Thermoforming Machine Research Articles

Bonding positional accuracy of attachments and marginal adaptation of in-house aligners - A quality improvement laboratory study.

To evaluate the 3D accuracy of attachment positioning and the adaptation of aligners to attachments using in-house templates made with either polyethylene terephthalate glycol (PETG) or ethylene-vinyl acetate (EVA) and either pressure or vacuum thermoforming machines. Overall, 140 test specimens were resin-printed. Templates for the attachment bonding were made with 1-mm EVA or 0.5-mm PETG laminates. Orthodontic aligners were manufactured with 0.75-mm PETG. The thermoplastification process was carried out using either vacuum or pressure machines. The positional differences between the virtual and bonded attachments were assessed in the X, Y and Z coordinates. The marginal adaptation between the aligners and the attachments was measured. Minor inaccuracies in the positioning of the attachments were observed in all combinations of thermoforming machines and plastic laminates used to fabricate the templates, mainly in the superior-inferior (Z) dimension. PETG performed better than EVA in the anterior region (p < .05). No association was found between thermoplastification machines and the accuracy of the positioning of the attachments (p > .05). While small misadaptations between the aligners and the attachments were observed, the EVA templates performed better than the PETG templates. The inaccuracy of the attachment positioning and the misadaptation of the aligners to the attachments were slight. The vacuum and pressure thermoplastification machines showed no difference in attachment positioning accuracy. The PETG template was better than the EVA template in the anterior region, but the EVA attachments presented a better adaptation to the aligners than the PETG attachments.

Maintenance Strategies for Industrial Multi-Stage Machines: The Study of a Thermoforming Machine.

The study of reliability, availability and control of industrial manufacturing machines is a constant challenge in the industrial environment. This paper compares the results offered by several maintenance strategies for multi-stage industrial manufacturing machines by analysing a real case of a multi-stage thermoforming machine. Specifically, two strategies based on preventive maintenance, Preventive Programming Maintenance (PPM) and Improve Preventive Programming Maintenance (IPPM) are compared with two new strategies based on predictive maintenance, namely Algorithm Life Optimisation Programming (ALOP) and Digital Behaviour Twin (DBT). The condition of machine components can be assessed with the latter two proposals (ALOP and DBT) using sensors and algorithms, thus providing a warning value for early decision-making before unexpected faults occur. The study shows that the ALOP and DBT models detect unexpected failures early enough, while the PPM and IPPM strategies warn of scheduled component replacement at the end of their life cycle. The ALOP and DBT strategies algorithms can also be valid for managing the maintenance of other multi-stage industrial manufacturing machines. The authors consider that the combination of preventive and predictive maintenance strategies may be an ideal approach because operating conditions affect the mechanical, electrical, electronic and pneumatic components of multi-stage industrial manufacturing machines differently.

High-capacity stacking apparatus for thermoforming machine – Part II: Structural design of the adjustable stacker driving mechanism

Part II presents the structural design of a high-capacity adjustable stacker mechanism for thermoforming machines which enables the receival, transport and stacking of cup-like products. It was previously established (please see Part I) that a four-bar linkage mechanism with a one-way clutch is the optimal solution for realizing the intermittent motion of the stacker conveyor. The main objective here is to enable the change of the stacker work parameters, with the goal of changing and adjusting the work stroke of the conveyor. Accordingly, there are two main requirements the solution needs to fulfill. The first is that of the regulation characteristic’s function – the relationship between the change of the work stroke and the change of the regulation parameter, must be linear, and the second is that it allows for regulation within a wide range. Due to this, the adopted solution proposed that two links have variable lengths. The input link should have discreet length values which correspond to different values of the conveyor work stroke, while the output link length should be continuously variable, within a narrow range thus ensuring linear regulation characteristic. Finally, it should be noted that this solution makes the stacker compatible with a wide array of products, which increases the productivity and flexibility, adjusting the stacker to receive a different product can be done quickly and easily and avoiding a halt in the production as it takes less time to adjust the stacker than the thermoforming machine.

