Abstract In the manufacturing, metal casting industry is one of the oldest basic principal and most important industries. The casting process is hindered by the occurrence of various defects. High casting reject levels and customer returns have a considerable adverse effect on productivity, delivery performance, customer satisfaction and employee morale. In addition excessive rejection reduces yield, wastes valuable raw materials and involves management time in problem solving. All foundry processes generate a certain level of rejection that is closely related to the type of casting, the processes used and the equipment available. This paper seeks to establish the extent to which cost of quality can impact on continuous improvement of the products and the relationship with the customers of the organization. To determine the cost of quality (COQ) at casting company X, the researchers used existing company records, publications and historical evidence of the company. The researchers utilized techniques such as, bar charts and tables in presenting and interpreting data. The above techniques have the ability to provide methods for collecting, presenting, and analysis and meaningfully interpret data. The research findings estimated the COQ to be 6.6% of sales revenue.

primarily on the COQ literature and its applicability at casting company X as a management eye opener.

Most of the foundries have no precise knowledge of the main causes of rejection because they fail to maintain a satisfactory quality control system. There is a need for an organized system of collecting information on the process parameters relating to the potential casting defects. Also, there is a need for developing a database of solutions for eliminating undesirable casting artifacts. Internal and external failure costs contribute to over 70% of the total quality costs in foundries. Quality costs in a foundry can vary between 5% and 25% of the total sales volume. Any attempt to reduce these costs is an immense benefit to metal casting companies. Any reduction in the scrap and rework also positively influences the environmental impact of our industry.

II. RELATED LITERATURE

A. Metal molding process

Metal moulding is an old production method that has been practiced time immemorial. It utilizes molten metal which is poured into prepared molds and is left to solidify and take the shape of the mould. After cooling the runners and risers are removed. The casting is then cleaned and in some cases machining takes place to give the required surface finish. In the event that the product becomes a reject it is recycled back to furnace to be reprocessed consuming more energy and labor hours. It is as the product passes through any of the mentioned stages that defects are produced.

B. Cost of Quality historical background

Quality cost was expanded by introducing numerous quality-oriented staff departments [1], [2]. Studies from previous research revealed that quality costs where (10 30) percent of sales or 25 to 40 percent of operating costs, these were as a result of poor quality products. This data used to justify quality improvement proposals and to track the cost data over time. The widely accepted Feigenbaums PAF Model classifies cost of quality into three categories Prevention cost, Appraisal cost and Failure cost [3]. Failure cost is further divided into external and internal failure cost. As stated by [3], the PAF model is the most commonly used COQ model in the United States and Great Britain. The American Society for Quality (ASQ) adopted the classification of COQ by four categories (where failure cost is divided into external and internal failure costs), based on PAF model [4]. Cost of quality is the deviation of actual costs of a company from the ideal one [5], that is, defined as costs of non conformance [6]. Quality costs are a tool that displays trends for management to act on. It is important to

Index Terms Cost of quality; casting; continuous improvement

I. INTRODUCTION

The growth of interest in product and services quality as a key contributor to competitiveness and marketability has stimulated organizational concern for economic effects of quality costs. Companies are now beginning to amass and use quality cost data mainly scrap, reworks and warranty claims. Cost of quality provides a means to gauge the return on quality by reducing business cost. In general cost of quality also known as the poor quality costs is defined as the sum of costs incurred to prevent non conformances from happening and the cost incurred when non conformance in products and services occurs. This paper will focus

Manuscript Received on January 2012

Davison Zimwara, Dept. Industrial and Manufacturing Engineering, National University of Science and Technology, Bulawayo, ZIMBABWE.

Lameck Mugwagwa, Dept. Industrial and Manufacturing Engineering, National University of Science and Technology,Bulawayo, ZIMBABWE.

Daniel Maringa, MSc student, Dept. Industrial and Manufacturing Engineering, National University of Science and Technology, Bulawayo, ZIMBABWE.

Albert Mnkandla, MSc student, Dept. Industrial and Manufacturing Engineering, National University of Science and Technology, Bulawayo, ZIMBABWE.

Lindleen Mugwagwa, MSc student, Dept. Industrial and Manufacturing Engineering, National University of Science and Technology, Bulawayo, ZIMBABWE.

Tendai Talent Ngwarati, MSc student, Dept. Industrial and Manufacturing Engineering, National University of Science and Technology, Bulawayo, ZIMBABWE.

carry out quality cost analysis in an organization and this information can be used by management to identify quality costs, prioritize quality cost reduction activities and measure the success of such activities.

Figure 1: Casting process flow chart adapted from company X

There are many ways that have been proposed by various researchers on how to measure Cost of Quality. Through the years the COQ models have been developed and many authors agree on the following classes of COQ models;

Figure 2: Quality costs categories

P-A-F model Crosbys model Opportunity cost models Process cost models

ABC models

Components of Cost of Quality

Step 1 Step 2 Step 3 Step 4

Step 5

Step 6 Step 7

Step 8 Step 9

E.

