Chapter 4: Lean Systems Flashcards
Lean systems
Operations systems that maximize value added by each of a company’s activities by removing waste and delays from them
Encompass the entirety of a company’s operations
Just in time system
JIT
A key foundation of a lean system. Represents a collection of practices that eliminate waste (aka muda) by cutting excess capacity or inventory and removing non-value-added activities
Eight types of waste
- Overproduction
- Inappropriate processing
- Waiting
- Transportation (excessive movement/ material handing)
- Unnecessary Motion
- Excess Inventory
- Defects
- Underutilization of employees
Goal of lean systems
To eliminate the eight types of waste
Produce services and products only as needed
Continuously improve value-added benefits of operations
Kaizen
Japanese, means “change for the better”
An approach to process improvement that centers the understanding that excess capacity/inventory hides underlying problems in a process. Excess capacity/inventory is removed to better spotlight areas for improvement
often uses “PDCA” process (plan, do, check, act)
Techniques to identify areas for continuous improvement
-maintaining low inventories
- periodically stressing the system
- focusing on the elements of the lean system
Supply chain considerations in lean systems
- close supplier ties
- small lot sizes
JIT II system
Aka vendor-managed inventories
Supplier is brought into the plant to be an active member of the purchasing office of the customer, empowered to plan and schedule replenishment of their materials
Fosters an extremely close interaction with suppliers
Benefits of small lot sizes
- reduces average inventory level
- inventory moves faster
- if defect discovered, less items to inspect
- helps maintain uniform workload and prevent overproduction
- makes it easier to rearrange workflow order
Disadvantages of small lot sizes
Increased setup frequency
Single digit setup
The goal of having a setup time of less than 10 minutes
Process considerations in lean systems
- pull method of workflow
- quality at the source
- uniform workstation loads
- standardized components and work methods
- flexible workforce
- automation
- five S (5S) practices
- total productive (preventative) maintenance (TPM)
Pull method of material flows
A method in which customer demand activated the production of a service or item
Commonly used in lean operations
Push method of material flows
A method in which production of the item begins in advance of customer needs
Dependant on forecasting
Quality at the source
A philosophy whereby defects are caught and corrected where they are created.
Goal for workers to act as their own quality inspectors and never pass defective units to the next process
Jidoka
A visual management system that Automatically stops the process when something is wrong and then fixing the problems on the line itself as they occur
Separates worker and machine activities by freeing workers from tending to machines constantly, allowing a single worker to staff multiple operations simultaneously
Poka-yoke
Mistake-proofing methods aimed at designing fail-safe systems that minimize human error
Andon
A system that gives machines and machine operations the ability to signal the occurrence of any abnormal conditions
Ways to achieve uniform workstation load
- reservations for service processes
- differential pricing to manage demand
- scheduling to same daily workload for manufacturing (capacity planning –>master production schedule –> daily workload)
Takt time
Cycle time of a process needed to match the rate of production to the rate of sales or consumption
Heijunka
Leveling of production load by both volume and product mix.
Instead of building to actual flow of orders builds to overall demand leveled out so same amount being made each day
Mixed- model assembly
A type of assembly that produces a mix of models in smaller lots
Five S (5S)
A methodology consisting of five workplace practices:
- sorting
- straightening
- shining
- standardizing
- sustaining
Conducive to visual controls and lean production
Enabler/foundation of lean systems
Why are line flows recommended for designing lean systems layouts?
- eliminate waste
- reduced frequency of setups (if volume is large enough setups may be eliminated entirely)
One-worker, multiple-machines cell
OWMM
A one person cell in which a worker operates several different machines simultaneously to achieve a line flow. Some tasks are automated and operator performs non-automated tasks
Reduces inventory queues and overall labor needed
Used when volumes are insufficient to keep multiple line workers busy
Group technology
GT
An option for achieving line-flow layouts with low volume processes; technique creates cells not limited to just one worker and has a unique way of selecting work to be done by the cell
Groups part or products with similar characteristics/processing requirements in families and sets aside groups of machines for their production (minimizes setup)
Kanban
A Japanese word meaning “card” or “visible record” that refers to the cards used to control the flow of the production through the factory
Goal to ensure company has minimum amount of inventory to keep production running and that production is being pulled by customer demand
Basic kanban system
- card attached to each container of items produced
- each container holds a given percent of the daily production requirement of that item
- when container is emptied card is moved to a receiving post, signalling the need to produce another container of the part
- when container refilled the card is out back on the container
General operating rules of the kanban system
Designed to facilitate flow and maintain control of inventory levels
- a full container must always have a kanban card
- the preceding process will never produce parts without a kanban card
- the following process must post the kanban card at the receiving post before beginning consumption of the parts inside the containers
- the containers should always be standard and contain the same number of good parts (described on the kanban card)
- only non-defective parts should be put into inventory with the kanban card (quality at the source)
Little’s law
Average inventory = average demand rate x average demand time
How to determine the number of containers in a kanban system
of containers = ((expected daily demand for units)(fraction of the day spent in materials handling and waiting during the production process+ fraction of a day it takes to process each container)(1+ variable set by policy for safety stock)) / quantity of units in a standard container
Average lead time per container (kanban system)
= waiting and materials handling time + production time
May be decreased by improved operations
Alternate Kanban signals
- the empty container itself
- in a container less system a painted area in a workbench
Value stream mapping
VSM
A qualitative lean tool for eliminating waste (muda) that involves a current state drawing, a future state drawing and an implementation plan
Visual mapping of every process involved in materials and information flows in a products value stream
Steps of building a future state map
1) determine if the process steps are capable of producing according to required takt time (if not apply constraint management methods)
2) identify where in the value stream inventories may be eliminated (creation of cell)
3) design pull systems to manage remaining inventories
4) preparing and using implementation plan to achieve the future state
Organizational considerations for lean systems
- potential for workers to feel stressed and like they have lost autonomy
- importance of cooperation and trust between teams, workforce and management
- realignment of reward system may be difficult given labor contracts
Process considerations for moving to lean systems
Need to change existing layout can be expensive
Inventory and scheduling considerations for lean systems
- lean systems require schedule stability and do not respond quickly to scheduling changes (in high volume environments)
- small lot sizes require a large number of set ups at significantly reduced times. Not flexible for sudden changes in set up time
- low levels of raw materials inventory requires reliable ordering/shipping/receiving (recovery may be difficult after supply chains are disrupted)
what is waste?
