Mechanical Fastening Mechanical Fastening ProcessesProcessesBrazingBrazing BrazingBrazing – joining process where – joining process where

just the filler material’s heat is just the filler material’s heat is raised to its melting raised to its melting temperature to join materialstemperature to join materials

First used as far back as 3000 to First used as far back as 3000 to 2000 B.C.2000 B.C.

Filler material has a lower Filler material has a lower melting temperature than melting temperature than components that you are joining.components that you are joining.

Mechanical Fastening Mechanical Fastening ProcessesProcessesBrazingBrazing Brazing uses a flux in order Brazing uses a flux in order

to prevent oxidation during to prevent oxidation during the joining processthe joining process

Factors that affect braze Factors that affect braze strengthstrength Joint clearanceJoint clearance Joint areaJoint area The bond formed between The bond formed between

the filler material and the the filler material and the base metalbase metal

Proper use of fluxProper use of flux

BrazingBrazingVarious MethodsVarious Methods

Torch – uses oxyfuel thru a torchTorch – uses oxyfuel thru a torch Furnace – parts preloaded with Furnace – parts preloaded with

consumable inserts then placed in consumable inserts then placed in furnace for uniform heatingfurnace for uniform heating

Induction – Heats thru use of High Induction – Heats thru use of High freq ACfreq AC

Dipping – dips entire base Dipping – dips entire base material into molten filler metal material into molten filler metal bath (used for very small parts)bath (used for very small parts)

Mechanical Fastening Mechanical Fastening ProcessesProcessesSolderingSoldering Main difference between soldering and Main difference between soldering and

Brazing lies in Temperature.Brazing lies in Temperature. Uses primarily tin-lead as filler materialUses primarily tin-lead as filler material Main use is for electronics which can’t Main use is for electronics which can’t

withstand extreme heat of brazing.withstand extreme heat of brazing. Uses same techniques as brazing as Uses same techniques as brazing as

well as that of Wave soldering – very well as that of Wave soldering – very useful for circuit boards.useful for circuit boards.

(b)(b)

Adhesive BondingAdhesive Bonding Types of AdhesivesTypes of Adhesives

Natural adhesives-starch, dextrin, soya Natural adhesives-starch, dextrin, soya flour, and animal productsflour, and animal products

Inorganic Adhesives-sodium silicate and Inorganic Adhesives-sodium silicate and magnesium oxychloridemagnesium oxychloride

Synthetic organic adhesives-Synthetic organic adhesives-thermoplastics, thermosetting polymers thermoplastics, thermosetting polymers (most important in manufacturing)(most important in manufacturing)

Adhesive BondingAdhesive Bonding Electronically Conducing Electronically Conducing

AdhesivesAdhesives Developed to replace lead-Developed to replace lead-

based solder, added metal based solder, added metal particles (40% to 70%)particles (40% to 70%)

Used in electronics such as Used in electronics such as calculators, TVs, and LCDscalculators, TVs, and LCDs

Adhesive BondingAdhesive BondingTABLE 30.4Type Comments ApplicationsAcrylic Thermoplastic; quick setting; tough bond at room

temperature; two component; good solvent chemicaland impact resistance; short work life; odorous;ventilation required

Fiberglass and steel sandwich bonds,tennis racquets, metal parts,plastics.

Anaearobic Thermoset; easy to use; slow curing; bonds at roomtemperature; curing occurs in absence of air, will notcure where air contacts adherents; one component; notgood on permeable surfaces

Close fitting machine parts such asshafts and pulleys, nuts and bolts,bushings and pins.

Epoxy Thermoset; one or two component; tough bond;strongest of engineering adhesives; high tensile and lowpeel strengths; resists moisture and high temperature;difficult to use

Metal, ceramic and rigid plastic parts.

Cyanoacrylate Thermoplastic; quick setting; tough bond at roomtemperature; easy to use; colorless.

“Crazy glue.” ™

Hot melt Thermoplastic; quick setting; rigid or flexible bonds;easy to apply; brittle at low temperatures; based onethylene vinyl acetate, polyolefins, polyamides andpolyesters

Bonds most materials. Packaging,book binding, metal can joints.

