DESIGN FOR MANUFACTURING – MEE 550

Project Report

On

DESIGN FOR MANUFACTURING AND ASSEMBLY OF

FOLDING CHAIR

By

Group-5

Akhil Soman (13MMF00)

Yalamoori.N.Nitin (13MMF0028)

Vijay Kumar (13MMF)

Shubhankar Das (13MCD)

Arun Saco (13MCD)

1. INTRODUCTION

1.1 WHAT IS DESIGN FOR MANUFACTURE AND ASSEMBLY?

The term "design for manufacture" (or DFM) means the design for ease of manufacture

of the collection of parts that will form the product after assembly and "design for assembly"

(or DFA) means the design of the product for ease of assembly. Thus, "design for manufacture

and assembly" (DFMA) is a combination of DFA and DFM.

DFMA is used for three main activities:

1. As the basis for concurrent engineering studies to provide guidance to the design team

in simplifying the product structure, to reduce manufacturing and assembly costs, and

to quantify the improvements.

2. As a benchmarking tool to study competitors' products and quantify manufacturing and

assembly difficulties.

3. As a should-cost tool to help negotiate suppliers contracts.

1.2 DESIGN FOR MANUFACTURING:

Design for manufacturing is the general engineering art of designing products in such a

way that they are easy to manufacture. The basic idea exists in almost all engineering

disciplines, but of course the details differ widely depending on the manufacturing technology.

This design practice not only focuses on the design aspect of a part but also on the

producibility. In simple language it means relative ease to manufacture a product, part or

assembly.

DFM describes the process of designing or engineering a product in order to facilitate

the manufacturing process in order to reduce its manufacturing costs. DFM will allow potential

problems to be fixed in the design phase which is the least expensive place to address them.

The design of the component can have an enormous effect on the cost of manufacturing. Other

factors may affect the manufacturability such as the type of raw material, the form of the raw

material, dimensional tolerances, and secondary processing such as finishing.

1.3 PRODUCT DESIGN GUIDELINES

A number of general design guidelines have been established to achieve higher quality,

lower cost, improved application of automation and better maintainability. Examples of these

DFM guidelines are as follows:

1) Reduce the number of parts to minimize the opportunity for a defective part or an assembly

error, to decrease the total cost of fabricating and assembling the product, and to improve the

chance to automate the process

2) Foolproof the assembly design (poka-yoke) so that the assembly process is unambiguous

3) Design verifiability into the product and its components to provide a natural test or

inspection of the item

4) Avoid tight tolerances beyond the natural capability of the manufacturing processes and

design in the middle of a part's tolerance range

5) Design "robustness" into products to compensate for uncertainty in the product's

manufacturing, testing and use

6) Design for parts orientation and handling to minimize non-value-added manual effort, to

avoid ambiguity in orienting and merging parts, and to facilitate automation

7) Design for ease of assembly by utilizing simple patterns of movement and minimizing

fastening steps

8) Utilize common parts and materials to facilitate design activities, to minimize the amount of

inventory in the system and to standardize handling and assembly operations

9) Design modular products to facilitate assembly with building block components and sub-

assemblies

10) Design for ease of servicing the product

In addition to these guidelines, designers need to understand more about their own

company's production system, i.e., its capabilities and limitations, in order to establish

company-specific design rules to further guide and optimize their product design to the

company's production system. For example, they need to understand the tolerance limitations

of certain manufacturing processes.

