Design and Fabrication of a Cost Effective Four Cavity Plastic Injection Mould for Bottled Water Handle

This work was carried out in collaboration between all authors. Author HEC designed the study, performed the statistical analysis, wrote the protocol, wrote the first draft of the manuscript and managed literature searches. Authors HCG and MCN scrutinized and managed the analyses of the study and literature searches. All authors read and approved the final manuscript. ABSTRACT Design and fabrication of a cost effective four industries is expected to increase due to public acceptability. Also, the introduction of handle allowed for better convenience in carrying bottled water especially the 1.5 litre sizes.

industries is expected to increase due to public acceptability. Also, the introduction of handle allowed for better convenience in carrying bottled water especially the 1.5 litre sizes.

INTRODUCTION
Nowadays, Injection moulding represents a large portion of the entire plastics processing industry and plastic is now one of the most widely used material in the world, according to Pattnaik et al. [1]. Among various plastic production technologies, injection moulding counts for a significant proportion of all plastic products from micro to macro components stated by Garvey [2].
Today, medical experts are encouraging people to drink water always for vitality. Because of this, demand for bottled water has increased as people tend to carry water about.
According to Weissmann [3], the introduction of handle on bottled water started with the introduction of handles on large size extrusion blow moulded containers which made them more user-friendly, especially where the total weight of the package reached several kilos in household product containers, and where larger weights of 5 to 20-litre containers were involved. Therefore, it is no wonder that handles can be found on most large bottles today, including household chemicals, garden chemicals, automotive fluids, beverage containers (non-carbonated), edible oil bottles, and even the 1.75-litre liquor bottles.
In Nigeria today, the standard sizes for bottles of bottled water are 20 liter, 1.5 liter, 0.75 liter and the 0.5 liter Polyethylene Terephthalate (PET). The 20 liter bottles are for water dispensers which cannot be carried about while the 1.5 liters, 0.7 liters and the 0.5 liters are used to package other things, including bottle water, and they can easily be carried about. The bottles are usually blow moulded.
Introduction of injection moulded polyethylene handles to be attached on the neck of the bottled water of smaller sizes of 1.5 liters and the 0.75 liter sizes has become necessary to enhance better convenience in carrying bottled water and increased acceptance by consumers.
This paper presents the design and fabrication of a four cavity Bottled Water Handle Mould. Also the impact of the handle on a sampled company was ascertained to show the level of public acceptability.

DESCRIPTION OF THE MOULD
Just like most moulds, the "four cavity bottled water handle mould" is separated into two sides at a parting line, the "A" side, and the "B" side, to permit the part to be extracted. Plastic resin enters the mould through a sprue in the "A" plate, which branches out between the two sides through channels called runners, and enters each part cavity through a gate. Inside each cavity, the resin flows around cores and conforms to the cavity geometry to form the handles. The amount of resin required to fill the sprue, runner and cavities of a mould is a shot. When a core shuts off against an opposing mould cavity or core, a hole results in the part. Air in the cavities when the mould closes escapes through very slight gaps between the plates and pins, into shallow vents created along the ejection pin.
To permit removal of the part, none of its features was allowed to overhang one another in the direction that the mould opens. Sides of the handles that appear parallel with the direction of draw are typically angled slightly with draft to ease release of the handles from the mould. Because areas in the cavities with bucket-like features tend to shrink onto the cores that form them while cooling, and cling to those cores when the cavity is pulled away; the mould is designed so that the moulded handle reliably remains on the ejector "B" side of the mould when it opens by making the bucket-like features remain on the "B" side, and draws the runner and the sprue out of the "A" side along with the handles. The handles then fall freely when ejected from the "B" side. The resin for the handle is thermoplastic, therefore, coolant, usually water with corrosion inhibitors, will circulates through passageways bored through the main plates on both sides of the mould to enable temperature control and rapid part solidification.
To ease maintenance and venting, cavities and cores are divided into pieces, called inserts, and subassemblies, also called inserts, blocks, or chase blocks. Fig. 2

Design Specifications
The following design specifications were taken into consideration: a. Mould should be able to withstand loading of 5 tons. b. Density of material used must be less than that of lead c. The clamping position of the mould must be inculcated during design to prevent it from slipping. d. Material used must withstand the melting temperature of resin (about 200°C) e. The mould is designed to have a proper resting base on the machine platens. f. Tough and stiff Materials were selected to withstand maximum loading of 5 tons and ensured material does not wear easily. g. The cavity must have uniform wall thickness. h. Avoided sharp corners in the design.
Sharp inside corners concentrate stresses from mechanical loading, substantially reducing mechanical performance. i. Provided minimum draft angles or tapers of 0.5° on all product features such as walls, ribs, posts, and bosses that lie parallel to the direction of release from the mould to ease part ejection. j. The mould is designed so that the cores can separate from the part in the mouldopening direction.

