Many companies today have either a quality department for inspection of their product, or inspection is build in as part of the process. Even if they perform a 100% inspection of every product that leaves their facility, there are no guarantees that the product will meet the customer's quality requirements all the time. Each product you produce is different in some way from the one you made prior. There are thousands of variables that affect thousands of characteristics of your product. We live in an environment that is constantly changing. This reality exists for manufacturing as well as the service sector. It is not feasible to measure every characteristic of the product. There are no tools to detect every characteristic. What is critical is to control the important parameters of the process throughout the product life cycle. This helps to ensure that the quality is built into the product as it is manufactured.
What most companies do is select a handful of characteristics that they believe are important to their customer. They measure those few to ensure that they meet customer requirements. They perform their 100% inspection, and if the product passes it is shipped to the customer. They are very surprised when they get a phone call from the customer that their product ruined the customer's lot, and their customer not only wants their money back but wants to be compensated for the losses as well. At that point the quality manager will retrieve the test results from the product, which shows that the product passed all quality inspection requirements before shipment. He or she will kindly forward those results to the customer with a word of advice "The problem is not ours it's on your end."
The dispute may go on for years or be resolved quickly when the customer vows never to buy any products from this vendor again. Either way the cost will be substantial to our manufacturer. What went wrong? The 100% inspection was performed and product passed? Whose fault was it? Costly investigations are performed many times without a resolution. The reason for the failure may not have been anyone's fault. It could be that a change in your process or manufacturing environment affected a characteristic of the product that you were not measuring. The customers may not be aware that this particular characteristic affects the performance of their manufacturing process. Something in customers manufacturing process changed that made their process more sensitive to this characteristic.
The best way to ensure that product quality is consistent is to monitor and control process characteristics. This includes the manufacturing process as well as measurement process. Consistent process delivers consistent product. Those who choose to rely only on the final inspection to ensure quality of the product will pay in loss of business, disagreements, and loss of market share. Therefore, even though you can't inspect quality into the product, you can ensure that quality is built into your product. Controlling process parameters and responding to changes quickly ensures that the product characteristics do not vary.
The best example of this is the frustrating process of trying to duplicate the recipe of your family's traditional thanksgiving stuffing. It never seems to taste as good as what your predecessors made. Unfortunately all the recipes include is the ingredients, sequence of the steps, appliance settings and time. The process is usually not described and process adjustments that are made throughout are not described either. The characteristics that are measured throughout the process are affected by the accuracy of measurement of the ingredients, the quality characteristics of the ingredients themselves, the size of each ingredients (1 cup of celery cut to 1/4 inch size will contain more celery than 1 cup of celery cut to 1/2 inch size), duration of each step, the temperature of the stove top, the type of pan used, the ingredients in a brand of bread, oven temperature accuracy and heat distribution, etc. You might say your predecessors had the same issues. You would be right. The difference is they have gained the experience and ability to monitor their process and make adjustments throughout the process. The recipe does not capture these adjustments.
No matter what process you are responsible for, you need to monitor and control it. Monitored and controlled manufacturing process will produce the most consistent product. Monitoring and controlling service product will deliver consistent service. Monitoring and controlling measurement and inspection process delivers consistent results.