Especially in the automotive industry, high-performance polymers are increasingly replacing assemblies made of metal and conventional engineering plastics, but their properties often present new challenges for joining technology. With novel laser system technology, even demanding materials can be joined.

Cross-section of a weld seam: The microsection of the seam shows a joining zone and characteristic melt flow for quasi-simultaneous welding

Novel Laser Welding Technology Can Also Be Used for Higher Filled PPS Types

Laserschweißen

Verbindungstechnik Verfahren

Thermisches Fügeverfahren

Laserschweißanlagen

Verbindungstechnik

Schweißanlagen

Lasertechnik

Glass Fiber-Reinforced Polyphenylene Sulfide Made Weldable

Transparent functional and design elements often consist of glass and plastic materials. But there may be problems in bonding them. High-strength hybrid connections are made possible with a two-step process, in which a laser first creates micro- and nanoscale structures in the glass, into which the plastic melt can subsequently penetrate.

Laser structuring of a glass sample by means of CO2 laser radiation: the microstructures are introduced into a glass substrate with a thickness of 3 mm at spacings of 1 mm. This is performed by means of a scanner system, which guides the laser beam over the glass substrate in multiple passes at high speed. When the laser beam impinges on it, the material is vaporized; the ablated particles can be seen as a yellow jet of flame 

Innovative Glass-Plastic Hybrid Combinations through Precise Laser Structuring

Hybridtechnik

Kunststoffverarbeitung: Verfahren

Spritzgießen

Laserstrukturieren

Oberflächentechnik

Laserbearbeitungen

Uniting Glass and Plastic

Carbon fiber-reinforced plastics (CFRP) are being used in more and more components. Their production is also becoming more and more effective. In the event of damage, however, business continues to be carried out manually. For this reason, greater automation is desirable when repairing CFRP. Automated laser processes could be one way of doing this.

Stepped scarfing on slat demonstrator: scarfing is a challenging step in CFRP repair

Automated Repair of Carbon Fiber-Reinforced Plastics

Kohlenstofffasern / -matten

Kunststoff Werkstoffe

Verstärkungsstoffe

Verbundwerkstoffe / Werkstoffverbunde

Faserverbundwerkstoffe

Andere Werkstoffe

Laser Substitute Manual Work

Touch-sensitive lighting modules that are the size of a palm and about as thin as a matchbox can create varying light mosaics thanks to digital control. The electronics behind this construction are situated in a flat plastic housing and are securely welded using laser technology for their protection.

When the mosaic surface is swiped, the modules light up in the desired colors in the touched areas

Luminous Mosaics with Laser Welded Electronic Modules

Elektronik-Fertigung

Elektronik

Colors at Your Fingertips

Thanks to technical advances which have made implementation easier, laser butt welding which was invented in the 1990s is now about to make the breakthrough. Aside from high-wall parts, it can be used to weld same-material polymers using precision laser technology.

Turn2Weld technique: the newly developed welding machine uses one laser per part and swivels the machine tables through 90° toward the laser scanners with the aid of servo motors

Advanced Laser Butt Welding for Joining High-Wall and Same-Material Parts

Halbleiterlaser, Diodenlaser

Photonik

Polycarbonat

Thermoplaste

Welded from the Ends

Since 1 November, Okke Ottenlinger has been the new Managing Director of the Chinese subsidiary Evosys Suzhou Laser System Co. Ltd.

Okke Ottenlinger, General Manager of Evosys Suzhou Laser System in China

Evosys Appoints Okke Ottenlinger General Manager in China

Since the beginning of the year, Evosys Laser with its representatives TRUmachines in Poland and Tamsa Makina in Turkey has strengthened its global presence.

Since the beginning of the year, the company Tamsa Makina from Istanbul is an Evosys representative.

Evosys Expands Presence in Poland and Turkey

Wide Area of Application. Up until now, laser-welding of clear-transparent components was not possible, because these materials did not absorp the laser beam. A new method involving the application of a special dispersion yields almost invisible welding seams. 

Laser Welding Transparent Parts 

Previously mainly diode lasers were used as beam sources for welding plastic. The spectrum of plastic welding has been expanded enormously thanks to advances in the field of fiber lasers. 

Welding: Laser Beams Precisely Controlled 

The great range of combinations of plastics in association with a steadily growing diversity of colors is constantly followed by advances in laser welding technology. The joining process is now usable in almost all common sectors. 

