The Design For Manufacture Engineering Essay

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A manufacturing system contain a large number of different processes or stages which independently and jointly, affects product cost, product quality and productivity of the overall system. The interactions between these various aspect of manufacturing systems are complex and decisions made concerning one aspect have result which extend to the others shown in fig below.

Fig:- Manufacturing Interactions [4]

Design for manufacture is concerned with understanding these interactions and using this information to optimize the manufacturing systems with respect to cost, quality and productivity. More specially DFM is concerned with understanding how product design cooperate with the other components of the manufacturing system and in defining product design alternatives which help make easy global optimization of the manufacturing systems as a whole. [4]

Design for Manufacturability (DFM) is a improvement program that can minimize labor, materials, process, and production costs without sacrificing the quality of the product. DFM focuses on how the product design interacts with the other components of the manufacturing system and in defining design alternatives.

In designing for manufacturability the elements of a product and a process are analyzed to develop a manufacturing system that meets the needs of organization. In most companies designers and manufacturing facilities are separated and have small interaction. The basic principle of DFM is to join the two into a functional group that will understand and understand the possible drivers of manufacturability that produces quality products for the customer.

So in our case, as the component to be manufactured is a cylinder block and is bespoke designed and a very low volume production for which design for manufacture concepts need to be applied. So, in this case the design for manufacture concepts relating to large volume production cannot be directly applied and hence DFM concepts relating to rapid prototyping will be more applicable. And, due to the nature of the manufacturing requirements of this concept, there will be different challenges than those of a mass production requirement.

Prototyping, the first physical byword of a design concept, frequently requires a large investment of time and money to describe the processes and tooling. The design goes through modification during the part manufacture as a result of the information added during the prototyping phase. Thus the time taken from the concept stage to the end products is longer with respect to that for job shop manufacturing. These restriction suggest the need for a design for manufacturability atmosphere to decrease the total cost and the manufacturing lead time for the first part.

When a idea is transformed to an actually manufacturable part design, many changes are common. The manufacturing process is frequently selected on the basis of part shape and size, material properties and production volume. Such change in manufacturing processes is common in the batch and mass production. But in prototyping and job shops it is generally not easy to make common or major changes in the manufacturing processes.

When conventional manufacturing method is used to create prototype, the long lead time and the high cost reduce the number of thoughts that are really converted into prototypes and models. For example in our case the cylinder block needs to have structural rigidity, wear resistance, corrosion resistance, high thermal conductivity and thermal stability and light in weight. This requires a use of the different materials, manufacturing processes, analyses, and finally testing over a wide range of operating conditions for each design alternative. High speed digital computers have helped the design engineer to analyze the alternatives. However, as long as conventional processes are used. It is not possible to prototype a large number of design concepts, each requiring specialized tooling and machine tools. This look like one of the major problems in decreasing the total growth time. [1]

Design for Manufacturing - Guidelines [6]

The heart of any design for manufacturing system is a design principles or guidelines that are prepared to help the designer decrease the cost and complexity of manufacturing of product. The guidelines are:

lessen the total number of parts

Homogenize components

Use common parts across product lines

Homogenize design features

Aspire to maintain designs functional and simple

Design parts to be multifunctional

Design parts for simplicity of manufacture

Avoid extremely tight tolerances

Lessen secondary and finishing operations

Employ the special characteristics of processes.

General Design Rules:-[6]

Design for small - workers -cost operations

Design a part so that as many manufacturing operations as possible can be achieved with no relocation it.

Design for general-purpose tooling whenever possible

Avoid sharp corners

Design light weight

Measurement from surfaces whenever possible

Avoid thin walls, thin webs, or similar characteristics that will result in dimensions due to manufacturing.

Avoid small holes and threaded characteristics because tool crack and part scrap raise.

Avoid undercuts that will need a special tools and operations.

Design round the standard cutters, drill bit sizes of other tools.

For threaded hole;

Design for full thread depth. Typically 1.5 x major diameters gives sufficient holding power.

Drilled hole depth is suggested to be at least equal to the full thread plus ½ major diameter, but never less than 0.050''.

When material thickness permit, thru holes are favoured

The design of the cylinder block is already exist based on basic function required. So in that design it is very hard to change anything. But some of the design shape can be change for Ease of machining with using the DFM guidelines and design rules .For example the design shape of oil passage way in the reference model block (AJ-V8) is half rectangular and half curvature can be redesign using DFM guidelines for ease of machining in to the hole shape. So previously design (rectangular/Curvature) needed the casting or slotting and drilling operation while new design (Hole) is just needed the drilling operation. This both design provides the same function of oil path from head to oil pan.

