Which manufacturing method is best for enclosures?

Manufacturing enclosures: CNC machining vs injection moulding vs 3D printing vs sheet metal fabrication

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An enclosure, sometimes known as a housing, is a box-like structure and essential component of many products. Enclosures usually provide protection and containment of internal components.

Electronic enclosure - 6082 T6 - powder coated

The process of manufacturing enclosures requires careful consideration regarding the design and material selection, as well as the manufacturing method. 

With various manufacturing methods available, choosing the right one for a particular application can be a challenging task. 

In this article, we will examine the most common manufacturing methods for enclosures, including CNC machining, injection moulding, 3D printing, and sheet metal fabrication. 

We will explore the advantages and disadvantages of each method, the materials suitable for each process, and the considerations when designing an enclosure for each manufacturing method. 

This article is intended for buyers and design engineers who are researching ways to manufacture an enclosure or housing for use in their final product. 

By the end of this article, you will have a better understanding of the best manufacturing method for your enclosure needs.

CNC Machining

 
What is CNC machining?

 

CNC machining is a subtractive manufacturing method. It uses pre-programmed computer software to relay a toolpath which tells a machine how and where to extract material from a block of material. The extraction is undertaken by motorised cutting tools.

 

For a full overview of CNC machining including what it is and how it works, the benefits and limitations, choosing materials and design parts for machining, see our CNC Machining Guide.

 

CNC miller working with CNC milling machine

 

Advantages of using CNC machining to manufacturer enclosures


There are several benefits of CNC machining custom enclosures, the main ones outlined here.

Accuracy and tight tolerances

Where tight tolerances are required, CNC machining can be very effective. The use of CAD results in extremely high accuracy parts.

 

A general machine tolerance of +/-0.1mm geometric tolerance is usually easily achieved with a surface finish of 1.6µm (micrometer) but tolerances tighter than 0.01µm can be accomplished where required.

 

Cost efficiency

CNC machining is suitable for prototypes, one-offs and small to large batch production although most cost-effective on small to medium runs.

 

There are significantly fewer upfront costs associated with CNC machining than there are with 3D printing and injection moulding.

 

There are also several ways that you can cut costs when machining an enclosure including:

  • Material selection – balancing the required properties with cost
  • Opening tolerances where appropriate
  • Specify surface finishes to reflect customer and non-customer facing surfaces
  • Specify as large a corner radius as possible
  • Specify the correct size and depth tapped hole - Going longer than optimum will not bring any additional strength, but will add cost through custom tooling requirements
  • Consider the position of PCB upstands, islands or bosses with tooling in mind

 

Time efficiency

The process of CNC machining an enclosure or batch of enclosures is reasonably quick. The set-up time is famously fast compared to other manufacturing methods. It is also easily repeatable; once the design is created, it can be accurately repeated.

 

It is worth noting that lead times may vary according to the popularity of your chosen CNC machined parts supplier. Sought after companies will invariably have longer lead times so it’s worth factoring this into your process where possible.

 

Superior quality

There’s a reason why CNC machining is sometimes called ‘precision machining’. It is a precise manufacturing method and is associated with exceptional quality and excellent physical properties.

 

Where high performance is required for your enclosure, CNC machining may be an obvious choice.

 

Range of materials

Whether you want to manufacture your enclosure in metals such as aluminium or stainless steel or an engineering plastic, CNC machining offers the broadest range of material options.

 

This means you can select the most appropriate material for their desired properties and cost with few limitations which cannot be said for other manufacturing methods. More information about material options can be found below.

 

Material options for CNC machining enclosures


Enclosures can be machined in a range of materials, namely aluminium, stainless steel and engineering plastics.

 

Aluminium

Aluminium is the most popular choice when it comes to CNC machining enclosures because it’s lightweight, the raw material is comparatively low cost and it’s available in a broad range of sizes.

 

Add to this that it is highly machinable; it generally has shorter run times due to the high rate of material removal and tight tolerances are easily achieved.

 

Tip: A high quality finish can easily be achieved with aluminium 5083 and finished with anodising.

 

Aluminium soft sulfuric blue anodised enclosure

 

Stainless steel

You may wish to use stainless steel for your machined enclosure where certain properties are required. For example, if your enclosure is going to be used in a harsh environment or come into contact with chemicals, stainless steel may be a more obvious choice.

 

Tip: We recommend stainless steel grades 304 and 316 to our customers for their balance between corrosion resistance and value for money.

 

Engineering plastics

Plastic is often chosen for enclosures that need to be lightweight and it can be a cost-effective choice.

 

If plastic is desired, sometimes it is suitable to choose an off the shelf moulded enclosures and then modify it to your specific requirements with machining.

 

The two most common grades of engineering plastics for CNC machined enclosures are Acetal, such as Delrin®, and ABS (Acrylonitrile Butadiene Styrene).

