McGraw-Hill Machining and Metalworking Handbook 3rd ed - R. Walsh_ D. Cormier (McGraw-Hill 2006) WW Part 14 docx

These nuts are also used on thin sheet metal parts where astrong joint is required, and not enough material thickness is avail-able for tapping the sheet metal.. 14.46 is extensive,the m

aluminum alloys, and stainless steels Figure 14.38 shows the sizesand dimensions of standard clamp-collars, and Fig 14.39 showsthe data for the internally threaded clamp-collar series.

Split-collars and threaded split-collars are also available and usedwidely in machine design The data for these types of clampingcollars are shown in Figs 14.40 and 14.41

Note: Figures 14.37 through 14.41 were extracted from theRuland catalog of collars and couplings (Ruland ManufacturingCompany, Inc., Watertown, MA 02172)

14.7 Machinery Bushings, Shims,

and Arbor Spacers

14.7.1 Machinery bushings

Machinery bushings are a special form of flat washer commonlymade of low-carbon mild steel They are used as spacers betweengears, pulleys, and sprockets and as filler spacers for parts mounted

on shafts These bushings are manufactured in the following gaugesand diameters:

14.7.3 Steel arbor spacers

Steel arbor spacers are thin steel rings with a keyway center holethat are used for accurately spacing milling cutters, slitter knives,and gang saws on keyway arbors Steel shims and steel arbor spacersare made of AISI 1010, fully hardened, cold-rolled low-carbon steel.Figure 14.42 also lists the sizes and thicknesses of steel arbor spacers

Figure 14.38 Clamp-collars (Ruland, Inc.)

14.8 Specialty Fasteners

The specialty fastener component lines available today are great innumbers and types This section will detail only those specialty fas-teners which have become common and which are used widely in newproduct design and manufacturing

A partial listing of some of the common specialty fasteners wouldinclude

■ Acorn nuts

■ Floating nuts

Figure 14.39 Threaded clamp-collars (Ruland, Inc.)

Figure 14.40 Split-collars (Ruland, Inc.)

■ T-slot nuts and bolts

■ Push nuts (pal nuts)

Figure 14.41 Split threaded clamp-collars (Ruland, Inc.)

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■ Various types of weld studs

■ Sheet metal nuts

■ Nylok bolts

■ Flanged “whiz” bolts

■ Turnbuckles

14.8.1 Specialty fasteners in common use

Figure 14.43 shows the different types of SEMs (screw and captivewasher assemblies) available today Note that on the SEM, the screw

is either thread-forming or thread-tapping This makes this class offastener useful and economical in rapid-assembly applications such

as automotive equipment manufacturing SEMs are specified inANSI Standard ANSI/ASME B18.13

Figure 14.44 shows some of the widely used Tinnerman types ofspeed nuts, which are made of high-carbon, spring-tempered steel.These types of speed nuts are produced in sizes from 6-32 through

5⁄16-18 or larger in special cases The Tinnerman type U and J nutsare used widely to fasten sheet metal screw covers onto sheet metalenclosures The flat and round types are used on through-bolt sheetmetal applications, such as automotive equipment and electronicchassis work These are economical, efficient fasteners whose appli-cations are limitless

Another specialty type of fastener that is used widely is the swagenut The swage nut is produced in several different styles, one of

which is shown in Fig 14.45a The swage nut is extremely useful in

applications where the thread cannot be produced efficiently or tively in a parent metal that must be fastened to another part Swagenuts are used in switch-gear equipment where copper bus bars arefastened together, and it is not practical to tap the soft copper bars forbolting These nuts are also used on thin sheet metal parts where astrong joint is required, and not enough material thickness is avail-able for tapping the sheet metal The swage nut normally is madefrom carbon steel with zinc or cadmium plating, stainless steels, and

effec-aluminum alloys Figure 14.45a shows a typical PEM-type nut.

The Rivnut and Plusnut, which are produced by B F Goodrich

Company, are shown in Fig 14.45b and c These types of “blind”

fasteners have countless applications in industry and are also duced with sealed ends for liquid-proofing applications The Rivnut

pro-is used widely in the aerospace industry

14.8.2 Electroplating fasteners

High-quality fasteners such as the Unbrako series of socket-headcap screws and shoulder bolts, which use the UNR thread profile,may be precision plated according to Table 14.2 Other types of fas-teners also may use the plating specifications shown in Table 14.2

Figure 14.43 Types of SEMs

(Text continued on page 922.)

