Mfg Tooling -08 Fixtures

Manufacturing Tooling6. Fixture DesignNageswara RaoPosinasettiFixtures A fixture is a means through which apart is securely fastened to themachine tool table to accurately locate,support and hold the part during themachining operation.February 26, 20082Fixtures In addition to the function of holding thework piece, the fixtures also provide forsetting the cutting tool for the actualmachining operation. Generally a fixture is supposed to besecurely fastened to the machine tooltable.February 26, 200831

Fixtures Fixtures are widely used in large batchproduction to ensure the easy setup andachieving the desired accuracy. It can be used in a variety of machine toolssuch as Lathe, milling, grinding, etc. thoughthe milling fixtures are the most widely usedin view of the complex requirements for themilling operation.February 26, 200842

Typical fixture used for milling a flatTypical fixture used for milling a flatFixtures are named on the machine toolin which it is being usedAssemblyBoringBroachingGrindingHeat ngFebruary 26, 200893

Machine Considerations Physical characteristics of workpiece– Round– Irregular– Large– small Types of motions– Linear– RotaryFebruary 26, 200810Fig. From Dr. John G. Nee (revised by), Fundamentalsof Tool Design, Fourth Edition, 1998, SMEProcess considerations Direction of the cutting forcesFebruary 26, 2008124

Fig. From Dr. John G. Nee (revised by), Fundamentalsof Tool Design, Fourth Edition, 1998, SMEFig. From Dr. John G. Nee (revised by), Fundamentalsof Tool Design, Fourth Edition, 1998, SMEFig. From Dr. John G. Nee (revised by), Fundamentalsof Tool Design, Fourth Edition, 1998, SME5

Types of Fixtures Plate fixtures Angle plate fixtures Vise jaw fixtures Indexing fixtures Multipart fixturesFebruary 26, 200816Plate Fixtures From a plate by adding locators andclamps Reference surface is parallel to themounting surfaceFebruary 26, 200817Fig. From Dr. John G. Nee (revised by), Fundamentalsof Tool Design, Fourth Edition, 1998, SME6

Plate fixtureFig. From Donaldson, and Lecain, Tool Design,McGraw HillAngle Plate Fixtures Modified form of plate fixture Reference surface is perpendicular tothe mounting surfaceFebruary 26, 200820Angle plate fixtureFig. From Dr. John G. Nee (revised by), Fundamentalsof Tool Design, Fourth Edition, 1998, SME7

Fig. From Dr. John G. Nee (revised by), Fundamentalsof Tool Design, Fourth Edition, 1998, SMEFig. From Dr. John G. Nee (revised by), Fundamentalsof Tool Design, Fourth Edition, 1998, SMEFig. From Dr. John G. Nee (revised by), Fundamentalsof Tool Design, Fourth Edition, 1998, SME8

Fig. From Dr. John G. Nee (revised by), Fundamentalsof Tool Design, Fourth Edition, 1998, SMEFig. From Dr. John G. Nee (revised by), Fundamentalsof Tool Design, Fourth Edition, 1998, SME9

Milling Fixtures Milling fixtures are the most commontype of fixture in general use today. The simplest type of milling fixture is amilling vise mounted on the machinetable. However, as the work piece size,shape, or complexity becomes moresophisticated, so too must the fixture.February 26, 200828Milling Fixtures The design should permit as manysurfaces of the part to be machined aspossible. without removing the part. Whenever possible, the tool should bechanged to suit the part. Moving thepart to accommodate one cutter forseveral operations is not as accurate oras efficient as changing cutters.February 26, 200829Milling Fixtures Locators must be designed to resist all toolforces and thrusts. Clamps should not beused to resist tool forces. Clearance space or sufficient room must beallotted to provide adequate space tochange cutters or to load and unload thepart. Milling fixtures should be designed and builtwith a low profile to prevent unnecessarytwisting or springing while in operation.February 26, 20083010

Milling Fixtures The entire workpiece must be located withinthe area of support of the fixture. In thosecases where this is either impossible orimpractical, additional supports, or jacks,must be provided. Chip removal and coolant drainage must beconsidered in the design of the fixture.Sufficient space should be permitted to allowthe chips to be easily removed with a brush.February 26, 200831Milling Fixtures Set blocks or cutter setting gages mustbe provided in the fixture design to aidthe operator in properly setting up thetool in production.February 26, 200832Fig. From Dr. John G. Nee (revised by), Fundamentalsof Tool Design, Fourth Edition, 1998, SME11

Fig. From Dr. John G. Nee (revised by), Fundamentalsof Tool Design, Fourth Edition, 1998, SMEFig. From Dr. John G. Nee (revised by), Fundamentalsof Tool Design, Fourth Edition, 1998, SME12

