21st Century Manufacturing Part 2 ppt

-General principlesdriven by designer TABLE 2.2 Subprlnclpl ••of Manufacturing Process Selaetfon Implied considerations for Ihe manufacturing processmechllJljca1manufactqriogproce.~.es A

Ftpre2.2 The market adoption curve,modified to include several products

cloned sheep would be way down in the bottom left corner.) Whether or not one ofthese technologies will climb the market adoption curve depends on the following:

• The cost benefit to the consumer

• The robustness and usefulness of the technology to the consumer

this may well mean other applications or software that can run on the newdevice)

• Whether or not the device falls in line with industry standards

Such projects bring out the difficulties associated with launching radically new

emphasize this (Figure 2.3) In the early stages of a product's life, there will always

be some measure of a market There is a small group of consumers who love nology enough to buy a new product, no matter how useful it is perhaps just foramusement or to be able to show off to their friends that they have the latest "cool"thing on the market But this early market of impressionable "technology nuts" or

first bullet above, namely, the cost benefit to the average consumer This begs the

question, How can a product survive across this chasm between the early

now-familiar personal pager Apparently, medical doctors were the first real market

adopters of the pager, and once the general public saw how useful they were, the

product "crossed the chasm" and accelerated rapidly up the S-shaped curve inFigure 2.2

Flgure2.3 The concept of "crossing thechasm" (from Geoffrey Moore, 1995).

Purchasing by

compulsive

"technophiles"

Maturity tmontha)

and Flexibility (CQDFI

This brief and informal introduction illustrates a wide spectrum of market nities with a wide variety of quality levels and consumer choices Thus, inevitably, any

opportu-company must face the rising costs (C) of adding higher quality (Q), faster delivery

Despite the rising costs of quality, delivery, and flexibility, today's customers aremore informed and they expect more than they used to For example, they expect aPentium chip to perform perfectly and yet be competitively priced So how do man-trade-offs to simultaneously achieve high quality and fast delivery in small lot sizes,while still maintaining low cost For example:

fabricated quickly and in small lot sizes and then sold at CompUSA in a pricerange suitable for families and college students

• A Lamborghini Or a Ferrari cannot be fabricated quickly and in small lot sizesand then sold at the price of a Honda Accord or a Ford Taurus.However, on closer inspection, the marketplace does set up a compromise sit-uation between the engineering constraints and the broader economic goals Thisdesign and fabrication systems that can appropriately address each market sector In

in the luxury car sector, the industry leaders will be those who refined their design

Purchasing by realmarket adopters I

Figure2.4 Schematic graph of risingcosts for adding more quality to theproduct, faster delivery (schematicallymeasured on the.r axis by the shortness

in days or weeks to deliver) and moresystem flexibility (CQDF).Also comparewith Figure 2.10

of course, highly influenced by cost, which must be clearly related to the benefits that

two main sections The relationship between cost, delivery, and flexibility will follow

In this general equation the terms are:

design, and prototyping

• T=tooling costs This particularly includes costs for production dies.These first two costs are amortized over the number of products made and

every product, and finally there are the overhead costs

packaging

including loan payments for machinery

Quality orfast delivery

or Jlexibilny

Q,llD,F

Figure 2.5 Cosl breakdowns for manufacturing, similar to Equation 2.I-not toS<;:1I1e(courtesyofOatwald,1988).

monthly costs, electrical and other physical services, general advertising, andeventually be allocated per component Reviewing this list of potential over-heads, it is not surprising that many small companies build the first prototypes

in the garage or basement of one of the founders

Another view of the above equation is shown in Figure 2.5 from Ostwald

manufacturing, and selling a product At the bottom of the chart, the prime costs are

accounts for the labor costs to run the overall factory, consumable materials such asother overhead type charges for running the organization Included in the engi-

neering costs are the design and development costs for a particular product in

=.

'PrUnecost.

