is needed to convey geometric descriptions from various CAD packages to Additive Manufacturing (AM) system. For the last three decades, the STL file format is used to exchange information between design programs and AM systems[10].
Figure 12. A sample STL file[10]
The STL file consists of the unordered list of triangular facets representing the outside skin of an object. There are two STL file formats. One is the ASCII format and the other is binary format, but it is human readable. In a STL file, triangular facets are described by a set of X, Y and Z coordinates for each of the three vertices and a unit normal vector with X, Y and Z to indicate the side of the facet. Moreover, many commercial CAD models are not robust enough to generate the facet model and frequently have problems as a result[10].
There are several advantages of the STL file:
1. It provides a simple method of representing 3D CAD data.
2. It is already a de facto standard and has been used by most CAD systems and AM systems.
3. Finally, it can provide small and accurate files for data transfer for certain shapes.
There are several disadvantages for STL as well:
1. The STL file is many times larger than the original CAD data file for the given accuracy parameter. The STL file carries much redundant information such as duplicate vertices and edges.
2. The geometry flaws exist in STL files because many commercial tessellation algorithm used by CAD vendors, which are not sufficiently robust.
3. The STL file carries limited information to represent colour, texture material, substructure and other properties of manufactured end object.
4. The subsequent slicing of large STL files can take many hours.
2.2 RepRap
Replicating Rapid Prototype (RepRap) is a device that is capable of self-replication and fast Prototyping. The project was founded in 2004 Dr.Adrian Bowyer at the University of Bath in the UK. Gradually, RepRap became an international project on the principle of open hardware and software, which means the assembly instructions RepRap products are freely open to anyone in the world[5]. Under this, license it can also available for everyone to improve the project and re-run it freely. A large part of the components needed to build a new 3D RepRap printer is possible Print to another 3D printer. The fact that the printer is capable of partial self-replication and instructions for building such a device are freely available, resulting in substantial drop in prices for commercial FDM devices[11].
2.3 Pre-processing
The first pre-production step is to get the model in STL (Standard Triangulation
several websites currently offering ready-to download models, in many cases free of charge.
2.3.1 Slicing and G-code
The basic information about the print, such as the diameter of the filament, the melting temperature of the material, or the temperature of the print environment, must be passed to the slicer.
After loading the model in the slicer, the 3D model is split into individual layers and translated into G code, which contains all the information to control the entire process.
In this file, there are commands (G-codes) where the extruder is located, how much material should be pushed at the specified temperature and in how much speed it’s moving. The G-code also contains the print commands that have been configured in the slicer settings (for example, the required print media temperature before the print is started). Popular software open slicers are Cura, Slic3R, Simplify3D and Skeinforge.
2.4 Post-Processing
Ideally, it is possible to remove a finished printout from the pad after overheating and gentle cooling. However, it is often necessary to remove support, either mechanically or by dissolving support material. The next step may be the surface finish of the model.
For example, ABS used to immerse the model in an acetone vapour bath, creating a shiny surface of the model. When printing larger models that are larger than the print area of the printer, it is possible to divide them into several smaller parts before printing, which then sticks together after printing.
2.5 Stratasys Fused Deposition Modelling 2.5.1 Company
Stratasys Inc. was founded in 1989 in Delaware and developed the company’s AM system based on Fused Deposition Modelling (FDM) technology. The technology was first developed by Scott Cramp in 1988 and the patent was awarded in the USA in 1992. FDM uses an extrusion process to build 3D models[10].
2.5.2 Products
Stratasys manufactures 3D printing equipment and materials create physical objects directly from digital data. The system range from affordable desktop 3D printers to large advanced 3D production systems. All of Stratasys 3D printer build parts layer by layer.
2.5.3 Process
In Stratasys patented process, a geometric model of a conceptual design is created on CAD software which uses .STL or IGES formatted files. The formatted files can be imported to the workstation where it is processed using InsightTM software, or Catalyst software for the dimension series, which automatically generate supports.
Within this software, the CAD file is sliced into horizontal layers after the part is oriented for the optimum build position, and any necessary support structures are automatically detected and generated[10].
