exploring advanced manufacturing technologiesany loose part can have as many as twelve degrees of...

Exploring Advanced Manufacturing Technologies

Copyright 2004, Industrial Press, Inc., New York, NY

SECTION

4

WORKHOLDING DEVICES

In this age of precision manufacturing, it is very important that part-holding acces-sories be suited to the part being held, be accurate and repeatable, and hold the partsecurely. Being able to maintain these qualities during manufacture will result in lowerscrap rates, reduced cycle rates, increased machine uptime, and lower cost per part.

There are many types of workholding devices available to suit the great variety ofparts manufactured. Modern workholding devices should be able to transmit greatholding forces, open and close at lightning speed, and be programmable since mostmanufacturing is now performed on CNC machine tools. To make them more accept-able to industry, they should be as compact as possible and modular enough to fit onvarious machines with slight modifications.

The workholding and material handling devices used on CNC turning and chuck-ing centers can range from simple and automatic chucks, special spindle-mounted fix-tures, to part-feeding systems. On CNC machining centers, they include multiple partvises, special fixtures, rotary tables, tombstones, and automated programmable palletsystems.



The objective of any manufacturing system is to produce avariety of parts using as few tools as possible. This usuallyinvolves operations of metal removal or forming, material han-dling and clamping, and assembly. An important part of allthese operations is the ability of the holding device to locate thepart accurately and securely enough to stand the external forcesapplied during the machining. Only if these factors are presentis it possible to have a continuous production of high-qualityparts produced to the required accuracy. Since a variety of partshapes and sizes are produced, it is important that the part fix-ture be versatile enough so that, with slight modifications, itcan accommodate different parts.

With the state-of-the-art tools available today, most of thehand-clamping methods of the past are being replaced becausethey were the source of potential bottlenecks in the productionprocess. A new breed of quick-change chucks and fixtures,indexing and modular workholding systems, pallet changers,automatic part loading and unloading, and their flexibilitymake it possible to consistently produce high-quality partsquickly and at low production costs, Fig. 4-1-1. They can:

■ Decrease downtime during setups because of the ease,speed, and accuracy of part setup.

■ Increase the spindle productivity due to short part-changecycles.

■ Better use of machine tool uptime increases throughputand productivity.

■ Reduces rework time and scrap through increased accura-cy of the finished part.

■ Improvement in overall manufacturing efficiency.

FIXTURE DESIGN CRITERIAThe speed, accuracy, and repeatability of modern machine

tools are largely due to the qualities of the design and accuracyof modern fixtures. These must have the qualities shown in Fig.4-1-2.

■ Positive Positioning. The part must be held securelyenough to prevent any movement in the X, Y, and Z axes.

■ Rigidity. It must be strong enough to withstand themachining forces and the stress of loading and unloadingof numerous parts.

■ Repeatability. Each part should be located in exactly thesame position in the fixture.

■ Versatility. They should be useful for a variety of machin-ing operations and be as low as possible to reduce vibrationand avoid coming into contact with the machining path.

■ Easy to Design and Build. Modular fixtures should usestandard elements that can be reused when other similarfixtures are required. Wherever possible, standard guides

Types of Workholding Devices 4-1-1

TYPES OF WORKHOLDING DEVICES

(Arthur Gill, Consultant – (Kelmar Associates)

UNIT

4-1

Fig. 4-1-1 Many types of workholding devices are used to locate and holdparts for machining. (Rohm Products of America) Fig. 4-1-2 The qualities that modern fixtures must possess. (Kelmar Associates)



and templates should be used to reduce design and con-struction time.

■ Designed for the Part. There may be slight variation inpart contours, the fixture should be versatile enough toaccommodate these and still be able to hold the partsecurely and accurately.

■ Loading and Unloading. It is essential that the part beable to be loaded and unloaded quickly, and preferablyautomatically, to reduce the amount of nonproductivemachine time.

■ Part Distortion. The part should be held and properlysupported to avoid distortion after it is machined andremoved from the holding fixture.

