Metalcasting operations are comprised of many processes and literally thousands of variables, and so the idea of gaining control over these processes and variables may seem impossible. But, with customers, competitors, and suppliers all providing different sorts of encouragement, foundries pursue process control in many ways — more than you may think.
Let’s start by organizing them, and then by naming them. The first thing to understand is that variables come in two basic types: input variable and output variables. Input variables are those inputs to the process that vary, such as metal pouring temperature, which is an input variable to the pouring process. Then there are output variables, outputs of a process that vary. Output variables in the process of wax injection are the dimension of the pattern, or the surface finish the pattern.
We can now easily categorize all foundry variables into input variables and output variables, and we can link them to a process step (or steps) of the foundry.
While sorting the entire list of variables into inputs and outputs might make them easier to understand, it certainly doesn’t lessen the load of the large quantity of variables in the casting processes. However, the next step in organization will do that. We only need to control some of these variables. These may be referred to as “key” variables, and they come in two different types, Key Input Variables (KIVs) and Key Output Variables (KOVs).
What are key process output variables?
Key process output variables can be defined by examining two different perspectives: first from the customer’s perspective, and then from the foundry supplier’s perspective.
The foundry customer perspective — Key process output variables (often referred to as Key Characteristics) are traits or features of a part, piece of material, assembly, subsystem or system in which variation has significant influence on its outcome. Outcomes may include a particular part’s fit, performance, reliability, manufacturability, assembly, etc. In short, they are characteristics that have a significant impact on efficiency and/or customer satisfaction. Consequently, the risk for variation in key process output variables leads to lower levels of quality and reliability, and ultimately, higher costs.
The foundry supplier perspective— Suppliers to the casting industry are the beginning of the metalcasting process. Like any other product company, they differentiate themselves from their competitors through product features and performance. These product features and performance claims become the KOV of our supplier process and a key input variable (KIV) to the casting processes. The casting industry in general relies heavily on many suppliers to help define the KOVs of the supplier process and help to determine appropriate tests to monitor these KIV to our processes.
Identifying Key Variables — The basic process to identifying the key variables (KIV and KOV) consists of performing the following:
- Map the process from suppliers to shipment of casting;
- Begin with the customer KOV;
- Work backward from the customer KOV;
- Verify the relationship between the customer KOV and a KIV in your process through experimentation, observation, or data collection;
- Establish control levels and methods for the verified KIV;
- Using the verified KIV as a KOV of other upstream process steps repeat the previous steps to control other KIV upstream in the process.