Universidad de Los Andes
UNDERGRADUATE THESIS
Submitted in partial fulfillment ofthe requirements for the award of the degree of
BACHELOR IN MECHANICAL ENGINEERING
Submitted by
JOHN JAIRO GOMEZ SANCHEZ
201314101
TUBE BENDING IMPROVEMENT FOR BOGBIBICYCLES USING JD-32 MANUAL BENDING
MACHINE
Director
EDGAR ALEJANDRO MARANON LEON, Ph.D.
Department of Mechanical EngineeringFaculty of Engineering
Bogota, Colombia
June 2018
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Abstract
In this work a 304 stainless steel tube bending was studied for 1.5in outer diameterwith the desire to improve the results providing a more standard and uniform bendingfor the JD-32 manual bending machine which belongs to a Colombian-Norway companycalled, Bogbi. In this process, a research was done focused on the cause and preventionof the damage to which the tubes were exposed. Afterwards, a design was establishedand manufactured making the proper corrections of the problem presented on the bentarea. This improvement was made on the bending clamp of the bending machine wheretheoretical geometry criteria was applied. Finally, the new clamp was assembled andtested. The results found a better bending with no deformation on the bend area anda softer transition between the clamping area and on the bent area, and at the sametime the new tube got less diameter reduction.
Resumen
En este trabajo se estudio el doblaje de un tubo de acero inoxidable 304 para un tubocon diametro de 1.5 pulgadas, con el deseo de mejorar los resultados generando undoblaje uniforme y estandar para la maquina de doblar tubos manualmente JD-32 lacual pertenece a la empresa Colombo-Noruega llamada Bogbi. Durante este proceso,una investigacion fue hecha enfocada en las causas y la prevencion del dao surgido enlos tubos. Posteriormente, se establecio un diseo y se manufacturo teniendo en consi-deracion las correcciones adecuadas para solucionar el problema surgido en el area dedoblaje. Esta mejora fue realizada en el sujetador de tubos de la maquina de doblaje,en donde criterios teoricos de la geometrıa fueron aplicados. Finalmente, el nuevo suje-tador fue ensamblado y probado. Los resultados obtenidos mostraron un mejor doblajesin deformaciones y suavidad en la transicin del area de sujecion y de doblaje, y almismo tiempo en el tubo se genero una reduccin menor del dimetro.
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Acknowledgments
In first place I would like to thank my advisor Professor Edgar Alejandro Maranon,due to his commitment, patience, and his advising on my thesis using all his knowledge.
In the second hand, I will give my fully thanks to my family: My mom, Martha LilianaSnchez, my sister, Liliana Gomez and my grandma, Maria Eva Sanchez,who gave meall their support all these years and always believed in my capabilitiess and knowledge.
At the same time, I am very thankful to Bogbi company for letting me use their cargobicycles, tools, equipment, staff and facilities. Therefore, I would like to thank EduardoMoreno, Sigurd Kihl, Johannes Hedgahl, David Duarte and Robinson Heredia, whogave me all their support in the development of my thesis.
Also, out of the staff of the laboratories at the the university, I would like to express mythanks to Andres Salgado, Carolina Coy and Ramiro Beltran. Furthermore, my sinceregratitude to Julio Hernandez, who gave me access to the laboratories and his advice inthe develop of my design.
Thank you.
