Rule based DFM analysis for deep drawing

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Rule based DFM analysis for deep drawing. Deep drawing is a widely used cold sheet metal forming process to draw the sheet metal in forming dye of desirable cross-section using mechanical force of the punch. DFM refers to design for manufacturability. DFA refers to design for assembly. DFMA stands for design for manufacture and assembly. It is a practice for designing the engineering components keeping manufacturing and assembly aspects in mind. DFMA tries to tackle the problems that may come during the manufacturing and assembly at the design stage itself. Changes in the parts design to remove these problems while keeping the functionality of the parts intact. This is done to reduce the cost of iterations thus making the manufacturing of components more efficient and economical.

Contents

In the deep drawing process, a blank of sheet metal (usually circular) is placed on the die. The die is fixed to the base. The metal blank is held in position on the die using blank holder. Mechanical force is applied on the part of the metal blank above the die cavity through a punch. As the punch force increases the metal flows from the flange region in to the die cavity.

Here is the Rule based DFM analysis for Deep drawing process. These rules can be incorporated at the design stage to improve the efficiency of the process:

Material of Sheet Metal

As the deep drawing is a cold forming operation, the germane properties of the sheet metal are formability, ductility and yield strength. The material should have good formability and ductility so that it can be drawn into the desired shape without any cracks. The yield strength of the material should be low facilitating initiation of the flow of metal without tearing near the punch radius.

Clearance between Punch and Die

Clearance between the punch and die guides the flow of the metal into the die. Clearance should be more than the metal thickness to avoid concentration of metal at the top of the die cavity. Clearance should not be as large so that the flow of metal into the die region becomes unrestricted leading to the wrinkling of wall. [1]

Die corner radius

Radius of curvature at the die where the metal enters from the flange region into the die region is an important geometrical parameter. If the die corner radius is small than wrinkling near the flange region becomes more prominent. Too small die corner radius results in cracks due to sharp change in the direction of metal flow. Generally it should be 5-10 times the sheet thickness. [2]

Punch corner radius

As the metal draws into the die the thickness of the sheet decreases near in the lower region of the punch. Maximum reduction happens near punch corner because the metal flow decreases significantly here. Too sharp corner results in cracks near the punch base. Corner radius of punch should be 4-10 times the sheet thickness. [3]

Blank holding force

The friction in the flange region is mainly affected by blank holding force. Blank holding force is required for checking the amount of the metal flow in to the die. The low value of blank holding force results in wrinkling in the flange region and too high value of holding force results in increase in the drawing force due to the increase in the friction between the flange region. The blank holding force should be just enough to restrict the flow of the metal.

Drawing Ratio

Measurement of the amount of drawing performed on a sheet metal blank is quantified using drawing ratio. The higher the drawing ratio, the more extreme the amount of deep drawing. Due to the geometry, forces, metal flow and material properties of the work, there is a limit to the amount of deep drawing that can be performed on a sheet metal blank in a single operation. The drawing ratio is roughly calculated as, DR = Db/Dp. Db is the diameter of the blank and Dp is the diameter of the punch. For shapes that are noncircular the maximum diameter is sometimes used, or occasionally drawing ratio is calculated using surface areas. The limit to the drawing ratio for an operation is usually 2 or under . [4]

Related Research Articles

A die is a specialized tool used in manufacturing industries to cut or shape material mostly using a press. Like molds, dies are generally customized to the item they are used to create. Products made with dies range from simple paper clips to complex pieces used in advanced technology.

Sheet metal Metal formed by an industrial process into thin, flat pieces. Sheet metal is one of the fundamental forms used in metalworking, and it can be cut and bent into a variety of shapes.

Sheet metal is metal formed by an industrial process into thin, flat pieces. Sheet metal is one of the fundamental forms used in metalworking, and it can be cut and bent into a variety of shapes. Countless everyday objects are fabricated from sheet metal. Thicknesses can vary significantly; extremely thin sheets are considered foil or leaf, and pieces thicker than 6 mm (0.25 in) are considered plate steel or "structural steel".

