Abstract
Metal casting industries are actively involved to reduce the scrap rejection and rework during the manufacturing process of the components. To achieve this, the production concerns must follow the quality control procedures correctly and perfectly without any negligence. Timely implementation of the modified techniques based on the quality control research is a must to avoid defects in the products. In this review paper, some of the solutions and quality control aspects are explained in a simplified manner to eliminate the unawareness of the foundry industrial personnel who work in the casting manufacturing quality control departments. This review paper provides very valuable information to the young manufacturing and mechanical engineers who have interest to start their career in the manufacturing concerns of medium and large scale captive foundries. This paper discusses all about the general quality control aspects in a detailed manner. Besides, statistical quality control (SQC) is also highlighted to understand its recent application and techniques adopted in the developing metallurgical engineering foundries. © 2005 Elsevier B.V. All rights reserved.
Keywords: Quality control; Statistical quality control (SQC); Quality circle; Quality assurance; Control charts; Captive foundries; Total quality control (TQC)
1. Introduction
Quality is defined as the fitness for use or purpose at the most economical level. It is an integral part of the process of design, manufacture and assembly. It can be assured by having effective procedures and controls at various stages. Manufacturing industries like foundries do not enjoy monopoly but they have to face competition. To overcome this problem andtoretaintheshareofthemarket,itisnecessarytoconstantly improve the quality of the cast product without the increase in the price of the products [1,2]. The price is influenced by the cost of production, which in turn is influenced by rework or rejection. Attention to quality assurance can reduce the wasteful rework. Aiming for quality in the first instance can reduce the cost of casting production. This quality production results in the company’s growth and profitability. Quality in a product is difficult to define and invariably involves a consideration of the service environment. The most meaningful definition involves the concept of fitness for a given purpose
∗ Corresponding author. E-mail address: hamouda@eng.upm.edu.my (A.M.S. Hamouda).
or application at a prescribed life of number of hours, months or years in service. For a given set of service conditions, quality and reliability are interrelated to a certain extent. The minimum quality acceptable in any application is that level of quality necessary to ensure that the prescribed portion of the components will pass through the predicted service life without failure. If all the cast components survive the designed period of service under the given environmental conditions, then this constitutes 100% reliability [2]. The basic concepts of qualityarethatthefinishedcastproductsmustmeetestablished specifications and standards and hence customer’s satisfaction will be derived from the quality products and services. Both of these can be attained by integrating quality development, quality maintenance and quality improvement of the product. These three aspects of a product can be achieved through a sound foundry quality control system [3,4]. The various meanings of quality are the fitness for purpose, conformance to requirements, grade, degree of preference, degree of excellence and measure of fulfillment of promises. The cast products should have certain abilities to perform satisfactorily. The factors governing are suitability, reliability, safe and foolproof workability, durability, affordability, maintainability, aesthetic look, satisfaction to customers, economical and versatility. ThT.R. Vijayaram et al. / Journal of Materials Processing Technology 178 (2006) 39–43
factors controlling the quality of casting design depends on the type of the customer in the market, profit consideration, environmental conditions and special requirements of the cast products. There exists a close relationship between quality and reliability. It is given as the sum of the quality now and quality later, which equals to reliability. The quality circles help in the improvement of product quality and productivity [5,6]. It implies the development of skills, capabilities, confidence and creativity of the people through cumulative process of foundry engineering education, pertinent training, work experience and participation [3]. A quality circle is defined as a way of capturing the creative and innovative power that lies within the work force and it is a group of employees, 3–12 doing similar work.
2. Emphasis of quality and quality control in foundries
The inspection of castings has the dual purpose of ensuring that the product confirms to design requirements and of providing information needed for quality control in foundry. Although foundry production and technical staff are concerned inmanyaspectsofqualitycontrol,thesystematiccollectionand interpretationofqualitydataisfrequentlychanneledthroughan inspectiondepartment,whichhasaspecialresponsibilityforthe administrationofstandardsembodiedincontractsandcommercialrelationships[7].Anoutlinechartforafoundryorganization ofinspectionandqualitycontrolfunctionsisillustratedinFig.1 [7]. The increasing weight given to the latter aspect, however, hasledtonewapproachesinwhichabroaderviewistakenofthe entire issue of quality design and management. A modern qualitycontrolfoundryisthusconcernedwithagreatdealmorethan the routine sorting of properties in relation to specified limits. Much data is obtained by the use of highly sophisticated equipment and techniques and more detailed treatment than simple go or no-go tests is required in interpreting the results. In the chartofFig.2shownbelow,duetoQuilter[29],thisisformally recognized in the titles applied to the various functions and to the staff involved.
Fig. 1. Functional organization of inspection and quality control activities [7].
Fig. 2. Revised concept of foundry organization for inspection and castings quality [7,29].
