POLISHING OF MOULD STEEL - Voestalpine · 2018. 5. 7. · MIRRAX ESR MIRRAX 40 ORVAR SUPREME VIDAR 1 ESR UNIMAX DIEVAR POWDER METALLURGY PROCESS UDDEHOLM STEEL GRADES: VANADIS 4 EXTRA

POLISHING OF MOULD STEEL

SS-EN ISO 9001SS-EN ISO 14001

This information is based on our present state of knowledge and is intended to provide generalnotes on our products and their uses. It should not therefore be construed as a warranty ofspecific properties of the products described or a warranty for fitness for a particular purpose.

Classified according to EU Directive 1999/45/ECFor further information see our “Material Safety Data Sheets”.

Edition 6, 07.2014The latest revised edition of this brochure is the English version,which is always published on our web site www.uddeholm.com

© UDDEHOLMS ABNo part of this publication may be reproduced or transmitted for commercial purposes

without permission of the copyright holder.


3

CONTENTS

Why strive for a high surface finish 4

Factors that affect the surface finish 4

Surface preparation of tool steels 6

Guidelines 7

Polishing problems can be solved 10

Measuring surface roughness and quality 11

4


overcome by an optimal choice oftool steel and preparation strategy.

Functional polishingMost cold work applications do notneed high gloss polished tool sur-faces, but it is always advantageous tocreate functional surfaces for a pro-longed tool life. In forming operationswhere lubricants are involved apreparation strategy may consist ofremoving larger peak formations onthe surface and preserving a control-led depth of valleys as lubricationpockets, which then will contributeto a reduced friction during forming.However, it is always important toconsider the final tool steel surfacequality in relation to the application.If a high quality surface coating isgoing to be applied, then it is alwaysrecommended to perform high glosspolishing of the tool surface beforethe coating process.

The polisher isextremely importantThe results from the tests that havebeen carried out during the workwith this brochure shows that theskill, experience and technique of thepolisher plays an extremely impor-tant role in achieving the desiredsurface finish.

Why strive for ahigh surface finish?Plastic and metallic components aremanufactured with various surfacefinishes all from shiny and glossy tofunctional surfaces of differentappearances. In this brochure we willinform about the factors that havethe biggest impact on the polishabilityof tool steels and give recommenda-tions on how to obtain the requiredsurface finish on moulds, dies,punches and metallic components/parts. The most common defects areshown in the Uddeholm brochure“Defect Chart and Hints for HighGloss Polishing of Steel Surfaces”

Depending on the application andrequirements we can distinguish be-tween two types of surface finishingmethods; high gloss polishing andfunctional polishing.

High gloss polishingTools for plastic moulding do requirea high surface finish especially whenextreme transparency and/or highgloss are aimed for. In such cases it isof utmost importance to choose aproper tool material and establish asuitable surface preparation tech-nique. To achieve a reflective surfacewith mirror finish the preparationprocess must involve several grindingand diamond polishing steps andthese have to be performed in aclean workplace. The use of properworking tools facilitates the processa lot.

High surface finish reduces the riskof local corrosion and fracture orcracking due to temporary over load-ing or pure fatigue.

The tool surface finish may alsohave an impact on productivity as inthe case of injection moulding. Here,the release forces of the plastic com-ponent from the tool steel surfaceare dependant on the adhesion prop-erties of the polymer to the mouldsurface. An improved smoothness ofthe tool surface may lead to higherrelease forces and eventually to stick-ing phenomena, which partly can be

Factors that affectthe surface finishTool steels are used in many applica-tion fields within plastic moulding,cold and hot working and as engi-neering components. For properfunctionality, but also to minimize themanufacturing cost of the tool orcomponent it is vital to specify therequired surface finish on the engi-neering drawing. Especially in applica-tions of plastic moulding it is impor-tant to have access to material datarelating to surface finish capabilities.However, it should be noted that thesurface finish of the end product isnot only determined by the tool steeland the applied surface preparationprocess, but also the applicationprocess itself has a big impact on theresult. Polymers have different mate-rial characteristics at plastic mouldingand this will definitely influence thefinal surface finish, as illustrated inFigures 1 and 2.

Fig.1. A number of factors have inf luence on thesurface f inish of the f inal end product.

Polishingtechnique

Application

Type of polymer

Type of tool steel

Pre-preparationof the surface

Heat treatmentProcess route

Surface quality

Fig 2. The photos show differently holes/pits on tool surface replicated on the plastic plaquedue to different material characteristics in different polymers. Fewer peaks is detected onthe Makrolon plaque whereas the Bayblend plaque had visible peaks all over the surface.

