Effects of forming velocity on micro deep drawing performance with different blank thickness

Micro deep drawing is a promising manufacturing method to produce the hollow, thin walled, cup or box like products at micro scale. Forming velocity can affect the products’ quality significantly due to the size effect, and this effect can be various with different thickness material. In this study, 30, 40, and 50 µm thickness stainless steels were annealed at 950 °C for 2 min under protection of argon gas ambient respectively. These different thickness steels were utilized in the micro deep drawing with different forming velocities. The experimental results show that, the profile accuracy and surface quality of the micro product are affected by changing the forming velocity with different thickness blanks. The micro cup has a less indentation area at the bottom and becomes rounder and more symmetrical with a thicker blank. Besides, the wrinkling phenomenon turns distinct with a thinner blank, and the earing becomes more significantly when increasing the drawing velocity or decreasing the blank thickness. When the drawing velocity or blank thickness increases, the surface of the micro cup becomes smooth and even. The experimental results are in good agreement with the simulation results, which confirms the developed finite element simulation model is applicable.

Experimental Investigation on Micro Deep Drawing of Stainless Steel Foils with Different Microstructural Characteristics

In the present work, austenitic stainless steel (ASS) 304 foils with a thickness of 50 µm were first annealed at temperatures ranging from 700 to 1100 ℃ for 1 h to obtain different microstructural characteristics. Then the effects of microstructural characteristics on the formability of ASS 304 foils and the quality of drawn cups using micro deep drawing (MDD) were studied, and the mechanism involved was discussed. The results show that the as-received ASS 304 foil has a poor formability and cannot be used to form a cup using MDD. Serious wrinkling problem occurs on the drawn cup, and the height profile distribution on the mouth and the symmetry of the drawn cup is quite non-uniform when the annealing temperature is 700 ℃. At annealing temperatures of 900 and 950 ℃, the drawn cups are both characterized with very few wrinkles, and the distribution of height profile, symmetry and mouth thickness are uniform on the mouths of the drawn cups. The wrinkling becomes increasingly significant with a further increase of annealing temperature from 950 to 1100 ℃. The optimal annealing temperatures obtained in this study are 900 and 950 ℃ for reducing the generation of wrinkling, and therefore improving the quality of drawn cups. With non-optimized microstructure, the distribution of the compressive stress in the circumferential direction of the drawn foils becomes inhomogeneous, which is thought to be the cause of the occurrence of localized deformation till wrinkling during MDD.

Effects of TiO2 nanoparticle lubricant on micro deep drawing performance

Micro deep drawing is a process to manufacture the thin walled, hollow, box or cup like products at micro scale. Lubricant can affect the products’ quality in micro deep drawing at micro scale due to the decrease of coefficient of friction between the material and tools, it is crucial to enhance the forming efficiency. In this study, 40 µm thickness stainless steel 301 (SUS301) was annealed at 980 ℃ for 2 min under protection of argon gas ambient, and this stainless steel was selected as the specimen material. The micro deep drawing was conducted on a micro press machine under dry and 4% TiO2 nanoparticle lubrication conditions with different forming velocities. The experimental results showed that the micro cup’s profile is affected by changing the forming velocity under the dry and nanoparticle lubrication conditions. Under the dry condition, the surface became rough with the increase of the forming velocity, and then the micro forming efficiency under application of nanoparticle lubricant increases with a rise of drawing velocity.

Micromanufacturing Technology and its Practice

In order to make micro composite drills (Fig. 1), cemented tungsten carbide (WC-10Co) and high strength (AISI 4340) steel were successfully bonded by hot compaction diffusion bonding at a low temperature. The effects of holding time, pressure and temperature on microstructure and mechanical properties of the sintered carbides and bonding strengths of the bimetallic composites were examined, and a transitional layer was found at the interface as a result of elemental inter-diffusion. The optimal bonding parameters were determined to achieve the maximum bonding strength of 226 MPa of the WC-10Co/AISI 4340 steel joints, which is helpful in producing micro composite drills. Microforming is introduced to produce lighter and more energy effective products. In this study, Magnesium-Lithium (Mg-Li) alloy, new material in microscale, was chosen to superior formed micro-cup due to its ultralight weight with outstanding ductility. The dry and oil lubrication conditions were chosen as benchmarks to investigate effects of a novel oil-based nanoparticle lubricant in micro deep drawing (MDD) process of Mg-Li alloy. Finite Element (FE) modelling was conducted and the simulation results of the drawing force were in a good agreement with the experimental results. The formed cup quality with consideration on the surface roughness has been extensively evaluated and the results illustrated the quality improvement was substantial.

Effect of process parameters on micro flexible deep drawing of stainless steel 304 cups utilizing floating ring: Simulation and experiments

Due to its simplicity, versatility of process and feasibility of prototyping, using flexible tools in sheet forming seems appropriate for producing cups at microscales. This article presents a novel micro deep drawing technique in which a cooperation of a floating ring, as a primary rigid die, with a rubber pad, as a main flexible die, is employed for forming micro-cups. The function of the floating ring is to overcome minor wrinkles that commonly occur at flange portion, while the flexible die is to complete the forming stroke. The influence of initial sheet thickness, drawing ratio, punch corner radius and rubber height is studied through simulations and experiments. Furthermore, three size scales are adopted to investigate the possibility of using the proposed technique under different process dimensions. The code ABAQUS/Standard is utilized to build the finite element models and thereafter micro-forming experiments are carried out to verify the numerical results. For this purpose, a special setup is developed to be compatible with simulation models. The results show that the formed cups are characterized by very accurate dimensions, high surface quality, homogeneous wall thickness distribution in terms of maximum thinning and thickening and relatively large aspect ratio.