Development of a Combined Bulging-Piercing Technique to Reduce Forming Load for a Long Semi-Hollow Stepped Part

This paper aims to develop a new forming technique to manufacture a long semi-hollow stepped part. Traditionally, hot backward extrusion is used. This technique is not suitable, because it requires a very high forming load acting on the die and punch especially at the contact between punch and workpiece. As a result, the service life of the punch is very low. Therefore, a new technique to overcome this problem is needed. A combined bulging-piercing technique was proposed and developed in this research. The main concept of this technique is to bulge the part by upsetting the workpiece between the punch and the counter-punch to generate high frictional contact pressure which will help to restrain the material sliding down to the die cavity during the piercing step. In other words, this technique utilizes frictional force at the die-workpiece interface to reduce the forming load of the punch. Finite element modeling was employed to investigate and determine the suitable level of the bulging which can reduce the forming load without generating any significantly high force to the counter-punch. Only experiments with the minimum forming load were selected and implemented to validate this concept, because other conditions with high load will risk to damage the punch and the machine press of the product line. The results show that this technique can reduce the forming load by almost 40%, and also control a good concentricity of the part and reduce the wall thickness variation.

Development of smart cold forging die life cycle management system based on real-time forging load monitoring

Cold forging dies are manufactured through the shrink fit process to withstand high pressure loads, but fatigue failure eventually occurs due to repeated compressive stresses. The life cycle until fatigue failure was defined as the limit life, and attempts were made to predict the die life based on finite element method (FEM). However, accurate prediction was impossible owing to uncontrollable environmental variables. Consequently, it is impossible to clearly determine the die replacement cycle, resulting in negative consequences such as poor quality, production delay, and cost increase. Various environmental factors affecting the prediction of die life cycle result in the increase or decrease of the forming load, which is an important variable that determines the die life cycle. In this study, a system for monitoring load data generated from forging facilities was developed based on a piezo sensor. In addition, the die life cycle was more accurately predicted by using the forming load data measured in real time, and a die life management system that can determine the die replacement cycle was applied to the automobile steering parts production line.

Simulation and Experimental Study on a New Successive Forming Process for Large Modulus Gears

A successive tooth forming process for producing large modulus spur gears (m>2.5 mm) is firstly proposed in this paper to break the restrictions of large forming load and large equipment structure of traditional plastic forming. It contains the preforming stage and the finishing stage. In the first stage, the die with a single-tooth preforms gear teeth one by one through several passes. In the second stage, the other die with multi-teeth refines the preformed teeth into required shape. The influence of total pressing depth and feed distribution in preforming stage on final forming quality is analyzed by numerical simulation, and the reasonable process parameters are presented. Successive tooth forming experiments are carried out on the self-designed gear forming device to verify the optimal simulation results. Gears without fold defects are well formed both in simulations and experiments, proving the feasibility of this method. Compared with the whole die forging process, the new technology has advantages of smaller load and simpler tooling, which shows a good potential for manufacturing large modulus and large size spur gears.

Design of a Combined Redrawing-Ironing Process to Manufacture a CNG Pressure Vessel Liner

The liner of a compressed natural gas pressure vessel is manufactured by D.D.I. (Deep Drawing and Ironing), which is a continuous process that uses deep drawing to reduce the diameter of a billet and ironing to reduce the thickness of the billet. In the second stage of the existing D.D.I. process, drawing and two steps of ironing have been performed separately with different dies, which requires a long processing time, high manufacturing cost, and installation space. To solve the above problems, this study suggests a new second stage using a combined redrawing-ironing die. A theoretical formula to calculate the forming load of the combined redrawing-ironing process was established and verified with finite element analysis results. The forming load, maximum thickness reduction ratio in the second stage, and forming defects in the third stage were analyzed by varying the redrawing-ironing ratio in the second stage. The results show that the number of dyes (3 → 1), punch diameter (394.1 mm → 383 mm), and processing time (39.8 s → 20 s) in the second stage were obtained to save production time and cost.

Deformation Behavior and Microstructural Evolution of T-Shape Upsetting Test in Ultrafine-Grained Pure Copper

Ultrafine-grained (UFG) materials can effectively solve the problem of size effects and improve the mechanical properties due to its ultra-high strength. This paper is dedicated to analyzing the deformation behavior and microstructural evolution of UFG pure copper based on T-shape upsetting test. Experimental results demonstrate that: the edge radius and V-groove angle have significant effects on the rib height and aspect ratio λ during T-shape upsetting; while the surface roughness has little effect on the forming load in the first stage, but in the second stage the influence becomes significant. The dynamic recrystallization temperature of UFG pure copper is between 200 °C and 250 °C.

Evaluation of Different Tools of Precision Finishing for Cold Extruded Sun Gear With Internal-External Tooth Shapes

Due to the complex metal flow in the cold extrusion of sun gear, the teeth accuracy of formed sun gear is poor. In order to improve the accuracy of the extruded sun gear, a novel precision finishing method with different tools was proposed in this study. Finite element simulations were performed using DEFORM, and a new finite element (FE) prediction strategy was developed to obtain an in-depth understanding of the deviation distribution laws of the finished sun gear. Then, the influences of different finishing tools on tooth deformation, tool stress, forming load and tooth accuracy were examined. The investigation results show that the profile accuracy of external gear can be improved from ninth to seventh class, lead accuracy can be enhanced from tenth to eighth class, and total M value deviation of internal spline is reduced to 72.3 μm by the precision finishing method with interference mandrel. Therefore, the interference mandrel is recommended as the optimal reshaping tool for commercial production of sun gears. The simulation results are well agreed with the experimental results, which verifies the feasibility of the precision finishing method and the reliability of the FE prediction strategy.

Study on Effect of Shapes of Serration of Joining Plane on Joining Characteristics for the Aluminum–Steel Multi-Materials Press Joining Process

Recently, mechanical joining processes have received much attention for joining multi-materials. In particular, these processes have a great demand in the automobile industry for weight reduction. The press-fitting process is a representative mechanical joining process. In this process, the shape of the interfacial serration on the joining plane is very important because it has a significant effect on the joining strength. In this study, the characteristics of the aluminum–steel press joining process were investigated according to the shape of the interfacial serration of the joining plane. The deformation of the material and the forming load were investigated by conducting finite element analysis. In addition, the unfilled height of the material, joining force, and torque were measured experimentally.

A New Successive Forming Process for Large Modulus Gears

A successive tooth forming process for producing large modulus spur gears (m＞2.5 mm) was firstly proposed in this paper to break the restrictions of large forming load and large equipment structure of traditional plastic forming. It contains the preforming stage and finishing stage. In the first stage, the die with a single-tooth preformed gear teeth one by one through several passes. In the second stage, the other die with multi-teeth refined the preformed teeth into required shape. The influence of total pressing depth and feed distribution in preforming stage on final forming quality was analyzed by numerical simulation and the reasonable process parameters had been presented. Gears without fold defects were well formed both in simulations and experiments, proving the feasibility of this method. The new process has advantages of smaller forming load and simpler tooling set, which shows a good potential for manufacturing large modulus spur gears.