Charting and Diagramming Techniques for Operations Analysis. How to Analyze the Chart or Diagram. Checklist of Questions - Example

Transcription

1 Chapter 9 Charting and Diagramming Techniques for Operations Analysis Sections: 1. Overview of Charting and Diagramming Techniques 2. Network Diagrams 3. Traditional Engineering Charting and Diagramming Techniques 4. Block Diagrams and Process Maps Gantt Charts? Objectives of Charts and Diagrams Used in Methods Engineering 1. To permit work processes to be communicated and comprehended more readily 2. To use algorithms specifically designed for the particular diagramming technique 3. To divide a given work process into its elements for analysis purposes 4. To provide a structure in the search for improvements 5. To represent a proposed new work process or method How to Create / Develop the Chart or Diagram? Analyst is intimately familiar with the process and develops a graphic to represent it Analyst observes and records information about the process One-on-one interviews with those familiar with the process A graphic model of the process is developed based on these interviews Group meetings with personnel familiar with process The analyst records the discussion of the meeting. A graphic model of the process is developed based on the group meetings How to Analyze the Chart or Diagram Algorithmic analysis Line balancing, critical path methods Checklists General questions applied to the particular process to assess whether they can be applied to the problem of interest Brainstorming Team activity in which participants contribute recommendations Separating value-added and non-value-added operations Value added steps: 1. Important to customer 2. Physically change the product or service Checklist of Questions - Example What alternative starting material could be used? Should the part be produced or purchased? Can this operation be eliminated, combined, or simplified? Could a different joining method be used? Could the inspection task be automated? Categories of Charts and Diagrams 1. Network diagrams 2. Traditional industrial engineering charts and diagrams Operation charts Process charts Flow diagrams Activity charts 3. Block diagrams and process maps 4. Gantt charts 1

2 Network Diagrams Consist of: Nodes representing operations, work elements, activities or other entities Arrows connecting the nodes indicates relationships among the nodes Direction of work flow between nodes Precedence among nodes Used to represent Work elements in assembly line balancing Work activities in CPM and PERT Two-way flows (movement of materials): Maximum number of arrows = n(n -1) Precedence diagram Network Diagram - Precedence Constraints Restrictions on the order in which work elements can be performed One-way arrows (precedence): Maximum number of arrows = n( n 1) 2 Traditional IE Charts and Diagrams Operation charts Process charts Flow diagrams Activity charts Operation Charts Graphical and symbolic representation of the operations used to produce a product The time to accomplish the operation is sometimes also included. Two types of operations: 1. Processing and assembly operations Changing the shape, properties or surface of a material or workpart Joining two or more parts to form an assembly 2. Inspection operations Checking the material, workpart, or assembly for quality or quantity Operation Chart Component Subassembly 2

3 Checklist of Questions Used to Analyze an Operation Chart Operation Charts The focus of the operation chart is on the materials of a product and the operations on them Questions related to material What alternative starting material could be used? Make or buy decision: should the part be produced in the factory or purchased? Questions related to operations Is this processing operation necessary? Can this operation be eliminated, combined, or simplified? Could a different joining method be used? Questions related to inspection Is this inspection necessary? Could the inspection task be automated? Process Charts Graphical and symbolic representation of the processing activities performed either on something or by somebody. The chart consists of a vertical list of activities using symbols to represent operations, inspections, moves, delays and storage and other activities. Principal types of process charts: 1. Flow process chart analysis of a material or workpiece being processed 2. Worker process chart analysis of a worker performing a task 3. Form process chart analysis of the processing of paperwork forms All these charts are used to examine for possible improvements of operations Flow Process Chart Uses five symbols to detail the work performed on a material or workpart as it is processed through a sequence of operations and activities: Operation processing of a material Inspection check for quality or quantity Move transport of material to new location Delay material waiting to be processed or moved Storage material kept in protected location Flow Process Charts If the processing operation combined with an inspection at the same workstation: combine symbols - a circle inside a square Provides more detail about the steps required to process a material than in the operation chart: is used to study a single work part rather than the multiple components of an assembly The chart also indicates distances for move activities and time values for other activities 3

4 Form for Flow Process Chart Checklist of Questions Used to Analyze a Flow Process Chart Questions Related to Material Make or buy decisions: Should the part be produced in the factory or purchased from an outside vendor? Questions Related to Operations and Inspections Is the operation time too high? Is the inspection operation necessary? Questions Related to Moves How can moves be shortened or eliminated by combining or eliminating operations? Can the level of mechanization in material handling be increased? Questions Related to Delays Is the delay avoidable? What is the reason for the delay? Can the reason be eliminated? Questions Related to Storage Is the storage necessary? Why can t the material be move immediately to the next operation? Flow Process Chart Flow Process Chart Unplanned vs. Planned stoppage Worker Process Charts Used to analyze the activities of a human worker as (s)he performs a task that requires movement around a facility. Form Process Charts Used to analyze the flow of paperwork forms and office procedures Also known as process chart-person analysis The symbols are the same as flow process chart Storage activity is omitted since it is difficult to interpret in the context of human work activity 4

