The Mikron HPM 1850U has a tool magazine with 238 pockets. This means that sufficient tools and sometimes the necessary sister tools can be stored, even if the individual pallets have different requirements. © GF Machining

The Mikron HPM 1850U is also accessible by crane. This means that all pallets are accessible for heavy workpieces and can be hydraulically lowered to a comfortable working height and rotated 360° in the two set-up stations. The lifting and lowering movements of the pallets are well damped and do not interfere with milling.

A special feature of the machine is its construction: instead of resting on a concrete bed, which was poured on site, its one-piece cast-iron frame stands on three legs. The effect is similar to that of a three-legged tripod: the frame does not tilt. The machine is inherently very rigid.

High precision in toolmaking

The sheet metal parts to be produced with the tools have high accuracy requirements for very complex contours. As they have to be produced in the tool over several stages, the required dimensional accuracy increases. The tolerance chain begins with the base plate: a suitable machine is required to produce it precisely. The HPM 1850U CNC milling machine was able to meet the qualitative expectations in the panel range over 1,000 mm.

The swivel axis of the Mikron HPM 1850U also allows optimum access to the workpiece from the side. © GF Machining

"First of all, a very precise machine has a rigid design," explains Seifert. "Because in the milling process, you have to eliminate expansion and distortion above all." These occur in every processing machine as a result of mechanical loads and thermal influences. The extent to which a body expands depends largely on its size and shape. With the well thought-out machine concept, the machine designers have realized a rigid, low-torsion machine structure: Among other things, the machine bed is made from a single piece. Two levels and a guide distance of over 800 mm in the X-axis guarantee torsional rigidity and stability during roughing. This is particularly important when heavy workpieces cannot be clamped centrally on the rotary table and the latter is rotated. The symmetrical design and a jacket-cooled spindle ensure that no thermally induced inaccuracies occur. The expansions have almost no influence on the position of the tool in the X and Y axes. And in the Z-axis they are suppressed by the constant temperature.

Another measure is particularly precisely manufactured bearings in the axles. This allows the arrangement as a fixed-fixed bearing as opposed to a fixed-loose bearing. The preload resolves this overdetermination, which in turn increases the rigidity. Despite the size of the machine, a repeat accuracy of 6 μm X, 5 μm Y and 4 μm Z is achieved. A positive side effect of the increased rigidity is the optimum cutting values of the tools.

The Mikron HPM 1850U from GF Machining Solutions enables the production of large yet precise individual parts from batch size 1 and is therefore used for base plates.

According to documents from GF Machining Solutions / ag