Metal Parts - Rapid Prototyping (RP) and Low Volume Production
Prototype or low volume parts in metal are generally manufactured by means of machining or bending. The high accuracies and surface finishes that are available continue to make this an attractive single stage process.
However, rapid prototyping (RP) is making headway, both directly with processes such as Direct Metal Laser Sintering (DMLS), and indirectly through the generation of patterns for both sand and investment casting.
The impact of global sourcing also brings processes usually only associated with high volume production, such as die casting into the prototype equation.
All these and others are covered through the links opposite to assist you in sourcing the most applicable option for your requirement. If you are in doubt, then please contact Plunkett Associates directly.
Machining has several significant strengths; it offers the greatest flexibility in terms of materials sought, is more widely available than any other process, and can deliver very accurate parts with high surface finish. Additionally, when used to prototype castings, there are no issues with material porosity. The limitations are that complexity drives cost (unlike RP methods) and that as a subtractive process, cutter access is a necessity.
Direct metal laser sintering (DMLS)
DMLS is analogous to plastic sintering except that build volumes are currently restricted to 250 x 250 x 150mm and that support structures are required. As a process that is gathering acceptance, particularly for medical and high complexity applications, DMLS has a lot to offer. Predominant limitations relate to the slow build speed and need to remove the support structures post build.
Sheet metal is very common in low volume production applications due to the negligible associated tooling costs. There are no short cuts when prototyping, and no pertinent RP processes to consider. The key is a high quality supplier who is set up to run prototype batch quantities on tight deliveries.
As the name implies, this process creates a mould for the molten metal from sand. The process is relatively quick and can be made faster through the use of RP patterns to create the cope and drag (core and cavity). Surface finish is a function of the sand system used and casting size is only limited by the foundries maximum casting weight. Post machining will be required to achieve any tight tolerance dimensions.
Investment casting 'invests' a sacrificial pattern in a ceramic shell through a series of dipping and coating processes. Drying and firing gives the shell strength whilst melting or burning out the pattern. The resulting cavity can now be filled with molten metal. Surface finish and accuracy are better than for sand casting, although some post machining may still be required.
This is similar to investment casting in that the pattern is sacrificed to create the mould. However, instead of creating a ceramic shell, plaster casting tends to use the block or flask technique. More often found amongst prototype shops for casting Aluminium and Zinc, surface finish is good.
This is a production technique that is usually associated with high volume production. A metal mould is used into which liquid metal (aluminium or zinc) is injected in a manner similar to the injection moulding of plastics. The reason it is considered here is that through global sourcing the cost of die casting, and hence the breakeven point for using the process, can be much lower than expected. As with injection moulding the cost is proportional to size and complexity.