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Indice general
Abstract II
Acknowledgements IV
1. Introduction 21.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.2. Problem Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.3. Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3.1. Sub-objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Background 42.1. Processes and techniques . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1.1. Compression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42.1.2. Die less: U-bend . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.1.3. Draw Bending: JD-32 . . . . . . . . . . . . . . . . . . . . . . . . 52.1.4. Murata Ohashi Suzuki . . . . . . . . . . . . . . . . . . . . . . . 62.1.5. Ram and press bending . . . . . . . . . . . . . . . . . . . . . . . 62.1.6. Roll Bending . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2. Restrictions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.2.1. Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.2.2. Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.3. Improvement methods . . . . . . . . . . . . . . . . . . . . . . . . . . . 92.3.1. Problem appearance: Corrective solutions . . . . . . . . . . . . . 9
3. Methodology 103.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103.2. Actual bending . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103.3. Selection of corrective solution . . . . . . . . . . . . . . . . . . . . . . . 133.4. Work Done . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
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3.4.1. Creating a design . . . . . . . . . . . . . . . . . . . . . . . . . . 133.5. Design validation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.5.1. Criteria of failure . . . . . . . . . . . . . . . . . . . . . . . . . . 193.5.2. Selecting material . . . . . . . . . . . . . . . . . . . . . . . . . . 203.5.3. Selecting heat treatment . . . . . . . . . . . . . . . . . . . . . . 20
4. Results and Discussion 21
5. Conclusion 26
References 27
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Indice de figuras
2.1. Schematic illustration of compression bending method. . . . . . . . . . 42.2. Schematic illustration of die-less U-bend method. . . . . . . . . . . . . 52.3. Schematic illustration of drawing bending method. . . . . . . . . . . . . 52.4. Schematic illustration of Murata Ohashi Suzuki (MOS) bending method. 62.5. Schematic illustration ram and press bending. . . . . . . . . . . . . . . 62.6. Schematic illustration of roll bending method. . . . . . . . . . . . . . . 72.7. JD-32 manual bending machine in Bogbi facilities . . . . . . . . . . . . 82.8. JD-32 bending die set. . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.9. types of damage presented on rotary draw bending with the the specific
corrective solution for each case. . . . . . . . . . . . . . . . . . . . . . . 9
3.1. Soft Wrinkles throughout bend area. . . . . . . . . . . . . . . . . . . . 113.2. Hard Wrinkles throughout bend area. . . . . . . . . . . . . . . . . . . . 113.3. Scratches throughout bend area. . . . . . . . . . . . . . . . . . . . . . . 123.4. Scratches inside bend area. . . . . . . . . . . . . . . . . . . . . . . . . . 123.5. Original clamp of the JD-32. . . . . . . . . . . . . . . . . . . . . . . . . 143.6. Original clamp of the JD-32. . . . . . . . . . . . . . . . . . . . . . . . . 143.7. New Design for clamp on the Jd-32 composed by 2 parts. . . . . . . . . 153.8. Top part of new clamp. . . . . . . . . . . . . . . . . . . . . . . . . . . . 153.9. Bottom part of the new clamp . . . . . . . . . . . . . . . . . . . . . . . 163.10. Bottom part of the new clamp attached to the bending die . . . . . . . 163.11. Pin-Cam mechanism on clamp for the JD-32 clamp. . . . . . . . . . . . 173.12. Destaco 323 pull action latch clamp for the JD-32 clamp . . . . . . . . 173.13. Complete assembly with the clamp and the pull action latch clamps . 183.14. Tube Bending simulation on Ansys®Workbrench. . . . . . . . . . . . . 183.15. Von Mises stress shown on the clamp. . . . . . . . . . . . . . . . . . . . 193.16. Von Misses stress shown on the only on one part. . . . . . . . . . . . . 19
4.1. Components of the clamping mechanism. . . . . . . . . . . . . . . . . . 21
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4.2. Clamping mechanism assembly. . . . . . . . . . . . . . . . . . . . . . . 224.3. Clamping mechanism assembled with the JD-32 bending machine. . . . 224.4. Clamping mechanism assemble with the JD-32 bending machine. . . . . 234.5. Tube sample bent with the new clamp. . . . . . . . . . . . . . . . . . . 234.6. Tube geometry reference system. . . . . . . . . . . . . . . . . . . . . . 244.7. Measurements of tube diameters. . . . . . . . . . . . . . . . . . . . . . 244.8. Measurements of tube thickness. . . . . . . . . . . . . . . . . . . . . . . 244.9. Measurements of tube diameters percentage. . . . . . . . . . . . . . . . 254.10. Measurements of tube thickness percentage. . . . . . . . . . . . . . . . 25
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Capıtulo 1
Introduction
1.1. Motivation
Bogbi is a Colombian company founded by Eduardo Moreno and Sigurd Kihlin 2016. Both are parents and have their kids in a kindergarten school, therefore, theywanted to develop a cargo bike in order to take and pick up their kids. As there is noindustry in Bogota, Colombia, that designs that type of bikes, they started togethera co-working with a Norwegian industrial designer, Colombian engineers and Norwe-gian investors. So, the main goals of Bogbi were: Contribute to the development ofsustainable and greener cities all over the world, create collaborations and synergiesbetween Nordic industrial designers and Colombian counterparts while promoting anew impression of Colombia around the world.
