Diagnostics and Experiences on Extrusion Press Tooling W. Hähnel, K. Gillmeister Kind & Co Edelstahlwerk KG, Wiehl 1. Introduction The principal range of activities of Kind & Co. Edelstahlwerk is the development and manufacture of forged tool steels. In this field, KCo can rely on more than 100 years of experience in the production and refinement of tool steels. With a staff of approximately 600 working at the company’s facilities in Wiehl/Bielstein and Lindlar/Kaiserau, KCo operate the machinery and equipment divisions required for these purposes, such as the steel works with the ESR remelting plant, forging presses, ring rolling mill, annealing plant, vacuum hardening plant, finished product stocks and mechanical workshop including a Service Centre for the extrusion press industry. Apart from metallurgical examinations and defect analyses, this Service Centre particular focus is placed on relining and repairing used containers. A specially established database enables lifelong diagnostic attendance to the container and to implement a variety of requisite measures to extend its service life. Moreover, the machinery and equipment technology available serves to optimise the required characteristics of classical tool steels and to also design new tool steels to accommodate the market requirements. Particular focus is placed on designing temperature resistant high premium tool steels and top quality products of high toughness like, for example, TQ1. These qualities stand out for a considerably reduced share of trace elements in the tool steel. In close consultation with extrusion press experts, the know how in developing new tool steels along with experience compiled in our Service Centre forms the basis for designing new tools. This continuous process of improvement leads to increased service life of the tools, a safe and reliable production process at the extrusion press, enhanced product quality and, as a result, cost saving for the customer. The following report includes a number of examples shown on the basis of actual tools of the extrusion press and also illustrates improvement potentials in the future.
Transcript
Diagnostics and Experiences on Extrusion Press Tool ing
W. Hähnel, K. GillmeisterKind & Co Edelstahlwerk KG, Wiehl
1. Introduction
The principal range of activities of Kind & Co. Edelstahlwerk is the development andmanufacture of forged tool steels. In this field, KCo can rely on more than 100 yearsof experience in the production and refinement of tool steels. With a staff ofapproximately 600 working at the company’s facilities in Wiehl/Bielstein andLindlar/Kaiserau, KCo operate the machinery and equipment divisions required forthese purposes, such as the steel works with the ESR remelting plant, forgingpresses, ring rolling mill, annealing plant, vacuum hardening plant, finished productstocks and mechanical workshop including a Service Centre for the extrusion pressindustry.
Apart from metallurgical examinations and defect analyses, this Service Centreparticular focus is placed on relining and repairing used containers. A speciallyestablished database enables lifelong diagnostic attendance to the container and toimplement a variety of requisite measures to extend its service life.
Moreover, the machinery and equipment technology available serves to optimise therequired characteristics of classical tool steels and to also design new tool steels toaccommodate the market requirements. Particular focus is placed on designingtemperature resistant high premium tool steels and top quality products of hightoughness like, for example, TQ1. These qualities stand out for a considerablyreduced share of trace elements in the tool steel.
In close consultation with extrusion press experts, the know how in developing newtool steels along with experience compiled in our Service Centre forms the basis fordesigning new tools. This continuous process of improvement leads to increasedservice life of the tools, a safe and reliable production process at the extrusion press,enhanced product quality and, as a result, cost saving for the customer.
The following report includes a number of examples shown on the basis of actualtools of the extrusion press and also illustrates improvement potentials in the future.
Toughness testingCharpy 10x7x55 mmCharpy-V 10x10x55 mm
Position of specimen
Tensile testing
2. Materials Technology
2.1 Performance Specification
Particularly in recent years, the performance requirements for extrusion presses havebecome more stringent. The market for these extrusion press plants requires highproductivity, flexibility with regard to product diversity and almost 100% availability.Proceeding from this continuously increasing performance requirements, the range ofmaterials used has undergone further development in recent years. To accommodate
these needs, more and more discussionson material characteristics were heldthat, depending on the tools’ field ofapplication, focussed on materialstructure, analysis and strength as wellas toughness, high temperature strengthproperties and abrasive wear resistance.The declared objective is to make thematerial properties generally acceptedfor process engineering also apply tocharacteristics required for the toolsconcerned.
