production problems of ASPH products and high index materials

[essegn]

Hi,

I'm the new member of optiboard forum, so i hope that somebody will help me :)

I'm working in small lab for lens production (400 lenses per day) and we have some problems to produce:

• ASPH products
• high index materials

We use two ways of production:

• conventional generator + grinding + polishing machine (Satisloh)

• Freeform technology (Optotech)

The percentage of failure production of low index materials on the both machines (conventional generator or Freeform) is up to 15 percent. So it's ok i think.

But when we try to produce high index or ASPH materials the failure percentage is about 50 percent or more.

The time for cooling after lenses blocking at high index is about 1 hour. The cutting parameters for generator are decreased as well as parameters for grinding and polishing.

We use different grinding and polishing foils on high index lenses.

In case of ASPH products, surface's topography is the same like datas from producers of semi finished materials.

It is the same when we produce high index material lenses on Freeform - 50 percent of falure products and more. (especially ASPH products)

The most common failures of lenses are:

• unrwanted cylinders
• increased or decreased power
• wrong lens thiknesses

The calibration of the mentioned machines is performed correctly. As i already wrote we don't have any problems to produce low index materials..

Used semi finished materials are being bought from well known producers (LTL, Essilor).

Did anybody the same experience and managed the problem?
What could be wrong ?

Many thanks for your responses

Peter

[IC-UC]

Hi Peter,

Hope I can help in some way. If your normal indeces are OK, then I would make sure that the software is calculating for high index materials for your tools (on the conventional line)
Not sure what index your tools have been cut on, but you must make sure your software accounts for this.

Are the pads you are using for your ASPH lenses too rough, perhaps using a Poly pad? We typically use a 15micron pad for CR and 30 for Poly.

Also you can check that your pressure on the fining mahines are constant and proper. Too much and you will get wrong thicknesses, powers etc.

Is your fining water chilled or cool enough? Is the polish at the right temp and baume?

Hope this helps a bit. let me know if you need more info.

[gemstone]

Hi,



The percentage of failure production of low index materials on the both machines (conventional generator or Freeform) is up to 15 percent.


Peter

Should be below 4%.

[IC-UC]

Yeah forgot to say 15% is not good! If we are only looking at surfacing it should be around 1-2%.
Hope we can help you somehow get this down.