In order to satisfy their goals, Bogbi produced and manufactured their cargo bikes inBogota, where they had acquired machines and tool for the manufacturing process.One of the machines they had, was the JD-32 from JD SQUARED INC., which is amanual tube bending machine that has an easy operation, a die locking mechanism anda degree pointer to produce high accuracy in the bending. In order to use the JD-32model in their factory they had to customize that model with a static structure madeby themselves, that helped in the bending process.
In the procedure of design, they took into account the fact that their bikes would notbe only for Bogota market, it would be worldwide, therefore, they chose a stainlesssteel for the bike frame that would be able to be in places where corrosion leads in theenvironment. However, using stainless steel made harder the process of bending dueto the mechanical properties these materials have. It started to appear some undesired
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deformation that gave a bad appearance to the bikes. Nevertheless, they affronted thatchallenge, but by doing research in the world industry, they found a company in Chicago,Illinois, where they could get the tubes bent correctly for a higher price. Although, somequestions showed up during research, such as: Is it possible to improve the bending ofthe tube with the machine that is in Bogbi facilities? What involves not producing thebending in Bogota in terms, of resources, such as time and costs?
This project will try to develop a solution to get rid of the undesired deformation solvingthe questions above and giving a silver lining in the subsistence of Bogbi goals.
1.2. Problem Definition
Using a manual bending machine to bend stainless steel without the additionof other processes to get a correct bending for the Bogbi cargo bike frame.
1.3. Objectives
This project targets to improve the tube bending of a 304 stainless steel forthe Bogbi cargo bike frame by solving the undesired deformation applying the correctiveadjustment in the process for the type of problem in the bending.
1.3.1. Sub-objectives
Find the corrective adjustment for the type of damage presented in the stainlesssteel tubes.
Design an improvement in the JD-32 machine in terms of process and componentsof it.
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Capıtulo 2
Background
2.1. Processes and techniques
2.1.1. Compression
Figura 2.1: Schematic illustration of compression bending method.
The tube in this method is bent around a die using a movable wiper shoe, which worksas a compressive force that enlongs the tube. This is a common method, usually byhand and for heavier wall thickness. Since there is little stretching of the outer surface,plated and painted tubing can be bent with this method and on the other side, 4 timesthe tubing diameter is the normal minimum centerline radius for compression bends.Figure 2.1 shows a schematic illustration of compression bending method.
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2.1.2. Die less: U-bend
Figura 2.2: Schematic illustration of die-less U-bend method.
A straight tube is held by a clamp and feeding rolls at the beginning of bending. Then,the arm in which the tube is attached starts rotating and at the same time, the rollersrotate synchronously with the arm in order to create the bent. This method is used intubes with big curvatures. Figure 2.2 shows a schematic illustration of die-less U-bendmethod.
2.1.3. Draw Bending: JD-32
Figura 2.3: Schematic illustration of drawing bending method.
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In this method, the tube is clamped against a pressure die which is still and the clampis fixed to the bending die which rotates and sticks the tube to it and in that waygenerates the bending. This method is the one used by Bogbi. Figure 2.3 shows aschematic illustration of drawing bending method.
2.1.4. Murata Ohashi Suzuki
Figura 2.4: Schematic illustration of Murata Ohashi Suzuki (MOS) bending method.
This is an innovative technological method, which is called MOS for its abbrevation,does not use bending dies. It works by pushing the tube through a guide cylinder andwhat gives the curvature is the die inside the spherical bearing which can be controlled.Figure 2.4 shows a schematic illustration of Murata Ohashi Suzuki (MOS) bendingmethod.
2.1.5. Ram and press bending
Figura 2.5: Schematic illustration ram and press bending.
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The ram and press bending method work using 2 supports and a roundedform die, which push the tube against it. The two supports pivot maintaining supportof the tube. It is not accurate due to the lack of control of tube flow and is used on heavytubing which permits distortion on section. Three times the diameter is the minimumcenterline bending radius for ram bending and 4 to 6 times the preferred radius. Figure2.5 shows a schematic illustration ram and press bending.
2.1.6. Roll Bending
Figura 2.6: Schematic illustration of roll bending method.
