Optimizing the design and development of thick film heaters for consumer products

Abstract

Ferro Techniek specializes in the use of enameling techniques in heating elements for consumer and industrial applications. They distinguish themself by delivering customized sub-assemblies for consumer products in the form of Thick Film Heaters (TFHs). These TFHs are used in several consumer products like Nespresso machines, food processors, steam ovens, and many others. The TFHs are flat heating elements that consist of a stainless steel plate, an enamel layer, and a printed electrical circuit protected by a glass insulating layer. The current development of these thick film heaters requires a large amount of prototype and testi iterations, taking up valuable time. Ferro Techniek wants to improve the current product development process by reducing the amount of iterations in the development process and shortening the duration of a project. TFHs are more expensive than the competing heating technologies, but offer benefits that other heating solution cannot, such as a very high power density, compact size and high energy efficiency. These benefits allow designers of consumer goods to design with more freedom and produce more energy efficient products, design aspects which are especially important in the high-end of the market. A very important trend in the consumer goods market is the shortening of the product life cycle caused by consumers who expect original equipment manufacturers (OEMs) to shorten the time between new product introductions. Ferro Techniek, as supplier of heating elements to these OEMs can improve its market position by shortening its own development time. The current development process roughly exists of four stages; initiation, study, development and implementation. Mainly during the study and development stages, there are many design iterations needed to obtain a proof of working principle under operating and extreme conditions. Two case studies of recent product development processes show that the total development time of one heating element can take up to 3 years and it shows what kind of technical challenges occur. The introduction of simulation in the form of a finite element analysis of the TFH to the current development process, especially in the study and development stages, can partially replace the iterations needed in the development process and reduce development duration. To be able to simulate the TFHs, the production process is analyzed, because it causes an initial deformation and stress in the enameled plates. A method for determining the elasticity of the enamel is presented, because suppliers of enamel do not supply any. The bond between enamel and metal is also studied from literature, but could only be defined in a general way, because there is currently no qualitative method of determining the bond strength. Also, anisotropic behavior of the metal substrate is studied to be able to obtain material specification for the input of the simulation. With the results for the enamel’s elasticity, the metals anisotropic behavior and the bond between the two materials defined, a number of square test plates have been simulated and validated, and subsequently the TFH plates. From these plates, the pre-stress and deformation, caused by a difference in thermal expansion of both materials, could be determined. The stress profile show that it is most likely that the enamel will fail during usage at the edges of the plates, due to a lower compressive pre-stress at those points. The thin layered structure of the TFH required a high amount of elements in the mesh, which requires high computing power to solve the simulations. A transient thermal analysis is used as a thermal load input for a transient structural analysis, but due to the lack of computing power available during this project, no conclusions about the deformation and stress development in the usages of a TFH can currently be made or validated. The study does however show a method of simulating and evaluating the TFHs usage, which can in the future be executed by a specialized external company. Two major conclusions can be drawn from redesigning the product development process with simulations. The first is that implementing simulation can be seen as an additional problem solving strategy next to the current deduction strategy (e.g. formalized knowledge of laws of physics) and induction strategy (knowledge obtained from testing and prototyping). The second conclusion is that the benefits of simulations go further than the obvious time saving, i.e.; (1) Experiment new and non-conventional possibilities and designs (2) Gain insights in physical properties that otherwise cannot be measured, like internal stress development (3) Discover relations between design parameters (4) Clearly communicate test results By adding simulations to the development process, Ferro Techniek can improve and shorten their development time, possibly find new heating solutions and thereby improve their market position.