60型熔融沉積 FDM3D 打印機設計含4張CAD圖
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International Conference on Manufacturing Engineering and Materials, ICMEM 2016,
6-10 June 2016, Novy Smokovec, Slovakia
Reconstruction and development of a 3D printer using FDM technology
Krisztián Kuna
* a Kecskemét College – Faculty of Mechanical Engineering and Automation – Department of Vehicle Technology, 10 Izsáki st., Kecskemét 6000, Hungary
Abstract
This study, we detail the constructional selection of a machine, which operates with FDM technology. We outline the milestones of the reconstruction of the printer, the restoration of the technical documentations (Reverse Engineering), and then the calibrations and the measurement results. Based on what we have learned from the construction, we started to design our own FDM printer, which is a compact, user demand-driven device.
? 2016 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the organizing committee of ICMEM 2016 Keywords: FDM; design; 3D printing; RE-RP; reconstruction;
1. Introduction of the FDM technology [1], [3], [4]
3D printing is additive, which means it creates the desired form with a built-up manner. This means, that the body is built up as a thin layer without a preform. The applied materials are usually some kind of plastics. There are several methods of the 3D printing technologies depending on the layer creation manner.
The FDM (Fused Deposition Modeling) 3D printing technology (Figure. 1.) works on an "additive" principle by laying down material in layers; a plastic filament is unwound from a coil to produce a part. The technology was developed by Scott Crump in the late 1980s. The FDM technology needs software which processes an STL file (stereolithography file format). After that we have to slicing the model with another program for the build process. If required, support structures may be generated. The model is produced by extruding thermoplastic material to form layers as the material hardens after extrusion from the nozzle. A plastic filament is unwound from a coil and an extrusion nozzle turn the flow on and off. There is a worm-drive that pushes the filament into the nozzle at a controlled rate. The nozzle is heated to melt the material. It can be moved in both horizontal and vertical directions by a numerically controlled mechanism. The nozzle controlled by a computer-aided manufacturing (CAM) software package, and the part is built from the bottom up, one layer at a time. The stepper motors are employed to move the extrusion head. The mechanism uses an X-Y-Z rectilinear movement.
1.1. Advantages-Disadvantages of the technology
The FDM printing technology is very flexible, and it is can handle with the small overhangs on the lower layers. The FDM generally has some restrictions and cannot produce undercuts without support material. Many materials are available, such as ABS and PLA among many others, with different trade-offs between strength and temperature properties. We picked the most advantageous technology from the 3D printing methods, while considering the printing quality and the level of difficulty of the building process. This technology is the FDM, i.e. the 3D extrusion. Thereafter, the next main concern was the structure of the 3D printer, more specifically: what structure we want to conform to.
Fig.Conceptual sketch of FDM
2. Constructional selection [1]
The most important premise is the mobility, in order to ensure a simple and fast usage of the 3D printer. Because of the mobility, it is essential to have a massive frame to prevent the printer for any kind of damage during the transportation. It was intented to make the printer out of simple parts to facilitate easy assembly and fast maintenance. Furthermore, it was an expection to make the printer compatible with electronic parts, such as standardized limit switches and to be able to print PLA and ABS.
The selected construction from the founded printers was the FELIX 2.0. This printer satisfied our premises the most. We introduce the building of this printer in the following phase.
Before we started building the printer itself, we made a sketch of which parts should be bought and which parts could be manufactured by us. Thanks to the manufacturer, building kits were available, so the project could be more cost-efficient, than we had bought the complete printer. By using the above mentioned, 3D printed parts and the own made ones, we created the FDM printer based on the construction of Felix Ltd., which is shown on Figure 2.
Fig.2 The built FDM 3D printer
We wanted to make the 3D printer in a virtual version. The purpose of this was to measure the parameters of the printer in a 3D model form, while simulating digital manufacturing. Since we bought the printed parts from the official dealer, their documentations were missing.
If there would be accurate models of every part, those could be used for manufacturing spare parts or even a second 3D printer. In order to implement this, we had to use Reverse Engineering, which helped us to get the original documentation and dimensions. The essence of the manner is detailed in the next phase.
3. Reverse Engineering [1], [2], [5]
Reverse Engineering is an engineering labour process, where we define the CAD geometry of a physically existing object with 3D digitalization. Reverse Engineering uses the end product to start off. Its purpose is reconstruction.
