Product designers and process engineers considering laser welding as an alternative to more conventional types of welding, such as MIG/TIG arc welding, will find each has its plusses and minuses. But for many applications laser welding is a cleaner, more precise, and more controlled method of welding and is especially much faster and better controllable.
Before comparing the two methods in detail, it’s helpful to review how each of them works:
In laser welding a laser beam is focused to a point usually just below the surface of the metals to be welded, causing the metals to heat and melt at the point of the weld. In their liquid state the two metals combine so that when they cool they are bonded. The laser beam has a high-power density (typically 10 MW/cm²) producing very small, Heat-Affected Zones or HAZ zones. These are typically fractions of a millimeter to a few millimeters in diameter and they heat and cool very rapidly.
Say the word “welding” and most people will immediately think of a person holding an acetylene torch like the kind they may have used in high school shop class. Today’s industrial welding, however, is typically arc welding in which the heat source is an electric arc formed between an electrode and the base metals being welded. The two main types of arc welding are TIG and MIG.
In TIG (Tungsten Inert Gas) an inert gas flows around the electrode to protect the weld from contamination. In addition to the electrode the welder also holds a stick of filler (flux) that melts in the heat of the arc and that, when cooled, bonds the metals. Excess filler that solidifies around the weld, called slag, must then be removed, usually by grinding. As filler sticks are con- sumed during welding they are replaced.
MIG (Metal Inert Gas) is similar to TIG except that the electrode itself is composed of the filler material. The electrode is therefore consumed during welding and must be replaced when depleted.
Types of material to be welded. Lasers can weld many types of materials together including many types of stainless steel, titanium, copper, and aluminum (although the two pieces being welded must be different kinds of aluminum). However, not all metal combinations are “bondable.” In conventional welding the metals don’t bond directly with each other but with the filler. So metal-to-metal compatibility is not an issue — which is why conventional welding can weld more types of metal than laser welding.
Material thickness. Laser welding is suitable for jobs ranging from as thin as 100µm up to about 8 mm (in the case of steel). That means that laser welding can be used for jobs where the metal is so thin that conventional welding would destroy it. On the other hand, conventional welding can easily handle large pieces — such as large pipes or structural beams in a building — that laser welding can’t.
Precision. The power output, size of weld, depth of weld, speed of weld, and the track of the laser beam on the metal surface are all highly controllable. The result is a very precise weld — you heat just what you want to heat to the degree you wish to heat it. Among other advantages versus conventional welding, there’s less likelihood of damaging or deforming the surrounding surfaces or components like electrical components that may already be installed.
Automation. Another benefit of a highly controlled process is that laser welding is highly programmable and robotic. Since it’s easier to automate compared to MIG or TIG welding methods, greater repeatability and faster throughput can be achieved.
Contamination. With laser welding, the only materials involved are the metals to be welded. For best results the metals must be cleaned of any oil and dirt prior to welding. The welding itself introduces no filler or slag that could contaminate application environments, such as an operating room in the case of surgical instruments.
Environmental impact. A cleaner process also means there’s much less impact on the environment.
Corrosion. With some metals such as steel, aluminum and titanium alloys, brittleness can result from conventional welding if the electrode used for welding contains traces of moisture. The heat of the welding causes the water to decompose and release hydrogen that enters the metal causing it to become brittle. This can’t happen with laser welding because there is no electrode.
LASER WELDING ADVANTAGES
- Cleaner — no excess bonding material or slag to clean off
- Less possibility of contamination
- Can weld more complex shapes
- More precise — for smaller objects, tighter spaces
- Can weld thinner metals
- More highly repeatable results
- Easier to automate
- Less chance of deforming or damaging nearby areas
- More environmentally friendly
- Less likely to corrode
ARC WELDING ADVANTAGES
- More suitable for welding large structures
- Wider range of materials can be welded
- Can weld thicker materials
Arc welding as a production process took a long time to become established, but has nevertheless been around since the 1940s. Although the laser was only invented in 1960, it quickly became established as a production process and by the 1980s was starting to be used in high volume manufacturing. Recent advances which have improved the beam quality and efficiency of lasers, make the laser an even more advantageous solution to high volume or automated industrial joining.
