Jigs and Fixture Essay Example for Free

Jigs and fixation analyseJigs r provided with slit guiding elements such as drill bushes.These direct the tool to the correct couch on the w/p. Jigs argon rarely clamped on the m/c hedge bcz it is necessary to cause the jig on the table to align the various bushes in the jig with the m/c spindle. holdfast hold the w/p securely in the correct position with respect to the m/c during operation. There is sometimes a provision in the fixture for trimting the tool with respect to the w/p, but the tool is not guided as in a jig. Fixture are very much clamped to the m/c table. Elements of JF( spatial relation,Clamping,Tool Guiding Setting Elements ) Adv of JF(Productivity,Interchageability,Skill Reduction,Cost Reduction) Limits Fits Diff b/w high and low limit , is called tolerance(unilateral,bilateral). miscellany of Fits (Running,Push, ask Fit,Force Fit) Cost Estimation(Matl,M/cing,Heat Treatment, Assembling Cost) Principles of Location (1 Location must be related to the d imensional rqmts stated on the comp binglents drawing 2) It is prefable to use a more stainlessly m/chined surface than a less accurate surface Location, 3) The w/p should be prevented from moving along and rotating around X,Y and Zaxes 4) Location sys should facilitate lite and quick loading and unloading of the w/p and aim at motion economy 5) bare(a) Locators must be avoided 6) Location sys should positevely prevent wrong loading of the w/p by foolproofing. Locating Methods of Plane Surfaces 1 A reasonably flat suface can be located by 3 pins of equal height having spherical surfaces at the fix points 2 A rough, uneven or diminish plane should be loacted by 3 adaptable location pins having spherical ends 3 Additional adjustable supports are neccesary to prevent vibrations or distortion of the w/p during m/c operation. The force for adjusting the supports should be kept minimum so that the w/p doesnot get dislocated or lifted from the location pins 4) A machined surface can be located by pads having flat surface.5 There should be tidy clearance for burr or dirt to ensure proper seating of the workpiece surfaces. 6 A cube can be prevented from linear movement and rotation around axes X,Y,Z by six location Pads. Profile 1 can be located approx by aligning it with a slightly bigger sighting case 2 Locating pins can be used to locate a indite or cylindrical w/p 3 Variations in w/p sizes ffrom stool to batch can be taken care of by exploitation eccentric locators whose eccentricity can be set to suit the batch. 4 W/p with little variation can be located but with nesting plates with suitable provision for unloading or ejection Cylinder Spigots used for locating bores should have ample lead for easy entry and their length should be short to prevent jamming of the w/p 2 Long locators for fragile w/p should be relieved at the centre 3 Location Posts which are also used for clamping , should be retained by a nut or a grub screw 4 When two location pins ar e used,the less important one should be made infield shaped .The important full pin should be longer than the diamond pin in order to facilitate easy loading of the w/p. 5 Rough cored holes and bosses are located by conical locators, which often have integral clamping arrangement and drill bush 6 Fixed V blocks are used to locate approx the outside surface of a cylinder. 7 For little location, an adjustable guided V block is necessary.The V Block can be adjusted by a screw or a cam. It can be with drawn quickly by using a swinging eyebolt. 8 V blocks should be positioned in such a way that the varition in the w/p would not affect the location for the operation. For drilling central holes, the centre line of V should be vertical. 9 Clearance grooves should be provided at flash line of cast, forged and moulded w/p .Principles of Clamping(Position, strength , prdouctivity,operator fatique, workpiece variation) Types of Clamps 1 Screw , 2 Strap (Retractable strap,swinging strap, edge , pivoted, hinged,swinging latch 3 Quick natural action (cam,bayonet, quarter turn screw, toggle) 4 Multiple Double, stacking, power clamping pnumatic,hydraulic,magnetic 5 Non Conventional Clamping (adhesive, Fusion- cast of low melting point bismut alloy) Indexing is a process of quick, accurate location of a w/p or fixture in a no of specific positions. Indexing involves periodic linear or dress circle movement of the indexed part precisely in each position.Rqmt of a good drill jig 1 Quick accurate location of the w/p 2 Easy loading and unloading of the w/p and prevention of wrong loading 3 Prevention of bending or movement of the w/p during drilling 4 Ample chip clearance with facilities for swarf removal and cleaning 5 watery weight to minimise operator fatique due to repeated handling 6 Prevention of loss of unwarranted parts by chaining them to the jig body 7 Clearance for overshoot of the drill Drill Bushes( Press Fit, Renewable, Slip, Threaded, Special) Various types o f Jigs(Plate jigs and channel jigs with w/p pots, Angle Plate jigs, Turn Over Jigs, Leaf or latch jigs, Box Jigs, Trunion , Sandwich and pump jigs, Jigs for multispindle m/cs Milling Fixtures Essentials (Strength, Thrust, Cutter Setting, Machine tennons, unmitigated Clamping, Motion economy,swarf disposal)Facing Fix , Sloting Fixture Boring Fix Chucks(Self centring 3 jaw , Independent 4 jaw, combination, power operated, special jaws, soft jaws) case Plate, Collets( Push out, pull in, dead length) Mandrels( Tapered, Axial, Expanding, Threaded) Fixture Module send off Concept. A criterion self contained unit. It is jargon for standardised, easily connectable, replaceable, sub assembled unit alike a timekeeper or acontractor.Modular construction assembles the commercially available modules in an arrangement suitable for the rqd applications. Modular Construction is like universal setup but not built on m/c Modular Fixture base can have t Slots or no of reamed holes. Modular tooli ng eliminates nned for manufacture procurement of standard parts neccesary accesories like fasteners, springs, washers, etc. Inspection Devices Standard Gauges(Go not go, Calliper , snap), Special Gauges(Key way and slot checking, Flush surface gauge for tapered hole, snap gauge for checking centre dist)Reciever gauges for assembly W/p marking and setting gauge Universal Jig- T nut stud as T Bolt,Universal Clamp,edge calmp, Face plate Universal Fixture Transfer Machines(in Line tranfer machines (Walking beam, poered roller conveyor, chain drive), Rotary Indexing table m/c (Rack and pinion, ratchet and pawl, Geneva ) Tranfer Devices Conveyor system(Roller , Wheel, Chute, Belt, Chain, Magnetic, Bucket ) Die is a specialized tool used in manufacturing industries to cut or shape material using a press. (Die block, Punch plate ,Blank cowpoke, Pierce poking,Stripper plate, Pilot, Guide / Back gage / Finger stop, Setting (Stop) Block , Shank) . General Die Design(Strip layout and plec trum of tooling, Economies of the strip- acc to tool shape also, tonnage calculation and selection of the press, Die shoe size, Method of Parts Ejection) continuous tense Die Design(Washers and Round Blanks- 19.5, 30 , Feed=Blank dia. +Sp/tan 19.5 and strip width Pilots and pilot Holes, Skipping of stations, Nesting and Locating) duncish Drawing(Blank Holding- clearance 5%, pressure- minimum force necessary to prevent wrinkling, Drawing Ratios-Blank dia/throat dia of die. Punch load increases with blank dia in linear manner ,Die profile radius-sharper the die radius the greater is the max punch load bcz of the inreased process work due to plastic bending under tension, Punch profile radius- t-1.5 t 0.5t over 3.25mm sheetMore generous the punch radii , the more gradual is the rise of punch load and longer punch travel, but the max punch load is almost unaffected., Radial clearance-1.2t 30% for general purpose. Ironing-10%, Drawing pelt along can affect the yield stress of the mater ial and efficiency of the lubricant, lubrication.