Professional model making is a core activity for us. In fact, Prototype Projects started in model making before expanding to provide CNC vowin.cn/en/News/news1251.html' target='_blank'>machining, 3D printing, vacuum casting and laser cutting. While these other services are self-explanatory, customers can view model making as something of a ‘black art’. In this article, therefore, we will explain how we go about making models – and how it is, in fact, a fine art.
Start at the beginning
Model making projects typically start with a customer enquiry followed by a discussion, as it is more difficult to quote for models than, say, parts made by CNC machining or 3D printing. This discussion is essential because no two projects are the same. It will cover issues such as the intended use for the model: will it be a display model in a case, is it for testing a function or ergonomics, or is it intended for usability trials or for handling by large numbers of visitors to a trade exhibition? Maybe the model will be a theatrical prop for a stage production or a movie, or perhaps it is required for filming or photographing an advertisement. Furthermore, whether the customer needs one model or several can have a bearing on the production technologies selected.
Something else we will discuss is whether the model incorporates components or sub-assemblies provided by the customer. These could be an existing product that needs modifying, or specialist prototype parts such a PCB or custom digital display.
Once we understand the required aesthetics, functionality, robustness and quantities, we can talk about materials, manufacturing technologies and finishes.
At the end of the discussion, we will determine how we would make and finish the model, and only then can we prepare a quote.
Model making technologies
A vital aspect of model making is choosing the optimum technologies for making the various parts, and this is where the experience of our highly skilled and experienced model making team proves invaluable. In most cases, a professional model making project will employ multiple technologies, and certain parts may also be fabricated by hand.
3D printing: parts can be 3D printed in a variety of plastic materials, including hard, tough and elastomeric grades. We can also print parts in clear materials for polishing to achieve glass-like clarity. 3D printing is highly versatile for both one-offs and multiple parts. With five different 3D printing technologies in-house, and a choice of materials, 3D printing plays a key role in our model making capability. For models incorporating small parts with high accuracy, extremely fine details and exceptionally smooth surfaces, we have recently invested in a PµSL 3D printer.
CNC machining: this technology is more accurate than 3D printing technologies (other than PµSL) and enables parts to be made in a much wider choice of materials. These include specialist plastics such as PTFE and PEEK, as well as a metals ranging from aluminium, stainless steel, mild steel and brass, through to phosphor bronze, tool steels and titanium alloys. If multiple parts are required, CNC machining achieves excellent part-to-part repeatability. Depending on the model’s requirements, we can also machine Tufnol composites, modelling foams, MDF and tooling board. Note that our CNC machining capability covers both milling and turning.
Vacuum casting: when customers need multiple models, we can create a master pattern – usually by 3D printing – then use vacuum casting to produce multiple castings. Parts are cast in polyurethane resin, but this material’s properties can be specified to replicate anything from soft elastomers through to glass-reinforced nylon. Another application for vacuum casting is overmoulding when, for example, a model needs soft elastomeric grips on selected areas of the exterior surfaces.
Laser cutting: we can cut a variety of thin materials, though we outsource laser cutting (and photochemical etching) of metals. Laser cutting is very quick and cost-effective for low volumes and it can also be the best option for cutting one-offs such as elastomeric gaskets for liquid- or gas-tight assemblies.
To complement these technologies, our model makers can adapt or modify existing production components, as well as source and repurpose or modify standard off-the-shelf components. We can also procure specialist custom parts such as springs and pressings.
Putting it all together
Assembly of the components parts is just as important as the manufacture of the individual parts if the finished model is to have the required aesthetics and functionality. The parts might need a small amount of fettling during the assembly stage to ensure surfaces are aligned correctly and mechanisms operate smoothly and have the desired feel.
If the assembly is likely to require subsequent dismantling for modification or adjustment, threaded fasteners can be used. Permanent joints can be made with adhesives. Snap fits can be 3D printed successfully, depending on the material, but are used less frequently for professional model making because of the added complexity of the joint design.
How we finish models
The choice of finishes depends on several factors such as the model’s intended use and operating environment, its materials of construction and the production technologies. Sometimes secondary finishes are not necessary, such as vacuum cast parts for which the polyurethane resin has been dyed a specific colour, or if parts have been CNC machined from stainless steel or brass.
SLS parts can be dyed in almost any colour. Plastic parts made using other 3D printing technologies can generally be spray painted in gloss, matt or eggshell finishes. In addition, parts can have a rubberised soft-feel finish applied.
3D printed parts might be lightly bead blasted prior to being dyed or painted, though sometimes the bead blast finish is sufficient on its own.
Parts 3D printed in clear grades are often polished and lacquered to give a glass-like appearance, but they can also be polished and tinted for parts such as automotive light lenses.
SLS parts can be slightly porous, so we can lacquer these to seal the surface.
We can make elastomeric parts using our PolyJet 3D printer but, because of the parts’ flexibility, we do not apply secondary finishes to these.
For functional parts, we can apply a blackout/RFI/EMC coating to the internal surfaces.
Parts 3D printed using PµSL technology benefit from high accuracy, extremely fine detail and exceptionally smooth surfaces. We therefore do not apply secondary finishes to these parts because doing so would compromise the part’s inherent characteristics.
The finishes outlined above relate primarily to 3D printed parts but can also be appropriate for parts CNC machined from plastics, depending on the material. When we CNC machine parts from metals, the choice of finishes is somewhat different, depending on the material and intended use for the model. If the parts are primarily functional, they might simply be deburred and cleaned.
Other options include hand polishing or bead blasting for aluminium, stainless steel and brass parts. Mild steel parts can be primed and painted.
The finishing facilities that we have in-house suit most customer requirements. However, we can also outsource specialist finishes. Examples include vacuum metallisation, electroplating, electrochemical polishing of stainless steel parts, clear and coloured anodising of aluminium alloy parts, powder coating, chemical blacking of steel parts, and heat treatments or other surface hardening processes for tool steels.
If the model is required to look identical to a production item, we can apply text, logos, symbols, or other graphics. This is usually done using rubdowns (dry transfers), waterslide decals and screen printing.
To complement and protect the models we make, we can also supply transit and display cases. These can take many forms, such as shadow foam-lined boxes or carry cases for small models, customised flight cases for large models, and any size of clear display cases with the model mounted on a base board.
Where necessary, transit cases and display cases can also accommodate accessories that would be used with the model. Cases can be finished with labels and logos, and display cases can be equipped with integral lighting.
No two the same
Compared with producing parts by 3D printing or CNC machining, model making projects are far more involved. No two projects are the same, which is why the skill and experience of the model making team is so important. Identifying the optimum way to make the various parts of a model is key to the success of a project, and also minimises the cost and ensures the model is delivered on time.
Talk to us
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