Rapid Tooling Process Research Articles

Computer aided rapid tooling process selection and manufacturability evaluation for injection mold development

Injection mold development lead time has been reduced presently by over 50% by employing rapid prototyping based tooling methods. Rapid tooling methods however, have certain limitations in terms of mold material, accuracy, surface finish, and mold life. The relevant process knowledge, especially for newer routes, is not very well established, resulting inconsistent or inappropriate rapid tooling (RT) process selection and mold design incompatibility. This paper presents a computer aided rapid tooling process selection and manufacturability evaluation methodology for injection molding, supported by mold cost estimation models and RT process capability database. Rapid tooling process selection is based on process capability mapping in quality function deployment (QFD) against a set of tooling requirements that are prioritized through pairwise comparison using analytical hierarchal process (AHP). The mold manufacturability for the selected RT process is carried out using fuzzy-analytic hierarchy process (fuzzy-AHP) to identify problem features, if any. This is followed by estimating the cost of RT mold and comparing it with a conventional mold, using cost models developed based on the concept of cost drivers and cost modifiers. The entire methodology has been implemented in a software program using Visual C++ in Windows environment and demonstrated on an experimental mold as well as industrial cases. The proposed methodology enables selecting an appropriate rapid tooling process for a given injection mold requirement, and identifying critical features that could be modified to improve manufacturability, thereby achieving better quality and lower cost of molded parts along with shorter lead time.

Rapid tooling form accuracy estimation using region elimination adaptive search based sampling technique

PurposeThe purpose of this paper is to present the results of an investigation on the straightness, flatness and circularity achievable on two direct RT methods: direct metal laser sintering (DMLS) and stereolithography (SLA).Design/methodology/approachThe steps included manufacturing of samples in eight custom designs with widely used geometric features, intelligent sampling of measurement data, and estimation of corresponding form tolerance by the least square method (LSM). The region elimination adaptive search‐based sampling method involved selecting additional sampling points around the maximum deviation in both positive and negative directions from the corresponding reference feature. The LSM solutions, which are commonly used in metrology, are used to estimate the form tolerances considering the best points along with initial measurement data points.FindingsApplication of the region elimination search‐based sampling method enables form tolerance estimation from a limited number of sample measurements. The study of the DMLS and SLA processes suggested that form accuracy of SLA samples are relatively poor, though their dimensional accuracy is much better than DMLS.Research limitations/implicationsThis paper was focused on estimating the form tolerances based on limited number of measurement data using region elimination search‐based sampling technique. It was assumed that build process parameters suggested by the material and RP systems vendors gives optimum results, presently it does not cover the effect of geometry and other causes of errors on form accuracy.Practical implicationsThere are two major applications of this investigation and the corresponding knowledge base: evaluating the process capabilities of different rapid tooling processes for comparison and for selecting an appropriate process; and allocating tolerance based on manufacturability considerations, so that the designs are compatible with the process, leading to fewer iterations. A similar approach can be used for updating the capabilities of an improved process as well as include newer processes to develop a comprehensive database of RT process capabilities.Originality/valueIn most of the previous benchmarking studies, a given RT process is compared with conventional practice or a limited number of other RT processes, the capabilities in terms of dimensional accuracy, form tolerance, and surface properties (surface finish, wear, and scratch resistance) have not been studied very well. To the best of authors' knowledge, no efforts have been made to estimate form tolerances of the parts or tooling produced by rapid prototyping and tooling processes. Application of the region elimination search‐based sampling technique enables estimation of form tolerances that saves costly experimentations. It appears to be completely new in the rapid prototyping and tooling domain.

Rapid tooling manufacturability evaluation using fuzzy-AHP methodology

Rapid tooling (RT) processes driven by rapid prototyping (such as stereolithography and selective laser sintering) can reduce mold development lead-time by 50% or more, though there are certain limitations in terms of mold materials, accuracy, and surface finish. This paper presents a systematic approach for manufacturability analysis of molds produced by rapid tooling methods, based on three aspects: mold feature manufacturability, secondary elements compatibility, and cost effectiveness. The geometric features of functional elements of the mold (core, cavity, side core, etc.) are evaluated for manufacturability using fuzzy-analytic hierarchy process (Fuzzy-AHP) methodology. The secondary elements of mold (parting surface, ejectors, cooling lines, etc.) are checked for compatibility with RT mold properties (machinability, wear resistance, and surface evenness). Finally, the cost of RT mold is estimated using a semi-empirical model based on cost drivers and cost modifiers, and compared with that of a conventional mold. The methodology has been demonstrated with an experimental mold. It is useful not only for RT mold process selection, but also for identifying minor modifications to a mold design to improve its manufacturability and economy.

