High-Precision Transmission Gears: DIN 4 Case Study

Client Background#

The customer is a manufacturer of automotive transmissions. It was looking for a stable supplier of high-precision gears for volume production, with a requirement of 2000 pieces per month. What a transmission gearbox needs is not the accuracy of a single sample but the same accuracy in batch after batch, so consistency across the batch was the central requirement of the project. The enquiry was handled as a volume programme from the start, which means the working question was never whether the accuracy could be reached once, but whether it could be repeated across the whole monthly requirement.

Requirement & Challenge#

• Batch accuracy held to DIN 4 grade
• Tooth surface roughness Ra ≤ 0.4 μm
• A full dimensional inspection report for every piece
• Stable lead times and high batch-to-batch consistency

Any one of these four points on its own is manageable. Holding all four at the same time in volume production is what the customer was assessing when it selected its supplier, and it is also what decides whether a gear programme stays in production or falls back into rework.

Solution & Process#

1. Process route - hobbing, then gear shaving, then heat treatment, then gear grinding. Grinding is placed after hardening so that the distortion introduced by heat treatment is corrected rather than produced, and the accuracy that leaves the shop is the accuracy that was measured.
2. Process control - SPC (statistical process control) is applied to the critical operations, so that any drift in size or geometry is detected while the batch is still running and before it reaches final inspection.
3. Inspection - Key parameters are checked on every part on a gear measuring centre, and a full dimensional inspection report is issued with each piece, so the customer receives the measurement record together with the gears.

Result & Feedback#

• Batch accuracy held at Grade 4, with a first-pass yield of 98.5%
• Monthly capacity of 2000 pieces, with an on-time delivery rate of 99%
• Zero defects recorded over a six-month period
• Three years of continuous cooperation, with more than 70,000 pieces delivered in total