Freeform Parts Research Articles

A new method to assess the accuracy of a Cone Beam Computed Tomography scanner by using a non-contact reverse engineering technique

AimToday Cone Beam Computed Tomography (CBCT) has become an important image technique for dento-maxilla facial applications. In the paper a new method to assess the geometric accuracy of these systems was proposed. It uses a free form benchmark model and a non-contact Reverse Engineering (RE) system. MethodThe test geometry chosen for this study was designed in such a way that it simulated human spongy bone, cortical bone, gingiva and teeth and it composed of removable free form parts. It was acquired with a high-resolution laser scanner (D700 Scanner – 3Shape, Denmark). The reference 3D surface models obtained with the laser scanner was compared with the 3D models that were created from a CBCT system (Scanora 3D – Soderex, Finland) and from a traditional Multi-Slice Computed Tomography (MSCT) scanner (LightSpeed VCT 64 Slice – General Electric, USA) at different reconstruction settings, using an iterative closest point algorithm (ICP) in Geomagic® software. ResultsThe comparison between the different pairs of CAD models clearly shows that there is a good overlap between the models. ConclusionsAlthough the results obtained in this study could lead to increase the use of CBCT for an increasing number of dental procedures, the publication of the European Commission guidelines represents a baseline on which the clinicians should rely heavily when considering the use of CBCT in their practice. Clinical SignificanceThe results of this research show that the accuracy of CBCT 3D models is comparable to MSCT 3D models.

Position-oriented process monitoring in freeform abrasive machining

Process monitoring is necessary for the identification and avoidance of process disturbances that could cause poor surface integrity at selected machining parameters. In this paper, a position-oriented process monitoring strategy is introduced which enables determination of process characteristics for freeform abrasive machining. Through correlation of internal machine data of position and power during machining with laser displacement measurement, position-orientated maps of power and specific energy can be generated to enable an evaluation of the machining efficiency of the abrasive machining process. Measurement chains are described, and experimental results reveal that the measurement system provides a significant insight into the process by identifying regions of high power, depth of cut, engagement and specific energy on freeform parts.

Modelling and Control of Inverse Dynamics for a 5-DOF Parallel Kinematic Polishing Machine

Currently, about 60% of the finishing works for freeform parts are done manually, in this paper a parallel kinematic polishing machine (PKPM) with five degrees of freedom (DOFs) and with structural configurations of the type T3R2 (three translations and two rotations) is presented. The PKPM is a variation of the existing METROM Pentapod. The PKPM has a large yaw angle space and, with the aid of an NC rotation table, it can access any given point of the freeform part. A kinematic analysis is developed, an inverse dynamic model based on Kane's equation and the affine projection method is set up in detail, and a real-time and highly efficient inverse dynamic algorithm is developed; the simulation results show that the presented PKPM could achieve an acceleration which is twice that of gravity. A mixed ℋ2/ ℋ ∞ control method is presented and investigated in order to track the error control of the inverse dynamic model; the simulation results from different conditions show that the mixed ℋ2/ ℋ ∞ control method could achieve an optimal and robust control performance. This work shows that the presented PKPM has a higher dynamic performance than conventional machine tools.

Performance study of dimensionality reduction methods for metrology of nonrigid mechanical parts

The geometric measurement of parts using a coordinate measuring machine (CMM) has been generally adapted to the advanced automotive and aerospace industries. However, for the geometric inspection of deformable free-form parts, special inspection fixtures, in combination with CMM’s and/or optical data acquisition devices (scanners), are used. As a result, the geometric inspection of flexible parts is a consuming process in terms of time and money. The general procedure to eliminate the use of inspection fixtures based on distance preserving nonlinear dimensionality reduction (NLDR) technique was developed in our previous works. We sought out geometric properties that are invariant to inelastic deformations. In this paper we will only present a systematic comparison of some well-known dimensionality reduction techniques in order to evaluate their accuracy and potential for non-rigid metrology. We will demonstrate that even though these techniques may provide acceptable results through artificial data on certain fields like pattern recognition and machine learning, this performance cannot be extended to all real engineering metrology problems where high accuracy is needed.