2.5.4 Principle
The principle of FDM technology is based on surface chemistry, thermal energy and layer manufacturing technology. It is known for its reliability and durable parts, and extrudes fine line of molten thermoplastic that solidify as they deposit. 3D printers that run on this technology build parts layer by layer by heating thermoplastic wire to semi liquid state[10]. FDM uses two materials to execute a print job, namely modelling material, which consists of finished piece and support material, which acts as a support for finished piece.
2.5.5 Strengths and Weaknesses
The main strength of the FDM technology are as follows:
1. Fabrication of functional part: FDM process is able, to fabricate prototypes with materials that are similar to that of actual product. With ABS, it is able, to fabricate fully functional parts that have strength of about 85% for the moulded part.
2. Minimal wastage: FDM process builds parts directly by extruding molten semi-
3. Ease of material change: Build materials, supplied in cartridge form, are easy to handle and, also can be changed easily. This keeps the operation of the machine simple and maintenance is easy for this process.
The weakness of FDM technology are as follows:
1. Restricted accuracy: Parts built with the FDM process usually have restricted accuracy due to the shape of the material used, i.e. the filament form. The newer FDM machines however have made some improvements in easing the problem by using better machine control.
2. Slow process: The building process is slow, as the whole cross sectional area needs to be filled with building materials. Building speed is restricted by the flow rate of the build material from the extrusion head.
2.5.6 Applications
FDM models can be used in following application areas:
1. Educational use: Educators can use FDM technology to elevate research and learning science, engineering, design and art[10].
2. Customisation of 3D models: Entrepreneurs and hobbyists use FDM 3D printing to expand manufacturing into the home, where we can create gifts, novelties, customised devices and inventions.
2.6 MANAGEMENT 3D PRINTER
To operate extrusion head, we need some other components to run. Those components are as follows
2.6.1 Control board
Control board is the brain of the entire 3D printer. Most of them are based on the board Arduino prototyping platforms and includes 8-bit microcontroller family of AVR from Atmel and the number of other support circuits. Firmware for the Arduino individually programmed by the user on a desktop computer and then to the Arduino recompiling. Inside Arduino firmware runs again and again in a loop, which discovers their status and by appropriate control firmware to stimulate the
environment responds. Since the flat-form is performed, there is a huge amount of Arduino derived constructions and designs for the control board of 3D printers.
They are inherently very similar and the choice of the particular solution is always individual due to the requirements with the device. One of the most widespread solution is to use plate Arduino Mega 2560 (processor ATmega2560), along with additional module called RAMPS (currently in version 1.4.2), where the Arduino takes care of the logical part of the process and RAMPS provides all power components and sensors. In this configuration, it is possible to control two extrusion head and stepper motors for all three axes. It is also possible to connect a heated pad, LCD display, SD card reader and fans. RAMPS stepper motor must install properly[12].
Figure 13. Arduino MEGA 2560 and RAMPS 1.4[12]
Another option is to use a control board named Rambo, currently in version 1.3. It consists of similar components (procesorATMega2560) as previous solutions. The difference, however, the different lies in integrating all components, including stepper motors drivers into one plate. As already mentioned, there are large number of control boards. In addition to the above, it is worth mentioning the following:
Sanguinololu, Gen7, Megatronics, Minitronics[13].
Figure 14. Sanguinololu[14]
3 Available solutions of extrusion head
There are many solutions for the extrusion heads according to the RepRap project, many users adjust the extrusion head according to their own needs and provide they are achieving their own solutions. The most common extrusion head designs are listed below. It should be noted that the solutions are combined.
3.1 Types of extruders
The extruders are divided into categories by the means of feeding element using feeding mechanism into the hot part of the extrusion head. Majority of the extruders for printing the material uses the following solutions.
3.1.1 Geared extruders
Geared extruders uses a gear reduced feeding mechanism to feed the filament. Because of the geared one the extruder offer higher torque than direct extruders and hence bigger diameter (3mm) of the wire is used for printing. The disadvantage for the geared extruder has more robust structure and size. The transmission ratio of the wheels may differ but it must be properly calibrated. This method says that the driving wheel is mounted on the output shaft of the stepper motor which drives the driven wheel mounted on the feed screw. This screw is placed in between the two bearings and has its own special line, which provides feed filament. Proper pressure ensures filament to screw hinged bracket with a bearing for the screw presses of the two springs[15, 16].
