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Plastic optics are growing in popularity: How small series and flexible production processes can be achieved with ultra-precision technology

Glass bottles are now the trend. The shocking images of packaging and plastic waste in the world's oceans are clearly causing many consumers to rethink. Glass bottles are tasteless, do not take on odors, do not pass on any odor and can be reused up to 50 times. Optical inspection systems with high-precision plastic optics make this possible.

, Lars Dick
Glass water bottles are subjected to an optical quality inspection

When manufacturing glass bottles, it is important that the bottle, which is cast and then pressed, slowly cools down in the cooling oven for two hours or more. If the bottle cools down too quickly, it can become deformed, and invisible hairline cracks may develop that can later lead to chipping or other damage. Optical inspection systems are used to identify such cracks early on during the manufacturing process and to prevent damaged bottles from coming into circulation. These inspection systems can identify damage to the bottle base or neck, for example, and sort out the corresponding bottles. With high-precision plastic optics, Jenoptik supplies an important optical key component for these inspection systems.

Special processes such as ultra-precision technology are required to manufacture plastic optics or polymer optics for optical inspection systems and other applications. This is a special process that Jenoptik uses to achieve polymer-optical prototypes and pre-series as well as customer projects that require such special technology.

Advantages of ultra-precision technology for high-precision plastic optics

The advantages of ultra-precision technology (UPT) are its flexibility, time saving and high accuracy. Depending on the customer's requirements, Jenoptik can adapt the prototype and therefore the plastic optics requested by the customer with high precision and flexibility by making suitable parameter adjustments. Furthermore, the production of plastic optics with this process is much faster and the customer can promptly check them for functionality and the required optical quality. This process is the optimal method of choice, especially in the prototype phase or preliminary phase of series production. It is also possible to manufacture tool inserts for plastic injection molding at Jenoptik using ultra-precision technology.

Many customer projects with very specific optics requirements, for example in terms of dimensional accuracy or internal stress, can only be achieved using ultra-precision technology. Ultra-precision technology is used where the classic injection molding processes for plastic optics reach their limits. Jenoptik has been deploying ultra-precision technology for many years and is able to produce small series up to an annual quantity of 1,000 pieces.

The four paths to precision polymer optics

Create rotationally symmetrical plastic optics using the diamond turning process
Jenoptik currently uses four different processes in ultra-precision technology:

Ultra-precise plastic optics with rotational symmetry thanks to diamond turning

The process of "two-axis diamond turning" is particularly suitable for plastic optics with rotational symmetry. The component is aligned with respect to the center of rotation and the optical surface geometry is then processed with the utmost precision using two linear axes. As a result, in addition to spherical and aspherical smooth surfaces, rotationally symmetrical structured surfaces, such as diffractive surfaces and Fresnel surfaces, can also be processed. In addition, asymmetrical surfaces, such as cylinders or toric surfaces, can also be achieved by clamping the component outside the center of rotation, i.e. outside the axis.
Creating application-specific free-form optics with slow tool servo processes

Slow tool servo processes create free-form surfaces

The "slow tool servo" supported turning process is used for fast production of free-form components on an ultra-precision machine. A rotation axis is integrated into the programming together with the linear x and z axes. This enables the machine to process three-dimensional surfaces with great precision. This process allows the asymmetrical shrinkage for injection molding tools to be compensated for by specially calculated free-form surfaces. This increases the accuracy in the injection molding process. The result is free-form surfaces, cylinders, toric surfaces or NURBS surfaces with very high precision, a roughness of up to <2 nm Rq and a form deviation of up to <0.5 µm.

Optical free-form surfaces are specifically used in the automotive industry, for example as head-mounted devices (HMDs), head-up displays (HUDs) and LED lighting optics.

High-precision grating structures using fly cutting

The "fly cutting" method is used for both linear structures and grating structures on flat surfaces. These are used in prism arrays, diffraction gratings, cylinder arrays, pyramid array reflectors with a typical grid spacing between 2 µm and 2 mm in beam shaping and distance measurement, but also in the field of sensors or safety technology.

For this purpose, the component is positioned with a vacuum chuck. A diamond tool rotates on the circumference of the tool holder. A linear structure is created by the rotation of the spindle and the linear movement of the x-axis. This linear structure has the negative form of the diamond tool and becomes a grating structure through repetition of this process. In terms of precision, Jenoptik achieves a minimal form deviation of up to <10 µm and surface roughness of up to <0.2 nm Rq.

Creating lens array forms using ultra-precision turning

Creating lens arrays with ultra-precision milling

"Ultra-precision milling" is suitable for particularly curved free-form surfaces and lens arrays. These optical functional surfaces are used, for example, in LED lighting technology, for beam shaping or for efficient lighting.

In ultra-precision milling, the milling process is carried out on an ultra-precision machine with at least three CNC-controlled axes. Very high spindle speeds of up to 80,000 rpm are used for optical surfaces, while simultaneously using a very small milling radius of up to 80 µm. In terms of precision, Jenoptik achieves a minimal form deviation of up to <0.5 µm and surface roughness of up to <5 nm Rq.

Jenoptik, an expert in the manufacture of high-precision plastic optics, has been offering ultra-precision technology since 1997 and can therefore look back on its many years of experience. As a reliable partner, Jenoptik offers individual solutions of the highest quality, taking into account the ISO standards.

If you would like to find out more about ultra-precision technology and our plastic optics, or if you would like to know that we can support you in achieving your specific optics requirements, please do not hesitate to contact us.

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Dr. Lars Dick

About Lars Dick

Lars Dick is graduated in mechanical engineering focusing on optics and precision engineering. As head of the ultra precision technology group and head of the tool center group at Jenoptik. His interests include diamond machining, molds, replication techniques, coating, and metrology of optical surfaces.

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