Tailored Placement of Fibres around Pores · 2015. 5. 14. · 3D surface a path created in Rhino and Grasshopper. The path reproduced a porosity gradient on the surface ... Sewing

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Tailored Placement of Fibres around PoresRobotic Fabrication Possibilities

Course Name: Computational Design and Digital FabricationCourse Number: 49780

Term/Year: Summer Term/2014Examination Number: 2918051

Tutors: Karola Dierichs, Marshall Prado, Tobias SchwinnInstitute: Institute for Computational Design

Eva Espuny

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Contents

Chapter 1: Introduction________________________________________Page 05

Chapter 2: Path Drawing______________________________________Page 09

Chapter 3: Robotic Fabrication Research_________________________Page 15

3.1: Fibre Winding_____________________________________Page 17

3.2: Stitching Pre-impregnate Fibres_______________________Page 19

3.3: Pinching of Unidirectional Pre-impregnate Fabrics_________Page 26

3.4: Robotic Application of Resin on Unidirectional Fabrics_____Page 28

3.5: Fibre placement between fingers______________________Page 30

Sources__________________________________________________Page 36

References_______________________________________________Page 37

4 5

Chapter 01

6 7CHAPTER 01 CHAPTER 01

INTRODUCTION

This research has been developed during the summer semester 2014 seminary Computational design and Digital Fabrication, as a part of the ITECH Master pro-gram of Stuttgart’s University.

Having the topic been chosen to give answer to the fab-rication aspects of my thesis preparation about inducing variable stiffness through porosity, this research focuss-es on the possible processes of laying fibres following curvilineal paths around a predetermined configuration of pores, conforming 3D surfaces, and using a Kuka ro-bot.

FIGURE 01: Lobster exoskeleton: chitin fiber arrangement around honeycomb structure of pores

8 9

Chapter 02

CHAPTER 02

x

Pore size increasement

Distance from external point to pore center on surface

10 11

FIGURE 03: A kinematic simulation of the robot task was performed using Grasshopper

CHAPTER 02 CHAPTER 02

PATH DRAWING TEST

The first test consisted on drawing with the Kuka on a 3D surface a path created in Rhino and Grasshopper.

The path reproduced a porosity gradient on the surface of a cylinder parametrically determined by the distance from the surface to a generic point.

FIGURE 02: Porosity gradient created with Grasshopper

12 13CHAPTER XX

FIGURE 03 and 04: Kuka robot performing the path drawing at the Robolab of Stuttgart University

CHAPTER 02 CHAPTER 02

Half a cylinder was built with cardboard and covered by a white paper. An ink pen was installed as effector on the Kuka´s head. Due to the rigidity of the support, an ink pen with a slightly movable point was chosen to al-low for certain tolerance.

Firs of all, the right position of the cylinder to permit the robot’s reach needed to be found.Second, a survey of the cylindrical surface was carried out, then transferred to grasshopper to recalculate the path.

Then a kinematic simulation of the robot was performed with Grasshopper. The path generated in grasshopper was then translated into Kuka’s language KRL.

The robot performed the drawing task perfectly after some small effector adjustment.

FIGURE 05 and 06: The resulting path drawn by the robot

14 15CHAPTER 03

Chapter 03

Woolen thread layed following a honey comb like structure

Control points

Half a sphere as scaffolding

16 17CHAPTER 03CHAPTER 03

Sample 1

Sample 5 Sample 6 Sample 7 Sample 8

Sample 2 Sample 3 Sample 4

Sample 1

Sample 5 Sample 6 Sample 7 Sample 8

Sample 2 Sample 3 Sample 4

ROBOTIC FABRICATION RESEARCH

As part of the Master’s thesis, five types of handmade samples, presenting different approaches to laying fi-bres creating pores, were produced and studied to pro-pose a robotic fabrication for each of them:

FIGURE 07: Catalog of handmade samples

Fibre winding

The first sample was created using half a sphere out of plaster as scaffolding. The goal was to lay down a continuous woolen thread following a honey comb like structure. Nails were used as control points.

