6-4 Section 6 Designing DESIGN DECISION -- ADVANTAGES WITH ALUMINUM EXTRUSIONS There are any number of ways in which extruded aluminum can be applied to meet design challenges more effectively, more efficiently, or more economically than alternative methods of manufacture. The following illustrations offer just a few common examples. 1. As shown, several rolled shapes, riveted together, can be replaced by a single extruded profile, resulting in higher strength while eliminating joining costs. 2. Machining costs often can be reduced by extruding the desired component to exact size and shape requirements. 3. Weight can be greatly decreased by putting the metal only where needed. The extrusion process can put the metal exactly where needed. 1 2 3
Transcript
66--44Section 6 Designing
DESIGN DECISION --ADVANTAGES WITH ALUMINUM EXTRUSIONSThere are any number of ways inwhich extruded aluminum can beapplied to meet design challengesmore effectively, more efficiently, ormore economically than alternativemethods of manufacture. The following illustrations offer just a fewcommon examples.
1. As shown, several rolled shapes,riveted together, can be replaced by asingle extruded profile, resulting inhigher strength while eliminatingjoining costs.
2. Machining costs often can bereduced by extruding the desiredcomponent to exact size and shaperequirements.
3. Weight can be greatly decreasedby putting the metal only whereneeded. The extrusion process canput the metal exactly where needed.
1
2
3
GUEST
66--55Aluminum Extrusion Manual
Advantages
4. Welded assemblies frequently canbe eliminated by designing an appro-priate extrusion. In this way, costscan be reduced while both strengthand accuracy are increased.
5. Sturdy multi-void hollow profilesare available to replace roll-formedalternatives, often at reduced set-upcosts and shortened lead times.
6. Improved stiffness and strengthcan be achieved through extrusion.Here, a detailed hollow profilereplaces a crimped tubular section, ata reduced manufacturing cost.
5
6
4
GUEST
Section 6 Designing
Most common profiles are less than18 inches in diameter, but a fewextruders are capable of producingextrusions with a much larger circumscribing circle diameter(CCD), some as large as 32 inches.
Circumscribing Circle SizeOne common measurement of thesize of an extrusion is the diameter of the smallest circle that will entirelyenclose its cross-section--its circumscribing circle.
This dimension is one factor in theeconomics of an extrusion. In general, extrusions are most economical when they fit within amedium-sized circumscribing circle:that is, one with a diameter betweenone and ten inches.
The example shown here would be classifiedas a 3-to-4-inch circle-size shape.
2”
4”
5”6”
8”
9”10”
18”+
7”
3”
Not to scale
66--1100
GUEST
Keep Metal Thickness As Uniform As PossibleExtrusion allows you to put extrametal where it is needed--in high-stress areas, for example--and stillsave material by using normal dimensions elsewhere in the samepiece. Adjacent-wall thickness ratiosof less than two-to-one are extrudedwithout difficulty, but large differ-ences between thick and thin areasmay create dimensional control prob-lems during extrusion. It is best tomaintain near uniform metal thick-ness throughout a shape if possible.When a design combines thick andthin dimensions, streamline the tran-sitions with a radius (a curve, ratherthan a sharp angle) at junctionswhere the thickness changes sharply.
66--1111Aluminum Extrusion Manual
Practices
DESIGN DECISION --PRACTICESTo develop a good extrusion design,the following key characteristicsshould be addressed:
• Specify the appropriate metal thickness
• Keep metal thickness as uniform as possible
• Use metal dimensions for tolerances
• Design with surface finish in mind• Smooth transitions• Use webs where possible• Use ribs to straighten• Round corners wherever possible,
avoiding sharp edges• Incorporate indexing marks.
Specify the Most Appropriate Metal ThicknessesSpecify metal thicknesses that are justheavy enough to meet your structuralrequirements. Even in low stressareas, however, keep sufficient thick-ness to avoid risking distortion ordamage. Some shapes tend to invitedistortion during the extrusionprocess (such as an asymmetric pro-file or thin details at the end of along flange); such tendencies exertmore influence on thin-walled shapesthan on those with typical metalthickness.
Metal thicknesses should be appropriate.
Rounded corners ease the flow of metal.
GUEST
66--1122Section 6 Designing
Use Metal Dimensions for BestToleranceDimensions measured across solidmetal are easier to produce to closetolerances than those measuredacross a gap or angle. So rely on so-called metal dimensions as much aspossible when designing close-fittedmating parts or other shapes requir-ing closer tolerances. Standardindustry dimensional tolerances areentirely adequate for many applica-tions, but special tolerances can bespecified if necessary.
Design with Surface Finish in MindAlways indicate "exposed surfaces" on your design drawing so theextruder can give them special attention and protect their finishduring both extrusion and post-extrusion handling.
As a general rule, the narrower theexposed surface, the more uniformits finish.
Webs, flanges, and abrupt changes in metal thickness may show up asmarks on the opposite surface of an extrusion, particularly on thin sections. The marking of exposedsurfaces can be minimized bythoughtful design.
A "Metal Dimension"can be extruded toclose tolerances.
An "Open SpaceDimension" is moredifficult to hold toclose tolerances.
Modifying the shapeby rounding the transitions reducesthe chance of oppo-site-side streaking.
This shape, with sharpangular transitions,risks show-throughstreaks on the oppositesurface.
