Maritime University of Szczecin
Akademia Morska w Szczecinie
2011, 27(99) z. 1 pp. 92–97 2011, 27(99) z. 1 s. 92–97
Quality control tools functioning in integrated management
system in the automotive branch company. Case study
Narzędzia kontroli jakości funkcjonujące w zintegrowanym
systemie zarządzania w przedsiębiorstwie branży
motoryzacyjnej. Studium przypadku
Katarzyna Midor
Silesian University of Technology, Faculty of Organisation and Management Institute of Production Engineering
Politechnika Śląska, Wydział Organizacji i Zarządzania, Instytut Inżynierii Produkcji 41-800 Zabrze, ul. Roosevelta 26, e-mail: katarzyna.midor@polsl.pl
Key words: Integrated Management System, methods and quality management tools, SPC, control cards Abstract
The article focused on the role of quality control methods in designing and production processes, on the example of the automotive company, in providing a product’s parameters in accordance with a client’s requirements. Methods and tools used in a process of production, which are instruments controlling and diagnosing quality during production, were analyzed. Much attention was paid to SPC methods that statistically describe a production process.
Słowa kluczowe: Zintegrowany System Zarządzania, metody i narzędzia zarządzania jakością, SPC, karty
kontrolne
Abstrakt
W artykule zwrócono uwagę na rolę metod kontroli jakości w procesie projektowania i produkcji, na przykła-dzie przedsiębiorstwa branży motoryzacyjnej, w zapewnieniu parametrów wyrobu zgodnych z wymaganiami klienta. Przeanalizowano zastosowanie metod i narzędzi w procesie produkcji, które są instrumentami nadzo-rowania i diagnozowania jakości podczas produkcji wyrobu. Zwrócono uwagę na metody SPC, które opisują w sposób statystyczny proces produkcji.
Introduction
Common market, fast growing competition, and even more radical legal determinants, which de-velop in a direction of a bigger human life protec-tion, health and natural environment, forced com-panies to take a comprehensive attitude towards a company management issue. International Stan-dards Organization ISO made an effort to meet these requirements, establishing standards con-cerning the following aspects, quality management system, environment management and management system of safety at work. The aim of introducing Integrated Management System into an
organiza-tion is a company’s aspiraorganiza-tion for improving all fields of activity and processes carried out in a firm [1].
Implementing the requirements of quality management systems, environment protection and safety at work allow to achieve a lot of notable benefits, among which one may count: using the same methods of implementation, verifying, approving and supervising documents, limiting the amount of systemic documents in use. Thanks to a possibility of taking into consideration, at the same time, aspects of quality management, environ-ment and safety at work, a uniform system of documentation is introduced, achieving a high
quality standard that can ensure the increase of a company’s competitiveness on the market, limiting the costs of systems’ maintenance [2, 3].
Quality, treated as a priority goal in a company, may be a key factor in the conditions of high com-petitiveness on the market. Quality management is a collective effort of an organization that aims at increasing quality and improving overall activity of a corporation, in order to achieve optimal effects. Quality ought to be a priority in a producer’s, a supplier’s and a recipient’s activities. It should be expected that a company’s activities were a process of a constant creative learning, which serves to gain skills of adjusting to every customer’s require-ments, and to changing competitive surroundings [4].
A very important factor, from the perspective of ensuring a stable level of products’ quality in a company, is implementing methods and quality control tools, when used properly, through prevent-ing the imperfection of a product’s life cycle on its every stage. These methods and tools have a very big influence on reducing losses and a company’s costs efficiently. Using quality control tools enables providing and confirming a product’s, or even a whole production system conformity with the guidelines and norms, which is an important infor-mation for a customer that a given product was designed and produced in a way assuring a user’s safety. It is significantly important in case of com-panies producing for automotive industry. Preven-tive activities bring more benefits than after the fact ones, which are related with advertising costs, selection or correcting activities [5].
Therefore, the author of this article pays atten-tion to methods and quality control tools, used in the company being analyzed, and to possible causes of lack of compliance.
The characteristic of the analyzed
company1
The analyzed company is a concern delivering products on the automotive market. It was founded in 1972. Nowadays, the company produces steering systems for Fiat Renault, Volkswagen, Mazda and Ford, slat transmission gears with hydraulic sup-port, slat transmissions for electric support system “Column Drive” type, steering columns “Tube in Tube” type, and components like casings, ratchets and slats.
