Additional opening hours for students

In addition to our opening hours for the Open Lab every Wednesdayfrom 2 p.m. to 8 p.m., this summer term we also have times when the Lab is openspecifically for students.
As of now, students can also work in the Fab Lab on Tuesdays and Thursdaysduring the following times:

Tuesdays from 1 – 4 pm

Thursdays from 14 – 17

These extended opening hours are directed towardsstudents of the University of Siegen in order to offer additional times to work on their projects. Individuals not affiliated with the university are welcome to come to the Open Lab on Wednesdays as usual.

The same recommendationsapply here as for the Open Lab:

  • no more than 20 guests in the lab
  • 3G recommended (genesen, geimpft, getestet = recovered, vaccinated, tested)
  • the mask is kindly requested to be worn at all times
    (Exception: drinking and eating in certain areas).
first Open Lab held in April on the 6th of April 2022

Reopening of the Fab Lab

Finally, we are back with good news! The Fab Lab will re-open at the beginning of the summer semester. We are thus happy to announce the date for the next Open Lab:Wednesday, April 06.

However, given the still very high number of corona cases, we have a few recommendations for visitors to the Lab:

Within the Lab we recommend to maintain the3G rule(genesen, geimpft, getestet = recovered, vaccinated, tested). Furthermore, it is recommended to wear a mask at all times. Of course, the mask may be removed for drinking, but we would kindly ask you to put it back on immediately afterwards. For this reason, open drinks (e.g. coffee/tea cups) are currently viewed with caution, as experience has shown that these lead to “Kaffeeklatsch” 😉
Instead of eating right at your workplace, we would like to ask you to consume your foodat the open (!) windows in the lobby at Startpunkt to ensure the safety of everyone staying here.

The number of visitors in the Fab Lab is limited to a maximum of 20 guests.

In summary:

  • maximum 20 guests in the lab
  • 3G recommended (genesen, geimpft, getestet = recovered, vaccinated, tested)
  • wearing the mask all the time is kindly requested
    (Exception: drinking and eating in certain areas).
first Open Lab held in April on the 6th of April 2022
View into the Fab Lab

Open Lab temporarily closed

Given the current incidences, we have decided to keep the Fab Lab closed until further notice for the safety of all of us.

Aconcrete date for reopening cannot be set at the moment. As soon as the pandemic situation allows us to safely open the lab again, we will announce this here on the website, via email and social media.

In urgent cases, e.g. for work on a thesis or other projects, please contact us and we will find a solution.

In the view of the anticipated course of the pandemic in the coming weeks, the University of Siegen has adjusted its measures. All buildings of the university will therefore remain closed to the public up to and including 06.02.2022. At this point it is not yet clear what will happen after that.

Regarding the Fab Lab, this means that there will be no Open Lab until at least the 06th of February. Contrary to our previous statement, there will therefore not be an Open Lab on Wednesday, January 19.
We hope that we can see you again on 09.02., but we can’t yet promise this.

Take care of yourselves.

Extension of rotary draw bending to a partially kinematic process with reduced tool surfaces

“If you know plastic, take steel!”

A well-known saying in our steel-dominated region. But how much steel does a production tool really need? This is the question we at the Chair of Forming Technology (UTS) asked ourselves in the DFG project “Extension of Rotat ion Tension Bending to a Partially Kinematic Process with Reduced Tool Surfaces.

Processes and tools

Pipe bends are manufactured in everyday industrial production by means of rotary draw bending. In rotary draw bending, the profile is bent around an internal bending shape. To ensure that the moment required for bending can be applied, the profile is guided through the counterholder on one side. The other end of the profile is clamped to the pivoted bending mold with the clamping jaw.

Schematic representation of the rotational tension bending process (left). Process video (right)

The task in the DFG project was to geometrically resolve and simplify the existing shape-bound tool elements of rotary draw bending.

This enables:

  • Increased flexibility of the forming process
  • economical production of smaller lot sizes
  • individualized products

An area reduction method was used to derive angled contact surfaces instead of the previous fully enclosing tools.

For direct comparison with the conventional design, these novel tools were initially made of tool steel. For direct comparison with the conventional design, these novel tools were initially made of tool steel. Pipes made of stainless steel and brass were examined. The wall thickness was 1 mm and 2 mm.

Deliverables

Compared to conventional tools, the deformation of the tubes is more pronounced and increases with decreasing wall thickness.

Deformation comparison after 90 ° bending: Difference conventional to simplified tools (a). Deviation scan of the manufactured pipe bends (b).

All specimens have a crease on the inner curve in front of the jaw. This can be attributed to the lack of support in the bending mold base, which was also shown in the simulations in a weakened form and represents an acceptable extent of the tolerance feature for the quality.

