Impact Fatigue Characteristics of Valve Leaves for Small Hermetic Reciprocating Compressors

This paper presents an investigation on the impact fatigue characteristics of valve leaves that are prevalently used in hermetic reciprocating compressors especially for the household type refrigerators. The investigation relates the impact fatigue lifetime of the valve leaves that is the heart of the compressor, with the working temperature, material type (carbon steel, stainless steel and improved stainless steel grade) and tumbling duration after the manufacturing process. The investigation provides a better understanding of the impact fatigue characteristics of valve leaves while designing a high performance compressor to decrease the energy consumption. \ud A unique automated impact fatigue test system was designed and produced, which enables to carry out impact fatigue tests of the compressor valve leaves under the desired impact velocities. In the test system, original valve plate and valve leaf couple was utilized through the experimentation in order to simulate the real behavior in the compressor. A fixture was designed to mount the valve plate. The main principle of the system is to create pulsating airflow through a high frequency solenoid valve. The impact fatigue life was determined for various impact velocities and at different operating temperatures

Temperature Effects on Grinding Residual Stress

AbstractResidual stress is a key factor that influences the reliability, precision, and life of final products. Earlier studies have alluded to the fact that the grinding process is usually the source of a tensile residual stress on the part surface, while there exists a temperature level commonly referred to as the onset tensile temperature beyond which the tensile profile of residual stresses starts to be generated. In this paper, a physics-based model is proposed to predict the onset temperature as a function of residual stress on an analytical and quantitative basis. The predictive model is based on the temperature distribution function using a moving heat source approach. Then, the thermal stresses are calculated analytically using Timoshenko thermal stress theory [1] followed by an elastic-plastic relaxation condition imposed on these stresses, thus leading to the resulting residual stresses. The model-predicted results have been experimentally validated using data of the grinding of AISI52100 hardened steel with subsequent X-ray and Neutron diffraction measurements. The model was shown to predict the residual stress profile under given process conditions and material properties, therefore providing an analytical tool for grinding process planning and optimization based on the understanding of onset tensile temperature for control of tensile residual stresses

Dynamic Build Bed for Additive Manufacturing

Compared to subtractive manufacturing, additive manufacturing generally has low material waste. However, models with large overhangs require manufacturing of support structures which ends up as waste material. This paper proposes the use of a dynamic build bed for reducing support structures. The bed consists of an array of actuated pins which move in the build orientation. Each pin can be individually moved to the correct height for supporting the given model. Two separate applications of the build bed are investigated. In the first application, the dynamic build bed is used as support structures in deposition-based AM methods. The pins individually raise out of the build bed to support the overhang geometry at the given deposition height. The second application is in powder-based AM methods. In the second application, the pins are used to fill the space of the powder where the geometry will not occupy. The pins are individually lowered in the build orientation to make space for a new powder layer. Thus, saving excessive deposition of powder.Mechanical Engineerin

Additive Manufacturing with Modular Support Structures

Additive manufacturing is praised to have low material waste compared to conventional subtractive manufacturing methods. This is not always the case when the computer aided design (CAD) model consists of large overhangs. In such cases, fabrication of support structures are required to fill the space between the CAD model and the manufacturing bed. In post processing, these support structures must be removed from the model. These supports become waste and reduce the buy-to-fly ratio. In this paper, we present a pre-fabricated reusable modular support structure system which minimizes the fabrication of conventional support structures. The conventional supports are replaced with modular support blocks wherever possible. The blocks are stacked under the overhang with a robot arm until the overhang of the model is reached. Conventional supports can be fabricated on top when needed with fused filament fabrication. This strategy reduces fabrication of conventional supports. Thus, faster fabrication times are obtained with higher buy-to-fly ratios.Mechanical Engineerin

Analysis of Build Direction in Deposition-Based Additive Manufacturing of Overhang Structures

Additive manufacturing (AM) has gained repute as a direct method of fabrication of complex parts. However, the requirement for each layer to be structurally supported can make parts with overhangs hard to produce without alterations to the parts. This work proposes using multi-axis additive manufacturing to fabricate and analyze freeform overhangs such as bridge structures. Multi-axis AM allows reorientation of the build direction so that overhangs can be 3D printed. Consequently, decision on the build orientation is necessary and its result should be analyzed. The effect of the AM build direction with respect to the overhang’s local surface directions will be studied. A Rhinoceros® plugin is designed to generate the path of the multi-axis AM for the unsupported components like roofs, bridges and protrusions. The effects of the build direction on the surface quality and deformation of the components are studied.Mechanical Engineerin