Money. We earn it, find it and spend but do we ever really stop to think how it is made? The United States Mint in Denver, CO, thinks about how coins are made every single day. That is their business and has been since the United StatesMint in Denver began its first year of operation in 1906. Today, the Denver Mint’s daily output can exceed 50 million coins a day. The United States Mint in Denver manufactures coins of all denominations for general circulation; coining dies; regular uncirculated coin sets; and commemorative coins as authorized by Congress. The composition of these coins range from copper-plated zinc, cupro-nickel and manganesebrass, depending on the coin. The weights of the final coins span from 2. 268 grams to 11.34 grams. Finished coin diameters begin with .705 inches for the dime up to 1.205 inches for the half dollar. Coin thicknesses begin at 1. 35 mmagain for the dime and extend to 2.15 mm for the half dollar. The coin edgesmay be plain, reeded or edge-lettered, depending again on the specific coin. Coins are manufactured in a basic six-step process. This process includes blanking, annealing-washing-drying, upsetting, striking, inspecting and counting-bagging. Blanking Blanks are punched from coiled strips of metal approximately 13 inches by 1,500 feet in a blanking press. The left over webbing is chopped up and recycled. The penny is the only coin stamped onto pre-made blanks. Annealing, Washing and Drying The blanks are heated in an annealing furnace to soften them. They are then run through a washer and dryer. Upsetting The good blanks go through an upsetting mill that raises a rim around their edges. Striking The blanks go to the coining press where they are stamped with the designs and inscriptions of a particular coin, making them official United States coins. Inspecting Press operators spot-check each batch of newly struck coins. Counting and Bagging An automatic counting machine counts the coins and drops them into large bags. Forklifts move the pallets of sealed bags to vaults for storage. Trucks then take new coins to Federal Reserve Banks and then to local banks. Die Manufacturing However, before a single coin can be struck, someone has to make the coining dies. A coining die is a tooled metal piece that contains the designs and inscriptions. Dies are used to strike both sides of a coin blank. The designs and inscriptions on the dies are transferred to the metal blank converting it to a coin. Dies are made out of hardened steel and can produce hundreds of thousands of coins before they wear out and are retired and defaced. The process of making working dies at the United States Mint in Denver begins when the Denver Die Manufacturing Division receives a master die from the Philadelphia Mint. From that master die, several working hubs are made. The working hubs are used to press the images into the dies with hydraulic presses. As with any detailed and precision- machined component in manufacturing, machining coins is no exception. The need for improved processes resulting in a quality coining die provided the challenge for David Croft, Plant Manager and Randy Johnson, Chief, Die Manufacturing Division, United States Mint in Denver. Croft, Johnson and the manufacturing team at the Denver Mint envisioned this challenge as an opportunity and labeled their new initiative as a “Kaizen Opportunity”. Kaizen, a Japanese word referring to a business philosophy surrounding working practices and efficiency, reflected the goal of improvement the team was searching for. “This is an all-encompassing project with several detailed components,” said Randy Johnson. After months of recording die manufacturing data and analysis, Johnson and his team determined that within their current manufacturing processes, they needed to transform to a single box flow from hubbing to heat treat and also needed to establish single piece flow at the machining lathes by designating technology to complete all turning operation sequences on one machine tool. The Denver Mint die manufacturing team wrote a carefully detailed project overview and enlisted the knowledge of Hartwig Incorporated and Gosiger Automation. This lathe operation project was branded as the “Three-Operation Lathe Cellular Manufacturing with Single-Piece Flow.” Also included in the operation was the use of lean tools including cellular manufacturing and Single-Minute Exchange of Die (SMED). Croft, Johnson and the team also determined that previous lathe machining caused defects that in turn impacted grind. The quality of the lathes needed to be improved while at the same time focusing on the causes of the off-center coin defects. Improvements were also needed in the measuring methods in order to minimize passing defects further down the inspection line. Upon recommendation from Hartwig Incorporated and approval by the Denver United States Mint die manufacturing team, the Okuma LT2000 EX horizontal lathe was chosen to be incorporated into the “Three-Operation Lathe Cellular Manufacturing” initiative. “I had to use all 27 years of my experience during this project,” said Randy Jokerst, Applications