Last updated on September 2nd, 2026 at 01:31 pm
Many sheet metal manufacturing problems can be traced back to decisions made during the design stage. A feature may look perfectly reasonable in CAD but become difficult, expensive, or even impossible to manufacture once material behavior, tooling, forming, hardware, welding, and finishing are considered.
At Approved Sheet Metal (ASM), we regularly review RFQs containing features that can increase cost, extend lead time, or create manufacturing challenges that could have been addressed earlier in the design process.
Five common areas deserve particular attention:
- Tolerances
- Material selection
- Embossments and special formed features
- Press brake access and bend sequence
- Holes, hardware, and finishing requirements
For additional sheet metal design guidance, download our Design for Manufacturing eBook.
1. Applying Machining-Style Tolerances to Sheet Metal Parts
Sheet metal tolerancing requires a different approach from CNC machining because fabricated parts are produced through a sequence of cutting, bending, hardware insertion, welding, finishing, and other operations.
A dimension established entirely during flat laser cutting behaves differently from a dimension that crosses one or more bends. Likewise, a dimension on a welded assembly may be affected by fit-up, heat input, weld shrinkage, and fixturing.
Formed dimensions can be influenced by factors including:
- Material thickness variation
- Material type and temper
- Bend radius
- Bend angle
- Springback
- Flange length
- Press brake tooling
- Number and orientation of bends
- How the dimension is established and measured
The more manufacturing operations involved between two features, the more important it becomes to consider the complete tolerance stack rather than treating every dimension independently.
How to Improve Sheet Metal Tolerancing
Apply tighter tolerances where they are necessary for fit, alignment, or function rather than applying the same restrictive tolerance to every dimension on the drawing.
Pay particular attention to:
- Mating hole patterns
- Mounting surfaces
- Dimensions across multiple bends
- Features that locate another component
- Interfaces between fabricated and machined parts
- Critical dimensions on welded assemblies
If machined and fabricated components must mate closely, review the complete assembly and tolerance stack before releasing either component for production. This can prevent a situation where one finished component forces unnecessarily difficult changes to another.
You can also reference ASM’s Recommended Default Sheet Metal Tolerances when developing your drawing.
2. Choosing Material Without Considering Formability
Material selection should be based on more than strength, hardness, or corrosion resistance. If the part will be formed, the material must also be compatible with the required bend geometry.
For example, 5052-H32 and 6061-T6 are both commonly used aluminum alloys, but they behave differently during forming. 5052-H32 generally offers better formability than 6061-T6, making it a common choice for enclosures, brackets, covers, and other formed sheet metal components.
6061-T6 offers higher strength for appropriate applications, but tighter bends can be more challenging. Required bend radius depends on factors including material thickness, temper, bend orientation, and geometry.
When selecting a sheet metal material, consider:
- Strength and stiffness
- Formability
- Material thickness
- Bend radius
- Temper
- Grain direction where applicable
- Corrosion resistance
- Weldability
- Finish requirements
- Material availability
- Cost
Material databases are useful for comparing mechanical and physical properties, but those properties are only part of the manufacturing decision. A material that looks ideal based on strength or hardness may require a larger bend radius or create other fabrication challenges.
How to Avoid Material Selection Problems
Start with the functional requirements of the finished part, then evaluate whether the selected alloy, temper, and thickness are compatible with the required manufacturing operations.
If multiple materials could satisfy the application, involving your sheet metal fabricator before the design is finalized can help identify options that balance performance, formability, availability, cost, and lead time.
3. Designing Embossments and Formed Features Without Considering Tooling
Embossments, louvers, knockouts, offsets, and other formed features can add strength, ventilation, clearance, alignment, or other functionality without requiring separate components.
However, these features cannot be treated like ordinary CAD geometry. Their manufacturability depends on both material behavior and the tooling available to produce them.
Important factors include:
- Material type
- Material thickness
- Feature height
- Feature width
- Corner radii
- Feature geometry
- Distance from bends and nearby features
- Forming direction
- Available punch and die tooling
As a practical ASM design guideline, the height of a punched formed feature should generally remain within approximately three times its smallest feature dimension unless the specific geometry and tooling have been reviewed.
