What is Die Casting_ _ Die Casting Design _ Die Casting Manufacturer
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11/18/2014 What i s Di e Casti ng? | Di e Casti ng Desi gn | Di e Casti ng Manufactur er http://www.paceind.com/die-casting-101/introduction whati s 1/3 Search: 1-888-DIE-CAST Home Pace Advantage Pace Facilities Pace Services Die Casting 101 Contact Us Careers Associates Ho me Di e Cas ti ng 10 1 About Alloys Glossary of Terms NADCA FAQ NADCA Tolerances Die Casting 101 F.A.Q. Introduction to Die Casting « Back to FAQ Q - What is Die Casting? A - Die casting is a manufacturing process for pr oducing accurately dimensioned, sharply defined, smooth or textured-surface metal parts. It is a ccomplished by forcing molten metal under high pressure into reusable metal dies. The proce ss is often described as the shortest distance between raw material and finished product . The term "die casting" is also used to describe the finished part. The term "gravity die casting" refers to castings made in metal molds under a gravity head. It is known as permanent mold casting in the U.S.A. and Canada. What we call "die casting" here is known as "pressure die casting" i n Europe. How Are Die Castings Produced? Types Of Machines for Die Casting Hot Chamber Machines Cold Chamber Machines Casting Dies and Their Construction Die Terminology Types of Dies Automation in Die Casting Quality in Die Casting Continuous Computerized Process Monitoring HOW ARE DIE CASTI NGS PRODUCED? First, a steel mold capable of producing tens of thousands of c astings in rapid succession must be made in at least two secti ons to permit removal of castings. These sections are mounted securely in a machine and are arranged so that one is stat ionary (fixed die half) while the other is moveable (injector die half). To begin the casting cycle, the two die halves are clamped tightly together by the die casting machine. Molten metal is injected into the die cavity where it solidifi es quickly. The die halves are drawn apart and the casting is ejected. Die casting dies can be simple or complex, having moveable slides, cores, or other sections depending on the complexity of the casting. The complete cycle of the die casting process is by far the fastest known for producing precise non-ferrous metal parts. This is in mark ed contrast to sand casting which requires a new sand mold for each ca stin g. While the permanent mold process uses iron or steel molds instead of sand, it is considerably slower, and not as precise a s die casting. top TYPES OF MACHINES FOR DIE CAS TING Regardless of the type of machine used, it is essential th at die halves, cores and/or other moveable sections be securely locked in place during the casting cycle. Generally, the clamping force of the machine is governed by (a) the projected surface area of the casti ng (measured at the die parting line) and (b) the pressure used to inject metal into the die. Most machines use toggle type mechanisms actuat ed by hydraulic cylinders (sometimes air pressure) to achieve locking. Others use direct actin g hydraulic pressure. Sa fety interloc k systems are used to prevent the die from opening during the casting cycles. Die castin g machines, large or small, vary fundamentally only in the method used to inject molten metal int o the die. These ar e classified and described a s either hot or cold chamber die casting machines. top HOT CHAMBER MACHINES Hot chamber machines ( Fig.1) are used primarily for zinc, and low melting point alloys whic h do not readily attack and erode metal pots, cylinders and plungers. Advanced technology and development of new, higher tempera ture materials has extended the use of this equipment for magnesium alloys. In the hot chamber machine, the injecti on mechanism is immerse d in molten metal in a furnace attached to the machine. As the plunger is raised, a port opens allowing molten metal to fill the cylinder. As the plunger moves downward sea ling the port, it forces molten metal through th e gooseneck and nozzle into the die. After the metal has solidified, the plunger is withdrawn, the die opens, a nd the resulting casti ng is eje cted. Hot chamber machines are rapid in operation. Cycle times vary from less than one second for small components weighing less than one ounce, to thirty seconds for a casting of several pounds. Dies are filled quickly (normally between five and forty milliseconds ) and metal is injected at high pressures (1,500 to over 4,500 psi). Nevertheless, modern technology gives close control over these values, thus producing castings wit h fine detail, close tolerances and high strength.
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Transcript of What is Die Casting_ _ Die Casting Design _ Die Casting Manufacturer
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Home Pace Advantage Pace Facilities Pace Services Die Casting 101 Contact Us Careers Associates
Home Die Casting 101
About Alloys
Glossary of Terms
NADCA FAQ
NADCA Tolerances
Die Casting 101F.A.Q.
Introduction to Die Casting
« Back to FAQ
Q - What is Die Casting?
