The engineer’s guide to 3D printing

Steven Parham takes looks at 3D printing.  This process has literally been a game changer for thousands of engineers and other professions over the past decade, thanks to the possibilities that the technology has brought to the fore.

Something that would have been considered fanciful or downright impossible up until a few years ago is not only a reality, but an affordable proposition.  Steven takes a look at what is involved, how some of these processes work, and how to go about making your own 3D prints.

Introduction

In the last 10 years, 3D printing has finally come of age. The technology has become both widespread and a cost effective way to prototype all manner of solid objects, which can be used in the real world for any number of applications.

So, what is the technical definition of 3D Printing? In short, 3D printing is the mechanical manufacturing process where objects are built up in layers or formed with other means, which means that a solid physical object can be created from a digital design such as a CAD drawing or model.

As you would imagine, there are various 3D printing technologies and materials that are in use, but in effect have the same ultimate goal – turning a digital model into a solid three-dimensional physical object by adding material layer by layer (an additive process).

It is easy to believe that 3D printing is a relatively new thing. The truth is that the technology has been around for more than 30 years.

An inventor at the University of Colorado, Chuck Hull was working on a process to cure table top varnish using an ultraviolet light process. What he discovered in the process was that he could build materials up in a controlled layered fashion. This was in fact the first 3D printing process which he christened Stereolithography back in 1983. Soon after, he filed a patent, defining stereolithography as ‘a method and apparatus for making solid objects by successively printing thin layers of the ultraviolet curable material one on top of the other’.

Hull’s original patent described ‘printing’ by means of a light curable liquid. When Hull founded his company 3D Systems in 1986, it dawned on him that stereolithograhy was not merely confined to liquids, so he redefined the principles of Stereolithography as ‘any material capable of solidification or capable of altering its physical state’. And thus, a new technology was born – Additive Manufacturing.

The process

All 3D prints begin at the digital 3D design file stage. The model has to be created using modelling software such as a CAD package. Once this is produced, that model is processed, and very thin slices that will build the final model are processed and sent to the 3D printer to build up. Some printers work by melting a plastic extrusion from a reel through a head, which acts in much the same was as a normal printer head, except that for each layer it moves in the third axis, the Z plane, as it builts up the model. Others use a vacuum forming process, or work by sintering metal powder with a laser beam at high temperature to create the model.

Even then, these models need some form of tidying up and finishing once completed, and creating a model take different amounts of time from system to system. There is also the cost of printing in 3D. Filament extruding methods are comparatively cheap these days, whereas laser sintering is still financially prohibitive for the small engineering firm. Even so, a 3D model file can be sent off to be printed professionally.

The range of materials that can be used in 3D printing is also increasing. Houses can even be built using a large scale 3D printer. The applications of this technology are staggering, and some of the materials that can now be used include metals and alloys, plastics and rubber, sandstone, silicates: the list goes on.

Ten years ago, 3D printing was severely restricted to those that could just about afford to use it. That was until the patent for Fused Deposition Modeling (FDM) expired in 2009. This suddenly made 3D printing affordable – as a result. the cost of the average 3D printer dropped through the floor. What cost £100,000 originally for 3D printing could now be done by a similar machine for £1000 or less.  That cost has come down drastically in the last two years alone.

3D printing is a fast moving technology, and as such has its advantages and disadvantages. Any new manufacturing process often takes time to gain traction, and more often than not, comes with a variety of pros and cons for its use in the real world. Let’s take a look at some of them.

Rapid prototyping

One of the main advantages of 3D printing is that the final objects often require very little in the way of tooling or finishing. Which means that it is a very cost effective way of producing bespoke and small production runs. It also makes design modifications an easier, less expensive proposition. For example, if you went to a manufacturer with a design, and then it needed to be modified, it would incur extra costs. By modifying the design yourself, you minimise those costs.

Bespoke options and customisation

Using traditional manufacturing processes, it’s more cost effective to sell products at an affordable price to the customer with a fixed set of options, such as small, medium or large. 3D printing on the other hand allows you to customise every piece that you manufacture to your customer or technical requirements while at the same time minimising the cost impact of those modifications.

Controversies

It is very apparent that 3D printing is what is referred to as a disruptive technology, and to date has definitely courted some considerable controversies. Back in 2013,  a group of American gun campaigners called Defense Distributed successfully designed, printed and fired a gun built by a 3D printer made from ABS plastic with only the firing pin made from metal. They then made the blueprints open source on the internet for anyone to download.  

The printers themselves also use a lot of energy – if you’re worried about your carbon footprint, these are guaranteed to bump that up a shoe size or two, and in some cases, the airborne particle emissions from some desktop printers are comparable to smoking a cigarette.  Then, there’s the issue of physical digital piracy; if you have a Lego set, and are missing the odd component, you can print off your own – the intellectual property issues then become very apparent.

