Stereolithography Molds Research Articles

SLA-Based Injection Molding Tool Inserts: Challenges, Innovations, and Future Prospects

Stereolithography (SLA), a key technology in additive manufacturing, has transformed the production of injection molding tool inserts by enabling rapid prototyping and cost-effective smallscale production. SLA utilizes photopolymer resins to fabricate intricate, high-precision molds, reducing lead times and costs. However, challenges such as limited mechanical strength, lower thermal resistance, and slower heat dissipation compared to traditional materials constrain its broader adoption. This paper reviews the application of SLA in injection molding, emphasizing advancements in high-performance resins that improve durability, thermal stability, and mechanical properties. Key factors affecting mold performance, including material flowability, cooling times, and injection pressure, are discussed alongside optimization strategies like modular designs and post-processing techniques. While SLA molds may not rival traditional tools for high-stress applications, they excel in rapid tooling and prototyping. As material and process innovations continue, SLA is poised to play a transformative role in modern injection molding, bridging additive and traditional manufacturing.

Quick-Delivery Mold Fabricated via Stereolithography to Enhance Manufacturing Efficiency.

The ever-growing demand for reducing costs and decreasing the time to market in today's plastics industry makes rapid tooling and rapid prototyping highly researched areas. Stereolithography (SLA)-manufactured injection mold inserts make it possible to produce prototype parts rapidly and cost-effectively. To utilize SLA in the injection molding industry, two steps have to be considered. The first is to identify suitable SLA process and post-thermal curing process parameters to enhance the mechanical and thermal characteristics. The second is to verify the applicability of SLA-manufactured molds for use in the injection molding industry. IA comprehensive study was performed to find the optimum process parameters for an SLA mold with excellent mechanical and thermal properties and to verify the applicability of the mold. First of all, the mechanical and thermal properties of samples manufactured based on various laser powers and heat treatment at different temperatures were analyzed with a tensile test, DSC, and TMA according to the degree of cure. On the basis of the results from those tests, an SLA mold was designed and fabricated with the optimum mechanical and thermal properties. In addition, the SLA mold was assembled into an injection machine, and an injection molding test was conducted. The SLA mold endured during the injection cycle, and 500 shots were successfully injected without damaging the mold, which resulted in reaching the quick-delivery mold standard. Finally, we demonstrate that SLA is an effective technology to produce molds for use in the injection molding industry.

Tissue transformation mold design and stereolithography fabrication

PurposeTo obtain a vascularized autologous bone graft by in-vivo tissue transformation, a biocompatible tissue transformation mold (TTM) is needed. An ideal TTM is of high geometric accuracy and X-ray radiolucent for monitoring the bone tissue formation. The purpose of this study is to present the TTM design and fabrication process, using 3D reconstruction, stereolithography (SLA) and silicone molding.Design/methodology/approachThe rat mandible, the targeted bone graft, was scanned by micro-computed tomography (CT). From the micro-CT images, the 3D mandible model was identified and used as the cavity geometry to design the TTM. The TTM was fabricated by molding the biocompatible and radiolucent silicone in the SLA molds. This TTM was implanted in a rat for in vivo tests on its biocompatibility and X-ray radiolucency.FindingsSLA can fabricate the TTM with a cavity shape that accurately replicates that of the rat mandible. The bone formation inside of the silicone TTM can be observed by X-ray. The TTM is feasible for in vivo tissue transformation for vascularized bone reconstruction.Research limitations/implicationsResearch of the dimensional and geometrical accuracy of the TTM cavity is required in the future study of this process.Practical implicationsThe TTM fabricated in this presented approach has been used for in-vivo tissue transformation. This technique can be implemented for bone reconstruction.Originality/valueThe precision fabrication of the TTMs for in-vivo tissue transformation into autogenous vascularized bone grafts with complex structures was achieved by using SLA, micro-CT and silicone molding.

