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FOUNDRY TECHNOLOGY

INVESTMENT CASTING

INVESTMENT CASTING

INVESTMENT CASTING

• ZOLLERN Castings Technology – performance, experience and innovation 3

• The Process 4

• Tolerances and Surfaces 6

• VDG Specification P 695 8

• VDG Specification P 690 9

• Shaping 14

• Applications 22

The Zollern factories

The ZOLLERN GmbH & Co. KG is a company with world-wide operations, employing over 2400 employees in thebusiness fields of transmission technology (automation,gears and winches, friction bearing technology), engi-neering elements, foundry technology and steel profiles.

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In the field of castings technology, theZOLLERN Company is not only one of theforemost names in Europe but also a highlyrespected exporter to some of the mostimportant industrial notions in the world. Afterall, we have been making castings for aroundone hundred years. ZOLLERN helped to shapeevery stage in the development of the techno-logy, from the production of simple cast ironat the end of the 19th century to the mostmodern technologies in use today.

Our origins, however, go a lot further back.Prince Meinrad II of Hohenzollern founded thesmelting plant which bore his name and con-sisting of a blast furnace and hammer mill aslong ago as 1708. During the 280 years since

then, the original iron works at Laucherthal (nearSigmaringen) has developed into a Companyemploying 2000 people and operating on aninternational scale. Today, ZOLLERN concentratesprimarily on producing castings by a variety ofmethods (investment, sand, shell, mould, Shaw,continuous and centrifugal); it also has forgingand drawing facilities at its disposal.

At the same time, ZOLLERN is also well known as a manufacturer and supplier of drive systems,handling equipment and machine components,with the result that the expertise obtained from all the industrial sectors which the Companysupplies is utilised synergically to the advantageof customers for ZOLLERN castings.

ZOLLERN CASTINGS TECHNOLOGY – PERFORMANCE, EXPERIENCE AND INNOVATION

INVESTMENT CASTING

THE PROCESS

Investment casting is taken to mean casting into single-piece ceramic shell moulds, eliminating the mould (pat-tern) parting line and the imprecision and flash associatedwith it. The characteristic feature of Investment casting isthat the pattern is melted away and thus lost. The processis described by the following detail production steps.

Investment castings is a precision casting method which isgrowing steadily in international significance for reason ofeconomy. The method is being used to produce larger andlarger castings. Investment castings is also employed on an increasing scale for so-called super alloys which requireever more complex smelting processes. Due to the economicbenefits it offers, increasing weight is being attached toinvestment casting in comparative value analyses. Its scopefor optimum shaping is unmatched by any other castingmethod. Investment castings-oriented design frequentlyoffers an answer to technical problems which would beeither impossible or far more expensive to implement usingany other method.

Material selectionAll castable materials can be processed using this method.Investment casting is particularly suitable for use withmaterials unsuited to machining.

Surface qualityThe casting are produced without any trace of flash, and with an excellent surface finish. In many cases-expect forproducing the required seat dimensions – there is no needfor a follow-on machining process.

Piece weightsGenerally speaking, the investment casting technique is usedfor small piece weights of between 1 g and 10 kg. Largerworkpieces up to 150 kg are also possible.

SummaryThe investment casting technique is characterized by • Almost unlimited scope for the shaping of castings• Hardly any restrictions in terms of materials• A high degree of dimensional accuracy due to elimination

of the mould parting line usually responsible for castingimprecision

• Facility for complex shaped inner contours due to the useof ceramic cores

• Low material allowance on surfaces to be machined• A high standard of surface quality

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1 For every casting, a wax pattern has to be produced.Pattern are manufactured using an injection mouldingmachine in metal moulds made of soft metal alloy,aluminium or using wax.

2 The Patter are glued either individually (in the case of largeworkpieces) or in groups forming ‘clusters’ to a gatingsystem (sprue, gates, feeder) which is also manufacturedusing wax.

3 up to 5 By repeated immersion of the patterns in a ceramicslurry followed by packing in sand, after drying and wherenecessary chemical hardening, the patterns are surroundedby a refractory ceramic cell between 6 and 10 mm thick.

6 and 7 After drying and curing of the mould material, thewax patterns are melted and the moulds fired at tempera-tures up to 1100° C.

8 Casting is carried out by pouring into the moulds while hot. As even the finest details of the mould are completelyfilled, a compact casting result is achieved.

9 up to 12 After cooling and knocking out of the filledmoulds, the casting are separated, machined and subjec-ted to a final inspection.

4 Packing in sand

5 Shell mould 6 Melting out of pattern 7 Firing 8 Casting

9 Casting ejection 10 Release 11 Machining 12 Inspection

1 Patternmaking 3 Immersion2 Assembly of the casting unit

INVESTMENT CASTING

TOLERANCES AND SURFACES

Using the investment casting method, economical dimen-sioning means ensuring that no tolerance is selected closerthan necessary for the intended purpose. Dimensional tole-rances, surface and machining allowances are generally laiddown by the Technical Memorandum of the VDG (GermanAssociation of Foundry Specialists), P 690. The accuracylevel D 1 is generally taken to be the free size tolerance forcasting which demonstrate an average degree of complexity.Accuracy level D2 applies to casting dimensions within toler-anced limits. Accuracy level D3 corresponds to the range ofvariation between different production batches and appliesonly to dimensions for largescale series which have beenagreed with the producer. In order to achieve D3 tolerances,it is often necessary to correct or ‘redress’ the tool by meansof trail gating processes. For this reason, it can be more eco-nomical to adjust the counter-part when mating for toleranceto the actual dimension of the casting.

Linearity, evenness, parallelismTolerances for linearity, evenness and parallelism as well as line and area shape are specified in Table 1 on the right.Small local irregularities in the surface such as shrink marksor pimples are not taken into account.