Can it be one layer more?

Following the positive project results with the reduced tooling, we thought, “If you know plastic, you’ll use plastic!”

So all tool parts were also additively manufactured from polylactide (PLA) at Fab Lab Siegen on 3D printers. The project’s flexibility to bend with reduced tooling surfaces is further enhanced by the additive tooling approach, which allows simplified tooling inserts to be printed on-demand from lower-cost plastic.

From the point of view of the profile, a better / smoother surface is achieved. The wrinkle expression is also in the same order of magnitude. But who wants to have wrinkles? A look at the trowel lying in the inner arch showed that it could not withstand the high load.

Reduced-area tool set made of PLA for rotational tension bending of metal tubes (top)
Deformation comparison: difference between conventional and PLA tools (bottom).

In an adaptation of the tool concept, it was finally possible to bend a tube of comparable quality to that produced with the conventional tools.

The question remains how much profile can be bent with a PLA tool. If you want to answer this, come to us.

Here again a big thank you to the team of Fab Lab Siegen for the support.

Corona

Because there were some questions we would like to clarify under which conditions you can come to the Lab.

We would like to share with you some more detailed info about how to access the Fab Lab. The 3G rule applies, which means whoever is fully vaccinated, recovered or tested negative may visit the lab. However, not all tests are the same. Valid are official PCR tests with a QR code as well as rapid tests from the approved sites (not self-performed tests). University students and employees, for example, can take advantage of the university’s offer of free self-testing through Nov. 30. .
The current regulations for the Fab Lab can be found here.

The Fab Lab opens again – at Reichwald’s corner!

Finally the time has come, from Wednesday, October 13 we open once a week on Wednesdays from 2 to 8 pm. We are very excited to welcome you to the new Lab at Sandstraße 26, on Reichwald’s corner, and to work (and drink mate) with you again.

The 3G rule applies, which means whoever is vaccinated, recovered or tested negative may come by. However, seating is limited to a maximum of 20 people at any one time. Masks are mandatory throughout the Lab (except at the workplace) and safety distance. Use of the Fab Lab is still free, but as always, everyone brings their own consumables.

It is also important that everyone, including those who have worked in the lab before, must take a safety instruction. Therefore, we are offering additional safety instructions on October 13 at 2 p.m., 4 p.m. and 6 p.m.. After that, there will be regular safety instruction on Wednesdays only at 4 p.m.

As usual, you don’t need to register or pay anything for the visit or the safety briefings.

Tensile Test

If you’ve always wondered what a plastic component from a 3D printer can withstand, you’ve come to the right place. As part of the SmaP research project, we teamed up with the UTS Chair of Forming Technology and literally put our prints to the test (yes, well, maybe more like clamped).

The Attempt

The test we have carried out is the tensile test according to DIN EN ISO 527-1. This DIN standard contains the basic information about the exact execution of the tensile test for plastics.

The Sample

The specimen was dimensioned according to DIN EN ISO 527-2. This standard specifically defines the test conditions for molding and extrusion compounds. In our case, it is an extrusion compound, which is due to the manufacturing process (FDM 3D printers like the ones used extrude liquid plastic into an extrusion compound). Our specimen is a flat specimen of type 1A, this has a rectangular shape with so-called heads for clamping wedges. The width is 10 mm and a thickness of 5 mm.

Test Execution

3 different materials from 2 different printers were tested. 5 samples each were made. Samples of polylactide (PLA) and polyethylene terephthalate (PETG) were printed on one of our Prusa i3 MK3s printers. Furthermore, samples of onyx were produced on the Markforged MarkTwo. Onyx is a nylon with portions of carbon short fibers. For the test, a material sample in standardized form is inserted into a tensile testing machine. This machine stretches the specimen during the test until it breaks or elongation occurs without breakage (looks then like an elongated chewing gum). The specimen is stretched at a standardized speed (1 mm/min). The tensile testing machine continuously pulls the specimen apart during the test. The force that the specimen opposes this imposed strain is meanwhile recorded via the strain. The values in the evaluation can then be determined from the measured data. In the video below, you can see the experimental procedure and the tearing of a sample.

Results

The evaluation contains all essential information about the test and its boundary conditions, as well as a stress-strain diagram, the images of the specimens, and the data on material properties obtained from the test.

PLA

In the stress/strain diagrams of PLA, the range of elastic deformation can be seen in the range of about 0 – 1.8 %, which then stops abruptly when the tensile strength is reached, and changes to plastic deformation. From the area of plastic deformation, approximately between 1.8 and 2%, the quite pronounced part of the necking begins. The material still allows about 1.5% elongation until it finally breaks.

