Zicheng Zhu

A review of hybrid manufacturing processes – state of the art and future perspectives

Today, hybrid manufacturing technology has drawn significant interests from both academia and industry due to the capability to make products in a more efficient and productive way. Although there is no specific consensus on the definition of the term ‘hybrid processes’, researchers have explored a number of approaches to combine different manufacturing processes with the similar objectives of improving surface integrity, increasing material removal rate, reducing tool wear, reducing production time and extending application areas. Thus, hybrid processes open up new opportunities and applications for manufacturing various components which are not able to be produced economically by processes on their own. This review paper starts with the classification of current manufacturing processes based on processes being defined as additive, subtractive, transformative, joining and dividing. Definitions of hybrid processes from other researchers in the literature are then introduced. The major part of this paper reviews existing hybrid processes reported over the past two decades. Finally, this paper attempts to propose possible definitions of hybrid processes along with the authors’ classification, followed by discussion of their developments, limitations and future research needs.

A Methodology for the Estimation of Build Time for Operation Sequencing in Process Planning for a Hybrid Process

The on-going industrial trend toward production of highly complex and accurate part geometries with reduced costs has led to the emergence of hybrid manufacturing processes where varied manufacturing operations are carried out in either parallel or serial manner. One such hybrid process being currently developed is the iAtractive process, which combines additive, subtractive, and inspection processes. The enabler for realizing the hybrid process production is the process planning algorithm. The production time estimation for the additive process, namely build time, is one of the key drivers for the major elements in the algorithm. This paper describes a method for predicting build times for operation sequencing for process planning of the iAtractive process. An analytical model is first proposed, theoretically analyzing the factors that affect build times, which is used to help with the design of four test parts together with 64 sets of variations. The experimental results indicate that part volume, and interactions of volume and porosity, height and intermittent factor have significant effect on build times. Finally, the build time estimation model has been developed, which were subsequently evaluated and validated by applying a wide range of the identified influential factors.

Using formal methods to model hybrid manufacturing processes

The on-going industrial trend towards high value sustainable manufacturing has led to the emergence of hybrid manufacturing processes and resources. This new generation of processes and resources combine the capabilities of a number of older technologies on a single platform. This increase in capability, however, comes at the cost of increasing complexity. Manufacturing processes, in general, can be categorised into subtractive processes, additive processes and transformative processes. While traditional machines supported a single type of these processes (e.g. a turn-mill machine that supports multiple metal removal - subtractive - processes), the new hybrid machines combine multiple types in one device. As a result, the current process and resource models have many shortcomings in representation of hybrid processes and hybrid machines. In this research formal methods are used to construct a new type of model for hybrid manufacturing processes. Formal methods are mathematically based techniques that allow clear and nonambiguous specification, development and, most importantly, verification of software and hardware systems. This paper utilises the ISO-standardised Z notation (named after Zermelo-Fraenkel set theory) to construct a formal model for hybrid manufacturing processes. The capabilities of the model in specification and verification of a hybrid device is then discussed through the use of a case study based on a prototype parallel kinematics hybrid manufacturing platform.

A novel decision-making logic for hybrid manufacture of prismatic components based on existing parts

The on-going industrial trend towards high value sustainable manufacturing has led to the emergence of hybrid manufacturing processes. This new generation of processes combines the capabilities of a number of individual manufacturing processes on a single platform. Despite the fact that the drawbacks of individual processes have been significantly reduced, the application of hybrid technology has always been constrained by the capabilities of their constituent processes, in particular the capability to utilise various raw materials in terms of shape and size. This paper introduces a novel concept of hybrid process, which consists of combining additive, subtractive and inspection processes. A feature-based decision-making logic is developed, enabling the hybrid process to reuse existing parts/legacy products. An existing part is first measured for obtaining its geometrical information. Feasible manufacturing strategies are provided and then additive, subtractive and inspection processes are utilised interchangeably to add and/or remove material, transforming the existing part into the final part. This indicates that the iAtractive process is not restricted by raw material geometries. Three identical test parts were manufactured from three existing different shaped parts, demonstrating the efficacy of the proposed hybrid process and the decision-making logic in material reuse. New features can be added onto the existing parts and existing features can be removed or further manufactured, giving these parts additional lives, new uses and increased functionality.

A novel process planning approach for hybrid manufacturing consisting of additive, subtractive and inspection processes

In recent years, hybrid manufacturing technologies that combine different processes (e.g. additive and subtractive processes) together have gained significant attention. This is due to their ability to capitalise on the advantages of each individual process, whilst minimising their disadvantages. However, there are limited process planning methods that are able to effectively utilise manufacturing resources for hybrid processes. In this paper, a hybrid process entitled iAtractive, combining additive, subtractive and inspection processes, along with part specific process planning is proposed, aiming to provide the designer with greater manufacturing capability and flexibility. This novel process planning approach enables a plastic part to be manufactured in a proper way in terms of process capabilities, production time and material consumption. This approach can be also adopted to remanufacture and reincarnate exiting parts or legacy products into other products. In this paper, the principle and framework of this process planning approach is presented and a test part was manufactured to validate this innovative approach.

A new algorithm for build time estimation for fused filament fabrication technologies

The manufacture of highly complex and accurate part geometries with reduced costs has led to the emergence of hybrid manufacturing technologies where varied manufacturing operations are carried out in either parallel or serial manner. One such hybrid process being currently developed is the iAtractive process, which combines additive (i.e. fused filament fabrication, which is sometimes called fused deposition modelling. However, the latter term is trademarked by Stratasys Inc. and cannot be used publicly without authorisation from Stratasys) and subtractive (i.e. computer numerical control machining) processes. In the iAtractive process production, operation sequencing of additive and subtractive operations is essential. This requires accurate estimation of production time, in which the fused filament fabrication build time is the determining factor. There have been some estimators developed for fused deposition modelling. However, these estimators are not applicable to hybrid manufacturing, particularly in process planning, which is a vital stage. This article addresses the characteristics of fused filament fabrication technologies and develops a novel and rigorous method for predicting build times. An analytical model was first created to theoretically analyse the factors that affect the part build time and was subsequently used to facilitate the design of test parts and experiments. The experimental results indicate that part volume, interaction of volume and porosity and interaction of height and intermittent factor have significant effects on build times. Finally, the estimation algorithm has been developed, which was subsequently evaluated and validated by applying a wide range of identified influential factors. The major advantage of the new proposed algorithm is its ability to estimate the build time based on simple geometrical parameters of a given part. The key factors that drive the algorithm can be directly obtained from part dimensions/drawings, providing an efficient and accurate way for fused filament fabrication time estimation. Test part evaluations and analysis have clearly demonstrated that estimation errors range from 0.1% to 13.5%, showing the validity, capability and significance of the developed algorithm and its applications to hybrid manufacture.