BUS606: Operations and Supply Chain Management

3.1. Strategic Development of the New Operational Availability Model

In TPS, the inventory buffer between each step is low so the overall impact of all previous steps affects the final throughput through short time (manufacturing starvation) to following step. Each step also affects the throughput of previous steps through full time (manufacturing blockage). The impact of each step or certain type of downtime can be evaluated by analyzing relationships between the so-called manufacturing blockage (Full) and manufacturing starvation (Short) of each step, as shown in Fig. 3.

Figure 3. Proposed Operational Availability Model

The throughput contribution factor of any step in the whole production line, from first step to last step, can be quantified. This evaluation method can be utilized with historical data for productivity improvement as well as real time data for floor management (real time bottleneck visual display). This model can be applied for one production line, as well as one plant or between plants and supplier.

3.2. Development of New Operational Availability Model to Link the Impact from One Step to Following Step

The authors have proposed a method to link throughput impact between steps, as shown in Fig. 4. The impact of any step to following step is consisted of two parts: The one is introduced by this step and the one is inherited from previous step. In this model, each impact factor to following step is calculated proportionally. The inherited impact of Step 3 to Step 4 is calculated in Equation (2). The introduced impact from Step 3 to Step 4 is calculated in Equation (3). The impact from each different downtime causes of this step is also can be quantified individually. Equation (4) and (5) show how to calculate equipment downtime impact and work delay impact from Step 3 to Step 4.

Figure 4. Model to link impact between two steps

$inherited\ Impact = \frac{ST3}{ST3+WT3+ET3} \times ST4$

$WT3$ is work delay at Step 3

$ET3$ is equipment downtime at Step 3

$ST4$ is Short time to Step 4 from Step 3

$Introduced\ Impact = \frac{WT3+ET3}{ST3+WT3+ET3} \times ST4$

$Introduce\ Impact\ due\ to\ Equipment\ = \frac{ET3}{ST3+WT3+ET3} \times ST4$

$Introduce\ Impact\ due\ to\ Work\ Delay\ = \frac{WT3}{ST3+WT3+ET3} \times ST4$

Based on this model which links impact between steps, the impact of each step to whole system with multiple steps can be developed. The calculation is applicable to large or small scale systems.