A - Die casting is a manufacturing process for producing accurately dimensioned, sharply
defined, smooth or textured-surface metal parts. It is accomplished by forcing molten metalunder high pressure into reusable metal dies. The process is often described as the shortestdistance between raw material and finished product. The term "die casting" is also used todescribe the finished part.
The term "gravity die casting" refers to castings made in metal molds under a gravity head. Itis known as permanent mold casting in the U.S.A. and Canada. What we call "die casting" hereis known as "pressure die casting" in Europe.
How Are Die Castings Produced?Types Of Machines for Die CastingHot Chamber MachinesCold Chamber MachinesCasting Dies and Their ConstructionDie TerminologyTypes of DiesAutomation in Die CastingQuality in Die CastingContinuous Computerized Process Monitoring
HOW ARE DIE CASTINGS PRODUCED?
First, a steel mold capable of producing tens of thousands of castings in rapid succession must
be made in at least two sections to permit removal of castings. These sections are mountedsecurely in a machine and are arranged so that one is stationary (fixed die half) while the otheris moveable (injector die half). To begin the casting cycle, the two die halves are clampedtightly together by the die casting machine. Molten metal is injected into the die cavity where itsolidifies quickly. The die halves are drawn apart and the casting is ejected. Die casting diescan be simple or complex, having moveable slides, cores, or other sections depending on thecomplexity of the casting.
The complete cycle of the die casting process is by far the fastest known for producing precisenon-ferrous metal parts. This is in marked contrast to sand casting which requires a new sandmold for each casting. While the permanent mold process uses iron or steel molds instead of sand, it is considerably slower, and not as precise as die casting.
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TYPES OF MACHINES FOR DIE CASTING
Regardless of the type of machine used, it is essential that die halves, cores and/or othermoveable sections be securely locked in place during the casting cycle. Generally, the clampingforce of the machine is governed by (a) the projected surface area of the casting (measured atthe die parting line) and (b) the pressure used to inject metal into the die. Most machines use
toggle type mechanisms actuated by hydraulic cylinders (sometimes air pressure) to achievelocking. Others use direct acting hydraulic pressure. Sa fety interlock systems are used toprevent the die from opening during the casting cycles.
Die casting machines, large or small, vary fundamentally only in the method used to injectmolten metal into the die. These are classified and described as either hot or cold chamber diecasting machines.
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HOT CHAMBER MACHINES
Hot chamber machines (Fig.1) are used primarily for zinc, and low melting point alloys which donot readily attack and erode metal pots, cylinders and plungers. Advanced technology anddevelopment of new, higher temperature materials has extended the use of this equipment formagnesium alloys.
In the hot chamber machine, the injection mechanism is immersed in molten metal in a furnaceattached to the machine. As the plunger is raised, a port opens allowing molten metal to fill thecylinder. As the plunger moves downward sea ling the port, it forces molten metal through thegooseneck and nozzle into the die. After the metal has solidified, the plunger is withdrawn, the
die opens, and the resulting casting is ejected.Hot chamber machines are rapid in operation. Cycle times vary from less than one second forsmall components weighing less than one ounce, to thirty seconds for a casting of severalpounds. Dies are filled quickly (normally between five and forty milliseconds) and metal isinjected at high pressures (1,500 to over 4,500 psi). Nevertheless, modern technology givesclose control over these values, thus producing castings with fine detail, close tolerances andhigh strength.
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Figure 1: Hot Chamber Machine. Diagram illustrates the plunger mechanism which issubmerged in molten metal. Modern machines are hydraulically operated and equipped withautomatic cycling controls and safety devices.
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COLD CHAMBER MACHINES
Cold chamber machines (Fig. 2) differ from hot chamber machines primarily in one respect; theinjection plunger and cylinder are not submerged in molten metal. The molten metal is poured
into a "cold chamber" through a port or pouring slot by a hand or automatic ladle. Ahydraulically operated plunger, advancing forward, seals the port forcing metal into the lockeddie at high pressures. Injection pressures range from 3,000 to over 10,000 psi for bothaluminum and magnesium alloys, and from 6,000 to over 15,000 psi for copper-based a lloys.
In a cold chamber machine, more molten metal is poured into the chamber than is needed tofill the die cavity. This helps sustain sufficient pressure to pack the cavity solidly with castingalloy. Excess metal is ejected along with the casting and is part of the complete shot.
Operation of a "cold chamber" machine is a little slower than a "hot chamber" machine becauseof the ladling operation. A cold chamber machine is used for high me lting point casting alloysbecause plunger and cy linder assemblies are less subject to attack since they are notsubmerged in molten metal.
