|Home | Articles | Forum | Glossary | Books|
3. Lean Manufacturing
Lean manufacturing is a management philosophy derived from the Toyota Production System. It is focused on the elimination of waste in various forms from the production process. The Toyota Production System originally identified seven different types of waste, or Muda--a Japanese term meaning uselessness, futility, or wastefulness.
The seven wastes describe resources that are often wasted in the manufacturing process:
1. Transportation: Every time a product is moved in a process it adds time. It also runs a risk of being lost, damaged, or delayed, and it does not add any value to the product that is being transported.
2. Inventory: Raw materials, works in progress (WIPs), and completed products represent capital outlay that is producing no income. If items are not being actively processed, they are considered to be wasting time and capital.
3. Motion: Excess motion of machinery contributes to wear on equipment, while excess movement of operators can contribute to repetitive stress injuries. Motion also increases the possibility of accidents that can damage equipment or injure personnel.
4. Waiting: If a product is not being processed, it is waiting- wasting both time and space. Most products spend most of their lifetime in a manufacturing plant waiting.
5. Overprocessing: Anytime more work or operations are performed on a product than is necessary, it is considered to be overprocessed. This includes tools that are more precise or expensive than required or machinery that is overly complex.
6. Overproduction: When more goods are produced than is required by existing orders from customers, the product is overproduced. Creating large batches of product often creates this condition since customer needs can change while product is being made. Many consider this to be the worst from of waste since it can hide and generate the other forms of Muda. Overproduction leads to excess inventory, more storage space, and additional movement of product.
7. Defects: Extra cost is incurred in handling the part, wasted material, rescheduling of production, and extra transportation of defects.
Lean manufacturing uses a number of tools in identifying and eliminating waste. The application of the lean methodology is often paired with that of Six Sigma and used within the management, manufacturing, and quality departments. This gives rise to the term Lean Six Sigma as an approach to business and manufacturing. The two systems can be used together to complement and reinforce each other as a strategy to make systems more efficient.
One of the basic tenets of the Toyota Production System and lean philosophies is that of just-in-time (JIT). This is an operation system where materials are moved through a system and are delivered with precise timing just as they are needed. This reduces in-process inventory and the associated carrying costs. To accomplish this, information about the process must be monitored carefully to ensure that product flows smoothly.
Another Japanese term used in the Toyota Production System is Mura, which means "unevenness" or "irregularity." Leveling production and eliminating waste through the application of the proper techniques should lead to a smooth and predictable workflow.
Mura is avoided by applying JIT techniques properly.
A third Japanese term describing waste is the word Muri, meaning "unreasonableness" or "impossible beyond one's power." Another way to describe Muri is the overburdening of machinery or personnel.
Examples of Muri are workers performing dangerous tasks or working at a pace beyond their physical limits. The concept also applies to machinery and running a system or production line beyond its designed capabilities.
3.1 Kanban and "Pull"
To meet the objectives of JIT, one of the techniques used is Kanban.
This is a manual system that uses signals between different points in the manufacturing process. Kanban applies to both deliveries to the factory and to individual workstations. The signal may consist of cards or tickets that indicate the status of a bin or storage area or simply an empty bin. These act as a trigger to replace the bin with a full one and order new parts.
Electronic methods of Kanban are sometimes used within enterprise software systems. Triggers in this case may be manual or automatic. If stock of a particular component is depleted by the amount of the Kanban card, electronic signaling can be used to generate a purchase order with a predefined quantity to a vendor.
Arrangements are made with the vendor to ensure that material is delivered within a defined lead time at a specified price. The result of a successful Kanban system is the delivery of a steady stream of containers of parts throughout the workday. Each container usually holds a small supply of parts or materials, and empty containers are replaced by full ones. An example of the implementation of Kanban might be a three-bin system, where one bin is on the factory floor in use, one bin is in the storeroom, and a third bin is always ready at the supplier's location. When the bin being used has been consumed, it is sent with its Kanban card to the supplier. The bin is replaced on the factory floor with the bin from the storeroom. The supplier then delivers a full bin to the factory storeroom, completing the loop.
To track Kanban cards, a visual scheduling tool called a Heijunka Box is sometimes used. This is a rack or series of boxes placed on a wall to hold Kanban cards. A row for each component is labeled with the name of the component or product. Columns are used to represent time intervals of production. Cards are often made in different colors to make it easier to identify the status of upcoming production runs.
