Message from the Chair
JOINING NEWS NEWSLETTER OF THE SOCIETY OF PLASTICS ENGINEERS JOINING OF PLASTICS AND COMPOSITES SPECIAL INTEREST GROUP
Volume 20, No. 2 (Fall 2009)
Message from the Chair ANTEC 2009 in Chicago, Illinois, was held in conjunction with NPE. This synergy contributed to a very successful meeting and a wonderful opportunity to see new machinery and processes not usually available at ANTEC. For our SIG, we can be very pleased with our four sessions, containing new and interesting developments, as well the Industry Panel on Advances in Plastic Joining Technologies for Medical Applications. None of this would have been possible without the initiative and hard work from the authors, as well as our loyal team of reviewers. Anyone who has written a paper or has reviewed one knows how much time and creativity is required, but this effort can result in the kind of information transfer that makes it worth while for not only the ANTEC attendees, but also those who only read the Proceedings. Sincere thanks to all of you for a great job of bringing exciting new discoveries to light in clear and comprehensive papers. This work enhances the development of joining as a science and improves the dependability of the products that result. As will be noted in the Technical Paper Chair’s report that follows, we have two ways of acknowledging excellence in the submitted papers. One is the awarding of a plaque to the Best Paper, based on the written article. The other is the Best Student Presentation, based on the presentation of the material during the sessions. The Best Paper award, which is chosen in advance of ANTEC, went to Helmut Potente and his group for the paper “In-Line Process Optimization Of Hot-Plate Welding Using An Innovative Actuation Concept” presented by Reinhild Hoffschlag. The Best Student Presentation was given by Mingliang Chen, the award being presented following the last technical paper session. We want to thank Jeff Frantz at Branson Ultrasonics, who has continued to organize the Best Paper plaque to honour our authors. Not only have we the authors and reviewers to thank, we also thank the industrial partners, who gave short papers and participated in discussions during the Industry Panel. More details will appear later in the Newsletter, but this Panel Discussion was certainly a high point for our SIG. At this point I want to especially thank the past executive of our SIG, who have put many hours into making the Joining Sessions so successful. The hard work of our Technical Paper Chair for the past 2 years, Alex Savitski, cannot be praised enough; ANTEC would not be possible without the work of all of the TPC’s of the various divisions and SIG’s. Further, the Newsletter Editor of these 2 years, Marc St. John, is well deserving of our thanks. Marc has been a good supporter of all of our efforts, and we will miss him next year. Many thanks to Chung Wu, who has volunteered to step into Marc’s place as upcoming Technical Paper Chair, when Alex moves on to become Chair and I move into retirement. This Newsletter is also an opportunity to remind all of our past authors plus hopefully many new ones that the Call for Papers has already been announced on the SPE website, and the deadline for submission of an Abstract is coming soon. Please look over your past year’s research to see whether there is an interesting paper there that you can present in Orlando this upcoming May. We plan to have another Industry Panel, this time on Aerospace Applications, which will be discussed later in this Newsletter. No matter what your particular interest, I join with the rest of the executive in encouraging your attendance in May in Orlando for ANTEC 2010. Thank you very much for your support of our SIG.
Bobbye Baylis Chair, Joining SIG
JOINING NEWS NEWSLETTER OF THE SOCIETY OF PLASTICS ENGINEERS JOINING OF PLASTICS AND COMPOSITES SPECIAL INTEREST GROUP
Volume 20, No. 2 (Fall 2009)
ANTEC® 2009 TPC Report As was mentioned in the message from our distinguished Chair, we were all pleased with our SIG performance at ANTEC 2009. This year we had four sessions, including the Industry Panel on Advances in Plastic Joining Technologies for Medical Applications. 21 papers were presented and we had one no-show. As in the last several years our largest session and the largest number of papers were on laser welding – 6 technical papers plus 1 commercial paper presented at our Industry Panel session by Dilas. Dilas - a well known vendor of laser diodes, and in the recent years, of a cutting edge plastic welding technology, presented two very good papers on close-loop control in laser welding of plastic components. One was presented by Rick Davis in Laser Welding technical session, and another by Wolfgang Horn, on the Industrial Panel. Both papers were strong contenders in our SIG’s Best Paper award. And probably for the first time in many years we did not have research papers on ultrasonic welding. However two commercial papers presented by Herrmann Ultrasonics and Dukane on our Industry Panel were very enlightening, both focused on expanding this wellknown technology’s capabilities. The selection of a research subject mix was also very interesting. Excluding a small number of papers on laser welding technology, and two thought provoking and innovative papers presented by Helmut Potente’s group “In-Line Process Optimization Of Hot-Plate Welding Using An Innovative Actuation Concept” on and by Sergio Amancio on a novel Fricriveting process, most of the research papers -13 of them, were focused on investigating joining processes application to various materials, or effect of specific properties on joint formation and factors affecting joint quality. The resulting impression of a good mix of practical applications and innovation was very favourable. I would also like to note the overall high quality of all the papers sent and presented this year. This was noted by all the reviewers, which deserve our great THANKS for the enormous job they are carrying out year after year, helping TPC to put together next technical conference. Given the exceptionally high quality of most of the papers, this year it was especially challenging to select the winner of The Best Paper award, which is chosen in advance of ANTEC. But at the end we all agreed that The 2009 Best Paper award should be given to Helmut Potente and his group from Paderborn University for the paper “In-Line Process Optimization Of Hot-Plate Welding Using An Innovative Actuation Concept” presented by Reinhild Hoffschlag. Best Student Presentation award went to Mingliang Chen for presenting paper “Finite Element Modeling and Microstructure Analysis for Contour Laser Transmission Welding of Glass Fibre Reinforced Nylon 6”. In order to facilitate this selection process for Best Student Presentation award in future years, we are asking the authors to note the student presenter during the submission process, if the paper is planned to be presented by a student And the closing note is about coming ANTEC 2010 in Orlando, FL. As everybody’s impression that the Industry Panel (even they are not always easy to organize) is a great way to bring new technologies and ideas to our Technical Conferences and enrich the mix of our research papers, we would like to continue this undertaking, Next year we plan to have another Industry Panel, this time on Aerospace Applications. The details are still being worked out, and Chung – Yuan Wu, who has graciously agreed to take the role of our SIG’s TPC for the next two years, will have his hands full. I am wishing him best of luck in this role and also taking this opportunity to ask everybody to greet him in this position and give him all the support possible in preparing new Technical Conference in Orlando in 2010.
