Blank forming process
The molding of the blank of optical parts plays a significant role in improving the efficiency of optical cold processing, improving the utilization rate of optical glass, saving labor and reducing costs.
Since 1970s in foreign countries, the blank technology of optical parts has completely broken through the bondage of classical method, realizing continuous smelting and material drop molding, which has increased the utilization rate of optical glass to over 90%, while the supply of raw material blank accounts for more than 80% of the whole raw material of optical parts.
The blank forming of optical parts can be divided into two methods. That is secondary molding method and primary molding method. Secondary molding is also called hot pressing molding method, and primary molding is also called dripping molding.
The technological process of hot-press molding is to process the optical glass into blocks first, then cut and adjust the weight, then heat and soften the glass, press, annealing and test it. In the whole process, there are several important concepts to be introduced.
● Blank precision
The blank processed by hot pressing method mainly controls its geometric precision, dimensional precision and surface quality. The main factor affecting the precision of the blank is the process condition. The weight fluctuation of the pressed glass parts, the thermal expansion of the mould, the contraction of the glass after pressing, the cooling speed after pressing, etc.
● Thickness tolerance
The thickness tolerance is the key precision of molding parts. It can mainly control the weight of glass material to meet the requirements. However, adopting conventional balance weighing and drum processing methods can not meet the precision requirements.
Now we often use bars to process, which can achieve higher precision.
● Surface quality of molding parts
On one hand, it depends on the surface quality of the cavity surface; on the other hand, it also depends on the pressing temperature and anti-adhesive.
In foreign countries, micro-vibration has been applied to the center of the shape to make it easy for the die-forming part to be uncoated, and the center is in place to ensure the geometric shape of the die-forming part.