EXPERIMENTAL RESEARCH ON ULTRASONIC WELDING OF MATERIAL COMBINATIONS COPPER-COPPER

Transcription

1 EXPERIMENTAL RESEARCH ON ULTRASONIC WELDING OF MATERIAL COMBINATIONS COPPER-COPPER As. dr. ig. Corelia LUCHIAN, as. dr. ig. Delia GÂRLEANU, cof. dr. ig. Gabriel GARLEANU, prof. dr. ig. Florea DUMITRACHE Politehica Uiversity of Bucharest, Romaia, corelia Abstract:This paper presets the optimum ultrasoud weldig parameters of copper sheets usig static aalysis methods results ad microscopic structural aalysis. Also it get the coclusio that weld formatio it s produced after the plastic deformatio process of metals because the actio of ultrasoic eergy i the joit area. KEYWORDS:Ultrasouds, Optimum tehology, Copper 1. THEORETICAL CONSIDERATIONS Ultrasoic weldig of metallic materials is part of the processes of weldig pressure i solid shape. Eergy required for weldig is itroduced i welded compoets, the challege of combiig vibratios istead, with a appropriate frequecy ultrasoud( Hz), welded compoets are pressed with a ormal force o their surface cotact. The simultaeous actio of vibratio ad pressig force producig oscillatig tesio i the eighborig areas of cotactless. This leads to slip ad frictio betwee the two compoets soldered, to expel oxides ad impurities from the surfaces i cotact, thus remai, easier hardware implemetatio of metal ties of the two compoets. I area a-a a weldig poit formed whose size depeds o the time of weldig (peetratio is mm). Area b-b, where the metal particles vibrate, is 3 more the i area a-a. [1],[3]. Processes occurrig i ultrasoic weldig of metallic materials must be uderstood as a series of pheomeals, which ifluece each other: developmet of heat ad pressig superficial surface layers uder the actio of pressig ad of frictio; plastic deformatio; hardeig ad recrystallizatio; diffusio ad micro-weldig cotiues traiig betwee those two welded metals. The most importat part of a ultrasoic weldig equipmet is the ultraacoustic system. It cotais the trasducer, acoustic cocetrators ad tool. I geeral, the choice of weldig parameters it s made from table, diagrams or omogrames. The chose values of parameters represets just oe startig poit, because for each material ad weldig equipmet type it sets optimal parameters of weldig regime oly experimetally. I most cases the quality of welded jois is estimated metallographic way by determiig the shearig-tractio force F, eeded to break the joi of two welded bars. The statistic aalysis of the results presumes the calculatio of the followig measures[1]: - the medium value of the tractio break force, that is calculated with the relatio: 1 F Fi (1) i 1 - the corrected dispersio, with: 75 Fiabilitate si Durabilitate - Fiability & Durability No 1/ 1

2 1 1 i 1 - the corrected medium square deviatio, with: s ( Fi F) () s 1 ( Fi F ) 1 i 1 (3) - the variatio coefficiet W, with: W s 1 F (4) where: is the tested value ; - umber of measuremets To exclud the result of a reject we use the studet criterio: Fj F t s (5) where: is the tested value (the highest or the lowest i the measuremets); - the medium value of the tractio break force. To verify the hypothesis that two radom medium values ad belog to the same real value, first the F test is used: F s 1 /s (6) ad the the t test,uder the form : F 1 F 1 t s (7) where:, are the studied medium values; ; the umber of experimets where were determied; - the corrected medium square deviatio, calculated as such: f1 s1 f s s (8) f where: f 1 = 1-1; f = -1; f=f 1 +f = are the degrees of freedom.. EXPERIMENTAL RESULTS To obtai high quality joits is sufficiet degreasig copper specimes [1,,3]. The samples were also determied optimum values of force ad time pressure weldig coditios: f = 1.6 khz frequecy ad amplitude of the oscillatio of the tool Geometrical form of the active part is represeted i Fig.1. Amplitude of the oscillatio measuremet tool 1 has bee established through the pressig force eeded for weldig copper samples(444n).for values greater tha his magitude is practically ascertaied. 76 Fiabilitate si Durabilitate - Fiability & Durability No 1/ 1

3 Fig. 1. Geometrical form of the active part Fig. Depedece of oscillatio amplitude of the tool ad dowforce Usig the pressig force ad weldig times t=,5 s, 3 s, 8 s ad reproducible values were obtaied resistace weldig poits (Table 1) Time of weldig (N) (N),5 3, 8, Table 1 Depedece of resistace weldig poits by time of weldig Tesile stregth of base metal 41,6 4,6 44,3 4,38,9 3, W (%) 15 Degree of deformatio i the welded zoe % 11,4 16,6 37, 8x Fig.3 welded joits micro structure Copper-copper t=. s 8x Fig. 4 welded joits micro structure copper-copper t=s 77 Fiabilitate si Durabilitate - Fiability & Durability No 1/ 1

