Robert R. Inman

Designing production systems for quality: Research opportunities from an automotive industry perspective

We explore the intersection of two research areas: quality and production system design. Conventional wisdom holds that a products quality is affected much more by its design than its production. Nevertheless, we argue that the production system used to manufacture a product does indeed affect its quality. We briefly review the limited literature on the intersection of quality and production system design and suggest several new research issues that are important to industry.

Chained cross-training of workers for robust performance

Training workers to perform multiple tasks can improve workforce agility for dealing with variations in workload. However, cross-training can be costly, time consuming to implement, is limited by worker learning capacity, and can lead to ambiguity about work responsibilities. Therefore, it is important to implement cross-training in the most efficient way and especially, due to the training time required, in a way that is robust to system changes. We use queueing and simulation analysis to investigate cross-training in the context of maintenance in a manufacturing plant. The tasks are independent and can be represented as a set of parallel queues that are served by dedicated and cross-trained workers. We propose a cross-training strategy called chaining, in which a few workers are strategically cross-trained, and show that it yields most of the benefits of cross-training all workers, with much less effort. Most importantly, we demonstrate that cross-training workers to form a “complete chain” is extremely robust in the following ways: (i) it is insensitive to the variety of ways a complete chain can be formed; (ii) it performs well even if there are major changes to or uncertainty in system parameters (such as mean task arrival rates); and (iii) performance is insensitive to control decisions that, without complete chaining, can significantly harm performance.

Chained cross-training of assembly line workers

To function properly, assembly lines require the presence of every worker. When a worker is absent, management must scramble quickly to find a replacement. Cross-training workers to perform multiple tasks mitigates this difficulty. However, since cross-training is costly and limited by learning capacity and can confound the search for quality problems, it should be used judiciously. The present paper proposes a training strategy called chaining in which workers are trained to perform a second task, and the assignments of task types to workers are linked in a chain. It is shown that chaining is a practical and effective strategy for prioritizing cross-training to compensate for absenteeism on assembly lines.

Survey of recent advances on the interface between production system design and quality

Product designs impact on quality is widely recognized. Less well recognized is the impact of production system design on quality. As quality can be improved by integrating it with the design of the product, so it can be improved by integrating quality with the design of the production system. This article provides evidence of the production systems influence on quality and surveys recent advances on the interface between quality and production system design including the design of the production systems quality control process. After mapping the literature, we identify opportunities for future research.

ASRS sizing for recreating automotive assembly sequences

Since a mixed model assembly lines efficiency depends on the sequence of jobs moving down the line, manufacturers spend considerable effort optimizing the sequence of jobs entering the plant. In automotive assembly plants however, repair loops and parallel stations scramble the sequence before it reaches the final assembly stage. Many automotive assembly plants use an automatic storage and retrieval system to revamp the scrambled sequence before final assembly. One plant even goes so far as to reconstruct the original sequence by completely undoing the sequence scrambling. We derive a relationship between the sequence scrambling information, the variety of model-colour configurations, and the size of the automatic storage and retrieval system needed to reconstruct the initial sequence. We enunciate this new ASRS sizing problem actually facing industry, show how to model it, present a solution approach, and demonstrate the approach on actual sequence scrambling data from an automotive assembly plant.

Product complexity and supply chain design

To assemble a product, each and every part is required. Hence, the more parts in the product, the greater the risk of disruption. Compared with retailers or assemblers of simple products, manufacturers of complex products are much more sensitive to supply chain delays. This heightened vulnerability to supply chain disruptions should lead complex product assemblers to design less risky supply chains. Supply chain design should depend on the complexity of the product assembled or manufactured. This paper models how product complexity drives the likelihood of disruption for given component supply chain reliabilities. The paper provides insights for supply chain design that comprehends the impact of product complexity.

Cross-training hospital nurses to reduce staffing costs.

Abstract: There are advantages and disadvantages of cross-training hospital nurses. The financial benefit of reducing reliance on supplemental agency staff can be quantified. Cross-training policies can be compared. Simulation shows that the strategic cross-training principle of chaining performs particularly well. Practical formulas (that can be solved in a spreadsheet) are provided for quickly evaluating the economic performance of staffing and cross-training scenarios.

Algorithm for agile assembling-to-order in the automotive industry

Traditional automotive assembly initiates the assembly of a vehicle based on a specific order and keeps that order coupled with the vehicle as it moves through the plant. However, due to parallel stations and rework loops in the plant, the build sequence becomes scrambled by the time it enters final assembly. The sequence that reaches final assembly may not be suited for efficient assembly because it might cause very unlevel material usage and workload. Conventional scheduling optimizes the build sequence before the body shop, attaches an order to a physical vehicle as it enters the body shop, and keeps the order and vehicle coupled throughout the plant. Decoupled assembly allows the plant to change the customer order associated with a particular physical vehicle. An algorithm is presented for scheduling and matching customer orders to vehicles to take advantage of this decoupling and quantify its advantages via simulation.

Quick and dirty sequencing for mixed-model multi-level jit systems

Abstract We extend an intuitive level part usage measure to the multi-level case and provide a practical yet powerful algorithm. The measure assigns an ideal due-date to each unit of each part type of each level and sums the squared deviation between these ideal due-dates and the actual completion times. The algorithm schedules the final products in earliest ideal due-date order. This algorithm entirely ignores the lower levels and is consequently extremely fast. Surprisingly, in addition to being many times faster than other algorithms, this quick and dirty algorithm performs very well with respect to both the new ideal due-date measure and the multi-level goal-chasing measure.

Scheduling duplicate serial stations in transfer lines

Abstract To support the production rate, some transfer line stations with long cycle times must be duplicated. A job is processed in only one of the duplicate stations. If laid out in parallel, this duplication essentially doubles the capacity, but, for practical reasons, these duplicate stations are often laid out in a series. The serial layout has a capacity less than the parallels, and also raises some operational questions. We enunciated and analysed this actual problem of operating duplicate stations in series. We simulated an existing closed-loop transfer-line with duplicate stations in series using the actual failure and repair characteristics of the automated stations, and compared a new heuristic with three simple policies.