Laser marking provides a fast, high contrast mark on a variety of surfaces. That’s easy if that surface is static; but what if it is moving rapidly past the laser?
Andy Hales, Project Sales Engineer at Pryor Marking Technology explains how laser marking ‘on the fly’ can be integrated into a fast-moving production environment.
Fast, accurate, high-contrast marking using specialist laser systems that apply, for example, two-dimensional Data Matrix codes on components, is widely deployed in industry for part or material identification. A clear, easily read mark is essential and nowhere more so than for industries that must achieve 100% traceability of manufactured parts or materials, such as aerospace, automotive and pharmaceuticals.
Where the manufacturing process is of a stop-start nature or confined to a single assembly cell, components are easily marked in situ when they are in a stationary position.
However, many manufacturing processes involve fast-moving production lines and in order to maintain product flow rates without interruption for marking, parts must instead be marked while they are in motion. This process of laser marking a component as it moves rapidly past a fixed laser is called ‘marking on the fly’, a technique that can avoid additional cycle time in the manufacturing process.
The below video shows a demonstration production line with Integrated On-the-Fly Laser Marking:
While clearly desirable for fast moving production lines, marking on the fly does require a special hardware configuration and appropriate software control. The static laser head needs to track the speed of the component in order to mark in the correct place without distortions arising from variations of line speed. The laser set-up is further complicated depending upon whether discrete components are being conveyed or raw material such as metal strip or extrusion is being continuously fed.
Where discrete components are concerned, proximity sensors detect each component as it approaches the laser marking site. In order to establish the correct sequence of events, the sensor detects the leading edge of the component and, based upon the instantaneous conveyor speed, the software determines the moment the laser is fired to apply the mark correctly. For continuous raw materials, such as coiled steel strip, line speed must be tracked using an encoder fitted to the conveyor in the vicinity of the laser station. The control software will initiate marking at predetermined intervals based on line speed.
Mark on the fly systems normally have a predefined marking ‘window’, which is an area of the component within which the mark, be it text or Data Matrix code, must be wholly contained. Pryor’s standard marking window, for example, is 100 square millimetres. The laser receives its marking initiation when the leading boundary of the window arrives; the marking must be completed before the trailing boundary of the window passes.
In both cases, discrete component and continuous raw material, the rate at which the laser etches the mark will be synchronised with the line speed to ensure that there is no distortion of the mark. Line speeds vary enormously. The major part of Pryor’s work in this area has concentrated on the marking of metallic components and raw materials, the former passing the laser station at anything up to two parts per second (the marking duration being 0.2 seconds or less), and the latter ranging in the hundreds of metres per second. For much faster line speeds, the marking window can be enlarged, a higher power laser deployed or multiple lasers to make alternating marks. Pryor’s marking on the fly stations use fibre lasers as the preferred option because of their relative simplicity, controllability and precision.
As with all marking systems, static or on the fly, it is essential to verify the format and quality of the mark, as soon as it has been applied.
Pryor offers a solution in the form of a dedicated verification system called VeriSmart 2.0, which can be integrated with the marking equipment or positioned downstream of the marking station. This operates on a similar principle to conventional code reading systems, but instead of a Data Matrix reader it uses a high resolution imaging camera in combination with a controllable lighting arrangement.
In addition to checking that the correct data has been marked on the part, these systems also ensure compliance with international marking standards; and they can do all that within the cycle time of up to two parts per second. One of the biggest challenges, however, is getting the lighting intensity and colour right. Modern verification systems such as VeriSmart can adjust their lighting and calibration settings automatically to provide a robust reading for every part.
Other than the basic hardware, there is no ‘off-the-shelf’ solution to satisfy all marking on the fly needs. Each application is unique, often requiring close integration into existing production lines and control systems. In such cases the advice of an experienced supplier (like Traceability Solutions Asia) can be an invaluable aid to successful implementation.