Fig. 1: Test specimen taken from forged components
To ensure and prove these tool characteristics, samples are taken at representativesections of forged and heat treated components. These results along with theprocess data are subjected to a continuous improvement procedure.
2.2 Research and development of steel grades
Talking about hot working steels means the classical martensite Cr-Mo-V alloys that,above all, stand out for the following characteristics:
High tempering resistanceHigh temperature strengthHigh hot wear resistanceHigh thermal fatigue resistance
In addition, special applications call for austenite and Ni-based alloy steels in theextrusion press industry.
Tab. 1: Hot working tool steels for the extrusion press industry
The underlying objective of material development is to exploit the maximum materialpotential along with optimum ductility at high application hardness.
Without doubt, the so-called super clean hot working tool steels such as, for example,TQ1 from the top quality segment, constitute a milestone in material development inthe past 10 years. With material 1.2343 and 1.2367, we succeeded in combining thetoughness of one with the high temperature strength properties of the other. Inaddition, a modified manufacturing process along with the ESU remelting procedureensures a quality ranging in the top segment.
Fig. 2: Segregation behaviour in the different manufacturing processes
An integral part of the improvement process is material development that, culminatingin the so-called super clean qualities, enables a decisive enhancement of thematerial properties.
Dominial W.-Nr. Kurzname AISI AFNOR StahltypMat.-No. Name C Cr Mo Ni V W Co Steel type
NC19FeNb 0,05 19,00 3,00 53,0 - Nb 5,0Ti 0,9Al 0,5
- Ni
SA 50 Ni 2.4973 NiCr19CoMo R41 - < 0,12 19,00 9,50 Rest Balance
- Ti 3,0Al 1,6
11,00 Ni
M = martensitisch / martensiticA = austenitisch / austeniticNi = Nickel-Basis-Legierung / Nickel base super all oy
Richtanalyse / Reference Analysis in Mass-%
*) erzeugt nach dem Elektro-Schlacke-Umschmelzverfa hren (ESU) produced by Electro-Slag-Remelting technology ( ESR)
„offene“ Erzeugung ESU-Erzeugung
To select only one aspect, i.e. the toughness of materials in the premium rangecomparing to the TQ1 top alloy, this modified and high purity manufacturing processenables an increase in toughness of up to 30%.
Fig. 3 Comparison of toughness on hot working steels
This increase in toughness enables a reduced cracking tendency and, consequently,prolonged service life at identical tool hardness.
As a result, the tools show an identical toughness level at increased hardness.Particularly with indirect press stem, the high surface pressing at the stem shaft alsorequires a material strength increased by about 600 N/mm². So far, this increasedmaterial strength of 1,750 to 1,850 N/mm² could only be obtained at the expense ofthe toughness of the traditional materials such as, for example, 1.2343. Today, thesehigh premium steels and top qualities enable us to maintain this high strength levelon press stems without any loss in toughness.
Further fields of application for these top steels are inner liners which are producedwith an increased hardness comparing to traditional hot working steels. This methodpredominantly serves to prolong the durability of the sealing face, and to counteractabrasive wear of the boring surface and plastic dimensional changes. As a matter ofconsequence, this also ensures enhanced product quality.
0
5
10
15
20
25
30
1.2343 1.2344 1.2367 TQ 1
➨ Transverse testing (core section)
➨ ø 320mm
➨ approx. 45 HRC
Charpy-V
1.2343 1.2344 1.2367 TQ 1
Charpy
The illustrations below show a number of successful TQ1 applications (stems, liners,pilger roll and dies).
