Using Monitoring Systems to Improve Stamping 'Batting Average'
What do baseball players, weather forecasters, and typical stamping plants have in common? Most are less than 60 percent effective.
Unlike baseball players who can continue to make millions of dollars if they can maintain a .300 batting average (only 30 percent effectiveness) and weather forecasters who are considered good if they are right only half of the time, stamping plants must continuously increase their efficiency and effectiveness to survive in today's increasingly competitive global market.
The changes and modifications necessary to improve productivity are unique to each individual stamper, but the first and most important step in every improvement program is to understand and document thoroughly the current production process and the individual factors that affect it.
Without accurate information, stampers may make decisions about which actions to take based on perceptions and subjective or biased measurements rather than actual facts. For this reason, implementing a production monitoring system to continuously monitor production efficiencies and utilizing current technology to increase production capabilities are the first steps toward continuous improvement.
Initially, implementing a simple, manual monitoring system may be the most cost-effective method. Eventually, however, the simplest and most cost-effective way to collect and analyze data is with an automated system that categorizes production uptime and downtime by machine, operator, tool, job, shift, and time period. This resulting information is as vital to running a successful stamping plant as a player's statistics are to a baseball team. It distinguishes profitable "players" from those that need attention or should be "traded."
Automated systems can collect large amounts of data accurately for each production parameter directly from the machine's programmable logic controller or from a separate machine monitor that is directly wired into the press control. This data, along with more specific downtime data input by the operator, is analyzed by the system to determine tooling and equipment uptime, downtime, efficiency, profitability, and overall effectiveness.
Production monitoring can provide so much information that it is easy for an operator to become lost in data minutia. This can be avoided by utilizing the system's customizable reporting feature to determine and focus on the areas that are likely to yield the quickest return, such as job profitability or downtime reduction.
When stampers estimate the cost of stamping a new part, they consider the production speed or the number of parts it can stamp per hour. To calculate this, most companies estimate the running speed in strokes per minute (SPM) and then multiply this number by a plantwide efficiency factor.
Once the part is put into production, most stampers check to see if the estimated running speed is achieved, but few monitor or modify the estimated efficiency factor for that job. Unfortunately, using a plantwide efficiency factor to estimate the cost/profit of an individual job is equivalent to a baseball team using a teamwide batting average to estimate the chances of an individual player getting a hit. Similarly, monitoring only the production speed is equivalent to monitoring how fast a pitcher throws but not tracking his earned run average.
These practices skew the cost/profit information for all jobs and can lead to bad decisions. For example, for a job that is more efficient than average, these methods would calculate a higher cost and lower profit than it actually achieves, and vice versa for a less efficient job. This misinformation prompts companies to underprice less efficient jobs (thus increasing their chances of receiving them) and overprice more efficient jobs, which decreases their chances of receiving this more profitable work.
A production monitoring system can compare the actual production rate to the standard rate.
A production monitoring system can resolve this issue by continuously calculating the efficiency rates of each individual tool, job, machine, operator, and shift and comparing the actual parts produced to the standard rate (see Figure 1).
Once each job's actual profit is known, attention can be focused on increasing the job's efficiency by reducing its unscheduled downtime. The most difficult part of eliminating downtime is identifying the root causes and their resulting costs. An automated monitoring system simplifies this task by collecting information on the downtime for each piece of equipment and providing reports that analyze in detail each specific machine, tool, job, and operator.
For example, the summary report in Figure 2indicates that scrap removal is the greatest single source of downtime. During this 10-month time period, production was stopped 1,947 times for a total of 297 hours. Additional analysis of the detailed downtime logs revealed that more than 60 percent of this downtime was on only two presses. In addition, 95 percent of the scrap removal incidents on these presses took less than 15 minutes, but the remaining 5 percent of the incidents accounted for more than 15 percent of the total scrap removal downtime.
Armed with this information, the company then could increase its overall efficiency by concentrating on improving scrap removal on just two machines and reducing scrap removal time to less than 15 minutes.
A production monitoring system isolates downtime by machine, operator, tool, job, shift, and time period.
Although automated production monitoring can indicate the causes and related costs of downtime based on the data input, unscheduled downtime that occurs as a result of press breakdowns often is not highlighted on automated monitoring systems because companies record these incidents as separate, independent items.
For example, downtime caused by motor, control, lubrication, hydraulic, and mechanical issues all may be tracked separately, when in fact the same preventive and predictive maintenance programs can address them all. In these cases, performing basic trending analysis on the downtime created by these interrelated events can help stampers evaluate the effectiveness of current maintenance programs and help justify the cost of a proposed program.
After a job's profitability has been determined and the current process's downtime has been minimized, the next step is determining if and how the process can be changed significantly to increase production speed. In general, an operation's maximum production speed is based on a single limiting factor. In stamping applications, the most common limiting factors are drawing and forming speeds, part and material movement, and the maximum equipment operating speed. A few methods are available for analyzing each of these factors.
Determining the potential maximum drawing speed has been an area of focus for many decades. Current predictive technologies include virtual tooling programs (see Figure 3), finite element methodology (FEM), and flow analysis. These technologies can determine the maximum running and drawing speeds obtainable for current designs and the speeds potentially obtainable as a result of design changes, including clearance modifications, differing amounts and types of lubricant (see Figure 4), different stroke lengths, and alternate slide motions.
Often either the material handling equipment is the limiting speed factor or the material or part moves at a rate of speed that results in continual quality problems or die jams. Typically the best—or part of the best—available solution is to increase feed and part transfer speeds. However, if erratic material or part movement occurs, speeding up the process will only worsen the situation. In this case, the production speed of the feed or transfer equipment must be increased without decreasing the time available for part and material transfer.
In most applications, the feeding or transfer angle already has been maximized for the given conditions, but certain press enhancements may make it possible to further increase this angle. For example, if the feed or transfer must be completed by a certain angle to allow enough time for die sensing before material contact, retrofitting the press with a high-performance hydraulic clutch and brake may decrease the press stopping time and provide increased time for material transfer.
Other ways to increase the available material transfer time include increasing stroke length or using a link motion that has been customized to spend more time in the upstroke position.
Alternative ways to increase press speed are limited, but it should not be assumed that the only way to increase press speed is by purchasing a new press. In some cases, a press manufacturer may help stampers retrofit or upgrade their current presses to increase speed capability. If the press speed cannot be increased, it may be possible to do more with each stroke.
For example, tools and processes can be modified to produce more parts per stroke to increase production without increasing SPM. Additionally, incorporating secondary operations such as assembly, tapping, and welding into the die can result in production and profit increases.
This article provides only a few, general recommendations on how to improve efficiency. There are as many different ways to address this issue as there are different stampers. Regardless of the situation, the key to process improvements is being able to accurately identify and document key production parameters. Continually obtaining and analyzing this information will provide the direction and focus required to win the game.