Sheet Metal Fabrication：The Overview, Process And Design
However, a thorough grasp of design concepts and best practices is necessary to guarantee the success of any sheet metal manufacturing job. We will offer a thorough overview of sheet metal fabrication design in this post, along with advice on material choice, geometric restrictions, and economical design techniques.
Whether you’re a skilled engineer or a beginner designer, this tutorial will assist you in producing top-notch sheet metal components that satisfy the demands and standards of your project.
Introduction to Sheet Metal Fabrication
Sheet metal, categorized as anything thinner than 0.25 inches, serves a crucial role in manufacturing. The consistent width requirement of sheet metal parts, although limiting in some applications, ensures the resulting components meet stringent standards of durability and longevity.
Typically found in applications such as automobile chassis, where the strength-to-weight ratio is critical, sheet metal parts exhibit lower thickness and are often hollow. This characteristic imparts reduced weight while maintaining the capacity to withstand substantial loads.
Precision processes may be unnecessary for straightforward applications, but for high-value applications, avoiding precision sheet metal fabrication is impractical. Neglecting precision in such cases can lead to wear and tear, potentially damaging sensitive equipment.
Working Principle
The underlying principle of sheet metal fabrication is straightforward, relying on the elasticity of the metal and the superior durability of cold-rolled metal. The fabrication process involves two main methods: cutting and forming.
Cutting involves removing a portion of the sheet to achieve the desired shape.
Forming, a more intricate method, encompasses three distinct processes that collaboratively shape the desired object. Careful consideration of design and manufacturability is essential to minimize waste and ensure perfection.
Manufacturers often utilize CAD files in DXF or DWG formats to ensure alignment with the intended design. In many projects, cutting and forming processes are synchronized for expedited results. While sheet metal fabrication typically requires minimal post-processing, some finishing and joining may be necessary based on the application.
The Four Primary Techniques in Sheet Metal Fabrication
The sheet metal fabrication process revolves around two key methods: forming and cutting. These techniques collaborate to shape the final product. While cutting is a straightforward process, forming further divides into stamping, bending, and punching.
Here’s an overview of the main techniques used in creating sheet metal parts:
Cutting:
The cutting process removes excess sheet metal to achieve the final form. Three primary cutting approaches include: Laser cutting, Plasma cutting, Water jet cutting.
Bending:
Bending applies significant force at a specific point on the sheet metal to attain the required shape. In some cases, preparation of the area under the bend, such as bend notches, aids in both identifying the bend location and facilitating the bending process.
Stamping:
Stamping is a complex formative process used to create intricate parts quickly. It involves various techniques, including shearing, bending, and stretching, to shape sheet metal into new forms.
Punching:
Similar to stamping, punching is a complex process utilizing shearing, bending, and stretching to create diverse shapes from sheet metal. Some stamping processes even involve joining multiple pieces using various techniques.
Main Advantages and Limitations of Sheet Metal Fabrication
Sheet metal parts designs are widely favored in various industries due to their perceived advantages, but they also come with limitations. These factors are crucial design considerations for manufacturers, influencing the appropriate applications of sheet metal.
Advantages:
- Quick Turnaround: Compared to other manufacturing methods.
- High-Quality Parts: Suitable for both production and prototyping.
- Versatility: Compatible with various metals like steel, aluminum, and copper.
- High Strength-to-Weight Ratio: Achieved through the hollow design.
- Minimal Post-Processing: Typically requires no additional finishing.
Limitations:
- Complex Design Challenges: Difficulty in creating intricate details limits the range of shapes and forms.
- Significant Investment: Substantial upfront costs for tooling and equipment, acting as a barrier for small-scale production.
- Longer Lead Times: Multiple stages, including cutting, forming, and finishing, contribute to extended production timelines.
- Skilled Labor Requirement: Skilled workforce comes at a higher cost, adding to overall production expenses.
Design Guidelines for Sheet Metal Fabrication
Designing for sheet metal fabrication involves careful consideration of various requirements, particularly dictated by the overall product design. The complexity of the design determines the number of processes needed to prepare the product for the market. Embracing best practices in sheet metal fabrication ensures optimal results and high-quality output within a short timeframe. Here are five key categories of general guidelines:
Tolerances
Tolerance is a critical parameter for various applications, with the general principle being that increased precision requires more resources and incurs additional costs. Tolerances must align with the specific application’s requirements. For instance, the precision needed for an automobile door differs from that required for the chassis.