0 500 1000 1500 2000 2500 µm 0

250

500

750 1000

1250

1500

1750

2000µm

0

250

500

750 1000

1250

1500

1750

2000µm

0 500 1000 1500 2000 2500 µm

0

250

500

750

1000

1250

1500

1750

2000

µm

0 500 1000 1500µm

Tool surface, inverted Makrolon AL2647(Medium viscosity)

Bayblend T45(Low viscosity)


5

The remelting processes direct thecasting structure in such a way thatmacro segregations are drasticallyreduced and a more uniform micro-structure is created, which is benefi-cial from polishing point of view.

PM ESR

Total number of particles per mm2 * (oxides + sulphides + carbides + nitrides) 1000

100

10

1

0.1

DEFECTS IN TOOL STEELS

Various types of defects emanatingfrom the production process may befound in the steel. During steelmakingnon-metallic inclusions are formed asa result of the deoxidation process.Other sources are entrapped exo-genous material from refractory inthe ladle or at casting. A fast solidifi-cation rate is normally beneficial bygiving less time for inclusions andparticles to grow and reducing segre-gation patterns.

In the special remelting processessuch as VAR and ESR the cast ingotare remelted under controlled condi-tions. Non-metallic oxide inclusionsare effectively removed from thesteel and sulphides are reducedsubstantially via the basic workingslag in the ESR-process altogethergiving tool steels of high cleanliness.

Tool steel quality

PROCESS ROUTES FOR TOOL STEELS

Tool steels are found in various alloycombinations to fit usage in differentapplication fields. Common manufac-turing process routes are conven-tional ingot casting (IC), continuouscasting (CC), electro slag remelting(ESR), vacuum arc remelting (VAR)and powder metallurgy (PM). Remelt-ing processes and PM processes pro-duce materials of higher homogeneitywith a low non-metallic inclusioncontent, whereas ingot cast materialsnormally have a higher degree ofsegregation patterns and also containmore non-metallic inclusions.

Recommendations

To produce highly reflective andglossy surfaces ESR-remelted or PMsteels are to be used. However,conventional ingot cast steels cangive a very good surface finish, ifboth steel manufacturing andpolishing are performed accordingto a good practice.

Fig. 4. A low defect content is benef icial from polishing point of view.

Fig 3. Process routes for tool steels andexample of steel grades produced by thedifferent routes.

CONVENTIONAL PROCESS

UDDEHOLM STEEL GRADES:

CALMAX

RIGOR

IMPAX SUPREME

NIMAX

RAMAX HH

ORVAR 2 MICRODIZED

CORRAX

ELECTROSLAG REMELTINGPROCESS


STAVAX ESR

MIRRAX ESR

MIRRAX 40

ORVAR SUPREME

VIDAR 1 ESR

UNIMAX

DIEVAR

POWDER METALLURGYPROCESS


VANADIS 4 EXTRA

VANADIS 10

ELMAX

Conventional

INGOT

CAST

STEEL

Polishability rank 5

4

3

2

1

Bad

Good

Low High

Defect content by inclusions and carbides

ESR REMELTED STEELPM

*oxides and sulphides >3µm carbides and nitrides >4µm

6


POLISHING

The abrasives are more or less fixedin the carrier material and will cutand/or plough the surface.

BUFFING

The abrasive adhere loosely to aflexible carrier (soft disk made ofcloth or hide). This step is consideredamong some polisher to be the lastpolishing step performed in order toobtain a mirror like surface.

HEAT TREATMENT

Heat treatment can affect polish-ability in many ways. Decarburizationor recarburization of the surfaceduring heat treatment can producevariations in hardness, resulting inpolishing difficulties.

In order to avoid this it is recom-mended that the hardening is carriedout in vacuum furnaces or furnaceswith controlled protective gas atmos-phere or salt baths. It is also of im-portance to secure that the time ataustenitizing temperature is not toolong and the quenching speed is nottoo slow to avoid grain growth andgrain boundary precipitations.

Surface preparationof tool steelsThe following four terms are com-monly used when it comes to surfacepreparation of tool steels. Theessential characteristics of thesemethods are explained below.

GRINDING

The abrasive particles are firmlybonded to a carrier such as grindingpaper, stones and the discs.

LAPPING

The abrasive particles are notbonded but move freely between thecarrier and the work piece.

Hints for grinding

OPERATION SURFACE FINISH

Ground Ra 0.5 µm Rz 5 µm

Milled Ra 0.5 µm Rz 5 µm

High speedmachined Ra 0.2 µm Rz 1.5 µm

EDM Ra 3.0 µm Rz 15 µm

Table 1. Typical initial surface roughnessvalues Ra and Rz.

