Axiomatic Design: 30 Years After

In 1977, Nam P Suh proposed a different approach to design research. Suh’s approach was different in that it introduced the notions of domains and layers in a 2-D design thinking and stipulated a set of axioms that describes what is a good design. Following Suh’s 2-D reasoning structure in a zigzagging manner and applying these axioms through the design process should enable the designer to arrive at a good design. In this paper, we present our own experiences in applying Suh’s theories to software design, product design, organizational design, process design, and more in both academic and industrial settings. We also share our experience from teaching the Axiomatic Design theory to students at universities and engineers in industry, and draw conclusions on how best to teach and use this approach, and what results one can expect. The merits of the design axioms are discussed based on the practical experiences that the authors have had in their application. The process developed around the axioms to derive maximum value (solution neutral environment, design domains, what-how relationship, zig-zag process, decomposition, and design matrices) is also discussed and some updates are proposed.

Resistance Welding Process Development and Optimization for Recycled High-Density Polyethylene (HDPE)

Large recycled high-density polyethylene (HDPE) structural members, difficult to manufacture by extrusion processes, have been created by the hot plate welding of simple plastic lumber sections. Hot plate welding generates better joint strength than any other welding method currently employed in plastic manufacturing. However, to achieve the desired temperature of the thick plate to melt the polymer uniformly, the process needs a high amount of heat energy requiring furnace (or resistance) heating of a considerable mass. A new method which could combine the heating element and a thin plate into one source could be more efficient in terms of heat loss and thus energy used. The premise of this investigation is to replace the hot plate with a very thin piece of high resistance nickel-chromium alloy ribbon to localize the application of heat within a plastic weld joint in order to reduce energy loss and its associated costs. This resistance ribbon method uses electrical current to reach an adequate temperature to allow for the welding of the HDPE plastic. The ribbon is only slightly larger than the welding surface and very thin to reduce the loss of excess heat through unused surface area and thick sides. The purpose of this project was to weld recycled high-density polyethylene (HDPE) using resistance welding and to match the tensile strength results considered acceptable in industry for hot plate welding, that is, equal to or greater than 80% of the base material strength. Information obtained through literature review and previous investigations in our laboratories established welding (heating) temperature and time as testing factors. Designed experimentation considered these factors in optimizing the process to maximize the weld tensile strength. A wide-ranging full-factorial experimental design using many levels was created for the initial testing plan. Tensile strengths obtained after welding under the various condition combinations of weld temperature and time revealed a region of higher strength values in the response surface. After the wide-range initial testing, the two control parameters, heating temperature and heating time, were ultimately set up in a focused Face Centered Cubic (FCC) Response Surface Method (RSM) testing design and the tensile strength response was then analyzed using statistical software. The results obtained indicated a strong correlation between heating time and heating temperature with strength. All welded samples in the final testing set exhibited tensile strength of over 90% base material, meeting the goal requirements. A full quadratic equation relationship for tensile strength as a function of welding time and temperature was developed and the maximum tensile strength was achieved when using 280°C for 60 seconds.

Automated Gaging of Surface Texture on Engine Components

Surface texture of engine components such as crankshafts and camshafts is one of the most important factors that determine the performance, efficiency and the operating life of an internal combustion engine. Current practices and the challenges faced by design engineers in specifying the target surface topography to meet these goals have been reviewed. Once specified, the surface texture must be measured fast, accurately and repeatably in the rough environment of an engine manufacturing plant. The key components of an automated skidded surface finish measuring gage designed with these criteria in mind are described in this paper. The gage has 7 axes of motion and 3 stylus probes oriented in the axial and radial directions to take axial and facial measurements on journal and cam lobe surfaces and thrust bearing surfaces. The selection of surface texture parameters to best describe the desired surface texture of these engine components was investigated. The final stage of surface preparation is often the superfinishing process. The measurement gage must be able to provide the sensitivity and repeatability that are required for measuring the finely finished surfaces generated by this process. Typical surface texture results of a superfinishing process achieved on crankshafts are described. The results of a Gage Repeatability and Reproducibility (R&R) study performed on the surface texture measuring gage are presented.

