COMPUTER AIDED DESIGN OF GATING SYSTEM FOR A DIE-CASTING DIE E-Book

Dr. Chandan Deep Singh

• Herausgeber: BookRix
• Kategorie: Fachliteratur
• Sprache: Englisch

Veröffentlichungsjahr: 2018

Beschreibung

Design of a die-casting die is a critical activity for its manufacturing and further downstream activities. Further, in design of a die-casting die, activities like cavity design, cavity layout and design of gating system are essential components. Design of gating system for a die-casting die is dependent upon a number of parameters which are influenced by part design and die-casting alloy. Gating system design takes much time of the die-casting expert since it requires lot of manual input and a number of iterations to finalize the design. This requires a good knowledge of die-casting process, making this activity completely dependent on the user. In modern day industry lot of CAD/CAM tools are being applied for design, development and manufacturing of a die-casting die. However, dependency on a die-casting expert throughout design and manufacturing of die-casting die makes it a quite lengthy process. Gating system design being one of the major activities in die design also takes much time. Therefore, it would be quite beneficial to automate the activity of the gating system design. This work is about computer aided design of gating system for die-casting die. Proposed system takes CAD file of the die-casting part as input and uses die-casting process knowledge to determine different parameters for the gating system. Designs of the components of the gating system like runner, gate and overflow have been attempted. A feature library has been proposed as a part of this work which together with parametric design of the gating system generates CAD model of the components of the gating system. The system has been tested on a number of industrial parts and results found are quite encouraging. The system would go a long way in bridging the gap between designing and manufacturing of die-casting.

Leseprobe

Dr. Chandan Deep Singh, Dr. Jatinder Madan

COMPUTER AIDED DESIGN OF GATING SYSTEM FOR A DIE-CASTING DIE

, , , BookRix GmbH & Co. KG80331 Munich

Chapter 1

In the era of mechanization, every new dawn witnesses the launch of enterprising products and technologies. This has been made possible due to adoption of improved design and manufacturing processes by the manufacturing companies. Modern design and manufacturing processes are quite different from the traditional ones. The traditional ones were manual, involved lot of paperwork and traditional machine tools. Now the things have changed a lot with the introduction of computer systems, NC machine tools and the advent of information technology in design and manufacturing processes. Today design sections have acquired an all new look due to hi-tech computer workstations with 3-D design software support like CATIA, Pro. E. etc. NC, CNC and DNC machine tools have re-invented the outlook of shop floor.

This new look is the result of development in the field of CAD and CAM. CAD/CAM is the term that stands for computer-aided design (CAD) and computer-aided manufacturing (CAM). CAD deals with generating and managing the design information and CAM is responsible for planning, managing and controlling the manufacturing activities.

Although CAD and CAM have been significantly developed over the last three decades, they have traditionally been treated as separate activities. Many designers use CAD with little understanding of CAM. This, sometimes, results in design of non-machinable components or use of expensive tools and difficult operations to machine complex geometries. In many cases, design has to be modified several times, resulting in increased lead times and cost. Therefore, great savings in machining times and costs can be achieved if designers can solve machining problems of the products at the design stage. This can only be achieved through these fully integrated CAD/CAM systems [8].

The following paragraphs throw some light on the design manufacturing integration, die-casting process and design manufacturing integration of die-casting process.

1.2 Design - Manufacturing Integration

In compliance with the need of design manufacturing integration, this section explains the idea in detail and gives insight into the integration process. Design-manufacturing integration involves the generation of manufacturing information and data from the design data of a product.

Attempts for integration of CAD/CAM have been made by many researchers [9, 12]. There are some systems available that are capable of generating manufacturing data from the CAD model. But human intervention is required at some steps. The main focus of present CAD/CAM integration is to generate the manufacturing data i.e. NC codes for NC and CNC machines. Besides the generation of CAM data base, we can also integrate the other functions such as process planning, factory management and robotic control.

The benefits that can be derived from the integration of CAD/CAM are many. Some of the benefits are: shorter lead times, improved productivity, fewer design errors, better design analysis, greater accuracy in design calculations, standardization of design, reduced data redundancy, scheduling of tools and components, better product planning and control, application in product forecasting etc.

Die-casting is the manufacturing process which is capable of producing products quite close to net shape products. Parts made from die-casting are extensively used in automobiles, aerospace products, electronic equipment, optical and household items. Design of a die- casting die is the first step for manufacturing parts using this process. However, it has been seen that a lot of human expertise and knowledge is involved for designing a die casting die. This makes die-casting die design activity very expensive and time consuming. The succeeding section discusses about the following:

Die-casting process

Main stages in die-casting process

Die-casting machines

1.3 Die-casting Process

Die-casting process is an example of permanent mold casting. In die-casting process molten metal is forced into the die cavity at pressures ranging from 0.7MPa to 700MPa and finally ejected out after solidification of the metal [23].