Alex Savitski SIG 012 Technical Panel Chair, 2008-2009
JOINING NEWS NEWSLETTER OF THE SOCIETY OF PLASTICS ENGINEERS JOINING OF PLASTICS AND COMPOSITES SPECIAL INTEREST GROUP
Volume 20, No. 2 (Fall 2009)
Introduction We want to take the opportunity to inform everyone of what happened during ANTEC 2009, which was held in conjunction with NPE last June. Certainly, grouping those two events together made attending even more appealing. I am sure that everyone will agree that it also made it difficult to choose what to see, as so many interesting things where going on at the same time! We are very happy with the turnout at our various sessions. The quality of the papers and presentations made it difficult for the judges to identify the best in both categories. At the end of the sessions, the SIG awarded the Best Paper to Helmut Potente and his group from Paderborn University for the paper “In-Line Process Optimization Of Hot-Plate Welding Using An Innovative Actuation Concept” presented by Reinhild Hoffschlag. Please see below a copy of this very interesting paper. The Best Student Presentation went to to Mingliang Chen for presenting a paper titled “Finite Element Modeling and Microstructure Analysis for Contour Laser Transmission Welding of Glass Fibre Reinforced Nylon 6”. The SIG is already in preparations for ANTEC 2010 which will be held in Orlando May 16-20. We are working on setting up an Industrial Panel to cover plastic joining in the Aerospace Industry. We are counting on benefiting from the proximity of NASA to get some good participation on the subject. We will ask presenters to make short 15-20 min presentations which would then be followed by a two hours discussion. No papers will be required. There are some executive organizational changes in our Joining SIG. Bobbye Baylis will be retiring soon from her position as Chair. Alex Savitsky has gracefully accepted taking on this very demanding position, and Chung-Yuan Wu will replace him as TPC (Technical Paper Chair). Also, Sergio Amancio will be Secretary, while I will be Newsletter Editor for the next two years. Finally, if you have not yet submitted a technical paper for the upcoming ANTEC (deadline was September 4th), we still encourage you to send one in. The final paper submission deadline is November 13th (5PM Eastern time). Your participation is essential in maintaining and growing the technical vitality of our SIG.
Sophie Morneau Newsletter Editor
Alex Savitsky present the Best Student Presentation award to Mingliang Chen of Queen’s University, Kingston, Ontario.
Bobbye Baylis congratulating Mingliang Chen
Page 1 of 5
In-Line Process Optimization of Hot-Tool Welding using an Innovative Actuation Concept H. Potente**, V. Schöppner**, R. Hoffschlag**, S. Gövert* and J. Schnieders* **University of Paderborn, Institute of Polymer Engineering, KTP * 3Pi Consulting and Management, Abstract This paper looks into the initial steps of the development of a self-optimizing hot-tool welding machine. By employing a new machine concept, it is possible to ensure displacement speeds counter to the direction of joining. This then allows the strength of the weld to be assessed while it is still in the molten state. To be able to use this data for self-optimization, it was necessary to establish a correlation between the short-time strength of the parts in the cooled state and their shorttime strength in the still molten state. Taking these correlations, a systematic approach can be worked out to allow the welding machine to find an optimum processing window with just a few test welds. The results show that the optimum of the joining displacement to the melt layer thickness ratio (sF/L0) can be established for the parameter setting by measuring the tear forces on the welding machine, even without knowing the short-time strength in the cooled state. The same applies for the ratio of the melt layer thicknesses to the wall thickness. Based on these results, the next steps are now to develop a means of selfoptimization and quality assurance during the running hottool welding process.
Problem and Aims Welding complex parts or assembling thermoplastics constitutes a key process step in plastics processing. Hottool welding is one of the techniques employed most frequently [1]. The current trend in joining technology, towards optimizing the methods employed economically and thus reducing the production costs for serial production to a minimum, is gaining increasing significance. In order to employ hot-tool welding successfully, it is essential for the requirements placed on the weld to be fulfilled. These include compliance with the tolerances of the molded part, tightness and the most important quality characteristic of all – the weld strength. To achieve this, the optimum setting parameters for the welding process must be established in advance and suitably tailored to the material and the geometry of the parts to be joined. Guide values published in 1987 are used to determine the optimum point of operation [2]. These guide values for optimizing the process parameters (joining displacement/melting depth, melting depth/wall
thickness) are used as reference values, and do not always lead to the optimum point of operation. It is thus standard practice to carry out parameter studies on the basis of the statistical optimization criteria and to conduct a subsequent test on the weld strength in a short-time tensile test. In the same way, quality tests must be conducted at specific intervals during running serial production in order to monitor the process and the associated quality characteristics. If any deviation is established here, the optimum point of operation must be established once again. Apart from the high costs involved, this also is very time consuming. To overcome this problem, process monitoring and the verification of the associated quality characteristics are to be implemented inline in running serial production. This research project establishes the fundamentals for a systematic method of adaptive process optimization, based on process data from the hot-tool welding machine. The aim is to simplify the determination of the point of operation, and also to monitor this point of operation on a self-optimizing machine by capturing and monitoring the dynamic optimization criteria. By employing a linear drive, it is possible to achieve very slow displacement speeds counter to the joining direction. Based on this, and by using a twin-carriage concept, the tear forces can be determined directly on the welding machine. To allow the new drive concept to be used for self-optimization, it was first necessary to identify correlations between the process data on the hot-tool welding machine and the weld strengths determined in the short-time tensile test.
Materials The investigations were first performed using two materials. One was a PMMA from Degussa and the other an HDPE from Basell. The following table provides an overview of the material properties.
Page 2 of 5
Table 1. Measured material properties Material Basic Glass transition material temperature strength
PMMA HDPE
Mean density
Tg[°C]
σG[N/mm2 ]
ρm[g/cm3]
117 132
81.62 28.736
1.186 0.951
Half dumbbell specimens [Figure 1] were used for the
starts after a constant cooling (tK). Care should be taken to ensure that the welding zone has not cooled down completely, since the machine will otherwise not be able to generate the necessary tearing force. This means that the parts being joined are torn apart directly after the stillmolten welding lugs come into contact with each other. Different cooling times of tK=5 s, 10 s and 15 s were observed to begin with. Material: Pretreatment:
PMMA Welded
Test point
test.
L0/d
Figure 1. Standardized test specimen This test specimen geometry was designed on the basis of existing standardized specimens (DIN EN 61, Type 1; now DIN EN ISO 527) [3].
