Re-Engineering Casting Production Systems.
Foundries must reduce their costs. With today's global competition and the year-after-year customer requests for reduced casting prices, foundries are required to drive every possible penny out of production so they can compete on the open market for jobs.
But from which area of the foundry is that savings generated? Does your foundry look for reduced cost options for raw materials? Do you look to streamline production in melting, molding and coremaking? Do you look to human resources to determine if manpower can be trimmed? Although each of these areas probably has provided some relief and reduced costs in the past, often foundries have removed every excess penny from these operations except for an upgrade in technology and automation.
One area of the foundry that often is neglected in pursuit of cost savings is the post-casting production area--from shakeout to shipping. For traditional job shops, this area requires the greatest amount of manual labor and, as a result, the highest manhours/ton. In addition, this area of the foundry often also exhibits the highest non-value-added work performed on castings such as rework, cleaning and finishing, inspection and material handling from station to station.
In a Steel Founders' Society of America and Cast Metals Coalition study, 21 steel foundries' post-casting production systems were examined (133 weeks of total system performance). This article takes a look at the results from that examination and discusses the success that can achieved by developing a flowpath of an operation for analysis.
Two of the greatest problems facing foundries in post-shakeout production are work-in-progress and lead times.
Foundries maintain too much work-in-progress, which results in problems with:
* Material Handling--Castings typically don't follow a smooth flow through a plant. A direct result of the increased material handling is increased casting inventory;
* Space Requirements--All work-in-progress eats up valuable floor space;
* Tied Up Capital--Every casting sitting on the floor represents idle money;
* Hidden Quality Problems--If a casting isn't finished and inspected until three weeks after production, then it is difficult to tie quality issues back to their source, whether they are molding-, pouring-or coremaking-related. One of the problems associated with lead time is the frequent expediting of orders to appease customers. The sales force is often responsible for expedited casting orders in which one customer's lot will take precedence over all other work-in-progress. In a survey conducted as part of this project, an average of 18% of casting orders reportedly were expedited. Expediting results in castings being shuffled around post-shakeout production to appease one customer. These expediting problems occur because customers need castings sooner, they ordered too late to fit into normal production, original casting orders had quality problems and a reorder is necessary, tool/design changes, equipment breakdowns and/or foundry personnel shortages.
Although customer satisfaction is critical, foundries must produce castings using the most efficient method possible. Expedited orders destroy the efficiency of an operation and force the expediting of other future casting orders that were pushed aside. From the survey conducted, the average time it took a casting to travel from shakeout to shipping is depicted in Fig. 1.
Reduction of material handling and the unnecessary movement of castings must be the focus of the future. Figure 2 shows that a large percentage of casting value is consumed by material handling costs at the foundries studied. The values expressed in this chart are conservative as it assumes that material-handling equipment (forklifts, cranes, etc.) is in use 100% of the time. A constant value of $1.30/lb also was assumed for this figure. Each point on the graph represents the material handling costs associated with a particular flowpath and the average weight for the castings represented by the flowpath.
For foundries to prepare for this future, they must first understand the true production flow of their castings.
One of the first steps a foundry should take to determine its production flow is to develop a flowpath. This process details the life of a casting by describing what happens to it every moment from coremaking to shipping. This includes:
Process Steps--This is any step in which some operation is performed that creates or changes an object. For example, making a mold and grinding a casting are processes since they create and change something, respectively. On the other hand, casting cooling is not a process because no operation is required to enact the change the casting is undergoing. Also, inspecting or changing the location of an object is not a process step since the object itself remains unaffected.
Inspection--This is the evaluation of casting quality and includes steps such as visual inspection, hardness testing and magnetic particle inspection.
Material Handling--This denotes an operation that moves a casting from one location to another. The greatest contribution of flowpath design may be to quantify the details of each of these movements. For each material-handling step, the mode of transportation (fork truck, conveyor, etc.), the horizontal distance and the time taken by the move should be included. For manual moves, the vertical distance also should be recorded. Material handling accounts for 80% of the steps in most of the flowpaths.
Queues--This refers to castings that are waiting according to the following criteria:
* castings must wait for an extended amount of time (more than 24 hr) for a process;
* a significant amount of work-in-progress inventory is accumulated in a particular area;
* castings enter a buffer zone between operations from which castings typically are not selected according to the first in, first out rule.
For example, if a batch of castings typically must wait for several hours before heat treatment, then a queue exists. If waiting time for castings is short, but there are a dozen bins of castings waiting in front of an area to be processed, then there is a queue by criteria two. Even if the waiting time is short and the work in process is small, if castings enter a waiting area where processing order is not a function of order of arrival, then a queue exists according to the third criteria.
Flowpaths serve several purposes for foundries. First, they are a valuable way to better understand the production process at a foundry. While most foundries are aware of their process steps (often from process plans), flowpaths fill in the details between these processes. These details, which often are overlooked, are the majority of the total steps. By seeing the sequence of steps on paper, foundries can easily identify areas for improvement.
