Differences between push and pull manufacturing

Push Manufacturing: manufacturing activities are planned based on a market forecast rather than actual customer demand.
• Emphasis on central planning
• Little communication between various stakeholders
• Material flows through in batches following a prescribed route in the work order
• Rely on heuristics
• Service levels assured by increasing and decreasing finished goods in inventory levels

Pull Manufacturing: manufacturing plan is based on actual customer demand.
• Control of manufacturing execution is at working level, which leads to much communication
• Material flows through the factory based on visual queues triggered by customer "pull"
• Rely on hands-on management
• Service levels are assured by increasing or decreasing levels between workstations

The 7 Wastes of Lean Enterprises

The main driver for a Lean Enterprise is to compress the time period from customer order to receiving payment from the customer. This is achieved by identifying and eliminating waste or non value added activities. In a conventional supply chain and in individual enterprise, there are potentially huge amounts of different wastes, famously known as The 7 Wastes. Recently an eighth waste, underutilized people, has been added to this category. Taiichi Ohno (developer of Toyota Production System) suggests that these account for up to 95% of all costs in non-Lean manufacturing environments.


These wastes are:

1. Overproduction – Producing items for which there are no customer demands. The Lean principle is to use a pull system, or producing products just as customers order them. Service organizations operate this way by their very nature. Manufacturing organizations, on the other hand, have historically operated by a Push System, building products to stock (per sales forecast), without firm customer orders. Anything produced beyond the customer demand (buffer or safety stocks, work-in-process inventories, etc.) ties up valuable labor and material resources and hence is a waste.


2. Waiting – Time during production (service) when no value is added to product (service). This includes waiting for material, information, equipment, tools, stock-outs, lot processing delays, equipment downtime, capacity bottlenecks, etc. The Lean principle is to use a just-in-time (JIT) system– not too soon, not too late.


3. Transportation – Unnecessary moving and handling of parts. This includes transporting work-in-process (WIP) long distances, trucking to and from an off-site storage facility. Lean demands that the material be shipped directly from the vendor to the location in the assembly line where it will be used. Material should be delivered to its point of use. The Lean term for this technique is called point-of-use-storage (POUS).


4. Over-Processing – Unnecessary processing or procedures than necessary to meet customer demand. Common examples deburring and multiple inspecting. Statistical process control techniques can be used to eliminate or minimize the amount of inspection required. Value Stream Mapping is another lean tool that can be used for this purpose also. This tool is frequently used to help identify non-valued-added steps in the process (for both manufacturers and service organizations).
   
5. Excess Inventory – Excess raw material, Work-In-Process (WIP), or finished goods. Inventory beyond that needed to meet customer demands negatively impacts cash flow and uses valuable floor space. Lean concepts like supermarket, and kanban can be used to tackle this waste.
   
6. Defects – Scrap, rework, replacement production, and inspection. Production defects and service errors waste resources in four ways. First, materials are consumed. Second, the labor used to produce the part (or provide the service) the first time cannot be recovered. Third, labor is required to rework the product (or redo the service). Fourth, labor is required to address any forthcoming customer complaints. Total Quality Management (TQM) is one of the lean tools that can be used to for reducing defects.


7. Excess Motion – Unnecessary motion of people or equipment that adds to value to product (service). This is caused by poor workflow, poor layout, housekeeping, and inconsistent or undocumented work methods. Value Stream Mapping (see above) is also used to identify this type of waste. Tools like 5S, cell design and Ergonomic workspace design can be used to eliminate this waste.


8. Underutilized People – Underutilization of mental, creative, and physical skills and abilities of employees of the organization. Some of the more common causes for this waste include – organizational culture, inadequate hiring practices, poor or non-existent training, and high employee turnover.

5 Principles to Characterize a Lean enterprise

The spotlight of any new concept is often on its application and results. In almost all successful concepts some fundamental assumptions and basic principles underlie the results. This holds true for Lean concept too. A copycat mentality without understanding the fundamentals behind lean can lead to phony gains and such a strategy will be ineffective. So this blog is focused on understanding the fundamental principles of a lean enterprise.

A set of five basic principles that characterize a lean enterprise are (as defined by Womack and Jones in their 1996 book Lean Thinking):

1. Define value precisely from the perspective of the end customer. The value should be defined in terms of a specific product, with specific capabilities, offered at a specific price and time.


2. Identify the entire value stream for each service, product or product family and eliminate waste. The value stream is all the specific actions required to bring a specific service or product through three critical activities in any business: Product/Service definition – from concept through detailed planning through launch Information management – from order taking through detailed scheduling to delivery Physical transformation – initial concept, to the receipt of the service/product by the customer Identifying the value stream almost always exposes enormous amounts of waste in the form of unnecessary steps, backtracking, and scrap, as the throughput travels from department to department and from company to company.


