Designing sheet metal parts can be frustrating. Small mistakes in the design often waste materials, increase costs, and cause delays. Engineers and manufacturers frequently face these problems when parts do not meet specifications or cannot be produced efficiently. These issues create stress, missed deadlines, and extra expenses.
You can avoid the most common mistakes from the beginning. Doing so saves time, lowers costs, and keeps production running smoothly. This guide highlights the top errors in sheet metal design and explains how to prevent them.
1. Overlooking Material Selection
The material you choose determines a part’s strength, cost, and lifespan. Many designs fail because the wrong material is selected from the start. This can lead to weak parts, higher expenses, or products that wear out quickly.
Thickness has a significant impact on strength and formability. If the sheet is too thin, the part can bend, deform, or break. For example, steel below 0.8 mm often warps during stamping. On the other hand, sheets thicker than 5 mm usually require more expensive machining tools than simple stamping.
Sheet metal parts often encounter moisture, heat, and chemicals. Ignoring corrosion resistance can cause parts to fail sooner, especially outdoors or in industrial environments. For instance, untreated mild steel can start rusting in as little as 48 hours in humid conditions.
Common choices include stainless steel, which naturally resists corrosion, or aluminum with anodizing for extra protection. Coatings such as powder paint or galvanization can further extend a part’s life.
2. Neglecting Bend Radii
Bend radii are crucial for the strength and accuracy of sheet metal parts. Ignoring them can cause cracked edges, uneven bends, or parts that do not fit properly. Correct bend radii also reduce stress on tools, extending tool life and lowering production costs.
If the rayon de courbure is too small, the metal stretches too much and cracks. For example, cold-rolled steel usually needs a minimum bend radius equal to its thickness. Harder metals, like stainless steel, may require 1.5 to 2 times the thickness. Skipping this guideline leads to weak bends and higher scrap rates.
Dos d'âne happens when metal tries to return to its original shape after bending. Aluminum alloys can spring back 2–3 degrees, while high-strength steels may spring back even more. If designers ignore this, the final part can be out of tolerance and need expensive rework. To prevent issues, always include springback in calculations or adjust tooling angles to compensate.
3. Designing Without Considering Tolerances
Tolérances determine how precisely each part must be made. Poorly chosen tolerances increase costs, cause delays, and create assembly problems. Good tolerance design balances function with manufacturability. Designers should base limits on how the part will be used, not just what looks perfect on a drawing.
Unnecessarily tight tolerances raise inspection time and require advanced machines. For example, holding ±0.01 mm on a simple bracket can cost up to three times more than using ±0.1 mm. Many sheet metal parts, especially non-critical components, do not need such precision. Loosening tolerances where possible cuts costs without affecting performance.
Loose or inconsistent tolerances can cause gaps, misfits, or extra manual work during assembly. Even a 0.5 mm hole placement offset can prevent bolts from aligning, slowing production. In high-volume manufacturing, such errors can lead to thousands of rejected units.
4. Ignoring Hole and Slot Requirements
Holes and slots are standard in sheet metal parts, but poor placement or sizing can weaken the part, damage tools, or increase costs. Good design ensures parts are strong and easy to produce.
If holes are too close to an edge, the surrounding material may tear or deform during forming. A common rule is to keep the edge distance at least 1.5 times the hole diameter. For bends, holes should be offset by at least 2 times the material thickness to prevent distortion. Ignoring these guidelines reduces part strength and increases scrap.
Tiny holes are challenging to punch or cut with a laser. A good rule is that the hole size should not be smaller than the material thickness. For example, cutting a 1 mm hole in 2 mm steel can break punches and cause excessive heat with laser cutting. Oversized holes also cause problems, often requiring extra machining steps.
5. Overcomplicating Part Geometry
Complex designs may look impressive, but often increase costs and slow production. Every extra bend, cutout, or feature adds tooling, setup, and processing time. Usually, these additions do not improve the part’s function.
Extra bends increase production steps and raise the chance of misalignment. For example, adding three bends instead of one can double the forming time and wear on tools. Features like decorative cutouts or tight corners make parts weaker and more complicated to handle. Designers should focus on function and remove features that do not improve performance.
Some shapes need special dies or secondary machining. Sharp corners, deep channels, or complex curves may not work with standard press brakes or rollers. In these cases, manufacturers need custom tooling, which can cost thousands of dollars and add weeks to production. Designing parts to fit standard tooling helps keep projects on schedule and budget.
6. Forgetting About Fastening and Joining Methods
Fastening and joining are critical in sheet metal design but often overlooked. Poor planning can cause assembly problems, weak joints, or expensive redesigns. Considering joining methods early helps create stronger parts and speeds up production.
Soudage needs space for tools and heat control. If designs leave little room for welders or robotic arms, joints may be incomplete or uneven. For example, narrow corners can trap heat, causing warping or weak welds. A simple 10–15 mm clearance often makes welding easier and more reliable.
Attaches also need proper hole sizing and spacing. If screws or rivets are too close together, the sheet may crack under load. A general rule is to leave at least 2 times the fastener diameter between holes. Inserts like PEM nuts require extra clearance for installation tools.
7. Overlooking Grain Direction and Anisotropy
Sheet metal is rolled during production, which creates a grain in the material. This grain affects how the metal bends, stretches, and resists cracking. Ignoring grain direction can lead to weak bends, distortion, or part failure during forming.
Bending against the grain increases the risk of cracks, especially in harder metals like stainless steel or aluminum alloys. Tests show that bending across the grain can reduce ductility by up to 50% compared to bending along it. A safe approach is to place bends parallel to the grain whenever possible to keep parts strong and reduce failures.
Anisotropy means the metal behaves differently depending on the direction. If ignored, parts may warp or twist during forming. For example, an extended flange bent across the grain can distort by several millimeters, requiring rework. Designers can reduce this risk by increasing bend radii, choosing softer tempers, or aligning the part orientation with the grain.
8. Failing to Optimize Flat Pattern Layouts
Flat pattern layouts determine how efficiently parts are cut from sheet metal. Poor layouts waste material, increase costs, and slow production. Designers who skip this step often face higher scrap rates and longer lead times.
Parts placed randomly on the sheet leave significant gaps, wasting valuable material. If layouts are not optimized, scrap can reach 10–20% of raw material. Using software or careful manual planning to nest parts tightly reduces scrap and costs.
Sheet metal comes in standard sizes, such as 4×8 ft (1.22×2.44 m) or 5×10 ft (1.52×3.05 m). Designing parts without considering these sizes may require cutting from oversized sheets, which raises material costs and processing time. Aligning part dimensions with available sheets improves efficiency and reduces waste.
9. Neglecting Finish and Post-Processing Needs
Surface finishes and post-processing affect sheet metal parts’ quality, performance, and lifespan. Ignoring these needs during design can lead to parts that do not fit, corrode quickly, or fail inspection.
Les revêtements comme powder paint, anodisation, ou Revêtement en zinc add thickness to the part. If this is not accounted for, holes may become too small, bend too tightly, or loosen assemblies. For example, powder coating can add 0.05–0.2 mm per side. Including this in the design prevents interference and ensures proper fit after finishing.
Sharp edges can cause injuries, assembly problems, or premature wear. Ébavurage and edge rounding smooth edges and improve safety. Skipping these steps may save time initially, but it often leads to returns or rework. Designing with edge treatment in mind avoids delays and ensures consistent quality.
No single rule can prevent every sheet metal design issue, but these nine tips highlight the most common pitfalls. Following them will help you create stronger, more efficient parts and reduce production delays.
For more guidance, consult an experienced sheet metal engineer who can review your design and suggest improvements. To get started on your next project, prepare your 3D CAD model and request a fast, interactive quote to see how your design performs in production.
Hey, je suis Kevin Lee
Au cours des dix dernières années, j'ai été immergé dans diverses formes de fabrication de tôles, partageant ici des idées intéressantes tirées de mes expériences dans divers ateliers.
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Kevin Lee
J'ai plus de dix ans d'expérience professionnelle dans la fabrication de tôles, avec une spécialisation dans la découpe au laser, le pliage, le soudage et les techniques de traitement de surface. En tant que directeur technique chez Shengen, je m'engage à résoudre des problèmes de fabrication complexes et à favoriser l'innovation et la qualité dans chaque projet.
