Handle with care

Zwiesel in the Bavarian Forest is well known for its glass industry. The handcrafting of glass products, which is still practiced here in part, is today considered to be a national treasure. A glance into the machine shop of a glass mold maker reveals that the latest machine tools are used here.

Mold making for the glass industry

Peter Olinger Formenbau e. K. specializes in molds for high-quality domestic glass in the crystal and lead crystal sector. The company has constantly adapted its production methods to the latest technological standards. While in the past molds were usually eroded and polished by hand, milling has now become prevalent. "We have always milled molds for large vases because the electrodes required would have been too large, too heavy and too expensive," explains managing director Peter Olinger. "Now, we mill almost everything - with excellent results in terms of quality and surface finish."

Inconsistent material, high requirements

Engravers have very high standards for their machining centers. They need to be just as suitable for high-speed roughing as they are for the finest engraving work. This requires not only a certain torque on the spindle but also high speeds for the precision work. The stainless steel used as a mold material is also very demanding: "It is an inconsistent material, because chromium makes it harder and nickel makes it softer," explains Olinger.

The latest milling machine was put into operation in January 2013. The Microcut MC 800LL was modified specifically to meet Olinger’s requirements: it has higher-quality bearings and a more powerful motor to ensure the required high speed and torque. For him, a prerequisite in purchasing the machine was that it be equipped with a Siemens CNC. The more powerful control version of Sinumerik 828D (PPU 281) brings faster block processing times and 5 MB of internal memory for user data.

The faster way to finished molds

To create the required surface finish quickly and without any additional optimization, the Microcut control system is equipped with the Sinumerik MDynamics milling technology package. This includes the High-Speed Setting Cycle (Cycle832). This provides all the important functions and G-code commands for High-Speed Cutting (HSC). After the machining strategy (roughing, prefinishing or finishing) and the tolerances have been entered, the respective dynamic parameters are automatically activated in the background. With the Advanced Surface option, which is part of the milling package, the control system calculates the speed profile in advance for short track sections and simultaneous fast feed rates. The more uniform speed profile achieved as a result optimizes the machining of free-form surfaces in the HSC area with regard to accuracy, speed and surface quality.

The Microcut machining center comes from Tusch & Richter GmbH & Co. KG of Obertraubling, Germany, which predominantly distributes cutting machines from Taiwan. Robert Pickl, managing director at Tusch & Richter, is confident: "The applications at Peter Olinger show that a Sinumerik-controlled standard machine from Taiwan meets the high demands of a mold maker."

Fragile part removal

The orders received by Peter Olinger vary greatly. The construction of the mold must always align design requirements with part removal possibilities. After all, it must be possible to remove the fragile glass product from the mold without damaging it. Olinger draws the expertise required for this from years of experience with material and manufacturing processes. And even though glass producers are increasingly trying to save on molds and therefore reduce costs, there are many products for which they cannot avoid mold makers. It is therefore an advantage if a mold maker has efficient equipment in order to produce good-quality molds cost-effectively.