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are expected to be most widely equipped with numerical controls. Table VI-1 shows the productivity gains experienced with numerically controlled equipment in a wide range of industries and operations. These productivity figures are for low-to-medium volume applications, some of which include toolmaking activities.

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NOTE: Total number of machines in survey: (1) Point-to-point, 1,289; (2) Continuous path, 555; Total, 1,844.

Source: 1967 Numerical Control Society Survey.

While numerical control's unprecedented rate of growth is based solidly upon many technological advantages, it is not expected to antiquate overnight conventional, general-purpose machines. Shops manufacturing large and complex dies will find numerical control of increasing importance; however, shops machining one-of-a-kind, small and simple parts. will likely find conventional drills, mills, lathes, planers, and shapers useful for some time.

NUMERICAL CONTROL-AN INTEGRATED SYSTEM

Thus far numerical control has been evaluated in its machining function alone. It has, however, a total manufacturing impact which affects costs in several related areas. Frequently, ancillary benefits, such as reduced inspection and assembly labor, were reported by survey respondents to far outweigh the significant machining advantages. A complete evaluation of numerical toolmaking can only take place in this broader context.

Chapter Seven

TRANSITION TO NUMERICAL TOOLMAKING

The most significant contribution of numerical control to production technology has been the introduction of the computer. The first industrial revolution was characterized by the introduction of machines which supplemented man's muscle; the computer is now augmenting his intellect. The computer in metalworking may initiate a second industrial revolution; it will certainly change die processing radically. Since two-thirds of the surveyed firms concentrate their sales in dies and associated fixtures, computer applications present a particularly significant alternative for Michigan toolmakers.

Numerical control has precipitated the use of computer-aided methods from the outset of product development to manufacture-further integrating automotive design and toolmaking. Experience with computerized toolmaking, though still sketchy, shows benefits comparable to those achieved in varied computer applications, from aircraft and rocket design to the balancing of automotive assembly line work assignments.

LEAD TIME PROBLEM

The auto industry is working vigorously to prune the frustrating, costly delays created by the model changeover cycle. The length of the present cycle so impairs the chance of a new style's catching fluid consumer tastes that technological refinements which cut the time, such as numerical control, may be worth millions of dollars even if they replace less expensive processes. The complex changeover cycle consists of 1,400 to 1,700 discrete, yet highly interdependent events. It begins with the definition. of the new model parameters and ends three and one-half years later with automobile parts produced from the new tooling.

The tooling phase, which is the longest of any in the changeover cycle, takes about two years to complete. Some typical lead times required to design and produce tooling successfully for model changeover are illustrated in Table VII-1.

The lead times necessary for changing various components give a more specific demonstration of the time involved in tooling for a model changeover. A tail lamp, for instance, and associated sheet metal require 18 to 24 months for styling, design testing, and preparation of tools. The manufacture of tooling for a new bumper takes 9 to 13 months after designs and tests are completed. Changes in the instrument panel tooling require one year after the completion date of the product design and engineering, with tool construction taking about 30 weeks.

TABLE VII-1

TYPICAL SCHEDULE OF SELECTED MODEL CHANGEOVER EVENTS
(Introduction Date of New Model: Sept. 1968)

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The dates shown are times when all activities in a category must be completed; components or assemblies may be required months before the final date. Extensive parallel effort is necessary to meet these dates.

PORTENT OF NUMERICAL CONTROL

It is already possible, even with the unrefined computerized design and numerical methods, to reduce the toolmaking phase from the standard 21 to 24 months' to as low as 18 months. As the numerical techniques improve, this phase of the changeover cycle may be reduced to 14 months; a reduction to about 17 months appears possible within five years.

One technological barrier to the 14-month goal is the problem of transforming clay model contours into a digital system of coordinate datum points. Approximately 10,000 datum points must be extracted to build a basic mathematical model necessary for defining the shape of the clay model. Millions of calculations are required to expand these basic reference points into a system of tightly laced values.

Compared to the many complex steps in conventional automotive toolmaking, the advantages of numerical methods are readily apparent. For a full appreciation of this, a comparison of the following steps is offered: the construction of the clay model, lofting, template and surface development, construction of wood models, making plastic patterns, die casting, and die machining. Special notice will be given to the elaborate manual techniques in conventional die processes, which account for substantial time losses.

THE OLD PROCESS

The creation of a new model begins when management, with information from market research, describes the characteristics of a car expected

1 Tooling for a few American cars (e.g., Valiant and Mustang) was developed on a crash basis in 17 to 19 months, but the extraordinary effort so strained toolmaking resources that the changeover cycle of other models was stretched out.

A coordinate datum point is the position of a point in space with respect to the x, y, and z axes of the Cartesian coordinate system.

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to meet developing consumer tastes. This description, including height, weight, length, width, etc., must be specified at least 42 months prior to the introduction of the new model.

Having established initial stylistic and performance objectives, several designers produce hundreds of charcoal sketches portraying their interpretations of management's instructions. After weeks of evaluation and comparison, the best renditions are made into small models for more thorough consideration. Approval of the miniature models must be given at least 30 months prior to new model production.

Clay Models

In the succeeding months, one or two of the miniature models are chosen for full size modeling in clay. During model construction the sculptors continually consult the stylists on minor changes needed to correct surface inconsistencies. This early work is inevitably tedious and expensive: tedious because it depends on the approval of many departments, including engineering, market research, and interior designing; expensive because it requires thousands of work hours by highly skilled craftsmen.

Clay has traditionally been the material used for making models because, unlike wood or metal, it can readily be altered to include new design features. Clay is also reusable. This is important in view of the number of models needed: one or more three-eighths scale representations for many of the 250 American models available in 1967 and 10 to 15 full-scale models for each automotive manufacturer. One manufacturer spends approximately $150,000 a year on clay. Although clay is too easily marked and temperature changes cause dimensional variations, no more suitable medium has been found.

Clay Model Surface Refinement

The clay model is constructed over a wooden frame on a level platform where its symmetry can be checked with a styling bridge, a large manually operated measuring instrument which slides along parallel rails. As shown in Figure VII-1, graduated scales on the horizontal beam and the vertical columns allow direct readings of the dimensions for any datum point on the model. An electronic scanner is also used for this purpose. The scanner's signal drives a servo-controlled pen that draws the outline followed by the scanner. With this information the more pronounced model asymmetries are isolated and corrected. This drawn-out, manual technique fails to detect some inaccuracies, which, as they affect subsequent activities, are quite expensive to correct.

The model is dressed with colored plastic film for paint, and foil for chrome to simulate a finished car. By this time, a general seating arrangement and instrument panel layout has been determined and management is called in to review the mock-up. One company makes plaster casts of

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FIGURE VII-1.

Reading Dimensions for a Datum Point on the Model.

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