CONTRIBUTIONS TO ULTRASONIC WELDING OF INTELLIGENT COMPOSITE MATERIALS USED IN VEHICLE MANUFACTURING

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1 The 4th International Conference Advanced Coposite Materials Engineering COMAT October 01, Brasov, Roania CONTRIBUTIONS TO ULTRASONIC WELDING OF INTELLIGENT COMPOSITE MATERIALS USED IN VEHICLE MANUFACTURING Z. Apostolescu 1, G. Aza 1, M. Dragoir Groza 1, S.L. Paise 1 Polytechnic University of Bucharest, Roania, aza@cais.pub.ro, zoia@cais.pub.ro. Abstract: The paper presents ain ethods of peranent joining of sart coposite pulling into obvious advantages of using ultrasonic energy. Experiental results are presented ultrasonic welding used in the construction of intelligent coposite autootive buper protection and soe intelligent auto stops. Key words: sart, coposite, welding, ethod. 1.INTRODUCTION Making sart coposite parts through assebly welding technology is very coplex because it ust take into account a nuber of factors related to the intelligent processing of coposite aterials and technological paraeters, echanical and acoustic influencing a greater or lesser extent sall welding process. The ain eleents to be taken into account, related to sart coposite aterials processing are: the nature of the coponents that ake sart coposites, atrix sart coposites, reinforcing eleents, sensors or sensor syste used, the geoetric configuration of the surfaces to be joined, overall diensions the surfaces to be joined, the properties of each coponent of sart coposite aterials and overall syste properties, how to obtain coposite aterials sart grid sensors, productivity required.. WELDING PROCESS PARAMETERS OF SMART COMPOSITES Ultrasonic welding sart coposites depends on three categories of paraeters: acoustic and echanical. The ain technological paraeters of welding process are: the nature of atrix sart coposites, the reinforcing nature of the ite, condition of cobined surface, thickness cobined aterials, the requireents of the functional role; welding ethod, the nuber of acoustic energy concentrators etc. Acoustic paraeters are related ultrasound syste used for ultrasonic welding syste, they are: type ultrasonic oscillations excited in the syste, oscillation aplitude, oscillation frequency, intensity ultrasonic energy, energy density ultrasound, size, shape and aterial sonotrode and anvil acoustic for factor of ultrasonic energy concentrator, reflection and absorption qualities of the support, pre-heating teperature, etc. sonotrode. Mechanical paraeters with significant influence on the welding process are: pressed static force, local contact pressure surfaces cobined, ultrasound etc during activation. Synthesis welding process paraeters shown in figure 1. /1/,//. To optiize the ultrasonic welding of a sart coposite aterial is to find an objective function that includes all factors shown in figure 1 and deterine the iniu cost and axiu productivity of the process in ters of a outstanding quality of the welded joint. In ost cases, investigating the influence of various paraeters on the quality of welded joints ultrasound is done by deterining the breaking strength and tensile shear tests at an angle of 45 and 90 to the plane of the joint. Reproducibility is ade by cobining quality variation coefficient kv, given by: k v 100 N (1) 85

2 where: σ is the standard deviation of effort shear or tension, N - arithetic ean value of shear or tension, which is deterined by the relationship: 1 n N N i n i1 () where n is the nuber of individual easureents, Ni - the value of individual easureents. deviation σ is deterined by the relationship: n i 1 N N n 1 i and its value is particularly significant because the deterination error is ± 1.5%.. (3) Figure 1: Ultrasonic welding process paraeters of sart coposites This work ais to establish the influence of acoustic paraeters of the welding process on the quality of welded joints. /1/,//,/3/. Types of sensors and their distribution network have direct influence on the actual welding paraeters nor the quality of welded joints obtained. But bear in ind that the sensor network ust be designed so as to not interrupt or welded joints are not affected sensors during welding, thus indicating sart coposite aterial and property of intelligence. It is iportant when designing the track to consider how to place sensor network (actuators) and sensors, so that the functional role of the part to be observed and the continuity of the network is not affected. Research undertaken using optical fiber sensors and piezoceraic plates showed that if they are included in the joint, there is a deterioration of the fiber surface protection and a depolarization of plates with piezoceraic sensors loss properties. /4/, /5/, /6/, /8/. 86