Test Setup The welding machine employed is equipped with a linear drive rather than the conventional hydraulic, pneumatic or rotational servomotor drives. This permits accelerations up to 4.5 times the acceleration due to gravity and a maximum speed of 2500 mm/s. A twin carriage concept was developed. With this concept, the clamping device is uncoupled from the actual carriage, thus avoiding any recording of disturbances due to friction and loss forces. By applying a force-measuring system to the guide carriage, it is possible to establish the tear forces between the parts being joined when the carriages are moved apart. Conducting an experimental design [Figure 2], the optimum process parameters for hot-tool welding were established. The following parameters were varied: the temperature of the heated tool (TH), the residual melt layer thickness (LR), the pressureless heating time (tE), the melt layer thickness (L0), the ratio of the melt layer thickness to the wall thickness of the part being joined (L0/d) and the ratio of the joining displacement to the melt layer thickness (sF/L0). The short-time tensile strength was tested after each run with standard tensile tests. In a further step, specimen parts were welded and torn apart on the welding machine. This tearing process
Testing speed welding machine: Testing speed tensile test:
4.1 4.9 4.17 4.25 4.33 4.41 4.49 4.57 4.65 5.1 5.9 5.17 5.25 5.33 5.41 5.49 5.57 5.65 6.1 6.9 6.17 6.25 6.33 6.41 6.49 6.57 6.65
0.5 0.5 0.5 1.4 1.4 1.4 1.5 1.5 1.5 0.5 0.5 0.5 1.4 1.4 1.4 1.5 1.5 1.5 0.5 0.5 0.5 1.4 1.4 1.4 1.5 1.5 1.5
L0 [mm] 1 1 1 2.28 2.28 2.28 3 3 3 1 1 1 2.28 2.28 2.28 3 3 3 1 1 1 2.28 2.28 2.28 3 3 3
Pressureless heating time t'E [s] 5.5 5.5 5.5 16.5 16.5 16.5 26 26 26 5.5 5.5 5.5 16.5 16.5 16.5 26 26 26 5.5 5.5 5.5 16.5 16.5 16.5 26 26 26
Time to tearing tk [s] 5 5 5 5 5 5 5 5 5 10 10 10 10 10 10 10 10 10 15 15 15 15 15 15 15 15 15
50 mm/min 5 mm/min
SF/L0 0.3 0.75 0.9 0.3 0.75 0.9 0.3 0.75 0.9 0.3 0.75 0.9 0.3 0.75 0.9 0.3 0.75 0.9 0.3 0.75 0.9 0.3 0.75 0.9 0.3 0.75 0.9
Joining displacement SF [mm] 0.3 0.75 0.9 0.684 1.71 2.052 0.9 2.25 2.7 0.3 0.75 0.9 0.684 1.71 2.052 0.9 2.25 2.7 0.3 0.75 0.9 0.684 1.71 2.052 0.9 2.25 2.7
Figure. 2. Sample experimental plan without repeats The tearing operation on the welding machine is performed on a velocity-controlled basis, with the test velocity being set at 50 mm/min for all materials. The relevant measuring data (displacement, force measuring data) are captured online on the welding machine. The force-measuring system installed transmits the measuring data at intervals of 100 ms. On the basis of these data, it is possible to compile a displacement and force measurement curve over the cycle time for each parameter setting [Figure 3]. Using these curves, the required forces and work on the welding machine were read off and were then used to identify correlations with the force curves gained from the short-time tensile testing unit.
Page 3 of 5
thickness of part being joined) and the contact surface (AK) that develops between the two welding beads.
180 Bereich für die Area for the spätere Ermittlung subsequent der zum Zerreißen Determination of the verwendeten Kräfte forces applied und Arbeiten auffor der Schweißmaschine Tearing and work on
190 180
130
80
Wegmesskurve
displacement measurement curve
the welding machine
170
Kraftmesskurve curve force measurement
30
160
0 -20
150 140
K K
200
[N][N] ForceKraftmessdaten measuring data
Wegmessdaten [mm] Displacement measuring data [mm]
Weg- undand Kraftmesskurven aufgetragencurves über die over Zykluszeit Displacement force measurement the cycle time
d
-70 0
50
100
150
200
250
300
l-Phase
Cycle time[s/10] [s/10] Zykluszeit Heating time Erwärmzeit
Tearing time Zerreißzeit
Umstellzeit Switchover time
b
Schweißzeit Welding time
Section Schnitt A-A A-A
Figure 5. Diagram of a load-bearing cross-sectional area Figure 3. Sample displacement and force measurement curve plotted over the cycle time Once all the relevant results were available, it was possible to plot the characteristics of relevance to quality (short-time tensile strength, force on the welding machine and work) over the ratio of the joining displacement to the residual melt layer thickness, or the ratio of the residual melt layer thickness to the wall thickness of the part being joined.
Results The initial results have shown that, in comparison to the curves from the short-time tensile testing unit, simply plotting the forces and work on the welding machine is not sufficient for low-value dimensionless variables [Figure 4]. Optimum Optimum tensile Zugprüfanlage testing unit
Force theder tensile testing unit [N] Kraftonauf Zugprüfanlage [N]
PMMA T H = 277°C LR = 0,57 mm
-20
tensile Zugprüfanlage
-21
testing unit
2500
-22 2000 -23 1500 -24
1000
Schweißmaschine Welding machine
Apparent optimum scheinbares Optimum welding machine Schweißmaschine
Kraft on aufthe der welding Schweißmaschine [N] Force machine [N]
3000
-25
500
-26 0,4
0,6
0,8
1
1,2
1,4
1,6
L0/d - Verhältnis
L0/d ratio
Figure 4. Comparison of the short-time tensile strength with the tearing force on the welding machine via the L0/d ratio and a constant LR of 0.57 mm In a second step, it was thus necessary to identify factors that influence the forces and work on the welding machine. These factors can then be used to apply a correction. Alongside the load-bearing cross-sectional area (A) another correction value that was found to be of relevance is the dimensionless joining displacement (sF/L0). Figure 5 shows the load-bearing cross-sectional area. This is obtained from the starting area (AB = width *
Since more material is displaced into the welding bead with an increasing joining displacement is increased, there is also a bigger cross-sectional area, which must be taken into account through an appropriate area correction. Working on the basis of the investigations, a statistical study was conducted of the correlations. The target variables here were the forces on the tensile testing unit (FZug.). The influencing variables were the tearing forces (FZer.) and the tearing work (WZer.) on the welding machine, in conjunction with the correction values (A and sF/L0). Working on the basis of this data, a statistics program provided a numerical model in each case (see Eqn. 1). s s FZug . = b0 + b1 ⋅ F + b2 ⋅ Fzer . + b3 ⋅ A + b4 ⋅ ln F L 0 L0 s + b6 ⋅ exp F + b7 ⋅ exp FZer . L0
b0 = -10750196,6029 b1 = 1590544,3538 b2 = 1118,7479 b3 = 10942,1493
+ b5 ⋅ ln A (1)
b4 = 383739,2178 b5 = 2782003,5842 b6 = 1374403,2898 b7 = 21697192804342,4766
Using this statistics program, it is possible to achieve a coefficient of determination in excess of 99.52 %. Figure 6 shows a comparison of the statistically evaluated forces and work on the welding machine, set against the forces on the tensile testing unit. The joining displacement (sF) and the melt layer thickness (L0) were varied here, while the residual melt layer thickness was kept constant at LR = 0.57 mm. The heated tool temperature was 277 C. The curve profiles display clear similarities. The forces increase with the sF/L0 ratio, attaining a maximum value at sF/L0 of 0.68. If the sF/L0 ratio increases further, the forces will fall again.