COSI of goodsmanufactured'Cost of manufacturing,development.and sales,

at the "conceptual product" stage in Figure 2.1 and (b) the moment the product is soldmarket extends all the way around the diagram to the "9 o'clock position." Colloqui-ally speaking, there are many opportunities to run up huge debts and "go broke"before selling anything Section 2.5 on delivery therefore examines the time-to-market issue in more detail.

Given these introductory remarks, an interesting question now arises: Are somemanufacturing processes cheaper to use than others?

If so, since the designers and the production planners have a wide variety ofpossible methods to choose from, why not choose one that gets the cheapest andmost predictable results?

The book now reviews the manufacturing processes of the "mechanical world"and discusses the constraints that arise For a reader unfamiliar with mechanicalincluded in Chapters 4, 7, and 8

The Manufacturing Advisory Service at <cybercut.berkeley.edu> shows trations and related information The first entry is the solid freeform (SFF) family

categorized in that way by the Unit Manufacturing Process Research Committee ofthe National Academy (Finnie, 1995)

The analysis that follows is based on personal experiences in the metal cessing industries and could probably be refined to suit other domains of manufac-turing such as semiconductors Also, the texts by Kalpakjian (1997) and Schey (1999)cover similar material in their last few chapters Some of their diagrams and conceptsthe time of writing is a "process selector" by Esawi and Ashby (1998)

• Should it be near-net-shape cast or forged and then finish machined?

• Should it be welded or riveted together from several pieces of standard stock?These are only three of many possible manufacturing routes The route tochoose usually depends on a rather complex interaction between guiding eubpnncl-pies of manufacturing process selection shown in Table 2.2

TABLE 2.1 A Brief Taxonomy 01 Mech8nlca/ Manuf&cturing Proceue. (Courte8y of

Flnn •• ,l~)

BriefexplanalionofprocessesProcesses

These processes remove shapes from a solid block calledthe stock LA simple drill from the hardware store createsholes of different depth and diameter 2 A milling cutterhas a flat end and can cut on its sides It can carve out flatpockets in a block to make an "ashtray." 3 Turning is done

on a lathe The stock is round The turning tool passes upnnd down the rotating stock removing layers "A round bar

abrasives to remove thin layers of metal to greater accuracythan processes 1 4.5 Electrodischarge machining useselectric arc: Electrochemical machining uses chargedchemicals to remove fine layers

I In casting, mollen metal is poured into a hollow cavity insand, initially created from a mold 2.lnjeclion molding

"shoots" hot liquefied plastic into a mold

1 Hard surface coatings can be deposited chemically orphysically on softer or tougher substrates-c-chrome plating

is an example 213.Alloying or shot blasting toughens.ur{a"es.

1 Slabs can be rolled down to strip as thin as everyday

"aluminum kitchen foil." 2 Such sheets can be cut and ben!into office furniture, filing cabinets, or soup cans 3 Likelarge-scale hot toothpaste, extrusions of different crosssections can be made if the die (the hole at the end) is apremade shape-using milling or EDM 4 Hot or coldforging involves "slamming" metal into a die cavity Themetal stock plasticaUy deforms to the desired shape

1 Powdered metal is formed in a die and then aintered togive full strength 2 Layers of different carbon fiber sheetsare an example of composite materials 3.Welding involveslocal melting and "mini casting together" of adjoiningplates Brazing uses solid-state bonding between a fillermelalannth ••twnplales

makes sense to begin with the criteria that make the most impact on the costs

-General principles

driven by designer

TABLE 2.2 Subprlnclpl ••of Manufacturing Process Selaetfon

Implied considerations for Ihe manufacturing process(mechllJljca1manufactqriogproce.~.es)

A need for high strength drives the choice toward metal processing over plastic molding, Even higher strengths/performance will force the choice toward forging or machining over casting A need for light weight may drive the choice to plastic, aluminum, or titanium In general, costs will increase when high strength and performance are required Materials such as titanium are very costly.

