Implementing Rapid Prototyping Using CNC Machining (CNC-RP) Through a CAD/CAM Interface

This paper presents the methodology and implementation of a rapid machining system using a CAD/CAM interface. Rapid Prototyping using CNC Machining (CNC-RP) is a method that has been developed which enables automatic generation of process plans for a machined component. The challenge with CNC-RP is not the technical problems of material removal, but with all of the required setup, fixture and toolpath planning, which has previously required a skilled machinist. Through the use of advanced geometric algorithms, we have implemented an interface with a CAD/CAM system that allows true automatic NC code generation directly from a CAD model with no human interaction; a capability necessary for a practical rapid prototyping system.Mechanical Engineerin

Process planning for fixturing of custom machined implants

This thesis presents a process planning methodology for orienting and fixturing bone prior to the rapid machining of custom bone implants. The motivation is to automatically create custom bone implant fragments that will fill voids caused by extreme trauma. Fixturing can be one of the biggest challenges of any manufacturing process, in particular, for custom components. CNC-RP is a Subtractive Rapid Prototyping (SRP) process which employs the concept of sacrificial supports for fixturing. The support structures are added to the CAD model prior to tool path planning and subsequently created during the machining process along with the other part features. This method of adding support structures has been proved successful for the machining of industrial components out of cylindrical stock material. Due to the unique position of the implant corresponding to the density distribution within natural bone (stock), it is a challenge to create the same support structures. An alternative approach has been identified which will uniquely address this problem by adding supports externally, in the form of metal screws. A set of existing algorithms identify the harvesting site of the implant; the algorithms also yield the location and the direction of the support structures in the form of co-ordinates and vectors. The methodology presented in this work provides a novel method to physically add the support structures at precise position and direction utilizing a five axis fixture. Using the principles of inverse kinematics, the rotations and translations are determined. The resulting co-ordinates of the support positions are used to insert the supports

The reverse guillotine tribometer for evaluation of sliding wear of Additive Manufactured fixtures

Purpose – The purpose of this paper is to present a custom-built tribometer that mimics the wear of additive manufactured fixtures used in inspection of sheet metal components. Design/methodology/approach – Referring to the inspection of sheet metal parts, the fixture undergoes sliding wear during loading and unloading phases of the quality control operation. A new wear test is proposed to mimic the actual wearing conditions of the fixtures because the standards are deemed insufficient. In the tribometer, a cylindrical Alumide cantilever beam is made to slide back and forth inside a slightly bigger hole cut into a nickel-plated steel sheet. The sheet is spring loaded such that it applies a force on the specimen. The wear on the beam is measured after every 500 cycles of the beam motion. Findings – Results of some first test trials are reported to evaluate the durability of Alumide fixtures fabricated by selective laser sintering. The results are also compared to those obtained for a machined fixture made of an Al-Cu alloy. Practical implications – The proposed wear test estimates the life time of additive manufactured fixtures in terms of numbers of inspected components. The test can be extended to different materials to compare their durability. Originality/value – Today, the fabrication of custom fixtures by means of additive manufacturing technologies is a reality in many manufacturing industries. The advantage of using those production technologies for custom fixtures is well assessed in literature in terms of manufacturing times and costs, whereas little attention was given to the life time and wear behaviour of fabricated fixtures. For its practical implication, the fixture durability is indeed very important for manufactures

Automated fixture design for a rapid machining process

Rapid prototyping techniques for CNC machining have been developed in an effort to produce functional prototypes in appropriate materials. One of the major challenges for rapid machining is to develop an automatic fixturing system for securing the part during the machining process. The method proposed in this paper is the use of sacrificial fixturing, similar to the support structures in existing rapid processes like Stereolithography. During the machining process, sacrificial supports emerge incrementally and, at the end of the process, are the only entities connecting the part to the stock material. This paper presents methodologies for the design of sacrificial support structures for a rapid machining process and illustrates them using a complex sample part machined in the laboratory

EFFICIENCY OF FLEXIBLE FIXTURES: DESIGN AND CONTROL

The manufacturing industries have been using flexible production technologies to meet the demand for customisation. As a part of production, fixtures have remained limited to dedicated technologies, even though numerous flexible fixtures have been studied and proposed by both academia and industry. The integration of flexible fixtures has shown that such efforts did not yield the anticipated performance and resulted in inefficiencies of cost and time. The fundamental formulation of this thesis addresses this issue and aims to increase the efficiency of flexible fixtures.To realise this aim, the research in this thesis poses three research questions. The first research question investigates the efficiency description of flexible fixtures in terms of the criteria. Relative to this, the second research question investigates the use of efficiency metrics to integrate efficiency criteria into a design procedure. Once the efficiency and design aspects have been established, the third research question investigates the active control of flexible fixtures to increase their efficiency. The results of this thesis derive from the outcome of seven studies investigating the automotive and aerospace industries. The results that answer the first research question use five criteria to establish the efficiency of flexible fixtures. These are: fundamental, flexibility, cost, time and quality. By incorporating design characteristics in respect of production system paradigms, each criterion is elaborated upon using relevant sub-criteria and metrics. Moreover, a comparative design procedure is presented for the second research question and comprising four stages (including mechanical, control and software aspects). Initially, the design procedure proposes conceptual design and verification stages to determine the most promising flexible fixture for a target production system. By executing detailed design and verification, the design procedure enables a fixture designer to finalise the flexible fixture and determine its efficiency. Furthermore, a novel parallel kinematics machine is presented to demonstrate the applicability of the design procedure’s analytical steps and illustrate how appropriate kinematic structures can facilitate the efficiency-orientated design of flexible fixtures.Based on the correlation established by the controller software’s design procedure, the active control of flexible fixtures directly affects the quality criterion of flexible fixture efficiency. This provides the answer to the third research question, on general control strategies for active control of flexible fixtures. The introduction of a system model and manipulator dynamics proposes force and position control strategies. It is shown that any flexible fixture using a kinematic class can be controlled, to regulate the force and position of a workpiece and ensure that process nominals are preserved. Moreover, using both direct and indirect force control strategies, a flexible fixture’s role in active control can be expanded into a system of actively controlled fixtures that are useful in various processes. Finally, a position controller is presented which has the capacity to regulate both periodic and non-periodic signals. This controller uses an additional feedforward scheme (based on the Hilbert transform) in parallel with a feedback mechanism. Thus, the position controller enables flexible fixtures to regulate the position of a workpiece in respect of any kind of disturbance