Ultra High-Speed Micro-Milling of Aluminum Alloy

Small precision parts with miniaturized features are increasingly used in components such as sensors, micro-medical devices, micro-fuel cells, and others. Mechanical micromachining processes, e.g., turning, drilling, milling and grinding are often used for fabrication of miniaturized components. The small micro-tools (50 μm to 500 μm diameter) used in micromachining limit the surface speeds achieved at the cutting point, unless the rotational speeds are substantially increased. Although the cutting speeds increase to 240 m/min with larger diameter tools (e.g., 500 μm) when using the highest available spindle speed of 150,000 rpm, the cutting speed with the smaller 50 μm tools is limited to 24 m/min. This low cutting speed at the tool tip is much smaller than the speeds required for efficient cutting. For example, in macro-milling of aluminum alloys the recommended speed is on the order of 60–200 m/min. The use of low cutting speeds limits the production rate, increases tool wear and tendency for burr formation, and limits the degree of dimensional tolerance and precision that can be achieved. The purpose of the present paper is to provide preliminary results that show the feasibility of ultra high-speed micro-milling of an aluminum alloy with respect to surface quality and burr formation. A new ultra high-speed spindle was used for micro-milling of an aluminum alloy with micro-end-mills ranging in diameter from 51 μm to 305 μm. Straight channels were machined to obtain an array of square patterns on the surface. High surface cutting speeds up to 340 m/min were achieved at 350,000 rpm. Inspection of the machined surfaces indicated that edge quality and burr formation tendency are related to the undeformed chip thickness, and therefore the cutting speed and feed rate. The quantity of burrs observed on the cut surfaces was generally small, and therefore, the burr types were not systematically determined. Cutting with the 305 μm tool at a cutting speed of 150 m/min produced an excellent cut quality using a chip thickness of 0.13 μm. However, the cut quality deteriorated as the chip thickness was decreased to 0.06 μm by increasing the cutting speed to 340 mm/min. This result is consistent with published data that show the dependence of bur formation on ratio of chip thickness to tool tip radius. The channel widths were also measured and the width of channels cut with the small diameter tools became larger than the tool diameter at higher speeds. The dependence of the channel widths on rotational speed and the fact that a similar variation was not observed for larger diameter tools, suggested that this phenomena is related to dynamic run-out of the tool tip, which increases the channel width at higher speeds.

The Genesis of Tool Wear in Machining

This paper presents a series of experimental and theoretical efforts that we have made in unraveling the tool wear mechanisms under steady state conditions in machining for the last few decades. Two primary modes of steady state tool wear considered in this paper are flank and crater wear. We preface this paper by stating that flank wear is explained as abrasive wear due to the hard phases in a work material while crater wear is a combination of abrasive wear and generalized dissolution wear which encompasses both dissolution wear as well as diffusion wear. However, the flank wear was not a function of the abrasive cementite content when turning low alloy steels with pearlitic microstructures. The machined surfaces of these alloys are examined to confirm the phase transformation (ferrite to austenite), which diminishes the effect of cementite content. In particular, the cementite phase present in low alloy steels dissociates and diffuses into the transformed austenitic phase during machining. Dissolution wear is claimed to describe the behavior of crater wear at high cutting speeds. The original dissolution mechanism explains the crater wear in the machining of ferrous materials and nickel alloys at high cutting speeds, but the generalization of the dissolution wear is necessary for titanium alloys. In machining titanium alloys, the original dissolution mechanism did not show a good correlation with experimental results; generally the diffusivity of the slowest diffusing tool constituent in titanium limits the wear rate. The phase transformation from alpha (HCP) to beta (BCC) phases can also take place in machining titanium alloys, which drastically increases the crater wear due to the few orders of magnitude increase in diffusivity. The most puzzling issue is however the presence of the scoring marks even though no hard inclusion is typically present in titanium alloys. This is finally explained by the heterogeneity in the microstructure due to the anisotropic hardness of alpha (HCP) phase (the hardness in c-direction is 50% higher than the hardness in other directions) and the presence of lamellar microstructure (alternating layers of alpha and beta). The lamellar microstructure has not only the in-plane anisotropic hardness but also a greater hardness than other phases. Even though we cannot claim to fully understand the physics behind tool wear, our combined approaches have unveiled some elementary wear mechanisms.

