The Fusion Welded Joint 3 distinct zones of weld are: base metal heat-affected zone (HAZ) fusion zone

Weld quality Discontinuities that affect weld quality are: 1. Porosity trapped gases, chemical reactions, contaminants 2. Slag inclusions Slag is trapped in the weld zone.

Weld quality 5. Cracks 4. Weld profile 3. Incomplete fusion and incomplete penetration 4. Weld profile Affects the strength and appearance of the weld. 5. Cracks

Design for Welding http://www.youtube.com/watch?v=pVyYvcEqkcQ&feature=related

Ex) Design frame for welding

Ex) Welding Gas metal arc welding

Problem of Fusion Welding Composition change Cavity, inclusion Grain growth, phase transformation Residual stress, crack Most failures start at heat affected zone Sharpness of variation of heat affected zone may be reduced by preheating When C is more than 0.3%, Martensite may form

Solid State Welding Cold Welding (냉간압점) Ultrasonic Welding (초음파용접) Friction Welding (마찰용접) Diffusion Bonding (확산접합)

Cold Welding (냉간압접) Localized pressure is applied to mating faces of parts through dies or rolls. Used to join small workpieces made of soft and ductile metals. Roll welding Pressure for long pieces or continuous strips is applied through a pair of rolls. Rolls Separating agent (graphite)

Ultrasonic Welding (초음파용접) Ultrasonic vibration of transducer & Pressure  Temperature rise to 0.3~0.5 melting point. Restricted to thin, small, delicate parts like electric components. Mass Force Coupling system Tip Workpiece Anvil Direction of vibration Power supply AC Transducer DC polarization Toolholder Roller Workpieces Support ©정하림 GNU

Vibration Welding Vibrate two plastic parts to be joined by friction heat http://ma.gnu.ac.kr/vod/Joining/Vibration_welding_plastic.MP4

Friction Welding (마찰용접) Heat required is generated from friction at the interface of the 2 members being joined. http://www.youtube.com/watch?v=-aEuAK8bsQg&p=9B6D9EAE75875D9D Friction Welding http://ma.gnu.ac.kr/vod/Joining/Friction_Welding.WMV Friction Welding

Diffusion Bonding (확산접합) Diffusion bonds two different materials in high pressure, elevated temperature, long time. High bond strength, slow process. Good for Ti, superalloy (Aircraft components) Introduction Diffusion bonding is a solid-state joining process capable of joining a wide range of metal and ceramic combinations to produce both small and large components. The process is dependent on a number of parameters, in particular, time, applied pressure, bonding temperature and method of heat application. Other examples of solid-state joining include cold pressure welding, friction welding, magnetically impelled arc butt (MIAB) welding and explosive welding. Diffusion bonding itself can be categorised into a number of variants, dependent on the form of pressurisation, the use of interlayers and the formation of a transient liquid phase. Each finds specific application for the range of materials and geometries that need to be joined. Process mechanism In its simplest form, diffusion bonding involves holding pre-machined components under load at an elevated temperature usually in a protective atmosphere or vacuum. The loads used are usually below those which would cause macrodeformation of the parent material(s) and temperatures of 0.5-0.8Tm (where Tm = melting point in K) are employed. Times at temperature can range from 1 to 60+ minutes, but this depends upon the materials being bonded, the joint properties required and the remaining bonding parameters. Although the majority of bonding operations are performed in vacuum or an inert gas atmosphere, certain bonds can be produced in air. An examination of the sequence of bonding (Fig.1) emphasises the importance of the original surface finish. To form a bond, it is necessary for two, clean and flat surfaces to come into atomic contact, with microasperities and surface layer contaminants being removed from the bonding faces during bonding. Various models have been developed to provide an understanding of the mechanisms involved in forming a bond. First they consider that the applied load causes plastic deformation of surface asperities reducing interfacial voids. Bond development then continues by diffusion controlled mechanisms including grain boundary diffusion and power law creep. Copper - Stainless Aluminum - Stainless

Brazing (경납접) & Soldering (연납접) Solid base, liquid filler Filler material: different composition, low melting point, lower strength

Brazing (경납접) Filler metal is placed between faying surfaces where the temperature is raised to melt the filler metal. Workpieces must melt in the weld area for fusion. Clearance is important as it affects the strength of the brazed joint.

Soldering (연납접) Filler metal (solder) fills the joint by capillary action. Can be used to join various metals and to thicken parts. Temperatures are low and have a low strength as they are for load-bearing structural members. Solders are tin-lead alloys.

Soldering

Design for Brazing

Adhesive Bonding Numerous components and products can be joined and assembled. Adhesive are required to be strong and tough, resistance to fluids, chemicals and environmental degradation.

Design for adhesive bonding