Pressure sensitive Thermoplastic; variable strength bonds. Primer anchorsadhesive to roll tape backing material, a release agenton the back of web permits unwinding. Made ofpolyacrylate esters and various natural and syntheticrubber

Tapes, labels, stickers.

Adhesive BondingAdhesive BondingSurface Prep, Process Capabilities, and Surface Prep, Process Capabilities, and

ApplicationsApplications Surface PreparationSurface Preparation

Surface must be free of dirt, dust, Surface must be free of dirt, dust, oil and any other contaminantsoil and any other contaminants

Porous or rough surface is Porous or rough surface is desirable, improve adhesiondesirable, improve adhesion

Process CapabilitiesProcess Capabilities Used to bond metallic and non-Used to bond metallic and non-

metallic materialmetallic material Do not subject to peelingDo not subject to peeling

Adhesive BondingAdhesive BondingSurface Prep, Process Capabilities, and Surface Prep, Process Capabilities, and

ApplicationsApplications ApplicationsApplications

Used in most industriesUsed in most industries Allows bond between dissimilar Allows bond between dissimilar

metals and reduces vibration and metals and reduces vibration and noisenoise

Distributes the load eliminating Distributes the load eliminating local stresses that usually result local stresses that usually result from mechanical fastenersfrom mechanical fasteners

External appearance is unaffectedExternal appearance is unaffected Thin and fragile components can Thin and fragile components can

be bonded without weight be bonded without weight increaseincrease

Adhesive BondingAdhesive BondingDesign for Adhesive BondingDesign for Adhesive Bonding

Ensure that joints are subjected only Ensure that joints are subjected only to compressive, tensile, and shear to compressive, tensile, and shear forces, not to peeling or cleavageforces, not to peeling or cleavage

Mechanical FastenersMechanical Fasteners Preferred over other methods Preferred over other methods

because of the following:because of the following: Ease of manufacturingEase of manufacturing Ease of assembly and Ease of assembly and

transportationtransportation Ease of disassembly, Ease of disassembly,

maintenance, part replacement, maintenance, part replacement, or repairor repair

Ease in creating designs that Ease in creating designs that have movable jointshave movable joints

Lowers costLowers cost

Mechanical FastenersMechanical Fasteners Hole PrepHole Prep

Using different methods to create the Using different methods to create the hole produces different characteristicshole produces different characteristics

Hole with some residual stress is Hole with some residual stress is desirable, improves fatigue lifedesirable, improves fatigue life

Threaded FastenersThreaded Fasteners Common bolts and screwsCommon bolts and screws

RivetsRivets Most common method of permanent Most common method of permanent

and semipermanent mechanical joiningand semipermanent mechanical joining Works by placing rivet through hole and Works by placing rivet through hole and

deforming enddeforming end

Mechanical FastenersMechanical Fasteners Other Fastening MethodsOther Fastening Methods

Metal Stitching and staplingMetal Stitching and stapling Similar to ordinary staplingSimilar to ordinary stapling

SeamingSeaming Folding two pieces of material togetherFolding two pieces of material together

CrimpingCrimping Physically forcing on piece onto anotherPhysically forcing on piece onto another

DesignDesign Use fewer, but larger, rather than many Use fewer, but larger, rather than many

smallsmall Fit between joined partsFit between joined parts Use standard sizes and keep holes away Use standard sizes and keep holes away

from edges or cornersfrom edges or corners

Mechanical FastenersMechanical Fasteners

Joining Plastics, Joining Plastics, Ceramics, and GlassesCeramics, and Glasses

Joining ThermoplasticsJoining Thermoplastics Thermal MethodsThermal Methods

Using heat to soften or melt two pieces at Using heat to soften or melt two pieces at the interface to ensure good bondthe interface to ensure good bond

Many way to apply the heatMany way to apply the heat Adhesive BondingAdhesive Bonding

Uses adhesives previously discussed to Uses adhesives previously discussed to attach the plasticsattach the plastics

Joining ThermosetsJoining Thermosets Joined using threads, mechanical Joined using threads, mechanical

fasteners, solvent bonding, co-curing fasteners, solvent bonding, co-curing and adhesive bondingand adhesive bonding