The metal, typically a non-ferrous alloy such as aluminum or zinc, is melted in the furnace and then injected into the dies in the die-casting machine. The die-casting method is especially suited for applications where a large quantity of small-to-medium-sized part is needed with good detail, a fine surface quality, and dimensional consistency. This level of versatility has placed die casting among the highest volume products made in the metalworking industry [26].

A die-casting die consists of two halves named as core half and cavity half. Cavity half is the fixed one while core part is movable. Injection of the metal is done using a gating system which is provided in the cavity half of the die. The following paragraphs give a brief idea about stages in die-casting process, die-casting machines and the die-casting die. There are five main stages in die-casting process which are:

1.3.1 Main Stages in Die-casting Process

The five main stages in die-casting process are explained as below:

Clamping

Injection

Cooling

Ejection

Trimming

Clamping

The first step is the preparation and clamping of the two halves of the die. Each die half is first cleaned from the previous injection and then lubricated to facilitate the ejection of the next part. After lubrication, the two die halves, which are attached inside the die-casting machine, are closed and securely clamped together.

Injection

The molten metal, which is maintained at a particular temperature in the furnace, is transferred into a chamber from where it can be injected into the die. The method of transferring the molten metal depends upon the type of die-casting machine, whether a hot chamber or cold chamber machine is being used. The difference in hot chamber or cold chamber machines has been discussed in the next section.

Cooling

The molten metal that is injected into the die will begin to cool and solidify once it enters the die cavity. When the entire cavity is filled and the molten metal solidifies, the final shape of the casting is formed.

Ejection

After the predetermined cooling time has passed, the die halves can be opened and an ejection mechanism can push the casting out of the die cavity. Once the casting is ejected, the die can be closed again for the next injection.

Trimming

During cooling, the material in the channels of the die will solidify and would remain attached to the casting. This excess material, along with any flash that has occurred, must be trimmed from the casting either manually via cutting or sawing, or using a trimming press.

1.3.2 Die-casting Machines

There are two main types of die-casting machines –

Hot chamber machines

Cold chamber machines

 Hot chamber machines

These machines are used for alloys with low melting temperatures, such as Zinc, Tin, and Lead. The molten metal is contained in the holding pot which is placed into furnace. The molten metal flows through shot chamber into the goose neck and finally injected through the nozzle into the die with the push of plunger. Figure 1.1 shows the important parts of hot chamber die-casting machine.

Figure 1.1 Hot chamber die-casting machine [24]

 Cold chamber machine

Cold chamber machines are used for alloys with high melting temperatures, such as, Aluminum, Brass, and Magnesium. The metal is poured from the ladle into the shot chamber through a pouring hole. The plunger forces the metal through shot chamber into the die. Figure 1.2 shows the important parts of cold chamber die-casting machine.

Figure 1.2 Cold chamber die-casting machine [24]

1.3.3 Die-casting Die

A die-casting die consists of two halves termed as cavity (cover die) and core (ejector die). The cavity half is fixed and the core half is movable. The core half is moved towards the cavity half to assemble the die. Molten metal is poured into the space left between the two halves termed as cavity. Figure 1.3 shows the various parts of a die with shot sleeve and plunger.

Figure 1.3 various parts of die [14]

Having discussed the die-casting process, the next paragraph discusses the design-manufacturing integration of die-casting process.

1.4 Design-Manufacturing Integration of Die-casting Process.

Die-casting processes involve extensive use of CAD tools in part and die design. The normal process is to prepare a CAD model of the part and use this CAD model for designing and making the CAD model of the die. Designing of die-casting die requires lot of knowledge and expertise on the behalf of the die designer. Design –manufacturing integration can be realized if we develop such a system that is capable of generating die design from the 3-D model of the part itself. The system would take 3-D model of the part as input, recognize various features of the part model and determine different aspects of die such as, parting direction, parting surface, gate runner design, cavity layout etc.

The processing theory defines a step-by-step analytical procedure to design the energy exchange functions necessary to make a useful piece part. The results are the specifications for the die design and the process control set points. Cooling and heating channels plus the heat flow paths must be designed to focus the correct amount of energy through the cavity surface to achieve the required heat flux. Hence, the die design is derived from the defined required final condition of the solidification pattern.

The design of the die includes the following aspects

mechanical aspect: material selection, insert seams, and clearance space;

in the thermal exchange: location, size, length of the cooling=heating channels, and the flow rate of the medium used; and

in the fluid flow arena: the location and size of the gating and venting, as well as configuration of the metal feed system. This term is also used to define the net shape produced from this process.

The following section throws some light on the die-casting die design process that could be beneficial in understanding the principles of die design process and formulating the objectives for the present work. The succeeding section describes about the die-casting die design.