Historically, sectors such as the electronics, medical and micromechanics industries have been pioneers in the area of miniaturisation. Products in these sectors are continuously being developed to be thinner, lightweight, energy efficient, less invasive and more accurate. To meet these demands, the company Ewag AG in Etziken, Switzerland, which is a member of the UNITED GRINDING Group, offers the LASER LINE ULTRA machining centre depicted in Fig. 1.
Figure 1
EWAG LASER LINE ULTRA ultrashort pulsed laser machining centre
This machine specialises in the laser fabrication of cutting tools made of hard and ultrahard materials such as tungsten carbide (WC), polycrystalline diamond (PCD), chemical vapour deposition diamond (CVD-D) and cubic boron nitride (CBN). The capabilities of the machine includes cutting edge preparation, post-sharpening, fabrication of chip breakers and cylindrical margins as well as laser-modification of ground cutting tools.
Owing to its 8-axis kinematic concept and the use of an industrial laser source emitting pulses in the picosecond time regime, complex micro geometries can be machined. Two examples to prove this claim include cutting tools made by the EWAG Drill and Mill Module software options.
- Spiral Tools
The EWAG Drill and Mill Module are software options which enable users of the LASER LINE ULTRA to fabricate spiral tools made of WC or PCD between Ø0.4mm to Ø3mm. Analog to HELITRONIC TOOL STUDIO from WALTER, programming is parametric and recommended laser processing parameters are automatically determined enabling a significant ease of programming.
- Micro Drill Bits
Applications of micro drill bits are manifold and include the drilling of gallium- or silicon-based wafers, sintered ceramic components, multilayer composite printed circuit boards (PCBs) or spray nozzles. To ensure homogenous hole quality, wear-resistance of the tools is of utmost importance and can only be achieved by micro cutting tools made out of ultrahard materials. By using ultrashort laser pulses and the EWAG Drill Module, the LASER LINE ULTRA can achieve this task with ease. An example in Fig. 2, depicts a micro drill bit made out of a carbide body and a PCD tip which is completely lasered from a cylindrical blank.
Figure 2
Ø0.4mm lasered PCD drill bit with the head of a matchstick for reference
The advantages of using laser technology compared to conventional techniques especially for micro cutting tools include:
- Diameter to length aspect ratios of up to 1:20
- Ability to process additional small features, e.g. tip thinning, tip chamfers, etc.
- Owing to the force-free process, no waste from tool breakage occurs and no steady-rest support is necessary
- High degree of geometrical flexibility since brazed plate-based tools and spiral tools can be fabricated without any retooling
Laser processing removes material according to thermal-based mechanisms. However, by using ultrashort laser pulses and correct laser parameters, a phenomenon arises in which the pulse is so short that there is insufficient time for a significant amount of heat to conduct into the cutting tool. As a result, there is a negligible heat-affected zone. To prove this claim and to further demonstrate the flexibility of the LASER LINE ULTRA, carbide drill bits are laser-fabricated and are subsequently coated by the physical vapour deposition (PVD) process with a single layer of either a TiAlN- or an AlTiN-alloy. During PVD coating, the processing chain and processing recipe were not adapted, i.e. laser-fabricated cutting tools are treated equally to ground cutting tools. Results depicting the evolution of the micro drill bit, from a cylindrical blank to a coated micro drill bit are given in Fig. 3.
Figure 3
Evolution of carbide drill bit from left to right: Ø0.5mm carbide blank, Ø0.45mm carbide drill bit after laser processing, carbide drill bit after TiAlN-coating and carbide drill bit after AlTiN-coating
EWAG has studied extensively the coatability of laser processed micro cutting tools and has worked closely with two of Switzerland’s biggest surface technology companies to ensure successful coating. To confirm that coating adhesion is comparable to ground tools, measurement methods such as optical microscopy, scanning electron microscopy, energy-dispersive x-ray spectroscopy, hardness indentation tests and destructive break tests were all used.