Joining Plastics, Joining Plastics, Ceramics, and GlassesCeramics, and Glasses

Joining Ceramics and GlassesJoining Ceramics and Glasses CeramicsCeramics

Treat surface with coating that is easily Treat surface with coating that is easily bondedbonded

Braze tungsten carbide and titanium Braze tungsten carbide and titanium carbidecarbide

Join during their primary shaping processJoin during their primary shaping process GlassesGlasses

Are bonded easilyAre bonded easily Done by softening and pressing two pieces Done by softening and pressing two pieces

together and coolingtogether and cooling Can be bonded to metals due to diffusion of Can be bonded to metals due to diffusion of

metal ions into the glass sturcture.metal ions into the glass sturcture.

32.7 Economics of Joining 32.7 Economics of Joining OpsOps

Cost from highest to lowest of Cost from highest to lowest of various Joining Operationsvarious Joining Operations

Highest: Brazing, bolts, nuts, and other fasteners.

Intermediate: Riveting and adhesive

Low: Seaming and crimping

Closer look at Brazing Closer look at Brazing CostsCosts

Manual Brazing: Basic equipment costs $300 $50,000+ for automated systems

Furnace Brazing: Wide range from $2,000 for batch furnaces to

$300,000 for continuous vacuum furnaces. Induction Brazing:

$10,000 for small units

Closer look at Brazing Closer look at Brazing CostsCosts

Resistance Brazing: $1,000 for simple units $10,000+ for larger units

Dip Brazing $2,000 to $200,000+, depends on equipment

which may be computer controlled Infrared Brazing:

$500 to $30,000 Diffusion Brazing:

$50,000-$300,000

Closer look at Brazing Closer look at Brazing CostsCosts

High End Convection CAB Brazing Furnace

High End Vacuum Furnace

Surface TechnologySurface Technology

How do we react How do we react to surfaces?to surfaces? TouchTouch

Roughness Texture Scratches

SightSight Waviness Color Reflectivity

Surface Technology Surface Technology

Jargon: “Jargon: “Surface IntegritySurface Integrity”” Describes the Describes the physical, chemical and mechanical physical, chemical and mechanical characteristics of surfacescharacteristics of surfaces

Influences on surfacesInfluences on surfaces Friction and wear of tools, molds, dies and of

the products themselves. Effectiveness of lubricants during

manufacturing and throughout the products life.

Thermal and electrical conductivity of contacting bodies.

Surface TechnologySurface Technology

Influences on surfaces (cont.)Influences on surfaces (cont.) Appearance and geometric features of the

part and their role in subsequent operations, such as welding, soldering, adhesive bonding, painting, coating and corrosion.

Crack initiation as a result of surface defects like roughness, scratches, seams, and heat–affected zones. These can lead to weakening and premature failure of a part.

Chapter 33 Surface Chapter 33 Surface Roughness and Roughness and

Measurements of Friction, Measurements of Friction, Wear and LubircationWear and Lubircation

33.2 Surface Structure and Integrity33.2 Surface Structure and Integrity Metal surfaces generally contain several layersMetal surfaces generally contain several layers

1ST Layer: Bulk Metal (substrate) has a structure that depends on the composition and processing history.

2ND Layer: Above the bulk metal is “Surface Structure” that is plastically deformed and work hardened more so than the Bulk Metal. The depth & properties of this layer depend on processing method and friction.

33.2 Surface Structure 33.2 Surface Structure and Integrityand Integrity

33RDRD layer: layer: Is the “Oxide Layer.” The only way to avoid this is to keep the metal in an oxygen free environment or work with a noble metal (gold, platinum).

44THTH layer: layer: is the “Absorbed Layer.” This layer absorbs gas and moisture.

55THTH layer: layer: Is the outermost layer that may be covered with contaminants such as dirt, dust, grease, various residues and other environmental pollutants.