1 The analyzed company did not give a permission for presenting its name, therefore, identification data will not be given in the following article.
Bearing in mind the aim of increasing the effi-ciency of organization’s management, Integrated Management System has been gradually imple-mented by the top management, which now in-cludes:
ISO/TS 16949:2002, ISO 14001:2004, PN-N-18001:2004, BS OHSAS 18001:2007.
Integrated Management System described in the Book applies in all organizational sections, and spreads throughout the company’s production: steering transmissions; components (slats, ratchets, and casings): for an internal production and corpo-rate customers.
Apart from the Book of Integrated System, there is also Company’s Perfection of Activities Plan that includes complementing elements, which serve as supporting tools in development and improving processes, and achieving better results.
Company’s Perfection of Activities Plan in-cludes:
Business management, Products’ improvement, Quality improvement,
Operating improvement, (LEAN), Cooperation with customers, Finance management, Personnel management, IT systems,
Cooperation with suppliers.
The company’s policy, following the norms ISO/TS 16949:2002, ISO 14001 and PN-N-18001, was included in a document Management Rules and announced to all workers. One of its key elements is the responsibility for products and actions taken, which is reflected in a slogan “Quality is me”. The analysis of the company’s systemic documentation points to the fact that the company uses a variety of management instruments, which allow to develop constantly and to increase the quality of the compa-ny’s products. However, the top management still does not achieve a satisfactory low level of rejects in the organization.
Quality control tools inside a company
Control in its wide perspective means: examin-ing, measurement, assessment attempt, checking or verification of a few or only one characteristic of an analyzed product or a process. The results are compared with a customer’s demands and require-ments in order to verify, and to estimate if the ac-cordance with the assumed level was achieved [6].
On every stage of a product’s life, quality control takes different forms.
On the stage of parameters’ design, the methods used aim at designing a product without defects causing incorrect functioning during its operation. The most common method in this phase of a pro-duct’s life cycle is FMEA or DOE.
FMEA analysis is used successfully in automo-tive companies on the initial stage of projecting technological processes, on a construction stage of a product, while starting a trial and also a serial production. This method may also be used success-fully to analyse a professional risk and to asses environmental aspects inside a company, therefore, it is a significant management instrument in an organization, in which Integrated System of Quality, Environment and Safety Management is implemented.
FMEA method is used to identify potential defects of a product or a process, and its causes. A team conducting an analysis, by means of their knowledge and experience, make a risk assessment of a potential defect, inconsistency or mistakes; and then they try to find their causes and predict possi-ble consequences. Afterwards, the team implement preventive and correction actions. After introducing these actions, the analysis is conducted again, and another risk assessment of a potential defect is made. Thanks to FMEA analysis, actions are taken inside a company in these sections where high risk appears.
The outcome of a properly conducted FMEA is planning efficient control and production process supervision. A well prepared control plan is a practical document shaping an overall view of supervision of a product’s important characteristics and its parameters, which influence a final product’s quality in a production process. The control plan includes: control method, criteria, frequency, a sample’s size, a contractor, controlling facilities, a goal, controlling procedure, a way of registering and a way of reaction to deviation.
The most common method of controlling pro-duction processes’ parameters in an organization is SPC, that is Statistical Process Control. This is an instrument that may help to monitor efficiently if a given process is statistically possible to control, in other words, if it is predictable in its course. What is more, it enables to verify disturbances, which take place for special reasons, different from a natu-ral variability of a process.
As part of SPC, X-R cards are used to control a product’s and a process’s characteristics. They use the laws of probability calculus or mathematical statistics that allow to find unfavourable deviations
or trends in a process analyzed. A chart of a stable process does not cross UCL and LCL limits, and trends cannot be seen. If there are any signals of inconsistency, another control is made, and the following elements are analyzed: a size of sample, frequency of control, measuring device, correctness and a method of measurement registering. It is also dependant on a product’s complexity and a produc-tion process, as well as on a company’s financial possibilities, but most of all on a customer’s re-quirements and expectations.
