Sheet metal fabrication is the process of creating parts and structures from thin metal sheets. This manufacturing process is advantageous because it creates lightweight components with good mechanical properties. Sheet metal fabrications utilizes various techniques to reshape the metal sheets into the desired shape and structure of the part.
Manufacturing often integrates techniques like CNC machining and laser cutting to enhance its precision and quality standards. However, like other manufacturing processes, it is also susceptible to defects. This article explores eight sheet metal fabrication defects in engineering.
What is Sheet Metal Fabrication?
Sheet metal fabrication is the manufacturing process that involves creating parts and structures using thin metal sheets. The technique consists of a series of operations such as cutting, stamping, bending, forming, and assembling to create parts and structures from these metal sheets. Due to its versatility and cost-effectiveness, it is widely used across industries like automotive, aerospace, and construction.
However, as we hinted earlier, despite the high precision and advanced technology involved, sheet metal fabrication is not without its flaws. Sheet metal fabrication defects refer to the imperfections or issues that arise during the manufacturing process, affecting the quality and functionality of the final product. These defects can range from minor surface imperfections to significant structural problems.
Potential causes of sheet metal fabrication defects include operator error, incorrect material selection, and inadequate tooling, among others. Below, we discuss eight common sheet metal fabrication defects.
Deformation
-
Descriptions
Deformation refers to the unwanted alteration of the shape or structure of sheet metal during fabrication. This sheet metal fabrication defect can occur in the form of warping, bending, or twisting of the metal sheet, leading to parts that do not meet the required specifications or tolerances.
-
Causes
Deformation is often a result of excessive or uneven force during the bending or forming stage of sheet metal fabrication. Other contributing factors include wrong material selection, inadequate support during processing, improper tooling, and thermal stress during welding or cutting.
-
Solutions
To prevent deformation, ensure proper material selection and use suitable tooling for the specific sheet metal. Also, the machinist should employ uniform force application during bending and forming processes, using fixtures or supports to hold the material in place, and controlling the thermal environment can also help minimize this defect. Regular maintenance and calibration of equipment further enhance process stability.
Burring
-
Descriptions
Burring is the formation of rough or slightly raised edges on sheet metal after cutting, drilling, or punching operations. These small, jagged projections can affect the appearance and function of the fabricated parts, potentially leading to assembly issues or safety hazards.
-
Causes
This sheet metal defect occurs due to improper cutting techniques, using dull or worn-out tools, and incorrect tool alignment. High cutting speeds and inadequate clamping of the sheet metal during machining can also contribute to the formation of burrs.
-
Solutions
To reduce or eliminate burring, ensure that sharp cutting tools are used and properly aligned to the workpiece. Modifying cutting speeds and feed rates to optimal levels and using appropriate clamping methods to secure the sheet metal during processing will also prove effective. In addition, post-processing techniques like deburring, sanding, or tumbling are effective means of removing any remaining burrs and smoothing the edges.
Scratches and Surface Marks
-
Descriptions
Scratches and surface marks are imperfections that appear on the surface of the sheet metal during fabrication. This defect typically compromises the aesthetics and quality appearance of the final product. Depending on the severity of the contact or force applied, scratches can range from light abrasions to deep gouges.
-
Causes
Common causes of scratches and surface marks include improper handling of material and cutting tools, contact with rough or contaminated tools, and debris on the work surface. Also, poor storage of raw materials and stacking of sheet metal can lead to surface damage, even before any fabrication process.
-
Solutions
To prevent scratches and surface marks, ensure proper handling and storage practices are followed. Use clean, well-maintained tools and work surfaces. Implement protective coverings or coatings during fabrication and transport. Regularly inspect and clean equipment to minimize the risk of debris causing damage. The solution to scratches and surface marks on machined parts is to apply appropriate surface finishing such as polishing, brushing, painting, etc.
Cracks
-
Descriptions
Cracks are linear fractures or fissures that occur in sheet metal during fabrication. These defects can range from small outline cracks to larger, more significant fractures that compromise the structural integrity of the products.
-
Causes
Excessive stress or strain during forming or bending operations is a common cause of cracks in sheet metal fabrication. Other material defects, such as inclusions or impurities, may also cause cracks, as may machining parameters, such as rapid cooling rates during welding or heat treatment processes.