3.1.2 Direct drive extruder
Direct drive extruder is characterized by placing the feed wheel directly on the output shaft of the stepper motor. Unlike in the previous solutions, the feeding mechanism is not geared and hence offers less torque, however, it is sufficient for filament feeding with the diameter of 1.75 mm.
Figure 16. Direct drive extruder[17]
3.1.3 Bowden extruders
Bowden extruder is one of the special cases. Most probably in the Bowden extruder the feeding mechanism is not located in the head together with the hot part, but anyway its mounted on the printer frame. The filament is being fed into the hot part through the tube. Feed filament can be implemented either as a direct or geared[18]. The advantage of this solution lightens the moving part, so that it allows the printer to print faster and better. Bowden extruder has a disadvantage that initially it is less accurate for feeding the material and some of the more flexible material cannot be used for printing with this extruder type. Problems may occur during retraction.
Figure 17. Bowden extruder[18]
3.2 Dual extrusion head
The term dual extrusion head states that it offers two independent materials (filaments) that can be automatically exchanged without the need of manual operation. Any of the design can be used to feed the material into the extrusion head, for example the extrusion has the combination of direct drive extruder for the first nozzle and Bowden for the second one.
The second material is often used as a supporting material on parts with large over- hangings, where the support-less print is not possible. In case of simple extrusion head, it is possible to create the supports from the same material as the model with the smaller density of the applied material[19]. When printing the parts, these supports must be cleaned mechanically which is not possible to do every time like that and they may also cause damage to the printed part. Using another different material as a supporting may minimise the risk. Generally, there are various dual extrusion head designs which are categorised as follows:
• Extruder duplication
• Two independent nozzle in one cooler
3.2.1 Extruder duplication
One of the easiest solutions to print on a 3D printer using more materials during one session is to duplicate the extruder. For example, the carriage head is fixed with two identical extruders used separately. In case if the small objects are being printed (their size on corresponding axis is smaller than the nozzle spacing), the print can be configured such a way that both extruders work synchronously that is two identical models are printed next to each other. For this solution, it requires twice the number of components necessary to implement one dual head. Using two independent stepper motor leads in decreasing the printing space, also total weight of the extrusion head will increase as well, which causes deterioration of print dynamics[19].
Another difficulty lies in the nozzle being in the same height, after switching from one nozzle to another so that the small amount of filament may leak from the previous nozzle, which leads to bad impression of the printing quality. This process can be prevented by means of cleaning the nozzle with the help of brush but unfortunately that leads to the increased complexity of process control. Also, it’s important to set the height of two nozzles correctly.
Figure 18. Extruder duplication[19]
Advantage is to have two independent nozzles, why because each of them contain two different materials with different melting temperature, so that its easy print more
complex objects, since one of the nozzle is used for supporting material. When using this solution, the amount of nozzle can be increased by more than one nozzle, which leads to increase in weight and reduction of printing space of the printer.
3.2.2 Two independent nozzles in one cooler
Another possible solution for dual extrusion head. Two independent nozzles with optional diameters are locked in heating blocks that are independently heated by its own heating elements. In heat break one end is locked with the heating element and the other end with the cooler which is in block shape, while the cooler is fitted with fan and used for both the nozzles. Two stepper motor which is solid, equipped with a fan and is common to both nozzles. The material supply is provided by two stepper motors, which are independent, and each of them gives the material just for one nozzle.
Figure 19. Two independent nozzles in one cooler
Advantages and disadvantages are same as the previous one whereas in this spacing of the nozzle is smaller, which allows the printer to print on large area with same feed rates.
3.2.3 One nozzle for two filaments
This concept utilizes a print for two filaments, one nozzle, which receives two filaments. This solution is suitable only for mixing two colours of the same material,
decrease the maximum print area. Additionally, the non-used nozzle will not be blocked by the printed object.
Figure 20. One nozzle for two filaments[19]
3.2.4 Manual Deployment during Printing
Another solution came from the Czech company Prusa Research, which specifically modified the Marlin firmware for this purpose. When using this procedure, first you need to generate a G code, then enter the web application and upload the G code. In this application, it also determines, in which layer the colour changing occurs and the modified G code is downloaded again.
Printing occurs in a layer that has been pre-defined to stop printing and extruding material. The extruder head moves away from the print area, and the beep sound indicate that a new filament needs to be inserted. All communication takes place via the LCD display, the user confirms, whether a clean new filament is coming out of the nozzle[20]. In case the material coming out of the nozzle is still mixed with the previous filament, the extrusion will occur again. Once confirmed, the extrusion head returns to the last position and continues printing.
