Recibido: 12/11/2024 Aceptado: 28/01/2025

performance. All three machines were consistently generating major rejections on a daily basis including a high volume

of purging rejections from the PVC soft extrusion machine, excessive trimming of oversized magnets during the

optimization and standardization, improvement of production execution planning and storage availability, temperature

controls on welding machines and encoder wheel knurling for magnetic insertion machine. The main objectives were

to deal with problems including material waste, variance in magnetic strip size, issues in welding machines and

frequent machine stoppages caused by improper production scheduling because of improper availability of storage

space for batch production independent of door pre-assembly plan. Following implementation, results show a

considerable decrease in extrusion machine rejection %age from 12% to 4.06%, a reduction in purging waste from 17

kg/day to 6.9 kg/day and an increase in machine efficiency from 50.1% to 83.3%. Furthermore, welding machine

rejection %age fell from 7% to 3.7% as a result of enhanced temperature management and equipment maintenance.

Size variation issue in magnet insertion machine was resolved by knurling of encoder wheel. Overall, these changes

resulted in an annual cost savings of roughly 1.5 million PKR for the extrusion process and 1.2 million from magnet

while simultaneously enhancing production efficiency and product quality (A Paramasivam, 2022). Six sigma

methodology (Tjahjono, 2010) (Hill, 2017) (S. Reosekar) (Patel, 2021) in its essence was first introduced in 1986 by

Bill smith and Mikel harry, the two engineers from Motorola in 1986. The term "Six Sigma" originates from a statistical

concept that describes a process with no more than 3.4 defects per million opportunities (Noori, 2018). Six sigma

methodology (Macias-Aguayo, Garcia-Castro, Barcia, McFarlane, & Abad-Moran, 2022) as evident from its name is

a six step-based data driven approach which aim to reduce the defects and variability in manufacturing process by

sigma methodology that is being used in manufacturing sector is DMAIC and it stands for define, measure, analyze,

improve and control (Monika Smętkowska B. M., 2018). It is a closed loop process in which impact of improvement

measures is evaluated and improved until the desired results are obtained. After achieving the desired results final

phase is control which is of utmost importance as continuous improvement is only possible if is sustainable over longer

durations. This DMAIC approach is applicable in broad range of industries including manufacturing, software, sales,

quality, service and marketing (LM, 2022).

Gaskets that are produced through extrusion process are very critical part of refrigerator product as they provide sealing

of freezer and refrigerator compartments from the atmosphere thus keeping the cooling inside the refrigerator. The

profile is made up of polyvinyl chloride (PVC) (Lewandowski & Skórczewska, 2022) material and it contains a magnet

has been facing lots of challenges regarding rejection and rework issues during extrusion process for gasket profile

manufacturing from PVC material, size variation issue during magnet cutting and magnet insertion station and poor

PVC weld joints issue. These issues not only increase process waste at the gasket manufacturing station, leading to

significant costs for Company A, but also negatively impact the efficiency of the gasket manufacturing process.

3- Enhance the quality and consistency of the gasket profiles

4- Cost savings by waste minimization

5- Reduction in magnet wastage because of size variation issue

6- Reduction in rejection and rework at welding machine station

of rising material costs, fluctuation in demand, more competition from emerging markets (Most. Asikha Aktar, 2021).

These issues lead to increase in manufacturing cost and reduction in profit margins as product prices can only be

increased up to a certain because purchasing power of general public is also going down (Bailey, 2016). So, in order

to make the business sustainable, increase profit margins and bring the cost of manufacturing down, more and more

Motorola are a few of these businesses. By applying the six-sigma methodology, these businesses have drastically

decreased their defect rates and multiplied their profits by many folds (T. Costa F. S., 2017). Numerous studies have

demonstrated the importance of Six Sigma and Lean techniques in driving quality improvements and minimizing

process variability. Smętkowska and Mrugalska (2018) successfully applied Six Sigma DMAIC to reduce rejection

rates in manufacturing operations (Monika Smętkowska B. M., 2018). Similarly, Macias-Aguayo et al. (2022) stressed

the use of Six Sigma and Industry 4.0 principles to improve operational efficiency (Jaime Macias-Aguayo, 2022).

