Design 3D printing - your route to prototype enclosures

Design 3D printing - your route to prototype enclosures

2013/08/06

Beneath the hype, 3D printing is a cost-effective way to build prototype parts for electronic prototypes. And you don’t have to be a CAD genius to generate the necessary design data.

3D printing is particularly suitable for constructing custom enclosures, but knobs, air ducts, and motor mounts are the next items on an infinitely long list.

“All day every day we are making PCB housings,” Nick Allen, director and founder of London-based 3D Print UK told Electronics Weekly.

3D printers come in all shapes and sizes. You can assemble a kit for a few hundred pounds, buy a capable printer for a few thousand, or you can email your design to someone who has paid a few hundred thousand and will make it for you.

“You can buy a printer for £500 or £600,” said Allen. “You get what you pay for.”

3D Print UK is one of several companies offering printing services – email the design in, and receive the finished item by post a few days later.

His particular printer, from German firm EOS, cost a quarter of a million pounds. He offers printing for as little as 10p/cm3 (volume of the rectangular block the item can be made within 8-10 days. 20p for two day service).

Do-it-yourself

Lower-cost printers tend to build up layers using something like a mechanised hot-melt glue gun – a hot nozzle fed from a reel of plastic fibre on an X-Y gantry, over a table that can be incremented downwards for each successive layer.

This type of printer builds up structures in free space, so it you want to make an inverted pyramid you have to add support features or it will fall over in the printer.

Results can be remarkably good ( scroll down)

More expensive printers are based on layers of powder in a box. Each new layer has a pattern drawn in it, for example by powerful laser, which sinter or melts the particles to their neighbours.

With sintering, powder particles remain solid, but melt where they touch neighbours to form a solid structure with voids. Depending on the process, the voids can approach negligibly small.

Unused powder remains packed around the structure as it is built up, so support structures are unnecessary.

Other processes can involve moving the focus point of a laser through a transparent liquid bath to polymerise it into solid, printing with an ink-jet print head – which can produce full colour models in some materials, and stacking/gluing paper cut-outs.

Unless you are a Formula One team or NASA, you are unlikely to be able to afford to have metal printed, so your choice is from various plastics, or plaster-like materials.

That said, there is an aluminium/nylon mix called Alumide which looks somewhat like metal, even if its thermal conductivity is 0.5-0.8 W/mK so it is hopeless for heatsinks (aluminium is 200W/mK).

And last month, in what was purely a technology demonstrator, North Carolina State University printed small conductive metal 3D structures using an alloy called EGaIn (75% indium, 25% gallium, melting point 15.7°C).

Plastics tend to be robust, handle-able, and limited to one or a few colours in their raw printed state. It is even possible to form elastomer objects on some printers.

Plaster-like materials are: easy to paint (or sometimes multi-colour printable) and can be detailed, but are brittle and therefore better for static things – table-top models for example.

“There is no perfect printer,” said Allen. “It is like cars. Not all cars are the same, and every printer has advantages and disadvantages. For example: “printed nylon has a 173°C melting point. Some resins melt at 50°C, but will take much more detail than nylon”.

With his company’s focus on low-cost printing, it offers any colour and material you want, so long as it is white nylon.

“We regularly get asked why we don’t do full colour printing, and the answer is simple, full colour printing can only be done in a plaster material, it has no flexibility, it’s brittle and has a rough texture,” said Allen. “We feel that nine times out of ten, you’re better either having plain white, or painting yourself. We will add black soon.”

The chemistry of nylon, unlike most other plastics, makes it colour well with certain fabric dyes. It is a simple process involving boiling water – Allen recommends looking it up on YouTube, and points out his products might absorb dye, but are waterproof.

With the right primer, plastics can also be painted.

What 3D printing is not going to deliver is a smooth polished surface. All of the printing processes leave signs that the object was built in layers. Some printing firms offer surface finishing as an additional service, some leave it to the customer.

What is the natural surface finish of Allen’s EOS selective laser sintering?

“It looks and feels like Extra Strong Mint,” he said. “Although it is not brittle like a mint, not on our machine. It is fantastic for non-aesthetic items unless you want to do post-processing.”

Building items in layers also gives them a ‘grain’ to a greater or lesser extent, so this anisotropic behaviour needs to be taken into account where strength is important.

A right-angled joint between a 1mm thick horizontal sheet and a tall vertical wall 1mm thick is going to be marginal at best.

However, finished objects in the right material can be strong enough for any human handling. Allen shows a video of a man failing to break a 3mm-thick object printed in nylon.

Different processes and materials have different physical design limitations.

In Allen’s process, 0.1mm or better local resolution is possible, but temperature gradients in the chamber can make for lower longer-distance precision.

Some bowing is possible in long thin objects, but can be minimal “0.5mm on a 30cm strip sometimes. 1mm is thinnest we recommend on short things, it can be thinner. On longer things, thickening them up will prevent warpage”, said Allen. “We have never have problems with PCBs fitting in enclosures, and we make a lot of Raspberry Pi cases.”