Page 4 of 5
1600
1600
welding machine 0,4
0,45
0,5
0,55
0,6
0,65
0,7
0,75
0,8
0,85
sF/L0 ratio
Zugprüfanlage Tensile testing unit 1400
1200
1200
Schweißmaschine Welding machine 1000
1000
800
800
600
600
400
400
200
200
0
Figure 6. Comparison of the short-time tensile strength with the tear strength on the welding machine versus the sF/L0 ratio and a constant LR of 0.57 mm The difference between the curve profiles that is seen with bigger sF/L0 ratios can be attributed to the area correction that is employed. It becomes clear, however, that, by measuring the tearing forces directly on the welding machine, it is possible to determine the optimum sF/L0 ratio for the parameter setting without having to have recourse to an elaborate parameter analysis with subsequent tensile tests on the short-time tensile unit. Corresponding statements can also be made on the melt layer thickness/wall thickness ratio (L0/d). Here too, virtually parallel curve profiles can be observed [Figure 7]. In the same way, the parameter optimum, which is achieved with an L0/d ratio of 0.9, can be determined without knowledge of the short-time tensile strength. With the data that has been determined and a specified wall thickness, it is now possible to calculate the melt layer thickness and the joining displacement.
(korrigiert mit sF/L0 und A) (Corrected with sF/L0 and A)
optimum welding machine
Force on auf the der tensile testing unit[N] [N] Kraft Zugprüfanlage
tensile testing unit
1400
(corrected by sF and A)
force on the welding machine
force on thetensile testing unit
PMMA TH=277°C LR=0,57 mm
HDPE T H = 217 °C LR = 0,17 mm
Kraft Schweißmaschine Force on auf theder welding machine [N]
optimum tensile testing unit
0 0,1
0,15
0,2
0,25
0,3
0,35
0,4
0,45
0,5
0,55
LL0/d Verhältnis /d- ratio 0
Figure 8. Comparison of the short-time tensile strength with the statistically established tear strength on the welding machine (corrected with sF/L0 and A) over the L0/d ratio and a constant LR of 0.17 mm
Prospects To achieve a self-optimizing hot-tool machine, the optimization tests presented have to be integrated in the process control. A schematic sequence plan for parameter optimization and quality control is set out in the following Figure 9. 1. Establishment of the melting curves Regression equation 2. Internal software calculation Experimental plan
optimum welding machine
0,4
0,6
0,8
tensile testing unit
welding machine 1
1,2
1,4
Tolerance exceeded (corrected with sF and A)
optimum tensile testing unit
PMMA TH=277°C LR=0,57 mm
force on the welding machine
force on the tensile testing machine
3. Tensile tests on the machine
1,6
L0/d ratio
Figure 7. Comparison of the short-time tensile strength with the tear strength on the welding machine versus the L0/d ratio and a constant LR of 0.57 mm The presentation of the results taking the example of PMMA shows clearly that the optimum process parameters can be determined without tensile tests on the short-time tensile testing unit [Figure 8]. Further-reaching investigations show that a close approximation of the curves can be achieved for a semi-crystalline thermoplastic too, which would permit a statement to be made on the optimum machine setting parameters.
Optimized setting Parameters within tolerance
5. Quality control via SPC
4.Series welding
Figure 9. Schematic diagram of the sequence plan for parameter optimization and quality control, including the tensile test on the hot-tool welding machine [4] To achieve this, the machine must be put in a position to compile an experimental plan itself. The knowledge of the melting behavior that is required for this can be acquired from just a few experimental measurements. The result obtained is a function that can be used to calculate the necessary pressureless heating time (Point 1). With this function, an experimental plan can be compiled and conducted by the machine program. (Point 3). To this end, the parts being joined are torn apart while still in the molten state, and a point of operation is
Page 5 of 5
established from the measured forces, which is then used as the starting point for serial production (Point 4). This point can be employed in the sense of SPC (Statistical Process Control) to perform quality control (Point 5). For the optimum point of operation a tolerance band has to be allocated for the forces and the work. The welded parts can be inspected at regular intervals directly on the welding machine and, through the tolerance band that has been set, conclusions can be drawn regarding the quality of the weld. At present, further-reaching investigations are being conducted with amorphous and semi-crystalline materials (filled and unfilled) in order to identify generally-valid correlations and to describe these with statistical methods and, if possible, with mathematical models.
Conclusion From the investigations, it has become clear that, by using a linear-drive hot-tool welding unit, it is possible to verify the point of operation directly on the machine. Since the parts being joined have to be torn apart while still in the molten state, on account of the low tensile and clamp forces available on the machine, it is necessary to create an underlying basis showing that correlations exist between the short-time tensile tests employed as standard and those carried out on the welding machine. Correcting the tearing forces with physical influencing variables and subsequently assessing them in a statistical assessment program has shown that it is possible to describe the short-time tensile strength by means of the numerically determined equations with a prediction of up to 99 %.
References 1.
Potente, H.: "Grundlagen des Fügens von Kunststoffen" Skript zur Vorlesung, Institut für Kunststofftechnik, Universität Paderborn 2. Kreiter, J.: "Optimierung der Schweißfestigkeit von Heizelementstumpfschweißungen von Formteilen durch verbesserte Prozessführung und Selbsteinstellung". Dissertation am Institut für Kunststofftechnik (KTP), Universität-GH Paderborn, 1987 3 Potente, H.; Brüssel, A.: "Qualitätsrelevante Parameter beim Schweißen von gefüllten und verstärkten Systemen mittels Heizelement". AIFAbschlussbericht No. 9802, 1997 4 Potente, H.; Wilke, L.; Schnieders, J.: "Neue Perspektiven beim Heizelementschweißen“ SKZ Seminar „Heizelement", Würzburg Mai 2006, Institut für Kunststofftechnik, Universität Paderborn
Key Words: Hotplate Optimization
Welding,
In-Line
Process
JOINING NEWS NEWSLETTER OF THE SOCIETY OF PLASTICS ENGINEERS JOINING OF PLASTICS AND COMPOSITES SPECIAL INTEREST GROUP
Volume 20, No. 2 (Fall 2009)
SIG 2010 Executive Committee Chair Alex Savetsky Baxter Healthcare TPC Chung-Yuan Wu Visteon Corporation Newsletter Editor Sophie Morneau Branson Ultrasonics Corporation Secretary Sergio Amancio GKSS Forschungszentrum GmbH Institute of Materials Research - Germany
Board Members Alexander Savitsky -- Chair Engineering Specialist Baxter Healthcare Baxter Healthcare, RLT-04 25212 w. Route 120 Round Lake, IL 60073 USA Phone: +1 847-270-2187 Fax: +1 847-270-4966 [email protected] Sergio Amancio -- Secretary GKSS Research Centre Max-Planck Str 1 D-21502 GEESTHACHT GERMANY Phone: +49 4152 87 2066 Fax: +49 4152 87 2023 [email protected] Sophie Morneau -- Newsletter Editor Manager, Applications Laboratory Branson Ultrasonics Corporation 41 Eagle Road Danbury, CT 06813 USA Phone: +1 203-796-0305 Fax: +1 203-796-0363 [email protected] Chung Yuan Wu -- Tech Program Chair Technical Fellow Visteon Corporation 3023 Gallinger Drive Ann Arbor, MI 48103 USA Phone: +1 734-710-2383 Fax: +1 734-736-5576 [email protected] James S. Griffing -- Executive Committe Liaison Technical Fellow Boeing Co. 6609 234th Street SW Mountlake Terrace, WA 98043 USA Phone: +1 425-717-1203 [email protected]