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Figure 14.44 Tinnerman speed nuts.

Figure 14.44 (Continued )

Figure 14.45 (a) Clinch or swage nut (b) Rivnut installation (c) Installed

Plusnut

For more complete information on electroplating, see Chap 13,

“Plating Practices and Finishes.”

14.9 Welding, Brazing, and Soldering

Welding, brazing, and soldering are all important methods of ing and fastening metals and alloys This section will detail thevarious methods or processes and materials used in these threetypes of joining techniques

join-14.9.1 Welding

Welding is a fusion process for joining metals The heat of

applica-tion causes mixing of the joint metals or of the filler metal and thejoint metal The resulting joint is as strong as the parent metal,provided the weld is made correctly

Numerous welding methods or techniques are in common use for

a vast array of applications Modern welding methods or techniquesare categorized in Fig 14.46, which shows the process and theAmerican Welding Society (AWS) designation Both welding andcutting processes for metals are shown in the figure

Although the list of processes shown in Fig 14.46 is extensive,the majority of welding is done by the following methods:

■ Stick welding (fluxed rod)—SMAW

■ MIG (metal inert gas) welding—GMAW

■ TIG (tungsten inert gas) welding—GTAW

■ Stud arc welding—SW

Whether the welding process is gas or arc, the welder may

pro-ceed to do the weld in the forward or backward direction, as shown

in Fig 14.47 The direction of welding is left to the judgment of thewelder based on the configuration of the object being welded Whenthe welder is looking down at the welded joint, this is normally

called in-position welding When the welder is looking up at the joint, this is called out-of-position welding Any orientation not looking

down at the weld can be considered as out-of-position welding

Each of the various welding processes produces physical teristics that allow the process to be identified by direct eye inspec-tion Figure 14.48 shows an assembly welded using the MIG process(GMAW) Here, the weld is rather rough looking and was difficult

charac-to clean mechanically The welding heat setting and the diameter

of the weld wire play important roles in producing a neat, clean weldthat is also mechanically sound Figure 14.49 shows the same type

of joint (using the same parts) that has been welded using the TIGprocess (GTAW) It is immediately apparent that the TIG process ismore advantageous in this application, from the point of view ofboth strength and cosmetic appearance This joint is comprised ofparts manufactured from AISI 304 type stainless steel Figure14.49 shows the welded assembly sand-blasted after welding TheTIG weld in this application was made efficiently and correctly by

a skilled welder Welding is an art as well as a science, and a goodwelder needs a great deal of practice and experience

Figure 14.46 Welding processes and designations

In a welded assembly of numerous parts, the welder’s skill andexperience play an important role in producing an acceptable finalweld assembly Many welded assemblies require additional machin-ing after the welding process because of the strains produced whenthe welded joints cool to room temperature Allowance must bemade in the design of such an assembly to accommodate these weld-ing distortions, which are sometimes unavoidable.

Figure 14.47 (a) Forward (b) Backward.

Figure 14.49 TIG-welded assembly.

Figure 14.48 MIG-welded assembly

Welding procedures and electrode sizes. The correct electrode size isone that, when used with the proper amperage and travel speed,produces a weld of the required size in the least amount of time Theelectrode diameter selected for use depends largely on the thick-ness of the material to be welded, the position in which welding is

to be performed, and the type of joint to be welded In general, largerelectrodes will be selected for applications involving thicker mate-rials and for welding in the flat position in order to take advantage

of their higher deposition rates

For welding in the horizontal, vertical, and overhead positions, themolten weld metal tends to flow out of the joint owing to gravity.This can be controlled by using small electrodes to reduce the weldpool size Electrode manipulation and increased travel speed alongthe weld joint also aid in controlling the weld pool size

Weld groove design also must be considered when electrode size

is selected The experience of the welder often has a bearing on thesize of the electrode This is particularly true for out-of-positionwelding because the welder’s skill determines the size of the moltenpool that the welder can control