5 Flow Diagram Drawing of the facility layout with the addition of lines representing movement of materials or workers within the facility Arrows on the lines represent direction of movement Often used in conjunction with a process chart Operations, inspections, delays, and storages at specific locations are identified by numbers referenced to the activity number Flow Diagram The flow diagram reveals problems in the work flow that may not readily be identified using the process chart alone. For example, if the work flow involves considerable backtracting, this can be identified in the flow diagram, whereas it is indicated only as distances in the process chart. Thus, it can be used to detect excessive backtracking (which might be missed in a process chart), excessive travel, possible traffic congestion, points where delays typically occur and inefficient layout. Flow diagram for worker setting up a milling machine: Note the large number of trips back and forth between the milling machine and the tool crib Flow Diagram Activity Charts A listing of the activities of one or more subjects (e.g., workers, machines) plotted against a time scale to indicate graphically how much time is spent on each activity These activities are generally repetitive. Types of activity charts: Right-hand/left-hand activity chart (a.k.a. workplace activity chart) Worker-machine activity chart Worker-multimachine activity chart Gang activity chart (a.k.a. multiworker activity chart) Shading Formats for Activity Charts Instead of using symbols for the work activities, as in the other charts, the activities are indicated by vertical lines or bars When bars are used, they are shaded or colored to indicate the kind of the activity being performed. Activity Chart Activity charts usually have more than one time scale e.g., activity time and cumulative time Activity chart for a worker performing a repetitive task: 5

6 Multiple-Activity Charts Used to track several participants working together They consists of multiple columns, one for each participant. Objective: to analyze how the workload is coordinated and shared among the entities. Right-hand/left-hand activity chart Worker-machine activity chart Worker-multimachine activity chart Gang activity chart (a.k.a. multiworker activity chart) Right-Hand/Left-Hand Activity Chart Shows contributions of the right and left hands balance of the workload between the right and left hands Remember the example with pegs Task involves placing pegs into a peg board Note that left hand is used as a workholder Worker-Machine Activity Chart Shows how work elements are allocated between a worker and a machine Help to identify opportunities for cycle time improvements e.g., replacement of external work elements by internal work elements Worker-Multimachine Activity Chart Can be used to indicate machine interference (when a machine must wait for service because worker is currently servicing another machine) Gang Activity Chart This chart indicates activities in which two or more workers performing together as a team Also known as multiworker activity chart Can be used to analyze the operations of different stations in the the same chart Objective: To better coordinate the activities and balance the workload among the workers Block Diagrams Graphic consisting mostly of blocks and arrows to portray the relationships among components of a physical system Commonly used in linear control theory, where Arrows represent the flow of signals or variables in the system Blocks contain transfer functions that define how input signals are mathematically transformed into output signals 6

7 x Block Diagram Used to depict flows and interrelationships among components in complex systems Block diagrams are commonly used in linear control theory, as shown below for a feedback control system 2 = x1 Cx3, x3 = Ax2 x3 = Ax1 ACx3 Output y AB = = Input x 1+ AC 1 Process Maps A process is a sequence of tasks that add value to inputs to produce outputs Basic process map is a block diagram showing the steps in a process Widely applied to business processes Also applicable to production, logistics, and service operations Levels of detail: High-level process map macroscopic view of process and includes only the most important steps Low-level process map used to map each of the steps in a high-level process map Symbols in the Basic Process Map Basic Process Map Process map symbols: (a) beginning/ending point of the process, (b) task or activity step, (c) decision point Symbols are connected by arrows to indicate sequence Alternative Forms of Process Maps Relationship process map block diagram that shows the input-output connections among departments (or other functional components) of an organization Cross-functional process map block diagram showing how the steps of a process are accomplished by various departments Departments listed as rows separated by dashed lines Also called a swim-lane chart Relationship Map Block diagram that shows the input-output connections among departments (or other functional components) of an organization 7

8 Cross-Functional Process Map Block diagram showing how the steps of a process are accomplished by departments Gantt Charts A graphical display of schedule project activities on a time axis Project activities are listed on a vertical axis Activity time durations are shown as horizontal bars with starting and ending times Gantt Chart: Planned Activities Shows planned activities for a construction project Gantt Chart: Progress Shows actual work accomplished at some point during week 7 Gantt Chart Showing Precedence Arrows can be used to indicate precedence relationships among activities 8