Heijunka is a Japanese term meaning production smoothing. It originates from the Toyota Production System and the concept that production flow will vary naturally and that the capacity of machinery and personnel will be forced or overburdened at certain times (Muri).
In supply chain management, one of the concepts that drives production is "push" versus "pull." In a push strategy, product is pushed toward the consumer. Forecasting of customer demand is used to predict how much of a product will be needed. This can lead to excess or insufficient inventory since there is always inaccuracy in forecasting. In a pull strategy, production is based on consumer demand and response to specific orders. Material or parts are replaced on demand, and only what is needed is produced.
This does not mean that products must be made to order to satisfy JIT and the pull system. A limited inventory is often kept on hand or in process and is replenished as it is consumed. A Kanban system is a means to this end.
Continuous improvement, or kaizen, is a major element of the TQM system and is used in manufacturing, engineering, and business management. It involves all employees of a company, from the CEO to production workers. By improving and standardizing processes, waste is eliminated, achieving the goals of lean methodology.
Kaizen is a daily process that teaches employees to apply a scientific method to the identification and elimination of waste. It can be applied individually, but often small groups are formed to look at specific applications or work areas. The group may be guided by a line supervisor but may also be assisted or led by people trained in Six Sigma techniques.
Kaizen events are often organized as a weeklong activity to address a specific issue. They are sometimes referred to as a "Kaizen Blitz." They are generally very limited in scope and involve all personnel involved in the process. Results from a kaizen event are often used in later events after careful evaluation.
A kaizen cycle can be divided into several steps. The first is to standardize an operation or its activities-in other words, ensuring that a system is in place in the beginning. The next step is to measure the operation using whatever measurement is appropriate. Examples include cycle time, waste material, in-process inventory, or defective parts. These measurements are then compared to the design requirements of the operation. Innovations and improvements can then be applied to the process and, hopefully, improve productivity.
In turn, the results of this cycle become the new standard, which is used as the basis for the next kaizen, and the cycle repeats.
Another name for this cycle is PDCA-an acronym for Plan-Do Check-Act or Plan-Do-Check-Adjust. The planning stage is used to establish the objectives and processes necessary to achieve the desired results. Doing involves implementing the plan, executing the process, or making the product. Data collection about the process is also performed during this step. The checking stage studies the results gathered during the previous step. Comparing the results to what was expected is made easier by charting the data and making it easier to spot trends. The acting or adjusting stage is used to apply corrective actions to the process. The PDCA cycle predates kaizen by many years and has its roots in the origination of the scientific method hundreds of years ago.
Safeguards that are built into a process in order to reduce the possibility of making an error are referred to in lean manufacturing by the Japanese term poka-yoke. This error-proofing technique is used to prevent, correct, or draw attention to mistakes as they occur.
The originator of the term was a Japanese industrial engineer named Shigeo Shingo who acted as a consultant to Toyota in the 1960s and 1970s. Shingo believed that errors were inevitable in any manufacturing process, but if mistakes were detected or prevented before products were shipped, the cost of these mistakes to the company would be reduced. Detecting a mistake as it is being made is known as a warning poka-yoke, while preventing the mistake is called a control poka-yoke.
Three types of poka-yoke are recognized as methods of detecting and preventing errors in a production system. The contact method tests a product's shape, color, size, weight, or other physical property.
This method is often implemented in automated processes by using sensors and test stations. The fixed-value, or constant number, method alerts the operator if a number of movements have not been made.
The motion-step, or sequence, method determines whether the required steps in a sequence have been followed. In automation, this method is performed by creating a fault in a system when a step is either not completed within a prescribed time or if an actuator does not complete its movement correctly.
In manual assembly, there are several techniques that are used to error-proof assemblies. Pick-to-light systems use signals to guide operators through the correct assembly process by blinking a light at the correct bin location for the component that is to be installed.
Sensors are used to detect whether a part was removed from the proper location and/or installed correctly. Manual tools, such as torque drivers, can be used to ensure that the proper angle and torque are achieved when installing screws. Carefully shaped fixturing and tooling are used to prevent parts from being placed incorrectly, and embedded sensors validate placement.
Ideally, mistakes are detected as they occur. Production lines often have test stations at several points in the process to eliminate further processing of reject parts. Test devices, such as gauges, leak testers, machine vision, and weighing systems, are used to flag parts or mark them for removal. Reject bins or reject spurs are equipped with sensors or identification systems to ensure parts do not proceed through production.