Then there are issues regarding responsibility and culpability.  If you print a 3D gun or knife, and somebody else kills someone with it, there are the obvious moral implications. And then there’s biotechnology.  Surgeons are already beginning to use 3D printing to create medical scaffolds for replacement bones and ligaments, soon it will be organs, created with synthetic collagen structures that help tissues form structures and biomechanisms.

In extremis, we could take this argument to the ‘n’th degree, and eventually start printing spare parts for ourselves.  In theory at the cutting edge of what would be possible, we might extend our lives with such processes.  Need a new hip? Print one off.  Your liver has almost packed up? Grow a new one in a jar after building a cartilege scaffold online.  Need a replacement heart valve? That’s not that far away technically speaking. Literally at the time of writing this, another article appeared on the University of Manchester’s website, announcing that scientists had successfully created functioning kidney tissue that could produce urine.  The technology is now in place that will eventually allow surgeons to print human organs to order.

Complexity and costs

Tooling and manufacturing complex shapes and components is often a lengthy process using traditional methods. With a 3D printer and a CAD package however, you can create and build very complicated structures with reasonably little effort. In terms of physically machining and tooling such items normally, they may prove to be a costly build. With a 3D printer, you not only are able to build complex objects, you can repeat the process with precision.

One of the ways in which complex objects can be made in a normal manufacturing process is by using casting or injection moulding techniques, or even vacuum forming. For casting or moulding, you would often require a new mould or former for each piece produced, which forces your costs up. One of the ways that companies can recover these costs is to do large production runs. With 3D printing, this all goes out of the window. It doesn’t matter how simple or complex a piece is, the process is the same throughout.

Manufacturing costs are reduced drastically. And as a result, waste is also substantially reduced. If you think that most conventional manufacturing techniques are subtractive, in other words they take a block of material, shape it and by various processes reduces it to the final product. There will be waste products, chips, dust and unless it can be recycled, it is when you look at it, an unacceptable overhead. In some cases, it’s not uncommon to lose 80%-90% of the initial raw material when creating a single object.

3D printing is an additive process, in that it creates objects by layers with the raw material, thus negating most of the waste that you would normally associate with a manufacturing process. And those materials by their very nature are themselves recyclable.

The downside of course is that for large production runs, the 3D printing process doesn’t compete effectively. After a 1000 unit run, depending upon the final materials used and the complexity of the design, the costs creep up again. Even so, the cost of 3D printing is still going down and we will almost certainly see this technology being used for larger production runs in the future.

Choice of materials for printing

There are more than six hundred types of material that are used for 3D printing in use currently. These however tend to be plastics, metals, or solvent based. In some cases, concrete is being used to print much larger 3D structures such as houses. There are 3D printers available that can print using chocolate. And in medicine, surgical prosthetics can be printed using collagen which can then be inserted into the human body to act as a scaffold which structures such as bones and ears can be rebuilt. In dentistry, creating dentures and dental fittings is often done using 3D printing techniques.

The disadvantages of 3D Printing

Although the precision with 3D printing is still relatively low in engineering terms, that precision is anywhere from 100 microns to as much as 20 microns. Not much when consider the thickness of a single sheet of paper. As a prototyping tool, this is brilliant in terms of creating and developing conceptual designs or small run items. Even so, if you need to reproduce something more complicated, requiring much greater precision, 3D printing may not be up to the job.

Repeatability is very much an issue here. If you print one design on one 3D printer, email it to a friend who then prints it on their printer, and the print platform is calibrated differently, the base level of that component will be skewed from the original. No two items, no matter the design, will match exactly, even with the best printing equipment.

Another issue is the way in which the fabrication process works. Printing layer by layer adds weakness to components; for example, turning a piece of metal or plastic on a lathe means that you are using a solid piece of material with all the strength of that material intact.

By building up objects in terms of substrates, you add areas which may be prone to fracture or even error. This error can creep in, in the form of a speck of dust or chemical contamination such as moisture.

Even so, there have been vast improvements in these processes over the past few years, and the gap is closing between 3D printing techniques and traditional manufacturing.

The types of 3D printing

Even though the basic method of transferring a CAD model to the printer may be virtually universal in 3D printers, the methods and materials differ significantly across the board. As we have already mentioned, there are a number of materials that can now be used with 3D printers. Let’s take a look at some of them and the processes involved in creating the final product.

Fused Deposition Modelling (FDM)

Most desktop 3D printers currently in use work using this method. FDM printing involves a reel of filament, guided from a reel attached to the printer, which is them feed through a nozzle heated to 230°C that melts the material and acts as the printer head. As it prints, it immediately cools and solidifies, and it is by building up each layer as a substrate that the foundation of the object being printed is created. One of the main advantages of this method of printing is that it is very cost effective.

Poly Lactic Acid (PLA) is probably the most cost effective of the materials, comes in any colour and can be produced in transparent form. PLA is bio-degradable, manufactured using plant-based materials such as corn starch and sugar cane – in effect, it’s virtually edible and totally recyclable.

Fused Deposition Modelling is the ideal choice for the hobbyist and small engineering firm that needs to prototype objects at a low cost, quickly, and that can be used in a wide range of applications.