Springback Prediction and Compensation for Thick Freeform Surface Parts Forming

The springback phenomenon of thick freeform surface steel plate forming occurs consequentially after unloading, which reduces the accuracy of the parts manufacturing and the processing efficiency. This paper developed a numerical simulation solution to the springback of thick freeform surface parts forming process using PAM-STAMP 2G at 20°C, 200°C, 400°C, 600°C, 700°C and 800°C, respectively. The maximum springback value of freeform surface parts decreases with increasing temperature, at 600°C, the minimum extreme value, and then the value with increasing temperature continues to rise higher. PAM-STAMP 2G offers a Die Compensation module, which is used to modify the die surface of thick freeform surface steel plate forming focused on springback defects. The approach based on iteratively comparing a target part shape with a numerical simulated part shape following forming and springback can be effective in reducing springback error. With it, the new tooling shapes will ensure the geometric accuracy of the thick freeform surface parts.

Application of CAD/CAM Technology on the Modeling of Freeform Surface Parts

To improve the design of complex curved parts and the shortage of reading two-dimensional drawings. This paper explicitly discussed modeling the bottom of a bottle by enhanced modeling and rendering techniques of CAD/CAM. Established the bottom with freeform surfaces in UG to solve the problem of design a part with freeform surfaces, and rendered the bottom of the bottle to express the result of three-dimensional stereoscopic of a part with freeform surfaces. Rendering is setting the material and texture for the model, and then adding lights and setting the background, etc to help solving the problem of identifying a part with freeform surfaces. Finally, we got the features of UG, the advancement, applicability of CAD/CAM and the necessity of expanding it.

Genetic B-Spline approximation on combined B-reps

We present a genetic algorithm for approximating densely sampled curves with uniform cubic B-Splines suitable for Combined B-reps. A feature of this representation is altering the continuity property of the B-Spline at any knot, allowing to combine freeform curves and polygonal parts within one representation. Naturally there is a trade-off between different approximation properties like accuracy and the number of control points needed. Our algorithm creates very accurate B-Splines with few control points, as shown in Fig. 1. Since the approximation problem is highly nonlinear, we approach it with genetic methods, leading to better results compared to classical gradient based methods. Parallelization and adapted evolution strategies are used to create results very fast.

Variable Geometry Casting of Concrete Elements Using Pin-Type Tooling

Today, free-form parts are made in small production volume with time consuming methods and a significant amount of material waste. These methods include computer numerical control (CNC)-machining and the layered rapid prototyping techniques stereolithography apparatus (SLA), selective layer sintering (SLS), fused deposition modeling (FDM), 3D print, etc., which are well suited for smaller parts that are rich in detail. Variable geometry molds (VGMs) offer a different approach to small production volume. A die or mold can change shape between the castings, and parts with a different geometry can be made in the same mold. VGM is used in a multitude of applications such as sheet metal forming of parts for aircrafts, trains, and cranial prostheses. The present project focuses on VGM for free-form concrete facade elements, which, in contrast to previous VGM projects, uses a liquid raw material and involves the use of only a small amount of force. The present VGM process is based on the so-called reconfigurable pin-type tooling (RPT) principle. The geometric possibilities have been examined using a proof-of-concept RPT test mold. Sixty closely packed adjustable pin-elements with hemispherical tops and a square section of 43.3×43.3 mm2 create a dimpled surface that is evened out using an elastic interpolating layer. Castings with concrete and plaster are made on an elastic membrane that is sucked toward the pins using a vacuum. The shape of the cast elements and the mold surface have been measured and compared. The RPT test mold can produce a large variety of free-form geometric shapes. It is possible to make straight vertical surfaces and even horizontal surfaces with dimples of only 0.3 mm. Part details can be made down to the size of a pin with hole depths up to 65 mm and protrusions up to 19 mm. Repeatability is better than the measurement uncertainty. VGMs using the RPT principle can be used for making scale models of a range of free-form cast concrete façade elements. It is almost possible to remove the imprints from the pins by using the right interpolators, but the dimples could also be a visually attractive characteristic of the process that could be valued by architects. Large hole depths and smaller protrusions are possible.

Develop a Robot-Aided Area Sensing System for 3D Shape Inspection

Dimensional inspection using a contact-based coordinate measurement machine (CMM) is time consuming because the part can only be measured point-by-point. A 3D sensor may replace the traditional CMM technology because it can measure a surface patch-by-patch. Therefore, the automotive industry has been seeking a practical solution for rapid surface inspection using a 3D sensor. However, the challenge is the capability to meet all the requirements including sensor accuracy, resolution, system efficiency, and system cost. In this paper, we develop a robot-aided 3D sensing system, which can automatically allocate sensor viewing points, measure the freeform part surface, and generate an error map for quality control. The measurement accuracy meets the industrial standards. This paper briefly describes the system architecture, design principle, calibration methods, and the present results.

