Jan 30, 2012
Today’s know-how, together with new developments in control technology and machine production technologies allow to utilise automotive glass grinding and cutting machines in new ways.
This equipment with its more flexible use, can reach higher quality and/or much shorter cycle times as well as it is open for new applications.
New equipment with direct drive technology is able to preprocess glass in a higher quality and at the same time faster than in the past. Thanks to the drives the gearboxes can be eliminated, higher torque can be achieved and higher resolution encoders can be used. Eliminating the gearboxes menas eliminating the mechanical play totally. The accuracy is given by the measurement system and the performance of the drive regulator. The measurement systems can resolve down to micrometers or micronarcs for polar systems.
Using the new technology the customers do not have to decide between productivity and quality to a given price. The new controls allow to adapt the production quality to the desired level. For example a customer can start its venture in the less demanding replacement segment, where high output is critical. If he is looking for new opportunities later it is possible to reprogram the machine to the highest quality levels. The customer is able to compete on the highest quality levels which allow asking for a higher price for the manufactured product. Todays new electronic developments allow an easy and riskless adaption of parameters. The technology, accuracy and flexibility can be applied in other glass production fields like solar or architectural production as well.
Technical basis of champ’speed
Working with two cutting bridges allows to separate relief cuts and form cuts. Furthermore the customer can separate cutting and breaking if needed. Using the correct combination distributing the processes allows moving the bottleneck process in cutting and grinding from the cutting/breaking into the grinding operation. The best combination depends on the design of the end product. In most of the cases the best solution is to do the relieve cuts on the first station and the cutting and breaking on the second station. Having two independent cutting heads with one breaking ball head gives room for the very best possible combination to increase the quality and accuracy to the maximum with the lowest possible cycle time.
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| Figure 1: Example windscreen |
Producing a form with an accuracy of 100 percent is possible but physical parameters limit the cycle time. If needed, the machine can follow the contour exactly. This will result in a very accurate glass, but takes its time. In theory, the relation between grinding speed and forward movement should be constant. To reach a constant grinding surface the speed has to be reduced at each point where the grinding spindle makes a turn or goes around an edge. This means: the smaller the radius, the lower the speed. As the grinding wheel has a diameter, the speed of its centre point has to increase, because it has to travel a much longer way than the grinding point of the glass. In an inner arc, the travelling speed has to be reduced, because otherwise the wheel would take too much glass and will get choked.
Today there are two ways, to achieve high speed and accuracy. Firstly it is possible to make the design of the form in a way that the end result will still be in specs. This means that the design is not in the middle of the tolerance field designed, but will touch the limits with working in lower tolerance bands. The achieved result is still the same (faster production cycle, in given tolerance), but the result does not depend on factors like speed or grinding wheel diameters anymore. Secondly one can do the same like in the past i.e. opening the contour error and allow bigger deviation. But with these methods the resulting form will then depend again on process parameters like speed. This method is not recommended but is very easy to do and does not require additional know-how or skill, but the production cycle improvement can still be considerable.
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| Figure 2: Cutting path with new equipment can increase corner speeds, improve quality and is reproducible |
Additional to the improvement in cycle time due to the higher moment of the motor, a well designed grinding path can add considerable cycle time advantages. Together with using two bridge cutting and direct drive grinders, the cycle time can come from 27 seconds for a windshield down to 16 seconds, for the same design.
Higher torque and higher accuracy allow on polar machine to increase the diameter range. Not only windshields for trucks and busses but also solar glasses or other high end glass with diagonals up to 3.6m are possible to grind with accuracies below 0.1mm around the whole circumference. This accuracy can be achieved with low cost process due to low cycle times, automotive approved equipment and low cost consumables.
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| Figure 3: Trajectory speed of the grinding wheel center |
Commercial applications
The investment is not much different than in the past, but the cycle times improve a lot on the same production space. This alone can justify a replacement of machines. Higher torque motors allow running the grinders faster and more accurate. Adding the possibility to use the tolerance band in improving cycle time gives more flexibility. The decision to invest in accurate or fast equipment has not to be taken anymore. The equipment can be bought and during the time of use switched by parameters to either use the machine in a mode with very low tolerances or in a mode with very high precision.
A company can start of in producing replacement glass with very high output and low cost for example and switch for other projects to OEM manufacturing parameters with high machine and process capabilities and insuring six sigma tolerances or more. The characteristic of the equipment can cater for different markets and customers by simply pushing a button or by an intelligent design. Using this way also small companies can invest and be sure, that the equipment keeps its value for all future ventures and supports future expansions. For solar glass new dimensions of accuracy can be achieved by low costs. The flexibility is there to adjust in the future to all needs of forms or accuracy. Proven process capabilities are given out of the automotive industry.
With this equipment producing changing models is possible without making test glasses. It is possible to change from one model to the next, without wasting one glass and without tweaking parameters. Change over time is dramatically reduced and lower skilled personal can handle the machines.
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| Figure 4: Example of a new automotive glass preprocessing equipment – champ’speed-line of Bystronic glass |
Conclusion – Limitations and things to consider
Due to the fact, that the machine does what the program defines, it means that a form has to be defined 100% correctly. The machine follows the drawing exactly. The CAD-drawing must include all detail and the transition from one drawing element to the next. Transitions of elements have to be correct and tangents have to be handled with care and accuracy. This higher demand in designing capabilities might allow to reduce the capabilities of the machine operator.
About Bystronic Glass
Bystronic glass is the most competent and reliable partner for services, machinery, plants and systems in the glass processing sector. Bystronic glass supplies its well-proven machine technologies also in important areas of the photovoltaic industry. This includes preprocessing, front-end and back-end solutions. Bystronic glass is an international brand with globally operating companies that support their customers on site and through own sales and service companies. Since 1994, Bystronic glass is part of the Conzzeta AG, a renowned Swiss industrial holding company.
Source: Glass on Web
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