Welds that are larger than necessary are more costly and, in tain instances, actually are harmful to the joint Any sudden change

cer-in section size or contour of a weld, such as that caused by ing, creates stress concentrations An improperly welded assembly

overweld-of parts will distort on cooling, and an experienced welder can vent this to a certain degree by applying the welds at the correctpoints and in the correct sequences Tooling fixtures and weld jigs play

pre-an importpre-ant role in controlling the distortion of welded assemblieswhen they are designed and applied properly

Shielded-metal arc welding can be accomplished with either nating current (ac) or direct current (dc) when the appropriate elec-trode is used The melting rate of any given electrode is directlyrelated to the electrical energy supplied to the arc via the weldingcontroller apparatus

alter-Direct current (dc) always supplies a steadier arc and smoothermetal transfer than alternating current (ac) Most covered electrodesoperate better on reverse polarity (electrode positive), althoughsome are suitable for and are even designed for straight-polaritywelding (electrode negative) Reverse polarity produces deeperweld penetration, whereas straight polarity produces a higher elec-trode melting rate Direct current is particularly suitable for thin-section welding and is preferred for vertical and overhead welding

(out-of-position welding) If arc blow is a problem when welding with

dc, change the current to ac

For SMAW, ac offers advantages over dc; one is the absence of arcblow, and the other is the cost of the power source for producing theweld (the welding machine or apparatus) Without arc blow, largerelectrodes and higher welding currents can be used.

Welding technique. In SMAW welding, you first select the properequipment, materials, and tools for the job The type of weldingcurrent and its polarity then must be selected, and the powersource set accordingly The power source must be set to give theproper voltampere (VA) characteristic for the size and type of elec-trode being used

Strike the arc, for the weld to begin, by tapping the end of theelectrode near the beginning of the weld joint; then quickly move it

to produce an arc of proper length at the beginning of the weld joint.Then move the electrode uniformly along the joint, keeping a con-stant arc length as the electrode melts to produce the welded joint

A good deal of practice is required, especially in out-of-position typeweld joints To break the welding arc, when the weld joint is com-pleted, stop the forward motion of the electrode and abruptly with-draw the electrode away from the joint or move the electrode into theweld pool quickly to kill the arc and then abruptly remove the elec-trode, thus breaking the arc

Note : Complete welding procedures and data for all weldingprocesses are prepared by the American Welding Society (AWS) and

are available in handbook form in its Welding Handbook, eighth

edition, in three volumes

Weld strength: Related equations and tables. Here we will presentthe equations for determining the approximate strengths of weldedjoints Any equation involving a process with many variables, such

as welding, can only be an approximation With this in mind, fore, one should allow a factor of safety when designing and calcu-lating the strengths of welded joints

there-Fillet welds. Refer to Fig 14.50a The basic welding equations forthe fillet weld are as follows:

where l leg dimension of fillet weld, in

L length of fillet weld, in

h weld throat height, in

t material thickness, in

d width of butt welded joint, in

For minimum leg sizes for fillet welds, see Figure 14.51b For

allowable design strengths and shear forces for fillet welds and

partial penetration groove welds, see Fig 14.51a.

Example: The allowable unit force for a fillet weld with a 0.25-in leg,using 80,000-lb/in2weld rod or wire, is 16,500  0.25  4125 lb/in Thus,

if the weld joint is 3 in long, the force allowable is 4125  3  12,375 lb

Plug welds. Plug welds (Fig 14.52) are useful in sheet metal andstructural design applications Plug welds are used primarily forshear loads, although they are not limited to this type of load Aplug weld may be subjected to a combination of shear and tensileloads The typical sizes of plug welds are shown in Fig 14.51c forvarious applications or combinations of material thicknesses Fig-ure 14.52 illustrates a typical plug weld

Note: It should be noted that the weld-strength figures and tables, allowables, and examples are for static loads only When the

welded members are dynamically or cyclically loaded, a factor ofsafety should be applied A safety factor of 3 should be applied forgeneral dynamic conditions In other words, if the weld joint wascalculated to withstand a load of 3000 pounds force, for dynamicconditions this load should be reduced to a 1000 pounds force max-imum (Divide the calculated load by 3 to arrive at the allowableload with the factor of safety applied.)