Verification of 3D freeform parts by registration of multiscale shape descriptors

Precision inspection of freeform parts takes an important role in manufacturing quality control. The aim of this inspection is to verify that the geometric dimensions and produced part tolerances meet quality requirements. This is achieved by fitting the scanned data to the computer-aided design (CAD) model. This verification is complicated since the produced part includes defects and distortions. Currently, industry uses semimanual verification, which is expensive, often inaccurate, and very time-consuming. This paper describes a new method for automatic registration and alignment of two 3D freeform shapes, one from the scanned data and the other from the CAD model. The method makes no assumptions about their initial positions. Instead, the proposed algorithm uses a multiscale shape descriptor to select features on the scanned data and identify their corresponding features on the CAD model. The proposed shape descriptor is invariant with respect to local shapes and is robust to noise. A coarse alignment is computed by finding and registering the best matching triplet of features. The iterative closest point algorithm uses resulting coarse alignment to achieve a tuned alignment. The proposed method is automatic, efficient, and straightforward to implement. The algorithm can also be effective in the case of partial scanned inspected shapes. The feasibility of the proposed method is demonstrated on a blade model.

Automatic recognition of intersecting features of freeform sheet metal parts

This paper presents an approach for recognizing both isolated and intersecting geometric features of freeform surface models of parts, for the purpose of automating the process planning of sheet metal forming. The developed methodology has three major steps: subdivision of B-spline surfaces, detection of protrusions and depressions, and recognition of geometric features for sheet metal forming domain. The input geometry data format of the part is based on an IGES CAD surface model represented in the form of trimmed B-spline surfaces. Each surface is classified or subdivided into different curvature regions with the aid of curvature property surfaces obtained by using symbolic computation of B-spline surfaces. Those regions satisfying a particular geometry and topology relation are recognized as protrusion and depression (DP) shapes. The DP shapes are then classified into different geometric features using a rule-based approach. A verified feasibility study of the developed method is also presented.

A METHOD OF 3D FREEFORM FABRICATION USING A CURING OF PHOTOPOLYMER RESIN

Recently, Study of 3D freeform fabrication method was working in the various applications. For example, in the powder base, it's laminated using a binding method or laser sintering method. However, the demerits of these methods are to take long time for post process and not enough to keep high strength of manufacturing part. The binding method needs the post process and the time for post process needs longer time than a manufacturing time. The sintering method has huge size of system with module of the laser. In this paper, we introduce a method of 3D freeform fabrication using a curing of photopolymer resin. A photopolymer curing method has simply fabrication process and high strength of manufacturing part. So, we are configuration the system with compact type module for the office environment and experiment a UV curing test with photopolymer resin in the 3D freeform fabrication method. In the conclusion, we fabricate the 3D freeform part, which is suitable to the office environment using a photopolymer curing method.

An effective method for multi-material part design

Injection moulding is the most commercially important of all plastic processing methods. In recent years, multi-material over-moulding has become one of the fastest growing sectors of the injection moulding industry mainly due to its in-mould assembly and in-mould decoration features. Unlike the rapid development of multi-material over-moulding technologies, research in computer-aided design of multi-material parts lags far behind. This paper reports initial thoughts and preliminary results about a computer-aided design method for multi-material parts. Haptic modelling has been developed into the computer-aided design system for quick and intuitive design concepts generation and evaluation. Some of the tedious and difficult tasks such as free-form surface painting, part decompositions, and stiffness evaluation can now be done in the proposed system.

Rheological Behavior of Alumina Aqueous Suspension for Extrusion Gelation Freeform Fabrication

Extrusion gelation freeform fabrication (EGFF) is a new solid freeform fabrication technique to fabricate ceramic parts. The study of ceramic suspensions rheological behavior is essential to a better understanding of parts fabrication through EGFF process. In this paper, the effects of dispersant concentrations, solids loading and binder composition on the rheological behavior of alumina suspensions were examined. The optimal amount of dispersant was found to be about 0.1 wt.%. The suspensions with 50 vol.% alumina and 1wt.% sodium alginate show shear thickening behavior. Such behavior is unfavorable for extrusion gelation freeform fabrication. By addition of PVA or styrene-acrylic latex, the rheological behavior of suspensions was changed. The addition of PVA or latex has a great effect on the viscosity of the suspensions and the type of their rheological behavior. The ceramic suspensions with PVA or latex were found to be shear thinning more suitable for EGFF.

