Considerations for designing sheet metal enclosures

Customized design of metal plate shells can provide low-cost and rapid market launch solutions for shell electronic products. When purchasing components has become a small matter, local choices are available and can provide high-quality solutions.

When selecting or designing a metal plate shell, the following six things need to be considered:

• Why use metal plates?

• 2. Which material is used?

• 3. Which shape is most suitable for application?

• 4. Dimensional tolerance

• 5. Completion Options

• 6. What assembly and testing are required?

• Consideration 1: Why choose a metal plate shell?

• When is it best to use metal plates to seal the equipment? This is fundamentally related to your application and the outcome you want.

• The manufacturing of custom designed shells using metal plates is usually cost-effective as it does not require a significant amount of cost-effectiveness. Metal plates can be cut by fast methods, such as turret stamping or laser cutting, where the metal is melted by precision laser.

  

• The decision to use a punch or laser depends on whether you need to form a cut or irregular shape. Many manufacturers can choose both.

  
  

• If any of the following statements apply to your application, you should consider using a metal sheet shell:

• Need custom design without high investment in tools.

• The development process needs to allow for low-cost changes to the shell design.

• The shell needs to provide sturdy protection and good mechanical stability.

• This application is suitable for challenging environments such as high chemical resistance and temperature resistance.

• The application requires EMC shielding and conductive connection for grounding.

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• Consideration 2: sheet metal materials

• The type of sheet metal material and its thickness defines the best method for designing and manufacturing an enclosure solution. The two most common sheet materials used for enclosures aresteel and aluminium.

• Steel

• An alloy of iron made by adding small amounts of carbon and other elements to make suitable for forming and fabrication. Typically, the types of steel used for enclosure production are:

• Mild steel: Natural mild steel is generally not suitable for wet or high-corrosion environments.

  Surface treatments such as paint or heavy treatments like zinc anneal or galvanising can help. It is important to be aware of the environment if this material is to be used.

• Stainless steel: Grade 304 can be considered the most common grade of stainless. Grade 316 offers vastly superior corrosion resistance to chlorides and acids and so is better suited to applications in corrosive environments or medical enclosures where solvents and heavy cleaning is required.

  
  

Aluminium

Compared to soft steel, aluminum is lighter and can resist corrosion even in unfinished situations. Although not as sturdy as stainless steel, it is much lighter and is a better thermal and electrical conductor. Aluminum is more reactive than stainless steel, therefore it is not suitable for certain chemical and food environments.

• 5005 and 5052 alloys are the most commonly used shells in Australia. Both have good weldability, formability, and corrosion resistance in marine environments. 5052 is much stronger than 5005, but has slightly better conductivity. Both are good choices for shells.

• The shell can use a harder and more corrosion-resistant 6061, but it must be carefully formed because if the bending radius is too small, 6061 will crack.

Consideration 3: shape of enclosure

It is important to think of the shape of the enclosure at the system design and PCB level process to avoid some common pitfalls. When compared to a moulded plastic enclosure, sheet metal is limited. However, it is possible to design cost-effective, functional and aesthetically appealing enclosures from any of the following common shapes.

Consideration 4: dimensional tolerances

Sheet metal enclosures require cut-outs and folds. Things to consider when specifying dimensional tolerances are:

• Keep your tolerance as wide as possible to allow some flexibility in tooling.

• Unless critical, avoid tight clearance around I/O components and fold to fold.

• If possible, provide symmetric tolerances for all clearances.

• Highlight critical dimensions and tolerances in your CAD drawings.

• Keep in mind that fold allowance factors will vary between manufacturers.
  

• Review how easy it will be to produce the cut-outs required.

• Are there any unusual or formed shapes or holes?

• Are small burrs or ‘nibble’ marks acceptable inside the shape?
  

• Avoid distortion.

• Check cut-out sizes and spacing. Distortion can occur if cut outs are too close.

• Check that folding allowance will not distort holes close to the fold or edge.

Consideration 5: finishing options

The look and function of a sheet metal enclosure can be greatly enhanced with the right finish.

Plating

• Mild steel

• Zinc plating provides corrosion protection, but it does not improve the look so usually paint is also required.

• Aluminium

• Chromate conversion can improve corrosion and electrical conductivity, but is prone to marking

• Anodising is an oxide film on the surface to make it more scratch resistant and more durable.

Painting

• Wet spray (rarely used) can provide a smooth or textured finish but requires a highly skilled operator to perform.

• Powder coat, which is easier to apply, is very durable with a large array of colours and finishes available as standard.

Labelling

The labelling will largely depend on the design of the enclosure.

• Screen printing — Costly for multicolour as each screen must be separated.

• Digital print — Works well on flat services and has some height restrictions.

• Decals or labels — Wide range of options available.

• Laser marking — Indelible, monochromatic labelling.

Consideration 6: assembly and testing

Consider enhancing the design by adding other custom sheet metal parts or assembly of certain elements during the fabrication process.

A few examples are:

• Brackets

• Fasteners

• Cable glands
  

When it comes to testing, consider:

• IP test/IK test

• Climatic and corrosion test

• Flatness testing

• EMC testing
  

This can all be considered in the design of the enclosure and may even be facilitated by the manufacturer since many can provide a one-stop source for custom, fully finished and partially assembled enclosures.

Yishang designs and manufactures large and small enclosure solutions for a wide range of applications. For more information, visit:https://www.zsyishang.com/products.html