GOALS OF DFM:

1) Early cost estimating

2) Material selection and Process planning

3) Early visualization of manufacturing process and impact on product design

4) Avoiding expensive and time consuming manufacturing process

5) Considering environmental issues

1.4 DESIGN FOR ASSEMBLY

DFA is a systematic analysis process primarily intended to reduce the assembly costs of

a product by simplifying the product design. It does so by first reducing the number of parts in

the product design, and then by ensuring that remaining parts are easily assembled. This close

analysis of the design is typically conducted by a team of, design and manufacturing engineers,

although other functional groups such as field service and purchasing may also be involved. DFA

techniques can be applied manually or with software. Both approaches lead to a simpler

product structure and assembly system. DFA is used for discrete manufacturing products, and

primarily for durable goods, but occasionally for consumer products. DFA was developed with

the assumption that the bulk of manufacturing costs are set in the design stage, before any

manufacturing systems analysis and tooling development is undertaken. DFA provides a

quantitative method for evaluating the cost and manufacturability of the design during the

design stage itself. DFA analysis roughly calculates expected unit material and labor (and/or

equipment) assembly cost, and also finds an efficiency which is a relative measure of the

product's ease of assembly.

PRINCIPLES OF DFA

1) Minimize part count

2) Design parts with self-locating features

3) Design parts with self-fastening features

4) Minimize reorientation of parts during assembly

5) Design parts for retrieval, handling, & insertion

6) Emphasize ‘Top-Down’ assemblies

7) Standardize parts

8) Encourage modular design

9) Design for a base part to locate other components

10) Design for component symmetry for insertion

1.5 SOFTWARE

DFM Concurrent Costing is a software tool to generate cost estimates for both piece

part cost and tooling investments. Unlike existing parametric cost estimating models, DFM

Concurrent Costing does not rely on historical data and therefore allows you to generate

accurate cost estimates for new designs and explore alternative materials and processes.

DFM complements Design for Assembly (DFA). Engineers use DFA software to reduce

the assembly cost of a product by consolidating parts into elegant and multifunctional designs.

DFM software then allows the design engineer quickly to judge the cost of producing the new

design and to compare it with the cost of producing the original assembly. Used together, DFM

and DFA software give engineers an early cost profile of product designs, providing a basis for

planning and decision making. Such analysis, when performed at the earliest stages of concept

design, has the potential to greatly influence manufacturing and other life cycle costs before

they are locked in.

Product engineers know that 85 percent of manufacturing costs are determined in the

early stages of design. When you make informed design decisions during the concept stage, you

avoid costly corrections later on.

Design for Assembly is a methodology for evaluating part designs and the overall design

of an assembly. It is a quantifiable way to identify unnecessary parts in an assembly and to

determine assembly times and costs. Using DFA software, product engineers assess the cost

contribution of each part and then simplify the product concept through part reduction

strategies. These strategies involve incorporating as many features into one part as is

economically feasible. The outcome of a DFA-based design is a more elegant product with

fewer parts that is both functionally efficient and easy to assemble. The larger benefits of a

DFA-based design are reduced part costs, improved quality and reliability, and shorter

development cycles.

DFA complements Design for Manufacture (DFM). Engineers use DFA software to

reduce the assembly cost of a product by consolidating parts into elegant and multifunctional

designs. DFM software then allows the design engineer quickly to judge the cost of producing

the new design and to compare it with the cost of producing the original assembly. Used

together, DFM and DFA software gives engineers an early cost profile of product designs,

providing a basis for planning and decision making. Such analyses, when performed at the

earliest stages of concept design, have the potential to greatly influence manufacturing and

other life-cycle costs before the costs are locked in.

2. FOLDING CHAIR

2.1 INTRODUCTION TO FOLDING CHAIR

A folding chair is a light, portable chair that folds flat, and can be stored in a stack, row,

or on a cart. Folding chairs are generally used for seating in areas where permanent seating is

not possible or practical. This includes outdoor and indoor events such as funerals, college

graduations, religious services, and sporting events and competitions. Folding chairs are also

used in the home for any situation requiring extra seating. This includes parties, card games,

and temporary seating at the dinner table.

2.2 HISTORY

Folding chairs were already being used in Sweden, Ancient Egypt, Greece and Rome. The

frame was mostly made of wood, and seldom made of metal. The wood was inlaid with artistic

carvings, gilded, and decorated with ivory. In Northern Europe, the remains of more than 18

folding chairs are known dating back to the Nordic Bronze Age such as the Daensen folding

chair.