Specifying welds. The type of welding, weld-rod strength and type,fillet or bead size, location, and length of welds all must be specified

on the welding drawings of a part or assembly Standard weld bols recognized by the American Welding Society (AWS) should beused on the engineering drawings (see “Standard Weld Symbols”below)

sym-Thin-section parts or any part or assembly that may pose a welddistortion problem should be reviewed in coordination with thewelding department or welder prior to final design or beginningthe work Experienced welders usually know or can determine weld-ing sequences to prevent distortion or keep it to a minimum Weldingsequence instructions may be required on the welding drawing

Secondary machining operations usually are performed on awelded part or assembly after the welding operation to correctunavoidable distortion or dimensional changes that take place

Figure 14.51 (a) Allowable shear (b) Weld leg sizes (c) Plug weld sizes.

(a)

(b)

(c)

during welding To reduce cost and save welding time, the amount

of welding on a part or assembly should be kept to a minimum, inaccordance with the strength requirements of the design or sealingrequirements

Standard weld symbols. The basic weld symbols shown in Fig 14.53should be used on all welding drawings, especially if the welded part

is sent to an outside vendor or subcontractor If in-house symbols areused, these should be noted on the welding drawings so that outsidevendors or subcontractors know their exact meaning The symbolsshown in the figure are those recognized by the American WeldingSociety (AWS), the American Iron and Steel Institute (AISI), theAmerican Society of Mechanical Engineers (ASME), the Society ofAutomotive Engineers (SAE), and other authorities and specificationagencies

Figure 14.52 (a) Section of plug (b) Plug-welded plates.

(a)

(b)

Elements of the welding symbol. When a weld is specified on anAmerican standard engineering drawing, it should conform to cer-tain characteristics, which are shown in Fig 14.54 In this way,uniformity and complete understanding are maintained between thewelder and the design engineer Typical welding drawing call-outs

Figure 14.53 Weld symbols

Figure 14.54

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or symbols are shown in Fig 14.55 with an explanation of theirmeaning.

Types of weld joints. There are many types of weld joints or designs,and the basic ones are shown in Fig 14.56 The various joints havebeen designed for different applications and strengths Other charac-teristics are designed into the weld joint, such as minimal outgassing,dynamic strength, deep penetration, pressure-vessel applications,and others Weld joints that require special preparation, such asmachining, filing, or grinding, are more expensive to produce andthus are used for special applications The majority of industrialwelding consists of the simple fillet- and butt-welded joints, followed

by the single-V and double-V joints

Figure 14.55 Typical weld call-outs (welding drawings)

Welding applications data. Welding is one of the most common andimportant means of fastening Its applications are limitless, and thetechnology is constantly changing Given here is a listing of variouswelding process applications that are helpful in design as well aswelding work.

Figure 14.56 Basic weld-joint geometry

Thin-gauge metal welding. Small welding flames or small arcs arerequired for welding thin-gauge metals The TIG process is especiallyuseful for producing small, accurate welds on thin materials, under

11 gauge (0.1196 in) To prevent buckling of large-area, thin

mate-rials, heat sinks are useful Heat sinks may take the form of wet

burlap bags or large blocks of metal clamped to the welded parts or

sections Applying tack welds in a specified sequence also may help

to prevent buckling of large, thin sections prior to beginning thefinal seams

Preheating. Large sections or masses of metal usually require apreheat stage, where the parts are heated a few hundred degreesFahrenheit prior to beginning the welding process This preventsthermal shock and minimizes distortion and possible cracking ofthe welds

Air cooling. Welded parts or assemblies normally are allowed tocool to ambient temperature after the welding process is com-pleted Do not water quench welded parts immediately after weld-ing Because of the high temperatures generated in the weldingprocess, cracking or distortion may occur Changes in the grainstructure of the metal may occur if the hot, welded part is cooledsuddenly by water quenching

Welding bases or platforms. A flat, level area is required for weldinglarge assemblies This is usually provided by structural beamsembedded in the weld shop floor The beams must be straight andleveled with a transit or leveling instrument For smaller weldedparts and assemblies, the standard welding table is used Figure14.57 shows a typical steel-grid welding table, which is used in manywelding departments This type of table is level and has square open-ings where different types of clamping and squaring tools may beattached to hold the welded assembly prior to the welding operation.Notice the screening and plastic shielding located around thewelding table area This shielding prevents the intense ultravioletradiation generated by the welding arc from reaching the eyes ofother personnel The intensity of the welding arc radiation is highenough to damage the membrane covering the human cornea andeyeball It is not necessary to look directly at the welding arc for dam-age to occur to the eye The arc rays can penetrate the side of the eyeindirectly and cause damage The usual effect of looking at a weld-

ing arc is the feeling that sand has entered the eye This usuallybegins to show some hours after exposure to the arc, either directly orindirectly, and is the result of scar tissue formation in the damagedeye.