 

Cerakorte coated aluminium 6082 T6 enclosure base

 

Design considerations for CNC machining enclosures

 

Tolerances

Designers should carefully consider the tolerances of their enclosure design. Where more open tolerances are suitable, it is recommended to state this on the drawing as this can reduce machining time and therefore cost.

 

It may be that there are some areas of the design where a tight tolerance is critical to the function and others where fit and tolerance can be relaxed.

 

Surface finish

Another important consideration on your enclosure drawing is surface finish. Often the inside of an enclosure is not ‘customer facing’ and therefore the surface finish could be relaxed to Ra3.2µm or greater. This will reduce time on the machine and ultimately reduce unit cost.

 

Corner Radii

Specifying as a large a corner radius as possible will allow a machinist to use a larger, standard, off the shelf cutter which will save time as well as costs on specialist cutters.

 

Tapped Holes and PCB Upstands

Generally, to get the maximum strength from a tapped hole, the thread depth needs to be 2.5 x Ø. For example, an M3 x 0.5mm pitch tapped hole needs a maximum thread depth of 7.5mm (3x2.5mm).

 

Going longer than this will not bring any additional strength, but it will add cost through custom tooling requirements.

 

Similarly, the location of features such as PCB upstands, islands or bosses within enclosures should be considered with tooling in mind. Siting such features close to the wall of your enclosure design will make it much more complex to machine. Grouping these features together can be the most efficient design for machining.  

 

Our blog Electronic Enclosure Design for Machining in 2023 contains a comprehensive rundown of our expert tips and advice when it comes to designing enclosure for CNC machining.

 

 

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Injection Moulding


What is injection moulding?


Injection moulding is an additive manufacturing process where a material in liquid form is quite literally injected into a mould. The material is then solidified which results in the finished component.

Injection moulding enclosure

Advantages of using injection moulding to manufacturer enclosures

 

Cost efficiency

Injection moulding can be a cost-effective manufacturing method for custom enclosures but only when a very high volume of components are required.

 

A lot of initial work goes into injection moulding: a prototype of the part needs to be machined, then a mould can be created using the prototype and only once a mould is available can the injection moulding process begin.

 

Less wastage

Due to being an additive manufacturing process, a reasonably small amount of material is likely to be wasted when injection moulding an enclosure.

 

Consistency

Once all the groundwork has been carried out, injection moulding is very good for producing bespoke enclosures that are as close to identical as is possible. This is particularly beneficial if your enclosure is to be used as part of an assembly.

 

Material options for injection moulding enclosures

 

Injection moulding is traditionally carried out using plastics. Metal injection moulding (MIM) can allow parts, including enclosures, to be moulded using steel, stainless steel and high temperature alloys but it is considered to be a complex and expensive process.

 

Engineering plastics

A wide range of plastics are suitable for injection moulding enclosures including: ABS, polycarbonate, thermoplastic polyurethane (TPU), acrylic (PMMA), nylon polymide, polyethylene and acetal.

 

Design considerations for injection moulding enclosures

 

Is your part being machined or 3D printed first?

If your part started its life being manufactured through CNC machining or 3D printing, there is a good chance it will require at least some tweaks to the design.

 

If you are in the early stages of designing a part for CNC machining or 3D printing with a view to moving over to injection moulding once economies of scale allow, it is recommended that you create your design in a way that suits both manufacturing methods.

 

A detail specification should be supplied to your chosen injection moulding supplier. This should include temperature requirements, aesthetics and structural integrity.

 

Wall thickness

It is more cost effective to maintain the same wall thickness throughout the enclosure.

 

The thickness of the wall will depend on the application and required performance, but it is worth bearing in mind that thin walls are at higher risk of manufacturing issues and very thick walls are more expensive.

 

Ribs and bosses

Bosses and ribs can be used to improve the structural integrity of thinner-walled areas. This can reduce the amount of material required and cycle time, potentially reducing the overall cost.

3D Printing


What is 3D printing?

 

3D printing is another kind of additive manufacturing. A part is produced by building it up layer by layer using specialist machinery such as a laser or heated extruder.

 

There are several different 3D printing manufacturing methods including FDM (Fused Deposition Modelling) for rapid prototyping, material jetting, SLA (Stereolithography) and SLS (Selective Laser Sintering).

 

3D printer for manufacturing enclosures

 

Advantages of using 3D printing to manufacturer enclosures

 

Complexity of design

3D printing can be a good option if your enclosure design is particularly complex. Intricate geometries, curves, and hollow structures can be created, which can be challenging or unattainable using alternative techniques.

 

Range of connection options

There are a number of options when it comes to securing 3D printed enclosure assemblies including snap-fits and push-fits, interlocking joints, threaded fasteners and living hinges.

 

Quantities

3D printing is much more suitable for smaller quantities of enclosures and other components as it is not usually economically viable to 3D print at scale.

 

It is therefore more often used for prototypes and then scaled up using CNC machining or where appropriate and for very high quantities, injection moulding.

