Eliminating waste in medical box-build production.

Contract manufacturers typically have to find middle ground in the use of Lean manufacturing principles. Unless a customer is completely committed to a holistic Lean environment, there will also be some level of waste (muda) in the process attributable to customer-related constraints. That said, use of Lean principles to minimize the seven wastes can help mitigate defects and lower costs that would otherwise occur as a result of inefficiency.

These seven wastes are defined as:


  1. Waste of Overproducing (no immediate need for product being produced).
  2. Waste of Waiting (idle time between operations).
  3. Waste of Transport (product moving more than necessary).
  4. Waste of Processing (doing more than what has been agreed upon).
  5. Waste of Inventory (excess above what was required).
  6. Waste of Motion (any motion not necessary outside of production).
  7. Waste of Defects (producing defects requiring rework).

Focus on minimizing the seven wastes aligns well with the 5S Plus discipline, which includes:

  • Seiri (sort) focuses on sorting and cleaning up by defining which tools and materials are needed at the job site and throwing away anything that is not needed.
  • Seiton (set in order) focuses on straightening and arranging necessary information, tools and materials in the correct order for their designated areas.
  • Seison (shine) recognizes that problems and inefficiencies are more visible when everything is neat and clean.
  • Seiketsu (standardize) focuses on establishing a discipline of cleaning tools, equipment and the job immediately after use.
  • Shitsuke (sustain) is the most important discipline because employees must continue to maintain the 5S discipline continuously.

The sixth S in the 5S Plus process is normally Safety and Environmental Health. While technically much of this is incorporated in Shitsuke, which mandates following all company rules and regulations, it helps put greater emphasis on worker safety and environmental responsibility.

SigmaTron applies these Lean principles in its medical box-build areas to eliminate non-value-added activity and reduce defect opportunities. Operational synergy is also evaluated to achieve better economies-of-scale.

In one project involving a patient assistance device, an ergonomic work cell has been designed that handles ongoing production and repair and upgrade operations. That minimizes raw material inventory requirements and capital equipment requirements, since the programming and test equipment supports both types of production activities. It also minimizes the transport that would occur if manufacturing and repair operations were handled in separate work areas. Finally, it also helps mitigate defects, since a core group of trained production operators and technicians familiar with the entire production process support the entire project.

Printed circuit board assembly (PCBA) has three separate models. The SMT area is treated as a supplier that ships to a Kanban in the stockroom. PCBAs are pulled from the Kanban and kitted as part of the top-level assembly as orders are released. This helps minimize overproduction since the SMT area is able to replenish the Kanban based on pull signals.

The top-level assembly process uses a fixture to minimize process variation and wasted motion in fan assembly, which is the most complex assembly step. Most other operations are simple assembly steps. The work cell structure is a metal frame that is adjustable to facilitate ergonomics. It can be adjusted so operators can sit or stand to perform their tasks based on their personal preference. The ergonomic element provides two benefits. First, from an operator safety standpoint it minimizes the potential of repetitive stress injuries. This aligns well with the facility’s 5S Plus program. Second, it gives production operators more control of their working environment in a way that doesn’t impact the process, enhancing workplace quality of life. The adjustable framing also makes it easy to arrange work surfaces, raw materials and work-in-process in ways that minimize clutter and foreign object damage (FOD) risk, in line with good 5S Plus discipline.

Programming, test and pack are an integrated operation. This ensures serialization integrity. The serial numbers are stored in both an Excel database and SigmaTron’s proprietary Wallaby program. The product is traceable through the serial number, and the customer utilizes this information for warranty verification.
Colocating these operations also minimizes transport, motion, waiting and overprocessing, since the operation is performed as products complete assembly in the same work cell. Colocation also eliminates potential mix-ups that can occur when products are tested and packed in separate areas of the production floor.

The work cell also handles repair and upgrade operations. In some cases, units are returned in bulk shipments from the customer for a retest and software upgrade. In other cases, units are returned from the field for warranty repair, which involves troubleshooting and repair. Repaired or upgraded units have their existing serial number annotated in the database, and a new serial number (traceable to the original) is issued.

Several operators in the work cell are cross-trained on similar projects, enabling them to shift to other work cells if demand drops. This flexibility also adds to worker quality of life and job focus by adding some variety to production activities.

The result of incorporating Lean manufacturing philosophy and 5S Plus disciplines into this type of production is a scalable work area with minimal defect opportunities. Worker quality of life is improved; resources are more efficiently utilized, and non-value-added cost is reduced.

Sonny Krishna is manufacturing manager at SigmaTron International’s Union City, CA, facility (;

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