bielomatik turns to fiber lasers for faster welding of plastics

Sept. 5, 2006
A fiber laser platform helps tackle the problem of plastics welding for a number of critical applications in automotive, medical, commercial, and environmental fields.

bielomatik Inc. of New Hudson, Michigan, has adopted a fiber laser platform in order to help tackle the problem of plastics welding for a number of critical applications in automotive, medical, commercial, and environmental fields.

The fiber laser has matured over the last few years into a robust industrial tool with a unique series of capabilities that enable a wide range of precision materials processing manufacturing methods. Fiber lasers offer low running costs, a fast ROI, a small footprint, and high reliability, and thus enjoy a growing acceptance within the laser-based manufacturing industry as a cost-effective alternative to conventional laser design.

Plastics welding
Laser welding of plastics is today an established process in the mass production of a wide spectrum of components.

For example, many components from the automotive sector that need to combine high reliability with environmental robustness are joined and sealed using laser welding techniques--in particular pressure vessels, tanks, pumps and housings, components with integrated sensors, and other electronic or electro-mechanical assemblies. Other sectors of industry include components for medical technology, household appliances such as telephone displays, biotechnology, and even sport articles.

Now in it's 60th anniversary year, bielomatik has specialized for many years in the welding of plastic parts using a variety of technologies, including hotplate, vibration, and ultrasonic techniques. Any plastics that can be welded using conventional thermal methods can also be welded using lasers, and bielomatik can provide the custom laser welding systems necessary to match customer needs. The company's patented and industry-proven laser welding technique is Quasi-Simultaneous Laser Welding (QSLW).

Some of the advantages claimed by bielomatik over alternative plastics welding methods include a high degree of finish quality, little or no debris, small weld thicknesses, small hear affected zone, and the ability to produce three-dimensional weld seams. Small sensitive parts of thermally sensitive materials as used in the medical and electronics industries can also be effectively handled, and the technique is readily adaptable to both small and large production runs.

In general, a wide variety of small and larger, soft, and even flexible components can be readily joined using a wide variety of bonding geometries, including micro-parts used in high-tech applications. bielomatik has seen the need to swiftly, effectively, and durably weld plastics rapidly increase and diversify for many industrial segments in recent years, in particular for automotive and medical applications.

Laser welding techniques
One common laser welding approach employs a transmissive technique where one component of the joint is transmissive and the other absorptive. The components are held together in a jig and the laser is used to generate heat at the interface--controlled wetting or melting forms the weld. Almost all basic molding is sufficiently transparent for this process. To achieve effective results the absorptive material is often compounded with an additive such as black carbon, talcum, chalk, soot, or glass fibers. Welding seam strength can closely match base material strengths, and is comparable to those achieved in hotplate and vibration welding.

Typical "light and dark" applications include automotive rear lights and headlights and other products comprising a transparent and an absorbing molding. The dominant materials in use are PA 6, PA 6.6, PBT, and various specially developed thermoplastics, for example polypropylene. These components can be colored as required, and even the absorbing molding can have almost any color. The use of special plastics to enhance the process, for example those that appear dark but in reality transmit enough of the laser light, is increasing.

A new process utilized by bielomatik involves the welding of clear or light-colored plastics. In this case, a special coating between the two surfaces to be joined is irradiated with the laser beam. Careful control of clamping forces and the laser parameters ensures proper absorption in the coating with minimum heat generation in the neighboring material. A controlled melting occurs and ultimately a strong, transparent weld.

This type of welding is suitable across a wide range of industries such as micro-medical parts, mobile phone components, and industrial batteries, where welds can be achieved in up to 10mm-thick polymer sheets when using highly intense fiber laser sources.

An important advantage of the Clear-Weld technique is that the coating used to absorb the laser light degrades and the join assumes the appearance of the surrounding material, even transparency.