More aggressive features may require different geometry, multiple operations, or custom tooling. Custom tooling can add both cost and lead time, which can be especially significant for prototypes and low-volume orders.
Use Existing Tooling When Possible
ASM customers can use our sheet metal CAD tooling library to access downloadable CAD models for louvers, embossments, and other features that correspond with tooling available in our shop.
Designing around existing tooling can eliminate the need to purchase dedicated tooling and gives engineers known geometry to incorporate into the CAD model.
4. Designing Bends Without Considering Press Brake Access
One of the most important sheet metal DFM concepts is also easy to overlook in CAD: a part that can be modeled successfully is not necessarily formable on a press brake.
During forming, the punch and die must physically reach each bend. The partially formed part must also clear the press brake tooling, machine, and previously formed features throughout the bend sequence.
Common problem geometries include:
- Deep boxes
- Tall opposing flanges
- Narrow U-shaped channels
- Return flanges
- Back bends
- Closely spaced bends
- Features that interfere with the punch or tool holder
- Parts that become trapped around the tooling after forming
Bend sequence matters as well. The first few bends may be straightforward, while a later bend becomes inaccessible because an earlier flange blocks the required tooling.
Design for the Complete Forming Sequence
When designing complex formed parts, consider:
- Minimum flange requirements
- Inside bend radius
- Tooling clearance
- Previously formed flanges
- Part rotation between bends
- Whether the part can be removed from the tooling
- Hardware or formed features located near bends
Specialized tooling such as gooseneck punches can provide additional clearance for some geometries, but tooling should not be assumed to solve every interference condition.
When a deep or complex enclosure cannot be formed as one piece, another option may be to divide it into multiple manufacturable components and join them through welding or mechanical fastening.
5. Designing Holes and Hardware Without Considering the Manufacturing Process
Hole diameter and location can affect cutting, forming, hardware insertion, assembly, and final part performance.
There is no single minimum hole diameter, hole-to-edge distance, or hole-to-bend distance that applies to every sheet metal design. The appropriate geometry depends on the material, thickness, manufacturing process, hole function, bend geometry, and any hardware being installed.
Laser-Cut vs. Punched Holes
Laser-cut holes are programmed digitally, so engineers generally do not need to select arbitrary “standard drill sizes” simply to make the feature economical.
For punched holes, existing punch tooling may influence the most economical feature size. If a specific punched feature is flexible, designing around available tooling can sometimes eliminate custom tooling requirements.
Holes Near Bends
Holes and cutouts located close to a bend can distort as the surrounding material stretches and compresses during forming.
How much clearance is needed depends on factors including:
- Material and thickness
- Hole size and shape
- Inside bend radius
- Hole orientation relative to the bend
- Tooling
- Whether minor distortion affects the function of the feature
If a hole must remain dimensionally critical near a bend, identify that requirement so the fabricator can evaluate the appropriate manufacturing approach.
Self-Clinching Hardware Requires Exact Hole Specifications
Hardware holes require additional attention because the mounting hole is part of the fastening system.
For self-clinching hardware such as PEM® nuts, studs, and standoffs, specify the exact manufacturer and part number whenever possible.
The selected hardware should be checked for:
- Required mounting-hole diameter and tolerance
- Minimum sheet thickness
- Sheet material and hardness
- Minimum edge distance
- Clearance from bends and nearby features
- Installation side
- Required thread size and length
- Finish and masking requirements
Do not scale the mounting hole based only on thread size. Different hardware families can require different mounting-hole dimensions even when they use the same thread.
Finishing Is Part of the Design
The finish specified for a sheet metal part can affect much more than appearance.
Finishing requirements can influence:
- Cost
- Lead time
- Finished dimensions
- Hole and slot clearances
- Threads
- Masking
- Electrical grounding and bonding surfaces
- Hardware installation sequence
- Cosmetic appearance
- Corrosion performance
When possible, use established finishing processes and clearly identify the performance or cosmetic requirements that matter to the application.
Specify Powder Coat Requirements Clearly
For powder-coated parts, a RAL number provides a standardized way to communicate color, but it does not completely define the coating.
