Volumes of production
Production runs of up to tens of thousands of components are possible using this type of micro-mold.
Unit price vs. capital investment
The CAD-driven nature of this process means that the setup costs are low.
Speed
It takes about seven hours to deposit a layer 100 microns thick, but several thousand micro-molds can be made concurrently on a single glass plate.
Surface
It is possible to achieve high levels of detail and a fine finish on micro-molds made in this way.
Types/complexity of shape
It is not possible to make molds that are capable of making shapes with tapered, or anything other than straight vertical, sides. Steps can be produced but require longer timings.
Scale
It is possible to create blocks of as little as 100 cubic microns, with embedded channels 30 microns wide. The largest parts are 4 by 2 inches.
Tolerances
± 2 microns.
Relevant materials
The micro-mold itself is made from gold with a nickel alloy coating. The molded parts are generally made from polyacetals (POM) and acetal resins.
Typical products
As you might expect, the micro-molds are used to produce very small parts for biomedical devices and electronics, watchmaking, and telecommunications components.
Similar methods
Wire EDM (p.44) and micro-milling techniques.
Sustainability issues
Although the process can be very slow, the molds produced using this method require no heat treatment or further processing such as polishing, which can significantly reduce energy consumption. As the component is built up in layers to the exact contours of the design, no cutting or machining away of materials is necessary, so the process makes very efficient use of resources and eliminates waste. The molds have an above-average life expectancy to ensure continuous use.
Further information
www.mimotec.ch
Selective Laser Sintering (SLS)
with selective laser melting (SLM)
Product |
sample of a hierarchical structure produced using SLM technology |
Designer |
not applicable |
Materials |
stainless steel |
Manufacturer |
Renishaw PLC |
Country |
UK |
Date |
2005 |
This structure, only 11/8 inch high, was produced to demonstrate the small scale of work that is achievable using selective laser melting (SLM) technology.
Innovation in production techniques has recently been dominated by advances in rapid prototyping. Designers are increasingly able to exploit the potential to make unique objects directly from a CAD file on a computer and selective laser sintering (SLS) is just one of the significant developments, opening up a world of rapid prototyping.
Sintering (see p.168) is a significant part of the field of powder metallurgy and it can be used in a number of different production methods. Selective laser sintering is an adapted (and refined) form of sintering in which a laser is used to solidify precise areas in a powder block in order to produce lightweight components. As in any sintering process, a powdered material (in the case of the implants illustrated here, a metal) acts as the starting point. A laser, driven by a CAD file, is fired repeatedly into the powder, fusing the particles together layer by layer until the specific component is built up. The process is also known as selective laser melting (SLM) for obvious reasons.
This, however, is only the beginning for the team at Renishaw PLC in the UK who use the technology to produce a type of microscopic scaffolding. They are able to exploit the design potential of a CAD file to produce components with a tiny, but complex, lattice-like structure. This results in forms that are made up mainly of air, like a sponge. The advantage of this type of microscaffolding is that it enables components to be produced in metals with a very high strength-to-weight ratio—the density of stainless steel parts, for instance, can be reduced by as much as 90 percent compared with conventional processes.
– Allows lightweight components with high strength to be produced.
– Easily customizable.
– Can be used with a range of metals and other materials.
– Fully automated system.
– High unit costs.