Recommendations

To facilitate the finishing steps andto minimize the risk of losingdimensional tolerances of the toolthe initial surface finish should havea roughness value of maximumRa / Rz = 0.5/5 µm. This will elimi-nate the need of using coarse grind-ing media in the first preparationstep.

Manufacturingof initial surfacesIt should be emphasized that thegrinding operation forms the basis fora rapid and successful polishing job. Ingrinding, the marks left by the rough-machining operation are eliminatedand a metallically pure and geometri-cally correct surface is obtained.

The finishing preparation steps canbe very time consuming and costly,but can be controlled to a certainextent by a proper manufacturing ofthe initial tool surface. Normally thestarting surface is ground, milled orelectro discharge machined (EDM).Typical initial surface roughnessvalues, as Ra/Rz, are approximately0.5/5 µm for the two former and3/15 µm for an EDM surface. Recentdevelopments in high speed machin-ing has made it possible to producesurface finishes better than Ra =0.2 µm and by using the latest tech-niques in EDM the Ra falls below0.07 µm. After EDM processing it isimportant to remove the heat affec-ted layers by either a fine sparkingand/or by grinding. If not doing socrack initiation may appear duringtool use.

Sample

A

B

Suspension

Support

A

BSample

GlueBacking

A

B

Sample


7

Recommendations

Material removal in hardened steelsis more consistent and repeatablewhen diamond products are used.Precision hand tools incorporatinglinear movement of the workingtools, grinding files and polishingstones, give a less troublesomepreparation process. A good prac-tice is to work perpendicular tothe grooves in all preparation stepsand to verify with optical examina-tion that all scratches from theprevious step have been completelyremoved. Note, that heavy coldworked material beneath the sur-face needs to be removed for aperfect end result.

3. Silicon carbide (SiC)Has a needle like blocky structure.Used for rougher surface finishes.

4. Boron carbide (B4C)Is hard and has a blocky crystal struc-ture. Fast material removal generatingmoderate surface finish.

5. Cubic Boron Nitride (CBN)Is produced basically in the same wayas synthetic diamond and is usedwhen grinding hard materials like HSSand hardened high carbide toolsteels.

PRACTICAL HINTS FOR GRINDING

It should be emphasized that thegrinding operation forms the basis fora rapid and successful polishing job.In grinding the marks left by therough machining operation are re-moved and a clean and geometricallycorrect surface is obtained. The prac-tical hints mentioned below apply toboth mechanical grinding and manualstoning.• To avoid adding heat and stress into

the surface, do not use too muchpressure and use plenty of coolant.

• Use only clean and free-cuttinggrinding tools with soft stones forhard surfaces.

• It is very important that the work-piece and the hands of the polisherare carefully cleaned between eachchange of grain size. This is done toprevent coarse particles and dustfrom being carried over to the nextgrinding step.

GuidelinesNo general recipe exists for all typesof steels, but the experience andability to adjust the polishing tech-nique to every single mould and tominor variations in the surface is ofcrucial importance for the end result.As a general guideline the procedurefor high gloss polishing shown belowcan be adopted i.e.;

• starting from a ground surfacewhere the roughness Ra/Rz shouldbe maximum 0.5/5 µm

• use stones/grinding papers for thefirst steps, stepwise grinding to1200 Mesh

Description of abrasives

THERMAL STABILITY

HARDNESS IN AIRABRASIVE KNOOP °C °F

Diamond 7 000 650 1200

Aluminiumoxide 2 100 2000 3630

Siliconcarbide 2 500 1200 2190

Boroncarbide 2 900 2700 4890

CBN 4 700 1300 2550

Table 2.

It is important that the abrasivefulfills requirements with respect to:

• hardness

• sharpness

• thermal resistance

• chemical stability

Today, the following five main groupsof synthetic abrasives are used, ful-filling the above requirements togreater or lesser extents.

1. Diamond designation SD

2. Aluminium oxide designation A (SG)

3. Silicon carbide designation C

4. Boron carbide designation B4C

5. Cubic boron nitride designation B

1. DiamondThe hardest material known, has asharp and angular structure. Fastmaterial removal and the best possi-ble planarity in combination withexcellent surface finishes.

Distinguish between mono andpolycrystalline diamonds. Mono-crystalline are best for lapping, sincethey are round and have many cuttingedges. Natural gives better cuts whilesynthetic are harder, a mix is the bestsince it last longer.

2. Aluminium oxide (Al2O3)Is relatively hard and has a sharpangular structure. It is often usedduring the last polishing step since itgives excellent and highly glossy sur-face finishes. Is relatively inexpensive.