Angular tolerancesAs the permissible misalignment can occur to either side, no± signs are specified in the VDG Memorandum. The respecti-ve tolerance value of the table in mm per 100 mm applies tothe shorter arm of the angle at the workpiece and must berounded up to the next full tenth.

Machining allowancesFor closer tolerances than those specified above, machiningallowances are necessary. Table 2 provides guideline valuesfor this. These must be added to or deducted from the res-pective limiting dimensions. The machining allowance ineach individual case depends on the material used and thetype of machining process, and therefore must be agreedseparately with the producer.

Accuracy Length of toleranced elementlevel

up to 25 mm 25 to 50 mm over 50 mm

Permissible dimensional variation

D1 0.15 mm 0.25 mm 0.6%

D2 0.10 mm 0.20 mm 0.4%

D3 0.10 mm 0.15 mm 0.3%

Table 1: Tolerances for linearity, flatness, parallelismand line area shape*

*Without/with reverence dimensions toleranced in accordance with immersion casting principles

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Table 3: Surface qualities to DIN ISO 1302

CLA Ra1) Rz

1) Rt1)

[µinch] [µm] [µm] [µm]

N 1 1 0.025 0.22–0.30 0.24–0.40

N 2 2 0.050 0.15–0.60 0.49–0.90

N 3 4 0.1 0.8–1.1 0.85–1.45

N 4 8 0.2 1.0–1.8 1.10–2.40

N 5 16 0.4 1.6–2.8 1.75–3.60

N 6 32 0.8 3.0–4.8 3.2–6.0

N 7 63 1.6 5.9–8.0 6.3–10.0

N 8 125 3.2 12–16 13.0–19.5

N 9 250 6.3 23–32 25–38

N 10 500 12.5 46–57 48–68

N 11 1000 25 90–110 95–130

N 12 2000 50 180–220 190–250

Inve

stm

ent

cast

ing

Mac

hini

ngSa

nd c

astin

g

Sure characteristicsThe surfaces are free of scoring and comply with two surfacecategories/classes N7 to N9 according to table 3. Unlessotherwise agreed, N9 in a sand-blasted surface finish issupplied as standard (see VDG Memorandum point 5).

Table 2: Machining allowances depending on thetype of machining (all values in mm)

Greatest nominal dimension Allowance per surface

over up to coarse fine

– 50 0.5

50 80 0.8 0.3

80 120 1.0

120 220 1.5 0.5

220 500 2.0 1.0

500 – > 2.0 > 1.5

1)Ra, Rz and Rt are approximated valuesFormation of relationship between Ra, Rz and Rt is not permissible.

Part 1: General conditions

1. ApplicationsVDG Specification P 695 lays down the general technicalterms of delivery for investment castings made by the lostwax method from standard and non-standard casting mate-rials or metals. Additional, specific requirements relating tocertain materials are laid down in separate standards.

The purchaser specifies his requirements for the casting inaccordance with its intended purpose. Appendix A of the spe-cification contains a check list providing negotiators withrapid information about various points which can be agreedwhen an order is placed. These refer to corresponding sub-sections and extracts from the VDG specification.

We expressly recommend that only materials be chosenwhich qualify as casting materials in official standards.

Part 2: Quality grades

1. GeneralThe present specification lays down various grades of externaland internal quality for the condition of materials on delivery.The grades are subdivided in accordance with the require-ments which the results of non-destructive tests must meet.

2. Quality grades2.1 Allocation of quality gradesThe allocation of external quality grades is determined inaccordance with tests based on the magnetic leakage-fluxmethod or dye method.

The allocation of internal quality grades is determined by a radiographic test and/or X-ray examination.

Extract from the guideline drawn up by the InvestmentCastings Committee of the VDG (Association of GermanFoundrymen).

INVESTMENT CASTINGS: TERMS OF DELIVERY

INVESTMENT CASTING

VDG SPECIFICATION P 695

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P690, 4th edition, February 1992Directive compiled by the Special Committee on ‘InvestmentCasting’ GERMAN ASSOCIATION OF FOUNDRY SPECIALISTSAvailable from VDG-Center of InformationSohnstr. 70, 40237 Düsseldorf Tel. +49 (0) 211/68 71-254Fax. +49 (0) 211/68 71-364 Email [email protected]

Slightly abridged version with the permission of the GermanAssociation of Foundry Specialists.

1. Definition and scope1.1 Investment casting is a process by which a high surfacequality can be manufactured through the formation of dimen-sionally accurate casting. The patterns produced by injectionmoulding are heat disposable and are melted out aftermanufacture of the ceramic moulds. The ceramic moulds aredestroyed after casting. For this reason, both the pattern andthe moulds are designated ‘lost’ using this method. Castingusually takes place into hot moulds.

1.2 Metals and iron, aluminium, nickel, cobalt, titanium, cop-per and magnesium-based alloys can be used for investmentcasting. Depending on the type of alloy, casting is performedexposed to the air, under inert gas in a vacuum.

1.3 This technical memorandum does not apply preciousmetals cast using the dewaxing method, to products of thejewellery industry, dental laboratories or to art casting.

2. Purpose2.1 This technical memorandum defines dimensional toler-ances, specifies machining allowances and surface roughnesscorresponding to the start of the art in the field of investmentcasting. It serves as a basis for optimum economic coopera-tion between investment casting suppliers and buyers.

2.2 The specifications mentioned here refer to sandblastedpreserved or pickled surfaces in their delivered condition.Exception must be agreed where work processes are involvedwhich alter the dimensional tolerances.

2.3 Unless otherwise agreed, initial samples are supplied forfirst-time orders. These are used to permit concrete mutualagreement between supplier and purchaser. Initial samplesmust be appraised by the buyer, followed by a written releaseto the foundry for series production. Deviation acknowledgedby the release or with positive appraisal of the initial samplesare binding for the production process and must be enteredinto the (casting) drawing.

