Cost Reduction Through Honing Stone Quality Control

The Challenge

Cummins’ Darlington works faced puzzling inconsistencies in their wet liner honing operations. Cycle times varied from 1 to 5 minutes. Glazing appeared unpredictably on cylinder bores. Stone sets sometimes lasted a full shift, other times needed replacement after just 30 minutes. The culprit: stones supplied as a single grade actually varied across more than six hardness grades—a 240-point spread when tested, spanning readings from 800 to 1100.

The Solution

Engineer Ken Claybourne implemented GrindoSonic testing to classify every honing stone before use. Testing 1,800 J-grade stones revealed the true variation hidden within nominal grades. The solution was straightforward: use only stones reading between 850 and 950, classified into narrow bands of just 10 points. All eight stones in each set now come from a single category, ensuring uniform load distribution and consistent cutting action.

Results

The matched-stone program transformed honing operations:

• Service life: Extended from 400 liners/set to 1,500–2,000 liners/set
• Stone consumption: Dropped from 133 stones/week to 148 stones/month—a 40% reduction per component
• Production rate: Increased from 270 to 500+ liners/shift with consistent sub-60-second cycles
• Oil consumption: Reduced from 4 oz/h to under 1 oz/h
• Blow-by: Improved by a factor of four
• Piston ring wear: Decreased from 0.07 gm to 0.01–0.03 gm
• Surface finish: Consistently 14–23 μm rms, eliminating glazed marks and bell-mouthing