Regrind Loop Coverage for a Gear Hobbing Cell
Pinnacle Gearworks runs a gear hobbing cell with six hobs. Each hob is new at 1,200 pieces, can be reground four times, and after each regrind has 650 pieces of life. The cell must produce 4,800 pieces next week. The tool crib shows: two new hobs on the shelf, one reground hob, one hob on the machine with 90 pieces remaining, and three hobs at the regrind vendor with no confirmed return date. The planner has a purchase requisition for two new hobs with a 10-day lead time. A customer expedite would cost 35% more but arrive in four days. The operation can run only one hob at a time, and a tool change takes 25 minutes. Quality requires the regrind count to be recorded before the hob is used.
1. Calculate whether next week's requirement can be covered with current and confirmed tooling, showing assumptions. What action do you recommend?
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Available life is 2 new hobs x 1,200 = 2,400, plus 1 reground x 650 = 650, plus 90 on the machine = 3,140 pieces. The requirement is 4,800, so the confirmed position is short 1,660 pieces. Even if the three vendor hobs return, each adds 650; two returns add 1,300 and still leave a 360-piece gap, while three returns add 1,950 and cover the week with 290 pieces of buffer.
The two-new-hob requisition at 10 days is too late. Recommended action: get firm return dates from the regrind vendor today; if at least three hobs can return before the run, schedule with a buffer; otherwise expedite two new hobs at the 35% premium and compare that cost with the customer expedite or missed shipment. Do not plan to run beyond the 650-piece regrind life.
2. What tool management records and statuses must be updated when hobs return from regrind?
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When a hob returns, receive it against the regrind PO and update the tool record before it is available: increment the regrind count, reset remaining life to 650 for this regrind cycle, record the vendor, receipt date, measured diameter or inspection result, and change status from at vendor to available only after quality release. Keep the serial or tool ID history so the certificate can trace which regrind cycle ran the parts. If the inspection fails, status should be quarantined or scrapped, not available. Also update the expected return date and cost. This prevents a returned hob from being used with the prior cycle's life or without the required regrind count.
3. How should scheduling and the 25-minute tool change affect the decision, beyond the raw piece count?
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Tool changes consume capacity and create a hard stop if tool life runs out mid-run. The cell must plan one hob at a time, reserve the hobs to the job, and sequence the longest-life tools first. With a 650-piece reground cycle, covering 4,800 pieces requires at least eight tool uses if all tools are reground; that means multiple planned changes totaling over three hours. If the plan depends on three vendor returns arriving on the same day, the schedule has no recovery time. Build in buffer life, set a life-limit stop in the operation, and document the expedite decision so the cell is not forced to run a hob past its validated life to protect the due date.