Shear Droop Research Articles

Effect of local heating by ultrashort pulsed laser on Fe–Si–B–Cr amorphous alloys and its influence on blanking machinability

We propose a novel blanking method to improve the machinability of amorphous alloys by taking advantage of changes in mechanical properties during local heating. The local heating is achieved through an ultrashort pulsed laser with a low thermal effect, allowing us to control the size and structure of heat-affected zones by adjusting laser power, pulse width, and shot numbers. This method hence causes phase transformation only in the blanking area. Namely, heat storage effects increased with a prolonged ablation process, and crystallization was observed at a repetition rate of 200 kHz or more. A fully crystallized microstructure, which formed at elevated temperatures, was seen at the center of the laser irradiation, while, as the distance from the irradiation point increased, small crystallites are found to disperse in the amorphous matrix. In addition, a thin crystalline phase appeared on the surface layer of the crystallized region. In general, the locally heated area was embrittled by the aforementioned structural changes, and consequently, the blanking resistance decreased with an increase in the crystallized area. Yet, it was found that laser irradiation which did not bring about crystallization also led to a decrease in the blanking resistance, showing that thermal effects below the crystallization temperature are still effective in reducing the blanking resistance. Additionally, the blanked cross-section of the locally heated specimen showed good surface quality without defects such as a large shear droop, which often occurs when punching amorphous alloys.

Dimensioning of the Clearance as a Means of Avoiding Burr and Film Formation during the Punching of PC/ABS Cable Ducts

The production of staple articles such as cable ducts offers reductions in resource and production energy consumption if the process is optimized. Side recesses made of polyvinyl chloride (PVC) have already been punched successfully as one of the process steps during the production of cable ducts. However, punching cable ducts made of flame-retardant polycarbonate/acrylonitrile–butadiene–styrene (PC/ABS) is challenging because increased burr and film formation occurs. This study introduces the correct dimensioning of the clearance as a means of reducing the burr and film formation and presents the ideal clearance dimensions. This new process design approach comprises the dimensioning of the clearance and its subsequent successful application. Tools with clearances in the relevant size range were purchased and examined by means of punching tests. The punch-outs were evaluated regarding the quality characteristics, such as the burr, film, cut surface quality, shear droop, and plastic flow characteristics. Excerpts from high-speed recordings were used to assess the punch-outs qualitatively. The burr formation is significantly decreased by the use of a correctly dimensioned clearance, allowing for the crack initiated at the punch side and the crack initiated at the die side to meet perfectly. It is assumed that film formation can be avoided via a significant reduction in the friction or heat input during the punching process.

Impact Joining of Pure Copper C1100 and Aluminum Alloy A6061-T6 Plates at Edges

Joining of pure copper C1100 and aluminum alloy A6061-T6 plates of 5 mm thickness was investigated. The method was developed by one of the authors, in which the newly created surfaces of a pair of plates obtained by high-speed shear were immediately in contact with a sliding motion with a small overlap length. The total processing time was just about a few milliseconds. To create the new surface, high-speed shaving was also tested. The joining was not possible for the full thickness of the plates. A sharp notch was observed at the joint boundary due to a large shear droop in the copper. Shaving decreased the shear droop, and the joint length through the plate thickness became longer. The joining performance was evaluated by a uniaxial tensile test. The joint efficiency reached 100% using the specimen cut out from the really joined boundary. The affected zone of joining was confirmed by the hardness distribution near the boundary. It was about 30% of the thickness of the plate, which was much smaller than that in welding by heat, and no softened zone was found in both materials.

Friction-Stir Spot Mechanical Joining between Hot-Dip 55% Aluminum–Zinc Alloy-Coated Steel Sheet and A5083 Aluminum Alloy Plate Using Conventional Punching

In this study, we fabricated a mechanical joining with spot friction-stirring between an aluminum alloy plate and an aluminum–zinc alloy-coated steel sheet; this was achieved by utilizing a conventional press-punching preprocess. In the preprocessing, a hot-dip 55% aluminum–zinc alloy-coated steel sheet was punched using a press and an inclined surface was generated at the wall of a punched hole due to shear droop. Subsequently, an A5083P-O aluminum alloy plate was positioned against it, and friction stirring was conducted on its rear surface. The hole was filled with the aluminum alloy to generate a mechanical interlock at the tilt of the wall. Further, we evaluated its cross tensile strength (CTS) and tensile shear strength (TSS) and obtained an average CTS and TSS of 368 kN and 1470 kN, respectively.