Society of Plastics Engineers
Volume 20, No. 2 (Fall 2009)
Message from the Chair ANTEC 2009 in Chicago, Illinois, was held in conjunction with NPE. This synergy contributed to a very successful meeting and a wonderful opportunity to see new machinery and processes not usually available at ANTEC. For our SIG, we can be very pleased with our four sessions, containing new and interesting developments, as well the Industry Panel on Advances in Plastic Joining Technologies for Medical Applications. None of this would have been possible without the initiative and hard work from the authors, as well as our loyal team of reviewers. Anyone who has written a paper or has reviewed one knows how much time and creativity is required, but this effort can result in the kind of information transfer that makes it worth while for not only the ANTEC attendees, but also those who only read the Proceedings. Sincere thanks to all of you for a great job of bringing exciting new discoveries to light in clear and comprehensive papers. This work enhances the development of joining as a science and improves the dependability of the products that result. As will be noted in the Technical Paper Chair’s report that follows, we have two ways of acknowledging excellence in the submitted papers. One is the awarding of a plaque to the Best Paper, based on the written article. The other is the Best Student Presentation, based on the presentation of the material during the sessions. The Best Paper award, which is chosen in advance of ANTEC, went to Helmut Potente and his group for the paper “In-Line Process Optimization Of Hot-Plate Welding Using An Innovative Actuation Concept” presented by Reinhild Hoffschlag. The Best Student Presentation was given by Mingliang Chen, the award being presented following the last technical paper session. We want to thank Jeff Frantz at Branson Ultrasonics, who has continued to organize the Best Paper plaque to honour our authors. Not only have we the authors and reviewers to thank, we also thank the industrial partners, who gave short papers and participated in discussions during the Industry Panel. More details will appear later in the Newsletter, but this Panel Discussion was certainly a high point for our SIG. At this point I want to especially thank the past executive of our SIG, who have put many hours into making the Joining Sessions so successful. The hard work of our Technical Paper Chair for the past 2 years, Alex Savitski, cannot be praised enough; ANTEC would not be possible without the work of all of the TPC’s of the various divisions and SIG’s. Further, the Newsletter Editor of these 2 years, Marc St. John, is well deserving of our thanks. Marc has been a good supporter of all of our efforts, and we will miss him next year. Many thanks to Chung Wu, who has volunteered to step into Marc’s place as upcoming Technical Paper Chair, when Alex moves on to become Chair and I move into retirement. This Newsletter is also an opportunity to remind all of our past authors plus hopefully many new ones that the Call for Papers has already been announced on the SPE website, and the deadline for submission of an Abstract is coming soon. Please look over your past year’s research to see whether there is an interesting paper there that you can present in Orlando this upcoming May. We plan to have another Industry Panel, this time on Aerospace Applications, which will be discussed later in this Newsletter. No matter what your particular interest, I join with the rest of the executive in encouraging your attendance in May in Orlando for ANTEC 2010. Thank you very much for your support of our SIG.
Bobbye Baylis Chair, Joining SIG
JOINING NEWS NEWSLETTER OF THE SOCIETY OF PLASTICS ENGINEERS JOINING OF PLASTICS AND COMPOSITES SPECIAL INTEREST GROUP
Volume 20, No. 2 (Fall 2009)
ANTEC® 2009 TPC Report As was mentioned in the message from our distinguished Chair, we were all pleased with our SIG performance at ANTEC 2009. This year we had four sessions, including the Industry Panel on Advances in Plastic Joining Technologies for Medical Applications. 21 papers were presented and we had one no-show. As in the last several years our largest session and the largest number of papers were on laser welding – 6 technical papers plus 1 commercial paper presented at our Industry Panel session by Dilas. Dilas - a well known vendor of laser diodes, and in the recent years, of a cutting edge plastic welding technology, presented two very good papers on close-loop control in laser welding of plastic components. One was presented by Rick Davis in Laser Welding technical session, and another by Wolfgang Horn, on the Industrial Panel. Both papers were strong contenders in our SIG’s Best Paper award. And probably for the first time in many years we did not have research papers on ultrasonic welding. However two commercial papers presented by Herrmann Ultrasonics and Dukane on our Industry Panel were very enlightening, both focused on expanding this wellknown technology’s capabilities. The selection of a research subject mix was also very interesting. Excluding a small number of papers on laser welding technology, and two thought provoking and innovative papers presented by Helmut Potente’s group “In-Line Process Optimization Of Hot-Plate Welding Using An Innovative Actuation Concept” on and by Sergio Amancio on a novel Fricriveting process, most of the research papers -13 of them, were focused on investigating joining processes application to various materials, or effect of specific properties on joint formation and factors affecting joint quality. The resulting impression of a good mix of practical applications and innovation was very favourable. I would also like to note the overall high quality of all the papers sent and presented this year. This was noted by all the reviewers, which deserve our great THANKS for the enormous job they are carrying out year after year, helping TPC to put together next technical conference. Given the exceptionally high quality of most of the papers, this year it was especially challenging to select the winner of The Best Paper award, which is chosen in advance of ANTEC. But at the end we all agreed that The 2009 Best Paper award should be given to Helmut Potente and his group from Paderborn University for the paper “In-Line Process Optimization Of Hot-Plate Welding Using An Innovative Actuation Concept” presented by Reinhild Hoffschlag. Best Student Presentation award went to Mingliang Chen for presenting paper “Finite Element Modeling and Microstructure Analysis for Contour Laser Transmission Welding of Glass Fibre Reinforced Nylon 6”. In order to facilitate this selection process for Best Student Presentation award in future years, we are asking the authors to note the student presenter during the submission process, if the paper is planned to be presented by a student And the closing note is about coming ANTEC 2010 in Orlando, FL. As everybody’s impression that the Industry Panel (even they are not always easy to organize) is a great way to bring new technologies and ideas to our Technical Conferences and enrich the mix of our research papers, we would like to continue this undertaking, Next year we plan to have another Industry Panel, this time on Aerospace Applications. The details are still being worked out, and Chung – Yuan Wu, who has graciously agreed to take the role of our SIG’s TPC for the next two years, will have his hands full. I am wishing him best of luck in this role and also taking this opportunity to ask everybody to greet him in this position and give him all the support possible in preparing new Technical Conference in Orlando in 2010.