33.2 Surface Structure 33.2 Surface Structure and Integrityand Integrity

Surface IntegritySurface Integrity

Surface integrity describes topological, Surface integrity describes topological, physical, and chemical as well as their physical, and chemical as well as their mechanical, metallurgical properties and mechanical, metallurgical properties and characteristics. Various surface defects characteristics. Various surface defects can weaken the Sruface Integrity can weaken the Sruface Integrity Cracks:Cracks: internal, external and microscopic Craters:Craters: shallow depressions Heat-affected zonesHeat-affected zones

Surface IntegritySurface Integrity

Surface Defects (continued)Surface Defects (continued) Inclusions:Inclusions: small nonmetallic elements Intergranular attack:Intergranular attack: the weakening of

grain boundaries Laps, Folds and Seams:Laps, Folds and Seams: overlapping of

material during processes Metallurgical transformations:Metallurgical transformations:

microstructural changes caused by temperature cycling of the material

Pits: shallow surface depressions from chemical or physical attack

Surface IntegritySurface Integrity

Surface Defects (continued)Surface Defects (continued) Residual stresses:Residual stresses: Either by tension or

compression and causes nonuniform deformation and temperature distribution.

Splatter:Splatter: Small resolidified molten metal particles on the surface.

Surface Plastic deformationSurface Plastic deformation: Severe surface deformation caused by high stress from friction, tool and die geometry, worn tools, and processing methods.

Surface Texture are characteristics that define a surface. These can be separated into four categories which are:

•Flaws or defects: random irregularities, such as scratches, cracks, holes, depressions, seams, tears, or inclusions

•Lay (directionality): direction of the predominant surface pattern

•Roughness: closely spaced, irregular deviations on a small scale

•Waviness: recurrent deviation from a flat surface

Surface roughness is usually described in two ways:

1. Arithmetic mean value (R a) – the schematic illustration of a rough surface

2. Root-mean roughness height – was known as RMS

3. Maximum roughness height (R t) – the height from the deepest trough to the highest peak; indicates how much material has to be removed to obtain a smooth surface

Coordinates used for surface-roughness measurements

R a = ( a + b + c + d + ….)/ n

R q = sq rt [(a2 + b2 + c2 + d2 + ….)/n]

Some symbols used to represent surface finish

Standard terminology and symbols used to describe surface finish

When measuring surface roughness, instruments called surface profilometers are used. Profilometers are tipped with a diamond stylus which usually has a 10 micon diameter. The way profilometers are used is they travel over the surface in a straight line recording about 10 to 15 roughness irregularities. The distance travel maybe anywhere from .08 to 25 mm. The most common distance used is .8 mm.

There are other ways of measuring surface measurement. This is done by using either an Optical-interference microscope or an atomic-force microscope.

•Optical-interference microscopes: shine a light against a reflective surface and record the interference fringes that result from the incident and its reflective waves

•Atomic-force microscopes (AMFs): it’s a very fine surface profilometer with a laser.

There are several theories that explain friction. Two of the more commonly accepted theories are the adhesion theory and the abrasion theory.

•Adhesion theory: theory that states that the contact of two items is actually only a fraction of their apparent contact area.

•Abrasion Theory: theory that states that the asperities of a harder surface penetrates and plows through a softer surface.

Another thing to take in to account is that all friction dissipates energy. This energy is converted into heat. Sometimes the heat may soften or even melt the material in use

Plastics generally possess low frictional characteristics. This is better for creating items such as bearings, gears, seals, prosthetic joints. But, an important consideration is that plastics have a low melting point. So, any heat caused by friction must be taken into account. Ceramics on the other hand have generally the same frictional characteristics as metals.

Some ways of reducing friction are :

1. Selection of materials used

2. Lubricants or solid films (such as graphite)

3. Ultrasonic vibrations

The coefficient of friction is found during the manufacturing process or in laboratory tests using smaller versions of various sizes of the material. One of the common tests used is called the ring-compression test. This is where a flat ring is upset plastically between two flat platens. If the both the diameters of the ring expand outward then the friction is zero. If the inner diameter becomes smaller, then there’s an increase of friction.

33.5 Wear33.5 Wear

Wear changes the shapes of tools and Wear changes the shapes of tools and dies, affects the tool life, tool size, and dies, affects the tool life, tool size, and the quality of the parts produced. the quality of the parts produced.

Importance of wear is evident in the Importance of wear is evident in the number of parts and components that number of parts and components that continually have to be replaced or continually have to be replaced or repaired.repaired.

i.e. dull drill bits, worn cutting tools and i.e. dull drill bits, worn cutting tools and diesdies

33.5 Wear33.5 WearRunning InRunning In period removes the peaks period removes the peaks

from asperities.from asperities.

