polishing of uddeholm mould steel · 4 treatment polishing of mould steel be overcome by an optimal...

TREATMENT POLISHING OF MOULD STEEL 1

POLISHINGOF UDDEHOLMMOULD STEEL

TREATMENT POLISHING OF MOULD STEEL2

This information is based on our present state of knowledge and is intended toprovide general notes on our products and their uses. It should not therefore beconstrued as a warranty of specific properties of the products described or awarranty for fitness for a particular purpose.

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

Edition 6, 08.2016

© UDDEHOLMS ABNo part of this publication may be reproduced or transmitted for commercialpurposes without permission of the copyright holder.


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


be 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 advantageousto create functional surfaces for aprolonged tool life. In forming opera-tions where lubricants are involved apreparation strategy may consist ofremoving larger peak formations onthe surface and preserving a controll-ed depth of valleys as lubricationpockets, which then will contribute toa 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 work withthis brochure shows that the skill,experience and technique of thepolisher plays an extremely importantrole in achieving the desired surfacefinish.

WHY STRIVE FORA HIGH SURFACEFINISH?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 have thebiggest impact on the polishability oftool steels and give recommendationson how to obtain the required surfacefinish on moulds, dies, punches andmetallic components/parts. The mostcommon defects are shown in theUddeholm brochure “Defect Chartand Hints for High Gloss Polishing ofSteel Surfaces”

Depending on the application andrequirements we can distinguishbetween two types of surface finish-ing methods; 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 a cleanworkplace. The use of proper workingtools facilitates the process a 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 surface aredependant on the adhesion proper-ties of the polymer to the mouldsurface. An improved smoothness ofthe tool surface may lead to higherrelease forces and eventually tosticking phenomena, which partly can

FACTORS THATAFFECT THESURFACE 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 appli-cations of plastic moulding it isimportant to have access to materialdata relating to surface finish capa-bilities. However, it should be notedthat the surface finish of the endproduct is not only determined by thetool steel and the applied surfacepreparation process, but also theapplication process itself has a bigimpact on the result. Polymers havedifferent material characteristics atplastic moulding and this will defi-nitely influence the final surface finish,as illustrated in Figures 1 and 2.

Fig.1. A number of factors have influence onthe surface finish of the final 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 plasticplaque due to different material characteristics in different polymers. Fewer peaks isdetected on the Makrolon plaque whereas the Bayblend plaque had visible peaks allover 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)


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 in theladle or at casting. A fast solidificationrate is normally beneficial by givingless time for inclusions and particlesto grow and reducing segregationpatterns.

In the special remelting processessuch as VAR and ESR the cast ingotare remelted under controlled condi-tions. Non-metallic oxide inclusionsare effectively removed from the steeland sulphides are reduced substan-tially via the basic working slag in theESR-process altogether giving toolsteels of high cleanliness.

TOOL STEEL QUALITY

PROCESS ROUTES FORTOOL STEELS

Tool steels are found in various alloycombinations to fit usage in differentapplication fields. Common manu-facturing 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 processesproduce materials of higher homo-geneity with a low non-metallic inclu-sion content, whereas ingot castmaterials normally have a higherdegree of segregation patterns andalso contain more non-metallicinclusions.

RECOMMENDATIONSTo produce highly reflective andglossy surfaces ESR-remelted orPM steels are to be used.However, conventional ingot caststeels can give a very goodsurface finish, if both steel manu-facturing and polishing areperformed according to a goodpractice.

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

Fig 3. Process routes for tool steels andexample of steel grades produced bythe different routes.

CONVENTIONAL PROCESSUDDEHOLM STEEL GRADES:

CalmaxRigorImpax SupremeNimaxRamax HHOrvar 2 MicrodizedCorrax

ELECTROSLAG REMELTINGPROCESS

UDDEHOLM STEEL GRADES:

Stavax ESRMirrax ESRMirrax 40Orvar SupremeVidar 1 ESRUnimaxDievar

POWDER METALLURGYPROCESS

UDDEHOLM STEEL GRADES:

Vanadis 4 Extra SuperCleanVanadis 8 SuperCleanElmax SuperClean

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 >3 µm carbides and nitrides >4 µm


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

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

HEAT TREATMENTHeat 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.

SURFACEPREPARATION OFTOOL STEELSThe following four terms are com-monly used when it comes to surfacepreparation of tool steels. The essen-tial characteristics of these methodsare explained below.

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

LAPPINGThe abrasive particles are not bondedbut move freely between the carrierand 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.

RECOMMENDATIONSTo facilitate the finishing steps and

to minimize the risk of losing

dimensional tolerances of the tool

the initial surface finish should have

a roughness value of maximum

Ra / Rz = 0.5/5 µm. This will

eliminate the need of using coarse

grinding media in the first prepara-

tion step.

