CAREER CLIPS to be answered within days. What are the Constant pressure exists on the manufac- not taught in a typical materials science normal operating conditions for the part? turing floor. Schedules for shipments must program: just-in-time manufacturing, cycle How do we accelerate the corrosion be made. New products must be released time, statistical process control, self-directed mechanism and predict the lifetime of the before the details of manufacturing can be work teams, assurance of supply, contin- part in the field? This problem sounds worked out. A key learning point for me in gency plans, WIP, kanban*, ergonomic interesting and challenging from a materi- moving from research and development design, design for manufacturability, als standpoint but there is no time to set (R&D) to manufacturing is the concept of design for reliability, design for test, cost, up a reasonable experiment. manufacturability. As an R&D engineer, absorption variance, and yield variance. creating one or two or even a dozen work- In other ways, skills I developed in ing prototypes is sufficient. Yet the ability acquiring a PhD degree have been useful Suggested Resources to make a consistent product over and over in my other positions. Such skills as pro- Robert H. Hays and Steve C. may have very different requirements. The ject management, literature searches, tech- Wheelwright, Restoring Our Competitive key to manufacturability is process stabili- nical writing, and oral presentations are Edge, Competing through Manufacturing, ty. It is critical to limit the variation in a essential. The ability to approach a prob- (John Wiley and Sons, New York, 1984). process. Yet variation is a fact of life on the lem logically and lay out an action plan to manufacturing floor. Different operators, resolve issues is critical. I have also found Richard Schonberger, World Class different shifts, different technicians, even that the contacts I have made in the Manufacturing, (Macmillan, New York, different engineers lead to variation. Also, research community have provided valu- 1986). variation occurs from incoming materials able input when I have faced many differ- Peter Senge, The Fifth Discipline, or from the upstream processes. These ent manufacturing problems. (Doubleday Books, Garden City, NY, variations can result in low yield, ineffi- 1994). cient operation of equipment, line stops, or *Kanban is a Japanese term for a way to manage poor reliability. It is enough to keep one Eliyahu Goldratt and Jeff Cox, The Goal, the production floor. It basically results in a pull awake at night—every night. of material through the process instead of a (North River Pr., New York, 1992). In many ways, the skills needed to be push. Usually kanbans are implemented with a Gordon MacKenzie, Orbiting the Giant successful in manufacturing are the oppo- card system or by limiting the space where Hairball, A Corporate Fool’s Guide to Sur- work can be staged. Its real positive impact is site of what we learn in graduate school. that it is a simple system which stops material viving with Grace, (Penguin Putnam, Decisions must be made quickly and often from piling up at a bottleneck process because it New York, 1998). with an incomplete set of data. The lan- limits the amount of product that can be staged guage and concepts in manufacturing are in front of any operation. HISTORICAL NOTE John Harrison’s “Sea Clocks” Despite centuries of experience navigat- 1714 Act of Queen Anne established a top understand the clockwork of the heavens ing on the open seas, prospects for a safe prize of £ 20,000 (the equivalent of millions to the necessary precision, while artisans journey were still grim in 1714. Whereas of today’s U.S. dollars) to anyone who worked to solve the mechanical difficul- latitude, the distance (measured in could determine the longitude to the accu- ties of keeping time on a rolling sea. No degrees) north or south of the equator, racy of half a degree on a routine 60-day less an authority than Sir Isaac Newton was easily determined from astronomical voyage from England to the West Indies. expressed his skepticism that a mechani- observations, longitude (the distance in For several centuries the best scientific cal solution would ever be found. degrees east or west of some arbitrary minds had wrestled with the dilemma of But John Harrison (1693–1776), a car- meridian), yielded to no such easy solu- longitude determination. In its essence, it penter and clockmaker from the town of tions. Sailors relied on a method called was a problem of timekeeping. Since the Barrow Upon Humber with little formal “dead reckoning” whereby estimates of Earth rotates 15 degrees in an hour, two education, used a combination of mechani- the ship’s speed and the elapsed time at locations an hour apart by the Earth’s cal skills and basic materials research to sea were combined with the captain’s rotation are separated by 