5_UndetachJoints.pdf

Gépelemek 1. UNDETACHABLE JOINTS Authors: Dr. Kerényi György Molnár László, Dr. Marosfalvi János, Dr. Horák Péter, & Dr. Baka Ernő Anyaggal záró kötések| GÉPELEMEK 1. előadás 1 Undetachable joints Gépelemek 1. − Welding − types − method − Calculation − Glueing − pros&cons − method − Calculat...

Gépelemek 1. UNDETACHABLE JOINTS Authors: Dr. Kerényi György Molnár László, Dr. Marosfalvi János, Dr. Horák Péter, & Dr. Baka Ernő Anyaggal záró kötések| GÉPELEMEK 1. előadás 1 Undetachable joints Gépelemek 1. − Welding − types − method − Calculation − Glueing − pros&cons − method − Calculation − Soldering − types − method Anyaggal záró kötések| GÉPELEMEK 1. előadás 2 Welded joints Gépelemek 1. In metalworking, a welding joint is a point or edge where two or more pieces of metal or plastic are joined together. (with same materials) They are formed by welding two or more workpieces according to a particular geometry. Advantages. • Big strenght (nearly same as the component strenght), • Indispensable for special manufacturing, • Maintenance for cracked & weared elements, • Productive, can be easily automated with robots, • Advantageous shapes can be designed from deflection & strenght point of view. Anyaggal záró kötések| GÉPELEMEK 1. előadás 3 Welded joints Gépelemek 1. Disadvantages: • Just for certain materials, • Warpage occurs because of the high local heat concentration, • After-welding process is needed, • No damping effect, • At quality welding the non-destructive control of the joint is cost effective. Welding techniques of metals: • MMA Metal manual Arc, • MIG Gas Metal Arc Welding, • TIG Gas Tungsten Arc Welding, • FCAW Flux Cored Arc Welding • SAW Submerged Arc Welding • SMAW Stick Shielded Metal Arc Welding, • Resistance welding, • Forge welding (e.g.: spot welding), • Friction welding, • Induction welding. Anyaggal záró kötések| GÉPELEMEK 1. előadás 4 Welded joints (Main Types) Gépelemek 1. Anyaggal záró kötések| GÉPELEMEK 1. előadás 5 Welded joints Gépelemek 1. Anyaggal záró kötések| GÉPELEMEK 1. előadás 6 Different Welded joints Gépelemek 1. Anyaggal záró kötések| GÉPELEMEK 1. előadás 7 Welded joints Gépelemek 1. (HAZ) Heat affected zones of welded joints 1) Weld metal (bead): In fusion welding, a portion of the base metals surrounding the junction is melted and re-solidified. The zone around the junction that melts and re-solidifies. 2) Heat affected zone: is a part of the base metal that is not melted during the fusion welding but is heated to an elevated temperature (below the melting temperature of the concerned material) before cooling down to room temperature 3) Base material: no chemical or mechanical material alteration. Anyaggal záró kötések| GÉPELEMEK 1. előadás 8 HAZ, Heat Affected Zones Gépelemek 1. Anyaggal záró kötések| GÉPELEMEK 1. előadás 9 Heat Affected Zones & Weld Metals (bead) Gépelemek 1. Weld Metal Heat Affected Zone (HAZ) Weld metal is usually treated as a separate part in the welded sample, rather than considering it as a part of the base metal. Weld metal region exists at the junction of two parent components. In fusion welding, weld metal undergoes phase change due to meting and subsequent solidification (solid to liquid and once again liquid to solid). HAZ is usually considered as an integrated part of the base metal. It contains significant portion of filler material (except in autogenous welding). Chemical composition of weld bead may differ from that of the parent metals. Properties of the weld metal can be improved during welding in several ways (such as appropriately selecting filler composition, shielding gas, etc.). It does not contain any filler material. It is purely a part of the base materials. Chemical composition of HAZ is mostly same with that of the parent metals. Properties of the HAZ cannot be improved favourably during welding (its width can only be controlled to some extent). HAZ exists within the parent components surrounding the weld bead. HAZ is never melted. It always remains solid. So no phase change occurs in HAZ. Weld bead produces in both fusion welding and solid HAZ is noticeable particularly in fusion welding state welding processes. However, it is narrow in processes. With solid state welding, HAZ is very solid state welding. narrow and is mostly not detectable. Geometry of the weld metal is characterised by three Only geometrical parameter of interest of the HAZ is parameters, namely (i) depth