Process Planning, Scheduling and Control for One-of-a-Kind Production
5.1 Introduction
Process Planning, Scheduling and Control for
It is observed that customer expectations today do not include an emphasis on longevity in commodity products. Today’s customers do not seem to want to pay the cost for long-lasting but prefer their disposable nature so that they can avail themselves of newer models with improved appearance and functionality. Product examples include such items as cell phones and motor cars. Together with environmental consciousness, this leads to additional requirements in design and in the process of improving the disposal and recycling of products.
One way to be successful in this type of manufacturing process is to develop products in such a manner that they can easily be customised and have opportunities for improvement. For example, the cell phone can be customised both in its appearance and its functionality (e.g. the cell-phone plan has many options such as voice mail, call forwarding, call display and others). Cell phone functionality has developed since its first introduction with the addition of text messaging, MP3 players and video displays. The case study in this chapter focuses on a manufacturer of customised windows and doors that uses an incremental product development method and a product production structure similar to that described by Tu et al.
[5.1][5.2]. Gienow’s integrated system was developed over the last ten years since 1995. It was instrumental in Gienow being able to reduce their production cycle from 10–12 days to 24 h.
Gienow’s products can be customised in numerous ways including size, geometric shape, appearance options and functional options. Over the product’s lifecycle, new innovations are introduced. In the past they have included extended glazing options, grill patterns and add-on options.
First, the base product is designed and tested in its basic form. In the case of windows and doors this includes the basic frame, other components and the glass.
The product is tested to ensure that it meets technical specifications and the prescribed building codes according to the geographic location where it will be installed. The design of the base product is also based on market studies that determine appearance and functional requirements. Once the base product is designed and tested, the limits of the product variations are determined and established as design constraints. These constraints include such properties as size (minimum and maximum), shapes, combinations, and options that are inclusive and/or exclusive. Consequently, the various customised windows that meet the technical specification and building codes of the base product can be designed and mass produced through the variations of the base product within these predefined limits. This production mode is called one-of-a-kind production (OKP), which is a very efficient means to realize so-called mass customisation. It has much higher flexibility than the batch-production mode that normally uses standard modules to achieve limited customisation with a required minimum production batch size to compensate its production cost. Compared with a job shop, an OKP company has nearly the same flexibility but with much higher production efficiency.
In terms of the base product, the product improvement program and process can also be defined. This can include warranty and maintenance services programs, and the ability to add on new improvements after installation or complete replacement programs. This process should be a collaborative process that includes the customers and suppliers so that any improvements developed by suppliers are included as soon as they become available. Customer involvement ensures that new requirements and
expectations are registered once they occur. This collaborative process leads to the design improvement process becoming shorter and more effective.
An OKP company normally demonstrates the following characteristics [5.3]:
1. “Once” successful approach on the product, i.e. no prototype or specimen will be made in OKP, and the batch size can be one.
2. Product is usually designed by modifying and combining existing products to avoid the risk of long lead time and high costs for developing a radically innovative product.
3. Frequent changes of product design, manufacturing processes, and production schedules due to changes in customer requirements, arrivals of customer orders or raw materials, and manufacturing process, as well as machine breakdowns.
4. Mixed-product production.
5. Frequent changes of production system to adapt customised product production requirements.
6. Optimally utilising technologies and resources to continually improve production efficiency and reduce the production costs.
Dedicated manufacturing systems, e.g. mass or batch production systems, are characterised by rigid equipment designed specifically for a product or a restricted family of products. Typically, processes are manual with limited use of CNC equipment. They have high production rates and are expensive to change. Included in these systems are dedicated machines and dedicated flow lines. The latter is used in mass production.
Flexible manufacturing systems [5.4] are defined by CECIMO (Commit Europeenne de Cooperation des Industries de la Machine Outil) as automated manufacturing systems capable, with minimum human action, of producing any part type of a predefined family; these are generally adopted for the production at small to medium volumes, in variable lots sizes that differ also in their composition. The system flexibility is usually limited to the family of parts on which the system was conceived. FMS are characterised by their use of CNC equipment and low volume or small batch sizes. Mass customisation uses FMS in dedicated flow lines in order to achieve some economies of scale at the same time as attaining some customisation. An OKP system is an FMS with a lot size of one. It is a customisation that produces a unique variation from one kind of product.
OKP companies are normally different from one-off and job-shop manufacturing companies mainly in two aspects:
1. OKP companies are product-oriented manufacturing companies, whereas one-off or job-shop manufacturing companies are capability-oriented manufacturing companies.
2. OKP companies often adopt automated and highly efficient manufacturing processes, e.g. product flow line processes, whereas one-off or job-shop companies normally adopt high flexibility but low-efficiency manufacturing process, e.g. universal and functional equipment and job-shop process.
Due to these differences, OKP companies are able to effectively compete with
large mass-production manufacturing companies and gain market shares through customisation, fast delivery and low-cost production, to realise mass customisation.
The EEC (European Economic Community) research program, “ESPRIT basic research action 3143 – Factory of Future (FOF) production theory”, envisaged that OKP would become a novel manufacturing paradigm in this century along with a clear market trend toward customisation and responsiveness [5.5].
The characteristics of OKP result in great uncertainties and complicated product data flow, which leads to a longer product development cycle and higher production costs. Particularly along with the OKP, companies are moving to so-called virtual manufacturing systems (VMS) that logically consist of manufacturing resources belonging to different physical manufacturers. Uncertainties increase and product data flow becomes even more complicated as a result. Computer Aided Design (CAD) and production control systems currently available either overlook these problems or are not developed to meet OKP needs. This complex data flow requires good communication channels and electronic data interchange (EDI) methods. If a customised product is ordered then there is likely to be customised sub-components that are outsourced. These outsourcings need to be manufactured in a similar customised manner by the suppliers. Distribution of manufacturing further complicates data requirements and the whole supply-chain management.
The various processes of mass customisation have been identified by MacCarthy [5.6]. These processes are summarised in Table 5.1.
Table 5.1. Processes of mass customisation
Process Definition: The process of
Order taking and coordination Defining the order and product specification Product development and design Designing the product and its compliance with
internal and external standards Product validation and
manufacturing engineering
Confirming manufacturability
Producing the BOM, routing and processing instructions
Order fulfilment management Managing the order fulfilment by determining when production can start
Managing the value-added supply chain
Scheduling, monitoring and controlling the process Order fulfilment realisation Executing the production and delivery
Realising the supplier activities Post order process Installation
Warranty claims Service
Central to these processes is the products’ manufacturing engineering knowledge.
Without accurate information about the bill of materials, routings, engineering constraints and data requirements, it will be impossible to manage a mass- customisation process for one-of-a-kind products. This information is required for all the processes from order taking to service. The method of developing this knowledge is beyond the scope of this chapter, but it is assumed to be available in order to manage the planning, scheduling and control processes.