WORKHOLDING SYSTEMSModern CNC machines and manufacturing processes

require high-performance toolholders, cutting tools, and work-holding systems to consistently produce high-quality parts.Regardless of how well a machine is designed and built or howgood the cutting tools used, the success of any machining oper-ation depends upon whether the part is located accurately andheld securely. The most important function of any workholdingdevice is to hold the part so that the surface to be machined isin the correct relationship to other surfaces, as indicated on thepart drawing, Fig. 4-1-3.

The workpiece must be securely fastened, and the setupmust be safe and rigid enough to withstand the forces that willbe present during the machining operation. If the workpiece orthe holding device becomes loose during machining, damagecan result to the tooling and the machine.

The machine operator should be sure that all workholdingdevices are free from chips and burrs before use. The work-holding devices, generally specified by the programmer,should be located in the proper position on the machine table.Failure to follow these instructions may result in operator

injury, damage to the machine, or scrap workpieces.

LOCATING SYSTEMAn important function of any workholder is to ensure that

parts are located accurately, within certain limits, every time.Therefore, the workholder must contain locators, be strategi-cally placed, that perform three functions: support, locate, andhold the part.

■ Supporting the Part. Supporting a part refers to posi-tioning the locators under the part in the Z axis to preventmovement during the machining cycle and distortionwhen the part is removed.

■ Locating the Part. The purpose of locators is to properlyposition the part in the workholding device in its relationto the horizontal X and Y axes.

■ Holding the Part. This function occurs when the locatorsposition the part properly and prevent any movement. Themain purpose of the clamping mechanisms is to hold thepart securely against the locators.

DESIGNING THE LOCATING SYSTEMAny loose part can have as many as twelve degrees of free-

dom or movement, three main axes (X, Y, and Z), and nineradial axes, Fig. 4-1-4.

Since most workpieces have three axes (X, Y, and Z) andfour degrees of freedom on each axis, the easiest way of pre-venting movement is by the six-point, or 3-2-1 locationmethod. This is the most efficient and accurate method of stop-ping movement on three axes, by placing locators on threesides. As a result, three degrees of freedom are restricted.

■ In Fig. 4-1-5, the primary surface is located on threepoints that establishes a plane, restricting five degrees ofmovement. The part cannot move down or rotate in eitherthe X or Y axes.

4-1-2 Types of Workholding Devices

Fig. 4-1-3 Horizontal machining center and automated pallet cell. (CincinnatiMachine, A UNOVA Co.)

Fig. 4-1-4 The different ways (freedom of movement) an unclamped part canmove. (Modern Machine Shop)



■ The secondary locating surface is located on two points,restricting another three degrees of movement. The twolocators stop axial movement on the Y axis and radialmovement around the Z axis.

■ The part-clamping device controls the last three degrees ofmovement.

Since part shapes vary greatly, the previous guidelinesshould be used only as a guide when designing a fixture. Theoverall goal when placing locators is so that the part is heldaccurately and that it is easy to load and unload.

TYPES OF WORKHOLDING DEVICESAlthough workholding devices differ due to the shape and

size of the part, or the type of machine tool they are being usedon, the most common are: vises, chucks, and fixtures.

A workholding system must do more than hold the partsecurely and prevent distortion; consideration must be given toclearances for the cutting tools as well as the cutting forces cre-ated by the machining process. Although experienced machin-ists and programmers constantly calculate the cutting forceloads, keep in mind that force loads change when cutting toolsare changed. Replacing a carbide end mill with a high-speedsteel (HSS) end mill, or a carbide drill with a HSS drill can havea disastrous effect on the machining process. The new tool coulddouble or triple the cutting forces exerted on the tool. The exist-ing workholding fixture could allow the workpiece to warp orbecome dislodged from the fixture, causing tool breakage, dam-age to the equipment, and possible operator injury. Whenever thedecision is made to change cutting tools, analyze the effects ofthe cutting forces on the workholding design.

