Functionality Manufacturing Processes Likely Failures Engineering Essay

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This paper addresses the design review and re-design of a Mini Chopper evaluating technical aspects of the product. Certain evaluation techniques are used such as QFD Quality Function Deployment for ensuring the quality of the product, FMEA (Failure Mode Effective Analysis) for analysing the failure modes in the product and Boothroyd and Dewhirst assembly analysis for quantitative evaluation of the design.

Introduction

Mini choppers (blenders) are commonly used household appliances to chop foods into a mixture. The blender described in this report is analysed to determine functionality, manufacturing processes, likely failures and materials of the components in the product. First, QFD analysis is conducted by focusing on true requirements and interpreting the customer needs. Also, areas of improvement in the product are also identified, where assembly process should be made simpler and safer thereby reducing manufacturing costs. Second, a Failure Mode Effective Analysis is carried out to identify possible methods and consequences of failure. It can be seen that highest risk factors are result of possible user error. Finally, Boothroyd and Dewhurst DFA analysis is conducted to determine the theoretical minimum part count and theoretical minimum assembly time. The assembly difficulties are also identified for elimination which may lead to manufacturing and quality problems. In this, the chopper was disassembled and broken into its unique component parts. The each part is analysed to determine its material and manufacturing process and this analysis is tabulated in the paper.

From the difficult disassembly of the chopper, it can be concluded that this chopper was intended to be discarded at the end of its life cycle rather than recycled. The improvements could be made by increasing the efficiency of the chopper motor resulting in energy cost savings.

Design Review of a Mini Chopper

The main function of the product is to chop through foods that are placed in the bowl using knife blades. It has a simple and easy-to-use design with milky white body. It consists of a coupling unit (bowl) with lid to open/close, a single control power on/off

Button and a set of knife blades (chopper). The performance level of the product is mediocre with the minimal speed level as there is no setting to adjust the speed to obtain optimal results. The bowl has 350 ml capacity, great for chopping various foods and the power of 120 watts. The lid can be airtight with an integrated safety lock feature that prevents any accidental use of the chopper.

Quality Function Deployment (QFD) for a Mini Chopper

Quality Function Deployment is a structured approach which translates the voice of the customer into the voice of an engineer. It is a set of powerful product development tools which transfer the concepts of quality control from the manufacturing process into the new product development process.

By using this tool in mini chopper, we are focussing on meeting market needs by using actual customer statements (referred to as the "Voice of the Customer"), its effective application of teamwork and the use of a comprehensive matrix (called the "House of Quality") for documenting information, perceptions and decisions.

This product can fail mainly for various reasons that the development team did not anticipate and these can be addressed by following such systematic QFD methodology. This analysis also develops the group of people to share a set of needs or assumptions, thereby evaluating the alternatives and making trade-offs.

From the House of Quality, according to the relative weight of the part characteristic in analysis, most of the customer requirements have strong relationship with product size, reliability, safety and lifespan of the chopper.

Failure Mode Effect Analysis for Mini Chopper (FMEA)

By carrying out FMEA for the mini chopper, we can document the key functions of a design, the primary potential failures relative to each function and the potential causes of each failure mode. This analysis allows the design team to document what they know and suspect about a product's failure modes prior to completing the design and then use this information to design out the causes of failure.

The purpose of FMEA chart is to assess the risks involved in the process of using a product and also to determine the causes and effects of each mode of failure. This is done by estimating a value that indicates severity, occurrence and detection of each error and then multiplying those values to obtain risk priority number (RPN). From this analysis table, possible actions to rectify the failures are also taken in so that further improvements can be made.

From analysing the table below, it can be observed that these failures can lead to issues which would make the chopper unable to use and also become more of a nuisance to the customer. These failures are very important to consider and their respective importance are tabulated below. The malfunction of the motor, wiring and the wear/deformation of the teeth would fail the chopper entirely while the cracks or breaks in other components are not that significant. From the values, it is clear that overheating of the motor is one severe issue, which results in a value of 8 though it is not likely to occur resulting in a value of 6. The motor in the chopper is not easily accessible to the user thus making it difficult to detect the failure. This example is a clear justification of the FMEA to determine the following values. These failure modes can be further resolved by conducting tests to make the product cost effective and satisfaction to the customer.

The table below illustrates FMEA for a Mini Chopper:

 

 

 

 

 

 

 

 

 

 

 

FAILURE MODE AND EFFECTS ANALYSIS

 

Item:

Mini Chopper

Responsibility:

 

Model:

 

Prepared by:

ASWIN PONNAN VARKEY

Core Team:

 

 

 

 

 

 

 

 

 

 

Item

Potential Failure Mode

Potential Effect(s) of Failure

Sev

Potential Cause(s)/ Mechanism(s) of Failure

Occur

Current

Process

Controls

Detec

RPN

Recommended Action(s)

