A Ring for Eternity

Whose eyes do not sparkle with joy when they think of beautiful wristwatches, necklaces or rings? It comes as no surprise, then, that the jewelry industry makes billions in sales worldwide. Many of these valuable pieces are castings, as they can be designed very freely. 

However, the artisan approach combined with highest quality requirements from customers lead to repairs, material losses of precious metals, and unnecessary time and energy consumption amounting to several million dollars every day. It is therefore a great challenge for jewelry manufacturers to find a good compromise between perfect casting quality and cost efficiency. 

Figure 1: Four different gating designs were analyzed

Figure 1: Four different gating designs were analyzed

ProTech is a company that provides innovative casting machines for the jewelry industry in Thailand and Southeast Asia. In a joint project with M5 Engineering, they demonstrated that MAGMASOFT® offers the jewelry industry comprehensive solutions for process optimization in investment casting processes.

The ring to be investigated was made of the silver alloy AgCu7. After understanding the jewelry manufacturer’s existing casting problems, the partners proposed a two-step process. In step 1, the gating for one ring was to be optimized. In step 2, the casting design for the entire tree of rings was then to be checked.

Figure 2: Correlation matrix for 4 different gating designs

Figure 2: Correlation matrix for 4 different gating designs

On this basis, in step 2, two trees with different runner diameters were analyzed, Fig. 3. It was important to maintain a good ratio of stem to gate to casting cross sections in the tree to reduce possible porosity. An incorrectly designed tree could also increase the risk of further casting defects, such as gas inclusions, oxides or misruns. 

Figure 3: Variants analyzed for the optimization of the tree

Figure 3: Variants analyzed for the optimization of the tree

Therefore, the casting process for both designs was analyzed, additionally considering the minimization of misrun problems. Cold run or misrun defects occur if, during mold filling, the mold cavity is not completely filled as a result of premature solidification due to an insufficient pouring temperature or preheating of the shell.

 

 

 

Figure 4: Comparing the two designs based on the selected criteria

Figure 4: Comparing the two designs based on the selected criteria

The evaluation of the two designs for all criteria clearly indicated that design B was the better choice (Fig. 4):

  • Compared to design A, design B showed a lower risk for shrinkage porosity due to better directional solidification (Fig. 5).
  • With under 4 minutes, the solidification time for design B was shorter than for design A (>5 minutes), resulting in a higher productivity.
  • In addition, the correlation matrix revealed that design B presented lower turbulence during filling, lower porosity, a higher yield and no increased tendency for misruns. 
    With design B, the yield increased from 16 % (design A) to 26 %.
Figure 5: Comparing shrinkage porosity in design A (left) and design B (right)

Figure 5: Comparing shrinkage porosity in design A (left) and design B (right)

Subsequently, both designs were cast for validation purposes. The inspection confirmed the results of the prior virtual decision-making process.

By using MAGMASOFT®, ProTech was able to help the jewelry manufacturer to design a robust casting layout. This means that customers can enjoy highly durable rings that last a lifetime, as it should be: forever and ever!

Figure 6: Predicted and real porosity defects in design B

Figure 6: Predicted and real porosity defects in design B

About ProTech Transfer Co., Ltd.

Founded in 1991, ProTech Transfer Co., Ltd. provides innovative and efficient machinery “Made in Germany”  and a highly professional technical support, sales and after sales service to its customers in the jeweler industry. The ProTech headquaters is located in Bangkok, Thailand. Other subsidaries are located in Chiang Mai/Thailand, Yangoon/Myanmar and Phnom Phen/Cambodia.

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