Figure 14.58 shows a welder performing the TIG welding process

on an aluminum electrical reactor core This is a precision processrequiring great skill by the welder Figure 14.59 shows a welderusing a pneumatic grinder to smooth the edges of a welded sheetmetal assembly that was completed using the MIG process Inmany companies, smoothing of the completed welds by grinding isconsidered part of the welding process and is performed by thewelders Small subassemblies as well as large welded assembliesare treated in this manner

Welding stainless steels. The electrode used to weld stainless steelsalso should be stainless steel, matching the application Types AISI

300 through 303 should not be welded because these are machininggrades Type AISI 304 is a preferred stainless steel for welding

Figure 14.57 A cast iron grid welding table

applications, with AISI type 304L, a special low-carbon grade for ical applications such as those used on aerospace vehicles Too muchcarbon or sulfur in a stainless steel produces cracking during thewelding process AISI types 308, 309S, 310S, 316, and 316L are alsosuitable for welding applications because they are low in carbon con-tent AISI types 316 and 316L stainless steels are used widely inhighly corrosive environments such as chemical and food-processingapplications The 300 series stainless steels are austenitic (nonmag-netic) and cannot be hardened by heat-treatment procedures SeeChap 4 for more information on stainless steels.

crit-Figure 14.58 A welder welding an aluminum reactor core using the TIGprocess on aluminum alloy

Welding carbon and alloy steels. The low-carbon grades from AISI

1010 through 1020 are readily weldable because they are low incarbon content Some of the medium-carbon grades are weldablewith caution, whereas the high-carbon grades are not recommendedfor welding (AISI 1045–1095) The higher carbon content in thesteel causes cracking during the welding process Low-alloy- andalloy-grade steels are weldable according to type and welding processemployed See Chap 4 for more data on the low-alloy and alloysteels, including tool steels

Cutting metals. Oxyacetylene cutting (OFC-A) is the most commonwelding process for cutting ferrous metals Most ferrous metalscut cleanly using this method, except the stainless steels, high-manganese steels, and special alloy steels To cut these difficult mate-rials, special techniques are required wherein the molten metal can

Figure 14.59 A welder grinding and smoothing the edges of a welded sheetmetal assembly for an electrical power distribution product

be blown away from the flame or arc during the cutting process.Laser beam cutting (LBC) is a modern method of cutting difficultmaterials and extremely thin materials Figure 14.60 shows smallparts made of carbon steel that were cut using the laser beammethod These parts are approximately 2 in long and 0.18 in thick.The quantity required did not justify building a stamping die forthis part, and milling the part from stock was expensive; therefore,laser beam cutting was selected for the method of manufacture.

Many branches of industry rely on the welding processes for ducing their equipment and machinery economically Figure 14.61shows a typical electrical power distribution industry lineup ofswitch gear that relies heavily on the welding processes to fastenand join the many sheet metal parts and structures required

pro-14.9.2 Brazing

Brazing employs a nonferrous filler metal, usually in wire or pasteform, to join metal parts at a temperature above approximately800°F but below the melting point of the base metals being joined.Various fluxes are used in the brazing process to remove oxides on

Figure 14.60 Laser-cut steel parts

the base-metal parts so that the filler metal can adhere to themstrongly Sal ammoniac is a good general-purpose flux for brazingcopper, phosphor-bronze, and stainless steels.

The brazing of tungsten alloys to various base metals is plished by pretinning the brazing surfaces of the tungsten alloy part

accom-in a nitrogen-atmosphere furnace before joaccom-inaccom-ing the tungsten alloypart with the base-metal part This is done because it is extremelydifficult to remove oxide layers that form on the tungsten part unless

it is pretinned and protected from the atmosphere Many of the ious designs of electrical contact points are brazed to their base-metalmountings, although riveting is sometimes employed

var-Brazing heat. Heat for brazing parts may be supplied by the lowing methods: