If the metal has been cold-rolled or -worked, the crystals elongate in the direction of rolling (see Figure 1). I am trying to explain grain direction and need a picture of L, LT & ST to define. In a seminar I went to many years ago the instructor said that the metal was stronger in the direction of rolling than it was across the direction of rolling. There seems to be two things related to this when its concerned with PCB. A grain is a region where the atoms are aligned. I am assuming the grain would run the long 8' direction of a sheet 4' x 8' I need to bend the parts across the grain and the material has not shown up yet but I want to nest the parts in the sheet. The grain is on both sides of the sheet, and run the same direction, but there is only protective film on one side. Should the strains in the grain direction exceed the shear fracture strains of the wood, discontinuous chips are … Another is the grain direction on the copper which decides the dirction of least resistence so most traces are to go in that direction. The grain direction of board (thicker paper) can be determined by checking the resistance of the board by bending slightly from end to end. It is the direction in which the metal was produced, so when you look at … One direction offers considerably more resistance than the other. The structure and size of the grains determine important physical Stroke the cat (or board) one way and the cat will purr, and your tool will produce a … Short of looking at the microstructure, there isn't a good way to tell. When bending metal along this grain there’s an increased risk of cracking, especially when putting-in a tight radius. Individual grains are elongated in the direction of the metal flow or plastic deformation. That is why when used in applications requireing max strength, forging is used for the primary shaping. Randomly oriented, the grains contact each other at surfaces called grain boundaries. I often tell people that the grain direction in a board is like the fur on a cat. CoryPad (Materials) 12 Dec 09 01:30 The horizontal lines are grooves that form during etching (was this chemical or electrical?) These are few examples of grains that are easily seen by naked eye or could be observed with a use of a simple magnifying glass. Be careful not to confuse this with surface finishes produced by grinding of other finishing operations. Understanding Grain Direction We show you two ways to read grain direction (even in rough stock) that will help you get tear-out-free surfaces. When a metal solidifies from the molten state, millions of tiny crystals start to grow. Work-hardening. RE: Metal Grain Direction Test? Like the grain in wood, a metal’s grain affects how the piece behaves. If they have sheared edges, then the short direction is the grain direction. Am I correct in stating that for a rectanglar bar, L = Longitudinal or actual grain direction, ST = Short Transverse = Thickness and LT = width. The longer the metal takes to cool the larger the crystals grow. Most grain boundaries are preferred sites for the onset of corrosion and for the precipitation of new phases from the solid. Since metal rolling affects grain orientation, a part can be rolled in a way as to create grains oriented in a direction such that they give directional strength … These crystals form the grains in the solid metal. that follow chemical segregation and other structural irregularities that form during thermomechanical processing. What sheet metal shops wish you knew: Reasonable tolerances, grain direction, and the base flange; Share. 2. Grind and then fine polish any of the resulting surfaces—exposed top or bottom, edge parallel to rolling direction, or edge perpendicular to the rolling direction. What is the grain direction is a pcb? Grain direction. Slight, but is there. And if I remember correctly it was weakest in the through thickness direction. The grain direction of the paper is important when binding books, because paper is scored and folded. It depends. Read on Mobile Enter Reading Mode. Cut a small coupon of sheetmetal. Cold rolling processes as discussed earlier, are useful for imparting strength and favorable grain orientation. RE: Grain direction in bending sheet metal berkshire (Aeronautics) 16 Aug 07 04:50 5052 is a pretty soft alloy and if the part is air bent there should be no cracking problems either with the grain or … Sorry for the dumb question I have had these parts cut in the past by someone else with a waterjet and this will be my first try on my router. Parallel to the grain direction the resistance is far less than against the grain. Grain size is not generally used to control strength in the aluminium alloys, although it is used extensively in reducing the risk of hot cracking and in controlling both strength and notch toughness in C/Mn and low-alloy steels. Longitudinal (the directional force is across the grain): it is harder to fracture the specimen and therefore takes more energy to fracture the steel across the grain. The weld-metalgrain structure can be refined by makingchanges in theprocess variables andthe useof externaldevices suchas it will take more joules (or foot pounds) of absorbed