Alex Savitski SIG 012 Technical Panel Chair, 2008-2009
JOINING NEWS NEWSLETTER OF THE SOCIETY OF PLASTICS ENGINEERS JOINING OF PLASTICS AND COMPOSITES SPECIAL INTEREST GROUP
Volume 20, No. 2 (Fall 2009)
Introduction We want to take the opportunity to inform everyone of what happened during ANTEC 2009, which was held in conjunction with NPE last June. Certainly, grouping those two events together made attending even more appealing. I am sure that everyone will agree that it also made it difficult to choose what to see, as so many interesting things where going on at the same time! We are very happy with the turnout at our various sessions. The quality of the papers and presentations made it difficult for the judges to identify the best in both categories. At the end of the sessions, the SIG awarded the Best Paper to Helmut Potente and his group from Paderborn University for the paper “In-Line Process Optimization Of Hot-Plate Welding Using An Innovative Actuation Concept” presented by Reinhild Hoffschlag. Please see below a copy of this very interesting paper. The Best Student Presentation went to to Mingliang Chen for presenting a paper titled “Finite Element Modeling and Microstructure Analysis for Contour Laser Transmission Welding of Glass Fibre Reinforced Nylon 6”. The SIG is already in preparations for ANTEC 2010 which will be held in Orlando May 16-20. We are working on setting up an Industrial Panel to cover plastic joining in the Aerospace Industry. We are counting on benefiting from the proximity of NASA to get some good participation on the subject. We will ask presenters to make short 15-20 min presentations which would then be followed by a two hours discussion. No papers will be required. There are some executive organizational changes in our Joining SIG. Bobbye Baylis will be retiring soon from her position as Chair. Alex Savitsky has gracefully accepted taking on this very demanding position, and Chung-Yuan Wu will replace him as TPC (Technical Paper Chair). Also, Sergio Amancio will be Secretary, while I will be Newsletter Editor for the next two years. Finally, if you have not yet submitted a technical paper for the upcoming ANTEC (deadline was September 4th), we still encourage you to send one in. The final paper submission deadline is November 13th (5PM Eastern time). Your participation is essential in maintaining and growing the technical vitality of our SIG.
Sophie Morneau Newsletter Editor
Alex Savitsky present the Best Student Presentation award to Mingliang Chen of Queen’s University, Kingston, Ontario.
Bobbye Baylis congratulating Mingliang Chen
Page 1 of 5
In-Line Process Optimization of Hot-Tool Welding using an Innovative Actuation Concept H. Potente**, V. Schöppner**, R. Hoffschlag**, S. Gövert* and J. Schnieders* **University of Paderborn, Institute of Polymer Engineering, KTP * 3Pi Consulting and Management, Abstract This paper looks into the initial steps of the development of a self-optimizing hot-tool welding machine. By employing a new machine concept, it is possible to ensure displacement speeds counter to the direction of joining. This then allows the strength of the weld to be assessed while it is still in the molten state. To be able to use this data for self-optimization, it was necessary to establish a correlation between the short-time strength of the parts in the cooled state and their shorttime strength in the still molten state. Taking these correlations, a systematic approach can be worked out to allow the welding machine to find an optimum processing window with just a few test welds. The results show that the optimum of the joining displacement to the melt layer thickness ratio (sF/L0) can be established for the parameter setting by measuring the tear forces on the welding machine, even without knowing the short-time strength in the cooled state. The same applies for the ratio of the melt layer thicknesses to the wall thickness. Based on these results, the next steps are now to develop a means of selfoptimization and quality assurance during the running hottool welding process.
Problem and Aims Welding complex parts or assembling thermoplastics constitutes a key process step in plastics processing. Hottool welding is one of the techniques employed most frequently [1]. The current trend in joining technology, towards optimizing the methods employed economically and thus reducing the production costs for serial production to a minimum, is gaining increasing significance. In order to employ hot-tool welding successfully, it is essential for the requirements placed on the weld to be fulfilled. These include compliance with the tolerances of the molded part, tightness and the most important quality characteristic of all – the weld strength. To achieve this, the optimum setting parameters for the welding process must be established in advance and suitably tailored to the material and the geometry of the parts to be joined. Guide values published in 1987 are used to determine the optimum point of operation [2]. These guide values for optimizing the process parameters (joining displacement/melting depth, melting depth/wall
thickness) are used as reference values, and do not always lead to the optimum point of operation. It is thus standard practice to carry out parameter studies on the basis of the statistical optimization criteria and to conduct a subsequent test on the weld strength in a short-time tensile test. In the same way, quality tests must be conducted at specific intervals during running serial production in order to monitor the process and the associated quality characteristics. If any deviation is established here, the optimum point of operation must be established once again. Apart from the high costs involved, this also is very time consuming. To overcome this problem, process monitoring and the verification of the associated quality characteristics are to be implemented inline in running serial production. This research project establishes the fundamentals for a systematic method of adaptive process optimization, based on process data from the hot-tool welding machine. The aim is to simplify the determination of the point of operation, and also to monitor this point of operation on a self-optimizing machine by capturing and monitoring the dynamic optimization criteria. By employing a linear drive, it is possible to achieve very slow displacement speeds counter to the joining direction. Based on this, and by using a twin-carriage concept, the tear forces can be determined directly on the welding machine. To allow the new drive concept to be used for self-optimization, it was first necessary to identify correlations between the process data on the hot-tool welding machine and the weld strengths determined in the short-time tensile test.
Materials The investigations were first performed using two materials. One was a PMMA from Degussa and the other an HDPE from Basell. The following table provides an overview of the material properties.
Page 2 of 5
Table 1. Measured material properties Material Basic Glass transition material temperature strength
PMMA HDPE
Mean density
Tg[°C]
σG[N/mm2 ]
ρm[g/cm3]
117 132
81.62 28.736
1.186 0.951
Half dumbbell specimens [Figure 1] were used for the
starts after a constant cooling (tK). Care should be taken to ensure that the welding zone has not cooled down completely, since the machine will otherwise not be able to generate the necessary tearing force. This means that the parts being joined are torn apart directly after the stillmolten welding lugs come into contact with each other. Different cooling times of tK=5 s, 10 s and 15 s were observed to begin with. Material: Pretreatment:
PMMA Welded
Test point
test.
L0/d
Figure 1. Standardized test specimen This test specimen geometry was designed on the basis of existing standardized specimens (DIN EN 61, Type 1; now DIN EN ISO 527) [3].