This sample is proposed to be robotically fabricated by wet or prepreg filament winding.

Various wet winding experiences have already been carried out at the University of Stuttgart by the ICD and ITKE Institutes to build the Research Pavilions 2012 and 2013. For the first, a temporary auxiliary structure made out of wood was used to create the control points needed for the geometry winding.

A similar set up and winding head could be used to fab-ricate this sample.

The problems will come from the huge amount of con-trol points needed in this case due to the particular cur-vilinear paths around the pores, and the subsequent dif-ficult disassembling of the auxiliary structure.

Since the goal is to create curvilinear paths, another disadvantage will be the fact that the fibre paths created by this method will be poly-lines instead of curves.● Fibre winding (sample 1)

● Stitching pre-impregnate fibres (samples 2 and 3)● Pinching of unidirectional pre-impregnate fabrics (sample 4)● Robotic application of resin on unidirectional fabrics (samples 5 and 6)● Fibre placement between fingers (samples 7 and 8)

FIGURE 08 and 09: Sample1


RESIN BATH

ROVING

PART

ROTATING TABLE

WINDING HEAD

FIGURE 11: Winding head. ICD / ITKE Pavillion 2012 preliminary testing (Source: http://www.designboom.com)

FIGURE 10: Wet winding of carbon fibre. ICD / ITKE Pavillion 2012 preliminary testing (Source: http://www.designboom.com)

Stitching pre-impregnate fibres (samples 2 and 3)

To elaborate the second type of handmade samples, first an elastic fabric was tensed over half plastic sphere used as auxiliary base. The paths were created by sew-ing wool thread to the elastic fabric. Then the thread was painted with resin.

For the sample 2, the resin used was polyurethane with the result of an homogeneously flexible structure.

At the sample 3, showing a gradient of porosity, the woolen thread was painted with epoxy resin. The cured sample was stiffer on the non-porous area and more flexible in the porous one.

The fabrication proposed for this samples consists in a robot able to stitch fibres pre-impregnate with a thermo-plastic resin, on a thermoplastic foil over a 3D auxiliary surface. The thermoplastic foil would melt afterwards during an autoclave process of consolidation becoming part of the composite matrix.

FIGURE 12 and 13: Sample 2 FIGURE 14 and 15: Sample 3

Homogeneously Flexible StifferDeformable and able to recover its initial shape

Depending on porosity and fiber density

VARIABLE STIFFNESS


FIGURE 21: Source: http://www.compositesworld.com/

FIGURE 20: Taylored fibre placement. Leibniz-Institut für Polymerforschung Dresden e. V.

FIGURE 16: Sewing machine FIGURE 17: Sewing machine shuttle hook FIGURE 18: Sewing machine for shoes: Blind stitching

Although there exist already machines which stitch fi-bre to a flat fabric or foil reproducing a path digitally created, the fabric has to be laid out over the machine table in a set up in which the position of the sewing head is fixed and the fabric is moving underneath using numeric control.

In this process of taylor fiber placement, the special fi-bre placement machine lays out bundled fibers, tow/Ro-ving in front of a sewing head, attaching them by needle and thread onto a base material that is held in a frame of the machine.

The base material can be a 2D-textile such as a woven fabric or for thermoplastic composites a matrix-compa-tible foil material. The consolidation of TFP-Preforms to

FIGURE 19: How it works a sewing machine

composites can be done with conventional processing techniques such as resin transfer molding, vacuum bag molding, pressing and autoclaving.

In case of thermoplastic composites the matrix mate-rial and the reinforcement fibers can be placed simul-taneously e.g. in the form of films or fibers. The base material can then be a thermoplastic foil which melts during the consolidation process and becomes part of the matrix.


FIGURE 24: KSL Two needle head RS 530

FIGURES 22 and 23: KSL sewing head KL 500, for Kuka robot

Some sewing heads for Kuka robots have been devel-oped which are used to sew together carbon fibre fab-rics over 3D surfaces.

