Abstract—This paper presents a work undertaken in a metal structures production system in a company producing several assorted products for the civil construction. The work aim was to improve the production process, solving several productive problems encountered in the production system, such as: deliveries delays, long lead times, too many material handling, high stocks, errors and defects in metal structures assembly and production, and unnecessary motions. The identified problems were analyzed and improvement actions were scheduled and subsequently implemented. These improvement actions were based on Lean production organizational model and some Lean tools. The 5S methodology was implemented in the workplace as well as mistake proofing mechanism, standardized procedures, production activity control system and layout reconfiguration. These actions led to a reduction of the lead time, work in progress, transports, delivery delays, defects and errors in assembly and production. Index Terms— Lean production, Kaizen, 5S, VSM. I. INTRODUCTION EAN production is a well established organizational model implemented in companies through all the world. Since the publication of the “Machine that changed the world” [1], “Lean” is the word that had been used to refer Toyota Production System (TPS) [2]. This word was used by a MIT researcher [3] because TPS was “doing more with less”: less human effort, less space, less inventories, less investment in new tools. This was achieved through tools and principles: Just-In-Time (JIT), autonomation, flexible work force and creative thinking [2]. Later, these were renewed in Lean Thinking principles: i) create value for the customer; ii) map the value stream; iii) create flow; iv) pull the production and v) pursuit perfection [4]. This last principle has to do with waste (muda, in Japanese) continuous search and continuous improvement (kaizen, in Japanese) [5]. TPS considered seven “deadly” kind of wastes: overproduction, unnecessary motion, unnecessary transport and handling, defects, inventories, waiting, over- processing [6]. Eliminating such wastes and putting in action the principles referred require diverse tools like Value Stream Mapping (VSM) [7]; 5S [2]; pull system [2]; standardized operating procedures (SOP) [8], [9], mistake R. Carvalho is with the Novo Modelo Europa, S. A. company (e-mail: rogeriorc08@gmail.com ). A. C. Alves is with the University of Minho, EE-DPS, Campus of Azurém, 4800-058 Guimarães, Portugal (phone: +351-253510766; fax: +351-253510343; e-mail: anabela@dps.uminho.pt ). I. Lopes is with the University of Minho, EE-DPS, Campus of Gualtar, 4710-057 Braga, Portugal (phone: +351-253604762; fax: +351-253604761; e-mail: ilopes@dps.uminho.pt ). proofing or poka-yoke mechanisms [2], to mention only a few. The work objective was to improve production processes in a metal structures production system, through identifying wastes and, applying Lean principles, tools and techniques, to reduce/eliminate these. Basic tools like ABC analysis, cause and effect diagrams, process flow diagrams, sequence diagrams and other, and more recent tools like Value Stream Mapping (VSM), were used to diagnose the production system. Kaizen, mistake proofing mechanism, 5S, Constant work in process (CONWIP) production activity control system [10], standardized operating procedures were implemented to solve the encountered problems and eliminate waste. Some performance measures were improved. The work described in this paper was developed in a context of an Industrial Management and Engineering (IME) master thesis final project. The methodology used by the researcher was the Action Research [11] where he participated actively in the company action, collaborating with all intervenient in action. This methodology involves a five phase’s cyclical process: 1) diagnosing; 2) action planning; 3) taking action; 4) evaluating and, 5) specifying learning. Other projects with these purposes had been developing using the same methodology [12], [13], [14]. This paper is organized in six sections. This first section introduces the objectives, reviews the main concepts about Lean production and presents the research methodology and paper organization. The second section describes the production system current situation and diagnoses this focusing one product: the metal frames. The actions planned for the improvement and its implementation were discussed in the third and fourth section. The fifth section evaluates and presents the results, and, finally the sixth and last section presents some conclusions. II. DIAGNOSTIC PHASE A. Product identification The production system target by this study produces on demand several types of product for the civil construction, such as: footbridges, spatial trusses, stairs, gutters, gates, grids and frames. The production system is organized into five sections: cutting, welding, drilling, bending and deburring. The materials or semi-finished products flow between sections depends on the product that is manufactured. Therefore, a product has been selected using the ABC analysis, based on invoicing for each product of the production system (see fig.1). Principles and Practices of Lean Production applied in a Metal Structures Production System R. Carvalho, A. Alves, and I. Lopes L Proceedings of the World Congress on Engineering 2011 Vol I WCE 2011, July 6 - 8, 2011, London, U.K. ISBN: 978-988-18210-6-5 ISSN: 2078-0958 (Print); ISSN: 2078-0966 (Online) WCE 2011