The use of various plastics in manufacturing has grown immensely in the last 15 or so years. Weight savings, optical requirements, and flexibility to name a few reasons push the envelope of legacy materials and often times leave plastics as the only logical choice to meet design requirements.
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As a designer or an engineer, you may find yourself trying to decide which joining method is the right one for your next plastic widget and happen to stumble across this revolutionary and seemingly &#;new&#; technology called Laser Polymer Welding (also called Laser Plastic Welding.) What is it you may ask? How does it work? What are the advantages? Will it work for my application?
What is it?
Laser Polymer Welding can be defined as: &#;A method of joining two plastics by subsequent transmission and absorption of laser energy.&#;
While Laser Polymer Welding really isn&#;t a new technology, it is still not quite as well-known or widely adopted as the legacy joining solutions for plastic components such as gluing, fasteners, snap fits, and ultrasonic welding. It is interesting to note that the German automotive industry was one of the first to adopt this technology around 19 years ago. In spite of the fact that it was (and still is) a revolutionary technology, it took many years for other industries to adopt it. I fully believe that in today&#;s market, medical device manufacturers and consumer electronics companies stand the most to gain from implementing Laser Polymer Welding.
How does it work?
When two plastics are clamped tightly together, a laser beam in the nm range penetrates the upper layer and is absorbed by the lower layer which in turn is heated by the laser energy and transfers this heat to the upper layer resulting in both of the plastics melting and mixing to form a bond that is virtually as strong as the base material.
Key advantages of Laser Plastic or Polymer Welding (among others of course):
Laser Polymer Welding picks up where other joining technologies leave off&#;
Will it work for my application?
With the above advantages of laser plastic welding being so attractive, quite often engineers will inquire looking to see if Laser Polymer Welding might be able to replace their current joining solution on a product that is already in mass production. In these cases, I counsel them that if the current joining solution is working and there are no prevalent issues such as excessive-quality fallout or cosmetic irregularities, then Laser Polymer Welding may not be the best approach because of the relatively high cost to implement it this late in the game.
It is highly recommended that designers and engineers reach out to an expert long before a design is frozen so they can receive proper guidance to design a laser-weldable joint and eliminate the potential for costly mistakes.
For those that are researching Laser Polymer Welding for implementation into a new product that has not been designed frozen, it would be beneficial to consider the below points:
I would like to conclude this article with the following:
If there is a need to eliminate quality problems and miniaturize designs, all while avoiding damage to sensitive electronics&#; Than Laser Polymer Welding is the right choice for your design!
Aluminum has certain properties which make it more challenging to weld than other metals. Its relatively high thermal conductivity (approx. 209 W/m K) and low melting point (1,221°F/660.3°C) make it such that only fusion welding processes can be used to weld it.
Fusion welding processes, such as MIG, TIG, Laser, and Electron Beam, generate intense heat in a small area to melt the material in the desired weld area. This small heat affected zone is essential as aluminum&#;s high thermal conductivity tends to result in heat traveling throughout the work piece, either melting too much material or deforming the entire part. The amount of heat applied and the location to which it is applied must be controlled very precisely. Manual welding processes, such as MIG and TIG, rely on operator skill and heat sinking to control these factors. Because aluminum doesn&#;t change in appearance as it approaches its melting point, welding processes which require visual judgment of material readiness can be unreliable. Automated methods, such as Laser and Electron Beam, which use computers to control feed rate, power, and weld location, offer more precise and consistent weld quality.
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Another challenge of welding aluminum involves the formation of oxide film on the work surface. The melting point of aluminum oxide is approximately 3x the melting point of pure aluminum, which can result in particles of aluminum oxide contaminating the weld and leading to porosity issues. In most cases, oxide film must be removed either by mechanical or chemical means prior to welding. Aluminum oxide can affect laser welding: oxide films can change the reflectivity of the parts surface, which negatively impacts the amount of laser energy making it to the base metal.
