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CHAPTER 15

CHAPTER 15. Shop Floor Control. ã 1998 South-Western College Publishing. Chapter Outline. I. Introduction II. Shop Floor Control in Continuous and Repetitive Operations III. Shop Floor Control in Intermittent Job Shop Operations IV. Scheduling Intermittent Job Shop Processes

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CHAPTER 15

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  1. CHAPTER 15 Shop Floor Control ã1998 South-Western College Publishing

  2. Chapter Outline I. Introduction II. Shop Floor Control in Continuous and Repetitive Operations III. Shop Floor Control in Intermittent Job Shop Operations IV. Scheduling Intermittent Job Shop Processes V. Data Collection and Order Disposition VI. Innovative Control: Theory of Constraints

  3. Shop Floor Control involves determining a production plan and routing for each manufacturing order, releasing that order to the production or service facility, tracking its progress and reporting its status when needed, and measuring the performance of the facility based upon the timely, cost effective completion of those orders.

  4. Shop Floor Control in Continuous Process perations: Objectives: Maintaining “linearity” by producing a consistent product a t a consistent rate of production. Decision areas: Choice of technology, and replacement and maintenance of the technology. Key Activities: Routine reporting of system status and prediction of ability of system to meet order requirements on-time.

  5. Shop Floor Control in Repetitive Operations: Objectives: Increase repetitiveness through all phases of the system to make the system more predictable and easier to manage. Decision areas: Reduce variability of the product and increase flexibility of the system. Key Activities: Routine reporting of system status and prediction of ability of system to meet order requirements on-time.

  6. Shop Floor Control in Job Shop Operations: Objectives: Meeting job due dates while maintaining high utilization of resources. Decision areas: Job due dates and routings. Key Activities: Determining lead times for orders, determining routings of jobs, and determining job release times.

  7. Shop Floor Control Terminology • Job or Order - a unit of production that follows some sequence of operations. • Production Lot - the number of units in the order that are produced between process setups. • Operation Processing Time - the estimated time that is required at an operation. • Total Processing Time - the sum of the operation processing times for a job.

  8. Shop Floor Control Terminology • Planned Lead Time - the estimated time it will take to complete an order including processing time and delays. • Flow time or Cycle Time- the time that an order actually takes to flow through the shop. • Completion Date - the actual time when an order is completed.

  9. Performance Measures in Job Shop Floor Control • Work-in-process inventory • orders that have been released but not yet completed • Throughput • total volume of output form a process • Utilization • percentage of time that resources are busy

  10. Work-in-process inventory should be reduced because... • it represents a commitment of raw material and processing time that has not yet generated any cash flow from the customer. • it is an indication of long flowtimes or cycle times. • it contributes to shop congestion and confusion.

  11. Methods of Reducing Non-value Adding Activities • Reduce Setup Times • Reduce Queue Times • Reduce Material Handling

  12. Sequencing is the process of prioritizing jobs that are waiting to be processed. • First Come, First Served • Shortest Processing Time • Earliest Due Date • Slack Time Remaining • Critical Ratio Commonsequencing or dispatching rules:

  13. Common Measures of Job Shop Performance • Average Flowtime • Average Number of Jobs in the System • Average Lateness • Maximum Lateness

  14. Johnson’s Rule provides an optimal solution to a fixed sequence, two machine problem.

  15. Johnson’s Rule Steps 1. Identify the minimum operation processing time for the unsequenced jobs. 2. If the minimum time is for the first operation, place the job as early as possible in the sequence. If the minimum time is for the second operation, assign it to the latest unassigned position in the sequence. 3. Break ties judiciously. 4. Repeat from step 1.

  16. Theory of Constraints is about identifying bottleneck operations, or constraints, which have fixed capacity and cannot be rushed. These bottleneck operations are critical to determining the throughput of the manufacturing system.

  17. TOC Process Steps Step 1: Identify the system’s constraints. Step 2: Decide how to exploit the system’s constraints. Step 3: Subordinate everything else to the decisions made in Step 2. Avoid keeping non-constraint resources busy doing unneeded work. Step 4: Elevate the system’s constraints. If possible, reduce the effects of the constraints. Step 5: If a constraint is relaxed in Step 4, go back to Step 1. Do not let inertia become a constraint.

  18. TOC: Performance Measures • Throughput - the rate at which the system generates money through sales. • Inventory - the money invested in things it could or plans to sell. • Operating expense - any money spent in the transformation process which converts inventory into throughput. Goal: Maximize throughput while minimiz-ing inventory and operating expense.

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