DIMENSIONAL TOLERANCES, SURFACES, MACHINING ALLOWANCES

VDG SPECIFICATION P 690

INVESTMENT CASTING

3. Dimensional accuracy3.1 Contraction and shrinkage During the solidification and cooling of cast metals, a con-traction of the volume naturally occurs as a result of shrink-age. Other factors influencing the production of instrumentcastings can result from the shrinkage of the lost pattern andthe expansion of moulds during heating. The sum of theseinfluencing factors is taken into consideration in the shrink-age allowance during the manufacture of injection moulds.The shrinkage allowance is based on experience values,depending on the contour of the casting, the ceramic shelland the casting materials, as well as the casting techniquesused in the individual foundries.

Fig. 1The primary reference plane ‘A’ is fixed by three referencepoints A1, A2 and A3. These should represent the largest sur-face area of the casting. The secondary reference plane ‘B’ isfixed by two reference points B1 and B2, which should bearranged along the longitudinal axis. The tertiary referenceplane ‘C’ has only a single reference point C!, which shouldlie at or near the centre of the casting.

Fig. 2The reference planes are laid through the symmetrical axisof the casting.

3.3 Overdefinition According to DIN 406, overdefinition must be avoided.Wall thicknesses must always be specified.

3.4 Mould and draught angles Mould and draught angles are not necessary as a generalrule. Exceptions to this for reason of mouldmaking or castingnecessity must be agreed between the investment castingsupplier and the buyer.

3.2 Reference planes and reference pointsDrawing used in the manufacture of casting must be gaugedsystematically using reference or locating points in order toensure that dimensional checks and subsequent machiningare in agreement. Reference points must be determined rightfrom the early design stage and coordinated between thezero position of the reference planes is precisely defined bymeans of the reference point dimensions. All reference pointsmust be arranged in such a way that they are not removed oraltered during the subsequent machining process. Referencepoints should be positioned on the outside surfaces of theinvestment casting. They may take the form of raised orreference points are beneficial when dealing with castingswith restricted shape and position tolerances. When deter-mining the reference points, attention should be paid toensuring that they do not fall in the area of a sprue. In caseof complex shaping, it is possible in this way to position thecasting precisely by (pre-) machining the locating points.

A3

A plane

C plane

B plane

B2 C1A2

A1

B1

Reference plane locating points

Fig. 1 Fig. 2

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4. Dimensional tolerances 4.1 Linear dimensional tolerances Achievable dimensional tolerances on investment casting are dependent on the following factors:• Casting material • Dimensions and shape of the casting• Validity of the accuracy grade

4.1.1 Casting materialIn production, the varying characteristics of the materialsaffect the spread of the tolerance fields. For this reason,different rows of tolerance apply in table 1 to the differentmaterial groupings:

Degree of accuracy

Material group D D1 to D3Iron, nickel, cobalt and copper-based alloys

Material group A A1 to A3Aluminium and magnesium-based alloys

4.1.2. Dimensions and shape of the casting The achievable accuracy level of the rated dimensions of aninvestment casting depends on the greatest dimension andthe shape of the casting. If the rated dimension (GTA)exceeds the rated dimension range indicated for a certainaccuracy level, the overall tolerance of the casting must betoleranced at the accuracy level (greatest tolerance field).Deviation outside the accuracy level must be agreed bet-ween the supplier and the buyer.

4.1.3 Validity of the accuracy levelIn each of the material grouping D and A, there are three accuracy levels specified.Accuracy level 1 applies for all untoleranced dimensions.Accuracy level 2 applies for all toleranced dimensions.Accuracy level 3 can only be adhered to for individual dimen-sions and must be agreed with supplier, as for other additionalproduction steps elaborate tool corrections are also necessary.

4.1.4 Location of the tolerance zoneThe location of the tolerance zone relative to the nominal sizecan be freely selected. It is advisable to lay the tolerance zoneevenly about the nominal size. In the case of surfaces which areto be machined, the sum / difference of the tolerance zone andmachining allowance must be taken into account (see point 6).

Range of D1 D2 D3 A1 A2 A3nominal size

Zone GTA Zone GTA Zone GTA Zone GTA Zone GTA Zone GTA

up to 6 0.3 0.24 0.2 0.3 0.24 0.2

6 up to 10 0.3614

0.2813.5

0.2213

0.3614

0.2813.5

0.2213

10 up to 18 0.44 0.34 0.28 0.44 0.34 0.28

18 up to 30 0.52 0.4 0.34 0.52 0.40 0.34

30 up to 50 0.8 0.62 0.5 0.8 0.62 0.5

50 up to 80 0.9 14.5 0.74 14 0.6 13.5 0.9 14.5 0.74 14 0.6 13.5

80 up to 120 1.1 0.88 0.7 1.1 0.88 0.7

120 up to 180 1.6 15 1.3 14.5 1.0 14 1.615

1.314.5

1.014

180 up to 250 2.415.5

1.915

1.514.5

1.9 1.5 1.2

250 up to 315 2.6 2.2 1.6 2.6 2.2 1.6

315 up to 400 3.616

2.815.5

2.8 15.5 2.4 15 1.7 14.5

400 up to 500 4.0 3.2 3.2 2.6 1.9

500 up to 630 5.4 4.4 4.4 3.4

630 up to 800 6.2 16.5 5.0 5.016

4.0 15.5

800 up to 1000 7.2 5.6 4.6

1000 up to 1250 6.6

Table 1: Linear tolerances (dimensions in mm)

The general casting tolerance series GTA correspond to DIN 1680 Part 2For wall thickness tolerances, see table 2.