The company KSL is using a two needle head (fig. 24): a single thread chain stitch seam is formed with only one single needle thread, which is brought into the material by two needles from the top side of the material.

Number of needles: 1 sewing and 1 catcher needleStitch type: modified chain stitchStitch length 4 - 8 mmMaterial thickness: 2 - 15 mm

KSL has patented as well a blindstich head.The blindstitch seam is formed with only one single needle thread, which is brought into the material by one curved needle from the top side of the material.

Number of needles: 1 curved needle d = 50 mmStitch type: blindstitch (KSL patent)Stitch length 5 - 12 mm (depending on material thick-ness)Material thickness: 2 - 7 mm (depending on stitch length)

This blindstich head could be used as the starting point to develop an sewing effector for Kuka robot incorporating a fibre roving.

FIGURE 25: KSL Blindstitch head RS510


FIGURE 26: KSL Blindstitch head RS510

The advantages of this fabrication system would be: the absence of control points as in the previous example, eliminating the laborious an tedious process of disassembling the part; the complete freedom in the fibre placement only subjected to the reach limitations of the robot; the possibility of true curvilinear fibre paths;

Amongst the disadvantages would be: the difficulty of the fibre blind stitching head to be developed; the slowness on the action of laying and sewing the fibre, comparing with the speed of a winding process; the lower level of possible pretension of the continuous fibre.

FIGURE 27: Blind stitch sewing machine Patent EP 1182287 A2 FIGURE 28: Blind stitching. Patent US5829373 A

34. Needle shaft.36. Needle holder40. Needle126. Drive gear150. Guide154. Adjustment plate156. Base plate170. Supporting roller172. Circunferential groove174. Pivoting lever182. Spring


Depending on porosity and fiber density

VARIABLE STIFFNESS

Partial Honey-comb structureFabric gripping to produce pores.

Epoxy resin was applied over the flax fabric

Unidirectional flax non woven fabric

FIGURE 31: Robotiq 2-finger adaptive robot gripper 200

Effector:

Hot surface GRIPPER: Pressure + heat:

Heatable tongs to press and heat the pinched fabric

ROBOTIC GRIPPER

Requirements: - Temporary scafolding - Non woven unidirectional fabric prepeg with: Heat curing epoxy

Three distinct gripping modes:- parallel- encompassing - internal

A third kind of samples was produced by hand using the same auxiliary base as in the previous example: an elastic textile tensed over a half plastic sphere.In this case an unidirectional flax fabric was laid up over the base. To create pores in a honeycomb like structure the fabric was pinched in specific points and then stitched to the textile base. Epoxy resin (in a pro-portion with hardener of 100:30) was then applied over the linen fabric.

The cured sample was showing higher stiffness on the porous areas, due to the higher fibre density of the pores borders compared with the non-porous area fibre density.

The robotic fabrication proposed consists in robot with a gripper having two heatable fingers which will be pinch-

FIGURE 29: Sample 4 before applying resin. FIGURE 30: Sample 4 after resin has cured

ing and then heating and pressing together specific points of an unidirectional fibre fabric, pre-impregnate with heat-curable resin, to create the desired distribu-tion of pores.

One of the advantages of this method would be the low-er complexity in the effector development as well as in the fabrication process, comparing to the stitching one.

The complexity would consist in achieving the right ac-curacy of the gripper to pinch exactly the specific areas of the successively laid up layers of fibre fabric one on the top of the other.

One inconvenient would be the need of a posterior con-solidating process as autoclave to cure completely all the pre-impregnate fibre fabric.

Pinching of unidirectional pre-impregnate fabrics (sample 4)

FIGURE 36: Diagram showing the areas painted with glue (yellowich) in sample 5. FIGURE 37: Diagram showing the areas painted with glue (yellowich) in sample 6. FIGURE 38: Craft Class 4 Robots Workshop. Robarch 2014.