On the Design of a Sustainable Production Line: The MetaCAM Tool

Nowadays, manufacturing enterprises face enormous environmental challenges, due to complex and diverse economic trends, including shorter product life cycles, rapid advances in science and technology, increased diversity in customer demands and globalization of production activities. Consequently, the cost is highly affected by environmentally related factors. Energy efficiency is one of the main factors, which together with waste management, affect manufacturing decisions. The complexity and diversity of the factors that determine energy efficiency require intelligent systems for their optimization at each “manufacturing level”. Manufacturing decisions should be taken as fast as possible and with the highest possible accuracy. Artificial intelligence/machine learning tools have made significant progress during the last decade and are suitable for such applications. The main objective of the current study is that an architecture for the development of a networked, online, decision support tool, be provided towards achieving sustainable value chain management. The main idea behind the proposed design is that stakeholders be assisted in taking decisions towards improving the energy and eco-efficiency of the entire value chain or parts of it. This is suggested within the context of a multi-objective optimization procedure, taking into account other important decision making attributes, such as flexibility, quality and time for the final reduction in the overall cost. This architecture incorporates real time information modules that interact with online monitoring systems, using any available information within the value chain and the existing IT tools. A partial realization of the proposed idea is implemented in the form of a user friendly software tool (the MetaCAM tool). This based, decision support tool aiming to optimize a current production line or to propose alternatives for the manufacturing of a product. The tool performs optimization based on a set of predefined criteria, namely energy, waste, cost and time. For each of these criteria, the end-user selects the desired weight factor in order to drive the optimization procedure accordingly. The tool presents the characteristics of the setup of the proposed optimized line and maintains all used data and calculations in order to be reused when necessary. For the tool’s validation, three real case studies from different industrial sectors have been used. The first case study comes from the domestic appliances sector (refrigerator door panel), the second one from the automotive sector (a two seat bench for light commercial vehicles) and finally, the third case study derives from the aeronautics sector and deals with the production of the loading ramp hinge of a military aircraft.

On the Laws and Theories of Sliding Friction

The many seminal contributions made by Professor Nam P. Suh to the theories of wear, such as the delamination wear and the solution wear, are well known. The contributions made by him and his associates to the theories of friction, however, are less known; but they are equally significant. In this article, I first briefly survey, to provide an historical context, the laws and theories of sliding friction as proposed over the past centuries and decades. Then the contributions of Prof. Suh and his associates in recent decades are reviewed. Specifically, the role of wear particles in the frictional phenomena of dry and boundary-lubricated sliding is examined. A novel concept of undulating, or patterned, surfaces has been advanced to minimize friction in both dry and boundary-lubricated sliding. The undulating surfaces trap wear debris and thus minimize plowing friction in dry sliding, above the transition temperature in boundary-lubricated sliding, and even in hydrodynamic bearings during start/stop operations. The concept is especially appropriate for heavily loaded tribological systems with tighter clearances in which the likelihood of seizure is imminent.

Evaluating Functional Coupling in Aeration Basin Air Distribution Systems

Axiomatic Design provides a set of axioms and corollaries to help make system design decisions. In this paper, the independence axiom is applied to evaluate alternate low pressure air (LPA) distribution system designs to serve the aeration basins of a wastewater treatment plant. The airflow to each air zone is defined as a functional requirement (FR) in the functional domain. A design parameter (DP) in the physical domain is selected to achieve each FR. The DPs include the LPA motor operated valve (MOV) damper positions and a process air blower inlet guide vane (IGV) position. Three design alternatives are developed and evaluated with the respect to the independence axiom. Each subsequent alternative attempts to reduce the amount of functional coupling. Reduced functional coupling in an LPA system results in a more stable treatment process and greater system longevity through reduced component wear.

Independence Measure (IM) Using Independence Priority Number (IPN) in Axiomatic Design Framework

Axiomatic Design is becoming a preferred system design process tool for insuring the quality and efficiency of design processes for products and services. One aspect of Axiomatic Design is modeling and analyzing the functional independence of proposed solutions. Axiomatic Design provides for comparing and ranking solutions by three categories of functional coupling: Uncoupled, Decoupled and Coupled (1). However, given two potential solutions within the same functional coupling category, Axiomatic Design technology cannot further rank these solutions without additional information. This paper proposes that the degree of functional coupling can be assessed to provide further discrimination between solutions within the same coupling category. Using complexity concepts, this paper proposes two additional metrics, the Independence Priority Number (IPN) and the Independence Measure (IM) to further rank the potential robustness of alternative solutions using the Independence Axiom of the Axiomatic Design process. With IPN and IM metrics, design professionals can better assess the functional robustness of their proposal at the earliest phase of design, conceptual design synthesis.