How to build a diesel engine

Manufacturing Engineering, Sep 2001 by Destefani, Jim

Team approach speeds design, manufacturing process development

In buisness since 1919, Cummins Inc. is known today as one of the top diesel engine builders in the world. But over its long history, Cummins has produced relatively few engine models, so a new product launch is a big deal for the Columbus, In, comapny.

Case in point: the company's Signature and ISX series of engines. Designed to replace the legendary N14 engines developed in the early 1970s, the 15-L, in-ine six-cylinder engines were designed to meet stringent emissions reglulations and staisfy the requirements of various end-use applications.

A fully integrated design covering air control, electronics, and engine breaking on the double-overhead-- cam engines results in 30% fewer parts than other engines in its class. The engines boast a million-mile range between overhauls and a two-year, 250,000-- mile protection plan for automotive applications. Cummins assembles Signature and ISX engines with different components, mainly electronics, to produce 14 variants rated from 400-600 hp (300-450 kW).

A primary goal in development of the new engine line was to shorten time to market by implementing a simultaneous engineering effort across the Cummins organization. The company put together a cross-functional team that included marketing, design, manufacturing, materials, purchasing, and customer service personnel.

Team members started with general performance goals for the engine, including displacement, overall package size and weight, and horsepower goals. These parameters were defined by the company's Marketing division, which determines much of how a product looks, how OEM customers will use the product, and other development guidelines.

"The Marketing group sets a lot of product goals, and they're typically very adamant when it comes to power, size, weight, and fuel economy," says manufacturing engineer Joe Birt. "They sometimes bring us conflicting goals, because the engines are used for various applications."

For example, he points out, a bulldozer operator has different expectations for an engine than a Class 8 truck operator. "The bulldozer operator doesn't care about weight," Birt says. "He wants strength, durability, and reliability. The truck operator is concerned about even half a pound of extra weight." About 30% of engines are sold for nonautomotive applications, including off-road equipment as well as stationary applications such as power units, pumps, and emergency generators.

Development of machining processes for the engine's cast iron blocks and heads also was a team effort. A group consisting of several manufacturing engineers, control engineers, quality engineers, machine operators, and skilled tradesmen made up the core team, which was further divided into teams for development of the block and head machining processes. Birt was the block team leader, and Jim Smith, who's currently director of simultaneous engineering at the Columbus plant, was the team leader for heads.

Smith, Birt, and other engineers interviewed for this article stressed the importance of the team approach in Signature and ISX engine development. "This project was much bigger than just Joe or me," says Smith, who was a manufacturing engineer at the time the project was initiated. "I don't want it to sound like we did it all, when we had an excellent team working with us."

Because they were starting with a clean sheet of paper, the machining teams put a lot of effort into determining what the best overall approach to machining the blocks and heads would be. "We spent almost two years, looking at everything from pure flexible systems to hybrid systems to pure dedicated transfer equipment," says Smith. "So we went the full spectrum from an analysis standpoint."

Factors that helped determine the machining approach included both planned volume and how quickly production was expected to ramp up. "We are not automotive, where we're going to do 150 engines an hour," says Smith. "And we're not going to do three or four a day. So we're in that area where we could consider a flexible system, a transfer line, or a hybrid system."

The selection process included benchmarking similar operations in other Cummins plants and outside facilities. "We looked for direct comparisons of the processes used down to specific features and tooling, and how the tools were operated," says Birt.

Transfer lines with some degree of flexibility built in proved to be the eventual machining solution. Supplied by Lamb Technicon (Warren, MI), the 10-operation, 1100' (335-m) line for blocks and 14-operation, 1400' (427-m) line for head machining combine traditional transfer line operations with CNC stations to provide flexibility and capability to machine up to 240 blocks and heads per day.

"We faced a dilemma in that we're at kind of an odd volume," says Birt. "These are complex products that would take a tremendous amount of flexible equipment to machine. But likewise, the investment in dedicated, single-function tooling is huge. So we had to try to find some middle ground."