CH4 = 0.8 hour * 20 CFH * $0.00347 = $0.056/100 $0.526/100 or $0.0053 per part
Te cost per part at the time of the experi- ment was $0.0053, which is significantly less than the other methodologies. If the calculation were altered to assume 100% cut time, it would yield:
O² = 350 * $0.004 = $1.40/100 CH4 = 20 * $0.00347 = $0.07/100 $1.47/100 or $0.015/part
At 100% cut time, this method was still significantly less
expensive than using cutoff wheels. With a 4 sq. in. part, the cold wheel cost $0.24/part, the hot wheel was $0.36/part and the oxy-fuel torch was $0.02/part.
AUTO-BAND SAW TEST
Te auto-band saw cutoff method has shown an ability to save Eagle Alloy money primarily because the operator can leave the operation and perform other duties. Although the facility has to normalize the parts prior to cutting and the contacts have to be configured, it attempted a case study to determine whether it was less expensive than the typical torch/snag operation. Rigid fixtures were required to elimi- nate cleanup, and that allowed the experimenters to skip the abrasive wheel operation. Labor costs for the torch method and snag grinder clean- ing totaled $1.97 per hour, whereas the auto-saw cell at Eagle Alloy cost $1.36 per hour with two men working. Te auto- saw method incurred an additional $0.32 for heat treating, whereas the torch method required none. Te consumables costs were $0.35 per part for the torch method and $0.15 for the auto-saw. Taken all together, the total costs were $2.32 per part for the torch method and $1.83 per part for the auto-saw, a difference of $0.49 per part. Te savings for the auto-band saw with consumables and normalization of the part before cutoff was $70,560 per year, given an annual volume of 144,000 parts.
SNAG VS. ARC CLEAN UP
When assessing the costs of cleaning gate areas after cutoff, the snag grinding operation was performed using a 30 in. wheel with different minerals. Employee variability occurs primarily due to wheel dressers, as Eagle Alloy found some employees preferred using wheel dressers, while others did not. Two methods of measurements were used: the cost per
Te auto saw offered savings over the torch for some parts.
March 2011 MODERN CASTING | 37
square inch of the wheel and the cost per pound. Cost per pound was the preferred methodology, as it was easier to weigh the wheel before and after grinding the parts. Te cost of the wheel at the time of the experiment was $3.19 per pound of usable wheel. Te experimenters determined that grinding 118 pieces of part A used 31 lbs. of wheel, or 0.2627 pounds/part, a consumables cost of $0.84/part. When arcing the same part smooth, the experimenters
were able to complete 105 pieces using 21 arc rods. At $0.70/ rod, this yielded a consumables cost of $0.14/part. Including labor, arcing was therefore $0.70, or 83%, less expensive than snag grinding.
Fig. 3. The gate configura- tion shown here is condu- cive to belt grinding the gate contacts smooth.
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