FREE-FORM SURFACE MACHINING AND COMPARING FEEDRATE SCHEDULING STRATEGIES

This article presents mathematical models of cutting forces and surface-form errors for machining of free-form surfaces. Besides the predictive models of cutting forces and surface deflections, a newly developed force based feedrate scheduling (FFS) technique is compared with material removal rate (MRR) based feedrate scheduling method that was used in feedrate optimization packages. With the experimental validations in free-form surfaces, it is shown that the mechanic models predict the forces and surface-form errors quite well. Moreover, by modifying the CNC programs with the new FFS technique, cycle times of the free-form parts can be decreased significantly.

Analysis of Kinematics and Dynamics for a Novel Hybrid Kinematics Machine

In this paper a novel 4 Degree-of-Freedom (DOF) parallel mechanism with the configuration of 4PUS-1RPU is first proposed, the mechanism is composed of four symmetrical driving chains and one central passive subchain. Based on the proposed 4-DOF parallel mechanism a 5-axis Hybrid Kinematics Machine (HKM) scheme is developed with an additional linear motion is combined, which can perform the 5-axis machining for freeform parts. The inverse kinematics of the 4-DOF parallel mechanism and the direct kinematics for the serial central sub-chain are then presented. The dexterity and the workspace analysis for the mechanism are also carried out. The dynamic characteristics of the PKM are investigated in detail. The simulation results show that the first four fundamental frequencies are the dominant factors that influence the dynamic characteristics of the developed PKM. The research provides the basis for the further parametric design with consideration of dynamic performances.

Fixtureless Sensor Standoff Control for High-Precision Dimensional Inspection of Freeform Parts

High-precision, noncontact dimensional inspection requires sensor standoff control due to the working range limitation posed by high-precision range sensors. Constant sensor standoff with the surface of the part is necessary to ensure accurate measurement. This paper presents a novel computer-aided design (CAD) independent approach to sensor standoff control called “fixtureless sensor standoff control (FSC),” which contrary to current methods does not require a fixture or manual intervention for registration. This approach to sensor standoff control will enable rapid, flexible, and high-precision inspection of freeform parts, thus catering to the needs of future manufacturing systems. In the FSC methodology, the sensor’s position for the next measurement is estimated based on immediate previous measurements. The method was implemented on a four-axis machine used to inspect turbine blades. Results from measurement of an example turbine blade showed the deviation from desired standoff to be significantly smaller than the working range of the sensor.

Kinematics and Simulation for a High-Precision Parallel Kinematic Platform

To meet the high speed and high precision requirements of machining freeform workpieces, a 4-DOF parallel kinematic platform with the configuration of 4 actuated legs plus a passive leg is proposed in this paper. Inverse kinematics and the calibration algorithm are developed, and virtual prototype modeling and kinematic simulation using MSC/ADAMS are carried out. The simulation results exhibit that the proposed structure is capable of implementing the high-precision machining requirements of freeform parts.

2차부재가 포함된 다수의 1차부재를 가공하기 위한 레이저 토치의 절단경로 최적화 알고리즘

A hybrid genetic algorithm is proposed for the problem of generating laser torch paths to cut a stock plate nested with free-formed parts each having a set of sub-parts. In the problem, the total unproductive travel distance of the torch is minimized. The problem is shown to be formulated as a special case of the standard travelling salesman problem. The hybrid genetic algorithm for solving the problem is hierarchically structured: First, it uses a genetic algorithm to find the cutting path f3r the parts and then, based on the obtained cutting path, sequence of sub-parts and their piercing locations are optimally determined by using a combined genetic and heuristic algorithms. This process is repeated until any progress in the total unproductive travel distance is not achieved. Computational results are provided to illustrate the validity of the proposed algorithm.

Determination of the optimal part orientation in layered manufacturing using a genetic algorithm

Several important factors must be taken into consideration to maximise the efficiency of rapid prototyping (RP) processes. The ability to select the optimal orientation of a build direction is one of the most critical factors in using RP processes, since it affects the quality of the prototyped part, the support structure and the build time. This study aims to determine the optimal part orientation that improves the average weighted surface roughness (AWSR) generated from the stair stepping effect. It also minimises the build time including the structure of the support in fabricating a completely freeform part. To avoid pre-selection operation, which is often troublesome and time-consuming, the genetic algorithm, that considers the fuzzy weight for surface roughness and build time, is used to determine the optimal orientation. The validity of the proposed algorithm is demonstrated by several examples using different RP systems and compared with previous works. The algorithm can help RP users select the best orientation of the part and carry out efficient process planning.