In this section we briefly review the literature on the two main subjects of this paper which are direct digital manufacturing and production planning and control.
2.1 Direct Digital Manufacturing
Direct Digital Manufacturing (DDM) technologies are a set of novel manufacturing techniques that produce the final parts from a computer aided design (CAD) file. These technologies which started to appear during the 1980s also have been known as additive manufacturing and 3D printing production techniques. In most of these technologies the computer software slices the three dimensional model of the part to very thing two dimensional cross sections and send them one at a time to the printing machines. The machine then utilized various technologies to produce these parts a layer at a time to reach the final geometrical form factor [1, 10].
The application of these CAD based technologies in the beginning was focused on the production of design models and prototypes. However, as the material range expanded and production quality and precision increased the application shifted to functional prototypes and recently final parts. Still there are obstacles to overcome before this method of production can enter the mainstream use and realize a wide application. For instance the cost intensiveness of the production machines as well as raw material, low throughput of the processes, limited range of available material and labour intensiveness of the pre and post production steps are among the most notable issues that need to be addressed .
However, DDM has a number of unique characteristics which makes it a very useful manufacturing method for a number of industries even at the current cost levels. DDM enables the production of very small batch size (as small as the batch of one in medical applications) while also removes the design for manufacturing limitations to a high extent. This means the production of very complex parts with moving parts is possible in a single run, which translates to designers’ freedom to take advantage of design for performance instead. This is very relevant especially to the aerospace industry which searches for any opportunity to cut weight from the components and increase the fuel efficiency of airplanes. The other important features of this production method are the significant reduction in the amount of raw material waste through the production, the nonexistence of economics of scale (no tooling) and high flexibility for modifications on the fly [1, 9].
As the DDM attracts more attention and investment the new advancements will emerge which may turn it to a common production method for small and medium volume production batches in distributed settings which also has the potential to enable on-shoring of the manufacturing to the world’s developed countries and cut the costs of transportation of goods significantly . Therefore we see the urge to study the impact of this technology on various aspect of production management to illustrate the potentials and refute the myths.
2.2 Production Planning and Control
Production planning and control (PPC) are a set of activities which have been designed to make the production and delivery of products more smooth and efficient both time and cost-wise. Planning sets the goals for the production’s long, medium and short term goals with regard to product and processes, in order to satisfy the customers’ needs on time and uninterrupted. Production control is responsible to check the performance of the organization with regard to its production schedules and deliveries to alert any sign of derailment from the established plans. Moreover, the healthy functioning PPC can keep the inventories in check and customers satisfied through the optimum utilization of labor, material and machinery [7, 8].
Planning, routing, scheduling and loading are the main tasks in the production planning while, dispatching, follow up, inspection and corrective action are the production control practices. Planning is concerned with the processes which are required to be done to enable the production of the product, routing is the task of determining a path for the movement of the production lots in the factory while it is being made. Loading of the works on the machines is related to the capacity utilization of machines. Scheduling which is the last action in the production planning function, determines when and for how long a machine will be occupied with the production of specific parts or batches .
Dispatching deals with authorization of machine starts on various jobs based on the routing and scheduling. The action of controlling the start and stop of the works on the machines is called follow-up. Moreover, inspection of products acts as the problem detection method which will be fixed through the corrective actions on planning of the processes .
2.3 Literature Gap
The current literature on the impact of DDM on PPC is quite limited and mostly is focused on the utilization of PPC practices also on direct digital manufacturing technologies . However, there is no critical study of the PPC to evaluate the actual necessity of those concepts in the new production management . We tend to address this literature gap through this paper.