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LEAN INVENTORY PRACTICES AND MANUFACTURING CYCLE TIME REDUCTION: ALUMINUM FABRICATION COMPANIES IN IKEJA AND BENIN CITY

CHAPTER ONE

INTRODUCTION

Abstract

Aluminium fabrication companies located in Ikeja, Lagos, and Benin City, Edo exhibit prolonged manufacturing cycle times averaging between 38 and 47 days despite processing identical extrusions and profiles. This inefficiency stems from excessive work-in-progress inventory, reliance on batch-and-queue production methods, and suboptimal facility layouts. The present study examines how lean inventory practices influence cycle time reduction within a sample of 26 fabricators over the period 2021 to 2025. Implementation of lean methodologies including value stream mapping, pull systems, one-piece flow cell arrangements, and visual inventory controls yielded substantial operational improvements. These interventions reduced average cycle times from 42 days to 9.4 days, increased inventory turns from 4.1 to 14.7 rotations annually, and enhanced on-time delivery performance from 61% to 96%. Comparative analysis revealed that companies in Ikeja achieved lean transformation 28% faster than their Benin City counterparts, attributable to superior access to training programs and geographic proximity to aluminium import suppliers. Both geographical clusters nevertheless confront shared operational constraints, notably unreliable electrical power infrastructure and high turnover rates among skilled workers. The research contributes a context-specific Lean Aluminium Fabrication Framework tailored to Nigerian operating conditions, integrating solutions for generator-supported cellular manufacturing and mobile workforce training initiatives. This framework demonstrates potential to reduce industry-wide cycle times by 64% while generating estimated annual throughput gains of N94 billion.

1.1 Background of the Study

Nigeria’s aluminium fabrication sector demonst

rates significant regional disparities in production capacity and operational efficiency. The sector generates an annual output exceeding 847,000 tonnes of fabricated products, including architectural and industrial components. Geographically, Ikeja and Benin City collectively represent nearly three-fifths of national production capacity, though their operational characteristics differ substantially.

Ikeja is characterized by larger enterprises with export-oriented production strategies, benefiting from advanced manufacturing infrastructure such as automated extrusion systems and powder-coating facilities. These firms operate within a more formalized industrial ecosystem, supported by logistical advantages including proximity to major ports and access to specialized technical expertise. In contrast, Benin City’s fabrication landscape is dominated by medium-scale indigenous operations, which primarily serve regional construction markets with less capital-intensive production methods.

Conventional fabrication processes in Nigeria adhere to a functionally segmented workflow, where materials undergo sequential batch processing stages. This approach results in significant inefficiencies, with work-in-progress inventory occupying the majority of production floor space and extending lead times beyond six weeks. Empirical research indicates that non-value-adding activities, particularly those arising from excessive inventory and overproduction, account for the overwhelming majority of cycle time in the sector.

The implementation of lean manufacturing methodologies presents a potential pathway to operational improvement, as evidenced by international case studies demonstrating substantial cycle time reductions. However, contextual challenges such as unreliable power infrastructure, equipment maintenance issues, and informal labor practices necessitate localized adaptation of these principles.

Regional disparities extend beyond production methods, with Ikeja-based operations enjoying distinct advantages in supply chain responsiveness, technical workforce availability, and institutional support for modern management practices. Conversely, fabricators in Benin City face prolonged material procurement delays and comparatively limited exposure to contemporary operational strategies, despite lower fixed operational costs.

1.2 Statement of the Problem

Aluminium fabricators operating in Ikeja and Benin City continue to employ batch-and-queue production methods despite increasing customer expectations for shorter delivery windows of seven to fourteen days. The reliance on excess inventory as a hedge against intermittent power supply, workforce skill gaps, and supplier reliability issues paradoxically generates the same delays it intends to mitigate. This manifests through prolonged setup durations for oversized production batches, undetected quality issues in large work-in-progress inventories, persistent expediting of orders, and continuous reactive problem-solving.

Value-creation activities such as cutting, bending, and welding account for a mere six percent of the total production cycle duration, with the overwhelming majority ninety-four percent consumed by idle periods between processes or during storage. Productive floor area that could accommodate additional machining capacity remains occupied by semi-processed aluminium profiles representing several months’ worth of output. Capital remains immobilized in aluminium inventories that degrade through oxidation and handling damage, even as customers increasingly migrate to competitively priced Chinese alternatives offering three-week delivery guarantees.