Weld quality and consistency
Laser welding enables the quality and consistency of welding to be readily controlled and consistently maintained. Since the laser head makes no contact with the workpiece and there is no electrode which can become worn, eroded or damaged there is no need for a tool change where the electrode needs to be reground or sharpened, as is the case with TIG. The lack of electrode dressing in laser welding results in higher uptime and longer time between maintenance interventions. Also, there is no risk of contamination of the weld material with Tungsten from the TIG electrode tip when striking the arc.
Lower heat input
With laser welding the heat input to the metal being welded is lower which means there is a smaller heat affected zone (HAZ) and the distortion of the assembly is vastly reduced making complex and accurate assembly more achievable, especially in an automated setting. In addition, the lower heat input means that a weld can be placed close to sensitive electronics or other heat-sensitive materials without risk of damage or failure. An example of this is in cardiac pacemakers and defibrillators where the external weld seam is directly above a heat-sensitive battery and micro-electronics which cannot withstand a temperature over 80 degrees C.
Throughput – higher welding speed
Weld speeds are generally higher with laser welding, especially with modern high power continuous wave (CW) fibre lasers. A high welding speed sometimes means that the motion system, for example the CNC system or robot contouring speed, is the limiting factor on cycle time rather than the process.
Cost per metre of weld
In processes where throughput is high it is common to find that the laser solution is more efficient and results in a lower cost per metre of weld. Interestingly, there are processes which combine laser and arc welding to achieve deeper penetration and higher welding speeds. These hybrid processes typically use a combination of laser welding to heat the metal efficiently to melting point and arc welding to provide deposition of droplets into the weld pool and enhanced penetration and weld strength over either process as a stand-alone procedure.
No finishing of the weld
With inert gas shielding, a laser weld in stainless steel or aluminium normally requires no post-processing (grinding or dressing) after welding, the weld finish is bright and oxide free and can be typically coated or painted without further cleaning steps.
Access difficult areas
Since the laser beam is a “line of sight” process, the laser can pass through gaps in a structure to weld areas from the rear, where it would not be possible to introduce a TIG electrode. Using a camera to view through the laser optics, it is easy to align the beam to a precise feature and perform welds in difficult-to-reach parts of the structure.
What about gaps?
One disadvantage of laser welding is that it tends to rely on good contact and minimum gap between parts to be joined, but with the wobble solution, this disadvantage disappeared completely. With either a laser process or even more with a TIG weld, there is a need to ensure that gaps are minimised or avoided to ensure good results. With the addition of wire feed, which adds a certain complexity to the process, it is possible to fill gaps or build up areas for additional strength.
For ease of automation, consistent quality and lack of post-processing there are clear advantages to using laser welding. Where welding is to be applied manually, TIG welding has greater flexibility and lower capital cost for the equipment.
The value of laser cutting, welding, marking, drilling, and other laser machining techniques has become increasingly known in the medical industry, causing further evolution of laser machining technologies to serve medical device manufacturing needs. Laser working resolutions/tolerances have improved dramatically, speed has increased.
Following are eight key benefts of laser machining that applies to many different medical industry applications.
1. Precise Temperature Control.
The high-performance materials used today in the industry often have desired material properties that are extremely sensitive to severe temperatures. Many special metals behavior are adversely affected by the temperature profles typical in Tig and Mig welding processes. Fortunately, laser welding of this special metals, and other delicate materials can be performed reliably with minimal heat-affected zones (HAZ) by laser welding. The temperature exposure of a material during laser manufacturing can be controlled in the range of micrometers, including how deeply the beam penetrates a material. The ability to program and precisely control the laser's output power and material exposure time, makes laser cutting a highly reliable and repeatable process.
2. Incredible Geometric Tolerances.
High-Tech device's geometric features are becoming more complex and new applications and techniques are being pioneered. Moreover, these new geometries often require much tighter manufacturing tolerances that are extremely repeatable. Modern laser machining beam widths are extremely small, some laser frequencies are even small enough to provide tolerances in the realm of tens of micrometers. Laser machining controllers are also extremely precise and consistent in the cap X and Y plane, allowing for complex and tightly spaced curves and segmentation during laser welding of fine wires. Automation features available with laser welding tools also enable much smaller tolerances with software-driven operation based on CAD Models. Benefts : technology is advancing rapidly with designers exploring various metal combinations for longer resistance and durability. Combinations like titanium and steel become challenging to weld properly and cleanly with any other method than fiber laser welding.
