¶ … operations process a bus manufacturing business project. The aim analyze operation develop methods improvement. Bus manufacturing is quite a slow and tedious process, for most companies, the manufacturing process is divided into two. First, most of the vehicle component are manufactured outside the parent enterprise and are purchased for assembly. Then the second phase of manufacturing, which now takes, place at the enterprise is the assembly part of it.

Bus manufacturing process goes through three stages; they include chassis manufacture, body works, and interior fitting. All these stages take place in a sequence where when a certain process is done with the vehicle moves to the next stage in the manufacturing process.

Most companies dealing with vehicle manufacture have nowadays shifted to opening more assembly factories; where all they do is to assemble some of the imported parts from specialized manufacturer then assemble them according to the country's standards. There are some advantages and disadvantages that these locally assembly plants go through. The advantages include; cheaper manufacturing cost of the bus compared to importing of already manufactures bus, this comes about because the plant experiences low labor costs and reduced transport cost of the parts since a cargo container are able to carry all the parts at a cheaper price with less damages. Some of the disadvantages these buses assembly companies go through include; limited choice of models available, poor quality of locally produced components, poor assembly quality due to low skilled workers also they experience delays in the acquiring of spare parts or the assembly parts they offered hence they are unable to meet the customers' satisfaction (Iles, 2005).

Chassis manufacturing combines the following parts, these include; the structural under frame of the designed bus, the radiator and engine, the axle, wheel and suspension, the gearbox and transmission and lastly there is the steering wheel, dashboard, and driver's seat. In most cases, the chassis is built as a single unit, where it can be mid-engine, front-engine or rear-engine. Many of the chassis models are in different standard length depending on the specification allowed by a given country, the radiators are mostly fitted at the front part of the bus to offer maximum cooling process irrespective of where the engines is situated.

Chassis manufacture involves various processes; first the manufacturing company has to design the type of chassis they intend to manufacture which will suit their specifications. In the next phase, the chassis is then assembled. Some companies with the capability of producing their own chassis also produce their own mechanical units such as the engine, axles and gear box, but in most scenarios, these items are mostly produced by more specialized manufacturers (Iles, 2005). Therefore, in the vehicle manufacturing industry, one is expected to find identical gearboxes, engines, and axles from different manufacturers but one outstanding part in the manufacturing process is that the chassis is always unique to a particular manufacturer.

Problem statement

Most bus manufacturing companies do not build the chassis part of the buses themselves. They would rather import parts and assemble the components. Those, which are involved, in the manufacture of their own chassis are faced with productivity issues since the production of this chassis incorporate a lot, therefore, becoming rather slow and expensive process. Even after importation of chassis parts from specialized manufacturers, these companies are still faced with several challenges in their assembly process, which has led, to decreased productivity all the same.

Methodology

This is the description of the different methods used during the study and the results for the analysis carried out. The basic methods used for information collection was through the use of literature studies, interviews and empirical studies, which brought out an understanding of operations in a bus manufacturing company and its potentials.

The information was collected about the operation of the factory and its limitation on a fast hand observation of the company's onsite operations. Thereafter a thorough literature review comprising of textbooks and scientific articles were used. Empirical studies were then performed to the plant as a basis for analysis.

The method used to evaluate the current systems, and even future possibilities is the use of Value Stream Mapping (Hines, 1997). All these were used to find out some of the flaws to the factory's operations and hence recommendation for improvement.

In order to have clarity of the chassis manufacturing processes involving, each aspect of the processes was analyzed both qualitatively and quantitatively.

Qualitative analysis

To gather an understanding of the processes in chassis manufacture, a series of semi-structured interviews were conducted with key logistics and operation personnel involved in the flow. Empirical studies and observation of the onsite activities were also conducted.

Quantitative analysis

Quantitative measurements were carried out through observations, time studies and calculations. Data was then added into the value stream map. The value stream map was then used as a point for commencement of discussion...