PETG

With PETG, the result cannot be reconstructed quite as nicely as with PLA. Sample PETG_P1, the upper outlier in the diagram, changes from the elastic to the plastic range at about 55 MPa, which then leads to necking at 60 MPa and ends in fracture of the sample at an elongation of 5.1%. The four other specimens behave similarly for the most part and also have only a small area of plastic deformation and pronounced area of necking. Compared to PLA, the elastic range of PETG is more pronounced.

Onyx

The onyx material also has a continuous transition from elastic to plastic deformation, although the region of elastic deformation is difficult to discern. Apparently, this ends at about between 8 and 10 MPa and then turns into a very pronounced part of plastic deformation, which subsequently leads to fracture with only slight necking.

Comparison

In this comparison, all evaluated specimens are summarized in a stress-strain diagram.

Here it can be seen that the specimens made of onyx (black) allow almost twice as much strain until fracture occurs, compared to the specimens made of PETG (red). Compared to the other two materials, the samples made of PLA allow even less elongation and are all already torn at an elongation of ε = 3.4 – 3.8 %. The comparison diagram also shows how much stress the materials can withstand, with PLA being the best performer except for the one outlier (PETG_P1). This is followed by PETG and in third place by the onyx material. Comparing all three materials with each other, it can be seen that PLA allows the least elongation in its elastic deformation range, but also quickly leads to breakage of the specimen after exceeding this range. Therefore, it can be said that PLA is certainly the material with the most brittle behavior. If you now want to realize one of your projects, you can follow these results to some extent, at least as far as tension and elongation are concerned, although the three materials naturally have other strengths and weaknesses.

Production of a prototype for a bending machine (Master thesis mechanical engineering)

As part of my master’s thesis at the Chair of Micro- and Nanoanalytics in cooperation with the Chair of Forming Technology at the University of Siegen, I developed and subsequently commissioned a bending machine for plastic forming in the scanning electron microscope.

The bending machine will be used to perform three-point bending tests to investigate the crack initiation of bent specimens in order to better utilize materials in bending forming. Forming processes are used in the manufacture of products in many areas of daily life: Cars, aircraft, ships, piping, sheet metal forming and many more.

For a detailed examination of the bending specimens during the bending test, I built the bending machine to fit the scanning electron microscope (SEM). Since there is little space available in a scanning electron microscope, the machine had to be relatively small and light – it fits on the palm of a hand. Initial bending tests in the SEM have already been carried out.

Rapid Prototyping

During the design phase, I used 3D printing as a rapid prototyping process. Compared to machining processes, this method has the advantage of fast production of parts based on CAD models. The first 1:1 scale prototype was designed and 3D printed during a planning and development project, also as part of my studies.

Especially at the beginning of the project, it was important to quickly get a good idea of the real dimensions of the components to be manufactured later. Thanks to the friendly support of the Fab Lab in the person of Fabian Vitt, the required components were printed quickly and without any problems. Thanks to the friendly support of the Fab Lab in the person of Fabian Vitt, the required components were printed quickly and without any problems. In this way, all those present can get a very good picture of the shape and details of the component that will later be manufactured through the 3D printouts. This is less possible with the otherwise often used printed construction drawings. 3D prototyping can lead to new fitting ideas and facilitate the identification of necessary optimizations.

A short animation video of the bending process:
https://lmn.mb.uni-siegen.de/in-situ-em/

Soviet hand drill repair

Pre Story

My father bought the thing at the flea market sometime. The price of 5 rubles (Ц. 5Р.) is incorporated in the handle, because at that time in the Soviet Union there was the planned economy and you could get a pack of butter for the same price in the big whole country.

Problem

The drill always did its job. It is particularly suitable for small jobs and you can dose the torque manually. Only at some point the drill got stuck somewhere and my father exerted too much momentum on the big bevel gear until a few plastic teeth sheared off, rendering the thing useless. The old bevel gear consisted of two parts: The front side with the teeth was made of a plastic casting and the back side was made of some kind of metal, which was somehow connected to the plastic (unfortunately no photo). So a new bevel gear was needed.

Solution

First, the teeth of the bevel gear had to be counted. There are 60 teeth. The driven bevel gear has 15 teeth, so there is a ratio of 1:4. In addition, all dimensions, such as the height of the teeth, their width and the bore diameter of the bevel gear had to be measured with a caliper gauge. The problem: the teeth are not simply arranged in a straight line, and their “focal point” is somewhere in the air. They are also wider at the outermost diameter than at the inner diameter of the bevel gear. So the geometry is a real challenge and you can’t just build the thing with a CAD program if you’re not a professional.
But what to do? Fortunately, I happened to come across a solidworks tutorial on the internet. It shows how to create configurable standard parts using the solidworks (SW) design library. And that worked well!

