13 - Production part 3 - Plastic parts

Submitted by ehanuise on Mon, 05/06/2017 - 10:07

Board games Production. part 3 : Plastic parts.

Including plastic components in board games only makes sense if you will have a large print run. As for many other components and techniques the setup and tooling costs are high so you need volume to keep unit costs under control.

Plastic

Plastic is a very generic term that covers a large range of materials. This is again a topic that could fill several books, so I will only cover the basics and I encourage you to do further research on your own.

The term ‘plastic’ covers a very wide array of polymers, many of them oil-based. The colloquial appellation plastics comes from the fact that most of these polymers exhibit good plasticity properties — meaning they are malleable enough to be shaped, bent, cast, pressed or extruded in many shapes and forms. Non oil-based plastics have been developed, from corn starch, cotton, vegetable fats and oils and even living organisms.

Two important families of plastics are thermosetting plastics (polymers that are fluid until cured by heat, radiation or chemically by a catalyst and then become definitively solid) and thermoplastics (that will melt again when heated at their fusion temperature). Thermoplastics are easier to recycle, but thermosetting plastics exhibit superior mechanical properties that make them a requirement for some applications.

Here are some of the most commonly used plastics for boardgames:

  • Polyvinyl Chloride (PVC, also commonly called Vinyl - 1872) is used for many miniatures, in conjunction with chemical agents that make it less brittle and more ‘bendy’. Yes, this is the same material used to make records. It is also used for modern mah-jong tiles. And roof gutters, and piping, and a lot of other applications.
  • Polystyrene (PS - 1839) and High impact polystyrene (HIPS) are used to make rigid, hard components and transparent things, such as transparent cubes. Also notable is their use as thermoplastic for vacuum forming of trays. When you get low-detail hard plastic parts in a cheaply produced game, it’s usually PS/HIPS.
  • Polyethylene (PE - 1898) and Low Density polyethylene (LDPE) are notably used for blisters and clamshells
  • Acrylonitrile butadiene styrene (ABS - 1948) is used for parts that must have good mechanical strength and show some flexibility. This is a very common material.
  • Polycarbonate (PC - 1953) is hard and transparent, and can be used for lenses, filters and other optical applications. It’s the medium used for Compact Discs.
  • Urea-formaldehyde (UF, also commonly called Urea - 1884) is a hard thermosetting plastic, notably used for moulded dice.
  • Polylactic acid (PLA - 1932) is not widely used for boardgames but is well known because of its use as filament for 3D printers. I included it here because these are increasingly used for prototyping.

Additives are usually added to these polymers to change their colours and to change their properties: make them harder or softer, make them more resistant to the ultraviolet radiation from sunlight, make them more resistant to moisture, etc.

The correct vocabulary for polymers is rarely used, and the terms ‘plastic’ and ‘resin’ are often used to refer to different polymers. Always ask your manufacturer what kind of plastic they offer in their quotes, as the differences in applications and prices are substantial.

Injection moulding

Injection moulding is the most common process to turn polymers into a finished objects. The bulk material used is usually pellets. Pellets are small beads of about 5mm, and can be bought by the ton by plastic manufactures. These pellets are heated to the melting point temperature of the polymer used (usually between 200°C and 500°C) and fed using an Archimedes screw pump into a metal mould. The molten plastic is injected into the mould under very high pressure, up to several tons per square centimetre, to make sure if lows in all parts of the mould. This process in called injection moulding.

Here is a video from Bill Hammack at engineerguy.com that explains the process:

https://youtu.be/RMjtmsr3CqA

Once the polymer has been injected it is allowed some time to cool down and harden, then the mould is split open and the part is ejected. For some complex parts, the mould will have more than two parts, and may also require to have built-in ejectors and actuators to release the finished part. The more complex, the more expensive of course.

Here is another video that focus on the moldmaking process:

https://youtu.be/seZqq1qxW30

Designing a mould for injection is a very complex process, and moulds are a very high precision tool with tolerances than can be as low as a few microns. The manufacturer will need to crate a computer model of the mould, and make complex simulations of the flow, heat and pressure inside the mould during the injection cycle. If the mould is not carefully designed, it might break and damage the injection machine. Special industrial software is required to do these simulations, and this is way out the scope of this book.

