The CIRP (International Academy for Production Engineering) Conference on Computer Aided Tolerancing (CAT) is initiated and supported scientifically every two years by two CIRP Scientific Technical Committees (STCs): Design (STC Dn) and Precision Metrology (STC P) to address the emerging problems of CAT, which has a prominent role at the interface between product design and manufacturing. The 13th CIRP CAT Conference held at Zhejiang University, Hangzhou, China during May 11–14, 2014 was the successor to the twelve earlier conferences. We are pleased to publish in this special part issue a selection of six papers that were presented at the conference in Hangzhou. These papers cover a wide spectrum of current international research in CAT.

For purposes of automating the assignment of tolerances during design, a math model, called the Tolerance-Map (T-Map), has been produced for most of the tolerance classes that are used by designers. Each T-Map is a hypothetical point-space that represents the geometric variations of a feature in its tolerance-zone. Of the six tolerance classes defined in the ASME/ANSI/ISO Standards, profile tolerances have received the least attention for representation in computer models. The objective of this paper is to describe a new method of construction, using computer-aided geometric design, which can produce the T-Map for any line-profile. The new method requires decomposing a profile into segments, creating a solid-model T-Map primitive for each, and then combining these by Boolean intersection to generate the T-Map for a complete line profile of any shape. To economize on length, the scope of this paper is limited to line-profiles formed from circular arc-segments. The parts containing the line-profile features are considered to be rigid.

Tolerance analysis consists of analyzing the impact of variations on the mechanism behavior due to the manufacturing process. The goal is to predict its quality level at the design stage. The technique involves computing probabilities of failure of the mechanism in a mass production process. The various analysis methods have to consider the component’s variations as random variables and the worst configuration of gaps for over-constrained systems. This consideration varies in function by the type of mechanism behavior and is realized by an optimization scheme combined with a Monte Carlo simulation. To simplify the optimization step, it is necessary to linearize the mechanism behavior into several parts. This study aims at analyzing the impact of the linearization strategy on the probability of failure estimation; a highly over-constrained mechanism with two pins and five cotters is used as an illustration for this study. The purpose is to strike a balance among model error caused by the linearization, computing time, and result accuracy. In addition, an iterative procedure is proposed for the assembly requirement to provide accurate results without using the entire Monte Carlo simulation.

In tolerancing, it is important to obtain recommendations from tolerance simulation results for optimizing tolerance values or the tolerance scheme. For this purpose, sensitivity analysis identifies the importance of single input parameters for received simulation results. This paper presents a method to adopt global sensitivity analysis methods on convex hull based tolerancing techniques, such as deviation domains. The focus of this paper lies on assemblability studies, in which the simulation output is a clearance. A method to estimate the influence of single part tolerances on the assembly clearance is proposed and performed for a pin-hole connection.

The geometric and spindle errors inevitably affect the quality of the end turning surface. These errors cause resultant positioning errors at the tool tip, which are defined as the difference between the actual and commanded tool tip position. This paper proposes an approach for modeling and simulation of the surface generated in end turning process. The model incorporates the effects of the positioning errors between the tool tip and the part being machined. It provides the possibility to simulate the surface topography for given errors. Based on the proposed model, groups of simulation experiments are conducted to investigate the effects of geometric and spindle errors on the topography of end turning surface. To further analyze the effect of these errors on the surface roughness, a set of simulation experiments have been designed according to the Taguchi method. The simulation results show that the surface roughness of end turning surface is more sensitive to the spindle displacement error compared with other error components. At the end of this paper, a simple method to find the principal error component is proposed.

With the development of precision manufacturing, the understanding of tolerance has become a research hotspot in the field of manufacturing. An adaptable design method for understanding tolerance in the precision stamping process is proposed in this study. First, fluctuations of tolerance which are caused by differences in the stamping process are analyzed, such as differences in material and thickness, which can lead to changes in the metal flow stress curve. Second, a condition-driven adaptive design method is constructed based on a monitoring system and hydraulic control system. The mapping rules between multiple disturbance factors and the execution strategy are established by the hidden Markov model algorithm. Third, executive parameters, such as velocity, pressure, and gaps, are calculated and optimized by the data statistics of partial tolerance fluctuations in the control module. Then disturbances of various conditions could be adaptively controlled timely and effectively by the executive parameters. Finally, the adaptive design method for tolerance of one precision stamping part is applied, and the effect of the application is proved by the optimized results.

As one of the tools for surface analysis, morphological operations, although not as popular as linear convolution operations (e.g., the Gaussian filter), are really useful in mechanical surface reconstruction, surface filtration, functional simulation, etc. By introducing the slope transform originally developed for signal processing into the field of surface metrology, an analytic capability is gained for morphological operations, paralleling that of the Fourier transform in the context of linear convolution. Using the slope transform, the tangential dilation is converted into the addition in the slope domain, just as by the Fourier transform, the convolution switches into the multiplication in the frequency domain. Under the theory of the slope transform, the slope and curvature changes of the structuring element to the operated surface can be obtained, offering a deeper understanding of morphological operations in surface measurement. The analytical solutions to the tangential dilation of a sine wave and a disk by a disk are derived respectively. An example of the discretized tangential dilation of a sine wave by the disks with two different radii is illustrated to show the consistency and distinction between the tangential dilation and the classical dilation.

A high noise level is one of the prominent shortcomings of an axial piston pump which is widely used in industrial and mobile applications. In this paper, a simulation model of an axial piston pump is developed based on a single piston chamber model, for capturing the dynamic characteristics of the discharge flow rate. The compressibility of fluid and main leakages across different friction pairs are considered. The simulation model is validated by a comparison of discharge flow ripple with the measured results using the secondary source method. The main cause of flow ripple is identified by a comparison of the frequency spectrums of actual and kinematic flow ripples. Flow rates with different index angles are analyzed in time and frequency domains. The findings show that an index angle of 20掳 is the most effective in reducing the flow ripple of a tandem axial piston pump, because the frequency contents at odd harmonics can be cancelled out. A sensitivity analysis is conducted at different pressure levels, speeds, and displacement angles, which reveals that with an index angle of 20掳, the sensitivity of flow ripple can be reduced by almost 50% over a wide variety of working conditions.

In this paper, we propose a shield cutterhead load characteristic forecast method and apply it to optimize the efficiency of the cutterhead driving system. For the forecast method, wavelet transform is used for preprocessing, and grey model GM(1,1) for forecasting. The performance of the wavelet-based GM(1,1) (WGM(1,1)) is illustrated through field data based load characteristic prediction and analysis. A cutterhead mode control strategy (CMCS) is presented based on the WGM(1,1). The CMCS can not only provide operators with some useful operating information but also optimize the stator winding connection. Finally, the CMCS is tested on a cutterhead driving experimental platform. Results show that the optimized stator winding connection can improve the system efficiency through reducing the energy consumption under part-load conditions. Therefore, the energy-saving CMCS is useful and practical.