Reverse Engineering is applied in the following cases:
l If the new design is based on an existing part,
l Hand-made master pattern,
l ?Outdated” plans (no computer data, CAD drawing),
l Part, tool reproduction,
l Rapid prototype making.
We could not have measure workpieces – with complicated geometries – with conventional measuring tools, since the caliper is not able to define complex geometries. In our case, the parts were only physical and the virtual documentations were missing. In order to make these parts re-manufacturable, we had to apply Reverse Engineering.
Steps of Reverse Engineering:
1. Scanning,
2. Making a point cloud,
3. Coating, surface fitting,
4. Inspection, correction,
5. Manufacturing
3.1. Scanning
Initially, we had to perform spatial scanning, alias 3D digitalization. The result of the scanning process was a point cloud, placed into a coordinate system. The CCD camera process was given for us, which is a non-contact technology. We did the measurement with a Steinbichler Optotechnik VarioZoom 200-400 3D scanner. With this manner, we were able to reproduce the virtual documentations of the existing parts. The technology is shown on the extrusion head holder unit (Figure 3.), but the other printed geometries are also made by the same manner.
Fig.3 Extrusion head holder unit
The projector of the scanning device – capable for accurate surface scanning – projects black and white, parallel light strips onto the surface of the object, which are deformed there. The scanner’s CCD camera initializes the breakage of the reflected light strips. The computer evaluation system calculates the attitude of the lined-up strips and then makes a point cloud.
3.2. Preliminary processing of the point cloud after scanning
For the final version of the cloud, we needed 34 photographs (Figure 4.), which were combined together by finding their corresponding points. When the point cloud has been completed, it was necessary to remove the parts which did not connect to the object. (clamping elements, workbench, risers, etc.)
Fig.4 Matching the recordings: The first recording is on the left,while on the right we can see the assembly of the 34 pictures.
3.3. Final processing of the point cloud
The most commonly used manner of reproduction is the triangle – STL file format – coating, since it creates a simple and universal file format for every designing software. We approach the points of the point cloud with triangles (Figure 5.). The smaller the triangles, the more accurate the shape analysis.
Fig. 5. Approximation of the points with triangles
On the picture, we can see grey and blue surfaces at the same time. The grey surfaces give us an accurate picture of the surfaces of the part, while the blue ones refer to surface discontinuity. Here the scanning was unsuccessful, since the camera didn’t get a proper view into these areas.
3.4. The usage of RapidForm XOR for creating a model
The previously created model is not yet useable directly on CNC machining or 3D printing, since the triangles have not fit perfectly onto the point clouds during the coating process, which caused dimensional errors. The software of the scanning device analyzed these errors during the triangle-coating process according to Figure 6.
Fig.6 The amount of errors occured during the triangle coating process
We imported the .STL file – generated by the software of the scanner device – to Reverse Engineering software (specialized on these purposes). The name of the software is: RapidForm XOR. We picked the base planes of the model. It is necessary to recognize during the usage of the software, that which steps did the previous designer follow to create the entire model. Thereafter, we used the Mesh Sketch command, which provided us cross-sectional sketches of the surface. We round drawed these sketches with approximate lines, then the real mesh size of the sketch has become definable after dimensioning them.
We reconstructed the 3D CAD model with the help of the sketches (Figure 7.). We used the usual basic commands of a 3D modeling software, namely the Extrude and the Cut commands. By the result of these processes, we got the CAD model, which dimensions’ are changeable and measurable on every surface
Fig. 7. CAD model of the extrusion head unit holder
3.5. Virtual prototype
After using the manner – presented in the 3.4. subsection – we had complete 3D models of every printed part. After this, we created the virtual construction of the printer in an assembly environment (Figure 8.) by using Autodesk Inventor. In this way, we were able to measure the parameters of the printer in 3D model format as well, and we also found it capable for a digital manufacturing simulation.
Fig.8 3D assembly of Felix 2.0
4. Constructional design of a parameterized workspace printing unit [1]
The biggest disadvantage of the built construction emerged from the dimension of the printing area. The area of the tempered, heated workbench is not isolated from the environment, so there is no chance of increasing the dimensions of the printing area, because of the increased heat loss.
Further problem was the transverse movement (Y) of the bench based on the below mentioned reasons:
l A bench, bigger than a certain size, and the movement of a printed object would overwhelm the stepper motor of the shaft.
l Further problem can be, that the overall dimension of a closed constructional frame would be increased in both directions by a formation like this.