MANUFACTURINGOF INITIAL SURFACESIt should be emphasized that thegrinding operation forms the basis fora rapid and successful polishing job.In grinding, the marks left by therough-machining operation areeliminated and a metallically pure andgeometrically correct surface isobtained.

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


RECOMMENDATIONSMaterial removal in hardened steels

is more consistent and repeatable

when diamond products are used.

Precision hand tools incorporating

linear movement of the working

tools, grinding files and polishing

stones, give a less troublesome

preparation process. A good

practice is to work perpendicular to

the grooves in all preparation steps

and to verify with optical examina-

tion that all scratches from the

previous step have been completely

removed. Note, that heavy cold

worked material beneath the surface

needs to be removed for a perfect

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 crystalstructure. Fast material removalgenerating moderate 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 GRINDINGIt should be emphasized that thegrinding operation forms the basis fora rapid and successful polishing job.In grinding the marks left by the roughmachining operation are removed anda clean and geometrically correctsurface is obtained. The practicalhints mentioned below apply to bothmechanical 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 doneto prevent coarse particles anddust from being carried over to thenext grinding 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 surface

where the roughness Ra/Rz shouldbe maximum 0.5/5 µm

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

DESCRIPTION OFABRASIVESIt is important that the abrasive fulfillsrequirements 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 SD2. Aluminium oxide designation A (SG)3. Silicon carbide designation C4. Boron carbide designation B4C5. Cubic boron nitride designation B

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

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 appear atRa/Rz approaching 0.1/1 µm, and thefinal surface roughness Ra/Rz shouldbe less than 0.005/0.04 µm for a highgloss polished surface.

FINE GRINDINGFine 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.

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.


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 FORPOLISHINGAbove all, cleanliness in every step ofthe polishing operation is of suchimportance that it cannot be overem-phasized.• Each polishing tool should be used

for only one paste grade and keptin dust proof containers.

• Paste should be applied to thepolishing tool in manual polishing,while in machine polishing thepaste should be applied to thework-piece.

• Polishing pressure should beadjusted to the hardness of thepolishing tool and the grade ofpaste. For the finest grain sizes,the pressure should only be theweight of 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 becareful with sharp corners andedges so they are not rounded off.

Fig. 6. The hardness of the carrieraffects the exposure of the diamondgrains and the removal rate.

TYPICAL POLISHINGSEQUENCESThe 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 figureshows example of howthe polishing sequencecan be selected.

Soft Medium Hard

Felt Wood Steel

Hardened steel

Rough Grainnumber

Rough

Rough Micronsize

Grain

FEPA

Roughgrinding

MillingTurningEDM’ing

Fine Fine

Fine Polishing with diamond paste

• Finish polishing step should, ifpossible, be carried out in therelease directional of the mouldedpart.

• 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 6below.

• When changing to the next finergrain size, it is recommended thatthe grinding direction be changedto 45°. Cross-grinding is verysimple, but extremely effective. Itincreases stock removal and itmakes it easier to detect scratchesfrom the previous steps and im-prove the dimensional 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


STEP TECHNIQUE TYPE OF TOOL LUBRICATION

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


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


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

Table 3.

EXAMPLE OF DIFFERENTPOLISHING STRATEGIES ATHIGH GLOSS POLISHINGAll polishers have their own proce-dures for high gloss polishing. Thedata, in Tables 3–5, reflects that

Table 4.

Table 5.

different manual polishing strategiescan be adopted to reach the samefinal surface finish by using rigorousand well proven working procedures.The achieved surface finish is lowerthan Ra 0.01 µm

The tables 3 and 4 show

examples of specific step-by-

step information regarding

high gloss polishing of

Uddeholm Stavax ESR and

Uddeholm Unimax.

Observe carefully, during the

polishing steps, if any deep

marks are visible in the

polished surface. If this

problem occur it is needed to

immediately reduce the

pressure, put on polishing oil

or if more diamond paste

needs to be added.


POLISHINGPROBLEMS CANBE SOLVEDThe predominant problem in polishingis so-called “overpolishing”. Thisterminology is used when a polishedsurface gets worse the longer youpolish it. There are basically twophenomena which can appear whena surface is overpolished: “orangepeel” and “pitting” (pin holes). Theseproblems often occur when changingfrom hard to a soft tool (felt/brush).

A material at higher hardnesscan better withstand a high polishingpressure compared with prehardenedsteel. Subsequently material with lowhardness 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 lastpolishing steps. A material at highhardness is less sensitive to problemswith “orange peel” compared toprehardened or soft annealed mate-rial.• If a polished surface shows signs

of an appearance like “orangepeel”; stop polishing! There is noidea to increase the polishingpressure and continue to polish.Such a course of action will onlyresult in a worse set of problems.