If important to the application, additional requirements may include:
- Gloss level
- Texture
- Coating chemistry
- Approved manufacturer or product
- Masking requirements
- Cosmetic requirements
- Environmental or performance specifications
For plating, anodizing, chromate conversion coating, and other finishes, identify the required specification, type, class, color, or performance requirement where applicable.
If an exact proprietary coating or unusual specification is required, confirm availability early because specialty finishing requirements can affect both cost and lead time.
Review the Complete Sheet Metal Part, Not Just Individual Features
Good sheet metal DFM requires looking at how features interact throughout the complete manufacturing process.
A hole may be easy to laser cut but distort when the flange next to it is formed. A self-clinching hardware hole may have the correct diameter but be incompatible with the selected panel thickness or hardness. A bend may look simple until another flange blocks press brake tooling. A standard powder coat may create problems if it covers a grounding surface, thread, or tightly fitting interface.
That is why design reviews should consider the entire manufacturing sequence:
- Material selection
- Flat cutting
- Forming
- Hardware insertion
- Welding
- Finishing
- Inspection
- Assembly
Providing both a 3D CAD model and a fully dimensioned drawing gives our team the information needed to evaluate geometry, tolerances, material, hardware, finish, and other manufacturing requirements before production begins.
Get DFM Feedback Before Your Design Is Locked In
Addressing manufacturability questions during the design stage is generally easier than making changes after mating components, tooling, or other parts of an assembly have already been produced.
Approved Sheet Metal works with mechanical engineers and buyers to identify potential fabrication challenges and suggest practical alternatives for prototype and low-volume sheet metal parts.
For additional guidance, download our Sheet Metal Design for Manufacturing eBook.
Have a part ready for review? Request a quote and send us your 3D model and drawing.
Recommended Default Sheet Metal Tolerances
| DIM | Tolerance (MM) | Tolerance (Inches) | Description |
| A | ± 0.13 | ± 0.005 | Sheared Edge to Hole |
| B | ± 0.13 | ± 0.005 | 2 Holes on One Surface |
| C | ± 0.25 | ± 0.010 | Formed Edge to Hole |
| D* | ± 0.76 | ± 0.030 | Holes Across 2 Bends |
| E* | ± 0.76 | ± 0.030 | Holes Across 4 Bends |
| F | ± 0.25 | ± 0.010 | Sheared Edge to Bend |
| G | ± 0.38 | ± 0.015 | Across 2 Bends |
| H* | ± 0.76 | ± 0.030 | Formed Part |
* Dimensions D, E and H are not recommended forms of dimensioning
These tolerances are recommended and best practices. We can obtain tighter tolerances (depending on part geometry/ construction), contact us for more information Download PDF
Common Design Mistakes in Sheet Metal Fabrication FAQ
What are the primary design challenges that often arise in sheet metal fabrication?
The most common challenges revolve around tolerancing, embossments/features, material selection, and finishing. Misunderstandings in these areas can lead to delays, increased costs, and compromised quality in the final product.
How do tight tolerances impact sheet metal fabrication, and what solutions are available?
Tight tolerances in sheet metal fabrication can pose significant challenges. When callouts exceed achievable tolerances, it’s crucial to engage in proactive discussions with a fabrication partner. A “sheet metal first” approach, reviewing designs before machining other parts, and referring to the fabricator’s standard tolerance documents are beneficial strategies.
What considerations should be made when selecting materials for sheet metal parts?
Choosing materials for sheet metal parts involves more than just mechanical properties. The fabrication process, such as bending and forming, plays a crucial role. Consulting with fabrication experts can ensure that material selection aligns with both design requirements and manufacturability.
Unique features often present challenges in standard sheet metal fabrication due to tooling limitations. Accessing a tooling library provided by a fabrication partner can offer pre-designed CAD templates for such features, reducing costs and lead times significantly.
What are some key considerations when selecting finishes for sheet metal parts?
Choosing finishes wisely can prevent budget and timeline disruptions. Standard finishes like standardized powder coatings and in-house plating capabilities are advisable, while relying on obscure or outdated finish specifications from online sources can lead to complications.