Casting Quality Control

CASTING QUALITY CASTING QUALITY CONTROLCONTROL

VINAY . SVINAY . S

AGENDAAGENDA

INTRODUCTION TO CASTING QUALITY INTRODUCTION TO CASTING QUALITY CONTROL.CONTROL.

CASTING DEFECTS, FACTORS RESPOCASTING DEFECTS, FACTORS RESPONSIBLE , REMEDIES.NSIBLE , REMEDIES.

CLEANING OF CASTINGSCLEANING OF CASTINGS INSPECTION METHODS AND TESTING INSPECTION METHODS AND TESTING

METHODS TO EVALUATE A CASTMETHODS TO EVALUATE A CAST.. Q / A Q / A

Sand Casting Steps

IntroductionIntroduction Reduces total output, increases the cost of Reduces total output, increases the cost of

production.production. Casting defects may be defined – Casting defects may be defined – those those

characteristics that create a deficiency or characteristics that create a deficiency or imperfection to quality specifications imposed by imperfection to quality specifications imposed by design and service requirements.design and service requirements.

Even in modern foundries the rejection rate – as Even in modern foundries the rejection rate – as high upto 20% of the number of casting produced.high upto 20% of the number of casting produced.

Hence all efforts must be taken to bring down the Hence all efforts must be taken to bring down the percentage of rejection.percentage of rejection.

For this to happen one should have sound For this to happen one should have sound knowledge of principles of casting, casting design, knowledge of principles of casting, casting design, potential defects, causes, remedies for same, potential defects, causes, remedies for same, inspectional methods, testing methods.inspectional methods, testing methods.

Types of Defects

ƒ Based on Location: ƒ Based on Cause: External Raw materials Internal Product design

Tooling design ƒ Based on Type:

Process parameters Geometric

Process control Integrity

ƒ Based on Stage: ƒ Based on Size/Severity:

Casting Small/Minor

Rough machining Large/Major

Finish machining ƒ Based on Process: Service

Moulding-related ƒ Based on Reparability: Filling-related Repairable Solidification-related. Irreparable

CLASSIFICATION OF CASTING CLASSIFICATION OF CASTING DEFECTSDEFECTS

Casting Defects

Based on nature of defects

Based on contributing factors

Surface defects

Internal defects

Incorrect chemical compo.

Unsatisfactory mech. properties

Defects caused by pattern Making & molding

Defects caused due to improper

Gating & rise ring

Defects caused by molten metal

Surface defectsSurface defects : may be visible on : may be visible on surface surface

incorrect shape & size, laps, flashes, poor incorrect shape & size, laps, flashes, poor surface finish.surface finish.

Internal defectsInternal defects : these are present in : these are present in interior of cast. Can be revealed through interior of cast. Can be revealed through NDT techniques.NDT techniques.

Incorrect chemical compositionIncorrect chemical composition – – formation of undesirable microstructure.formation of undesirable microstructure.

Unsatisfactory mechanical properties – Unsatisfactory mechanical properties – low quality, poor percent of usage.low quality, poor percent of usage.

BASED ON NATURE OF BASED ON NATURE OF DEFECTSDEFECTS

BASED ON CONTRIBUTING BASED ON CONTRIBUTING FACTORSFACTORS

Defects caused by pattern making and Defects caused by pattern making and mouldsmoulds::

results in incorrect dimensions, poor surface results in incorrect dimensions, poor surface finish, flash, mismatch. finish, flash, mismatch.

Defects – improper gating & riseringDefects – improper gating & risering

results in cold shut, misrun, inclusions, pulls, results in cold shut, misrun, inclusions, pulls, shrinkage cavities.shrinkage cavities.

Defects caused – molten metalDefects caused – molten metal

results in cold shut, metal penetration, porosity. results in cold shut, metal penetration, porosity.

CAUSES FOR DEFECTSCAUSES FOR DEFECTS

Unsuitable and unsatisfactory raw Unsuitable and unsatisfactory raw materials.materials.

Application of unsatisfactory casting Application of unsatisfactory casting principles.principles.