By keeping this perspectives in mind, we started to design an own printing unit. Our goal was to create a structure, where the extrusion head unit does the X-Y movement at the same time. The way of printing without a supporter unit also highly restricted the feasible geometries, since the undercut surfaces collapsed after the printing process. That is why we wanted to make the designed printing unit out of two extrusion head units.
4.1. Design of the extrusion head unit
Important requirement is the running on linear bearings as well as the holding of the two extruders. The easy strain adjustment of the leading belt is an advantageous attribution as well as the adjustment of the grip during the retortion – done by the motor. The diameter of the string is 1,75 mm.
4.1.1. The retortion unit
We started the design with the retortion unit, because it was relevant to know what is the distance between the output shafts of the two motors, when placing them next to each other. The mesh size of the retortion unit is based on this dimension, where we took into consideration the dimensions of the output PTOs (?5), the standardized bearing dimensions (?8), and also the thickness of the string (?1,75). By placing the motor housing next to each other demanded the need of guide cylinders (?20,55) on each of the shafts. The mesh size is shown on Figure 9. These dimensions also directly affected the distance between the extruders. . Fig. 9. Mesh size structure
Fig.9 Mesh size structure
It is also relevant to ensure an easy removal of the string at the retortion unit. We managed to solve this by clenching the string with the guide cylinder and the bearings – both can be found at the end of the motor. In this way we ensure the holding. We designed the retortion unit according to these perpectives, which model is shown on Figure 10.
Fig.10 Model of the retortion unit
4.1.2. Structure of the extrusion head unit
Since the distance between the extruders’ axes has been defined during the evolving of the retortion unit, we started building the holder unit by using these dimensions. Important perspectives were:
l Minimalization of the dimensions,
l Placement of the linear bearings,
l Ensurance of the cooling for the protection of the elements connected to the heated units,
l The slight adjustment of the strain on the leading belt.
We kept in mind all requirements during the design of the extrusion head unit (Figure 11.). The head unit’s design ensures the accurate guidance, fast material flow as well as cooling.
Fig. 11. The extrusion head unit
We displaced the axes of the leading linear bearings in order to maintain an accurate guidance and the carrying capacity of the parts, so while it carries the weight of one motor, the other two prevent the transverse axial movement. We actualized the cooling in the following ways:
l We used standardized fans
l We separated the heated unit with porcelain sleeves
l We created heatsinks on the stem of the extrusion unit
l We created surfaces on the extrusion head holder unit for deflecting the air to the required place.
l We designed an air control surface onto the workbench for instant cooling of the freshly printed material.
Fig.12 Cooling around the heated area
4.2. Implementation of the X-Y movement with the new extrusion head unit
The biggest challenge of the construction was to maintain two-axis movement of the head unit. Our goal was to create a paremetrized workspace, which replaces the movement of the bench and with a few modifications of certain values, it is possible to make an adequate printing area according to the desired demands. We achieved this by replacing the linear elements with beam (grinded) guided linear bearings on the X axis as well. We designed an assembly of the model (Figure 13.) in Inventor 2016 Pro software, where the entire construction refreshes itself when we modify a dimension on it, so everyone can adjust the coverage of the printing area on their own preferences.
Fig. 13. The Assembly of the printing unit
The dimension driven parametrization works both on X and Y axes by changing the dimensions of the appropriate beam. The shafts are moved by separate electric motors on both sides along the X axis. The motors are connected in series. In this way the path that can be done is controlled by only one limit switch. (Figure 14.)
Fig.14 The Assembly of the printing unit
4.3. Belt tension
We had to introduce the belt drive – applied to the moving unit – which ensures an accurate positioning. It is essential to keep the belt in the adequate tension in order to maintain the accurate guidance. For this, it is indispens able to strain the belt in the easiest way. The designed method oversimplifies the maintenance as well as the calibration. Figure 15. also shows the essence of the system in 3D.
Fig. 15. Demonstration of the belt tensioning
5. Summary
We detailed the building process and the Reverse Engineering of a machine which operates with FDM technology. After the experiences, gained on the builded printer, we started to design an experimental printer unit, which correct the earlier’s deficiencies. The designed printing unit is a compact, user-friendly jog unit and a head-holder console. Our goal was to create a structure, where the extrusion head unit does the X-Y movement at the same time, and to be able to print support material. That is why we designed the printing unit with two extrusion head. In conclusion, we have designed a unit to be a great assembly of an existing or a whole new machine.
