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Kreischer Optics - Transmitted Wavefront Correction: MRF Eliminates Hit or Miss Polishing

 

 

 

Company:

Kreischer Optics, Ltd.

 

Company Background:

Kreischer Optics, Ltd., has been located in the Chicago area since its inception in 1948.  The growing company employs a staff of 14 today, and has recently expanded its facility from 8400 square feet to 16,200 square feet.  Kreischer Optics specializes in precision test glasses, cylinders, spheres, flats, and is now recognized as a world leader in the manufacture of aspheres.  Kreischer Optics purchased a Q22-XE MRF system in 2007 and continues to expand their capacity and enhance their capability with the recent addition of a Q22-X MRF system which will be installed in early 2009.

 

Kreischer Optics Manufacturing at a Glance:

  • Founded in 1948, today employs 14 people
  • Purchased Q22-XE MRF machine in 2007, purchased Q22-X MRF in 2009
  • Markets served: master precision test glasses, cylinders, spheres and flats, and is now recognized as a world leader in the manufacture of aspheres
  • Reason for purchase:
    Kreischer recognized the increasing demand for asphere manufacturing and decided MRF was the right tool to help them manufacture to higher precisions deterministically
    • Deterministic polishing of aspheres
    • Increased production capacity
    • Advanced technical capabilities
    • Reduced costs
    • Eliminate manufacturing uncertainty

 Kreischer’s MRF Experience:

Within a week of getting their Q22-XE MRF machine on the floor and in production, they saw immediate impact on their business – with the very first lenses that come off the machine. Those first lenses were part of a 24-piece order that needed to be polished to a .2-micron accuracy.  They shipped the initial batch to the customer, who called before even completing their testing.  Cody Kreischer, CEO, told us, “Our parts were so much better than their previous vendor, they placed an order for 32 more.”  Kreischer went on to describe how this success has opened other doors for Kreischer Optics. “Although they are still in the pre-production phase, they anticipate ordering over 400 next year.  In addition, we have orders for spherical and cylindrical optics that go into the same system!”

 

Transmitted Wavefront Correction

Having MRF in place has helped Kreischer to expand its manufacturing capabilities. Another area in which MRF has made a big impact is the correction of transmitted wavefronts. The ability to specify transmitted wavefront is important to many of Kreischer’s customers because it is a measure of quality of the overall optical assembly. 

 

Before using MRF, correcting transmitted wavefronts was problematic. They were challenged with lower yields, longer lead times, cost of reworks and replacements and uncertain shipping schedules. Adding MRF allowed them to transform their process, make better surfaces on time, within specification, while reducing their costs, all to the delight of their customers. Once MRF was in place they found they could use MRF to deterministically polish individual surfaces to lower precisions and then use MRF to do a one-pass correction of one surface to remove transmitted wavefront errors of the final assembly. Kreischer found that the direct correction of transmitted wavefront error using actual measurement data resulted in much better surfaces with much less effort.

 

Improving yield

Correcting transmitted wavefront by conventional polishing techniques was a "hit and miss" process. In fact, the Kreischer’s miss rate was 25-50% on meeting specifications. In order to achieve the necessary yield, they would increase their normal planned overage of 10% to 50%.

 

With MRF, they could predictably and reliably meet their specifications every time.

 

Reducing precision requirements

Before MRF, Kreischer also found that they had to polish individual surfaces to a much higher level of precision to ensure that the transmitted wavefront of the final assembly was in tolerance.  Previous polishing techniques required that they reach 1/20th wave surface quality on all elements.  Even with these stringent specifications, Kreischer found that after assembly, some assembled components did not meet 1/8th  wave tolerances.

 

MRF allowed Kreischer to relax individual surface specifications from 1/20th wave to 1/8th wave tolerances. Then, by using MRF to do a one-pass correction of one surface to remove transmitted wavefront errors of the final assembly, most final assemblies are now qualified at 1/16th  wave .

           

Reducing “re-works” and costs

Since so many of the components fell out of specification, Kreischer estimated that they spent a lot of time and money on reworks and replacement of bad surfaces. They estimate that reworks increased unit cost by as much as 33%. 

 

Meeting deadlines

Meeting shipping schedules and customer deadlines was difficult, with uncertainties at every step of the process.

 

Although bringing the surfaces to lamba/8 adds about 10% to MRF time, the increased time in this single step is more than compensated for by a 1/3 reduction of overall work load in other steps.

 

 

 

Before MRF

After MRF

Yield

50-75%

90-100%

Planned overages

50%

10%

Individual surface requirement

1/20th wave

1/8th wave

Reworks costs

+ 33%

--

Reduction in overall work load

--

33%

Final precision

1/8th wave

1/16th wave

 

 

Kreischer continues to be delighted with the addition of MRF polishing to their robust manufacturing capabilities.  Kreischer Optics Ltd., continues to grow and will soon add a second MRF machine (a bigger Q-22X) to help them keep up with demand. Adding MRF into their production lines has allowed them to work faster, create better surfaces, save money and even go after (and win!) new work.

 

 

Company Contact:

Cody Kriescher, CEO

optics@kreischer.com

www.kreischer.com

 

 



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