Pseudo linear joining for dissimilar materials utilizing punching and Friction Stir Forming

This study presents a new technique for pseudo-linear joining of dissimilar materials. First, multiple holes on a joined material, such as a steel plate, are pierced with a press or a punching machine. The holes have an inclined surface owing to the breakout angle. The breakout side of the joined material is then brought into contact with a backing plate to enclose the holes. Next, a base material such as an aluminum alloy plate is placed on it, and friction stirring with horizontal tool traveling is conducted on it to fill the holes with the deformed material. Eventually, a pseudo linear mechanical joint is created by the undercut in the holes, which is derived from the shear droop. Herein, the pseudo-bead-width and strength of the joints were investigated with a 3 mm-thick A5083 aluminum alloy plate and a 1 mm-thick perforated SPCC steel plate.

Investigation of shear droop formation around convex portions of blanked components

A large shear droop generated in the convex portions of blanked components leads to functional problems, such as a decrease in the effective thickness of gear parts. In this study, the cause of this issue was investigated by comparing half-blanked workpieces with circular and rhombic profiles. The large shear droop at the convex tip was closely related to the tip radius, specifically the indented deformation occurring at the convex tip. The experimental results were verified by the finite element method, and the numerical results agreed closely with the experimental ones. The cause of the increase in shear droop at the convex tip was quantitatively explained using a deformation model and corresponding stress distributions.

Effect of use of protrusion punch on length of burnished surface in piercing after half punching

Shearing is a cutting method with high productivity. The cut surface consists of a shear droop, a burnished surface, a fractured surface and burr. Press shaving removes the shear droop and fractured surface on the cut surface obtained by shearing to increase the length of the burnished surface. In press shaving, the trimming allowance is set to a small value. The amount of chips obtained by press shaving is very small. The occurrence of small chips is a problem for press working. Therefore, it is desirable that a large burnished surface is obtained without the occurrence of small chips. When piercing with a small trimming allowance was previously carried out after half punching, a chip was connected to the sheet material under the punch. However, the length of the burnished surface was decreased. In this study, piercing using a protrusion punch after half punching was carried out to increase the length of the burnished surface. The effect of the use of a protrusion punch on the length of the burnished surface and the shape of the chip was investigated.

Electromagnetic Piercing of Aluminum Sheet Using Flat-Plate One-Turn Coil

A processing technology for microholes in sheet metal is required for small electronic devices such as micropumps. Recently, hole processing by electromagnetic piercing has been considered. The flat-plate one-turn coil we use can generate high electromagnetic power, because a strong magnetic field of high frequency can be formed in a narrow linear region. In this report, the results of many simultaneous electromagnetic piercing experiments for different diameters (dh ) and different thicknesses (τ) of A1050-H24 are presented. The minimum energy of piercing (Wp ) and the characteristics of deformation are determined from the results. The relationship between Wp and dh /τ is indicated by one curve. A negligible amount of burr after piercing is observed, but the width of shear droop was 80% of the thickness. A method to determine the maximum magnetic pressure at piercing (Pm ) from the maximum current Im at Wp is described. Pm and Wp exhibit the same tendency with respect to dh . As mentioned above, the results are discussed with respected to both electrical and mechanical engineering.

Precision stamping process of metal micro gears

Precision blanking processes suppress shear droop, fracture, and burr generated on a cut blank surface. However, as the blank size becomes extremely small, as in microgears, the technology involved becomes extremely difficult, particularly in die-and-punch making. More specifically, the punch itself may easily snap off or buckle. The present press precision blanking is very innovative in that we made the die-and-punch system for stainless-steel microgear parts, where an extremely small punch can penetrate into the work material yet remain unbroken.

平押し法における材料への拘束が分離成功条件域ならびに切口面に及ぼす影響

The cut surface obtained by blanking has burrs, whose occurrence should be prevented. Push-back blanking is one of the burr free blanking methods. This method was consists of two stages. The first stage is a half-blanking stage, and in the second stage the product is separated from the scrap by pushing the half-blanked material. It is known that the range of successful blanking conditions decreases with decreasing scrap width. In this paper, the effects of constraint of the sheet material on the range of successful blanking conditions and the cut surface are discussed on the basis of the results of an experiment when the scrap width is small. The experiment was carried out using a disk-shaped specimen whose outer peripheral surface was constrained in the first stage. This study clarified the following. The constraint of the specimen in the first stage was effective for increasing the range of successful blanking conditions when the scrap width was small. It is considered that the increase in the range of successful blanking conditions is caused by the decreased the bending deformation and the compressive deformation of the scrap in the second stage from the observation of a cross section of the specimen. The shear droop formed in the half-blanking stage and separating stage was decreased when the specimen was constrained in the first stage.

