11-1

11 ASSEMBLY

11.1 AIMS OF THE LECTURE

To describe the characteristics of module, unit and block

To examine methods of assembling modules, units and blocks

To give particular attentions on the assembly hazards

11.2 WHAT IS ASSEMBLY

Assembly is a process of building up a product from various parts, equipment, and machinery in arranged sequences of operations.

In the case of shipbuilding assembly can be defined as an arrangement of processes to building up a ship structure from various sub-assemblies, panels, and outfits to form a module, unit, or a block, and even grand-block, which can be illustrated as follows:

Figure 11.1 Panel

Figure 11.2 Sub-block

11-2

11.3 CHARACTERISTICS OF THE ASSEMBLIES

The structures have been built up can be categorised into four different products i.e. module, unit, block, and grand-block, each of this product has its typical characteristics as follows:

a) Module Module is a compact structure of typical system of the ship some examples of it are: fresh water pumping system module, main engine module, accommodation cabin module etc.

Typical characteristics of a module is that the structure is made up of several outfits which support the particular system and are grouped together, so that it can be attached to the block easily.

Figure 11.3 Block

Figure 11.4 Grand-block

11-3

b) Unit

Unit is a complex built-up section of a ship, which may consists of several panels and/or sub-assemblies, such as complete fore end structure of the ship forward of collision bulkhead; wheel house unit, double bottom unit, etc. Unit can weigh up to 50 to 100 tonnes; its size sometimes is limited by the availability of the transportation and lifting capacity of the existing facilities in the shipyard.

Figure 11.5 Pipe module

Figure 11.6 Accommodation module

11-4

c) Block and grand-block Block is a large structural part of a ship. It is built up of several panels and sub-assemblies as well as ships outfits. The block may range from just part of double bottom to a full ship structural compartment such as engine room, cargo hold, or accommodation structure. A very large and fully outfitted block which is made up of several smaller blocks sometimes is called a Grand-block.

It is a trend in large and modern shipyard to build the block as big and as complete as it is allowed by the availability of transport and lifting facilities in the shipyard.

The main aim of building large and complete block prior to its erection onto the building dock or berth is to minimise works to be carried out on the dock or berth which might cause more production and safety hazards.

Example of make up of a grand-block is as follow:

Figure 11.7 Fore end unit

Figure 11.8 Aft end unit

11-5

11.4 ASSEMBY METHODS

In conventional method ship structure was formed piece by piece frames first, then the shell plates and decks, after that the inner parts. All these took place on the building berth, which made the work inefficient and took long time to accomplish.

To increase productivity and to minimise the influence of disturbing weather block system was introduced, where the blocks were assembled in the covered workshop, and joined one by one on the berth or dock. With the introduction of advanced outfitting and Integrated Hull construction Outfitting and Painting (IHOP) the block can be built up including its outfits and painted prior being transferred to the berth or dock.

Figure 11.9 Make up of a grand-block

Figure 11.10 Example of an IHOP block

11-6

Basically assembly involves joining panels and subassemblies to form a larger and more complex structure, and outfitting several machineries and equipment and their supporting system parts. Welding is the most process involves in assembly, then aligning, fitting, and occasionally cutting too.

Methods of assembling the ship structure are dependent on the type and characteristics of the structure to be formed. In general these methods can be categorised into two main groups i.e.: structure that contents more outfit parts such as module structure, and structure that contents less outfit parts such as cargo hold block.

a) Structure with more outfit parts In assembling structure that contents more outfit parts attention should be given to the function and characteristics of each outfit part so that it can be fitted in properly to the structure and can be joined with other parts in the same system in different structure. In conjunction with the implementation of advanced outfitting, the outfitting works should be carried out in as early stage as possible, such as in the construction of panel, when the structure is still relatively simple and more access is available.

b) Structure with less outfit parts For assembling structure with less outfit parts the sequential approach is usually employed. Panels are joined to each other, then some other sub-assemblies are welded in. Attention should be made that as far as it is possible the assembled panel would self supported, so that the worker may gain more access to carry out their tasks.

