Measuring a Part That Is Not Held the Way It Will Be Used

ZEISS Industrial Quality Solutions has extended the Virtual Clamping app within its ZEISS INSPECT 3D metrology platform and paired it with a new Guided Holding Kit that fixtures parts on up to four contact points, working alongside the existing universal pneumatic clamping device. Parts can be repositioned in under ten minutes, with the software automatically generating measurement sequences and alignment procedures for robotic implementation and inserting virtual extensions and collision bodies into the measurement environment. It supports weight-force-compensated mesh analysis with deformation modelling referenced to measurement data, covering injection-moulded, die-cast and sheet metal components including vehicle body panels, and integrates with the ZEISS ScanBox optical measuring machine. The stated aim is to reduce both fixture cost and labour.

The problem this addresses is one of the more counter-intuitive in dimensional metrology. A flexible part — a body panel, a thin die-casting, a large moulding — has no single shape. Its geometry depends on how it is supported, because gravity and clamping forces deform it. A panel measured lying flat on a table is not the panel that will be bolted into a car, and the deviations found on the table may be entirely artefacts of the support. The traditional answer is a rigid fixture that holds the part exactly as the assembly does, which is why automotive quality departments own warehouses of steel fixtures, each specific to one part, each costing tens of thousands and taking months to build.

Virtual clamping inverts that. The part is held in a simple generic fixture at a few points, scanned, and the software then computes what the measured surface would look like if it were constrained the way the assembly constrains it — using a deformation model of the part referenced to the measurement data, with the part's own weight compensated out. The physical fixture becomes a holder rather than a datum, and the datum scheme moves into software where it can be changed without machining anything.

The consequences are worth spelling out for anyone running inspection on flexible parts. A change to the clamping strategy becomes a software change rather than a new fixture, which means a design revision no longer strands a fixture investment. New parts can be measured before their fixtures exist, which moves inspection earlier in a programme. And the ten-minute repositioning figure matters because it is what makes a single scanner economic across many part numbers rather than dedicated to one. The caveat is the model: results are only as good as the deformation behaviour assumed, which for a part with non-linear stiffness, a thick-to-thin transition or significant springback deserves validation against a real rigid fixture at least once. That comparison is worth doing on the first part family, and worth writing down, because it is the evidence the method is trusted on afterwards.