Which manufacturing method is best for enclosures?

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.

 

 

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.

 

 

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).

 

 

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.

 

 

 

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).

 

 

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.