Many operators and manufacturers shaketheir heads when form cutter tolerancesof ± 2 μm or runouts of less than 2 μm

are required. It is these precise and expensivemills, however, that allow great savings in moldconstruction. This is because high speed cutter

(HSC) technology, using high performance mills,allows one-pass machining of the finished mold(Fig. 1). When the substrate, geometry and coatingare right, then modern micromills can directlymachine hardened steel. This avoids the produc-tion of very complex electrodes and the slow ero-sion process. The surface quality, dimensions andform accuracy, however, must be nearly perfect.Therefore, the requirements placed on the millsare very high.

For such mills, some parameters are particular-ly critical for a perfect cut. The precision of theshaft has a great influence on the quality of thecut, because the grinders use the shaft as a guideduring grinding. The runout of the shank is alsoparticularly important for preventing vibrations,because the miniature mills are run in the rangefrom 20,000 to 60,000 rpm.

Cutting depths of 20 to 50 μm are typical in final

22 QMT January/February 12www.qmtmag.com

In micromachining, even the slightest deviations can disturb the process anddrive up costs. Sensitive and expensive tools must, therefore, meet extremelytight requirements. To monitor quality, high precision optical or multisensor

measuring machines can be used. By Christopher Morcom.

OPTICAL METROLOGY

Figure 2. Similar to the tool magazine

on a machining centre,Werth tool measuring

machines have a wideselection of sensors, such as

the Werth Fibre Probe, toprecisely measurable micro-

geometries.

Why microtools must be soprecise

Figure 1. Complete machining,using HSC high per-

formance mills toobtain the final shape,

is possible only withform cutter tolerancesof ±2 μm and runout

of less than 2 µm.Image: Zecha

P23,24,25 Werth.qxp 06/02/2012 18:21 Page 22

machining. Cutting tool radii tolerances of 5 μmand lower are therefore necessary to keep all thecutting edges equally engaged. These tight radiitolerances greatly affect surface quality and elimi-nate costly intensive manual reworking. This alsogreatly increases the usable life of the mold.

To obtain these advantages, the mills must be ofthe best quality. Everything must be right; the sub-strate, the macro geometry (shank and neckshape), the shape and the quality of the cuttingedges. The required quality can be assured only

by combining high end grinding technology withhigh precision, simple measurement technology.The ability to monitor shape integrity, runout,edge quality and surface quality of the cutting andprimary surfaces is the deciding factor. Tool MTGmbH provides solutions in this area.

Tool metrologySince 2009, MT Microtool GmbH and WerthMesstechnik GmbH have joined forces in theiractivities in tool metrology under the name ToolMT GmbH. The cooperation provides newmachine solutions for high precision measure-ment of tools up to 300 mm in diameter, includ-ing application specific sensors, such as imageprocessing, lasers, or touch and scanning probes,with repeatability of less than 1 μm and compli-ance with VDI-VDE 2617 and ISO10360 specifi-cations. All measuring machines are traceable tothe length standard of the Physikalisch-Technische Bundesanstalt (PTB - NationalMetrology Institute). Therefore, the measurementresults are absolutely reliable.

Well known manufacturers in the tooling indus-try use these systems in over a hundred installa-tions, including Sandvik, Kennametal, HAM,Hitachi, OSG, Walter, Krupp Widia, Seco, Nachi,Wolf and Zecha. The products of these manufac-turers include; indexable cutters, drills, mills,threading tools, medical and dental tools. All tools

QMT January/February 12

OPTICAL METROLOGY

www.qmtmag.com

Figure 3. The special tool

mount, in a sap-phire-lined V-

groove, allowsmeasurement with-

out pendulumerrors.

Figure 4. NanoMatic: fast, simple,precise measurement oftools, directly in the pro-

duction environment

24Verisurf 1011(new number) indd 1 10/5/2011 3:43:09 PM

P23,24,25 Werth.qxp 06/02/2012 18:22 Page 24

are subjected to strict quality controland all relevant dimensions are docu-mented.

To reliably ensure precision, high endmeasurement systems and non-contactprocesses are required. High magnifica-tion levels are required to measurediameters and small radii at a precisionof less than 1 μm.

The critical factors for the perform-ance of microtools are; form accuracy,runout, dimensional accuracy of thecutting and relief angles, and the coat-

ing used. Form and runout measurements havebeen performed for several years using the trans-mitted light scanning method. Tool MT relies onthe experience with microscopy, illumination,image processing algorithms and sensors fromWerth Messtechnik in Giessen (Figure 2).

Tight shape tolerances can be inspected only bymeans of the best tool holding technology.Classical chucks are often not precise enough.Because their runout is too big, they cause pendu-lum errors. The tools can be rotated for accuraterunout in a precise, sapphire lined V-groove witha motor drive (Figure 3). The captured shape ofthe mill does not include any chucking error, itonly shows only errors in the cutting edges of thetool or in the shank.

To adapt to the precision and tool size, theimage processing optics are equipped with auto-matic magnification and working distance adjust-ments. They can measure the smallest details reli-ably, even for microtools. In addition to optics,laser and fibre probes are also used for measuringmicrotools. The fibre probe, with a probe sphereas small as 20 μm, is particularly useful for meas-uring drop-off and thread profiles on small taps orimplants.

Only high precision 3D sensors make it possibleto set up a control loop with the grinder to manu-facture the cutting and relief angles to tolerance of± 1° in a reliable process. The highest quality stan-dards are a prerequisite for success against thebackground of globalization and rising costs, par-ticularly for German and European tool manufac-turers. To gain a time advantage in the productionprocess, it is critical that the geometry data (2D or3D) that are entered in the grinder software canalso be used directly for automatic measurement.Data transfer takes place, for example, via aNumroto, Rollomatic, or Anca interface. The fea-tures to be measured can be selected graphically.This measurement software can be used both inmachines in the production environment(ScopeCheck and NanoMatic) and in the high endmeasuring machines (VideoCheck HA) (Figures 4and 5).

The measurement results are fed back into thegrinder programming software and are availablefor automatic process correction.�

www.werth-tool-mt.de

25QMT January/February 12

OPTICAL METROLOGY

www.qmtmag.com

Figure 5. VideoCheck V-

HA: Toolmeasurementsat resolutions

of 10 nm andlength meas-

urement devia-tion less than

0.25 µm

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