The next experiment was to apply glue on two pieces of unidirectional linen fibre fabric following two different reticulated patterns, similar to a chessboard pattern. Once dried, the fabric was manually stretched with the result of openings of the fabric in the areas left without glue.

Such a concept could be further developed and fabrica-ted using a robot to paint with resin a fabric reproducing a digitally created pattern.

Applying paint with a robot is a normal task carried out at the car industry, and more artistic robotic painting ex-periences have been tried, as the one showed during the Robarch 2014 workshops.

An effector more accurate than a brush could be deve-

loped to apply resin on the laying flat fabric.Before the curing of resin, the fabric would be stretched over the desired auxiliary 3D geometry with the subse-quent fabric opening and pores creation.

Robotic application of resin on unidirectional fabrics (sample 5 and 6)

FIGURE 32: Sample 5. The glue has been applied on the fabric. FIGURE 33: Sample 5. The fabric is stretched opening the pores. FIGURE 34: Sample 6. The glue has been applied on the fabric. FIGURE 35: Sample 6. The fabric is stretched opening the pores.

Area of fabric painted with glue

Area of fabric without glue


FIGURE 40: Checking the placement of fibre in between the silicon fingers. FIGURE 41: Fabrication of sample number 8. FIGURE 42: View of sample 8

Polyurethane foam fingers

Seconnd layer of flax fibre thread (orientation 45º)

Flax fibre thread

First layer of flax fibre thread (orientation 90º)

FIGURE 39: Sample7

For the sample number 7, a scaffolding was builded by sewing cylinders of polyurethane foam on a polyu-rethane foam sheet. This foam was placed and fixed over a plastic sphere to curve it. Then a flax thread was layed around/between the cylinders/fingers.

For the last handmade sample, (sample 8), a pre-mould was created using clay and an adjustable wooden fra-me. The clay was pierced creating a regular pattern of circular holes following an hexagonal grid. Then a mould was created pouring silicon over the clay, producing a flexible mat with fingers.The silicon mould was then stretched and hold over a

cardboard cylinder.At the shorter edges of the mould screws were placed to act as edge control points. A release agent was applied over the silicon mould and control points.A resin bath was improvised to impregnate the linen fi-bre just before to be placed around and in between the silicon fingers, to create the “fibre around pores” organi-sation. The continuous fibre was placed in position with the help of a thin plastic tube through which the fibre was running.

The laying of the fibre was fast and easy. Once the resin was cured, the disassembling process of the fibre com-posite was presenting no difficulty.

The fibre was pre-stressed around the fingers and con-trol points, and its path was truly curvilinear.

Fibre placement between fingers (samples 7 and 8)

cardboard cilinder

silicon mold

silicon mold with fingers

flax fibre thread

hollow tube to place the fibre in between the fingers

first layers fibers+PU

screws as control points

last layers fibers+epoxy

hinge

Depending on porosity, fiber density and matrix

VARIABLE STIFFNESS


Wet filament winding RESIN BATH

ROVING

PART

ROTATING TABLE

WINDING HEAD

95 m

m

72 m

m

40 mm 10 mm

33 mm

Ø40 mm Ø12 mm

Ø6 mm

50 m

m

150

mm

+

FIGURE 47: Steel piece builded to add to the existing winding head. Plans and elevations. FIGURE 48: Render of the final winding head.

FIGURE 43: Wet winding of carbon fibre. ICD / ITKE Pavillion 2012 preliminary testing. FIGURE 44: Winding head made out of steel.FIGURE 45: Collage showing the idea for modification of ICD/ITEKE Pavillion 2012 Final effector. FIGURE 46: Perspective of the piece to add to the existing winding head

For the robotic fabrication of this kind of samples an effector was built: the winding head used to produce the ICD/ITKE Research Pavilion 2012 was modified by adding to it a thin steel tube. The fibre will be guided to the interior of this tube by two plastic spools.

