High-mix Environment Research Articles

Data-Driven Scheduling Optimization for SMT Lines Using SMD Reel Commonality

Optimizing production efficiency in Surface-Mount Technology (SMT) manufacturing is a critical challenge, particularly in high-mix environments where frequent product changeovers can lead to significant downtime. This study presents a scheduling algorithm that minimizes changeover times on SMT lines by leveraging the commonality of Surface-Mount Device (SMD) reel part numbers across product Bills of Materials (BOMs). The algorithm’s capabilities were demonstrated through both simulated datasets and practical validation trials, providing a comprehensive evaluation framework. In the practical implementation, the algorithm successfully aligned predicted and measured changeover times, highlighting its applicability and accuracy in operational settings. The proposed approach integrates heuristic and optimization techniques to identify scheduling strategies that not only minimize reel changes but also support production scalability and operational flexibility. This framework offers a robust solution for optimizing SMT workflows, enhancing productivity, and reducing resource inefficiencies in both greenfield projects and established manufacturing environments.

An experimental investigation of Lean Six Sigma philosophies in a high-mix low-volume manufacturing environment.

This article experimentally examines methods for implementing the philosophies of Lean Six Sigma (LSS) in a High-Mix Low-Volume (HMLV) manufacturing environment. HMLV environments present unique challenges to LSS paradigms because of the need for extraordinary operational flexibility and customer responsiveness. The subject HMLV manufacturer for this experimentation manufactures (among 8500 others) an example component for which 3 machines work independently to perform the necessary operations to manufacture this component. The experiment that is the subject of this research seeks to adapt LSS philosophies to develop treatments to improve the performance of the manufacturing of this component. These LSS-inspired treatments included 1) using cellular manufacturing methods, and the 3 machines as a single work cell to manufacture the component, and 2) using a single multipurpose machine to perform all operations required to manufacture the component. The results of this experiment demonstrate that the cellular manufacturing method was the most effective to reduce costs, to standardize operations at a process level, and to increase throughput. The single machine processing method improved production rates and on-time delivery relative to the baseline, but greatly increased lead time, thereby increasing total cost per part. These results highlight the importance of critically assessing the application of LSS within HMLV environments compared to the Low-Mix High-Volume (LMHV) environments where LSS is traditionally successful. HMLV manufacturers and researchers can use these findings to identify the most effective methods for their specific needs and to design interventions that will improve system-level manufacturing performance in high mix environments.

Manufacturing Variety: Economies of Scope in a Low-Volume, High-Mix Environment

Increasingly, the Holy Grail in manufacturing is the ability to combine the flexibility of customized production with the efficiency of mass production to achieve “mass customization.” Our research has identified an innovative method of customized manufacturing in an unlikely place – contract manufacturers that provide electronic manufacturing services (EMS). We conduct an in-depth case study of two EMS firms in the Pearl Delta Region of China who have created value-added by providing variety in production to their customers through adaptive, or flexible, manufacturing techniques. The firms’ success in these techniques is derived from investment in repeatable and robust routines, rather than from low-cost labor or from high tech equipment. Specifically, by investing in organization and technological routines in three key areas – customer relations, supplier relations, and labor relations – the EMS providers are able to create a production process that is relatively independent of changes in customers and workforce as well as changes in the design, technology, and markets of the products they produce.

Implementation of Nonthreaded Estimation for Run-to-Run Control of High Mix Semiconductor Manufacturing

Semiconductor processing consists of many different unit operations that are combined in a sequence to create the finished product. Many of these unit operations utilize run to run control in order to keep the process within the required manufacturing constraints. Typically, the difference, or bias, between the desired and actual result of processing a particular wafer is affected by not only the particular product being produced, but the prior processing path. Each possible effect is called a context category, and the particular context items relevant for a wafer is called a thread. Because of frequent changes and updates in semiconductor products as well as a large number of product lines, run to run control must deal with a high-mix environment of products, and a large number of threads. Previously, several authors have discussed a method of describing the bias for a particular thread as a sum of context item biases and using a Kalman Filter to estimate these biases. However, two issues with previous implementations have been the observability of the state realization of the bias model, and the computational cost of the Kalman filter. In this paper, we introduce a model formulation that does not require model reduction or the specification of special reference threads, thus easily allowing new threads to be added and old threads removed. In addition, we describe how the problem structure allows the information form of the Kalman filter to be much more computationally efficient. Simulation results illustrate the proposed method.