3.00±.024
3.00±.057
GUEST
66--1133Aluminum Extrusion Manual
Smooth All Transitions in ThicknessTransitions should be streamlined bya generous radius at any thick-thinjunction.
Web Gives Better DimensionalControlMetal dimensions are more easilyheld than gap or angle dimensions.The web also allows thinner wall sec-tions in this example.
Ribs Help Straightening OperationWide, thin sections can be hard tostraighten after extrusion. Ribs helpto reduce twisting, and to improveflatness.
Rounded Corner Strengthens TongueThe die tongue is less likely to snapoff when the corners of the profileare rounded at the narrowest area ofthe void.
Built-In Indexing MarkShallow extruded grooves makedrilling, punching, and assembly easier by eliminating the need forcenter-punching. An index groovecan also be used to help identifypieces that are similar in appearance,or to distinguish an inside (ratherthan an outside) surface.
Smooth transitionscan be achievedthrough rounding corners.
The hollow conditionof the part can beavoided by makingthe component in twopieces as shown bythe dotted line.
Rounded corners arestronger corners.
An extruded groovecould eliminate theneed for center-punching.
Ribs reduce twisting.
GUEST
66--1144Section 6 Designing
DESIGN DECISION --ASSEMBLYExtruded shapes can incorporateessential design features such as screwbosses, card slots, or drill guides.Thus, aluminum profiles enhance theusefulness of the part produced.
The joining of aluminum extrusionscan be accomplished by way of ninedistinct methods that can bedesigned into the profiles themselves.
Nesting JointsNesting joints which include lapjoints and tongue-and-groove joints,have mating elements that are shapedto be assembled with little or no self-locking action.
Interlocking JointsThe interlocking joint is, in effect, amodified tongue-and-groove. Butinstead of being straight, the two mat-ing elements are curved; therefore,they cannot be assembled or (moreto the point) disassembled by simplestraight-line motion. They are assem-bled by a rotating motion and willnot separate without a correspondingcounter-rotation. As long as the partsare held in their assembled position,they strongly resist separation andmisalignment in both the horizontaland the vertical directions.
A nesting joint.
An Interlocking joint.
Heat Sink
Groove forscrew or rivetSlot for nut or bolt
Groove forrubber molding
Grooveto acceptprintedcircuitcards
Fluted Surfacefor appearance
“Christmas Tree”for joining withwood or plastic
Screw Bosson leg
Hinge
PatternedSurface forappearance
IntegralTube on leg
Snap-fitassembly
Dovetailassembly
Drill grooves
Anti-skidtraction patternScrew Boss
GUEST
Assembly
Aluminum Extrusion Manual 66--1155
Snap-Fit JointsA "snap-fit" or "snap-lock" joint is onewhich is self-locking and requires noadditional fasteners to hold the jointtogether.
The mating parts of a snap-fit jointexert a cam action on each other,flexing until one part slips past araised lip on the other part. Oncepast this lip, the flexed parts snapback to their normal shape and thelip prevents them from separating.After it is snapped together, this jointcannot be disassembled unintentionally.
A Three-Piece Interlocking JointA three-piece joint can be designedwith a blind (hidden) fastener inter-locking the two principal extrusions.Such a design presents one side witha smooth appearance and no visiblemounting hardware.
A snap-fit joint
A three-piece interlocking joint.
In the example below, a single extruded shape is designed for matingwith identical parts that are rotated into assembly and then snap-lockedrigidly into position without auxiliary fastening. The tight surface-to-surface contact in this design also provides resistance to slidingbetween the parts.
Combination JointsNesting, interlocking and snap-fitjoints can be combined in the sameextruded assembly.
For example, snap-fit elements caneasily be combined with rotating elements.
Assembles with self
GUEST
66--1166Section 6 Designing
Slip-Fit JointsSlip-fit joints are assembled by slidingtwo extruded mating parts togetherin the direction of their length.They are generally classified either asclose-fitting, rigid dovetail joints oras loose, freely-rotating hinge joints.
Dovetail joints are useful in manyproducts where a simple, strong, permanent connection is required.
Hinge JointsThe cross-section of the componentsof a hinge joint have ball-and-socketshapes that allow them to rotate with-out separating. Hinge actionthrough 60 to 90 degrees is easy toobtain; incorporating adequate rein-forcement, hinge joints may bedesigned to rotate beyond 90degrees. Since the hinge joint is rel-atively "loose," provisions should bemade to prevent lateral (side-to side)slippage.
This dovetail joint is a type of slip-fit joint.
A pair of extruded components make up this hinge joint.
A number of profiles could be assembled in series for this type of hinge joint.
GUEST
This unique key-locked joint won an awardin an international extrusion design competition cosponsored by The AluminumAssociation and the Aluminum ExtrudersCouncil.
66--1177Aluminum Extrusion Manual
Key-Locked JointsThese unusual joints have two ormore primary elements which arelocked together only when an addi-tional specialized part, the key, is slidinto position.
The joint shown here is used to connect two or more panels. In theillustration, two panels and theirextruded joining elements are seenedge-on from the top or bottom.The three hook-profiled extrusionsnest together, but are not in factjoined until an extruded pin with aspecial profile is inserted into thespace at the center, locking them inplace.
Keyed interlocks of this type permitrapid, easy assembly and disassembly,making them particularly adaptable totemporary and portable installations, aswell as relatively permanent structures.
