Soldering…………………………………………….………………Pages 3-4

Joining Methods9

Contents:

Bonding…………………………………………….…………..….……Page 2

Brazing………………………………………………………...... …..Page 5

Welding……………………………….…………………..………..Pages 6-8

Fastening………………………………..…………..……….…..Pages 9-12

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BONDING Bonding is a joining technique where parts are connected with adhesive non-metallic material – organic polymer in a liquid state which becomes solid after curing or hardening. Different geometries and materials can be joined this way without deformation or damage. Product weight, number of parts and cost are reduced, tension stress equally distributed, metal grinding is eliminated, as well as corrosion associated with joining metals with different galvanic potential, for example steel with aluminum. Various formulations available can be used to increase the resistance to impact and fatigue, reduce noise and vibration and offer sealing function and protection against corrosion. Special adhesives can conduct electricity or act as electrical insulator. Main disadvantage is related to safety and environment associated with handling chemical compounds. Bonding is not recommended for joining electrical conductive parts. Removal or disassembling cannot be done without damaging the mating parts. Use of adhesives usually calls for skilled technicians and controlled procedures as well as time for surface preparation and curing. The aerospace area was the first sector that promoted the use of adhesives in the aircraft manufacturing process, due to its advantages over traditional methods such as welding or bolting. In the automotive industry, during the manufacturing process of the racks of the car, interior parts are bonded with adhesives instead of being welded and riveted, making cars lighter and safer in crash tests.

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SOLDERING Soldering is used for joining conductive materials and on applications where mechanical strength is not critical. An alloy is melted around leads of work pieces at temperatures below 840°F to create permanent bond without melting the parts. The best alloy for soldering is tin-lead in the following ratios: 60-40, 50-50 and 40 percent tin to 60 percent lead (40-60). The European Union’s Waste Electrical and Electronic Equipment Directive (WEEE) and Restriction of Hazardous Substances Directive (RoHS) came into effect in 2006 prohibiting the inclusion of significant quantities of lead in most consumer electronics used in the EU. Mercury (Hg), cadmium (Cd), hexavalent chromium (CrVI), polybrominated biphenyls (PBB) and polybrominated diphenyl ethers (PBDE) are also restricted. In the US, lead is prohibited in plumbing applications for drinking water use according to the Safe Drinking Water Act (SDWA). For other applications, manufacturers are encouraged to reduce the lead- based solder through tax benefits. The most common lead-free solder used is tin/silver/copper - SAC (from Sn-Ag-Cu). Lead-free solder may still be less desirable for critical applications, such as aerospace and medical projects, because its properties are less thoroughly known. Mass-production printed circuit boards (PCBs) are mostly wave soldered or reflow soldered, though hand soldering is still widely used. In wave soldering, components are installed on the PCB, occasionally kept in place with small dabs of adhesive or secured with a fixture. The

Joining Methods9 assembly is passed over flowing solder in a bulk container so that solder stays on pins and pads.

Wave Soldering Reflow soldering is a process in which a solder paste (a mixture of solder powder and flux) is used to stick the components to attachment pads, after which the assembly is heated. It is common to use two or more processes for a given PCB. For example, surface mounted parts may be reflow soldered first, with a wave soldering process for the through-hole mounted components next, and bulkier parts hand-soldered last.

Reflow soldering oven

Joining Methods9

BRAZING

Brazing is considered as one of the strongest bonding joining methods. Two metal pieces are permanently joined together with the use of heat above 840°F to melt a filler alloy (copper with either zinc or silver being the most common) without melting the base metal.

Joining Methods9

WELDING Welding is a fabrication process of joining materials by melting and adding a filler into the weld pool which produces a joint stronger than the base material.

Some of the best known welding methods are:

Oxy-fuel welding. Fuel gases and pure oxygen are used to weld and cut metals. It has been declining in almost all industrial uses due to arc welding methods with more consistent weld properties and faster application.

Shielded metal arc welding (SMAW) – also known as stick welding or electric welding, uses an electrode that slowly melts away.

Gas tungsten arc welding (GTAW), also known as TIG (tungsten, inert gas), uses a non-consumable tungsten electrode to produce the weld. The weld area is protected from contamination by an inert gas such as argon or helium.

Joining Methods9 Gas metal arc welding (GMAW), commonly termed MIG (metal, inert gas), uses a gun that feeds wire at an adjustable speed and flows an argon-based shielding gas or a mix of argon and carbon dioxide (CO2) over the weld puddle to protect it from atmospheric contamination. Flux-cored arc welding (FCAW) almost identical to MIG welding except it uses a special tubular wire filled with flux.

Submerged arc welding (SAW) uses an automatically fed consumable electrode and a blanket of granular fusible flux. The molten weld and the arc zone are protected from atmospheric contamination by being "submerged" under the flux blanket.

Electro slag welding (ESW) is a highly productive, single pass welding process for thicker materials (between 1-12 inches).

Joining Methods9 Electric resistance welding (ERW)

Forged welds created by combination of heat and pressure are made by ERW. The heat is generated by the resistance of material to the flow of electrical current. The two main types are high frequency and rotary contact wheel.

The two high frequency (HF) welding processes are HF contact and HF induction. In both cases the equipment providing the electrical current is independent from the equipment supplying the forge pressure. Impeders, which are magnetic components located inside the tube being welded, are used to focus the weld current in the strip edges.

In the case of HF induction welding, the weld current is transmitted to the material through a coil which is not in contact with the material being welded. The electrical current is induced through magnetic field that surrounds the work piece, usually a tube. HF induction welding eliminates contact marks and reduces the setup required when changing a tube size. It also requires less maintenance than contact welding. It is estimated that 90 percent of tube mills in North America use HF induction welding.

HF contact welding transfers weld current to the material through contacts that ride on the strip. The weld power is applied directly to the work piece, making this process more electrically efficient than HF induction welding and better suited for heavy-wall and large-diameter tubes.

HF welding machines are classified by how they generate power. The two types are vacuum tube and solid-state, the later having the prominence.

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F A S T E N I N G Fastening is a joining method with future disassembling in mind. With the exception of rivets and pins, fasteners are removable without damaging mated parts. Fasteners can be permanent (rivets), semi-permanent (cotter pins) and removable (screws, bolts and nuts). Permanent fasteners cannot be removed without damaging the components. Semi- permanent fasteners can be removed and replaced with some damage being done to the parts. Depending on a joint type, fasteners may require a) clearance holes, b) tapped holes or c) pilot holes for installation. Fasteners pass smoothly through clearance holes and engage with tapped holes with threads. Pilot holes are pre drilled to prevent material from splitting during installation of self-tapping or thread-cutting screws.

Joining Methods9 Types of fasteners

Bolts Machine screws Partially threaded fasteners, Smaller than bolts, usually fully assembled with nuts and washers, threaded, may be used without installed in predrilled clearance nuts. In some cases hole does not holes. Torque is applied on the have to be predrilled. nut.

Sheet metal screws have sharp Wood screws have larger threads points and threads. Designated to than sheet metal screws and be driven directly into sheet metal smooth shank. or softer materials.

Joining Methods9

Cap screws Studs Bolts with larger head, a washer Fully threaded or threaded on face under the head and the ends, without head. Typically chamfered end. Torque is applied fastened into a tapped hole and to the head and one mating part secured with a nut on other the needs a tapped hole. side.

Screw Head types:

Joining Methods9 Nut types:

Cage nuts:

Washer Types:

The Unified Thread Standard (UTS) is the main standard for bolts, nuts, and a wide variety of other threaded fasteners and is controlled by ASME and ANSI. It defines standard thread form and series, allowances, tolerances, and designations for screw threads commonly used in the US and Canada.