Use of improper tools, equipment, Use of improper tools, equipment, appliances or patterns.appliances or patterns.

Unprofessional management.Unprofessional management. Unsatisfactory setting up of procedures, Unsatisfactory setting up of procedures,

poor work discipline, lack of training.poor work discipline, lack of training.

CASTING DEFECTS ,FACTORS CASTING DEFECTS ,FACTORS RESPONSIBLE FOR THEM AND RESPONSIBLE FOR THEM AND

REMEDIESREMEDIES CORE SHIFTCORE SHIFT WRAPED CASTINGWRAPED CASTING SWELLSWELL FINFIN BLOW HOLESBLOW HOLES PIN HOLESPIN HOLES GAS HOLESGAS HOLES SHRINKAGE CAVITYSHRINKAGE CAVITY HOT TEARHOT TEAR INCLUSIONSINCLUSIONS MISRUN AND COLD SHUTMISRUN AND COLD SHUT EXPANSION SCABSEXPANSION SCABS

CORE SHIFTCORE SHIFT

Results in mismatch of the section.Results in mismatch of the section. Usually easy to identify.Usually easy to identify. Can be repaired provided with in Can be repaired provided with in

tolerable limits.tolerable limits. Misalignment of flasks is a common Misalignment of flasks is a common

cause.cause. Can be prevented by ensuring proper Can be prevented by ensuring proper

alignment of pattern, die parts, alignment of pattern, die parts, molding boxes.molding boxes.

CORE SHIFTCORE SHIFT

WARPED CASTINGWARPED CASTING

Warpage - Undesirable deformation in Warpage - Undesirable deformation in a casting.a casting.

Large cross sections or intersections Large cross sections or intersections are particularly prone to warping.are particularly prone to warping.

Can be reduced by proper casting Can be reduced by proper casting design, judicious use of ribs.design, judicious use of ribs.

Cannot be eliminated but allowances Cannot be eliminated but allowances can be given along with machining can be given along with machining allowance, to remove by machining.allowance, to remove by machining.

SWELL SWELL Swell- enlargement of the mould cavity by Swell- enlargement of the mould cavity by

metal pressures, results – localized or metal pressures, results – localized or overall enlargement of castingsoverall enlargement of castings

Caused due to insufficient ramming of the Caused due to insufficient ramming of the sand.sand.

Also due to rapid pouring of molten metal.Also due to rapid pouring of molten metal. Also due to insufficient weighting of Also due to insufficient weighting of

mouldmould Remedies – avoid rapid pouring, provide Remedies – avoid rapid pouring, provide

sufficient ram on sands , proper weighting sufficient ram on sands , proper weighting of moulds.of moulds.

FINFIN

A thin projection of metal – not a part A thin projection of metal – not a part of cast.of cast.

Usually occur at the parting of mould Usually occur at the parting of mould or core sections.or core sections.

Causes - Incorrect assembly of cores Causes - Incorrect assembly of cores and moulds, improper clamping, and moulds, improper clamping, improper sealing.improper sealing.

Remedy is proper clamping of cores Remedy is proper clamping of cores and mould.and mould.

FINS OR FLASH

BLOW HOLESBLOW HOLES They are entrapped gases.They are entrapped gases. This is result of gases from mould, This is result of gases from mould,

molten metal and steam sand.molten metal and steam sand. Remedy is to provide sufficient Remedy is to provide sufficient

permeability, making vent holes, use permeability, making vent holes, use minimum quantity of water.minimum quantity of water.

Also use of dry sand moulds, use of no Also use of dry sand moulds, use of no bake sands.bake sands.

BLOW HOLE

SHRINKAGE CAVITYSHRINKAGE CAVITY

It is a void or depression in the It is a void or depression in the casting caused mainly by casting caused mainly by uncontrolled solidification.uncontrolled solidification.

Remedy is apply principles of Remedy is apply principles of casting, provide adequate risers, casting, provide adequate risers, feeders, which supply the molten feeders, which supply the molten metal to compensate the shrinkage.metal to compensate the shrinkage.