• spend more time on the coarsesteps before changing to the finersteps

• polishing with diamond compoundfrom 15 µm down to 1 µm grain,use as short time as possible

• always be careful when using softcarriers (felt, brushes, cloths) asthere is a risk of “orange peel”formation on the polished surface

A reflective surface starts to appearat Ra/Rz approaching 0.1/1 µm, andthe final surface roughness Ra/Rzshould be less than 0.005/0.04 µm fora high gloss polished surface.

FINE GRINDING

Fine grinding should smooth thesurface before the diamond polishingstage commences. Working tools andcompound media are built up arounddifferent kinds of abrasives whichconsists of small and hard particleswith sharp edges and irregularshapes.

Abrasives have different applicationareas, depending on their particularcharacteristics, as shown partially intable 2 below.

8


Standard

45°

90°

Irregular overlapping

Fig. 5. Grinding directions.

A

B

C

D

50

80

120

180

220

320

800

1200

45 µm

25

15

9631

PRACTICAL HINTS FOR POLISHING

Above all, cleanliness in every step ofthe polishing operation is of suchimportance that it cannot be over-emphasized.

• Each polishing tool should be usedfor only one paste grade and keptin dust proof containers.

• Paste should be applied to thepolishing tool in manual polishing,while in machine polishing the pasteshould be applied to the work-piece.

• Polishing pressure should beadjusted to the hardness of thepolishing tool and the grade ofpaste. For the finest grain sizes, thepressure should only be the weightof the polishing tool.

• Work with hard carriers for asmany steps as possible and workfor as short a period as possiblewith soft carriers.

• Polishing should start in the cor-ners, edges and fillets but be carefulwith sharp corners and edges sothey are not rounded off.

Figure 6. The hardness of the carrieraffects the exposure of the diamond grainsand the removal rate.

TYPICAL POLISHING SEQUENCES

The choice of grinding and polishingsequences are determined by theexperience of the operator and theequipment he/she has at his/herdisposal. The properties of the toolmaterial can also influence thesequence.

Fig. 7. This f igureshows example of howthe polishing sequence

can be selected.

Soft Medium Hard

Felt Wood Steel

Hardened steel

Rough Grainnumber

Rough

Rough Micronsize

Grain

FEPA

Roughgrinding

MillingTurningEDM’ing

Fine Fine

Fine Polishing withdiamond paste

• Finish polishing step should, if possi-ble, be carried out in the releasedirectional of the moulded part.

• With softer carrier the abrasive isable to penetrate deeper into thecarrier. This will result in that thesurface will be finer for the samesize of abrasive. See Figure 6 below.

• When changing to the next finergrain size, it is recommended thatthe grinding direction be changed to45°. Cross-grinding is very simple,but extremely effective. It increasesstock removal and it makes it easierto detect scratches from the pre-vious steps and improve the dimen-sional accuracy. Figure 5 A–C.

• Select the sequence of movementsso that all surface segments areprocessed for an equally longperiod. With a rotating grindingdisc there will be a risk that therewill be less stock removal on theedge than in the centre of thesurface. Figure 5 D.

Finegrinding


9

STEP TECHNIQUE TYPE OF TOOL LUBRICATION

1 Ground

2 Hand-held unit SiC paper K320 Dry



5 Hand-held unit Acryl D fluid 6 µm Polishing oil

6 Hand-held unit Acryl D fluid 3 µm Polishing oil

7 Hand-held unit Cotton D fluid 3 µm Polishing oil

Table 3.

EXAMPLE OF DIFFERENT

POLISHING STRATEGIES AT HIGH

GLOSS POLISHING

All polishers have their own proce-dures for high gloss polishing. Thedata, in Tables 3–5, reflects that differ-

Table 4.


1 Hand-held unit Stone 320 Dielectric oil



4 Hand-held unit Paper 400 Dry

5 Hand-held unit Paper 600 Dry

6 Hand-held unit Paper 800 Dielectric oil

7 Hand-held unit (linear) Brass 5 x 5 mm DP 9 µm Dielectric oil

8 Hand-held unit (linear) Wood 5 x 5 mm DP 9 µm Dielectric oil

9 Hand-held unit (linear) Wood 5 x 5 mm DP 6 µm Polishing oil

10 Hand-held unit (rotational) Hard felt 10 mm DP 3 µm Polishing oil

11 Hand-held unit Piece ofcotton wool DP 1 µm Polishing oil


1 Reciprocating machine 9500 Rpm Brass carrier DP W 15 µm Polishing oilAmplitude movment 0.2 mm Plastic carrier




5 Turning tools Wool blankets DP W 1 µm Polishing oil

Table 5.

ent manual polishing strategies canbe adopted to reach the same finalsurface finish by using rigorous andwell proven working procedures.The achieved surface finish is lowerthan Ra 0.01 µm

The tables 3 and 4 showexamples of specific step-by-step information regard-ing high gloss polishing ofUddeholm Stavax ESR andUddeholm Unimax.

