**4. Parametric ALTs with corrective action plans**

232 Energy Efficiency – The Innovative Ways for Smart Energy, the Future Towards Modern Utilities

(Table 3).

Item

**Table 3.** Operating number of a drawer

approximately 4.0 using equation (13).

**Figure 5.** ALT equipment and duty cycles.

life of *B1* = 10 years. Assuming the shape parameter

confidence that it would fail less than once during 67,000 cycles.

number of operating cycles for one day was approximately 5; the worst case was 9. Under the worst case, the objective drawer open/close cycles for ten years would be 32,850 cycles

Drawer 5 9 18,250 32,850

For the worst case, the food weight force on the handle of the drawer was 0.34 *kN*. The applied food weight force for the ALT was 0.68 *kN*. With a quotient, *n*, of 2, the total *AF* was

The parameter design criterion of the newly designed drawer can be more than the target

and test sample numbers calculated in Equation (7) were 67,000 cycles and 3 units, respectively. The ALT was designed to ensure a *B1* life of 10 years with about a 60% level of

(a) ALT equipment and controller

(b) Duty cycles of repetitive food weight force on the drawer

β

was 2.0 and *x* was 0.01, the test cycles

Number of operations (times) 1 day 10 years Normal Worst Normal Worst

> Figures 6(a) and 6(b) show the failed product from the field and the 1st accelerated life testing, respectively. The failure sites in the field and the first ALT occurred at the drawer handle as a result of high concentrated stress. Figure 7 shows a graphical analysis of the ALT results and field data on a Weibull plot. For the shape parameter, the estimated value on the chart was 2.0. For the final design, the shape parameter was determined to be 3.1. These methodologies were valid for pinpointing the weak design responsible for failures in the field and 1st ALT.

(a) Failed product in field (b) Failed sample in first accelerated life testing

**Figure 6.** Failed products in field and first ALT

The Reliability Design and Its Direct Effect on the Energy Efficiency 235

The fracture of the drawer in the first and second ALTs occurred in the handle and slide rails (Figure 6(b) and Figure 8). The missing or improper parameters of the handle and slide rails in the design phase are listed in Table 4. These design flaws can result in a fracture

**CTQ Parameters Unit**

To prevent the fracture problem and release the repetitive stresses, the handle and slide rails were redesigned. The corrective action plan for the design parameters included: (1) increasing the width of the reinforced handle, C1, from 90mm to 122mm; (2) increasing the handle hooker size, C2, from 8mm to 19mm; (3) increasing the rail fastening screw number, C3, from 1 to 2; (4) adding an inner chamber and plastic material, C4, from HIPS to ABS; (5) thickening the boss, C5, from 2.0mm to 3.0mm; (6) adding a new support rib,

The parameter design criterion of the newly designed samples was more than the target life,

the recalculated test cycles and sample size in Equation (7) were 32,000 and 3 units, respectively. In the third ALT, no problems were found with the drawer after 32,000 cycles and 65,000 cycles. We therefore concluded that the modified design parameters were

Table 6 provides a summary of the ALT results. Figure 9 shows the results of the 1st ALT and 3rd ALT plotted in a Weibull chart. With the improved design parameters, the *B1* life of

, on the Weibull chart was 3.1. For the second ALT,

β

the samples in the third ALT was lengthened to more than 10.0 years.

KNP N1 Consumer food loading kN

C1 Reinforced handle width - C2 Handle hooker width - C3 Fastening screw number - C4 Slide rail chamber mm C5 Slide rail boss thickness mm C6 New added rib -

when the repetitive food load is applied.

KCP

**Table 4.** Vital parameters based on ALTs

*B1*, of ten years. The confirmed value,

Fracture

C6 (Table 5).

effective.

**Figure 7.** Field data and results of 1st ALT on Weibull chart.

**Figure 8.** Failed slide rails in second ALT

The fracture of the drawer in the first and second ALTs occurred in the handle and slide rails (Figure 6(b) and Figure 8). The missing or improper parameters of the handle and slide rails in the design phase are listed in Table 4. These design flaws can result in a fracture when the repetitive food load is applied.


**Table 4.** Vital parameters based on ALTs

234 Energy Efficiency – The Innovative Ways for Smart Energy, the Future Towards Modern Utilities

**Figure 7.** Field data and results of 1st ALT on Weibull chart.

**Figure 8.** Failed slide rails in second ALT

To prevent the fracture problem and release the repetitive stresses, the handle and slide rails were redesigned. The corrective action plan for the design parameters included: (1) increasing the width of the reinforced handle, C1, from 90mm to 122mm; (2) increasing the handle hooker size, C2, from 8mm to 19mm; (3) increasing the rail fastening screw number, C3, from 1 to 2; (4) adding an inner chamber and plastic material, C4, from HIPS to ABS; (5) thickening the boss, C5, from 2.0mm to 3.0mm; (6) adding a new support rib, C6 (Table 5).