Fabricating hollow turbine blades using short carbon fiber-reinforced SiC composite

The development of hollow turbine blades fabricated by nickel-base superalloy is limited by its high density and low operating temperature (<1,100 °C). A new technology for fabricating hollow turbine blades of fiber-reinforced SiC composite was put forward. The chemical corrosion process of DSM Somos 19120 resin mold was investigated, and the pyrolysis of phenolic resin and the infiltration of liquid silicon were analyzed by using scanning electron microscope and X-ray diffraction. The influence of carbon fiber content on fracture strength and fracture toughness of fiber-reinforced SiC composite was investigated using the measurement of three-point flexural strength test. Results showed that stereolithography molds of photosensitive resin were corroded perfectly using KOH alcohol water solution. The porous carbon preforms were obtained after phenolic resin was pyrolyzed from 400 to 800 °C, which were then infiltrated with molten silicon to gain SiC matrix at the temperature of 1,450 °C in 1 h. The fracture strength and fracture toughness of SiC ceramic matrix were enhanced with the increase of short carbon fiber content. The maximum fracture strength and fracture toughness of samples were about 270 MPa and 5.1 MPa m1/2, respectively. Finally, hollow turbine blades were successfully fabricated using short carbon fiber-reinforced SiC composite.

Rapid casting of turbine blades with abnormal film cooling holes using integral ceramic casting molds

Film cooling is an important cooling method to decrease the turbine blade surface temperature, and its average cooling efficiency is mainly dependent on the cooling structures of internal passageways and the shapes of film cooling holes. Compared with standard cylindrical film cooling holes, abnormal film cooling holes have higher average cooling efficiency. But it is difficult to manufacture these holes using traditional machining methods. In this paper, a novel process was developed to fabricate turbine blades with abnormal film cooling holes by combining stereolithography (SL) technology with gelcasting technology. To decrease the drying shrinkage, the freeze-drying technique was applied to treat the wet ceramic casting mold green body surrounded by the SL mold, and the proper sintering process parameters were determined for lowering the sintered shrinkage. Finally, the integral ceramic casting mold was obtained, and a turbine blade with converging–diverging film cooling holes was rapidly cast to verify the feasibility of the proposed process.

우레탄레진(TSR-755)을 이용한 시작형몰드의 냉각채널 배치에 따른 영향 해석

본 연구에서는 시작형 몰드재료로 우레탄 레진(TSR-755)을 이용하여 레이저 조형으로 다양한 형태의 냉각 채널을 가진 몰드로 가공했을 경우, 사출성형 상용패키지(Simpoe-Mold)를 사용하여 냉각채널 변화에 따라 사출물의 냉각시간과 변형량을 비교 검토 하였다. 해석결과, 사출물 주변의 적절한 냉각채널배치로 기존 금속재질의 시작형 몰드 대비 19% 최대 변형량 감소와 46%의 냉각시간 단축이 가능한 것으로 나타났다. The urethane based on prototype mold is very useful for making prototype. Especially, the method of stereolithography mold was turned out to be rapid and accurate 3-dimensional modeling data. Urethane resin (TSR-755) has heat resistant and is good for make hundreds of prototypes. In this study, we compared with various designed cooling channel and analyzed of cooling effect and deformation using commercial code Simpoe-Mold for injection mold. As a result, efficiently arranged cooling channel could make 19% of shrinkage to reduce and 46% cooling time to reduce.

The experimental study on the defects occurrence of SL mold in injection molding

Past experience has shown that the defects occurrence in injection-molded parts of metal mold included weld line, flow mark and solid skin. In this study, a thin wall cavity is designed as flow path for plastic injection mold. The injection molding tests were performed by using metal mold and stereolithography (SL) mold to compare with the flow behavior and defects occurrence of flat parts. The experiments were performed with various process parameters to investigate the defects occurrence in the injection-molded parts. The experimental results showed that defects occurrence has close relation with injection speeds and mold temperatures. Flow marks of SL mold occur more easily when the mold temperature and the injection speed are low. Moreover, the injection-molded parts were examined whether the surface defects (flow mark and weld line) occurred and analyzed as the reference for the future SL mold design.

Stereolithography mold life extension using gas‐assisted injection

PurposeThe purpose of this work is to extend the life of plastic injection molds made by stereolithography through the use of gas‐assist technology.Design/methodology/approachPolypropylene parts were made by injection molding in stereolithography molds with and without gas‐assist technology. The mold life was evaluated by observing the number of parts produced before the breakage of each of small core pins and the ejection force was measured.FindingsWhen using gas‐assisted injection molding (GAIM), the core pin life was approximately doubled, the average cavity pressure and the average mold temperature were reduced, and there was a three‐fold increase in ejection force. Also, the core pin location had a very dramatic effect on the life.Research limitations/implicationsThis study suggests research into understanding the relationship between ejection force and mold failure, testing the mechanical properties of the parts and identifying reliable design rules for parts produced by GAIM. Research into other low pressure injection techniques and the viability of using a wider set of polymer materials also appears promising.Practical implicationsThe result of this research encourages molders who have abandoned the use of stereolithography tools after a few unsuccessful attempts to consider using GAIM with stereolithography molds.Originality/valueThis is a novel use of GAIM technology to extend the lives of molds fabricated by stereolithography.