The folding chair became especially widespread during the Middle Ages. It was

treasured as a liturgical furniture piece. Since the 15th and 16th centuries the folding chair has

mostly had arm and head rests. Of course, newer chairs which are often found in functions and

events are also called folding chairs. The folding chairs were very easy to use and bring to

different places such as parties or family gatherings.

In the United States, an early patent for a folding chair was by John Cham in 1855. In

1947, Fredric Arnold created the first aluminum folding chair with fabric strapping for the seat

and back. By 1957, the Fredric Arnold Company of Brooklyn, New York, was manufacturing

more than 14,000 chairs per day. Today, the folding chair is mostly made of hard plastic or

metal or wood. Folding chairs can be divided into different categories.

3. OLD DESIGN

3.1 OLD DESIGN

Fig: 3.1 Folding Chair (Old Design).

3.2 COMPONENTS AND MANUFACTURING PROCESS

S. No Component Material used Quantity Manufacturing process

1 Frame1 Generic low carbon steel 1

Machined/cut from the

stock

2 Frame2 Generic low carbon steel 1

Machined/cut from the

stock

3 Cross braces Generic low carbon steel 3 Machined/cut from the

stock

4 Spreader Generic low carbon steel 4 Compound Die Stamping

5 Seat Generic low carbon steel 1 Compound Die Stamping

6 Back rest Generic low carbon steel 1 Compound Die Stamping

7 Stability

caps

ABS Plastic 2 Injection Molding

8 Foot caps ABS Plastic 4 Injection Molding

9 Fasteners Generic low carbon steel 24 Assembly fabrication

Total 42 (Including Fasteners)

18 (Excluding Fasteners)

Table 3.1 Manufacturing process and materials used for various components of old design

3.3 DFMA ANALYSIS OF OLD DESIGN

Recently, the availability of SLDPRT file outputs from CAD systems has enabled some of

the geometric data required for various models for early cost estimation to be obtained

automatically. The link between CAD systems and the DFM software is the SolidView program

that has been developed for the visualization and measurement of objects defined in SLDPRT

and other formats.

Specific routines can be used to determine the following:

Overall envelope dimensions

Part volume (weight)

Projected area in the direction the die or mold closure where appropriate

Number of surface elements or patches.

This means that cost estimates for manufacture by various manufacturing processes can be

obtained from an initial CAD description of an object.

3.3.1 BACK REST

Figure 3.2 Shows the backrest visualized from a SLDPRT file representation using SolidWorks.

Table 3.2 Shows the cost breakdown for manufacturing this part by Compound Die Stamping

using the DFM Concurrent Costing software tool.

Fig 3.2

Table 3.2

3.3.2 CROSS BRACES

Figure 3.3 Shows the Cross Braces visualized from a SLDPRT file representation using

SolidWorks.

Table 3.3 Shows the cost breakdown for manufacturing Cross Braces by Machined/cut from the

stock Process using the DFM Concurrent Costing software tool.

Fig 3.3

Table 3.3

3.3.3 FOOT CAPS

Figure 3.4 Shows Foot Caps visualized from a SLDPRT file representation using SolidWorks.

Table 3.4 Shows the cost breakdown for manufacturing of Foot Caps by Injection Molding

Process using the DFM Concurrent Costing software tool.

Fig 3.4

Table 3.4

3.3.4 FRAME 1

Figure 3.5 Shows FRAME 1 visualized from a SLDPRT file representation using SolidWorks.

Table 3.5 Shows the cost breakdown for manufacturing of FRAME 1 by Machined/cut from the

stock Process using the DFM Concurrent Costing software tool.

Fig 3.5

Table 3.5

3.3.5 FRAME 2

Figure 3.6 shows FRAME 2 visualized from a SLDPRT file representation using SolidWorks.

Table 3.6 shows the cost breakdown for manufacturing of FRAME 2 by Machined/cut from the

stock Process using the DFM Concurrent Costing software tool.

