21st Century Manufacturing Episode 2 Part 7 ppsx

7.6.1Precision Manufacturing Services and Their Clients Today's clients for "high-tech" machine shops and metal fabrication shops include the medical industry, the biotechnology industry

d=grid circle diameter before pressing

d;= major diameter of ellipse after pressing

d,=minor diameter of ellipse after pressing

It is frequently more convenient to express the resulting principal strains in terms of engineering rather than true or natural strain definition-that is,

eZ=-d-If the analysis is made for the circles immediately adjacent to necked or frac-tured regions a plot of major strain (el) against minor strain (ez) will yield a curve that separates the strain conditions for successful pressings from those that result in weakness or fracture (i.e., forming limits will be established)

Thus as indicated in the experimental press shop data of Figure 7.31, "safe" regions and "fail" regions for different materials and thicknesses can be established,

It is informative to consider some day-to-day uses of the fanning limit diagram, The die setter can quickly determine, from a single pressing on a gridded sheet, whether a new component with its given set of tools is going to be easy, hard, or

140

0.35mm

Thickness 1.95=

0.93mm

20

MinorsuIface strain (%)

Fipre 7.31Forming limit diagram Different sheet thicknesses shown on right

impossible Then it might be possible to argue quantitatively for a design

modifica-from failure to success by increasing one of the strain components through a slight change in die geometry

In many cases, special lubricants containing molybdenum disulfide can be locally applied to critical areas of the pressing, just to change the strain distribution near potential thinning and fracture points In a different scenario it might be found that the material being used is too good and that a cheaper grade of sheet could be introduced

By keeping a satisfactory reference pressing, the die setter can also locate a source of trouble if, later on in the production run, the press gets out of adjustment

or the properties of the sheet change Finally, the training of press operators and die setters can be made considerably easier and quicker if gridded blanks are available for reference and demonstration

7.6.1Precision Manufacturing Services and Their Clients

Today's clients for "high-tech" machine shops and metal fabrication shops include the medical industry, the biotechnology industry, mold-making industries that create the plastic casings of electromechanical consumer products, the aerospace industry, and the special-effects companies for Hollywood's movie industry

Small-batch high-precision machine shops are also the key suppliers of equip-ment for the semiconductor industry (Chapter 5) and PCB industries (Chapter 6) The stepper machines that increment the masks in photolithography are an excellent example of $1 to $2 million machines that are initially fabricated by metal machining This review of the "client base" for machining brings out a key historical

obser-vation that will hold true in the future Namely, the machine tool industry is a key building block for industrial society, since it provides the base upon which other indus-tries perform their production This fact was especially true in the decades that

fol-lowed the first industrial revolution (approximately 1780 to 1820) Throughout the period to the 19208, the machine tool industry was the foundation for the ship-building, railroad, gun-making, construction, automobile, and early aircraft industry Since then it has also become the foundation for semiconductor fabrication and all forms of consumer product manufacturing As these devices become more specialized and miniaturized, the construction of equally specialized equipment will still be performed at these "high-tech" machine shops and metal fabrication shops Given this range of services, it is not surprising that a new awareness of preci-sion and optimization is emerging Also, processes such as laser machining that were once regarded as specialized are now being used on a day-to-day basis for precision hole drilling (Chryssolouris, 1991)

Overall, best practices include rapid links from design to G andMcodes as indicated in Section 7.2.5, highly tuned economically operated machine tools as

indi-machining-for example, the prediction of the cutting forces in Section 7.3.1-result

in sensible investments in machine tools, forming machines, and rolling mills 7.6.2 Open-Architecture Manufacturing

At the same time, more sophisticated control of the metal (cutting and metal)

the SFF technologies described in Chapter 4 Some new developments in the last

described

Today, factory-floor CNC machines are supplied by the machine tool compa-nies with "closed controller architectures." Fanuc, Mazak, and Cincinneti-Milaoron are some of the most often seen controllers Specifically this means that a user or pro-grammer is constrained to work with the predefined library of G and M codes (now the RS 274 standard) that are supplied with each machine tool company's

vendor-These are adequate today for routine production machining but they are not "open"

for new CAD geometries or new machining sensors coming onto the market

A broader "openness" to any outside third-party developer is one of the design goals of several U.S government projects (Schofield and Wright, 1998; Greenfeld et al., 1989) The aim is to improve the productivity of the U.S machine tool industry, not just by focusing on machine tool companies alone but also by expanding market opportunities for CAD companies, sensor companies, diagnostic software devel-open and all ancillary product suppliers The paradigm is the vastly expanding PC

number of third-party product s will be supported commercially, hence increasing the productivity of standard CNC machines and flexible manufacturing systems