VisesMachine vises are the most widely used workholding

device for conventional and CNC milling operations. Machinevises are available in many sizes and styles, making them a

quick and economical way to hold the workpiece and findwide use on indexible tombstone fixtures for machining mul-tiple parts. Plain vises supplied with quick-change features,Fig.4-1-6 A and B are widely used. For repeat positioning ofparts, adjustable stops can be attached to either side of thevise.

Multiple-Part Workholding SystemsMultiple-part machining can be made easy when using a

multiple-part workholding system Fig. 4-1-7. These vises pro-vide a means of rapid loading with positive and equalizedworkholding pressure. Parts can be pre-loaded into slidingjaws; a retaining wire is used to hold the parts in place whilethe sliding jaw is loaded and unloaded. Clearance for theretaining wire is ground into the compensating jaw. Thesevises provide a cost-effective solution for maximizing pro-duction on high volume repetitive milling, drilling, or grind-ing operations.


Fig. 4-1-5 Locating positions to stop a part from moving during machining.(Modern Machine Shop)

Fig. 4-1-6 Plain vise fixturing systems: (A)vise jaws; (B)vise stop. (Toolex Systems, Inc.)

Fig. 4-1-7 A rapid load system combines fast loading with positive, equalizedworkholding pressure. (Lassy Tools Inc.)



Multipart FixturingCreative workholding techniques enable a manufacturer to

reduce the cost per part and speed cycle time in multipart oper-ations. Some examples of these are:

■ Multi-fixtures and small workholding systems for partscan minimize setup time and improve machining efficien-cy, Fig. 4-1-8A.

■ A number of vises or small workholding pallets, fastenedto the faces of a tombstone set on an indexible rotaryworktable on a machining center, allow a number ofmachining operations to be performed in one setup, Fig. 4-1-8B.

It is important to follow good design principles when select-ing or building any workholding device or fixture. Before a newfixture or workholding device is put into actual production, it is

wise to test the complete machining cycle either manually orwith the CNC jog mode dry run to check that the fixture andclamping devices do not interfere with the machining operation.

Magnetic Workholding DevicesMagnetic workholding devices have been around for many

years, and the most common use has been for grinding appli-cations. The use of magnetic devices for workholding has notreally been accepted for other areas of machining, although theholding force is more than enough to hold the workpiece forturning and milling operations. Magnetic chucks have alsobeen used on ram type vertical electrical discharge machines tohold mold and die components during machining.

Magnetic workholding technology can provide a viablealternative workholding solution, Fig 4-1-9, for reducing setuptime and simplify workholding. The workholding device needsto hold and support the workpiece securely and provide a clearmachining area to perform the machining operations. Magnetsgenerate a uniform pulling force across the entire work surface.Holding force is only on one side of the workpiece, allowingcutting tools to access the other five sides of the workpiece. Byfully supporting the workpiece, increased speeds and feeds canbe used without creating vibration or chatter. Although non-magnetic material applications cannot be used directly on themagnet, workholders can be used to hold the non-ferrous parts.

Vacuum WorkholdingOn many occasions the machinist or shop is faced with the

problem of holding workpieces that are thin, flat, or made fromnonferrous and non-metallic materials. This is when the dou-ble-faced tape is brought out of the cupboard, and usually withthe aid of clamps, the job is completed without cutting into theworktable. However, there is another alternative and that is avacuum-operated workholding system, Fig. 4-1-10, that isdesigned to securely hold thin, flat workpieces.


Fig. 4-1-8B A number of vises fastened to the faces of a tombstone allow a num-ber of machining operations to be performed in one setup. (Kurt Manufacturing Co.)

Fig. 4-1-8A Multi-fixtures can minimize setup time and improve machining effi-ciency. (Chick Workholding Solutions, Inc.)

Fig. 4-1-9 Magnetic workholding technology can provide a viable alternativeworkholding solution.



The system includes a modular vacuum chuck plate and anexpendable plastic mat.

■ The vacuum plate is attached to the machine table as asub-plate.

■ The modular chuck plates can be used singularly or placedtogether to accommodate larger workpieces.

