POLISHING OF UDDEHOLM MOULD STEEL

TREATMENT POLISHING OF MOULD STEEL 1 © UDDEHOLMS AB No part of this publication may be reproduced or transmitted for commercial purposes without permission of the copyright holder.

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

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Edition 6, 08.2016

2 TREATMENT POLISHING OF MOULD STEEL 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

TREATMENT POLISHING OF MOULD STEEL 3 WHY STRIVE FOR be overcome by an optimal choice of FACTORS THAT tool steel and preparation strategy. A HIGH SURFACE AFFECT THE FINISH? FUNCTIONAL POLISHING SURFACE FINISH Plastic and metallic components are Most cold work applications do not Tool steels are used in many applica- manufactured with various surface need high gloss polished tool sur- tion fields within plastic moulding, finishes all from shiny and glossy to faces, but it is always advantageous cold and hot working and as engi- functional surfaces of different to create functional surfaces for a neering components. For proper appearances. In this brochure we will prolonged tool life. In forming opera- functionality, but also to minimize the inform about the factors that have the tions where lubricants are involved a cost of the tool or biggest impact on the polishability of preparation strategy may consist of component it is vital to specify the tool steels and give recommendations removing larger peak formations on required surface finish on the engi- on how to obtain the required surface the surface and preserving a controll- neering drawing. Especially in appli- finish on moulds, dies, punches and ed depth of valleys as lubrication cations of plastic moulding it is metallic components/parts. The most pockets, which then will contribute to important to have access to material common defects are shown in the a reduced friction during forming. data relating to surface finish capa- Uddeholm brochure “Defect Chart However, it is always important to bilities. However, it should be noted and Hints for High Gloss Polishing of consider the final tool steel surface that the surface finish of the end Steel Surfaces” quality in relation to the application. product is not only determined by the Depending on the application and If a high quality surface coating is tool steel and the applied surface requirements we can distinguish going to be applied, then it is always preparation process, but also the between two types of surface finish- recommended to perform high gloss application process itself has a big ing methods; high gloss polishing and polishing of the tool surface before impact on the result. Polymers have functional polishing. the coating process. different material characteristics at plastic moulding and this will defi- HIGH GLOSS POLISHING THE POLISHER IS nitely influence the final surface finish, Tools for plastic moulding do require EXTREMELY IMPORTANT as illustrated in Figures 1 and 2. a high surface finish especially when The results from the tests that have Application been carried out during the work with extreme transparency and/or high Polishing Type of polymer gloss are aimed for. In such cases it is this brochure shows that the skill, technique of utmost importance to choose a experience and technique of the proper tool material and establish a polisher plays an extremely important suitable surface preparation tech- role in achieving the desired surface Type of Surface quality tool steel nique. To achieve a reflective surface finish. with mirror finish the preparation Pre-preparation process must involve several grinding of the surface and diamond polishing steps and Process route these have to be performed in a clean Heat treatment workplace. The use of proper working tools facilitates the process a lot. Fig.1. A number of factors have influence on the surface finish of the final end product. High surface finish reduces the risk of local corrosion and fracture or 0 500 1000 1500µm cracking due to temporary over load- 0 0 500 1000 1500 2000 2500 µm 0 500 1000 1500 2000 2500 µm 250 ing or pure fatigue. 0 0 The tool surface finish may also 250 250 500 500 750 have an impact on productivity as in 500 750 750 1000 the case of injection moulding. Here, 1000 1000 1250 1250 1250 1500 the release forces of the plastic com- 1500 1500 ponent from the tool steel surface are 1750 1750 1750 2000 2000 2000 dependant on the adhesion proper- µm µm µm ties of the polymer to the mould Tool surface, inverted Makrolon AL2647 Bayblend T45 (Medium viscosity) (Low viscosity) surface. An improved smoothness of the tool surface may lead to higher Fig 2. The photos show differently holes/pits on tool surface replicated on the plastic plaque due to different material characteristics in different polymers. Fewer peaks is release forces and eventually to detected on the Makrolon plaque whereas the Bayblend plaque had visible peaks all sticking phenomena, which partly can over the surface.

