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What is Surface Roughness

Introducing the best values of TDC mirror finishing and basic knowledge about surface roughness.

Click here for the actual values of surface roughness.
Metal(133)
Resin(23)
Ceramics(32)
Glass(8)
Semiconductor(21)
Coating(12)
Others(4)

What is surface roughness?

The surface of the workpiece has complex undulations with continuous peaks and valleys of different heights, depths, and intervals. Those with large undulations are called “flatness”, and those with small undulations are called “surface roughness”.
Surface roughness affect not only the precision of processed products, but also the gloss and texture of the surface, so they are one of the factors that influence the product image and product brand.
Especially in the field of ultra-precision machining, not only machining accuracy but high surface treatment ability is required, so the surface roughness is extremely important.

Measurement Methods

There are basically two types of Measurement Methods for surface roughness; one is contact type that uses a stylus and non-contact type that uses a laser or light.

Contact measurement method

A method of measuring the surface condition of a part by bringing the tip of a stylus into contact with the object to be measured. Detects vertical changes and displacements of the stylus and records the surface roughness.
In addition to being able to obtain a clear shape waveform because it is touched directly, it has the advantage of being able to measure long distances.
The standard for evaluating and analyzing surface roughness is “JIS B 0601 (ISO4287)”.

 Non-contact measurement method

The “non-contact type” is a method of measuring surface roughness using light or laser instead of a stylus. There are multiple measurement methods for non-contact type due to the difference in the principle of measurement method. In addition to surface roughness, there are many that measure the shape, and by converting the measurement results into three-dimensional data, various measurements such as “height”, “flatness”, and “plane profile” can be performed.

The non-contact type has the major advantage of being able to solve the problems of the contact type, such as wear of the stylus, indentation on the object, and limitation of the minimum measured value. Is also a feature.

The standard for evaluating and analyzing surface roughness is “ISO 25178”.

Surface Roughness Parameters

Surface roughness use different calculation formulas (parameters) depending on the measurement content.
Typical parameters for surface roughness are as follows.

Ra

It is a parameter in the height direction called “arithmetic mean roughness”, and the arithmetic mean roughness when the contour curve is a roughness curve is called “Ra”.
A part of the roughness curve is used as the reference length, and the unevenness of that section is expressed as an average value.
Since the average value is used, it is not easily affected by one scratch, and it is a parameter that can obtain stable results when evaluating surface roughness.
It is written as Sa in “ISO 25178”.

Rz

It is a parameter in the height direction called “maximum height”.
A part of the roughness curve is used as the reference length, and it is calculated by the sum value of the highest part and the deepest part in the section.
It is possible to check the presence or absence of protruding scratches, and together with Ra, it is one of the indicators of quality stability.
In “ISO 25178”, it is written as Sz.

Rq(Rms)

This is a parameter called “root mean square roughness”.
There are always peaks and valleys in the surface roughness of an object, and the average roughness on the peak side (height direction) is calculated.
In “ISO 25178”, it is written as Sq.

Standard ISO 25178 JIS B 0601-2001
(ISO 13565-1)
Maximum profile peak height Sp Rp
Maximum profile valley depth Sv Rv
Maximum height of profile Sz Rz
Arithmetical mean height Sa Ra
Root mean square deviation Sq Rq
Skewness Ssk Rsk
Kurtosis Sku Rku
Spatial Parameters Sal、Str、Std
Hybrid Parameters Sdq、Sdr RΔq

Necessity of smooth surface

Measurement of surface roughness is important not only for controlling the finished state and appearance quality of processing, but for controlling product life and mechanical efficiency.

By measuring surface roughness such as Ra / Rz / Rq, you can mainly know the following functionality.

・ Appearance
Appearance such as scattered light reflection and glare.

・ Air density
The roughness between the contact surfaces has an effect on leakage from gaps.

・ Texture

・ Friction force

・ Adhesiveness
Optimal coating for packaging and adhesives. Coating adhesion.

・ Print quality
Paper texture and ink ride.

・ Noise / vibration
Vibration of the surface that rolls at high speed.

・ Easy to peel off
Easy to peel off the mold and molded product.

・ Optical performance
Disturbance or scattering of refraction of luminous flux.

·Abrasion resistance
Ease of scraping due to load concentration during sliding.

・ Fatigue fracture / strength
Strength against fatigue fracture due to stress concentration.