■ The mat size is 12- by 8-in. (300 by 200 mm) and about.090 in. (2.3 mm) thick. The mat acts as a buffer betweenthe bottom side of the workpiece and the vacuum chuck.

■ The .090 in. thickness of the mat provides sufficient roomfor the Z axis feed to stop without damaging the vacuumchuck below. If the cutting tool hits the rubber mat, it sim-ply cuts the rubber without damaging the chuck.

■ If the mat gets cut beyond re-use it can be replaced withanother one.

■ The mats, inexpensive to replace, are biodegradable andnot affected by cutting fluids.

The work holding side of the mat is covered with evenlyspaced small and large suction cups. Each of these suction cupsis connected to the external vacuum pump by air lines that aremolded into the mat. The vacuum required for an average mat(12 x 8 in.) is 3.5 cubic feet per minute. When machining smallparts, make sure that as many holes as possible are covered inorder to provide the best gripping force. Vacuum chucks canalso be mounted in a vertical position clamped to an angle plateor held in a vise to allow access to the edge of the workpiece.

AUTOMATIC WORKCHANGERS (AWC)

Twin-Pallet Carrousel WorkchangerHorizontal machining centers equipped with an automatic

workchanger (AWC) keep work in front of the machine spindle

almost constantly, Fig. 4-1-11. Machines using twin pallet AWCwith a quick 180º turn can simultaneously move a queued-uppallet into the workzone for processing, at the same time bring-ing a finished pallet of parts into the part load and unload zone.Pallet registration systems on the pallet-forward Z axis ensurenear perfect alignment (radial location to .0001 in.) or (0.0025mm) each time a new pallet is brought into position.

To keep production moving and ensure multi-face process-ing in one setup, the table indexes in the B axis in 1º incrementsat a speed of 2.6 seconds per 90º increments. An optional fullforth axis contouring table is also available programmable in.001º increments. Standard X Y Z positioning and repeatabili-ty are ±.00006 in.; with optional digital scales, precision can beincreased to ±.00012 and ±.00004 in.(1 micron).

Modular Automatic WorkchangerHorizontal machining centers with modular automated

workchangers redefine productivity and high definitionmachining. These machine tools are designed for maximumpart throughput and quality while compressing product time tomarket. Off-line pallet park stands increase spindle utilizationand part throughput by reducing spindle idle time. Mix andmatch square and rectangular pallets are available for flexabil-ity in setup. Standard X Y Z positioning and repeatability are±.0002 and ±.00008 in., with optional digital scales precision isimproved to ±.00016 and ±.00006 in.(1 1/2) micron.

Machine tools equipped with Automatic Work Changers(AWC) and Automatic Tool Changers (ATC) provide randomtool selection (access by the shortest path search). The hori-zontal machining center provides the ideal solution for ultimateproductivity and flexibility, machining more parts in less timewith less inventory and labor costs.

Automated Pallet Cell (APC)The automated pallet cell (APC) is an ideal machining and

workholding solution to maximize productivity and profit. Thehorizontal machining center (HMC) with an APC allows parts to


Fig. 4-1-10 Vacuum workholding system used to hold thin, flat non-metallicparts. (IBAG North America)

Fig. 4-1-11 Automatic workchanger with off-line load/unload station. (CincinnatiMachine, A UNOVA Co.)

AWC + ATC = Higher Part Throughput



be machined in less time, reducing cost as well as reducinginventory. Workpieces are easily loaded and unloaded at an off-line station. Pallets can be manually indexed, allowing access toall sides of the fixture for part load and unload. The APC, Fig. 4-1-3, is a flexible machining solution that allows manufacturersquick response to changes in production design and product mix.

CHUCKSThe demand for heavier metal-removal rates and higher

spindle speeds has created a need for high-performancechucks. Along with these performance requirements is the needfor better and more secure gripping of the workpiece, quick-change jaws, and chucks that can handle different size work-pieces, etc. The most common workholding device on turningand chucking centers is some type of chuck. These come in awide variety such as self-centering, counter-centrifugal, high-precision chucks for turning and grinding, power chucks,indexing and collet chucks to suit various workpieces andmachining conditions. Self-lubricating and sealed chucks arevirtually maintenance free, providing better accuracy and dura-bility while reducing the maintenance necessary to keep pro-duction equipment functioning accurately.