3.4 Tools and Terms
Lean manufacturing tools have been developed over years of refinement to improve the efficiency of production. In addition to the techniques of Kanban, kaizen, and poka-yoke, other methods to aid in the organization of the workplace and analysis of data have been adopted by many manufacturers.
Standardized work instructions (SWI) allow processes to be completed in a consistent, timely, and repeatable manner. This technique involves testing work processes in order to determine the most efficient and accurate way to accomplish a task. Work instructions are created using photos, simple text, and diagrams to clearly indicate what an operator is to do. Employees often want to do things their own ways, but developing the most appropriate method to accomplish a task is a critical element of process improvement. Workers should be encouraged to challenge the instructions and help make improvements, but consistency is reinforced when everyone is completing tasks in the "current best way." The 5S system creates a workplace that is clean, organized, and free of materials not needed for production. The 5S system, sometimes called the "visual workplace" or "visual factory," is a housekeeping tool with five behaviors intended to make the workplace more effective.
Sort 1. : Decide which items are needed to accomplish the task and remove all others.
Straighten/Set in Order 2. : Organize the items in a work area so that they can be accessed quickly. Make a place for everything, and put everything in its place.
Sweep/Shine 3. : Clean and inspect everything in the work area.
Perform equipment and tool maintenance regularly.
Standardize 4. : Use standard procedures and instructions for all work. Use discipline and structure to maintain consistency.
Sustain/Self-Discipline 5. : Continue to maintain the 5S efforts through auditing and documentation. Ensure that employees understand company expectations and the need for an uncluttered and organized workplace.
Value stream mapping (VSM) is used to design and analyze the flow of products or information between key work processes. This technique is used to differentiate value adding activities from non value-adding ones and reduce waste. Software tools and templates are available for accomplishing this task, but VSM is often performed by teams drawing diagrams by hand. Shigeo Shingo suggested that value-added steps be drawn horizontally across the center of a page and non-value-added steps represented by vertical lines at right angles to the value stream. Shingo referred to the value-added steps as the process and the "waste" steps as operations. Separating the steps allows them to be evaluated using different methods; VSM often leads to the discovery of hidden waste activities.
OEE is used to monitor and improve the effectiveness of manufacturing processes. It is described in terms of its application to machinery.
Statistical process control (SPC) refers to the application of statistical tools to the monitoring and control of a process in order to ensure it operates at full potential. The goal of a process is generally to produce as much conforming product as possible with a minimum of waste. Inspection methods detect defective product after it is made, while SPC emphasizes early detection and prevention of problems. SPC is not only used to detect waste; it can reduce the time that it takes to produce a product. It is used to identify bottlenecks in a process, waiting times, and sources of delay. SPC can be used on any process where the output of conforming product (product meeting specifications) can be measured.
SPC monitors a process by using control charts. Control charts use objective criteria to distinguish background variation ("noise") from significant events. The first step in SPC is to map the process, breaking it down into individual steps. This can be done using a flowchart or a list of subprocesses. Typical variables identified during the process mapping step include downtime, defects, delays, and cost. The next step is to measure sources of variation using control charts. A common type of control chart is a line chart. The line chart is used to correlate measurements over time or a number of samples.
By adding an average line to the line chart, a run chart is generated.
A run chart shows the variations of the process from the average over time. Adding upper control limits (UCL) and lower control limits (LCL) creates a control chart.
The type of data that is being collected determines the type of control chart to use. Attribute control charts include p charts, np charts, c charts, and u charts. Types of variable control charts include Xbar-R charts, Xbar-s charts, moving average and moving range charts, individual charts, and run charts. Descriptions and further treatment of these can be found in SPC books or online.
Control charts provide a graphical method of viewing when a process exceeds control limits, but there are many rules that must be applied to the statistical results to determine whether a process is stable or not. If none of the various detection triggers occurs, the process is determined to be stable. If a process is found to be unstable other tools, such as Ishikawa diagrams, designed experiments, and Pareto charts, can be used to identify sources of excessive variation. Ishikawa diagrams, also known as fishbone or herringbone diagrams, are line drawings that show the causes of a specific event. Causes are usually grouped into categories such as people, methods, machines, materials, measurement, and environment, which are then further subdivided into potential factors contributing to error.
Factors Contributing to Defect Measurements Inspectors Calibration Devices Suppliers Plastic Fasteners Operators Training Shifts Defect Temperature Humidity Environment Methods Machines Tooling Speed Tip Angle Ultrasonic Weld Pick & Place Materials Personnel
The information and discussion in this section of the section is solely the opinion of the author after observation of the working methods used in various companies.
