1. Introduction

Additive manufacturing (AM) can significantly reduce the development time for small batch parts or parts with complicated geometries, especially for polymer components [1]. Today, many polymer components are produced on a single AM machine, where the parts are manufactured directly to meet engineering requirements (e.g. geometric dimensions and mechanical properties). Producing a product on a single production resource yields significant benefits such as reducing material handling and in-process control. However, the most significant benefit associated with producing a product on a single production resource could be the reduction

in process engineering time. For many of these polymer components, the mechanical properties come directly from the combination of the polymer material and the processing parameters. The geometric shape and dimensions comes from a combination of the computer-aided design (CAD) model developed during Product Engineering and the dimensional capabilities of the AM machine used.

combination takes advantage of the capabilities of both processes. However, the

racies as compared to casting alone. For example, parts often exhibit better flatness and smaller radiused corners when machined. Machining using computer numerical control (CNC), means that the process is highly repeatable and easily scalable due to the incorporation of computer-guided automation. While the accuracy is better for machined components, there is a sharp reduction of the geometric complexity possible, particularly with internal features, when compared to cast parts. This is because machining is limited to a straight line of sight from the cutting tool, which limits the features that are accessible for finishing. Additionally, unless combined with another process, machining is associated with larger amounts of material waste from transforming rectangular or cylindrical billets into final

Combined, these two processes can produce parts that are better able to meet the final part specifications in an economical way as outlined by the advantages mentioned previously. In this category of HMP, there are special considerations that must be given to the incorporation of machining after casting. For example, engineers should decide if small holes in the casting should be filled (i.e. not produced in the casting) to ensure drills would be able to accurately finish holes without tool walking. Another possible consideration is the method for fixturing cast parts to a milling machine, since each individual castings' defects (flash, shrinkage, pores, etc.) could impact this. Additional factors and where they should be addressed in the casting-subtractive category of HMP are outlined

geometries.

in Figure 1.

Figure 1.

119

Process flow of casting-subtractive category of HMP.

Since the material flows into a mold cavity, casting enables the production of complex internal and external geometries that are net- or near-net shape. Parts fabricated using casting are often limited in other ways. For example, the surface roughness of castings is directly correlated to the roughness of the mold cavity walls, which in the case of sand casting is the roughness of the sand. Additionally, consideration must be given to process inherent defects that affect the mechanical performance and geometrical and dimensional accuracy of the casting such as shrinkage cavities, inclusions of air or foreign matter due to turbulence from pouring, etc. Machining can allow users to manufacture parts with increased accu-

material properties can be sacrificed compared to just machining.

Advanced Manufacturing Using Linked Processes: Hybrid Manufacturing

DOI: http://dx.doi.org/10.5772/intechopen.88560

Unfortunately, polymers have a limited use for only certain products. As better mechanical properties and finer geometric tolerances are required, the use of metals becomes necessary. Although metal AM has been around for two decades, the geometric accuracy of metal AM frequently falls short of the engineering specifications and the mechanical properties of AM produced metal parts are often highly dependent on the surface conditions. The result of these specifics is that metal AM production typically requires multiple post-production processes and machines. Metal AM machines have typically been used to create "near net-shape" components that require additional processes to enhance both the tolerances and surfaces as well as the mechanical properties of the AM printed component. This has slowed the adoption of metal AM for many high-performance components, especially those requiring certification.

To increase the performance of engineered parts with complex geometries which use processes such as metal AM, Hybrid Manufacturing Processes (HMP) are used which incorporate a secondary post process. HMP can significantly reduce time to customer, waste, and tooling costs per part while increasing possible part geometries and material availability for small batch parts. Examples of hybrid manufacturing for this chapter include Casting-Subtractive, Injection-Molding-Subtractive, and Additive-Subtractive processes. HMP usually have accurate results but require extra layers of complexity including process plan development.

This chapter outlines several hybrid manufacturing processes and the intricacies required to design parts and develop process plans for the complex processes. Although HMP is largely comprised of an additive process followed by a subtractive process, two other manufacturing methods are discussed since they have similar complexities in the process planning phase. Finally, a feature-based advanced hybrid manufacturing process planning system (FAH-PS) is discussed. This framework uses feature-specific geometric, tolerance, and material data input to generate automated process plans based on user-specified feature precedence for additivesubtractive hybrid manufacturing, a hybrid manufacturing process. Plans generated by FAH-PS can optimize process plans to minimize tool changes, orientation changes, etc., to improve process times. A case study of a patient-specific bone plate is described at the end of the chapter for proof of concept of the framework. Imploring a strategy of minimizing tool and orientation changes generated a process plan that demonstrated automation of an optimized process plan.
