Choosing the right pulse in laser micromachining

Related Vendors

HASCO Hasenclever GmbH + Co KG

BORIDE Engineered Abrasives

AMPCO METAL Deutschland GbmH

GFH Gesellschaft für Fertigungsprozessplanung mbH

The pulse duration has no effect on quality

In addition to the removal rate, the quality and surface structure were examined as these parameters are significant for some functional requirements of components. During testing, the quality as a factor of pulse duration was examined and compared to a repetition rate of 1.1 MHz for a range of fluence (pulse energy per unit surface area) values.

Gallery

Gallery with 5 images

It was found that the quality remains virtually constant even as the pulse duration is varied. Only stainless steel exhibited a poorer surface quality when the pulse duration was increased to 10 ps. In addition, increasing the fluence resulted in a higher removal rate for all studied materials. However, the fluence value cannot be set to an arbitrary high value since the quality drops as this value is increased. Good settings were found to be 0.2 J/cm² for stainless steel, 0.5 J/cm² for carbide and aluminium nitride. It may be possible to use even higher fluence values for these materials, since 0.5 J/cm² is the highest value used during the tests and still produced good quality results. Another effect which was observed for all of the tested materials is that the removal rate increased with the repetition rate. But there is also an optimal value for this parameter, and an excessively high repetition rate reduces the quality on account of heat build-up. A rate of 1.1 MHz proved to provide good results in the tests. The effect of the pulse duration on the efficiency of laser micromachining is due to the different properties of the materials: For metals, the lattice heats up approx. 900 fs to 1 ps after the start of the laser pulse, before that only the electron system gets hot. If a pulse duration greater than 900 fs is selected, then additional energy is introduced into the material by the laser beam after this time even though the lattice is warm already. This leads to energy losses to the surrounding material, causing it to melt. With shorter pulse durations, however, the entire energy of the laser pulse is used for removal since the lattice isn't warm yet, only the electron system. In this case the material transitions to the gaseous state directly without melting. However, selecting a short pulse duration with a high fluence value produces the same effect observed with longer pulses. Due to the large amounts of applied energy, the surrounding material starts to melt.

No waste - Fashion show vividly reflects the plastics industry's pursuit of zero waste

But a different effect is responsible for the optimal pulse duration of 10 ps for ceramics: Since no material is removed here at lower fluence values, a lot of energy and thus higher fluence is required for machining in this case. Ceramics are also good at retaining heat, which means that the material heats up more and stores the heat when the pulses are longer. This results in a higher amount of energy in the material during the next pulse, since heat from the first pulse adds to the energy of the second pulse.

Selecting the right laser for the material

Tests with different materials have shown that it is certainly possible to achieve a high level of efficiency with simultaneous good quality through laser machining – if the right pulse duration for the material is selected. This means that the choices for the most suitable laser can be narrowed down on the basis of the material being machined and the required machining process – drilling, cutting or removal. The tests also showed that a pulse duration below 900 fs isn't required for any of the studied materials, since the removal rate is constant below this value. This also translates into an economical removal rate in this regard, since lasers with a longer pulse duration are also more cost-effective. Longer pulse durations are also less susceptible with regard to stability.

In addition to the pulse duration, pulse energy and repetition rate parameters, however, there are additional criteria which have to be considered when selecting a beam source. Among other things, they include the power output stability, pulse stability, robustness with regard to fluctuations in the environment, in-field service, the mean time before failure (MTBF), the mean time to repair (MTTR) and other so-called soft specs. In order to select the most suitable laser system for the respective application despite the wide range of requirements, GFH draws on an extensive knowledge base and the experience gained from several kilowatts of installed short pulse laser power. Since the company's system technology isn't limited with regard to the laser source used, the same system solution can be used to provide the customer with different laser systems and configurations according to the application.

(ID:43380500)