Self-Centering ChuckChucks are designed to move all jaws equally and simulta-

neously to center the part in the chuck. Self-centering chucks,Fig. 4-1-12, normally have higher gripping forces and are moreaccurate than other chuck types. These chucks are recommend-ed for bar stock, forgings, castings, or turned parts that arelocated from the gripping diameter. Some self-centering powerchucks are equipped with centrifugal force counterbalance thatmaintain the gripping force at high speeds.

Counter Centrifugal ChuckThe counter centrifugal chuck is one way manufacturers have

met the need to better grip the workpiece at high speeds. The

counter centrifugal chuck reduces the centrifugal force developedby the high r/min, counterweights pivot so that the centrifugalforce tends to increase the gripping pressure, thus offsetting theoutward forces developed by centrifugal force of the chuck jaws.

One of the disadvantages of these chucks is the tendency toincrease the gripping pressure as the turning center slowsdown, which may damage the workpiece. An alternativemethod is to use elements of the chuck to lock the chuck jawsmechanically in their original position.

Counter centrifugal chucks come in a variety of sizes from 8to 18 in. (200 to 450 mm) in diameter and can operate at spin-dle speeds of 5500 r/min for an 8 in. (200 mm) diameter chuckand 3500 r/min for a 12 in. (300 mm) diameter chuck. Therepeatability of these chucks is .001 in. (0.02 mm).

Power ChucksPower chucks are an essential part of the automatic manu-

facturing process. Power chucks provide an even grippingforce and their performance does not rely on the skill of theoperator. The gripping power is provided by hydraulic or pneu-matic cylinders that cause the chuck’s jaws to increase theirgrip on the workpiece before the machining forces can causethe workpiece to slip out.

Indexing ChucksIndexing chucks were developed specifically for accurately

clamping workpieces requiring more than one surface to bemachined. When using conventional chucking equipment, eachsurface to be machined requires the repositioning and re-grip-ping of the part, which greatly increases the potential for inac-curacies and machine downtime. With an indexing chuck, thecomplete machining process only requires one gripping opera-tion, Fig. 4-1-13. Once the workpiece is gripped, it is pivotedto the required machining position the program needs, usuallywithout the machine spindle even stopping.


Fig. 4-1-12 Self-centering chucks move jaws simultaneously to center a part;power chucks with centrifugal counterbalance maintain their gripping pressure athigh speeds. (Forkardt International)

Fig. 4-1-13 Hydraulic-actuated indexing chuck used to clamp valve bodies.(Rohn Products of America)



Collet ChucksWorkpieces that are easily deformed, or those that can be easi-

ly surface damaged, cannot always be held optimally using apower chucking system. Machining delicate workpieces or per-forming delicate tasks is sometimes best solved using colletchucks, which are particularly well suited to gripping cylindricalworkpieces. Collet chucks grip the workpiece from the outsideand are usually designed for a specific workpiece diameter, pro-viding repeatability of .0008 in. (0.02 mm) or less radial deviation.

Collet chucks, Fig. 4-1-14, are available in a variety of sizesand styles (round, square, hexagonal), covering a wide clampingrange while achieving the high accuracy expected from a colletchuck. High turning speeds do not cause a loss in clamping force.

Gripping Force MetersGripping force meters are used to determine the static and

dynamic gripping force of the chuck, Fig 4-1-15. The staticgripping force is the force per jaw exerted by the chuck on theworkpiece when the spindle is stopped. The dynamic grippingforce is the force per jaw exerted by the chuck on the work-piece when the spindle is running.

Gripping force meters are electronic/mechanical devicesused to make routine maintenance checks of workholdingequipment and to enhance the safety and productivity of themanufacturing process.