Test Setup The welding machine employed is equipped with a linear drive rather than the conventional hydraulic, pneumatic or rotational servomotor drives. This permits accelerations up to 4.5 times the acceleration due to gravity and a maximum speed of 2500 mm/s. A twin carriage concept was developed. With this concept, the clamping device is uncoupled from the actual carriage, thus avoiding any recording of disturbances due to friction and loss forces. By applying a force-measuring system to the guide carriage, it is possible to establish the tear forces between the parts being joined when the carriages are moved apart. Conducting an experimental design [Figure 2], the optimum process parameters for hot-tool welding were established. The following parameters were varied: the temperature of the heated tool (TH), the residual melt layer thickness (LR), the pressureless heating time (tE), the melt layer thickness (L0), the ratio of the melt layer thickness to the wall thickness of the part being joined (L0/d) and the ratio of the joining displacement to the melt layer thickness (sF/L0). The short-time tensile strength was tested after each run with standard tensile tests. In a further step, specimen parts were welded and torn apart on the welding machine. This tearing process
Testing speed welding machine: Testing speed tensile test:
4.1 4.9 4.17 4.25 4.33 4.41 4.49 4.57 4.65 5.1 5.9 5.17 5.25 5.33 5.41 5.49 5.57 5.65 6.1 6.9 6.17 6.25 6.33 6.41 6.49 6.57 6.65
0.5 0.5 0.5 1.4 1.4 1.4 1.5 1.5 1.5 0.5 0.5 0.5 1.4 1.4 1.4 1.5 1.5 1.5 0.5 0.5 0.5 1.4 1.4 1.4 1.5 1.5 1.5
L0 [mm] 1 1 1 2.28 2.28 2.28 3 3 3 1 1 1 2.28 2.28 2.28 3 3 3 1 1 1 2.28 2.28 2.28 3 3 3
Pressureless heating time t'E [s] 5.5 5.5 5.5 16.5 16.5 16.5 26 26 26 5.5 5.5 5.5 16.5 16.5 16.5 26 26 26 5.5 5.5 5.5 16.5 16.5 16.5 26 26 26
Time to tearing tk [s] 5 5 5 5 5 5 5 5 5 10 10 10 10 10 10 10 10 10 15 15 15 15 15 15 15 15 15
50 mm/min 5 mm/min
SF/L0 0.3 0.75 0.9 0.3 0.75 0.9 0.3 0.75 0.9 0.3 0.75 0.9 0.3 0.75 0.9 0.3 0.75 0.9 0.3 0.75 0.9 0.3 0.75 0.9 0.3 0.75 0.9
Joining displacement SF [mm] 0.3 0.75 0.9 0.684 1.71 2.052 0.9 2.25 2.7 0.3 0.75 0.9 0.684 1.71 2.052 0.9 2.25 2.7 0.3 0.75 0.9 0.684 1.71 2.052 0.9 2.25 2.7
Figure. 2. Sample experimental plan without repeats The tearing operation on the welding machine is performed on a velocity-controlled basis, with the test velocity being set at 50 mm/min for all materials. The relevant measuring data (displacement, force measuring data) are captured online on the welding machine. The force-measuring system installed transmits the measuring data at intervals of 100 ms. On the basis of these data, it is possible to compile a displacement and force measurement curve over the cycle time for each parameter setting [Figure 3]. Using these curves, the required forces and work on the welding machine were read off and were then used to identify correlations with the force curves gained from the short-time tensile testing unit.
Page 3 of 5
thickness of part being joined) and the contact surface (AK) that develops between the two welding beads.
180 Bereich für die Area for the spätere Ermittlung subsequent der zum Zerreißen Determination of the verwendeten Kräfte forces applied und Arbeiten auffor der Schweißmaschine Tearing and work on
190 180
130
80
Wegmesskurve
displacement measurement curve
the welding machine
170
Kraftmesskurve curve force measurement
30
160
0 -20
150 140
K K
200
[N][N] ForceKraftmessdaten measuring data
Wegmessdaten [mm] Displacement measuring data [mm]
Weg- undand Kraftmesskurven aufgetragencurves über die over Zykluszeit Displacement force measurement the cycle time
d
-70 0
50
100
150
200
250
300
l-Phase
Cycle time[s/10] [s/10] Zykluszeit Heating time Erwärmzeit
Tearing time Zerreißzeit
Umstellzeit Switchover time
b
Schweißzeit Welding time
Section Schnitt A-A A-A
Figure 5. Diagram of a load-bearing cross-sectional area Figure 3. Sample displacement and force measurement curve plotted over the cycle time Once all the relevant results were available, it was possible to plot the characteristics of relevance to quality (short-time tensile strength, force on the welding machine and work) over the ratio of the joining displacement to the residual melt layer thickness, or the ratio of the residual melt layer thickness to the wall thickness of the part being joined.
Results The initial results have shown that, in comparison to the curves from the short-time tensile testing unit, simply plotting the forces and work on the welding machine is not sufficient for low-value dimensionless variables [Figure 4]. Optimum Optimum tensile Zugprüfanlage testing unit
Force theder tensile testing unit [N] Kraftonauf Zugprüfanlage [N]
PMMA T H = 277°C LR = 0,57 mm
-20
tensile Zugprüfanlage
-21
testing unit
2500
-22 2000 -23 1500 -24
1000
Schweißmaschine Welding machine
Apparent optimum scheinbares Optimum welding machine Schweißmaschine
Kraft on aufthe der welding Schweißmaschine [N] Force machine [N]
3000
-25
500
-26 0,4
0,6
0,8
1
1,2
1,4
1,6
L0/d - Verhältnis
L0/d ratio
Figure 4. Comparison of the short-time tensile strength with the tearing force on the welding machine via the L0/d ratio and a constant LR of 0.57 mm In a second step, it was thus necessary to identify factors that influence the forces and work on the welding machine. These factors can then be used to apply a correction. Alongside the load-bearing cross-sectional area (A) another correction value that was found to be of relevance is the dimensionless joining displacement (sF/L0). Figure 5 shows the load-bearing cross-sectional area. This is obtained from the starting area (AB = width *
Since more material is displaced into the welding bead with an increasing joining displacement is increased, there is also a bigger cross-sectional area, which must be taken into account through an appropriate area correction. Working on the basis of the investigations, a statistical study was conducted of the correlations. The target variables here were the forces on the tensile testing unit (FZug.). The influencing variables were the tearing forces (FZer.) and the tearing work (WZer.) on the welding machine, in conjunction with the correction values (A and sF/L0). Working on the basis of this data, a statistics program provided a numerical model in each case (see Eqn. 1). s s FZug . = b0 + b1 ⋅ F + b2 ⋅ Fzer . + b3 ⋅ A + b4 ⋅ ln F L 0 L0 s + b6 ⋅ exp F + b7 ⋅ exp FZer . L0
b0 = -10750196,6029 b1 = 1590544,3538 b2 = 1118,7479 b3 = 10942,1493
+ b5 ⋅ ln A (1)
b4 = 383739,2178 b5 = 2782003,5842 b6 = 1374403,2898 b7 = 21697192804342,4766
Using this statistics program, it is possible to achieve a coefficient of determination in excess of 99.52 %. Figure 6 shows a comparison of the statistically evaluated forces and work on the welding machine, set against the forces on the tensile testing unit. The joining displacement (sF) and the melt layer thickness (L0) were varied here, while the residual melt layer thickness was kept constant at LR = 0.57 mm. The heated tool temperature was 277 C. The curve profiles display clear similarities. The forces increase with the sF/L0 ratio, attaining a maximum value at sF/L0 of 0.68. If the sF/L0 ratio increases further, the forces will fall again.