4 TREATMENT POLISHING OF MOULD STEEL TOOL STEEL QUALITY CONVENTIONAL PROCESS PROCESS ROUTES FOR UDDEHOLM STEEL GRADES: TOOL STEELS Calmax Tool steels are found in various Rigor combinations to fit usage in different Impax Supreme Nimax application fields. Common manu- Ramax HH facturing process routes are conven- Orvar 2 Microdized tional ingot casting (IC), continuous Corrax casting (CC), electro slag remelting (ESR), vacuum arc remelting (VAR) and powder (PM). Remelt- ELECTROSLAG REMELTING ing processes and PM processes PROCESS produce materials of higher homo- UDDEHOLM STEEL GRADES: geneity with a low non-metallic inclu- Stavax ESR sion content, whereas ingot cast Mirrax ESR materials normally have a higher Mirrax 40 Orvar Supreme degree of segregation patterns and Vidar 1 ESR also contain more non-metallic Unimax inclusions. Dievar

RECOMMENDATIONS To produce highly reflective and PROCESS glossy surfaces ESR-remelted or PM steels are to be used. UDDEHOLM STEEL GRADES: However, conventional ingot cast SuperClean Vanadis 8 SuperClean steels can give a very good Elmax SuperClean surface finish, if both steel manu- facturing and polishing are performed according to a good Fig 3. Process routes for tool steels and practice. example of steel grades produced by the different routes.

DEFECTS IN TOOL STEELS Various types of defects emanating The remelting processes direct the from the production process may be casting structure in such a way that found in the steel. During macro segregations are drastically non-metallic inclusions are formed as reduced and a more uniform micro- a result of the deoxidation process. structure is created, which is benefi- Other sources are entrapped exo- cial from polishing point of view. genous material from refractory in the ladle or at casting. A fast solidification Total number of particles per mm2 * rate is normally beneficial by giving Polishability rank (oxides + sulphides + carbides + nitrides) less time for inclusions and particles 5 1000 Bad to grow and reducing segregation 4 100 patterns. 3 In the special remelting processes 10 INGOT CAST STEEL such as VAR and ESR the cast ingot 2 are remelted under controlled condi- 1 1 Good ESR REMELTED STEEL tions. Non-metallic oxide inclusions PM 0.1 are effectively removed from the steel Low High PM ESR Conventional and sulphides are reduced substan- Defect content by inclusions and carbides *oxides and sulphides >3 µm carbides and nitrides >4 µm tially via the basic working slag in the ESR-process altogether giving tool Fig. 4. A low defect content is beneficial from polishing point of view. steels of high cleanliness.

TREATMENT POLISHING OF MOULD STEEL 5 HEAT TREATMENT SURFACE MANUFACTURING Heat treatment can affect polish- PREPARATION OF OF INITIAL SURFACES ability in many ways. Decarburization It should be emphasized that the or recarburization of the surface TOOL STEELS grinding operation forms the basis for during heat treatment can produce The following four terms are com- a rapid and successful polishing job. variations in hardness, resulting in monly used when it comes to surface In grinding, the marks left by the polishing difficulties. preparation of tool steels. The essen- rough-machining operation are In order to avoid this it is recom- tial characteristics of these methods eliminated and a metallically pure and mended that the hardening is carried are explained below. geometrically correct surface is out in vacuum furnaces or furnaces obtained. with controlled protective gas atmos- GRINDING The finishing preparation steps can phere or salt baths. It is also of im- The abrasive particles are firmly be very time consuming and costly, portance to secure that the time at bonded to a carrier such as grinding but can be controlled to a certain austenitizing temperature is not too paper, stones and the discs. extent by a proper manufacturing of long and the quenching speed is not the initial tool surface. Normally the too slow to avoid grain growth and A starting surface is ground, milled or grain boundary precipitations. electro discharge machined (EDM). Sample Typical initial surface roughness B values, as Ra/Rz, are approximately Glue Backing 0.5/5 µm for the two former and 3/15 µm for an EDM surface. Recent developments in high speed machin- ing has made it possible to produce LAPPING surface finishes better than Ra = The abrasive particles are not bonded 0.2 µm and by using the latest tech- but move freely between the carrier niques in EDM the Ra falls below and the work piece. 0.07 µm. After EDM processing it is important to remove the heat affec- A ted layers by either a fine sparking and/or by grinding. If not doing so B Sample crack initiation may appear during Suspension tool use. Support HINTS FOR GRINDING

