Bending

Introduction

Bending is a process by which metal can be deformed by plastically deforming the material and changing its shape. The material is stressed beyond the yield strength but below the ultimate tensile strength. The surface area of the material does not change much. Bending usually refers to deformation about one axis.
Bending is a flexible process by which many different shapes can be produced. Standard die sets are used to produce a wide variety of shapes. The material is placed on the die, and positioned in place with stops and/or gages. It is held in place with hold-downs. The upper part of the press, the ram with the appropriately shaped punch descends and forms the v-shaped bend.
Bending is done using Press Brakes. Press Brakes normally have a capacity of 20 to 200 tons to accommodate stock from 1m to 4.5m (3 feet to 15 feet). Larger and smaller presses are used for specialized applications. Programmable back gages, and multiple die sets available currently can make for a very economical process.
Air Bending is done with the punch touching the workpiece and the workpiece, not bottoming in the lower cavity. This is called air bending. As the punch is released, the workpiece ends up with less bend than that on the punch (greater included angle). This is called spring-back. The amount of spring back depends on the material, thickness, grain and temper. The spring back usually ranges from 5 to 10 degrees. Usually the same angle is used in both the punch and the die to minimize setup time. The inner radius of the bend is the same as the radius on the punch.

Bottoming or Coining is the bending process where the punch and the workpiece bottom on the die. This makes for a controlled angle with very little spring back. The tonnage required on this type of press is more than in air bending. The inner radius of the workpiece should be a minimum of 1 material thickness in the case of bottoming; and upto 0.75 material thickness, in the case of coining.

CNC Cutting, Engraving and Dispensing Solutions -- The fastest router for 3D applications

Precix Advanced Cutting Technologies designs and manufactures computerized XYZ CNC tables for cutting, engraving and dispensing. Our router tables are the fastest in 3D routing.
Precix also develops the 3 to 6 axis CNC motion control systems that drive these cutting, engraving and dispensing tables.
Precix has over 1300 CNC users in 40 countries around the world. Precix CNC tables can be set up as CNC routers, CNC dispensers, CNC lasers or for any other CNC applications. They are used by signmakers, architects, custom cabinet makers and pattern makers. Other uses include trimming plastic, CNC machining and fabricating as well as automated cutting for the vacuum forming industry. Precix CNC tables are used in Industries that range from the home appliance manufacuring to the automotive parts, to the point of purchase market.
Precix OEM customers use our technology to integrate into CNC printing tables, liquid dispensing machines, CNC laser cutting systems and computerized mat cutters for the picture frame industry. We also OEM controllers for CNC equipment manufacturers.

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Laser cutting

Introduction

Laser cutting machines can accurately produce complex exterior contours. The laser beam is typically 0.2 mm (0.008 in) diameter at the cutting surface with a power of 1000 to 2000 watts.
Laser cutting can be complementary to the CNC/Turret process. The CNC/Turret process can produce internal features such as holes readily whereas the laser cutting process can produce external complex features easily.
Laser cutting takes direct input in the form of electronic data from a CAD drawing to produce flat form parts of great complexity. With 3-axis control, the laser cutting process can profile parts after they have been formed on the CNC/Turret process.
Lasers work best on materials such as carbon steel or stainless steels. Metals such as aluminum and copper alloys are more difficult to cut due to their ability to reflect the light as well as absorb and conduct heat. This requires lasers that are more powerful.

Design Considerations


Lasers cut by melting the material in the beam path. Materials that are heat treatable will get case hardened at the cut edges. This may be beneficial if the hardened edges are functionally desirable in the finished parts. However, if further machining operations such as threading are required, then hardening is a problem.
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A hole cut with a laser has an entry diameter larger than the exit diameter, creating a slightly tapered hole.
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The minimum radius for slot corners is 0.75 mm (0.030 in). Unlike blanking, piercing, and forming, the normal design rules regarding minimum wall thicknesses, minimum hole size (as a percent of stock thickness) do not apply. The minimum hole sizes are related to stock thickness and can be as low as 20% of the stock thickness, with a minimum of 0.25 mm (0.010 in) for upto 1.9 mm (0.075 in). Contrast this with normal piercing operations with the recommended hole size 1.2 times the stock thickness.
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Burrs are quite small compared to blanking and shearing. They can be almost eliminated when 3D lasers are used and further, eliminate the need for secondary deburring operations.
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As in blanking and piercing, considerable economies can be obtained by nesting parts, and cutting along common lines. In addition, secondary deburring operations can be reduced or eliminated.