Under controlled conditions, wear Under controlled conditions, wear may be regarded as a type of may be regarded as a type of smoothing or polishing process.smoothing or polishing process.

Adhesive WearAdhesive WearA tangential force is applied and A tangential force is applied and

shearing takes place either at shearing takes place either at a) the original interfacea) the original interfaceb) along a path below or above the b) along a path below or above the interfaceinterface

*adhesive bonds often are stronger *adhesive bonds often are stronger than the base metals.than the base metals.

Schematic illustration of (a) two contacting asperities, (b) adhesion between two asperities, and (c) the formation of a wear particle.

Abrasive WearAbrasive WearCaused by a hard rough surface sliding Caused by a hard rough surface sliding

across another surface. Microchips and across another surface. Microchips and slivers are produced, leaving grooves slivers are produced, leaving grooves or scratches on the softer surface.or scratches on the softer surface.

*processes: filing, grinding, ultrasonic *processes: filing, grinding, ultrasonic machining and abrasive jet machining machining and abrasive jet machining act in this manneract in this manner

Other types of WearOther types of Wear Corrosive.Corrosive. Fatigue-when the surface of a Fatigue-when the surface of a

material is subjected to cyclic material is subjected to cyclic loadingloading

Erosion-caused by loose abrasive Erosion-caused by loose abrasive particles on a surfaceparticles on a surface

FrettingFretting ImpactImpact

33.6 Lubrication33.6 Lubrication4-Regimes of Lubrication in 4-Regimes of Lubrication in

Manufacturing Ops.Manufacturing Ops.1)Thick-film:1)Thick-film: surfaces separated completely by surfaces separated completely by a film of lubricant. Results in dull, grainy a film of lubricant. Results in dull, grainy surface appearance after forming operationssurface appearance after forming operations

2) Thin-film:2) Thin-film: Load between the die and work Load between the die and work piece increases, or the speed and viscosity of piece increases, or the speed and viscosity of fluid decrease, the lubricant becomes thinner fluid decrease, the lubricant becomes thinner raising friction and results in slight wearraising friction and results in slight wear

33.6 Lubricants33.6 Lubricants3)Mixed:3)Mixed: a significant portion of the load is a significant portion of the load is carried by the physical contact of the two carried by the physical contact of the two surfaces. The rest is carried by the fluid film surfaces. The rest is carried by the fluid film trapped in the valleys (asperities).trapped in the valleys (asperities).

4) Boundary4) Boundary: load supported by contacting : load supported by contacting surfaces covered with boundary film of lubricant. surfaces covered with boundary film of lubricant. The lubricant is attracted physically to the metal The lubricant is attracted physically to the metal surfaces, thus preventing direct metal-to-metal surfaces, thus preventing direct metal-to-metal contact and reducing wear.contact and reducing wear.

33.7 Metalworking Fluids33.7 Metalworking Fluids Reduce frictionReduce friction Reduce wearReduce wear Improve material flowImprove material flow Act as a thermal barrier between the Act as a thermal barrier between the

workpiece and its tool and die workpiece and its tool and die surfacessurfaces

Act as a release or parting agentAct as a release or parting agent

Oils and EmulsionsOils and EmulsionsOils Oils are very effective in reduction of friction and wear are very effective in reduction of friction and wear

and have low thermal conductivity but they do not and have low thermal conductivity but they do not conduct away the heat generated by friction conduct away the heat generated by friction effectively. effectively.

**It is difficult and costly to remove oils from component It is difficult and costly to remove oils from component surfaces that are to be painted or welded, and is surfaces that are to be painted or welded, and is difficult to dispose of.difficult to dispose of.

Emulsion:Emulsion: mixture of oil and water in various mixture of oil and water in various proportions along with additives. aka water-soluble proportions along with additives. aka water-soluble oils or coolantsoils or coolants1)direct: mineral oil dispersed in water in very small 1)direct: mineral oil dispersed in water in very small dropletsdropletsImportant in metalworking b/c the presence of water Important in metalworking b/c the presence of water gives them high cooling capacity.gives them high cooling capacity.