This is a method that employs grooved rollers arranged in a way in which adetermined curvature is produced after the bending, it can do the process continuously,butthe only limitations is that it is just used on a heavy walled surface. Figure 2.6shows a schematic illustration of roll bending method.
2.2. Restrictions
2.2.1. Methods
In order to understand what could be done to try to solve the damage onethe tubes, Bogbi staff named some methods in which they were not interested to workwith:
As a very common technique, sand was discarded by Bogbi as a solution in viewof the mess produced by that element and the lack of experience using it.
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Another fact to be taken into account was that the improvement had to be on away in which grease was used in less amount or non at all.
2.2.2. Geometry
For instance, In the case of the geometry it has a big importance on anychange on the process because it rules the bending process, for instance, the gap insidethe mechanism of bending limits the size range. As it is shown in the Figure 2.7, wherethe JD-32 machine owned by Bogbi can be appreciated and the set of the die is shownon Figure 2.8.
Figura 2.7: JD-32 manual bending machine in Bogbi facilities
Figura 2.8: JD-32 bending die set.
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2.3. Improvement methods
2.3.1. Problem appearance: Corrective solutions
Headed for fixing the main problem presented on the tube area, there is aspecification on the research of the most common problems that have appeared on tubebending. In this case, for instance there are 12 most common problems shown on 2.9with their respective correction on the process, technique and equipment usage.
Figura 2.9: types of damage presented on rotary draw bending with the the specificcorrective solution for each case.
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Capıtulo 3
Methodology
3.1. Introduction
In order to analyze what is happening on the bending that Bogbi had made,I took some samples in which could be appreciated the deformation throughout thetube bending area. After that, I established the direct relation between the procedureor technique and what could be helpful according the type of damage. Subsequently,the main focus on the project got to rid of the cause generator of the issue presentedon the tube.
3.2. Actual bending
First of all, to face the problem involved on the project, I started to take adocumentation of the process of bending the tubes. As I had said before, the resultsof the tubes were no satisfactory. For instance, on figure 3.1 it can be observed smallswrinkles on the bending area and a significant reduction on the tube diameter, it issomething that should have happened due to the displacement of material, but thedesirable transition should have have been in a softer form.
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Figura 3.1: Soft Wrinkles throughout bend area.
On the other hand, I took another specimen figure 3.2, in which the type of wrinklewas presented in a higher way than the one shown on the last figure. In contrast to thesofter wrinkles, these can be felt and also another fact was that when the bending wason the process, sounds on the rotation of die could be heard in a high level.
Figura 3.2: Hard Wrinkles throughout bend area.
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At the same time, it was possible to observe some scratches on the surface at 90 degreefrom the contact area of the die and the tube. Not only did it appear on the outsidesurface, it also showed up in a significant proportion on the inner side, this can be seenon Figures 3.3 and 3.4 .
Figura 3.3: Scratches throughout bend area.
Figura 3.4: Scratches inside bend area.
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3.3. Selection of corrective solution
As a result of the detailing of the failure on the bending area, the performance of thedamage gets me to established the problem 12 on the Figure2.9, where wrinkles arepresented and some linear scratches in grip area indicating clamp slippage. Hence, thecorrections that this problem should have are shown hereafter [8]:
Pressure reduction in die force.
Check location of mandrel and wiper die.
Increase pressure on clamp die.
Use serrated or carbide spray in tube groove of clamp die. Therefore, in this caseI focused on increasing pressure on clamp die
3.4. Work Done
3.4.1. Creating a design
Observing the original clamp on the figure 3.5, it doesn’t approve the restrictions inwhich the minimum tube length of contact has to be 3 times the outer diameter ofthe tube[6]. Therefore, in order to reduce and make the pertinent correction of theimprovement of the bending, I proposed a design in which the new part would beassembled with the die of the JD-32 bending machine, that would be rough enough andwon’t slip on the tube, as the one original does. For example, in the figure 3.5 Bogbistaff had to place some marks in order to notice if there is a big displacement, due tothe fact that small displacements can’t be seen by the eye. Also, they had to drill ahole in the tube for placing a circular plate that could hold the other side of the tube,as it’s shown on figure 3.6.
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Figura 3.5: Original clamp of the JD-32.
Figura 3.6: Original clamp of the JD-32.