The parameter design criterion of the newly designed samples was more than the target life, *B1*, of ten years. The confirmed value, β, on the Weibull chart was 3.1. For the second ALT, the recalculated test cycles and sample size in Equation (7) were 32,000 and 3 units, respectively. In the third ALT, no problems were found with the drawer after 32,000 cycles and 65,000 cycles. We therefore concluded that the modified design parameters were effective.

Table 6 provides a summary of the ALT results. Figure 9 shows the results of the 1st ALT and 3rd ALT plotted in a Weibull chart. With the improved design parameters, the *B1* life of the samples in the third ALT was lengthened to more than 10.0 years.

The Reliability Design and Its Direct Effect on the Energy Efficiency 237

**Figure 9.** Results of 1st ALT and 3rd ALT plotted in Weibull chart


**Table 5.** Redesigned handle and right/left slide rail

**Figure 9.** Results of 1st ALT and 3rd ALT plotted in Weibull chart

C1: Width L90mm → L122mm (1st ALT) C2: Width L8mm → L19mm (1st ALT)

**Table 5.** Redesigned handle and right/left slide rail

Handle Right/left slide rail

ALT)

C3: Rail fastening screw number 1→2 (2nd

 Plastic material HIPS → ABS (2nd ALT) C5: Boss thickness 2.0 → 3.0 mm (2nd ALT)

C4: Chamfer: Corner chamfer

C6: New support rib (2nd ALT)


The Reliability Design and Its Direct Effect on the Energy Efficiency 239

The case study focused on a mechanical structure consisting of several parts subjected to repetitive stresses under consumer usage conditions. The same principles developed for the new reliability design methodology could be applied to other mechanical systems, including construction equipment, automobile gear trains and engines, forklifts, washing machines, vacuum cleaners, and motor fan systems. We recommend that the missing or improper controllable design parameters on these systems also be studied for reliability design. These parameter studies would also include failure analysis, load analysis, and a tailored series of accelerated life tests. These methodologies could then predict part life quantitatively

through accelerated factors and exact sample size.

**7. Nomenclature** 

*e* effort

*f* flow

*h\**

*AF* acceleration factor *BX* durability index

*C3* back rib of slide rail

*Ea* activation energy

*h* testing time (or cycles)

*KCP* Key Control Parameter *KNP* Key Noise Parameter

*n* the number of test samples

Δ*P* pressure difference, *MPa*

*r* failed numbers

*F(t)* unreliability

*i* current, *A*

*C5* inner chamber of slide rail *C6* material of slide rail

*C7* screw number of slide number

*C1* width of reinforced handle, mm *C2* width of handle hooker, mm

*C4* screw boss height of slide rail, mm

*e0* effort under normal stress conditions *e1* effort under accelerated stress conditions

*Fdraw* open/close force of the freezer drawer system, *kN F1* weight force under accelerated stress conditions, *kN*

*F0* weight force under normal conditions, *kN*

*k* Boltzmann's constant, 8.62 x 10-5 *eV*/*deg* 

non-dimensional testing cycles, \* <sup>1</sup> *<sup>B</sup> h hL* = ≥

*LB* the target *BX* life and *x* = 0.01X, on the condition that *x* ≤ 0.2

*N1* consumer freezer door drawer open/close force, *kN*

**Table 6.** Results of ALTs

#### **6. Conclusions**

We developed a new reliability design method based on a study of a defective refrigerator drawer and handle system that was failing under field use conditions. The failure modes and mechanisms for the drawer in the field and in the ALTs were identified. Important design parameters were studied and improvements were evaluated using ALTs.

Based on the products returned from the field and the results of the first ALT, we found that the handles were fracturing because of design flaws. The handle design was corrected by increasing the handle width. During the second ALT, the slide rails fractured because they did not have enough strength to endure the repetitive food storage loads. The slide rails were corrected by providing additional reinforced ribs, reinforced boss, and an inner chamber. As a result these modified design parameters, there were no problems in the third ALT. We therefore concluded that the values for the design parameters were effective to meet the life cycle requirements. The yearly failure rate and *B1* life of the redesigned drawer and handle system, based on the results of ALT, were under 0.1% and more than 10 years, respectively. The study of the missing or improper design parameters in the design phase, through the inspection of failed products in the field, load analysis, and ALTs was very effective in redesigning more reliable parts with significantly longer life.

The case study focused on a mechanical structure consisting of several parts subjected to repetitive stresses under consumer usage conditions. The same principles developed for the new reliability design methodology could be applied to other mechanical systems, including construction equipment, automobile gear trains and engines, forklifts, washing machines, vacuum cleaners, and motor fan systems. We recommend that the missing or improper controllable design parameters on these systems also be studied for reliability design. These parameter studies would also include failure analysis, load analysis, and a tailored series of accelerated life tests. These methodologies could then predict part life quantitatively through accelerated factors and exact sample size.