Figure 21. LCD display for replacing filament[20]
This solution, however, is the same as the prior art solution of one multi-purpose nozzle which is suitable for multi-colour printing of the same materials as the heater is heated to the same temperature. Therefore, it is not suitable for printing different materials. Another disadvantage is the impossibility of printing automation. The filament must be loaded manually. When replacing the filament, it is always necessary to extrude the remaining material manually from the hot part of the extrusion head, which can be considered as a waste material. In addition to this one nozzle solution, it does not reduce the maximum print area of the printer as same in the previous case.
4 Materials & Methods 4.1 Extrusion head
Extrusion head is the most important components of the whole printer and it consists of two parts cold and hot part. The material will be in the form of thermoplastic wire which fed by the feeding mechanism from the cold part to the hot part, Where the wire is being melted.
Figure 22. Principle of the printing head[21, 22]
4.2 Feed mechanism
The feeding mechanism belongs to the cold part of the extrusion head. The task is to bring the filament to a warm section in a controlled manner. A feeding wheel is used to provide with the material, while this wheel slightly cuts into the filament during rotation. Filament is moved due to the contact pressure from the other side, where the wire is fed in the desired direction. The feed of the material is controlled by a stepper
motor on which the feed wheel is mounted. During printing, it may be advantageous for a short time to remove the material from the hot part, which is achieved by reversing the feed mechanism - this phenomenon is called as retraction.
The main parameter of the feed mechanism is the size of the filament pressure feed wheel. If too little pressure is set, it may occur to the material slip, and thus to its incorrect or no dosing into the hot portion of the extrusion head. If the thrust is too large and the teeth of the feed wheel are too much cut into the material, may occur at the site of their contact with the spinning of the filament, which subsequently clogs the grooves of the feed wheel. The result is a filament slip in the feed mechanism and possible degradation of the printed model[22].
Figure 23. Feed mechanism
4.3 Stepper Motor
Stepper motor are DC motor that moves in discrete steps. They of plenty of coils that are organised in groups called “Phases”. By energizing each phase in sequence, the motor will rotate one step at a time. In computer, stepping can be controlled for positioning and speed controlling. In the stepper motor, the wire is connected to the
Figure 24. Stepper motor
4.4 Servo drive
A servo drive is a special electronic amplifier used to power electric servomechanism and continually adjusts for deviation from expected behaviour. A sensor attached to the servo motor reports the motors actual status back to the servo drive. The servo drive then compares the actual motor status with the command motor status. It then alters the voltage frequency to the motor so as to correct for any deviation from the command status.
Figure 25. Servo drive
4.5 Heat break
The filament is being fed into called as “heat-break”. The task of the component is to transfer less amount of heat from the heating block to the cold part of the head as much as possible. That is why the top part of the heat break is mounted with the cooler, the bottom part of the heat break ends with a thread which is screwed to the heating block in which the material passes into the nozzle[12]. The temperature in place of contact of the heat break and the nozzle is in hundreds of degrees, the filament input into the heat break is a requirement for the lowest temperature (ambient temperature). For the printer, RepRap is used to produce the part of the extrusion head, the material often used is stainless steel, why because the thermal conductivity is about 3 times smaller than that of commonly used steel.
Figure 26. Heat break[12]
4.6 Cooler
The cooler is the largest component for the extrusion head. It is used for extracting the heat away from the heat break so that the filament is not melted as much and does not choke the heat break up. Generally, for the better result the cooler is often fitted with additional fan. According to the manufacturer and type of extrusion head, coolers are of various shapes which have been used, generally will be in cylinder or block shape.
Figure 27. Cooler
4.7 Heating block
The heating block is a major connecting link of several parts of the extrusion head.
Dimensionally it is a small component. The molten material passes from the heat break to the nozzle which is arrested by means of a heating block thread. Additionally, it consists of own heater element and thermistor for measuring and regulating of filament melting temperature[12]. The most often used heater element for RepRap type 3D printer is ceramic core element with 40 W of power and 12 or 24 V of operational voltage. The heating element consists of a resistor which converts electrical energy to thermal. This heat the heating block in which the heater is armed. Heater block is usually fitted with a single heater element.