Page 4 of 5
1600
1600
welding machine 0,4
0,45
0,5
0,55
0,6
0,65
0,7
0,75
0,8
0,85
sF/L0 ratio
Zugprüfanlage Tensile testing unit 1400
1200
1200
Schweißmaschine Welding machine 1000
1000
800
800
600
600
400
400
200
200
0
Figure 6. Comparison of the short-time tensile strength with the tear strength on the welding machine versus the sF/L0 ratio and a constant LR of 0.57 mm The difference between the curve profiles that is seen with bigger sF/L0 ratios can be attributed to the area correction that is employed. It becomes clear, however, that, by measuring the tearing forces directly on the welding machine, it is possible to determine the optimum sF/L0 ratio for the parameter setting without having to have recourse to an elaborate parameter analysis with subsequent tensile tests on the short-time tensile unit. Corresponding statements can also be made on the melt layer thickness/wall thickness ratio (L0/d). Here too, virtually parallel curve profiles can be observed [Figure 7]. In the same way, the parameter optimum, which is achieved with an L0/d ratio of 0.9, can be determined without knowledge of the short-time tensile strength. With the data that has been determined and a specified wall thickness, it is now possible to calculate the melt layer thickness and the joining displacement.
(korrigiert mit sF/L0 und A) (Corrected with sF/L0 and A)
optimum welding machine
Force on auf the der tensile testing unit[N] [N] Kraft Zugprüfanlage
tensile testing unit
1400
(corrected by sF and A)
force on the welding machine
force on thetensile testing unit
PMMA TH=277°C LR=0,57 mm
HDPE T H = 217 °C LR = 0,17 mm
Kraft Schweißmaschine Force on auf theder welding machine [N]
optimum tensile testing unit
0 0,1
0,15
0,2
0,25
0,3
0,35
0,4
0,45
0,5
0,55
LL0/d Verhältnis /d- ratio 0
Figure 8. Comparison of the short-time tensile strength with the statistically established tear strength on the welding machine (corrected with sF/L0 and A) over the L0/d ratio and a constant LR of 0.17 mm
Prospects To achieve a self-optimizing hot-tool machine, the optimization tests presented have to be integrated in the process control. A schematic sequence plan for parameter optimization and quality control is set out in the following Figure 9. 1. Establishment of the melting curves Regression equation 2. Internal software calculation Experimental plan
optimum welding machine
0,4
0,6
0,8
tensile testing unit
welding machine 1
1,2
1,4
Tolerance exceeded (corrected with sF and A)
optimum tensile testing unit
PMMA TH=277°C LR=0,57 mm
force on the welding machine
force on the tensile testing machine
3. Tensile tests on the machine
1,6
L0/d ratio
Figure 7. Comparison of the short-time tensile strength with the tear strength on the welding machine versus the L0/d ratio and a constant LR of 0.57 mm The presentation of the results taking the example of PMMA shows clearly that the optimum process parameters can be determined without tensile tests on the short-time tensile testing unit [Figure 8]. Further-reaching investigations show that a close approximation of the curves can be achieved for a semi-crystalline thermoplastic too, which would permit a statement to be made on the optimum machine setting parameters.
Optimized setting Parameters within tolerance
5. Quality control via SPC
4.Series welding
Figure 9. Schematic diagram of the sequence plan for parameter optimization and quality control, including the tensile test on the hot-tool welding machine [4] To achieve this, the machine must be put in a position to compile an experimental plan itself. The knowledge of the melting behavior that is required for this can be acquired from just a few experimental measurements. The result obtained is a function that can be used to calculate the necessary pressureless heating time (Point 1). With this function, an experimental plan can be compiled and conducted by the machine program. (Point 3). To this end, the parts being joined are torn apart while still in the molten state, and a point of operation is
Page 5 of 5
established from the measured forces, which is then used as the starting point for serial production (Point 4). This point can be employed in the sense of SPC (Statistical Process Control) to perform quality control (Point 5). For the optimum point of operation a tolerance band has to be allocated for the forces and the work. The welded parts can be inspected at regular intervals directly on the welding machine and, through the tolerance band that has been set, conclusions can be drawn regarding the quality of the weld. At present, further-reaching investigations are being conducted with amorphous and semi-crystalline materials (filled and unfilled) in order to identify generally-valid correlations and to describe these with statistical methods and, if possible, with mathematical models.
Conclusion From the investigations, it has become clear that, by using a linear-drive hot-tool welding unit, it is possible to verify the point of operation directly on the machine. Since the parts being joined have to be torn apart while still in the molten state, on account of the low tensile and clamp forces available on the machine, it is necessary to create an underlying basis showing that correlations exist between the short-time tensile tests employed as standard and those carried out on the welding machine. Correcting the tearing forces with physical influencing variables and subsequently assessing them in a statistical assessment program has shown that it is possible to describe the short-time tensile strength by means of the numerically determined equations with a prediction of up to 99 %.
References 1.
Potente, H.: "Grundlagen des Fügens von Kunststoffen" Skript zur Vorlesung, Institut für Kunststofftechnik, Universität Paderborn 2. Kreiter, J.: "Optimierung der Schweißfestigkeit von Heizelementstumpfschweißungen von Formteilen durch verbesserte Prozessführung und Selbsteinstellung". Dissertation am Institut für Kunststofftechnik (KTP), Universität-GH Paderborn, 1987 3 Potente, H.; Brüssel, A.: "Qualitätsrelevante Parameter beim Schweißen von gefüllten und verstärkten Systemen mittels Heizelement". AIFAbschlussbericht No. 9802, 1997 4 Potente, H.; Wilke, L.; Schnieders, J.: "Neue Perspektiven beim Heizelementschweißen“ SKZ Seminar „Heizelement", Würzburg Mai 2006, Institut für Kunststofftechnik, Universität Paderborn
Key Words: Hotplate Optimization
Welding,
In-Line
Process
JOINING NEWS NEWSLETTER OF THE SOCIETY OF PLASTICS ENGINEERS JOINING OF PLASTICS AND COMPOSITES SPECIAL INTEREST GROUP
Volume 20, No. 2 (Fall 2009)
SIG 2010 Executive Committee Chair Alex Savetsky Baxter Healthcare TPC Chung-Yuan Wu Visteon Corporation Newsletter Editor Sophie Morneau Branson Ultrasonics Corporation Secretary Sergio Amancio GKSS Forschungszentrum GmbH Institute of Materials Research - Germany
Board Members Alexander Savitsky -- Chair Engineering Specialist Baxter Healthcare Baxter Healthcare, RLT-04 25212 w. Route 120 Round Lake, IL 60073 USA Phone: +1 847-270-2187 Fax: +1 847-270-4966 [email protected] Sergio Amancio -- Secretary GKSS Research Centre Max-Planck Str 1 D-21502 GEESTHACHT GERMANY Phone: +49 4152 87 2066 Fax: +49 4152 87 2023 [email protected] Sophie Morneau -- Newsletter Editor Manager, Applications Laboratory Branson Ultrasonics Corporation 41 Eagle Road Danbury, CT 06813 USA Phone: +1 203-796-0305 Fax: +1 203-796-0363 [email protected] Chung Yuan Wu -- Tech Program Chair Technical Fellow Visteon Corporation 3023 Gallinger Drive Ann Arbor, MI 48103 USA Phone: +1 734-710-2383 Fax: +1 734-736-5576 [email protected] James S. Griffing -- Executive Committe Liaison Technical Fellow Boeing Co. 6609 234th Street SW Mountlake Terrace, WA 98043 USA Phone: +1 425-717-1203 [email protected]
Society of Plastics Engineers
