Comparing 'Micromanufacturing' Processes

New micro processes are emerging, but some of the most reliable ones have been around for decades.

Micromanufacturing is a hot topic these days, but it raises a question: What qualifies as "micro?"

The answer: It depends on who you ask. A 2010 survey conducted by MICROmanufacturing found that there is no true consensus as to what makes a part or design feature "micro." The survey said 33  percent of the respondents said any part or feature up to .039" is "micro." 24 percent said up to .078", while 15 percent said up to .157". A shocking 24 percent considered .314" to be the upper limit for micro parts.

Most of the respondents were from shops using conventional cutting and stamping processes, where metal is still cutting metal. But non-conventional photochemical processes have been at the micro level for decades, largely as a result of imaging advances driven by the rapidly evolving semiconductor industry..

Stamping
Stamping is a popular fabrication method when OEMs need high volumes of small metal parts. With mechanical or hydraulic presses, energy is transferred from a flywheel or hydraulic system to the work piece. A stamping guide by Jonathan Zhang shows some of the design capabilities of this process:

• Minimum hole diameter should be at least 20% greater than stock thickness. For stainless steels, it should be two times the material thickness.
• In most cases, size tolerance of .002" can be held.
• Slot or tab widths should be greater than 1.5 times the stock thickness. The length can be a maximum of 5 times slot/tab width. These rules can be bent, though your tooling costs will increase.

Stamping can run into some issues: A burr height of up to 10% of metal thickness is to be expected, in addition to hold-down marks, which designers must account for ahead of time. Parts with a large number of small holes in a tight space can end up with mechanical distortions due to the material stretching and extreme pressure caused by holding the material down.

The products that use these components are getting smaller all the time, so burrs can lead to dysfunctional products if they interfere with other parts. Mitigating these effects is possible, but it will require extra operations or different tooling which means higher costs and longer production times.

Microstamping
Microstamping is essentially the same process as stamping, but as the name implies, it's better suited for micro parts.

Precision micro stampers use ultra thin materials and sometimes unusual metals to create micro parts and features of about .078" and smaller. They can handle some complex applications with the ability to make cuts and holes with an aspect ratio of less than 1-to-1 and can also hold tight tolerances - as low as .0003".

But microstamping is still vulnerable to the same downsides as stamping: Long lead times, mechanical distortions, high upfront tooling costs and a lack of flexibility for design changes once the tooling is finished.

Stamping and microstamping are a viable choice for certain applications, but for complex precision micro parts, there are non-conventional methods that OEMs should know about.

Many industries are turning to nonconventional processes for their micro needs

Photo etching
What we consider to be micro in the etching business is still not feasible for most conventional processes. We can make parts down to about .020" using sheets that range from .001" to about .080" in thickness. When it comes to holes, our minimum hole/slot dimension must be at least 110 percent of metal thickness, though we can easily adjust the aspect ratio to make them different sizes on each side of the sheet. Here are some other advantages photo etching has when it comes to micromanufacturing:

• Most photo tools are about $300 or less. They can also be reused, allowing for large batches from just one tool.
• We can have your tools ready in about a day, keeping lead times short.
• Etching does not alter the composition of the metal or expose it to heat - parts come free of mechanical distortions and burrs.

Find out if photo etching fits for your application:

Electroforming
ASTM B892-93 defines electroforming as "the production or reproduction of articles by electrodeposition upon a mandrel or mould that is subsequently separated from the deposit."

Through electroforming, we can build a new part one particle at a time, with a high level of control over the process and keeping these miniscule parts to print. Electroformed parts can have a thickness between .0005" and .010". Holes and other design features can be brought down to about .0002" in diameter, while holding tight tolerances of about +/- .0002"

Both photo etching and electroforming have been used in the MEMS, RF & Microwave and medical fields to create sieves, meshes, screens, ligatures and other parts that have to fit in spaces that are just a few microns wide.

Learn more about micromanufacturing.  Download our FREE guide:

If you're an engineer or designer with micro designs, call us at 800-443-5218 or email us at sales@conardcorp.com to see how we can help you.