MIC-206 Inspection: Intro and Process Control

• NDT means Non-Destructive Testing
• Indian Institute of Technology Roorkee is the institute where this module is taught
• MIC-206 is the module code for Theory of Production Processes

Inspection Intro

• Inspection involves measuring, examining, testing and gauging product characteristics.
• Results are compared to requirements to check conformity, per ISO 2859.
• Objectives are to assess conformity with design specifications, and improve product quality and reliability.
• Inspection occurs throughout production, from raw materials to finished goods.
• Inspection is a maintenance strategy for continuous manufacturing systems.

Inspection vs Process Control

• Inspection uses customer requirements and specification drawings.
• Inspection methods are used with judgement criteria.
• Products can be accepted or rejected.
• Process Control uses ongoing processes, benchmarked with standards.
• Control charts are used to measure and establish UCL and LCL control limits.
• Man, method, machine and material characteristics are taken into account
• Processes can be stable or abnormal
• Aims to measure and prevent repetition and check for cause of problems

Inspection Cost Analysis

• Achieving 100% good quality needs 100% inspection.
• All defects are screened and only good quality parts are accepted.
• Inspection cost equals fixed cost plus variable cost.

Inspection Process Stages

• Ensuring product quality at different stages in manufacturing is crucial for maintaining standards.
• This reduces defects, and meets customer expectations.
• The Quality Inspection Process has 3 primary types:
• Receiving Inspection
• In-Process Inspection
• Final Inspection
• All 3 play a vital role in identifying and resolving quality issues as early as possible.
• They minimize production costs, and ensure reliability.

Receiving Inspection

• Ensures raw materials and components meet quality standards before production.
• Objectives include ensuring materials meet quality standards.
• Objectives include preventing defective materials from entering production.
• Objectives include confirming supplier compliance.
• Objectives include tracking recurring issues.
• Key Activities:
• Sampling Inspection: Randomly selecting samples for quality evaluation.
• Measurement & Testing: Using tools to assess materials against standards.
• Documentation & Records: Maintaining inspection reports for traceability.
• Acceptable/Rejection Decision: Materials accepted, rejected, or returned based on inspection results.
• Tools Used: Calipers, Micrometers, Height Gauges, Verification Software and Barcode Scanners.
• Quality Inspectors, Procurement Specialists and Supply Chain Managers key roles.
• Supplier Quality, Incoming Defect Rate (IDR) and Lead Time for inspection relevant KPIs.

In-Process Inspection

• Detects and addresses quality issues during manufacturing.
• Ensures each step is performed correctly.
• Objectives include identifying defects or deviations early in production.
• Objectives include minimizing rework, scrap, and production delays.
• Objectives include monitoring processes for consistency and adherence to specs.
• Key Activities:
• Regular Inspection: Checks dimensions, tolerances, and parameters.
• Process Monitoring: Ensures operators follow standard procedures.
• Control Plans: Follows documented plans specifying inspection points, frequencies.
• Corrective Actions: Implements CAPA if deviations are detected.
• Visual Inspection tools, gauges, fixtures and measuring instruments Tools Used.
• Process control charts are also used for monitoring.
• Quality Engineers, Weld Inspectors and Production Supervisors key roles.
• In-process Defect Rate, First Pass Yield (FPY) and Rework Costs are relevant KPIs.

Final Inspection

• Ensures products are defect-free and compliant before shipment.
• Objectives include providing verification of product quality, preventing defective products from reaching customers.
• Objectives include certifying compliance with customer and regulatory requirements.
• Key Activities:
• Visual and Dimensional Checks: Ensures fit, form, & functional requirements meet standards.
• Functional Testing: Tests under conditions the product will face.
• Packaging Inspection: Verifies correct labeling and packing.
• Final Documentation: Generates certificates of conformance.
• Examples of tools used are Final inspection checklists and functional testing rigs.
• A Quality Management System (QMS) is used for tracking & reporting.
• Key roles are Quality Engineers, QMS and Testing rigs
• Relevant KPIs are Final Defect Rate, On-Time Delivery Rate and Customer Complaints.

Non-Destructive Inspection

• Process of inspecting, testing, or evaluating materials and components.
• It detects discontinuities or characteristic differences without destroying serviceability.
• Terms like non-destructive examination (NDE) and evaluation (NDE) describe this technology.
• A high value technique that saves money and time in product evaluation.
• Also useful in troubleshooting, and research.
• NDT allows inspection without interfering with a product's final use.
• NDT provides a balance between quality control and cost-effectiveness.
• Used in manufacturing and in-service inspections to ensure product integrity.
• NDT ensures reliability, controls processes, lowers production costs and maintains uniform quality.