For supporting the assembly process the availability and capacity of lifting and transferring facilities play very important role. Panels, sub-assemblies, and outfits have to be lifted to the assembly floor, and to transfer the completed structure to the building berth or dock. Electric overhead travelling cranes are usually employed in various lifting capacity ranging from 20 to 100 tonnes. To transfer the blocks to the building berth or dock multi-wheel transporter is usually being used.

Figure 11.11 Overhead crane

11-7

11.5 ASSEMBLY HAZARDS

a) Type of hazards Block and grand-block are comprised of large, heavy, and complex structural members that should be constructed in the right position, involving a great number of equipment and workers in a restricted working environment. This inconvenient condition is very vulnerable to any kind of hazards such as:

Use of flame and electricity Insecure laying of tools and structural parts Improper support of structural parts Unsafe and toxic working environment Inaccurate position of the structural parts

b) Risks related to assembly process Risks related to the assembly processes based on the identified hazards would include safety and production risks as follows:

Injury of the workers Reworks Delay in the completion of the interim products Products do not meet the required standards

c) Risk reduction To reduce any risk that might happen during the assembly process especially when the units or blocks become more complex as the members are increasing, an intensive planning of assembly sequence is required. Several considerations would include:

The shape of the interim products to be assembled The functional system of the outfits involved The size and weight of the assembly members

Figure 11.12 Transporter

11-8

The lifting and transfer facilities available in the shop The size and weight of the completed unit or block

With regard to the works to be carried out in the assembling process herewith some considerations that need to be taken:

Positioning of the block should not disturb the activities being undertaken Maximising the possibility of the block members to be self supported Provide good access to the people working in the block Provide good safety environment

11.6 ACCURACY CONTROL a) What is accuracy control? Accuracy control is not quality control; it is a way of using statistical method to predict the measurements accuracy of the interim products being processed, so that precautions could be taken to anticipate the probability outcomes of the product after being joined with the others. The accuracy control is aimed to increase the efficiency and productivity of the tasks being undertaken by minimising rework and plate margins.

b) Why accuracy control? Accuracy control is important in ship production, because shipbuilding involves the fabrication of large and complex structure, thus there are so many hazards involved in ship production processes such as late of delivery, product does not meet the required standards, and spending of unnecessary costs, and accuracy control is one of the approaches for reducing the risks of the hazards.

There are the trend of completing many tasks in the block construction (IHOP), and the involvement of thin structural members, that very easy to deform, therefore accuracy measurement and positioning of these parts become very crucial in order to achieve high efficiency in work processes.

c) Principles of accuracy control Statistical methods are used to predict the trend and possible deviations of the products being processed by calculating the standard deviations and variances of the normal distribution data gathered from previous production information.

Accuracy is defined as the difference between the achieved mean dimension and the target specification.

The variation of the distribution around its mean tells us to what degree the process is capable of achieving the desired performance; the smaller the dispersion around the process mean, the more capable the process. The reciprocal of the variance is the process precision, which measures the ability to execute identical performances and the ability of people and procedures to direct the fabrication process.

Sources of variation lie in materials, machines, people and procedures. Therefore in order to minimise the variation process control is implemented. The application of process control

11-9

requires an understanding of the kinds of variation that can occur, their sources, and the means by which they can be managed.

Process control can be considered as comprising the following five activities:

1. Establishing Performance Standards 2. Measuring Actual Performance 3. Comparison of Actual Performance Against Established Standards 4. Implementation of Corrective Action 5. Continuous Improvement

11.7 CONCLUDING REMARKS

a) Assembly is a process of building up a product from various parts, equipment, and machinery in arranged sequences of operations.

b) The assemblied structures can be divided into: module, unit, block, and grand-block. c) Mothods of assembling ship structure can be categorised into: structure that contents more outfit parts, and structure that contents less outfit parts.

d) Typical hazards related to the assembly process would include: Use of flame and electricity Insecure laying of tools and structural parts Improper support of structural parts Unsafe and toxic working environment Inaccurate position of the structural parts

e) Risks related to the assembly include safety risks and production risks.

f) Proper planning of assembly sequence is important in reducing the assemby risks.

g) Accuracy control is one of the approaches that could improve the quality of assembly processes.