3. High Repeatability.
The level of automation and software control driving some robotized laser welding processes, as well as the very tight tolerance control, provides a level of repeatability and quality diffcult to achieve with other manufacturing technologies and methods. The precise control of laser power, pulses, and processing temperature further enhances the overall repeatability of laser machining. Laser machining systems also have very high up-times with little need to re-tool processing components, which means there is little variation in the machine itself from part-to-part and batch-tobatch. Laser machine operators familiar with mechanical manufacturing qualifcation requirements may also have expertise in methods to enhance overall repeatability and qualifcation assurance protocols.
4. Faster Processing Speed and Shorter Lead Times.
As many mechanical devices designers may be interested in iteratively improving a design with a short delivery window, or prototyping several design variations simultaneously, cost effective and rapid manufacturing is often a necessity. Traditional precision manufacturing technologies, such as CNC machining, EDM, and
casting sometimes require substantial lead times for fxture, tool, and mold designs. Making modifcations to these processes can also incur large extensions on lead times, as well as huge costs in the case of mold making. The software driven approach to laser machining systems and simplifed setup enables much shorter lead times and faster job processing speeds. Also, the high up-time of laser machining tools means that there is very little lost time, and job-to-job transitions can be performed without long tool cool-downs and warm-ups. As with most manufacturing and mechanical technologies, time is money, and laser welding tools provide competitive advantage for prototyping and production volume manufacturing.
5. Reduced Contamination from Flux, Pigment, and Debris.
Many mechanical device and appliance technologies are required to pass strict safety requirements and quality assurances protocols. Areas where contamination
is a particular concern are with high-tech appliances. Most traditional machining technologies produce a substantial amount of debris, or involve complex chemical processing stages. Flux, pigments, and solvents must thoroughly be removed to meet the stringent quality requirements. In the case of laser machining, many of these steps are unnecessary, as laser welding, and other laser processes don’t require any chemicals, ﬂux, or pigments and the laser machining produces minimal debris.
6. More Durable Weldings.
The rigorous sanitation requirements for many high-tech appliances and tools frequently requires the tools to be placed in extremely harsh sanitization chemicals or under high heat and moisture environments. Most welding technologies, and even early laser welding, had diffculty maintaining welding that doesn’t ﬂake, erode, or develop oxides or corrosion byproducts. The latest laser welding techniques are precise and controlled enough to produce marks that don’t produce debris.
7. Reduced Machining Costs and More Cost Effective Validation.
High-tech devices and appliances requirements often place them in a high cost category for traditional machining. The levels of precision, repeatability, and
purity expected for this complex applications may be far too expensive to be performed by technologies other than laser machining. Modern laser machining
tools require very little maintenance and can readily be automated, reducing the overall cost of operation compared to many machining technologies.
Validation protocols required by quality assurance standards can also often be performed easily with laser machining technologies high controlled processing features, further reducing the manufacturing overhead for laser machining services, respectively.
8. Enables Advanced Materials and Approaches.
The latest mechanical devices are often high-mix parts with a wide range of materials in a single part. Part sealing, mixed material welding, and machining of a wide range of materials is often required to produce a single device. The precise control over the laser beams frequency, power, and pulse enable laser machining technologies to operate on a very wide range of materials. Various and mixed metals and polymers can be laser welded, including clear polymers and the latest in organic bio-absorbable material
- Are you looking for a very precise weld?
- Do you require an intricate weld pattern or is the area to be welded difficult to reach?
- Is minimal cleanup, low contamination risk, and low environmental impact important?
- Do you need to integrate welding with other manufacturing steps — so automation and high repeatability are both key?
If you answered yes to any or all of these questions then you may wish to consider laser-welding, especially if the metals to be welded together are thin. One way to know for sure which method of welding is best is by discussing your application with a laser-welding expert first, before you commit to a process.