The Development of Direct Metallic Rapid Tooling System

In recent years, rapid tooling (RT) has become increasingly important because of the requirement of rapid manufacturing. RT can be used to produce temporary molds as well as permanent molds in mass production. RT provides more benefits from the design stage to mass production. The objective of this research is to develop the direct metallic RT system and identify process parameters of laser cladding. A 2.5-kW Nd-AG laser system, a metallic powder feeder system, a lateral powder nozzle system, a PC-based motion controller, and a shielding gas-supply system are incorporated for the hardware architecture in the proposed RT system. The critical process parameters influencing the dimensional accuracy were analyzed with Taguchi's experimental design. From the analysis of variance computational results, the factors Scanning speed and Tool path offset are the influential factors affecting the layer thickness of RT parts. From the experimental results, the dimensional accuracy of the dual nozzle RT system is better than the single-nozzle RT system. Finally, the proposed RT system could fabricate the mold inserts. After finishing the mold inserts and assembling the plenary injection mold, the injection molding machine can generate acrylonitrile butadiene styrene plastic parts with excellent quality. Note to Practitioners-Rapid prototyping (RP) technologies have provided a new way of making models or producing visualization prototype in a fast fashion. However, there is an urgent demand from the industry for much faster ways to make physical prototypes, with the desired material using the appropriate production method. RP technologies have introduced a new generation of RT processes. Producing tooling directly from computer-aided-design (CAD) models is regarded as an important process of reducing the cost and time to market for new products. In this paper, a direct metallic rapid tooling (RT) system is developed to fabricate the metallic parts and molds directly from 3-D CAD models. The experimental investigations are implemented to study the proposed RT system. Using Taguchi's method, the critical performance process parameters have been analyzed. The analysis of variance method is used to decide the important process parameters. The developed RT system can produce the mold inserts directly. After assembling the plenary injection mold, the Acrylonitrile butadiene styrene ABS plastic parts have been generated from this RT mold to demonstrate the success of the process. In the future, it is possible to develop a grading alloy RT system, which can control the ratio of the alloy grading layers. Because the grading alloy rapid mold can use varied metallic powders with varied ratio, the cooling time and the residual stress can be reduced. Furthermore, the RT system can also adopt the coaxial nozzle which can be integrated with the optical system. The advantage of the coaxial nozzle is the independence of the powder supply direction in which the workpiece moves

Rapid hard tooling process selection using QFD‐AHP methodology

PurposeTo provide a systematic framework for mold designers, that can be used for rapid tooling (RT) process selection and prioritization of process parameters.Design/methodology/approachThis paper presents a QFD‐AHP methodology which has three phases. The first phase involves prioritizing the tooling requirements (driven by customer preferences) against a set of die/mold development attributes (such as product material, geometry, and die material and production order) through pair‐wise comparison using analytical hierarchal process (AHP). These priority ratings are used for selecting the most appropriate tooling process using quality function deployment (QFD) in the second phase. Finally, QFD is used again for identifying critical process parameters (such as layer thickness, scan pitch and laser power) for the selected RT process.FindingsThe QFD‐AHP methodology has been illustrated with industrial examples on RT for molded parts. The molds were fabricated using direct metal laser sintering and spray metal tooling processes, for example, 1 and 2, respectively, to prove that the methodology can be easily implemented in tool rooms. The issues noted in these experimental studies are also discussed for the benefit of researchers.Research limitations/implicationsThe capabilities of the RT processes presented in the paper reflect the experience of the research team in RT development. The QFD‐AHP methodology will give progressively better results with a growing body of RT process knowledge.Practical implicationsThis investigation is a key step towards the goal of developing a comprehensive system for RT process selection and manufacturability evaluation. The mold designer can use this QFD‐AHP process selection methodology, prior to detailed manufacturability analysis, to better realize the benefits of RT technologies.Originality/valueThe proposed QFD‐AHP methodology is a new approach for the tooling process selection domain, and has not been reported earlier; this can be easily used for similar applications for any manufacturing domain.

PERMANENT RAPID PROTOTYPED MOLDS FOR THIN WALL MAGNESIUM CASTING

Rapid tooling processes are now well known and largely implemented in the plastic injection industries. Harsh conditions related to metal casting or injection do not allow such rapid tooling processes to be directly applicable. This paper focuses on magnesium alloy casting in rapid prototyped mold with thin walls created by Direct Metal Laser Sintering. Such molds are anisotropic, due to special laser exposure between their skin and core. Hence, experimental results from casting are described and analyzed. The results can help companies improve their rapid prototyping means in the field of magnesium casting of precise parts in permanent molds.

