Table 4. Cause and Effect Matrix for Casting Defect Analysis—Example Shrinkage Parameter
X
Furnace Temperature Ladle Temperature Pouring Temperature Transfer Time in Ladle Pouring Time Gating Ratio
Modulus Ratio
X1 X2 X3 X4 X5 X6 X7
Type
Personnel Equipment Personnel Personnel Personnel Method Method
Root Cause Operator Error
Probe Position and Depth Operator Skills Operator Skills
Operator Training
Inadequate Knowledge Inadequate Knowledge
Frequecny of scale: 0-Never; 1-Rare; 3-Sometimes; 9-All the time Severity of Scale: 0-No influence; 1-Very small effect; 3-Moderate effect; 9-Severe effect
of the parameter. For a stable process, the upper and lower control limits for the parameter will be plus or minus 3 sigma. For a process capability of 1, the upper and lower specification limits for the parameter would be the same as the upper and lower control limits. Generally, it is desirable to have a process capability of 1.33. Te metalcasting facility needs to establish whether the response associ- ated with the factor will be acceptable if the factor’s value fluctuates with plus or minus 3 standard deviations of the factor. If not, the standard deviation must be reduced to a low enough value that the fluctuation will not affect the response related to the concerned variable. By looking at process knowledge in
terms of factors and responses, met- alcasters identify only the parts of the process that affect whether they pro- duce a good casting. Variation is okay, so long as a good casting is produced. But high variation cannot be tolerated if it results in a bad casting. Similarly, while 40-plus types of defects can occur in castings, it is necessary only to determine the factors and part-specific range for the handful of defects a specific part may exhibit. Metalcasters may review all the fac- tors listed in the tables that have been created for Maynard Steel Casting at
www.moderncasting.com and use them as guidelines to create product specific tables. Eventually, you will
have collected additional factors and whittled out the non-relevant fac- tors. Te data collected on the factors for part specification limits should have traceability to the responses on the castings made in the plant. Such part specific process knowledge will help minimize scrap and rework and improve profitability.
Frequency 9
9 9 8 9 9 9
Severity 4
6 6 4 5 9 8
RPN 36
54 54 32 45 81 72
ONLINE RESOURCE
Visit
www.metalcastingtv.com to watch a video of Dr. Hathibelagal Roshan discussing process knowledge.
Fig. 2. In a hierarchy of manufacturing process levels, the Process kingdom has three families: joining, shaping and finishing.
May 2013 MODERN CASTING | 29
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