Facility Layout Chapter 6

Facility Layout

• Refers to the configuration of departments, work centers, and equipment, with emphasis on movement of work (customers or materials) through the system.
• Involves an optimum arrangement of facilities, including man, machine, equipment, materials, etc.
• Critical due to substantial investments, long-term commitments, and significant impact on operational costs and efficiency.

The Need for Layout Decisions

• Inefficient operations, high costs, and bottlenecks.
• Changes in product or service design, introduction of new products or services, accidents, and safety hazards.
• Changes in environmental or legal requirements, output volume, or product mix.
• Changes in methods and equipment, and morale problems.

Facility Layout Requirements

• Specification of objectives in terms of output and flexibility.
• Estimation of product or service demand.
• Processing requirements in terms of operations and flow between departments and work centers.
• Space requirements for elements in the layout.
• Space availability within the facility.

Basic Layout Types

1. Product Layout

• Used with product-focused (repetitive) processes.
• Facility organized around product.
• Achieves smooth and rapid flow of large volumes of goods or customers through the system.
• Advantages:
  • High output, faster processing, and less unproductive time.
  • Low unit cost due to high volume and low material-handling cost.
  • Fairly routine accounting, purchasing, and scheduling.
  • High utilization of labor and equipment.
• Disadvantages:
  • Breakdown in a machine can cause shutdown.
  • Little satisfaction to workers.
  • Difficult to avoid machine interference.
  • Difficulty of applying individual-based incentive plans.
  • The system is fairly inflexible.

2. Process Layout

• Used with process-focused processes; low volume, high variety.
• Designed to process items or provide services that involve a variety of processing requirements.
• Causes discontinuous work flow, referred to as intermittent processing (non-repetitive processing).
• Place departments with large flows of material or people close together.
• Similar processes and equipment are located in close proximity.
• Advantages:
  • Flexibility: Allows wide variety of products.
  • Low fixed costs for general-purpose equipment.
  • Breakdown of a machine or worker does not stop processing.
  • Can handle a variety of processing requirements.
  • Possible to use individual incentive plans.
  • More satisfaction to workers.
• Disadvantages:
  • In-process inventory costs can be high.
  • Challenging routing and scheduling.
  • Equipment utilization rates are low.
  • Material handling slow and inefficient.
  • Complexities often reduce span of supervision.
  • Special attention for each product or customer.
  • Employees more loyal to their department than to the company.

3. Fixed-Position Layout

• Used for projects in which the product can't be moved.
• Layout in which the product or project remains stationary, and workers, materials, and equipment are moved as needed.
• Workers and equipment come to the site.
• Widely used in farming, firefighting, road building, home building, and drilling for oil.

Combination Layouts

• A combination of the three basic layout types to satisfy the needs of a particular situation.
• Hospitals, for example, use a combination of process and fixed-position layouts.

Service Layouts

• Different types of service layouts, including:
  • Warehouse Layout
  • Storage Layouts
  • Retail Layouts
  • Office Layouts
  • Restaurant Layouts
  • Hospital Layouts, etc.

Scheduling

• Scheduling is the process of determining the starting and completion times for jobs, and allocating resources (labor, equipment, and facilities) to produce a product or provide a service.
• It specifies the timing and sequence of production, and must be realistic and clearly differentiated from aggregate planning.

Work Loading

• Loading is the assignment of work to specific resources/machines, and can be classified into two types:
  • Finite loading: assigns only as much work as can be done with available capacity, but doesn't prepare for inevitable slippage.
  • Infinite loading: ignores capacity constraints, but helps identify bottlenecks in a proposed schedule to enable proactive management.

Forward and Backward Loading

• Forward loading: starts processing when a job is received.
• Backward loading: begins scheduling the job's last activity so that the job is finished on the due date.

Job Sequencing

• Sequencing is concerned with developing an exact order (or sequence) of job processing.
• It determines the order in which jobs at a work center will be processed, taking into account the workstation, job time, and setup and processing time.

Gantt Charts

• Developed by Henry Gantt in the early 1900's, load charts illustrate the workload relative to the capacity of a resource, and are used as a visual aid for loading and scheduling.
• They show today's job schedule by employee, and help determine which jobs should be scheduled first.

Priority Rules for Allocating Jobs

• Priority rules are used to select the order in which jobs will be processed, and can be simple or complex, using one or more pieces of information.
• Commonly used priority rules include:
  • First Come, First Served (FCFS): orders are run in the order they arrive in the department.
  • Shortest Processing Time (SPT): run the job with the shortest completion time first.
  • Earliest Due Date (EDD): run the job with the earliest due date first.
  • Critical Ratio (CR): calculated as the difference between the due date and the current date divided by the work remaining.
  • Random Order: the supervisors or operators select which job to run based on their preference.
  • Last Come, First Served (LCFS): orders are placed on top of the stack, and the operator usually picks up the order on top to run first.
  • Slack Time Remaining (STR): calculated as the difference between the time remaining before the due date minus the processing time remaining.

Service Scheduling

• Service scheduling is encountered in manufacturing systems, and is complex due to the inability to store or inventory services, and the random nature of customer requests.
• Scheduling the workforce involves managing capacity for service, while scheduling multiple resources involves coordinating the use of more than one resource.