OPERATION SURFACE FINISH

POLISHING Ground Ra 0.5 µmRz 5 µm The abrasives are more or less fixed Milled Ra 0.5 µmRz 5 µm in the carrier material and will cut High speed and/or plough the surface. machined Ra 0.2 µmRz 1.5 µm EDM Ra 3.0 µmRz 15 µm

Table 1. Typical initial surface roughness Sample values R and R . A a z

B RECOMMENDATIONS To facilitate the finishing steps and to minimize the risk of losing BUFFING dimensional tolerances of the tool The abrasive adhere loosely to a the initial surface finish should have flexible carrier (soft disk made of cloth a roughness value of maximum or hide). This step is considered Ra / Rz = 0.5/5 µm. This will eliminate the need of using coarse among some polisher to be the last grinding media in the first prepara- polishing step performed in order to tion step. obtain a mirror like surface.

6 TREATMENT POLISHING OF MOULD STEEL DESCRIPTION OF 3. Silicon carbide (SiC) • spend more time on the coarse ABRASIVES Has a needle like blocky structure. steps before changing to the finer It is important that the abrasive fulfills Used for rougher surface finishes. steps requirements with respect to: • polishing with diamond compound 4. Boron carbide (B4C) • hardness Is hard and has a blocky crystal from 15 µm down to 1 µm grain, • sharpness structure. Fast material removal use as short time as possible • thermal resistance generating moderate surface finish. • always be careful when using soft • chemical stability carriers (felt, brushes, cloths) as 5. Cubic Boron Nitride (CBN) there is a risk of “orange peel” Today, the following five main groups Is produced basically in the same way formation on the polished surface of synthetic abrasives are used, ful- as synthetic diamond and is used filling the above requirements to when grinding hard materials like HSS A reflective surface starts to appear at greater or lesser extents. and hardened high carbide tool Ra/Rz approaching 0.1/1 µm, and the 1. Diamond designation SD steels. final surface roughness Ra/Rz should 2. Aluminium oxide designation A (SG) be less than 0.005/0.04 µm for a high 3. Silicon carbide designation C gloss polished surface. 4. Boron carbide designation B4C 5. Cubic boron nitride designation B RECOMMENDATIONS FINE GRINDING Material removal in hardened steels Abrasives have different application Fine grinding should smooth the is more consistent and repeatable areas, depending on their particular surface before the diamond polishing when diamond products are used. characteristics, as shown partially in Precision hand tools incorporating stage commences. Working tools and table 2 below. linear movement of the working compound media are built up around tools, grinding files and polishing different kinds of abrasives which stones, give a less troublesome consists of small and hard particles THERMAL STABILITY preparation process. A good with sharp edges and irregular HARDNESS IN AIR practice is to work perpendicular to shapes. ABRASIVE KNOOP °C °F the grooves in all preparation steps Diamond 7 000 650 1200 and to verify with optical examina- PRACTICAL HINTS Aluminium tion that all scratches from the oxide 2 100 2000 3630 FOR GRINDING previous step have been completely Silicon carbide 2 500 1200 2190 removed. Note, that heavy cold It should be emphasized that the Boron worked material beneath the surface grinding operation forms the basis for carbide 2 900 2700 4890 needs to be removed for a perfect a rapid and successful polishing job. CBN 4 700 1300 2550 end result. In grinding the marks left by the rough Table 2. machining operation are removed and a clean and geometrically correct surface is obtained. The practical 1. Diamond hints mentioned below apply to both The hardest material known, has a GUIDELINES mechanical grinding and manual sharp and angular structure. Fast stoning. material removal and the best possi- No general recipe exists for all types • To avoid adding heat and stress into ble planarity in combination with of steels, but the experience and the surface, do not use too much excellent surface finishes. ability to adjust the polishing tech- pressure and use plenty of coolant. Distinguish between mono and nique to every single mould and to • Use only clean and free-cutting polycrystalline diamonds. Mono- minor variations in the surface is of grinding tools with soft stones for crystalline are best for lapping, since crucial importance for the end result. hard surfaces. they are round and have many cutting As a general guideline the procedure edges. Natural gives better cuts while for high gloss polishing shown below • It is very important that the work- synthetic are harder, a mix is the best can be adopted i.e.; piece and the hands of the polisher since it last longer. • starting from a ground surface are carefully cleaned between each where the roughness Ra/Rz should change of grain size. This is done 2. Aluminium oxide (Al O ) 2 3 be maximum 0.5/5 µm to prevent coarse particles and Is relatively hard and has a sharp • use stones/grinding papers for the dust from being carried over to the angular structure. It is often used first steps, stepwise grinding to next grinding step. during the last polishing step since it 1200 Mesh gives excellent and highly glossy sur- face finishes. Is relatively inexpensive.