References
[1.] K. Kun, I. Miskolczi. A. Fodor. 3D nyomtató építése és fejlesztése. Gradus Vol 2, No 2 2015. p. 155-159.
[2.] J. Kodácsy, Zs. Pintér, P. Pokriva. Reverse Engineering módszerrel el?állított felületek min?sége. Kecskemét; 2003. p. 1-7.
[3.] J.G. Kovács. Gyors prototípus eljárások II. Gyakorlati megvalósítások. 2002. p. 103-107.
[4.] L. Morovic. Rapid technológie. Rapid Technologies. In Automation and CA Systems in Technology Planning and Manufacturings. Pozna? University of Technology, 2004, p. 177-183. ISBN 83-904877-8-0.
[5.] L. Morovic. A lézeres 3D szkennelés. Fiatal m?szakiak tudományos ülésszaka. Kolozsvár; 2005. 185-188. p. ISBN 973-8231-44
國際制造工程與材料會議，ICMEM 2016，
2016年6月6日至10日，Novy斯莫科維奇，斯洛伐克
基于FDM技術(shù)的3D打印機的重建與開發(fā)
Krisztian庫納
* a Kecskemét學院-機械工程和自動化學院-車輛技術(shù)系，10 Izsáki st.， Kecskemét 6000，匈牙利
摘要
在本研究中，我們詳細介紹了使用FDM技術(shù)的機器的結(jié)構(gòu)選擇。我們概述了打印機重建、技術(shù)文檔恢復(逆向工程)、校準和測量結(jié)果的里程碑。根據(jù)我們從建造設計中所學到的知識，我們開始設計我們自己的FDM打印機，這是一種緊湊的，用戶需求驅(qū)動的設備。
?2016作者。
關(guān)鍵詞:FDM;設計;3 d打印;RE-RP;重建;
1. FDM技術(shù)介紹
3D打印是累加的，這意味著它以一種疊加的方式創(chuàng)建所需的形式。這意味著，打印體是沒有預制的薄層。應用的材料通常是某種塑料。根據(jù)不同的圖層創(chuàng)建方式，3D打印技術(shù)有多種方法。
FDM(熔融沉積建模)3D打印技術(shù)(圖1)通過將材料分層放置在“添加”原理上工作;將一根塑料燈絲從線圈上松開來制造一個零件。這項技術(shù)是斯科特·克倫普(Scott Crump)在20世紀80年代末開發(fā)的。FDM技術(shù)需要處理STL文件(立體光刻文件格式)的軟件。在此之后，我們必須使用另一個程序?qū)?gòu)建過程中的模型進行分割。如果需要，可以生成支撐結(jié)構(gòu)。該模型是通過將熱塑性材料從噴嘴擠壓后硬化而形成層狀而制成的。塑料燈絲從線圈中解開，擠出噴嘴打開或關(guān)閉流量。有一個蝸桿驅(qū)動裝置以可控的速度將燈絲推入噴嘴。噴嘴被加熱以熔化材料。它可以在水平和垂直方向通過數(shù)控機構(gòu)移動。噴嘴由一個計算機輔助制造(CAM)軟件包控制，零件是自下而上的，一次一層。使用步進電機來移動擠出頭。該機構(gòu)采用X-Y-Z直線運動。
1.1. FDM技術(shù)的優(yōu)點與缺點
該技術(shù)的優(yōu)點-缺點FDM印刷技術(shù)非常靈活，可以處理下層的小懸垂。FDM通常有一些限制，并且不能在沒有支持材料的情況下產(chǎn)生底價。許多材料是可用的，如ABS和PLA等，在強度和溫度性能之間有不同的權(quán)衡。我們從3D打印方法中選擇了最具優(yōu)勢的技術(shù)，同時考慮了打印質(zhì)量和建筑過程的難度。這種技術(shù)就是FDM，即3D擠壓。此后，下一個主要問題是3D打印機的結(jié)構(gòu)，更具體地說:我們想遵循什么結(jié)構(gòu)。
圖1 FDM概念示意圖
2. 結(jié)構(gòu)選擇[1]
