Finite element modelling of the coupled pressure volume phenomena during inflation

In industrial blow molding machines, the inflation pressure is only controlled in the upstream blowing device and not inside the cavity. However, observations show that the inside measured pressure is considerably lower than the nominal one captured in the upstream air feeding system. Several recent investigations show that if the volume of the enclosed gas changes significantly during the inflation stage, then the assumption that the internal pressure is know and constant can be incorrect. In this case, the internal pressure becomes a function of the unknown cavity volume. This paper presents a thermodynamical model used for predicting the pressure evolution in molded cavities during the inflation process. A brief recall of the FEM formulation and implementation is also presented. Experimental validation of the numerical approach is performed on a one-stage stretch blow-molding machine.Peer reviewed: NoNRC publication: Ye

Modelling of solidification deformation in automotive formed parts

The accurate prediction of part deformation due to solidification in automotive formed parts is important to help achieve an efficient production. Forming processes are those where a molten preform is deformed to take the shape of a mould cavity and subsequently solidified. Tolerance issues are critical in automotive applications and therefore part deformation due to solidification needs to be controlled and optimized accordingly. Formed parts can have a wide range of deformations according to the conditions of solidification. Both a small displacement and a large displacement formulation are developed for prediction of part deformation due to solidification. Experimental results obtained on a simple as well as complex automotive part are compared to determine whether the small displacement theory or the more complex approach is more appropriate.Peer reviewed: YesNRC publication: Ye

Modelling of solidification deformation in automotive formed parts

The accurate prediction of part deformation due to solidification in automotive formed parts is important to help achieve an efficient production. Forming processes are those where a molten preform is deformed to take the shape of a mould cavity and subsequently solidified. Tolerance issues are critical in automotive applications and therefore part deformation due to solidification needs to be controlled and optimized accordingly. Formed parts can have a wide range of deformations according to the conditions of solidification. Both a small displacement and a large displacement formulation are developed for prediction of part deformation due to solidification. Experimental results obtained on a simple as well as complex automotive part are compared to determine whether the small displacement theory or the more complex approach is more appropriate.Peer reviewed: YesNRC publication: Ye

Micro-blow moulding and micro-thermoforming: simulation and validation

Peer reviewed: YesNRC publication: Ye

Enhancement of angioplasty balloon performance through annealing

Angioplasty balloons are used to implement stenting of atherosclerosed blood vessels and put in place heart valve systems. The balloons are required to have thin walls and high burst pressure while having a given compliance (e.g., given balloon diameter at a nominal pressure). In this study 3 by 15 mm and an 8 by 30 mm balloons are formed through a micro-blow moulding process. The balloon forming machine process (BFMP) starts by stretching an extruded tubing of thermoplastic elastomer into a'parison' by means of a specially instrumented balloon forming machine. The BFMP is identified as a three step stretch micro blow moulding process, where the 'parison' is stretched under pressure and at controlled temperatures to form a 'balloon': Forming of the cylinders, forming of the balloon's cones and annealing of the balloon. In this article we show how the elastic and mechanical properties of the balloon can be fine tuned to the specifications of the medical suppliers. A balloon design method and suggestion for an in-line control method for the balloon forming process are also presented

Process optimization of automotive blow molded parts

The key quality requirements of automotive blow molded parts include weight distribution, geometric tolerance and mechanical performance. This work deals with the optimization of an automotive filler panel used in a sports utility vehicle. The part is molded with an insulating material (carpet) on one side, which renders the design of the part complex, due primarily to the non-uniform solidification of the part and the tight tolerance requirements of automotive OEM's. The proposed optimization consists of the manipulation of the die gap programming points and the mould temperature in order to optimize the part thickness distribution and to minimize the part warpage.Peer reviewed: YesNRC publication: Ye

Process optimization of automotive blow molded parts

The key quality requirements of automotive blow molded parts include weight distribution, geometric tolerance and mechanical performance. This work deals with the optimization of an automotive filler panel used in a sports utility vehicle. The part is molded with an insulating material (carpet) on one side, which renders the design of the part complex, due primarily to the non-uniform solidification of the part and the tight tolerance requirements of automotive OEM's. The proposed optimization consists of the manipulation of the die gap programming points and the mould temperature in order to optimize the part thickness distribution and to minimize the part warpage.Peer reviewed: YesNRC publication: Ye

Micro-blow molding: Designing of an angioplasty balloon

Angioplasty balloons are used to enlarge narrowed blood vessels; the balloons are required to have thin walls, and yet high burst pressure, and also be semi-compliant (e.g., limited increase in balloon diameter past the nominal pressure). In this study, the 3 X15 mm and 8X30 mm balloons are formed by a unique micro-blow molding process. The process starts by stretching an extruded tubing of thermoplastic elastomer, into a 'parison' by means of a Double End Stretching Machine. The balloon forming is accomplished through a process called stretch blow molding, where the 'parison' is stretched under pressure and at elevated temperatures to form a 'balloon'. Following the formation of the balloon, a secondary temperature is applied over a dwell time; this annealing step prevents shrinkage of the balloon once it is removed from the mould. The current study focuses on the effects of heat treatment during micro blow molding process to achieve semi-compliant balloons with thin walls and high burst pressure. To this end, the balloons prepared under different processing conditions are characterized in terms of mechanical properties. An ideal process condition is proposed

On-line adaptive control for thermoforming of large thermoplastic sheet

Large sheet thermoforming is widely used for the manufacture of parts such as twin sheet formed gas tanks, body panels and windshields. These complex technical parts require a precise temperature map to be realized prior to forming. In particular, the material used for forming gas tanks incorporates an EVOH barrier layer that is susceptible to tearing when exact processing conditions are not strictly respected. The problem is compounded by the fact that the temperature is presently controlled at the heating elements, while the temperature distribution across the thickness of the sheet is the main process variable. This makes the thermoforming process very susceptible to perturbations and greatly increases the number of rejected parts. In order to increase productivity and quality, the actual sheet temperature distribution before forming must adhere to the optimized temperature map as predicted by a process simulation or the recipe as determined by previous runs. The system presented here controls the amount of energy received by every sheet zone, which is equivalent to controlling the sheet temperature. It is tuned on-line by identifying the heating zone to sheet zone gains matrix using a flux meter and by correlating the matrix to the output of an infrared scanning thermometer located at the exit of the heating oven. The control system will realize the map of the required sheet surface temperature by adjusting the heating elements temperature. The system has been implemented on a Monark twin-sheet thermoforming machine that has dual 1.8mx1.8m square ovens and 504 heating elements in re-configurable zones.Peer reviewed: NoNRC publication: Ye