Energy supply volatility intensifies these operational inefficiencies. During generator operation periods, production staff prioritize completing large batches before the next interruption, thereby perpetuating overproduction cycles. The absence of effective visual management systems leads to workers spending twenty to forty minutes locating appropriate tooling dies and material profiles, further extending production timelines. These systemic inefficiencies result in consistent failure to meet delivery commitments, elevated rework rates ranging from eleven to eighteen percent, and severely constrained profitability margins of four to seven percent, notwithstanding a twofold increase in aluminium commodity prices since 2022 (Adebayo & Ibrahim, 2024).

1.3 Objectives of the Study

General Objective To evaluate the impact of lean inventory practices on manufacturing cycle time reduction in aluminium fabrication companies located in Ikeja and Benin City.

Specific Objectives

1. To measure current cycle times, inventory levels, and waste profiles across companies operating traditional batch systems versus those implementing lean practices
2. To quantify the contribution of specific lean tools (value stream mapping, pull systems, cellular manufacturing, visual controls, SMED) to cycle time reduction and throughput improvement
3. To identify location-specific enablers and barriers to lean adoption in Ikeja and Benin City and develop a Nigeria-adapted Lean Aluminium Fabrication Framework suitable for power-unstable environments

1.4 Research Questions

1. What is the magnitude of cycle time reduction achievable through systematic application of lean inventory practices in Nigerian aluminium fabrication?
2. Which lean tools deliver the highest impact on lead time and inventory turns in the context of frequent power outages and informal workforce practices?
3. How do infrastructure, training access, and supply proximity explain the observed differences in lean maturity between Ikeja and Benin City fabricators?

1.5 Research Hypotheses

H₀₁: Implementation of lean inventory practices has no significant effect on manufacturing cycle time in aluminium fabrication companies H₀₂: There is no significant relationship between work-in-progress inventory reduction and throughput improvement under lean systems H₀₃: No significant difference exists in lean transformation outcomes between Ikeja and Benin City aluminium fabricators when provided identical tools and training

1.6 Significance of the Study

The research constitutes the inaugural comprehensive longitudinal investigation into lean implementation within Nigeria’s metal fabrication sector, utilizing empirical factory-floor data as opposed to survey methodologies. Anticipated findings demonstrate that the validated framework facilitates a reduction in average cycle time from 42 days to fewer than 10 days. Furthermore, this framework enables the liberation of 70–80% of factory floor space, which can be reallocated to accommodate additional value-adding equipment. Sector-wide projections indicate an annual throughput increase amounting to N94 billion. The resulting blueprint possesses immediate applicability not only within metal fabrication but also extends to steel fabrication, furniture manufacturing, and plastic processing industries.

1.7 Scope and Delimitation

Scope: 26 aluminium fabrication companies in Ikeja and Benin City producing windows, doors, roofing, and partitions Period: January 2021 – June 2025 Focus: Internal manufacturing processes from billet cutting to packing Delimitation: Excludes primary extrusion and anodising plants

1.8 Definition of Key Terms

Lean Inventory Practices: Systematic application of pull production, one-piece flow, visual management, and waste elimination to minimise non-value-adding stock Manufacturing Cycle Time: Total time from release of raw aluminium billet to completion of finished product ready for dispatch Cellular Manufacturing: Physical rearrangement of machines into U-shaped cells enabling one-piece flow

References

Adebayo, R. A., & Ibrahim, M. U. (2024). Power instability and lean implementation in Nigerian metal fabrication. Journal of Manufacturing Technology Management, Advance online publication. https://doi.org/10.1108/JMTM-09-2024-0456

Afolabi, A. A., & Eze, P. (2024). Value stream mapping in African SMEs: Evidence from aluminium fabrication clusters. African Journal of Economic and Management Studies, 15(4), 567–584.

Erdil, N. O., & Erbiyik, H. (2023). Lean transformation in aluminium extrusion and fabrication: A 10-year longitudinal study. International Journal of Lean Six Sigma, 14(5), 890–912.

Ogunleye, T. A., & Adebayo, R. A. (2025). Cellular manufacturing under infrastructure constraints: The Nigerian experience. Production Planning & Control, Advance online publication. https://doi.org/10.1080/09537287.2025.2345671

Okonkwo, I. P., & Musa, A. (2025). Regional disparities in lean adoption: Ikeja vs Benin City industrial clusters. Journal of Operations and Supply Chain Management, 18(2), 123–145.

Singh, B., et al. (2025). Lean practices in emerging market metal fabrication: A systematic review 2020–2025. International Journal of Production Research, 63(8), 2789–2814.