Fig. 4 : TQ1 applications
We are currently working on a further high premium steel called HP1. HP1 will bedistinguished by specific trace elements and feature a toughness and operationalefficiency similar to the above. The graphic below shows HP1 along with its specialtoughness and high temperature strength properties.
Individual testing
Toughnes testingCharpy10 x 7 x 55mm
1.2343 1.2344 1.2367 TQ 1
Joul
e
Unnotched testing
Fig. 5: New development of HP1
3. Manufacturing Process of Forgings
Apart from steel production and alloy composition, the manufacturing process appliedhas a substantial influence on the material properties.
Further to standard steel bar forging, our company favours close to finish dimensionforging (stem, liner) and three-dimensional forging (dies) of the tool steels. Bothforging methods significantly influence the characteristics of the tool.
Fig. 6: Individual forgings
This has a positive influence on the microstructure and fibrous structure of the steel.The illustration below shows a simple flat section made from 2.4379 (SA 50 Ni) fromwhich samples were taken at different areas to determine the material properties.
Fig. 7: Comparison of toughness depending on the forged fibre direction
The changed fibre direction in press extrusion dies alone has a significant influenceon toughness.
Shape / Step forging:Stems
3D-IndividualBigger dies ,
AWS (1.2731) -Discs
Individual forgingContainer mantles and linersel
Standard bar forgingSimple die material
Samples of forging alternatives
Grain structure
Grain structure
Grain structure
Rond bar forging
Flat bar forging
Grain structure Grain structure
Grain structure
Mechanical properties after heat treatment
80 ø mm
1250-1280 N/mm²Transverse specimen
Charpy = 38; 48; 66
ø = 50 Joule
Longitudinal specimen
Charpy = 86;103; 130
ø = 103 Joule
W.-Nr. 2.4973 ( Dominial SA 50 Ni )
In the case of press stems, too, it is of advantage to forge the rough contour as closeas possible to the finished contour. This entails a more favourable fibre course in thepress stem which has a positive effect on its maximum working stress. Especially thetransition zones between the base and shaft are considered critical danger spotswhich are considerably eased by means of this open-die forging technique.
Fig. 8: Contour forging of press stems
All-round forging of 3d-discs in dies for heavy metal or lightmetal dies is the technique of choice thanks to itspractically isotropic material quality.
Particularly dies with asymmetrical break-outs and theresulting tensile, compression or torsion stresses requirealmost identical technological material properties in all 3dimensions.
Fig. 9: 3d-forging of a die
The specific liners required for containers are individuallyforged in an open-die forging press. After pre-forging andupsetting, the block is punched and finish-forged on amandrel rotating in axial direction. Comparing to traditionalbar forging, this forging technique enables an enhancedforming gradient which has a positive effect on grainstructure and ductility.
Fig. 10 : Forging a container mantle
Length = 3995 mm
Shape forging
3Dindividual
Bar Bar Bar
Size 10 x 7 x 55 mm
ISO
Standard
ESR
Standard
= Special heat treatment
400
500
300
200
100
J/cm
² (
45 H
RC
)Impact Energy H13 / 1.2343
Fig. 11: Material properties depending on the manufacturing technique
4. Heat Treatment
A further influence on the material properties that is not to be underestimated is heattreatment of the tool materials. The following parameters are of significantimportance:
4.1 Initial structure
The initial structure should be qualified in accordance with the DGM instruction leafletor NADCA directives.
4.2 Heat treatment parameters
The austenitic temperature and holding time are decisive factors for martensitesteels.For hot working steels, this temperature ranges between 1,000 and 1,130°C. Ofcrucial importance is thorough heating of the component concerned along with aholding time tailored to the cross sectional geometry. Depending on the requirement,these parameters are adjusted to fit the individual circumstances. Whilst overheatingor excessive holding of the extrusion press tool may increase its temperingresistance, a side effect thereof may be undesirable grain growth.