To supervise and to make processes in a com-pany stable, as part of SPC, different control cards are used. A suitable control card is used to monitor production, which depends on a method of taking sample, a kind of a parameter measured, a number of parameters controlled and a characteristic of a process being controlled. In a company analyzed, the most common control cards include [7]:
single-track X card, with a numerical assessment of a property;
double-track X-R card, with a numerical as-sessment of a property, average value (X) and gap (R);
double-track X-S card, with a numerical assess-ment of a property, average value (X) and stan-dard deviation (S);
single-track p card, with alternative assessment, a card of incompatible fraction units;
single-track c card, with a gradual assessment, a card of incompatibles.
The completion of a component’s quality control in the analyzed company
Creating a product’s quality in the analyzed company takes place on every stage of a product’s life, starting with a concept and a project, through designing production processes, distribution and finishing with its use. While designing a product by means of FMEA method, a recipient’s requirements are converted into a specificity of a given product. Not only financial limitations, but also organiza-tional, technological and technical ones are taken into considerations. Of big importance are desig-ners’ experience and their knowledge. On this stage a possibility to assess critical places is highly important.
Control plans in a company, which are based on FMEA analysis, are fundamental for activities being part of TQ-X procedure. This procedure describes very precisely a line of quality control statistical techniques in a company, which are used to verify a product’s and a process’s characteristics. SPC enables a company to limit incompatibilities
on each stage of a process, supervising systemati-cally a production process, maintaining a required level of quality, allowing the process to be im-proved.
In the following article the use of SPC in a com-pany will be presented on the example of a frag-ment of a serrated slat product – figure 1. The points, which are determinants of a customer’s requirements encompassed in a product’s specifi-city, are marked on figure 2. They refer to the tilt angle of a serration line, and the length on grooves. These two characteristics of a product are subject to control, as they can significantly influence the final quality of a produced component.
Fig. 1. A product, a component – slat [8] Rys. 1. Wyrób, komponent – listwa [8]
Fig. 2. A fragment of a serrated slat product [8] Rys. 2. Wycinek z wyrobu listwy zębatej [8]
In Control Plan on Slat Line, on a workstation teeth broaching, on a machine Pull Broach Varinelli 5056 Broach 90014 the following were included: control characteristics, criteria, frequency, a sam-ple’s size, a contractor, controlling devices, a goal, control procedure, register method, as well as a way of reaction to deviation. On account of this docu-ment’s complexity, it is not possible to present it in the following article. A production process control of a serrated slat starts with presenting OPDS. It is a document confirming the first properly produced item on a given post. A leader of a given manufac-turing cell or an operator, having an appropriate training, controls the parameters of the first item. If he finds them correct, he gives this item to a laboratory for further measurements.
Presenting a certificate of the first good item is very important, as it prevents starting a mass production of a product having incorrect parame-ters. OPDS is given not only after devises’ retool-ing for a new model of a product, but also after repairs, maintenance staff interventions, serious failures disturbing a process or stoppages. OPDS on a Slat Line is conducted by an operator or a quality controller with a frequency described in a Control Plan, depending on a control procedure which is subject to a characteristic’s control.
After starting a mass production of a Serrated slat, X-R card is used in a company, in order to monitor key parameters, such as: tilt angle of a serration line and length on grooves. On figures 3 and 4 model X-R control cards are presented for chosen parameters (these cards are presented frag-mentarily on account of a possibility that the company might be identified). The parameters that directly influence a final quality of a product, or
Fig. 3. X-R Card, measurement of tilt angle of a serration line [8] Rys. 3. Karta X–R, pomiar kąta pochylenia linii uzębienia [8]
significantly affect a further course of a production process were controlled. It is possible to directly influence on these parameters, thanks to steerable factors in a process. Monitored features have determined minimum tolerance limits (DLT), as well as maximum tolerance limits (GLT) in the range, in which their compliance or their lack is marked, according to precisely defined require-ments beforehand.
The sizes, that decide if the information gained from these cards is credible, are: a constant size of a sample, and its proper amount, a normal layout of results, frequency, a regularity of sample taking, initial adjustment of a machine, an operator’s dili-gence and knowledge and finally measuring device. In the company analyzed, keeping X-R control cards is based on regular sample taking, in defined time intervals and given numbers, measuring the value of an analyzed parameter (in this case length on grooves and tilt angle of a serration line). It is done by means of measuring the average value X and the gap R in a sample, with a previous assump-tion that analyzed sizes have a normal layout.
