Town-City
Arguably the ideas of Just-in-time (JIT) have had the most significant influence on operations of the manufacturing industries in the past twenty years. It has also had a significant impact on the service operations, specifically the ‘back office’ operations. In most management circles JIT is now being referred to the lean operations practice. As such it has broadened to a philosophy of how organization’s operations should be managed. This Philosophy emphasizes on the avoidance of all forms of waste, maintaining high levels of quality and reliability and on the need of reduced throughput time of resources already transformed.
The APICS dictionary defines JIT as a manufacturing philosophy anchored on elimination of all forms of waste and adoption of continuous improvement ideas on productivity. It has also been defined as an approach with the overall aim of producing what is needed, at the time it’s needed and in the actual quantity needed.. In JIT supplies and the required components are ‘pulled’ through the system to reach their destination (workstation) when they are required. This is unlike the traditional system which was a ‘push system’ and more often resulted in many non value adding activities thus resulting in wastage. In the words of the Toyota president, Waste is ‘anything over and above the minimum quantity of materials, space, equipment, parts and employee’s time, which is absolutely important to add value to the product.’- Schoichiro Toyoda, Toyota President.
Just in time improves profits and return on investment of the organization by reducing inventory levels to the minimum required for any production, improving the product quality, reducing delivery and production lead times and reducing any unnecessary costs that do not add value from the customer’s perspective. The excess capacity that results in a JIT system is used to hedge against problems that may arise instead of buffer inventories.
JIT applies mainly to manufacturing processes that are repetitive in which same components and products are produced again and again. The basic idea is to create a flow process by linking work centers so that there is an even and balanced flow of materials throughout the whole production process. To achieve this, effort is made to drive the entire buffer inventory to zero.
Toyota developed the basic elements of JIT in 1950’s, which became known as the Toyota Production System (TPS). By the early 1970’s JIT was well-established in most factories in Japan. In the US JIT was adopted in the 1980’s with GE being the early adopter.JIT is now widely accepted and used in most manufacturing companies. The basic elements of JIT are;
Stabilize and level the Master Production Schedule (MPS) with uniform plant loading: Establish a uniform load on all work stations (or load centers) through a uniform daily production (freeze windows are established to avoid changes in the production plan for some duration) and a mixed assembly model (this ensures that roughly the same mix of products are produced each day, using some repeated sequence in cases where several products are produced on the same production line). The demand fluctuations are met through end-term inventory instead of meeting the same through variations in the production level. The use of a constant production schedule allows for the use of back flushing in inventory management.
Eliminate or reduce the setup time: JIT aims to reduce the setup time to a single digit (below 10 minutes). This is achieved through better planning, redesign of the processes and product.
Reduce Lot Size: By reducing the setup time, the economical production of small lot sizes is made feasible. To achieve reduction in order quantities a close cooperation with the suppliers is critical since this will call for frequent deliveries. Besides the suppliers need to maintain high quality of the supplies to avoid any returns.
Reduce lead times: To reduce production lead times Work stations are moved closer together , cellular manufacturing concepts and group technologies are effectively applied, queue length reduction (reducing the quantity of jobs awaiting processing at any given machine), and increasing the coordination and operation between processes. Whereas delivery lead times are reduced by increasing cooperation with suppliers.
Preventive Maintenance: During idle time of the machine and the workers the equipment maintenance and preventive breakdowns are done. This prevents wastage of productive time.
Flexible Work force: JIT calls for a very flexible work force. This is achieved by training the employees to operate several machines. Generally JIT requires competent, empowered teams of employees who have greater responsibility for their individual work. The TPS maxim of “respect for people” leads to a good relationship between the employees and management.
Require quality assurance from the suppliers and implementation of a zero defect quality program: JIT requires that all errors that could result in defective items be eliminated, since there are no idle stocks to cover any unnecessary excess parts resulting from defect items. Quality at the source program has to be implemented to ensure workers have a personal responsibility of their work and the powers to stop any production when something is wrong. The suppliers have to guarantee high quality raw materials to ensure that no defective items result as a result of defective inputs.
Small-lot conveyance: JIT uses control systems such as a kanban system or other systems of signaling to convey parts between work centers in small numbers (ideally one at a time).
The Kaban System
The “kanban System” is a production control method that plays a critical role in the Toyota Production System (TPS). This system is also referred to as the “supermarket method” since the underlying idea was borrowed from supermarkets. This system uses simple visual signs to control material movement between work centers. As implemented in the TPS a kanban refers to a card attached to the container for storage and transport. The card identifies the container capacity and the part number together with other information. The card is used to provide easy to understand signal on the specific activity required. Sample of the kanban cards are shown below.
At Toyota two main types of kanbans are in use; the Production Kanban which authorizes the production of more parts/products and the. Conveyance Kanban which authorizes the movement of products/parts from one work center to the next.
The dual-card kanban operated by Toyota is based on some basic rules: Every container part should have a Kanban card (i.e. each container has exactly one kanban). Only on receipt of a production kanban can production commence. The implication of this rule is that no part is made without a production kanban. A procedure remains idle if there is no production kanban, and the workers are given other duties. The third rule is that all the containers have their standard quantities and only the standard container for the part is available for use. Similarly as a rule the using work center must come to providing work center and not vice versa i.e. parts are always pulled. For any part to be obtained there has to be a conveyance card. In Toyota JIT has provided a smooth, continuous and optimal workflow. This has resulted in a carefully planned and stable work-cycle time. The system has also resulted in the on-demand movement of products, and a reduction on the time, materials and capacity wasted. All this saving to the organization have resulted in better service delivery to customers and improved product quality with an overall improvement on the company’s profits and competitive advantage over its competitors. Employees can now focus on their tasks with little or no interruption thus increased productivity levels from individual employees. Toyota customers enjoy high quality products and timely delivery.
Bibliography
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Toyota Motor Corporation, 2013. Toyota. [Online] Available at http://www.toyota global.com/company/vision_philosophy/toyota_production_system/just-in-time.html [Accessed 04 July 2013].
