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Additive manufacturing What is rapid prototyping?

| Editor: Steffen Donath

Optimising the transition from concept to full-scale model and beyond. How do modern businesses test their ideas out effectively? Here's how fast prototyping techniques power innovation.

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Different additive manufacturing methods are the key to rapid prototyping.
Different additive manufacturing methods are the key to rapid prototyping.
(Source: Ines Álvarez Fdez (Unsplash))

The manufacturing realm is unique in that there are many viable routes from an idea to a market-worthy product. Although the fabrication techniques that get innovators from point A to point B vary widely, there are a few consistent trends. For massive companies, inventors and entrepreneurs alike, the name of the game is minimising the lead time needed to create viable prototypes.

Accelerated prototyping plays an essential role in making such objectives attainable. Encompassing a range of distinct techniques, it empowers fabricators to leverage a variety of production and testing methodologies as they hone their ideas.

Defining the fundamentals

Rapid prototyping refers to a number of independent strategies that dramatically reduce the fabrication time needed to create full-scale, three-dimensional shapes. Starting with CAD, or computer-aided design, files, rapid prototype hardware automates fabrication to bypass the traditional manual labour associated with building mock-ups and figures. This may involve various techniques, such as 3D printing and carving using CNC or computer numerical control, machinery.

What makes it necessary?

Faster prototyping only came into prominence in the1980s with the development of technology that could quickly translate digital designs into real-world objects. Before then, things like vehicle mock-ups were typically created by artists, such as sculptors who made partial-scale replicas from clay.

The rise of quick prototyping methods reflected a number of relevant factors. For one thing, the use of computers as industrial tools was gaining steam as these systems grew more readily accessible and understandable. Since companies no longer needed to pay for time-share servers or hire software engineers and computer scientists to accomplish simple tasks, they could experiment with unprecedented new fabrication methods at all stages of the product life cycle. The prototyping stage, with its minimal risk, was a natural place to start applying this technology.

Another important issue was the fact that the manufacturing world was getting a lot more competitive. Whereas nations like the United States had once held sway in the realm of machine tooling, the 1970s saw the rise of companies with increasingly globalised backgrounds. In short, more players were joining in, and those that took advantage of nascent technology would ultimately prove themselves the fittest survivors.

What are the benefits?

Quicker prototyping gave its adopters an edge that few could deny. The advantages were by no means limited to one domain:

Intensified speed and heightened accuracy

Depending on the complexity of the item, a manual mock-up can be made fairly quickly. The problem is that conventional processes, such as clay sculpting and foam board construction, often lack durability and strength. These weaknesses limit their efficacy at creating items that need to be tested alongside other components, such as fittings, housings and gears.

Traditional methods aren't always very repeatable either. For instance, even though an engineer with carving skills can rapidly knock out a basic representation of a relatively complex object, they might not be quite as precise the second or third time around. This tendency makes it harder to use and share prototypes effectively.

Rapid fabrication techniques solve these problems handily. Since these methods can create prototypes in everything from wood-infused PLA, or polylactic acid, to UV-cured resins and metals, it's a lot simpler to build a prototype that bears more similarities to the intended final product. When properly calibrated, these machines are also remarkably consistent.

Significant cost reductions

Devices like high-end 3D printers come with hefty price tags. Fortunately, the rise of new prototyping types also resulted in new prototyping services.

Third-party prototyping firms lowered the barrier to entry by making it easy to outsource the prototyping process. Since these enterprises specialised in creating mock-ups, they could produce high-quality output in a short span and have their work shipped back to the purchasing company within days.

This shift contributed to the proliferation of a novel variety of tech start-up: These businesses didn't necessarily have to retain their own fabrication departments to make and test new products. Since places like Shenzhen, China, were emerging as huge hubs for outsourced components like electronics, these firms could extend the same logic to other aspects of their supply chains.

Achieving previously unattainable techniques

Another big advantage of rapid fabrication was that it empowered more experimental types of creation. For instance, 3D printers that deposit biological substances now make it possible to create everything from medical devices that imitate real tissues to artificial organs that prove critical to new lifesaving technologies and drug tests.

Other techniques, such as electron beam melting, or EBM, and selective laser sintering, or SLS, make it possible to modify the physical properties of materials with fantastic precision. From changing an object's density to altering its crystal structure, these methods are revolutionising not only the way firms build prototypes but also the way they think about engineering.

Exploring techniques and technologies

There's no universal winner when it comes to choosing an accelerated prototyping method. Instead, different techniques have distinct advantages that make it critical to select your weapon on a case-by-case basis. Although there's no way to cover all of the options in one short article, exploring the two major classes,additive and subtractive manufacturing, is a good way to get yourself oriented.

