Quality Control (QC) is a system of routine technical activities, to measure and control the quality of the inventory as it is being developed. The Quality Control system is designed to:
- Provide routine and consistent checks to ensure data integrity, correctness, and completeness;
- Identify and address errors and omissions;
- Document and archive inventory material and record all QC activities.
Seven Quality Control Tools
The following seven quality control tools are considered basic tools for achieving quality.
- Flow Chart: It is a visual representation of process showing the various steps. It helps in locating the points at which a problem exists or an improvement is possible. Detailed data can be collected, analyzed and methods for correction can be developed. A sample is shown below lists out the various steps or activities in a particular job. It classifies them as a procedure or a decision. Each decision point generates alternatives. Criteria and consequences that go with decision are amenable to evaluation for purposes of assessing quality. The flow chart helps in pin-pointing the exact at which errors have crept in.
- Check Sheet: These are used to record the number of defects, types of defects, locations at which they are occurring, times at which they are occurring, workmen by whom they are occurring. It keeps a record of the frequencies of occurrence with reference to possible defect causing parameter. It helps to implement a corrective procedure at the point where the frequencies are more, so that the benefit of correct will be maximum.
- Histogram: Histograms are graphical representations of distribution of data. They are generally used to record huge volumes of data about a process. They reveal whether the pattern of distribution — whether there is a single peak, or many peak and also the extent of variation around the peak value. This helps in identifying whether the problem is serious. When used in conjunction with comparable parameters, the visual patterns help us to identify the problem which should be attended to.
- Pareto Analysis: This is a tool for classifying problem areas according to the degree of importance and attending to the most important. Pareto principle, also called 80-20 rule, states that 80 percent of the problems that we encounter arise out of 20 percent of items. If we find that, in a day, we have 184 assemblies have given problems and there are 11 possible causes, it is observed that 80 per cent of them i.e. 147 of them have been caused by just 2 or 3 of them. It will be easy to focus on these 2 or three and reduce the number of defects to a great extent. When the cause of these defects have been attended, we will observe that some other defect
- Scatter Diagram: These are used when we have two variables and want to know the degree of relationship between them. We can determine if there is cause and effect relationship between and its extent over a range of values. Sometimes, we can observe that there is no relationship, in which we can change one parameter being sure that it has no effect on the other parameter.
- Control Charts: These are used to verify whether a process is under control. Variables when they remain within a range will render the product maintain the specifications. This is the quality of conformance. The range of permitted deviations is determined by design parameters. Samples are taken and the mean and range of the variable of each sample (subgroup) is recorded. The mean of the means of the samples gives the control lines. Assuming normal distribution, we expect 99.97 per cent of all values to lie within the UCL when we take 3 standard deviations — Upper Control Limit — and LCL — Lower Control Limit. The graphical representation of data helps in changing settings to bring back the process closer to the target.
- Cause and Effect Diagram: This is a diagram in which all possible causes are classified on quality characteristics which lead to a defect. These are arranged in such a way that different branches – the causes are — leading the stem in the direction of the discovery of the problem. When each of them is investigated thoroughly we will be able to pinpoint some factors which cause the problem. We will also observe that a few of them will have cumulative effect or even a cascading effect.
Download: Quality Control Tools (ppt)