But when you are paying by overall volume, and there is no need to worry about the shape limitations of injection moulding, stiffening webs are for free, as are mounting holes, board guides, lugs, spigots, trunnions, and any number of other Victorian-sounding projections,

Every detail, mount or hole you add to the enclosure in the design stage is one you will not have to engrave, screw-on or drill later on.

This said, threads are best formed by tapping a hole after construction, or by adding a pocket for a push-in threaded insert.

Maximum size varies from printer to printer. At 3D Print UK, it is 300x230x190mm, and 1x1x8mm, or 8x8x1mm, minimum. Recommended minimum height there for surface detail to show is 0.4mm.

Maximum recommended thickness is 5mm.

The object will be close, but not identical, to something made from the same design information by normal production techniques.

“Materials can behave differently than they do in an injection moulding,” he said.

What shouldn’t people expect?

“There is too much hype, a lot of things out there won’t live up to expectations. People seem to think you will have a printer in every room and print everything.”

He sees 3D printing as perfect for one-offs, or maybe five items, or 10-20 units in a limited production run.

Design-in-yourself

3D printers generally want their data in an STL file, which describes a solid shape as a series of inter-connected surface triangles.

SolidWorks and AutoDesk Inventor are professional packages well suited to producing files for 3D printing, according to Allen.

Then there are free packages: Autodesk 123D (check conditions) and SketchUp (once Google SketchUp, now owned by Trimble).

SketchUp is particularly easy to use, even from a standing start, and there are plenty of enclosure-related how-to videos on YouTube – try searching for ‘subwoofer SketchUp’.

There are a number of CAD school boy errors that will mess-up the end product: one is leaving infinitely thin gaps between adjacent shapes rather than connecting them into one solid shape. Another is constructing a solid shape out of surfaces, but leaving a side off or a hole in one of the surfaces.

“We check STL files here,” said Allen. “We generally do this for free. We will sort it out if it is easily do-able, or tell them.”

If your prototype PCB already exists, it is possible to use its design data to produce a 3D model of it suitable to design the enclosure around.

Distributor Element14 advocates the use of Eagle as a free (check licencing) PCB tool, and there is EagleUp, an Eagle to SketchUp converter, and a tutorial at Dangerous Prototypes.

RS Components has something similar: a PCB design suite and converter for SketchUp

Element 14 has a 3D printing community, and RS offers 3D CAD models of its products.

For hundreds of examples of what is possible with 3D CAD, try looking through the Thingiverse (a site linked to New York printer firm MakerBot) – view the gadget and hobby categories. There is an enclosure with added lugs and other features, for example, an enclosure for an LCD, or a servo mount.
And although printing bearings in-situ is a bit risky, watch this video to see what is possible at the limits of 3D printing.

Welcome to SUV System Ltd!

SUV System Ltd is ISO 90012008 Certified electronics distributor with 10 years of experiences.

We have built up long term business relationship with about many companies which are stockers and authorized agents. we have a steady and reliable supply to meet customer's demands to the greatest extent .Confidently, we are able to lower your cost and support your business with our years of professional service.

SUV System Ltd is Electronic Components Distributor Supplies,Find Quality Electronic Components Supplies Products IC(Integrated Circuits),Connectors,Capacitor,Resistors,Diodes,Transistors,LED at Suvsystem.com. Sourcing Other Energy, Environment, Excess Inventory Products from Manufacturers and Suppliers at Suvsystem.com

Electronic Components distributor:http://www.suvsystem.com

Connectors Distributor:http://www.suvsystem.com/l/Connectors-1.html

IC Distributor:http://www.suvsystem.com/l/IC(Integrated-Circuits)-1.html

LED Distributor:http://www.suvsystem.com/l/LED-1.html

Capacitor Distributor:http://www.suvsystem.com/l/Capacitor-1.html

Transistor Distributor:http://www.suvsystem.com/l/Transistors-1.html

Resistor Distributor:http://www.suvsystem.com/l/Resistors-1.html

Diode Distributor:http://www.suvsystem.com/l/Diodes-1.html

SUV System Ltd insists on the managing faith ofsincereness,speciality,foresight, win-win,so we build up stable-relationship customers located all over the world, including the States, Europe, Argentina, UAE, Malaysia, Australia,and India etc

we are focus on the following fields,and hope we can help you.

ST Transistors Infineon Technologies Transistors Vishay resistors Ligitek LED Kingbrigt LED Connectors IC(Integrated Circuits) ELPIDA IC Fast Recovery Diodes Thin Film Resistors INFLNEON Diodes IR transistor TI IC Switches components Electronic News Current Sensors Resistors High Precision Resistors Renesas parts IC Atmel IC LED Fleld Effect Transistors YAGEO Resistors LITTELFUSE Diodes LINEAR IC Zener Diodes Military IC NXP Diodes TDK IC Metal Can Packages Transistors MAXIM IC Resistor Arrays ST Diodes FAIRCHILD diodes Schottky Diodes Diodes TOSHIBA Transistors NXP Transistors Transistors Freescale Discrete Semiconductor Transistors
http://www.suvsystem.com/a/4684.aspx