The Dirt On Cleaner Crankshafts

Historically, U.S. automakers machined the five Cs of engines—crankshafts, connecting rods, cylinder heads, cylinder blocks and camshafts—in house. Over the last 20 years, there has been a trend to offload this work to vendors. Recently, that trend has accelerated. Firms that supply the automotive industry have welcomed the increased work, but in many cases it has come with strings in the form of stringent quality requirements.

Norton Manufacturing Company, Fostoria, Ohio, a firm that manufactures crankshafts for diesel and gasoline engines, compressors and pumps, was one of the early beneficiaries of the above trend. It began machining prototype crankshafts for Ford, General Motors and Chrysler as early as 1982, and it received its first production crankshaft order (from Chrysler) in 1986.

Norton specializes in limited production of crankshafts—quantities ranging from prototypes to 100,000 units per year. Where automakers would install a dedicated crankshaft machining line designed to produce completely machined crankshafts from raw castings or forgings, Norton requires greater flexibility because of its job shop nature and the relatively small quantities of cranks it produces. Accordingly, the firm manufactures its cranks in a series of operations on a mix of machines, including dedicated crankshaft-machining equipment purchased from the automobile manufacturers and modernized, and more conventional CNC lathes, grinders and machining centers.

Recently, Norton received an order from one of the big-three automakers for a steel crankshaft for a new engine program. The order quantity was larger than usual for Norton, and the automaker specified that the crankshafts had to be within a 5 millipore rating, a cleanliness level that the firm found difficult to achieve with its existing slush washing equipment.

The slush washer accepts from one to four crankshafts at a time, raising them up and down in a cleaning solution to flush chips and fines from the various passages. The process is not without some problems, however. “Because of the many grinding operations performed on the crankshaft, grinding swarf can accumulate in the oil passages,” explains Les Lipski, Norton’s CFO. “The grinding swarf is difficult to remove under the best of circumstances, but the difficulty is compounded when the cranks are allowed to sit for any length of time, for example, over a weekend. The swarf hardens in place, and to remove it the oil passages must sometimes be brushed out by hand.”

To meet the cleanliness specs for the new crankshaft, Norton manually brushed the oil passages three times, with intervening washings. At 10 to 11 minutes per brushing, the procedure was not only time consuming, but it still fell short of required cleanliness levels.

Another problem with the slush washing method is that it doesn’t remove burrs. Removing burrs, particularly those produced at intersecting oil passages, required another operation, increasing the unit processing time and labor cost for crankshaft cleaning.

Let’s Talk

Norton consulted with its customer about implementing a more efficient cleaning process—hopefully one that would perform the cleaning and deburring in one operation. As a result, the slush washer was replaced by a Jet-Flex Center CNC waterjet deburring machine, produced by Sugino Corp. (Schaumburg, Illinois).

Norton’s Jet-Flex Center is a six-spindle, turret-type CNC machine with an interesting capability. The turret stations can be loaded with drills, taps, end mills, brushes, reamers, and so on, for conventional machining and hard tool deburring operations, OR fitted with nozzles capable of directing a high-powered blast of water, OR any combination of the two. A 30-hp motor drives a positive displacement pump capable of producing water pressures to 5,000 psi.

One or more of the machine’s turret stations can be fitted with a lance or straight nozzle to reach into the smallest passages to dislodge even tough burrs. Fan and manifold nozzles are used to clean and deburr contaminants from interior and exterior surfaces. Special nozzles are available for specific deburring and cleaning applications.

Currently, Norton uses the Jet-Flex Center exclusively as a cleaning and deburring machine. Using prototypes of the crankshaft complete with all of the oil passages, drilled and tapped holes and other machined features, Sugino created the cleaning program, installed the machine at Norton and debugged it on-site. The firm also trained Norton personnel to program and operate the machine.

Machined crankshafts are loaded and cleaned in the Jet-Flex one at a time. The operator uses an electric hoist (a crankshaft can weigh as much as 75 pounds) to load a crankshaft onto a fixture on a pallet extending from the front of the machine. Machined features on the crankshaft prevent it from being loaded in the fixture in any but the correct position for cleaning.