Synthetic solutionsSynthetic solutionsSoaps, greases, waxesSoaps, greases, waxes

Synthetic Solutions:Synthetic Solutions: chemical fluids that chemical fluids that contain inorganic and other chemicals contain inorganic and other chemicals dissolved in water (contain NO mineral dissolved in water (contain NO mineral oils) Oil found @ Pepboysoils) Oil found @ Pepboys

Soaps:Soaps: reaction products of sodium or reaction products of sodium or potassium salts with fatty acids. Effective potassium salts with fatty acids. Effective boundary lubricants. Alkali soaps are boundary lubricants. Alkali soaps are soluble in water but metal soaps are soluble in water but metal soaps are generally insolublegenerally insoluble

Greases:Greases: solid or semisolid lubricant that solid or semisolid lubricant that consists of soaps, mineral oil, and consists of soaps, mineral oil, and additives. Highly viscous and adhere well additives. Highly viscous and adhere well to metal surfaces.to metal surfaces.

Waxes:Waxes: Less greasy and more brittle. Less greasy and more brittle. Limited to metalworking operationsLimited to metalworking operations

AdditivesAdditivesMetalworking fluids usually blend with Metalworking fluids usually blend with

various additives:various additives:

• Oxidation inhibitorsOxidation inhibitors• Rust-preventing agentsRust-preventing agents• Foam inhibitorsFoam inhibitors• Wetting agentsWetting agents• Odor-Controlling agentsOdor-Controlling agents• AntisepticsAntiseptics

Solid LubricantsSolid LubricantsGraphite:Graphite: effective at elevated temps, effective at elevated temps,

however friction is low only in the however friction is low only in the presence of air presence of air

or moisture. or moisture.

Molybdenum disulfide:Molybdenum disulfide: lamellar solid lamellar solid lube, similar appearance to graphite lube, similar appearance to graphite however has a high friction coefficient however has a high friction coefficient in an ambient environment. Oils in an ambient environment. Oils commonly used with MoScommonly used with MoS22..

Metallic & polymeric Films:Metallic & polymeric Films: Thin Thin layers of soft metals and polymer layers of soft metals and polymer coatings. Suitable metals include lead, coatings. Suitable metals include lead, indium, tin, silver, PTFE(Teflon).indium, tin, silver, PTFE(Teflon).

Selection of Selection of Metalworking FluidsMetalworking Fluids

Considerations of several factors:Considerations of several factors:

1)1) Particular manufacturing processParticular manufacturing process

2)2) Work piece materialWork piece material

3)3) Tool or die materialTool or die material

4)4) Processing parametersProcessing parameters

5)5) Compatibility of the fluid with the tool and die Compatibility of the fluid with the tool and die materials and the work piece.materials and the work piece.

6)6) Required surface preparationRequired surface preparation

7)7) Method of fluid applicationMethod of fluid application

8)8) Removal of fluid and cleaning after processingRemoval of fluid and cleaning after processing

9)9) Contamination of the fluid by other lubricantsContamination of the fluid by other lubricants

10)10) Storage and maintenance of fluidsStorage and maintenance of fluids

11)11) Treatment of waste lubricantTreatment of waste lubricant

12)12) Biological and Environmental considerationsBiological and Environmental considerations

13)13) Costs involved in all of the aspects listedCosts involved in all of the aspects listed

Biological and Economical Biological and Economical ConsiderationsConsiderations

Potential hazards may be involved by Potential hazards may be involved by contacting or inhaling some fluid. contacting or inhaling some fluid. Improper disposal of fluids may cause Improper disposal of fluids may cause adverse effects on the environment. adverse effects on the environment.

Much progress has been made in Much progress has been made in developing environmentally safe developing environmentally safe fluids, technology, and equipment for fluids, technology, and equipment for their proper treatment, recycling, and their proper treatment, recycling, and disposal. disposal.

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page8convectionphoto.jpg page8convectionphoto.jpg Convection CAB Brazing FurnaceConvection CAB Brazing Furnace http://www.malichaudatlantique.com/images/v6.gif vacuum furnacehttp://www.malichaudatlantique.com/images/v6.gif vacuum furnace