Sorting & Kitting System Project
A manufacturer of heat exchangers has an assembly area with three main feeder departments: Sheet Metal, Tubes and Fins. The factory is a high mix, low volume shop, and most of the products they sell are replacements that are field measured and designed from the obtained dimensions. With the high mix & low volume environment, designing plant layout and WIP storage solutions is a challenge, as is developing a one piece flow through the shop. Depending on the product mix, the capacity bottleneck of the factory would change between Assembly and the next process.
The Old Workflow
For the sheet metal area, the metal parts would be bent on a press brake, and all of the sheet metal for a heat exchanger would be taped together with the production order number written on the tape. Then, the bundle would be loaded into any available rolling cart at the press brake area. Once full of metal from different orders, these carts would then periodically be rolled to the assembly area.
For the tubing area, the operators would run the tubing machines, tape bundles of tubes together and write the production order number on the tape. Then the bundles of tubes would be placed into any available rolling cart in the tubing area. The cart would be pushed to a common area with the other tubing carts.
For the fins, they were stamped on a press. Tape was put onto the fins with the production order number written on the tape, and then the fins were placed onto a pallet. The pallets were organized based on the diameter of the holes in the fins.
Once an assembler was ready to begin work on a heat exchanger, they would have to walk to the tubing area, and try to find the tubing bundle for their job. At any given time, there could be 6 to 10 carts full of tubes, so finding them could take quite a while. Often, multiple orders would be in one cart, which made the search even more difficult. Once the tubes were located, the assembler would pick them up and take them to the assembly area, or push the cart to their build table.
Then, the assembler would locate the sheet metal. At any given time, there could be 3 to 5 carts full of sheet metal. The assembler would have to dig through all of the orders to find the metal for the job they were working on. The assembler would pick the bundle up and take it to their work area.
The assembler would then locate the fins. The fins were split apart based on hole diameter, so finding them wasn't quite as difficult as the others. The assembler would pick up the bundle and take it to their work area. After all three components were brought to the work table, the worker would build the heat exchanger.
The New Workflow
The majority of the improvements made to this process were reductions in searching time. It is important to note that the searching time of the assemblers was decreased, which is one of the two capacity bottlenecks of the manufacturing plant. This increased the % of Value Added Time of an Assembler’s shift, thus increasing the % Value Added Time of the capacity bottleneck of the plant, which increased the capacity of the facility as a whole. Several actions were undertaken to reduce the searching wastes involved with the old process:
Several actions were undertaken to reduce the searching wastes involved with the old process:
The Sheet Metal Carts were named. The Tubing carts had signs fabricated with a unique number for each cart. Also, the tubing carts were modified with flip over trays so that sheet metal could be loaded onto the same cart as the tubing for the same Production Order number, allowing the kitting of tubes and sheet metal together where possible.
Lanes were established for each assembly table. These lanes were for the kitted carts.
The production lead for that area was responsible for kitting, when they had time.
A rack was constructed. This rack was used for Production Orders that had tubing under a certain length. So, instead of placing shorter tubes onto a cart, the tubes were placed into the rack, and the operator would write the production order number on a whiteboard strip in front of where they placed the order in the rack. This made smaller orders easier to find.
A “Locator” program was made and installed on the computers at the Sheet Metal, Tubing and Assembly areas.
At the Sheet Metal and Tubing areas, the operator at that area would input the Production Order Number, and which Cart the order was placed into.
At the assembly area, the assembler types in the production order number, and the program tells them which cart the sheet metal and the tubes are in, greatly reducing the time involved with searching.
A Note Regarding Scheduling and One Piece Flow
One key component to any factory is the scheduling of work. One piece flows are ideal, but not always possible. In this particular instance, the major roadblock to establishing a one piece flow of all three components is the changeovers required for all three feeder areas to run the same order at the same time. Optimizing the schedule for one feeder area would cause additional changeovers at another feeder area. At the time of the improvements discussed in this case study, the changeovers required to make this possible were too labor intensive to establish this flow. The tradeoff was holding approximately two shifts of WIP (Work in Place) between the feeder areas and the assembly area. This WIP has a cost, but reducing changeover times can have a cost as well.
Savings from Reduction in Waste
Adding the Locator program to the workflow for the Sheet Metal and Tubing workers added an additional 5 seconds to their workflow per Production Order. However, this was easily offset by the huge reductions in searching time for the assemblers.
When the orders were not kitted, time spent searching for sheet metal decreased by 75%, and time spent searching for tubing decreased by 90%. When the orders were kitted, searching for the assemblers was reduced to the fins only. The variation for the fins made it difficult to kit them with the tubes and the sheet metal on the same cart.