Observe carefully, duringthe polishing steps, if anydeep marks are visible inthe polished surface. If thisproblem occur it is neededto immediately reduce thepressure, put on polishingoil or if more diamondpaste needs to be added.

10


Polishing problemscan be solvedThe predominant problem in polish-ing is so-called “overpolishing”. Thisterminology is used when a polishedsurface gets worse the longer youpolish it. There are basically twophenomena which can appear when asurface is overpolished: “orange peel”and “pitting” (pin holes). These prob-lems often occur when changingfrom hard to a soft tool (felt/brush).

A material at higher hardnesscan better withstand a high polishingpressure compared with prehard-ened steel. Subsequently materialwith low hardness will become“over-polished” more easily.

Orange peelThe appearance of an irregular, roughsurface, which is normally referred toas “orange peel”, might depend ondifferent causes. The most commonis polishing with high pressure andprolonged time during the last polish-ing steps. A material at high hardnessis less sensitive to problems with“orange peel” compared to prehard-ened or soft annealed material.

• If a polished surface shows signsof an appearance like “orange peel”;stop polishing! There is no idea toincrease the polishing pressure andcontinue to polish. Such a course ofaction will only result in a worseset of problems.

• Following steps are recommendedto restore the surface. Remove thedefective surface layer by regrindingit, by using the last grinding stepprior to polishing. Use a lowerpressure and shorter time duringthe polishing steps than what wasused when the problems occurred.

PittingThe very small pits (pin holes) whichcan occur in a polished surface gener-ally result from non-metallic inclu-sions or hard carbides which havebeen torn out from the surfaceduring the polishing process. Pittingcan also be caused by hard particlesembedded in a softer matrix. Duringpolishing the matrix will be removedat a more rapid rate than the hardparticles. Polishing will gradually“undermine” the hard particles untilthey are torn out of the material byfurther polishing. The problem ismost often encountered when polish-ing with diamond paste grain size lessthan 10 µm and soft polishing tools(felt, brush).

If pitting occurs the followingmeasures should be taken:• regrind the surface carefully using

the last grinding step prior topolishing

• use a hard coarse tool and repeatthe polishing process

When using grain size 10 µm andsmaller:• the softest polishing tools should

be avoided• the polishing process should be

carried out for the shortest possi-ble time and under the lowestpossible pressure

0.5 mm

“Orange peel”

0.5 mm

“Pitting”


11

SURFACE ROUGHNESS ACC. TO DIN/ISO 1302 SURFACE ROUGHNESS ACC. TO SPI

ROUGHNESS ROUGHNESS Ra, µm Rmax, µm ACHIEVED AFTER GRINDING/POLISHING WITH

N 1 0.025 0.1–0.3 A-1 3 µm Diamond PasteN 2 0.05 0.3–0.7 A-2 6 µm Diamond PasteN 3 0.1 0.75–1.25 A-3 15 µm Diamond Paste

N 4 0.2 1.5–2.5 B-1 600 Grit PaperN 5 0.4 2–6 B-2 400 Grit PaperN 6 0.8 6–10 B-3 320 Grit Paper

N 7 1.6 10–20 C-1 600 Grit StoneN 8 3.2 20–40 C-2 400 Grit StoneN 9 6.3 ~60 C-3 320 Grit Stone

N 10 12.5 ~125 D-1 600 Stone Prior to Dry Blast Glass Beads #11N 11 25 ~250 D-2 400 Stone Prior to Dry Blast #240 Alminium oxideN 12 50 ~500 D-3 320 Stone Prior to Dry Blast #24 Aluminium oxide

Measuringsurface roughnessand qualityPolished mould surfaces are tradi-tionally estimated by the naked eyeand/or measured by mechanicalprofilers for surface roughness, com-monly described with the Ra, Rz andRt values.

Table 6. Approximate comparison between requested surface roughness measured by mechanical prof ilers andinternational standards.

Surface assessment byroughness parametersThe benefit to measure surfaces isboth the possibility to study them inthe micro- and nano-scale, and a wayto quantitatively evaluate them. But,there is a huge amount of available2D- and 3D parameters (abbreviatedR- and S-parameters, respectively), sohow do you know which to use?

