Process Improvement Through SQC Supplier Selection

Article

Hutchinson, William E.   (1988, ASQC)   Lord Corporation, Erie, PA

Annual Quality Congress, Dallas TX    Vol. 42    No. 0
QICID: 3521    May 1988    pp. 811-816
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Article Abstract

The use of simple charting techniques for evaluating, accepting, and analyzing natural rubber (SMR CV60), carbon black, and various rubber chemicals will be discussed. This discussion will begin with a brief introduction to familiarize the audience with some tests used to evaluate and accept these materials, how the tests are conducted and their significance. Data will then be presented, based on these tests, to demonstrate how process decisions are made relative to acceptance of material, choice of suppliers and use of skip lot testing.

Three separate sources of natural rubber were evaluated using cure rate data based on a standard ACS-1 formulation. These data were analyzed using X & R charting techniques and indicated considerable variations among the sources. The data will be presented along with the rationale used to remove one supplier from the approved listing. Additionally, histograms and rationale used to remove one supplier from the approved listing. Additionally, histograms and control charts for viscosity will be presented for the other two suppliers. Of these two, one is preferred for more critical process applications. This rationale will also be presented.

Two carbon black suppliers were also evaluated using process control chart analysis obtained for N-330 black, our largest user. A control chart for individuals using a moving range and a moving average was used. Based on these data, one supplier was chosen over the other for primary purchases. In addition, we evaluated our internal process testing results versus the supplier certification data using curve fitting techniques. This evaluation demonstrated very good correlation between our incoming quality control data and the supplier's data. Because of this good correlation, skip lot testing was initiated on our four major carbon blacks.

Melting point testing is used for approving most rubber chemicals. We also evaluated our internal testing results versus supplier certification data for melting points. As in the case of carbon blacks, these data indicated very good correlation between our data and the supplier's data. Skip lot testing was also initiated on our major rubber chemical types. Supplier use of charting techniques has also provided us with additional input to help substantiate our reduced testing levels.

Using simple charting techniques we have been able to:

  1. Discover and remove a supplier of poor natural rubber from our approved supplier listing.
  2. Define the supplier of natural rubber for use in aerospace process applications.
  3. Specify the primary supplier of the carbon black most used in our processes.
  4. Reduce testing costs by initiating skip lot testing on certain carbon blacks and rubber chemicals.
  5. Work with suppliers to obtain similar data for use in assuring that raw material needs for our processes are met.

Keywords

Chemical and process industries,Customer supplier relationships


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