Breaking the Honing Bottleneck

The Challenge

For years, the Cummins engine plant in Darlington struggled with chronic honing problems on cylinder liners. Bores glazed unpredictably, retraction marks appeared, and cycle times dragged from the target of one minute out to five minutes. The honing operation became a production bottleneck, limiting output to just 270 liners per shift.

The problems cascaded: glazed bores caused sizing issues, operators compensated with higher honing pressures, and those pressures split the rubber bushes in the hydraulic fixtures. When glazing occurred, stones might be changed at any point in their life—sometimes after only half an hour—driving up rejection rates and abrasive costs. Engineers from both the abrasive supplier and machine tool company visited Darlington repeatedly over the years, but no one solved the problem permanently.

The Solution

A GrindoSonic sales engineer introduced the technology to Cummins, and the plant decided to characterize their honing stones. Testing a batch of 1,800 stones—all nominally the same GC-320-J-VTNS grade—revealed a 300-point spread in GrindoSonic readings (800 to 1100), equivalent to six hardness grades within a single “grade” designation.

Controlled honing tests with stones grouped by GrindoSonic number told the story clearly:

The hardest stones (reading 800) glazed and extended cycle times. The softest stones (reading 1100) eroded so rapidly they wore down to the steel shoe after just 35 liners—sometimes requiring replacement after mere minutes. But stones in the middle range (850-950) performed excellently: consistent 55-second cycles, good texture and surface finish, and tool life extending to 3,000 liners.

The mystery of random failures was solved. When hard and soft stones were mixed in the same set, the soft stones wore faster, leaving the hard stones proud of the honing head guides—causing the glazing on retraction that had plagued production for years.

Results

By specifying a GrindoSonic spread of 850-950 for incoming stones, Cummins transformed their honing operation. During one full day’s observation with properly selected stones, 120 liners were honed within the hour on a two-spindle machine—each completing in 55 seconds with excellent texture and finish.

Carborundum initially resisted GrindoSonic specifications, but eventually achieved batches with fall-out rates down to 5%. Atlantic of West Germany guaranteed a 100-point spread and flew stones directly to Teesside for testing.

The same approach proved valuable for cam grinding wheels. Tracking E-modulus on over 100 wheels revealed that Norton had quietly changed their abrasive mix. When Cummins reverted to the original 23A series based on GrindoSonic verification, grinding times improved by 30 seconds and dressing frequency dropped by 50%.