First of all, using the restrictions found on the literature, also using the machine workspace as a limitation of size. I started a design mated with the bending die at the
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position of the clamp, in that way It could substitute the original clamp and would beable to hold in a better way the stainless steel tube. Bearing this in mind, I designedit in AutoDesk Inventor ®, it that can be observed on Figure 3.7, where for an easierunderstanding of the components of the new clamp, the parts are with different colourson the CAD, blue for the part that will be on the top and green for the one on thebottom. Each part by itself is shown on Figure 3.8 and Figure 3.9 respectively.
Figura 3.7: New Design for clamp on the Jd-32 composed by 2 parts.
Figura 3.8: Top part of new clamp.
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Figura 3.9: Bottom part of the new clamp
In addition, for a clearer observation of the type of mated of the assembly, on figure3.10 it is possible to take a look on how the clamp is attached to the bending die.
Figura 3.10: Bottom part of the new clamp attached to the bending die
At the same, the clamp needed to hold the tube very tight, so a clamp mechanism had
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to be applied. This mechanism was divided into 2 parts. The first one was a replacementof an alignment pin, in which the die and the clamp were joined. This mechanism hadthe advantage to work as an fast clamp mechanism that could be adjusted by a bolt anda cam system as is shown on figure 3.11. The second one is a pull action latch clampthat will help to maintain the pressure on the opposite site of the clamp distributingthe pressure that wield the bending process on the clamp, on figure 3.12 is displayed.
Figura 3.11: Pin-Cam mechanism on clamp for the JD-32 clamp.
Figura 3.12: Destaco 323 pull action latch clamp for the JD-32 clamp
As a final result, the new clamp mechanism is shown on Figure 3.13 where the tubeclamp and the latch clamp is joined to the bending tube and the die as a completeassembly.
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Figura 3.13: Complete assembly with the clamp and the pull action latch clamps
3.5. Design validation
In first place, I recreated the scenario of the bending, where all the impor-tant components in the bending process were measured and drawn in a CAD format.Then, the assembly of the process was created. Afterwards, this assembly was conver-ted into a suitable format(.STP) in order to make a simulation of the bending usingAnsys®Workbrench. This simulation was done using each material of every componentand establishing the right restrictions until it got to final stage of bending, where thestainless tube was bent 90 degrees as is presented on Figure 3.14.
Figura 3.14: Tube Bending simulation on Ansys®Workbrench.
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After the bending simulation, it was used the Von Mises stress analysis that can beappreciated on Figure 3.15 for both parts of the clamp and on Figure 3.16 it is shownonly one of the part due to the fact both components should perform equally and for abetter looking of the area with higher stresses.
Figura 3.15: Von Mises stress shown on the clamp.
Figura 3.16: Von Misses stress shown on the only on one part.
3.5.1. Criteria of failure
First of all, the component design is going to be loading and unloading everytime, therefore, the failure in which the component will be prone is fatigue.
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Furthermore, as the component should be designed with infinite life, the maximumstress found on the clamp by the simulation was used a safety factor, S.F., in whichthis number should be at least 4, so that there could be a range far away from thefailure zone using the limit fatigue strength. This safety factor is shown on Equation3.1[7], where Se is the stress endurance of the material and σ max is the maximumstress shown on the simulation.
S.F. =Se
σmax
(3.1)
For this case, the maximum stress found during the simulation is 12.7 MPa and theSe of the 1020 steel is half of the ultimate tensile strength, so the value is 220 MPa[7].Therefore, using the Equation 3.1 the S.F. will be approximately 17, that represents avalue far away from of the failure zone.
3.5.2. Selecting material
After finishing the design, another decision had to be taken, in this case thematerial in which the clamp should be done. In the research done, I found that mostlyall the clamps die are made from low-carbon steel[6]. That is because this type of steelis ideal for parts in machines that are in contact with a harder material, that is usefulfor wear outs on the clamp and not on the tubes. Therefore, for solving this problem Ichose a 1020 steel for all the component.
3.5.3. Selecting heat treatment
In addition to choosing the right material, a heat treatment should be neces-sary in order to reduce the wear on the surface of the material and prolong the life cycleof the part. So, after doing a research of which heat treatment would adjust the beston the component, I get to decide that the tennifer will be the right one. It is mainly abath where a diffusive process of nitrogen and carbon, during this bath the material isstill in a ferritic phase, which was an advantage[10]. In overall, this process makes thecomponent with a better surface against the wear, it improves fatigue properties andincrease corrosion resistance.