"Open-architecture" machinery control (Figure 7.32) will allow faster access between high-level computer aided design (CAD), computer aided process planning (CAPP), and computer aided manufacturing (CAM)

• As a first example, especially for mold making and some aerospace parts, it is crucial to be able to take interesting, highly complex geometries from CAD and convert them into cutting tool motions For example, a particular goal of the work by Hillaire and associates (1998) is the ability to take NURBS

on a standard three-axis milling machine By contrast, with "closed architec-tures" it is likely that the user would be confined to the geometries and stan-dard interpolations in the machine tool company's lib:rary

• As a second example, open architectures allow a machine tool to automatically compensate for errors in the positioning of the workpiece and make possible the active control of the machining process by accepting inputs from external sensors-c-sometfung that the previous generation of controllers could not do This results in faster production, more flexibility, and more opportunity for

Tool path

Cutter locations t

( Servo loop )

Voltage to drives

F1glIre 7.3Z Control loops for open-architecture machine tools Sensors and feedback are shown at six levels on the right (I-VI): (I) at tbe lowest level vibration and force sensors monitor levels, and changes in speed or feed can be made "on the fly"; (II) at the next level, "on-the-machine touch probing after machining" can suggest changes in the cutter locations to compensate for form

can be compensated for by changing the entry and exit angles of the milling cullen: (JV) at Ihe ne1[1level_now within the process planing domain-it is often desirable to reallocate the proportion of roughing versus finishing cuts so that the last "slab" milled into the bottom of a pocket creates the desired surface fmish; (V) at the next level-e-still within the process planning domain-it is often desirable to reorder the sequence in which the several features of the part are cut,

new graphics routines can be directly sent to the open-architecture machine

Path planning Microplan Macroplan

Design

Constraint informatior Design features

Plan

Machine

Ordered slabs

Machining features

Reference generation

Since the mid·1990s.open-architecture machine tool controllers have thus been ccnuuerclally launched by some industrial companies including Hewlett-Packard, Allen-Bradley, Delta Tau, and Aerotech [e.g., see Delta Tau, 1994) Such

and are open to third-party suppliers of sensors, diagnostic systems, programming interfaces, and software tools

Thrgeted at sophisticated users in industries such as aerospace, these open-architecture machine tools will be very useful as stand-alone machines,andthey will provide powerful, networked-based machines for agile manufacturing As individual systems they will be capable of producing small lot sizes of components with high accu-racy They will also be the factory-floor building blocks of systems in which machines

sized that such bidirectional knowledge exchange is the key to implementing TQM,

lIT,and 6 sigma procedures, for the total integrati.on of quality in the factory

To close with an analogy, a banking machine or a telephone is useful not only because the machine itself is sophisticated but because it has been designed to allow bidirectional knowledge exchange all over a global network Access to the network and all its services is actually more important than the local characteristics of the machine itself

7.7 GLOSSARY

7.7.1Cemented Carbide Cutting Tools

A family of sintered cutting tools that use a few percent of cobalt as the binder phase and a variety of hard carbide particles as the high-temperature, abrasion resistant phase.These may be tungsten carbide, titanium carbide, or tantalum carbide Com-monly, these cemented carbide materials are additionally coated with thin, abrasion-resistant layers

7.7.2Ceramic and Cubic Boron Nitride (CBNI Cutting Tools

A family of hard, nonmetallic stntered cutting tools that have higher abrasion resist-ance than carbides but relatively low toughness

7.7.3Chatter

A machine tool vibration initiated by resonance with a machine tool element but worsened as the part surface becomes undulated and regenerative chatter occurs 7.7.4 Chuck

The clamping device in a lathe

7.7.5 Cup

The test part shape in methods that assess the stretching (Erichsen) and drawing

7.7.6 Deep Drawing

Essentially the same as drawing hut often related to processes that use several repeated drawing operations so that long products can be formed

7.7.7 Drawing

The general term for sheet-metal forming and more specifically the behavior of material in the flange of a product that gets drawn into the die wall

7.7.8 Deformed/Undeformed Chip Thlckne ••

The geometry of machining can be described by the chip dimension (t e)and the

uncut dimension (t) If the rake angle is zero, then tan 4J=tlte.

