Injection moulding

G. Tosello (a), A. Schoth (b), H.N. Hansen (a)

(a) Technical University of Denmark (DTU), Department of Mechanical Engineering, Produktionstorvet, Building 427S, DK-2800 Kgs. Lyngby, Denmark
(b) Laboratory for Process Technology, Department of Microsystems Engineering (IMTEK), University of Freiburg, George-Koehler-Allee 103,79110 Freiburg, Germany

Abstract

In polymer micro manufacturing technology, software simulation tools adapted from conventional injection moulding can provide useful assistance for the optimization of moulding tools, mould inserts, micro component design, and process parameters. Conventional implementation methods of simulation are not suitable for micro injection (μIM) application and are limiting the possibility to extend the use of existing packages for the modelling and the simulation of polymer micro parts. Different strategies optimized for the set-up the simulation of a miniaturized part with micro features are presented. Model design and mesh issues are discussed, as well as dynamic implementation of the flow constrains for the creation of an effective interface between the machine and the polymer flow in the simulation software. The results of the different methods are evaluated by means of a quantitative study which compares the simulated results and the actual micro injection moulding experiments.

C.A. Griffiths, S.S. Dimov, E. B. Brousseau and M. S. Packianather
Manufacturing Engineering Centre, Cardiff University, Cardiff CF24 3AA, UK

Abstract

Micro injection moulding as a replication method is one of the key technologies for micro manufacture. The understanding of process constraints for a selected production route is essential at both the design stage and during mass production. In this research, an existing Finite Element Analysis (FEA) system is used to study the effects of four process parameters, namely melt and mould temperature, injection speed and part thickness. A special attention is paid to the melt flow sensitivity when filling micro channels, particularly the factors affecting shear rate and flow front temperature. The results obtained from two different simulation models are presented for two polymer materials, PP and ABS and conclusions are made about the important factors affecting part quality.

W. Michaeli (a), F. Klaiber (a), S. Scholz (b)

(a) Institute of Plastics Processing, RWTH Aachen University, Aachen, Germany
(b) The Manufacturing Engineering Centre, Cardiff University, Cardiff, CF24 3AA, UK

Abstract

Telecommunication, information and medical industries have a high growth potential. A key technology for those industries is the replication of microstructures. Precise microstructured parts with functional surfaces can be produced economically by injection moulding. The whole process chain (thermal mould condition, moulding, demoulding, measurement and analysis) must be analysed carefully to ensure the highest precision and reliability. To enable the precise production of such structures fundamental studies were conducted at the Institute of Plastics Processing (IKV). The studies considered several polymers (PMMA, POM) on the one side and various test structures on the other side. In addition an innovative external inductive heating unit was analysed and implemented into the process to heat the cavity surface efficiently. Using this technique cavity surface temperature increase rates of up to 60 K/s have been achieved. A pyrometer was implemented for contact less instant temperature measurement, and controller was used to realise preset cavity temperatures by regulating the inductor power. With the dynamic inductive heating system the moulding accuracy of the microstructures could be increased drastically. The final step of the process chain comprises of the measurement and analysis of the microstructured moulded parts. To analyse the microscopic deviation between the mould cavity and the surface of the moulded part scanning electron microscopy (SEM) and white light interferometry (WLI) was used.

C.A. Griffiths (1), S. S. Dimov (1), E.B. Brousseau (1), C. Chouquet (2), J. Gavillet (2), S. Bigot (1)

(1) Manufacturing Engineering Centre, Cardiff University, Cardiff CF24 3AA, UK
(2) French Atomic Energy Commission (CEA), Laboratory of Innovation for New Energy Technologies and Nanomaterials (LITEN), 38054 Grenoble, France

Abstract

Micro injection moulding as a replication method is one of the key technologies for micro manufacture. The understanding of process constraints for a selected production route is essential at both the design stage and during mass production. In this research a tool surface treatment is used to study the effects of demoulding a part with micro features. In particular a tool coated with diamond like carbon (DLC) will be compared to an identical tool without coating. Through a range of experimental trials the effects of four process parameters, namely melt and mould temperature, and cooling and ejection time will be used to evaluate the demoulding process. Using two polymer materials PP and ABS, a special attention is paid to the forces present in demoulding and conclusions are made about the influence of DLC surface treatments and the factors affecting demoulding.

W. Michaeli, T. Kamps
Institute of Plastics Processing at RWTH Aachen University, 52056 Aachen, Germany

Abstract

Micro injection moulding is established as one of the most common manufacturing processes for thermoplastic polymers due to its high degree of automation and the short cycle times. With micro assembly injection moulding, offline joining process steps can be avoided by overmoulding components of the micro system directly in the injection mould. Overmoulding can be used to generate movable or fixed combinations of different materials. One of the materials combined in a hybrid micro system is thermoplastic polymers, whereas the other one can be selected from a wide range of materials, e.g. technical ceramics, glass, or metals. Micro assembly injection moulding provides several advantages compared to other joining processes. However, functional integrity of the micro system is an end requirement. In the case of a joint micro structure, the bonding strength between two components affects the stability of the whole micro system and is thus important for the part’s quality. As tests conducted at IKV show, a plasma treatment (plasma activation) of the insert parts significantly increases the bonding strength. Inserts of metal and glass have been overmoulded with several polymers, and the influence of different plasma gases and duration of the treatment on the feasible bonding strength is shown.