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Capıtulo 4
Results and Discussion
As a final stage on the project, the manufacture of the plate clamp and the pinmechanism was done and afterwards, a verification process was set, where the completemechanism was assembled and tested. The result are shown on the figure 4.1 where allthe parts of the clamping mechanism can be observed.
Figura 4.1: Components of the clamping mechanism.
At the same time, on figure 4.2 all the mechanism assembly itself can be seen.
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Figura 4.2: Clamping mechanism assembly.
On the other side, on figure 4.3 and on figure 4.4 the mechanism is assembled and readyto be tested bending stainless steel.
Figura 4.3: Clamping mechanism assembled with the JD-32 bending machine.
After setting up the assembly, the bending process was done. During it, the force requi-red by the operator felt less in comparison to the one sensed with the original clamp.At the end of the bending, the clamp was taken of and the tube was analyzed. On theobservation perceived figure 4.5, the tube had a bending with no deformation on thebending area, in addition to the transition between the bending area and the clamparea felt softer, it means that the sizes of the neck produced by every bending weresmaller with the new clamp.
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Figura 4.4: Clamping mechanism assemble with the JD-32 bending machine.
Figura 4.5: Tube sample bent with the new clamp.
In order for make a comparison between the previous results before the deploy of theclamp mechanism and afterwards, measurements of the diameters and thickness of thewalls on the inner side and the outer side of the tube was done. The results can be seenon figure 4.7 and on figure 4.8.
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Figura 4.6: Tube geometry reference system.
Figura 4.7: Measurements of tube diameters.
Figura 4.8: Measurements of tube thickness.
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In order to compare the change of size that the bending has on the tubesdiameter and thickness, all the data were plotted on a graph establishing the originalmeasures as a point of reference, for the diameter can be appreciated on figure 4.9 andfor the thickness on figure 4.10.
Figura 4.9: Measurements of tube diameters percentage.
Figura 4.10: Measurements of tube thickness percentage.
On the results achieved, the rate of change is proportional for each case and the worstdata was from the wrinkles tube. The final bending with the clamp mechanism gaineda lower difference of the nominal diameter, which represents a better result in terms ofthe geometry and the previous bending made.
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Capıtulo 5
Conclusion
The new clamp improved the appearance of the bending area, getting rid of thewrinkles and the scratches, producing a tube without these deformations.
In terms of bending process, the stage of drilling a hole and adding material wasdefeated, therefore, the new clamp mechanism helped taking out these operationsand letting the operator use the time he wasted on it to accelerate the production.
The dimensions of the tube after the bending improve getting just a difference of25 % in comparison to the tubes with wrinkles and scratches that have 50 % and75 % respectively. At the same time the thickness got a similar trend.
The operator expressed that the force he had to use in order to use the machinewas less with the new clamp. Therefore, as the force wasn’t measured, followingthe research done previously, as the pressure on the die increase with the design ofthe new clamp, the force required should be less when the bending was made[8].
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References
[1] Bogbi, www.bogbi.co/about/
[2] JD Squared INC., www.jd2.com/model-32-bender
[3] James G.Bralla. Design for Manufacturability Handbook,Second edition. TheMcGraw-Hill Companies Inc. Boston,Massachusetts, 1999.
[4] Uday S. Dixit, R. Ganesh Narayanan. Metal Forming Technology and Process Mo-delling. McGraw-Hill Education Private Limited. New York, 2013.
[5] Taylan Altan, A. Erman Tekkaya. Sheet Metal Forming: Processes and Applica-tions. ASM International. Materials Park, Ohio, 2012.
[6] Gregory Miller. Tube Forming Processes: A Comprehensive Guide . Society of Ma-nufacturing Engineers. Dearborn,Michigan, 2003.
[7] Nombres. Shigley’s Mechanical Engineering Design, Nine Edition. McGraw-Hill,New York, 2008.
[8] Hwaiyu Geng. Manufacturing Engineering Handbook. McGraw-Hill, New York,2004.
[9] Muammer Ko. Hydroforming for Advanced Manufacturing. Editorial. Cambridge,UK: Woodhead, 2008.
[10] John Schey. Procesos de Manufactura. Tercera edicion. McGraw-Hill, Mexico, 2002.
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