Effect of Edge Shape of Tool in Finish Blanking

In the present paper, the finish-blanking method is taken up because it is an easy-to-use method by using a tool with rounded edge and a small clearance between the punch and die. In finish blanking, the process parameters such as the tool shape and clearance are significant. The purpose of the present work is to clarify the effect of tool shape of PW punch in finish blanking. In the present paper, a high-tensile-strength-steel plate with a thickness of 6mm was used. The edge shape of punch was changed, and the clearance was changed within the range of 0.65%t - 12%t. The experimental results show that the edge angle of PW punch should be in the range of 30° - 60°, and the clearance should be less than 2.0%t to obtain the ratio of the burnished surface more than 80%. The edge shape of the punch has a very limited effect on the shear droop, when the clearance is less than 2.0%t. It was also found that the PW punch is more suitable to control the burr depth than Rounded punch.

かえりなしせん断加工の成功条件および切り口面品質に及ぼす材料延性の影響

In push-back blanking, burr-free products are produced by compressing a half-blanked sheet between platens, where success conditions are affected by the ductility of materials. In this study, the mechanism of success and the cut edge quality in the push-back blanking process using a ductile and a brittle steel sheet were discussed. Experiments were carried out, varying the punch penetration and clearance in the half-blanking step. Brittle steel showed a wider successful range and less shear droop on the cut edge than ductile steel. Corresponding simulations were conducted and the damage value based on a ductile fracture criterion was calculated around the shear zone. Negative clearance was effective in keeping the damage value low and allowed deep punch penetration without fracturing in the half-blanking step. In the following push-back step, a rapid increase in the damage was observed when the high mean stress zone prevailed over the half-blanked portion. The timing of increase in damage was earlier for brittle steel owing to the localization of deformation, resulting in a wider successful range than that of ductile steel.

Analysis of Shear Droop on Cut Surface of High-Tensile-Strength Steel in Fine-Blanking Process

The fine-blanking process is used in the production of automobile parts and other metal components. Although the fine-blanking process can produce sheared surfaces with higher precision than the punching process, shear droops on cut surfaces are also formed, as in the punching process. It is important to determine the causes of the formation of shear droops, but the mechanism is difficult to determine experimentally. Here, the finite element method (FEM) is adopted to study the causes of the formation of shear droops. The cut surfaces in the present experiments have fine sheared surfaces but no fracture surfaces. Although a combination of the fracture criterion and element-kill method is used for many simulations of the fine-blanking process, fine sheared surfaces cannot be evaluated by the combination of these methods. In the present calculations, an adaptive remeshing technique for FEM is used to create fine sheared surfaces. The shear droop is associated with the initial compression by and the subsequent clearance of the punches and dies. Results are obtained for various clearances and initial compressions in the fine-blanking process for high-strength steel, and the experimental and calculation results are compared. In the present paper, we show that the shear droops are affected by the clearance of and initial compression by the punches and die. [doi:10.2320/matertrans.P-M2010828]

Butt Joining of High Strength Steel Sheet and Dissimilar Metal Sheet by Shot Peening

In the shot peening process, the substrate undergoes large plastic deformation near the surface due to the hit with many shots. A large plastic deformation characterized by a shear droop occurs at the edge of the substrate. When the dissimilar sheets with the edge of the notch geometry are connected without level difference and then the contact area are shot-peened, the sheets can be joined due to the plastic flow generated by a large plastic deformation during shot peening. This method is similar to joining by caulking. The aim of this paper is to investigate the butt joining of high strength steel and dissimilar metal sheets using a shot peening process. The shot velocity and the coverage were controlled in the experiment. The shots used were made of high carbon cast steel and cemented carbide with an average diameter of 0.1 mm. The sheets were high strength steel and aluminum alloys. The influences of processing conditions on the joinability were mainly examined. The joint strength increased with the kinetic energy of shots. Tensile test was also examined to evaluate bond strength. It was found that the present method can be used to enhance the butt joining of high strength steel and dissimilar metal sheets.

Butt Joining of Magnesium Alloy Sheet by Shot Peening

Magnesium and its alloys are very attractive for light weight applications. However, their use is complicated by the fact that dissimilar metals are joined by fusion welding. In the present study, the ability of shot peening to enhance butt joining of a magnesium alloy sheet with dissimilar material sheets was investigated. Shot peening improves the performance of the engineering components. In this process the substrate undergoes a large plastic deformation near its surface when hit by many shots. The substrate material close to the surface flows during shot peening. This plastic flow is characterized by a shear droop at the edge of the substrate, namely, the peened material overflows at the edge. When the dissimilar metal sheets with notched edges are connected without a level difference and then the connection is shot-peened, the sheets can be joined by the plastic flow generated by the large plastic deformation during shot peening. In this experiment, an air shot peening machine was used. The influences of air pressure and peening time on the joinability were examined. The joint strength increased with peening time, i.e., the amount of plastic flow. It was found that the present method can be used to enhance the butt joining of a magnesium alloy sheet with a dissimilar material sheet.