Experimental Study of Demolding Properties on Stereolithography Tooling

Direct tooling using stereolithography (SL) photopolymer has been developed as rapid tooling for short-run injection molds. However, the tool strength, thermal conductivity, and erosion resistance of SL mold are lower than that of the conventional metal mold. Previous study has showed that the tool life was limited under 200 shots and tool damage often occurs during part ejection. In this paper, experimental data from a demolding properties test are presented and discussed. The experiments were performed using various cooling time, hold pressure, and mold temperature. The experimental data were analyzed by measuring demolding force and surface roughness to evaluate tool life and failure mechanism in order to obtain a working range for the process parameters. The test result shows that the demolding force has close relation with cooling time and mold temperature.

Numerical Molding Simulation for Rapid-Prototyped Injection Molds

: Injection molding is a very mature technology, but the growth of layer-build, additive, manufacturing technologies (rapid prototyping, RP) has the potential of expanding injection molding into areas not commercially feasible with traditional molds and molding techniques. This integration of injection molding with rapid prototyping has undergone many demonstrations of potential. What is missing is the fundamental understanding of how the modifications to the mold material and RP manufacturing process impact both the mold design and the injection molding process. In addition, numerical simulation techniques have now become helpful tools of mold designers and process engineers for traditional injection molding. But all current simulation packages for conventional injection molding are no longer applicable to this new type of injection molds, mainly because the property of the mold material changes greatly. In this paper, an approach to accomplish numerical simulation of injection molding into rapid-prototyped molds is established and a corresponding simulation system is developed. For verification, an experiment is also been carried out with an RP fabricated SL mold. Stereolithography (SL) is an original and typical rapid-prototyping method, which is chosen as the study object in the paper.

Integrated simulation of the injection molding process with stereolithography molds

Functional parts are needed for design verification testing, field trials, customer evaluation, and production planning. By eliminating multiple steps, the creation of the injection mold directly by a rapid prototyping (RP) process holds the best promise of reducing the time and cost needed to mold low-volume quantities of parts. The potential of this integration of injection molding with RP has been demonstrated many times. What is missing is the fundamental understanding of how the modifications to the mold material and RP manufacturing process impact both the mold design and the injection molding process. In addition, numerical simulation techniques have now become helpful tools of mold designers and process engineers for traditional injection molding. But all current simulation packages for conventional injection molding are no longer applicable to this new type of injection molds, mainly because the property of the mold material changes greatly. In this paper, an integrated approach to accomplish a numerical simulation of injection molding into rapid-prototyped molds is established and a corresponding simulation system is developed. Comparisons with experimental results are employed for verification, which show that the present scheme is well suited to handle RP fabricated stereolithography (SL) molds.

The use of stereolithography rapid tools in the manufacturing of metal powder injection molding parts

The utilization of stereolithography molds in the manufacture pre-series for injection molded plastic parts aims to reduce costs throughout the product life-time, but mainly during design and manufacturing phases. The use of this Rapid Tooling technique in powder metal injection molding is evaluated in this work. One of the greatest differences between traditional and stereolithography tools is related to the heat conductivity of the materials employed. For example, steel molds have a heat conductivity coefficient 300 times higher than molds made with the photosensitive resin used in the stereolithography process. The discrepancy regarding the cooling rate of the molded parts during the injection cycle must be compensated with adjustments in the injection molding parameters, such as temperature, pressure and speed. The optimization of these parameters made it possible to eject green parts from the mold without causing defects which would become evident in debinding and sintering stages. The dimensional analysis performed at the end of each case study showed that the shrinking factor of the component after the sintering had the same value obtained for components using traditional metallic molds. Moreover, the dimensional error remains under 2% which can be considered low for a pre-series of components (or prototype series).