Hydroforming Method of shaping metal through pressurized water

Hydroforming is a cost-effective way of shaping ductile metals such as aluminium, brass, low alloy steel, and stainless steel into lightweight, structurally stiff and strong pieces. One of the largest applications of hydroforming is the automotive industry, which makes use of the complex shapes made possible by hydroforming to produce stronger, lighter, and more rigid unibody structures for vehicles. This technique is particularly popular with the high-end sports car industry and is also frequently employed in the shaping of aluminium tubes for bicycle frames.

Drawing is a metalworking process which uses tensile forces to stretch metal glass, or plastic. As the metal is drawn (pulled), it stretches thinner, into a desired shape and thickness. Drawing is classified in two types: sheet metal drawing and wire, bar, and tube drawing. The specific definition for sheet metal drawing is that it involves plastic deformation over a curved axis. For wire, bar, and tube drawing, the starting stock is drawn through a die to reduce its diameter and increase its length. Drawing is usually done at room temperature, thus classified a cold working process, however it may be performed at elevated temperatures to hot work large wires, rods or hollow sections in order to reduce forces.

Punching metal forming process that uses a punch press to force a tool, called a punch, through the workpiece to create a hole via shearing

Punching is a forming process that uses a punch press to force a tool, called a punch, through the workpiece to create a hole via shearing. Punching is applicable to a wide variety of materials that come in sheet form, including sheet metal, paper, vulcanized fibre and some forms of plastic sheet. The punch often passes through the work into a die. A scrap slug from the hole is deposited into the die in the process. Depending on the material being punched this slug may be recycled and reused or discarded.

Design for manufacturability

Design for manufacturability is the general engineering practice of designing products in such a way that they are easy to manufacture. The concept exists in almost all engineering disciplines, but the implementation differs widely depending on the manufacturing technology. DFM describes the process of designing or engineering a product in order to facilitate the manufacturing process in order to reduce its manufacturing costs. DFM will allow potential problems to be fixed in the design phase which is the least expensive place to address them. Other factors may affect the manufacturability such as the type of raw material, the form of the raw material, dimensional tolerances, and secondary processing such as finishing.

Stamping (metalworking) metalworking

Stamping is the process of placing flat sheet metal in either blank or coil form into a stamping press where a tool and die surface forms the metal into a net shape. Stamping includes a variety of sheet-metal forming manufacturing processes, such as punching using a machine press or stamping press, blanking, embossing, bending, flanging, and coining. This could be a single stage operation where every stroke of the press produces the desired form on the sheet metal part, or could occur through a series of stages. The process is usually carried out on sheet metal, but can also be used on other materials, such as polystyrene. Progressive dies are commonly fed from a coil of steel, coil reel for unwinding of coil to a straightener to level the coil and then into a feeder which advances the material into the press and die at a predetermined feed length. Depending on part complexity, the number of stations in the die can be determined.

Bending (metalworking) metalworking term

Bending is a manufacturing process that produces a V-shape, U-shape, or channel shape along a straight axis in ductile materials, most commonly sheet metal. Commonly used equipment include box and pan brakes, brake presses, and other specialized machine presses. Typical products that are made like this are boxes such as electrical enclosures and rectangular ductwork.

Deep drawing

Deep drawing is a sheet metal forming process in which a sheet metal blank is radially drawn into a forming die by the mechanical action of a punch. It is thus a shape transformation process with material retention. The process is considered "deep" drawing when the depth of the drawn part exceeds its diameter. This is achieved by redrawing the part through a series of dies. The flange region experiences a radial drawing stress and a tangential compressive stress due to the material retention property. These compressive stresses result in flange wrinkles. Wrinkles can be prevented by using a blank holder, the function of which is to facilitate controlled material flow into the die radius.

Press brake Machine pressing tool for bending sheet and plate material, most commonly sheet metal. It forms predetermined bends by clamping the workpiece between a matching punch and die.

A press brake is a machine pressing tool for bending sheet and plate material, most commonly sheet metal. It forms predetermined bends by clamping the workpiece between a matching punch and die.