An Evaluation of the Benefits of Integrating Run-to-Run Control With Scheduling and Dispatching Systems

The benefits of run-to-run control are commonplace and well known: improved process and device performance, increased process tool utilization, improved throughput, reduction of non production (pilot) wafers, etc. Likewise, the benefits of intelligent scheduling and dispatching methods have been shown to reduce cycle time and improve resource utilization. In this paper, we will consider the potential additional benefits that can be obtained through sharing information between a run-to-run control system and a fab dispatch system. Many factors can be taken into consideration when deciding how to dispatch material to process resources-equipment availability, equipment states, time constraints, due dates, bottleneck resources, etc. However, in practice, the decision for lot-to-tool assignment is often based on identifying the highest priority lot and the next available tool. For a process area that has deployed run-to-run control, a number of factors available from the control system can enhance the effectiveness of the dispatch tool. Likewise, the selection of equipment for a given process can affect a controller's efficiency. A controller's state is commonly partitioned by context, such as process tool, product, layer, etc. When this information is used in the dispatch decision, the material can be assigned to a tool with an existing or recently updated partition. The wrong dispatch decision can result in an unnecessary look-ahead run, especially in high-mix environments. This paper will discuss the impact of control-oriented dispatching on factory performance metrics. We describe simulation results where traditional dispatching techniques are compared with a process metrics-based approach, using cycle time and utilization as the key metrics, based on actual production data from a chemical-mechanical planarization process area. We describe a single-resource constrained (process tools only) process and suggest possible enhancements. We illustrate how dispatching can impact batch processes, process cycle time, and controller performance. Practical considerations for integrating these types of systems, such as scalability constraints, will also be discussed.

Optimization of high-mix printed circuit card assembly using genetic algorithms

The purpose of this paper is to present an overview of the factors affecting the cycle time of printed circuit card assembly (PCCA) in high-mix environments and demonstrate a technique for improving machine throughput. We have concentrated our research on optimizing the portion of the PCCA manufacturing process performed by high-speed placement machines (chip shooters). A crucial factor affecting the throughput of a chip shooter is the assignment of components to the feeder slots. Genetic algorithms were employed to find a near optimal assignment of the feeder carriage. Results for various genetic operators in this problem domain are presented.

Analysis of partial setup strategies for solving the operational planning problem in parallel machine electronic assembly systems

In this paper, we analyse the operational planning problem in an electronic assembly system with multiple placement machines operating in parallel. The partial setup strategy is proposed as an effective methodology for this problem. This strategy attempts to determine the balance between processing time and changeover time during system operation. The Tour primary issues are determining the assignment of products to machines, the sequence of products on each machine, the assignment of components to feeder locations for each product, and the component placement sequence for each product. Four solution procedures for unique and partial setup strategies are developed and tested. The computation results show that for low to medium volume high mix environments, the partial setup procedures offer significant improvement over the unique setup strategies. The results also show that no single fixed strategy dominates in all scenarios, and therefore, an adaptable procedure that will choose the best solution for eac...

Progressive Hand Assembly of Circuit Packs in a Small-Lot, High-Mix Environment

Progressive assembly is widely used to hand-assemble components on circuit packs. However, this method is normally used whenever lot sizes are large and the production volume is high enough to justify the effort required to set up the operation. When the manufacturing environment consists of small lot sizes and many circuit pack codes, progressive assembly is usually not the method of choice. It is a manufacturing truism that the benefits of progressive hand assembly do not extend to small-lot production where many code changeovers and setups are required. The prevailing view is that the benefits derived do not exceed the effort required to prepare and update the manufacturing information for each circuit pack type. This paper describes the application of progressive hand assembly to a manufacturing shop that typifies small-lot production and high product variability. It shows that the benefits from a high-volume operation can be achieved in a small-lot operation when component preforming, kitting, and setup issues are appropriately addressed.

A simple, low-risk, approach to JIT

Abstract The movement to just-in-time (JIT) manufacturing philosophies and techniques will be critical to the survival of many manufacturing entities that compete in the world-wide marketplace. Unfortunately, the process of converting to JIT can be a survival-threatening experience in itself, but this need not be the case. This paper will describe several simple, low-risk, and low-cost approaches used at the Lake Stevens Instrument Division (LSID) of Hewlett-Packard to successfully achieve a work-orderless JIT manufacturing environment. In particular, the paper will describe how to gain most of the benefits of JIT in a low-volume, high-mix environment without incurring the complexities and risks associated with a complete post-deduct (backflush) JIT implementation. Three phases of implementation will be described: a pull process with work-orders, a work-orderless pull process with distinct stores and WIP inventories, and a partial implementation of a post-deduct process with online storage of combined sto...