Hot embossing glass -- to the nearest micrometer

December 2, 2010
The finished lens array is at a slant behind the lower die set of the hot embossing equipment. (© Fraunhofer IWU)

The lens is what matters: if lens arrays could be made of glass, it would be possible to make more conveniently sized projectors. Fraunhofer researchers have now developed a process that allows this key component to be mass produced with extreme accuracy.

Projectors are getting smaller and smaller. Now that pictures are available in digital format almost everywhere, we need projectors to beam giant photos and films onto walls. Projectors contain lenses that spread the light from the pixelated source in such a way as to illuminate the image area evenly. Until now, this was done using complicated arrays of lenses placed one behind the other. Recently, the same effect has been achieved using flat lens arrays made up of thousands of identical microlenses. This kind of array takes up much less space and does not need to be painstakingly assembled and aligned. To date it has only been possible to manufacture these lens arrays from plastic, but the in conventional projectors is hot enough to melt them.

To get around this problem, Jan Edelmann and his team at the Fraunhofer Institute for Machine Tools and IWU in Chemnitz have developed a process for manufacturing lens arrays from glass, whereby the of the array is hot embossed into viscous glass at temperatures of between 600 and 900 degrees Celsius. “The main challenge is to keep the material exactly at the where it is malleable but not yet molten,” explains the project manager. “That is the only way to guarantee that components made from it will be within the prescribed tolerances to within a few micrometers.”

The first step is to produce the forming die equipment, using tungsten carbide which is machined with ultra-precise grinders. “Of course, we have to take into account right from the beginning that the high temperatures will cause both the glass and the equipment to expand, but at different rates”, says Edelmann. “So the die has to be a slightly different shape from the workpiece that we are looking to produce.” Considering that 1700 absolutely identical square microlenses must fit into an area of just five square centimeters, it is not hard to imagine the level of precision that is required, and it is no surprise that it takes hours to produce the die. Once it is finished, the die is given a wear-resistant coating of precious metal.

During hot embossing, which takes place in a vacuum chamber, it is important for the glass and the equipment to be kept at a constant temperature until the workpiece has been ejected from the mold. The reason for this is that, during the cooling process, the glass shrinks more than the equipment. Tensions would otherwise arise and the lenses, only millimeters thick, might shatter. For ease of handling, the IWU researchers have given the workpiece an edge. Here, too, precision is of the utmost importance. Both stamping dies must be aligned exactly with one another, and there must be no slippage or distortion when they are pressed together.

The team from IWU has overcome all these problems and succeeded in producing arrays from high refraction that have extremely smooth surfaces and where alignment faults across all 1700 microlenses are smaller than 20 micrometers. “This is a world’s first,” says Edelmann happily. The process is suitable for use in mass production, and could bring the price of such components down to a tenth of what current lenses cost. Furthermore, arrays of this kind are not only important for projectors. They could also be used to broaden and homogenize laser beams, for example in industrial welding machines.

Explore further: Custom-Sized Microlenses

Related Stories

Custom-Sized Microlenses

August 30, 2004

Optical components have joined the trend towards miniaturization. There have, however, been no methods available thus far to produce custom-sized glass lenses. A new process now enables the low-cost, high-volume manufacture ...

Mini-projectors -- maximum performance

May 20, 2010

( -- The number of mini-projector devotees keeps growing. The combination of a new kind of optical structure with high-performance LEDs enables completely new compact and brilliant lighting and projection systems.

Measuring in 3-D

April 16, 2008

Today, complex optical free-form geometries are used primarily in car headlamps and in optics for cameras and digital projectors. These optical components are expensive to manufacture and to test. At Hannover-Messe on April ...

Heart of glass

November 24, 2010

What’s the best way to keep track of medicines or luxury goods? Just give them a number, of course. But what if the item you want to keep your eye on is made of glass?

World' First Transparent Ceramic Lens

August 2, 2004

CASIO, Inc., in conjunction with its parent company, CASIO COMPUTER CO., LTD., Tokyo, Japan today announced that using its proprietary optical technology, CASIO COMPUTER CO., LTD., has developed the world’s first lens using ...

A robot with finger-tip sensitivity

December 1, 2010

Two arms, three cameras, finger-tip sensitivity and a variety of facial expressions – these are the distinguishing features of the pi4-workerbot. Similar in size to a human being, it can be employed at any modern workstation ...

Recommended for you

A not-quite-random walk demystifies the algorithm

December 15, 2017

The algorithm is having a cultural moment. Originally a math and computer science term, algorithms are now used to account for everything from military drone strikes and financial market forecasts to Google search results.

FCC votes along party lines to end 'net neutrality' (Update)

December 14, 2017

The Federal Communications Commission repealed the Obama-era "net neutrality" rules Thursday, giving internet service providers like Verizon, Comcast and AT&T a free hand to slow or block websites and apps as they see fit ...

US faces moment of truth on 'net neutrality'

December 14, 2017

The acrimonious battle over "net neutrality" in America comes to a head Thursday with a US agency set to vote to roll back rules enacted two years earlier aimed at preventing a "two-speed" internet.

The wet road to fast and stable batteries

December 14, 2017

An international team of scientists—including several researchers from the U.S. Department of Energy's (DOE) Argonne National Laboratory—has discovered an anode battery material with superfast charging and stable operation ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.