Shrinkage cavity

HOT TEARHOT TEAR If the mould surface is rigid, it If the mould surface is rigid, it

restrains solidifying casting from restrains solidifying casting from contraction and resulting in contraction and resulting in development of cracks or tear, also development of cracks or tear, also called pulls.called pulls.

Remedy is avoid excessive ramming.Remedy is avoid excessive ramming. Controlled ramming should be done.Controlled ramming should be done.

Hot Tears

ME 6222: Manufacturing Processes and Systems 7 Prof. J.S. Colton

METAL PENETRATIONMETAL PENETRATION

When molten metal penetrates in the When molten metal penetrates in the spaces between sand grains.spaces between sand grains.

Result - sand will be tightly held to Result - sand will be tightly held to the casting.the casting.

Remedy – good optimum mould Remedy – good optimum mould hardness.hardness.

MISRUN & COLDSHUTMISRUN & COLDSHUT

Misrun occurs particular section of Misrun occurs particular section of casting is solidified before filling .casting is solidified before filling .

when two streams of molten metal when two streams of molten metal which are too cold to meet and do which are too cold to meet and do not fuse then results in coldshut.not fuse then results in coldshut.

Prevented by proper casting design.Prevented by proper casting design.

Casting Defects


EXPANSION SCABSEXPANSION SCABS

This is due to expansion property of sand.This is due to expansion property of sand. Due to high temperature sand will expand.Due to high temperature sand will expand. Low thermal stability of sand used.Low thermal stability of sand used. This expansion is prevented by mould This expansion is prevented by mould

condition, results in cracks, poor surface condition, results in cracks, poor surface finish.finish.

Remedy is to reduce use clay content.Remedy is to reduce use clay content. Use of additives which reduce thermal Use of additives which reduce thermal

expansion of sand.expansion of sand.

Casting Defects


CLEANING OF CLEANING OF CASTINGSCASTINGS

This operation is also referred a fettling.This operation is also referred a fettling.

Operations may beOperations may be Knocking out of dry sand cores.Knocking out of dry sand cores. Removal of gates and risers.Removal of gates and risers. Extraction of fins and unwanted Extraction of fins and unwanted

projections.projections. Cleaning and smoothening of surface.Cleaning and smoothening of surface. Repairing the casting, to fill up defects.Repairing the casting, to fill up defects.

Knocking out of dry sand Knocking out of dry sand corescores

Dry sand cores can be removed by Dry sand cores can be removed by rapping or knocking with an iron rapping or knocking with an iron bar.bar.

For quicker removal hydraulic and For quicker removal hydraulic and pneumatic equipments can be used.pneumatic equipments can be used.

These devices also helps in cleaning These devices also helps in cleaning and smoothening.and smoothening.

Removal of gates and Removal of gates and risers.risers.

Choice of removal methods – depend Choice of removal methods – depend upon size and shape, type of cast.upon size and shape, type of cast.

Using hammer to knock off, this is Using hammer to knock off, this is particularly suitable for brittle materials.particularly suitable for brittle materials.

Sawing- may be band saw, circular saw, Sawing- may be band saw, circular saw, power hacksaw.power hacksaw.

Using flame generated by oxyacetylene Using flame generated by oxyacetylene gas.gas.

Employing abrasive cutting machines.Employing abrasive cutting machines.

Extraction of fins and Extraction of fins and unwanted projectionsunwanted projections

This operation is also called This operation is also called snagging.snagging.

Methods include – using grindersMethods include – using grinders Chipping with hand tool.Chipping with hand tool. Flame cutting.Flame cutting. Using electric arc equipment.Using electric arc equipment. Filing.Filing.

Cleaning and smoothening Cleaning and smoothening of castingof casting

Manual methodManual method – – Done using wire brushDone using wire brush Extremely tedious and time Extremely tedious and time

consuming.consuming. As a result mechanical methods are As a result mechanical methods are

employedemployed

Cleaning and smoothening Cleaning and smoothening of castingof casting

Mechanical methods include – Mechanical methods include – o TumblingTumblingo Compressed air impact cleaningCompressed air impact cleaningo Mechanical impact cleaning or shot Mechanical impact cleaning or shot

blastingblastingo Hydro blasting.Hydro blasting.

