How does off-site manufacture improve quality?
The McGraw-Hill Construction SmartMarket Report on Prefabrication and Modularization found that "the quality of materials is one of the major benefits of prefabrication." In fact, in their survey of building owners, they found that even those who find no compelling cost benefit to prefabrication or modularization often choose to use it because of the dependable quality. This improved quality in modular units is also testified to by all of our clients.
Modular construction companies consistently attribute this improved quality to the following factors:
• access to technology in the factory environment
• tighter tolerances
• monitoring and quality control
• increased cooperation between trades that are usually performed by separate sub-contractors
• division and repetition of work
• improved physical access to the work
• improved working environment
Access to technology
As a result of the product passing through work stations (rather than labour going to the product, as is necessary on a construction site), there are more opportunities in a modular construction environment to introduce jigs and other less mobile technologies, like pneumatics and CNC equipment.
A jig is any type of apparatus for holding work and for guiding tools while working. We use them extensively to make plumbing and electrical harnesses and for welding components and frames together. The image to the right demonstrates a large welding jig that ensures that the structural steel frame is made square to a tolerance of less than 4mm over 7m.
Monitoring and quality control
The compact production line environment and the ease of moving around the modules allows for the increased visibility of work by supervisors. A team leader is able to easily see all the modules under their care at any given time and to move from one module to the next. This increased monitoring leads to the improved quality of tasks.
The production environment with its work stations through which each module passes facilitates a quality assurance step at the completion of each stage. Fixing errors as a result of this assurance process means that the final product is intrinsically better constructed from the core and services all the way to the finishes.
Key risks and any specific requirements of the clients can be incorporated into the quality assurance and testing process, like pressure testing the water suppply system (as indicated on the right).
Firstly, the materials used in a modular environment (like boards, steel or panels) are inherently made to tighter tolerances than those used on site (like bricks).
Secondly, the assembly of these materials can be made to greater tolerances in a manufactuing environment. Consider the difficulty with placing and pouring concrete accurately or laying bricks to tolerances of less than a few milimeters on site. Compare this to a modular approach that seeks to componentise key elements of a building. Where possible, each sub-component is made using CNC equipment that integrates with CAD design software. For example, steel studs and brackets are made using rolling equipment or cutting and bending equipment that are integrated with the design software. CNC machines are used to cut key timber components. This results in components that are made to tighter tolerances than those found on site and leads to a more consistent product with fewer installation defects than its conventional alternative.
Co-operation between trades
One of the fundamental benefits to modular bathrooms or room modules is that they align multiple trades. On site, each of these trades is usually subject to separate contracts. In the factory, waterproofing, tiling, plumbing, electrical, HVAC, glasswork and finishing are performed by one team. Co-operation is not negotiable, so alignment of process and performance is secured.
Division and repetition of work
The movement of modules through workstations allows for tasks to be broken down more fully than they can be on a construction site. So, plumbing can be broken down into pipe cutting (on a jig), assembly of sub-harnesses and then installation into the walls. The greater division of tasks that are then performed by one person leads to greater efficiency as well as quality as the task is mastered more easily and then perfomed with greater consistency.
Improved physical access to work
Modules passing through each work station have adequate space to move around. In addition, the module is desiged to ensure that it can be optimally assembled. The physical restrictions and limitations in gaining access to the work space that are on site are removed and with it, quality is improved.
Improved working environment
Tools and materials are located appropriately for each work station. Having these readily available at the work station as the module passes through ensures consistency in performing the required tasks.
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