D. Clay Whybark

The Impact of Environmental Technologies on Manufacturing Performance

Management of the natural environment is becoming an increasingly important issue to manufacturing firms, yet their managers are also challenged to implement changes that improve competitiveness. T...

Lot-sizing under uncertainty in a rolling schedule environment

SUMMARY This paper presents results from a simulation experiment evaluating 14 different single stage lot-sizing procedures. Uncertainty in the form of forecast errors was used as one factor in the experiment. In order to prevent different service levels from confounding cost comparisons, enough safety stock to achieve a 100% service level in all situations was introduced. The ranking of the rules under uncertainty turned out to be very different from the ranking when no demand uncertainty was present. Statistical differences were found between the six best lot-sizing procedures when there was no uncertainty. When forecast errors were present, however, no differences existed for the six best rules in this situation. Thus, uncertainty not only changed the relationship between the lot-sizing rules, but also the character of this relationship.

Barriers to the management of international operations

Abstract The purpose of this research was to define and rank key barriers to the effective management of international manufacturing operations. An international panel of experts, composed of practitioners, academics and consultants, was surveyed using a Delphi process to identify the key barriers, to explain the rationale for their selection and to rank them. The highest ranked barrier was general lack of a global view by management. Among the other highly ranked barriers were contemporary managerial issues like manufacturing strategy and managing international factory networks. Some traditional technical concerns like cultural and language differences and managing global logistics were also highly ranked. The responses clustered into two groups with the largest group focusing more heavily on contemporary manufacturing concerns while the other group emphasized more traditional technical topics. The results help establish priorities for developing research agendas, orienting teaching programs and focusing company resources.

GMRG survey research in operations management

The Global Manufacturing Research Group (GMRG) is an informal group of researchers conducting operations management research throughout the world. Describes aspects of their survey research on manufacturing practices. Presents the background of the project, a bit about the group itself, and specifics on getting involved in the group. Presents the principles which guided the first and second rounds of the GMRG global survey and the theory underlying their survey instrument and its revision. Finally, provides several details of the research methodology and some of the research findings.

Material requirements planning (MRP) and purchase discounts

Abstract This paper reports the results of a simulation experiment that compares alternative procedures for determining purchase quantities in MRP systems when quantity discounts are available. The procedures are least unit cost (LUC), McLarens order moment (MOM) and a “traditional” procedure that ignores the time-phased information available from an MRP system. One of the factors in the experiment was requirement uncertainty, a factor heretofore not incorporated in MRP lot-sizing research. The results of the experiment confirm MOM (and to a lesser extent LUC) as an effective lot-sizing procedure. In addition, the work shows that the differences between the procedures tend to vanish as the amount of uncertainty in the requirements increases.

Searching for the sandcone in the GMRG data

Over the last few years, several international studies have independently shown a significant correlation between the number and intensity of manufacturing practices in use and the performance of a firm. The conclusion is an unsettling: “the more the better.” This paper uses the Global Manufacturing Research Group’s (GMRG) second round database to deepen our understanding of this relationship. The shape of a scatterplot of practices versus performance resembles the shape of an American or rugby football and is often called the “performance football”. The performance football seems to be a general phenomenon so, as practices are added, a firm should garner earlier performance improvements if it followed the upper edge of the performance envelope. This is consistent with the “sandcone” model or sequential capability building model that suggests that a firm should first invest in quality practices and then add others over this base. We first demonstrate the relationship between practices and performance holds for the GMRG data and then we make detailed comparisons of the firms along the upper and lower edges of the football. The comparisons provide some evidence that there is a sandcone effect.

GLOBAL RELATIONS BETWEEN INVENTORY, MANUFACTURING LEAD TIME AND DELIVERY DATE PROMISES

Abstract This paper reports a study of the inventory, lead time and delivery promise data from the Global Manufacturing Research Group. It finds that manufacturing lead time increases as work-in-process inventory increases, as theory suggests. Also, many companies promise delivery in less time than it takes to produce the product and the difference is not explained by finished goods inventory. The research also shows that the chief benefit of JIT, for those few firms that are achieving benefits, seems to be reduced raw materials.

American and European manufacturing practices: An analytical framework and comparisons

This paper presents a general analytical framework for making bilateral comparisons of manufacturing practices. The approach suggests a grouping of the data, defines a conservative test called a pure regional effect, and matches the data types to the appropriate statistical tests. The methodology is used to compare manufacturing practices in North America with those in Western Europe using data compiled by the Global Manufacturing Research Group. The broad hypothesis tested is that the two regions are more similar than different. For the two industries studied (small machine tools and nonfashion textiles), this hypothesis holds. Fewer than 10% of the 119 variables investigated have a significant pure regional effect. This suggests that the lack of success of joint ventures between North American and European firms must be attributed to factors other than differences in manufacturing practices. These variables for which significant effects were found reflect differences in external orientation, asset utilization and the management of details. Despite the overall similarities, differences in these factors could be important for American Managers contemplating partnerships with European companies.

Material requirements planning in hierarchical production planning systems

Abstract Material requirements planning (MRP) is a way to develop the time phased material and other resource requirements to satisfy the needs of a master production schedule. Hierarchical production planning (HPP) is a framework for analysis and decision making in complex production environments. They are complementary approaches to the decision support system needs of multi-stage production systems. The hierarchical approach provides for efficient management review of proposed plans at corporate, plant, and shop levels while MRP provides a sound and detailed basis for understanding the implications of proposed plans and for executing the selected plan. The relationships between these two approaches are illustrated with an example application.

Inventory and capacity trade-offs in a manufacturing cell

This paper describes an investigation into the trade-off between capacity, inventory and variance reduction techniques for buffering against uncertainty and model mix fluctuations in a manufacturing cell. The cell is patterned after one that produces engine blocks which feed directly on to the assembly line at a plant manufacturing large diesel engines. A simulation model is used to evaluate the effect of different buffering techniques on capacity utilization, throughput time and output rate. Two production control systems are used in the cell, one based on a pull approach, the other on a push approach. The results show that variance reduction and capacity increases are serious alternatives to using inventory for buffering in either system.