This contains information an the smallest lateral length of asurface, which is authoritative in determining the wall thick-ness tolerance, for each material grouping.

INVESTMENT CASTING

Table 2: Wall thickness tolerances4.2 Dimensional tolerance for wall thicknesses The wall thickness tolerance depend on • the size of the (ceramic) walls of the mould • their uninterrupted surface area • their possible thermal distortion • the metalostatic pressure of the molten metal.

The wall thickness tolerance are, for this reason, not depend-ent on the level of accuracy. They are restricted (or reduced)by thicker edge sections, break-throughs (openings, holes),webs to be included in the casting, ribs and similar, whichserve to ‘relieve’ the wall thickness. The tolerance range inquestion in each case is indicated in Table 2.

Smallest Material Materiallateral length group D group Aof a surface Fe, Ni, Co, Cu Al and Mg

(Fig. 3) based on alloys based on alloysmm mm mm

< 50 ± 0.25 ± 0.25

50 up to 100 ± 0.30 ± 0.30

100 up to 180 ± 0.40 ± 0.40

180 up to 315 ± 0.50 ± 0.50

> 315 ± 0.60 ± 0.60

4.3 Shape and position tolerancesShape and position tolerances presume the determination of reference planes and reference points as defined by DIN ISO 1101. They are dependent on the material and shape of the casting and must therefore be agreed betweenthe supplier and buyer.

4.4 Angular tolerances for material groups D and AAngular tolerance deviating from table 3 must be agreedwith the supplier and entered in the drawing I accordancewith DIN ISO 1101.

Case AThe surface formed by the dimension a and b is not interrup-ted. Dimension b determines the wall thickness tolerance.

Case BThe surface formed by the dimensions a and b is interruptedby a borehole in the centre. The non-interrupted surface inthis case is therefore formed by the dimensions b and c. Thedimension c is smaller than b, and therefore c determinesthe wall thickness tolerance.

Table 3: Angular tolerances

Accurancy Range of nominal sizes1

levelup to 30 mm 30 up to 100 mm 100 up to 200 mm over 200 mm

Permissible misalignment

Angular mm per Angular mm per Angular mm per Angular mm perminutes 100 mm minutes 100 mm minutes 100 mm minutes 100 mm

1 30 2 0.87 30 2 0.87 30 2 0.87 20 2 0.58

2 30 2 0.87 20 2 0.58 15 2 0.44 15 2 0.44

3 20 2 0.58 15 2 0.44 10 2 0.29 10 2 0.29

Case A Case B

Wall thickness s

b

a a

b

c

c

4.5 Dimensional tolerances for cast-on or cast-in prefabricated parts

These must be determined in agreement with the foundry.

1 For the range of nominal sizes, the length of the short arm is authoritative.2 The angle may deviate in both directions.

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5. Surface properties For cast surface, Ra (CLA) should be used in according withTable 4. Classes N 7, N 8 and surface treatments must beagreed separately and entered into drawing in accordancewith DIN ISO 1302. Unless otherwise agreed, class N9 withsandblasted finish is assumed to be the condition on delivery.

6. Machining allowances For sizes of fit on surface or low surface roughness factorswhich cannot be achieved by investment casting alone,machining allowance must take into account material-specific properties and the computational unfavorableposition within the tolerance field.

Table 4: Surface roughness factors

Surface Material group D Material group Aroughnessstandards CLA Ra CLA Ra

(µinch) (µm) (µinch) (µm)

N 7 63 1.6

N 8 125 3.2 125 3.2

N 9 250 6.3 250 6.3

7. Supplementary remarks and data7.1 Inside radii Radii on inside corners and inside edges (fillets) help to avoidcasting faults and reduce notch stress in the casting duringlater use.

The minimum radius should amount to around 20% of thegreatest wall thickness, but be no less than 0.5 mm. An idealinside radius should correspond to at least the smallest wallthickness.

7.2 Outside radii and outside chamfersInvestment castings have no sharp edges with R = 0. For thisreason, outside radii and outside chamfers should always bespecified as maximum radii, for example R ≤ 0.5.

Table 5: Dimensions for holes, blind holes and channels

Width Greatest depth, bottom

Open Closedb (mm) l t

≥ 2 up to 4 ≈ 1 x b≈ 1.0 x b

> 4 up to 6 ≈ 2 x b

> 6 up to 10 ≈ 3 x b ≈ 1.6 x b

> 10 ≈ 4 x b ≈ 2.0 x b

Table 6: Dimensions for slots and grooves

dia. / or similar Greatest length or depth

Through hole Blind holed (mm) l t

≥ 2 up to 4 ≈ 1 x d ≈ 0.6 x d

> 4 up to 6 ≈ 2 x d ≈ 1.0 x d

> 6 up to 10 ≈ 3 x d ≈ 1.6 x d

> 10 ≈ 4 x d ≈ 1.6 x d

7.3 Holes, blind holes, channels, slots and grooves In order to allow through holes, blind holes, channels, slotsand grooves to be most beneficially included in the casting,i.e. without the need for pre-formed ceramic cores, thevalues specified in Tables 5 and 6 must be taken intoaccount.

7.4 Identification of castingIf casting are to be identified, the lettering size (‘medium’ to DIN 1451) and the position of the marking on the castingmust be agreed. Identifying marks may be raised or recessed,or raised within a recessed field. If there are no specificationscovering this in the drawing, the manner in which identifyingmarks is made must be determined by the supplier.

Inside contours and undercuttingThe highly developed core technology used in conjunctionwith investment casting permits varied and economical sha-ping when working with inside contours and undercutting.It is often possible to join several construction elements toform one part ‘from a single mould’ saving complex fittingwork and assembly, and the extensive equipment requiredfor these work processes. It is possible to form inside con-tours which impossible or extremely difficult to manufactureusing other methods . For this purpose, manual insert, coreslides and/or knock-out cores are used in the tool. It is alsopossible to assemble patterns from individual elements.Depending on the shape of the workpiece, the most econom-ical of these possibilities can be used.

