Case Study: Solving a Chronic Tolerance StackUp Issue
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Case Study: Solving a Chronic Tolerance StackUp Issue
In the world of precision CNC machining for highvolume production, few challenges are as persistent and costly as tolerance stackup. This issue, where the cumulative effect of individual part tolerances causes an assembly to fail, can halt production lines and damage supplier relationships. We recently partnered with a client in the automotive sector who faced exactly this chronic problem with a critical sensor mounting bracket assembly.
The client’s previous supplier was manufacturing the three component parts—a base plate, a spacer, and a mounting arm—each within their specified individual tolerances of ±0.05 mm. However, when assembled, the final position of the sensor was consistently out of specification, leading to a 23% rejection rate at their quality control stage. The root cause was a classic tolerance stackup: the variances from each of the three components were adding up in the same direction, creating an unacceptably large total deviation.
Our engineering team was tasked not just with manufacturing the parts, but with solving the underlying designformanufacturability (DFM) flaw. We initiated a thorough analysis using advanced metrology and statistical software to model the assembly process. The solution was multifaceted:
1. Tolerance Analysis: We performed a worstcase and statistical tolerance analysis, which revealed that the original design did not account for the interaction between the datums and features of the three parts.
2. DFM Recommendation: We proposed a key change: converting the design to use a single datum reference frame across all critical features. This controlled the relationship between features from a common origin, preventing errors from accumulating.
3. Process Optimization: On our production floor, we implemented stricter statistical process control (SPC) on our multiaxis CNC machines for these parts. By ensuring each feature was machined in a single setup relative to the new datum, we minimized locational variation at the source.
CNC machining
The results were transformative. The rejection rate for the assembly plummeted from 23% to under 0.5%. The client achieved a significant reduction in waste, assembly line downtime, and overall cost per unit. More importantly, this case solidified their trust in our capability not merely as a parts supplier, but as a true engineering partner.
For any business facing similar precision challenges in bulk, this case underscores a critical lesson: solving tolerance stackup requires a proactive, analytical approach from a supplier with deep DFM expertise. It is this valueadded engineering that turns a chronic problem into a reliable, highvolume production success.
In the world of precision CNC machining for highvolume production, few challenges are as persistent and costly as tolerance stackup. This issue, where the cumulative effect of individual part tolerances causes an assembly to fail, can halt production lines and damage supplier relationships. We recently partnered with a client in the automotive sector who faced exactly this chronic problem with a critical sensor mounting bracket assembly.
The client’s previous supplier was manufacturing the three component parts—a base plate, a spacer, and a mounting arm—each within their specified individual tolerances of ±0.05 mm. However, when assembled, the final position of the sensor was consistently out of specification, leading to a 23% rejection rate at their quality control stage. The root cause was a classic tolerance stackup: the variances from each of the three components were adding up in the same direction, creating an unacceptably large total deviation.
Our engineering team was tasked not just with manufacturing the parts, but with solving the underlying designformanufacturability (DFM) flaw. We initiated a thorough analysis using advanced metrology and statistical software to model the assembly process. The solution was multifaceted:
1. Tolerance Analysis: We performed a worstcase and statistical tolerance analysis, which revealed that the original design did not account for the interaction between the datums and features of the three parts.
2. DFM Recommendation: We proposed a key change: converting the design to use a single datum reference frame across all critical features. This controlled the relationship between features from a common origin, preventing errors from accumulating.
3. Process Optimization: On our production floor, we implemented stricter statistical process control (SPC) on our multiaxis CNC machines for these parts. By ensuring each feature was machined in a single setup relative to the new datum, we minimized locational variation at the source.
CNC machining
The results were transformative. The rejection rate for the assembly plummeted from 23% to under 0.5%. The client achieved a significant reduction in waste, assembly line downtime, and overall cost per unit. More importantly, this case solidified their trust in our capability not merely as a parts supplier, but as a true engineering partner.
For any business facing similar precision challenges in bulk, this case underscores a critical lesson: solving tolerance stackup requires a proactive, analytical approach from a supplier with deep DFM expertise. It is this valueadded engineering that turns a chronic problem into a reliable, highvolume production success.