GravityCasting

Background:

A customer that sells flags came to us because they had problems with their die cast aluminum flagpole bracket. The bracket would break in severe weather. After discussion with the customer, we learned they actually needed two brackets – a strong bracket they could sell to retailers at a low price point and an even stronger bracket they could sell to commercial users at a higher price.

Our Approach:

First we figured the strength of the customer’s current bracket. We devised a simple test using a steel pipe, steel cable, a load cell and several pulleys. The steel cables allowed us to apply force to the bracket, which the load cell measured; this helped us determine how much force was needed to break the bracket. We repeated the test several dozen times, and we discovered a wide range in the results. Based on our observations we believed this was due to severe porosity in a small portion of the castings, poor design in the pouring of the casting, and inconsistencies in the alloy. The median bracket was fairly strong, but there were several brackets with strength values less than a quarter of the average. This wide distribution led to an exaggerated perception of poor quality – remembered the end user would remember the one bad bracket and not the eight good ones.

The second step was to determine the root causes of the failures found in testing. This process was not difficult. Almost all castings failed at the same section of the part, indicating a weakness in the overall design and possibly a problem in the channels where the molten metal flowed. Many of the failed castings exhibited extreme air entrapment, most likely resulting from impurities in the metal used on the castings.

Success in the Retail Market:

Consistency was the key to our success in the retail market.

First, we used only raw materials that met the composition guidelines defined by the alloy we were casting. We checked samples from the ingots we received against the certificates from the mill and determined the accuracy of the inspection process at the mill. The higher quality raw materials had no foreign matter entrapped in the melt. Gasified foreign matter can be a huge source of voids and porosity in the casting, and this was a major reason the previous vendor’s castings had been so inconsistent.

Second, we redesigned the casting to eliminate the weak spot in the design. The “spot” was actually two separate problems. Besides the weak spot in the finished casting and the sharp transition angle associated with it, the flow of the metal in the mold exacerbated the weakness in the design. We created better paths for the molten metal to flow into the die, which led to less turbidity in the flow and less porosity in the finished casting. At the same time, we eliminated the weak spot in the design and created a smoother transition between the barrel and the arm.

By improving the design, process control, and attention to detail, we were able to make parts that were consistently better than what the customer had been receiving. We were also able to eliminate a substantial portion of the parts that exhibited defects. More closely monitored parts led to a more consistent experience, which in turn eliminated retail customer complaints.

Success in the Commercial Market:

We learned that the commercial market required a much stronger bracket than the retail market. Die casting alone was not going to be enough, and in any case, the smaller quantities of brackets consumed by commercial users made die casting expensive.

Gravity casting seemed to be the best solution. Gravity casting was possible in smaller quantities, as the process is more flexible, and able to accommodate unusual alloys without a complex, expensive changeover process. Gravity cast alloys are readily heat treated, a process that adds substantial strength. We combined gravity casting and heat treating with a shot blasting process that yielded a strong, bright, and attractive part.

The final result was a production process conducive to small runs and optimized for strength.

Conclusion:

Listening was the first key step. Only then were we able to completely understand the customer’s needs in each market. Quantifying the results was the second key step. Without that process we could not have measured our success. Diligent attention to detail resolved the problems for the retail market, while creative application of an alternate process allowed us to find success in the commercial market.

We want to work with you to overcome whatever challenges you are currently facing. Call us today to learn how we can help!