How to control laser focus in real time

New materials, component design and manufacturing, along with requirements for high quality products are the dominant drives for continuous performance improvements in laser drilling, cutting and welding systems.

For example, the protection of aircraft engine components relies on the accurate positioning of the laser-drilled holes as well as the consistent air flow through the holes. These holes must be very accurate in their width, depth and angle.

In these types of applications the laser beam focal point must be accurately positioned.  Optimet’s unique technological properties allow the sensor to be incorporated with the customer’s laser beam delivery optics. In this case, the sensor is implemented as an autofocus device which continuously and accurately measures the distance to the object.

The Auto focus can be implemented in two ways, pre-process and in-process. In the pre-process application the sensor takes a profile measurement of the object or creates a 3D scan if needed, and maps out the area of interest. It passes that data to the welding or engraving laser and tells it where to position the laser in order to receive the result required.

The in-process application can be implemented by having the sensor on the same arm as the laser but slightly ahead of it, that way it always tells the welding laser where its next step is. Another way to implement this is having the sensor’s detection beam go through the lens (TTL) of the laser welding or drilling system and gather the measurement in-between the pulses of the drilling laser. This allows real in-process inspection as well as immediate feedback to the laser system in order to adjust optics accordingly.

Laser-drilled holes permit film cooling in this first-stage V2500 nozzle guide vane
Laser-drilled holes permit film cooling in this first-stage V2500 nozzle guide vane (CC BY-SA 3.0, via Wikimedia Commons)

Other applications where Autofocus can be implemented are:

Blind Hole Measurement – The sensor is used to examine the depth and diameter of blind holes in PC Boards or metallic parts. Blind holes are drilled holes which cannot be measured while drilling them, since the drilling system fills up the whole diameter and another probe cannot be inserted while in process. The collinear approach of the Conoscopic Holography technology enables entering holes with even the smallest diameter.

Another type of blind hole is when the measured surface is not directly under the sensor
Another type of blind hole is when the measured surface is not directly under the sensor. This type of hole can only be drilled by a laser and the measurement can be done only using a collinear sensor.

In-process Measurement of Hole DepthThe sensor is used to examine on-line, the depth of laser drilling in soft materials. The measurements are synchronized between the engraving laser pulses, providing a feedback of the depth of the drilled hole. The highly precise measurements are performed through the laser focusing lens.

microscopic picture of a slope done with laser engraving technology
A microscopic picture of a slope done with laser engraving technology () and a 3D scan of the slope.

In-process welding of 3D moldsLaser welding of free-form 3D objects is limited by the operator’s ability to adjust the Z axis along the welding path. The sensor’s autofocus maintains the effective focal length of the welding laser’s objective at its optimal position regardless of the mold’s shape. The sensor measures the distance to the object between the laser pulses and predicts the position of the next point, bringing the welding laser’s beam   to the center of the next welding position. The sensor’s autofocus operates collinear to the welding laser and through the system objective lens.

diagram of an auto-focus laser system based on Optimet's sensor
A diagram of an auto-focus laser system based on Optimet’s sensor. This kind of setup is used in various laser machine companies around the world

There are many applications in which this technology is useful and it becomes more and more relevant with every advance in laser systems. The CNC world is moving to laser-based systems, and this requires more advanced solutions with quicker and more accurate control and feedback.

Accurate laser machining requires precise laser inspection.


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  • Reply

    Can we control the depth of laser for specified length (ex: 3cm or 3 ich or 3 mtr)

  • Fernando Carlos

    We are a portuguese lead crystal and “normal” glass manufacturer .

    We have already a Trumpf laser marking machine, engraving lead crystal and glass products.

    We want to know if you have any sensor to perform auto focus, that can be mounted on a Trumpf machine and if it is able to detect lead crystal and glass products.

    Looking forward to your answer , ASAP.


    Fernando Carlos

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