Cees Van Eldijk_TDI

8/2/2019 Cees Van Eldijk_TDI

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Advanced High Strength ThinDuctile Iron - A Breakthroug

C. van EldijTDIvalueWeb the Netherlan

ABSTRACT

Thin Ductile Iron, TDI, is a spheroidal graphite steelmatrix composite with wall thickness from 4 down to 2mm and a microstructure with a nodule count from 1000up to 7000 nodules per mm2. The much finer graphiteparticles cause an increase in fatigue strength, somelowering of fracture toughness and a shift in the Tough-Brittle-Transition-Temperature to lower temperaturescompared to standard ductile iron grades.

This positions TDI as a superior solution vs. steel

weldments and aluminium castings in compact, complexgeometries where fatigue strength and weight reductionare critical.

Exploitation of the potential for (fatigue) strength criticalfunctions in TDI require new design concepts and canbe realised with new procedures for integratedengineering techniques such as geometry optimisation,simulation of mould filling and solidification including(residual) stress analysis, rapid prototyping andthermographical stress analysis.

A market share boost for DI including TDI is expected.

For strength critical applications, TDI is a technicaldesign material par excellence

INTRODUCTION

Thin Ductile Iron, TDI, can be defined as a graphite/steelmatrix composite with 1000 to 7000 spheroidal graphiteparticles in wall thickness down from 4 to less than 2mm. Thin Ductile Iron with various matrixmicrostructures ferritic to austempered TW(A)DI ispart of the Fe-C family and has an enormous potential inadded value creation and market volume expansionproviding up to 50% cost and/or weight savings vs.aluminium, steel and regular ductile iron in applications

where (fatigue) strength is critical and geometry iscomplex. Confronted with new scarcities, rocketing alloymaterial prices and tightening of environmentalregulations, TDI is a best practice answer to these newchallenges.

More than just weight savings and total cost savings,TDI provides improved functional performance (strength,volume, maintenance, life span, noise reduction,environmental aspects). Exploitation of this potential of

TDI has just started and will be illustrated in this paperwith a case study from the transportation sector.The production of TDI castings with a wall thicknessdown to 1.5mm is possible with modern, standardfoundry practices. However, a full realisation oeconomic, commercial, technical and environmentagains can be realized in newly developed, specializedTDI(TADI) casting lines. At this moment, all elementsfor the start of large scale TDI series production areavailable: controlled casting procedures, new productiontechnology and equipment as well as appropriateengineering software and new non destructive inspection

techniques for quality control. To develop optimalquality controlled, strength critical TDI castings, a designprocedure is warranted involving the different partners inthe TDI value chain, ranging from the engineering officeto the OEM. Exploitation of the full potential of TDI ismore than just a simple change of the recipe. Tomaterialise, the potential of TDI, investments need to bemade in the actual organisation and orchestration of TDproduction. At the end of this paper, a shororganizational outlook will be given.

BACKGROUND

Several development projects concerning TDI with

grants from the European Community, the Flemish andDutch governments and Corus steelworks in theNetherlands in the period of 1987-2000 have beencoordinated by the author. The outcome of theseprojects was more knowledge about improvedproduction procedures for TDI, fracture mechanicsproperties for TDI as well as computer simulationmodels for mould filling, solidification and residual stressanalysis. Several pilot projects have validated newlydeveloped technologies. At this moment, a value webfor strength critical TDI castings is starting up incooperation with a number of partner organisations.

PRODUCTION / METALLURGYSerious attempts to produce thin wall Ductile Iron, TDIstarted more than 20 years ago using the availableinoculants, raising the pouring temperature to impracticahigh values and sometimes using insulating mouldingmaterials. The results were not repeatable, themicrostructure not much finer than regular ductile ironand carbides that required annealing had to beaccepted.