Bottom Cover Screws

Loosening

Expose electronics

6

User error/Tampering

6

Use screw that requires specialised tool to unscrew

1

36

Screw the bottom back on

Bottom cover

Cracks, missing sections

Expose electronics

4

Dropping, Hitting

7

Use stronger or thicker plastic for the bottom

1

28

None

Electrical Cord

Missing insulation, Frayed wiring

Electrocution of user

9

User error, accidental cutting, wear of the insulation

4

Stronger insulation, retractable cord

1

36

Swap out electrical cord if possible

Circuit board

Liquid coming in contact with the board

Sparking, chopper failure

8

Dripping from pouring over chopper base and getting into the sockets

6

Put a sealing over the console

1

48

Pour the contents over the sink

Bowl

Cracking/Breaking

Unusable chopper without bowl

7

Dropping, Hitting

3

None, already very thick glass

1

21

Replace with new bowl

Bowl Lid

Cracking/Breaking

Incomplete bowl resulting in some mess

6

Dropping, Hitting

3

None, already very thick glass

1

18

Replace

Spring

Breaks or does not reform after compression

Power switch stops working

8

Metal Fatigue, Manufacturing error

1

Make springs out of resilient material

3

24

Replace spring

Blade Assembly

Not locking blade in during use assembly

Free blade

8

Improper use

7

Make locking mechanism that locks blade when it is put in shaft

1

56

Reassemble chopper

Motor Rotor

Bending motor shaft

Severe vibration, jamming

4

Dropping, Hitting, wear, exceeding manufacturing tolerances

3

3

36

Replace chopper

Blades

Breaking shards; Blade edge dulls

Shards in food; Takes longer time and makes it difficult to chop

9

Improper use

2

Stronger blade material

2

36

Do not use chopper

Gears

Wear, deformation of teeth

Unusable chopper

8

Lifespan, liquid coming in contact

2

2

32

Replace gears

Motor

Motor Overheating

Motor will not be able to turn the blades and make the chopper useless

8

Motor could overheat if it is left on too long when chopping thicker foods

6

Testing fan output as well as testing motor at speeds with different loads.

8

384

Add a switch that would turn off the chopper if the maximum speed approached

Table 1: FMEA for a Mini Chopper

Materials and Manufacturing Processes

The materials and manufacturing processes are suggested from the assumptions depending on the shape, density and visual indications on the parts.

The materials and manufacturing processes for each component in the mini chopper are tabulated below:

Table 2: Materials and Manufacturing Processes

Part Name

Materials

Manufacturing Processes

Bowl

Acrylonitrile styrene

Molding

Bowl Cover/Lid

Acrylonitrile styrene

Molding

Spring

Steel

Extrusion, Coiled

Blade

Steel

Milling and Stamping

Blade Shaft

Steel

Extrusion

Bearing

Brass

Extrusion/Turning

Motor Assembly

Stainless Steel, Aluminium, Plastic, Steel

Power Cord and wiring- Molded/ Stamped; Coil- Extrusion;

Base

Polypropylene

Two Part molding

Motor cover

Polypropylene

Two part molding

Cover screws

Aluminium

Extrusion/rolled

Base Screws

Aluminium

Extrusion/rolled

Button

Polypropylene

Two part molding

Stator

Steel, Copper

Stamped, Coiled and Assembled

The mini chopper is mainly composed of five major components such as bowl, motor, base, blade assembly and a button. The bowl is made up of acrylonitrile styrene and made by molding. This is assembled with the use of fasteners which increases the ease of assembly. There is also a blade holder assembly made up of polypropylene connecting the bowl to the body of the chopper. The two identical blades are setup on the assembly made from a slab of steel that are kept on top of one another riveted on it. The other major component is a motor which is inside the base and problem is that it is not sufficiently mounted. The other parts of the motor are glued directly to the motor assembly. The other main component is the base made up of polypropylene most likely by injection molding (two part molding). The last component is a simple on/off button made up of polypropylene which is assembled with snap on fit along with a spring made of steel by extrusion.

The majority of the parts of the chopper are made up of plastic and most of them are made through injection molding as flashing lines are an indication of this type of manufacturing

Boothroyd and Dewhurst Assembly Analysis for Mini Chopper

This assembly analysis does the following:

Determines the theoretical minimum part count by applying minimum part criteria.

Estimate actual assembly time.

Determines DFA by comparing actual assembly time with theoretical minimum assembly time.

Identify assembly difficulties and others for elimination which may lead to manufacturing and quality problems.

Product Disassembly

In order to begin the assembly analysis, the chopper was disassembled and divided into its unique component parts and is tabulated below (Table 3). Each part is analysed and reassembled to determine assembly operational time according to the estimated handling time and insertion time of each component thus evaluating the design efficiency of the chopper (Reverse Engineering) shown in Table 4. The handling and insertion times are obtained for each component according to the assembly sequence, geometry and its dimension. The assembly operation cost is calculated by taking manual assembly operation cost rate as £40/ hour.

