Automated system for designing gating system of sand casting E-Book

Dr. Chandan Deep Singh

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

Veröffentlichungsjahr: 2018

Beschreibung

Designing in sand casting is a critical activity for manufacturing. Further, activities like cavity design, cavity layout and design of gating system are essential in design. Design of gating system in sand casting is dependent upon a various parameters. Gating system design requires lot of manual input and a number of iterations to finalize the design. This requires a good knowledge of casting process, making this activity completely dependent on the user. In present day industry, lot of CAD/CAM tools are applied for design, development and manufacturing. However, need of sand casting expert throughout design and manufacturing makes it a quite lengthy process. Gating system design being one of the major activities also takes much time. Therefore, it would be quite beneficial to develop a system for automated generation of gating system. Proposed system takes CAD file of the die casting part as input and uses sand casting process, machine and alloy 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 would go a long way in bridging the gap between designing and manufacturing of die-casting.

Leseprobe

Dr. Chandan Deep Singh, Rajdeep Singh

Automated system for designing gating system of sand casting

BookRix GmbH & Co. KG81371 Munich

Chapter 1

CHAPTER 1

INTRODUCTION

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.

Computer-Aided Design and Manufacturing

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 [Lin and Tai, 1996].

Computer-aided design is the use of computer systems to help in creation, modification, analysis, or optimization of a design. CAD creates a technical drawing with the use of computer software and used to increase the productivity of the designer, improve the quality of design, improve communications through documentation, and to create a database for manufacturing. It used to design curves and figures in two-dimensional (2D) surfaces, and solids in three-dimensional (3D) with the help of CATIA, Pro-E or Solid Works software’s. In a traditional CAD setting, the computer primarily serves as a precise drafting and visualization tool, permitting the designer to view the emerging geometry from different angles and in different projections. A digital representation also makes it possible to carry out some analytical tasks such as determining volume or surface area of a part. [wikipedia.org]

CAM is the use of computer software to control machine tools and related machinery in the manufacturing of work pieces. CAM is a subsequent computer-aided process after computer-aided design as the model generated in CAD and verified can be input into CAM software, which then controls the machine tool. CAD and CAM work together in that the digital model generated in CAD is inputted to the CAM software package for manufacturing the part created in CAM software. [wikipedia.org]

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 [Madan et al., 2007]. 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.

Designof tooling for Sand Casting involves parting line generation, gatingsystem design calculations, addition of shrinkage allowances andlayout. These all tasks are completed to some extent by theapplication of CAD/CAM techniques to mold design. Database providedin the software include data on material most commonly used for SandCasting, the information about material properties like shrinkage%,cast temperature, specific gravity etc. and the gating informationsuch as fill time, gate velocity and gate thickness. And at last thedatabase of machine using; like it may be cold chamber Sand Castingmachine or a hot chamber Sand Casting machine specifications.

1.3 Sand Casting

Sand casting, also known as sand molded casting, is a metal casting process characterized by using sand as the mold material. The term "sand casting" can also refer to an object produced via the sand casting process. Sand castings are produced in specialized factories called foundries. Over 70% of all metal castings are produced via sand casting process.

Molds made of sand are relatively cheap, and sufficiently refractory even for steel foundry use. In addition to the sand, a suitable bonding agent (usually clay) is mixed or occurs with the sand. The mixture is moistened, typically with water, but sometimes with other substances, to develop the strength and plasticity of the clay and to make the aggregate suitable for molding. The sand is typically contained in a system of frames or mold boxes known as a flask. The mold cavities and gate system are created by compacting the sand around models, or patterns, or carved directly into the sand.

Basic Process

There are six steps in this process:

Place a pattern in sand to create a mould.Incorporate the pattern and sand in a gating system.Remove the pattern.Fill the mould cavity with molten metal.Allow the metal to cool.Break away the sand mould and remove the casting.

Components

Patterns

From the design, provided by an engineer or designer, a skilled pattern maker builds a pattern of the object to be produced, using wood, metal, or a plastic such as expanded polystyrene. Sand can be ground, swept or strickled into shape. The metal to be cast will contract during solidification, and this may be non-uniform due to uneven cooling. Therefore, the pattern must be slightly larger than the finished product, a difference known as contraction allowance. Pattern-makers are able to produce suitable patterns using "according to the percentage of extra length needed). Different scaled rules are used for different metals, because each metal and alloy contracts by an amount distinct from all others. Patterns also have core prints that create registers within the molds into which are placed sand cores. Such cores, sometimes reinforced by wires, are used to create under-cut profiles and cavities which cannot be molded with the cope and drag, such as the interior passages of valves or cooling passages in engine blocks.

Paths for the entrance of metal into the mold cavity constitute the runner system and include the sprue, various feeders which maintain a good metal 'feed', and in-gates which attach the runner system to the casting cavity. Gas and steam generated during casting exit through the permeable sand or via risers, which are added either in the pattern itself, or as separate pieces.

Tools

In addition to patterns, the sand molder could also use tools to create the holes.

Molding box and materials

A multi-part molding box (known as a casting flask, the top and bottom halves of which are known respectively as the cope and drag) is prepared to receive the pattern. Molding boxes are made in segments that may be latched to each other and to end closures. For a simple object—flat on one side—the lower portion of the box, closed at the bottom, will be filled with a molding sand. The sand is packed in through a vibratory process called ramming, and in this case, periodically screeded level. The surface of the sand may then be stabilized with a sizing compound. The pattern is placed on the sand and another molding box segment is added. Additional sand is rammed over and around the pattern. Finally a cover is placed on the box and it is turned and unlatched, so that the halves of the mold may be parted and the pattern with its sprue and vent patterns removed. Additional sizing may be added and any defects introduced by the removal of the pattern are corrected. The box is closed again. This forms a "green" mold which must be dried to receive the hot metal. If the mold is not sufficiently dried a steam explosion can occur that can throw molten metal about. In some cases, the sand may be oiled instead of moistened, which makes casting possible without waiting for the sand to dry. Sand may also be bonded by chemical binders, such as furane resins or amine-hardened resins.

Chills