TREATMENT POLISHING OF MOULD STEEL 7 • When changing to the next finer PRACTICAL HINTS FOR • Finish polishing step should, if grain size, it is recommended that POLISHING possible, be carried out in the the grinding direction be changed Above all, cleanliness in every step of release directional of the moulded to 45°. Cross-grinding is very the polishing operation is of such part. simple, but extremely effective. It importance that it cannot be overem- • With softer carrier the abrasive is increases stock removal and it phasized. able to penetrate deeper into the makes it easier to detect scratches • Each polishing tool should be used carrier. This will result in that the from the previous steps and im- for only one paste grade and kept surface will be finer for the same prove the dimensional accuracy. in dust proof containers. size of abrasive. See Figure 6 Figure 5 A–C. • Paste should be applied to the below. • Select the sequence of movements polishing tool in manual polishing, Soft Medium Hard so that all surface segments are while in machine polishing the processed for an equally long paste should be applied to the Felt Wood Steel period. With a rotating grinding work-piece. disc there will be a risk that there • Polishing pressure should be will be less stock removal on the adjusted to the hardness of the Hardened steel edge than in the centre of the polishing tool and the grade of surface. Figure 5 D. Fig. 6. The hardness of the carrier paste. For the finest grain sizes, affects the exposure of the diamond the pressure should only be the grains and the removal rate. weight of the polishing tool. Standard •Work with hard carriers for as many steps as possible and work TYPICAL POLISHING A for as short a period as possible SEQUENCES with soft carriers. The choice of grinding and polishing • Polishing should start in the cor- sequences are determined by the ners, edges and fillets but be experience of the operator and the 45° careful with sharp corners and equipment he/she has at his/her edges so they are not rounded off. disposal. The properties of the tool B material can also influence the sequence.

Milling Turning 90° EDM’ing Rough grinding Rough Grain C number 50

80

Irregular overlapping 120 Fine FEPA 180 grinding Rough Grain D Fine 220 Polishing with diamond paste Rough Micron 320 size 45 µm Fig. 5. Grinding directions.

25 800

1200 15 Fig. 7. This figure 9 shows example of how 6 3 the polishing sequence 1 can be selected. Fine Fine

8 TREATMENT POLISHING OF MOULD STEEL EXAMPLE OF DIFFERENT different manual polishing strategies POLISHING STRATEGIES AT can be adopted to reach the same HIGH GLOSS POLISHING final surface finish by using rigorous All polishers have their own proce- and well proven working procedures. dures for high gloss polishing. The The achieved surface finish is lower data, in Tables 3–5, reflects that than Ra 0.01 µm

STEP TECHNIQUE TYPE OF TOOL LUBRICATION

1 Hand-held unit Stone 320 Dielectric oil

2 Hand-held unit Stone 400 Dielectric oil

3 Hand-held unit Stone 600 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) 5 x 5 mm DP 9 µm Dielectric oil

8 Hand-held unit (linear) Wood 5 x 5 mm DP 9 µm Dielectric oil The tables 3 and 4 show 9 Hand-held unit (linear) Wood 5 x 5 mm DP 6 µm Polishing oil examples of specific step-by- step information regarding 10 Hand-held unit (rotational) Hard felt 10 mm DP 3 m Polishing oil µ high gloss polishing of 11 Hand-held unit Piece of Uddeholm Stavax ESR and cotton wool DP 1 µm Polishing oil Uddeholm Unimax.

Table 3.