An advanced cutting trajectory algorithm for laminated tooling

PurposeTo provide an advanced cutting trajectory algorithm for the profiled edge laminae (PEL) rapid tooling (RT) process, which is ideally suited for large‐scale dies and molds. The process involves assembling an array of laminae whose top edges are simultaneously profiled and beveled using a line‐of‐sight cutting method based on a CAD model of the intended tool surface.Design/methodology/approachThe cutting profiles for an individual tool lamina are based on intersection curves obtained directly from the CAD model, and generated with exact geometrical accuracy. Two adjacent slice profiles, which define a lamination's top edge and are represented as polylines, are stitched together using an adaptive surface reconstruction algorithm. A cutting trajectory algorithm then develops a series of suitable cutting vectors (i.e. position and cutting direction) that minimize abrasive waterjet (AWJ) cutting errors due to non‐uniform motion and variations in kerf geometry resulting from process parameter variations. The proposed cutting trajectory generation process is demonstrated virtually for an actual production tool.FindingsThe proposed algorithm yields well‐behaved AWJ cutting trajectories for individual lamina used in a PEL tool that are better than those obtained using any other algorithm found in the literature.Research limitations/implicationsThe algorithm is intended for use with AWJ cutting of PEL tool surfaces. Suggested future research includes assessment of the algorithm for other lamina cutting methods including laser cutting and wire‐type electro‐discharge machining, extending the algorithm to handle conformal cooling/heating channels and internal cavities, and application of the algorithm to several industrial tool case studies.Practical implicationsThe algorithm generates cutting trajectories directly from CAD geometry that are ideal for AWJ cutting of profiled edge lamina. It will simply make industrial implementation of the PEL RT process easier.Originality/valueThis paper provides a new cutting trajectory algorithm for the PEL RT process that is a significant improvement over comparable algorithms proposed in the literature.

Statistical process design for hybrid adaptive layer manufacturing

PurposeThis paper discusses the optimization of the process parameters for the hybrid‐layered manufacturing (HLM) process during its weld layer deposition with subsequent surface machining in attaining the desired accuracy and contour profile of the deposited weld layer thickness.Design/methodology/approachThe HLM process integrates the synergic metal inert gas (MIG) – metal active gas (MAG) welding process for depositing the metal layer of a desired slice thickness and perform the computer numerical control (CNC) machining process on the deposited layer to enhance both the surface quality and dimensional accuracy of the deposited layer. For the HLM process the weld bead geometry plays a vital role in determination of the layer thickness, surface quality, build time, heat input into the deposited layer and the hardness attained by the prototype. A feasible weld bead width and heights are to be formulated for the exterior contour weld path deposition and for the interior weld cladding. Thus, Taguchi methodology was employed with minimum number of trails as compared with classical statistical experiments. This study systematically reveals the complex cause‐effect relationships between design parameters and performance.FindingsStatistical design of experiments using orthogonal arrays and signal‐to‐noise (S/N) ratios are performed to constitute the core of the robust design procedure. Experimental confirmations of the performance characteristic using the derived optimal levels of process parameters are provided to confirm the effectiveness of this approach.Research limitations/implicationsThe welding parameters such as current, voltage, arc length, wire feed rates, wire stick‐out distance, shielding gas, filler wire diameter, weld speed, etc. will influence on the deposited weld bead geometry. Further investigations are to be carried out during adaptive layer deposition on the induced thermal stresses and its influence on the hardness of the deposited weld layer.Originality/valueThis paper describes a low cost direct rapid tooling process, HLM. This unique methodology would reduce the cost and time to make molds and dies that are used in batch production.

Impact fracture study of epoxy-based composites with aluminium particles and milled fibres

Epoxy-based composites moulds are frequently used for wax and polymer materials injection. Tri-phase materials, composed by an epoxy resin, aluminium particles and milled fibres, were produced, with mechanical and thermal performances better than the single materials, increasing the competitiveness of the epoxy rapid tooling processes. Charpy impact tests were employed to obtain a qualitative indication of the composites toughness. The electronic instrumentation of these tests allows a more accurate differentiation of the impact behaviour of the neat resins, the aluminium filled resins and the tri-phase composites (composed by epoxy, aluminium particles and milled glass or carbon fibres), and to consequently tailor the composites mechanical properties for rapid tooling applications.

