Ch 26 Just-In-Time and Lean Production Sections: 1. Lean Production and Waste in Manufacturing 2. Just-in-time Production Systems 3. Autonomation 4. Worker Involvement What is Lean Production? Lean production means doing more work with fewer resources Adaptation of mass production in which work is accomplished in less time, smaller space, with fewer workers and less equipment Based on the Toyota Production System The term "lean production" was coined by researchers at Massachusetts Institute of Technology Structure of Lean Production System Taiichi Ohno's structure of the Toyota Production System Activities in Manufacturing 1. Actual work - activities that add value to the product 2. Auxiliary work - activities that support the value-adding activities 3. Muda (waste) - activities that neither add value nor support the value-adding activities Muda (Waste) Taiichi Ohno s seven forms of waste: 1. Production of defective parts 2. Production of more parts than needed (overproduction) 3. Excessive inventories 4. Unnecessary processing steps 5. Unnecessary movement of people 6. Unnecessary handling of materials 7. Workers waiting Keys to Eliminating Waste 1. Just-in-time production 2. Autonomation (automation with a human touch) 3. Worker involvement 1
Just-In-Time Production Requisites for JIT Production and delivery of exactly the required number of each component to the downstream operation in the manufacturing sequence just at the moment when the component is needed Minimizes: Work-in-process Manufacturing lead time 1. A pull system of production control 2. Setup time reduction for smaller batch sizes 3. Stable and reliable production operations Pull System of Production Control A system in which the order to make and deliver parts at each workstation in the production sequence comes from the downstream station that uses those parts JIT is based on a pull system of production control Alternative is a push system in which parts are produced at each station irrespective of the immediate need for those parts at the downstream station Kanban System Toyota s way of implementing a pull system of production control Kanban means card in Japanese Two types of kanbans: 1. Production kanban authorizes upstream station to produce a batch of parts 2. Transport kanban authorizes transport of the parts to the downstream station Operation of a Kanban System Operation of a Kanban System 1. Station i + 1 removes next P-kanban from dispatching rack. This P-kanban authorizes it to process a container of part b. A material handling worker removes the T-kanban from incoming container of part b and takes it back to station i. 1. At station i, the material handling worker finds the container of part b, removes the P-kanban and replaces it with a T-kanban. He then puts the P-kanban in the dispatching rack at station i. 2
Operation of a Kanban System Setup Time Reduction Starting point in setup time reduction is recognition that the work elements in setup are of two types: 1. Internal elements can only be done while the production machine is stopped 2. External elements do not require the machine to be stopped 1. The container of part b that was at station i is moved to station i + 1 as authorized by the T-kanban. The P-kanban for part b at station i authorizes station i to process a new container of part b, but it must wait its turn in the dispatching rack. Scheduling of work at each station is determined by the order of P-kanbans. External Work Elements Internal Work Elements Can be accomplished while previous job is still running Strategy: Design the setup tooling and plan the changeover procedure to permit as much of the setup as possible to consist of external elements Examples: Retrieve tooling for next job from tool crib Assemble tools for next job Reprogram machine for next job Use time & motion study and methods improvement to minimize the sum of the internal work element times Use two workers rather than one to accomplish the changeover Eliminate adjustments in the setup Use quick-acting fasteners rather than bolts and nuts Use U-shaped washers instead of O-shaped washers Design modular fixtures consisting of a base plus insert tooling that can be quickly changed for each new part style Base part remains attached to production machine Examples of Setup Reduction Setup time Equipment type Before After Reduction 1000 ton press 4 hr 3 min 98.7% Transfer line 9.3 hr 9 min 98.4% Punch press 2 hr 3 min 97.5% Machine tool 6 hr 10 min 97.2% 45 ton press 50 min 2 min 96.0% Stable and Reliable Production Operations Production leveling - distribute changes in product mix and quantity as evenly as possible over time On-time delivery of components Defect-free components and materials Reliable production equipment Workforce that is cooperative, committed, and crosstrained Dependable supplier base 3
Autonomation Automation with a human touch Production machines operate autonomously as long as they are functioning properly When they do not function properly (e.g., they produce a defect), they are designed to stop Autonomation topics: 1. Stop the process 2. Error prevention 3. Total Productive Maintenance (TPM) Stop the Process Jidoka Japanese word meaning machines that are designed to stop automatically when something goes wrong Stop the process when: Defective parts are produced Required production quantity has been completed Avoids overproduction Error Prevention Poka-yoke Japanese word meaning prevention of errors using low cost devices to prevent or detect them Common mistakes in manufacturing: Omitting processing steps Incorrectly locating a part in a fixture Using the wrong tool Neglecting to add a part in assembly Poka-Yoke Functions Performs 100% inspection for the following: Workpart deviations Processing and methods deviations Counting and timing functions Verification of steps during work cycle When an error or other exception is identified, the pokayoke responses are either or both of the following: Stops the process when an error or problem is detected Provides an audible or visible warning to alert operator and other workers Total Productive Maintenance Equipment Availability Curve Goal: zero breakdowns TPM = integration of preventive and predictive maintenance to avoid emergency maintenance Emergency maintenance = repair equipment that breaks down Preventive maintenance = routine repairs to avoid breakdowns Predictive maintenance = anticipating malfunctions before they occur Typical U-shaped availability curve for a piece of equipment during its life 4
Overall Equipment Effectiveness Measure that includes availability (reliability), equipment utilization, yield of good product, and operating capability OEE = A U Y r os where OEE = overall equipment effectiveness A = availability (proportion uptime) U = equipment utilization (time equipment is used relative to available time) Y = yield of good product = 1 - q, where q = fraction defect rate r os = operating capability (actual speed / design speed) Worker Involvement Components: Continuous improvement Visual workplace Standard work procedures Total productive maintenance Continuous Improvement Kaizen Japanese word meaning continuous improvement of production operations Usually implemented by worker teams, sometimes called quality circles Encourages worker sense of responsibility Allows workers to gain recognition among colleagues Improves worker s technical skills Visual Management and 5S Principle: the status of the work situation should be evident just by looking at it Objects that obstruct the view are not allowed Build-up of WIP is limited to a specific height Andon boards located above the assembly line indicate the status of the workstations Worker training includes use of photos and diagrams to document work instructions Worker Involvement through 5S Standardized Work Procedures Japanese word Seiri Seiton Seiso Seiketsu Shitsuke English equivalent Sort Set in order, simplify access Shine, sweep, scrub Standardize Self-discipline, sustain Three components: 1. Cycle time actual time required Takt time reciprocal of demand rate adjusted for available shift time 2. Work sequence Basically the same as a standard method 3. Standard work-in-process Minimum number of parts to avoid waiting of workers 5
Takt Time and Cycle Time Takt time defined T takt = EOT / Q dd where T takt = takt time EOT = effective daily operating time Q dd = daily quantity demanded In the Toyota Production System, the work must be designed so that the operation cycle time is consistent with the takt time Standard Operations Routine Sheet Shows the machines that must be visited by the worker during each work cycle U-shaped Work Cell Operations Routine Sheets Allocation of work at nine machines between three workers in a production work cell Allocation of work at nine machines for three workers in a production work cell Standard Work-In-Process Quantity Defined as the minimum number of parts necessary to avoid workers waiting Factors that affect the standard WIP quantity: If quality inspections must be performed as distinct steps, then additional parts must be provided If processing includes heating of parts, then additional parts must be provided for heating and cooling time If the worker's work sequence is in the opposite direction of the part processing sequence, then at least one workpart must be held between machines to avoid waiting time 6