Design Calculations
The method used for determining the required clamp force was to obtain the product of the projected area of the part to be moulded and a factor of 2 to 8 tons per square inch which is the maximum machine capacity (tonnage) the mould is being designed for. According to Hieber and Isayev, [6], the lower tonnage can be used for high flow materials and the higher tonnage for low flow (stiff) materials. High Density Polyethylene (HDPE) is used and it is a high flow material. Therefore, being on a safe side, an average of 5 tons/in 2 was used. 5 * 6.89 x 10 -3 MPa or N/mm 2 [conversion factor from lb f /in 2 (psi) to MPa (N/mm 2 )] Cavity Pressure = 3.45 x 10 -2 MPa. Each of the labeled areas is demarcated with a yellow line; for instance, label "A" represent a semicircular cross-section while label "B" represents a rectangular cross-section and so on.

Projected area determination
The average thickness of the product is estimated to be 2 mm, hence estimated shot volume =6409.06*2 =12818.12 mm 3 . Therefore, the projected area is 6409.06 mm 2 ; it substitute in equation (1) to obtain;

Determination of the reactions R A and R B at supports "A" and "B"
Taking moment about 'A', we have

Determination of Bending Moments (BM) on the mould
Note: However, @ x = ݈ 2 , M has its maximum value ∴ M ௫ = 5.87 Nm

Determination of maximum deflection on the mould
According to Bayer Corporation [4], Maximum elastic deflection (at the mid-point along l) of a beam under a uniform load is given as follows:

Fig. 2.4. Rectangular face plate showing details of deflection
Where,

Determination of maximum bending stress on the mould
The maximum bending stress for a rectangular cross section could be given as stated below according to Bayer Corporation [4].

The Material Selection
The choice of material to build a mould is primarily one of economics. To select the adequate material for the design, the first step was to translate the design requirements, which was done in section 2.1, into a material specification. Making reference to the Ashby's Chart according to Ashby [7], materials that fail constraints in the specification were screened out to obtain the go/no-go criteria. Then the next was ranking (an ordering of the materials that fall within the "go" criteria) by ability to meet objectives in other words called Material Indices. The promising candidates (materials) were sought for. The next step is to seek, from the subset of materials which satisfy the primary constraints, those which maximize the performance of the component. For instance, for the design of stiff components; the modulus E is plotted against density ρ, on log scales of the Ashby chart. The performance index (tension on stiff beam) is given as shown: Taking logs of equation (1), This is an equation of the form y = mx + b which is a family of straight parallel lines; one line for each value of the constant C. The slope is always 1 and log C is the y intercept. The index for bending on beam is: Equation (3) will gives another family of lines, this time with a slope of 2.
The index for bending on light-stiff plate is: Equation (4) will gives another family of lines, this time with a slope of 3.
All materials which lie on ISO-line of ா భ మ ρ will perform equally well.
To obtain the optimum material, other Ashby material selection charts that highlight other material qualities were considered. They as stated below: -Strength -Density chart: Finally steel was most favourd because it satisfies the criteria: Economic machinability Smallest change in size upon heat treatment Good polishability Great compressive strength High wear resistance Sufficient corrosion-resisting quality

Manufacturing Processes
Once the design is completed manufacturing begins. Mould making involves many steps which include: • Marking-Out • Milling and turning • Heat-treating • Grinding and honing • Electrical discharge machining • Polishing and texturing To save cost, common mould components are purchased from suppliers e.g. bolts.
When all of the parts are completed the next step is to fit, assemble and test the mould. The mould must have venting features added to allow the air to escape as earlier stated in the vent design. At last, the mould must be tested to insure the products are correct and that the mould is performing properly.

The Operation Process Chart
The Fig. 2.6 represents the operational process involved in the manufacture of the mould. The mould is made of two major parts, the cavity and the core. Under the cavity, are the female base plate, female face plate, the sprue bush and the locating ring. While on the core are the male base plate, male face plate, face plate support, locating pin, ejector plate and the ejector pin. Under each are circles and rectangular boxes that indicate the operations and the events taken to produce individual parts before finally assembling them to form the cavity and the core respectively.

Exploded View of Mould
Below is the exploded view of the manufactured mould showing all the parts arranged for assembly.

