🇪🇺 European Directives · Quality Control by Sampling

UNI 4842-1975

What is UNI 4842-1975?

UNI 4842-1975 defines the criteria for acceptance sampling in industrial processes. Its main purpose is to guarantee batch quality through inspection based on representative samples, reducing costs and time compared to a 100% inspection. The standard provides rigorous statistical criteria for selecting the quantity of samples and assessing their conformity.

This approach minimises the risk of product defects and ensures that the required technical specifications are met. Furthermore, UNI 4842-1975 promotes the use of statistical methods to determine the acceptable level of quality, improving the reliability of controls and optimising the resources used in the production process.

The final objective is to provide a structured method for quality control that can be easily integrated into company processes, contributing to improving competitiveness in the market.

Learn more about the UNI 4842-1975 Directive

Scope of Application

The standard applies to production processes where it is necessary to check the quality of a batch without checking each individual part. It uses two main parameters:

  • Sample size (n): Number of parts to be tested.
  • Acceptance number (na): Maximum number of acceptable defective parts.

UNI 4842-1975 is particularly useful in contexts where the production volume is high and a full inspection would be impractical or too costly. The criteria set out in the standard are designed to ensure that quality control is representative of the entire batch, avoiding waste of time and resources. The sampling approach also allows different severity levels to be defined, depending on the criticality of the product and the specific needs of the customer.

Conformity Criteria

UNI 4842-1975 classifies batches according to size and acceptable quality level (AQL). Samples are taken according to an established test plan, and the batch is accepted or rejected based on the test results. The AQL represents the maximum percentage of defects that can be considered acceptable in a batch. This criterion balances the risk between producer and customer, ensuring that the final product meets the agreed quality standards. The standard provides for different categories of sampling, including single, double or multiple sampling, depending on the needs and characteristics of the production process.

The use of a pre-established sampling plan reduces the risk of bias and increases both manufacturer and customer confidence in the results of quality control. In addition, the standard establishes procedures for the management of possible non-conformities, defining the steps to follow in the event of negative results, such as rejection of the batch or the need for further controls.

What SIMEL does to comply

SIMEL integrates the UNI 4842-1975 standard into its ERP system, which automatically generates control plans. The main actions include:

  1. Regular Sampling: First and last pieces of each batch are always checked, with intermediate samples selected according to statistical rules (1:15, 1:20, 1:50). This approach ensures that every stage of production is monitored, reducing the risk of defects and ensuring that any problems are identified and corrected promptly.
  2. Specific Testing: Each sample undergoes compliance testing for strength, inductance, dimensions and other parameters. These tests are designed to ensure that each component meets the required technical specifications and is able to meet customer expectations in terms of performance and reliability. Tests include mechanical, electrical and dimensional checks, carried out with instruments that are calibrated regularly to ensure maximum accuracy.
  3. Traceability and Recording: All tests are tracked and recorded in the ERP system to ensure transparency and continuity. Every batch, every sample and every test result are documented so that they can be easily traced and analysed. This level of traceability allows SIMEL to provide customers with detailed information on product quality and to intervene quickly in the event of problems.
  4. Staff training: Operators are trained to handle controls according to the specifications of the standard. Training includes both theoretical aspects, such as understanding the statistical principles behind sampling, and practical aspects, such as the use of measuring instruments and recording data in the ERP system. Continuous staff training is essential to maintain high quality standards and to adapt to technological and regulatory changes in the industry.

Quality Management at SIMEL

Quality process

SIMEL is committed to delivering high quality electric motors that exceed customer expectations, ensuring reliability, performance and durability. Each step is designed to minimise defects and ensure the highest quality standard. This integrated approach allows SIMEL to deliver customised, high-precision solutions, maintaining high levels of customer satisfaction and reinforcing trust in the brand.

Input (Incoming Materials):

  • Control of materials with instruments calibrated by external bodies to ensure compliance with the required quality standards.
  • Rigorous selection of suppliers, based on quality audits and certifications, to ensure that materials meet the required specifications.

In-Process (During Production):

  • Spot Checks: During each production stage, spot checks are carried out at a regulated frequency (1:15, 1:20, 1:50) depending on the criticality of the component and the specific process.
  • Advanced Machinery and Systems: Use of the latest CNC machinery and ERP systems to ensure precision, efficiency and continuous traceability throughout the production cycle. Machinery is regularly subjected to preventive maintenance to minimise downtime and guarantee product quality.
  • Technical Documentation and Control Plans: Each operation is supported by detailed technical documentation, including bills of materials, technical drawings and control plans describing the specifications to be met and verification methods.
  • FStaff Training: Operators undergo continuous training, both theoretical and practical, to ensure that they are always up-to-date on processing techniques, the use of new technologies and safety regulations. This ensures not only product quality, but also a safe and regulatory-compliant working environment.

Output (Finished Product):

  • 100% Compliance Testing: Each assembled winding and motor undergoes comprehensive testing for strength, operation and safety. These tests include absorption tests, electrical continuity and functionality under load.

  • Final Visual and Dimensional Checks: Before shipment, each product undergoes visual, dimensional and electrical checks to ensure that all specifications are met. The windings are 100% tested to ensure that there are no defects that could compromise motor life and reliability.

  • Product traceability: Each motor is labelled and registered in the ERP system to ensure complete traceability from production to delivery to the customer.

Quality Tools

  • UNI 4842-1975: Acceptance sampling for regular checks, ensuring that each batch meets quality requirements.

  • ERP Traceability: Each part is identifiable and monitored in real time, ensuring a complete record of all production steps and checks carried out.

  • Machinery Maintenance and Upgrade: Retrofit and replace equipment to ensure efficiency, precision and energy savings. This includes upgrades of machinery control systems to improve performance.

  • Continuous Training: Regular update programmes on safety, advanced technologies and production methodologies for personnel to ensure that operators are competent and prepared to meet production challenges.