Engineering Case: The Alternative That Simplified Manufacturing

Early in the pre-production run, the mechanical enclosure presented chronic fitment issues. The initial design relied on four stamped aluminum brackets welded to a structural rail, carrying the optical sensor mount and internal drive motor. While individual part fabrication met drawing tolerances, accumulated angular variations across consecutive bend radii created unpredictable 1.8 mm offset deviations across the mounting plane.

Assembly technicians were forced to manually shim every third subassembly during line trials. This manual adjustment ballooned build times from 8 minutes to nearly 26 minutes per unit. Instead of continuing patch-up rework routines or tightening stamping vendors to unsustainable micro-tolerances, the engineering lead paused tooling release to branch alternative manufacturing strategies.

The core objective shifted: eliminate human calibration during assembly without expanding the exterior envelope or driving piece-part costs beyond acceptable unit economic targets.

Three distinct design branches were created inside Onshape to test competing fabrication paths against cycle time, upfront tooling expenditure, and structural rigidity:

Running physical prototype cycles for Fork B and Fork C concurrently gave the team verified cycle data within nine days. Fork B proved that 5-axis machining reduced total unit assembly steps from 19 down to 3, while preserving precise sensor alignment without secondary fixture adjustments.

Detailed time studies and dimensional inspection reports confirmed substantial operational gains when migrating to the single monolithic machined unibody:

• Fastener Count Reduction: Dropped from 18 M3 fasteners and 4 weld beads down to 4 captured mounting bolts.
• Baseline Assembly Duration: Decreased from 24.5 minutes down to 7.8 minutes per completed chassis module.
• Datum Plane Variance: Sensor seating coplanarity tightened from ±0.45 mm down to ±0.02 mm across all units.
• Production Scrap Rate: Reduced from 6.2% pre-assembly rework scrap down to less than 0.3% line rejection.

Although raw billet machining raised individual piece-part material expense by $4.20 per unit, total manufactured cost dropped by $11.80 when factoring in saved labor hours, fixturing upkeep, and zeroed rework stations.