Bringing a new product to market involves a complex process of design, market research and manufacturing. Incorporate rapid prototyping into this process to create parts that develop working models of a product, allowing for testing of its features and limitations. For testing purposes, you can make these prototypes from the same materials as the final product or from different materials.

Some methods of making metal prototypes include:

  • 3D printing
  • Sand casting
  • Investment casting
  • Fabricating the part directly from metal stock
  • Machining the part directly from metal stock

Methods and applications for rapid prototyping

3D printing

In additive manufacturing, also known as 3D printing, you build a 3D component layer by layer until the final product is formed.Each layer can be around 100 microns thick. A computerized system controls the printer, taking a 3D design as input and generating the 3D product as output.

The technology has evolved over time and a wide range of materials have become available for printing. You can use plastics, nylons, resins, silver, titanium, steel, wax, photopolymers, and polycarbonates as materials for 3D printing.

There are three main types of 3D printers:

  • Selective Laser Sintering (SLS) uses a powdered build material. A laser melts the powder to form each layer of the part. New powder is applied to the partially completed part and the process begins again until the entire part is produced.
  • Fused Deposition Modelling (FDM) uses thermoplastic filaments that are melted and then extruded. The extrusion process is precisely controlled by a computer according to the three-dimensional design, printing each layer in turn.
  • Stereolithography also uses lasers, but in this case the liquid product solidifies layer by layer under the action of the laser and is controlled according to the design.

The reason 3D printing has become so popular for rapid prototyping is that the process is very resource efficient. There is no need to set up tooling on the production line, labour requirements are extremely low and there is very little waste. The disadvantages of 3D printing are that it is time consuming, taking hours, sometimes days, to produce complex parts. The print area of the machine limits the size of the part that you can produce. Also, due to the high melting point of some metals, it may not be possible to produce the part in the material required.

Sand casting

In metal foundries, craftsmen use patterns to create molds for casting metal parts. They craft prototype patterns in the simplest and most economical manner to facilitate testing and adjustments as needed. Typically, they opt for sand molds due to their affordability and speed of production. Using loose wood patterns, the entire process of creating prototypes can take 2 to 4 weeks from start to finish.

Wood pattern makers create loose wood patterns using techniques such as turning, tool making, mold making, and fine woodworking. They base these patterns on the prototype design and incorporate specific tolerances to account for shrinkage during metal cooling. When the prototype design necessitates parts with reverse airflow, they craft these parts into loose patterns and secure them in place with pins.

Crafters specially formulate modeling sand with the appropriate mix of ingredients to ensure it possesses the necessary properties for metal casting. It must maintain its shape, retain moisture appropriately, and yield a smooth surface finish. They then pack this sand around the loose wood pattern to create a mold, which is subsequently used for producing metal prototypes.

Casting a metal prototype is a standard casting process that involves melting metal, controlling the composition and pouring the molten metal into a mould. Once cooled, craftsmen remove the mold, leaving the metal prototype ready for finishing touches.

Rapid metal prototyping with loose wooden molds is popular due to its low production costs and the ease of adjusting and recasting the wooden mold if needed. Moreover, crafting the prototype from the same material as the final product eliminates the necessity for additional development. Manufacturers often find that the process of developing a prototype often requires only minor modifications to become the final production method.

Investment casting

In investment casting, a metal casting process, craftsmen employ various techniques to create the pattern from which the mold is formed. The initial step involves creating a wax pattern that corresponds to the prototype design. Traditionally, artisans used injection molding machines or wax presses for making the wax pattern, but advancements in materials and 3D printing technology have now facilitated simpler and quicker production of investment casting patterns.

After creating the pattern, craftsmen encase it in ceramic material, which solidifies to match the pattern’s shape. Subsequently, they heat the mold until the wax melts and drains out, a process also known as lost wax casting. The conventional casting procedure proceeds as molten metal is poured into the mold. Once the metal cools and solidifies, artisans remove the ceramic casting, unveiling the metal prototype for finishing.

The benefits of this rapid prototyping method are similar to those of lost wax, but with finer tolerances and surface finishes.

Fabricating metal prototypes

Stock metal materials include sheet, bar, tube, strip and wire. You can use any of these materials as raw materials to produce metal prototypes as a secondary step, rather than relying on a primary manufacturing process like casting or 3D printing.

In sheet metal prototyping, craftsmen have several processes at their disposal to create the prototype. They can start by flattening a physical model and using it as a template on a sheet of metal. Then, they use a laser or torch to cut contours, openings, and mark bends. A press is employed to bend the metal along the marked boundaries, and specialized welding equipment is utilized to join the parts together.

You can use tubing for prototyping by subjecting it to various operations to create a prototype part that matches the design.

  • Flaring – widening the opening at the end of a tube into a funnel shape
  • Swaging – reducing or increasing the diameter of the tubing
  • Dimpling – small deformations on the metal surface
  • Bending – creating shapes through inserting bends at defined points in the tubing
  • Flattening – using a press to compress the tubing
  • Piercing – creating holes in the material
  • Expanding – using heat and tools to open the diameter of the tubing

The main advantage of using stock materials to produce metal prototypes is that it is time efficient. No templates or molds are necessary, and you can easily find the raw materials. The disadvantage is that standard manufacturing processes cannot produce some complex prototype designs using this technique.

Machining metal prototypes

Machining cuts a piece of raw material into a desired shape and size through a controlled process of material removal, known as subtractive manufacturing. Use machining to produce various metal products, as well as items made from wood, plastics, ceramics, and composites. In modern manufacturing, implement machining using computer numerical control (CNC)

CNC is the computerised control of machining equipment to produce a part according to a 3D design. Machining equipment includes lathes, mills, routers, drills and grinders. The raw material for CNC machines is stock metal products such as steel plates and bars.

Convert a 3D design into a computer program, and then use this program to direct the machines through the control system. To create a prototype through machining, select a raw material larger than the intended prototype to allow for metal removal during the process. Advanced CNC machines control operations on all 3 axes (x,y and z) and can automatically rotate the part and change machining tools, resulting in a high quality finish and level of accuracy.

The advantage of CNC machines over other manufacturing techniques is that they operate automatically from a 3D design. Human intervention is minimized, and the prototype closely matches the design. CNC machines can produce more complex prototypes than manual methods. A disadvantage of machining parts is that the part is made by removing metal from the raw material, resulting in waste. Although the waste material can be recycled, there are cost implications and losses.

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