Experimental study of the deformation behaviour of compacted metal powders used in a new rapid tooling process

To examine the feasibility of a newly proposed rapid tooling process based on the backing of a metal shell with metal powders, the compressive deformation behaviour of selected metal powders and metal shells was investigated. It was found that the mechanical properties of the powder material and the mixing ratio of powders of different sizes had a significant effect on the compressive deformation behaviour of the compacted powders. Softer metal powders with the same compressive stress tended to produce greater plastic deformation and formed a block under a stress of 138 MPa. Mixing two or more powders of different sizes could significantly increase the deformation resistance of the compacted powders. Minimum plastic deformation was achieved when the fraction of the coarse powder in a binary powder mixture reached 0.77. Initial loading at a higher stress could minimize or eliminate the plastic deformation in subsequent loading cycles. This feature could be used advantageously in powder packing for the proposed new rapid tooling process. Some elastic properties of the compacted metal powders were also determined from the compression experimental data.

Feasibility study of a new rapid tooling process

The requirements for faster product development cycles, lower product cost and environmental sustainability are ever increasing in today’s globally competitive market. Tooling is a very important phase in the product manufacturing cycle. To overcome the shortcomings of long lead-time and high cost associated with conventional tooling processes, new tooling methods with shorter lead-time and lower cost are strongly under demand. In this study, the feasibility of the proposed new rapid tooling process based on back support of a metal shell with packed metal powders is examined. First, the effect of metal powder properties, such as powder shape, size, and size distributions, on powder-packing behaviour is investigated experimentally. Then, the compressive behaviours of the metal shell and the shell-powder assembly are analysed numerically with different compressive loading. The study indicates that the proposed new rapid tooling method can potentially be used for injection moulding applications.

Laser machining in die making—a modern rapid tooling process

Laser machining is a new, very flexible process in mould making especially, for the machining of filigree structures. This process is suitable for machining difficult-to-machine materials, like ceramics, carbide and hardened steel with excellent productivity and surface quality. Laser machining provides a number of advantages over the traditional electro discharge machining (EDM) in die making. It eliminates the expensive manufacture of electrodes, radically shortens the number of operations, reduces lead time from mould design to manufacture and provides excellent productivity and cost efficiency with good surface finish. The paper presents the investigation on surface quality, material removal, when machining with a combination of high-speed milling (HSM) and laser machining (LM) for roughing and finishing, respectively. The research covers the machining of a range of difficult-to-machine metallic and non-metallic materials used in the tool and die making industry. The input and output machining data, collected in a structured database, provide the key for process optimisation and allow for data update.

Some demands on rapid prototypes used as master patterns in rapid tooling for injection moulding

Injection moulded components are finding vigorously increasing applications in numerous sectors. The flexibility of the process allows complex components to be manufactured in high volumes in fully automated environments. Associated with such components are equally complex tools whose manufacture is both expensive and time consuming. It is therefore vital that the component design be evaluated thoroughly with regard to both performance and manufacturability before commitment is made to expensive production tooling. The use of a physical prototype often provides the best method of design evaluation. The major routes to prototype manufacture are; material removal, rapid prototyping and rapid tooling. Rapid tooling techniques provide the most representative route, with the ability to produce polymeric prototypes (often in final material) by an injection moulding process.Research has been undertaken into two rapid tooling processes; enhanced silicone moulding and sand moulding. Both processes involve casting material against a rapid prototype (master pattern) to form a mould which is then used in the manufacture of product prototypes by injection moulding. The focus of this paper is on the demands of these tooling techniques placed on rapid prototypes when used as master patterns. The demands are discussed in terms of surface finish, surface porosity, dimensional accuracy, thermal resistance and thermal expansion.

Dimensional accuracy of injection-moulded components produced in an enhanced silicone rubber mould