3 3. CONTRIBUTIONS ACOUSTIC PARAMETERS INFLUENCE THE QUALITY OF WELDED JOINTS ULTRASONIC SMART COMPOSITES One of the phenoena that cause sea quality is the eergence and developent of plastic deforation in the aterial layers cobine, on which a particular influence have joint training acoustic conditions. Different acoustic conditions can be produced by the action of the eleents that cobine different types of oscillation: longitudinal, shear, bending, torsion and cobinations whose exciteent in the joint is achieved through design, construction and systes specific ultrasound used for initiation and propagation of ultrasonic oscillations. /1/, //. Experiental research conducted has shown that the excitation of longitudinal waves in sonotrode, ie ultrasound syste for calculating the resonant frequency of longitudinal waves, cobining resistance and coefficient of variation kv depend on the length of the sonotrode properly and where the force is applied static push. Quality of welded joints obtained with systes that excite and propagate bending oscillations is lower than joints ade with longitudinal waves, this explaining the large variation in the input ipedance of the autoregulation syste frequency The experiental results obtained with soe sart coposite aterials with polyeric atrix showed that the ost effective systes are those in which ultrasound excites and propagates oscillations or oscillations longitudinal-transverse shear as it provides the best destruction and reoval of oxide layers surfaces to be joined, fail better to liit oxygen penetration in the contact area, producing a coplex oveent of the aterial in the contact area and creates favorable conditions for achieving the highest quality joints./1/, //, /3/, /4/, /5/ Influence of ultrasonic oscillation aplitude on the quality of welded joints The foration of the welded joint using ultrasonic oscillations depends to a large extent I sonotrode aplitude oscillations and static power pressing Ps. 1 is transitted oscillations sonotrode aterial cobined and 3 (Fig. ) and acoustic anvil 4, each vibrating with corresponding aplitudes fulfilling the condition: /1/, //. As > Aps > Api > An (4) P s S Al As A ps Api A Sn Figure : Schee when welding ultrasonic vibration of coposite aterials with polyeric atrix? E M a t e r i a l u l = A B S F r e c v e n t a = 0 k H z µ Figure 3: Energy loss ΔE, based on dry friction coefficient μ, the frequency of 0kHz Between sonotrode and top part triggers a force Fs, of the for: 87

4 Fs = I sin ωt (5) and between parts and 3 in contact and friction acting Ff, of the for: Ff = I sin ωt (6) pressure and static power Ps. Relationship exists between these forces: Ff μps (7) Ff μps as long as the two aterials overlap oscillates without it appearing only when Ff> Ps and the energy loss ΔE is the largest (Fig. 3). Experientally deterined optiu value for static pressure Ps force eight for: Ps eight = Sc σc (8) where: Sc is the contact surface sonotrode - top piece, σc - yield liit of the aterial at the reference teperature of 0 C. Knowing the pressure aplitude of the sonotrode can deterine the best optial, considering that the optiu tangential force Pt eight that appears is: P t opt = k μ Psopt (9) and leads to the appearance of the weld voltage shift τf, of the for: τf = τx sin ωt (10) The link between τx, Aps and Api is: x Aps Api 10 h k G (11) where: h is the height of the zone of plastic deforation, G - shear odulus, τx - yield shear in the joint and is expressed as: P s x s 1 3 a s (1) where: is a coefficient depending on the construction sonotrode ( = 0, 1,, 3); τs-shear yield strength of the aterial it is ade sonotrode, a - coefficient depending on the thickness of the welding parts ( a = s) s - thickness welding parts. /1/, //, /3/. For exaple, sart coposite aterials with polyeric atrix (ABS) to find optial link next relationship: x As 3,3 10 h k G (13) Breakthrough influence the aplitude of the ultrasonic welded joint shown in figure 4.6. It is noted that if the aplitude of the ultrasonic vibration is reduced and Fr joint resistance is also reduced, and the aplitude values lower than a iniu value I in, the cobination does not occur. The front of the sonotrode aplitude of the oscillations depends on dosage acoustic energy in the joint, which should be higher in the first stage to achieve intiate contact between the surfaces to be joined. After creating physical contact foci foration stage of interaction between the surfaces to be joined and increase their contact surfaces is necessary to reduce the aplitude of oscillations up to 50% of its initial value to prevent broken links that were fored. At this stage all acoustic energy is spent on speeding up the process of plasticization and elting the aterial in the joint. F r [ d a N ] t =. 0 s t = 1. 0 s t = 0. 5 s t = s A s [ µ ] Figure 4: Influence of sonotrode aplitude of Breakthrough As Fr, at different ties of welding. 88