Fig 3.6

Table 3.6

3.3.6 SEAT

Figure 3.7 Shows SEAT visualized from a SLDPRT file representation using SolidWorks.

Table 3.7 Shows the cost breakdown for manufacturing of SEAT by Compound Die Stamping

Process using the DFM Concurrent Costing software tool.

Fig 3.7

Table 3.7

3.3.7 SPREADER

Figure 3.8 Shows SPREADER visualized from a SLDPRT file representation using SolidWorks.

Table 3.8 Shows the cost breakdown for manufacturing of SPREADER by Compound Die

Stamping Process using the DFM Concurrent Costing software tool.

Fig 3.8

Table 3.8

3.3.8 STABILITY CAPS

Figure 3.9 Shows STABILITY CAPS visualized from a SLDPRT file representation using SolidWorks.

Table 3.9 Shows the cost breakdown for manufacturing of STABILITY CAPS by Injection Molding

Process using the DFM Concurrent Costing software tool.

Fig 3.9

Table 3.9

3.3.9 FASTENERS

Table 3.10 Shows the cost breakdown for manufacturing of FASTENERS by Assembly Fabrication

Process using the DFM Concurrent Costing software tool.

Table 3.10

3.4 COST BREAKDOWN PER CHAIR

The chart shows a breakdown of cost per product

3.5 PROBLEMS WITH OLD DESIGN

Not Efficient and Effective.

Expensive.

Lot of Parts.

Difficult to manufacture as multiple processes are required on single component.

Takes Lot of Time for Assembly.

Difficult to stack number of chairs together.

4. THE NEW CONCEPT

4.1 DESCRIPTION

The new concept is designed with an aim of reducing assembly time and effort by

keeping the number of individual parts to a minimum. The number of parts has been reduced

to three: two frames and a seat. The same material namely ABS is used for making the three

parts. This choice of material is done with a view of keeping the weight low while maintaining

the strength of the product. This also enables us to use the same manufacturing process for the

three individual parts. Similarly Polypropylene or High Density Polyethylene (HDPE) may also be

used.

Fig 4.1 New folding chair model.

The three individual parts can be seen more clearly in the folded view on the chair

below. The backrest has been built into the frame itself. The frames form complete loops. This

eliminates the use of cross coupling for stability. The frames have more contact area with the

floor as compared to four points in the old design. The weight is distributed along the entire

length of the frame in contact with the floor. As all the parts are made of the same material,

separate parts like stability caps and foot-caps are not required.

Fig 4.2 New folding chair model in folded mode.

The main frame has been provided with filleted holes into which the second frame and

the seat are snap-fitted. The second frame and seat have been provided with peg like

projections which fit into the holes provided in the first frame. The seat has a rounded pocket

into which the second frame sits in the unfolded position. The projections locate the second

frame and seat with respect to the first frame. The projections and pocket transmit the weight

of the person to the floor through frames.

Fig 4.3 Main Frame.

Fig 4.4 Secondary Frame.

Fig 4.5 Seat in wireframe view showing

pocket for seating second frame.

Fig 4.6 Filleted peg for location and load

transmission.

Pocket

Fillet

4.2 MATERIAL PROPERTIES

ABS is a terpolymer made by polymerizing styrene and acrylonitrile in the presence of

polybutadiene. The proportions can vary from 15 to 35% acrylonitrile, 5 to 30% butadiene and

40 to 60% styrene. The result is a long chain of polybutadiene crisscrossed with shorter chains

of poly (styreneco- acrylonitrile). The nitrile groups from neighboring chains, being polar,

attract each other and bind the chains together, making ABS stronger than pure polystyrene.

The styrene gives the plastic a shiny, impervious surface. The polybutadiene, a rubbery

substance, provides resilience even at low temperatures. For the majority of applications, ABS

can be used between −20 and 80 °C ( −4 and 176 °F) as its mechanical properties vary with

temperature. The properties are created by rubber toughening, where fine particles of

elastomer are distributed throughout the rigid matrix.

The most important mechanical properties of ABS are impact resistance and toughness.