of penetration, (ii) weld its lateral width. bead width, and (iii) reinforcement height. Anyaggal záró kötések| GÉPELEMEK 1. előadás 10 Types of welded joints Gépelemek 1. Butt joint: One of the best joints: − big strenght, reliable, cheap; − at metal sheets it requires rework. Lap joint: Poor quality not the best: − double weld metal; − more material, − additional bending. Strap joint: Resembles to riveted joint: − big load capacity; − quadrant weld metal; − more material; − no additional bending. Anyaggal záró kötések| GÉPELEMEK 1. előadás 11 Types of welded joints Gépelemek 1. Corner joints a) Best corner joint, least material, biggest load capacity. At sheet metal it requires additional rework. b) Cheap , but less load capacity. c) Bigger load capacity than previous one but more expensive because of theneed of accurate fitment. d) Good strenght but more expensive than the previous ones. Anyaggal záró kötések| GÉPELEMEK 1. előadás 12 Construction of welded joints Gépelemek 1. General principles in the design of welded assemblies: Select the material with high weldability Use of a minimum number of welds Do not shape the parts based on casting or forging Use standard components Avoid straps, laps, and stiffeners Select the proper location of the weld Prescribe the correct sequence of the welding Anyaggal záró kötések| GÉPELEMEK 1. előadás 13 Construction of welded joints Gépelemek 1. The „best” solution is the butt joint because the flow of flux is not deflected. Átlapolt Lap kötés joint Hevederes Strap kötés joint Butt Tompa joint varrat 1:4 1:4 In order to achieve the smooth flow of flux the steps in cross sections must be avoided. 1:4 Anyaggal záró kötések| GÉPELEMEK 1. előadás 14 Construction of welded joints Gépelemek 1. Do not place a welded joint in the proximity of the peak of stress! Stress distributiona in sheet metal Feszültségeloszlás lemezben Helyes varratelhelyezés Good joint placement: A varrat a feszültséggyüjtő the joint is relatively far fromtávol the hatást okozó saroktól helyezkedik peak of stress! el. Hibás Wrongvarratelhelyezés joint placement: A varrat a csúcsfeszültségi the joint is placed helyen van. in the peak of stress! Anyaggal záró kötések| GÉPELEMEK 1. előadás 15 Construction of welded joints Gépelemek 1. Avoid the welding lines crossings! Helytelen elrendezés Incorrectvarrat joint placement Helyes joint varratplacement elrendezés Correct Rossz Wrong Megfelelő Appropriate JóGood The fewer joints are the better! Anyaggal záró kötések| GÉPELEMEK 1. előadás 16 Construction of welded joints Gépelemek 1. v 5v r 5v r Hibás! Incorrect! A hidegen hajlított The joint is at thelehet cold szakaszon nem bended section hegesztési varrat. Correct! Jó. A hidegen hajlított The joint is mért at least 5v szakasztól far away from the cold távolság legalább 5v. bended section. At cold worked sheet metals, especially at corners or at bending curves welded joints must NOT be placed because of aging or rigid fracture. Anyaggal záró kötések| GÉPELEMEK 1. előadás 17 Construction of welded joints Gépelemek 1. Welded joint on fitted surfaces to be avoided! Incorrect Rossz Wrong Elfogadható Appropriate Correct JóGood The corner joint to be welded as double, At dynamic loads to be concave. Anyaggal záró kötések| GÉPELEMEK 1. előadás 18 Construction of welded joints Gépelemek 1. t 1. The rib must not have an apex point because it melts down during welding. b c a 2. At corner 3 joints are connecting. (weld accumulation) e b Hibás Incorrect Megfelelő Correct Avoid skew connection! Anyaggal záró kötések| GÉPELEMEK 1. előadás 19 Construction of welded joints Gépelemek 1. Avoid the tension forces on root side. Erők Forces HelyesCorrect megoldás Incorrect Helytelen At spot welded joints: Avoid the tension the joint to be designed for shearing! t Od t F Od F Anyaggal záró kötések| GÉPELEMEK 1. előadás 20 Weld nomenclature Gépelemek 1. Anyaggal záró kötések| GÉPELEMEK 1. előadás 21 Calculation for static loads Gépelemek 1. I. Dimensions of the welded joint: 1) throat size „a" 2) Lenght of weld „l” Anyaggal záró kötések| GÉPELEMEK 1. előadás 22 Calculation for static loads Gépelemek 1. II. Calculation of stresses in the weld: • tension  = F a l • bending  = M K • shearing 𝐹 𝜏ҧ = 𝑎⋅𝑙 • torsion Bredt-form = K is cross section factor; M cs 2 A0 a A0 : section drawn by the middle line of the weld all along the way. Anyaggal záró kötések| GÉPELEMEK 1. előadás 23 Calculation for static loads