Fig. From Dr. John G. Nee (revised by), Fundamentalsof Tool Design, Fourth Edition, 1998, SMEFig. From Dr. John G. Nee (revised by), Fundamentalsof Tool Design, Fourth Edition, 1998, SMEFig. From Dr. John G. Nee (revised by), Fundamentalsof Tool Design, Fourth Edition, 1998, SME13

Fig. From Dr. John G. Nee (revised by), Fundamentalsof Tool Design, Fourth Edition, 1998, SMEFig. From Donaldson, and Lecain, Tool Design,McGraw Hill14

Fig. From Donaldson, and Lecain, Tool Design,McGraw HillFig. From Donaldson, and Lecain, Tool Design,McGraw Hill15

Lathe Fixtures Similar to the design of milling fixtures. In milling, the workpiece is stationary and thecutting tool revolves. In turning operations,the workpiece revolves and the cutting tool isstationary. Tool designer must deal with-centrifugalforce. The complete fixture must bedesigned and constructed to resist theeffects of the rotational, or centrifugal, forcespresent in the turning.February 26, 200847Lathe Fixtures Since lathe fixtures are designed torotate, they should be as lightweight aspossible. Lathe fixtures must be balanced. Whileperfect balance is not normallyrequired for slow-speed turningoperations, high rotational speedsrequire the fixture to be well-balanced.February 26, 20084816

Lathe Fixtures Projections and sharp corners should beavoided since these areas will becomealmost invisible as the tool rotates and theycould cause serious Injury. Parts to be fixtured should, wheneverpossible, be gripped by their largestdiameter, or cross section. The part should be positioned in the fixtureso that most of the machine operation canbe performed in the first fixturing.February 26, 200849Lathe Fixtures Clamps should be positioned onsurfaces, or areas, which are rigidbefore and after machining. As with other fixtures, some means ofcutter setting should also beincorporated into the design. However,since the work holder will be rotating,this setting device should be removed.February 26, 200850Lathe Fixtures Whenever possible, standard latheaccessories should be adapted in thedesign of turning fixtures. Lathefaceplates are an ideal method tomount large fixtures. Likewise, astandard lathe chuck, or collets, canand should be modified for manyfixturing applications.February 26, 20085117

Fig. From Dr. John G. Nee (revised by), Fundamentalsof Tool Design, Fourth Edition, 1998, SMEFig. From Dr. John G. Nee (revised by), Fundamentalsof Tool Design, Fourth Edition, 1998, SMEFig. From Donaldson, and Lecain, Tool Design,McGraw Hill18

Fig. From Donaldson, and Lecain, Tool Design,McGraw HillFig. From Donaldson, and Lecain, Tool Design,McGraw HillFig. From Donaldson, and Lecain, Tool Design,McGraw Hill19

Surface Grinding Fixtures Surface grinding fixtures are similar indesign to milling fixtures, but made to muchcloser tolerances. Whenever practical, use magnetic chucks tohold the workpiece. Provide adequate room or slots to permit theescape of coolant and to allow easy removalof built-up grinding sludge.February 26, 200858Surface Grinding Fixtures Provide coolant containment devices orsplash guards to keep the fixture fromspilling coolant on the floor around themachine. Fixture elements which are in contactwith the magnetic chuck should bemade from ferrous materials.February 26, 200859Surface Grinding Fixtures Include provisions for rapid wheeldressing and truing in the design of thefixture, if not built into the machine. All locators must be accurately andpositively positioned.February 26, 20086020

Boring Fixtures These fixtures differ from boring normallyused for large parts with large holes wherethe boring bar is rigid enough to provideadditional support. A pilot bushing is notneeded. Boring fixtures, like milling fixtures, shouldhave some provision for setting the positionof the cutting tool relative to the part.February 26, 200861Boring Fixtures In cases where a boring fixture is to beused on a very large machine, such asa boring mill or vertical turret lathe it isalso good practice to include areas onthe fixture to insure proper alignmentwith the machine.February 26, 200862Angle type fixtureFig. From Donaldson, and Lecain, Tool Design,McGraw HillFebruary 26, 20086321

Fig. From Donaldson, and Lecain, Tool Design,McGraw HillFig. From Donaldson, and Lecain, Tool Design,McGraw Hill22

Milling Fixtures Milling fixtures are the most common type of fixture in general use today. The simplest type of milling fixture is a milling vise mounted on the machine table. However, as the work piece size, shape, or complexity becomes more sophisticated, so too must the fixture. February 26, 2008 29 Milling Fixtures