NDT Techniques

• Popular NDT techniques include Visual Testing, Liquid Penetrant Testing and Magnetic Particle Testing.
• Other such popular tests are Eddy Current Testing, Radiographic Testing and Ultrasonic Testing.
• More tests are Acoustic Emission Testing and Infrared Thermography.

Visual Inspection

• Detects and examines surface flaws like corrosion, contamination, and discontinuities.
• It include flaws like welds, seals, solder connections, and burning.
• It is the most cost-effective at detecting common welding and casting defects.
• Implemented easily, it helps eliminate simple errors to prevent follow-on effects..
• Visual inspection is a supplement for detecting surface cracks, when using other techniques.

Visual Inspection Classification

• Three Types of Visual Testing include:
• Direct Unaided Visual Testing
• Direct-Aided Visual Testing
• Remote Visual Testing

Direct Visual Inspection

• Direct visual examination is made in situations where there is interest and access.
• There is no possibility of injury to the inspectors.
• There is no interruption between the eye and the object.
• Detectable defects include cracks, corrosion layers and physical damage.
• Further defects include: surface porosity, and misalignment of mated parts.

Direct Aided Viaual Inspection

• The nature of the image is not modified.
• Modification of the image is only allowed by means magnification, eg mirror or lens.
• Otherwise use spectral or density filtering by a filter lens.

Remote Visual Inspection

• The nature of the image is modified.
• The optical image is converted into an electronic image by a camera.
• Equipment used: Camera, robotic device, fiber optics, portable video probes, etc.

Visual Inspection Basic Procedure

• Comprises of three steps:

1. Clean the inspection surface properly.

• Contaminants such as oil, grease, scale etc, may interfere with interpretation of results.

2. Adequately illuminate the specimen with light.
3. Examine the specimen with eyes or take the assistance of light-sensitive devices.

Visual Inspection Testing Equipment

• Different kinds of equipment are used to improve the inspection quality.
• Equipment categorized into two parts:

1. Optical Aids
2. Mechanical Aids

• Widely Used Optical Aids:
• Magnifiers (magnifying glasses, microscopes)
• Borescopes and fiber optic borescopes
• Inspection Mirrors (especially small and angled mirrors)
• Lighting or Illumination
• Other Equipment:
• Video borescope
• Robotic devices

Mechanical Aids

• Several mechanical gauges are also used to assist examinations.
• Included screw pitch gauge, measuring rules and tapes.
• Included thread, pitch & thickness gauges.
• Also included plumb lines plus angle measuring tools
• Includes calipers and micrometers with lever gauges for various applications.

Visual Inspection Advantages

• It is a routine procedure.
• The cost of visual inspection is low.
• Exam is effective before, during, and after manufacturing.
• Testing is simple, and testing speed is high.
• Testing is possible while the test object is being used.
• Records can be made with latest equipment.

Visual Inspection Limitations

• Limited to surface defects.
• Limited to the observers visual acuity
• Eye fatigue may cause the defects to remain undetected.

Magnetic Particle Inspection

• Detects surface and shallow subsurface discontinuities in ferromagnetic materials.
• Materials: iron, nickel, cobalt, and some of their alloys.
• MPI is fast, easy to apply, and part surface preparation is not as critical as for some other NDT methods.
• It uses magnetic fields and small magnetic particles (e.g., iron filings).
• The fields and particles are used to detect flaws in components.
• The method checks castings, forgings, and weldments.
• Many industries determine a component's fitness-for-use.
• Based on magnetic flux leakage caused by material discontinuities.
• The leakage collects magnetic particles to form indications.
• Direct/indirect methods magnetize the component for inspection.
• Necessary to demagnetize the component after inspection.
• It can interfere with manufacturing processes or service.

MPI Principle

• Magnetic moments in a ferromagnetic material will align parallel with each other.
• If a surface or subsurface discontinuity is present, magnetic flux leaks out of the material.
• Air cannot support as much magnetic field as metals.
• Magnetic flux collects ferromagnetic particles such as iron powder.
• It makes discontinuity size/shape easily visible.

MPI Field Orientation and Flaw Detectability

• Crack orientation against magnetic lines determines if the crack can be detected properly.
• Orientation of 45 to 90 degrees between magnetic field and defect is good to indication.
• Defects may occur in various directions, each part is normally magnetized in two directions at right angles to each other.
• Circular magnetization example: longitudinal defects are detectable.
• Transverse-type defects are not detectable.

MPI Basic Steps

• Magnetic particle inspection has 5 steps.