Gépelemek 1. III. Determining the stress components in the normal & transverse plane. The following stress components are derived:  ⊥ , II , II , ⊥ ⊥  ⊥   ⊥ ⊥  Butt joint Corner joint Anyaggal záró kötések| GÉPELEMEK 1. előadás 24 Calculation for static loads Gépelemek 1. IV. Resultant stress calculation The resultant stress is calculated from the components:  ⊥ ,  II , II , ⊥  ö =  ⊥2 +  II2 −  ⊥ II + 3( ⊥2 +  II2 ) V. Checking ö H Weld is correct if, where σH ultimate stress is dependent upon: • yield stress of the weaker material (ReH), • gain factor of the weld (φ), • safety factor of the weld (n). H ReH =  n Anyaggal záró kötések| GÉPELEMEK 1. előadás 25 Glued joints Gépelemek 1. Adhesive Bonding is the process of joining two surfaces together, usually with the creation of a smooth bond. This may involve the use of glue, epoxy, or one of a wide range of plastic agents which bond either through the evaporation of a solvent or through curing via heat, time, or pressure. Application field is almost the same as welding. Advantages: • No heat affected zone, no alteration in material • Small amount of space and weight is required • Applicable at different thickness of materials • Sealing and corrosion resistance is possible • Damping effect • No pre-drilling of metal sheets (no stress peaks) • Can be combined with other kind of joints Anyaggal záró kötések| GÉPELEMEK 1. előadás 26 Glued joints Gépelemek 1. Disadvantages: • Long preparation time (at max. 24h) • Preparation of the surfaces requires attention • Pressing machines, cleaning machines may be needed • Sensitive for high temperatures • It has much more lower strenght than welded joints • Ageing occurs • Sensitive for ultra violent & oxidation of the air • Harmful gases during processing and hazardous when recycled if can be... From the effect type: • phisical effect bonding • chemical effect bonding (reactive glueing) Anyaggal záró kötések| GÉPELEMEK 1. előadás 27 Glued joints Gépelemek 1. Phisical phenomenom: Pressure-sensitive adhesives (which are polymers) are 'sticky' because they are essentially very high viscosity liquids that also have some elastic characteristics, they are 'viscoelastic.’ and they will 'wet' a surface to which they are pressed. But then, because of their elasticity, they will resist separation when stressed. Thus, 'stickiness' is strictly a physical (viscoelastic) phenomenon, not a chemical one.„ Chemical phenomenom: "There are two fundamentally different components of tape's sticky nature; adhesion and cohesion. Adhesion is the binding force between two different materials, whereas cohesion is the binding force between two similar materials. When two materials are brought into contact with each other, the surface molecules interact, giving rise to attractive forces that may be physical, chemical or electrostatic (corresponding to adsorption, covalent bonding or van der Waals forces, respectively). Anyaggal záró kötések| GÉPELEMEK 1. előadás 28 Glued joints Gépelemek 1. Phisical effect: (τmeg = 5 – 10 N/mm2 ) • Contact glues: smear both surfaces, solvent evaporates, then press both strongly together. • Melt glues: in melted phase (generaly on 150-190Cº-degrees) to smear, then match both parts together before solidifying. • Plasticoles: no solvent, adhesive pasta to smear unto surface, and it hardens on 150-200Cº-degrees Chemical effect: • low strenght joints (τmeg ≤ 5 N/mm2 ). • Application: non-wet elements (dry), fine mechanics, furniture. • medium strenght joints (τmeg = 5 – 10 N/mm2 ). • Application: automotive & machinery • high strenght joints (τmeg ≥ 10 N/mm2 ). • Application: contact with water, oil, solvents, automotive, plane, ship industry, chemical appliances. Anyaggal záró kötések| GÉPELEMEK 1. előadás 29 Glued joints Gépelemek 1. Constructural considerations Below factors influence the strenght of glued joints: • Glue material, • Kind of substrates, • Operation conditions, • Geometry of glueing gap, • Load case. Engineering guidelines • • • • • Design the joint for shearing, To achieve homogenous load distribution, To avoid impact and peeling effects, To increase glueing surface, To avoid additional load cases. Anyaggal záró kötések| GÉPELEMEK 1. előadás 30 Glued joints design guidelines Gépelemek 1. Anyaggal záró kötések| GÉPELEMEK 1. előadás 31 Lap joints Gépelemek 1. One-way Reverse way One-way joint can carry apr. 2x load than the reverse-way joint, if the Young modulii are