4 8x Fig. 5. welded joits micro structure Coppercopper t=1 s; 8x Fig.6. welded joits micro structure coppercopper t=3s It is foud that weld stregth depeds o the umber of welded areas (microwelds) of the weldig poit (Fig. 3, 4, 5, 6). With icreasig weldig time icreases the umber ad size of these zoes icreases weld stregth. Thus the tesile stregth icreases from 47% of the base metal stregth for t =,5s, 7% for t = 3s to 76% for t = 8s. Of these statistically sigificat icreases i resistace. Depedece of tesile stregth ad weldig time, for differet values of the pressig force is represeted i Fig. 7. With icreasig weldig time from 3s to 8s icreases the degree of plastic deformatio apruvetelor welded area, which leads to lower their sectio i this area, makig them uusable. From these cosideratios it follows that the optimal weldig time is t = 3-4s. Stregth of welded joits depeds o the size of the pressig force F (Fig. 8).I example,for t=3s ad,fids that from 6 N to 444 N obtai a marked icrease of tesile stregth, ad from 444 N to 494 N the chagig of is ot sigificat statistically speakig. Physical sese of this reality is that the greater the dowforce tha the better coditios are created for the destructio of oxide layers, hece creatig a greater umber of welded parts. 78 Fiabilitate si Durabilitate - Fiability & Durability No 1/ 1

5 Microduritate HV F [N] P = 94 N P = 15 N P = 444 N P = 75 N P = 49 N t [s] Fig. 7 Depedece of tesile force F durig weldig t. 1 8 t =,5s t = 3,s t = 8,s Distata 1 1 [mm] Fig. 8 Depedece of breakig tractio force F pressig force Fp Fig. 9 The variatio of the H micro grid irregularity. 79 Fiabilitate si Durabilitate - Fiability & Durability No 1/ 1

6 a. b. Fig. 1. Ultrasoic weldig plat used for weldig. a-geeral view; b-ultrasoic block detail I additio, icreasig pressure icreases the degree of plastic deformatio, which produces udesirable pheomeo-weakeig of the weld sectio. As such the value Fp = 4-7 N provide optimum coditios for obtaiig quality welds. The measured values of microhardess (Fig. 9) show that for t =.5s ad 3s, hardeig occurs i the joit as a result of plastic deformatio of metals, which takes place whe the joits are made. For higher weldig speeds(t=8s) there is a decrease i the cocetratio of defects ad recrystallizatio. Ultrasoic weldig plat used for weldig,is represeted i Fig.1. 8 Fiabilitate si Durabilitate - Fiability & Durability No 1/ 1

7 3. CONCLUSIONS O ultrasoic weldig of metallic materials, vibratios produced by magetostrictive trasducer ad amplified by acoustic cocetrators are trasmitted at the joi by a parallel pla with the cotact surface. The simultaeous actio of vibratio ad pressig force is producig oscillatig tesio i areas eighborig the cotact. This leads to slidig betwee the two welded compoets at the expel of the oxides ad impurities from the surfaces i cotact, followig such the achievemet of metal coectios of the two compoets; The processes occurrig i ultrasoic weldig of metallic materials should be uderstood as a series of pheomea, which ifluece each other: developmet of heat ad pressig superficial layers uder the actio of pressig ad frictio, plastic deformatio, hardeig ad recrystallizatio, diffusio ad formatio of micro welds betwee the two compoets of the joit; Almost all materials ad metal alloys ca be welded with ultrasoud, but the procedure is ot always the most ecoomical. I each case, the optimal weldig parameters are established experimetally; Ultrasoic weldig process is already applied idustrially i the electrical idustry to maufacture miiaturized compoets of differet types of electrical cotacts.the compoets that lead electrical power made of differet materials, such as alumium, copper, silver must be well welded alog with calibrated thi wire with high power desity. REFERENCES [1] Corelia LUCHIAN, Cotributii teoretice si experimetale privid sudarea cu ultrasuete a materialelor compuse, Teza de doctorat, Bucuresti, 7; [] Gheorghe AMZA, Sisteme ultraacustice, Editura Academiei Bucuresti, 5; [3] Florea DUMITRACHE Ultrazvukove bodove zvaraie iektorych kombiacii ezelezycs kovov. Teza de doctorat Bratislava, Fiabilitate si Durabilitate - Fiability & Durability No 1/ 1