TumblingTumbling

Components are place sin barrel along Components are place sin barrel along with steel rodswith steel rods

Barrel is then rotated its central axis – Barrel is then rotated its central axis – peening action takes place – casting are peening action takes place – casting are cleaned.cleaned.

Care should be taken – not to charge very Care should be taken – not to charge very tightly to prevent any relative motions.tightly to prevent any relative motions.

Hard castings - are not fragile enough are Hard castings - are not fragile enough are suitable for tumbling.suitable for tumbling.

Compressed air impact Compressed air impact cleaningcleaning

Stream of suitable abrasive particles Stream of suitable abrasive particles along with compressed air is along with compressed air is directed – at high velocities.directed – at high velocities.

This is done in tightly closed This is done in tightly closed chambers.chambers.

Due to impact surface gets cleaned.Due to impact surface gets cleaned.

Mechanical impact cleaning or Mechanical impact cleaning or shot blastingshot blasting

Abrasive particles are thrown by Abrasive particles are thrown by centrifugal force.centrifugal force.

Has vane rotating at speed of 1800 to Has vane rotating at speed of 1800 to 2500 rpm.2500 rpm.

Abrasive particles are fed at angular Abrasive particles are fed at angular positions near the centre.positions near the centre.

Centrifugal force causes particles to move Centrifugal force causes particles to move outwards the periphery until it reaches outwards the periphery until it reaches the outer tips and is thrown at workpiece.the outer tips and is thrown at workpiece.

Due to impact surface is cleaned.Due to impact surface is cleaned.

Hydro blastingHydro blasting

High velocity stream – 15% sand and High velocity stream – 15% sand and 85% water is directed against the 85% water is directed against the surface through nozzle.surface through nozzle.

Thus by nozzle pressure increases – up Thus by nozzle pressure increases – up to 600 m / min.to 600 m / min.

Smallest casting that can be cleaned, Smallest casting that can be cleaned, weighs at least 120 kgs.weighs at least 120 kgs.

Provisions are made to recover sand.Provisions are made to recover sand.

INSPECTION OF INSPECTION OF CASTINGCASTING

PROCESS INSPECTIONPROCESS INSPECTION VISUAL INSPECTIONVISUAL INSPECTION DIMENSIONAL INSPECTIONDIMENSIONAL INSPECTION

PROCESS INSPECTIONPROCESS INSPECTION

Inspection done while parts are Inspection done while parts are being processed.being processed.

This is helpful to detect defects at This is helpful to detect defects at the start and allow the corrections.the start and allow the corrections.

This is an preventive act.This is an preventive act.

VISUAL INSPECTIONVISUAL INSPECTION

Simplest and most fastest Simplest and most fastest inspectional methods.inspectional methods.

Most commonly employed.Most commonly employed. Usually good to check surface Usually good to check surface

defects.defects. Fails to identify internal defects.Fails to identify internal defects.

DIMENSIONAL DIMENSIONAL INSPECTIIONINSPECTIION

Before casting are to be machined Before casting are to be machined dimensional inspection is done.dimensional inspection is done.

Castings are placed on surface plate Castings are placed on surface plate or surface table with angle - or surface table with angle - measuring instruments.measuring instruments.

Various measuring instruments are Various measuring instruments are employed for a first set of castings, employed for a first set of castings, so as to standardize subsequent so as to standardize subsequent castings. castings.

TESTING METHODSTESTING METHODS

PRESSURE TESTINGPRESSURE TESTING DESTRUCTIVE TESTINGDESTRUCTIVE TESTING NON DESTRUCTIVE TESTINGNON DESTRUCTIVE TESTING

PRESSURE TESTINGPRESSURE TESTING

Casting that is used for containing or Casting that is used for containing or conveying liquids, gases, such type are conveying liquids, gases, such type are subjected to pressure testing.subjected to pressure testing.

It is tested for any leaks through their It is tested for any leaks through their walls.walls.