the same. At one-way both sheets are tensioned, at reverse-way the above sheet is compressed the below sheet is tensioned. Anyaggal záró kötések| GÉPELEMEK 1. előadás 32 Internal stresses in lap joints Gépelemek 1. a. Unloaded b. Loaded situation Anyaggal záró kötések| GÉPELEMEK 1. előadás 33 Internal stresses in lap joints Gépelemek 1. a, b, a. Single lap joint b. Double lap joint Anyaggal záró kötések| GÉPELEMEK 1. előadás 34 Calculation of lap joints Gépelemek 1. The stress peak on the edge of joint is the starting point of Failures. To describe the stress peak the so-called stress congestion factor is introduced. (α):  max  F  = A = where τmax , is max and  is average stress: where F is shear force, Aτ is glueing surface. How to reduce stress congestion factor: • To apply one-way lap joints, • To use short joints, • To have soft glueing material and rigid substrates, • To create varying cross sections of substrates than applying constant cross sections. Anyaggal záró kötések| GÉPELEMEK 1. előadás 35 Calculation of lap joints (tapered lap joint) Gépelemek 1. The following equation describes the above condition: if the two strains & the two Young’s modulii are the same then the two thicknesses of the sheets are also the same. 𝐹0 𝐴10𝐸1 = 𝐹0 𝐴20𝐸2 Anyaggal záró kötések| GÉPELEMEK 1. előadás 36 Types of glued joints & nomenclature Gépelemek 1. Disturbed, as a joint topology with one or more offsets between the adherends, while undisturbed, such that the adherends are aligned (no offset). Anyaggal záró kötések| GÉPELEMEK 1. előadás 37 Design of lap joints Gépelemek 1. Taper cross section: laps & scarf joints in order to reduce the stress congestion factor. Improvement with a taper patch Scarf joints Glueing belt ends Improvement with taper substrate endings We reinforce the structure with material removal!!?? ☺ Anyaggal záró kötések| GÉPELEMEK 1. előadás 38 Design of glued joints Gépelemek 1. correct Helytelen megoldás incorrect Megfelelő megoldás Helytelen megoldás incorrect Megfelelő megoldás correct Anyaggal záró kötések| GÉPELEMEK 1. előadás 39 Design of glued joints Gépelemek 1. incorrect possible Rossz Rossz Lehetséges szerkezeti megoldások Lehetséges szerkezeti megoldások Rossz Rossz Lehetséges szerkezeti megoldások Lehetséges szerkezeti megoldások incorrect possible Anyaggal záró kötések| GÉPELEMEK 1. előadás 40 Design of glued joints Gépelemek 1. F M F F F F F F F s d F F M incorrect F/2 F F/2 correct Anyaggal záró kötések| GÉPELEMEK 1. előadás 41 Soldered joints Gépelemek 1. Soldering is the process of joining two metal objects together by a third soft metal alloy which is called solder. Solder is a metal alloy which melts at a lower temperature than the metals being soldered. Advantages: • Different metals with different thickness are bondable, • Low soldering temperature, • No heat peak & HAZ zones, deflections cracks, • Good sealing ability, • Good electrical conduction, • Proper for local assembly, because of short assembly time, • Available for mass production. Disadvantages: • Relatively small load carrying capacity, • Surface preparation is too expensive, • Small heat resistance. Anyaggal záró kötések| GÉPELEMEK 1. előadás 42 Soldered joints Gépelemek 1. Material of the solder and the melting temperature point of view we can make 2 types: • Hard soldering: t > 450 C°, solder material is brass alloy, & a borax based flux acts as a cleaning agent during the soldering process. (τB = 180 – 270 MPa) • Soft soldering: t < 450 C°, solder material is lead (tin) alloy, the flux is a resin based agent. (τB = 20 – 86 MPa) Create the joint The soldered joint - dependent upon its shape & location – in optimal cases it has shearing state of stress. At the parallel surfaces 0,05 – 0,6 mm, capillary action allows the deposition of molten substances like any alloy, metal, etc. in between the two metal surfaces. In the soldering process, the molten solder rises due to the capillary force into the cracks in between the parts that are to be joined. It allows the permanent joining of two metal pieces. (the magic of soldering!!!) Anyaggal záró kötések| GÉPELEMEK 1. előadás 43 Design of soldered joints Gépelemek 1. Vessel base Pipe attachment to sheet metal Beam attachment to sheet metal Shaft attachments Sheet metal to sheet metal Anyaggal záró kötések| GÉPELEMEK 1. előadás 44 Soldering variations Gépelemek 1. Machinery Plumbing Electronics Anyaggal záró kötések| GÉPELEMEK 1. előadás 45