STEP TECHNIQUE TYPE OF TOOL LUBRICATION

1Ground

2 Hand-held unit SiC paper K320 Dry

3 Hand-held unit SiC paper K800 Dry

4 Hand-held unit SiC paper K1500 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 4.

STEP TECHNIQUE TYPE OF TOOL LUBRICATION

1 Reciprocating machine 9500 Rpm Brass carrier DP W 15 µm Polishing oil Amplitude movment 0.2 mm Plastic carrier Observe carefully, during the 2 Reciprocating machine 9500 Rpm Brass carrier DP W 10 µm Polishing oil polishing steps, if any deep Amplitude movment 0.2 mm Plastic carrier marks are visible in the 3 Reciprocating machine 9000 Rpm Brass carrier DP W 5 µm Polishing oil polished surface. If this Amplitude movment 0.2 mm Plastic carrier problem occur it is needed to immediately reduce the 4 Reciprocating machine 7500 Rpm Brass carrier DP W 3 µm Polishing oil Amplitude movment 0.2 mm Plastic carrier pressure, put on polishing oil or if more diamond paste 5Turning tools Wool blankets DP W 1 µm Polishing oil needs to be added. Table 5.

TREATMENT POLISHING OF MOULD STEEL 9 POLISHING PITTING When using grain size 10 µm and PROBLEMS CAN The very small pits (pin holes) which smaller: can occur in a polished surface • the softest polishing tools should BE SOLVED generally result from non-metallic be avoided The predominant problem in polishing inclu-sions or hard carbides which • the polishing process should be is so-called “overpolishing”. This have been torn out from the surface carried out for the shortest possi- terminology is used when a polished during the polishing process. Pitting ble time and under the lowest surface gets worse the longer you can also be caused by hard particles possible pressure polish it. There are basically two embedded in a softer matrix. During phenomena which can appear when polishing the matrix will be removed a surface is overpolished: “orange at a more rapid rate than the hard peel” and “pitting” (pin holes). These particles. Polishing will gradually problems often occur when changing “undermine” the hard particles until from hard to a soft tool (felt/brush). they are torn out of the material by A material at higher hardness further polishing. The problem is most can better withstand a high polishing often encountered when polishing pressure compared with prehardened with diamond paste grain size less steel. Subsequently material with low than 10 µm and soft polishing tools hardness will become “over-polished” (felt, brush). more easily. If pitting occurs the following measures should be taken: •regrind the surface carefully using ORANGE PEEL the last grinding step prior to The appearance of an irregular, rough polishing surface, which is normally referred to • use a hard coarse tool and repeat as “orange peel”, might depend on the polishing process different causes. The most common is polishing with high pressure and prolonged time during the last 0.5 mm polishing steps. A material at high hardness is less sensitive to problems with “orange peel” compared to prehardened or soft annealed mate- rial. • If a polished surface shows signs of an appearance like “orange peel”; stop polishing! There is no idea to increase the polishing pressure and continue to polish. “Pitting” Such a course of action will only result in a worse set of problems.

• Following steps are recommended 0.5 mm to restore the surface. Remove the defective surface layer by regrind- ing it, by using the last grinding step prior to polishing. Use a lower pressure and shorter time during the polishing stepsthan what was used when the problems occurred.

“Orange peel”

10 TREATMENT POLISHING OF MOULD STEEL MEASURING However, these methods are both subjective and uncertain compared to SURFACE more advanced surface- and sub- ROUGHNESS AND surface measurement devices capable of measuring to fractions of QUALITY nano-metres. The use of 3D-instru- Polished mould surfaces are tradi- mentation with higher resolution tionally estimated by the naked eye provides more accurate surface and/or measured by mechanical measurements of moulds with profilers for surface roughness, complex geometries which in turn commonly described with the Ra, Rz means that quantitative surface and Rt values. quality controls can be performed.