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In the EU, Dutch and Flemish subsidized researchprojects during 1987-2000 an extended test programwas carried out with lab tests and several full scaleproduction runs on ten different foundry production lines.[1] This resulted in optimized controllable procedures forthe production of TDI with wall thickness from less than2 up to 4 mm including 7 mm. To secure a TDImicrostructure free of carbide under standard foundryconditions in SiO2-based moulding material a sufficienthigh nodule count is required as presented in Figure 1.To obtain this high nodule count a high %Si level isneeded (compared to regular ductile iron) as well as ahigher amount of inoculant with a sophisticatedprocedure for stepwise addition. The general conclusioncan be that TDI procedures can be operational withstandard modern foundry practices, but the allowableprocess windows for the various process steps aresignificantly smaller than for regular DI and even morecritical than for CGI castings.

Critical conditions that apply for TDI production include:- Inoculation potential (charge composition)- Hypereutectic final chemical composition (CE>4.7)- Nodulisation and pre-inoculation- Late inoculation in mould or stream- Low residual Magnesium content- High pouring temperature- High pouring rate- Fading effects- Controlled mould filling- No burrs on critical places

For the best and reproducible inoculation situation duringsolidification, nodulisation material and inoculationmaterials are important as well as the basic chargecomponents. A high pouring temperature is required toprevent cold run effects and to ensure full solution of thelate inoculation. However, it should not be too high soas to spoil the inoculation effects. A high pouring rate isvery effective in preventing cold run. A good fluid flowand heat flow simulation package for mould filling is amust for designing the optimal gating system. Theresidual magnesium content should be as low aspossible to prevent graphite deterioration and porosity,but high enough to prevent the negative effects of mouldmetal reaction.

The best practice in general terms for TDI production toachieve sufficient high nodule count is a Mg-treatmentwithout further alloying elements (FeSiMg, NiMg, Mg-coke), one or more inoculation (pre-conditioning)treatments containing and a late inoculation in the mould(insert in the mould or powder in the pouring stream).The most effective inoculant for ladle inoculation as wellas in the mould inoculation is a FeSi-based inoculant

containing some Rare Earth elements and Bismuth

Nodule Count vs. Wall thickness

0

1000

2000

3000

4000

5000

6000

7000

8000

0 1 2 3 4 5 6 7 8

Wall thickness (mm)

NoduleCount/m

2

A

B

NO

CARBIDES

RISK

RISK

FOR

CARBIDES

Figure 1: Series A: Lower limit for carbides freecastings produced with optimized and walthickness specific inoculation; Series B: uniforminoculation.

The moment of addition, sequence, amount and ratio forCerium-RareEarth and Bismuth is critical. The besconditions are to be established for each specificproduction situation. Narrow process windows fotemperature-time history, charge composition andminimized fading effects are required comparable tocompacted graphite iron.

GRAPHITE MORPHOLOGYUnder lab conditions [1] TDI material was produced forfurther material characterization (micro structurefracture toughness and fatigue properties) in verticallycast test plates with dimensions of 10 x 20 mm and walthickness of 2, 4 and 7 mm. In all cases a SiO2 basedmoulding material was used. In those test plates agraphite distribution was found as shown in Table 1.The composition of the iron was 3.7-3.9%C, 3.12.7%Si,


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The material was free of primary carbides (cementite)

for these high nodule counts.The major factor to prevent formation of metastablesolidification with primary carbides in TDI is generatingsufficient solidification heat and enlarging theundercooling region before carbides are formed. In orderfor this to happen, a large number of austenite nucleiand graphite nuclei are critical to provide a sufficientaustenite dendrite surface areaand prevent local criticalunder-cooling. A fine austenite dendrite distribution isalso right for good feeding properties. A high %Si isnecessary to allow larger undercooling and produce ahigher nodule count. [1] Of secondary significance toprevent formation of primary carbides is the metal-mouldheat transfer coefficient, the improved solid statediffusion possibility of carbon and the pouringtemperature, which in standard foundry conditions canbe changed in only a limited extent. The pouringtemperature should be high enough to prevent cold runeffects and complete solution of the inoculant.

