Q: How do you differentiate corrective action and correction? What are some best practices for handling corrective actions versus corrections?
Overland Park, KS
A: It’s important to first understand the differences between correction and corrective action.
Correction is an action taken to eliminate a detected nonconformity.1 If the detected nonconformity is a defective product or an incorrect invoice, for example, then reworking the defective product or the incorrect invoice is considered correction. You may be able to restore the intended requirement or function, but you are only correcting the situation.
Corrective action is taken to eliminate the cause of a detected nonconformity.2 This requires understanding the root cause of the detected nonconformity and taking action to eliminate the root cause(s) to prevent recurrence of the nonconformity.
Both correction and corrective action may be required in many scenarios. Correction addresses the short-term need and gets immediate attention, and most organizations do a good job of correcting the nonconformity. Corrective action, on the other hand, is a long-term solution. In my opinion, organizations do not invest adequate resources in addressing corrective action. Even if attempted, often due to organizations’ ad hoc approaches, only symptoms are addressed rather than root causes. There are proven root cause analysis tools and problem-solving methods that can be used to take effective corrective action. For correction, you need process-specific instruction. For corrective action, problem-solving skills are required.
If an auditee is just correcting the instance detected by the auditor, he or she is not addressing the overall impact. An auditee or process owner who is truly interested in improving his or her system will take additional samples and evaluate the current controls before concluding the detected nonconformance is indeed isolated. If a nonconformity is an isolated incident and is low risk to business and customers, investing time and resources for understanding the root cause is not a value-added activity. Correction of the situation may be adequate.
Table 1 shows some scenarios that illustrate the relationship between correction and corrective action and the applicability of each.
Director, quality assurance
SunPower Corp., San Jose, CA
- American National Standards Institute, International Organization for Standardization and ASQ, ANSI/ISO/ASQ Q9000-2005—Quality management systems—Fundamentals and vocabulary, clauses 3.6.5 and 3.6.6.
- Russell, J.P., and Terry Regel,
Closing the Loop on the Audit Process,
second edition, ASQ Quality Press, 1996.
Q: We know that there are many types of waste encountered by organizations. How can we measure waste? What are the tools or guidelines to find it and measure it?
Jeddah, Saudi Arabia
A: The essence of lean manufacturing can be summarized in two words: eliminate waste. Waste can be broadly defined as anything that consumes resources but does not add value to the finished product. Waste can take many forms. Let’s look at a few examples. Consider this all-too-common scenario:
Management wants to keep the workers busy, so production continues even if there are no orders for the product. Overproduction in manufacturing leads to excess inventory, which must be moved and stored. Material handling costs increase because product must be handled two or three extra times. Warehouse costs increase because more space is required, and this increases rent, utility charges and manpower required to manage the inventory. If the product has a limited shelf life, there is a possibility of future loss due to product degradation or changing consumer demand. Imagine a warehouse full of product that no one wants. It must be sold at a discount—or perhaps even at a loss.
Inventory can be measured, but can we measure the waste caused by excess inventory? One broad but unscientific rule of thumb is that annual inventory carrying costs are equivalent to 20% of the face value of the inventory. So, if a business has $100 million in inventory on average, it costs $20 million per year to carry the inventory.
Remember that the warehouse does not add any value to the product, so excess inventory is a huge source of waste. Many companies measure "inventory turns." This metric is usually calculated by dividing the cost of goods sold by the average inventory for a given period of time. Many automotive assembly plants have just-in-time systems and turn over their inventory several times per day. You can benchmark your industry to determine a competitive target for inventory turns.
We will not have much success reducing inventory until we understand the reasons for creating it. I once toured a plant that had only three inventory turns per year. The CEO explained that setup was time consuming, so management preferred long production runs to minimize the frequency of setups. The challenge is to reduce or eliminate the delays associated with setup time so that changes in the product mix are relatively quick and painless. If a NASCAR pit crew can change a set of tires in less than 10 seconds, surely we can figure out how to streamline the tooling changeover process.
Scrap is a highly visible source of waste in many plants. It is usually easy to measure but difficult to reduce. Be careful not to rely on plant standards that have a built-in allowance for scrap and other types of waste. If defective product is found during routine quality inspections, many facilities will react with 100% reinspection to ensure quality.
If your operation depends on rework and reinspection, it is time to focus on prevention. Customers do not want to pay extra for something that should have been done right the first time. Some cost-of-quality practitioners claim that prevention activities are about 10 times cheaper than the cost of internal failures and as much as 100 times cheaper than the cost of external failures.
Excess motion is another common source of waste. Spaghetti diagrams are a quick and easy way to discover and document wasted motion. Process mapping is a bit more complicated, but it usually uncovers hidden delays between operations. Delays lead to idle workers, underused machines and increased work-in-process time.
Down time is yet another big source of waste. Various metrics have been proposed to measure performance, but you should avoid optimizing one metric at the expense of another. Overall equipment effectiveness is a nice metric because it combines machine availability, performance and quality into a single, overall performance metric. Additional tools and techniques are described in the sources cited below.
Consultant, Master Black Belt
For more information
- Borror, Connie M., The Certified Quality Engineer Handbook, third edition, ASQ Quality Press, 2009.
- Monden, Yasuhiro, Toyota Production System, third edition, Engineering and Management Press, 1998.