Grinding_Center_RFI.pdf

United States Mint - HQ Sources Sought #USM-HQ-14-0050

Description: The grinding center serves as the final machining stage for die manufacturing. After heat treatment, the base, neck, and flange (for split-collar “chess piece dies” shown below) must be machined true with respect to the hubbed impression and true to each other with a high degree of accuracy for perpendicularity, cylindricity, and overall absolute dimensions.

To achieve the required accuracy and throughput for this stage of the die manufacturing process, it is necessary to finish grind all relevant surfaces without changing machine set

up. After extensive research, it was determined that the dual spindle with swiveling wheel heads cylindrical grinder was the only machine that was capable of satisfying the Mint’s requirements. Other machines could not perform the finish grinding for the “chess piece” dies, which requires “side wheel grinding” and “face wheel grinding”, with automatic rotational spindle positioning to access the relevant surfaces to be finish ground. Our typical dies have a straight die neck, however, the die neck for the “chess piece” dies is interrupted with a flange for operating a split collar. The flange adds a very difficult machining operation that cannot be accomplished with the typical single-spindle grinding center.

Factors required for the Grinders are as follows:

• grinder with a high precision rotating head.

• capable of mounting two (2) wheels simultaneously; one large wheel, one small wheel for various grinding operations.

• grinder capable of completing the undercut on the chess piece dies.

United States Mint - HQ Sources Sought #USM-HQ-14-0050