Statistical quality control
Introduction
SQC is the application of statistical technique to accept or reject products already produced, or to control the process and therefore, product quality while the part is being made. While the latter is called process control, the former is named acceptance sampling.
Meaning
SQC is the application of statistical technique to determine how far the product confers to the standards of quality and precision and to what extent its quality deviates from the standard quality.
Techniques of SQC
1. quality control during production : - the standard quality is determined through careful research and investigation. It is quite impractical to adhere strictly to the standards of precision, especially in cases where human factor dominates over the machine factor. Some deviation is therefore, allowed or tolerated they are referred to as tolerances. With in the limits, set by these tolerances, the product is considered to be of standard quality. SQC brings to lights the deviations outside these limits, i.e. the purpose is statistical quality control is to discover and correct only those forces which are also responsible for variations outside the suitable pattern through SQC techniques.
Their measurable characteristics such as length, diameter, hardness, tensile strength etc.
‘Fraction defectives’ “p”, when the characteristics cannot or need not to be measured.
Number of defects is sample.
The process is said to be with in control if the sample points fall with in the pre established control limits. The crux of the process control lies in establishing the appropriate control limits. The charts showing these control limits are called ‘process control charts’.
Control charts
One of the most important tools f production management and the control of quality in the manufactured product is the control chart techniques. These are two types of control charts;
1. Control chart for variable are;
Control chart for mean (x)
Control chart for range (r)
Control chart for standard deviation ()
2. Control chart for attributes are;
Control chart for fraction defectives, i.e. P chart
Control chart for number of defectives, i.e. np-chart or d chart
Control chart for number of defects per unit, i.e. c-chart
2. Quality assurance while purchasing
Acceptance sampling can be described as the post mortem of the quality of the product that has already produced. The term acceptance sampling relates to the acceptance of a consignment / batch of items on the basis of its quality; it is used for:
Acceptance / rejection of the raw material delivered.
Passing/ non passing of the batch of item manufactured.
Shipment of items for delivery to customer.
In modern industry it has become a necessity as it offers the following benefits;
It saves on rejection
In the absence of SQC technique, many products may be found defective and worthless at the manufacturing process and have to be thrown away as a scrap. SQC helps to avoid such a situation and thus saves the cost of labour and material involved in the production of defective items.
Measure the extent of defect
SQC technique measure the extent of defect and certain defective products may be approved with reworking to the level of acceptance standards. It helps in deciding whether to do reworking or not and hence helps in reduction of loses due to unnecessary working.
It maintain high standard of quality
It helps in removing rejections and improving through reworking whether felt necessary and hence the outgoing standard is quite higher as compared to in the absence of SQC technique. This increase the goodwill of the company which gives intangible benefits.
Reduce expenses of inspection
It reduce the expenses of as lot size to be inspected is very small as compared to 100% inspection and thus enables the product to be manufactured at lowest cost.
Ensure standard price
As the outgoing quality of the product is a standard /uniform hence the producer is able to secure the standard price for all standard products. Thus, it increases the profitability of the concern.
Felling of responsibility among the workers
Among the workers a feeling of responsibility develops because they begin to understand that their work is being inspected very minutely, hence they work carefully and it helps in increasing their morale.
Reduces monotony and necessary fatigue of inspection
As 100% inspection is very monotonous and is likely to cause unwillingness at the part of quality inspection, thus SQC which is a technique implying sampling/ acceptance plans is not monotonous and hence helps in reducing their unwillingness and increasing their quality.
Introduction
SQC is the application of statistical technique to accept or reject products already produced, or to control the process and therefore, product quality while the part is being made. While the latter is called process control, the former is named acceptance sampling.
Meaning
SQC is the application of statistical technique to determine how far the product confers to the standards of quality and precision and to what extent its quality deviates from the standard quality.
Techniques of SQC
1. quality control during production : - the standard quality is determined through careful research and investigation. It is quite impractical to adhere strictly to the standards of precision, especially in cases where human factor dominates over the machine factor. Some deviation is therefore, allowed or tolerated they are referred to as tolerances. With in the limits, set by these tolerances, the product is considered to be of standard quality. SQC brings to lights the deviations outside these limits, i.e. the purpose is statistical quality control is to discover and correct only those forces which are also responsible for variations outside the suitable pattern through SQC techniques.
Their measurable characteristics such as length, diameter, hardness, tensile strength etc.
‘Fraction defectives’ “p”, when the characteristics cannot or need not to be measured.
Number of defects is sample.
The process is said to be with in control if the sample points fall with in the pre established control limits. The crux of the process control lies in establishing the appropriate control limits. The charts showing these control limits are called ‘process control charts’.
Control charts
One of the most important tools f production management and the control of quality in the manufactured product is the control chart techniques. These are two types of control charts;
1. Control chart for variable are;
Control chart for mean (x)
Control chart for range (r)
Control chart for standard deviation ()
2. Control chart for attributes are;
Control chart for fraction defectives, i.e. P chart
Control chart for number of defectives, i.e. np-chart or d chart
Control chart for number of defects per unit, i.e. c-chart
2. Quality assurance while purchasing
Acceptance sampling can be described as the post mortem of the quality of the product that has already produced. The term acceptance sampling relates to the acceptance of a consignment / batch of items on the basis of its quality; it is used for:
Acceptance / rejection of the raw material delivered.
Passing/ non passing of the batch of item manufactured.
Shipment of items for delivery to customer.
In modern industry it has become a necessity as it offers the following benefits;
It saves on rejection
In the absence of SQC technique, many products may be found defective and worthless at the manufacturing process and have to be thrown away as a scrap. SQC helps to avoid such a situation and thus saves the cost of labour and material involved in the production of defective items.
Measure the extent of defect
SQC technique measure the extent of defect and certain defective products may be approved with reworking to the level of acceptance standards. It helps in deciding whether to do reworking or not and hence helps in reduction of loses due to unnecessary working.
It maintain high standard of quality
It helps in removing rejections and improving through reworking whether felt necessary and hence the outgoing standard is quite higher as compared to in the absence of SQC technique. This increase the goodwill of the company which gives intangible benefits.
Reduce expenses of inspection
It reduce the expenses of as lot size to be inspected is very small as compared to 100% inspection and thus enables the product to be manufactured at lowest cost.
Ensure standard price
As the outgoing quality of the product is a standard /uniform hence the producer is able to secure the standard price for all standard products. Thus, it increases the profitability of the concern.
Felling of responsibility among the workers
Among the workers a feeling of responsibility develops because they begin to understand that their work is being inspected very minutely, hence they work carefully and it helps in increasing their morale.
Reduces monotony and necessary fatigue of inspection
As 100% inspection is very monotonous and is likely to cause unwillingness at the part of quality inspection, thus SQC which is a technique implying sampling/ acceptance plans is not monotonous and hence helps in reducing their unwillingness and increasing their quality.
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