3D-printed prototypes are produced layer by layer.
3D-printed prototypes are produced layer by layer.
(Source: Ricardo Gomez Angel (Unsplash))

Additive manufacturing techniques

Additive manufacturing is the general term for techniques where objects are successively built up by sticking globs of material together. For instance, 3D printing creates an item by building individual layers and joining each one together as the work progresses. There are a number of different ways to go about additive manufacturing:

Fused-deposition modeling, or FDM, is what occurs with most plastic printing 3D printers. These machines extrude, or squeeze out, thin beads of plastic at sufficiently high temperatures to partially liquefy the material. As the plastic cools on a purpose-made bedplate, it solidifies. By squeezing out subsequent extrusions so that they come into contact with the previous beads and layers, it's possible to build a unified piece. Similar techniques enable the creation of prototypes using everything from glass and ceramics to edible materials and living cells.

Stereolithography, or SLA, involves the use of liquid polymers. These chemical mixtures are carefully chosen for their ability to photopolymerise, or create chemical bonds when they're exposed to certain wavelengths of light. Machinery connected to a vat of the fluid raises a build platform out of the liquid reservoir in small increments. Simultaneously, a light-emitting device selectively illuminates the resin in specific spots to form the hardened layers from below. SLA light emitters may take the form of lasers that cure a single point at a time, but digital light processing, or DLP, systems use projectors to complete an entire layer at once.

Powder bed methods begin, as their name implies, with a tray or bed of fine-grained source material. With substances such as gypsum plaster or starch, an inkjet head can be used to deposit a binder that joins the small particles into a solid. With powdered metal alloys and thermoplastics, EBM, SLS and other tactics use lasers to wholly or partially fuse the particles through the application of intense heat.

Subtractive manufacturing techniques

In subtractive manufacturing, a final object is created by removing unwanted parts from a uniform block of material. There are various ways to go about it:

CNC machinery is essential for the subtractive manufacture of prototypes. Devices controlled by computers can precisely carve away specified sections of metal, wood, plastic and other hard materials.

Lathing is a technique with its roots in hundreds of years of industrial development. It involves rotating a workpiece around a single axis at rapid speeds. The fabrication machine moves a sharp tool to gouge out sections of the item. This action is aided by the fact that the spinning brings new surfaces into contact with the cutting edge so that the tool can minimise unneeded motion for consistency's sake.

Routing involves a stationary workpiece. The router, a device with a fast, spinning head, is applied as necessary to remove sections. In addition to routers that travel along two axes, some manufacturing devices include robotic arms that feature extra degrees of freedom. Similar methods include cutting pieces from wood, composite and metal boards using pressurised waterjets and moving lasers.

In a lot of research and development departments, a 3D printer is a central component.
In a lot of research and development departments, a 3D printer is a central component.
(Source: Rob Wingate (Unsplash))

Comparing the options

Different fast prototyping techniques have distinct advantages. For instance, when using plastic, FDM is usually quicker and cheaper than SLA: These printers are less technically complex, and they tend to waste less material. SLA is notably more precise, however, because the minimum resolution is determined by the size of an optical projection point instead of a physical extrusion nozzle's diameter. SLA's lack of a moving print head also means that there are fewer unwanted forces that might cause stresses, misalignment or other irregularities.

With lathing and routing, each technique produces different kinds of shapes due to the differences in how they hold the workpieces. Lathes are typically more appropriate for creating forms with radial symmetry, whereas routers and cutters handle irregular shapes quite well. In many cases, the techniques are combined or used in conjunction with drilling and stamping.

Is additive or subtractive manufacturing best for prototyping? Such a debate is unlikely to yield useful results anytime soon. Each option has its pros and cons. For example, some objects, such as closed forms with interior volumes, are impossible to create using subtractive manufacturing. Additive fabrication, on the other hand, results in parts with inherent structural weaknesses where layers and extrusions connect.

When considering what works best for a given project, it's wisest to think about the physical constraints of the object and the intended use of the prototype. A pinion or other drivetrain component that must survive trials in a larger mechanical system might prove more functional when made from a solid piece via reductive techniques. Thin-walled enclosures and other geometrically simple forms might be easier to fabricate with water jet cutting, but they'll need bending and welding later.

Finally, remember that many fast prototyping types produce rough objects. Although it's possible to achieve a smoother surface finish by tweaking your 3-D printing settings or fine-tuning how you slice a CAD file, some techniques demand post-processing. For instance, objects that have overhangs, or areas that jut out into empty space, usually need to be printed with removable support structures and cleaned up afterward.

Drawing connections: rapid tooling, manufacturing and prototyping

Industrial processes often demand custom tools that need to be produced at scale. While accelerated prototyping makes it easy to create test versions of such hardware, the results aren't always strong or durable enough to serve as jigs, milling tools, dies, welding fixtures or other production aids.

Agile prototyping services help bridge the gap between the industrial design process and the casting, moulding and other methods used to make long-lasting parts. For instance, one common use of SLA printing is creating high-quality moulds that can then facilitate the mass production of tools with fine details. Using fast prototyping to create such a pattern is relatively easy because modern CAD software makes it possible to do things like subtracting one form from another, splitting molds into articulated, or multi-piece, forms and adding channels for injection molding.

Rapid prototyping not only speeds research and development but also streamlines the production stages that follow. By giving engineers and others the ability to explore the dynamics of their ideas outside the digital space, it lets thought leaders make quick changes to established fabrication systems and polish the way they work.

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