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Case Study - HPB4³ - Machine Specification

Several machine configurations were considered but in this instance there was no need for a long concept review. A very conventional axis arrangement has been chosen to accommodate components weighing as much as four tonnes enclosed in the workzone of four cubic metres. A full machine specification has been developed around a range of components from the largest LT3 workheads and wheelheads down to small bores on prismatic parts for other machine assemblies.

The final machine performance is predicted to improve on the component specification limited only by the individual parts of the error budget. Values input into the error budget are taken from historical data measured on machines recently made at Cranfield Precision. The magnification of the basic geometrical errors relates to the machine configuration, the Abbe offsets and the temperature control regime.

X Stroke About B Axis Centre Line± 1.0
Y Stroke1.1
Z Stroke1.25
Workzone Volume4M³
Workpiece Maximum Weight4 tonnes
Drift in any 24 HoursMicrons
X axis drift12
Y axis drift12
Z axis drift12
Displacement - All AxesMicrons
Full travel5
Within any 100mm2
Within any 2mm1
Horizontal and Vertical Straightness - All AxesMicrons
Full travel10
Within any 100mm5
Within any 2mm2
Pitch, Yaw and Roll - Full Travel Including ReversalArc Seconds
X axis5
Y axis3
Z axis4
SquarenessArc Seconds
Z to X, X to Y and Y to Z5
Parallelism C to ZArc Seconds
Vertical and Horizontal5
B Axis Rotary Table
Angular Displacement Accuracy± 1 arc sec
Command Resolution0,0001 deg
Average Radial Error Motion5 µm
Average Axial Error Motion5 µm
B-axis Squareness to X-Z plane< 0.5 arc sec
B table Top run out to X-Z plane swash< 1.0 arc sec
C Axis Spindle
Angular displacement2 arc sec
Average radial motion at nose0.5 µm
Average radial motion at 250mm2 µm
Average axial0.5 µm
Spindle growth after 30 min warm-up at 1000 rpm5 µm
Fluid Systems Temperature Control
High Pressure Hydrostatic Oil20°C ± 0.5°C
Low Pressure Coolant20°C ± 0.5°C

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