Water-soluble cores For inside contours which are not too narrow, water-solublecores are used . These each involve the manufacture ofanother tool and coated with the non-water soluble patternmaterial. When the core is dissolved after immersion in awater bath, the required inside contour is left.

INVESTMENT CASTING

Despite the wide scope open to designers in the manu-facture of investment cast components, it is advisable forconsiderations of economy to observe certain basic rulesto keep the production input as low as possible. As aresult, on the one hand the basic law of physics are obey-ed during the casting process and work sequence from thetool to the finished casting, while on the other hand theyindicate the scope of achievements possible using theinvestment casting process. In either event, a basic rule of thumb applies: The more complex the shape of a work-piece, the more difficult it is to process, the more economi-cal it is to produce it by investment casting. Investmentcast items are often cast ready for installation withoutfurther processing. Where this is not possible due to in-sufficient tolerances, conventional machining methods can be used. Far-thinking, sensible design simplifies themachining process, so reducing the input and improvingeconomy.

Core slides and manual insertsIf the contour to be created so permits, core slides and/ormanual inserts are provided in the tool. Where possible, thecore slides are automatically ejected. However, frequentlythese have to be drawn manually, particularly in the case ofhousings with multiple undercut inside contours.

SHAPING

Spatially curved surfacesSpatially curved surfaces can be precisely reproduced true toshape using the investment casting technique. What makesthis , method so economical is the fact that the relativelyhigh processing input is only necessary on one singleoccasion, i.e. during manufacture of the tool.

Curved channels A feature which can be produced particularly economicallyare curved channels, which are shaped in such a way thatthey can be manufactured in the tool using core sliders. Inother cases, watersoluble or ceramic cores must be used,which involve the manufacture ofa special tool.

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Ceramic coresCeramic cores are used for narrow or intricately shapedcavities in the casing involving undercuts which cannot bereached or properly filled out by the ceramic mould materialduring the mouldmaking process. They are inserted in thetool ready fired and, in contrast to water-soluble cores,remain in the mould until after casting.

Possible(with core)

R

R ≤ 0,1

Favourable(with core slides in tool)

Parting PartingGate

Gate

Favourable

Gate

Eliminated gate

Core

Possible

Assembled patternIn certain cases, it is possible to assemble patterns. With the aid of fitting marks, they are precisely assembled andconnected, so forming the undercut contours . This proce-dure is often used in cases where symmetrical patterns canbe assembled from two or more identical pattern compo-nents, as then only a single (part) tool is required.

= Knock-out direction of the core slide

BulkinessBy providing recesses (=farsighted design for casting), it is possible to reduce the number of gates; this makes the tools less bulky and reduces the complexity of the castingprocess.

Material: Al or Cu based alloy

Possible

Unfavourable

Heating edges

Favourable

Favourable

INVESTMENT CASTING

The modules for which casting is still possible depend on thesize of the casting and the type of material. The followinggeneral rule applies: m ≥ 1.0 mm for FE, I, Co based alloys,m ≥ 0.5 mm for Al and Cu based alloys.

In the case of serration and similar types of toothing, the teethwhich become finer towards the middle should be recessedat the places at which the pitch falls below the followingvalues:t = 1.0 mm with Fe, Ni, Co based alloys t = 0.5 mm for Al and Cu based alloys

Cooling finsCooling fins should have cross-sections wich taper towardsthe outside; this not only improves casting performance butalso the heat flow.

Notch effects, radiiNot only the designer but also the caster is anxious to avoidnotch effects, as sharp-edged notches (heating edges) inter-fere with the casting process. A casting with larger radiidemon strates a less marked stress gradient, making it morefunctionally reliable. The ‘rough’ surface of an investmentcasting demonstrates the same notch insensitivity as a finishmachined surface.

R

R

R

R

R

RR

R

ToothingThe rough and finish casting of special toothing arrangementsof all different types can be economically performed using theinvestment casting technique, in particular using heavy-duty,non-machinable materials. Applications include Gear andclutch toothing, serration, internal gears and gear-type profi-les which cannot be machined using the generation grindingmethod, bevel and chain wheels, worm gear wheels. If theinvestment casting tolerances are not sufficient for the pitchand diameter, the casting must be subsequently machined,for example by grinding.

Threads Threads are only included in the casting if the investmentcasting tolerances are sufficient for the pitch and profile. Thismeans that only the following special cases can be consideredfor casting :• Interrupted threads, e.g. for bayonet catches and quick-

action couplings;• Threads which mate with materials such as rubber or plastic • Coarse circular or trapezoidal threads; • Threads of alloy which are important to examine whether it

might not be possible to either avoid their use by a modifi-cation of the design, or to carry out subsequent grinding.

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Knurling, corrugated effectsKnurling, and corrugated, as well as fish skin effects can be included in the casting. The following pitches applyt = 0.8 mm with FE, Ni, Co based alloyst = 0.5 mm with Al and Cu based alloys.

The tips always demonstrate a small natural casting radiusof around 0.1 mm. All-round cross knurling demands adisproportionately high tool input and should therefore beavoided.

Inside edges, notchesSharp inside edges and notches are unfavorable for casting,as thy act as ‘heating edges’ which can result in porosity.Instead, these points should be shaped as radii or fillet for-mations of at least around 20% of the wall thickness, in thin-walled components at least 0.3-0.5 mm.