Only two of the machine’s six turret positions are equipped with nozzles; the other positions are empty. The first nozzle is a lance-type nozzle used to clean each oil hole in turn. Instead of simply directing the spray down the center of the hole, the lance traces a circle as it follows the periphery of the hole. The movement increases the turbulence in the hole, making for more effective removal of burrs and other machining residues.

Many oil holes are drilled at an angle, which makes cleaning them more difficult. However, the crankshaft rotates 360 degrees on the fixture, simplifying access to the holes. The second nozzle sprays the entire exterior of the crankshaft to wash away any chips, burrs, fines and other residue dislodged from the various holes.

Less Than 2 Minutes

Total cycle time for the cleaning and deburring operation is less than 2 minutes—or about 5 percent of the time required for cleaning alone by the slush cleaning method. On completion, the pallet returns to the load/unload position, and the operator offloads the crankshaft to a shipping container. Total elapsed time is about 3 minutes.

The Jet-Flex machine cleans and deburrs in the same operation, which enabled Norton to eliminate deburring the crankshafts as a separate operation. “The waterjet machine dislodges all but the most stubborn burrs,” Mr. Lipski explains. “And if a burr is able to withstand a 5,000-psi stream of water, there’s little likelihood of its coming loose in a sealed engine operating at 40 psi oil pressure.”

Most important, crankshafts cleaned by the waterjet machine are measurably cleaner. “With the slush washing method, we had difficulty meeting the 5 millipore cleanliness level specified by the customer,” Mr. Lipski continues. “With the waterjet cleaning machine, we’re getting millipore rates ranging from 0.2 to 3.8 .”

“The waterjet machine has also given our customer greater confidence in our process capability,” adds process engineer Andy Bowen. “When we were slush washing the crankshafts, our customer random sampled them. Now, waterjet cleaning has proven so reliable that our crankshafts go right to the assembly line, bypassing incoming inspection.”

Another Task

The Jet-Flex machine cleared up Norton’s crankshaft cleaning problems using only two of the machine’s six turret stations. However, plans are underway to make use of at least some of that unused capacity. Norton’s customer has asked it to permanently mark all crankshafts cleaned in the waterjet machine. The company is exploring the feasibility of mounting a stamping device in one of the machine’s unused turret positions that would stamp an ID on each crankshaft.

A Measure Of Cleanliness

Cleanliness is, simply, the absence of dirt, so one way—probably the only way—of measuring how clean something is is to measure how dirty it is. There are several methods for doing just that, one of which is the gravimetric or millipore method, mentioned in the accompanying article, which is used to measure residues on an object as well as to gage the effectiveness of a cleaning process.

In the millipore method, a just-cleaned workpiece is sprayed with a solvent to remove any contaminants that were left behind. The solvent bearing the contaminants is collected on a very fine membrane of known weight. The membrane is then heated in an oven to drive off the solvent, leaving the contaminants behind. Finally the membrane is then weighed a second time and any increase in weight is attributed to the contaminants.

At Norton, an inspector mounts a clean crankshaft between centers on an inspection fixture and places a pan beneath the crank to catch the solvent/cleaning solution that will be used for the cleanliness inspection. The inspector rinses each of the crankshaft’s oil passages with the solution, brushes three times with a nylon-bristled brush to dislodge any loosened particulates, and rinses again to flush any remaining residues.

Next, the inspector strains the solution through an 11-micron filter which has been oven-dried and weighed. He returns the filter to the oven, dries it a second time, and reweighs it. The difference between the initial and final weights of the filter is the weight of particulates (measured in milligrams) removed by the cleanliness inspection procedure. For the crankshafts described in the article, total weight of the particles from all 16 oil holes may not exceed 5 milligrams. If a reject is found, the entire lot must be rewashed. As indicated in the story, however, as a result of waterjet washing of the crankshafts, inspection results range from 0.2 milligram to 3.8 milligrams. How clean is that? To provide some perspective, acceptable levels of cleanliness for crankshafts for some diesel engines are in the range of 4 to 5 milligrams per oil passage.