Leaks may be detected by submerging Leaks may be detected by submerging the complete casting under water for gas the complete casting under water for gas pressures.pressures.

Or by visual inspection by liquid Or by visual inspection by liquid pressures.pressures.

DESTRUCTIVE TESTINGDESTRUCTIVE TESTING

This test is done causing harm to the This test is done causing harm to the casting i.e. by destroying it.casting i.e. by destroying it.

Various tests include fatigue tests, Various tests include fatigue tests, compression tests, creep tests etc.compression tests, creep tests etc.

NON DESTRUCTIVE NON DESTRUCTIVE TESTINGTESTING Here parts to be tested are inspected for Here parts to be tested are inspected for

internal defects and surface defects internal defects and surface defects without destroying the component.without destroying the component.

Various methods available are:Various methods available are: Liquid penetrate test LPILiquid penetrate test LPI Magnetic particle inspection MPIMagnetic particle inspection MPI X – Ray radiography XRRX – Ray radiography XRR Ultrasonic testing UTUltrasonic testing UT Eddy current test ECTEddy current test ECT Gamma ray radiography GRRGamma ray radiography GRR

Liquid penetrant testLiquid penetrant test

Surface preparationSurface preparation Penetrant applicationPenetrant application Penetrant dwellPenetrant dwell Excess Penetrant removalExcess Penetrant removal Developer applicationDeveloper application Indication developmentIndication development InspectionInspection Clean surface.Clean surface.

Magnetic Particle Magnetic Particle Inspection - MPIInspection - MPI

Most satisfactory method Used to Most satisfactory method Used to find surface and sub surface defects.find surface and sub surface defects.

It is quick, cheap, very sensitiveIt is quick, cheap, very sensitive Can only be applied to ferrous Can only be applied to ferrous

metals like steel, cast iron etcmetals like steel, cast iron etc

Principle - MPIPrinciple - MPI

When a metal placed in magnetic field, When a metal placed in magnetic field, magnetic flux are intersected by the defect magnetic flux are intersected by the defect – magnetic poles are induced on either side – magnetic poles are induced on either side of discontinuity.of discontinuity.

Abrupt change in path of flux – local Abrupt change in path of flux – local leakageleakage

This can detected when magnetic particles This can detected when magnetic particles are attracted towards defective region.are attracted towards defective region.

Magnetic particles piles up in defective Magnetic particles piles up in defective region.region.

ProcedureProcedure Preparation of specimenPreparation of specimen Surface should be cleaned thoroughly, Surface should be cleaned thoroughly,

free from rust, grease, oil, paint etc.free from rust, grease, oil, paint etc. Cleaning of surface can be done using Cleaning of surface can be done using

wire steel brushes, shot blasting wire steel brushes, shot blasting technique or by using solvents.technique or by using solvents.

MagnetizationMagnetization

To induce magnetic lines – two methods To induce magnetic lines – two methods – permanent magnet – electromagnet.– permanent magnet – electromagnet.

Electromagnet is proffered as it has Electromagnet is proffered as it has capability to produce stronger capability to produce stronger magnetic field.magnetic field.

Magnetization – two types – Magnetization – two types – longitudinal or for parallel defects – longitudinal or for parallel defects – circular or for perpendicular defects.circular or for perpendicular defects.

For a defect to be detected flux lined For a defect to be detected flux lined should pass perpendicular line.should pass perpendicular line.

Application of magnetic Application of magnetic particlesparticles

Magnetic particles are applied uniformly Magnetic particles are applied uniformly so that they move on the surface freely.so that they move on the surface freely.

The particles must be as fine as possible.The particles must be as fine as possible. Generally pulverized iron oxide, Generally pulverized iron oxide,

carbonyl iron powder are used.carbonyl iron powder are used. Powder can be of Powder can be of

Powder suspended in liquid petroleumPowder suspended in liquid petroleum Dry powderDry powder Fluorescent powder – can be viewed in UV Fluorescent powder – can be viewed in UV

light.light.