As result of an extended test program with many labtests and full scale foundry tests a relation could beformulated between nodule count and wall thickness asgiven in Figure 1 curve A. In all cases SiO2 basedmoulding or coring material was used. Curve Arepresents a (conservative) relation above which neverprimary carbides were found. The inoculation was

adapted for different wall thicknesses to get an optimalnodule shape and distribution as given in Table 1.In series B (Figure 1) the inoculation method adaptedfor 2 mm wall thickness was also used for the 4mm and7 mm thin test samples, which resulted in higher nodulecounts in the thicker samples, but with risks for graphitedeterioration and porosity.

Shrinkage defects in thin walls are absent or limited tosome centreline microporosity, which is not found on

crack initiation locations in the samples after fatiguetesting as described below.

a.

b.

a. b. c.Figure 2 : Typical microstructures for ferritic TDI with wall thickness of 2 mm (a), 4 mm (b) and 7 mm (c)

20m

20m


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Figure 3 : Microstructures for 3 mm TDI:a) sufficient inoculation; ~2000 nod/mm2b) insufficient inoculation; ~600 nod/mm2

Figure 2 shows representative microstructures for thetested material in wall thickness of 2, 4 and 7 mmrespectively with a ferritic matrix structure after anannealing treatment. For the 2-3 mm TDI material, agood, regular distribution of graphite particles is foundtogether with a rather perfect shaped spheroidal

graphite.Figure 3.a shows a representative microstructure in for3 mm TDI with ~2000 nod/mm2 in the as cast condition.Figure 3b shows a microstructure for the samecomposition and the same wall thickness of 3 mm, butshowing now only ~600 nod/mm2 and primary carbidesdue to an insufficient inoculation.

Conclusions:Controlled industrial production of TDI is now technicallypossible. Starting the production of TDI is not just asimple change of the recipe. In several foundryproduction stages, narrow process windows must beobeyed / accepted / followed comparable to those for ENGJS 500 or EN GJV.

FRACTURE MECHANICAL PROPERTIES

Fatigue and fracture toughness properties are importantperformance indicators for strength critical or safetycritical applications. For low temperature performance,the Tough-Brittle-Transition-Temperature has to beknown. TDI as a structural material can offer benefits incompetition with steel weldments or aluminium.

To determine the influence of the nodule count on the

material properties, test material was used with asignificant difference in nodule count (500 7000), afully ferritised matrix microstructure and essentiallyidentical chemical composition (Table 1).

FATIGUE LIMITThe fatigue limits have been determined at 4 millioncycles by using the staircase method for differentsurface conditions. Higher limits were found when thecasting skin was removed and crack initiation on the

edges could be excluded. The casting skin was taken ofby smoothly grinding and the sharp machined edgeswere rounded. For these conditions, crack initiationoccurred on the flanks of the sample and not on theedges. A short summary of this extended graduateresearch program is presented in Table 2. Thecalculated fatigue limits are based on the largest nodulesize found in the material and/or the size of the readefect found at the crack initiation location. The resultsare in accordance with the theoretical approach usingthe square root area model of Murakami and Endo. Theresults show a considerable increase in fatigueproperties with increasing nodule count (smaller nodulesize), which has been confirmed by others. [2]

TABLE 2 : Fatigue limits (measured and calculated)ferritic TDI, (UTS=574 MPa, ys=458 MPa).Thickness (mm)s-p=shot-peened

c-c=curved corner

w (MPa)Experiment

R= 0,1Calculnodule

R=0.1

Calculdefect

R=0.12 / c-c / no skin 183.6

5.9315 192

4 / s-p / no skin 161.2 2.8

265 131

7 / s-p / cast skin 121.0 7.9

226

Some examples of fatigue fracture surfaces of the 2, 4and 7 mm specimens are shown in Figure 4. with crackinitiation from the flank and from the edge.

Figure 4 : Fracture surfaces with crack initiationfrom cast skin and corner of the 2, 4 and 7 mm testsamples.

