Get the Most Out of Sheet Metal: DFM Best Practices
Design for Manufacturability (DFM) is a strategic approach that integrates manufacturing considerations into the design process, ensuring that products are easier and more cost-effective to produce. When working with sheet metal, DFM is essential, especially when creating complex forms. Complex geometries can pose challenges due to the inherent characteristics of sheet metal, such as its flatness, stiffness, and thickness limitations. By incorporating best practices into your design, you can successfully create intricate shapes while maintaining manufacturability.
This article focuses on key DFM best practices for creating complex forms in sheet metal, offering strategies that balance creativity with practicality.
1. Material Selection
The first step in DFM for sheet metal is selecting the right material for the project. Common materials include stainless steel, aluminum, galvanized steel, and copper, each with its own characteristics. Some metals are easier to bend and stretch than others, which will directly impact the ability to form intricate shapes.
Ductile materials: For complex shapes that involve deep drawing, bending, or stretching, opt for more malleable materials such as aluminum or mild steel. These materials can better withstand the stresses of forming without cracking or tearing.
Formability considerations: High-strength materials such as stainless steel may resist deformation, making them harder to form into complex shapes. If strength is necessary, ensure that the design takes into account the forming limits of these materials.
Selecting the correct material impacts the bending, cutting, and joining processes. Balancing formability with the functional requirements is key.
2. Bending and Forming
Understanding bending techniques is crucial to achieving your sheet metal design. Depending on cost goals it can limit what options are available to you, introducing challenges if not accounted for during the design phase. Creating complex bends requires careful design consideration, as bending introduces stresses that can result in cracking, springback, or surface distortions.
Bend radius: The inside radius of a bend should be at least equal to the thickness of the material to prevent cracking. Sharp bends can lead to material failure and difficulty in manufacturing.
Bend allowance and relief: Provide enough material for the metal to deform naturally during the bending process. Adding bend reliefs at corners reduces material stress, prevents tearing, and ensures clean bends.
Consistent bend direction: Whenever possible, align all bends in the same direction to minimize the number of tool changes during production, improving efficiency.
Segmented bends: For designs with multiple bends, break the bending sequence into multiple operations, each with a dedicated bend radius. This reduces the risk of material failure and helps maintain precision.
Use of bend reliefs: Include bend reliefs at the corners to avoid material tearing and to maintain clean, crisp bends. Bend reliefs are small cutouts near the bend area that allow the material to bend more easily.
Multi-axis bending: For intricate geometries, consider multi-axis bending machines. These machines can create complex bends in different planes without repositioning the part, ensuring greater accuracy.
Overbend compensation: Different materials exhibit varying degrees of springback. Softer metals will experience less springback compared to high-strength steels. It is important to design the tooling to overbend the material slightly according to its material properties. This ensures that the final shape conforms to the desired specifications.
3. Multi-Stage Forming and Progressive Dies
Complex forms often cannot be created in a single operation. Instead, multiple forming stages or progressive dies are required to shape the metal gradually without exceeding its deformation limits.
Progressive dies: These allow for the gradual formation of complex shapes over several stages. Each die in the sequence performs a specific operation—such as cutting, bending, or punching—on the sheet metal. This reduces stress on the material and improves precision.
Pre-forming operations: For deep-drawn or highly contoured parts, begin with intermediate forming steps to create partial shapes before final forming. This reduces the risk of material stretching or wrinkling.
Compound tools: Consider compound tools that combine several forming actions into one press stroke, allowing for faster, more efficient production of complex geometries.
Stretch forming: This method involves stretching the sheet metal over a die to achieve curved or contoured shapes. It is ideal for aerospace and automotive applications where smooth, large-radius curves are required.
Hydroforming: Hydroforming uses pressurized fluid to form sheet metal into complex shapes. This process is excellent for creating parts with uniform wall thickness and is especially useful for forming irregular or asymmetrical shapes.