Wide, thin cruss ~eL"tions will drive choice toward blow molding for plastic parts

or sheet-metal forming for metal parts "Chunky" cross sections drive the choice to castinglforginglmilling operations."Cylindrical" cross sections drive the choice to turning In general, parts with complex geometries will cause high manufacturing costs In small batches, the CNC programming and execution times will be long 10 large batches, dies are expensive to create and operate Tolerances tighter than +1-50 microns (0.002 inch) will begin 10 drive the choice to the machining/grinding/polishing family of processes Grinding and polishing are expensive operations-if possible the designer should avoid such fmishingcosts.

A desired long service life will probably drive the choice to metal processing over plastics Design constraints on fatigue properties may require special tooling and/or lapping processes Longer desired service life will almost certainly increase costs because of more or better materials used, improved surface finish, and more careful design optimizetlona

To deliver the part to the designer quickly, production planners hope to use standard processes and tooling Weird designs might require special tools and lengthy hand assembly and finishing Special tools and fixtures will rapidly drive up the costs and delivery time Any process that requires a die or mold will be more expensive and will take longer than machining or SFR The way in which an individual part is mated or fixed to another one in an assembly is also important Welding, riveting, and bolting costs are high, and these processes are often poorly controlled Thus, cost reductions may result from new assembly or single-piece manufacturing methods.

2.3.4.1 Batch Size of 1

If only one component is needed, then one of the rapid prototyping methods such as

(FDM), CNC machining, or casting is the obvious manufacturing choice The firstthree listed are collectively known as solid freeform fabrication (SFF) Note that

LC •••

create low strength metal parts, and FDM can create low strength ABS plastic parts.

because they do not require the time to make an expensive die or mold prior to duction Casting is also possible for large, complex single components that cannotfeasibly be made by machining However, an expensive mold of wax or wood isActually, if the batch size is as low as only one or two components and if thepart geometry is simple, a skilled craftsperson might even use a manual millingmachine or lathe because the programming time for a CNC machine might not beworthwhile However, if the part geometry is complex, it is worth the time spent toprogram the CNC machine even for one-off components The reason for this is rea-part is almost complete, "all is lost" -c-not only the piece of work material but all thetime that was invested up until that point But on a programmable machine, if anmetrical programming steps that were invested up until that point are stored in theanswer might be that part complexity increases with the number of lines of CNCcode needed to machine the part

pro-For a batch size of one, if the desired part has a complex geometry, SFF ratherthan machining processes will be used An object that resembles a doughnut will beeasy to make by the SFF methods but almost impossible to make by CNC machiningunless it can be made in two halves and joined along its equator Speaking very gen-

only viable alternatives if high strength is needed Selective laser sintering (SLS) canproduce a metal part, but it will he weaker than one produced by machining Fused

one that is weaker than a part from plastic injection molding

2.3.4.2 Batch Siz~ 2 to 10

If only a few components, say 2 to 10, are needed, then CNC machining is today themost likely choice, unless the geometry is highly complex and sculptured, in whichcase a batch of SLS or FDM components might be realistic and cost effective

2.3.4.3 Batch Size 10 to 500

A batch of 10 to 500 might well be done by CNC machining This batch size is

(Figure 2.6) However, manual transfer of parts between machines will be quite likelysince this batch size is not sufficient to warrant investments in automation

It should also be noted that if the customer is increasing its order from just one tothis higher batch size, it might be best to "backtrack" and make a good stereolithog-'These numbers for batch size are very approximate and depend on several factors including part

flJure 2.6 Trends from manual, to CNC, to reprogrammablesystems (FMS) and10"harder automation" (courtesy of Ostwald,1988).

raphy pattern that will then be used for castings.'This option will work if the desired process, rather than machining

tol-2.3.4.4 Batch Size 100 to 1U,OOO

(FMS), will be favored as batch size grows Perhaps robots Ofautomated guided cles (AGVs) will be used to move parts from one machine to another Efficiency will

system However, batch sizes of several thousands will begin to warrant the tion of an expensive die that can rapidly punch out products by a cold forging orstamping process While processes that require a premade die or mold are rarely, ifever, used for one-off or short batch runs, the cost of the die can be amortized over

