Vacuum clamping systems for woodworking centres are now widely used, both in small companies and, in particular, in industrial applications. New machines are now increasingly equipped with vacuum clamping systems, but users still have certain reservations about upgrading existing machines with this technology. However, as the following practical example shows, the arguments against upgrading cannot are rarely based on technical facts. It should be noted that it is a medium-sized company, rather than an industrial production facility, which has recognised the opportunities which result from upgrading a woodworking centre which has been in use for many years. Messrs. Krines GmbH in Sand am Main was founded as a joiner's shop in 1968: today. It has little in common with a traditional joiner's shop. Initially, the company founder, Peter Krines, concentrated above all on the classical area of interior completion of buildings; later, the emphasis moved to the manufacture, sales and installation of windows, doors and conservatories and, in particular, the production of these in accordance with the customers' specific wishes. Together with his sons Gunther (sales) and Jochen (production), Peter Krines today manages a company with 55 employees, of whom over 30 work in the production. The production of the company's products generally involves the manufacture of many individual parts and small lots, and the company's adoption of CNC technology about nine years ago was a logical step, since it promised the necessary flexibility. Since then, Krines has used an Italian woodworking centre for many application and with good results. However, the vacuum clamping system delivered with the machine often caused problems with handling of the workpieces and in the conversion from one workpiece to another. In addition, more and more customers demanded increasingly individual windows, house doors and conservatories, and this meant that many more different elements had to be produced, most of them on the woodworking centre, which thus became a bottleneck in the production sequence.

A new clamping technology or a
new CNC machining centre?

Due to the enormous demand for machining capacity, Jochen Krines, who is responsible for production, decided to look for an economical alternative. The first option was the purchase of a further CNC woodworking centre, but the company was not prepared, for various reasons, to invest so much money. Various attempts to optimise the existing clamping system were unsuccessful. For this reason, Messrs. Krines visited the Woodworking Trade Fair in Nuremberg to search for a better solution. They found this on the stand of the vacuum-technology specialists J. Schmalz GmbH in the form of a wide range of vacuum clamping systems. Detailed examinations and discussions were followed by a test with the Innospann vacuum clamping system. Due to its modular concept and the fact that it can be mounted on thin base plates made of stainless steel, this clamping system is ideal for retrofitting on many different types of CNC woodworking centres. The tests at the Krines factory were convincing and the company therefore decided to completely convert their CNC woodworking centre to the vacuum clamping system Innospann. Jochen Krines said, "We were faced with the choice of either buying a new CNC centre, which would have cost us several hundred thousand Euros, or upgrading our existing machining centre so that it could be used very productively and flexibly for several years. The Innospann system from Schmalz made our decision easy, since the conversion costs were only about 10% of what we could expect to pay for a new machine and the conversion would permit us to fully utilise the performance of the existing machine".

Flexible vacuum clamping technology for shorter
setup times and lower conversion and handling costs

With the clear objective of minimising the setup times and reducing the times needed for tool changing and handling, while providing the required flexibility in use, even in multishift operation, the vacuum clamping system Innospann for the CNC machining centre from CMS was configured as follows: two base plates Steel-Plate-T, 3 mm thick, with laser-cut slots and 420 valves (distributed on the two plates, each with the dimensions 2340 x 2520 mm), 24 suction blocks Quad-Base-T with the dimensions 175 x 175 x 22 mm, 48 standard suction cups 1 with 80 x 80 mm, 32 standard suction cups 2 with 80 x 40 mm, 64 adapter rings for standard suction pads and mounting materials, gaskets, valves and vacuum hoses. Later, 20 frame clamps and lifting cups were added, permitting Krines to clamp all conceivable workpieces rationally, safely and flexibly. Since the double table of the machine, each half with the dimensions 2340 x 2520 mm could not be covered with a single stainless-steel plate, two plates were used. This has the additional benefit that finished parts can be removed and new workpieces can be mounted on one half of the table while other workpieces are being machined on the other half. In order to keep the cost of converting the CMS machining centre to the Innospann system as low as possible, Krines employees milled the surface of the existing machine table and installed all of the vacuum connections. Both the existing vacuum generator and the laser-projection system for fast and simple positioning of the workpieces (and also the suction blocks) were retained. The very low and compact design of the Innospann clamping system and its suction blocks also ensured that there was no reduction in the usable Z height of the machine and this, in turn, meant that high workpieces and frames can still be machined.

Summary

According to Jochen Krines and Andreas Greulich, responsible for the CNC programming and the operation of the CNC woodworking centre at Krines, the purchase of the Innospann vacuum clamping system from Schmalz has already paid for itself. "The investment in vacuum clamping technology was amortised within just over eight months. The flexibility offered by this system helps us in our everyday work, because we rarely machine two identical workpieces in sequence. Due to the double table and the higher holding forces, we can manufacture even complex one-off workpieces very flexibly and with the maximum machine performance", said Jochen Krines about the economical and manufacturing aspects. Andreas Greulich added: "As a result of the conversion, we now work in 1.5 shifts with a machine loading of 120%. Before the conversion, the setup time for a new part was about 20 minutes; today, it is never more than 3 to 5 minutes. This 80% reduction in the setup times alone justifies the investment in such a practically oriented workpiece clamping system. In addition, we can now clamp even very narrow workpieces safely and without the need for templates, there are no hoses to get in the way, we can machine the parts from all sides without reclamping, and there are virtually no standstill times". To sum up, Jochen Krines said: "We are currently testing further tools because we wish to do everything possible with the machine and aim to start production in two or even three shifts in the future. The decision to invest in retrofitting our machine with vacuum clamping technology was one of the best we have ever made. A new machine would have cost us more than ten times what we paid for the upgrade, and it would probably not have made us more flexible or more productive. We are thus fully satisfied and profit in many ways from this future-oriented conversion of our existing machine". As a result of the increased productivity, Messrs. Krines are now in a position to accept production orders from dealers, etc. in addition to their existing customers.