Monday, November 28, 2016

Laser Solutions to the Transport and Aerospace Industry

With mounting pressure to speed production, advanced polymer thermoplastic composites are rapidly gaining acceptance amongst both the automotive and aerospace industries. These polymer materials are strong and lightweight, making them ideal for reducing weight and meeting stricter fuel efficiency and crashworthiness regulations. However, the inhomogeneous nature of composite materials is far from ideal for ablative lasers.

For example, polymer composites, by their nature, contain a variety of materials with at least one reinforcement material and at least one matrix which supports the reinforcement material. The mismatch between the conductivity of carbon fiber-reinforced polymer and the epoxy matrix makes traditional laser cutting nearly impossible. Epoxies are a type of thermoset polymer.

The challenge for laser processing involves the fact that each component has its own unique physical properties which are also highly anisotropic. Imagine a composite with two or three different melting points and how that might affect a traditional laser. These incompatibilities render traditional lasers ineffective for polymer composites.

Though challenging for the laser industry, solutions are emerging. Here's a brief overview of some of the new technologies and processes recently discussed in an article featured in Industrial Laser Solutions for Manufacturing.

Laser Solutions to Polymer Composite Challenges

Fiber Lasers - Fibers are commonly used as reinforcements due to their high surface-area-to-volume ratio and strength. Fiber lasers are emerging as the leading choice for composite processing. With a fiber laser, the beam is generated inside the fiber. With the light inside the fiber, the beam can easily and precisely be focused. Fiber lasers have the highest focusability and high average power, near infrared properties, making them suitable for cutting and welding of both metal and composite polymer materials.

Using Lasers to Improve Adhesive Bond Strength - The auto and aerospace industries also use lasers and other composite processes to improve adhesive bond strength. For example, lasers are now used to clean composite surfaces before applying adhesive bonds. Lasers eliminate the need for preparing materials for bonding with chemical or mechanical abrasion.

Localized Repair - One of the problems with composites involves localized damage. Lasers are starting to be used to repair this damage using ablation and adhesive injections. Localized repair is an emerging technique that is still being explored.

Laser Welding - According to Coherent, joining composite materials requires different approaches than when joining metal materials due to it the composite material's properties. For example, riveting can weaken or damage the composite material as discussed earlier. Laser welding becomes possible when at least one of the welding partners has a thermoplastic resin and one partner is transmissive to radiation. If the CFRP partner is a thermoset, it must be pre-processed prior to laser welding. This involves laser ablating of the reis to reveal the fiber structure. While the open fiber structure improves shear strength, it also affects absorption. Coherent recommends keeping the welding temperature constant with a pyrometer to improve weld quality.