The tools discussed in this section are just that: tools. Like any tool they can be misapplied and misused. Tools do not perform any work themselves; they have to be applied by people. Therein lies the problem: everyone does things differently. One of the key elements of implementing a successful business, project, or machine is systemization. This can be described as a method of ensuring that things are done the same "current best way" every time.
With all the tools and resources available, it is sometimes easy to arrive at "analysis paralysis," where a great deal of time is spent determining which solution or solutions to apply to a problem, but no solution is ever applied. A systematic method of choosing a solution involves careful analysis of the problem, establishing a deadline for selecting a method, and application of the solution based on a criteria such as most appropriate, least time-consuming, lowest cost, simplest, and so on. It is important not to implement multiple solutions that may be at cross-purposes with each other.
Many lean manufacturing and Six Sigma experts are very experienced in selecting the appropriate solution; bringing in outside help for defining and solving company problems can be a wise investment.
Even if the correct tools are used, incorrect inputs can lead to errors in output. There is an acronym for this used in the computer industry, GIGO, or "garbage in, garbage out." This not only applies to programs and algorithms; it also applies in the business world. As an example, when discussing a problem with involved personnel, their opinion can be colored by relationships with other people also involved. An unbiased opinion can be hard to obtain, and direct observation of operations is usually the preferred method. Ideally all information used as input to solve a problem should be quantifiable.
4.1 Job and Task Descriptions
The SWI described in the previous section apply to processes typically found in the manufacturing environment. They are often represented by pictures of activities and numbered, written descriptions of how a specific task is to be done. This same method can be applied to nearly any job function in the workplace, although it may not be necessary to post them in a public location as you might see on a factory floor.
All too often the most basic of job descriptions do not exist in many businesses. Employees are hired as "manufacturing engineers," "buyers," "sales," or "maintenance," as if these functions are the same in every business. This can lead to disappointment and frustration when jobs are not performed as expected.
Ideally job and job function descriptions should be provided to employees before the first day of work. This provides a list of expectations and general functional descriptions for each position in a company. This should be a "living" document that is updated on a regular basis as job functions evolve, which they generally do over time. The document should start with a general overall description of the position, the title of the person filling the position, where in the overall management hierarchy the position falls, and the names of employees that relate with the person in this position on a regular basis. This gives new employees a sense of belonging within the overall organization and within their department.
After the general description of the position, an outline of the functions within that job should be listed. This can be broken down into as many levels as necessary; again this should be an evolving document. The statement "it's not my job" should never occur within an organization that has a properly documented list of job function descriptions. As conflicts appear as to where a particular function falls within an organizational map, the issue should be documented for discussion at the next job function meeting. Of course, until the conflict is resolved someone still has to perform the task.
Job function meetings should be held at least on a monthly basis initially. They can be informal and last as little time as necessary, but they should never be put off or ignored. Input should be gathered from every person possibly affected by a change in function; members attending the meeting should include at a minimum immediate supervisors of the position being discussed; department heads should also be involved if possible.
Feedback from employees should be a part of the process. In the initial stages of documenting a job and its functions, it may take several kaizen-type meetings to produce a satisfactory initial document. As the document is fleshed out, the process can be done on a more periodic basis and with less involvement by non-affected personnel. Since the description falls under the "current best way" category, efforts should be made to keep the document as accurate as possible.
As part of daily activities in the workplace people engage in many different forms of communication. Verbal, electronic, printed, or handwritten and even nonverbal methods are commonly used.
Choice of the proper method of communications is a critical part of the business process.
Meetings are a major component of most business methods. They are intended to be a method of two-way communications between individuals or groups of people. All too often they end up being more of a one-way method, where a presenter provides information to a group of people without much feedback. This type of meeting is often more appropriately done through a written method for two important reasons. The first reason is that meetings take more time than reading a presentation. They are also less flexible in terms of timing; they are scheduled for a specific time during which everyone must stop what they are doing and attend. So the first disadvantage is that of time.
The second reason applies to more than just meetings: verbal presentations are often not documented. Sometimes an outline is presented to attendees; people may even take notes. The problem here is that there is no guarantee that the important information was received and understood by all attendees in the same way. This reemphasizes the importance of clear, written communications in business.