 

Time

Once a design is proven, an enclosure can be 3D printed very quickly. Depending on the size and complexity of your enclosure, you have the potential to shorten the printing time to hours or days.

 

Of course, lead times will vary between suppliers and good 3D printers may be booked up months in advance.

 

Material options for 3D printing enclosures


3D printing is somewhat limited in its material offerings. Traditionally 3D printed components, including enclosures, are manufactured from plastics such as a plastic resin or filament.

While more options to 3D print metals are being introduced, this is a much more expensive option.

3D printing materials include Nylon (PA11, PA12), thermoplastics such as PLA, PEI and ABS and thermoset photopolymer resins.

 

Design considerations for 3D printing enclosures

 

3D print internal components

When using 3D printing within prototyping, it is recommended to 3D print the internal components as well as the enclosure itself to check fit and positioning.

 

Wall thickness

A thickness of no less than 2mm is recommended for 3D printed enclosures with a tolerance of 0.5mm around internal components and ± 0.25mm for clearance.

 

Uniform wall thickness is good practice for 3D printing but is also necessary if your design will eventually be injection moulded.

 

Corner Radii
Similarly to CNC machining, it is recommended to add a radii to corners where possible. This will make the structure stronger as well as easier (and therefore quicker and cheaper) to 3D print.

 

Consider structural elements

While structural elements such as ribs and gussets aren’t absolutely essential as they are for injection moulding, they can still improve rigidity and help to distribute stresses throughout the part.

Sheet Metal Fabrication

 

What is sheet metal fabrication?


Sheet metal fabrication is a manufacturing process where flat sheets of aluminium, stainless steel, and occasionally mild steel, are formed into a desired shape.

There are three main processes: cutting, bending and assembly. Other processes include punching, folding and stretching.


Sheet metal fabrication is a common manufacturing method for enclosures within computers.

 

Sheet metal fabrication to manufacture enclosures

 

Advantages of using sheet metal fabrication to manufacturer enclosures

 

Professional finish

It’s relatively easy to achieve a professional finish with sheet metal fabricated enclosures because they lend themselves to powder coating. Powder coating is reasonably inexpensive and known for being highly durable and weather resistant.

 

Other commonly available finishes for sheet metal fabricated enclosures include anodising and chromate plating.

 

Lightweight

The process of manufacturing from sheet metal includes thin sheets of metal. Aluminium enclosures fabricated from sheet metal in particular are very lightweight.

 

Where weight is a key design consideration and your application requires below average weight, sheet metal fabrication may be the solution.

 

Cost-effective

Sheet metal fabrication can be cost-effective for prototypes all the way up to large batch production. It is very easy to scale up production.

 

Affordable materials

The sheet metals from which enclosures can be fabricated are generally affordable. Sheet metals that are held in stock are the best choice to reduce costs and improve lead times.

 

Material options for sheet metal fabrication enclosures

 

Enclosures can be fabricated in aluminium, stainless steel and mild steel. The material you choose will depend on your requirements.

 

Aluminium is often selected when a more lightweight and corrosion resistant enclosure is required.

 

Stainless steel is also corrosion resistant but it is particularly sought for its excellent strength and hardness. This does come at a cost.

 

See below for our summary of steels for sheet metal fabrication.

 

Aluminium

Aluminium 5251 is a popular sheet for fabrication; it’s lightweight, high strength and has good corrosion resistance.

 

Stainless steel

Stainless steel 316L and 304 are commonly used grades of sheet metal for fabrication. 304 is less expensive than 316L but has slightly lower mechanical strength and is corrosion resistant to a slightly smaller range of chemicals.

 

Steel

Hot rolled steel (HRS), cold rolled steel (CRS) and cold galvanised steel are commonly used.

 

HRS is easier to work with and suitable for large batch production but harder to keep to tight tolerances than CRS.

 

CRS is more expensive than HRS but has increased strength and hardness and tighter tolerances.

 

Cold galvanised steel has a protective zinc coating applied to its surface so provides extra corrosion protection and increases life expectancy of the enclosure.

 

Design considerations for sheet metal fabrication enclosures

 

Which shape?

There are only so many options available when it comes to the shape of a sheet metal fabrication enclosure design. The most common ones are:

 

  • Folder box – four-sided box shape with lid
  • L-shape – simple geometry and easy access
  • F-shape – simple to produce and suitable for PCBs that have connectors on either side
  • U-shape – simple to produce, solid base and easy access

 

Deviating from these and including complicated design elements will undoubtedly increase costs and lead times.

 

Sheet metal thickness

When designing an enclosure for sheet metal fabrication, you need to consider that you will be working with a uniform thickness.

 

Thus selecting the correct thickness for your enclosure application is imperative and will have a huge bearing on the final strength and weight of the enclosure.

 

Larger enclosures would usually lend themselves to a thicker sheet metal and smaller enclosures to a thinner sheet metal. The thickness you choose must be consistent on all faces of the enclosure.