The inherent technical limitations of rapid prototyping systems have led to the development of rapid tooling techniques. These techniques are capable of producing prototypes in final materials by the intended manufacturing process. One rapid tooling process that provides a low cost and rapid route to the manufacture of injection-moulded thermoplastic components is enhanced silicone moulding. During the moulding cycle the mould deforms under the pressures and temperatures experienced and components produced suffer a loss of dimensional accuracy. An analytical and experimental investigation was undertaken to quantify the dimensional accuracy of components produced by the process, and to identify the moulding parameters which contribute to the loss of dimensional accuracy. A mould was produced from a stereolithography master pattern and used to injection-mould components in high-impact polystyrene under various moulding conditions. Moulded components produced were typically oversized with a loss of dimensional accuracy of the order of 0.3–0.6 mm. Two parameters, namely injection pressure and mould temperature, were found to have an influence on dimensional accuracy. The injection pressure causes the mould cavity to expand and results in manufacture of components which are oversized. Components produced at an injection pressure of 16MPa were on average 0.34 mm (1.3 per cent) oversized in width and 0.36 mm (11.3 per cent) oversized in depth. Those produced at an injection pressure of 20 MPa were oversized by an average of 0.45 mm (1.8 per cent) in width and 0.59 mm (18.6 per cent) in depth. An increase in mould temperature caused a reduction in the size of the mould cavity. This was because the rubber mould was restricted in a metal mould frame. The rubber mould expands into the free space of the cavity. Components produced at mould temperatures of 50, 70 and 90°C were oversized in width by an average of 0.37mm (1.5 per cent), 0.34 mm (1.3 per cent) and 0.20 mm (0.8 per cent) respectively.

Conversion of rapid prototyping models into metallic tools by ceramic moulding - an indirect rapid tooling process

INEGI developed a process to convert models made by rapid prototyping or conventional techniques into metallic moulds. The main purpose is to rapidly obtain prototype tools by casting a metal into a ceramic mould produced by mixing in variable proportions, ceramic particles, a liquid binder and a catalyst added to start a sol-gel reaction. This liquid slurry is poured into the box containing the mould to be reproduced. After a short period of time the ceramic mixture acquires a rubber consistency. The pattern is removed from the ceramic mould, which is fired and sintered in order to generate an inert mould with the desired strength in which most alloys can be cast. The effect of ceramic materials (shape, granulometric distribution, chemical composition), sintering conditions (time and temperature) and casting conditions (mould preheating temperature and pouring temperature) were studied in order to obtain ceramic moulds and, subsequently, metallic moulds with tailored properties (accuracy reproduction of details, low roughness and high mechanical strength).

Shelling strategies to save time in a rapid tooling process

Selective laser sintering can be used to manufacture injection mould inserts using an indirect metal laser sintering process, such as the RapidTool™ process commercialised by 3D Systems. The volume of material to be laser processed for insert manufacturing is very high when compared to that for plastic prototype manufacturing. Consequently, the time involved in the laser processing is also very long. This paper describes the development and assessment of shelling strategies to be applied in an indirect rapid tooling process aimed at reducing time in the process. The feasibility of the shelling idea has been confirmed and although the scanning system offers some limitations to the idea two strategies are presented as successful, open shell and closed shell, with a great potential to save time.

The effect of laser pulse width on multiple-layer 316L steel clad microstructure and surface finish

Multiple layer laser cladding is a flexible rapid prototyping and tooling process that allows a fully dense wall or surface to be fabricated from the consolidation of a metal powder. The microstructure and resultant physical properties of the material are determined by process parameters, one of which is the pulse width of the laser used. In this work, a CO 2 laser, operating at different pulse widths and in continuous mode is used to assess this effect. Microstructural characterisation of multiple layers of consolidated 316L steel is carried out and the dimensions, surface roughness and hardness of the built samples compared with the generating pulse widths.

Calculation of molten pool shape on directed plasma fabrication

Directed Plasma Fabrication (DPF) is a rapid tooling process based on controlled deposition of molten powder particles according to computer controlled patterns. It makes fully dense, near net shape metal components without molds or dies, and without forming, pressing or forging systems.Experimental works were carried out using conventional low current Plasma Transferred Arc Welding system, and metallic powder was stellite #21. Cylindrical shapes were successfully deposited with dimensions of 0.8–1.2mm wall thickness. Critical parameters were plasma current stability and powder supply. Other key factor was the melting efficiency M, which is defined as the ratio of given heat input into base metal and required heat input to melting of deposited metal. The other was is a non dimensional operating parameter, n proposed by N. Christensen. Better deposition efficiency was obtained in case of lower melting efficiency M, this means shorter arc length and slower traveling speed when the same plasma current conditions are applied.

Rapid Prototyping and Tooling of Custom-Made Tracheobronchial Stents

Rapid prototyping (RP) and rapid tooling (RT) techniques can be applied to the field of medicine primarily because of their ability to produce customised profiles and geometries in relatively short lead times. In this paper, the process by which these techniques can be applied for the production of customised tracheobronchial stents for the purpose of maintaining patency in an occluded respiratory tract is described. A comparison of RP systems was carried out to establish the preferred RP method to produce the master model. The vacuum casting RT process was then used to produce the stent.

Digital Photoelasticity: Advanced Techniques and Applications

Digital Photoelasticity: Advanced Techniques and Applications