1. Part preparation: Pre-cleaning/degassing is done on the component.

• Contaminants may prevent particles from being attracted to leakage fields

2. Fine magnetic particles applied on the test surface are applied to the test surface.

• Particles used in MPI are are finely divided ferromagnetic materials with high magnetic permeability and low retention

3. Introduction of magnetic field: Direct and Indirect Magnetization
4. Examination of the component surface for defect
5. Demagnetization of the component.

MPI Demagnetization

• Parts inspected may have an objectionable residual magnetic field sometimes.
• Field may interfere with downstream manufacturing operations.
• Effects of residual magnetism are that machining is affected, causes chips to cling to a component.
• 'Arc blow' condition may also occur in welding.
• Arc blow may cause the weld arc to wander or filler metal to be repelled from the weld.
• Two methods of demagnetization as are:
• Heating Method: random orientation can be achieved best by heating material above Curie temperature
• Electrical Method: subjecting the component to a reversing and decreasing magnetic field will return dipoles to a nearly random orientation.

MPI Advantages

• It is rapid and economical, and staff can be trained rapidly.
• It can detect both surface and near sub-surface discontinuity.
• It can inspect parts with irregular shapes easily.
• Inspection and indications are fast and visible directly on the specimen surface.
• It is a portable method when used with battery-powered equipment.

MPI Limitations

• It can only be used on ferromagnetic materials.
• Only effective for seeking surface-breaking or near-surface defects.
• Components must be magnetized in at least two directions for full coverage.
• Weldments with different magnetic characteristics are difficult to inspect.
• Post-cleaning and post-demagnetization is required.

Dye Penetrating Testing

• Also called liquid penetrant inspection (LPI) or penetrant testing (PT).
• Widely applied and low-cost; used to locate surface breaking defects in all non-porous materials such as metals, plastics, or ceramics.
• Used to inspect casting, forging, and welding defects such as hairline cracks.
• Will locate hairline cracks, surface porosity and leaks in new products.
• Also detects fatigue cracks on in-service components.
• DPI is based upon capillary action.
• Low surface tension fluid penetrates into clean, dry surface-breaking discontinuities.

DPI Procedure

1. Pre-cleaning removes rust, dust, or oil-grease coatings from the test piece.
2. Penetrant is applied and soaked:

• Achieves dwell time
• HasHigh surface wetting ability

3. Test piece is rinsed, and left to dry
4. Apply developer, fine grained white powder is suspended in liquid with waiting time.

• The dye comes out and gets attached to powder particles.

DPI Advantages

• It has few material limitations, inspects metallic and non-metallic plus magnetic and nonmagnetic materials.
• It inspects conductive and nonconductive materials.
• Large areas and large volumes of parts/materials are inspected rapidly and at low cost.
• Parts with complex geometric shapes are routinely inspected.
• Indications are visual, directly on the surface,
• Aerosol spray cans make penetrant materials portable.
• Penetrant materials and equipment are inexpensive.

DPI Limitations

• Only surface-breaking defects are detected.
• Uses materials with a nonporous, smooth surface.
• Pre-cleaning is critical, contaminants can mask defects.
• Metal smearing from machining or blasting must be removed prior to DPI.
• Inspector must have direct access.
• Surface finish and roughness affect sensitivity.
• Post-cleaning of acceptable parts must take place.
• Chemical handling needs care and proper disposal.

Ultrasonic Inspection

• A non-destructive test method using ultrasonic waves.
• Used for examinations and measurements.
• Ultrasonic Waves are high-frequency sound waves.
• Waves vibrate above the upper audible limit, above 20 kHz (20,000 vibrations/second).
• Sound has similar properties, however ultrasonic waves are beyond human hearing range.
• Ultrasonic waves cannot travel through a vacuum.
• Wave speed remains constant, wave travels at the speed of sound in a medium with constant velocity.
• Reflection and Refraction behaves like light waves.
• Material Properties impact the velocity, wave speed depends on density and Young's modulus of material.
• Waves are faster in denser media with typical speed order: Vgas < Vliquidsolid

UI principles

• Acoustic Impedance (Z) = material density (p) * acoustic velocity (V)
• Ultrasound travels in a constant line.
• Is reflected when an interface between materials is encountered with different acoustic impedances.
• Strong vs Weak Reflection: large difference at interfaces, compared to a smaller difference
• These respective differences are strong and weak.

UI reflection

• Reflection Coefficient (R) = fraction of incident wave intensity reflected
• Calculated using R = [(Z2-Z1)/(Z2+Z1)]2
• Z1 and Z2 are the media acoustic impedances.