2D parameters, usually obtained bya mechanical profiler, can be used toquantify the surface quality in alimited extent. The most frequentused in practical work with moulds isthe Ra-value describing the averageheight of the measured surface.However, it is a rather poor descrip-tion of the mould surface sincesmaller defects and certain textureswill be “averaged out” and/or unde-tected. See figure 8.

Ra – the arithmetical mean deviation ofthe prof ile is the mean value of theabsolute value of the profile departurey within the reference length l.Source: The f igure to the left is fromT.R. Thomas book “Rough surfaces”2nd edition.

The A- & B-prof iles illustrate one ofthe major disadvantages of the 2Dprof ilometry; A – a surface with pores,and B – a “defect free” surface, i.e. theresults are strongly dependent on theprof ile location.

Illustration of different surfacetopographies with equal Ra-value;i.e. the Ra-value itself is not enough tofully describe the surface structureSource: Illustration from T.R. Thomasbook “Rough surfaces” 2nd edition.

Fig. 8.

Ra= 2.4 µm

Ra= 2.5 µm

Ra= 2.4 µm

0 100 200 300 400 500 600 µm 0 50

100

150

200

250

300

350

400

450

µm

However, these methods are bothsubjective and uncertain compared tomore advanced surface- and sub-surface measurement devices capableof measuring to fractions of nano-metres. The use of 3D-instrumenta-tion with higher resolution providesmore accurate surface measurementsof moulds with complex geometrieswhich in turn means that quantitativesurface quality controls can be per-formed.

12


advantages in laboratories due toits sensitivity to vibration, but newinstruments are comingthat can be used for in-linemeasurements. Typical outputare 3D maps and areal surfaceparameters (e.g. Sa and St whichcorrespond to the Ra and Rt re-spectively). Also other parameterfamilies are available, e.g. areal,volume and functional parameters.

Builds up 3D mapsbased on stacks ofimages recorded atdifferent heights,excluding points

that are out of focus. The techniqueis preferential for surfaces rougher

Typical outputparameters are theRa (arithmetic meanvalue of a profile),the Rz (mean peak

to valley height), and the Rmax (orRt, the maximum peak to valleyheight). Notice: most often R-valuesare filtered per default (connected toactual measurement length and cut-off).

MECHANICAL PROFILER (STYLUS)

The surface is illumi-nated and the re-flected/scatteredlight is detected.Simple glossmeters

measure reflections in defined angles,whereas scatterometers include thetotal reflection.

SCATTEROMETER (GLOSSMETER)

CONFOCAL MICROSCOPE

nm

85807570656055504540353025201510500

20

40

60 8

0 10

0 120

140

160

180

µm

90

0 20 40 60 80 100 120 140

µm

Y scatter angle (degree) X scatter angle (degree)

40 20 0 -20 -40 40

20

0

-2

0

-40

Measurement devices and analysis techniques available toquantify engineered surface topographies

µm

2.0

0

-2.0

Ra 0.083 µm Rz 0.78 µm

0.3 mm/div 1.3 mm

P000_007 PCD: R(LC GS 0.3 mm)

Sample D ground 15 rep Unimax 01

Lt 1.75 mmLs 2.5 µmVB 350 µmVt 0.50 mm/sPoints 3500Pick-up PHT 350

190

nm180

160

140

120

100

80

60

40

20

0 9

0 8

0 7

0 6

0 5

0 4

0 3

0 2

0 1

0 0

µ

m

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

µm

than optical quality. Typical outputare 3D maps and areal surfaceparameters (e.g. Sa and Stwhich correspond to the Ra andRt respectively). Also other param-eter families are available, e.g. areal,volume and functional parameters.

50

0

-50

Scattering data need to be corre-lated to roughness data by veri-fications with other measurementdevices. Typical output is e.g. anaverage rms-values, the ratio ofthe diffuse reflection or the re-flection of light at a defined angle.

Intensity db

INTERFEROMETER

Height deviationsare detected byutilising interferencepatterns formed/arised when tworeflected light

beams, one from the sample and onefrom a reference surface, interact.Features down to 1 µm in spatialresolution and sub-nm in height canbe detected. The technique is of


13

e

SEM/EDS

A focused electronbeam raster-scansthe surface; theenergetic electronsinteract with the

atoms in the sample within a few nmto several µm of the surface, i.e.scattering events take place (primaryelectrons loose energy and/or

change direction). The emittedelectrons are “collected” by differentdetectors. The EDS, a type of X-rayspectrometer, allows elementalanalysis. Typical output are thetopographical contrast (based on SE),chemical contrast (based on BSE) andphase composition (based on X-ray).