Flowpaths facilitate analysis of material handling and queues and can be used to identify unusually time-consuming or expensive movements. While these movements are often a consequence of a foundry's layout (and thus not easily subject to change), they also can point out opportunities for reducing material-handling expenses with minimal effort such as changing the location of an inspection station or shifting a grinder to do touch-up work.
After shakeout, the sum of all of the process times is generally significantly less than the time it will take that casting to move from shakeout to shipping. What accounts for this difference? Lead time is largely a function of how much time a casting spends sitting in queues. Reducing lead time is nearly equivalent (in most cases) to reducing the size of these queues. Thus, a strong incentive exists for further investigation of each queue identified on the flow chart.
Queues are not necessarily "bad" as they perform several useful functions, They serve as capacity buffers to ensure high utilization of people and equipment. They protect against unforeseen disruptions such as equipment failures. Queues allow certain operations (especially heat treatment) to be performed on large batches of castings, thereby lowering unit costs. A wise approach to queues is not to indiscriminately eliminate or reduce them, but to ask where queues are necessary and how big these queues need to be to fulfill their purpose.
Flowpaths also illustrate when deviations from the firm's process plan for a casting job occurred due to rework, an attempt to keep employees busy, equipment breakdowns or supervisor preferences. These deviations are what add unnecessary complexity to the production system and increase work-in-progress, lead time and material handling.
Beyond the story told by the sequence of steps, the flowpaths are valuable because they assist in quantifying the costs of material handling for different types of castings. They also provide answers to relevant questions: How far does a casting travel? How many times is it moved by overhead cranes? How much personnel time is required to move a large casting from shakeout to shipping? While aggregate measures of material handling expenses are readily available (number of employees engaged in material handling activity, annual maintenance expense for overhead cranes, etc.), the flowpaths have the added benefit of isolating costs for different types of castings and showing which moves are relatively expensive.
Due to the jobbing nature of most foundries, flowpath development may seem difficult due to the fact that every casting job is unique. However, during the study, only 2 to 8 flowpaths per foundry were required to account for 90% of the casting jobs performed by the foundries.
The reason behind this minimal figure is that even though casting shape and processing may be unique to each job, the majority of the steps in a flowpath are identical. Development of the flowpaths will help foundries to begin to think of their operations as efficient, continuous flow of similar products, rather than individual jobs that are unique.
Based on the analysis of the 21 foundries, several general recommendations beyond the development of flowpaths can be made for re-engineering the casting production system.
* Material handling costs can be reduced by moving people to castings rather than moving castings to people. This is especially relevant for inspections.
* Castings must be sorted at least once after pouring (often at shakeout). Additional sorting operations increase material-handling costs unnecessarily.
* Besides increasing lead times, rework substantially adds to material handling distance and cost. It must be tracked. The impact of rework justifies making an effort to reduce it. For the success of such efforts to be measurable, a system must exist for quantifying rework.
* Queues serve a valuable purpose as buffers and they help to ensure high utilization of key equipment and personnel. On the other hand, the majority of time between shakeout and shipping is spent in queues for most castings. Reducing lead time and work-in-progress requires working to reduce queue size by analyzing where strategic buffers are needed and how large these buffers should be. The size of the queue should only be large enough to keep key personnel and equipment busy most of the time.
* The survey of steel foundries revealed that many companies were planning to construct new buildings. At many of the companies, space within the existing foundries was "found" by eliminating unnecessary queues. In addition, layouts that are developed to reduce material handling also reduce the amount of floor space required.
* Since material handling may consume 10% or more of casting value, it requires personnel responsible for reducing it. The detailed flow paths have proven to be invaluable in identifying improvement areas.
This project was funded by the US Department of Energy (DOE) award No. DE-FC07-981D13614. However, any opinion, findings, conclusion or recommendations expressed herein are those of the authors and do not necessarily reflect the views of the DOE.
This article was adapted from presentations given at the AFS Wisconsin Regional Conference and the AFS Casting Congress.
Doing What Is Best
During the study, one foundry was purchasing a new blast cleaner for its finishing area. The floor supervisor, plant engineer and manufacturing engineer were asked where it should be located in the foundry. The responses were:
* Floor Supervisor: "I'll use it wherever they put it."
* Plant Engineer: "Put it where the old one was."
* Manufacturing Engineer: "Place it in the ideal location."
The decision was made to place it in a new location that was geographically near the steps in the flowpath. The result was a location only 200 ft away from where the old blast center was located. However, eliminating a back and forth trip by the forklift (200 ft each away) multiplied by 20,000 castings/yr saved 1500 miles/yr of driving for the forklift.
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|Title Annotation:||Steel foundries' post-casting production systems surveu|
|Comment:||Re-Engineering Casting Production Systems.(Steel foundries' post-casting production systems surveu)|
|Author:||Voorhis, Tim Van|
|Date:||Jul 1, 2001|
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