When the subject of inspection comes, we think about the manufacturing goods and types of inspection. Heavy emphasis is placed on inspection under the current environment of the global market and keen competition.
Inspection is not cheap. It costs to inspect and it is considered a non-value-added function, even though it protects customers. Inspection is also associated with non-manufacturing goods such as pre-buy inspection of a car or a house.
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Type of InspectionÂ
Inspection falls into four main categories, namely,
1. Visual ( appearance surface characteristics, size, shape, color, etc.)
2. Physical or dimensional measurements.
3. Testing ( Mechanical strength, material properties, electrical, etc.)
4. Sensory ( Touch, smell, taste, etc.)
Factors such as human judgment, environment, sample, size, etc. can influence the result. Visual inspection can be very subjective without some kind of standards. Visual inspection can be performed naked eye or can be aided by a microscope or magnifier. Automated visual inspection tools are available and are still in the development stage.
Physical or dimensional measurements can be performed by using tools such as micrometers, depth gages, coordinate measuring machines, comparators, dial indicators, etc. Testing involves electrical, mechanical, material strength, or characteristics measurements. Electrical testing includes opens, shorts, parametric, or functional characteristics.Â
Sensory testing involves smelling or tasting as in the case of wine or tea.
Destructive and Non-Destructive testingÂ
The inspection could be destructive or non-destructive (NDT). NDT testing is the examination of an object in a manner that does not affect its future and usefulness. NDT tests are performed to detect internal or external imperfections, to determine structure, composition, or properties, or to measure geometric characteristics without affecting the form, fit, or function of the test object. Visual inspection is a kind of Non-destructive testing.
NDT testing of the material quality and structural integrity of products or fabrications is now a major component of modern manufacturing and in-service maintenance practice. In recent years the added emphasis has been placed on the importance of NDT by the need to maintain reputations in increasingly competitive markets. Sophisticated data processing techniques are being used to reduce the degree of reliance on subjective interpretation of results.
Typical NDT techniques are X-ray radiography, Gamma-ray radiography, Ultrasonic testing using high-frequency sound waves, Magnetic particle, liquid penetrant, Eddy current, Leak testing, Acoustic emission, and Visual examination. Special NDT methods such as the use of microwaves, ultrasonic imaging, lasers, holography, liquid crystals, and infrared thermal testing techniques are popular.
Tests such as cross-sectional analysis or tensile strength fall under destructive tests. Random vibration testing is used in environmental testing laboratories for qualification, acceptance, and reliability demonstration tests to various standards.
Automation Inspection
Automated Inspection System (AIS) technologies include X-ray radiography, X-ray laminographic, Ultrasonic imaging, Automated optical inspection, Laser inspection, and Infrared inspection. AIS Can supplement but not replace manual inspection for low-volume, high-reliability surface mount solder joints. Each of these techniques has its own strengths and weaknesses. The results of the inspection can be affected by human-dependent or human-intended techniques being used.Â
Slef-Inspection Criteria
Standards play an important role in the inspection results. Results would be subjective without some kind of standard, particularly in the case of visual inspection. Note: Inspection Methodology will vary from industry to industry.
Assembly/manufacturing industries use more visual and testing techniques. Semiconductor industries require thorough visual and electrical testing. The chemical industry requires more laboratory testing.
Why do we do inspections?
The main objective of the inspection is to meet customer requirements in case of a final inspection. In the case of in-process inspection, the objective is to prevent defective products from flowing down the successive operation and prevent loss of yield. In many cases, some characteristics can only be inspected at the intermediate or sub-assembly stages.
When should we do the inspection?
Inspection should be done at a process stage when it is economical to detect defects. Naturally, a final inspection will be required to meet customer demands. Optimal inspection points are where critical criteria can be inspected without investing more into the product.
How should an inspection be performed?
Human-independent or automated systems should be sued to avoid subjectivity and gain productivity. Inspection results should not be judgmental.
Where should the inspection be performed?
Inspection should be performed at the source of operation to provide immediate feedback for corrective actions. priorities have to be set to perform receiving inspection, in-process inspection, or final inspection.
What should be inspected?
Inspection should be performed according to the established criteria and specifications. If something obvious is observed, it should not be neglected.
Who should perform the inspection?
Only well-trained and computable persons should be authorized to perform inspection functions. Inspection requirements must be understood by all responsible persons.Â
Conclusion
Orderly data collection and feedback of results are important criteria for the inspection function. Automation, simplicity, and training of inspectors become key priorities to compete effectively in the global markets. Preventive measures and standardized approaches will bring the desired results. A defect prevention strategy should be applied to produce quality products. A sense of confidence, unity, and early stabilization in the organization will satisfy customer requirements.
Ethics and code of conduct are important when performing an inspection. A professional attitude with high ethical standards will keep the image of the inspection profession.
