Weekly routines demystify production schedules, inventory levels
August 10, 2004
Although automakers' demands on automotive stampers fluctuate, under normal conditions, the variation in quantities of parts required is 20 percent or less. Most of the time the variation is substantially lower, although seasonal changes, such as holidays and plant shutdowns, can have an impact on demand.
This low fluctuation in demand gives stamping plants an opportunity to level out their weekly production based on demand history and rolling forecasts provided by the automakers and Tier 1 suppliers.
Automakers often require daily, semiweekly, or weekly deliveries from their stamping suppliers. When stamping plants run production on a weekly basis to meet this demand pattern, they can substantially reduce schedule variations. Stampers can smooth out the levels of incoming raw materials, encouraging more reliable, repeatable performance from their own material suppliers.
This is where sequence scheduling comes in. The sequence scheduling methodology is conducive to leveling production with a small buffer of finished-goods inventory to accommodate demand fluctuations, particularly increases. If inventory monitoring shows an increase in finished goods, the stamper can choose a corrective action: either skip a week of production of a part when the buffer reaches the level required to meet the next weekly demand, or lower the weekly production quantity until the buffer is consumed.
The relatively predictable demand and frequent delivery pattern in automotive stamping allow for the same parts to run every week in the same quantities while allowing for production quantity adjustments caused by demand variations. Traditionally, stamping plant personnel run the parts on the same press every week, despite the fact that dies may be used in other presses with the same or similar characteristics. Sequence scheduling is an ideal application in this environment.
A low production quantity may not justify weekly production runs. In this situation, stampers should schedule production runs every two weeks and maintain a sequence on that basis for parts in that category. The company would then repeat the same sequence each subsequent week.
Raw material can be delivered on a just-in-time (JIT) basis for the scheduled production runs. The timing for using production-ready tooling can be synchronized with the sequence scheduling pattern, providing time for tool maintenance between scheduled production runs.
The production sequence schedule should incorporate lead-time allowances for secondary operations, although it is not necessary to schedule those operations specifically. A modified kanban approach can be used to schedule them.
In a typical kanban operation, when parts are low for secondary operations, the empty container is returned to the upstream operations, which is the signal to make more parts, fill the container on a JIT basis, and return it to the operation that created the demand.
With sequence scheduling, the container is filled according to the sequence run pattern established, so that some time elapses before the container is refilled and returned to the secondary operation.
Weekly production quantities can be communicated to both internal and external providers of secondary operations. Secondary operations should begin as soon as the parts arrive from stamping operations.
Developing a sequence scheduling protocol requires a thorough analysis of production requirements, capacity utilization, efficiencies, production rates, delivery lead-times, customer demand, production frequency, delivery frequency, finished-goods buffers, production quantities, and inventory levels. After this analysis is complete, the sequence scheduling format can be developed.
During week 1 beginning on Monday, a stamper runs parts 101 and 102, runs part 103 on Tuesday and Wednesday, runs part 104 on Thursday, and on Friday runs part 105. The week 2 production schedule is the same as week 1 except for changes in demand.
For example, during week 1 beginning on Monday, the stamper can run parts 101 and 102, run part 103 on Tuesday and Wednesday, run part 104 on Thursday, and on Friday run part 105. The week 2 production schedule is the same as week 1 except for changes in demand (see Figure 1).
Excel spreadsheets can provide a viable scheduling solution on a stand-alone basis. The sequence scheduling format also can be easily integrated into an existing information technology system, which can download the electronic data interchange (EDI) data containing customer delivery requirements to the scheduling tools, reducing the requirement for manual data entry.
While EDI schedule data provides delivery quantities and due dates, sometimes it does not fit perfectly with the ideal production quantities and frequencies of production runs. In this situation, the production scheduler will have to edit the EDI data, applying some common sense based on knowledge of the customer delivery frequency patterns.
Establishing a production schedule routine on a sequence scheduling basis can provide an automotive stamping shop with:
The schedule regularity provided by sequence scheduling creates a routine the entire organization and outside secondary-operation providers can understand. Everyone will know the weekly expectations and tailor their production schedules, staffing, and capacity to meet them on a regular basis.
Frank G. Rubury is president of The Rubury Company, P.O. Box 1240, Dover, NJ 07802, 973-726-9007, fax 973-726-9490, email@example.com.