Construction of milling machines

Making light work of machining - Milling machine for lightweight construction plastics controlled by Siemens CNC

Materials used for lightweight construction are replacing metal in an increasing number of different industries. The development of suitable machine tools is complex, as the chips produced during machining are electrically conductive, and could not only be responsible for causing a short circuit but also have detrimental effects on health. As a result, their efficient extraction is vital. To address this issue, HG Grimme has developed its gantry rotary table milling machine / inclined bed (G-DT-F/SB), a 5-axis milling machine controlled by a Sinumerik 840 D sI. The machine is used for the manufacture of car components made of CFP.

In the G-DT-F/SB, different extraction systems suction the carbon chips and dust generated along the milling contour through extraction holes in the clamping fixture, while a brush extractor clears the milling head. In addition, an airborne dust extractor in the sealed-off machine cabin ensures that the air is purified to 99.99 percent by passing through a filtration system, after which it flows back to the building. As a certain proportion of the fine dust still manages to escape from the machine and a single chip could cause a short circuit, the control cabinets are afforded special protection by the creation of internal overpressure.

Equal attention to safety and efficiency
As an additional protection for operating staff, as well as the extraction system, the underlying design of the machine as a double gantry with inclined bed ensures that operators are not required to set foot in the work area during production. Instead, they are able to clamp a component for machining into position externally at one side of the machine, while a second one is being machined inside.
The extensive safety features in no way compromise the machine’s efficiency: In the G-DT-F/SB with double gantry and two milling heads, a workpiece is machined within just nine minutes – with a repeat accuracy of 0.08 millimeters, acceleration values of 3, 500 millimeters/second and traversing speeds of 55 meters/minute. These values are achieved through precise coordination of the mechanical design with the highly dynamic Sinamics S120 converter.

Alongside the G-DT-F/SB, the company also uses Siemens CNC controls in its machine tools and mold making machines, because with ShopMill they benefit from integrated work step programming optimized specifically for the production of one-off components and ultra-small production runs.

Captions
HG Grimme SysTech GmbH has developed a 5-axis milling machine specifically for machining CFP components which is controlled by a Sinumerik 840D sl from Siemens. Picture 1: Copyright HG GRIMME SysTech GmbH
One way of removing carbon chips immediately where they are produced is using a brush extractor mounted at the milling head.
Because a single carbon chip could cause a short circuit, the control cabinet will be as hermetically sealed as possible and overpressure created inside during subsequent operation.