-
Solutions
Machinists should optimize machining parameters, such as the bending radius, tooling clearance, and material temperature, during forming operations. They should also ensure the use of high-quality, defect-free materials and inspect for surface imperfections before fabrication. Finally, they should implement proper heat treatment processes to relieve internal stresses and improve material ductility.
Burn Marks
-
Descriptions
Burn marks are discolored or charred areas that appear on the surface of sheet metal during fabrication. They arise from overheating or localized heating of the material, leading to oxidation or thermal degradation of the metal surface. Depending on the severity of the heat exposure, burn marks can range from light discoloration to darkened, carbonized areas.
-
Causes
We already mentioned the causes of burn marks, which include excessive heat generated during welding, cutting, or grinding operations. It may also be a welding defect or arise from poor welding techniques (using incorrect welding parameters or insufficient shielding gas) can lead to overheating and burn marks. Likewise, improper cutting speeds or inadequate cooling during machining can also result in thermal damage and burn marks.
-
Solutions
To prevent burn marks, the machinist should optimize welding parameters, such as current, voltage, and travel speed, to minimize heat input and ensure proper shielding gas coverage. Sharp cutting tools and modulating cutting speeds should also reduce frictional heat buildup during machining.
Other methods of preventing burn marks include implementing effective cooling methods, such as liquid cooling systems, to dissipate heat and avoid localized overheating. Using appropriate lubricants and cooling fluids could also prove effective in minimizing burn marks.
Porosity
-
Descriptions
Porosity refers to the presence of voids or tiny holes within the structure of the sheet metal. These voids can be visible on the surface, appearing as pores, or they may be internal, affecting the material’s density and integrity. This sheet metal fabrication defect may compromise the metal’s mechanical properties, such as strength, ductility, and corrosion resistance.
-
Causes
Porosity in sheet metal results from various factors, including gas trapping during welding or casting processes. Other causes include inadequate degassing of molten metal, improper shielding gas coverage during welding, or contamination of the metal surface with oil, grease, or other contaminants.
-
Solutions
Proper welding techniques are essential to prevent and minimize gas porosity. Ensure adequate shielding gas coverage to prevent gas entrapment and adequate gas evacuation from the molten metal. Also, the manufacturer should clean and degrease metal surfaces before welding or casting to remove potential contaminants that can contribute to porosity. Use proper ventilation systems to remove gases and fumes from the welding area.
Distortion
-
Descriptions
Distortion refers to issues with the shape of the sheet metal parts. This defect is when there is a deviation from the intended shape or dimensions of the sheet metal part during fabrication. This defect can manifest as warping, twisting, bending, or bowing of the material, resulting in inaccuracies and inconsistencies in the final product.
-
Causes
The typical causes of distortion in sheet metal fabrication include uneven heat distribution during welding or thermal cutting and inadequate fixturing or clamping arrangements. Internal stress in the material, uneven heating or cooling, or excessive use of mechanical force during fabrication may also cause distortions.
-
Solutions
Addressing distortion issues involves careful control of heat input, maintaining uniform heating and cooling rates, and using appropriate fixturing and clamping methods to minimize material movement during fabrication.
Tool Marks
-
Descriptions
As the name suggests, tool marks are surface imperfections or irregularities left behind by the cutting tools in the sheet metal during the machining, forming, or finishing processes. These marks can vary in appearance and severity, ranging from shallow scratches to deep gouges or indentations. They typically diminish the metal’s aesthetic quality.
-
Causes
Tool marks are typically caused by improper tool selection, inadequate lubrication or cooling, excessive cutting speeds or feed rates, worn or damaged cutting tools, or incorrect machining parameters. Additionally, poor tooling setup or alignment, vibration during machining, or material inconsistencies can contribute to the formation of tool marks.
-
Solutions
To minimize tool marks, sharp, properly maintained cutting tools are essential. Machinists should select and optimize machining parameters and ensure adequate lubrication or cooling during cutting. Proper tool alignment, fixture clamping, and vibration damping measures are all effective measures for preventing tool markings on sheet metal surfaces.
Conclusion
Sheet metal fabrication suits the fabrication of high-quality and reliable products. However, when defects occur, they can compromise the part’s appearance, quality, or even structural integrity. Therefore, it is important to prevent sheet metal fabrication defects, and when they do, machinists and OEMs must be proactive about restoring the quality of the fabrication.
