Zinc base alloys are used for die castings for the economical manufacture of small complicated shapes, provided very little strain is applied. Zinc is used as a protective coating on bolts and wheel rims. Cadmium is also used as a protective coating on certain parts. Chromium is plated on surfaces to resist wear, tarnishing and corrosion. It is frequently plated over nickel on such decorative parts as radiator shells and lamp rims. Silver is commonly used to plate head-light reflectors, because of its effi ciency in reflecting light and its ability to take a high polish. Occasionally other metals with a lower reflecting efficiency are used because they are less likely to tarnish. Tin base alloys are used for the engine bearings. They provide a surface that permits the crankshaft to turn with a minimum of friction. Lead castings are used for battery plates. Their function is to enter into a re versible chemical reaction which alternately stores and supplies electrical energy for lighting and starting circuits.
The development of mass production of automobiles since the beginning of this century, especially since the beginning of the World War, has been remarkable and far-reaching, its influence being felt in almost every other line of manufacturing. This development has been due very largely to necessity, because in the early days of the industry, when io,000 cars a year was a big output, buildings were not designed to embody any specially i helpful feature, nor were they large enough to handle the increased volume under the old methods, where one workman did many operations, and the work moved slowly and at irregular intervals until it was finished. Among the pioneer companies which have been forced by the growth of their business to construct additional buildings and reorganize old ones the principle of progressive pro duction has been carried out to a fine degree. These buildings are laid out so that all parts and sub-assemblies move forward to the main or final assembly line with the least amount of duplicated travel possible. The phenomenal growth of the industry has pre sented the problems of inventory and material handling. If ma terial on hand and in process were handled to-day by the old methods, the inventory would be prohibitive and the production slowed down beyond belief.
The development of material handling within the plant has undergone many improvements. The following items show the evolution of these methods: (I) four-wheel truck; (2) hand-lift truck, with movable rack; (3) electric or gasoline truck, with mov able rack or trailer; (4) mechanical and gravity conveyor. While all of these methods are still in use for some phases of material handling, the last is being more and more used wherever the situ ation warrants. The use of the improved methods has relieved congestion, speeded up production and reduced inventory. The use of motor trucks for transporting materials between buildings is being superseded in many cases by conveyors. Distance alone is no barrier, for in certain cases conveyors a mile long are in use. Some companies operate their own fleets of motor trucks on regular schedule from supplier to their own plant, in preference to relying on the railroads. In this connection it is becoming
common practice to provide large loading docks to facilitate the loading and unloading of trucks, just as it is customary to provide loading platforms for railway trucks. (See CONVEYORS IN MASS PRODUCTION.) In many cases where the manufacturer is a quan tity producer, he makes all the various "units" going into the whole assembly, except those which are highly specialized, re quiring an enormous amount of floor space and capital as well, such as electrical equipment or tires. From this, then, it will be seen that the automobile manufacturer makes grey iron, alu minium, brass, and in some cases malleable castings, die castings, forgings, sheet-metal stampings, steels, tires, and glass; and does all kinds of plating, enamelling, painting and machining and as sembling. In addition, he has tool, die and pattern shops for mak ing and maintaining tool equipment.
It has become customary among many of the larger companies to bring out about every 1 2 months what are known as new models. These are either an entirely new series or the old series changed to embody the latest improvements and refinements. The development of the new line starts months before it is scheduled for manufacture. Experimental cars are built and tested through thousands of miles and as far as possible under all of the conditions to be experienced by the future owner. Each series frequently consists of as many as 15 or 20 models differing from each other in chassis or power plant or body. Each model may be built with a choice of several styles of wheels and many different body colours, all of which further complicate the prob lem of quantity production at low cost.
When the series is finally approved, the problem of the big pro ducer is how to finish the run on the old series and begin on the new with the least possible break or loss of time in between. This requires consideration of all the following subjects: Bill of material or list of every part in each model; designing and making of new tools, dies, patterns, etc. ; ordering and installation of new or special machines; relocation of old machines and equipment, if necessary to facilitate production of the new parts; routing of each part by operations; running ahead on parts to be discarded to give opportunity to try out new equipment; (a) time required for each operation and for moving from department to depart ment or building to building; (b) number of cars scheduled per day; (c) number of days float or quantity needed to keep the parts moving steadily from raw state to finished car; (d) amount required ahead of primary operation as a protection against un foreseen delays in transportation; (e) time required for supplier to make shipment ; (f) time required in transit. Then: Time—a plus e plus f equals number of days that material must be ordered in advance of shipment of automobile. Material—b times c, plus d, equals amount of material required in the plant at all times, c only varying inversely with a change of capacity.