最重要的前提是移動性，以保證3D打印機的簡單快速使用。由于機動性，必須有一個巨大的框架，以防止打印機在運輸過程中受到任何形式的損壞。它的目的是使打印機由簡單的部件，方便組裝和快速維護。此外，這是一個期望，使打印機兼容電子部件，如標準化的限制開關(guān)，并能夠打印PLA和ABS。
從創(chuàng)建的打印機中選擇的構(gòu)造是FELIX 2.0。這臺打印機最符合我們的要求。我們將在下一個階段介紹如何構(gòu)建此打印機。
在我們開始制造打印機之前，我們先畫了一張草圖，說明哪些零件應該買，哪些零件可以自己制造。多虧了制造商，建造工具是可用的，所以這個項目可能比我們買完整的打印機更劃算。我們使用了上述的3D打印部件和自己制作的部件，在Felix Ltd.的基礎(chǔ)上創(chuàng)建了FDM打印機，如圖2所示。
圖2 FDM 3D打印機
我們想在虛擬版本中制作3D打印機。其目的是在模擬數(shù)字化制造的同時，以3D模型的形式測量打印機的參數(shù)。因為我們從官方經(jīng)銷商那里買了印刷零件，他們的文件就不見了。
如果每個零件都有精確的模型，這些模型就可以用來制造零部件，甚至可以用來制造第二臺3D打印機。為了實現(xiàn)這一點，我們必須使用逆向工程，這幫助我們獲得原始文檔和尺寸。方式的本質(zhì)將在下一階段詳細說明。
3. 逆向工程[1][2][5]
逆向工程是一種工程勞動過程，我們通過三維數(shù)字化來定義一個物理存在對象的CAD幾何形狀。逆向工程以最終產(chǎn)品為起點，其目的是重建。
逆向工程主要應用于以下幾種情況:
l l如果新的設計是基于現(xiàn)有的部分，
l l手工制作主圖案，
l l“過時”的計劃(沒有計算機數(shù)據(jù)，CAD繪圖)，
l l零件，工具復制，
l l快速原型制作。
我們不能用傳統(tǒng)的測量工具測量復雜幾何形狀的工件，因為卡尺不能定義復雜的幾何形狀。在我們的例子中，這些部件只是物理的，而虛擬的文檔卻丟失了。為了使這些部件可再制造，我們必須應用逆向工程。
逆向工程步驟:
1. 掃描
2. 做點云
3. 涂料、表面擬合
4. 檢查、調(diào)整
5. 制造業(yè)
3.1掃描
首先，我們需要進行空間掃描，別名三維數(shù)字化。掃描過程的結(jié)果是一個點云，放置到一個坐標系統(tǒng)。給出了一種非接觸式CCD攝像工藝。我們使用Steinbichler Optotechnik VarioZoom 200-400 3D掃描儀進行測量。通過這種方式，我們能夠復制現(xiàn)有部分的虛擬文檔。該技術(shù)顯示在擠出頭支架單元上(圖3)，但其他打印幾何圖形也以同樣的方式制作。
圖3 擠壓頭固定裝置
掃描設備的投影儀——能夠進行精確的表面掃描——將黑白平行的光條投射到物體的表面，而物體的表面是變形的。掃描儀的CCD攝像機開始破壞反射光條。計算機評估系統(tǒng)計算出條形線的姿態(tài)，然后做出點云。
3.2掃描后點云的初步處理
對于云的最終版本，我們需要34張照片(圖4)，通過找到它們對應的點將它們組合在一起。當點云已經(jīng)完成，有必要刪除那些沒有連接到對象的部分。(卡緊元件、工作臺、隔水管等)
圖4 匹配:第一張在左邊，而在右邊我們可以看到34張圖片的組合。
3.3最后處理點云
最常用的復制方式是三角- STL文件格式-涂層，因為它為每個設計軟件創(chuàng)建了一個簡單而通用的文件格式。我們使用三角形來接近點云的點(圖5)。三角形越小，形狀分析越準確。
圖5 用三角形逼近這些點
在這幅畫上，我們可以同時看到灰色和藍色的表面?；疑谋砻娼o了我們一個準確的零件表面的圖像，而藍色的表面是指表面的不連續(xù)。這里的掃描是不成功的，因為相機沒有得到一個適當?shù)囊曇斑M入這些區(qū)域
3.4使用RapidForm XOR創(chuàng)建模型
之前創(chuàng)建的模型還不能直接用于數(shù)控加工或3D打印，因為在涂層過程中，三角形并沒有完全貼合到點云上，導致了尺寸誤差。掃描裝置的軟件根據(jù)圖6分析了三角涂層過程中的這些誤差。
圖6 三角涂層過程中出現(xiàn)的誤差量
我們導入了. stl文件-由掃描設備的軟件生成-反向工程軟件(專門針對這些目的)。軟件名稱為:RapidF
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