A variety of modifications can be made to improve impact resistance, toughness, and heat

resistance. The impact resistance can be amplified by increasing the proportions of

polybutadiene in relation to styrene and also acrylonitrile, although this causes changes in

other properties. Impact resistance does not fall off rapidly at lower temperatures. Stability

under load is excellent with limited loads. Thus, changing the proportions of its components

ABS can be prepared in different grades. Two major categories could be ABS for extrusion and

ABS for injection molding, then high and medium impact resistance. Generally ABS would have

useful characteristics within a temperature range from −20 to 80 °C (−4 to 176 °F).

The final properties will be influenced to some extent by the conditions under which the

material is processed to the final product. For example, molding at a high temperature

improves the gloss and heat resistance of the product whereas the highest impact resistance

and strength are obtained by molding at low temperature. Fibers (usually glass fibers) and

additives can be mixed in the resin pellets to make the final product strong and raise the

operating range to as high as 80 °C (176 °F). Pigments can also be added, as the raw material

original color is translucent ivory to white. The aging characteristics of the polymers are largely

influenced by the polybutadiene content, and it is normal to include antioxidants in the

composition. Other factors include exposure to ultraviolet radiation, for which additives are

also available to protect against.

4.3 INJECTION MOLDING PROCESS

Injection molding is a manufacturing process for producing parts by injecting material

into a mould. Injection Molding can be performed with a host of materials, including metals,

glasses, elastomers, confections, and most commonly thermoplastic and thermosetting

polymers. Material for the part is fed into a heated barrel, mixed, and forced into a mould

cavity, where it cools and hardens to the configuration of the cavity. After a product is

designed, usually by an industrial designer or an engineer, moulds are made by a mouldmaker

(or toolmaker) from metal, usually either steel or aluminum, and precision-machined to form

the features of the desired part. Injection Molding is widely used for manufacturing a variety of

parts, from the smallest components to entire body panels of cars. Advances in 3D printing

technology, using photopolymers which do not melt during the injection Molding of some

lower temperature thermoplastics, can be used for some simple injection moulds.

Fig 4.7 Injection mold setup.

Parts to be injection moulded must be very carefully designed to facilitate the Molding

process; the material used for the part, the desired shape and features of the part, the material

of the mould, and the properties of the Molding machine must all be taken into account. The

versatility of injection Molding is facilitated by this breadth of design considerations and

possibilities

4.4 DFMA ANALYSIS OF NEW DESIGN

The cost breakdowns of individual parts are shown:

4.4.1 FRAME 1

Table 4.1 Shows the cost breakdown for manufacturing of main Frame by Injection molding

process using the DFM Concurrent Costing software tool.

Table 4.1

4.4.2 FRAME 2

Table 4.1 Shows the cost breakdown for manufacturing of secondary Frame by Injection

molding process using the DFM Concurrent Costing software tool.

Table 4.2

4.4.3 SEAT

Table 4.1 Shows the cost breakdown for manufacturing of main Seat by Injection molding

process using the DFM Concurrent Costing software tool.

Table 4.3

4.5 COST BREAKDOWN PER CHAIR

5. CONCLUSION

DFMA analysis of Folding chair was performed using DFMA software by Boothroyd

Dewhurst Inc.

Using the DFA module, the old assembly was analyzed. The assembly method for each

component was specified to the software which later calculated the cost of assembling the

product. The design was modified for ease of assemble as is observed by the reduced DFA Index

in the new design. Consequently the cost of assembly has also been reduced $4.28 to $0.17 per

product. This shows a reduction in time required for assembling the new product as compared

to the old product.

DFM Concurrent costing module was used to analyze and optimize the materials used

for manufacturing the product. The cost of individual components of final product assembly

was calculated. By selection of proper material and manufacturing processes in conjunction

with optimized assembly, we were successfully able to redesign the Folding chair for lower cost.

The cost of the Folding chair was reduced from $143.32 per product to $104.65 per

product for a product life volume of 10000.