Tolerancing and quality control

Understanding Tolerancing

Tolerance: This term defines the acceptable limit or limits within which the physical dimension of a part can vary. It is the difference between the maximum and minimum sizes that a part can take while still functioning properly.
Unilateral Tolerance: This is when the tolerance happens only in one direction from the specified dimension. For example, a part could have a measurement of 10mm +0.5mm/-0mm.
Bilateral Tolerance: When the tolerance occurs in both directions from the specified dimension, it is described as a bilateral tolerance. For instance, a part could have a measurement of 10mm +0.5mm/-0.5mm.
Limit System of Tolerance: This system is used to determine the size of a part. The upper limit is the maximum allowable size, and the lower limit is the minimum allowable size.
Fit: This refers to the mechanical relationship between two or more parts. It could be a loose fit designed for easy assembly or a tight fit for precision.

Understanding Quality Control

Quality Control: This is a set of procedures that ensure that a manufactured product adheres to a defined set of quality criteria or meets the needs of the client or customer.
Inspection: This is a critical aspect of quality control, where physical measurements and checks are made to ensure the product matches the design specification.
Sample Inspection: Sometimes it’s not practical to inspect every single item in a large batch, so a representative selection is taken and inspected instead.
Quality Assurance: While quality control focuses on identifying and correcting defects in the finished product, quality assurance seeks to improve and stabilise production to avoid, or at least minimise, issues.
Total Quality Management (TQM): This is an approach that seeks to improve quality and performance in all services, departments and processes within a company to provide added benefits to both the organisation and its clients.
Quality Management System (QMS): This is the set of policies, processes and procedures required for planning and execution in the core business area of an organisation. It aims to ensure consistent quality in the production process.
Statistical Process Control (SPC): This involves using statistical methods to oversee and control the quality of manufacturing processes.
International Organisation for Standardisation (ISO): A body that provides standardised guidelines for production processes to ensure product quality, safety, and efficiency on an international scale.