When it comes to metal laser cutting, one crucial factor that often goes unnoticed is the impact of material stresses. These stresses can have a significant effect on the quality and accuracy of the cut, making it essential for laser operators and service providers to understand and manage them effectively.
To mitigate the effects of material stresses, laser operators employ various techniques such as material selection, using simplified cutting parameters, proper fixturing, and incorporating stress-relieving methods. By understanding the factors that contribute to material stress and implementing appropriate measures, operators can achieve higher precision, smoother cuts, and overall improved quality in their metal laser cutting processes.
Effects of material stresses on metal laser cutting process
The impact of material stresses on the metal laser cutting process can be far-reaching. One of the most common effects is the deviation from desired dimensions. As the material expands and contracts during the cutting process, it may deviate from the intended measurements, leading to inaccuracies and inconsistencies in the final product.
Laser heat induced stresses can also cause part features to warp, twist, or distort. Material that lifts while processing (changes the laser’s focal length or effective cutting height) can undesirably alter the cut kerf (width), generate uneven cutlines, or to lose the cutting process altogether.
Similarly, material memory or stress inherent to the raw material can have the same effect as laser induced stresses. This can be observed when a laser cut stencil or mask does not lay completely flat. Material memory can also take over when a significant percentage of the material is removed from a blank raw metal sheet.
Even if the part is cut perfectly while on the cutting table, the final part can lose shape or form when unconstrained due to the material stresses left in the material. A good example of a part losing form is laser cutting a narrow, serpentine pattern. If too much material stress is induced from the cutting process, the once flat serpentine part will lift up like a spring when free from the sheet.
Best practices for material stresses in metal laser cutting
To minimize the impact of material stresses in metal laser cutting, several strategies can be employed.
Proper laser cutting parameters are crucial in managing material stresses. Parameters such as laser power, cutting speed, and assist gas flow rate (provides localized cooling & debris removal) should be optimized based on the material properties and thickness. By finding the right balance, operators can minimize the heat input and subsequent material stresses, leading to more accurate and consistent cuts.
Incorporating stress-relieving methods is another effective strategy. This involves subjecting the material to controlled heat treatment before or after the cutting process, allowing it to relax and relieve any residual stresses. Stress-relieving can be done through techniques such as annealing or tempering, depending on the specific material and application requirements.
One of the most important factors to controlling material stresses during metal laser cutting is the material selection or type. Each metal type/temper and the various metal alloys have different densities and thermal properties, which affect how they transfer/dissipate the localized heat generated by the laser ablation process.
Mitigating Material Stress
Laser Cutting Parameters
Simplify Design and Cut Path
The metal thickness also plays a significant role in determining the level of material stresses. Thicker materials require higher laser power, which generates more heat that needs to be dissipated and can increase the likelihood of material distortion.
Another best practice is to consider simplifying the design and complexity of the cut. Designs with dense cut patterns that are limited to a small area can allow heat to build up as there is less area to dissipate the heat. Intricate designs with long narrow features are more prone to stress and less thermal transfer, leading to higher levels of distortion. An exaggerated example would be a heater wire that curls & twists as the wire temperature increases.
Laser programming techniques can be invoked by limiting the number of cuts and/or cutting time in any one area of the part being fabricated. This will allow some areas to cool before the laser moves back to the same area to continue processing.
This technique acts as a time delay between cuts. Additionally, using a specific assist gas, such as nitrogen or argon, can help cool the material as it is being cut and to reduce oxidation.
Ensuring proper fixturing and/or clamping of the material is also crucial for cut quality. Metal materials are provided in the form of sheets, strips, or coils. Metals with coil memory or warped metal sheets/strips must be held flat while processing. Securely holding the raw material in place during the cutting process helps to minimize part movement and maintain part tolerances.
Conclusion and future prospects
Material stresses play a critical role in metal laser cutting, significantly impacting the quality and designed part geometry. By understanding the factors that contribute to material stress and implementing appropriate stress mitigating strategies, one can achieve higher precision, smoother cuts, and overall improved quality in their metal laser cutting processes.
Micron Laser employs these stress relieving techniques and more when laser cutting metals.
Contact firstname.lastname@example.org today to discuss how we can help in the fabrication or optimal material selection for your next part.