15 degrees of rise to the challenge. Realizing that he first intuition to estimate longitudinal posi- longitude. Calculating a ship’s longitudi- had to understand and perfect timekeep- tions. Given that one degree of longitude nal position at sea requires a knowledge ing on land, which at that point was capa- equals 68 miles at the equator, even small of the time in two locations: that at the ble of an accuracy of only about a minute errors in judgment proved to be disas- ship’s current position, and at some arbi- a day in the best clocks available, he set trous: Sailors traveling through fog who trary reference position of known longi- about analyzing and improving upon the thought they had 50 miles to go to reach tude. Comparison of the time difference current technology. the shore frequently found it sooner than between the two locations yields the dis- The main problems with the existing they had hoped. Ships were running tance separating them. clocks of the time were the need for lubri- aground, lives and cargo were being lost, Two possible solutions emerged: the cants to minimize friction and the thermal and something had to be done. astronomical and the mechanical. Astrono- expansion of the metal pendulum rod In 1714 merchants and sailors petitioned mers such as Edmond Halley of the Royal altering the length, and hence the period, the British Parliament for a solution. The Observatory at Greenwich strove to of the pendulum’s swing. The primitive 70 MRS BULLETIN/APRIL 2000 HISTORICAL NOTE lubricants of the time (mostly animal fats) changed viscosity with variations in tem- perature, which alternately slowed down or sped up the internal mechanisms through changes in friction. Eventually, the lubricant dried out, making periodic cleaning a necessity. Harrison the carpen- ter used his intimate knowledge of wood types to select a naturally greasy variety called lignum vitae as the primary material for his gears and bushings. With careful attention to his craft, for the first time the need for lubrication was eliminated. The period of a pendulum is directly proportional to the square root of its length. A slight change in length due to temperature fluctuations would alter the Detail of the bimetallic strip of John Harrison’s sea clock labeled H3. period to an unacceptable degree if one Illustration by David Penney, Copyright. were aiming for the tolerances specified in Queen Anne’s Act. Harrison, no metallur- gist, borrowed the expertise and samples onds in 24 hours, which should have been a different position along the balance available from the foundries of London, good enough to claim at least part of the spring, effectively shortening or lengthen- and began performing basic experiments prize. However, Harrison, the perfection- ing it. Thus expansion and contraction of in the thermal expansion of metals. ist, already had improvements in mind, the balance spring were compensated by For temperature control, Harrison and he turned down a proposed test on the bimetallic strip, which maintained it at reports that he “prepared a Convenience the West Indies run that was stipulated in a constant length (see Figure). on the outside Wall of my House, where the act of 1714. With this last innovation Harrison had the Sun at 1 or 2 o’clock makes it very In H.2, the second sea clock, Harrison perfected the art of timekeeping to a suffi- warm.” Relying on cold winter mornings replaced the wooden gears with brass cient degree to claim his prize. However, and hot summer afternoons, he hung the ones that were precisely machined and it was not H.3 that finally brought him the samples of metals he was comparing— polished to minimize friction. In combina- reward, but an oversized pocket watch steel, iron, brass of various compositions, tion with anti-friction bearings and bush- dubbed H.4 that used the principles silver, and copper—and measured their ings he managed to craft the first all-metal developed in his previous efforts. During lengths as the temperature varied. He used clock that did not require lubrication. a voyage begun in October 1761 from the data obtained in this manner to devel- However, by the time H.2 was finished, England to Jamaica aboard the HMS op his first major innovation, the “grid- he had ideas for improvements, and it Deptford, H.4 lost only five seconds over iron” pendulum. Constructed of four rods was never given a test at sea. 81 days at sea. In 1765, having fought of brass layered between five rods of steel, For H.3, completed in 1757, Harrison many political battles, the 72-year-old the complementary thermal properties of substituted two massive circular balances Harrison collected £ 10,000—only half of the two metals kept the pendulum at a con- for the double-balance, and replaced the what he deserved—for solving the prob- stant length despite temperature fluctua- helical balance springs with a thin, coiled lem of finding the longitude at sea.