Intended learning outcomes: Explain the principle of overlapping within an operation. Describe the principle of operation overlapping.
We speak of overlapping within an operation when the individual units of a lot are not produced sequentially, or one after the other, but rather overlap one another.
Consider the example of an assembly operation for machines. The operation may comprise several partial operations. Figure 13.4.2.1 shows the situation for the lot as a whole.
Fig. 13.4.2.1 The principle of overlapping within an operation.
A later partial operation on the first machine of the lot may be worked on parallel to the first partial operation on a subsequent machine of the lot.
The run time offset, or offset of the next run time, is a measure for the overlapping within an operation.
Run time offset is expressed as a percentage of run time. The standard value for run time offset is 100%, or “no overlapping.”
For some production processes, you can overlap entire operations.
In an operation overlapping or an overlapped schedule, we begin the next operation on a portion of the lot before the entire lot is completed with the previous operation.
Figure 13.4.2.2 shows an example. Schedulers can use operation overlapping to accelerate a production order.
Fig. 13.4.2.2 The principle of operation overlapping.
The maximum offset of the next operation is a measure of operation overlapping. It is based on one operation and shows the maximum lapse of time before the next operation begins.
In practice, the next operation begins immediately after the setup time and run time for the first unit (or first units) of the order lot. (See, for example, near-to-line production in Figure 6.2.2.2).
The initial value of the maximum offset of the next operation is infinite, that is, “no overlapping.” If the time we calculate (based on operation time and interoperation times) until beginning the next operation is smaller than the actual value, we take the smaller time as the new offset time.
Course section 13.4: Subsections and their intended learning outcomes
13.4 Order Splitting, Order Overlapping, and Extended Scheduling Algorithms
Intended learning outcomes: Explain order or lot splitting, and overlapping. Present an extended formula for manufacturing lead time and extended scheduling algorithms.
13.4.1 Order Splitting, or Lot Splitting
Intended learning outcomes: Explain reducing lead time for operation i by using a splitting factor > 1. Describe how the split offset factor offsets the split lots in time.
13.4.2 Operation Overlapping and Overlapping Within an Operation
Intended learning outcomes: Explain the principle of overlapping within an operation. Describe the principle of operation overlapping.
13.4.3 An Extended Formula for Manufacturing Lead Time (*)
Present an extended operation lead time. Explain the corresponding extended lead time formula in its first and second version. Disclose the influence of overlapping of operations upon lead time.
13.4.4 Extended Scheduling Algorithms (*)
Intended learning outcomes: Identify various possible extensions of the scheduling algorithms. Describe possible cases arising in process industries.