The FORSAVE D measuring system, Fig. 4-1-16, is applica-ble to dynamic measuring, analysis, and reporting of grippingforce. The gripping force sensors are inserted instead of theworkpiece. The measuring unit can be used for fast run-ups onhigh-performance NC and CNC machines. The measurementstaken can be computer processed to generate gripping force dia-grams and machining programs for individual components.

Chuck Jaw Pressure LimitationsWhen the chuck jaw clamping pressure is set, the pressure

must not exceed the maximum pressure stamped on the warn-ing plate. If a greater pressure is used, high-stress forces are

created within the chuck, resulting in possible damage to thechuck or to the machine, and possibly personal injury.

Typically, front-actuated chucks can be operated between200 and 500 psi. Operating the chuck below 200 psi will causeinsufficient clamping force on the part. Always use the maxi-mum chuck clamping pressure unless the pressure applied willdamage the part.

Centrifugal Force and Speed limitationsCentrifugal force imposes speed limitations upon all types of

chucks. Centrifugal force, which increases, as the speed of rota-tion increases, tends to force the chuck jaws outward. Thisdecreases the amount of the clamping force on the part. Allchucks are affected by the high internal stresses caused by cen-trifugal force and therefore all have a recommended maximumrotation speed that should never be exceeded. Operating chucksat spindle speeds higher than recommended will result in higherinternal stresses and the loss of clamping force on the part. Highstresses can cause jaw or chuck component breakage that mayrelease the clamping pressure of the jaws on the workpiece.

Centrifugal force increases as spindle speed increases andas jaws are made heavier, resulting in the jaws trying tomove away from the centerline of rotation. Do not mount topjaws so that they extend beyond the diameter of the chuck.Also, reduce the spindle speed when using special top jawtooling.


Fig. 4-1-14 Collet chucks are used to machine delicate workpieces or perform-ing delicate tasks. (Forkardt International)

Fig. 4-1-15 Gripping force meter used to check static and dynamic grippingforce. (Forkardt International)

Fig. 4-1-16 Gripping force measuring system, dynamic measuring, analysis,and reporting of gripping forces. (Forkardt International)



Changing Chuck JawsAquick-jaw changing system can be used when it is necessary

to frequently change the chuck jaws for different size work-pieces, or when additional machining operations are required.This quick jaw-changing system, Fig. 4-1-17, can reduce thechanging time from 30 minutes to 1 1/2 minutes or less. With lessmachine downtime productivity of the machine improves dra-matically and results in payback in a very short time.

Chucking centers can also be equipped with an automaticchuck-changing system, Fig. 4-1-18. The more chuck changingthat is required, the more important the system becomes inreducing the downtime of the machine. When the CNC pro-gram calls up the automated-jaw changing system, it movesinto position in front of the chuck. The jaws mounted in thechuck are removed and returned to their position in the maga-zine, and those required for the next operation are mounted intothe chuck. Some automated systems change only one jaw at atime, while other systems are capable of changing all jaws atonce. Manually changing the chuck jaws could take the opera-tor 20 to 30 minutes, but with new quick-change designs, thejaws or the inserts can be changed in a minute or less.

TOMBSTONE FIXTURESTombstone fixtures are available in vertical and horizontal

styles, and square, hexagonal, and octagonal shapes, Fig. 4-1-19,for holding some type of flat part on machining centers. Parts canbe mounted on any or all of the available sides for machining,reducing setup time, and increasing machine uptime. There aremany variations of standard tombstone fixtures, such as special-ly designed models to suit specific workpieces. These fixturescan have locating features that provide accurate alignment, rowsof tapped holes, or plain smooth surfaces to hold the workpiece.

MODULAR WORKHOLDING STATIONThe Kurt ClusterTower™ modular workholding stations,

Fig. 4-1-20, consist of a highly rigid cast iron integral visetower providing excellent workpiece immobility while reduc-ing cutter induced vibration. The Kurt setup provides rigidityand flexibility to hold many different parts. They are ideal forholding multiple parts in eight clamping stations. This systemis very flexible because the vise jaws, fixtures, or accessoriescan be quickly and accurately changed to suit different work-pieces. Vise towers maximize machining center output whileproviding flexibility for handling changing part requirements.