7.7.9 Depth-ol-Cut (dl

In turning operations, the depth-of-cut is measured radially into the bar being machined In milling it is the vertical depth into the block

7.7.10 Feed R_If)

In turning, the feed rate (f) is measured longitudinally along the bar, usually in

mil-table speed in millimeters or inches per minute, so that it represents the relative motion between the tool and part in the plane being machined

7.7.11 Fixture

A work-holding device that supports, clamps, and resists the cutting forces between tool and work

7.7.12 Flank Face/Flank Angle

On a turning tool, the face is given a clearance angle at the side of a tool This pre-vents it from rubbing on the shoulder being cut (usually to the left of the tool) 7.7.13 Force

The main cutting force is F c'acting on the tool face from the advancing tool in milling

or the advancing work in turning The tangential force, Fn acts normal to the main

cutting force

7.7.14 Form Error

Ideally the walls of a milled pocket should be vertical However, form errors often occur because of fixture deflections, part deflections, or tool deflections, In the latter

shape Similar form errors can occur in turning if the bar is slender and pushes away

1.7.15 Forming Limit Diagram

A plot of minor strain, on a +/-x axis, and major strain, on ay axis The strains are

measured from small circles that are etched onto a sheet prior to the test The circles might become ellipses or bigger circles depending on the deformation that occurs The diagram also notes at which combination of major and minor strain failurebytearing

of the sheet occurs This locus of failure points is the forming limit curve or diagram 7.7.16 G Cod ••

The standard low-end machine tool command set that gives motion; for example,

G 1=linear feed

7.7.17 Jig

A modified work-holding device or fixture that additionally guides the cutting tool into ~ desired location on the surface of the part

7.7.18 Machinability

A relative term that judges the ease of machining of differentmateriaIs Usually, the tool wear or tool life is the main objective function that appraises relative machinability 7.7.19 M·Cod••

The standard low-end command set for machine tool operations that are not related

to x, y,or z motion of the axes; for example, M6 = call tool into spindle 7.7.20 Milling

A machining process suited to prismatic parts

7.7.21 nValue (the Work-Hardening Coefficient)

Defines the slope of the stress-strain curve plotted on log axes Physically, large n

values occur with materials that work-harden a great deal during deformation Austenitic stainless steels are in that category

7.7.22 Power

The power supplied by the lathe or mill is usually measured by the product of the main cutting force and cutting velocity

7.1.23 Rake Angle

The rake angle is measured from the face of the tool to the normal to the surface being cut

7.7.24 RValue

Defines a ratio between the strain in the plane of a sheet and the strain in the

thick-7.7.25Roll Gap

The area between the rolls where plastic deformation of the strip is occurring 7.7.28Roll Load

The force between the rolls related to the deformation of the strip

7.7.27Shear Plane Angle, $

The shear angle $ is not a single plane but a narrow zone identifiable in micrographs The shear angle is then measured between this zone and the direction of the tool/work velocity factor

• Primary shear: the main shear process that creates the chip

• Secondary shear: the shear zone between the bottom of the chip and the tool face

7.7.28 Strain

Defined as the extension divided by the original length:

• Engineering strain: the extension divided by the original length

• True strain: the extension divided by the current length as deformation increases

7.7.29Stress

Defined as the load divided by the area of contact of the two opposing load bearing elements:

• Engineering stress: the load divided by the original area

• True stress: the load divided by the current area as deformation increases 7.7.30Stretching

The deformation mode in sheet-metal forming in which an original square element

of the sheet surface is deformed in both thex and y dimensions to become larger in

all directions

7.7.31Surface Finish Surface Roughness

Cutting tools leave distinctive markings on the surface that are a function of feed rate and the nose radius of the cutting tool edge (see Armarego and Brown, 1969) A pro-filometer can be used to trace over the surface and measure the roughness (Imagine

following the tracks.)

The surface roughness can be measured by the arithmetic mean value

(R,,)-which used to be known as the centerline average-or the root-mean-square average

(R q).To obtain these values, imagine that a cross section is like a rough or uneven

A r1YCl\ f, h ij kl0 !II ~B

lIbCdeUIW \V "

Center (datum) line Figure7.]3 Surface finish

n, of amplitude or ordinate values of the rough sine wave (a + b + c+ +n) and dividing themby n.TheR qvalue is obtainedbytaking the square root of[(a 2+b 2 +

c2+ + n 2 )/nj.Typical values ofR"might be 125 rnicroinches for standard surfaces and 60 to 80 microinches for smoother, well-finished surfaces (Figure 7.33)

7.1.32 Taylor Equation (VT"=C1

The result of replotting cutting speed(V)against the tool life data(non log-log axes

