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Managing & Reducing Variability in Castings V


ariability in metalcasting is inherent to the pro- cess. Metallurgy, furnace

operation and melting, coremaking, molding, tooling, molding process, various operators, cleaning room processes—so many aspects are involved in making quality cast metal components that some level of varia- tion is inevitable. However, the best metalcasting facilities have refined processes and established quality control procedures to reduce and mitigate the impact of the variability. With proper diligence and imple- mentation of software and analysis, metalcasters can identify and mini- mize the sources of variability. A typical program to address

variability will aim to reduce cast- ing variation by improving casting quality, process variation by stan- dardizing processes, and operator variation by improving communi- cation and training.

Defect Mapping One starting point is utilizing

“fallout logs” (referring to castings that “fall out” of the process due to a quality problem) to help iden- tify casting defects. Metalcasting facilities can use visual inspection to document defect frequency for each part inspected and, based on fallout logs, engineers can work to reduce or eliminate the variables that cause defects. Fallout logs don’t always tell the whole story of the casting defect, but information about location, size or severity can help determine root causes of rework and defects. Computerized anomaly mapping software can be a valuable tool to assist iden- tifying and reducing defects. Solid models of parts can be imported into the map- per and allow inspectors to define anomalies and store details in the database

by part number. Typical programs will include analysis tools, such as a frequency map, that creates a topo- graphical representation of defect locations based on defect type and histograms that present the num- ber of instances of each defect type across a number of different castings. Inspection history can be reviewed at later times to help implement process improvements to reduce the defects.

Process Improvements

Implementing lean manufactur- ing methods is another way to reduce variability by standardizing pro- cesses and product flow. Each casting process can be examined to identify potential variation between operators, implement procedures to identify defects and variations, and suggest corrective action. For example, in one operation, the cleaning room was de- signed for typical batch proceeding, with castings moving from station to station using baskets and forklifts. Te castings were moved after the full order was completed at each operation and the average through- put of cleaning room operations was several days. If operators processed parts incorrectly, the defects were only caught after the entire batch was completed. After implementing a more lean approach, product moved from operation to operation by hand and conveyor. Te castings were

moved after each piece was completed at each operation and the average throughput per order in the lean cell measured in hours. Variability also was reduced due to greater visibility in the process. If an operator processes parts incorrectly, the defects were identified immediately at the next operation and feedback was immediate.

Work Instructions Detailed process instructions on job

cards and pictorial instruction guides help communicate process steps and requirements and minimize variability during inspection. Process instructions should all be current to reflect changes in processing and should include detailed instructions, as well as detailed general inspection requirements. Process instructions can be utilized to document tasks and times for each operation and can define average processing time per task. Marked images of castings highlight what the detailed instructions describe, and general inspection guidelines can be listed. Final application and end use of the cast part can be provided. Utilizing tracking tools such as

Mapping can identify defects and provide information for improvements. 48 | MODERN CASTING October 2015

fallout logs or mapping software can help engineers determine prevalent, recurring issues that impact cast- ing quality. Testing and analysis can identify variations between operators at each operation and implementing lean manufacturing methods can re- sult in measurable improvements. Communication tools can help reduce the impacts of operator and process variability. Although some variation may be inevitable in metalcasting processes, signifi- cant opportunity exists to reduce variability through data collection and analysis, process improve- ments and improved communica- tion and training. Based on the presentation, “Re- ducing and Managing Variability at Eagle Precision Cast Parts,” by A.J. Menefee, from the 119th AFS Met- alcasting Congress in Dayton, Ohio.

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