Custom metal enclosures for products - an alternative to injection moulding

Many designers rush to injection moulding when designing enclosures for electronic products. Often there are many other alternative options. Here we consider custom metal enclosures with a case study  using the PAT-IT Portable Appliance Tester. More examples can be seen in the book "From Prototype to Product - a Practical Guide for Electronic Engineers".

When this product was first planned in 2002, our expectation was to sell around 200 per annum. Hence we discounted an injection moulded case, for the same reasons as for the Microwave Checker. That is, we could not justify the cost of the tooling, as the product was speculative and we could not be sure whether we would recover the cost of our investment.

Instead we decided to go for a custom metal enclosure.

The benefits of this approach was that there was no tooling costs, it gave us a robust enclosure with all the necessary apertures for displays and buttons and cost less than £10 when purchased in volumes of around 100.

 

 

The case parts are powder coated to give them a nice finish. To complete the product, we used a custom label. The finished product can be seen below.

Although this approach gave us a good solution for the enclosure, the internal assembly gave us issues during maintenance. The top of the case held the switches, connectors and the display while the base held the main PCB assembly. When opening the case to gain access to the electronics, the length of the wire looms prevented an engineer from working on the PCB without disassembling the whole case. 

 

 

 

One way this could have been overcome is to assemble the PCB into the lid of the PAT-IT with the base just being a covering. This would have made access to the electronics a lot easier.

 

Design for disassembly

It is important to put some thought into what happens to the product after it has been sold. Many of the products that I have been involved with have been in use for more than 10 years. In this period, they are often returned for calibration or repair. A good design engineer will design in easy disassembly, to allow the repair technician quick access to the electronics.

In summary:

There are many altrnatives to injection moulding when designing enclosures for electronic products. A good engineer will make a decision based on forecast sales volumes.