New Products, New Empowerment

Product Background: The Bosch Servo twin Gen3 fully redundant electro-hydraulic hybrid power steering system is Bosch’s third-generation electro-hydraulic hybrid power steering (EPS) solution for heavy-duty trucks, launched in 2021. It supports Level 3 automated driving, transforming truck drivers from physically demanding laborers into light-duty operators in intelligent driving mode. This system is one of Bosch’s flagship offerings aimed at empowering China’s heavy-truck industry.

On the finished-product assembly and commissioning line at Bosch Steering (Jinan), the New Product Introduction (NPI) phase for the Servo twin Gen3 EPS has just been completed—yet China National Heavy Duty Truck’s flagship Howo model has already placed a bulk order, instantly bringing the Jinan plant’s production line to full capacity.

Incidental factors causing line outages:
During a night shift in late April 2023, assembly worker Xiao Liu discovered during commissioning that when using a torque wrench to tighten several M14 screws, the torque exceeded the specified limit and the screws still failed to achieve proper tightening, resulting in a nonconforming quality assessment. This was determined to be an isolated occurrence. The on-duty engineer and team leader convened an emergency on-site meeting, but no resolution was reached. Subsequent continuous monitoring over a period of time revealed that this issue occurred, to varying degrees, in the threaded connections of the entire product series; however, the incidence rate was only about 0.1%, which is significantly higher than the 15 ppm requirement for overall mechanical performance as stipulated in the design. In response, the customer representative and the Quality Department issued a corrective action notice, mandating that the process be implemented in accordance with the 15 ppm quality standard.

On the third day, Bosch (Jinan)’s Quality Department, Supply Management Department, and the Weifang Supply Chain Plant held a video conference to discuss and resolve the issue of loose screw fastening, which affects a range of threaded components across multiple product series: M10x1.5, M14x1.5, M16x1.5, M18x1.5, and M20x1.5, each accounting for approximately 0.1% of the total. Root-cause analysis was conducted simultaneously at both the assembly site and the component manufacturing facility.
Fine detritus (approximately 0.3 × 0.6 × 5 mm), as shown in the field photographs.

Inspections were conducted across the machining shop, including the on-machine cleaning stage, the ultrasonic cleaning stage, and the packaging, storage, and transportation stages; no deviations from the Standard Operating Procedures (SOP) or Standard Inspection Procedures (SIP) were identified in any of these stages. Furthermore, no root cause was identified through FMEA analysis.
In the end, we had no choice but to disassemble the product for inspection. At the bottom of the threaded hole, on the thread itself, three tiny chips—about 4 to 5 mm in size—were found, resulting from tapping with a fine tap.
With the issue identified, everyone breathed a sigh of relief; however, the supplier was left in a difficult position. The production processes and procedures had already undergone a second factory audit, and the manufacturing steps had been validated through new-product introduction and small-batch inspections. Moreover, the delivery deadline was extremely tight, involving numerous departments and personnel. In response, the PMC department submitted a quality-release request to the customer representative and Quality Manager Zhang. Following urgent negotiations, the customer agreed to grant a temporary release for three days, during which time an improvement plan must be developed to uphold the 15 ppm zero-defect standard.

A new village emerges after the willows and flowers.
During the concurrent FMEA meeting, all aspects—people, equipment, materials, methods, environment, and standards—were thoroughly reviewed, but no root cause was identified. The information from the meeting was relayed to the machining shop, where PE engineer Zhang Xinyong reasoned: since none of the above factors appeared to be at fault, the problem must lie in the process parameters.
The engineer provided a summary of the case to Du Chengyuan, ArrowStone’s tool-efficiency engineer. Following urgent consultations within the company, Du and his team developed a solution involving internal coolant for the tap, aiming to resolve the issue.
Process Improvement
1. Tooling system: Transition from conventional external-coolant tool holders to internal-coolant tool holders;
2. The tap tool has been changed from external cooling to internal cooling;
3. Machine tool: Upgraded from a Taichung Precision vertical machining center to a Mazak 6000-II dual-table horizontal machining center, with support for internal coolant pressure up to 15 kg.

The machine cycle time for this product’s housing is approximately 32 minutes. Four machines were simultaneously loaded with new taps, and after two days of emergency validation, it was confirmed that the thread quality and the issue of residual metal chips had been essentially resolved; we disassembled 11 parts (each costing several hundred yuan—such a waste!).
The supplier submitted the 8D report that same evening, which was reviewed on the spot by representatives from SINOTRUK and Bosch—and it was approved.

One year later, Arrowstone once again tracked the stability and continuity of subsequent developments and authored this article to attest to China’s quality, China’s speed, and China’s supply chain.
Submit “Arrow Stone Tap Trial Cutting Report – Botch, May 14, 2023”
For further questions about taps, please call Engineer Du at: 18265612588.

Cast Iron Tap Test Report Botch2023.6.14.xls