• Following steps are recommendedto restore the surface. Remove thedefective surface layer by regrind-ing it, by using the last grindingstep prior to polishing. Use a lowerpressure and shorter time duringthe polishing stepsthan what wasused when the problems occurred.

PITTINGThe very small pits (pin holes) whichcan occur in a polished surfacegenerally result from non-metallicinclu-sions or hard carbides whichhave been 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 is mostoften encountered when polishingwith 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 becarried out for the shortest possi-ble time and under the lowestpossible pressure

0.5 mm

“Orange peel”

0.5 mm

“Pitting”


0 100 200 300 400 500 600 µm 0 50

100

150

200

250

300

350

400

450

µm

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 #240 Aluminium oxide

MEASURINGSURFACEROUGHNESS ANDQUALITYPolished mould surfaces are tradi-tionally estimated by the naked eyeand/or measured by mechanicalprofilers for surface roughness,commonly described with the Ra, Rzand Rt values.

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

SURFACE ASSESSMENTBY ROUGHNESS PARA-METERSThe 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),so how do you know which to use?

2D parameters, usually obtained bya mechanical profiler, can be used toquantify the surface quality in a limitedextent. The most frequent used inpractical work with moulds is the Ra-value describing the average height ofthe measured surface. However, it is arather poor description of the mouldsurface since smaller defects andcertain textures will be “averaged out”and/or undetected. See figure 8.

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

The A- & B-profiles illustrate one ofthe major disadvantages of the 2Dprofilometry; A – a surface withpores, and B – a “defect free”surface, i.e. the results are stronglydependent on the profile location.

Illustration of different surfacetopographies with equal Ra-value;i.e. the Ra-value itself is notenough to fully describe thesurface structureSource: Illustration from T.R.Thomas book “Rough surfaces”2nd edition.

Fig. 8.

Ra = 2.4 µm

Ra = 2.5 µm

Ra = 2.4 µm

However, these methods are bothsubjective and uncertain compared tomore advanced surface- and sub-surface measurement devicescapable of measuring to fractions ofnano-metres. The use of 3D-instru-mentation with higher resolutionprovides more accurate surfacemeasurements of moulds withcomplex geometries which in turnmeans that quantitative surfacequality controls can be performed.


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 technique ispreferential for surfaces rougher than

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

to valley height), and the Rmax (or Rt,the maximum peak to valley height).Notice: most often R-values arefiltered per default (connected toactual measurement length and cut-off).

MECHANICAL PROFILER (STYLUS)

The surface isilluminated and thereflected/scatteredlight is detected.Simple glossmeters

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

CONFOCAL MICROSCOPE

nm

85807570656055504540353025201510500

20 40

60 80

100 120 1

40 160 1

80

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 2

0 0

-20 -4

0

MEASUREMENT DEVICES AND ANALYSIS TECHNIQUESAVAILABLE TO QUANTIFY 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 90

80

70

60

50

40

30

20

10

0

µ

m

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

µm

optical quality. Typical output are3D maps and areal surfaceparameters (e.g. Sa and Stwhich correspond to the Ra andRt respectively). Also other parameterfamilies are available, e.g. areal,volume and functional parameters.

50

0

-50

Scattering data need to becorrelated to roughness data byverifications with other measure-ment devices. Typical output ise.g. an average rms-values, theratio of the diffuse reflection orthe reflection of light at a definedangle.

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

SCATTEROMETER (GLOSSMETER)


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 emitted electrons are“collected” by different detectors. TheEDS, a type of X-ray spectrometer,allows elemental analysis. Typicaloutput are the topographical contrast(based on SE), chemical contrast(based on BSE) and phase composi-tion (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-updermination samples, ability to

image 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 figures shown should only be considered as guidelines.


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 / T

RY

CKER

I KNA

PPEN; KA

RLST

AD

2013101

DEFECT CHART AND HINTS FOR

HIGH GLOSS POLISHING

OF STEEL SURFACES

The most common defects foundwhen polishing are described inthe Uddeholm brochure “DefectChart and Hints for High GlossPolishing of Steel 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

50100150200250300350400450500550600

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

50100150200250300350400450500550600



UDDEHOLM DEFECT CHARTUDDEHOLM DEFECT CHARTUDDEHOLM DEFECT CHART


NETWORK OF EXCELLENCEUddeholm is present on every continent. This ensures you

high-quality Swedish tool steel and local support wherever

you are. We secure our position as the world’s leading

supplier of tooling materials.


UD

DEH

OLM

14/1609.200 / STR

OKIR

K KNA

PPEN

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 devel-

opment 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. We secure our position as the world’s

leading supplier of tooling materials. We act worldwide. For us it is all

a matter of trust – in long-term partnerships as well as in developing

new products.

For more information, please visit www.uddeholm.com

polishing of uddeholm mould steel · 4 treatment polishing of mould steel be overcome by an optimal...

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