Project initialization and preparation Assessment of current business performance Project organization and assignments Identification of major costs of conformance and costs of non conformance items Identification and provision of additional training needs Collect ,compile and process cost of quality data Analyze cost of quality to identify opportunities for improvements Organize and implement quality improvement and cost reduction programs Establish continuous improvement of the cost of quality performance

General benefits of implementing COQ [7]

Can be used to quantify qualitative improvements

Can be used to determine problem areas and action priorities Can be used for investment appraisal purposes and to asses overall effectiveness of the quality programmes

C.

Prevention costs: These are costs incurred by an organization when they try to investigate, prevent or reduce the risks of non conformity. These costs are planned and are associated with the design, implementation and maintenance of a total quality management system.

Appraisal costs: These are costs associated with evaluation and verification of purchased goods, services, and processes by an organization to ensure that they are within specified requirements. Examples of these costs include production trial test costs, test and measurement costs.

Internal failure costs: These are costs that arise from failure of products to conform to customer requirements. These can be categorized into costs of scrap, rework, retest, re-inspection, modification, downtime, overtime, corrective action and redesign costs.

External failure costs: These are costs an organization incurs after delivering to the customer non conforming products Examples of these costs includes equipment failure, downtime and warranty.

D. Stages in the cost of quality implementation

The steps to the implementation of COQ are shown in table1

I - Steps in implementing COQ Activities [7]

COQ reporting has the potential of bringing numerous benefits to the organizations but the organizations must also

Step 10

Conduct quality audits regularly and initiate document changes in response to improvements made in various processes

be aware of difficulties encountered during the implementation period so that they are better prepared to overcome the obstacles.

The major purpose of a cost of quality system is to reduce costs through identifying improvement opportunities[8]. According to [8], quality costs programmes fail because:

III: Failure Cost Internal failure

External failure

Rework Scrap Downtime Obsolescence Defect/failure analysis Re-inspection / retesting Downgrading

Complaints Warranty claim

F.

Some organisations use the COQ information as a scorekeeping tool rather than as a driver for continual improvement Preoccupation with perfection in determining the COQ figures

Underestimation of the depth and extend of commitment required to be made to prevention

Cost of Quality metrics

Phase 2: Quantification of Cost of Quality Records from Production, Operation, Accounting records were used in the gathering of information of quality costs at the company.

IV. RESULTS Results of the research are presented in the next section

A. Problems Identified

The problems can be classified into the following categories:

Core making; Poor surface finish and Completely damaged core

Moulding; Misalignment of cope and drag box

Melting and pouring; Short pouring, Slag and sand

inclusion The process was analysed by considering each step in the casting process. This was done to identify all the wastes in the shop floor. This helped to determine value adding and non value adding activities carried out in the casting process at the case study company. The non value adding activities are removed so as to reduce time wasting and also to meet customer demand on time. There are also some processes essential in the casting process which do not value to the final product but have to be carried out and these are called required non value added activities.

B. Prevention costs

Table IV summarises the results of prevention cost. Fig. 3 summarises the preventive cost for the period under review. As can be seen preventive costs are low indicating the system at company X is not proactive.

C. Appraisal Activities

The findings of appraisal costs are summarized in Table V. These findings are also illustrated in graphical format in Fig. 4. As can be seen appraisal costs are not significant which illustrates again the system has a feedback system that is not effective, resulting in poor preventive methods to avert failure.

D. Internal Failure Costs

The major cost elements are as detailed in Table VI.Fig. 5 gives the summary of internal failure costs. As can be seen internal failure costs are huge indicating that the system at company X is not yet mature. Measures need to be put in place to minimize the failure rate hence the COQ.

E. External Failure Costs

Table VII and Fig. 6 illustrate the quantum of external failures. This shows that the system at the case study company needs a proactive approach so that external failures are brought to a minimum.

COQ measurement systems have a mixture of global and detailed metrics [9]. Some examples of detailed metrics are given in Table II. Global quality metrics measure global performance; some examples are also given in Table II.

Cost of assets Cost of labour Cost of defects per 100 pieces Cost of late deliveries Time between service calls Number of complaints received

Return on quality Quality rate Process quality Cost of quality

III.

METHODOLOGY

Primary data was collected by direct observation during plant operation visits and during working hours; and through personal interviews with managers, superintendents, supervisors and general workers. The gathered information was used to quantify the quality cost in tabular format. Secondary data from existing records, publication and historical evidence of the company from the company library and recordings was collected. The researchers utilized techniques such as bar charts and tables in presenting and interpreting data. The above techniques have the ability to provide methods for collecting, presenting and analysis and meaningfully interpret data.

The following steps were used in identifying the costs of quality at company X:

Phase 1: Identification of non conformance costs These were categorized into internal and external failure. Table III shows what was considered in this section

C7 Downgrading: Downgrading of grinding media

V: Appraisal Cost