Hydrocarbon contamination of aluminum during storage and preparation of the material can cause problems when welding. Aluminum parts are frequently formed, sheared, sawed and machined prior to the welding operation. If a lubricant is used during any of these pre-weld operations, complete removal of the lubricant prior to welding is essential to avoid bad welds. Prudence dictates that aluminum parts which are to be welded should be pre-weld processed in such a manner that minimal to no lubricants are used &#; sawing and machining of aluminum should be performed dry, if possible, and if not, the parts must be thoroughly cleaned.
Laser beam welding is one of our most popular services for welding aluminum. The process is ideal for fast, clean welds. The heat affected zone is minimized and weld penetration can range up to 0.25&#; in aluminum. Laser beam welding can be used with crack sensitive materials, such as the series of aluminum alloys when combined with an appropriate filler material such as or aluminum. There are several different types of lasers that work well with aluminum, and often the use of a cover gas is prudent.
The amount of pre-weld preparation is largely dependent on the condition of the aluminum parts to be welded, and that is generally dependent on the storage conditions and the cleanliness of the machine procedures used to make the part thus far.
To avoid oxide films and hydrocarbon contamination, aluminum to be laser welded must be thoroughly cleaned. This is often achieved mechanically, using stainless steel wire brushes, grinding, filing or scraping to remove any oxides. Alternatively, there are chemical cleaning methods utilizing immersions in caustic solutions and water that are effective at removing aluminum oxide.
Hydrocarbon residue on aluminum parts can generally be removed using acetone or alcohol based solvents. Avoid using chlorinated solvents in the welding area because they may form toxic gases when heated. Hydrocarbon contamination must be removed before abrading the surface to remove aluminum oxide.
A very important aspect to welding aluminum is how the joint is fabricated. Special care in machining and assembly must be taken because aluminum is softer than most metals. Contaminants can easily be transferred to a part and then pushed under the surface of the joint.
Laser welding requires a fairly precise joint in order to maintain permissible gap and mismatch. Good weld fixturing is necessary so that the laser beam can be placed accurately. Laser welding and cutting are thus inherently machine guided processes.
There are four main categories of lasers that are suitable for welding aluminum:
All of these technologies are capable of producing high quality aluminum welds, and the method to be used is often dependent on operational costs rather than weld quality. However, each process has slightly different characteristics which can make some types of lasers preferable for certain applications, joint configurations, and aluminum alloy combinations.
Laser beam energy can be applied to the work piece either as a series of pulses, as a continuous beam, or in a laser stir weld configuration. The decision to use a particular method is dependent on the application, the properties of the materials, etc.
A pulsed laser is exactly that: the beam is switched on and off at a very high rate (10- hz) such that the energy applied to the work piece is a series of separate bursts. Each pulse creates an area of melted material, the work piece is then moved slightly and another pulse is applied, resulting in a series of overlapping welds creating a continuous bead. Each weld area created by a pulse cools quickly, which minimizes the amount of heat in the surrounding material, which in turn limits how hot the part might become, which in turn minimizes melting and distortion of the part. Because of aluminum&#;s high thermal conductivity, a pulsed laser is generally the best way to laser weld aluminum when low thermal input is required.
Continuous wave laser welding is used for deep penetration welds, and is often referred to as keyhole welding. A steady beam of laser light is applied to the work piece, which is then moved beneath the beam. Material on the leading edge of the laser beam melts as the trailing edge cools. Continuous wave lasers typically feed at speeds of 25 to 100 inches per minute in order to not overheat the parts. Because heat is applied at a constant rate, and the part is not subject to the constant heating and cooling of a pulsed laser, continuous wave welding may be better suited for some of the more crack sensitive alloys of aluminum.
Laser welding aluminum without cracking is a constant challenge. The standard technique when welding crack prone alloys is to use a filler wire or shim made from a more weldable alloy (such as ) in order to achieve quality weld joint. For welding heat sensitive components, such as electronics housings, using filler materials and welding with a pulsed laser is indicated. However, for welds with deeper penetration in crack prone aluminum alloys, we&#;ve had a lot of success using our proprietary Laser Stir Welding technique.
Laser stir welding is a process in which a continuous beam laser is oscillated at a relatively high frequency, which causes a stirring action within the molten weld pool &#; hence the term &#;stir welding.&#; The result is a manipulation of the weld pool/vapor cavity, which changes some key characteristics of the weld.
Benefits:
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