SURFACE ROUGHNESS ACC. TO DIN/ISO 1302 SURFACE ROUGHNESS ACC. TO SPI ROUGHNESS ROUGHNESS Ra, µmRmax, µm ACHIEVED AFTER GRINDING/POLISHING WITH N 1 0.025 0.1–0.3 A-1 3 µm Diamond Paste N 2 0.05 0.3–0.7 A-2 6 µm Diamond Paste N 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 Paper N 5 0.4 2–6 B-2 400 Grit Paper N 6 0.8 6–10 B-3 320 Grit Paper N 7 1.6 10–20 C-1 600 Grit Stone N 8 3.2 20–40 C-2 400 Grit Stone N 9 6.3 ~60 C-3 320 Grit Stone N 10 12.5 ~125 D-1 600 Stone Prior to Dry Blast Glass Beads #11 N 11 25 ~250 D-2 400 Stone Prior to Dry Blast #240 Alminium oxide N 12 50 ~500 D-3 320 Stone Prior to Dry Blast #240 Aluminium oxide

Table 6. Approximate comparison between requested surface roughness measured by mechanical profilers and international standards.

SURFACE ASSESSMENT BY ROUGHNESS PARA- Ra – the arithmetical mean deviation of METERS the profile is the mean value of the absolute value of the profile departure The benefit to measure surfaces is y within the reference length l. both the possibility to study them in Source: The figure to the left is from T.R. Thomas book “Rough surfaces” the micro- and nano-scale, and a way 2nd edition. to quantitatively evaluate them. But, 0 100 200 300 400 500 600 µm there is a huge amount of available 0 2D- and 3D parameters (abbreviated 50 100 The A- & B-profiles illustrate one of R- and S-parameters, respectively), 150 the major disadvantages of the 2D so how do you know which to use? 200 profilometry; A – a surface with 250 pores, and B – a “defect free” 2D parameters, usually obtained by 300 350 surface, i.e. the results are strongly a mechanical profiler, can be used to 400 dependent on the profile location. quantify the surface quality in a limited 450 µm extent. The most frequent used in practical work with moulds is the Ra- value describing the average height of Ra = 2.4 µm the measured surface. However, it is a Illustration of different surface rather poor description of the mould topographies with equal Ra-value; surface since smaller defects and i.e. the Ra-value itself is not R = 2.5 µm certain textures will be “averaged out” a enough to fully describe the and/or undetected. See figure 8. surface structure Source: Illustration from T.R. Thomas book “Rough surfaces” Ra = 2.4 µm 2nd edition.

Fig. 8.

TREATMENT POLISHING OF MOULD STEEL 11 MEASUREMENT DEVICES AND ANALYSIS TECHNIQUES AVAILABLE TO QUANTIFY ENGINEERED SURFACE TOPOGRAPHIES

MECHANICAL PROFILER (STYLUS) Lt 1.75 mm Typical output Ls 2.5 µm VB 350 µm parameters are the Vt 0.50 mm/s Points 3500 Ra (arithmetic mean Sample D ground 15 rep Unimax 01 Pick-up PHT 350 P000_007 PCD: R(LC GS 0.3 mm) value of a profile), µm the Rz (mean peak 2.0 to valley height), and the Rmax (or Rt, the maximum peak to valley height). 0 Notice: most often R-values are -2.0 filtered per default (connected to 0.3 mm/div 1.3 mm Ra 0.083 µm Rz 0.78 µm actual measurement length and cut- off).

SCATTEROMETER (GLOSSMETER)

The surface is Scattering data need to be Intensity db illuminated and the correlated to roughness data by 50

reflected/scattered verifications with other measure- 0 light is detected. ment devices. Typical output is Simple glossmeters e.g. an average rms-values, the -50

measure reflections in defined angles, ratio of the diffuse reflection or 40 20 0 -20 -40 whereas scatterometers include the the reflection of light at a defined total reflection. angle.

40 20 0 -20 -40 Y scatter angle (degree) X scatter angle (degree)

INTERFEROMETER

Height deviations advantages in laboratories due to nm 85 are detected by its sensitivity to vibration, but new 80 75 70 utilising interference instruments are coming 90 65 60 patterns formed/ that can be used for in-line 0 20 40 60 80 100 120 140 55 arised when two measurements. Typical output 50 45 reflected light are 3D maps and areal surface 40 35 µ beams, one from the sample and one parameters (e.g. Sa and St which m 30 25 from a reference surface, interact. correspond to the R and R re- 20 a t 15 µm Features down to 1 m in spatial spectively). Also other parameter 10 µ 5 resolution and sub-nm in height can families are available, e.g. areal, 0 20 40 60 80 100 120 140 160 180 0 be detected. The technique is of volume and functional parameters.