Diode Lasers: Diversity in Joining 

Despite the vast amount of joining elements and processing techniques available, the sector, while searching for gaps in the market, is continuously finding new elements and devices for manual or automatic joining processes. Producers’ endeavors are focused on meeting the strong demand for cheap joining techniques as well as paying account of the different requirements involved in special applications. 

Schmelzschweißen

Schraubtechnik

Joining Technology (Trade Fair Report Fakuma 2009): Joining and Dissolving 

Balloon dilation catheters used to expand the coronary vessels not only must be leak-proof but are also subject to tight tolerances. A CO2 laser integrated into a welding system ensures the requirements are implemented in series production, while making for a robust process that offers short cycle times. 

Medizintechnik

Medical Technology: Leak-Proof All Round 

Infusion pumps are used to administer drugs and must therefore be capable of accurate dosing. This places very high demands on the production process. A new, physically driven pump is now being assembled on the production line by laser transmission welding. 

Medical Technology: Clean Connection 

Laser staking is a new method for positive connection of two components by plastic deformation of one of the two components. The sturdy and matured basic technology of laser transmission welding offers the necessary reliability here for use in automated production. 

Laser Technology: Riveting with Light 

Selected plastic-metal joints can be produced with high strength using thermal joining methods. The fundamental principles for an improved process compared with the joining methods to date have been developed with the framework of a Cluster of Excellence at RWTH Aachen University. This method opens up new design possibilities, in particular for lightweight construction. 

Verbindungstechnik, hybride

Lightweight Construction: A Strong Connection of Unequal Partners 

Welding in Mind When Designing  a Product

Laser polymer welding offers several advantages over other joining methods, but implementing it right requires an understanding of the technology, and often benefits from discussions with a knowledgeable equipment supplier early on in the product development cycle.

The increasing use of polymer parts, especially in high precision products, is driving manufacturers to look for joining technologies that offer better welds, increased production throughput and reduced costs. Laser polymer welding promises to deliver in all of these areas. But, getting a laser process implemented so that it consistently produces optimum results and minimizes cost requires an understanding of the technology. And, it is often helpful to partner with a vendor that is expert with it as early as the product design phase to accomplish this. This whitepaper reviews the basics of laser polymer welding and outlines some of the key issues that should be considered before starting production.

Polymers offer several unique characteristics and advantages over other materials. These include a high strength-to-weight ratio, mechanical flexibility, corrosion resistance, biocompatibility, electrical and thermal insulating ability, and even optical transparency in some cases. In terms of manufacturing, polymer parts can often be produced using various molding techniques. These methods offer high production throughput and low unit cost.

All this has led to greater use of polymers in areas as diverse as packaging, automotive production, microelectronics, and medical devices. A common requirement across many of these applications is for joining of two or more polymer parts during product assembly. For applications involving sophisticated products, such as medical implants and electronic sensors, this joining must be accomplished with high mechanical precision, minimal particulate debris production, and excellent bond strength.

For volume production, this is usually done using some kind of welding, rather than simply gluing. This is because welding can usually be performed much faster and more accurately than adhesive bonding, and makes a stronger and more reliable connection.

There are numerous different polymer welding methods in use. Usually these involve selectively melting the material using applied heat, through friction or vibration, or even by the use of chemical solvents. Each of these techniques has its advantages and uses.

Laser polymer welding has become increasingly popular for the most demanding applications because it delivers a unique combination of advantages (Table 1).

Laser polymer welding utilizes a laser as the heat source to melt the material. There are many different ways this can be implemented depending upon the materials being joined, the specific requirements of the application, and various production considerations such as cost or speed.

One of the most useful and commonly employed techniques is called “through transmission laser welding” (TTLW). This method involves joining one part made from transparent plastic to another which is opaque. In this instance, “transparent” and “opaque” specifically refer to whether or not the parts absorb or transmit the wavelength of the laser being used, as opposed to being visually transparent or opaque (Fig.1).

There are several different ways that TTLW can be performed depending upon the part size and shape, the required throughput speed, the desired weld quality and characteristics, as well as other factors. One of the most useful and versatile of these methods is called quasi-simultaneous welding.

In quasi-simultaneous welding, the two parts are either clamped together or brought into direct contact, with the clear part on top. The laser is focused in through the clear part, and down towards the opaque one. The opaque polymer absorbs the laser light, heats up and melts. The heat from it also melts some of the clear part.

