Study of the Effects of Miniaturization on Static and Dynamic Form Errors in Desktop Milling Machines

Desktop and miniaturized machine tools are a new trend in small scale and customized manufacturing. The performance of these machines in terms of their energy consumption, machining fluid consumption and their precision have been investigated in the literature, but the effect of miniaturization on static deflection, stability against chatter and the resulting surface error has not been studied. In this paper, the performance of the desktop milling machine tool in terms of their static and dynamic form errors is studied. The performance of a miniature milling machine used for end milling of a typical workpiece is compared with a similar machine of conventional size through dimensional analysis and numerical modeling. The error of the surface finish generated is predicted and verified through simulation.

Producing HP Pump Barrels Utilizing Powder Metallurgy and Hot Isostatic Pressing

The fabrication of near net shape powder metal (PM) components by hot isostatic pressing (HIP) has been an important manufacturing technology for steel and stainless steel alloys since about 1985. The manufacturing process involves inert gas atomization of powder, 3D CAD capsule design, sheet metal capsule fabrication and densification by HIP in very large pressure vessels. Since 1985, several thousand tonnes of parts have been produced. The major applications are found in the oil and gas industry especially in offshore applications, the industrial power generation industry, and traditional engineering industries. Typically, the components replace castings, forgings and fabricated parts and are produced in high alloy grades such as martensitic steels, austenitic stainless steels, duplex (ferritic/austenitic) stainless steels and nickel based superalloys. The application of PM/HIP near net shapes to pump barrels for medium to high pressure use has a number of advantages compared to the traditional forging and welding approach. First, the need for machining of the components is reduced to a minimum and welding during final assembly is reduced substantially. Mechanical properties of the PM/HIP parts are isotropic and equal to the best forged properties in the flow direction. This derives from the fine microstructure using powder powder and the uniform structure from the HIP process. Furthermore, when using the PM HIP process the parts are produced near net shape with supports, nozzles and flanges integrated. This significantly reduces manufacturing lead-time and gives greater design flexibility which improves cost for the final component. The PM HIP near net shape route has received approval from ASTM, NACE and API for specific steel, stainless steel and nickel base alloys. This paper reviews the manufacturing sequence for PM near net shapes and discusses the details of several successful applications. The application of the PM/HIP process to high pressure pump barrels is highlighted.

Using the Fuzzy Method to Evaluate Manufacturing Productivity

This paper introduces a useful method for improvement of the time forecasting of production lines operating at full speed production time (FSPT) and dealing with uncertain time losses. The full speed production time is a major index of the production line’s performance because it enables direct evaluation of production line output. This measure is called as overall equipment effectiveness (OEE). The fixed theoretically available hours minus time losses such as holidays, broken equipment and raw materials or labor shortages give us the production lines’ full speed production time. The waterfall chart model (WCM) improves the measurement of FSPT and can thereby help decision-makers to evaluate OEE. Unfortunately, there are many uncertain and imprecise factors operating. The fuzzy method can be used to reduce the degree and effect of uncertainty and imprecision [1]. We therefore introduce fuzzy theory into our WCM chart. This will assist decision makers in evaluating uncertainty and imprecision and obtain improved OEE measurements as well as producing better production plans and master production schedules [2].

Advanced Design and Manufacture of Face-Hobbed Spiral Bevel Gears

The design and advanced manufacture of face-hobbed spiral bevel gears on computer numerical control (CNC) hypoid generating machines is presented. The concept of face-hobbed bevel gear generation by an imaginary generating crown gear is established. In order to reduce the sensitivity of the gear pair to errors in tooth-surfaces and to the mutual position of the mating members, modifications are introduced into the teeth of both members. The lengthwise crowning of teeth is achieved by applying a slightly bigger lengthwise tooth flank curvature of the crown gear generating the concave side of pinion/gear tooth-surfaces, and/or by using tilt angle of the head-cutter in the manufacture of pinion/gear teeth. The tooth profile modification is introduced by the circular profile of the cutting edge of head-cutter blades. An algorithm is developed for the execution of motions on the CNC hypoid generating machine using the relations on the cradle-type machine. The algorithm is based on the condition that since the tool is a rotary surface and the pinion/gear blank is also related to a rotary surface, it is necessary to ensure the same relative position of the head cutter and the pinion on both machines.

Investigation of Residual Stress Development During Swage Autofrettage, Using Finite Element Analysis

Swaging is one method of autofrettage, a means of pre-stressing high-pressure vessels to increase their fatigue lives and load bearing capacity. Swaging achieves the required deformation through physical interference between an oversized mandrel and the bore diameter of the tube, as it is pushed through the tube. A Finite Element model of the swaging process was developed, in ANSYS, and systematically refined, to investigate the mechanism of deformation and subsequent development of residual stresses. A parametric study was undertaken, of various properties such as mandrel slope angle, parallel section length and friction coefficient. It is observed that the axial stress plays a crucial role in the determination of the residual hoop stress and reverse yielding. The model, and results obtained from it, provides a means of understanding the swaging process and how it responds to different parameters. This understanding, coupled with future improvements to the model, potentially allows the swaging process to be refined, in terms of residual stresses development and mandrel driving force.