Figure 28. Heating block[12]
4.8 Thermistor
The most commonly used thermal sensor for a RepRap printer is a thermistor. This sensor works on a variable value of resistance that is dependent on Temperature change. The thermistor is distinguished into two types - NTC and PTC. When warming up NTC thermistor reduces its resistance while increasing the PTC type. Frequently used Thermistor for RepRap printers is a NTC thermistor with an internal resistance of 100 kΩ.
4.9 Nozzle
The nozzle is the last part of the extrusion head. In this nozzle part the melted filament leaves the extrusion head and is applied to the base plate or by the previous layers of the printed model. The basic condition for successful extrusion is to ensure that melt through the nozzle should be smooth as much as possible so that the melt do not accumulate, and the nozzle gives the least resistance. It is important that the nozzle is sufficiently tightened to the heater with heat break and thus prevent leakage of melt around the gaps between the individual parts. Materials for the manufacture of nozzles varies depending on what material is going to be printed. For printing the frequently used materials (ABS, PLA) are used for nozzle[12]. The nozzle opening ranges within tenths of millimetres. Generally, the smaller nozzle hole diameter is, the more detailed models where we can achieve. The nozzle diameter is smaller, so probably the print will take longer time to complete the task.
Figure 30. Nozzle[12]
4.10 Limit switches
Limit switches are used to define the movements of the individual axes of the 3D printer. Always before printing the printer moves in each of its axis to the zero point, initially coordinates should be as [0, 0, 0]. Always in contact with a limit switch axis is in its zero position. For defining the movement in each axis, sufficient terminal switches are always located in the zero position. In general, limit switches can be divided into several types, for 3D printer mainly mechanical and optoelectronic.
Mechanical limit sensors, which operate on the principle of micro switches, have simple design and lower cost. The disadvantage is the limited number of cycles and lower accuracy, which is particularly important for the Z axis, where the limit switch at the first layer indicates the position of the nozzle above the set plate.
The optoelectronic sensors operate on the principle of interruption the light barrier, compared with mechanical sensors, they are more expensive, more complex, but their accuracy tends to be higher.
5 Current state of 3D printer
The first step was to determine the current state of 3D printer, the construction of the printer is realized. This printer works on the principle of FDM, which has two extrusion independent nozzles with one cooler and allows you to print two materials.
Due to the damage or partially dismantled extrusion head, it is not possible to print.
Also, the control board of this printer is not functioning properly. Coordinate system of this construction is Cartesian type. Apparatus (measuring approximately 900 x 700 x 1000 mm) with closed structure. Initially, offered print space for this printer is 203 x 203 x 305 mm. The construction consists of 1. Die for two materials, 2. Provided for thread, 3. Guided rod, 4. Corners of the print area (space for printing area), 5. Brush is placed for cleaning the nozzle of the extrusion head, when changing the materials, 6.
Two coils of filament and display in the control panel, 7. Closed part of the printer to check the temperatures.
Figure 31. Scheme of existing temperature[23]
The control board can’t fix directly to the 3D printer. For that we need to design the connecting plate in order, to avoid some malfunctions. The connecting plate is printed with the material named ABS.
The wiring connections from the extruder head to control board (back side of 3D printer) is often getting entangled and leads to damage in wire. To avoid this kind of entanglement, the design was modified according to which the wire goes inside the extruder without any entanglement as much as possible.
The printing space is very low in this old design prototype of the extrusion head. There are lot of possibilities for firing, since the printer doesn’t have automatic temperature control unit. To avoid that kind of firing, thermal fuse is placed at the bottom of the extruder head (below cooler), so that temperature can be measured and controlled using control unit.
Kinematic arrangement of the whole printer contains 3 stepper motor. Two stepper motor for X and Y axis rope-friction gearing and one for the Z axis, which propelled three threaded rods across the belt. After removing the print cover, the name of the stepper motor and its parameter can be read as shown[23].
Figure 32. Stepper motor details[23]
Filaments with the diameter of 1.75mm was fed to the extruder head at the bottom of the printer construction. From the bottom position, the filament was fed into Teflon (PTFE) tubes, which feeds the flexible tube to the extrusion head in the Y axis. The communication was done via Ethernet. The control board with the source is located at
is placed in this printer gives very less space for the printer to print. The design for the dual head extrusion is quite simple and the filament wire passing through the extrusion head is quite complicated and wires are bending a lot in this design, which leads to breakage of filament wire.