MODULAR WORKHOLDING FIXTURESModular fixtures provide many of the advantages of perma-

nent fixtures, but are flexible enough to accommodate variousshapes of workpieces by changing certain components. A mod-ular fixture can be built from a set of standard components tohold a certain part shape, Fig. 4-1-21. After the production runis complete, the fixture can be disassembled to allow the com-ponents to be reused. A manufacturer can make fixtures at anytime to suit the part to be manufactured.

Modular fixturing systems include precision and nonprecisionpositioners and locators, mechanical, pneumatic, and hydraulicclamps. System manufacturers provide a wide range of standardcomponents that can be used to fixture most workpieces. Howev-


Fig. 4-1-17 Quick jaw-changing system replaces chuck jaws in one minute or less. (Rohm Products of America)

Fig. 4-1-18 Automatic chuck-changing systems reduce machine downtime andincrease productivity. (Forkardt, International)

Fig. 4-1-19 Various styles of tombstone fixtures used on CNC machining cen-ters. (Mid-State Machine Products, Inc.)



er, it may be necessary to create custom components to hold cer-tain parts. Although components in a system are standardized,there is no industry standardization of modular fixturing ele-ments. Therefore, components manufactured for one system can-not be interchanged with another system. However, the conceptbehind the system is the same. Components are mounted to a baseplate placed into position and tightened into place.

The T-slot system uses a series of evenly spaced crisscrossedT-slots and T-nuts to hold the components in place. This systemprovides flexibility in the location of the components, but doesnot provide repeatable locations to accurately recreate the fix-ture again.

The dowel-pin system uses a grid of accurately machinedalternating tapped and dowel-pin holes to locate and fasten the

components. This system offers an accurate and easy way torelocate components for fixtures that must be frequently dis-mantled and rebuilt.

Advantages of the modular fixturing system become appar-ent when used for prototype work or short-run jobs where indi-vidual fixtures can be quickly built or changed. Componentparts can be reused, and if the fixture configuration is properlydocumented, it can be reconstructed at any time eliminating theneed to store fixtures for future use.

ROTARY TABLES AND INDEXERSRotary tables and indexing heads have always been one of

the most important accessories to milling operations. Usedmanually or geared to the milling machine table for machiningcams, gears, and helical grooves. Some manufacturers havetaken this concept to the next level by providing high-speedindexers, Fig. 4-1-22, used for high-speed engraving, ordrilling and tapping operations where fast cycle times arerequired for repetitive small part machining.

The Haas trunnion rotary table, Fig. 4-1-22, is an easy solu-tion to convert a 3-axis machining center to 5-axis for complexmachining. The dual axis trunnion table, Fig. 4-1-23, boltsdirectly to the table of the mill, providing 5-axis simultaneous


Fig. 4-1-20 Cluster tower workholding system used for high-production fixturingapplications. (Kurt Manufacturing)

Fig. 4-1-21 Modular fixtures can accommodate a variety of part shapes bychanging fixture components. (Carr Lane Mfg. Co.)

Fig. 4-1-22 High-speed indexer for rapid cycle times of small repetitive parts.(Haas Automation, Inc.)

Fig. 4-1-23 The trunnion rotary table can convert a 3-axis machining center to5-axis for complex machining. (Haas Automation, Inc.)




motion or part positioning to nearly any angle for multi-sidedmachining. The dual axis provides ± 120º of tilt and the rotarytable 360º of rotation.

SUMMARYIn this technological age, it is important to consider all fac-

tors involved in the manufacture of a product to see that every-thing is functioning as near perfect as possible. Automatedworkholding systems must locate and hold the parts firmly to

prevent errors that result in scrap parts. The goal is towarderror-free manufacturing and avoiding the hidden costs ofscrap parts such as labor, material, inspection, sorting, rework,system stoppage, and supervisory costs.

For more information on WORKHOLDINGDEVICES see the Acknowledgment section for the Websites of an industry/organization listed.



exploring advanced manufacturing technologiesany loose part can have as many as twelve degrees of...

Documents