Moulds can be made from different metals, depending on the moulded pieces shapes and the pressure requirements for the shape and polymer used. The best material for making moulds is steel, but it is also the most expensive. Brass and Copper are softer and cheaper, but less durable and require special care to manage residual heat.

A steel mould can be used to produce millions of parts, and can be overkill for parts that will only be produced in the tens of thousands. Consult with your manufacturer, and make sure to compare prices from different sources. Some manufacturers will only use steel for moulds as they are ill-equipped for other metals, and will consequently be much more expensive than other manufacturers.

Moulds are nowadays almost exclusively produced by CNC machining. Some manufacturers still do manual mould carving, especially in Asia, but they are slowly disappearing. The shape to be cast is carved in the mould using milling tools, then a few channels are added for the plastic to flow into the mould or for sprues, and to let the air out when plastic is injected. Special features are added as needed such as actuated ejectors, articulated sections that allow to open the mould without breaking the newly cast part, and sometimes cooling fluid channels to manage the mould temperature during production.

wikimedia_pubdom_Standard_two_plate_injection_molding_tool.jpg

Very high precision moulds can be made using other high-tech methods, such as using electrolysis or milling on a copper or graphite bloc to shape it and then using that bloc as an anode to carve a bloc of steel using electric arcs and very high current — a process called electrical discharge machining (EDM) but this is very expensive and only used for very finely detailed miniatures. Keep in mind the level of detail in the finished pieces may be more limited by the properties of the polymers used than the actual detail level of your mould. Some plastics cannot pick up all the details a very high quality mould can have, and some companies specialised in miniatures boardgames have developed custom polymer mixes to get the best results.

The cost for a plastic mould will vary according to the complexity of the part, the level of detail required, and the size of the part. Your manufacturer should be able to suggest changes to your parts in order to get a better price.

A plastic injection machine is a very large and expensive piece of equipment, just as a printing press. It should be in operation 24/7 to amortize its costs, and require highly trained and skilled personnel to operate. This is why most manufacturers don’t have in-house plastic injection facilities and outsource this to specialized suppliers.

Plastic components design

There are a few important rules to keep in mind when designing plastic pieces. Following these rules will help you keep moulding and production costs to a minimum, and make sure your parts are well-sited to mass production.

Rule #1 — One cycle, one colour

One cycle consists in the mould being closed, molten plastic being injected, let to cool down, and then opening of the mould and ejection of the newly cast part or parts.

You will design your parts individually, but the manufacturer may elicit to group several parts in the same mould, or several copies of the same part in a single mould.

Each time the machine will perform one cycle, it will produce one unit of each part the mould has. If you have six miniatures in the same mould, each cycle will produce six miniatures.

However, each cycle can only use one kind of material. So if you have six different miniatures that can be produced in one cycle using the same mould, and you need 5000 of each miniature in green, 5.000 of each in blue, 5.000 in red and 5.000 in Yellow, it’s only one mould, which will perform 5.000 cycles for each colour, 20.000 cycles in total, and the total yield will be 120.000 miniatures in total. The mould will be set up only once on the machine, and each colour change will just waste a few cycles to replace one colour by the next in the feeding pump.

If you need 5.000 copies of miniature A in red, 5.000 of miniature B in Yellow, 5.000 of miniature C in blue, 5.000 or miniature D in green, 5.000 of miniature E in Orange and 5.000 of miniature F in purple you will need six different moulds (one for each miniature) and each will be used 5.000 times for a total of 30.000 miniatures. And this will be much more expensive than the above example for 120.000 miniatures. Not only will you need six moulds instead of one, but also you will need to change mould and set up the injection machine six times instead of just one. As for printing, setup costs matter a lot!