Procedure

Open Solidworks, open any assembly and throw out all the parts. Somehow it didn’t work out any other way for me. Then, on the right side of the screen, open the construction library and shimmy through the tree. Toolbox, ISO, power transmission, gears, degree bevel gear (driving).

Solidworks

For me, the ISO standard matched well with my Soviet part. Then the “Degree bevel gear (driving)” must be dragged and dropped into the assembly window. Now the “Configure component” dialog opens on the left. The module, the number of teeth, the pressure angle, etc. can be set. Here you have to experiment, have the bevel gear with the green check mark built again and again and measure it. (Tip: If you click on a component edge, the bottom info bar of SW conveniently shows the measured length directly).

SolidWorks-2

However, you cannot specify all dimensions and geometry properties in the configurator. And here’s where it gets a little tricky. If the tooth geometry of the blank created fits so far, the rest must now be added manually. I used the function “Attachment/Base rotated” to build a created sketch as a body of rotation to the blank (see screenshot). Again, I had to measure the old bevel gear over and over again.

SolidWorks-3

Once you are satisfied with the part, you need to export it to *.STL format for 3D printing. And off we go to the Fab Lab Siegen! Here Fabian helped me out, showed me the 3D printers and started the printing. Thanks a lot! 😊

Result

The first print was unsuccessful (of course). In 3D printing, for example, the holes are always slightly smaller compared to the model. The teeth were also too small, so that they could not engage deeply enough with the opposing teeth. These teeth also sheared off during initial attempts. In addition, the bracket for the crank was a bit too thin and is therefore broken off.

Gears printed

Drill machine open

But now it was possible to measure the printed bevel gear and improve the dimensions in SW and finally start a second attempt. However, the second time it went better than expected and the bevel gear installed beautifully. The hand drill runs very smoothly and if any problems should occur in a few years, I’ll just print out the bevel gear again 😉 .

Drill-machine-composed-1

Drill-machine-composed-2

A Child’s Book, or: Saving Plastic, Starting 3D Prints New

During the summer semester 2020, there was a printer in the Fab Lab that was constantly cancelled for testing. The printer with the name “Hades” had to serve as a test object for a children’s book. But what does a children’s book have to do with highly experimental, plastic-saving techniques? Let’s lunge a litte bit.

Earlier this summer semester, I decided to develop a children’s book for 3D printers. Together with my fellow student C. Ajiboye, this became a manual that tells a story on one side, one of Ursa, a girl exploring 3D printing through “Learning By Doing.” On the other side, there were explanations of how Ursa finds problems and what solutions it gives for each of them.
But the last page was special:

A WLAN-enabled (ESP32) microcontroller was embedded in this page. This one could feel touches via its touchpins. I then soldered these pins to copper surfaces and hid them under the page. One laser cut later, the copper surfaces could be seen shining through.

Thanks to these surfaces it was now possible to give commands to the ESP32. And thanks to the Octoprint servers, it was then possible to give commands to the printers. Yes, you read that right, this little book has a remote control for a 3D printer built in.

But What is the Point of All This?

Restarting a 3D print is not an easy task, so far there is not a single Octoprint plugin that dares to do this. The result is that when a print fails, which the sensors do not notice, a lot of time, sometimes days, and also up to kilos of plastic are lost. This book was intended to prevent that.

A book has many advantages: it’s quickly at hand, it’s often where you want it, and the software doesn’t change much. It is also lighter than a laptop and thus handier to use. What’s more, you don’t have to boot it up or preconfigure it. The interface is simply there.

But How do You Restart a Print With a Book Now?

A 3D print is stored in machine code. This “code” is written line by line and executed line by line afterwards. So a group of lines represents a layer, because a 3D print is done layer by layer. If a 3D print fails at one point, the commands could be executed again from this point. In the file, as well as in the real print, an exact height is defined for this. You could measure this height, but neither with the eye nor with a ruler you can find it exactly. With the 3D printer itself, on the other hand, you can find the exact height. Like calibrating old 3D prints, you can now use a piece of paper and the tip to determine to within 0.1mm where a print failed. So, with the book in your hand, you move the nozzle exactly over the pressure, lower it very slowly, and try to feel with a piece of paper placed in between when the nozzle touches the pressure.

The printer then knows exactly where this nozzle is located, if it is still referenced. Based on this height, the code is then split, the necessary initial steps are executed and then the printer prints again as if it had never stopped.

I Want This Too

After this semester I found the time to develop this project as a plugin for Octoprint. So you don’t need your own book and you can try it out in the web interface. But ATTENTION! This plugin is highly experimental and has also once caused damage to a 3D printer. I do not make any guarantees or take any responsibility for future damages and advise to always hover with your hand over the emergency switch until the first layer prints again and you are sure that the printer is working on the correct line.

Yours, Gerrit.