fo ssenkchTＴ：ecepssenkchecept iiiiit： iignkrowgnkroW※Tip perimeterTip shape A：L＝πP：A＝0.25πH：A＝0.25πH－0.25πM：A＝0.25πD：A＝0.25πD－0.25πM※Acreage of headPunchesH：head diameterM：screw hole diameterD：shank diameter h＝H＋Ttan15Heavy load punches·ejector heavy load punches·punches with centre hole h＝D＋Ttan15※Diameter after diffusionpunches・ejector punches・punches with centre holerenateRSunkenFrictionRepeatPunching forceShape recoveryFrictionAfter long-time useRemaining sunkenMounting holeis expandedUnstable tipTensile strength ofworking piece：σBPicture 1Picture 2Diameter after diffusion：hIntensity of pressureafter diffusion：σ2The diffused range of forceon backing plate is 30HeadIntensity of pressure：σ1Acreage：Atip perimeter：LCounterforce：FHeadRetainer sets for high-tensile strength materialFor automobile manufacture, the acting force between high-tensile strength material and punch is high. In order to extend the lifespan, coating treatment is applied to punch to improve the wearability. But the lifespan of punch is not only decided by tip wearability, but also retainers. High tensile strength of the material will lead to high counterforce to punch, and it will be transferred to the backing plate, even to the mold （casting part）. If the situation continues, the mounting hole of retainer will be expanded, and the mounting surface of retainer may even be sunken. Here punch shank will be loose, and the tip will be unstable. This may expedite the wear of punch, and shorten the lifespan （refer to the drawings below）. In order to diffuse the stress to retainers for high-tensile strength material, thickness alteration of backing plate is applied （from 5mm to 6～15mm）.Standard of selectionFor molds in useRetainers for high-tensile strength material are recommended for the following situations： 1 Sunken is found on the backing plate（Picture 1）. 2 Sunken is found on the mounting surface （casting surface） of mold while removing the retainer ※1. 3 Press-in punch can be easily demounted from the retainer. 4 Black mark （electrochemical corrosion） is found on the shank of demounted punch（Picture 2）. ※1 New retainer is recommended after flatting the mounting surface. ※2 Electrochemical corrosion is the phenomena of acidification（corrosion）occurred by potential difference caused by rubbing between 2 different type of metals.For new molds designingCalculate the bottom stress of punch according to the tensile strength and thickness of high-tensile strength material, as well as mounting hole shape （P・W dimensions of punch） and punch bottom acreage. If the stress is 49N/mm2 or more（5kgf/mm2 or more）（for the mounting surface of retainer is raw material or casting） or above, retainers for high-tensile strength material is recommended. For backing plates of entire quenching, the acting force P on the bottom of punch will diffuse in a range of 30°. And for retainers for high-tensile strength material, stress on the mounting surface will be lowered, and the lifespan is extended by using thicker backing plates. Selection of backing plate thicknessCalculate the stress on the bottom of punch according to ① and ②. If the target value is 5kgf/mm2 or more, please select retainers for high-tensile strength material, and calculate the backing plate thickness through ③. 1 Calculate the counterforce Counterforce F＝L（tip perimeter：mm）× t（thickness of working piece：mm）× σB（tensile strength of working piece：kgf/mm2）× 0.8. 2Calculate the intensity of pressure on the head σ1［kgf/mm2］ Intensity of pressure on the head σ1＝F（counterforce：kgf）÷A（sectional acreage of head：mm2） ・・・Retainers for high tensile material are recommended if the result is 5［kgf/mm2］ or more. 3 For retainers for high-tensile strength material, the intensity of pressure after diffusion is σ2≦5［kgf/mm2］ Please select backing plates with thickness T［mm］ Intensity of pressure after diffusionσ2＝F（counterforce：kgf）÷0.25πh（diameter after diffusion：mm）H：head diameterD：shank diameterT：backing plate thicknessF：counterforce For T dimension calculation, alter the above formula as follows: Punches・ejector punches・punches with centre hole･･･････････････T≧1.87（ 0.255F−H） Heavy load punches・ejector heavy load punches・ heavy load punches with centre hole････････････････････････････ T≧1.87（ 0.255F−D）Notes for designingBecause the body of retainer is unchanged, the mounting dimension is the same, too. But the thickness of backing plate is altered from 5mm to 6～15mm. For alteration of retainers for high-tensile strength material, please take the altered backing plate thickness and the length of punch into account when assembling with punches. Tip shape E：L＝πW＋2（P－W）Tip shape R：L＝2πR＋P＋W－4RTip shape D：L＝2（P＋W）Tip shape G：L＝2 P2－W2 ＋πPsin-1（W÷P）÷90Ejector punchesPunches with centre hole：A＝0.25πH－4.71Heavy load punchesEjector heavy load punchesEjector punches with centre hole：A＝0.25πD－4.71569Retainers for High-Tensile Material
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