High-capacity stacking apparatus for thermoforming machine – Part I: Synthesis of intermittent mechanisms as stacker driving units

The paper presents the type and dimensional synthesis of intermittent mechanisms for use in a thermoforming machine high-capacity stacking apparatus. The aim of this paper is to realize the intermittent motion of the working part of the stacker – conveyor, with a completely mechanical system that should enable the adjustment of the operating parameters of the stacker at a constant motor speed. Mechanical control ensures high positioning accuracy of the product ejection panel, as well as high repeatability of the motion cycle of the conveyor, which is key. Based on the set requirements, the concept of a planar mechanism of simple structure was chosen, which enables oscillatory movement of the output link for continuous motion of the input link, in combination with a one-way clutch (OWC). Four types of intermittent mechanisms have been proposed. However, multiple configurations of the same mechanism type can achieve the same output link motion interval, which is why 3 configurations for each mechanism type are considered, with a total of 4 output link motion intervals, which is 12 potential solutions for only one mechanism type. Afterwards, dimensional synthesis was performed for each type of mechanism by using the optimization method. Based on the analysis of the results, all of the mechanism types are potentially usable. After additional analyses, the optimal solution was chosen.

Application of parabolic blending for the estimation of thickness distribution in thermoformed products

The Parabolic Blending (PB) technique has been widely used in various research fields, such as rotor noise prediction, over the last few decades. However, in the literature, PB is not utilised for the thickness prediction of thermoformed products. In this study, Polystyrene (PS) sheets of various thicknesses were thermoformed using a lab-scale thermoforming machine. Firstly, thickness distributions in thermoformed PS products were obtained by the experimental method. Then, PB was used to estimate the thickness distribution of conical semi-finished thermoformed parts. The obtained results were then compared with the ones obtained experimentally. A comparison reveals that the use of PB provides more accurate thickness values than the experimental results. As a result, PB can be utilised for the prediction of thickness distribution in thermoformed products which have been formed by the same mould.

Reliability of a two‐dimensional demand‐based networked system with multistate components

AbstractExisting research on multistate system reliability has mainly focused on one‐dimensional systems such as parallel systems, linear sliding window systems, and linearly consecutively connected systems. However, two‐dimensional networked systems widely exist in real‐world applications such as lighting systems, monitoring systems, and computer network systems. This research considers a two‐dimensional networked system consisting of multistate components. The system fails if the cumulative performance of any row or any column cannot meet a predetermined demand. A novel reliability evaluation algorithm is proposed for the considered two‐dimensional networked system by extending the universal generating function technique. Furthermore, the proposed model and reliability evaluation algorithm are extended to a two‐dimensional networked system with phased missions. The proposed models and algorithms are illustrated by a matrix heating system in a thermoforming machine.

Thermoforming behavior of 3D-printed PLA sheets

Abstract Fused deposition modeling is one of the most well-known additive manufacturing methods. It might be considered the easiest way to produce particle reinforced composites or unreinforced sheets which are biodegradable and used in the packaging industry as well as for custom products. In this study, polylactic acid (PLA) sheets were produced by 3D printing and thermoformed using a lab-scale thermoforming machine. This article aims to determine the deformation behavior of 3d printed PLA sheets during thermoforming. In addition to experimental work, finite element analysis was performed to investigate the prediction capabilities of Mooney-Rivlin and Ogden models for PLA sheets. In addition, the initial thickness of the sheet was optimized using FEA and a python script to obtain final uniform thickness distribution. Thanks to 3D printing’s capability for printing sheets of variable thickness, sheets of variable thickness were printed to verify the material models. As a result, based on the thickness distribution obtained from the experimental study, Mooney-Rivlin and Odgen material models were found to be inadequate for representing the actual deformation behavior of PLA sheets.