Computer Numerical Control (CNC) fabrication

Introduction


The Computer Numerical Control (CNC) fabrication process offers flexible manufacturing runs without high capital expenditure dies and stamping presses. High volumes are not required to justify the use of this equipment.
Tooling is mounted on a turret which can be as little as 10 sets to as much as 100 sets. This turret is mounted on the upper part of the press, which can range in capacity from 10 tons to 100 tons in capacity.
The turret travels on lead screws, which travel in the X and Y direction and are computer controlled. Alternatively, the workpiece can travel on the lead screws, and move relative to the fixed turret. The tooling is located over the sheet metal, the punch is activated, and performs the operation, and the turret is indexed to the next location of the workpiece. After the first stage of tooling is deployed over the entire workpiece, the second stage is rotated into place and the whole process is repeated. This entire process is repeated until all the tooling positions of the turret are deployed.
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Advantages
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The process is very flexible in being able to produce many different configurations of parts due to the modular nature of the tooling employed. In most cases, most of the punches and dies are already available and they can be mixed and matched to produce a variety of configurations.
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Due to the fact that most of the tooling is "available"; the lead-time for tooling is reduced or non-existent. All that needs to be done is to schedule the work order in the production shop, after the programming of the CNC process is done.
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The quantities that can be economically made can be in the thousands depending on the complexity of the part. Simple outer contours and normal size holes will allow the use of this process for many thousands of parts. However, when the part design involves irregular outer contours or large holes requiring a long cycle time, then dedicated tooling can be justified for smaller production runs. Certain parts with tightly spaced hole patterns or slots require expensive dedicated tooling, however with the CNC turret press, these parts can be easily made using standard tooling.
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Design Considerations
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To maximize utilization of material, parts are nested as close to each other as possible. They are separated from one another by "micro-ties" which are small width strips that hold the parts together during the punching process. After punching, the parts are separated by vibrating them in a shaker. The parts are known as "shaker parts" or "shake a part". This is very cost effective since no special tooling is necessary for separating them.
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Burrs are inevitable in the stamping process. The burrs are formed on the side of the sheet metal where the punch exits. Properly maintained tools (proper die clearance and sharpening) have burrs that are less than 10 % of stock thickness. When designing parts, the burrs should be confined to areas that will not be exposed to handling and should be either folded away or otherwise shielded form the user. Otherwise, an added operation of deburring needs to be done at added cost.
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Flatness/bowing can be an issue if the hole pattern is tight, and/or where excessive material is punched out. This releases the residual stresses in the material, which causes bowing or twisting of the part. Proper use of clamping and strippers can minimize this, as can subsequent straightening operations. Recognizing which side the bow can occur can also allow some designs to accept this out of flat condition by designing features that are not sensitive to this condition.
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Edge conditions. Quite often, curves and other difficult features are produced by punching out small sections at a time. This process is called nibbling. This leads to triangular shaped features. These triangular shaped features give the edge a scalloped look. This scalloping can be pronounced if the nibbling pitch is coarse. The amount of scalloping that can be accepted is a function of tooling and product cost. Clamp marks are cosmetic in nature, and if objectionable, can be so positioned to cut them away in subsequent processing.
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Lockwashers for threads can be eliminated by forming a dome on the side opposite to the screw head. As the screw is tightened, the domed thread form locks against the male thread and prevents the screw from vibrating loose in service.
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Parts that need to be welded can be positioned very precisely using shear buttons. Shear buttons on one surface are snugly fitted inside the corresponding holes into the other surface. This allows the parts to be self-jigging and eliminate the need for fixtures and other hold-downs.
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Dimensioning. As in all part design, the designer should be aware of process strengths, weaknesses. Datums should be through hole centers rather than edges of parts. This is because edges can have tapers or roll-offs, which can skew a datum and subsequent measurement. Sound practice of tolerancing methods such as geometric dimensioning and tolerancing are appropriate for the dimensioning of these parts.
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Process Tolerances. Feature tolerances can vary from ±0.12 to ±0.38 mm (±0.005 to ±0.015 in). The program can be tweaked (a little!) to improve these numbers. Repeatability is 0.05 mm (0.002 in) as long as the machine lead screw advances only in one direction.


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