The laser beam is rapidly scanned to trace out the pattern of the desired weld seam. Typically it is scanned over the pattern numerous times, and has the effect of melting the entire weld path simultaneously (hence the name). After the entire weld path is molten, the laser is turned off, and the melted material quickly resolidifies to form the weld joint.

Quasi-simultaneous TTLW is a fast, versatile method that provides excellent bonds and high production throughput. It is most useful for welds seams that are entirely in a single plane (flat), or have minor height changes.

Works without Tight Tolerances: Collapse Rib Method

One particular part configuration frequently used for quasi-simultaneous TTLW is called the “collapse rib” method. Here the bottom part has a thin protruding rib which mates into a corresponding groove in the top part. However, the groove is a bit wider than the rib.

The bottom rib is partially melted by the laser during welding while clamps actively press the two parts together. Some of the bottom rib becomes molten, and this material flows and fills some of the gap between the top and bottom parts. This then resolidifies to make the weld joint (Fig. 2).

This particular embodiment of TTLW is especially useful because it delivers a good weld joint even if the parts are not perfectly flat or tightly toleranced. Moreover, the “collapse height” – that is, the amount that the top part moves down during the welding process – can be monitored and used for closed loop process control. This enables very consistent results in volume production, even in the presence of part-to-part variations in dimensions or material absorption of laser energy. It can even compensate for changes in laser output power or focused laser spot characteristics.

Criteria for Successful Transmission Laser Welding

When using transmission laser welding of polymers, some details have to be considered. Some of them have to be regarded already in the product development or before starting production:

<ul><li>Material selection: It is essential that there must be some temperature range over which both polymers (clear and opaque) will remain molten (but not decompose) for the method to work. The greater this overlap, the wider the process window. And, a wider process window makes production easier and more robust. Figure 3 summarizes which common polymer combinations are compatible with laser welding.</li><li>Design for manufacturing: For example, implementing the collapse rib method requires a part design having sufficient space in the appropriate location for the clamps to engage during welding, while also permitting unobstructed access to the entire weld path for the laser beam.</li><li>Dimensions and shapes of the rib and groove: They must also be chosen to provide enough material for the welding process and to accommodate the melt flash that is produced. In addition, it is necessary to design the parts to allow for a sufficient collapse height. For high precision applications, alignment features, such as locating pins, may have to be incorporated into the part design. The goal is to achieve a strong weld and good weld cosmetics, while eliminating the need for post-processing to trim or remove flash.</li><li>Process development: Picking the right laser source for the polymer materials to begin with, determining the optimum laser operating parameters, and identifying what process variables must be monitored or controlled to achieve the desired yields. There may also be various practical issues in terms of part handling, the mechanical and software interface of the polymer welding system with other production equipment, and, of course, cost of ownership.</li></ul>

Service Providers Support  System Configuration

The simplest way to address all these factors is to partner with a supplier who can provide applications development assistance. Specifically, this means finding a vendor who can run tests to determine what system configuration will yield best results, and perhaps even help identify the optimum laser parameters for the production process. Coherent Labs provides precisely that service, and Coherent also produces laser polymer welding systems that are readily integrated into production environments.

In conclusion, laser welding enables precision joining of polymer parts, and is a cost-effective method over a wide range of production volumes. It can help deliver on the promise of polymers to lower cost, save weight, and provide advanced functionality in a wide range of products.

Coherent Munich GmbH & Co. KG  

https://www.coherent.com

Ausgabenartikel

Fig. 3. Material combinations which are compatible with TTLW.

In quasi-simultaneous welding, the laser beam is scanned rapidly over the entire weld path in order to melt it all at once (simultaneously). 

16:9

Table 1. Advantages of laser polymer welding.

Fig. 1. In transmission laser welding, a laser beam passes through a clear plastic part and is absorbed by an opaque part beneath it. This heats the bottom part and melts it to weld the parts together.

Fig. 2. Schematic of the major steps in the “collapse rib” method of quasi-simultaneous TTLW. 

Name - Hauptartikel

 David Bosom is Product Line Manager for Polymer Welding Systems at Coherent.

Read the German version of the article in our magazine Kunststoffe or at <a href="https://www.kunststoffe.de/a/fachartikel/beim-produktdesign-schon-an-das-schweiss-2673726" target="_blank">www.kunststoffe.de</a>

issue 06/2022

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