When selecting a number of samples, the com-pany is guided by statistical and economical crite-ria. The number of samples, for statistical reasons, ranges between 3 and 12, in the case studied it is 5. The frequency of taking a sample depends on a function of a process’s stability. The more stable a process, the longer an interval (frequency). In both examples it is 1 item per 200.
In order to simplify the analysis of changes taking place, the following factors are marked on
a control card: central lines which are to determine a planned average value, and tolerance lines mean-ing requirements, which are set for a supervised value.
Using control cards, which are part of SPC method, is to minimise internal costs, as well as the external ones, by turning towards a necessity of eliminating rejects, failures. Moreover, it is a con-stant strive after perfection in a given task, in order to eliminate continuous error correction and con-trolling the number of rejects.
Despite the use of a lot of methods and tools to control and supervise quality in the analyzed com-pany, the costs of rejects on a serrated slat produc-tion are high. The costs the company incurs on sort-ing for incompatible production, which cannot be repaired, with reference to a whole company, remains on the level of 0.43% of the sales income in the last three quarters of the year 2010. It is far too much, taking into consideration so high costs of prevention means, such as using FMEA, OPDS or SPC method.
Presented on figures 3 and 4 X-R cards show that the process, despite small deviations, is stable. There are no fluctuations, which could cause such a level of rejects. As a consequence, it should be considered what influences these costs.
The reasons for this state may be different. The author suggests a necessity to analyse individual elements of a control plan. The following factors should be reconsidered: frequency of sample tak-ing, quantity, the quality of a control tool. Attention must paid to the fact that control is conducted by Fig. 4. X-R Card, measurement of length on grooves [8]
an operator very frequently, marking manually measurement data on a control card. Although the company aspires for a bigger involvement of all employees, as it decides about quality improve-ment, not every worker has the same professional competences or predispositions. Statistical tech-niques are not easy methods.
An individual training might be necessary – fitted for a specific workstation, as well as verifying methods of motivating employees. The question-naire conducted by the author, among workers filling in control cards, shows explicitly that data is not marked with a proper care. The company’s management ought to consider a necessity of investing in a specific programme, which could eliminate such a state of affairs. It is worth quoting Y. Kondo “....in order to produce a product with attracting quality that would increase the level of a customer’s satisfaction, an employee should feel satisfied with his work. And this is not possible without the efforts made by the management staff of a company...” [4].
Conclusions
Companies, which take into account both a profit and a long lasting cooperation with a loyal and faithful customer, have to meet the demand of products’ quality in a much wider meaning. Properly implemented and maintained Integrated Management System is used as a result of a well thought need to keep the optimal quality of pro-ducts, to have a positive influence on the environ-ment and to ensure the safety at work. It contributes to the development of an organisation’s condition and its image, both in the eyes of internal and external customers.
The lack of any failures of a product, in other words, providing a product in accordance with a specificity and a customer’s requirements is a desired state in all organisations, a state that gives benefits and satisfaction not only for a producer, but also for a recipient of a product.
A need for safety is very important from a cus-tomer’s point of view. The presented company pro-duces components used in automotive industry. They influence directly a user’s safety or even his life. It is reflected in a recipient’s behaviour and reactions in case of a lack of quality, which
influ-ences significantly a strive to avoid situations in which a final user’s safety could be in any way endangered. Finding that a product is incompatible with requirements may result in the cost of sorting for rejects and work repair, if the incompatibility will be detected inside a company. However, if a faulty product leaves a company, the conse-quences are much more serious: a necessity to pay a compensation to a customer, removing the results of a failure in a recipient’s company, possible loss of a company’s position on the market. In case of a recipient being exposed to serious losses, a loss of health or even a customer’s or other parties’ life the result may mean being brought to justice. The pre-sented situations can affect negatively a company’s functioning, disturbing its financial stability, cause the key customers’ withdrawal or ruin a company’s image. As a result, a company may lose its eco-nomic basis of existence.
Therefore, the analysed company must aspire after a maximum reduction of products’ defective-ness through the use of diverse methods and control quality tools, and also by means of a detailed analy-sis of all potential causes that might influence the production of faulty products.
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Recenzent: dr hab. inż. Zbigniew Matuszak, prof. AM Akademia Morska w Szczecinie