From the product disassembly, it can be concluded that there is only a little room for improvement in design for assembly. Most of the parts were made of polypropylene plastic that can be manufactured through injection molding, which is really cheap and fast. A very few screws are found on the chopper, mostly standard parts, which are easily available and these can be reduced with the use of rivets and tabs on the design which would reduce the number of part count. Blades were found to be stamped sheet steel, where stamping is one of the easiest and effective ways of manufacturing. Also, parts could be easily stacked on top of each other during assembly. One of the major exceptions are the addition of a sub-base which covers the motor and the control top holding the on/off switch which can be eliminated to reduce the part count.

One of the design defect found in the wiring (motor assembly) is that all the wires are bunched along with the motor towards the base, thus making it manually to bunch the wires, slowing down the overall assembly process.

The future redesign should be made to reduce the number of components to speed up the rate of manufacturing process and cost savings.

Part Number

Part Name

Quantity

Function

Bowl sub-assembly

01

Bowl

1

Holds foods to be chopped

02

Cover/Lid

1

Covers top of the bowl

Blade sub-assembly

03

Knife blade

1

Chops food

04

Blade shaft

1

Transmit rotation of blade

05

Blade holder

1

Connects blade to bowl lid

Motor Sub- assembly

06

Motor assembly

1

It is a housing that generates an alternating magnetic field with surrounding coils

07

Motor shaft

1

Rotates the blade

Gear Sub- assembly

08

Gears

3

Rotates the blade

09

Locking Nut

1

Attached blade to the shaft

10

Screw washer

1

Distributes load evenly to the shaft

User interface sub-assembly

11

Sub-Base (Motor cover)

1

Covers the bottom of the motor

12

Main Base

1

Covers the bottom of the body and provides stability for the chopper

13

Base cover screws

4

Holds base to motor cover and motor assembly

14

Main Body

1

Covers top of the motor and allows the user to interact with chopper

15

Control top

1

Hold the button in place

16

Button

1

Switch on/off chopper

17

Spring

1

Movement of button upwards and downwards respectively

Table 3: Product Disassembly

1

2

3

4

5

6

7

8

9

Nature of Assembly/

Component

Part Id No:

No of times

operation is carried out

2-digit

manual handling code

Manual handling time per part

2-digit manual insertion code

Manual insertion time per part

Operation time =

(2)*{(4)+(6)}

(secs)

Operation cost Manual assembly rate * (7) (£)

Figures for estimation of Theoretical minimum parts

Mini chopper

15

1

00

1.13

00

1.5

2.63

0.03

1

Main Body

14

2

00

1.13

00

1.5

5.26

0.06

1

Gears

13

1

02

1.88

38

6.0

7.88

0.09

0

Locking Nut

12

1

Blade shaft

11

1

Motor Assembly

10

1

00

1.13

01

2.5

3.63

0.04

1

Sub Base

09

1

00

1.13

06

5.5

6.63

0.07

1

Base

08

4

01

1.43

38

6.0

29.72

0.33

0

Screws

07

1

01

1.43

30

2.0

3.43

0.04

1

Spring

06

1

00

1.13

38

6.0

7.13

0.08

1

Control Button

05

1

00

1.13

06

5.5

6.63

0.07

0

Control top

04

1

10

1.5

09

7.5

9

0.10

1

Top cover

03

1

01

1.13

31

5.0

6.13

0.07

1

Blade Assembly

02

1

01

1.13

31

5.0

6.13

0.07

1

Bowl

01

1

01

1.13

31

5.0

6.13

0.07

1

Bowl Lid

85.47

1.12

10

Design Efficiency =

3 * NM/TM

TM

CM

NM

0.35

Table 4: Evaluating the design efficiency of the mini chopper

From the analysis table, design efficiency is obtained. This table gives a basic idea of how the cost of the mini chopper can be reduced through the simplification of its design. This can be achieved by reducing the number of components, ensuring that the parts are easy to assemble, increasing the use of standardised parts and material selection with respect to manufacturing processes. Also it can be concluded that design can be improved as the number in the column 9 is less than column 2 and assembly time can be reduced by examining column 4 and 6. According to the table, there are four components with the assembly operation time more than 7 seconds due to a very high insertion time. This is due to the position of holding the components down for orientation and location and also screw tightening takes longer time.

By comparing with the ideal time with the minimum number of parts and each part taking an average time of 3 second to assemble, the mini chopper has only 0.35 % design efficiency. This means that total assembly operation time in ideal condition is only 39% of the assembly operation for the existing mini chopper design and this design needed some improvement on assembly process.

Re-design of Mini Chopper

Redesign

The motor is made to fit under the base and is sufficiently mounted. The mounting clips are under the blender base and are made to withstand the movement associated with the vibrations from the motor. The mounting clips are extensions on the base allowing for more strength. However, many parts of the motor attachment are attached by gluing which may result in problems with reusing or taking apart the glued components during the assembly process.

Bowl and lid optimization

Removal of sub base (only one base required)

Reduction of screws snap on fittings

- Reduction of number of components

- Ensuring that parts are easy to assemble

- Increasing the use of standardized parts across entire product range

- Designing with widest possible tolerances

- Material selection must consider manufacturing also, not just function.

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