4. Deep Drawing Techniques
Deep drawing is one of the primary methods used to create complex three-dimensional shapes from sheet metal. The process involves pulling the metal into a die using a punch, forming it into a desired shape.
Material stretchability: Ensure the metal can stretch adequately to conform to deep-drawn shapes. Materials like aluminum and cold-rolled steel are often used in deep drawing due to their good elongation properties.
Minimize wrinkling and tearing: To prevent wrinkling or tearing during deep drawing, use features like fillets and radii instead of sharp corners. Increasing the blank holder force can also help prevent the material from wrinkling.
Uniform wall thickness: Maintain a consistent wall thickness throughout the design. Sudden changes in thickness can lead to uneven deformation, which can complicate the deep-drawing process.
5. Hole Placement and Sizes
Holes are common in sheet metal parts for fasteners, ventilation, or weight reduction, but improper hole placement can cause production issues.
Hole distance from edges: Place holes at least 1.5 times the thickness of the metal away from edges to prevent deformation during punching or cutting.
Minimum hole diameter: Avoid holes smaller than the thickness of the sheet metal; smaller holes are harder to punch cleanly and may require secondary processes.
Avoid distortion: If holes are too close to a bend, distortion may occur. Ensure that holes are positioned at a sufficient distance from bends and edges to maintain structural integrity.
6. Incorporating Stamped Features
Incorporating stamped features like louvers, ribs, and embosses can enhance structural rigidity while also adding functional or aesthetic elements to the part.
Add stiffness with ribs and embossing: When complex forms require additional strength, include ribs, beads, or embosses. These features not only reinforce flat surfaces but can also enhance the overall aesthetic without increasing material thickness.
Maintain uniform depth: When adding these features, maintain consistent depths to avoid creating stress points that could lead to cracking or tearing during manufacturing.
Avoid excessive complexity: While stamped features add value, avoid over-complicating the design. Excessive details may increase the cost and complexity of the stamping process.
For complex forms, laser cutting or CNC punching offers precise cutting of intricate shapes, including cutouts, slots, or complex patterns. These methods allow for the creation of highly detailed forms without the need for custom stamping dies.
7. Joining Methods
Sheet metal parts are often joined using welding, riveting, or fastening. Each method comes with specific design considerations to optimize manufacturability.
Weld-friendly designs: When using welding, ensure that the design allows for easy access to the weld joints and minimizes complex angles. Avoid designing joints that require precise alignment.
Rivets and fasteners: For parts that need to be disassembled, consider designing for rivets, screws, or bolts. Include features like tabs, flanges, or slots to ensure that the pieces can be accurately and securely joined without additional fixtures.
Avoid excessive fasteners: Reduce the number of fasteners or welds wherever possible to cut down on assembly time and costs.
8. Assembly Process Consideration
Maintaining realistic tolerances is essential to ensure that parts fit together properly while keeping production costs in check.
Tight tolerances: These increase production costs due to the higher precision required. Apply tight tolerances only where absolutely necessary.
Self-locating features: Use features like tabs, slots, or notches to ensure easy alignment during assembly or welding. These features help reduce the need for additional fixtures, speeding up production.
9. Surface Finishing
Surface treatments, such as painting, powder coating, or anodizing, are common in sheet metal fabrication to improve appearance or protect against corrosion.
Design for finishing: Ensure the design allows for easy application of surface treatments by avoiding sharp internal corners, intricate shapes, or areas that are difficult to reach.
Consistent finishes: Select materials and surface finishes that are compatible with the design, especially when using different metals in an assembly to prevent galvanic corrosion.
Consider grain direction: When specifying a brushed or directional finish, account for how the grain will appear on complex forms. Inconsistent grain direction can result in a non-uniform appearance.
Conclusion
Creating complex forms out of sheet metal requires a deep understanding of both material properties and manufacturing operations. At Acorn Product Development we leverage these best practices to balance creativity and manufacturability. We ensure that even intricate shapes can be produced efficiently and cost-effectively. Take advantage of our free consultation and learn more about our sheet metal design services by filling out the form below!