A process step (or operation) is an activity performed on one or more products. It includes both the actual process time and setup or changeover time. Process steps are assigned to routings and routings are assigned to items.
To Edit the Properties of a Process Step:
- Select a Process Step
- Open the panel on the right side of the User Interface called Properties
- Make desired changes to the input fields
Estimating Squared Coefficient of Variation
Squared Coefficient of Variation (SCV) is a measure of dispersion of a probability distribution. The SCV for a single variable aims to describe the dispersion of the variable in a way that does not depend on the variable’s measurement unit. The higher the SCV, the greater the dispersion in the variable. The SCV is equal to standard deviation squared divided by the mean squared.
Within the Production Optimizer, the user will be asked to provide an SCV for Process and Setup Times. For environments where Process and Setup Time data is not available, the user can provide estimated values dependent upon the perceived levels of variability.
| Type of Process | SCV |
|---|---|
| Automated (Low Variability) | 0.01 |
| Normal Manual Work (Moderate Variability) | 0.25 – 1.00 |
| Difficult / Complex Work (High Variability) | ≥ 1.00 |
Process Step Properties Data Element Description
| Data Element | Description | Constraints |
|---|---|---|
| Description | A description of the process center | |
| Estimated Yield | The percentage of good quality parts that leave this step | 0 – 100% |
| Include Queue Time | This selection tells the system to include queue time associated with the Process Center, Work Group, or maximum of the two. The user can also select NONE to signal to the system to ignore queue time at a process step. See additional comments below | Maximum WG/PC, Process Center, Work Group, NONE |
| Setup Cost | The out of pocket costs for each setup Out of pocket costs refer to the variable costs that occur with each setup such as assay material or plastic loss on an injection molding machine Labor costs or depreciation are very rarely counted as out-of-pocket costs due to a setup | ≥ 0 |
| Process Center | Select a predefined process center from the list | Process Center Table |
| Avg. Nominal Process Rate | The average rate in units per hour for this step per machine for sequential and conveyor batching processing. | > 0 |
| Avg. Nominal Process Time | The average time in hours that it takes for a simultaneous batching operation to complete | > 0 |
| SCV of Process Times for a Transfer Batch | The SCV of the process times for a Transfer Batch at the process center | ≥ 0 |
| Avg. Setup Time | The average time (hours) between process batches. Although setups usually indicate a change in product type, the model assumes a setup occurs between all process batches. All three machine types can have setup time. | ≥ 0 |
| SCV of Setup Time | The SCV of setup times | ≥ 0 |
| Work Group | The work group used at a process step | Work Group Table |
| Number of Workers for Process | The number of workers needed to process a transfer batch at a step. | Integer ≥ 0 |
| Number of Workers for Setup | The number of workers needed to perform a setup at this step | Integer ≥ 0 |
| Process Step Not Constrained by Labor | Check this box if labor is synchronized with machines such that the machine does not have to wait for labor to be available for the machine to run. If checked, work group labor is modeled as if labor is dedicated to machines so that labor utilization and queue time is ignored in determining capacity constraints and cycle time calculations. If not checked the Production Optimizer will: 1. Compute the queue time for waiting for however many workers are needed (as specified by the process step) from the work group 2. Compute the queue time for waiting for a machine in the process center 3. Set the queue time for the item when visiting this process center to be the larger of the two. | Check mark |
Additional Comments for “Include Queue Time”
Default selection is Process Center and the Process Step Not Constrained by Labor box is checked. In this case the Production Optimizer will include queue time for the Process Center only.
If Work Group is selected and the Process Step Not Constrained by Labor box is not checked, the Production Optimizer will include queue time for the Work Group only.
If the Maximum of Work Group or Process Center is selected, the Production Optimizer will use the queue time for the resource with larger capacity utilization.
The user can select NONE and the Production Optimizer will ignore any queue time for the process center and the work group. An instance of this would be when modeling the first process center in a routing that has work released as soon as it is needed and not before. In this case, there would never be a queue at the process center. However, the NONE selection is ignored when computing CONWIP cycle times. In the case of CONWIP, all of the queues are considered. For this reason, the Flow Optimizer can exhibit some strange results when the “Include Queue Time” selection is set to NONE. For instance, “WIP push” can be less than the “WIP min” because the “push” calculation ignores the queues for those steps for which the box is not checked.
To Edit the Custom Attributes of a Process Step:
- Select a Process Step
- Open the panel on the right side of the User Interface called Custom Attributes
- Make desired changes to the input fields
To Edit the DES Parameters of a Process Step:
- Open the Data Entry pane on the left side of the User Interface
- Select a Process Step
- Open the panel on the right side of the User Interface called DES Parameters
- Make the desired changes to the input fields
To Allocate a New DES Resource to a Process Step
- Select a Process Step
- Open the panel on the right side of the User Interface called DES Parameters
- Select the + Add button
- Select the resource from the drop-down list
- Make the desired changes to the input fields for the new resource
Process Step Data Element Description for Discrete Event Simulation
| Data Element | Description | Constraints |
|---|---|---|
| Resource | Pre-defined resources within the Resource Pool that are available to perform an operation. This is used for Discrete Event Simulation only. | Resource Pool Table |
| Number Available | This field reports the number of each available provided by the user in the Resource Pool menu | Integer > 0 |
| Number Required | The number of each resource required each time the process step is executed | Integer > 0 |
| Stay With Item | If this is checked, the resource used for a process step will stay with the item as it moves through the remaining process steps in the routing | Check Mark |
| Priority | An integer value that represents the priority of executing a process step when limited resources are available. Consider when two or more process steps require the same resource. Consider also, that the shared resource only has one available. If an item can be moved into each process step at exactly the same time, the process step with greater priority will be allocated the single resource and the item ready to move into the other process step will wait. | Integer values from 0 – 100 |
| Work Time Period | If this is checked, the resources assigned to a process step will follow the working and non-working durations set by the following three parameters | Check mark |
| Offset (Days) | The amount of time in days starting from the start of the simulation (Simulation Time = 0) that a process step will wait to begin working. | ≥ 0 |
| Working Duration (Days) | The amount of time, in days, that a process step will be available to work until stopping for a non-working period. | ≥ 0 |
| Non-Working Duration (Days) | The amount of time, in days, that a process step will remain idle before starting up again for a working period. | ≥ 0 |