Automotive Manufacturing: Body Shop and Press Shop Position

Displacement measurement in automotive manufacturing concentrates on two places, the body shop and the press shop. On the body-shop side are clamping and in-position stroke of fixtures, locating pins and press heads, which determine body-assembly accuracy and weld consistency. On the press-shop side are press-slide position and die shut height, which determine part-forming quality and die safety. The shared requirements of both lines are a high cycle rate, high repeatability and strong vibration, so vibration resistance and long-term consistency of displacement feedback are demanding.

Body shop: fixture and locating stroke

On a body line (spot weld, laser weld, adhesive) the fixture presses the panel onto the locating datum. Displacement feedback is used as the clamp-in-position criterion, for multi-station synchronisation monitoring, and for compensation after wear. Body accuracy is accumulated over many operations; if clamping at a single operation is not in position, the error is passed to the next. Multi-channel sensors of the same model and the same measuring range are recommended, with attention paid to repeatability (typically of the order of ±0.002 mm; see the three accuracy terms). The selection framework for pneumatically or hydraulically driven clamping mechanisms is given in why hydraulic cylinder position control uses magnetostrictive sensing; for cylinder-integrated types see Series 17 cylinder-integrated directly.

Press shop: slide bottom dead centre and shut height

Bottom-dead-centre position of the slide on a mechanical or servo press determines die shut height and part forming. Displacement feedback reads slide absolute position for bottom-dead-centre monitoring, shut-height setting and overload protection. A servo press places higher demands on the position loop; a 1-10 μm resolution grade is recommended (typical non-linearity <0.02% FS; see the three accuracy terms). After a power loss absolute position is retained, so re-zeroing is unnecessary after a die change (see absolute vs. incremental position).

Typical measuring-point layout in automotive manufacturing

Installation points in vibration and weld-slag environments

A body shop has weld-slag spatter and vibration; a press shop has periodic high shock. Countermeasures: keep the rod out of the direct slag-spray zone, specify connectors to IP67 or better (for the meaning of each rating see IP protection ratings), and at high-vibration stations specify Series 13 mobile hydraulic, rated 25 g vibration and 100 g shock; for cylinder-integrated types specify Series 17. Installation and anti-loosening practice is in installing and commissioning in practice; troubleshooting of abnormalities caused by weld slag is in common-fault troubleshooting.

Interfaces and line integration

Body and press lines are large and have many axes. Position feedback should preferably use a fieldbus type for centralised management. Multi-axis synchronous sampling should use EtherCAT with distributed clocks (Series 197 EtherCAT; configuration in the practical fieldbus guide). Matching cycle time and refresh rate is covered in matching response time to the control cycle. Similar demand for damping and brake displacement can be compared with high-speed rail and urban transit: damping and brake position.