An activity that adds cost or time but does not add value
consuming more resources than are necessary to produce the goods or services that the customer wants
Two types of waste
- Pure Waste
- incidental waste
Pure waste
“actions that could be stopped without affecting the customer (waste in processing that the customer never sees)
Incidental waste
Actions that need to be done based on how the current system operations that do not add value. Somehow inherent to the system and require a change to the whole system to fix them
Ryder Systems lean guiding principles
- people involvement (making use of employee knowledge)
- built-in quality
- standardization (document and follow best practices)
- short lead time
- continuous improvident
Characteristics of lean employees
- persist when confronted with difficulties
- adapt, are proactive and thrive under uncertainty
- take personal initiative
- understand what’s important at the moment and take appropriate action
- are deeply engaged with the organization
How to foster people involvement in a lean organization
- focus on communication
- empower the experts (people who do the work)
- cross training so people understand the whole process
What is built-in-quality
a focus on getting it right the first time
benefits the entire process
mistake-proofing to eliminate rework
FMEA
Failure mode and effects analysis
testing where the tester tries to break/ find the weak points of a process so they know what needs fixing
Why is standardization important to lean systems
everyone follows best practices so improvements multiply and are more sustainable
layered audit
Audit performed while the work is in progress to allow for immediate corrections of errors
visual management
visual tools to communicate with employees
ways to shorten lead time
- streamlining work
- eliminating steps that do not add value
- keep work flowing without impediment or waste
Elements that facilitate shorter lead time
- small lots
- level loading
- simple process flows
- pull system
implementing simple process flows
use Value Stream Mapping to break process down into its smallest step, diagram, and identify waste points to remove waste/ simplify flow
Level loading
work is structured so that pace and momentum stays steady throughout the process
important to keep processes in sync
ideally paced to meet customer demand
Pull system
customer consumption creates the signal that determines how much inventory to replenish, so system matches how demand changes
Continuous Improvement
based on the Idea that it is more effective to make many small gains over time rather than try to accomplish massive gains all at once
uses structured problem solving of identifying a problem, analyzing its root causes, and implenting solutions
Five Whys tool
Used to walk backwards through a problem to discover the flaw that created the problem. The idea being that if you ask “why” five times you will get to the root of an issue
use of automation in lean systems
have humans focus on high-value complex work and use automation to support these tasks by automating the basic, repetitive, low-value steps
Standard work
combines the elements of a job into the most effective sequence without waste to achieve the most efficient level of production
simplifies finding anomalies where the process deviates from standard
Andon cord
a way to empower front-line workers to address quality (or other) problems by stopping production until the defect is fixed. (to avoid problems compounding)
Six sigma
a statistical measure of defect - out of one million opportunities for defect how many defects occur (a non-linear function)
offers a way to compare across different processes
3- 4 sigma is average, 6 sigma is considered “best in class
sigma rage of average company/ person
3-4 sigma range
Six sigma textbook definition
a comprehensive and flexible system for achieving, sustaining, and maximizing business success by minimizing defects and variability in processes
Opportunities for defect
number of possible way for an item or process to be defective * number of times item or process is produced
defect (for purpose of six sigma)
any time a product or service does not meet the customer expectation
A six sigma process
one that eliminates the opportunities for defects
variability and sigma
a process with a higher variability will have a lower sigma - more defects per million opportunities. If can improve standardization can reduce variation and increase sigma
5S
a theory that focuses on effective workplace organization and standardization that allows people to easily spot variation from standard operating conditions
- sort
- stabilize (simplify or set in order)
- shine (regular cleaning and maintenance)
- standardize (develop a system)
- sustain (maintain the system)