FRACTURE TOUGHNESS

Fracture toughness values, Kc, were determinedaccording to ASTM E1152-95 (J-R curve) with a SENB(single edge notched bending) specimen for the 4 and 7mm materials. A modified J-integral, JM, was used withSENT (single edge notched tensile) specimens for the 2and 4 mm material to exclude geometry effects. For altests, material was used with identical chemicacomposition as specified above with a fully ferritic matrixmicrostructure after a ferritisation treatment. During an

A

2 mm 4 mm 7mm

B

2 mm


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extended graduate program valid JM-R curves could befound for 7, 4 and 2 mm TDI for SENB and SENTsamples. A short summary af the results and calculatedKc-values are presented in Table 3.

Table 3 : Fracture values JMC and estimated KC forferritic TDI with 2, 4 and 7 mm wall thicknesses.

Wallthicknessand

test geometry

JmCN/mm

Std.dev

N/mm

KCMPam

Std.dev

MPam

7 mm / SENB 20.7 2.2 60.8 5.44 mm / SENB +SENT

18.1 3.0 56.8 6.3

2 mm /SENT

12.9 3.0 47.9 6.4

The results indicate that fracture toughness of ductileiron decreases with decreasing nodule size, which wasfound to be in accordance with a model presented by

Rice and Johnson. [ 3, 4 ]

TOUGH-BRITTLE-TRANSITION-TEMPERATUREThe TBTT is an important value for strength/safetycritical applications at low temperatures. A lowering ofthe TBTT by an increasing nodule count is mentioned bysome reports using impact tests. For a nodule countvarying from 220 to 1700 nod/mm2, the TBTT shows asignificant shift to lower temperatures from -26C to-80C using the same sample geometry for impact testsof ductile iron with a fully ferritic matrix structure. For theresilience or upper shelf level of the impact test,decreasing values are found for increasing nodule

counts, which is in accordance with the results of theabove mentioned fracture toughness tests. [5]

A shift of the TBTT to lower temperatures is alsoreported for a ferritic ductile iron with a nodule countincreasing from 98 to 240 nod/mm2 and a Si-content of2.753.3%Si. [6]

For an austempered ductile iron, ADI, in comparisonwith a ferritic matrix, an increase is mentioned for theTBTT (-50C to -100C) [7] No information has beenfound for the influence of an increasing nodule count onthe TBTT for ADI. Further work concerning TADI isconsidered.

Qualitatively those results show an interesting shift ofimpact properties to relatively higher levels and lowertemperatures. It should be noted that the Charpy impacttest does not provide a realistic representation for thereal loading conditions in practice for almost allapplications such as trucks and cars. A fracturetoughness test gives a better representation and rankingof materials concerning toughness requirements. Ingeneral, TBTT values found with fracture toughness

tests show a shift to lower temperatures in comparisonto values found with (Charpy) impact tests.

DISCUSSIONWhen TDI is compared with structural steels andaluminium with identical mechanical properties (UTSYS) in strength critical complex shaped applicationslower fracture toughness properties are found foaluminium (castings) and higher fracture toughnessvalues for steel (in delivery condition). To achieve weighreduction, the new so called Low-Alloyed-AdvancedHigh-Strength-Steels are being used more and more forstructural applications instead of the S350 steel (YS350MPa). The new LA AHSSteels have very highstrength properties (UTS 600 to 1200MPa as hot rolledblanks) thanks to a multi phase microstructure with amixture of hard and soft phases (martensite, bainiteferrite, meta stable austenite). These steels miss thegood crack stopping properties of the former lowstrength structural steels (e.g. S350), have a limited

forming capacity and may generate submicro defectsinternally or at the surface during forming operations(bending, deep drawing or welding). These defectsusually provide a downswing in fatigue and toughnessproperties in the final application.

The results for TDI indicate that it will have a goodcompetitive position in product performance providing areliable robust fracture toughness and fatigue behaviourin addition to a low TBTT as required for transportationapplications.

Conclusions :- An increase in nodule count has a positive effect on thefatigue properties; which is found to be in accordancewith a theoretical model.- An increase in nodule count has some lowering effecton the fracture toughness properties, which is found tobe in accordance with a theoretical model.- An increase in nodule count shifts the Tough-BrittleTransition-Temperature to favourable lower values.- Fracture toughness (Kc or Jint) should be used insteadof Charpy impact tests for toughness testing.- TDI shows a superior potential for complex shapedparts with improved performance in comparison withaluminium and steel. TDI is an outstanding material fostrength critical and safety critical applications.

