1. Simulation of a Generic Cellular Manufacturing System Using Rockwell Arena Simulation Software This document provides a generic simulation model of a cellular manufacturing system that can be adapted to a particular system implementation. 1Cellular Manufacturing System Simulation © 2012 Mark Polczynski All rights reserved mhp.techforge@gmail.com

2. 2 This document contains the following sections: Part 1: Describe generic cellular manufacturing system. Part 2: Create variables and resources. Part 3: Build single station model. Part 4: Replicate stations. Part 5: Create alternative scenarios. Cellular Manufacturing System Simulation

3. 3 Some Terms - 1: Assemblies go through a series of operations which transform the assemblies into finished goods. Operations are performed at work stations, which consist of machines, equipment, and tools required to perform the operations. Operations and their associated work stations are grouped into manufacturing cells. Work stations are operated by cell operators. Cell operators are assigned to cells to operate the work stations in their cell. Multiple work stations can be assigned to an operation. For example, there may be several drill press work stations assigned to a drilling operation. Multiple cell operators can be assigned to a cell. For example, there may be one operator for each station in a cell.

4. Cellular Manufacturing System Simulation4 Some Terms - 2: Production of assemblies is performed in the sequence specified by the production schedule. Each type of assembly has a unique part number. The production schedule consists of a list of jobs, with each job specifying the part number and quantity of the specific assembly to be produced. Each job in the production schedule generates a shop order which travels through production along with the assemblies. The shop order specifies the part number, quantity, and sequence of operations for the job being worked on. The sequence of operations that will be performed on a specific assembly is called the part routing.

5. 5 Manufacturing System Cells and Operations: The manufacturing system being modeled here has 6 operations configured as 3 manufacturing cells, plus a stock room for finished goods. As will be shown, the model can be easily modified to simulate other cell configurations. Cellular Manufacturing System Simulation

6. 6 Manufacturing System Cells and Operations: For this model, each of the six operations can be performed by either of two stations assigned to the operation. Cellular Manufacturing System Simulation

7. 7 Manufacturing System Cells and Operations: For this model, each cell has two cell operators assigned to it. Cell operators can only operate stations assigned to the same cell. Each cell operator is qualified to run specific stations within their cell. For example, Cell Operator A may be qualified to run Station 1 and 2, but not Station 3 and 4. Cellular Manufacturing System Simulation

8. 8 Operator Requirements: An operation requires operators to set up the operation’s stations, and operators to run the stations. These operators come from the cell that the stations are assigned to (previous slide). For this model, it is assumed that all of the stations assigned to an operation are identical, meaning that the number of operators needed to set up a station and run a station is the same for all stations assigned to the operation This chart shows how many operators are required to set up and run the stations in each operation. Cellular Manufacturing System Simulation Note that for some operations, an operator can run more than one station at a time. Operator Requirements Operator Requirements

9. 9 Production Schedule: The manufacturing system builds parts according to a production schedule. The production schedule is composed of a sequence of jobs. Each job specifies the part number and quantity of parts to be produced for the job. Note: The sequence of jobs in the production order is established by a production scheduler, who may change the sequence at any time. The model built here does not include creation or revision of the production schedule. The model builds jobs in whatever sequence is shown in the schedule. Cellular Manufacturing System Simulation

10. 10 Part Routings: Part routings show the sequence of operations that a particular part number moves through as a job is worked on. For example: Part number 1 is routed from operation 1 to operation 2 to operation 5 to operation 6 to operation 100 (finished goods stock). Cellular Manufacturing System Simulation

11. 11 Shop Orders A shop order is created for each job in the production schedule. The shop order is a document which shows the job number, part number, quantity, and part routing for each job in the schedule. Production Schedule: Shop Orders: Note: Shop orders are the entities that will be moving through the model built here.

12. Cellular Manufacturing System Simulation12 Shop Orders Shop orders flow through a cell along with the parts being built to the shop order. Shop orders are worked on in the sequence that they arrive at the operation. If shop orders are waiting to be run at an operation, the cell operator or production scheduler may change the sequence of accumulated shop orders. The simulation being built here does not include manual shuffling of shop orders by a cell operator or production scheduler. The simulation runs shop orders in the order that they arrive at an operation.

13. Cellular Manufacturing System Simulation13 Sequencing of Shop Orders When more than one shop order is waiting to be worked on at a particular operation, sequencing of shop orders through the station is done as follows: For jobs that that are currently being worked on, shop orders go into a first-in/first-out queue (per previous slide). For jobs that have not been started, the job’s shop order moves to the first operation in its routing only when the first operation is not working on a shop order, i.e., when no other shop orders are in the operation queue. Example: Don’t start working on this job until Operation 5 is idle. Example: Don’t start working on this job until Operation 5 is idle.

14. 14 Run Times: Run time is the times it takes for an operation to complete work on 1 unit of a particular part number. For example, it takes 3 time units for operation 4 to complete work on 1 piece of part number 2. Cellular Manufacturing System Simulation Part Routings Run Times

15. 15 Operation Run Times vs. Station Run Times: Note that in reality, it is stations that are run, not operations. Here, it is assumed that all the stations assigned to an operation are identical, so have identical run times. This allows run times to be specified by operation vs. by each individual station assigned to an operation. This simplification will be used on the station set-up procedures and set-up times described on the next slides. Cellular Manufacturing System Simulation Run Times Run time is the same for each station assigned to an operation.

16. Cellular Manufacturing System Simulation16 Set-Up Procedures Each operation needs to be set up before being run. An operation is set up according to a set-up procedure for that operation and the particular part number to be worked on. The chart below shows which set-up procedure to use for each part number and operation. For example, when running operation 3 on part number 2, the operator uses set-up procedure 5. Set-Up Procedures

17. 17 Set-Up Times: Set-up time is the times it takes for an operator to set up an operation. For example, it takes 1 time unit for an operator to set up operation 4. Cellular Manufacturing System Simulation Set-Up Procedures Set-Up Times

18. Cellular Manufacturing System Simulation18 Operation 1 and operation 2 are in cell 1, which has 1 operator. All shop orders require 1 operator for set-up, and 0.5 operator to run. Operations 1 and 2 are both running shop orders, which requires 0.5 + 0.5 = 1 operator. Operation 1 finishes, releasing 0.5 operators. Operation 1 remains idle until operation 2 finishes, because operation 1 needs 1.0 operator to set up for the next order. When operation 2 finishes, both stations become idle. This leads to the following situation… Resource Conflicts A particular type of resource conflict occurs when an operation needs to be set up before running the next shop order in its queue. Consider the following situation:

19. Cellular Manufacturing System Simulation19 Resource Conflicts In the preceding example, operation 1 remains idle until operation 2 is finished. When operation 2 finishes, both operations will be idle at the same time, so the operator must choose which operation to set up next. The operator must decide whether to start running the operation that was just set up, or to set up the other operation before running either operation. If the operator chooses to run the operation just set up (consuming 0.5 operator), it will not be possible to set up the second operation (requiring 1.0 operator) until the first is done running (releasing 0.5 operator). For the model built here, all set-ups in a cell will be completed before any idle operations start running.