Unfavourable Better Favourable

Unfavourable

Favourable

Favourable

Favourable

(Not for Al or Ti alloys)

FavourableR

RR

R R

Unfavourable

Unfavourable Favourable

Gate

Molten Solidified

Solidification front

Casting

Parting cut

Shrinkage cavity

Heating edgeR R

R R~4 x t

l~4 x ht

hR R

R

RR

R

R

R

R R

Shrinkage cavities Shrinkage cavities are a natural occurrence on the solidi-fication of molten metal. The task of the producer is to usesuitable means to make them occur not in the castingitself but in the gates, which are parted off after casting.For reason of cost, it can happen that the designer toler-ates certain defined shrinkage cavities either because theyoccur at an uncritical location or because they will in anycase be removed by a subsequent machining process.However, this must be agreed expressly with the producer.The ‘ideal casting’ is shaped in such a way that its cross-sections diminish as they progress from the gate towardsmore distant sections of the casting; If this ideal constella-tion is achieved, the solidification process can take place inthe opposite direction to the gate. Castings which comeclosest to this ideal are those with walls of approximatelyequal thickness and those which offer the producer thepossibility to ‘gate’ them for optimum casting. The resultingpoints to observe when setting about the design of an opti-mum investment casting are illustrated in the following.

Mould and draught Mould and draught angles are only required in exceptionalcases. Only where extremely long inside contours or similarexist it is necessary to provide for a slight conicity or angle.

Gates Where possible, a suitable even outer surface at the thickestcross-section should be selected for the gates. This constel-lation will permit them to be separated off more economical-ly later. The gating surfaces can serve as gauge or referencepoints for subsequent machining.

INVESTMENT CASTING

Junctions Junctions should be configured so that no sharp internaledges or accumulations of material occur. For this reason,sloping and parallel walls should be joined to each otherwherever possible at right angels.

Without mould angle With mould angle

≤ 1°

Possible

Unfavourable

Better

Favourable

Favourable

Gate

Gate

18 19

Holes and channels Slots and groves

dia. / or similar Greatest length or depth Width Greatest depth, bottomThrough hole Blind hole open closed

d (mm) l t b (mm) l t

≥ 2 up to 4 ≈ 1 x d ≈ 0.6 x d ≥ 2 up to 4 ≈ 1 x b≈ 1.0 x b

> 4 up to 6 ≈ 2 x d ≈ 1.0 x d > 4 up to 6 ≈ 2 x b

> 6 up to 10 ≈ 3 x d ≈ 1.6 x d > 6 up to 10 ≈ 3 x b ≈ 1.6 x b

> 10 ≈ 4 x d ≈ 2.0 x d > 10 ≈ 4 x b ≈ 2.0 x b

Possible

To be avoided Favourable

R

R

R R R R

Rl

Naturally smaller casting radius

d

d

t

d d d

(b)

(b) (b) (b) (b)

(b) (b) (b) (b) (b)

d d d d d

Core pullerFavourable

t

b

Ø Ø

b

s>b possible

ss

t

Holes and slotsMould and draught angles are only required in exceptionalcases. Only where extremely long inside contours or similarexist it is necessary to provide for a slight conicity or angle.

Through holes It is advisable to configure through holes and slots in such away that they can be formed with an unsplit core slide.

Blind holesBlind holes and closed slots must be rounded off at thebottom. In the case of Al and Ti alloys, it is advisable to avoid blind holes.

Unfavourable Favourable

SlotsSlots can only be produced without ceramic cores if the ratiob:t or b:l as indicated in the diagram on the right can beadhered to; The dimension S can be selected as required.

Examples of design measures The exemplars on the right demonstrate how it is oftensimple to achieve the economically most favorable tablevalues through intelligent design.

Flat surfacesAlthough it is possible to cast relatively large surfaces, theseshould be avoided where possible, as they can only be exe-cuted with a dis-proportionate effort. They should conse-quently be ‘broken up’ by ribbing effects, recessing or break-throughs. This simplifies the casting process, increases theform strength of the casting under certain circumstances,and often also reduces the weight.

Knife edges at the casting Due to the surface tension of molten metals, it is not possi-ble to cast knives or sharp edges. These must be producedwith a machining allowance and then finish ground.

INVESTMENT CASTING

Division plane and ejector marksWhere patterns are produced using automatic tools, it canhappen that marks are created at the division plane andejectors; As these are raised areas, as a general rule theycan be ignored.

Knife edges in the toolIn cases where knife edges would be created in the tool oron the core slide, for example where boreholes with varyingdiameters collide tangentially with each other, then water-soluble or ceramic cores must be used. However, where thistype of transition in the cross-sectional area can be avoided,with a slight adjustment it is often possible to use core sli-des. This presents a particularly economical solution.

To be avoided Favourable

Machining allowance ≥ 3 mm

P

P

P

P

P

P

Ideal

Unfavourable

Unfavourable Favourable

Possible

Knife edge in bothcore slides

Core

Unfavourable

= Knock-out direction of core slides

20 21

To be avoided Favourable Possible

Possible Favourable To be avoided

Recessed lettering Raised letteringin recessed field

Raised lettering

Recessed lettering Raised letteringin recessed field

Raised lettering

Aluminium and steel tools

Soft metal tools

RecessesWhere the functional characteristics of the component sopermit, surface which will require subsequent machining canbe recessed from the initial casting stage, so reducing thedegree of stock removal (and also the workpiece weight).

Investment casting are frequently ready-to-mount compo-nents without need for subsequent machining. However,where extremely narrow tolerances make this impossible,components may require a machining cycle. Intelligentdesign can simplify the machining process, so improvingoverall economy.

UndercutsUndercuts can be arranged in such a way that they eliminatethe need for water-soluble or ceramic cores. The knock-outdirection in the pattern tool must be taken into considerationhere: As the illustration indicates, the undercut determinesthe knock-out direction.