Rule #2 — The cake mould rule

Think of your plastic parts as if they were cakes. When you bake a cake, you fill the mould with paste, cook it, and then remove the cake from the mould. Usually, cake moulds have shapes that are narrower at the top and wider at the bottom, and shapes that will not get stuck into the mould when removing it. For an injection mould, the same principle applies. The mould must be split in several parts that can each be removed from the cast part without breaking it apart. If you design your parts in such a way that the mould only need to be split in two parts, you will save a lot of costs and trouble. Some moulds have up to 8 parts to accommodate complex shapes, but this is very expensive, and all factories cannot handle that level of mould complexity. It is sometimes much cheaper to split your part in several smaller parts. Multi-parts miniatures can be assembled by the final customer, or they can be assembled at the factory (and they will usually be glues or welded together if assembled at the factory).

Always consult with your factory for optimisation of your parts for moulding and assembly. A good manufacturer will be able to get your files or models and handle all of the technical complexity of turning them into moulds, and then plastic parts.

Rule #3 — Don’t do it yourself

As stated above, creating a mould is a very complex process that require industrial equipment, and skilled engineers to run the pressure and flow simulations. Don’t fool yourself in thinking you can design the mould. It’s a custom part, and it’s bespoke to the actual injection machine that your manufacturer will use.

Creating a plastic part for your game

There are several ways to create the plastic parts for your games, which I will review here. Each part should be considered separately and you will end up using different ways for different parts for the same game.

The first way is to only provide drawings and sketches to the manufacturer, and ask them to create the parts from these drawings and sketches. If you do this, you should provide for each part several drawings at different angles: viewed from the front, from the side, from behind, from the top, the bottom, and a 3/4 view. This will allow the sculptor to understand the specifics of your part and create a model that matches your input. Also make sure to provide a scale reference so they know the size the part should have.

The manufacturer will have a sculptor create models for you, and will send you pictures of the models (photos of the clay models or renders of the computer models) for approval and feedback. They will do changes based on your comments, and after some back and forth you will approve the final models for production. If the models are computer-based (this is becoming the norm) you can request 3D-printed samples, or 3d-printable files to print samples locally.

The second way is to use a local sculptor that will provide you with clay or epoxy putty models, based on drawings and instructions you provide. The final models are called ‘masters’ and will be sent to the factory to be turned into an injection mould. The process will vary from factory to factory, they may 3D-scan the model and use a CNC machine to carve the mould, or they may do it manually.

If you do this you must be very careful to send the factory pictures of the models as they are sculpted so they can provide feedback. Some models are not suitable for moulding and require to be split in several parts or require complex and very expensive moulds. The sooner the factory is involved in the process, the less problems you will have. This is the most complex and risky way to design plastic parts.

The third way is to create 3D models from your sketches and instructions, or to design the parts directly in3D software. You could do this yourself, or hire a 3D modeller or artist for this. Once the parts are designed, you send the files to the factory and they will in turn create a mould from these files. The factory will provide or ask for changes to your models so they can efficiently be turned into a mould, and should again be included early in the loop.

The main advantage of this over the first way is that you can 3D print samples as needed during the creation of the part to have a good idea of the final results. It also allows you to manage one or several 3D artists directly, which can be easier than going through the factory each time.

Last but not least it allows you to start creating the 3D parts during playtesting and development, and see how they affect gameplay and ergonomics. For miniatures this is not very useful, but if your game has parts that greatly affect gameplay this is a huge advantage.

Keep in mind that your 3D files will not be instantly transformed into an injection mould. Actually, most 3D modeling software only handle surfaces and triangles (think of it as only the skin of your objects), whereas the software used to make the flow, pressure and temperature simulations and the software used to drive industrial CNC milling equipment handle volumes instead of surfaces. This means they speak a completely different language and your modeling work will be converted to another format. The factory will come back to you with a final model that is slightly different from what you sent them, and you will always need to carefully check everything and do some changes before it can be approved for mass production.

I ask a 3D modeling artist or the factory to model miniatures from sketches, and only design 3D models myself when they play a key part in the gameplay and when I am confident it actually has an added value to do it myself. It’s easy to get lost in the rabbit hole of 3D design, but I always keep in mind that my job is to make sure gameplay and development come first.