・ Joint surface rigidity
Increased deflection due to load concentration on the joint surface.

TDC’s surface roughness results

It is a list of surface roughness results of each material that has been mirror-polished by TDC.
We would gladly handle the materials that are not on this list.
Please feel free to contact us!

Feel free to contact us for any inquires.

Metal

材質 Ra (nm) Rz (nm) Sa(nm) Sz(nm)
FC250 2.179 11.58
Fe 0.529 3.357
Fe-Ni36 0.881 4.82
SPCC 1.01 5.457
DC53 0.794 7.267
S35C 2.503 13.42
S45C 0.608 3.727
S50C 0.518 3.543
SK-3 0.799 4.89
SK-4 0.769 4.74
SKD11 0.67 4.5
SKD61 0.608 3.017
SUS301 0.455 2.467
SUS303 0.342 2.109
SUS304 0.308 1.95 1.84 38
SUS310 0.494 3.513
SUS316 0.37 2.3
SUS321 0.498 2.653
SUS403 1.554 8.703
SUS410 0.673 4.677
SUS420J2 0.363 2.427
CENA1 0.442 3.19
CENA-V 0.551 3.163
MAT21 0.546 2.817
HAP10 1.364 7.987
M333 0.471 3.18
STAVAX 0.33 2.13
ELMAX 0.9 5.83
POLMAX 0.528 4.073
Pure Cu 0.219 1.213
C1011 0.48 2.76
C1020 0.303 1.61
C2801 6.825 34.043
Phosphor bronz 0.712 3.57
BeCu 0.88 5.05
Pure Al 0.23 1.6
A1050 0.815 5.043
A1070 0.957 5.217
A1100 0.87 4.85
A2219 0.962 6.343
A5052 0.404 2.24
A5056 1.265 6.55
A6061 0.627 4.287
A7075 2.589 12.553
Ni (Polycrystal) 0.376 2.43 3.5 35
Ni (Singlecrystal) 0.864 5.75
NiTi 0.628 3.377
Ni718 0.566 3.72
Ni720 1.502 9.383
NiCo 0.488 3.527
NiFe 12 169
Pure Ti 0.38 2.5
64Ti 0.328 1.81
βTi 0.349 2.18
TB340C 0.868 6.973
PK 1.57 9.36
SUJ2 0.527 3.45
SKS3 0.943 5.58
SCM415 0.604 3.567
SCM420 0.61 3.87
SCM420H 0.898 5.247
SCM435 2.324 14.103
SCM440 1.152 5.977
SCr15 3.337 19.13
SCr20 0.723 4.963
SCr420 1.845 10.883
SNCM20 1.152 6.147
SNCM439 0.596 3.977
SACM645 0.628 3.977
SNMN432 0.608 3.857
YSM 0.663 4.192
SKH51 0.47 3.4
SKH55 3.08 23.35
SKH57 3 18
Palladium 0.739 5.043
Vanadium 1.1 6.5
Niobium 0.495 3.33
Rhodium 0.545 3.577
Inconel® 0.417 2.623
HASTELLOY 0.421 2.597 3 34.6
42 Alloy 0.514 3.65
Ag 0.864 5.49
Au 1.767 13.357
Pt 0.586 4.237
Co 0.807 5.3
CoCr 47 470
CoNiCrMo 1.803 9.063
COBARION 0.423 2.493
Kovar 0.43 3.053
Stellite® 4.564 24.71
Ge 0.66 4.48
Mg Alloy 3.63 24.1
Sn 1.305 8.9
Zn 0.91 5.827
Metalic Glass 0.28 1.837
MA22 0.473 2.81
Cr 0.31 2.1
Te 3.976 23.253
80W-20Cu 8.3 47.2
Ta 0.25 1.87
Mo 1.064 7.203
W 0.455 2.833
W-Mo Alloy 1.641 10.843
Invar 0.711 3.74
Super Invar 0.405 2.367
Hf 0.751 4.48
Cemented Carbide 0.375 2.308
SPRON 0.26 1.101
ELGILOY 0.644
NdFeB 2.889 63.127
PD613 0.47 3.44
BiSbTe 4.162 72.26
VANADIS60 1.315 8.373
Nimowal 0.85 4.83
LEX-ZERO 0.746 4.307
Cu-T Alloy 3.2 18
Brass 0.96 5.12
PD613 0.471 2.18

