A die is a specialized tool used in manufacturing industries to cut, shape and form a wide variety of products and components. Like molds and templates, dies are generally customized and uniquely matched to the product they are used to create. Products made with dies range from simple paper clips to complex pieces used in advanced technology.
Die forming
Progressive die with scrap strip and stampings
Forming dies are typically made by tool and die makers and put into production after mounting into a press. The die is a metal block that is used for forming materials like sheet metal and plastic. For the vacuum forming of plastic sheet only a single form is used, typically to form transparent plastic containers (called blister packs) for merchandise. Vacuum forming is considered a simple molding thermoforming process but uses the same principles as die forming. For the forming of sheet metal, such as automobile body parts, two parts may be used, one, called the punch, performs the stretching, bending, and/or blanking operation, while another part, called the die block, securely clamps the workpiece and provides similar, stretching, bending, and/or blanking operation. The workpiece may pass through several stages using different tools or operations to obtain the final form. In the case of an automotive component there will usually be a shearing operation after the main forming is done and then additional crimping or rolling operations to ensure that all sharp edges are hidden and to add rigidity to the panel.
Die components
- Die block
- Punch plate
- Blank punch
- Pierce punch
- Stripper plate
- Pilot
- Dowel Pin
- Back gage
- Finger stop
Die operations and types
Die operations are often named after the specific type of die that performs the operation. For example a bending operation is performed by a bending die. Operations are not limited to one specific die as some dies may incorporate multiple operation types.
Press with bending die
- Bending: The bending operation is the act of bending blanks at a predetermined angle. An example would be an "L" bracket which is a straight piece of metal bent at a 90° angle. The main difference between a forming operation and a bending operation is the bending operation creates a straight line bend (such as a corner in a box) as where a form operation may create a curved bend (such as the bottom of a drinks can).
- Blanking: A blanking die produces a flat piece of material by cutting the desired shape in one operation. The finish part is referred to as a blank. Generally a blanking die may only cut the outside contour of a part, often used for parts with no internal features.
Three benefits to die blanking are:
- Accuracy. A properly sharpened die, with the correct amount of clearance between the punch and die, will produce a part that holds close dimensional tolerances in relationship to the parts edges.
- Appearance. Since the part is blanked in one operation, the finish edges of the part produces a uniform appearance as opposed to varying degrees of burnishing from multiple operations.
- Flatness. Due to the even compression of the blanking process, the end result is a flat part that may retain a specific level of flatness for additional manufacturing operations.
- Broaching: Broaching is the process of removing material through the use of multiple cutting teeth, with each tooth cutting behind the other. A broaching die is often used to remove material from parts that are too thick for shaving.
- Bulging: A bulging die expands the closed end of tube through the use of two types of bulging dies. Similar to the way a chefs hat bulges out at the top from the cylindrical band around the chefs head.
- Bulging fluid dies: Uses water or oil as a vehicle to expand the part.
- Bulging rubber dies: Uses a rubber pad or block under pressure to move the wall of a workpiece.
- Coining: is similar to forming with the main difference being that a coining die may form completely different features on either face of the blank, these features being transferred from the face of the punch or die respectively. The coining die and punch flow the metal by squeezing the blank within a confined area, instead of bending the blank. For example: an Olympic medal that was formed from a coining die may have a flat surface on the back and a raised feature on the front. If the medal was formed (or embossed), the surface on the back would be the reverse image of the front.
- Compound operations: Compound dies perform multiple operations on the part. The compound operation is the act of implementing more than one operation during the press cycle.
- Compound die: A type of die that has the die block (matrix) mounted on a punch plate with perforators in the upper die with the inner punch mounted in the lower die set. An inverted type of blanking die that punches upwards, leaving the part sitting on the lower punch (after being shed from the upper matrix on the press return stroke) instead of blanking the part through. A compound die allows the cutting of internal and external part features on a single press stroke.
- Curling: The curling operation is used to roll the material into a curved shape. A door hinge is an example of a part created by a curling die.
- Cut off: Cut off dies are used to cut off excess material from a finished end of a part or to cut off a predetermined length of material strip for additional operations.
- Drawing: The drawing operation is very similar to the forming operation except that the drawing operation undergoes severe plastic deformation and the material of the part extends around the sides. A metal cup with a detailed feature at the bottom is an example of the difference between formed and drawn. The bottom of the cup was formed while the sides were drawn.
- Extruding: Extruding is the act of severely deforming blanks of metal called slugs into finished parts such as an aluminum I-beam. Extrusion dies use extremely high pressure from the punch to squeeze the metal out into the desired form. The difference between cold forming and extrusion is extruded parts do not take shape of the punch.
- Forming: Forming dies bend the blank along a curved surface. An example of a part that has been formed would be the positive end(+) of a AA battery.
- Cold forming (cold heading): Cold forming is similar to extruding in that it squeezes the blank material but cold forming uses the punch and the die to create the desired form, extruding does not.