The manufacturing of the chassis platform was grouped into several sub-assemblies. During the manufacturing process, the sub-assemblies are the ones which were assembled on the main jig platform to form part of the chassis.
Designing of the Chassis

First the chassis was designed by the designing team, them the different parts of the chassis were brought together for assembly. The platform was the first part of the assembly process, it was noted that platforms sizes normally differ with the type of model of the bus they varied mostly in length and width. Within the bus manufacturing plant, an 8 wheel double decker bus had the following dimensions as shown in the table below (Somkiat Jongprasithporn, 2007).

Table 1: Table showing the dimensions of a Double Decker bus chassis platform

DIMENSIONS

UNITS IN METERS

Width

2.3 meters

Length

11.8 meters

Height

0.86 meters

While, in this other table, these are the dimension of a 6 wheel Single Decker bus chassis platform.

Table 2: Table showing the dimensions of a Single Decker bus chassis platform

DIMENSIONS

UNITS IN METERS

Width

2.35 meters

Length

11.8 meters

Height

0.77 meters

The type of steel that the chassis platform were made from were also varied in size, they were being made from stainless steel rectangle tube RST 4003, such as 80 by 4, 80 by 40 by 4 and 50 by 4. The chassis platform was divided into three zones, the front part, middle part and the rear part. The chassis platform for the rear and the front part are symmetry towards the longitudinal axis, they are rarely changed even by the customer's order, and they suit all models being manufactured (Itsara Rojana, 2008). The middle zone is the one that varies in most of the bus models available. It is this middle part that may be adjusted to suit the size of the bus the customer has ordered. Therefore, the middle part of the chassis is normally not considered as the sub-assembly part of the platform. The second stage in the chassis manufacturing process is the division and grouping together of the platform into sub-assemblies based on the similarity of sizes and shapes of each part.

Determining the stress and deformation of the Jig

The jigs composed of assembly table with clamps and support structure were then designed for each group of sub-assemblies. The support structure for the jig had two significances, the supported column had adjustable slot for the table height setting, and it also has manually rotating device on the structure that allows it to make a 360 degree rotation on horizontal for easier welding of some of the sub-structures (Vilasinee Leowarin, 2007). At this stage, the clamps were also fixed to the table at designated points to give way for the fixing of the sub-assembly's part elements.

Analysis of the jigs was done to determine its stress and deformation. A jig was made using two types of materials. The support structure was made from stainless steel RST 4003 while the assembly table was made from structural steel AISI 1020 material (Somsak Siwadamrongpong, 2010). Then the finite element method was used to analyze the structure stress, deflection and safety of factor in 3 cases.

Table 2: Table showing the stress and deformation properties of the jig material.

Properties

Modulus of Elasticity (GPa)

Poisson's Ratio

0.25

0.3

0.3

Weight Density (kg/m3)

Yield Stress (MPa)

Tensile Stress (MPa)

1930

Case 1: Analysis of stress of the Assembly Table

In the stage, considerations were given to the amount of weight exerted by the sub-assemblies. The following table shows the amount of load exerted by the sub-assemblies in the four trials conducted.

Table 4: Table showing the amount of load exerted by the sub-assemblies

JIG

1

2

3

4

Maximum Load of Sub-assemblies (N)

Support Area (m2)

0.76

0.41

0.59

0.23

Maximum Load of Sub-assemblies (Pa)

Reaction force (N)

Case 2: Analysis of the stress exerted on the assembly table.

In this case, considerations were given to the load of the sub-assemblies and the table itself that applied to the assembly table.

Table 5: Table showing the amount of stress exerted on the assembly table.

JIG

1

2

3

4

Maximum Load of Sub-assemblies (Pa)

Load of Clamp and Screw (N)

75.62

82.06

67.01

6.34

Load of Assembly Table (Pa)

Reaction force (N)

1938.71

Case 3: Analysis of the stress experienced on the Support Structures

In this section of the chassis assembly process, the following results were got for analysis of the stress of sun-assemblies and the table that…