Manager, Hartwig Incorporated.” I enjoyed analyzing problems and drilling down to the root cause. It has been a while since I have spent time digging through chips comparing colors and shapes.” The robot, implemented by Gosiger Automation in collaboration with Hartwig Incorporated, is a FANUC M-710iC. The Okuma LT2000 EX horizontal lathe provides four-axis operations with left/right spindles. The upper/ lower turrets can be combined with either spindle therefore providing a cycle balance of primary and secondary operations. Multitasking V16 turrets are standard on the Okuma LT2000 EX. The PREX 15/10 HP spindle motor on both left and right spindles provides a spindle speed of 6,000 min-1 and a milling tool HP of 7.3/5. The rapid traverse of the X-axis is 30m/min (1,181 IPM) and the Z-axis is 70m/min (1,575 IPM). The FANUC M-710iC is a six-axes robot that provides 2050 mm of reach with slim arm and wrist assemblies providing minimal interference with system peripherals, therefore allowing operation in confined spaces. How Does the Three-Operation Lathe Cell Manufacturing Process Work? The Three-Operation Lathe Cellular Manufacturing Process would be replacing three sequential lathe operations with lathe 1 doing the first operations, lathe 2 providing the second operations and lathe three completing the third and final operations. The process flow of the new cell is detailed as follows: 1) The lathe is changed over to the proper set-up for the coin die to be run. 2) Die blanks are loaded onto the inbound conveyor. 3) The bar code scanning sequence is followed, telling the system what parts are loaded onto which lane of the conveyor and how many to produce. 4) The system is started from the conveyor Human-Machine Interface (HMI). 5) The robot signals the lathe to begin running. Since there are no parts in the spindles, the lathe knows to run a gauging routine. This gauging routine calibrates the probe, calibrates every tool to be used with the tool setter and probes the workholding to ensure the correct workholding was mounted correctly. 6) The lathe signals the robot to load the left spindle with raw material. 7) Vision at the conveyor scans the part to ensure it is the correct part and to tell the robot the orientation of the part for proper loading. 8) Once loaded, the robot again starts the lathe. The part is machined in the left spindle and then transferred to the right spindle. 9) To complete the set-up part, the robot cycle starts the lathe again. 10) The part, machining completed in the right spindle, is unloaded by grippers in the upper turret. 11) The robot is signaled to unload the set-up part followed by loading another part into the left spindle. This setup part is taken to the output conveyor and the robot cycle starts the machine. 12) The part is machined in the left spindle and transferred to the right spindle. 13) The machining cycle ends. 14) The robot loads another part into the spindle and starts the machine. 15) At this cycle, both parts (one in the left spindle and one in the right spindle) are machined. The part in the right spindle is unloaded to the turret gripper and the part in the left spindle is transferred to the right spindle. 16) The machining cycle ends. 17) The part is unloaded from the turret gripper by the robot and raw material is loaded into the left spindle. 18) The finished part is taken to the outbound conveyor and the system is now in full production. Continued production loops back to step 17 until all the part run is complete through the machines, both left and right spindles. - Single-Piece Flow that reducesWork- In-Process (WIP) - Parallel operations resulting in increased line flexibility, therefore, reducing lot sizes and WIP - Are duction in WIP reduces Manufacturing Lead Time (MLT) - Labor savings increases piece count / Full-Time Equivalent (FTE) - WIP reduction reduces scrap rate - Auto-gauging reduces scrap rate The Bottom Line “When we began our lean journey, our MLT was 5.14 days, our scrap rate was 12.5%, we had frequent late deliveries and our dies used per FTE / year were 1,380,” said Johnson. “Today, our MLT is 2.86 days, our scrap rate is 2.8% (78% improvement), we have no late deliveries and our dies used per FTE / year is now 1,955 (a 42% improvement). Moving forward, we hope to achieve a MLT of .61 days, a scrap rate less than 1%, made-to-order deliveries and 2,225 dies per FTE/year.” “This machining cell will take productivity to another level at the United States Mint in Denver,” said Jokerst. “I am proud that I was involved with the Mint in taking a huge leap forward by reducing three operations to one with this process.” For more information contact: Guillermo Hernandez Chief, Public Affairs Office United States Mint 320 West Colfax Avenue Denver, CO 80204 303-405-4763 ghernandez@usmint.treas.gov www.usmint.treas.gov Randy Jokerst Applications Manager Hartwig Incorporated 10617 Trenton Avenue St. Louis, MO 63132 314-426-5300 randy.jokerst@hartwiginc.com www.hartwiginc.com Julie Murphy, Marketing Manager Okuma America Corporation 11900 Westhall Drive Charlotte, NC 28278 704-588-7000 www.Okuma.com