Search results

The purpose of this paper is to review additive and/or subtractive manufacturing methods for metallic objects and their gradual evolution from prototyping tools to rapid manufacture of actual parts.

Various existing rapid manufacturing (RM) methods have been classified into six groups, namely, CNC machining laminated manufacturing, powder‐bed technologies, deposition technologies, hybrid technologies and rapid casting technologies and discussed in detail. The RM methods have been further classified, based on criteria such as material, raw material form, energy source, etc. The process capabilities springing from these classifications are captured in the form of a table, which acts as a database.

Due to the approximation in RM in exchange for total automation, a variety of multi‐faceted and hybrid approaches has to be adopted. This study helps in choosing the appropriate RM process among these myriad technologies.

This review facilitates identification of appropriate RM process for a given situation and sets the framework for design for RM.

This paper seeks to detail the fabrication of a glass‐ceramic substrate, based on the LiO₂‐ZrO₂‐SiO₂‐Al₂O₃ (LZSA) system, by laminated object manufacturing (LOM) using water‐based cast tapes.

Small amounts of ZrSiO₄ were added to control the thermal expansion coefficient (TEC) of the original glass‐ceramic (LZSA5Zr: LZSA+5 wt% ZrSiO₄). In order to verify the influence of the amount and nature of crystalline phases on the thermal and dielectric behavior of the material, LZSA and LZSA5Zr laminates were sintered at 700°C for 30 min and crystallized at either 800 or 850°C for 30 min.

LZSA laminates (sintered and crystallized at 700 and 800°C, respectively) exhibited a relative density of ∼90 percent, a dielectric constant of 8.39, a dielectric loss tangent of 0.031 and TEC of 5.5×10⁻⁶ K⁻¹ (25‐550°C). The addition of 5 wt% ZrSiO₄ to original LZSA glass‐ceramics led to a nearly constant TEC value of 6×10⁻⁶ K⁻¹ throughout the whole temperature interval (25‐800°C). Dielectric properties of LZSA5Zr did not show any remarkable change when compared to original LZSA.

The thermal, mechanical and electrical properties of LZSA glass‐ceramic laminates fabricated by LOM makes them potential candidates for substrate applications.

Additively manufactured objects have layered structures, which means post processing is often required to achieve a desired surface finish. Furthermore, the additive nature of the process makes it less accurate than subtractive processes. Hence, additive manufacturing techniques could tremendously benefit from finishing processes to improve their geometric tolerance and surface finish.

Rotary ultrasonic machining (RUM) was chosen as a finishing operation for drilling additively manufactured carbon fiber reinforced polymer (CFRP) composites. Two distinct additive manufacturing methods of fused deposition modeling (FDM) and laser-assisted laminated object manufacturing (LA-LOM) were used to fabricate CFRP plates with continuous carbon fiber reinforcement. The influence of the feedrate, tool rotation speed and ultrasonic power of the RUM process parameters on the aforementioned quality characteristics revealed the feasibility of RUM process as a finishing operation for additive manufactured CFRP.

The quality of drilled holes in the CFRP plates fabricated via LA-LOM was supremely superior to the FDM counterparts with less pullout delamination, smoother surface and less burr formation. The strong interfacial bonding in LA-LOM proven to be superior to FDM was able to endure higher cutting force of the RUM process. The cutting force and cutting temperature overwhelmed the FDM parts and induced higher surface damage.

Overall, the present study demonstrates the feasibility of a hybrid additive and subtractive manufacturing method that could potentially reduce cost and waste of the CFRP production for industrial applications.

It is now possible to generate tooling for near net shape manufacturing processes directly from a CAD database by using computer numerical control (CNC) machining or a variety of rapid prototyping (RP) processes. These methods are widely referred to as rapid tooling processes because the tool geometry is created in a relatively short time. In particular, the use of RP processes has proved to be a cost‐effective and time‐efficient approach for producing patterns and core boxes for sand casting. However, the suitability of this approach depends on a variety of geometry and process related considerations. Investigates the use of the laminated object manufacturing (LOM) based rapid tooling process in sand casting. Issues discussed include geometry considerations, error sources and propagation, and shrinkage effects. A case study illustrating time and cost savings using the LOM approach is also presented.

Laminated object manufacturing (LOM) is a rapid prototyping process where a part is built sequentially from layers of paper. Studied in the present paper are the precision and accuracy of the LOM process and the dimensional stability of LOM parts. The process was found to exhibit both constant and random sources of error in the part dimensions. The dimensional error was the largest normal to the plane of the paper, exacerbated by the moisture absorption and subsequent swelling. The key process parameters were identified and optimized for sufficient bonding and cutting accuracy.

LOM is one of the techniques for rapid prototyping, which is used to build three‐dimensional solid objects. In this paper, a numerical analysis of the thermomechanical behavior of a laminate during the LOM process is presented. Models were developed to describe heat transfer and deformation phenomena. These models are incorporated into computer codes to generate numerical results. The numerical results show how the process parameters (e.g. roller temperature, velocity, indentation) are related to temperature and stress distributions within the laminate. By using this code, process conditions which are favorable to bonding are identified.