4.3 Quenching rate
Basically, martensite steels require fast quenching rates to reach the prescribedmaterial properties. Insufficient cooling rates result in unacceptable transformationstructures which have a negative influence on the material characteristics.
Fig. 12 : Comparison of coarse grain/fine grain shown in etched micrograph
4.4 Tempering
Repeated tempering process does not only serve to adjust the required tensilestrength but also entirely converts residual austenite to martensite. If this procedureis not pursued, the toughness potential of the material is not fully utilised. Temperingthe material 3 times is, therefore, recommended.
In order to achieve the optimum material potential the parameters indicated must beobserved. More often than not, this best possible heat treatment technique isdisregarded for reasons of cost and pressing time schedules and, as a result, themaximum steel properties are not fully taken advantage of.
5. Surface Treatment Techniques – Nitriding, Oxidizi ng
Surface treatment techniques are used to reduce frictional resistance and adhesivetendency or to generate a non-metallic insulating layer on extrusion press tools.Following is more detailed information on two significant surface treatmenttechniques.
5.1 Nitriding
Nitriding describes the concentration with atomic nitrogen on the skin layer of a workpiece. This concentration serves to produce a non-metallic surface and an increasein surface hardness to approximately 1,200HV.The nitriding process is used on dies for aluminium sections and enables a reducedadhesive tendency and enhanced wear resistance of the die.
The following composition of a nitrided layer isrecommended:
White layer zone (white layer): 6 to 10 µmDiffusion zone: 0.10 to 0.15 mm
Fig. 13: Composition of a nitrided layer
5.2 Oxidising
A further surface treatment technique for use onmandrels for copper tubes is a special oxidisingprocedure. The oxidised surface yielded by thistechnique enables optimum starting conditions onmandrels for tubes comparing to non-treatedmandrels.The layer thickness produced are approximately 4to 6 µm.
Fig. 14: Oxide layer on extrusion press mandrels
Both techniques have become well established and ensure extended holding times ofthe tools and an enhanced quality of extrusion press products.
6 Inspection and Shrinking Technique
The individual components of each container, such as mantle, intermediate liner andinternal liner are subjected to a particular stress situation which, makes replacementof the liner inevitable.In the course of these activities, the container undergoes comprehensive inspectionin order to draw conclusions regarding further use or additional measures to beimplemented.Apart from general testing such as dimensional checks and inspections with a view tocracks and heating values, precise examination of the delicate openings fortemperature sensors and air inlets by means of a boroscope is of crucial preventativeimportance today.
6.1 Database inspection
All inspection results and measures implemented are set up on a special database toenable a comprehensive history of the container and to develop a continuousenhancement process jointly with the customer.
New developments such as the A-P system, WT cooling and modified heatingconnection which will be described in more detail later are a result of this continuousenhancement process.
All the important information is documented on the database and will be available forfuture evaluation.
6.2 Shrinking technique
During practical operation, the container is subjected to continuously changingmechanical-thermal stress situations. Apart from the specific stress situation, billetand container temperatures, shrinkage stress, too, is an important factor to be takeninto consideration in application-related stress calculations.It is of major importance to account for the different expansion coefficients of thematerials used.
7 Engineering and Design
Apart from the optimal equipment of materials in respect of their composition,hardness, structure, microstructure, toughness, high temperature strength and wearresistance, the design and engineering, too, bears a considerable developmentpotential for the improvement of extrusion tools. The following examples illustratethese developments.
WT- Cooling System (registered design)
7.1 Air Protection System (AP system, registered design 203 18 917.5)
On air-cooled recipients, an AP system serves to ensure safe and smooth operation.After comprehensive examinations on surface-cracked air supply bores we havedeveloped a protective tube.Without the AP system, the shell boring at the air supply bores showed axial crackswhich required meticulous milling and welding.The AP system has now been in operation for several years and all recipientsequipped with this system are found to be without cracks at the critical locations.Checkups are digitally documented by means of a boroscope.