PolyJet/MultiJet Modelling

Similar to inkjet printing, polyjet or multijet modelling uses a jet mechanism to create layers of liquid photopolymer onto the building tray, curing it with ultraviolet light. The process begins when the printer jets the liquid material onto the build tray. As the process reiterates, the process builds up the model. In terms of complex shape creation where there are overhanging structures that need support, these printers jet removable gel in place of the photopolymer which can be removed after the print is finished. It also means that on the more advanced printers of this type, different photopolymers with specific properties – flexibility, transparency, durability and colour – can be interchanged in the process.

This is the process used in a number of industrial 3D printers, and has not only the physical advantages just described, but is also a very precise process, with as little an error in 3D printing terms of 15 microns (less than the cross width of a human hair).

Selective Laser Sintering (SLS)

This unsurprisingly uses a laser to melt layers of powdered material and manipulate that material into a final finished product. Its main advantage is the fact that structures support themselves as the printing process progresses, with the excess material supporting the object being printed. This can them be reused for the next print. It can produce incredibly complex structures, although the printed objects take longer to cool.

In this instance, an SLS printer has not one, but two printing beds known as pistons. As the printing process begins, the laser prints the footprint of the object in the powder, which is either nylon or other types of polyamide, polystyrene or thermosetting plastic, and sinters the material. It cools rapidly and solidifies, then the print bed moves down, as the other containing the powder moves up, with a roller dusting the previous layer with material. This process goes on until the final product is formed.

This used to be for the high end industrial market, but recently, affordable desktop versions have appeared.

Binder Jet Technology

Similar to SLS in that the process relies upon layering powdered material in printing an object, except that instead of a laser to sinter the material, Binder Jet printers use a chemical agent extruded from the print nozzle to bind the material together. Once printed the object has to be cleaned up and coated with a fixing adhesive to add strength and prevent any discolouration of the material. Again, this is an industrial printing process, and is used predominantly by architectural firms that require sandstone replicas and objects. It is comparatively inexpensive, uses little in the way of energy and can produce complex structures. Even so, the finished product is not that robust.

Getting started in 3D modelling

So, you want to build print a 3D model? Well, there are constraints as you would expect. Apart from the printer, you will need software to design the object, and that design has to be the right size to be printed. Some desktop printers can only print in an area the size of 150mm³.

Then there’s the cost. Some software, such as Sketchup or Autodesk’s TinkerCAD, can be downloaded for free, and from that you can create a model, save it as a DXF file, which can then in a number of instances be transferred to the software provided by the 3D printer manufacturer which can then create the final object. Alternatively, there are a number of designs already out there.

Because of the open source nature of 3D printing, you can trawl the internet for various designs and model files that you can download for yourself and build the object of your choice. There are literally thousands of designs out there waiting to be built, and if you’re after a specific design, this may save you time and money if there is already an open source design available.

Conclusions

If, like us, you’re an engineering company, the advantages of having a 3D printer is a no brainer. We can test ideas and concepts rapidly. It is the ultimate rapid prototyping tool. If you ever watched Star Trek, and wondered if there would ever be technology such as the replicator which could pull a meal or a tool out of thin air – it’s here virtually. OK, maybe it doesn’t use quite the same complex technology to manufacture items, but we have arrived at a crossroads in our technological evolution.

What used to cost thousands of pounds to design and develop, can be done in an hour in someone’s office or shed, cheaply, effectively and repeatably within reason. Although not new, it is only in the last few years that this technology is coming into its own. Companies are printing artificial limbs to order. Tools can be made by companies to their own specification almost instantly.

My advice is that if you need a 3D printer, look at how frequently you would be using it, and at the nature of the objects that you would be printing with it. You will also need room for it, and storage for the tools and materials that come with it. My Flashforge Finder takes up 420mm³ in the office, about twice the size of a laserprinter.

It’s printing footprint is approximately 150mm³, and the last print I made was for a holster for my Amazon Echo so it could be attached to an Ikea unit. It took 2 hours to print, but the result was a sturdy, robust and cheap solution to a problem that would have cost about £20 if bought elsewhere, and cost £3 in material in terms of the PLA filament needed to build it. Each reel of the filament costs under £15 if you buy it from reputable suppliers, and these come in a number of colours, tones, and also in transparent form. It is more than precise enough for prototyping and developing ideas, and since the Flashforge was priced at the time of purchase under £500, I considered it to be a sound investment, which indeed it was.

Using software to design an object first means that you can tweak your design to perfection before you print it. It also means that you can conserve materials, by working out where material is required in a design and where it adds nothing to the final product. In the case of the Flashforge, any solid object is layered up to a point, and then the software creates a lattice structure in the printed object. This means that the final object will be both strong and light, using the optimal amount of material.

For the hobbyist and small scale engineer, the facility to print in 3D will enhance your capabilities enormously.

 

Steven Parham

Women in Engineering

Useful Links

Thingyverse – Digital design resource

Pinshape – 3D printable files and designs

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