T in Equation 2.1) Sands (1970) presents a comprehensive analysis for different

forming processes showing at which batch size the use of a die becomes efficient Diecosts and manufacturing system costs increase from left to right in Figure 2.6 Thiscost factor places an important responsibility on the designer In an ideal situationthe newly designed component will be made on existing factory floor machinery,

IJoblotindust~

ModeratequantityindustriesMi"ss production industries]

Mechanization

~grammable, automatio~

Flexible workstationcsn

Work

station

Production-systems

2.3.4.5 Batch Size 5,000 to millions

As batch size increases automation plays a bigger role However.for extremely largebatch sizes, it might even be economic to revert to noncomputerized machines.Speaking colloquially, this batch size moves into the realm of "ketchup in bottles."

referred to as fixed or hard automation, literally because "hard stops" are fixed in

place with wrenches These hard stops establish the positions where components rest

in place while being filled or labeled Some basic computer control and sensors areneeded to keep things on track, but reprogramming will not be needed

The material that the designer chooses for the part will be influenced by weight siderations, cost factors and desired strength This desired strength of the finishedobject is obviously a key factor Even though metals are generally stronger than plas-sumer products such as household appliances, consumer electronics, and manyautomotive products

con-In general manufacturing costs for plastics are lower than those for comparablemetal products This is because plastic forming requires much lower forces thanlabor costs are often lower However, critical components such as transmission gearsstructure Finish machining completes the critical gear tooth involute profiles This

treat-ment, and in-process characteristics The latter include the work-hardening moment in the text to reemphasize that solid freeforrn (SFF') prctotyping techniquessuch as stereolithography create plastic components from a photo-curable liquid.This material from the SLA bath is by no means as structurally sound as standardstrength, but not with the same structural integrity as injection molded ABS

The product's geometry embodies the aesthetic qualities and functional properties

of the part, but it also restricts the selection of suitable manufacturing processes.Figure 2.7 is taken from Schey (1999) to show how one aspect of overall part geom-etry drives process choice.To quickly understand this graph, begin by noting that the

cold rolling process nearest the x axis produces a flat strip that is at the extremes of

wide and thin In fact the strips are often several feet wide and still only a few Cold rolling is thus one of the starting points for a large range of subsidiary processes

mm

Hot rulling :,Dit:cll~ting(Al)

Shell casting (sleel)

Minimum dimension of webw(in.)

FifW"lil2.7 Process capabilities related so part geometry.Very thinsectionstevorrolling and thermotorrmng: "cDunky"s<:ctiQus favor machining and injectionmolding (from fmroductivlIlIJ Manufacturing Processes by J, A Schey, if) 1987.Reprinted with permission of the McGraw-Hill Companies),

The thermoforming of plastic sheets is slightly above cold rolling in the graph.This also creates sections that are relatively thin, and thus it competes with coldThe middle part of the graph relates to processes that create more "chunky" lookingparts of greater thickness (theyaxis in the figure) Finally, note that the mold makingprocedures in sand casting prevent itfrom being selected if one of the dimensions isless than 5 millimeters (0.2 inch),

2.3.7 Accuracy, Tolerances, and FideUty between CAD and CAM

performance that is constrained by the physical and/or chemical processes that,during fabrication, are imposed on the original work material This begs the fol-lowing question: How much fidelity will there be between (a) the specified CADgeometry, tolerances, and desired strength and (b) the final physical object that ismanufactured? In the best case scenario, the CAD geometry will be perfectly trans-lated into the fabricated geometry Also, the properties of the original piece of workmaterial stock will be either unchanged or possibly work-hardened into an even

Accuracy microns

TABlE 2.3 Routine Accuracies for Mechanical Processes (One "Thou" Approximately =

25 Micronsl

Accuracy inches

Hot, open die forging

Hot, closed die forging

+/-0.05 inch+/-0.02mch+/-0.003-0.01 inch+/- 0,002-0.005 inch+/-0.001-0.005 inch+/-0.0005 inch+/-0.ססOO1inch