energy to break a longitudinal specimen). Individual grains are elongated in the direction of the metal … More importantly, non-metallic inclusions, particles and other impurities inherited during the casting process are elongated in the direction of grain flow. What is metal grain direction - Answers.com Metal Grain Direction is similar to Wood Grain Direction. The preferred grain selection process that occurs during welding promotes a columnar grain structure. Stuart Keeler President/owner Why Sheetmetal Grain Size is Important February 1, 2011. If the pieces are still covered in mill scale (edges too) the grain direction will be that of the 8ft length. It’s always best to bend across the grain. Individual grains are elongated in the direction of the metal flow or plastic deformation. The grain size has an important effect on the mechanical properties of a metal. Rolling metal into sheet form at the mill elongates the metal crystals and gives it a grain. Grain direction is an important consideration in printing processes such as sheet fed offset lithography (in particular multiple-colour work), especially in connection with dimensional stability (how well a particular sheet of paper will retain its original length and width upon exposure to moisture and pressure). In such a case, anisotropy may cause shear to occur preferentially along the grain direction rather than at the primary shear plane angle given by isotropic continuum mechanics. One is with the FR4 material where grain direction decides warpage direction. Each grain is a distinct crystal with its own orientation. The size of the grains depends upon a number of factors, but the principal one is the heat treatment to which the metal has been subjected. Acually, the grain direction is not just cosmetic, but adds only a little more strength than cross grain does, and does have a slight advantage over cross grain. Therefore, knowing the grain direction and how it will affect the layout of your project makes a big difference in the quality of your finished piece. Grain Direction A "grain" is formed in metal in the direction in which the sheet is rolled at the mill. In addition to the new "bounding box" sketch, there is a new option in the property manager for the Flat-Pattern feature: "Grain Direction".You can define a grain direction to use when calculating the bounding box for sheet metal parts. Grain in a sand is barely visible but a grain of a rice is quite visible. 1. A grain boundary is the interface between two grains, or crystallites, in a polycrystalline material.Grain boundaries are 2D defects in the crystal structure, and tend to decrease the electrical and thermal conductivity of the material. Varying from sheet to sheet and batch to batch, changing grain properties create many unforeseen challenges. Grain flow is a directional orientation of metal grains and any inclusions that have been deformed by forging. Also, the grain looks identical on the 304 and 430 stainless steel, but the protective film may be different colors. Therefore, knowing the grain direction and how it will affect the layout of a project makes a big difference in the quality of the finished piece. Grain direction is very important and makes a huge difference as to how the paper will react when attempting to fold, score and bind it. Grain, in metallurgy, any of the crystallites (small crystals or grains) of varying, randomly distributed, small sizes that compose a solid metal. Definition: Forging Flow Lines is a directional orientation of metal grains and any non-metallic inclusions that have been deformed due to forging. In metals, atoms are arranged in a crystal structure (it is not just a mess of atoms, the atoms line up in rows). For bookbinding, you should always fold with the grain direction parallel to the fold and the spine of your binding. Grain direction is very important and makes a huge difference as to how the paper will react when you attempt to fold, score and bind it. Grain flow is a directional orientation of metal grains and any inclusions that have been deformed by forging. The former is the grain direction; the latter is the cross direction. The size and number of grains a material has is guided by the rate of the metal’s solidification from its liquid state. The software determines the smallest rectangle (bounding box) that aligns with the grain direction to fit the flat pattern. In general terms, as grain size increases, the yield and ultimate tensile strengths of a metal … theheatflow direction in welds. When the metal has been cold-rolled or cold-worked, the crystals elongate and take a directional preference in the direction of roll, creating the grains we see. The areas between the grains are known as grain boundaries. Figure 4 shows both epitaxial growth and a columnar grain structure in an iridium alloy weld. If the material is to be hemmed, the protective film will be on the outside, unless it is specified to be different. Posted By" ">Steve on October 18, 2002 at 16:49:54:. Longitudinal test pieces therefore have higher notch toughness’ (i.e. Setup of that production line and the methods used to bend sheet metal are important to sheet metal design.