Industry Standards: Many industries prefer adhering to set quality standards to maintain consistency and performance. Compliance with industry standards, such as ISO 2768 for sheet metal fabrication, helps meet industrial requirements and build consumer trust in the brand.
General Tolerances
Industry-wide, certain tolerances are commonly used, though exceptions exist for sensitive applications like aerospace and automotive, where precision is paramount.
Wall Thickness: 0.9mm to 20mm
Offsets: 0.3mm to 0.7mm
Curls: >2x material thickness (Note: Lesser curl dimensions may compromise sheet integrity.)
Bends: Varying based on thickness (A +/- degree deviation is expected on all bends.)
Hems: Inside dia = material thickness with return length 4x the thickness
Countersinks: Major dia = +/- 0.254 mm, Minor dia > 2/3 thickness
Holes and Slots: Diameter > material thickness (Diameter less than thickness may cause sheet cracks.)
Notches and Tabs: Notch width > 1.5x thickness, Length > 5x thickness
These guidelines help maintain precision, adhere to quality standards, and ensure cost-effective and efficient sheet metal fabrication.
Fundamentals of Forming
In the forming process, a flat sheet of metal undergoes shaping by the application of pressure, with specific requirements varying based on the type of bending process employed. While numerous bending methods exist, three primary techniques stand out:
Brake Pressing:
A manual process utilizing a clamping bar and plate to shape the metal sheet.
Primarily suitable for prototyping and small-scale productions.
Roll Bending:
Similar fundamentals to brake pressing but results in cylindrical, conical, or other arc-shaped forms.
Press Brake Bending:
The most advanced bending method employing hydraulic machines with punches and dies.
Suitable for metal sheets up to 6mm thickness, providing precision in shaping.
Crucial Parameters for Sheet Metal Bending
In sheet metal bending, adherence to specific parameters is essential for optimal results. Six fundamental parameters characterize any sheet metal bend, influencing the quality of the final product:
Bend Line:
A straight line on the sheet’s surface marking the beginning and end on both sides of the bend.
Industry standard: Keep the distance between the inside edge and outside of the bend at 5 times the sheet thickness.
Bend Radius:
The distance from the bend axis to the inner surface between two bend lines.
Recommended to use a bend radius equal to or larger than the material thickness for optimal load-bearing capacity.
Bend Angle:
The angle formed by the bend concerning the imaginary perpendicular line from the axis.
Industry practice: Ensure flange length is 4 times the thickness; maintain consistency in bend angles.
Neutral Axis:
The portion of a sheet unaffected by stretching or compression.
Precision in bend radius and angle crucial for determining final product performance.
K-Factor:
A measure of material location, determined by the ratio of distance to thickness.
Optimal range: 0.25 to 0.50, influenced by material type, bending process, and angle.
Bend Allowance:
Measurement and accounting for arc length and distance between the neutral axis and bend lines.
Use accurate allowances based on material, thickness, and bending process for consistent results.
Essentials of Cutting
Cutting, another vital process in sheet metal fabrication, provides rapid results with acceptable precision. Key considerations during the design phase involve the following five parameters:
Material Selection:
Material characteristics determine the suitable cutting process.
Consider manufacturability alongside strength and durability.
Hole Diameter:
Ensure hole diameter equals or exceeds the overall thickness of the sheet.
Inadequate hole diameter relative to thickness may lead to cracks and durability issues.
Localized Hardening:
Heat generated during cutting can cause localized hardening.
Control cutting speed and use coolants to minimize the risk.
Distortion:
Warping, bending, or twisting of the metal sheet during fabrication.
Address factors like temperature, stress, and pressure to prevent dimensional inaccuracies.
Kerf:
Width of material removed by the cutting tool.
Consider the kerf’s impact on final dimensions and fabrication costs, adjusting designs accordingly.
Common Features Found in Sheet Metal Parts
Sheet metal design incorporates various features to meet industry requirements. Here are six prevalent features commonly found in sheet metal parts:
Corner Fillets
Corner fillets are curved edges or corners incorporated into sheet metal parts to eliminate sharp edges, which pose safety hazards and can induce stress concentrations in the metal, potentially leading to failure.
Size: Equal to or greater than the sheet metal thickness.
Symmetry: Fillets on opposing corners should be symmetrical.
Uniformity: Fillets should maintain uniform size throughout the part.