- Roll forming:
is a continuous bending operation in which sheet or strip metal is gradually formed in tandem sets of rollers until the desired cross-sectional configuration is obtained. Roll forming is ideal for producing parts with long lengths or in large quantities.
- Horning: A horning die provides an arbor or horn which the parts are place for secondary operations.
- Hydroforming: Forming of tubular part from simpler tubes with high water pressure.
- Pancake die: A Pancake die is a simple type of manufacturing die that performs blanking and/or piercing. While many dies perform complex procedures simultaneously, a pancake die may only perform one simple procedure with the finished product being removed by hand.
- Piercing: The piercing operation is used to pierce holes in stampings.
- Progressive die: Progressive dies provide different stations for operations to be performed. A common practice is to move the material through the die so it is progressively modified at each station until the final operation ejects a finished part.
- Shaving: The shaving operation removes a small amount of material from the edges of the part to improve the edges finish or part accuracy. (Compare to Trimming).
- Side cam die: Side cams transform vertical motion from the press ram into horizontal or angular motion.
- Sub press operation: Sub-press dies blank and/or form small watch, clock, and instrument parts.
- Swaging: Swaging (necking) is the process of "necking down" a feature on a part. Swaging is the opposite of bulging as it reduces the size of the part. The end of a shell casing that captures the bullet is an example of swaging.
- Trimming: Trimming dies cut away excess or unwanted irregular features from a part, they are usually the last operation performed.
Die casting
-
Main article: Die casting
For the casting of low melting point metals (such as pot metal, lead, aluminum, or magnesium) a multi-part die is used in a process called die casting. For automotive parts such as the cases of automatic transmissions these dies may be quite complex, as they must be disassembled in specific order to ensure that the workpiece is released freely from the casting die. Parts or products produced by this method are referred to as die cast. Compared to lost wax casting the marginal production can be quite cheap, once the substantial investment in tooling and materials handling equipment is made. Compared to sand casting the die casting method can reproduce fine details on complex parts and yield a smooth surface, greatly reducing machining and polishing requirements. As some small portion of metal may leak between the mating seams of the die this can result in a sharp edge of metal called flash, which must be removed by grinding and buffing. For small metal toys the term die cast is generally considered a mark of quality, especially when compared to the cheaper stamping of lithographed sheet metal, or bare stamped metal possibly later painted.
Products created by forming dies
- Metal spoon, fork, and knives
- Aluminum cans
- Car fender, bumper, door, hood, piston, rods, and frame
- Clothing zipper and buttons
Thread cutting
-
Main article: Taps and dies
Another device also called a die is a nut-like thread cutting device for making screw threads on rod stock. This device may also be used to restore damaged threads - a method called chasing. (Other methods are generally used to produce machine screws and small bolts in quantity — they are formed by a process called rolling.)
For high production a die head may be used. Its operation is very similar but does not require "unthreading" at the end of the cut. The head's construction permits the die head to expand at the required length of thread, disengaging the chasers (cutting tips) and permitting the tools retraction without interfering with the work pieces rotation. Die heads are available and are commonly used for both cut threads and rolled threads. A popular machine that regularly uses a die head is a screw machine.
Products created by threading dies
In contrast to forming dies, threading dies rarely produce a part from start to finish. Many operations are performed on the part in addition to the threading created by the die.
- Screws, bolts, threaded rod
- Pre-threaded metal plumbing pipe and male fittings.
- Tangs in fencing blades
Wire pulling
-
Wire-making dies have a hole through the middle of them. A wire or rod of Steel, copper, or other metals or alloy, enters into one side and is lubricated and reduced in size. The leading tip of the wire is usually pointed in the process. The tip of the wire is then guided into the die and rolled onto a block on the opposite side. The block provides the power to pull the wire through the die.
The die is divided into several different sections. First is an entrance angle that guides the wire into the die. Next is the approach angle which brings the wire to the nib which facilitates the reduction. Next is the bearing and the back relief. Lubrication is added at the entrance angle. The lube can be in powdered soap form. If the lubricant is soap, the friction of the drawing of wire heats the soap to liquid form and coats the wire. The wire should never actually come in contact with the die. A thin coat of lubricant should prevent the metal to metal contact.
For pulling a substantial rod down to a fine wire a series of several dies is used to obtain progressive reduction of diameter in stages.
Standard wire gauges used to refer to the number of dies through which the wire had been pulled. Thus, a higher-numbered wire gauge meant a thinner wire. Typical telephone wires were 22-gauge, while main power cables might be 3- or 4-gauge.
References
- J. R. Paquin and R. E. Crowley, CMfgE, PE (1987). Die Design Fundamentals. New York, New York: Industrial Press Inc. ISBN 0-8311-1172-0
- David T. Reid (1991). Fundamentals of Tool Design. Dearborn, Michigan: Society of Manufacturing Engineers. ISBN 0-87263-412-4
External links