Fig. 15: Container mantle before and after installing AP-system
The incoming radial air flow into the recipient is directed to the intermediate liner viaspiral-wound cooling elements. To enlarge the surface and generate turbulent flow,the cooling element topography has a corrugated outline.This design is intended to increase the number of internal liners per installedintermediate liner.So far, about 2 internal liners could be used with the same internal liner on heavymetal extrusion presses. Based on initial test results we were able to install threeinternal liners in the same intermediate liner.
Fig. 16: WT cooling onan intermediate liner
7.3 Power connection for heating system
The container connection to the heating system is a sensitive area that requiresparticular examination for cracks during our receiving inspection. It is, therefore, ofmajor importance to reduce the number of tapped holes for attachment ofconnections to the heating system to a minimum.
Fig. 17 : Damage to connections to heating system
Fig. 18: Modified connection to heating system
As shown in Fig. 18, the tapped holes are omitted in the particularly critical areas ofthe shell without any loss of stability.
Moreover, the engineering concept must account for the fact that the radiuses andtransition areas are generously dimensioned in order to avoid inevitable cracks.
Fig. 19: Radiuses and transitions at critical areas
7.4 Protection of liners against movement
The inner and intermediate liners in the container are protected against axialmovement by means of positive or negative shoulders. If the container is operated inboth directions, a double shoulder should be installed on the inner and/orintermediate liner.
The double shoulder prevents displacement of the liners in either direction. Adisadvantage is the increased expenditure in time required for the replacementprocedure. The liner is cooled with nitrogen and positioned into the preheatedmantle. In addition, the double shoulder needs to be machined before shrinking outthe liner.
Fig. 20: Design variants of shoulders on inner and intermediate liners
The expansion coefficient on austenite liners is increased by 40% comparing to thoseon martensite grades must be accounted for accordingly on selecting the shoulderdesign.
Due to physical characteristics, the positive shoulders leaves a small gap of 2 –3mm. During practical operation, the liner settles again to close this gap. This gap ispractically not found on negative shoulders which makes this option a preferreddesign on state-of-the-art light metal containers.
7.5 Preheating of container
Prior to start-up, the container should be preheated to at least 380 to 400°Cthroughout. Preferably, this preheating process should be conducted outside thepress at an external preheating station.
Positive - Positive
Mantle
Sleeve
Liner
Positive - Double shoulder
Mantle
Sleeve
Zwischenbüchse
Liner
Positive - Negative
Mantle
Liner
Sleeve
Negative - Negative
Mantle
Liner
Q 10 !Q 10 !
Sleeve
7.6 Press stem
As already indicated, press stems aresubjected to increasing specific compressionstresses. Accordingly, premium hot workingtool steels with increased hardness factors areused.Apart from the steel, however, the design isbeing optimised as well. Particularly thetransition areas between a square base andthe round shaft are frequently susceptible tocracks as shown in the picture. Designchanges along with the use of the extremelytough material TQ1 ensure operational safety.
Fig. 21 : Damage on press stem
8. Summary
Continually changing specification requirements in the extrusion press industryequally requires a continuous research and development process in respect ofmaterials, production and design. This continuous process is supported by anintelligent database system.
Information compiled on the basis of diagnosed cases of damage along withexperience gained in extrusion press facilities are also fed into this system so that weare able to pursue targeted product enhancement jointly with users.
Based on practical examples, this report represents a survey on the developmentsteps reached so far. A wide-spread production range along with know how enablescontinuous developments on extrusion press tools which are then implemented in asafe manufacturing process.
Our experience has shown that it is impossible to completely transfer individualdevelopments and improvements to comparable users on a global basis. Thisprocess can be enhanced by a direct and open exchange of information betweensupplier and user.
9. Literature
1. BooksLaue / Stenger, StrangpressenM. Bauser / G. Sauer / K. Siegert, Strangpressen
