Numerical, Analytical and Experimental Analysis of Combined Extrusion Forging Processes Applied to Collet Chuck Holders

Abstract

The material flow in the combined extrusion/forging process is an important phenomenon which controls the mechanical and metallurgical properties of any manufactured component. Collet chuck holder is a tool holding device used in different types of CNC milling machines. The chuck holder is described by a flange at the middle to fit into the machine, taper portion which is conical shaped area present at the bottom which enters the spindle for changing holder and collet pocket which fits the collet for holding the cutting tool. For manufacturing the tool holder an enormous amount of material is being wasted by the machining process which is almost equal to the volume of the product. Some manufacturer use casting, subsequently by machining to get the final shape. Both the used processes have their limitations as discussed earlier. To secure our material resources and to get better mechanical properties it is proposed to adopt the combined extrusion/forging and/or multi-stage processes for the production of different types of collet chuck holders.
In general, it is found challenging to predict the metal flow by 3D combined extrusion/forging process of complicated sections, collet chuck holder in particular, due to its complexity nature of analysis. From experiments it is observed that the complete process to get the first three components can be assumed to compose of four stages and fourth one of two stages with regard to forward/backward extrusion, forging, die corner filling, and flash formation. The mechanical, microscopic, micro hardness and residual stress analyses are performed for all the four components manufactured under different frictional conditions and ram velocities. The results confirm the advantage of the proposed processes to manufacture collet chuck holder. In the present investigation, upper bound method is used to analyze the combined extrusion/forging process of different types of collet chuck holders. A set of kinematically admissible velocity field is proposed to predict the metal flow pattern and the forging load. This work also employed 3D finite element formulation to simulate the combined extrusion/forging process for axisymmetric collet chuck holders. The forming loads obtained by proposed upper bound technique is in good agreement with the numerical and experimental results and lies in the range of 0-15%, 5-20%, 0-15% and 12-20% for first, second, third and fourth products respectively.
Experimental observations indicate that the collet chuck holder can be effectively manufactured by metal forming route of combined and/or multi-stage extrusion/forging to get its inherent advantages instead of following the present practice of machining and/or casting. The estimated loads obtained using proposed kinematically admissible velocity fields effectively take care of work hardening, friction effects and redundant work and are remain within engineering accuracy when compared with that obtained from FEA and experiments. The results confirm the suitability of the proposed techniques (FEA and upper bound) for the prediction of load in combined extrusion-forging processes studied in the present work applied to collet chuck holder.