COST ANALYSIS
For a 50 kg material, revenue accrued is given as: Revenue, R = Cost of Production, C + Profit, P R = C + P ሺ14ሻ  To obtain the time taken by a worker to fix one handle on a bottled water, work measurement, which involves motion and time study, was carried out as stated in

Tabulated Costs of Material for Conventional Bottled Water
The tables show the materials and their cost for making conventional bottled water without the consideration of the cost of handle.

Return on Investment (ROI) Analysis
In order to make decision on which of the investment regime to invest in, return on investment (ROI) analysis is used. This enabled us to choose which of the investment regime has a better return.

I ୡ െ Investment Cost
This analysis was done on the three regimes as stated below:

RESULTS
The design was done with the proper engineering design procedure and the following results were obtained.
The cost of introducing handle was determined; also the difference in the Cost/mass was obtained between the foreign and locally made handle and presented in the table.

Comparison of Locally Made Handle and Foreign Handle
The locally made handle showed a significant reduction in weight to that of the foreign made handle. This reduction also shows that the material usage is reduced from the cost/mass ratio column. This in turn shows a reduction in cost of production.

Financial implication of using bottle water handle
From section 3.2, the cost of handle was obtained as N 1.60per handle. This value was in turn used to obtain the cost of introducing handle into the bottled water company in section 3.3 to be N 27.13 /Dozen. Furthermore, with reference to the sales data presented in Appendix AI, the rate of return on investment (ROI) as a result of this extra cost.

Considering the response of the locally made handle
The graph above represents the response of the Locally Made Handle. The graph shows that before the introduction of handle, the ROI was approaching 30% and when handle was introduced, the ROI increased to 46.34%. However, the ROI took a nose dive when the handle was removed to the tune of 34.41%.

Considering the response of the foreign made handle
The graph above represents the response of the Foreign Made Handle. The graph shows that before the introduction of handle, the ROI was approaching 30% and when handle was introduced, the ROI increased to 46.05%. However, the ROI took a declined to 34.41% when the handle was removed.

DISCUSSION
The design results as obtained shows that maximum deflection is 2.33 x 10 -3 mm. Therefore, the deflection obtained is minimal, therefore is negligible. The maximum bending stress is 4.4677 x 10 5 N/m 2 this indicates that the material can withstand the stress as the yield strength, S y and ultimate tensile strength, S u of steels are within the values 5.1x10 8 N/m 2 and 7.1x10 8 N/m 2 according to Todd et al. [10].
The cost of introducing handle was determined; also the difference in the Cost/mass was obtained between the foreign and locally made handle and presented in the table.
It was presented that the difference in cost/mass ration is 0.3199 N/g. This means that in every 50 kg of handle, the bottled water company saves: 50000 x 0.32 = N 15995.
This amount of money saved is significant enough to encourage the bottled water companies in Nigeria.

Comparing the Responses of the Locally and the Foreign Made Handle
The graph above represents the superimposition of the responses of the locally and Foreign Made Handle. The graph curves show that before the introduction of handle, the ROI was approaching 30 % and when handle was introduced, the ROI increased to 46.34 % and 46.05 % for the locally and foreign made handles respectively. This 0.29 % difference during the introduction of handle could be attributed to N 0.90 (N 2.50 -N 1.60) in foreign and locally made handle price. However, the ROI took a declined to 34.41 % when the handle was removed in both cases though this is still higher than the response at the initial time before the introduction of handle. This is

CONCLUSION
This work has demonstrated the ability to design and manufacture an injection mould for bottled water handle from locally available materials. With the increase in the number of bottled water industries, this project would have a profitable application in bottled water production due to increased demand for bottled water. The simplicity of the design and the availability of materials for the mould design, and the handle from local petrochemical industries make this work practicable. The impact of the handle on the financial returns of the sampled company is enough reason to encourage bottled water companies to venture into the use of handle for their smaller sizes, 1.5 liter and 0.75 liter, of bottled water. Nevertheless, the cost incurred as a result of introduction of handle to the bottled water is small compared to the benefit accrued to the company. Commercializing this will be cheap and economically viable to the mould manufacturing industry, the plastic industry and the bottled water industry.
In the future, it is recommended that more work be done on the optimization of number of cavities for economic use of machines. Also, it is recommended that more research work be done to ascertain the acceptability of the product owning to the effect of the handle noticed on the company as reported in this work.
Therefore, we recommend that local plastic industries should embark on the production of bottled water handle for local consumption. Also, bottled water companies should patronize local manufacturers of bottled water handle at reduced cost. Application of computer simulation for finding optimum gate location in plastic injection moulding process.