Butt Joining of Dissimilar Sheets by Shot Peening

The butt joining of dissimilar sheets using a shot peening process was investigated. Shot peening is a surface treatment and improves the performance of engineering components. In shot peening, the substrate undergoes a large plastic deformation near its surface due to a hit with many shots. Thus, plastic flow characterized by a shear droop occurs at the edge of the substrate due to shot peening. When the dissimilar sheets with the edge of the notch geometry are connected without level difference and shot-peened the connection, the sheets can be joined due to the plastic flow generated by the large plastic deformation during shot peening. In the experiment, a compressed-air-type shot peening machine was employed. The influences of processing conditions on the joining of the dissimilar sheets were examined. The joint strength increased with the kinetic energy of shots. It was found that the present method using shot peening process was effective in joining dissimilar sheets.

2737 粒子衝突による薄板の突合わせ接合(S24-2 塑性加工(2),S24 塑性加工の動向とその展開)

The butt joining of thin sheets using a shot peening process was investigated. Shot peening improves the performance of engineering components. In this process, the substrate undergoes a large plastic deformation near its surface due to a hit with many shots. Thus, at the edge of substrate, large plastic flow characterized by a shear droop occurs. If the dissimilar sheets with the step edge are connected without level difference and then shot-peened the connection, the sheets can be joined due to the plastic flow generated by the large plastic deformation during shot peening. In the experiment, a compressed-air-type shot peening machine was employed. The influence of processing conditions on the joining of the dissimilar sheets was examined. The joint strength increased with the kinetic energy of shots. It was found that the present method using shot peening process was effective for butt joining dissimilar sheets.

Punchless punching of thin sheet metal by ultrahigh pressure gas for circular hole

Traditional punching of sheet metal is performed by punches and dies. If the thickness of the sheet metal is less than 0.1mm, the clearance between the punch and die has to be less than 0.005mm. As the clearance decreases, the punches and dies tend to suffer damage and wear away, and the extreme accuracy of the installation between punches and dies is necessary. As the hole diameter becomes smaller, the punch tend to be broken because of the reduction of punch rigidity. We have studied a new punching method for the thin sheet metal using ultrahigh pressure gas without punch. In this paper, the punching process of circular holes for the sheet is discussed experimentally. The workpieces are thin metal sheets of aluminum and copper. The thicknesses are 0.05 and 0.10mm, and the diameters of the holes range from 1.0mm to 5.0mm. The punching mechanism was clearly explained. The prediction of the minimum pressure required to punch the holes of given sizes could be calculated according to the sheet thicknesses and mechanical properties. The predicted pressure for punching agree well with experimental results for the hole sizes. The cut edge of punched holes have a large shear droop and small fracture surface with a good degree of accuracy in size. The diameters of punched holes are a little small for dies diameters. The differences between punched and dies diameters are about 0.025mm in spite of the material, thickness and hole diameters. The punching of the thin sheet metal was worked easily with high accuracy by our newly invented punchless punching method using ultrahigh pressure gas.

Precision Piercing and Blanking of Fiber Reinforced Plastics by Vibro-Punching

Summary Vibro-Punching is a newly developed precision shearing process in which the sheet material is punched reciprocatively in the state of half shearing by two couples of punch and die. This process was applied to the punching of the composite materials which can not be sheared precisely by any currently used precison shearing process. Experimental results show that all kinds of test composite materials including glass, carbon, aramid fibers and paper in the plastic-bases such as epoxy, phenol, polyimide polymers etc. can be successfully sheared. Sheared surfaces obtained by this process have a sharp edge without shear droop, an accurate right angle to the sheet surface and a glossy surface with the roughness Rmax of 3 - 8μm. Such a precise surface was confirmed to be copied from the side surfaces of punch and die after the softening of matrix polymer by the local temperature rise at the sheared region due to the friction between the sheared surfaces. This process could be applied to some of thermoplastics, PMMA, PC and ABS which are not punched well by a convetional way. As the other applications of this process, the half shearing and the welding of the polymer and its composite were also confirmed to be achieved by stopping the punch movement in the intermediate stage. The prototype machine was completed for punching the riveting hole of Kevlar composite and CFRP sheets for airplane.

アルミニウム薄板のゴム工具による孔あけ加工の研究

A1100P-O and A1100P-H14 of 0.5, 1.0 and 1.5mm in thickness were punched with the die hole diameters of 10, 15, 20, 25 and 30mm. Cutout is generally completed after two steps of fracture. Cutout is impossible in the following three cases from various die thickness conditions. (1) Td>Dd, (2) Td_??_Dd and (3) Td_??_Dd, where Td is die thickness and Dd is die hole diameter. If Td_??_Dd, the primary fracture does not occur. The length of shear droop in the horizontal orientation on the edges of punched products is nearly equal to the sheet thickness. The ratios of fracture surface to sheet thickness of A1100P-O and A1100P-H14 are from 20 to 30% and from 30 to 40% respectively.