A Reverse Glue Approach to Automated Construction of Multi-Piece Molds

Mold design can be a difficult, time-consuming process. Determining how to split a mold cavity into multiple mold pieces (e.g., core, cavity) manually can be a tedious process. This paper focuses on the mold construction step of the automated mold design process. By investigating glue operations and its relations with parting faces, an approach based on a new reverse glue operation is presented. The key to the reverse glue operation is to generate parting faces. A problem definition of parting face generation for a region is provided. Correspondingly, three face generating criteria are identified. Based on the parting lines of a region, our algorithms to generate the parting faces are presented. Our mold construction algorithms for two-piece molds and multi-piece molds are also presented with brief discussions. Some industrial examples are provided which illustrate the efficiency and effectiveness of our approach. We tested our mold designs by fabricating stereolithography mold inserts (a rapid tooling method) and molding parts.

Properties of rapid prototype injection mold tooling materials

AbstractEpoxy acrylate‐based sterolithography resins have been used successfully as tools for injection molding. Molds made out of these resins fail at distinct times: during the first injection of plastic; during the first part first ejection; during either injection or ejection, but after a certain number of parts have been produced, which can be compared to a fatigue process. This paper presents corelations between measured properties of stereolithography molds and injection molding processing conditions so as to understand and predict mold failure. The study focuses on two stereolithography resins (SL 7510 and SL 7510) and one epoxy‐based composite material used for the high speed machining of prototype molds (Renboard). Rapid tooling materials are studied in fatigue, tensile, and fracture at injection molding operating temperatures and at room temperature. Finally, a method to address failure of molds is proposed using the theory of fracture.

Release behavior for powder injection molding in stereolithography molds

Adhesion has been measured between a powder injection molded (PIM) part and the stereolithography epoxy mold surrounding it after cooling. Analysis of release behavior suggests a link to the thermal properties of the mold material. Subsequent measurements of cooling in the part and at the part/mold interface are consistent with a one‐dimensional heat transfer model. Adhesion development at the part/mold interface shows a complex dependence on the thermal characteristics of both the mold and the PIM feedstock.

Draft angle and surface roughness effects on stereolithography molds

Stereolithography (SL) is a rapid prototyping process, which allows one to build complex shapes quickly. Current research investigates the possibilities of using this process to make injection molds. This would allow designers to manufacture and test molds easily and rapidly. One of the main issues with this technique is the effects of its surface on the part. Molds built by SL have high roughness. This gives rise to a high friction force between the part and the mold, and increases the ejection force needed to eject the part from the mold. High ejection forces often lead to damage or breakage of the part and the mold. Research was undertaken on the effects of draft angle and roughness on ejection forces. It was found that increasing the draft angle does not necessary assist the ejection of the part. As the draft angle increases, the roughness and hence the friction force between the part and the mold also increase. There is a trade-off between draft angle and roughness. A model based on Glanvill's equation was developed to predict ejection force and was consistent with experimental results.

Studies in Direct Tooling Using Stereolithography

Rapid prototyping (RP) technologies are valuable for reducing product development cycle times by creating physical models for visual inspection and form-fit studies directly from a 3-D database. However, if the part is meant for volume production, tooling will be necessary. Tool development and fabrication using conventional techniques and materials is time consuming and expensive. Therefore, it is risky to commit to production tooling in the initial stages of product development. Low volume prototyping is highly desirable but requires a small number of parts (hundreds) to be produced quickly and economically. To meet this need, this paper studies direct tooling using the RP technology of stereolithography (SL) to produce photopolymer tools. Without modifications to improve thermal response, SL molds will not be able to produce production-quality parts. This experimental study quantifies the thermal characteristics of an SL mold for a simple part geometry. Several modifications that affect thermal properties are then studied and both thermal response and part quality are quantified. The data indicate that although it is possible to change the thermal response of an SL mold and obtain reasonable parts, the ability to duplicate traditional mold characteristics (and thus simulate part production before committing to high-volume tooling) is probably not practical. Similar results were achieved when using a more realistic final-part geometry on a production mold machine. Although mold process simulation using SL molds could provide useful design guidance for traditional high-volume part production, this work suggests that these SL molds can be used for low-volume part production. By reducing mold fabrication time and costs, low-volume part production could become cost-effective using traditional high-volume manufacturing techniques. [S1087-1357(00)00702-4]