ENGINEERING

TDI solutions offer maximal benefits for strength criticacomplex shaped applications in comparison withformed/welded steel. A steel part is considered to have acomplex geometry when it includes more than eighwelding and/or forming operations.


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The first TDI re-engineering experience is acquired withseveral brackets for trucks. [8] The results proved that acontrolled short series production is possible andweight/cost reductions of 30% are realistic with using anoperational state of the art engineering facilities andaccepting the limitation of the existing productspecifications. [9]

The real benefits of TDI solutions are much larger thanweight and cost reductions and can be formulated ingeneral terms as a reduction of total costs of ownership,improved competitive position and improved functionalperformance. The following distinguishing aspects canbe summed up in comparison with complex shaped steeland/or aluminium parts: improved strength, reducedmaterial volume, improved freedom of shaping, lessmaintenance, function integration, longer lifespan,improved corrosion resistance, improved noise damping,not easy to copy, low start up cost/time, low toolingcosts, low prototyping costs and last, but not least, a

reduced environmental footprint. Many of these benefitsare typical for castings in general.

To prove the benefits of TDI, the latest state of the artengineering techniques available were used to re-engineer two products: a shock absorber bracket for aheavy truck and a twist lock housing for a containertrailer. [10, 11]

SHOCK ABSORBER BRACKETFollowing reverse engineering, inclusive fatigue testingto measure the performance of a welded steel bracketwas completed for two different load cases. Thefunctional specification was casting directedreformulated and the design space was defined. Twopossible designs were developed with this design spaceusing an automated geometry optimisation tool(Optistruct).

One possible result was skipped due to an incompletefunctional specification and the other was furtherdeveloped in two versions, an open version and a closedversion. The residual stress distribution was predicted byusing a casting optimisation tool (Experto) and thenused as input for the FEM stress analysis. The TDIproduction procedure utilized a double ladle/moldinoculation [12] The FEM-model was validated with the

Lock-in Thermography-stress analysis tool at the firstprototypes.

Fatigue tests confirmed the calculated results that theopen version would perform just as well as theweldment. The closed version outperformed the originalsteel weldment. In other words, the closed TDI version isstill over-dimensioned against the existing conservativerequirements in the functional specification. Figure 5

gives an illustration ofthis development process leadingto a final weight reduction of ~50%.

Conclusions :- The latest state of the art techniques in engineering aresufficient for developing strength critical TDI castings.- The latest state of the art engineering techniqueswhich include fast (inexpensive) prototyping, computeassisted engineering and testing result in rapid andreliable prediction of fatigue performance for TDproducts and additionally provide for a short time andlow cost production start up.- Using TDI in combination with new developed designconcepts for TDI leads to over 50% weight savings incomparison with current approaches for welded steeassemblies.- Furthermore it reduces the total costs of ownership andimproves the competitive position.

MARKET FOR TDI

The strong position of TDI castings can be made cleaby using material performance indicators or comparinggrowth in production volumes.

Figure 5 : Shock absorber bracket; TDI designprovide a smoother stress distribution and ~50%weight reduction vs. a steel weldment.

In a comparison of performance, TDI scores the highespoints in comparison to steel forgings, steel weldmentsand aluminium castings on the aspects of cost, weightmaterial volume and mechanical performance. This isillustrated in Figure 6 with a wheel knuckle as anexample of a typical safety critical component. In almosall cars, TDI has replaced steel forgings.

SteelWeldment2.6 kg

Designspace

TDI1.45kg

TDI1.2kg


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Figure 6 : TDI scores highest vs. Al and steel forstrength critical complex shape parts.