T. Costa et al. (2017) used Six Sigma to optimize extrusion processes in tire manufacture, resulting in considerable

defect reduction, demonstrating the applicability of this methodology to extrusion-based industries such as gasket

production (T. Costa F. S., 2017). Furthermore, Hassan Araman et al. (2023) shed light on six sigma and gasket

aiming for practical process enhancements and measurable outcomes.

There are several other key philosophies in the manufacturing industry, such as Lean Manufacturing and Six Sigma.

Six Sigma is a data-driven methodology that utilizes statistical tools to minimize defects and reduce process variability.

Whereas Lean Manufacturing primarily focuses on eliminating waste and improving process flow. Lean practices

in which multiple statistical tools are used during different phases in order to achieve the desired result. All those tools

will be discussed in the methodology section in detail. Six Sigma is a statistical term that represents a process in which

minimal defects occur. “Sigma" (σ) stands for a process's standard deviation in Six Sigma terminology. A process that

achieves a Six Sigma level is said to produce less than 3.4 defects per million opportunities (DPMO), which is an

4.5

99.8700%

The X-bar line in Figure represents that normal data is distributed symmetrically around mean. A normal curve is

useful for determining the probability that a given data point in a population will fall within a certain range of the

distribution (Amaral, 2022).

The X-bar line in Figure represents the mean and normal data is formed symmetrically around it. A normal curve is

useful for determining the chance that a given data point in a population will fall within a certain range of the

distribution. Red arrow covers ±1σ from mean and (σ = standard deviation) represents that 68.26% of all data points

Gasket is an integral part of refrigerator product (Guoqiang Liu, A review of refrigerator gasket: Development trend,

heat and mass transfer characteristics, structure and material optimization, 2021) which help keep the refrigerator

freezer and refrigerator compartment insulated from environment. Gasket profile is manufactured from the polyvinyl

chloride (PVC) material through the extrusion process. Extrusion process is a manufacturing technique in which a

material is heated according to the required specifications in a barrel which is then forced through a die to achieve the

required profile (Guoqiang Liu, Research on test method of heat transfer coefficient for refrigerator gasket, 2020).

After exiting of PVC profile from die it is shifted to cooling station through conveyors where it is cooled down through

water jets. These profiles are then shifted to cutting station where they are cut to desired length as per requirement.

These profiles are then later on moved to stock area and then as per requirement to magnet insertion machine area

billion USD. Being a billion-dollar industry, no research has been conducted on combined optimization of extrusion,

magnet insertion and welding process. In this project six sigma methodology will be systematically applied in order to

identify the key problems in the whole gasket manufacturing process. These defects/problems will then be later

addressed by using six sigma DMAIC methodology.

industry, demonstrating the value of applying Six Sigma methodology not only in gasket production but potentially

across all manufacturing processes.

insights from various stakeholders specifically customer, process owner (production team). This helped in identifying

critical issues in the gasket manufacturing area. First step in define phase to make a project charter in which objectives,

goals, project deliverables, in-scope, out-scope and problem statement were defined.

Now in order to assist planning and keep the track of project during its various phases, a Gantt chart was setup with

deadlines of the project phase wise. Gantt chart is available in Figure .

In this comparison of VOB (Voice of the Business) and VOC (Voice of the Customer), common goals were identified

that were important to both the immediate customer, the door assembly line and management. Key objectives included

cost savings, improving production efficiency, optimizing machine energy consumption, controlling waste,

minimizing defects passed to the customer and reducing variations in the sizes of PVC profiles and magnetic strips.

After that a SIPOC (supplier-input-process-output-customer) was plotted in order to identify all the suppliers (internal

and external), inputs, process mapping, outputs and customer (internal). SIPOC is used to understand the process

components and relevance as it is a simple tool. This was developed through brainstorming session with the project

29th July, 2024

Extrusion machine rejection data is mentioned in the Table .