Shear forming

Shear forming, also referred as shear spinning, is similar to metal spinning. In shear spinning the area of the final piece is approximately equal to that of the flat sheet metal blank. The wall thickness is maintained by controlling the gap between the roller and the mandrel. In shear forming a reduction of the wall thickness occurs.

Blanking and piercing

Blanking and piercing are shearing processes in which a punch and die are used to modify webs. The tooling and processes are the same between the two, only the terminology is different: in blanking the punched out piece is used and called a blank; in piercing the punched out piece is scrap. The process for parts manufactured simultaneously with both techniques is often termed "pierce and blank." An alternative name of piercing is punching.

Tube bending

Tube bending is any metal forming processes used to permanently form pipes or tubing. Tube bending may be form-bound or use freeform-bending procedures, and it may use heat supported or cold forming procedures.

Formability is the ability of a given metal workpiece to undergo plastic deformation without being damaged. The plastic deformation capacity of metallic materials, however, is limited to a certain extent, at which point, the material could experience tearing or fracture (breakage).

Press tools are commonly used in hydraulic, pneumatic, and mechanical presses to produce the sheet metal components in large volumes. Generally press tools are categorized by the types of operation performed using the tool, such as blanking, piercing, bending, forming, forging, trimming etc. The press tool will also be specified as a blanking tool, piercing tool, bending tool etc.

Extrusion is a plastic deformation process in which raw material (billet) is forced to flow by compression through the die opening of a smaller cross-section area. The extrusion process is divided in two basic types: direct extrusion and indirect extrusion. In direct extrusion the billet is pushed through the die with ram pressure, whereas in indirect extrusion die moves relative to the container.

DFM Guidelines for Hot Metal Extrusion Process

Extrusion is a metal forming process to form parts with constant cross-section along its length. This process uses a metal billet or ingot which is inserted in a chamber. One side of this contains a die to produce the desired cross section and the other side a hydraulic ram is present to push the metal billet or ingot. Metal flows around the profile of the die and after solidification takes the desired shape.
Extrusion process can be done with the material hot or cold, but most of the metals are heated before the process, if high surface finish and tight tolerances are required then the material is not heated.

Rule based DFM analysis for metal spinning. Metal spinning is a lesser known metal forming and fabricating manufacturing process. It is more conventionally used for the manufacturing of axis-symmetric parts. Its ability to create parts that require high tolerance and high strength makes it an outstanding process to manufacture a wide range of parts for automobile, aerospace, defence and medical industries. Typical components produced by metal spinning are lamp bases, reflectors, hollowware, pots, bans bowls and components for electrical equipment. Design for manufacturability is the general engineering art of designing products in such a way that they are easy to manufacture. The concept exists in almost all engineering disciplines, but the implementation differs widely depending on the manufacturing technology. DFM describes the process of designing or engineering a product in order to facilitate the manufacturing process in order to reduce the manufacturing costs. DFM will allow potential problems to be fixed in the design phase which is the least expensive place to address them. Other factors may affect the manufacturability such as the type of raw material, the form of the raw material, dimensional tolerances, and secondary processing such as finishing.

Design of plastic components

Injection molding has been one of the most popular ways for fabricating plastic parts for a very long time. They are used in automotive interior parts, electronic housings, housewares, medical equipment, compact discs, and even doghouses. Below are certain rule based standard guidelines which can be referred to while designing parts for injection molding considering manufacturability in mind.

Rule based DFM analysis for forging. Forging is the controlled deformation of metal into a specific shape by compressive forces. The forging process goes back to 8000 B.C. and evolved from the manual art of simple blacksmithing. Then as now, a series of compressive hammer blows performs the shaping or forging of the part. Modern forging uses machine driven impact hammers or presses which deform the work-piece by controlled pressure.

References

  1. "Deep Drawing" . Retrieved 10 September 2015.
  2. "Metal Forming Process" (PDF). Archived from the original (PDF) on 2016-03-04.
  3. "Influence of process parameters in deep drawing" (PDF).
  4. "Deep Drawing".