When comparing the production volumes of structural

materials, the total cast iron production is about 10% ofthe total steel production, which is about 10% of the totalconcrete production. Steel production showed a ratherstable level of 700 800 million tons/yr during the periodof 19701990. Since then, it has exploded to more than1.2 billion tons/yr. Ductile irons share of the total 70million tons of cast iron production continues to grow,surpassing the 20 million ton/year mark in 2005. Since1950, ductile iron has replaced grey iron, malleable ironand forged steel. It is now replacing welded steelassemblies more often in safety-critical parts in the fullwidth of the transportation sector: trucks, trailers, railvehicles, pumps and pressure vessels.

An American-Japanese study for the period of 19851990 made the case for a 5-7% growth of DI in primarilystrength critical applications while including a muchlarger increase in added value. This estimated growthrate can be understood when analysing the market fortrucks and cars.

Market for TRUCKSA heavy, not optimised, European truck of 9 tonscontains about 1000 kg of brackets in welded steel,ductile iron and aluminium. A study completed in the1980s showed that re-engineering these parts in TDIwould provide a 50% weight reduction or 500 kg per

truck. If new concepts for trucks in steel and TDI aredeveloped, a total weight reduction is expected of 20 to30% for each vehicle.

Market for CARSA middle/large European car increased in weight from800 to 1300kg during the period of 1985 to 2000 with theamount of cast iron (130 kg [13]) remaining relativelyunchanged. The predicted increase in amount of Al, Mg

is not realised and in most applications where aluminiumis used, it is replacing steel and not cast iron [14]Substitution by TDI can save at least 50 kg per car. Newconcepts based on TDI could provide even more weighreduction.

This potential substitution by TDI of welded steeassemblies and over-dimensioned DI castings in trucksand cars world-wide makes for one million tons of TDI ora 5% volume growth for ductile iron. This is based onthe rough assumption of the production of 50 million carsand .5 million trucks yearly. In figures :

50x106carsx10kg+0.5x106trucksx500kg = (500 + 250

x106 kg = 0.75 x 106tons TDI/yr

Developing new concepts for trucks and cars wilmultiply this growth by replacement of one million tonsper year. A further multiplication of this growth can beexpected if we also consider potential volume increases

of TDI in other market sectors such as: trailersagricultural equipment, busses, light rail vehiclespumps, cranes, building, pipes and fittings.During the past ten years, increasing volume growth forregular ductile iron, the new materials such as ADI, TDITADI, CGI including permanent mould cast iron andcontinuous cast ductile iron has occurred. The growth othese materials should continue to occupy an evenlarger part of the total production volume for cast ironnow ~70.106 tons per year. This is mainly a shift fromgrey iron to the extended DI family to a predicted totatonnage of 40.106 tons per year in 2020.

All technology is available for the production of TDcastings which are just as reliable as forgings thanks tonew production sustaining techniques as developed forsteel production. For the estimated volume increase fothe following decades, this means an enormous extragrowth taking into account the potential of the extendedcast iron family of CGI, ADI, TDI, TADI and TCI as ispresented in Figure 7.

Wheel su


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Outlook

World production ductile iron

0

10

20

30

40

50

60

1950 1960 1970 1980 1990 2000 2010 2020 2030

YEAR

MillionTo

nnes

Transport

Pipes

Machines

Total DI

P r o g n o s i s

CGI

ADI

TDI

TADI

Figure 7 : Production of ductile iron worldwide andestimated growth including ADI, CGI, TDI, TADI.

Market for PIPESIn addition to the volume growth of centrifugal castpipes, the possible volume growth should of continuouscast pipes should be considered. Continuous casting ofTDI pipes is not yet an operational technique. In theory,there is no hindrance for a static or mobile continuouscasting process for pipelines to be used for the transportof water, gas or oil with savings in transport costs andmaterial use and possibly improved performance.Successful tests are reported for the production of TDIpipes with a static horizontal continuous caster. Lowercosts are claimed compared with centrifugal casting ofpipes (1994). [15] The only relevant patented process inthis field is a semi-continuous casting techniqueoperational for the production of piston rings. A bettercontrol of dimensional accuracy and finer microstructurewith improved properties are claimed [16]Conclusions:The volume growth of more than 5% yearly for ductileiron worldwide is not a temporary revival of an worntechnology. It appears to be a consolidation of the startup of the exploitation of the full potential of ductile ironnot yet including the role of TDI. Simply put, it is part ofthe start up of exploitation of the full potential of theextended Fe-C-family in structural applications.