Resin

Materila Ra (nm) Rz (nm)
Acrylic 0.99 7.04
ABS 4.972 29.637
COP 2.317 19.9
PTFE 1,918 12.663
PES4100G 1.698 11.247
PC 3.7 28.72
PEEK 2.39 17.4
PEEK450G 1.785 10.807
Vespel 1.96 14.1
Polyimide 1.42 11.9
polyester 3.693 33.963
PPS 1.41 9.96
PDMS 1.191 9.177
PP 1.615 10.13
ORGA 1.937 12.487
SUMI-EPOXY 5.256 82.863
Iupilon® 3.852 57.597
Polymer Monolith 0.054 500
Glass Epoxy 1.736 17.81
Epoxy 2.137 12.59
POM 48.0 489.0

Ceramics

Material Ra (nm) Rz (nm) Sa(nm) Sz(nm)
GDC 1.176 7.823
Alsima L 1.922 28.927
NEXCERA 2.722 81.173
SiC 0.401 2.1 1.6 15.7
CVD-SiC 0.488 3.25 2.107 27.38
Si3N4 0.507 4.32
Barium Titanate 0.549 1.816
AIN 0.798 6.057
ZrO2 0.474 2.773
Transparent Alumina 0.8 6.5
Carbon 4.5 26.4
92% Al2O3 3.797 25.6
99.5% Al2O3 1.017 7.987
99.6% Al2O3 8.294 34.247
99.7% Al2O3 2.6
Al2O3/ZrO2 7 39
Sintered Alumina 0.848 5.633
Ferrite 0.874 6.627
Sialon 7.908 208.59
Glassy Carbon 0.669 4.557
CEPLA 4.319 29.183
Ruby 0.724 5.107
Black Al2O3-ZrO2 107.0 945.0
Shapal® 158.0 1159.0
TiO2 0.884 10.42
SS501 1.984 10.297
Cordierite 44.432 394.537
Apatite 1.289 29.673
LLZT 0.848 15.28
Mg2SiSn 0.8 4.4

Glass

Material Ra (nm) Rz (nm)
Si 0.129 0.723
Fused quartz 0.295 2.047
BK7 0.725 5.647
TEMPAX Float® 0.67 4.503
Soda-Lime Glass 0.73 5.4
CLEARCERAM™-Z 0.609 3.757
Zerodur 0.541 4.217
borosilicate glass 0.707 7.181

Semiconductor

 

Material Ra (nm) Rz (nm) Sa(nm) Sz(nm)
AISi 0.775 6.17
Si 0.263 1.838
Quartz 0.6 4.41
GAGG 0.526 3.653
Sapphire 0.4 2.9 1.3 9.8
LiNb03 0.366 2.313
YIG 0.442 3.007
LiTa 0.232 1.18
YAG 0.783 6.79
GAN 0.573 4.15
SiC (Singlecrystal) 0.07  
PG 16 240
SiGe 0.829 4.477
CVD-SiC 0.675 3.68
Bi2Te3 4.335 29.93
Spinel 0.87 3.6
CTGS (Singlecrystal) 0.301 2.137
Ge 0.295 2
Diamond 0.38 2.03
Mg2SiSh 1.82 10

 

Coating

Material Ra (nm) Rz (nm)
Cr Plating 0.29 1.75
Ni-P 0.263 1.93
PFA 2.152 14.597
Cu 0.299 1.86
Alumite 1.407 12.947
Al 127.0 1218.0
PTFE 26.0 364.0
Al2O3 Thermal Spraying 0.638 75.453
TiC 1.01 4.91
FEP 8.15 65.557
PBI 6.46 70.93
YSZ Thermal Spraying 1.243 10.667

Others

Material Ra (nm) Rz (nm)
Stone Plate Thermal Spraying 267.0 2060.0
Pebble 171.0 1336.0
Lapis Lazuli 13.814 307.02
PCD 5.65 159.7

After mirror finishing, we will use the in-house surface roughness measuring machine and ship the data together.

We use AFM (Bruker), new view 9000 (ZYGO), Tali Surf CCI SunStar (Taylor Hobson), and Surf Test (Mitutoyo) according to the application and request.

Surface Roughness Data Sample

  • Measuring Instrument :Talysurf CCI SunStar
  • Taylor Hobson
  • Non-contact Optical 3D Profiler