nm 180 CONFOCAL MICROSCOPE 160

140 Builds up 3D maps optical quality. Typical output are 120 based on stacks of 3D maps and areal surface 190 100 images recorded at parameters (e.g. S and S a t 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 80

different heights, which correspond to the Ra and 60 m excluding points µ µ Rt respectively). Also other parameter 40 m that are out of focus. The technique is families are available, e.g. areal, 20

preferential for surfaces rougher than volume and functional parameters. 90 80 70 60 50 40 30 20 10 0 0

12 TREATMENT POLISHING OF MOULD STEEL SEM/EDS

e A focused electron direction). The emitted electrons are beam raster-scans “collected” by different detectors. The the surface; the EDS, a type of X-ray spectrometer, energetic electrons allows elemental analysis. Typical interact with the output are the topographical contrast atoms in the sample within a few nm (based on SE), chemical contrast to several µm of the surface, i.e. (based on BSE) and phase composi- scattering events take place (primary tion (based on X-ray). electrons loose energy and/or change

ATOMIC FORCE MICROSCOPE

µm Simply described as a tiny profiler/stylus 35 operating with 30 extremely small 25 probe tips barely 20 touching the surface resulting in 3D 15 resolutions close to atomic level. 10

Typical output are 3D maps and areal 5 surface parameters. 0 0 5 10 15 20 25 30 35 µm

SELECTION OF MEASUREMENT DEVICES AND GENERAL SPECIFICATIONS

LIGHT ATOMIC GENERAL 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 – Measurement area 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 –

Component analysis No No No No Yes No No

Usability Good Good Mid Mid Bad Bad Good

Measurement time – Long Short Mid Long Long Short

Size of Device Unlimited Device Device mm-cm Device Unlimited workpiece dependent dependent dependent dependent (often up to (often up to 2–10 kg) 2–10 kg)

Other Standardised Risk of surface Sensitive to Large depth of Work in vacuum, Noise sensitive, Only average methods for damage, fragile vibrations focus, problems needs solid and fragile roughness data cleanliness stylus/pick-up with artefacts conducting stylus/pick-up dermination samples, ability to image undercuts

Table 7. The figures shown should only be considered as guidelines.

TREATMENT POLISHING OF MOULD STEEL 13 DDEHOLM 120305.1000 / TRYCKERI KNAPPEN; KARLSTAD 2013101

DEFECT CHART AND HINTS FOR HIGH GLOSS POLISHING OF STEEL SURFACES

The most common defects found when polishing are described in the Uddeholm brochure “Defect Chart and Hints for High Gloss Polishing of Steel Surfaces”.

UDDEHOLM DEFECT CHART UDDEHOLM DEFECT CHART UDDEHOLM DEFECT CHART

PITTING 3D MEASUREMENT 3D MEASUREMENT DISCOLORATION/ 3D MEASUREMENT AND PROFILE RELIEF AND PROFILE AND PROFILE Scattered (pin) holes dispersed 0.5mm Hill-like formations in all kind of 0.5mm 0.5mm µm µm STAINING µm 0 0 0 over the majority of the surface. 50 geometries covering the majority 50 50 100 Discoloured areas; e.g. “milky 100 100 150 of the surface. 150 spots”. 150 200 200 HINTS 250 250 200 300 300 250 • Shorten the polishing time (use enough 350 HINTS 350 HINTS 300 400 400 350 450 • Choose a cleaner steel i.e. ESR steel grade 450 but short steps) • Inhomogeneous microstructure is adverse 400 500 500 • Use lower pressure 550 • Use harder carriers/tools 550 • Clean and dry the workpiece immediately 450 600 600 500 • Use harder carriers/tools – combination 0 100 200 300 400 500 600 700 800 µm • Choose a more homogeneous steel 0 100 200 300 400 500 600 700 800 µm after each preparation step, avoid hot 0 100 200 300 400 500 600 µm diamond paste and lubricants is important material. Softer areas tend to be more water •Avoid unidirectional movements during polished than harder ones (pre-stage to • Compressed air can contain oil or water, preparation of the surfaces orange peel) which might affect the surface •Dry the workpiece and store properly to • Decrease the polishing time (use enough •Cover the surface after polishing and avoid corrosion attacks on the surface but short steps) store properly • If the pitting defects only appears in a •Polishing cloths with low pressure reduce • Avoid overheating during previous pre- local area on the surfaces it probably due the risk paration steps which get visible during the to impurities in the material • Use lower pressure polishing process