Placement: Strategically placed in areas prone to stress concentrations.
Radius: Larger radii distribute stress more evenly.
Design: Should allow easy addition of fillets without compromising part integrity.
Ribs
Ribs are elevated features typically oriented perpendicular to the sheet metal part’s surface. Their purpose is to enhance strength and rigidity without significantly increasing the weight of the part.
Thickness: Limited to no more than 60% of sheet metal thickness.
Fillets: Use fillets to smooth transitions and distribute stresses.
Spacing: Avoid placing ribs too close together or near bends.
Shape: Consider tapered or variable-height ribs for even stress distribution.
Embossment
Embossments are recessed features usually parallel to the sheet metal part’s surface. They serve to introduce depth or texture to the part and may create space for accommodating another component.
Depth: Limited to no more than 50% of sheet metal thickness.
Fillets: Use fillets for smooth transitions and stress distribution.
Spacing: Avoid placing embossments too closely or near bends.
Aesthetics: Consider impact on overall appearance and alignment with design requirements.
Round Boss
A round boss is a raised circular feature employed in sheet metal fabrication to enhance the strength and stiffness of a part. This feature is commonly produced by punching or forming a circular depression, causing the surrounding metal to bulge and form the raised circular feature.
Size and Location: Carefully choose to provide support without interference.
Tooling: Use specialized tooling like punch and die sets for accurate formation.
Material Thickness: Consider the impact of sheet metal thickness on boss size and shape.
Dimple Feature
Dimples serve various purposes, including reinforcing the stiffness and strength of a sheet metal part, creating a smooth and flush surface for attaching fasteners or other components, and providing clearance for additional parts or components.
Size and Location: Place dimples strategically for maximum benefit.
Depth: Avoid overly large or shallow dimples for optimal reinforcement.
Tooling: Choose appropriate tools (punches, dies) based on dimple size and material.
Sheet Metal Thickness: Account for thickness variations and adjust tooling accordingly.
Louver Feature
Louvers are designed to enhance airflow and ventilation within enclosures or panels. They can be tailored for specific purposes, such as directing airflow, reducing noise, or offering protection against dust, dirt, or moisture.
Size: Choose louvers based on required airflow and available space.
Orientation: Align louvers with airflow direction, considering obstructions.
Shape: Optimize efficiency with a streamlined, aerodynamic louver design.
Material: Select materials (e.g., stainless steel, aluminum) based on intended application.
Manufacturing Method: Choose a method based on precision, consistency, and cost-effectiveness.
Round Knockout
Round knockouts are employed to create holes of varying sizes, determined by the punch and die dimensions. Widely utilized in sheet metal fabrication, they find applications in electrical boxes, HVAC systems, and enclosures.
Size: Use the correct punch and die size for the desired hole.
Material: Ensure compatibility with specific sheet metal types.
Sharpness: Maintain sharpness of punch and die for quality holes.
Thickness: Ideal for thinner materials; consider alternative tools for thicker sheets.
Burr Removal: Beware of burrs and use deburring tools for a clean finish.
Sheet Metal Thickness
The appropriate thickness for sheet metal is contingent on the material type and the intended application. In general, thicker metals offer increased strength and durability, whereas thinner metals exhibit greater flexibility and reduced weight. Sheet metal thickness typically falls within the range of 0.5 mm to 6 mm, though specific materials and purposes may warrant deviations from this range. The following outlines recommended material thickness for various commonly used metals in sheet metal fabrication.
Steel/Stainless Steel/Aluminum: 22Gauge 0.8 mm 0.031 inches
Steel/Stainless Steel/Aluminum: 20Gauge 1.0 mm 0.039 inches
Steel/Stainless Steel/Aluminum: 18Gauge 1.2 mm 0.047 inches
Steel/Stainless Steel/Aluminum: 16Gauge 1.6 mm 0.063 inches
Steel/Stainless Steel/Aluminum: 14Gauge 2.0 mm 0.079 inches
Steel/Stainless Steel/Aluminum: 12Gauge 2.5 mm 0.098 inches
Steel/Stainless Steel/Aluminum: 10Gauge 3.2 mm 0.126 inches
Common Sheet Metal Design Mistakes to Avoid
Sheet metal fabrication is a intricate process encompassing design, cutting, bending, and assembly to create a final product. Despite the proficiency of designers, errors can occur, leading to expensive rework or scrapped parts. To prevent these costly mistakes, it’s crucial to be cognizant of common design errors and take preventative measures.