3. Castings practice and quality control in foundries
Castingscanbedifficulttogetright.Importantrulesareproposedasnecessaryandsufficientforthemanufactureofreliable andqualitycastings[6].Itisproposedthattheyareusedinaddition to existing necessary technical specifications such as alloy type, strength and traceability via international standard qualitysystems,andotherwell-knownandwell-understoodfoundry controls such as casting temperature. The rules are summarized as follows [6].
• Start with a good quality melt. • Avoid turbulent entrainment of the surface film on the liquid. • Avoid laminar entrainment of the surface film on the liquid. • Avoid bubble entrainment by properly designed offset step pouring basin and a well designed gating system. • Avoid core blows by adequate venting. • Avoid shrinkage. • Avoidconvectionbyabsolutelyreducingtheconvectiveloops in the geometry of the casting and rigging. • Reduce segregation, particularly the channel segregation. • Reduceresidualstressbynotquenchinginwater:thenowater quench requirement. • Provide location points for pickup for dimensional checking and machining.
4. Objectives of quality control in metal casting industries
The aims and objectives of foundry quality control are to improve the casting industries income by making the product moreacceptabletothecustomersbyprovidinglonglife,greater usefulness, versatility, aesthetic concepts, maintainability to 41
reduce company’s cost through reduction of losses due to the defectstoachievelessscrap,lessrework,lesssortingandfewer returns from the customers [3]. In large scale captive foundries, quality control should help to optimum quality at the minimum price, to make inspection prompt, to ensure quality control at proper stages to ensure production of non-defective cast products [8–10]. Another important aspect of quality control is judging the conformity of the process by the established standards and taking suitable action when there are any deviations observed.Itscriticalaimistoimprovethequalityandproductivitybyprocesscontrol,experimentationandfromthecustomer’s feed back. This assists for developing quality consciousness in the engineering concerns [4]. The quality control concept has three major attributes. They are: quality control is a form of participative management, quality control is a human resource developmenttechniqueandqualitycontrolisaproblemsolving technique [11]. The basic organization structure of a quality circle should be effectively designed and hierarched for its efficient performance. The structure of quality control may vary from foundry to foundry, but it is useful to have a basic framework as a model. A quality circle will have a top-level steering committee and it will be coordinated by a coordinator through quality control facilitators. The facilitators are further supported by circle leader and circle members [12,13].
5. Quality and process control in foundries
Quality control is concerned with variation of a process or productcharacteristicaboutsomehypotheticalstandardstate.In assessing the significance of deviations from this state, distinction must be drawn between variations due to chance and those resulting from definite changes in production conditions and requiringcorrectiveaction[7].Controlchartsareprovidedwith limits designed to show when these conditions are reached, the limits being established by statistical methods which take into account the natural vibrations arising in process and product. These methods also give guidance in the use of sampling techniques to minimize the task of measurement [14,15]. A limited amount of information concerning variation is given by simple classificationintocategories,forexampleacceptanceorejection oninspection.Muchmoreinformationcanbederived,however, frommeasurementofsomepropertywhichcanbepresentedby a quantitative index, for example a linear dimension, temperature, composition or mechanical property. Collection of such data how the full nature of the variation and enables trends to be detected before a critical condition is reached. The spread of measurements obtained when a large number of minor causes combine to produce variations about some peak value is often characterized by the normal or Gaussian frequency distribution curve [7]. Once the particular Gaussian distribution characteristic of the process is known; therefore, this provides the means of finding whether any further set of readings confirms to the distribution and hence whether the process is operating under control [7]. The particular Gaussian distribution obtained under stable conditions illustrates the inherent variability of the process, or ‘process capability’. Since it represents the normal or chance variation when the process is operating satisfactorily,
it should govern the choice of the process in relation to specification requirements; it is necessary to know not only that a casting can be made, but it can be made with a high probability of success. Control charts are designed to facilitate continuous observationofthemagnitudeandspreadofmeasuredvaluesand to detect changes in either respect indicating that production is deviating from its characteristic stable state. Control charts for average and range are particularly applicable to the control of metalcompositionbyanalysis,tosandtestingandtothedimensional inspection of castings where precision is of maximum importance [7].
6. Steps involved in a foundry quality circle
The various steps in the foundry quality circle operations areproblemidentification,problemselection,problemanalysis, generating alternative solutions, selecting the most appropriative solutions, preparing the plan of the action, presenting the solutiontothemanagementandimplementationofthesolution. Inspection of the casting production technique and the products after manufacture form the basis of quality control [4]. Inspection programme is such that it gives the accurate measure of the efficiency of the whole system and ensures to reduce and sort out the defective products from the lot during processing. Feed back from both the interval inspection and the customers are obtainedregardingqualityfortakingcorrectiveaction[16].The emergenceofthemassproductionleadstothedevelopmentand the sophistication in the inspection techniques.