Two possibilities could be deeply explored: the place-ment of wet fibre or the use of fibre pre-impregnate with heat or UV curing resin.

This kind of samples and this robotic fabrication pro-cess has been the chosen to be further developed du-ring the Master’s thesis.

The next steps related to robotic fabrication will be to test the effector laying of fibre around different finger configurations focusing on the versatility of the suppor-

ting mould to create different porous systems.

34 35

233mm

310m

m5m

m50

mm

26.25mm

20mm

243mm

310m

m5m

m40

mm

5mm

CHAPTER 03CHAPTER 03

FIGURE 50: Different examples of fibre organisations around the fingers. FIGURE 49: Drawings of silicon scaffoldings with two different finger diametre to lay fibres.

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References

Raabe, D, Sachs, S & Romano, P 2005, The crustacean exoskeleton as an example of a structurally mechanica-lly graded biological nanocomposite material.

TFP-Principle. Available from: <http://www.ipfdd.de/Complex-Structural-Components-Tailored.424.0.html?&L=0>

Sewing lessons for aerospace engineers. Available from: <http://machinedesign.com/archive/sewing-lessons-ae-rospace-engineers>

KL 500 Robot Sewing Unit: Available from: <http://www.ksl-lorsch.de/fileadmin/user_upload/Produkte/Basic_3D-Roboter-Naehanlage_KL_500/Datasheet_KL_500_Dashboard.pdf>

RS 530 Two needle head: Available from: <http://www.ksl-lorsch.de/fileadmin/user_upload/Produkte/Zweinadel-Naehkopf_RS_530/Datasheet_RS_530.pdf>

RS 510 Blindstitch head. Available from: <http://www.ksl-lorsch.de/fileadmin/user_upload/Produkte/Blindstich-Naehkopf_RS_510/Datasheet_RS_510.pdf>

Sources

Figure1: Raabe, D, Sachs, S & Romano, P 2005, The crustacean exoskeleton as an example of a structurally mechanically graded biological nanocomposite material.

Figures 10, 11 and 43: Available from: <http://http://www.designboom.com/architecture/robotically-fabricated-carbon-and-glass-fibre-pavilion-by-icd-itke/>

Figure 16: Available from: <http://www.bsewinn.com/Totally_Stitchin_Summer_Camp.html>

Figure 17: Available from: <http://www.instructables.com/id/How-to-Sew-using-a-sewing-machine/>

Figure 19: Available from: <http://buckylab.blogspot.de/2013/02/how-it-works-sewing-machine.html>

Figure 20: Available from: http://www.ipfdd.de/Tailored-Fiber-Placement-Principle.446.0.html

Figure 21: Available from: <http://www.compositesworld.com/articles/tailored-fiber-placement-besting-

metal-in-volume-production>

Figures 22 and 23: Available from: <http://www.ksl-lorsch.de/en/products/produktgruppen/robot-sewing-unit/ba-sic-3d-robot-sewing-unit-kl-500/>

Figure 24: Available from: <http://www.ksl-lorsch.de/en/products/produktgruppen/robot-sewing-unit/two-needle-head-rs-530/>

Figures 25 and 26: Available from: <http://www.ksl-lorsch.de/en/products/produktgruppen/robot-sewing-unit/blindstitch-head-rc-510/>

Figure 27: R. Keilmann (2001). Blind stitch sewing machine, Patent EP1182287 A2. Available from: <http://www.google.com/patents/EP1182287A2?cl=en>

Figure 28: Baxter (1998). Blind stitching apparatus and composite material manufacturing methods, Patent US5829373A. Available from: <http://www.google.com/patents/US5829373>

Figure 31: Available from: <http://robotiq.com/en/products/electric-gripper>

Figure 38: Available from: <http://www.robarch2014.org/>

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Tailored Placement of Fibres around Pores · 2015. 5. 14. · 3D surface a path created in Rhino and Grasshopper. The path reproduced a porosity gradient on the surface ... Sewing