Thermoforming behavior of 3D-printed PLA sheets

Abstract Fused deposition modeling is one of the most well-known additive manufacturing methods. It might be considered the easiest way to produce particle reinforced composites or unreinforced sheets which are biodegradable and used in the packaging industry as well as for custom products. In this study, polylactic acid (PLA) sheets were produced by 3D printing and thermoformed using a lab-scale thermoforming machine. This article aims to determine the deformation behavior of 3d printed PLA sheets during thermoforming. In addition to experimental work, finite element analysis was performed to investigate the prediction capabilities of Mooney-Rivlin and Ogden models for PLA sheets. In addition, the initial thickness of the sheet was optimized using FEA and a python script to obtain final uniform thickness distribution. Thanks to 3D printing’s capability for printing sheets of variable thickness, sheets of variable thickness were printed to verify the material models. As a result, based on the thickness distribution obtained from the experimental study, Mooney-Rivlin and Odgen material models were found to be inadequate for representing the actual deformation behavior of PLA sheets.

The influence of temperature on sheet lamination process when fabricating mouthguard on dental thermoforming machine.

Laminated custom-made mouthguards tend to delaminate with use; this is a problem in clinical use. Insufficient bonding strength causes delamination, and bonding strength is strongly affected by heating temperature during lamination. The present study aimed to evaluate the influence of heating temperature on the sheet lamination process. Seven mouthguard sheet products were laminated together at different heating temperatures. To evaluate the bonding strength, a delamination test (n = 6) was performed, and the fracture patterns were inspected visually. To evaluate the shock absorption capability, a falling impact test (n = 5) was performed, and the specimen thicknesses were measured. All recorded values were analyzed using two-way analysis of variance and Tukey's Honest Significant Difference Test (P < 0.05). The present study confirmed that bonding strength was dependent on heating temperature: In ethylene-vinyl acetate copolymer products, the bonding strength was almost constant at 130°C and above, and it was constant at 110°C and above in polyolefin products. The thickness of every specimen decreased and, in some specimens, the shock absorption capability decreased with increasing heating temperature. The present study concludes that the heating temperature during the sheet lamination process when laminated custom-made mouthguards are fabricated may not be less than 120°C in ethylene-vinyl acetate copolymer products and 110°C in polyolefin products.

Jon M. Huntsman is dead at 80

Jon M. Huntsman Sr., the Huntsman Corp. founder, packaging innovator, and philanthropist, died on Feb. 2. He was 80 years old. To the chemical industry, Huntsman is best known for the company that bears his name. In 2016, Huntsman Corp. was the sixth-largest U.S. chemical company, with $9.6 billion in sales. Huntsman came to the chemical industry in the early 1960s as an egg salesperson in Southern California. Using a plastic extruder and an improvised thermoforming machine, he developed the first polystyrene foam egg cartons. This invention led to a packaging joint venture with Styrofoam giant Dow Chemical and the founding of Huntsman Container Corp. in 1970. That company would continue to innovate, inventing the polystyrene foam clamshell container used for the Big Mac and other takeout food. Huntsman founded Huntsman Corp. in 1983 with the purchase of a Shell polystyrene plant in Belpre, Ohio. He would grow to be

Numerical investigation of wrinkle for multi-point thermoforming of Polymethylmethacrylate sheet

The multi-point thermoforming (MPTF) machine and process of resin sheet were introduced, the glass transition temperature and stress relaxation curves of Polymethylmethacrylate (PMMA) sheet were tested, and the material parameters of PMMA sheet were got. Lots of numerical simulation of wrinkle for spherical part with MPTF of PMMA sheet were put forward, the effects of thickness, radius and forming temperature on the wrinkle were investigated, and the non-wrinkle forming limit diagram are determined. Then, MPTF experiments of spherical part with PMMA sheet was done to verify the numerical results. Consequently, the spherical part has good shape accuracy, which confirms that PMMA sheet formed by MPTF is feasible and the non-wrinkle forming limit diagram obtained by numerical simulation is practicable.