Meetings can serve an important function: when two-way communications are needed between individuals or groups, they are the most efficient way to exchange information or come to an agreement. Even here it is important to document them with written communications so that there is not later disagreement over what actually took place. Most people in larger organizations would agree that too much of their time is taken up by meetings. One way to reduce the number of meetings is to determine whether they can be replaced with written forms of communication.
Conversations between individuals should also often be documented by written communications. If an important decision or instruction is not documented, there may be disagreements later as to what was actually said. The statements "you never told me" or "that's not what I/you said" should never be made if proper communication methods are chosen. With the development of technologies such as personal communication devices able to send texts or e-mails, there is simply no excuse for miscommunication or misinterpretation.
Especially for project-based work, documented communication between coworkers and vendors/customers is critical.
4.3 Hiring and Training
The hiring process often includes rigorous analysis of a prospective employee's experience and skill set, suitability for a position, and ability to "fit in" with an organization. Candidates are often interviewed by multiple people, including (hopefully) peers familiar with the person's field of expertise. If an employee is being hired for a position that requires specific skills, testing of the candidate should be part of the process. Examples in the technical field might be generating CAD drawings, writing a short program, fabricating a part, or troubleshooting a machine. Decisions on whether a candidate for a position is to be hired are usually based on various factors, including personality, experience, skills, and compensation requirements.
Even with all this careful examination of a candidate, there is a variety of skills that will likely not match exactly. Every company has a different method of accomplishing tasks, and new employees often need guidelines or training to completely mesh with their new organization.
If the job and task descriptions described in Sec. 4.1 (above) are detailed enough they can serve as an important training tool. Examples of previous work or projects can also be a useful element in the training process. If an employee with a similar job function is available, he or she may also be assigned to help with the orientation process.
Even with all these internal resources, sometimes outside help must be obtained to facilitate the training process. Vendors such as distributors' and manufacturers' representatives can be an excellent resource for product-specific training. They will often provide "lunch and learn" activities in order to help promote their products. Trade shows also often provide hands-on training on many products.
Skills such as CAD/CAM and lean manufacturing techniques are often taught by independent companies and consultants. Establishing a budget for employee training can be a wise investment for a company provided employee retention is high. Training programs are often administered by the human resources department.
A common problem is balancing training with retention of employees. Companies often hire personnel at a relatively low pay rate with the intent of training them into a position, only to find that once the employee's skills have increased, he or she has become more marketable and goes to find a higher-paying job. It is important that companies stay competitive in the job market while still controlling their own bottom line.
4.4 Engineering and Project Notebooks
An important tool often used by inventors, engineers, and designers is the engineering or project notebook. The intent is to capture vital details of the engineering process and create an ongoing record of the project. Observations, ideas, and even meeting notes help provide a timeline for the project. Formal engineering notebooks are often used as a permanent record of a project accessible by all members; these are usually bound books (so that all pages are accounted for), written in ink (pencil and erasable ink are not acceptable), with all entries dated and signed. There are often formal methods of making corrections (no Wite-Out, a single line drawn through errors), and they may even contain signatures of team members who attended project meetings.
While formal engineering notebooks may be used in large companies and engineering firms, they are not common in factories and industrial plants. Perhaps people believe that they take too much time to maintain or they have simply never heard of them.
I have created a notebook for every project I have ever been involved with. While breaking nearly every rule listed above (mine are usually written in pencil, I use loose-leaf binders, and I do not sign anything or expect others to), I still find them very useful. I have often gone back to a project notebook to review how I solved a particular problem or wrote a piece of code.
In addition, I use a different notebook to keep records and ideas in that do not fall into a particular project. My project notebooks are always available for other team members or employees to look at, but my personal notebook contains scheduling information, random thoughts, and even passwords for the various web sites and unimportant accounts I am signed up for. In some ways it is a hybrid journal and life-project notebook.
As mentioned earlier in this section, I am a big believer in written communications and records. Many times I have visited a plant to evaluate a project only to find that there is insufficient information on a machine or system to be able to properly estimate the time it would take to solve the problem. Documentation is the primary and most important tool used in troubleshooting. This not only applies to the formal documentation that is supplied with a manufactured system, but also to the maintenance records and notes that operators and technicians keep on the equipment. For the cost of some paper and a little bit of time, it is possible to save thousands of dollars by simply recording the events in a system's history.
This can also be extended to the business world. By keeping written documentation of daily events, it is much less likely that tasks will be forgotten. There are various electronic devices such as personal data assistants (PDAs), laptops, iPads, or even cell phones that can aid in this task, but I personally still prefer the handwritten method.