Conventional Design and manufacture and different DFM methods

Fig:-Sequence of events prevalent in industry for the design and manufacture of product [2]

The above flowchart shows the various steps in the case of conventional model of design and manufacture of products. This is a very chronological way of producing components. This sequence start with the conception of an plan for a new or modified product. These ideas for new and enhanced products come from the customers, employees and new technology. After the approval of idea, the new or improved product is then designed, engineered and analyzed for function and performance. A design phase is consisting of industrial or product design phase and engineer design phase. Next an analysis of the design from point of view of function and performance takes place. Next the design is detailed as the remaining dimensions and tolerances are added, the material is specified, and production drawing is produced. Finally the product is twisted over to manufacturing where both production design and process design takes place. [2]

This sequential mode of the operation is still found in the industry today.

Design for manufacture elements

Fig:- Key elements of successful design for manufacture [3]

As it can be seen from the fig above there are various elements that make up the design for manufacture possible. These are:

Team Work

Simultaneous engineering

DFM Techniques

And in general the whole idea is based around the manufacturing process used in the making of the part in question.

Four components of DFM are represented in the diagram by overlapping circles to emphasis their interdependence and the need for them all to exist in a competitive product introduction process. By applying the DFM principal early in new product design, optimal use is made of materials and processes, when change is easier and less expensive and overall cumulative use and product introduction process lead time are reduced.

Modified DFM for this project

Various elements of a standard DFM which are not required for this project's design have been eliminated in order to keep only the ones that are required. These elements are:

Project Concept

Purchased components

Product Design

Material selection

Process selection

Production system design

End Product

Fig: - Modified DFM for Cylinder Block

The above diagram shows the modified DFM for the cylinder block. The aim is to design a cylinder block that is easily and economically manufactured as design precedes from concept design, to configuration and parametric design and to detail design, the material and process selection becomes more detailed. The DFM is controlling all 6 parameters and output of this whole process is an end product a cylinder block. The value of DFM is highlighted by the fact that about 70% of manufacturing costs like material cost and machining cost of a product is determined by design judgment, with production judgment for example tool and machine selection and process planning is responsible for simply 20%.

Purchased components

Normally the project main constraint is to use the facilities available in the Coventry University first. So in this project it been try to use the maximum facilities i.e. machine, materials, tools, workshops etc. available in Coventry University. But Some of the facility is not available in university and without that particular facilities it is impossible to complete this project (manufacturing of the cylinder block).For example to provide a proper wear resistance inner cylinder bore surface ,the casting technique is used typically, which facility is not available in university. The other and last option is to purchase the ready made cast iron or Al-Si A390 liners. The size of the engine is very small ,it is just a prototype model so its very hard to get the ready made cylinder liners from out side manufacturer, It need to order for manufacture and then purchase it.

Also the whole cylinder block is going to be manufacture from the aluminium alloys A356. (Why described later in deep).So need to purchase required size of billet material (block).And the material for the fixture plate and main bearing cap is cast iron(Why described later in deep).So need to purchase the cast iron billet bock from outside manufacturer as well.

In this project cylinder bore sleeve and the crank case will be purchase as the workshop facilities are not capable for manufacturing these components to the requisite specifications.

Material selections and processes

The identification of the importance of materials selection in design has increased in recent years. The importance given to quality and cost aspects of manufacturing in present day product design has highlight the fact that materials and manufacturing are closely related in shaping final product performance. The range of materials available to the engineer is much broader than ever before. This presents the opportunity for originality in design by using these materials to offer greater performance at lower cost. Getting these benefits needs a logical process for materials selection. Wrongly chosen material can lead not only to failure of the block but also to excessive life-cycle cost. Selecting the best material for a block involves more than choosing both a material that has the properties to supply the necessary performance in service and the processing techniques used to produce the finished part.

Fig- Modified Interrelationship between materials selections and manufacturing in Cylinder block design.

Fig shows the modified interrelationship between cylinder block design performance requirements, material properties, and manufacturing consideration in selecting the material and in designing the cylinder block. In this Block design, material properties and the manufacturing process area interrelated with each other. That means the any change in one of them affects the other two parameters. Step by step material selection process as per the detail design and the cylinder block performance requirements are described later in details. The material chosen here is the Aluminium alloys-A356-T4 for the cylinder block and aluminium alloys A390-T4 for the cylinder liners. The all properties of aluminium alloys are exactly fit with the performance required properties of cylinder block compare to the other materials. For example good machinability is the main requirement in material as decided that the whole cylinder block is going to be machined. And aluminium in general rate highly in the machinability table by most of the criteria. The reason for choosing the aluminium alloys are described later in deep.

A manufacturing process converts a material into a finished part or product. The changes that take place happen with respect to block geometry, or they can influence the internal microstructure and therefore the properties of the material. As followed the project condition or limitation the manufacturing process used here for the whole cylinder block is machining (3 axis milling machine).So any required software or other preparation/process to short out the suitable manufacturing process for the cylinder block is not needed here. A manufacturing process is divided whether the process is mass conserving or mass reducing. The milling machining process is a mass reducing process in which the mass of the start material is greater than the end product. Such process is form generation process because part form is created by the relative motion between the tool and the billet block. And material removed is caused by controlled fracture, melting, or chemical reaction.