Mistake 1: A CAD File with No Bends
Providing a CAD file lacking bends is a significant mistake. A sheet metal part sans bends may necessitate additional parts and labor to join multiple pieces. It is imperative to incorporate bends in the design, specifying bend angles and radii to ensure accurate fabrication.
Mistake 2: Features Too Close to a Bend
Misplacing features, such as holes or tabs, too close to a bend can result in deformed metal parts. Adhering to the 4T rule—keeping features at least 4 times the material thickness away from any bend line—prevents such issues.
Mistake 3: Perfectly Perpendicular Internal Bend Radius
Seeking perfectly perpendicular lines in CAD designs can lead to material deformation during bending. Specifying a minimum bend radius suitable for the material and thickness is recommended to ensure a smooth transition and prevent stress concentrations.
Mistake 4: Not Including Hardware Details in CAD File
Failing to include hardware details in a CAD file can lead to delays and increased assembly costs. Incorporating specific hardware specifications, sizes, and locations in the design facilitates a smoother fabrication process.
Mistake 5: Choosing an Unsuitable Finish
Selecting an unsuitable finishing option can impact both aesthetics and protection against rust or corrosion. Understanding the function of various finishes, such as protective coatings or aesthetic enhancements, ensures the right choice for the intended application.
Mistake 6: Selecting the Wrong Sheet of Metal
Consider the application and environmental factors when choosing sheet metal. Using the wrong metal in corrosive environments can lead to rust and corrosion. Understanding the technical requirements helps in selecting the appropriate sheet metal.
Mistake 7: Not Considering Material Strength for U Channels
Neglecting material strength when designing U channels can result in weak channels prone to bending or breaking. Selecting the right material and thickness, considering expected loads and additional stresses, is essential for U channel design.
Mistake 8: Designing Unachievable Welding Requirements
Overestimating welding capabilities can complicate designs and increase costs. Implementing strict design for manufacturing (DFM) practices ensures adherence to prevalent standards and avoids unrealistic welding requirements.
Types of Sheet Metals
The term “sheet metal” is broadly used in the industry, and the metal utilized typically falls into one of the following categories:
Stainless Steel: Renowned for its versatility and durability, stainless steel is a prevalent and popular option. It is the top choice for applications requiring a cost-effective, durable, and robust material.
Cold Rolled Steel: Ideal for applications where material strength is a primary concern for designers, cold-rolled steel offers excellent strength properties.
Pre-Plated Steel: Similar to regular steel but equipped with a special coating to prevent corrosion, pre-plated steel provides added protection against environmental degradation.
Aluminum: A lightweight and practically inert option, aluminum offers an excellent strength-to-weight ratio. It is widely used in various applications.
Copper: Despite being relatively expensive, copper is an effective material that does not react under normal conditions. It ensures long-lasting performance without succumbing to chemical or biological degradation.
Brass: An alloy of copper and zinc, brass combines corrosion resistance with sufficient hardness to withstand multiple impacts. It finds use in diverse applications.
Common Finishes for Sheet Metal Parts
While sheet metal often performs well without additional processing, certain applications may warrant post-processing for specific requirements. Some of the most common post-processing steps for sheet metal products include:
- Anodizing
- Brushing
- Polishing
- Bead Blasting
- Powder Coating
- Plating
- Passivation
- Chrome Coating
Additionally, custom finishes can be accommodated upon request to meet specific design or functional needs.
Sheet Metal Fabrication at Sungplastic
We are a skilled manufacturing partner that can assist you in bringing your design from the drawing board into reality. Our staff has the knowledge and resources to help you, whether you’re a startup trying to launch a new product or an existing business trying to optimize your manufacturing procedures.
We are aware of the significance of manufacturing viability and how it affects your product’s success. With the newest tools and technologies at their disposal, our team of professionals can give a thorough design for manufacturing (DFM) examination. We will collaborate closely with you to maximize your design’s manufacturability, seeing possible problems early on to reduce the possibility of delays in production or poor quality.
In addition to our sheet metal stamping service, we also specialize in CNC machining and metal injection molding. Our production facilities are equipped with the latest equipment and technology. We serve the needs of a variety of industries, including aerospace, automotive, medical and consumer products. By working with us, you can trust that your products will be delivered on time, on budget, and to the highest quality standards. Contact us today to learn more about how we can help you realize your design and get your product to market faster.
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