5 As Materialul = ABS Frecventa = 0kHz t [s] Figure 5: I sonotrode aplitude variation, while for different types of oscillations: 1 - longitudinal, - shear 3 - bending, 4 - longitudinal, torsional, 5 torsional Teperature increase in the contact area increases heat atos which favors the transfer of aterial in icropores existing daage diffusion process. Therefore, the aplitude variation in the two stages of the process of foration of the joint ust be of the for shown in figure 5, depending on the type oscillation excited and propagated in sonotrode./1/, //, /3/ Acoustic intensity influence the quality of welded joints Deterination of optial acoustic intensity is a rather coplex because it depends not only on output power and aplitude ultrasound the syste but also the nature of the sonotrode tip oscillation that propagates into the ultrasound, welded shape, size and nature of the surfaces in contact cobined aterials. F r [ d a N ] A s = 3 µ P s = 1 0 d a N D f = I u [ w / c ] Figure 6: Variation of tensile strength of welded Fr Is acoustic energy density,for different plastics Experientally it is found that as the acoustic energy density increases during joint training lowers and increases the tensile strength of the joint (Fig. 6) but there is an optiu, which is understandable because if it exceeds a certain acoustic energy density, greatly increases heat in the contact area and the aterial begins to destroy. How noise affects energy density is very different depending on the aterial to be joined and the diensions of the joint. It is noted that there is always an optial acoustic energy density depending on the nature of the aterial, the aplitude and static force pressing the sonotrode in the cobined./1/, //. 4. CONCLUSIONS The experiental results obtained in welding sart car stops and soe intelligent auto bupers allow the following conclusions: - The quality of welded joints is expressed priarily by tensile strength deterined by testing shear and tension at an angle of 450 and 900 to the plane of the joint; - Optiize welding process involves finding a sart coposite objective functions encopassing technological paraeters, acoustic and echanical and deterination of iniu cost and axiu productivity in ters of a outstanding quality of the weld; - The foration of welded joints with ultrasound depends to a large extent and aplitude of the oscillations sonotrode contact surfaces of icro irregularities surfaces to be joined. 89

6 REFERENCES [1] Aza Gheorghe, Ultrasound of high energy - Ed. Acadeiei, Bucureşti, [] Aza Gheorghe, Systes ultraacustice Ed. Tehnică, Bucureşti, [3]. Aza, Gh. Borda C., Marinescu M., Arsene D., Design of Ring Type Ultrasonic Motor Scientific Session of the University "Petru Maior" - Targu Mures, 7-8 oct. 001, vol.6, pa.7-14, Petru Maior University Press - Targu Mures, 001, ISBN , vol.6isbn [4] Berlin, A.A., et al. Principles of Polyer Coposite, Ed. Springer Verlag, New York 1986 (Polyer Properties and Aplications, vol. 10). [5] Dry M. Carolyn, Sottos, R. Nancy, Passive sart self-repair inpolaer atrix coposite aterials- Sart Structures abd Materials 1993, Albuquerque, N.M. USA- Proceedings of SPIE The International Society for Optical Engineering v , Publ by Society of Photo Optical Instruentation Engineers, Belligha, WA USA, p [6] Gandhi M.V. and Thopson B.S., A New Genertaion of Revolutionary Ultra Advanced Copostes Materials Faturing Electro-Reological Fluide, U.S Ary Research Office Workshop on Sart Materials Structures and Matheatical Issues, [7] Ki, J., Varadan V.V., Varadan V.K. and Bao X.Q., Finite eleente odelling of a sart cantilever plate and coparison with experients, Sart Materials and Structures, vol. 5, 1996, pag [8] Lawrence C.M., Nelson D.V., Spingarn J.R., Measureent of process-induced strain in coposite aterials using ebedded fiber-optic sensors, SPIE Vol. 718, San Diego, 1996, pag