VALUE CHAIN

The existing value chain for strength critical castings isworking sequentially, e.g.: an OEMs engineeringdepartment formulates a new set of specifications usingdesign concepts and materials based on knowledge andexpertise (K&E) of more than 10 years; the (strength)critical parts are obtained from a limited number ofcertified suppliers; this supplier (foundry or machining

partner) is asked to give input to convert the technicaspecification into a casting and provide prototypesWhen there is no supply contract, the foundrysexclusive K&E is not brought into this product. Thisprocedure is a guarantee for sub-optimisation. Is thefoundry supplier not willing to suggest a production linewhich is better lined up for a specific TDI production?Furthermore, this procedure is not using the latest stateof the art in the engineering of castings. When theengineering is outsourced using a specialisedindependent engineering company, the outcome will nobe different.

Conclusions:The current product development strategy isconservative guaranteeing multi-staged suboptimisation.The purchase department has a strong influenceEfficiency and costs reduction are leading and suppressor stop product innovations demanding initia

investments to realise financial benefits and astrengthened market position.

A viable commercial strategy to realise the economicbenefits of TDI needs involvement in a K&E-network andrelated engineering facilities (commercial operational).As main stakeholders in TDI productions, OEMs needto cooperate with and invest in K&E-networks with thenecessary engineering facilities for optimal TDproduction. A pivotal role in the coordination of such anetwork is the position for a TDI orchestrator (Figure 8).The TDI-Orchestrator monitors new developments in theworld and assures that the latest state of the art for TDessential K&E is implemented and that the facilities areoperational with sufficient capacity and qualityassurance. Another role of the TDI- Orchestrator isdeveloping continuous changing concepts for differenTDI castings groups. For each engineering project, theTDI-Orchestrator has the final responsibility of assuringthe needed input from partners on the right time, fittingand reserving adequate capacities up to and includingselection of production line and production capacity. Thisresponsibility ends with the first passed production runwith first article inspection.


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Figure 8 : Knowledge & Expertise basedorchestrated value web for strength critical castingsin TDI.

This approach creates an optimal situation for parallelengineering providing short development times in theorder of 3 months. This will position the TDI solution asa competitive solution versus welded/forged/formedsteel and/or aluminium castings in safety criticalfunctions with an improved quality position vs. regularductile iron and corresponding steel forgings. Theremaining question now is: which new, emerging criticalconcerns of the OEMs will boost activities inorchestrated TDI value webs?

SUMMARY

At this moment the author is involved in the furtherdevelopment of a TDI value web. A summary is givenbelow of the current state of the art concerningproduction, material properties, engineering andorganisation enabling the start-up of TDI.

PRODUCTION / METALLURGY- Controlled production of 2mm TDI is possible withinnarrow process windows.

FRACTURE MECHANICAL PROPERTIES- The increase in nodule count in TDI raises fatigueproperties corresponding to a theoretical model.- The increase in nodule count in TDI has some loweringeffect on the fracture toughness properties (Kc, Jint),corresponding to a theoretical model.- The increase in nodule count seems to shift the Tough-Brittle-Transition-Temperature to suitable lower values.

- Fracture toughness test (Kc or Jint) should be usedinstead of Charpy impact tests for ranking toughness.

MARKET- The volume growth of more than 5% yearly for ductileiron world-wide is the forerunner for further exploitationof the full potential of ductile iron, including TDI.

ENGINEERING- The latest state of the art techniques in engineering aresufficient for developing strength critical TDI castings.- Computer aided design, rapid prototyping andcomputer aided performance validation enables optimadesign at low costs with a short time to market.- Using TDI in combination with new developed designconcepts for TDI leads to over 50% weight savings incomparison with current approaches for welded steeassemblies.- TDI provides more benefits leading to reduction of thetotal costs of ownership and improvement o

competitiveness.

VALUE CHAINThe conversion from traditional sequential value chain toan orchestrated value web requires a partnershipattitude with all parties involved in a special per producproject-based organisation.

