Lean Manufacturing Essay
Definition: According to Taghizadegan (2006), Lean is a technique “used to accelerate and minimize the cost of any process by eliminating the waste in either manufacturing or service.” The waste may be “non-value added cost or unneeded wait time within the process caused by defects, excess production, and other processes.”
Lean Manufacturing, also called Lean Production, is a business philosophy that was originally developed by the Toyota Motor Company, and was referred to as the Toyota Production System or TPS.
Ehrlich (2002) states that basic goals of Lean are “high quality, low cost, short cycle times, flexibility, relentless efforts to drive waste out of the organization, and all value being defined by the customer.” The result is faster cycle time, less waste, and more efficiency. It also provides tools for reducing variability (Epply, 2000).
According to Carreira et. al. (2006), the six main Lean Manufacturing principles are: value, value stream, waste elimination, flow, pull and perfection.
Principle 1: Value. A given activity can add or deduct value to a specific product or service, based on the customers’ point of view. In other words, an activity can alter the product or the service to a more desirable one and thus generate revenue by adding to the profit line, or it can unnecessarily add cost, subtracting from the profit line, in which case it is referred to as non-value added task. These tasks may involve more time, labour, materials, or space but do not improve the product or enhance its value.
Principle 2: Value stream. This is “the total cycle of activity to provide a product or service, from initial customer contact to receipt of payment” (Carreira et. al., 2006). Improving individual areas of a process and analyzing their impact across the whole process, can improve the entire process. It can also provide an overall view of the activities, inputs, outputs, and disconnects, to allow for leveraging maximum financial improvement; system-wide and bottom line.
Principle 3: Waste elimination. Waste is defined as anything the customer is not willing to pay for, or, which does not add value to the process (Epply, 2000). There are seven types of waste in Lean Manufacturing.
Overproduction: indicates high productivity to demand ratio, which results from utilizing production equipment and machines faster than required. This can result in “dumping” the products at reduced price or selling them with difficulty (Epply, 2000).
Inventory: includes unprocessed components, finished product and work-in-progress. Any unnecessary work, excess inventory, and stockpiling inventory between processes, are wasteful and increase the cost (Ehrlich, 2002).
Waiting: waiting for the next stage of production can result in delays in the project. However, it is acceptable for the machine to wait for available operator but an operator should not wait on the machine (Ehrlich, 2002).
Motion: unnecessary operator motions and moving material can cause waste and affect process performance (Epply, 2000).
Transportation (Conveyance): refers to excessive movement of people or equipment during the production process; more than that required for performing the tasks in the process. This can create wasteful rework and damage to the parts (Epply, 2000).
Rework (Correction): refers to inspection and fixing any errors or flaws. This is wasteful, but it can be eliminated by error proofing (Epply, 2000).
Over processing: means process waste resulting from poor equipment, duplication of effort, inspections, and no value-adding activities, and inadequate product design. This can lead to failure and increase in cost (Epply, 2000).
Waste elimination reduces the production cycle time (time from receipt of order to receipt of payment) and results in higher quality, short delivery times and lower costs (Ehrlich, 2002).
Principle 4: Flow. It is necessary to ensure that all value creating steps can flow smoothly; by focusing on the customers’ viewpoints, ignoring boundaries and limitations of job descriptions, eliminating or handling bottlenecks, and synchronizing all activities (Caldwell et. al., 2009). Bottleneck or constraints are the slowest steps in the process, which are identified in order to be eliminated, so to increase the output of the whole process (Ehrlich, 2002).
Principle 5: Pull. It is “a technique where downstream customer triggers the need for the product or service” (Meisel et. al., 2007). Let customers pull value from the next upstream activity.
Principle 6: Perfection. Once the above steps are implemented, the last task is to achieve perfection by continuously reviewing the steps until a state of perfection is reached. In this stage no errors are made or defects generated (Meisel et. al., 2007).
Lean Manufacturing can also be divided into nine basic principles that assist and generate solutions to manufacturing problems. These are: Continuous Flow, Lean Machines, Workplace Organization, Parts Presentation, Reconfigurability, Product Quality, Maintainability, Ease of Access, and Ergonomics (cited from Bosch Rexroth Corporation (2007)). The nine principles are shown in appendix A, figure 7 in a typical U-shaped cell.