COMET TAILS PEAK/RAISING HAZE m 0.5mm µm 0.5mm µm 0.5mm µ 0 0 0 Scattered holes with a tail, Small outwardly directed feature, Areas with lower gloss than 50 50 25 100 100 50 dispersed over the majority of 150 often irregularly shaped, e.g. bare the surrounding (“silvery frosted 150 75 200 200 laid inclusions. 100 the surface. 250 appearance”). 250 300 125 300 350 150 350 400 175 400 HINTS 450 HINTS 200 HINTS 450 500 500 225 • Avoid unidirectional movements 550 • Choose a cleaner steel material • Choose steel with homogenous material 550 250 600 600 • Clean the workpiece to avoid surface 275 properties (e.g. without grain clusters in • Use higher rotational speed if manual 0 100 200 300 400 500 600 700 800 µm 0 100 200 300 400 500 600 700 800 µm polishing contamination 0 50 100 150 200 250 300 350 µm different directions and/or hardness • Use lower pressure, larger abrasive sizes, variations) polishing cloths with higher resilience • Might be correlated to previous process- and/or a lubricant with higher viscosity to ing (e.g. milling or welding operations) avoid embedded abrasives • Last polishing step discarded/cancelled • Unclean surface (insuffizient carrier, wrong lubrication and diamond paste)

µm HOLE 0.5mm µm ORANGE PEEL µm BURN MARK 0 0 0.5mm 0.5mm 0 Smaller irregular or circular 50 Physical destruction due too high 50 100 Randomly, smooth valleys and 250 100 shaped cavity, e.g. pores, pinholes 150 hills covering the majority of 500 surface temp. during surface pre- 150 200 750 200 and imprints by abrasives. 250 the surface. 1000 paration. On the sample surface 250 300 300 1250 350 three different defects are shown 350 1500 400 400 450 1750 HINTS e.g. dark bluish areas from high 450 500 HINTS 2000 • Choose a cleaner steel i.e. ESR steel grade 550 pressure during polishing, point 500 600 • Shorten the polishing time (use enough 2250 550 2500 600 0 100 200 300 400 500 600 700 800 µm shaped burns caused by EDM • Use softer carriers/tools (without lint) but short steps) 0 5000 1000 1500 2000 2500 3000 µm 650 process and linear and laminar 700 • Use lower pressure • Use harder carriers/tools 750 burns caused by grinding, welding 800 • Napless polishing cloths reduce the risk • Use lower pressure or other operations. 0 100 200 300 400 500 600 µm for pull-outs • Increase the lubrication in order to cool • Use a fluoride-free polishing cloth down the surface HINTS • Use lubrication in order to cool down the workpiece during surface preparation • Use lower pressure and/or speed during surface preparation GROOVE (scratches) 0.5mm µm 0.5mm 0.5mm 0 WAVINESS µm Longitudinal recession with 10 0 Longitudinal, smooth valleys 250 rounded/flat bottom. 20 CRACK 30 and hills covering the majority 500 40 of the surface. 750 Linear recession with a 50 1000 HINTS 60 1250 sharp bottom. • Clean the workpiece, tools etc. between 70 HINTS 1500 0 20 40 60 80 100 120 140 160 µm 1750 every polishing step; remaining abrasives •Work with tools that have a good 2000 HINTS Groove (Scratches) can scratch the surface by accident contact to the surface 2250 • Crack result from surface tensions build 2500 • Be sure that marks left from previous • If waviness occurs go back to the first 2750 up during the manufacturing process, preparation steps (e.g. turning or grinding polishing step and change to a larger 3000 i.e. change the preparation and/or the marks) are removed 3250 manufacturing process tool that fits better to the geometry 0 500 1000 1500 2000 2500 µm • Check if the hardness is too low of the surface to be polished

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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.

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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

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