Product design:-

With the traditional method, the designer would work out an initial thought and convert that into a product design, making small change as required to meet the specification. DFM need that the designer begin the process by bearing in mind various design thought alternative early in the route. At this stage, small has been invested in a design alternative and much can be gain if a more successful design process can be developed. Using some of the previous design system as a structure, the designer needs to productively develop design option. Then option is evaluated against DFM objectives. [5]

Basically the whole cylinder block is designed with taking reference of jaguar AJ-V8 cylinder block. Most of the design geometry in our case of the cylinder block similar to AJ-V8 except some complex geometry and the size of all design geometry. The new designed cylinder block size is 1/3 of the AJ-V8 cylinder block, means all the design features of designed cylinder block will be 1/3 of AJ-V8 design features. The cooling water jacket, cylinder bores, the main bearing hole, crankshaft passage(Bulkhead) and some other small design are complex and time consuming but the plain holes , threaded holes for mounting the accessories and other purpose are easy to machine. The main design of the cylinder block is depend on the requirement of the end product (Customers) i.e. light weight, cheap, on time etc. If the cylinder block is design with keep in mind of light weight concept then the design will be change and add some more time and complex operation in machining but lighter in weight than old design. Here in this project two different design of cylinder block is generated with keeping in mind of combination of easy machining and light weight concept. The design details are described later on in design section).

At the design stage of the cylinder block it would be beneficial to keep in mind some factors which makes easy and quick production. Those factors are Milling machining (specifications, limits, capacity etc.), Material (Properties, machinability, availability etc), Tooling's and mounting accessories and other special facilities. The improved main design geometry worked out on base of these factors and available facilities are;

Cooling water jacket

Crankcase/Bed plate /Skirt

Coolant drain hole

Main bearing cap

The above new modified designs features of cylinder block are described in design section in details.

Factors influencing the design of the cylinder blocks:

Cylinder block design is a complex activity which has to take into consideration a large number of varied factors. These factors are generally grouped in the following categories:

Factors related to product specifications, such as weight, expected service life of block reliability, human factor, ease of operation, frequency of failure, operating cost, styling, possibility of use after retirement.

Factors related to design specification such as complexity, design code, operating loads, flexibility, lubrication, thermal consideration, electrical consideration and expected life.

Material related factors such as strength, toughness, stiffness, density, corrosion and wear resistance, cost, availability, melting point, thermal conductivity, process ability and recycling.

And the manufacturing related factors such as available fabrication process, accuracy, surface finish, required quantity and quality, delivery time and cost.

Successful design should take into account the function, material properties and manufacturing processes as shown in the fig below. The fig also shows that there is secondary relationship between material properties and manufacturing processes, between function and manufacturing processes, and between function and material properties. The relationship between the design and material properties is complicated because the performance of the material in the finished product can be fairly different from that of the stock material used in making it. This is shown in fig .which shows the direct influence of stock material properties, production method and component geometry and external forces on the behaviour of materials in the finished component. Fig also shows that secondary relationship exists between geometry and production method, between stock material and production method, and stock material and component geometry. (Mahmoud m.farag)

Factor that should consider in a component Design

Fig:- Factors that should be considered in anticipating the behaviour of material in the component (Cylinder Block)

Production system design:-

Production system design is connected with the market analysis, product design, manufacturing, sales and distribution. In our case there is no marketing analysis and not even sales and distribution so the production system will be easy to design. Because of this is one-off product it doesn't required any big production line or special equipments. The production system in our case covers the machining, tooling and other work piece mounting accessories. The whole cylinder block is going to be machined on the 3-axis manual milling machine. The milling machine is located at Coventry university workshop. In the workshop CNC 5-axis milling machine is also available but due to the project constraint, the use of the other machine is not possible. The numbers of different tools and cutters are required for the machining of the cylinder block which is also available in workshop .The machine is always free for doing the job (machining).

For mounting the cylinder block on the machine, it is been decided to use dividing head, and fixture plate. Dividing head is already available in workshop and in good condition. And the fixture is going to be design first and then manufactured from the cast iron separately before the machining of cylinder block. The machining operation can be performed from 9.30 am to 4.30 pm in the university workshop.

[0] Boothroyd, G., 1988, Dewhurst, P., Product Design for Manufacture and Assembly

[1] Issue in design/manufacture integration 1990 ,Sponsored by ;The design for manufacture committee of the design engineer division,ASME,DE-Vol.29

[2]Design for manufacturing a structural approachby corrado poli, University of Massachsetts Amhest,2001

[3] Design for manufacture Congress seminar papers - 33 ,Chairman - J Ford Lucas car braking Systems.

[4] Design for manufacture Strategies,Principles and Techniques by john Corbett, mikedooner, John Meleka and Christopher Pym.-1991

[5] http://www.npd-solutions.com/dfm.html

[6]Engineering Design byGeorge E.Dieter and Linda C.Schmidt-4th Edition,McGraw Hill-2009.

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