UI operation

• Pulser/Receiver produce high voltage electrical pulses.
• Transducer is driven by a pulser providing high-frequency ultrasonic energy
• Energy is introduced to the examined material
• Propagates as waves pass flaws
• Discontinuities are measured by waves discontinuity (crack), with some energy reflecting
• Signal Transformation: Transduction turns wave signal into screen signal
• Signal analysis: Signal travel time is related to distance travelled, the signal's size helps determine flaws.

UI - couplant use

• Couplant material (usually liquid) facilitates the transmission of ultrasonic energy.
• It facilities transfer from the transducer into the specimen
• Acoustic Impedance Mismatch: The couplant is necessary because there is a large acoustic impedance mismatch between air and the test specimen.
• Function: It displaces air, allowing more sound energy to enter specimen.

UI techniques

• Two techniques are pulse-echo and and through transmission.
• Pulse-Echo Technique has ultrasonic waves, transmitted into the under-test material.
• Reflected waves (echoes) from discontinuities are received by the same or another transducer.
• Display: relative size and depth of is calibrated.
• Accessibility: useful where access to only one side of the material is possible.
• Through Transmission Technique has two transducers in use.
• One transducer is a transmitter,. the other is a receiver.
• Both are located opposite the test specimen.
• Transducer strength is measured with this method to determine discontinuities that are not good reflectors

UI Advantages

• Superior depth of penetration compared to alternatives.
• Only requires access to one side of the material when using pulse-echo.
• High precision in locating objects.
• Systems can make detailed automates images, and flaw presence impacts the severity assessment.

UI Limitations

• The surface must be accessible to transmit ultrasound.
• Requires more extensive skill and training compared to alternatives.
• Requires a couplant for the test specimen.
• Difficult to read and interpret rough, irregular, small, thin materials.
• Linear defects oriented to the sound beam are hard to detect.

Radiographic Inspection Intro

• Creates images through material and components inner structure
• Used to verify its internal structure and integrity
• Process begins with Roentgen's X-rays breakthrough by Roentgen by Becquerel in 1895 and Becquerel's Radioactivity in 1896
• Term radiography is used with processes producing film images.
• X-rays and Gamma are used in the process
• Radioactive processes produce greater photon energy than X-Ray generators
• This has broadened to usage to inspect industry/welds
• Castings reveal castings presence via H absorption.

Radiographic Inspection principles

• Short wavelength and high energy waves can achieve high penetration
• Waves run through some components, materials impact its transmission
• radiological densities of materials differ.
• Radiological density measure's material absorbtion
• Radiological density is calculated and represented as scales of grey.
• It's calculation is based on atomic structure, that is atom's # number
• Commonly used for Al (13) and Ti (22).

Radiographic Inspection Methodology

• Placed source radiation radiation passes part goes on film.
• The part stops some of the radiation, thicker regions resist radiation more
• Unabsorbed film emulsion is similar to photography, light reflects to take the imagine.
• Two-dimensional images are created through processing.
• Object variations caused through the image are varied,
• Density is based evaluation with known characteristics for film.

Basic Testing Elements

1. A penetrating X-Ray radiation source
2. Material being read in its component form
3. Film which processes photographic read process
4. trained reading professional
5. experienced read interpreter

Radiographic Inspection Factors

• Can be easy to detect of radiation
• Thin energy walls
• High and low radiation beams
• And respective readings
• It is difficult to source accurate readings

Computed Tomography intro

• Imaging technique for cross-sectional imaging for solid objects
• Technique developed from Greek words "tomos" for slice and "graphia" for description

RI Advantages

• Inspection of parts and composition
• Includes metals, composites and ceramics.
• Quantifies component results, and provides insights to structure and important data regarding integrity
• Record of inspection as image
• Works with large objects
• Sensitive to small defects

RI Disadvantages

• Concern over safety is a great factor, and correct safety and procedures need to be followed.
• Proper exposure steps must be taken, increasing time.
• Experience is needed.
• Cost of setting up and maintaining equipment.
• Environmental impact due to material handling.
• Portability and movement and usage is limited due to size.

Safety in NDT

• Radiographic Testing (RT)
• Radiation Exposure: control strict radiation rays protocols such as X-rays exposure with barriers and dosimeters.
• Ultrasonic Testing (UT)
• Electrical Safety: grounded tools, disconnected when not in use
• Couplant Handling: with non-toxic solutions/material
• Avoid skin irritants
• Magnetic Particle Testing (MT)
• Magnetic Fields: sensitive to pacemaker/magnetic tools
• Dust Control: exhausted to prevent magnetic particle
• Liquid Penetrant Testing (PT)
• Chemical Exposure: penetrants/developers
• Ventilation prevent fumes