7.7.33 Tool Utetn

UsuaUy defined by 0.75 millimeter (0.03 inch) of flank wear

7.7.34Turning

A machining process suited to axisymmetrical parts

7.7.35 Wear Mechanisms

Tool wearbyabrasion, attrition, and fracture occurs at lower cutting speeds At higher speeds diffusion occurs especially at the rake face, where high-temperature conditions exist

7.8 REFERENCES

Armarego, E 1 A and R H Brown.1969 The machining of metals Englewood Cliffs, NJ: Prentice-Hall

Asada, H., and A Fields 1985 Design of flexible fixtures reconfigured by robot manipulators

In Proceedings of the Robotics and Manufacturing AutomationASME Winter Annual Meeting,

251-257

Backofen, W.A.1972 Deformation processing. Reading, MA:Addison Wesley Cbryssolouris, G 1991 Laser machining. New York: Springer-Verlag

Cole, R E 1999 Managing quality fads: How American business learned to play the quality game New York and Oxford: Oxford University Press

Cook, N H 1966 Manufacturing analysis Reading, MA: Addison-Wesley

Delta Tau Data Systems Inc 1994 Product Literature: "PMAC-NC." Northridge, CA Ernst, H., and M E Merchant 1940-1945 In particular see M E Merchant 1945 The

Goodwin, G M 1968 Application of strain analysis to sheet metal forming problems in the

press shop In Proceedings of the Fifth Biennial Congress 1.UD.R.G., Torino, Italy.

Greenfeld, I., E B Hansen, and P K Wright 1989 Self-sustaining, open-system machine tools

In Proceedings oftke 17th North American Manufacturing Research Institution Conference, 17: 281-292

Grippo, P M., B S.Thompson, and M V Ghandi 1988 A review of flexible fixturing systems for computer integrated manufacturing.lnter1Ultional Journal of Computer Integrated Manu-facturing 1 (2): 124-135

Hill, R 1956 The mathematical theory of plasticity New York and Oxford: Oxford University Press

Hillaire, R., L Marchetti, and P K.Wright 1998 Geometry for precision manufacturing on an open architecture machine tool (MOSAIC-PC) In Proceedings of the ASME International Mechanical Engineering Congress and Exposition, 8: 605 610

Hoffman, E G 1985 Jig and fixture design Albany, New York: Delmar.

Johnson, W., and P B MeUor.I973 Engineering plasticity.London: Van Nostrand Reinhold

Lu, L., and S Akella 1999 Folding cartons with fixtures; A motion planning algorithm In

IEEE Conference on Robotics and Automation. Detroit

Meyer, R H., and 1 R Newby 1968 Effect of mechanical properties of bi-axial stretchability

on low carbon steel Paper presented at the SAEAutomotive Engineering Congress Paper No.

680094

1 R., M L Bohn, A R Kashani, and K 1 Weinmann 1995 Feedback control of the sheet metal formingprocess using drawbead penetration as the control variable.In Proceed-ings of the North American Manufacturing Research Institution, 23: 71-78

Miller, S M 1985 Impacts of robotics and flexible manufacturing technologies on manufac-turing cost and employment In The Management of Productivity and Technology in Manage-ment, edited by P R Kleindorfer, 73-110 New York: Plenum Press

Mueller, M E., R E DeVor, and P K Wright 1997 The physics of end-milling: Comparisons between simulations (EMSIM) and new experimental results from touch probed features In

Tra1l.!lactions of the 25th North American Manufacturing Research Institution, 25; 123-128 See

<http;/Imtamri.me.uiuc.edu>

Rose,F.A.1974 Grid strain analysis technique for determining the press performance of sheet

metal blanks In international Conference on Production Technology. Melbourne Institution

of Engineers

Rowe, G W 1977 Principles of industrial metalworking processes. London, Arnold Sarma, S., and P K Wright 1997 Algorithms for the minimization of setups and tool changes in 'simply Iixturable' components in milling Journal of Manufacturing Systems

15 (2); 95-112

Schofield, S M., and P K Wright 1998 Openarchitecture controllers for machine tools, part I: Design principles ASME Journal of Manufacturing Science and Engineering,

120; 425-432

Stevenson, M G., P K Wright, and 1 G Chow 1983 Further developments in applying the finite element method to the calculation of temperature distribution in machining and com-parisons with experiment Transactions of theASME, Journal of Engineering for Industry 105:

149-154

Stori,1.A.I998 Machiningoperation planning based on process simulation and the mechanics