Figure 33. Control board
5.1 Problems in the current state of 3D printer
The control board for the shown 3D printer is not functioning properly. The power source is not travelling to control board. It may be due to damage in connectors or control board.
So, it is necessary to change the control board as well as the connectors used in the 3D printer. There is no proper arrangement of wires in the extrusion head, for example stepper motor connectors, thermistor connectors are not fixed properly in the head, so that the connectors may get spoiled easily during operation.
There is lot of gap between the nozzle and brush approximately 4mm, it is necessary to bring the nozzle down to 4mm, so that the nozzle reaches the brush placed in the bottom.
The function of brush is clean the nozzle.
To bring the nozzle down to 4mm, it is necessary to change the design of the extruder head. According to which the nozzle will be seated with brush. Mainly, the wires are placed properly and it’s necessary to fix the wiring properly.
Thermistor is not fixed in the extrusion head may lead to firing. The function of thermistor is to measure the temperature and to control the temperature using control unit.
5.2 Resolving the problems in existing solution
There are some of the solutions which we have, to rectify in this thesis work. Some of the rectified solutions are explained as follows:
5.2.1 Change in Design of Extrusion head
The design of the extrusion head is changed according to which the nozzle touches the brush easily for the cleaning process. Initially in the design the length of the head is extruded by 4mm on the top of the profile and 4mm to the bottom of the profile. The comparison with the previous prototype to the new prototype is shown.
Figure 34. Previous design with 7mm[23] Figure 35. New design with 3mm
whenever it is necessary. The main advantage for reducing the length to 4mm is that the output model, what we get in the future will be in the finest form of structure.
Because of the change in new design to 3mm. The end of the nozzle is seated properly to the brush, which is meant for cleaning process. Whereas in the previous design with 7mm, was not having enough contact surface between the brush and nozzle.
Figure 36. Contact between nozzle and brush
5.2.2 Holes in the design
The holes are given at the back side of the design in extrusion head. The holes are meant for the wires to pass through on it. There are two big holes at the back side with the diameter of about 9mm. The function of this hole is to pass the Teflon tube through it (inside the Teflon tube the filament wire will be travelling). In that hole, the push-back bolt is fixed, so that the Teflon tube will fixed properly and it won’t come out until it removed manually. There is one projection for the hole, which is not meant for the Teflon tube to bend. Bending may lead in breakage of filament wire. The main advantage for the projection is to avoid bending in the Teflon tube and holes may lead to proper arrangement of the wire. The wires don’t get entangled with each other was the main advantage for the holes in the design.
Figure 37. Design holes for wiring
From the figure 36, we can see some holes and projection for the wirings to pass through in it.
Due to the holes and projection, the wires don’t get entangled. The orientation is given as we can see in the left side figure 36, meant for the round tube to join, together with screws in that orientation.
5.2.3 Fixing connectors to the extruder head
The connectors are soldered and it is fixed in the extruder head, where it is possible to fix without any collision. The wires from the stepper motor, servo-drive and thermistors are soldered and attached to the board in the extrusion head with corresponding stepper motor, servo-drive and thermistor wires, as shown. Next to the connector board there is hole in the head, which is meant for the wires to pass through on it uniformly. The advantage of fixing this connecting board is that, the wires will travel uniformly without any collisions and during printing process the wires and connectors don’t get disturbed.
The corresponding wires are soldered to the corresponding pins in which they are connected and meant for. The figure 37 shows that the connecting board is placed in the extrusion head.
Figure 38. Fixing connecting board to extrusion head
5.2.4 Fixing Thermistor at the bottom of the extrusion head
In the previous prototype the thermal fuse was not fixed in the extrusion head. The function of thermal fuse is to measure the temperature. In the previous prototype, thermistor was not placed, so that the temperature cannot be controlled, leads to firing.
In our case, it is necessary to fix thermistor at the bottom of the extruder head, so that the temperature is controlled using control unit with the help of thermal fuse. The thermal fuse is placed at the back side of the nozzle as shown in the figure 38. One end of the thermistor is joined with one red wire and the another, end of the thermistor is connected to another red wire respectively.
