February 10, 2015


 

As an Industrial Design student, I have a profound interest in manufacturing processes. Learning about how things are made is fascinating and really help to come up with innovative ways to make products. DFM (Design For Manufacture) is one of the subject that we are being taught at school, however, there is no better way to learn about that stuff than experiencing it first hand. Since access to manufactures is limited, I found incredibly helpful to just strip down products in order to understand how they are made, and more importantly, how they have been designed.

The speaker used as a case study here is mostly made of injection moulded ABS parts. Injection moulding is how most of the plastic products surrounding us are made and therefore is an important one to know for designers.

This process is used to produce everything from car bumpers to toothbrushes. It is so widely used because it allows to create complex objects at high speed. Although the tooling costs are very high (often tens of thousands), it will then be possible to mass produce those parts at a low production cost.

 

 
Image Source: LearnEasy

Image Source: LearnEasy

 

This is how it works: 
Granulated plastics are fed into the hopper. The screw pushes those granules through a heated tube and as they progress forward, they start melting up to a liquid state. The screw then translates towards the mould to build up the pressure inside the tube. Once the valves opened, the liquid plastic is injected in the mould at high pressure. The cycle time depends on the wall thickness of the parts and the type of plastic used but usually last between 30 and 60 seconds.

 

This speaker is manufactured by Iriver (formerly iRiver), a South Korean electronic company well known for their early MP3 players. I've purchased this model in Korea in 2012 for less than £100. I found this brand to be selling rather affordable and good quality products.

Dismantling electronic devices requires a few tools like precision screwdrivers, scalpel/knife, pliers, etc... And a camera!

Documenting every steps of the breakdown will become very handy when putting the product back together.

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We usually don't think about all those mechanisms and electronics living inside those shiny products. However designing the inside correctly is essential for the durability and recyclability of the product. This speaker was easy to take apart since most components were either screwed to the chassis of clipped to each other.. No glue at all!

Here the CD player was screwed to the bottom of the main ABS body and plugged to the circuit board on the left. I had to unplug a lot of wires and belts to be able to progress.

All this work was mainly to let me analyse how plastic parts were designed for injection moulding and assembly. Here we see the front panel clips which are designed to snap to the main body. Notice the bosses in which the circuit boards are screwed to.

The speaker mesh is stretched over a plastic chassis which is snapped to the main body. In order for the mesh part to hold onto the main body, the male/female clips need to be assembled tightly. This is achieved by adding tiny ribs around the male clip which will be forced into the bosses of the main body.

The polyester mesh is applied to the plastic chassis by burning its edges on the inside. Ingenious as it removes the need for another solvent but isn't the neatest method.

Undressed.

Electronics weaved between plastic parts.

Once all dismantled, you get a sense of all the thinking and designing that went into the production of such a complex product.

The beauty of plastic!
I am actually really amazed that such a complex part was produced in one mould.

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The ribs are those repetitive lines on the inside of plastic parts. Their main purpose is to add structural rigidity to the object and prevent it to break or bend too much. Note that it is better to have many thin ribs as deep ones may cause sink marks on the other side of the part.

Again, ribs and boss surrounding the speaker hole.

The ventilation holes were also produced in-mould to avoid time consuming and expensive process afterward.

One of the most important thing to consider when designing plastic parts are draft angles. If looked at closely, we can notice that the walls of the part are slightly slanted and not at 90˚. Without this small angle, the part wouldn't get ejected out of the mould. 

The smallest draft angles needed on vertical faces is usually 0.5˚ but this depends on the material and surface finish. A textured finish will need a greater draft angle.

 

Injection moulding allows various surface finishes in the same mould. Notice the transition between the glossy surface and the rough texture of the bottom of the body. This is achieved by machining the desired texture directly in the mould through EDM (mould machining process) so the liquid plastic can pick up all the little details.


Control Panel

The control panel is made of multiple plastic parts.

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The round buttons boast live hinges that permit the little sticks to press the electronic buttons on the circuit board.

This semi-transparent disc is added to add some opacity and softness to an LED. It is snapped on 4 little extrusions.

The design of those parts require rigorous consideration of all the components needed to the assembly of the product. This included fixtures for screws, holes for LEDS, and clear panels for screens.


Ribs

Ribs are like the skeleton of plastic parts. They help to hold everything tight together.


Split Lines

Last thing: split lines (or parting lines). They are those seams that we notice on the surface of the product. They are caused by the intersection of two parts in the mould. They are often polished off on high-end products but for fast consumer goods, manufacturers usually can't afford an additional expensive process. However, designers can find ways to use those seams cleverly as part of the design language of the product. On the picture above, the split line is clearly visible at the start of the rounded corner.


Rebuild

After dismantling the product, the not-so-fun part is to put it all back together. And making it work again!
I got a little scared with this one as the left speaker wouldn't work after reassembly. Fortunately it was just a connector unplugging itself when screwing the back panel back..

This is it for my first post on manufacturing processes. I hope that this was an informative or at least interesting read. If interested about this subject, I highly recommend a book written by my tutor Rob Thompson: Manufacturing Processes for Design Professionals. Probably the best volume written on manufacturing for designers. 

Posted
AuthorJonathan Gomez