Jose Luis Garcia

Even a high-volume shop can benefit from these process control steps.

A holistic approach to implementing Lean manufacturing philosophy in high-mix, low-to-medium volume production environments has significant benefits on efficiency. However, it also can have substantial efficiency and quality benefits in high-volume production environments that must also support production of spare parts.

Many customers in SigmaTron’s facility in Chihuahua, Mexico, require production of spares for up to 15 years after a product has ceased production. In a typical high-volume production facility, this cut-in of legacy product can create both opportunities for defects and inefficiency. The facility’s holistic approach to implementation of Lean Manufacturing principles, however, has made it easy to cut in small production lots of spares as needed. Some of the key elements driving efficiency in this area are as follows:

Computer-integrated manufacturing. One area where defect opportunities and the potential for inefficiencies exist is line changeover. This can be particularly problematic when legacy product is involved, since there may be less familiarity with products built infrequently. Legacy products also can create documentation control issues, particularly if there are multiple paper copies of the documentation.

The Chihuahua facility started its focus on improvements in line changeover by migrating from paper visual aids to electronic work instructions displayed on monitors at each workstation. This not only enabled fast line changeovers, it also ensured documentation integrity and gave production operators a higher quality visual aid. Additionally, should the headcount of a manual assembly line change, due to an increase or reduction in demand, the electronic work instructions automatically adjust the number of parts assembled by each operator. Today, that system has grown into an internal manufacturing execution system (MES) that links with capabilities already in Agile. Product is barcoded and tracked through each operation. Real-time production status monitors display data in each work area, so production personnel are aware of actual production vs. targeted goals. This system can also switch programs in SMT and on some test equipment. This speeds changeover, plus ensures the correct set of process steps is performed on each work order. It also provides the level of traceability needed to quickly analyze root cause and implement corrective action should a product failure be detected.

Additionally, SigmaTron utilizes an industry-standard ERP system enhanced by an internally developed suite of software tools, which facilitate goods inventory and supply chain management. Via the proprietary iScore system, the team in Chihuahua has visibility into forecasted demand, actual demand, inventory in the facility and inventory on order. Auto-replenishment tools supported by an MRP share system take “touches” out of this process.

Flexible production equipment. The facility has taken a slightly different approach to integrating Lean principles into its SMT production area than is typically found in a high-mix, low-to-medium volume operation. A newer SMT production line is reserved for low-volume product cut-ins, because the line’s production carts can be loaded with feeders capable of supporting multiple production lots, and the line’s software determines which feeders are used for a given production lot. Offline setup further optimizes line changeover time when carts must be changed out.

Cross-trained workforce. The Chihuahua team has long been focused on enhancing the productivity of each production operator. Production operators are cross-trained in multiple processes to allow shifts among lines to responsively support variations in demand.

Strong end-of-line controls. Lean philosophy also influences end of the line activities. The shop floor control system provides a strong check and balance in this area, because a barcode scan at each operation step determines whether all necessary prior steps have been completed. This added check-and-balance is particularly beneficial with legacy products, since many are built infrequently.

Programming is not integrated with test because, in most cases, it can be done faster as a separate operation than when integrated with a test program. Test is integrated with packing, and the shipping label printed after a barcode scan verifies the unit has passed test, plus completed all prior steps. This level of final inspection and correct product labeling verification is particularly important in spares production, as the units are typically stocked and sold standalone. In that situation, if mistakes are made, the first person to notice the issue is an end-customer trying to get a non-working product repaired.

Kanban utilization. The facility uses kanbans both in production and in finished goods. The shop floor control system uses a graphical illustration of bins to share production schedules, making it easy for all production personnel to understand production status and requirements.

Finished goods kanbans are held at a warehouse in Texas to eliminate added lead-time or costs associated with border crossing. Bins have been sized to customer requirements and are replenished as inventory is pulled.  

The metrics underscore the benefits of Lean manufacturing. The team has not had a shipment rejected by a customer in over seven years.

The team’s holistic approach to Lean manufacturing minimizes the potential for variation from required processes for each product type by automating configuration management. Flexible equipment, a cross-trained workforce and strong systems minimize the non-valued activity that might normally be caused by the cut-in of legacy product. Utilization of kanbans facilitates a pull system that minimizes overproduction and/or the need for reactive expediting.

Jose Luis Garcia is plant manager at SigmaTron International’s ( Chihuahua, Mexico facility;

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