Figure 39. Fixing Thermal fuse
5.3 Connecting Components to Control board
For connecting the RAMPS 1.4 and MEGA 2560 board, we need one connecting plate to connect those two types of control board to the 3D printer (back side). The back side of the printer is covered with steel surface, so the control boards cannot attach directly to the printer. The connecting plate is designed on our own with ABS material to avoid malfunction.
Figure 40. Connecting plate
5.4 Comparison of First and Second Prototype
In the previous design, the back side of the extrusion head is fully open. Because of that the wires passing from the extruder head to main control board are getting entangled often, due to the entanglement, the wires are getting damaged easily.
Heating filament made of Teflon (PTFE) tube passing from heat break to the
extrusion head was having insufficient design in the previous prototype, which leads to the breakage of filament wire.
In the new design prototype, the back side of the extrusion head is closed by giving some holes wherever its necessary, the holes are given for the wires to pass through from the head to the control board. In the first design, there were two block of holes with less space for Teflon tube (PTFE), leads to damage in filament wire. Whereas in the new design, one hole with more space is given for the Teflon tube to pass freely, in this case there won’t be any damage for the filament wire. The black filament wire is used for the new design head as shown in the above figure. There is no damage
during the travel of filament wire for the new design. The comparison of the previous design to the new design is shown.
Figure 41. Comparison of previous design to the new one
In the previous design prototype, the printing space was very less. In order, to increase print space the length of about 4mm is decreased from the previous design, so that the printer gives more space when compared to the previous design prototype. There are some projections of extruder in the bottom, which is meant for the wires to pass through in it. From the figure 42, the wiring connections are not arranged in the neat way. The entanglement of the wire may lead to damage in wire during printing sessions. Whereas in our new design prototype the wires are arranged in the neat manner, so that they don’t get entangled.
Figure 42. Previous Prototype of wiring arrangement
Figure 43. New Prototype of wiring arrangement
The above figure 43, shows clearly that the wiring connections are arranged in a neat manner, whereas in the previous design the wiring connections are not arranged properly leads to the damage in wire.
5.5 Practical Realization of Printing
After completing the design of dual extrusion head with respect to the original equipment design. The small control board for connecting thermistors, stepper motor is fixed inside the dual extrusion head. The connectors are soldered with respect to the number of wires connected in the previous variant, for example, the stepper have four wires with different colour, those four wires are joined with the connector. The wires are arranged in a way that, they don’t get entangled with each other from the extrusion head to the main control board. There are large number wires passing from dual extrusion head to main control board, namely heater wires, stepper wires, thermistor wires etc. Though the main focus of the thesis is on designing an extrusion head, it will be a justification for the design if it is tested. In the final stages of the research, it was discovered that connecting plate had not been printed for fixing it to the rear side of the printer. Attaching the new control board to the printer is expected to take some more time. Due to this, results are scheduled after the submission of the thesis. The results may be obtained in another two weeks. The things scheduled to be done are to 3D print the connecting plate first and then given wiring connections after fixing the control board to the printer. Once these steps are completed, final test results to be obtained.
6 Conclusion
This thesis work presents the result of dual extrusion head design for 3D printing using FDM technology. A detailed review of the existing solution was performed. Post that research, we decided to custom design a head that was smaller and lighter in weight as compared to the existing solutions available in the market. Additionally, it was important to have nozzle spacing as small as possible. This is necessary because nozzle size affects the size of printing space. In comparison to previous prototype, the length of extruder head was increased for 4mm so that the nozzle end touches the brush.
The design of the extruder has the proper space for the wires to travel from the head to control board. This will ensure there is no entanglement between wires. Whereas in the previous design, the possibilities of wire entanglement was very high.
The safety elements for the extruder head was given. Initially, in the first prototype, the temperature controller (thermistor) was not fixed which increased the possibility of burning of the head. To avoid the burning, the thermistor was fixed at the bottom of the extruder head (cooler). Because of this temperature controller, the system was automatic shutdown whenever the heat increased beyond the threshold temperature.
However, in the final solution, most of the part was replaced as work-pieces in order, to improve accuracy and service life of the whole printer.
The design head was used as the fundamental part of the experimental printer. In future, it will be necessary to change Teflon tube (PTFE) which is situated near to the extrusion head. Since the diameter of the Teflon tube is small now, if we increase the diameter of the Teflon tube, the filament wire will move freely inside the tube.
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