Using a retrofitting programme from Messrs. Arburg, the machine tool manufacturer Burkhardt+Weber used a new magnetic clamping device in order to modernise a special machining center. It was possible in this way to increase the output by 30 %.
„In spite of a very satisfactory growth rate and an increase in the automation of our mechanical production, we made a clear decision not to invest in a new machining center“, recalls Siegfried Finkbeiner, Production Manager of Arburg GmH & Co. KG at the commencement of the retrofitting project. This company in Loßburg in the North of the Black Forest is one of the world leaders in the manufacture of plastic injection moulding machines. Arburg machines are used in many different industries, e.g. in the production of one-way medical products such as syringes or infusion equipment. The car industry uses Arburg machines to process different kinds of plastics, to produce for example rain and light sensors or airbag components.
„My idea was to modernise the two very reliable machining centers from Burkhard+Weber, which we have been using since the 1980’s, the aim being to achieve an increased variety of products and a significantly higher output“, says Finkbeiner, referring to the specifications for Burkhardt+Weber. Up till then the Loßburg company had used the BW production plant to produce all machine base frames for the Arburg machines.
Because of the solid mechanical structure of the machining center, it seemed a natural decision for the retrofitting experts of Burkhardt+Weber to carry out a general overhaul and to add modern drive and control components.
Together with staff from Arburg, the Reutlingen machine tool manufacturer developed a suitable retrofitting concept which needed to be carried out within a tight time and cost schedule. At the same time they had to try to overcome the existing bottle-necks in the Arburg manufacturing processes by increasing production without lowering the quality.
Before the overhaul the BW plant had been assembled in the form of a classical double column machine. In the middle was a large clamping table with the dimensions 4000 mm x 1500 mm, on which pallets taken from a pallet storage could be selected in alternating mode. On each of the outer long sides was a 3-axis unit with a 4000 mm long X-axis. Each 3-axis unit was fitted with a 25 kW swivel head for horizontal and vertical processing, as well as a tool holder for 40 tools.
The solid clamping table needed to be still available for use after the overhaul. It was, however, necessary to replace both the moving columns by 2 powerful 3-axis units with fast travelling axes, modern high-torque swivel spindles and enlarged tool magazines. The reconditioning and conversion also included the addition of a Siemens Sinumerik NC control of the latest generation. The final machine should also include one new pallet storage, and the complete ergonomic design of the plant was to be improved.
In order to save time and money, the engineers at Burkhardt+Weber decided to use for the modernisation of the 2 moving columns existing components of the standard machining centers. The BW platform strategy proved to be a wise decision and ensured minimum development time using state-of-the-art technology. In order to reduce the actual renovation time, the retrofit experts completely prefabricated and tested both units in Reutlingen. Each was now fitted with a 2,5 s fast horizontal and vertical swivel head (8,000 min-1 and 37kW at 100 %), an impressive torque of 1,490 Nm and 60 m/min feed axes, and thus met the requirement for a significantly shorter processing time.
The technicians developed completely new chain magazines incorporating special tool changers, which, with a capacity of 60 tools each, were able to meet the requirements for fully automatic machining for an increased range of products. This deliberate use of new and innovative components significantly increased the dimensional stability of the machine frames. These include among others the Siemens 840D control, the possibility of operating via several switchable control panels, digital drive technology, absolute value measuring systems, tool taper cleaning, tool fracture control, a tool dialogue system and an electronic in-process measurement. It was possible to simplify the programming and the operation of the plant, and future problems can be avoided by, when necessary, replacing parts using standard BW replacement parts.
An important part of the modernisation plan was to improve the ergonomic design by means of faster tool change. For this reason, the experts from BW abandoned the previous concept of a hydraulic clamping device and instead introduced a completely new clamping device automatically adjustable in width, using magnetic clamping technology. By the use of this clamping device, the machine operator at Arburg can automatically centre and optimally twist-free tighten and clamp different widths and lengths of casings. The electro-mechanically adjustable side panels are switched off using torque limitation as soon as the 2 magnetic poles are in position. Subsequently the polarity of the magnetic poles is reversed so that they lock themselves, Because of the permanent magnetic force, the machine frames are clamped securely and twist-free.
The effort was worthwhile, and the goal was achieved. „The modernised BW plant has a 30 % higher output and much greater flexibility“, says Arburg Production Manager Siegfried Finkbeiner, proudly describing the successful retrofitting project.
Burghard+Weber are equally enthusiastic about the project. The job was carried out in less than the scheduled time thanks to close cooperation with the experts from Arburg and to the prefabrication of the important machine components
Norbert Kraas Journalist in Tübingen
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