Possible(with core)

Ø Ø Ø Ø

Possible(without core)

Peripheral undercuts Straight undercuts

Possible Favourable

Possible Favourable

= Knock-out-direction

Inscription Cast company loges, spare part numbers, detents, positionand flow marks as well as any other identifying symbols saveassembly and downtimes, and help to avoid mistakes whenexchanging and ordering spare parts. The type of lettering oridentifying mark depends financially on the type of materialused: recessed when using soft metals, raised for aluminumor steel tools. If a raised inscription is not possible for func-tional reason, the inscription field must be recessed and theinscription itself raised. Also for reasons of economy, thelettering should be positioned parallel to the division plane of tool where possible. In case of doubt, a remark in the (enquiry) drawing indicating the possible positions for the

inscription field is sufficient. For the nominal height of thelettering, the following regulation applies:h ≥ 22.5 mm for Fe, Ni, Co based alloysh ≥ 2.0 mm for Al and Cu based alloys.

Material types The investment casting technique permits the use of analmost unlimited spectrum of casting and also wroughtmaterials. A certain restriction is imposed by the fact that a large number of materials possess similar characteristicsand be ‘substituted’ by alternative materials which are atleast equivalent in value. On the other hand, investmentcasting also permits the use of a higher-grade material at no additional cost, so covering a wide range of possibleapplications. Accordingly, in the following explanation, typesproviding a representative selection have been specifiedunder the various material groupings. If the use of differentmaterials is stipulated expressly for certain applications, anenquiry is necessary with the producer. The data contained inthe tables are guideline values only. This applies also whereguaranteed minimum values are specified in standards orother regulations. As a rule, these regulations refer to othershaping techniques unless they explicitly specify the instru-ment casting method. Unless otherwise indicated, the valuesapply to separately cast test bars.

INVESTMENT CASTING

APPLICATIONS

1

2

3

4

22 23

Economy It makes economic sense to work with customarily usedinvestment casting materials. Particular reference is made to these in the following tables. In case of doubt, consult theproducer. If at all possible to use corrosion-resistant materi-als, in particular for small components, in order to eliminatethe need for costly surface finishing which is necessarywhen working with low-alloy and non-alloyed materials.This type of component remains chemically resistant even if the surface is damage.

It id frequently possible to procure the same componentsmade of different materials- even alloys on a different basis -with one and the same pattern tool. This permits, for exam-ple, the material used for identical fittings and pump com-ponents to be varied to match the aggressive properties ofdifferent media. However, this simple exchange of materialsalso makes sense in cases where greater levels of differentmedia. However, this simple exchange of materials alsomakes sense in cases where greater levels of strain occurthan were previously known or envisaged. In this case, it isalmost always possible to select a more suitable material.

5 6

7

1 Nozzle tips for hot runnerinjection nozzles used in theplastics industyMaterial Inconel 713

2 End piece for the steeringcolumn of the Fokker F100Material GF-AlSiMg 0.6 wa Material number 3.2384 Verification of mechanical-technological characteristics isprovided through trails from thecasting.

3 VDO housingElectronic housing for LCD screenused in an armoured defencehelicopter PAH2. The part is finishmachined. Wall thickness partiallyto 1.2 mm. Modular system withover 90 ‘movable components’.Material G-AlSiMg 0.6 wa.

4 Hand leverMaterial G-AlSi7Mg 0.6 wa Material number 3.2384 Door opening in the Airbus A330/A 340.

5 Bone clamps made of implant material ‘ZOLLERN SUPER N’ CoCrMoN

6 Steering column leverMaterial G-AlSi7Mg 0.6 wa Material number 3.2384 Weight 1350 g Foot of the steering column fortransmission of mechanical forces in the Do 328

7 Fixed and steering wings for missiles made of material 17/4 PH Material number 1.4549

INVESTMENT CASTING

The plant operates in the high vacuum range from 10-2 to 10 m bar, and is capable of producing component sizes of up to appr. 250 mm in diameter and a maximum of 300 mmin height.

The following maximum melting weights can be cast:15 kg of Ni-based material 15 kg of Co-based material 15 kg of steel alloys 15 kg of Cu-based material

The vacuum casting technique additionally offers the benefitof an extremely high degree of purity. Due to the special pro-cess technology used, it is also possible to achieved specificgrain refinement of castings.

The work sequence at the smelting stations is fully auto-mated with the exception of loading and unloading.

Vacuum remelt alloys exclusively are used as base materialsfor superalloys.

Vacuum investment casting Due to their chemical makeup, in particular their content ofoxygen-affine elements, highly heat-resistant materials haveto be smelted and cast under a vacuum.

The vacuum induction investment casting furnace atZOLLERN is designed as a tandem plant for smelting andcasting under vacuum, and intended for the series produc-tion of small-scale investment casting. It is specially adaptedfor the use of preheated ceramic crucible. Gating is perfor-med automatically through a plug hole in the floor of thecrucible after a thin metal plate which seals the plug holehas melted through. The metal plate is made of the samematerial type as the smelted alloy.

The crucible is either made of an oxide ceramic fibre ma-terial or forms an integral component of the mould.

8 Door fitting, internal Material G-AlSi7Mg 0.6 wa Material number 3.2384 Emergency exit in the Airbus

9 Vacuum castings made of the materials Inconel 713,Inconel 718 and Hastelloy for apparatus construction

8

9

24 25

10

11

13

13 Mounting casting for the epicy-clic gearbox in the gear system/starter stage of a jet engineMaterial 17/4 pH 1.4549 Weight approx. 1500 g Rm. approx. 1200 Mpa

11 Cut-away model demonstratingthe structural principle of theexhaust gas turbochargerThe turbine wheel (hot side) in the foreground and behind it thecompressor area (cold side) withaluminium impeller wheel

12 Aluminium compressor impellerfor an exhaust gas turbochargerMaterial number 3.2384 Strength values Rp 0.2 ≥ 270 N/mm2

Rm ≥ 330 N/mm2, A5 ≥ 3%

10 Aluminum electronic housing for an optical application in thefield of laser technology.Material FG-AlSiMg 0.6 wa Material number 3.2384 Weight 120 g The complex internal contour isachieved using various water-soluble wax cores.