This paper proposes sheet thickness determination in manufacturing of laminated dies as an optimization problem. The aim of this optimization procedure is finding the best set of thicknesses which minimizes the volume deviation between actual computer‐aided design (CAD) model and assembled slices.

This works uses a modified version of genetic algorithms for the optimization purpose. Each set of thicknesses that can cover the whole CAD model surface is considered as a chromosome. Genetic operators such as crossover and mutation have to be modified to be used in this application.

A new method for finding the total volume deviation between assembled slices and the actual CAD model was developed in this research. On the other hand, the results show how the program can automate the slice plane locations search process.

Premature convergence does not allow the algorithm to search the entire solution space before getting trapped in a local optimum. Even the mutation operator cannot postpone this untimely convergence.

The proposed method is a good substitute for the manual methods that are currently used in industry. These experience‐based methods are mostly based on the decision made by a well‐trained technician on picking up the thicknesses for a specific CAD model.

This is the first attempt at optimizing the slicing method in laminated tooling. Other methods are mostly based on rapid prototyping (RP) and they are not applicable in the laminated tooling process since, despite RP, here not all optimization outputs can be used in practical procedure.

A method for estimating the build‐time required by the laminated object manufacturing (LOM) process is presented in this paper. The proposed algorithm – taking into account the real process parameters and the information included in the part's STL‐file – performs a minimum manipulation of the file, and calculates total volume, total surface area and flat areas involved in fine cross‐hatching. A number of experiments performed verify the applicability of the algorithm in process build‐time estimation. The time prediction estimates are within 7.6 per cent of the real build‐times for the LOM process. It is believed that, through specific minor adjustments, the algorithm could well be employed in process build‐time estimation for similar rapid prototyping processes.

Due to an uncertainty between actual model and assembled slices, there is always an extra material on assembled slices in laminated tooling. Therefore, a post processing, usually CNC machining, is required to remove this extra material and reach the near net shape surface for final product. One of the issues in laminated tooling is to minimize the amount of this extra material and reduce the cost of the post processing. Direction of slicing is an important parameter in this issue. This research aims to introduce a method to find the best slicing direction based on CAD model surface geometry and minimize the amount of the extra material in the assembled slices. Researches on the best slicing direction investigation so far were mostly based on the extra volume calculation for a number of candidate directions. Since the time needed for the extra volume calculation is proportionally high, the number of candidate directions to be investigated was usually limited, whereas, in the proposed method, the best slicing direction is found based on CAD model surface geometry and there is no need to find the actual amount of the extra volume. Moreover, the suggested method is developed to the cases where having more than one slicing direction is desirable for more reduction in the amount of the extra volume. The proposed optimization method can be used to find the best slicing direction in laminated tooling. Moreover, the ability to suggest multiple slicing directions can provide more reduction for the amount of the extra material. However, the number of candidate directions in the case of multiple slicing directions is limited due to joining problems in laminated tooling.

The investigation is based on the situation of normal vectors on CAD model surface. The CAD model surface is considered as a combination of planar tiles and all normal vectors of these tiles are considered as the candidate directions. This provides a number of candidates that can cover almost all possible slicing directions. The best slicing direction is then found by estimating the amount of the extra material produced on the tiles by each normal vector.

The proposed method applied to some examples. The case studies included the simple predictable models to qualify the reliability of the proposed method. Also more applicable examples were provided to show how the suggested method acts in real cases.

The proposed method can be applied to each and every CAD model. Therefore, there is no limitation with regard to the type of model which can be investigated by the proposed method. However, there is limitation on the number of times the building direction can be changed in laminated tooling.

The proposed method can be employed to reduce the post processing time in laminated tooling.

Following the prior study researchers conducted in optimization of laminated dies, another parameter, slicing direction, is considered in this research. This brings a new approach on laminated dies optimization to reduce the production cost.

A novel rapid prototyping technology incorporating a curved layer building style was developed. The new process, based on laminated object manufacturing (LOM), was designed for efficient fabrication of curved layer structures made from ceramics and fiber reinforced composites. A new LOM machine was created, referred to as curved layer LOM. This new machine uses ceramic tapes and fiber prepregs as feedstocks and fabricates curved structures on a curved‐layer by curved‐layer basis. The output of the process is a three‐dimensional “green” ceramic that is capable of being processed to a seamless, fully dense ceramic using traditional techniques. A detailed description is made of the necessary software and hardware for this new process. Also reviewed is the development of ceramic preforms and accompanying process technology for net shape ceramic fabrication. Monolithic ceramic (SiC) and ceramic matrix composite (SiC/SiC) articles were fabricated using both the flat layer and curved layer LOM processes. For making curved layer objects, the curved process afforded the advantages of eliminated stair step effect, increased build speed, reduced waste, reduced need for decubing, and maintenance of continuous fibers in the direction of curvature.