Modern Machine Shop

JAN 2018

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CNC TECH TALK MMS JANUARY 2018 36 Processes and Programming DEBURR ANY CROSSHOLE with the offsets needing adjustment. In addition to documentation, task-simplifying engineering can include any studies and actions that improve the way a job is run. Setup and Cycle-Time Reduction Considerations I define setup time as the period from running the last part in the previous production run to running the first (good) workpiece in the next production run. Cycle time (per part) is the total time it takes to run the rest of the parts divided by how many parts have been run. Given similar program execution times, machines will be in setup for a greater percentage of production run time when running smaller lots. With very small lot sizes, for instance, it is not uncommon for setup time to far exceed the time required to run out the job. When trying to improve machine utilization given this scenario, you should first concentrate on setup time. As lot sizes grow, the percentage of time a machine is in setup will shrink. With large and very large lots, setup may be but a small part of the production run. In these cases, it would be better to target cycle time for improvement. While you should concentrate on things that happen during every cycle, like program execution time, part load/unload, cleaning/deburring and so on, don't forget about things that do not, like tool mainte- nance, sampling inspections and machine warmup. Personnel Utilization Considerations The larger the average lot size, the more tasks that can be performed off line in preparation for upcoming jobs. As lot sizes grow, there comes what I call a break-even point when there is ample time for someone (probably not the setup person or operator) to do all of legwork needed for upcoming jobs. Setup-related tasks could include acquiring related documentation, gathering components and measuring devices, assembling cutting tools, and taking certain cutting tool mea- surements. Production-run tasks could include gathering resources to complete the run, like inserts, raw material and coolant. This will mini- mize the amount of work a setup person or opera- tor must do while the machine is down. AUTHOR | Mike Lynch Founder and President, CNC Concepts Inc.

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