Tougher assignments
The applications team at bielomatik was recently presented with the challenge of welding water softening tanks made of an ABS material. Initial tests together with a research institute in Ohio using an Nd:YAG laser produced adequate results but weld speed was limited due to beam quality and intensity. For these same reasons, the usable stand-off distances typical of Nd:YAG lasers often restrict access in some welding applications.

SPI lasers plc of Southampton, UK, has been developing fiber lasers for the industrial market for several years, primarily for materials processing applications such as microwelding and microcutting, but also for marking applications.

Although the power requirements for welding plastics are in principal significantly lower than for metals, the 50¿200W range effectively covers most applications¿the wide pulse flexibility (from microseconds to CW) provided by the fiber laser, coupled with it's TEM00 beam quality, provides access to very fast scan speeds, thus also achieving high cm3 weld coverage rates. A 200 W CW/modulated fiber laser produced significantly better results as the beam quality allowed a greater stand-off distance from the work piece (and so greater 3D access) and the beam intensity allowed faster welding speeds or coverage compared to a Nd:YAG laser of equivalent power. According to Jeff Weddell, sales manager at bielomatik, "The difference in weld quality and usability of the fiber laser compared to the Nd:YAG laser was like night and day".

This result is typical of manufacturing requiring a complex mix of optical performance, system flexibility, high yield, high up-time, and exceptional reliability. While many different laser designs have found their way into materials processing applications, fiber lasers help minimize the balance that must be ordinarily struck between production quality and production line speed by providing an extended performance envelope.

Advantage of fiber lasers
Fiber lasers bring significant advantages for industrial applications. To begin with, they do not exhibit the shortcomings in spot size or focus drift performance found in other laser designs¿at all power levels, across all pulse sequences, and during the entire lifetime of the laser, the spot size remains small, predictable, and consistent.

A further advantage is that the small spot size and high beam quality translate to high irradiance at the focus. Coupling these factors with the wide range of control over pulse generation means that plastic welding tools equipped with fiber lasers can produce better results faster and at lower power levels.

The focused beam consistently melts a small area of plastic, with the benefit that very little heat is generated around the weld point. High-quality precision welding can be performed close (0.1 mm) to the most complicated and intricate component parts.

From an economics standpoint, the fiber laser minimizes operational costs with no lamp changes, alignment, or calibration requirements and so reduced maintenance costs, longer up-times, and improved production quality with less scrap. Fiber lasers are also exceptionally physically robust and stable and thus suitable for the most challenging of industrial environments.

These financial and performance advantages mean that fiber laser technology is now frequently chosen as an upgrade over conventional flashlamp-pumped solid state, or even DPSS laser technology in many other laser-assisted industrial manufacture segments. In addition, a small footprint and fast ROI open up markets that were previously out of reach for some applications.

Advantages for industrial manufacturing
In the plastics welding sector, not only are component assemblies becoming increasingly more complex, but at the same time, more and more demands are being placed on their quality and functionality. Today's market is increasingly seeking solutions to combine and integrate a variety of welding technologies.

bielomatik can provide end-users with one-source, integrated system solutions for all relevant welding processes, with capabilities now enhanced by the adoption of fiber lasers for more stringent applications. bielomatik's fast scanning optics are particularly suited for applications requiring high line speed, and this pairs ideally with the capabilities of the fiber laser.

In general, the choice of tooling for any application comes down to determining the required performance followed by a trade-off between initial outlay, component yield, uptime, and maintenance. Fiber laser welding tools enjoy rapid ROI due to high yield, near 100 percent up-time, and near-zero maintenance, meaning that the end-user can focus on business demands rather than having to become a laser maintenance expert.

Bielomatik Inc., New Hudson, Michigan, USA

John Tinson
Vice President Sales
SPI Lasers UK Limited
Tel. +44 1489 779668
Fax: +44 1489 779698
eMail: [email protected]

Gregory Flinn
Putting Photonics into Context, Munich, Germany
Tel. +49 89 95420457
eMail: [email protected]
web: [email protected]

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