12

Plants of the Zollern group of companies

Herbertingen plant

ZOLLERN GmbH & Co. KG

Mannheim plant

ZOLLERN ISOPROFIL GmbH & Co. KG

Portugal plant

ZOLLERN & Comandita

China plant

ZOLLERN (Tianjin) Maschinery Co., LTD.

Dorsten plant

ZOLLERN Dorstener AntriebstechnikGmbH & Co. KG

Braunschweig plant

ZOLLERN BHW GleitlagerGmbH & Co. KG

Osterode plant

ZOLLERN BHW GleitlagerGmbH & Co. KG

Drive TechnologyPlain BearingsAv. Manoel Inácio Peixoto, 2147BR-36771-000 Cataguases MGTel. +55 32 34 29 20 02Fax +55 32 34 29 20 26eMail [email protected]

Brazil plant

ZOLLERN LTDA

Drive TechnologyPlain BearingsRolandsweg 16 – 20D-37520 Osterode am HarzTel. +49 55 22 31 27 0Fax +49 55 22 31 27 99

Drive TechnologyGearsHüttenstraße 1D-46284 DorstenTel. +49 23 62 67 0Fax +49 23 62 67 40 3eMail [email protected]

No. 33, 7th AvenueTEDA-TIANJIN 300 457Peoples Republic of CHINATel. +86 22 25 32 38 11Fax +86 22 25 32 38 10eMail [email protected]

Steel ProfilesPostfach 24 03 59D-68173 MannheimTel. +49 62 18 45 90Fax +49 62 18 45 92 63eMail [email protected]

Foundry TechnologyRua Jorge Ferreirinha, 1095Apartado 1027P-4470-314 Vermoim MAIATel. +351 22 94 14 68 1Fax +351 22 94 14 69 5eMail [email protected]

Drive TechnologyPlain BearingsPostfach 32 13D-38022 BraunschweigTel. +49 53 12 60 50Fax +49 53 12 60 52 22eMail [email protected]

Mechanical Engineering ComponentsPostfach 12 65D-88322 AulendorfTel. +49 75 25 94 81 30Fax +49 75 25 94 81 00eMail [email protected]

Sales:Tel. +49 7571 70246Fax +49 7571 70275eMail [email protected]

France plant

ZOLLERN TLC SAS

62, Rue Pierre CurieB.P.No 1055F-78131 Les Mureaux CEDEXTel. +33 1 34 74 39 00Fax +33 1 34 74 28 52

Sweden plant

Kvalitetsstal AB

P. O. Box 233SE-73224 ArbogaTel. +46 58 91 60 35Fax +46 58 91 20 02eMail [email protected]

USA plant

ZOLLERN North America L.P.

9364 Wallisville Rd., Suite 150Houston, Texas 77013USATel. +1 71 36 73 79 02Fax +1 71 36 73 79 50eMail [email protected]

Romania plant

Zollern S.R.L.

RO 317235 PecicaFerma 20 FNJud. Arad

Switzerland plant

ZOLLERN-MIMTEC AG

Säntisstrasse 11CH-9401 RorschachTel. +41 71 844 16 88Fax +41 71 844 16 77eMail [email protected] www.mimtec.com

Aulendorf plant

ZOLLERN GmbH & Co. KG

France ZOLLERN S.à.r.l13, Rue AllwiesF-57200 SarregueminesTel. +33 3 87 95 35 14Fax +33 3 87 95 35 21

eMail [email protected]

Great Britain Zollern UK LimitedCastle HillKenilworthGB-CV8 1NBTel. +44 19 26 51 54 20 Fax +44 19 26 85 34 11

eMail [email protected] www.zollern.co.uk

Italy ZOLLERN Italiana S.r.L.Via C. Battisti, 1I-21045 Gazzada (VA)Tel. +39 03 32 46 20 59Fax +39 03 32 46 20 67

eMail [email protected]

Netherlands ZOLLERN Nederland B.V.Postbus 134NL-5150 AC DRUNENTel. +31 41 63 22 92 0Fax +31 41 63 20 93 6

eMail [email protected] www.zollern.nl

Sales offices

Drive TechnologyHeustraße 1D-88518 Herbertingen

AutomationTel. +49 75 86 95 95 86Fax +49 75 86 95 95 85eMail [email protected]

Gears and WinchesTel. +49 75 86 95 95 47Fax +49 75 86 95 95 75eMail [email protected] BearingsTel. +49 75 86 95 95 20Fax +49 75 86 9597 15eMail [email protected]

INVESTMENT CASTING

26 27

ZOLLERN GmbH & Co. KG

Foundry TechnologyPostfach 12 20D-72481 Sigmaringen

Laucherthal plant

CONTACT

We offer comprehensive project management:• Many years of project experience• CAD masters• Project meetings on-site and plant inspections• Detailed, binding offers

ZOLLERN GmbH & Co. KG

Foundry TechnologyPostfach 12 20D-72481 SigmaringenTel. +49 75 71 70 44 0Fax +49 75 71 70 60 1eMail [email protected]

Steel ProfilesDivisionTel. +49 75 71 70 24 6Fax +49 75 71 70 27 5eMail [email protected]

Foundry TechnologyDivisionTel. +49 75 71 70 44 0Fax +49 75 71 70 60 1eMail [email protected]

ZOLLERN GmbH & Co. KG

Postfach 12 20D-72481 SigmaringenTel. +49 75 71/70-0 Fax +49 75 71/70-601 [email protected] Z4

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