Reliability design of the hinge kit system subjected to repetitive loading in a commercial refrigerator

A newly designed hinge kit system (HKS) of a commercial refrigerator was subjected to a robust reliability methodology during the design phase of the system. This methodology included setting the overall parametric accelerated life test (ALT) plan of product and identifying failure mechanisms and modes in field.  The ALT included a sample size equation to improve several of the HKS design parameters. Reliability of the new HKS was targeted to be 10 years over B1. Failure sites in the HKS were identified through returned products from the field. The first ALT confirmed a failure that occurred at the housing of HKS. The missing design parameters of HKS housing for the refrigerator were that it had no support ribs in the original design. The supporting structure of HKS in the refrigerator was modified based on the action plan. Cracks were identified in a second ALT that was generated in the torsional shaft. Due to it having squared off corners, the HKS torsional shaft did not have not enough strength to withstand repetitive stresses. The shaft was modified as a consequence of the ALTs. The reliability of redesigned HKS is now guaranteed as B1 10 years. The design methods - load analysis and three ALTs were very effective in identifying the missing design parameters during the design phase. The robust design method presented in this paper might be applicable to the other mechanical systems

Improving the Reliability of Mechanical Components That Have Failed in the Field Due to Repetitive Stress

To improve the reliability of mechanical parts that have failed in the field, a reliability methodology for parametric accelerated life testing (ALT) is proposed. It consists of: (1) a parametric ALT plan, (2) a load analysis, (3) a tailored series of parametric ALTs with action plans, and (4) an evaluation of the final designs to ensure the design requirements are satisfied. This parametric ALT should help an engineer reproduce the fractured or failed parts in a product subjectedto repetitive loading and correct the faulty designs. As a test case, the helix upper dispenser of a refrigerator ice-maker fractured in field was studied. Using a load analysis, we discerned that the helix upper dispenser fracture was due to repetitive loads and a faulty design with a 2 mm gap between the blade dispenser and the helix upper dispenser. During the first and second ALTs, the fracture in the helix upper dispenser was reproduced. The failure modes and mechanisms found were similar to those of the failed sample in field. As an action plan, the design of the helix upper dispenser was modified by eliminating the 2 mm gap and adding enforced ribs. In the third ALT there were no problems. After three rounds of parametric ALTs, the reliability of the helix upper dispenser was guaranteed as a 10-year life with an accumulated failure rate of 1%

Reliability Design of Mechanical Systems Such as Compressor Subjected to Repetitive Stresses

This study demonstrates the use of parametric accelerated life testing (ALT) as a way to recognize design defects in mechanical products in creating a reliable quantitative (RQ) specification. It covers: (1) a system BX lifetime that X% of a product population fails, created on the parametric ALT scheme, (2) fatigue and redesign, (3) adapted ALTs with design alternations, and (4) an evaluation of whether the system design(s) acquires the objective BX lifetime. A life-stress model and a sample size formulation, therefore, are suggested. A refrigerator compressor is used to demonstrate this method. Compressors subjected to repetitive impact loading were failing in the field. To analyze the pressure loading of the compressor and carry out parametric ALT, a mass/energy balance on the vapor-compression cycle was examined. At the first ALT, the compressor failed due to a cracked or fractured suction reed valve made of Sandvik 20C carbon steel (1 wt% C, 0.25 wt% Si, 0.45 wt% Mn). The failure modes of the suction reed valves were similar to those valves returned from the field. The fatigue failure of the suction reed valves came from an overlap between the suction reed valve and the valve plate in combination with the repeated pressure loading. The problematic design was modified by the trespan dimensions, tumbling process, a ball peening, and brushing process for the valve plate. At the second ALT, the compressor locked due to the intrusion between the crankshaft and thrust washer. The corrective action plan specified to perform the heat treatment to the exterior of the crankshaft made of cast iron (0.45 wt% C, 0.25 wt% Si, 0.8 wt% Mn, 0.03 wt% P). After these design modifications, there were no troubles during the third ALT. The lifetime of the compressor was secured to have a B1 life of 10 years

Process to Establish the Enhance of Fatigue Life of New Mechanical System Such as a Drawer by Accelerated Tests

To extend the life of a mechanical system, parametric Accelerated Life Testing (ALT) is proposed as a procedure to identify design faults and reduce fatigue failure. It includes a derivation of generalized time to failure model by linear transport process and a sample size equation for the ALT. A refrigerator drawer was used as an example. After loading, the rail rollers broke and the center support was bent. Ribs were added to the center support and the rail roller support was extended. At the first ALT, the box cover failed near the intersection between the cover and body. The box was then modified by increasing the rib and fillet. At the second ALT, the rails and center support fractured. They were altered by increasing the rib and corner rounding. After the third ALT, there were no issues. The drawer lifetime was ensured to be B1 life 10 years

Process to Establish the Enhance of Fatigue Life of New Mechanical System Such as a Drawer by Accelerated Tests

To extend the life of a mechanical system, parametric Accelerated Life Testing (ALT) is proposed as a procedure to identify design faults and reduce fatigue failure. It includes a derivation of generalized time to failure model by linear transport process and a sample size equation for the ALT. A refrigerator drawer was used as an example. After loading, the rail rollers broke and the center support was bent. Ribs were added to the center support and the rail roller support was extended. At the first ALT, the box cover failed near the intersection between the cover and body. The box was then modified by increasing the rib and fillet. At the second ALT, the rails and center support fractured. They were altered by increasing the rib and corner rounding. After the third ALT, there were no issues. The drawer lifetime was ensured to be B1 life 10 years

Systematic Methods to Increase the Lifetime of Mechanical Products Such as Refrigerators by Employing Parametric Accelerated Life Testing

This investigation practically explains the implementation of parametric accelerated life testing (ALT) as an algorithm to recognize design imperfection and rectify it in creating a reliable quantitative (RQ) statement by sample size equation. It covers: (1) a module BX life that X% of a collection of system items is unsuccessful with an ALT plan, (2) design for fatigue, (3) ALTs with alterations, and (4) discernment as to if the final design(s) obtains the targeted BX lifetime. A (generalized) life–stress formulation by the linear transport process is recommended for the mathematical work of the parametric model. As a case study, an ice-maker including gear system in a refrigerator was utilized. The gear teeth made of cast iron (carbon, 3 wt% and silicon, 2 wt%) was fracturing in a refrigerator ice-maker. To reproduce the field failure and rectify the problematic designs in the marketplace, a parametric ALT was carried out. At the first ALT, the gear teeth made of cast iron partly cracked and fractured under severe cold conditions (below −20 °C) in the freezer. It was modified by changing the material from cast iron to a sinter-hardened powder metallurgy nickel steel because high fatigue strength in the low temperature was required. At the second ALT, we discovered the fractured helix made of polycarbonates (PC). As a modification, strengthened rib on the front and side of the helix the thickness of gear teeth was attached. At the third ALT, there was no concern, and the life of the auger motor including gear system was manifested to have a B1 life 10 years