ATOMIC FORCE MICROSCOPE

Simply described asa tiny profiler/stylusoperating withextremely smallprobe tips barely

touching the surface resulting in 3Dresolutions close to atomic level.Typical output are 3D maps and arealsurface parameters.

LIGHT ATOMICGENERAL OPTICAL INTERFERO- FORCE

SPEC./DEVICE MICROSCOPE STYLUS METER CONFOCAL SEM/EDS MICROSCOPE GLOSSMETER

Resolution (m) xy: 10-7 xy: 10-6 – 10-4 xy: 10-6 xy: 10-6 xy: 10-9 xy: 10-10

z: 10-6 z: 10-9 z: 10-10 z: 10-7 z: 10-9 z: 10-12 –

Measurementarea µm-mm µm-cm µm µm-mm µm-mm µm µm-mm

Height info No No Yes Yes No Yes Possible

2D/3D 2D 2D 3D 3D 2D/3D 3D –

Componentanalysis No No No No Yes No No

Usability Good Good Mid Mid Bad Bad Good

Measurementtime – Long Short Mid Long Long Short

Size of Device Unlimited Device Device mm-cm Device Unlimitedworkpiece dependent dependent dependent dependent

(often up to (often up to2–10 kg) 2–10 kg)

Other Standardised Risk of surface Sensitive to Large depth of Work in vacuum, Noise sensitive, Only averagemethods for damage, fragile vibrations focus, problems needs solid and fragile roughness datacleanliness stylus/pick-up with artefacts conducting stylus/pick-up

dermination samples, ability toimage undercuts

SELECTION OF MEASUREMENT DEVICES AND GENERAL SPECIFICATIONS

0 5 10 15 20 25 30 35 µm

µm

35

30

25

20

15

10

5

0

Table 7. The f igures shown should only be considered as guidelines.

14


This brochure and the related brochure Defect Chart and Hints for High Gloss Polishing of Steel Surfaces

have been produced in co-operation with the Functional Surfaces Research Group

at Halmstad University in Sweden.

DD

EHO

LM120305.1000 / TRY

CKERI KN

APPEN

; KARLSTA

D 2013101

DEFECT CHART AND H

INTS FOR

HIGH GLOSS POLISH

ING

OF STEEL SURFACES

The most common defects foundwhen polishing are described in theUddeholm brochure “Defect Chartand Hints for High Gloss Polishing ofSteel Surfaces”.

COMET TAILSScattered holes with a tail,dispersed over the majority ofthe surface.

HINTS• Avoid unidirectional movements• Use higher rotational speed if manual

polishing

HOLESmaller irregular or circularshaped cavity, e.g. pores, pinholesand imprints by abrasives.

HINTS• Choose a cleaner steel i.e. ESR steel grade• Use softer carriers/tools (without lint)• Use lower pressure• Napless polishing cloths reduce the risk

for pull-outs• Use a fluoride-free polishing cloth

GROOVE (scratches)Longitudinal recession withrounded/flat bottom.

HINTS• Clean the workpiece, tools etc. between

every polishing step; remaining abrasivescan scratch the surface by accident

• Be sure that marks left from previous preparation steps (e.g. turning or grinding marks) are removed

• Check if the hardness is too low

0 100 200 300 400 500 600 700 800 µm

µm0

50100150200250300350400450500550600

0 100 200 300 400 500 600 700 800 µm

µm0

50100150200250300350400450500550600

Groove (Scratches)

0 20 40 60 80 100 120 140 160 µm

µm0

10

20

30

40

50

60

70

0.5mm

0.5mm

0.5mm

RELIEFHill-like formations in all kind ofgeometries covering the majorityof the surface.

HINTS• Choose a cleaner steel i.e. ESR steel grade• Use harder carriers/tools• Choose a more homogeneous steel

material. Softer areas tend to be morepolished than harder ones (pre-stage toorange peel)

• Decrease the polishing time (use enoughbut short steps)

• Polishing cloths with low pressure reducethe risk

• Use lower pressure

0 100 200 300 400 500 600 700 800 µm

µm0

50100150200250300350400450500550600

0.5mm

PEAK/RAISINGSmall outwardly directed feature,often irregularly shaped, e.g. barelaid inclusions.

HINTS• Choose a cleaner steel material• Clean the workpiece to avoid surface

contamination• Use lower pressure, larger abrasive sizes,

polishing cloths with higher resilienceand/or a lubricant with higher viscosity toavoid embedded abrasives

0.5mm

0 50 100 150 200 250 300 350 µm

µm0

25

5075

100

125

150

175

200

225

250

275

ORANGE PEELRandomly, smooth valleys andhills covering the majority ofthe surface.

