Design for manufacturability (DFM) plays a crucial role in streamlining production and improving the overall quality of sheet metal parts. One of the primary benefits of DFM is cost reduction. By designing parts that are easy to manufacture, companies reduce material waste, labor costs and the need for specialized tooling. This helps in cost savings, especially for high-volume production runs.
Another key advantage of DFM in sheet metal design is improved product quality. By considering manufacturing processes during the design stage, issues such as warping, tearing and dimensional inaccuracies are identified and addressed proactively. This results in parts that meet the required specifications and perform reliably in their intended applications.
To ensure efficient and cost-effective production of sheet metal parts, careful consideration must be given to various design aspects. The following are DFM guidelines with respect to design.
Follow the guide
Material selection: Choosing the right material is crucial for functionality and manufacturability. Factors such as strength, formability and corrosion resistance should be considered, along with the material’s compatibility with the intended manufacturing processes. For example, some materials may be more suitable for bending or welding than others. Most CAD software includes a comprehensive materials library with detailed properties for various sheet metals.
Bend radius: The bend radius is the minimum radius to which a sheet metal part can be bent without cracking or deforming. Specifying appropriate bend radii is essential to prevent stress concentrations and ensure the structural integrity of the part. Bend radius is influenced by factors such as material thickness, type of bend and bending method. CAD systems can automatically calculate the minimum bend radius based on the chosen material and its thickness.
Hole placement: Proper hole placement is also critical for functionality and manufacturability. Holes should be positioned to avoid interference with bends or other features, and their size and spacing should be optimized for the chosen manufacturing process. For example, holes that are too close to a bend may distort during the bending process.
Tolerances: Specifying realistic tolerances is crucial for ensuring that parts can be manufactured consistently and meet the required functional requirements. Overly tight tolerances can increase manufacturing costs and lead to production delays, while loose tolerances may compromise the performance or interchange ability of parts. Designers use CAD to define and manage tolerances directly within the 3-D model.
Additional guidelines
Slot and tab design: Optimal slot and tab designs minimize assembly time and costs. Maintaining a minimum slot width 0.010 in. greater than the material thickness helps to avoid jamming during insertion. Positioning slots and tabs away from bend lines prevents deformation.
Equalizing tab and slot widths, with a slight overbend allowance factored into the tab, typically 0.003 in. to 0.005 in. per side, ensures a secure, snap-fit assembly. This minimizes manufacturing complexity and ensures robust assembly.
Corner design: Sharp corners in sheet metal parts induce stress concentrations during bending, leading to cracking or tearing, particularly in brittle materials. CAD software helps automatically generate corner reliefs or radii based on predefined rules or user-defined parameters.
Relief size should be at least the material thickness plus bend radius. Larger reliefs reduce material thinning at the bend, but excessively large reliefs can compromise part strength and aesthetics. Radius size selection depends on the material, bend angle and tooling limitations.
Flange design: Narrow flanges (less than three times the material thickness) challenge bending precision and increase tooling costs. Maintaining flange flatness mitigates distortion during bending and subsequent welding operations. Insufficient flatness leads to oil canning or pillowing, impacting assembly fit-up.
FEA analysis helps predict flange deformation and guide design optimization. Appropriate bend radii minimize stress concentrations and cracking, particularly for high-strength materials.
Embossing and coining: Embossing and coining modify sheet metal surfaces for functional or aesthetic purposes. Embossing raises or lowers the surface, maintaining constant sheet thickness. Coining, using higher forces, displaces material, creating a bas relief.
Depth impacts tooling and press selection; shallower depths simplify manufacturing. Sharp corners in emboss/coin designs increase stress, potentially causing tearing or fracture during formation. A larger radius minimizes these risks.
Surface finish: Surface finish impacts sheet metal manufacturing cost and lead time. Specifying finishes like powder coating or anodizing after forming helps to avoid damaging the coating. Taking into consideration the environment, for corrosion resistance, zinc plating (ASTM B633) or electro polishing (ASTM B912) offer viable solutions.
A brushed finish necessitates an oriented grain direction. Laser engraving, used for part identification for example, must account for material thickness and warping from heat. Unnecessary finishes increase cost so their functional necessity must be ensured. Consulting applicable standards, such as MIL-STD-171, is helpful.
Principles for best design
By incorporating DFM principles into the design process, manufacturers identify and resolve formability issues, such as splitting, wrinkling and springback. Addressing these virtually before production helps in optimize sheet metal design and prevents costly physical trials. For example, DFM can help prevent errors, such as incorrect material selection, improper bend radii, inconsistent hole placement and overly tight tolerances.
Error reduction translates directly to improved production yields, shorter lead times and enhanced part quality, ultimately lowering overall manufacturing costs.
DFM helps optimize the design for cost-effective manufacturing. By considering the manufacturing process early on, designers can make choices that minimize material usage, simplify assembly and reduce the need for specialized tooling.
Key DFM principles for cost-effective design include:
- Standardize parts and components
- Design for ease of assembly
- Using CAD tools, nest parts efficiently within the sheet to maximize material utilization
- Standardize features like hole sizes and bend radii to leverage common tooling, reducing setup costs
- Design self-locating features for simplified, tool-less assembly, minimizing labor
- Favor simple bends over complex forming operations
- Employ tab-and-slot features to reduce costs and assembly time
By adhering to these principles, designers create sheet metal parts that are functional and economical to produce.
Impact on efficiency
DFM in sheet metal design streamlines production by simplifying geometries for bend ability and minimizing forming operations, such as deep drawing. This reduces specialized tooling, which reduces costs and lead times, and simplifies assembly, such as snap-fit over welding.
Predictive forming simulations optimize blank layouts, minimize material scrap and maximize material utilization, directly impacting production throughput and profitability. Simplified designs reduce error-prone operations, ensuring faster production with fewer defects and reworks, shortening lead times, reducing machine downtime and improving overall productivity.
Hitech Cadd Services optimized sheet metal product design for a U.S.-based fabricator using CAD and DFM guidelines, reducing turnaround time by 56 percent. Deliverables included detailed 3-D models, assemblies and manufacturing drawings. A library-based approach helped cut customization errors and boosted efficiency for diverse fabrication needs.
When designing sheet metal parts, designers should prioritize DFM from the outset. Integrating DFM principles early in the design process allows them to optimize designs and catch errors before they happen during production.
This leads to lower costs, better product quality and increased production efficiency, making it a critical strategy for sheet metal manufacturing. Following DFM guidelines helps a company gain a competitive edge by bringing innovative, high-quality products to market faster and more affordably.
