Original Date: 07/09/2007
Revision Date: / /
Best Practice : Machine Cell Specification
Cell specialization based on similar products rather than similar processes has significantly increased the production capabilities at the Inpro/Seal Company. Cells creating similar products require less tooling changes and reduce machine downtime.
The Inpro/Seal Company implements several cell specification techniques to increase productivity by reducing the amount of machine downtime during production. This process is used to optimize production and increases one-day turnaround for which the company is known. Several different methods are employed to achieve specialization on various levels that reduce the manpower required for high-volume production or increase the efficiency of lower- volume production. Much of this specification is already being implemented, with one type of high-volume specification emerging in the near future.
The initial type of cell specification within Inpro/Seal’s manufacturing process relates to the material used in the production of an order. Inpro/Seal creates its isolators using two basic materials – stainless steel and bronze (the primary material). Since these two materials have very different properties and fewer steel parts are made, there is a specific cell dedicated to steel parts. This separation and cell specialization reduces downtime for CNC machines used for tooling since there are less tooling changes on each machine. This separation also helps to increase the life of cutting tools used for production of bronze isolators since bronze is a relatively soft metal. Because the steel cutting tools in the machines need to be changed more often, the tools in this cell are also fitted with quick adapters to reduce downtime of the machine. The adapters and lower-rate production of this cell also lend it to perform more custom production, freeing up the rest of the plant for normal production. The separation of material also increases the return on bronze scraps by $.05 per pound, since recycling of “clean” or uncontaminated pure bronze scraps yields a higher return.
Cells are also specialized by the tooling required for a specific design. By assigning only those models that require a specified or very similar tooling, machine downtime is greatly reduced. When switching from one design to another, tooling changes can take up to 45 minutes before a machine is up and running again. Without tooling changes, the same machine will take only 7-8 minutes to prepare for the next model/design. This keeps machines up and running longer and greatly decreases downtime. This decreased downtime is apparent in the fact that on average, 2.8 of the 3 machines in a typical cell are running all 8 hours per shift. Operators in these cells will also organize the orders in their cell to finish those using the same stock sizes to further reduce the time for tooling changes.
This order can be compromised by so-called “hot” orders sent into the cell, supporting a pull system within the cell. Even though the operator can organize longer-term jobs to create a more efficient schedule for tooling changes, some orders take priority due to schedule constraints and will be moved up in the queue. “Hot” orders are sent to a specific cell that is most capable of completing the order quickly so the change in queue order will not disrupt the production of the other orders within the cell. Queue changing ensures that priority orders are accelerated and pulled to shipping from the cell specialized to expedite the order.
Inpro/Seal also makes use of specialization for the quantity required for production in one order. There is currently one cell dedicated to only high-production, low-margin orders. This cell contains four CNC machines that perform all of the lathe work and milling for either rotor or stator in one machine all controlled by one operator. All four machines are equipped with bar feeders to allow longer pieces of stock to be loaded into each machine. With stock loaded and the program set on the machine, these machines can be left to create the number of parts needed. This allows the operator to run each machine while still having time to clean the parts and perform final assembly and quality control by spot-checking some parts. A quality control/ final assembly person also works in the cell performing dimension checks and assembling cleaned parts from the operators. This one cell currently produces almost half of the total parts produced each month. In the near future another cell will be added to complement the work done by this cell and increase production for large orders.
Since there is a cell specifically dedicated to high-level production runs, there must be a cell dedicated to one-offs and very low-volume production runs. Custom jobs are mostly accomplished in a manual-tooling cell. Here there are manual lathes and mills to complete jobs that would require tooling changes elsewhere. Rather than shutting down a CNC machine to change tooling for a single part, the manual tools are used to keep the other cells productive. This helps to keep machine downtime to a minimum while still completing small custom orders in a timely fashion. Manual cells follow the same procedures as the other cells, including their own quality control.
Control interfaces are also being specialized within cells and throughout the shop/production area. Inpro/Seal is moving toward standardizing the control interface of all new CNC machines to reduce the amount of training required for operators within each cell. Similar interfaces will not only increase production within a cell due to familiarity with the interface but will allow operator flexibility between cells. With similar control interfaces, operation of one machine should not differ much from the operation of a different machine, increasing operator confidence in using multiple machines and keeping the machines working at full speed.
Cell specialization will continue to be used to increase production rates at Inpro/Seal. An experimental cell is currently being used to test new ideas for the in-cell process that will increase productivity and reduce downtime. The specialization will continue to be more product-specific and less process-specific to further increase productivity.
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