This page contains a tutorial demonstrating how to build a production system model for a civil construction process. This tutorial assumes that the reader has read through the Map a Production System and Model a Production System sections and preceding articles within this section of the Help Menu, Optimize Flows. If not, please refer to those sections of the Help Menu before continuing.
Civil Contractor
A contractor is bidding for a job and wants to be sure that his available resources will have enough capacity to deliver the target scope within the scheduled time frame. The contractor cannot afford to incur any penalties from the project owner for any delays. If the contractor accepts the job, it would have to fabricate and install 500 rebar cages within 10 weeks.
Use the following information to develop a model of the rebar fabrication and installation production process and provide the contractor with an answer to whether it should accept the job.
Create a new production process called Rebar Fab and Installation.
Next, open the production process and draw a single production routing with the following characteristics. Add all relevant data depicted below. All input fields not mentioned in this section’s tables should be kept as their default values.
| Process Center Name | Work Schedule | Batching Type | Number Available |
|---|---|---|---|
| Assembly Machine | 1x5x8 | Sequential | 2 |
| Crane | 1x5x8 | Sequential | 2 |
| Helpers | 1x5x8 | Sequential | 2 |
| QC | 1x5x8 | Sequential | 2 |
| Trucks | 1x5x8 | Simultaneous | 1 |
| Shape | Shape Name | Sequence | Process Center | Average Nominal Process Rate per Machine (Units/Hour) | SCV of Process Times for a Transfer Batch |
|---|---|---|---|---|---|
| Stock | Rebar Stock Lengths | ||||
| Operation | Cut Rebar to Spec | 100 | Helpers | 10 | 1 |
| Operation | QC Rebar Cuts | 200 | QC | 20 | 1 |
| Stock | Ready to Assemble Rebar | ||||
| Operation | Assemble Rebar Cage | 100 | Assembly Machine | 0.75 | 1 |
| Operation | QC Assembly Spec | 200 | QC | 2 | 1 |
| Stock | Rebar Cages | ||||
| Operation | Move to Installation | 100 | Trucks | 0.5, (2 hours) | 1 |
| Operation | Place Rebar Cage | 200 | Crane | 0.8 | 1 |
| Operation | Inspect Placement | 300 | QC | 2.2 | 1 |
| Stock | Rebar Cages in Place |
Work Groups
Work groups will not be used in this model. Therefore, leave the default values as is. Refer to Work Groups for a complete description of work groups and their data elements.
Units
Next, open the Unit of Measure menu and create two units of measure named “Rebar” and “Rebar Cages” for the units that will flow through this engineering production system. The Default Unit of Measure can be renamed, or the user can create a new one. A unit of measure is required to account for various WIP types that flow throughout a production system. Refer to Unit of Measure for a complete description of UOMs and their data elements.
Product Flows
Next, open the Product Flows menu. By default, every new model will come with a product flow named “Default Product Flow”. Any routing generated will automatically be assigned to this product flow. Create three product flows containing the following information. Refer to Product Flows for a complete description of Product Flows and their data elements.
| Description | UOM | AICCR (%) | CONWIP |
|---|---|---|---|
| Assembly | Rebar Cages | 20 | 25 |
| Fabrication | Rebar | 20 | 100 |
| Installation | Rebar Cages | 20 | 26 |
| Description | Max WIP | Max Throughput | Max Cycle Time |
|---|---|---|---|
| Assembly | 100 | 5 | 50 |
| Fabrication | 400 | 50 | 25 |
| Installation | 50 | 5 | 25 |
Routings
Next, open Routings. There will be three routings generated. Change the names of the routings to “Rebar Cutting”, “Rebar Cage Assembly”, and “Rebar Cage Installation”. They should be assigned to the product flows according to the table below. Refer to Routings for a complete description of Routings and their data elements.
| Routing | Product Flow |
|---|---|
| Rebar Cutting | Fabrication |
| Rebar Cage Assembly | Assembly |
| Rebar Cage Installation | Installation |
Items
Recall that the Engineering Company needs to install 500 rebar cages in the next 10 weeks. This creates an average demand of 50 rebar cages per week. For each Installed Rebar Cage, the crew needs to assemble one rebar cage and for each assembled rebar cage the crew needs to fabricate 10 pieces of rebar. Be sure to generate a Bill of Materials for this relationship.
Now open the Items list. Replace the Default Item with one of the items mentioned below and create two more for the remaining two items. Update the following values in each item table. Refer to Items and Bill of Materials for a complete description of Items and their data elements.
| Parameter | Value |
|---|---|
| Description | Rebar |
| ID | Rebar |
| Unit of Measure | Rebar |
| Average Number of Orders (Per Period) | 0 |
| Variance of Orders (Per Period) | 0 |
| Transfer Batch (Units) | 25 |
| Current Reorder Quantity (Units) | 25 |
| Parameter | Value |
|---|---|
| Description | Assembled Rebar Cages |
| ID | Assembled Rebar Cages |
| Unit of Measure | Rebar Cages |
| Average Number of Orders (Per Period) | 0 |
| Variance of Orders (Per Period) | 0 |
| Transfer Batch (Units) | 5 |
| Current Reorder Quantity (Units) | 5 |
| Parameter | Value |
|---|---|
| Description | Installed Rebar Cages |
| ID | Installed Rebar Cages |
| Unit of Measure | Rebar Cages |
| Average Number of Orders (Per Period) | 50 |
| Variance of Orders (Per Period) | 30 |
| Transfer Batch (Units) | 5 |
| Current Reorder Quantity (Units) | 5 |
Item Routings
Next, open the Item Routings list. Item routings tell the model which routing to send each item. Create new Item Routings for each item. There should be three in total and every item should be assigned to only one routing. For this model, keep Fraction of Releases at its default value, 100%. Refer to Item Routings for a complete description of Item Routings and their data elements.
Current Production System Analysis
The model is now complete and ready to be analyzed. Select the Production System Analysis button to run the model. The production system analysis will reveal that the current system does not have enough capacity to meet the needed demand.
If the reader hasn’t already, read through the previous sections of the Help Menu (listed below). These sections will guide the reader on how to interpret, analyze and optimize this engineering production system using an assembly production process as an example.
- Model an Assembly Flow
- Interpret Flow Model Results
- Optimize an Assembly Flow
- Verify and Validate a Flow Model
Once finished with these sections, return to this model and decide if contractor should proceed with accepting this job. Which resource is the bottleneck? For an additional challenge, determine how to reduce cycle times for all items by at least 30% without further increasing resources, reducing demand, or changing process times.