Open source multi-Head 3D printer for polymer-metal composite component manufacturing

As low-cost desktop 3D printing is now dominated by free and open source self-replicating rapid prototype (RepRap) derivatives, there is an intense interest in extending the scope of potential applications to manufacturing. This study describes a manufacturing technology that enables a constrained set of polymer-metal composite components. This paper provides (1) free and open source hardware and (2) software for printing systems that achieves metal wire embedment into a polymer matrix 3D-printed part via a novel weaving and wrapping method using (3) OpenSCAD and parametric coding for customized g-code commands. Composite parts are evaluated from the technical viability of manufacturing and quality. The results show that utilizing a multi-polymer head system for multi-component manufacturing reduces manufacturing time and reduces the embodied energy of manufacturing. Finally, it is concluded that an open source software and hardware tool chain can provide low-cost industrial manufacturing of complex metal-polymer composite-based products

Reliability Analysis of On-Demand High-Speed Machining

Current trends in high-speed machining aim to increase manufacturing efficiency by maximizing material removal rates and minimizing part cycle times. This project explores three related technologies and presents a system design for rapid production of custom machined parts. First a reliability analysis in high-speed machining of thin wall features is put forth with experimental results. Second an implementation of on-demand manufacturing is presented with emphasis on flexibility and automation. Finally innovative manufacturing cell design is used to drive costs down by optimizing material and information flow. The resulting high-speed on-demand machining cell design employs effective techniques to reduce production time, meet changing customer needs, and drive down costs

Process planning for the rapid machining of custom bone implants

This thesis proposes a new process planning methodology for rapid machining of bone implants with customized surface characteristics. Bone implants are used in patients to replace voids in the fractured bones created during accident or trauma. Use of bone implants allow better fracture healing in the patients and restore the original bone strength. The manufacturing process used for creating bone implants in this thesis is highly automated CNC-RP invented at Rapid Manufacturing and Prototyping Lab (RMPL) at Iowa State University. CNC-RP is a 4th axis rapid machining process where the part is machined using cylindrical stock fixed between two opposing chucks. In addition to conventional 3 axes, the chucks provide 4th rotary axis that allows automated fixturing setups for machining the part. The process planning steps for CNC-RP therefore includes calculating minimum number of setup orientations required to create the part about the rotary axis. The algorithms developed in this thesis work towards calculating a minimum number of orientations required to create bone implant with their respective surface characteristics. Usually bone implants may have up to 3 types of surfaces (articular/periosteal/fractured) with (high/medium/low) finish. Currently CNC-RP is capable of creating accurate bone implants from different clinically relevant materials with same surface finish on all of the implant surfaces. However in order to enhance the functionality of the bone implants in the biological environment, it is usually advisable to create implant surfaces with their respective characteristics. This can be achieved by using setup orientations that would generally isolate implant surfaces and machine them with individual finishes. This thesis therefore focuses on developing process planning algorithms for calculating minimum number of orientations required to create customized implant surfaces and control related issues. The bone implants created using new customization algorithms would have enhanced functionality. This would reduce the fracture healing time for the patient and restore the original bone strength. The software package created using new algorithms will be termed as CNC-RPbio throughout in this thesis The three main tasks in this thesis are a) calculating setup orientations in a specific sequence for implant surfaces b) Algorithms for calculating a minimum number of setup orientations to create implant surfaces c) Machining operation sequence. These three research tasks are explained in details in chapter 4 of this thesis. The layout of this thesis is as follows. Chapter 1 provides introduction, background and motivation to the research in this thesis. Chapter 2 provides a literature review explaining different researches conducted to study the effects of different surface finish on the bone implants on their functionality. It also presents different non-traditional and RP techniques used to create bone implant geometries with customized surfaces, their advantages and limitations. Chapter 3 gives the overview of process planning algorithms used for CNC-RP and those needed for CNC-RPbio. Chapter 4 is the main chapter of the thesis including process planning algorithms for rapid machining of bone implants with customized surfaces using CNC-RP in details, while Chapter 5 provides Conclusions and Future work