In the worst case situation, a poorly controlled process will damage a perfectlygood work material Examples of tbis were widespread in the early days of welding,where beat-affected zones reduced the fracture toughness of materials Controllingthis envelope for each process is quite complex and relies on a number of factors,which include:

deposited

• The properties of the tooling/masking/forming media

• The characteristics of the basic processing machinery and its control structure

• The number of parameters in the physics or chemistry of the process

• Sensitivity of tbe process to external disturbances such as dirt, friction, andhumidity

Table 2.3 and Figure 2.8 convey the typical tolerances that can be obtained.Note that even witbin one particular process there can be subtle differences inperformance, resulting in a range of tolerance The darkest bars in the center of eachprocess are the normally anticipated values This range is given the namenatural tol- erance (NT) of the process and is crucially important in both design and manufac-turing work

It cannot be emphasized enough that the cost of manufacturing, and the sequent cost of any consumer product, is related to the designer's selection of partaccuracy and dimensional tolerance

sub-Once the design and its related tolerances reach a factory floor, the turers will be obliged to choose processes that deliver the accuracy and NT implicitdesigner has been overdemanding or just thoughtless Poor design decisions couldresult in the obligatory choice of an inherently expensive manufacturing process

family of manufacturing processes Examples of these are also shown on the Website

gradually achieve a highly accurate, smooth surface A common chain in mechanicalProcess

in.X 10-3

100 50Process

Traditional

Flame cutting

Hand grinding

Disk grinding or filmg

Turning shaping, or milling

Plasma beam machining

Electrical discharge machining

bulk shape Flame cutting could then be followed by a series of machining operations

to obtain further accuracy These can then be followed by grinding and polishing ifhigh accuracy and finish are desired by the designer

In Figure 2.8, the NTs of flame cutting, machining, and grinding are shown,moving across from left to right with finer accuracy Several points should be made:

• The designer should realize that these process chains exist, as summarized inthe simple diagram of Figure 2.9

• Each additional process is needed after a certaintransitional tolerance. If thedesigner is unaware of these transitions, unnecessary finishing costs may becreated, as shown in Figure 2.10 The other side of this coin is that manufac-turing costs can he saved if the designer is willing to loosen desired tolerances

• The manufacturing quality assurance at one step in the process chain must becarefully executed before moving on to the next process If a "parent" process

is "ended too early," the next "child" process may have too much or an sible amount of work to do (Imagine cleaning a rusty garden tool; heavy

015

Secondary process flat capability

FiJUre2.' Processchains with levelsof tojerance

grinding or heavy abrasive papers are needed before moving on to the finalpolishing steps.)

Recall that part strength is listed as the third criterion in Table 2.2 It is related to thedesign geometry, tolerances, material selected, and chosen manufacturing method

These factors also have a coupled influence on the long-term in-service life

Aero-space and structural engineers are probably the designers who are most concernedwith these long-term properties Hertzberg (1996) and Dowling (1993) describe thefatigue properties of metals and polymers The influences of material compositionand local-geometry effects are also described A fatigue failure always begins at astress concentration A sharp corner, a small hole, a rapid transition in diameter are

high integrity grades of steel and aluminum, will choose processes like forging and

IDrill IEDM

I Broach Ream I Bm",l

HoningIHole hierarchy

Surt rougjrin Itr-etncheDtm acc in Hr-s mcnes

Dim ace in 10_1inches Surf rough in Iu-e Inches

complexity metal parts with +/~50 microns (+1- 0.002 inch) accuracy can be

obtained from a production machine shop with a two- to three-week turnaroundtime, obviously depending on normal business conditions

However, several weeks of lead time will be experienced as soon as a seriousmold or die is needed For the processes like forging, sheet metal forming, and high-

die design, factors such as springback for metals and shrinkage for plastics need to

be incorporated Since the deformation stresses that build up during manufacturingare high, the die designer also has to create supporting blocks and pressure plates.The designer will also need to consider parting planes and the draft angles that giveslight tapers to any vertical walls: these are needed to ensure that the part can be