FINAL CONCLUSIONFor the critical production and engineering of strengthcritical TDI castings, mature technologies are availableIntegration of these technologies is taking place. Markedevelopments, such as scarcity/instability inmarkets/pricing for raw materials, increasing energycosts and tightening up of environmental regulationsshould push this TDI technology to a breakthrough.

ACKNOWLEDGEMENTS

This work is made possible by Corus steelworks in theNetherlands who provided the opportunity focoordinating extended R&D work concerning TDI withgrants from the European Community, the DutchGovernment and the Flemish Government in the periodof 1987 - 2000. Special thanks is also owed to IronFoundry Van der Burgt BV for doing extra experimentawork , to Jos van der Randen for sharing his extended

foundry expertise and to Ab van Eldijk for the input withregard to organisational aspects and internationapositioning the TDIvalueWeb.

REFERENCES

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CADLifetimePredictio

n

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on Rapid

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Manufacturing

FoundryOperatio

ns2nd

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Assembling

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by orchestrator controlledoperations

critical for knowledgenet

Conceptual

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ion

TDIOrchestrator

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2. Zuidema, J., Hoogen, M. van den, Effect of NoduleSize on Fatigue Properties of Ferritic Nodular Cast Iron,13th European Conf.on Fracture + Fracture MechanicsSanSebastian, Espana, 6-9 September, 2000,Laboratory for Materials Science, Delft University ofTechnology, The Netherlands.3. Janssen, M., Boone, H. Fracture Toughness of ThinNodular Cast Iron 12th Eur. Conf. on Fracture Fracturefrom Defects Sheffield / UK, Sept. 1998.4. Rice, R.C., Johnson, M.A., The Role of Large CrackTip Geometry Changes in Plane Strain Fracture, in:Inelastic Behaviour of Solids, eds. M.F. Kanninen,W.F. Adler, A.R. Rosenfield and R.I. Jaffee, McGraw-Hill, New York, 1969.5. Caldera, M., Massone, J.M. Impact Properties ofTWDI, ISIJ Int, Vol. 44 (2004), No 4, pp. 731-736.6. Bjrkegren, L.E., Hamberg, K. Si-gelegeerd gietijzer;bijzonder taai en uitstekend bewerkbaar, GietwerkPerspektief, 2004 nr 1,, pp 11-17.7. Fierro, V.E., e.o. Mechanical behaviour of spheroidal

graphite ci in the temperature range -100C and +100C.8. Eldijk, C. van, Kaspers, Lipzig, H., Velt, J. int, Thinductile iron castings for automotive applications; a strongpotential, 60 WFCongress, TheHague, Netherlands,sep-oct 1993, pp 12-1 tot 12-7.9. Eldijk, C. van, Kaspers, Lipzig, H., Velt, J. int, Thinductile iron castings for automotive applications; a strongpotential, 60 WFCongress, TheHague, Netherlands,sep-oct 1993, pp 12-1 tot 12-7.10. Eldijk, C. van, Erents, S., Productontwikkeling voorsterktekritische gietstukken, 28 nov 2002, NVvGT-Symposium, pp 21-38; Gietwerk Perspektief 2003 2, pp.11. Bulte, G. ten, Corus nieuw gietproces, 7-mei-2004vraag&aanbod redactioneel.12. Eldijk, P.C.van, Lietaert, F.B. Production of NodularCast Iron Involving a Preliminary Inoculation in theCasting Ladle EP 1 126 037 B1; US 6 533 998.13. Le Gal, J., Lallgement en automobile: Y a tilencore une place pour produits ferreux moules?,Hommes & Fonderie, Janvier 2003, No. 330, pp 11-14.14. Le Gal, J. Enjeux de lallegement danslautomobile, Hommes &Fonderie, Janvier 2002, No.320, pp 14-16.15. Sheng Da, Zheng Yongping, A study of themicrostructure and properties of continuous casting rareearth ductile iron pipes Journal of Alloys andCompounds, 207/208, (1994), pp 383-385.

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