- Micro End Mills
Applications of micro end mills are manifold and include profiling of PCBs, milling of enclosures such as mobile phone cases as well as the fabrication of moulds and dies for injection moulding. By using the EWAG Mill Module, the LASER LINE ULTRA is able to fabricate 4-flute PCD end mills from cylindrical blanks as depicted in Fig. 4. Primary and secondary clearance faces are fabricated both at the tip and circumference, the corners at the edges are broken by a chamfer, and with all lasered spiral tools, a smooth uninterrupted interface between PCD-WC is observed.
Figure 4
Ø0.5mm lasered PCD 4-flute end mill with the head of a matchstick for reference
- Quality of Spiral Micro Tools
An important quantity which defines the quality and chip evacuation performance of spiral tools is the surface quality of the helix flute. In this case, white light interferometry is used given a 20x 0.4NA objective lens. Surface roughness results of the helix flute are summarised in Fig. 5.
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Figure 5a
Surface quality results of the helix flute at the tip of a Ø0.4mm drill bit: (a) ground WC surface (b) lasered WC surface and (c) lasered PCD surface (Measurement conditions: measurement length = 400µm, roughness filter = FFT fixed, cut-off frequency = 250µm)
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Figure 5b
Surface quality results of the helix flute at the tip of a Ø0.4mm drill bit: (a) ground WC surface (b) lasered WC surface and (c) lasered PCD surface (Measurement conditions: measurement length = 400µm, roughness filter = FFT fixed, cut-off frequency = 250µm)
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Figure 5c
Surface quality results of the helix flute at the tip of a Ø0.4mm drill bit: (a) ground WC surface (b) lasered WC surface and (c) lasered PCD surface (Measurement conditions: measurement length = 400µm, roughness filter = FFT fixed, cut-off frequency = 250µm)
Interestingly to notice, the lasered surfaces are homogenous and do not show any form of periodicity or directionality compared to the ground surface. Furthermore, the surface quality of the lasered WC surfaces is 20% better than the ground WC drill bit. For lasered PCD surfaces, an excellent surface quality is also achieved, however, results are typically not comparable to that of WC. In general, lasered spiral tool surfaces, regardless of material, exhibit surface roughness values for Ra and Rz of <0.25µm and <1.5µm respectively.
Additionally, cutting edge radii are typically ≤5µm and are symmetric with a K-factor typically equal to 1±0.2. In terms of diameter stability, a tolerance of ±0.005mm can be achieved given a production run of 12 hours under climatised conditions.
- Outlook
The EWAG LASER LINE ULTRA provides an excellent basis to fabricate complex micro cutting tool geometries independent of their hardness and with negligible heat-affected zone. The presented examples would otherwise be difficult or impossible to fabricate by conventional manufacturing techniques or even with nanosecond laser pulses. With continuous improvements to the laser process and software, EWAG is actively developing in the following areas: fabrication of spiral tools made of CVD-D and CBN, additional spiral tool types and new process development. To exemplify the former, Fig. 6a depicts the fabrication of a 4-flute polycrystalline CVD-D end mill. By inspecting the image more closely, one can even notice the grain boundaries of the CVD-D polycrystalline structure. To exemplify the latter, Fig. 6b depicts a part made of PCD which has been laser-turned from a solid cylindrical blank. Applications of this part include chip-free machining of carbide and tool steel for a mirror finish, chip-free expansion of holes to achieve ultraprecise diameters or guide pins in the mould industry
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Figure 6a
(a) Ø1mm lasered polycrystalline CVD-D 4-flute end mill (b) Ø2mm laser-turned PCD part
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Figure 6b
(a) Ø1mm lasered polycrystalline CVD-D 4-flute end mill (b) Ø2mm laser-turned PCD part
The presented tools show very well that the use of an industrial picosecond laser source has the ability to process a wide range of materials and intricate geometries. In conclusion, the fabrication of spiral tools together with the ability of processing standard brazed plate-based tools, shows that the EWAG LASER LINE ULTRA is particularly well suited for the electronics, medical and micromechanics industries.