Formability of AZ31 Magnesium Alloy Sheet in Dry Press Forming Using Diamond-Coated Dies

Dry press forming which hasn’t used lubricants in the process is the attractive forming technique of zero emission for the lubricants. As one of the dry press forming techniques, the usage of dies coated with a chemical vapor deposition (CVD) diamond film, which are expected to be applied to forming tools owing to their high tribological properties, abrasion resistance and heat resistance, has been proposed. Magnesium alloys have attracted attention owing to their advantages over what such as, high specific strength and ease of recycling. However, they have intractable characteristics, and it is necessary to perform the forming technique at high temperature and to consider lubrication condition. In this study, diamond-coated dies were used in the deformation of magnesium alloy sheets without lubricants in press forming, and the formability of magnesium alloy and its effect on the surface texture of a formed-cup were investigated. Dry deep-drawing tests and dry ironing tests were carried out to estimate the effect of the diamond-coated dies on the formability of magnesium alloy sheets. Furthermore, the formability obtained using the above-mentioned tests was compared with that obtained in tests using non-lubricant dies with traditional lubricant. AZ31 magnesium alloy sheets (thickness: t0 = 0.5 mm) were deformed at 200 °C in dry deep-drawing tests. From the results, it was found that what can be deformed using diamond-coated dies. Moreover, a 20% reduction in drawing force was confirmed compared with the usage of the traditional lubricant (MoS2). Meanwhile, dry ironing tests were performed under conditions of 10% ironing ratio by a method similar to the dry deep-drawing tests. In general, the ironing process, which is the most difficult step in lubrication in sheet forming, has been enabled by the diamond coating technique. Furthermore, it was observed that the surface roughness of the formed-cup walls using the diamond-coated dies was 0.4 μmRz, and, 1.3 μmRz in case of MoS2. It was confirmed that the application of diamond-coated dies improved the surface roughness of the formed-cup. It produced an improvement in the formability of magnesium alloys compared with the traditional lubrication technique (use of MoS2). It was concluded that the validity of the use of diamond-coated dies became clear.

Thermal Elastohydrodynamic Lubrication Analysis for Point Contact Transmission

To investigate the thermal EHL (elastohydrodynamic lubrication) in point contact transmission, a model considering the two-dimensional surface velocity of tooth face and the running-in is proposed. The numerical solutions for pressure, temperature and film thickness distribution in the contact zone are obtained by solving equations including the Reynolds, Energy and the elastic displacement with variable dimension meshing method. The model was used to study the point contact transmission of the circular arc gear in a windlass. The main results show that it is pure rolling along the direction of tooth width, and the rolling speed plays a leading role in improving the lubricating performance and transmission efficiency of circular arc gear. The squeeze film effect makes the pressure peak tend to be gentle and the film thickness increase slightly.

Investigation of Corner Cavity Formation During Backward Cup Extrusion Process Using Finite Element Method

This study focuses on the finite element analysis of the formation of corner cavity defect during the Backward Cup Extrusion (BCE) process. In the final stage of this process, when the bottom thickness reaches to a critical value this defect will be appear as a circumferential defect in the corner of the cup. In addition, this research examines the temporal prediction of onset of corner cavity formation in the various amounts of the reduction of areas. The finite element simulation results were compared with those of the experimental, indicating that the amount of the reduction of area and that of the friction coefficient have considerable impact on the onset of corner cavity formation during the BCE process.

A Bi-Directional Ultrasonic Elliptical Vibration Actuator (BUEVA) for Micro Machining

Presented is the detailed design and implementation of a bi-directional ultrasonic elliptical vibration actuator (BUEVA) for micro machining. Removal of material occurs via a generated elliptical tool motion resembling a natural ‘spoon feeding’ action in contrast to in-plane, horizontal motion utilized by most existing setups. The motion is generated by two stacked ceramic multilayer actuator ring (SCMAR) piezo elements vibrating out of phase in the tool’s axial and transverse directions. The amplitude of vibration of the tool is controlled in order to vary the cutting depth according to the desired cutting parameters. To ensure precise tool positioning, the BUEVA actuator is fitted to a 3-axis precision machining center that provides the necessary tool path. The cutting forces and the resulting surface finish are both numerically modeled and then experimentally measured by a 3-axis mini dynamometer and a surface profilometer, respectively. Preliminary cutting results show good dimensional definition and surface integrity.

Influence of Lubricants on Advanced High Strength Steel Tubes in Bending Process

To reach safety, emissions, and cost objectives, manufacturers of automotive body structural components shape thin gauge, high strength steel tube using a series of manufacturing steps that often include bending, preforming and hydroforming. Challenging grades and bend severity require a sensitive optimization of the tubular bending process. Lubricants play a significant role in establishing a successful bending process. In this study, the performance of two lubricants, Hydrodraw 551 and HFO 20, were investigated for bending Dual Phase 780 (DP780) and High Strength Low Alloy 350 (HSLA350) thin-walled steel tubes. Formability success was evaluated in terms of wrinkling, thinning strain and final geometry. Lubricant performance was found to be sensitive to grade and application site. HFO 20 was found to be a poor choice for bending DP780 tube.