### **7. Nomenclature**

238 Energy Efficiency – The Innovative Ways for Smart Energy, the Future Towards Modern Utilities

7,500 cycles: 2/3 Fail 12,000 cycles: 1/3 OK

 = 26.6 %/year *B1* = 3.4 year

Width2: L8→L19.0

We developed a new reliability design method based on a study of a defective refrigerator drawer and handle system that was failing under field use conditions. The failure modes and mechanisms for the drawer in the field and in the ALTs were identified. Important

Based on the products returned from the field and the results of the first ALT, we found that the handles were fracturing because of design flaws. The handle design was corrected by increasing the handle width. During the second ALT, the slide rails fractured because they did not have enough strength to endure the repetitive food storage loads. The slide rails were corrected by providing additional reinforced ribs, reinforced boss, and an inner chamber. As a result these modified design parameters, there were no problems in the third ALT. We therefore concluded that the values for the design parameters were effective to meet the life cycle requirements. The yearly failure rate and *B1* life of the redesigned drawer and handle system, based on the results of ALT, were under 0.1% and more than 10 years, respectively. The study of the missing or improper design parameters in the design phase, through the inspection of failed products in the field, load analysis, and ALTs was very

design parameters were studied and improvements were evaluated using ALTs.

effective in redesigning more reliable parts with significantly longer life.

λ

Material & Spec. Width1: L90 →L122

In 32,000 cycles, Fracturing is less than 1

Drawer structure

**Table 6.** Results of ALTs

**6. Conclusions** 

**First ALT Second ALT Third ALT** Initial design First design iteration Final design

λ

16,000 cycles: 2/3 Fail

Rib1: new support rib boss: 2.0 → 3.0 mm Chamfer1: Corner Material: HIPS →ABS 32,000 cycles:

65,000 cycles:

λ = 0.1 %/year *B1* = 10 year

3/3 OK

3/3 OK

= 2.46 %/year *B1* = 7.3 year


The Reliability Design and Its Direct Effect on the Energy Efficiency 241

[2] Taguchi, G., Shih-Chung, T, 1992, Introduction to Quality Engineering: Bringing Quality Engineering Upstream, American Society of Mechanical Engineering, New

[3] Ashley, S., 1992, Applying Taguchi's Quality Engineering to Technology Development,

[4] Wilkins, J., 2000, Putting Taguchi Methods to Work to Solve Design Flaws, Quality

[5] Phadke, M., 1989, Quality Engineering Using Robust Design, Englewood Cliffs, NJ:

[6] Byrne, D., Taguchi, S., 1987, Taguchi Approach to Parameter Design, Quality Progress,

[7] Woo, S., Pecht, M., 2008, Failure Analysis and Redesign of a Helix Upper Dispenser,

[8] Woo, S., O'Neal, D., Pecht, M., 2009, Improving the Reliability of a Water Dispenser Lever in a Refrigerator Subjected to Repetitive Stresses, Engineering Failure Analysis,

[9] Woo, S., O'Neal, D., Pecht, M., 2009, Design of a Hinge Kit System in a Kimchi Refrigerator Receiving Repetitive Stresses, Engineering Failure Analysis, 16 (5), 1655–

[10] Woo, S., Ryu, D., Pecht, M., 2009, Design Evaluation of a French Refrigerator Drawer System Subjected to Repeated Food Storage Loads, Engineering Failure Analysis, 16 (7),

[11] Woo, S., O'Neal, D., Pecht, M., 2010, Failure Analysis and Redesign of the Evaporator Tubing in a Kimchi Refrigerator, Engineering Failure Analysis, 2010, 17(2), 369-

[12] Woo, S., O'Neal, D., Pecht, M., 2010, Reliability design of a reciprocating compressor suction reed valve in a common refrigerator subjected to repetitive pressure loads,

[13] Woo, S., Pecht, M., O'Neal, D., 2009, Reliability Design and Case Study of a Refrigerator Compressor Subjected to Repetitive Loads, International Journal of Refrigeration, 32 (3),

[14] Woo S, O'Neal D, Pecht M. Reliability design of residential sized refrigerators subjected to repetitive random vibration loads during rail transport, Engineering Failure Analysis

[15] Karnopp, D., Margolis, D., Rosenberg, R., 2000, System Dynamics: Modeling and Simulation of Mechatronic Systems, third ed. John Wiley & Sons, Inc, New York. [16] McPherson, J., 1989, Accelerated Testing, Packaging, Electronic Materials Handbook*,* 

[17] Ajiki, T., Sugimoto, M., Higuchi, H., 1979. A new cyclic biased THB power dissipating

ICs. In: 17th Annual Proceedings Reliability Physics. pp. 118–126.

York.

Mechanical Engineering.

Engineering Failure Analysis, 15 (4), 642–653.

Engineering Failure Analysis, 2010, 17(4), 979-991.

Progress, 33(5), 55-59.

Prentice Hall.

20(12), 19-26.

16 (5), 1597–1606.

1665.

379.

478-486

2011, 18(5), 1322–1332.

ASM International 1, 887-894.

2224–2234.



Greek symbols


Superscripts

βshape parameter in a Weibull distribution

$$n \qquad \text{stress dependence, } n = -\left[\frac{\partial \ln(T\_f)}{\partial \ln(S)}\right]$$

Subscripts

