Balancing an Assembly Line as part of Strategic Goals

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Welcome to our 'Lean in Action' series, where we bring you real stories from the field about the transformative power of value stream mapping (VSM). While we’ve taken care to keep identities confidential, the insights, successes, and lessons shared here are authentic accounts from lean experts and industry professionals across various sectors.?

Massimo Zucchelli

Increasing the Productivity of an Assembly Linen

Hoshin Kanri's "cascade" is the process of breaking down big strategic goals into smaller, clear objectives that are passed down through all levels of the organization. This means that every department, team, and individual knows their role in achieving the company's goals and aligns their efforts with the overall strategy.

As a cascade from the strategic objectives of a production facility, a tactical project was launched, with the goal of increasing the productivity of an assembly line. The specific focus was on reducing all sources of inefficiency, losses, and waste. The performance of the line showed efficiency KPI significantly below the benchmark of other plants within the group and lower than the performance of other lines in the same facility.

The assembly line was composed by 16 workstations where 7 versions of industrial machines were assembled, each with a high level of customization in terms of optional features. This complexity resulted in highly variable workloads (MURA), depending on the configurations chosen by customers.

Identifying causes of inefficiency in an assembly line

To achieve the goal of benchmark efficiency levels, an analysis was conducted to identify the causes of inefficiency (MURI, MURA, MUDA). The first step was to quantify how many of the total hours spent on the line over a defined period were actually used for product assembly - the overall cycle time spent to produce the mix of products planned in that period. This cycle time, however, still included non-optimized activities and wastes as per lean thinking; operator movements, for example, were still part of the cycle. It was found that cycle time was approximately only 50% of the total measured hours, leading a focus on identifying the causes of the remaining 50% of hours not used for product assembly.

The analysis included mapping operator activities through work sampling, data collection on tasks performed, and assessing whether the workload was evenly distributed across the different phases.?

This process led to the identification of the distribution of inefficiency (MUDA) as follows:

• 25% due to operator waiting caused by line unbalancing.
• 20% attributed to unplanned cycle losses (wastes), such as movement and transport to get non-standardized information, or materials not available at the workstation;
• 15% due to assembly errors that require rework;
• 12% related to aesthetic touch-ups on visible components;
• 12% due to end-of-line completion for missing parts.

The unbalancing of the line was mainly due to the variability in the workload (MURA), creating peaks that varied from phase to phase, shifting the bottleneck position along the line and resulting in waiting waste (MUDA). Additionally, some stations had to be large enough to accommodate all necessary components, leading to waste in operator movement (MUDA).

Kaizen workshop and quick wins

As a first step, a specific kaizen workshop was scheduled, involving the operational departments, to identify wastes through working sampling, map operator movements through spaghetti diagramming, and implement quick improvement actions (quick wins). The kaizen activities at the workstations recovered approximately 11% of the initial inefficiencies.

The cycle and product analysis, integrated with the planned countermeasures and insights from the kaizen wokshops, led to a redesign of the assembly line concept, layout, and workbenches. The variability in workload was concentrated at the beginning and end of the line, dividing it into three zones:

1. First zone: dedicated to variability due to design and customer-selected configurations. The tracking assembly concept was adopted in this area, where an operator assembled the same product through all stations in the section, creating a semi-finished product that feeds an intermediate buffer. The number of operators in this zone is calculated based on the required capacity and the mix of customer-requested configurations.
2. Second zone: consisting of operations with standardized work content across different models, enabling operations balancing. The number of phases was chosen to allow flexible capacity modulation, enabling operators to be assigned flexibly, according to the takt time needed (e.g., 12 phases allowing configurations with 12, 8, 6, or 4 operators).
3. Third zone: conceptually similar to the first zone. In this area, the semi-finished product from the buffer at the end of the second section is completed based on the customer configuration.

This new configuration eliminated almost all unbalance and improved work standardization in the second zone, reducing assembly errors. Additionally, a more compact layout, with less material variability in the second section, reduced motion and transport waste (MUDA).

As a result, the line redesign eliminated 18% of the initial losses, with an additional 4% improvement due to reduced human errors. The redesigned line, with the described concept, allowed for a zero-time setup change, adapting flexibly to customer demand.

Other inefficiency clusters were addressed with focused workshops and dedicated lean tools, allowing the team to meet and exceed the defined productivity targets.

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