Integral Logistics Management — Operations Management and Supply Chain Management Within and Across Companies

8.1.1b Manufacture of By-Products in Mechanical Production

Intended learning outcomes: Describe the manufacture of by-products in sheet metal working. Identify the production of collets from a steel cylinder as well as the “saucepan and lid” problem linked with temporary assembly.

Continuation from previous subsection (8.1.1).

The second example is taken from sheet-metal working. Here, washers are stamped from a strip of metal. In this case, beyond the technical process itself, by-product production makes economic sense: it allows the fullest possible utilization of the raw material. Figure shows a section of the metal strip after a typical stamping operation.

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Fig.        Washers stamped from a strip of sheet metal by a stamping press.

To utilize more of the strip when producing washer X, a small washer Y is stamped inside each large washer. In addition, the press stamps other washers, of a size determined by the honeycomb principle, between the larger washers. As a result, 5 parts are obtained from each pass of the stamping machine: 2 each of part X and part Y and 1 of part Z. This can be expressed as the goods flow shown in Figure The waste product obtained is the stamped sheet metal strip B′. There is an interesting parallel here to our first example: This stamping procedure makes sense only if the washers are separated out according to size. In the first example, it was necessary to separate the primary products (A, B, and C) from by-product (N).


Fig.        The manufacture of by-products in the sheet-metal working industry.

Exercise: Manufacture of by-products in mechanical industry
Try to produce a washer stamping pattern in such a way that the least amount of waste is produced. Be aware, however, that the need for the individual washers varies and over-production should be avoided.
The Flash animation shows a part of a continuous metal sheet from which the washers, etc. are cut.

The third example shows the production of split steel collets, which are used for tool holding and disengaging. Figure shows a typical production process that yields a number of different sizes of collets. Here, reasons of economy dictate the production of by-products.

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Fig.        Production of collets from a steel cylinder.

Collets S1, S2,…, Sn, each of different diameter d1, d2,…, dn, can be produced from a round bar M of diameter D. Here, again, the decision to produce by-products is based on economy. Once production has been set up, collets of various diameters can be produced with negligibly short setup times. Since various collet diameters are produced together, the possible batch size is relatively large. This minimizes the share of setup for each collet. At the same time, only a few collets of each size are produced, which keeps down the carrying cost for each size and for production as a whole. Figure shows the flow of goods for collet production.

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Fig.        Production of collets from a steel cylinder.

The fourth and last example is temporary assembly, taken from the manu­facture of precision machines. Here, components at low production structure levels may have to be put together for mutual adjustment, disassembled again, and sent on for further processing. At the latest at final assembly, the fitted components are rejoined. This is the typical “saucepan and lid” problem, as formally shown in Figure The saucepan and the lid have to be produced at the same time since they have to be matched to each other. However, they may then pass through other, quite different orders before they are finally assembled.

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Fig.         Temporary assembly: the “saucepan and lid” problem.

There are thus a number of reasons for producing by-products in the process industries. In many cases, the reason lies in the nature of the chemical, biological, or physical processes in the various stages of processing. However, there may be economic factors that demand appropriate processing techniques.

Course section 8.1: Subsections and their intended learning outcomes