CAD/CAM silicone auricular prosthesis with thermoformed stiffening insert

Purpose: Epitheses (facial prostheses) for large facial tissue defects manufacturedfrom silicones exhibit unsatisfactory rigidity and its stiffening is required, which createstechnological problems. Moreover, facial epitheses have to be replaced in a relatively shortperiod of use which creates a significant costs, often impossible to realize. The hypothesisof the study was that with use of additive manufacturing is possible to obtain the reusableform for thermoforming of the stiffening insert of auricular prosthesis and the mould whichallows multiple casting of silicone prosthesis with the insert.Design/methodology/approach: Manufacturing of the epithesis consisted of designingand manufacturing. In the first step, the auricular prosthesis and the stiffening insert weredesigned with use of engineering CAD software. In this first computer step, the split form forvacuum thermoforming of the stiffening insert and the split mould for casting of the siliconeear were designed. In the second step, additive printing was used for manufacturing thesplit and reusable model for vacuum thermoforming of the stiffening insert and the splitform of ear. In the third step, stiffening insert was made of thermoformed polyurethane sheetof 0.1 mm thick (Biolon, Dreve), where dental thermoforming machine (Drufosmart, Dreve)was used. In the fourth step, the stiffening insert was located in the mould and the ear wascasting of silicone.Findings: CAD/CAM of epitheses with stiffening insert for large tissues defect/loss wasproposed, where in case of re-producing, it required only thermoforming of insert andcasting silicone with use of the reusable models. Dental technician, in case of damage orloss of a forms, is not much involved in their creation.Research limitations/implications: Bond strength test between stiffening insert vs. softsilicone and manufacturing tolerance of epitheses have not been investigated.Practical implications: Method of casting in a negative form, despite the more timeconsumingwhen comparing with epithesis direct-printing, allows introducing a stiffeninginsert and performing a manual adjustment of margin shape and thickness. Method ofnegative form allows the use of a commercially available medical silicone without the needfor medical tests of a new printed materials.

Decreasing of the manufacturing time for a thermoforming mold by applying the DFM principles

In this paper it is analyzed a product machined at the S.C. ULMA PACKAGING S.A. company, which is a “Thermoforming mold” used in order to obtain plastic containers in which the food or non-food product is packed, making part of a thermoforming machine called TFS 200. The aims of this paper are to determine the optimal technological parameters and to study the effects of the DFM principles and the optimal tool path strategy usage on manufacturing time of the “Thermoforming mold”. A redesign of the thermoforming mold is presented based on the failed rules and recommendations given by the DFM program and followed by the analysis of the DFM’s benefic effect on the manufacturing time.

Design and Analysis of Connecting Rod of Die Pillar Station of Vacuum Thermoforming Machine

Design and Analysis of Connecting Rod of Die Pillar Station of Vacuum Thermoforming Machine

Development of a multivariable online monitoring system for the thermoforming process

The thermoforming industry has been relatively slow to embrace modern measurement technologies. As a result researchers have struggled to develop accurate thermoforming simulations as some of the key aspects of the process remain poorly understood. For the first time, this work reports the development of a prototype multivariable instrumentation system for use in thermoforming. The system contains sensors for plug force, plug displacement, air pressure and temperature, plug temperature, and sheet temperature. Initially, it was developed to fit the tooling on a laboratory thermoforming machine, but later its performance was validated by installing it on a similar industrial tool. Throughout its development, providing access for the various sensors and their cabling was the most challenging task. In testing, all of the sensors performed well and the data collected has given a powerful insight into the operation of the process. In particular, it has shown that both the air and plug temperatures stabilize at more than 80°C during the continuous thermoforming of amorphous polyethylene terephthalate (aPET) sheet at 110°C. The work also highlighted significant differences in the timing and magnitude of the cavity pressures reached in the two thermoforming machines. The prototype system has considerable potential for further development. POLYM. ENG. SCI., 54:2815–2823, 2014. © 2014 Society of Plastics Engineers

Study of the press forming mechanism of a thermoforming machine

The paper presents kinematic and dynamic investigations of the main press forming mechanism of a thermoforming machine. A multibody analysis of this press forming mechanism, which lifts and rotates a press bed, was carried out. Press bed lifting, which is necessary to form the component, is performed by means of a first rod and toggle mechanism. Press bed rotation to eject the formed component is produced by means of a second rod and must be appropriately shifted. These rods are oscillating followers driven by cams, making it possible to precisely define trajectories as a function of the motor shaft rotation angle. Analysis is performed by numerically solving the equations of motion. Cam synthesis on the basis of the oscillating followers’ trajectories makes it possible to obtain cam profiles in order to evaluate pressure angles and check that there is no undercutting. System dynamics is investigated in order to evaluate motor torque and analyse internal stresses on the hinges. In addition, some experimental results and those obtained with the dynamic model are compared. Performance improvement of the actual machine is carried out by modifying the trajectory of the press bed by means of a numerical code at the purpose developed. This approach is more convenient than the use of a commercial multibody code, which is not specifically built for parametric studies.

