Jit And Lean Manufacturing

The Revolution of Just-In-Time (JIT) and Lean Manufacturing

The essence of the JIT revolution and Lean Manufacturing • Try to reduce the system operational inefficiencies and the resulting waste by identifying the sources of these inefficiencies and working proactively to eliminate them as much as possible. • In the emerging philosophy, inventories should be carefully controlled and they should not function as the mechanism for accommodating the system inefficiencies => Just-In-Time (JIT) • The aforementioned effort should be an ongoing process towards continuous improvement rather than one-time/shot effort.

Targeting the sources of inefficiency – input • unreliable quality of raw material • unreliable delivery times – operation • unreliable processes in terms of – required processing times – process outcome • complex interacting process flows • long set-up times • unreliable (irresponsive and irresponsible) personnel – output • Highly variable production requirements in terms of – production volume, and – production scope

JIT enabling factors and practices •

Emphasis on quality at both the process and the supply side by promoting – Statistical Process Control (SPC) theory and practice – Quality certification programs – Deployment of stable automated processes and foolproof practices (like checklists and machines gauges) to guarantee the desired performance – Employee empowerment and knowledge management (quality circles)

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“Tightening” of the supply chain by promoting – Long-lasting and trustful relationships between the different parties in the supply chain – Timely and reliable information flow across these parties that takes advantage of modern IT technologies, like • Electronic Data Interchange (EDI), and e-commerce practices • Real-time communications and global positioning systems – Promotion of vendor owned and managed inventory practices that • Establish economies of scale and protection to variability through pooling • Enhance the demand visibility across the entire supply chain.

JIT enabling factors and practices (cont.) •

Simplification of the process flows by promoting cellular manufacturing practices – Dedication of separate production cells to product families with similar processing requirements – U-shaped layouts for facilitating employee sharing – Employee cross-training for more flexible and higher utilization

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Set-up time reduction through – The adoption of cellular manufacturing – Externalization of set-up times – Employment of flexible processes and pertinent auxiliary equipment like pertinent fixtures – Part standardization

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Focus on repetitive manufacturing and promote the establishment of stable production rates through – Smoothing of the aggregate production requirements by appropriate quota setting – Pertinent sequencing of the final assembly to support a desired product mix – Use of buffer capacity (planned overtime) to protect against slippages from the target production rates – Component standardization

Institutionalizing the JIT practice through the KANBAN-based Production Authorization Mechanism Station 1

Station 2

Station 3

Remarks: • The KANBANS at each station cap the WIP at that station and they offer a natural mechanism for reacting to various disruptions taking place in the system operation. • In particular, production at each station is “pulled” as a result of the downstream activity rather than “pushed” by an MPS-generated schedule. • The KANBANS at each station should be set at a level that enables production at the target rate • A safe approach to set the KANBAN level at each station is by setting it initially to the “historical” WIP level, and subsequently decrease it incrementally while observing its impact on the production rate • Frequent KANBAN changes are ineffective, since the production rate of the line is rather insensitive to these changes, and they should be avoided

From KANBAN to CONWIP Station 1

Station 2

Station 3

Why? • It maintains the WIP cap but at the same time it offers more operational flexibility than

FGI

KANBAN. • The unrestricted flow of WIP within the line enables better utilization of the (shifting) bottleneck, and therefore, higher throughput. • Less stress for the line operators since it enables them to work at the “natural pace” of the line. • It enables more flexible scheduling of the line, since in the CONWIP operational context, WIP is interpreted more generally as some aggregate amount of workload loaded into the line (even measured in time-units, rather than number of parts) – new parts are pulled from an available “work backlog” according to a pertinent set of dispatching rules. • Easier to analyze and parameterize through the theory of closed-queueing networks. • Remark: While the above features of CONWIP mitigate the rigidity of the KANBAN-based shop-floor control, its “pull” nature still implies that it requires stable target production rates in order to function well, and therefore, it is appropriate for repetitive manufacturing contexts.