Inspection of defectInspection of defect

Generally carried out in good light.Generally carried out in good light. If no defects then regular pattern, if If no defects then regular pattern, if

presence of defects then flux lines presence of defects then flux lines distorted.distorted.

Magnetic particles spreads out at Magnetic particles spreads out at the point of defects indicating the point of defects indicating presence of defect.presence of defect.

X – ray radiographyX – ray radiography X – Rays are produced when high energy X – Rays are produced when high energy

electrons collide with the nucleus of an electrons collide with the nucleus of an atom .atom .

The x – ray equipment ---which produces The x – ray equipment ---which produces incandescent light, placed near a highly incandescent light, placed near a highly charged cathode, causing the electrons to charged cathode, causing the electrons to flow from the cathode which is attributed by flow from the cathode which is attributed by the anode or target.the anode or target.

The intensity of x – rays produced is directly The intensity of x – rays produced is directly proportional to the number of electrons proportional to the number of electrons produced at the filament.produced at the filament.

The pattern of the x – ray so produced The pattern of the x – ray so produced depends on the shape of the target. depends on the shape of the target.

X – ray radiographyX – ray radiography A radiographic film is placed next to the part to be A radiographic film is placed next to the part to be

tested and x rays are directed against the part. tested and x rays are directed against the part. The x – rays will pass through the part to be tested The x – rays will pass through the part to be tested

proportional to the density and thickness of the part.proportional to the density and thickness of the part. The absorption of x – rays is directly proportional to The absorption of x – rays is directly proportional to

the density of and thickness of the part. If the part the density of and thickness of the part. If the part has no defects, the x- rays will pass uniformly has no defects, the x- rays will pass uniformly through the part. through the part.

However if there are any defects such as porosity However if there are any defects such as porosity which leads to lesser density, the penetration of x – which leads to lesser density, the penetration of x – rays will be move through them which shows as rays will be move through them which shows as darker areas on the film.darker areas on the film.

X – Rays technique is effective in locating cracks, X – Rays technique is effective in locating cracks, slay inclusions, porosity, blow holes, pin holes etc.slay inclusions, porosity, blow holes, pin holes etc.

X- Rays can be used for inspection of casting in all X- Rays can be used for inspection of casting in all type of metals, like steel, aluminum, magnesium etc. type of metals, like steel, aluminum, magnesium etc.

Ultrasonic TestingUltrasonic Testing Ultrasonic Testing (UT) uses high frequency Ultrasonic Testing (UT) uses high frequency

sound energy to conduct examinations and sound energy to conduct examinations and make measurements. make measurements.

Ultrasonic testing is based on piezoelectric Ultrasonic testing is based on piezoelectric effect which converts electrical energy to effect which converts electrical energy to mechanical energy thus generating ultrasonic mechanical energy thus generating ultrasonic waves waves

Ultrasonic waves are generated when a high Ultrasonic waves are generated when a high frequency alternating current of about a frequency alternating current of about a million times per second is impressed across million times per second is impressed across the forces of piezoelectric materials like quartz the forces of piezoelectric materials like quartz crystal. crystal.

The crystal expands in full half of the cycle and The crystal expands in full half of the cycle and contracts when the electric field is increased, contracts when the electric field is increased, thus producing mechanical vibrations.thus producing mechanical vibrations.

UT arrangementUT arrangement

Ultrasonic TestingUltrasonic Testing When there is a discontinuity (such as a crack) in the When there is a discontinuity (such as a crack) in the

wave path, part of the energy will be reflected back wave path, part of the energy will be reflected back from the flaw surface from the flaw surface

The reflected wave signal is transformed into an The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on electrical signal by the transducer and is displayed on a screen a screen

In the applet below, the reflected signal strength is In the applet below, the reflected signal strength is displayed versus the time from signal generation to displayed versus the time from signal generation to when an echo was received. Signal travel time can be when an echo was received. Signal travel time can be directly related to the distance that the signal traveled directly related to the distance that the signal traveled

From the signal, information about the reflector From the signal, information about the reflector location, size, orientation and other features can location, size, orientation and other features can sometimes be sometimes be

Education

Casting Quality Control