Model-Based Virtual Sensors and Core-Temperature Observers in Thermoforming Applications

In this paper, we present the notion of model-based virtual sensors (MBVSs) and virtual core-temperature observers in a thermoforming process. The concept of MBVSs allows for additional surface-temperature measurement points in addition to the already existing infrared sensors. This leads to improved controllability of the plastic sheet temperature and increased accuracy in temperature zoning, thus eliminating the use of extra infrared sensors, which significantly reduces the cost of the control system. The problem of core sheet temperature measurement is also addressed through the application of a closed-loop Luenberger core-temperature observer to estimate the center-plane temperature of the plastic sheet since it is not practical to have any kind of actual core-temperature measurement during the heating process. The two concepts of virtual sensors and virtual core-temperature observers are then combined to form an overall observer-based closed-loop control system. Finally, the functionality, performance, and robustness of the new system is investigated through simulation of an industrial-type thermoforming machine.

Thermal Field Analysis of Matrix Heating System on Thermoforming Machine

Thermoforming machine plays a very important role in industrial production, food packaging and other industries. In traditional thermoforming machine, highest temperature often appears in the center of the heating zone, and gradually reduces from the middle to both sides. It results in uneven heating, reducing the rate of finished products and a waste of resources. According to the finite element method, this article established the thermal field model of matrix heating system in thermoforming machine and simulated the temperature distribution of plastic in heating system under the conditions of “uniform heating” and “non-uniform heating” separately. It found that under the condition of “non-uniform heating”, the temperature distribution appeared uniform. The temperature of main region to be heated appeared approximately linear distribution, with the variation range of less than 5 °C, resulted in better effect than that under the condition of “uniform heating”

Modeling of Thermoforming of Low-density Glass Mat Thermoplastic

The glass mat thermoplastic (GMT) is made from random-chopped glass fibers and polypropylene in a sheet form. This low-density compressible material is used extensively in the automotive industry for making panels. The mechanical behavior of this material in large deformation and at thermoforming process temperature is far from being well understood. The objective of this research is to determine a constitutive law of this Azdel thermoplastic composite used for thermoforming process. A series of biaxial tests was performed to study the stress-strain behavior of the low-density thermoplastic sheet reinforced with 55% glass fiber. Different strain rates and temperatures were employed to study their effects on the mechanical behavior. Pressure-thickness model parameters were obtained using a laboratory press. A nonisothermal hyperelastic model was used for modeling this material. The results of the simulation are compared with data from a laboratory thermoforming machine and a small, simple mold.

Derivation of optimal processing parameters of polypropylene foam thermoforming by an artificial neural network

The effects of processing parameters on the thermoforming of polymeric foam sheets are highly nonlinear and fully coupled. The complex interconnection of these dominant processing parameters makes the process design a difficult task. In this study, the optimal processing parameters of polypropylene foam thermoforming are obtained by the use of an artificial neural network. Data from tests carried out on a lab-scale thermoforming machine were used to train an artificial neural network, which serves as an inverse model of the process. The inverse model has the desired product dimensions as inputs and the corresponding processing parameters as outputs. The structure, together with the training methods, of the artificial neural network is also investigated. The feasibility of the proposed method is demonstrated by experimental manufacturing of cups with optimal geometry derived from the finite element method. Except the dimension deviation at one location, which amounts to 17.14%, deviations of the other locations are all below 3.5%. POLYM. ENG. SCI., 45:375–384, 2005. © 2005 Society of Plastics Engineers