HINTS• Shorten the polishing time (use enough

but short steps)• Use harder carriers/tools• Use lower pressure• Increase the lubrication in order to cool

down the surface

0.5mm

0 5000 1000 1500 2000 2500 3000 µm

µm0

250

500

750

1000

1250

1500

1750

2000

2250

2500

WAVINESSLongitudinal, smooth valleysand hills covering the majorityof the surface.

HINTS• Work with tools that have a good

contact to the surface• If waviness occurs go back to the first

polishing step and change to a largertool that fits better to the geometryof the surface to be polished

0 500 1000 1500 2000 2500 µm

µm0

250

500

750

1000

1250

1500

1750

2000

2250

2500

2750

3000

3250

0.5mm

DISCOLORATION/STAININGDiscoloured areas; e.g. “milkyspots”.

HINTS• Inhomogeneous microstructure is adverse• Clean and dry the workpiece immediately

after each preparation step, avoid hotwater

• Compressed air can contain oil or water,which might affect the surface

• Cover the surface after polishing andstore properly

• Avoid overheating during previous preparation steps which get visible during thepolishing process

0 100 200 300 400 500 600 µm

µm0

50

100

150

200

250

300

350

400

450

500

0.5mm

HAZEAreas with lower gloss thanthe surrounding (“silvery frostedappearance”).

HINTS• Choose steel with homogenous material

properties (e.g. without grain clusters indifferent directions and/or hardnessvariations)

• Might be correlated to previous process-ing (e.g. milling or welding operations)

• Last polishing step discarded/cancelled• Unclean surface (insuffizient carrier, wrong lubrication and diamond paste)

0.5mm

0 100 200 300 400 500 600 700 800 µm

µm0

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BURN MARKPhysical destruction due too highsurface temp. during surface pre-paration. On the sample surfacethree different defects are showne.g. dark bluish areas from highpressure during polishing, pointshaped burns caused by EDMprocess and linear and laminarburns caused by grinding, weldingor other operations.

HINTS• Use lubrication in order to cool down

the workpiece during surface preparation• Use lower pressure and/or speed during

surface preparation

0.5mm

0 100 200 300 400 500 600 µm

µm0

50

100150200250300350

400450500550600650700750800

CRACKLinear recession with asharp bottom.

HINTS• Crack result from surface tensions build

up during the manufacturing process,i.e. change the preparation and/or themanufacturing process

0.5mm

– 2 – – 3 – – 4 –

PITTINGScattered (pin) holes dispersedover the majority of the surface.

HINTS• Shorten the polishing time (use enough

but short steps)• Use lower pressure• Use harder carriers/tools – combination

diamond paste and lubricants is important• Avoid unidirectional movements during

preparation of the surfaces• Dry the workpiece and store properly to

avoid corrosion attacks on the surface• If the pitting defects only appears in a

local area on the surfaces it probably dueto impurities in the material

0.5mm

3D MEASUREMENTAND PROFILE

0 100 200 300 400 500 600 700 800 µm

µm0

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UDDEHOLM DEFECT CHARTUDDEHOLM DEFECT CHARTUDDEHOLM DEFECT CHART

www.assab.com www.uddeholm.com

Network of excellenceUDDEHOLM is present on every continent. This ensures you

high-quality Swedish tool steel and local support wherever you

are. ASSAB is our exclusive sales channel, representing Udde-

holm in the Asia Pacific area. Together we secure our position

as the world’s leading supplier of tooling materials.

16

UD

DEH

OLM

140701.300 / STROKIRK KN

APPEN

1407

UDDEHOLM is the world’s leading supplier of tooling materials. This

is a position we have reached by improving our customers’ everyday

business. Long tradition combined with research and product develop-

ment equips Uddeholm to solve any tooling problem that may arise.

It is a challenging process, but the goal is clear – to be your number one

partner and tool steel provider.

Our presence on every continent guarantees you the same high quality

wherever you are. ASSAB is our exclusive sales channel, representing

Uddeholm in the Asia Pacific area. Together we secure our position as

the world’s leading supplier of tooling materials. We act worldwide, so

there is always an Uddeholm or ASSAB representative close at hand to

give local advice and support. For us it is all a matter of trust – in long-

term partnerships as well as in developing new products. Trust is

something you earn, every day.

For more information, please visit www.uddeholm.com or www.assab.com

Documents

POLISHING OF MOULD STEEL - Voestalpine · 2018. 5. 7. · MIRRAX ESR MIRRAX 40 ORVAR SUPREME VIDAR 1 ESR UNIMAX DIEVAR POWDER METALLURGY PROCESS UDDEHOLM STEEL GRADES: VANADIS 4 EXTRA