3. Make the remaining value-creating steps flow. Making steps flow means working on each design, order, and product continuously from beginning to end so that there is no waiting, downtime, or waste, within or between the steps. This usually requires introducing new types of organizations or technologies and getting rid of “monuments” – obstructions whose large scale or complex technology necessitates operating in a batch mode.


4. As flow is introduced let the customer pull i.e., to provide what the customer wants only when the customer wants it. Letting the customer pull the product/service from the value stream eliminates the following types of waste: designs that are obsolete before the product is completed, finished goods, inventories, elaborate inventory/information tracking systems, and “left overs” no one wants.


5. Pursue perfection. A lean thinking enterprise sets their sights on perfection. The idea of total quality management is to systematically and continuously remove the root causes of poor quality – with the ultimate goal of achieving Zero defects.

Standing Vs Seated Workstations in Lean Cells?

During the summer, I am consulting a company in lean manufacturing aspects. Currently I am working on creating “flow” in one of the assembly lines of the company. Yesterday, while finalizing the details of workstations in the assembly line, I was asked this question. Here are my two cents on this issue.

One of the most debated aspects of lean approach to assembly cell design is the requirement they be chair-free—that the assemblers stand rather than sit. In lean manufacturing the concept of standing workstation is popular. Given the choice between standing and sitting most people would prefer to sit.

There are numerous applications where standing is the preferred working posture, as opposed to sitting.

• Standing is preferred when the work area is too large. The maximum reach envelope when standing is significantly larger than the corresponding reach envelope when sitting. Have you ever seen a sitting workstation for checkout cashiers in stores like Wal-Mart? Do you ever cook on a sitting chair? Large work areas frequently are found in assembly environments, including auto assembly, packaging, welding, sheet metal, and paint lines. This also applies when the person works in more than one workspace to perform his/her job duties. In lean cells you want people to move frequently so that you can achieve “self-balancing” of the cell.


• Standing is preferred when the work surface obstruction does not allow the person to comfortably position his/her legs under the surface. This is often the case when working on a conveyor, using a workstation with a drawer located underneath the work surface or a wide front beam, or using specialized equipment.


• Ergonomics research shows that standing is recommended to maximize grip forces, and improve static or dynamic lifts. In general, more strength can be exerted while standing.

There is also an extensive lists of jobs that are most appropriately done standing, including construction workers, highway flaggers, medical personnel, painters, electricians, plumbers, loggers, firefighters, plant inspectors, and maintenance personnel.

Applications where seated workstation is preferred.

• Work that is highly dependent of fine motor functions—manual electronic assembly like soldering, writing, and sewing etc should be done at a seated workplace equipped with armrests.


• Work that require precise foot control movements.

Remember assembly and manufacturing line working requirements are different from the work requirements of office desks. The short term comfort of sitting does not translate to long-term well-being but instead leads to weight and back problems. In most of the manufacturing and assembly line scenario it is often un-ergonomic to perform your job while seated. From a strictly ergonomic standpoint sitting all the time is in fact no better than standing all the time.

So the rule of thumb…Use seated workstation only when fine motor skills are essential.

What is Lean Thinking?

John Krafcik, an MIT MBA student coined the term “Lean Manufacturing” to identify the Toyota methods, because the production system achieved more results with less resources. TPS, or lean production, was an after-effect of the competition in the Japanese automobile industry after World War II. The mass production techniques pioneered by Henry Ford were unsuitable for low volume production, so Toyota found it necessary to develop its own production system to build cars more cheaply with inbuilt quality. In essence, Lean production is the elimination of waste to produce more flexible and adaptable manufacturing processes. Lean Thinking extends lean production to go beyond manufacturing and to include the entire enterprise. Lean thinking extended the elimination of waste to include the creation of value at enterprise level.

This business philosophy goes by different names. Agile Philosphy, Just-In-Time (JIT), Synchronous Manufacturing and Continuous Flow are all terms that are used in parallel with lean thinking.The basic components and tools of the Toyota Production System (TPS) and lean production existed in literature much before publication of The Machine That Changed The World (Womack, et al., 1990). However advent of this book popularized the Lean concept and brought the ideas to masses. The key idea in the book (and one that is absent in earlier literature) is that of “Value.” Specifying value from customer's perspective (whether internal or external) is an important step in lean thinking. Lean thinking focuses on abolishing or reducing waste (or “muda”, the Japanese word for waste) on maximizing or fully utilizing activities that add value from customer’s perspective.

Value-Added: An activity that changes the size, shape, fit, form, of function of material or information to meet the customer requirement. The customer is willing to pay for it.

Non-Value-Added: Activities that take time and resources but do not add to customer requirements.

The value stream represents the end to end processes through the entire enterprise. The lean thinking focuses on every facet of the value stream by eliminating waste in order to reduce cost, generate capital, bring in more sales, and remain competitive in growing global market.