The production of moulds or dies is a tedious process that is and energy demanding. It involves a lot of processes that take time and waste human effort. Press steel die making is laborious and involves heavy metal for haulage. Manufacturing of engineering products with intricate shapes and requiring mass production necessitates production of moulds and dies. The use of moulds and dies in manufacturing cannot be overemphasized. Hence to facilitate quick moulds or die production, the need for automation through Computer Aided Design (CAD) and Computer Aided Manufacture (CAM), using Computer Numerical Controlled (CNC) machines and other semi-automatic machines cannot be neglected .
Development and modelling of a computer aided programme from a well detailed dimensional Auto CAD drawing allows the point-to-point co-ordinates of the pattern for the programming. This is presented in codes and instructions that are best understood by the machine. A programming language for the computer numerical controlled (CNC) machine is chosen by the manufacturer. Examples of these programming languages include Siemens Programming, GSK programming, and Aldehan and Sinumeric. Engineers should therefore be versatile with the pattern language and instructions that the type of CNC machine allows .
Advanced manufacturing through CNC programming and machining techniques facilitate human effort in this laborious die making activity, and save energy and man hours. It is also made possible through efficient integration of tool inspection for optimum tool performance. Hence, this yields good surface finishing .
To produce most geometry shapes, the process of formation and manufacturing of the die may be affected by limitations such as: material availability and cost, machine size, processing speed, dimensional accuracy, surface finishing and cost effectiveness. However, it is safer, convenient, energy and time saving to use automation such as CNC machines in mould or die production .
The advent of CNC and other semi-automatic machines makes mass production possible. This is also favored in rapid prototyping (RP) and rapid tooling (RT). Other machines are developed to ease moulds and die production which are also more technologically advanced than CNCs, such as Stereo lithography (SLA), Selective Laser Sintering (SLS), Fused Deposition Modelling (FDM), Three-Dimensional Printing, Direct Metal Laser Sintering (DMLS), Laser Engineered Net Shaping (LENS), Electron Beam Melting (EBM) as additive manufacturing processes. Conversely, the subtractive manufacturing processes are CNC milling, CNC wire EDM, drilling, grinding, and lathe-turning . All these machines can be fully utilized with the use of CAD, which provides a means of obtaining the programme for any operation, through the co-ordinate points obtained from the detailed design work .
Drop dies like this are meant for cold forming of materials into their desired shapes as the shapes of the dies. These drop dies are hence capable of mass producing quite a number of the products within minutes .
The die and mould making industrial development has been strong in recent years. Machine tools and cutting tools get more and more sophisticated every day and can perform applications at a speed and accuracy not even thought of twenty years ago. CAD/CAM has become popular for machining with High Speed Machining (HSM), which is a necessity for the die and mould making industry .
A die is a specialized tool used in manufacturing industries to cut or shape material using a press. Like molds, dies are generally customized to the item they are used to create (see Fig. 1). Products made with dies range from simple paper clips to complex pieces used in advanced manufacturing technology .
Forming dies are typically made by tool and die makers and put into production after mounting into a press. The die is a metal block that is used for forming materials such as sheet metal and plastic. For the vacuum forming of plastic sheet, only a single form is used, typically to form transparent plastic containers (called blister packs) for merchandise. Vacuum forming is considered a simple molding thermoforming process but uses the same principles as die forming .
For the forming of sheet metal, such as automobile body parts, two parts may be used. The first part, known as the punch, performs the stretching, bending, and/or blanking operation. The second part, known as the die block, securely clamps the work piece and provides similar stretching, bending, and/or blanking operation. The work piece may pass through several stages using different tools or operations to obtain the final form. In the case of an automotive component, there will usually be a shearing operation after the main forming is done, followed by additional crimping or rolling operations to ensure that all sharp edges are hidden and to add rigidity to the panel .
Machinability of most types of cast-iron involved in metal cutting production is generally good. The rating is highly related to the structure where the harder pearlitic cast-irons are somewhat more demanding to machine. Graphite flake cast-iron and malleable cast-iron have excellent machining properties, while SG cast-iron is not quite as good. The main wear types encountered when machining cast-iron are abrasion, adhesion and diffusion wear. The abrasion is produced mainly by the carbides, sand inclusions and harder chill skins. Adhesion wear with built-up edge formation takes place at lower machining temperatures and cutting speeds. This is the ferrite part of cast-iron which is most easily welded onto the insert, but which can be counteracted by increasing speed and temperature. On the other hand, diffusion wear is temperature related and occurs at high cutting speeds, especially with the higher strength cast-iron grades. These grades have a greater deformation resistance, leading to higher temperature . This type of wear is related to the reaction between cast-iron and tool and has led to some cast-iron machining being carried out at high speeds with ceramic tools, achieving good surface finish.
Typical tool properties needed, generally, to machine cast-iron are high hot-hardness and chemical stability but, depending upon the operation, work pieces and machining conditions, toughness, thermal shock resistance and strength are needed from the cutting edge. Ceramic grades are used to machine cast-iron along with cemented carbide. Obtaining satisfactory results in machining cast-iron is dependent on how the cutting-edge wear develops: rapid blunting will mean premature edge breakdown through thermal cracks and chipping and poor results by way of work piece frittering, poor surface finish, and excessive waviness. Well-developed flank wear, maintaining a balanced sharp edge, is generally to be strived for .
Modern CAD/CAM-systems can be used in much better ways if old thinking, traditional tooling and production habits are abandoned. If instead, new ways of thinking that also approach an application, there will be a lot of wins and savings in the end. If using a programming technique in which the main ingredients are to “slice-off” material with a constant Z-value, using contouring tool paths in combination with down milling, the result will be:
i. a considerably shorter machining time;
ii. better machine and tool utilization;
iii. improved geometrical quality of the machined die or mould; and
iv. less manual polishing and try out time.
In combination with modern holding and cutting tools it has been proven many times that this concept can cut the total production cost considerably. A human being cannot compete, no matter how skilled, with a computerized tool path when it comes to precision. Different persons use different pressures when doing stoning and polishing, resulting most often in too big dimensional deviations. It is also difficult to find and recruit skilled, experienced labour in this field. The machining process should be divided into at least three operation types; roughing, semi-finishing and finishing, sometimes even super-finishing in the context of mostly HSM applications .
HSM processes have underlined the necessity to develop both the CAM and CNC-technology radically. HSM is not simply a question of controlling and driving the axes and turning the spindles faster. HSM applications create a need of much faster data communication between different units in the process chain. There are also specific conditions for the cutting process in HSM applications that conventional CNCs cannot handle.
The typical structure for generating data and performing the cutting and measuring process is depicted in Fig. 2.
This type of process structure is characterized by specific configuration of data for each computer. The communication of data between each computer in this chain has to be adapted and translated. The communication is always of one way-type. There are often several types of interfaces without a common standard .