Principle 1: Continuous Flow. This concept requires minimum movement of work piece or assembly from one workstation to the next. For this reason the preferred shape of the Lean work cell is U-shape (as shown in appendix A, figure 7), connecting each subprocess to the next. In this way, all non-value-added movements are eliminated, by carrying work piece from one value-added operation to the next, either manually or mechanically, if the work piece is too heavy. Manual push or gravity conveyors are ideal for transportation of very heavy parts, although belt conveyors may also be used.
Principle 2: Lean Machines (Simplicity). It is important to design each workstation or machine to fit within a minimal envelope, in order to reduce unnecessary steps taken by the worker between subprocesses, and provide continuous flow, thereby resulting in “batch” processing. If this principle is not considered, it can increase the amount of work done in the process. The reason is that excess flat space increases the possibility of storing parts, or sub-assemblies, at the workstation or machine. Moreover, to enable continuous improvement of the work environment, the layout and design of the process should be flexible so that all workstations and work-cells can be easily modified, as areas for process improvements are identified. Optimizing machine base or workstation is also vital in Lean Manufacturing, since it can aid saving on cost and the environment, by using reconfigurable and reusable material in machines.
Principle 3: Workplace Organization. This involves everything in the work cell including tool holders and information boards. To achieve an efficient Lean work cell, it is vital to provide a smooth, uninterrupted flow of completed work pieces. Avoiding loss or misplacement of tools, and using separate tool holders for the tools in each workstation allows immediate awareness of the absence of a tool. It is also important that spare tools are stored at any automated workstation, in order to minimize downtime, and maintain a continuous flow, by replacing damaged tools quickly.
Using simple, easy to re-position and re-usable information boards at the workplace, to inform about repair procedures, work instructions, assembly processes, or even production targets, will allow workers to effectively carry out any task at hand.
Principle 4: Part Presentation. According to this concept, additional parts supplied to the workstations will minimize the number of interruptions. For instance, case lifters or bins (as shown in appendix A, figure 8 and 9 respectively) reduce interruptions because bins are ideal for small parts, whereas case lifters can be used to raise heavy and large parts to the proper height using pneumatic, electric or hydraulic power.
Principle 5: Reconfigurability. The design of the work cell must be such that it can be easily reconfigured, at times when the process needs to be altered in order to accommodate assembly of a new product. This concept also emphasizes the importance of quick changeover of a machine or workstation in order to decrease production time of the process.
Principle 6: Quality. For primary quality assurance, visual inspection by the worker or through gages (a measuring instrument or device) is required. The test fixtures and gages must be mounted onto the machine or workstation, and easily changed or replaced. The cause of poor quality may be a malfunctioning machine. This can be easily changed, if the Lean cell is designed in a way, such that there are no pneumatic or electrical connections between the machines. In this way the machine can be replaced quickly, whereas the need to disconnect lines would slow down the process. Another factor that can lower quality in Lean Manufacturing is flawed process. This can be avoided using a structural framing system, which would enable alterations to be carried out within minimum amount of time.
Principle 7: Maintainability. This refers to the ease of service. To provide optimal maintainability, a modular structural framing system is required. This would allow individual components to be reconfigured or replaced, or even, for the entire machine bases to be rebuilt, in minimum amount of time. In terms of maintaining the structure, the structural framing system provides minimum number of tools, and common components, in order to eliminate the need for a large inventory of spare parts.
Principle 8: Ease of access. This requires all necessary work components to be in easily accessible locations. To ensure all workers have access to the components, they need to be easily and quickly repositioned, and added to any workstation.
Principle 9: Ergonomics. This concept is concerned with the ergonomic problems of height, and lifting. It is required that the work cell is adequately designed to maintain, ergonomically, correct height, considering the average height of the workers. Also, the optimum height of a workstation or machine must be easily changed to accommodate the average height in different countries. In terms of lifting devices, if the weight of the parts exceeds lifting standards, then simple electric, hydraulic or pneumatic devices should be used. Finally, to prevent faulty design, and analyze ergonomic issues in the design stage, software packages that test ergonomics of a work cell can be used.
Lean Manufacturing principles can vary based on the organization. In other words, each organization develops, and uses principles, based on its requirement for improvement. Out of all of the principles illustrated above, the first six principles are more general, whereas the nine principles were specifically developed for Rexroth (Bosch Group).