7. Significance of quality control in the modern casting manufacturing world
In the modern era, quality is considered as an emergent property. The concepts like total quality control (TQC), quality assurance (QA), company wide quality and creativity (CWQC) and zero defect quality control (ZDQC) are developed inspection oriented approach by identifying the problems before they occurandsolvingthem.Thequalityassuranceengineeringplays a vital role in the quality control aspect [5]. The total quality assurance is equal to the sum of the quality of design, quality of manufacturing conforming to design and the quality of performance [17–19]. Fewer defects, lesser scrap, fewer complaints less inspection rejects, better quality, higher efficiency, higher productivity and good customer relations are the advantagesgainedfromthequalityassuranceengineering.Thequality rating of the outgoing cast product is explained by the monthly samplesize.Asitisdesirabletohaveanoverallqualityratingfor the product, the casting defects are further classified as major, minorandcritical,givingappropriateweightagetoeachtypeof the defects [20–22].
8. Inspection methods for quality control of castings in foundries

Inspection methods for castings are followed in terms of the measurement, go- and no-go checking, functional test, visual inspection, 100% inspection and sampling inspection
Inspection for foundry quality control is also classified as normal inspection, reduced inspection and tightened inspection [23,24]. To check and assess the quality, destructive test, non-destructive test and process inspection tests are performed in the casting engineering industries. In the quality control aspect of a cast engineering product, the particular reason for a defectisrepresentedbythecauseandeffectdiagram,otherwise called as Fish bone and Ishikawa diagram [5]. The various steps involved in the Ishikawa diagram analysis are identifying the effect or problem, noting down the main cause categories, manpower, machines, materials and methods, adding causes to the diagram, identifying most likely causes, identifying most probable causes and verifying the causes. Effective quality control makes a lot of financial savings in foundries. The quality control operations include process verification, process control and final inspection. The process verification reviews the specifications of the products, the proposed process and control procedures for compactability [25,26].
9. Responsibilities of foundry industrial personnel in quality control
Quality control responsibilities in foundry process control includeevaluationoftheincomingrawandproductionmaterials, performanceofselectedprocesscontrolinallthesub-processes involved and process control checks performed by the production personnel and information regarding the feed back should be communicated to the production department [2]. The final inspectionisonthedefectsobservation,propertiestesting,hightest frequency, statistical sampling and thorough evaluation for the suspect condition prior to being released to the finishing area or to being rejected [27]. The foundry quality control system comprises a set of procedures that should be followed to fulfill the quality policy. It has to be built in such a way that the best coordination of all the activities will be achieved without compromising any elements affecting the quality of the cast products in the metal casting industries [28,29].
10. Application of statistical quality control aspects at a glance
Afoundryqualitycontrolsystemperformsinspection,testing andanalysistoensurethatthequalityofthecastproductsmanufacturedisasperthelaiddownqualitystandards[5].Itiscalled as statistical quality control (SQC), when statistical techniques are employed to control, improve and maintain the quality or to solvethequalitybasedproblems.Basicstatisticaltechniquesare employed to develop statistical techniques of quality control. It ledtotheintroductionofsamplingtablesandcontrolcharts.Itis usedtocontrolthequalityofthecastproductsduringthevarious manufacturing stages. Statistical analysis is used as a feedback tobringtheappropriatechangesintheprocessandalsoforcontrollingtheprocess.Statisticalqualitycontrolisusedforfoundry inspectionandresearch.Itisbasedonthestatisticaltheorywith control charts and sampling plans forming the opening wedge fortheuseofstatisticsinfoundries[8,9].Moderntechniquesof statisticalqualitycontrolacceptancesamplinghaveanimportant
part to play in the improvement of quality, enhancement of productivity, creation of consumer confidence and development of industrial economy of the country. The most important benefits ofstatisticalqualitycontrolareexpressedintermsofefficiency, reduction of foundry scrap and foundry returns, easy detection of faults, elimination of bottlenecks, better customer relationships, efficient utilization of foundry personnel and machines, increases output and reduces wasted machine and man hours and adherence to specifications [10].
11. Conclusion
Itisconcludedthatcarefulsupervisionwitheffectmotivation of individual employees in achieving the quality is a must in reducingtherejectionandscrapinmetalcastingmanufacturing engineering industries. It is to be emphasized that quality is contributed to by all the members of an organization from the chief executive to the worker and is not the job of only foundry qualitycontrolstaffs.Infoundriesadditiontothequalitycontrol department, a scrap prevention team is needed to improve the quality and this should be felt by each employee.
Acknowledgement
TheauthorsexpresstheirsinceregratitudetotheDepartment ofMechanicalandManufacturingEngineering,UniversitiPutra Malaysia for the consent given to publish this paper.