If you are going to change your process in some fundamental way, you need to fully understand your current process.
Solving Problems Te right tools must be applied
for a specific problem. In cases where a process has been performing rea- sonably well over a long period, then suddenly exhibits a drop in quality or some other measure of performance shift, a rigorous 8D problem-solving effort is more appropriate than a full-blown Six Sigma project. Many such shifts in performance simply
require process experts to assess what key parameter has changed and bring it back into the normal operating range. To illustrate, the control chart
in Figure 1 shows a sudden, unplanned shift in a key process output measurable, in this case sand core tensile strength. Te appropri- ate questions for managers to ask are: what key input has changed
8D Problem Solving
D0: Plan D1: Use a Team D2: Define and Describe the Problem D3: Develop Interim Containment Plan, Implement and Verify Interim Actions D4: Determine, Identify, and Verify Root Causes and Escape Points D5: Choose and Verify Permanent Corrections (PCs) for Problem/Non-Conformity D6: Implement and Validate Corrective Actions D7: Take Preventive Measures D8: Congratulate Your Team
that could cause such a shift, and what can we do to bring it back to normal quickly? For example, has there been a change in resin supplier, resin batch, mixing cycle, tempera- ture, etc.? Tis is only one example where jumping to a Six Sigma project, or any other true process improvement (PI) project, is premature and unnec- essary. But more prevalent is the case where a process is exhibiting no obvious sudden shifts, but a subtle variability that would likely make a Six Sigma project a frustrating effort. Typically, a PI project team
determines the centerline and spread of the current process and evaluates whether the focus should be on reducing variability, shifting the process mean or both. The project outcome specifies what changes should be made to the current process to give a desired improvement in the process output. Those changes are intended to be fundamental modifications to mate- rials, design, process settings, pro- cedures and/or equipment, and they will be permanent. It only makes sense that if you are going to change your process in some fundamental way, you need to fully understand your current process.
Pursuing Process Stability Statistical Process Control (SPC)
is all but essential in determining whether a process is even a candidate for a PI effort. Te key requirement is stability. Process stability is a basic prerequisite in the two major com- ponents of a PI project: establishing baseline performance and evaluating process improvement alternatives. Establishing Baseline Perfor-
Fig. 1. This I-MR control chart shows a sudden process shift. 34 | MODERN CASTING April 2013
mance: Typically, a PI project involves establishing a baseline per- formance level for the key output(s). Examples of key outputs may be sig- nificant casting dimensions, a casting surface quality metric, or a physical attribute like tensile strength or tensile elongation. Tis baseline gives an assessment of the current state of the process and serves as a basis for comparison when evaluat- ing proposed changes. It must give
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