Figure 2: Cold Chamber Machine. Diagram illustrates die, cold chamber and horizontal ramor plunger (in charging position).
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CASTING DIES AND THEIR CONSTRUCTION
Die casting dies (Fig. 3) are made of a lloy tool steels in at least two sections called fixed diehalf and ejector die half. The fixed die half is mounted on the side toward the molten metalinjection system. The ejector die half, to which the die casting adheres, and from which it isejected when the die is opened, is mounted on the moveable platen of the machine.
The fixed die half of the die is designed to contain the sprue hole through which molten metalenters the die. The ejector half usually contains the runners (passage ways) and gates (inlets)which route molten metal to the cavity (or cavities) of the die. The ejector half is alsoconnected to an ejector box which houses the mechanism for ejecting the casting from the die.Ejection occurs when pins connected to the ejector plate move forward to force the castingfrom the cavity. This usually occurs as part of the opening stroke of the machine. Placement of ejector pins must be carefully arranged so force placed upon the casting during ejection will notcause deformation. Return pins attached to the ejector plate return this plate to its castingposition as the die closes.
Fixed and moveable cores are often used in dies. If fixed, the core axis must be parallel to the
direction of the die opening. If moveable, they are often attached to core slides. Should theside of a die casting design require a depression, the die can be made with one or more slidesto obtain the desired result without affecting ejection of the casting from the die cavity. Allmoveable slides and cores must be care fully fitted, and have the ability to be securely lockedinto position during the casting cycle. Otherwise, molten metal could be forced into theirslideways causing a disruption of operations. Although slides and cores add to the complexityand cost of die construction, they make it possible to produce die castings in a wide variety of configurations, and usually more economically than any other metalworking process.
Figure 3
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DIE TERMINOLOGY
Sprue holes are tapered with the small end located at the breaking point when the die isopened. A sprue pin, located in the ejector half, makes the sprue hollow and deflects metalentering the die into the runner system.
Runners are channels located at the parting line to route liquid metal from the sprue hole to thegate.
Gates are passages through which metal enters the die cav ity. They have an important functionin directing metal flow so that the cavity is correctly filled. Air is expelled through vents asmolten metal enters the die cavity.
Guide pins assure proper alignment of die halves and correct register of cavities.
Side walls and cores are designed to have a slight taper or dra ft. The largest diameter or crosssection of a cav ity must be located at the par ting line (unless slides are used) so the castingcan be removed from the die. A s molten metal in a die cavity solidifies, it shrinks away fromwalls onto core pins and other projections. The design of the die must permit withdrawal of core pins, and ejection without applying too much pressure which could cause deformation tothe die casting.
Cores, fixed or moveable, as well as "loose pieces," must be positioned to facilitate removaleither mechanically or by hand. Loose pieces used to form undercuts must be positioned by theoperator. This requires extra labor, and usually slows the casting cycle.
Inserts can be cast integrally to provide special characteristics.
Most dies are cooled by water circulating through channels drilled for that purpose
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TYPES OF DIES
Dies are classified as: single cavity, multiple cavity, combination and unit dies (Figures 4-A to4-D).
A single cavity die requires no explanation. Multiple cavity dies have several cav ities which areall identical. If a die has cav ities of different shapes, it’s called a combination or family die. Acombination die is used to produce several parts for an assembly. For simple parts, unit diesmight be used to effect tooling and production economies. Several parts for an assembly, orfor different customers, might be cast at the same time with unit dies. One or more unit diesare assembled in a common holder and connected by runners to a common opening or spruehole. This permits simultaneous filling of all cavities.
Figure 4
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AUTOMATION IN DIE CASTING
"Automation and Mechanization" are terms often used interchangeably by the die castingindustry. Automation of a manufacturing process is more sophisticated and complicated thanthe mechanization of various operations.
A die caster progresses towards automation by mechanizing various steps of the die castingprocess. For example:
1. Die lubrication can be accomplished by installing fixed or reciprocating spray systems.2. An automatic ladling device can replace the hand ladle.3. Castings can be removed from the die by ex tractors or robots, or by "drop through" to a
conveyor below the machine.4. Die casting machine operation can be integrated to cast, quench, trim and eject castings
and return scrap to the furnace by conveyor.
By closing the loop, the die casting process can be automated, utilizing feed-back controls andmicroprocessors which automatically self compensate for process variables. As die castingplants move toward automation, noticeable changes occur. The operation tends to becomesafer. Production and quality improves considerably. Automation upgrades the labor force byrequiring the development of new skills for machine set-up, programming, electronics,mechanics and maintenance.
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QUALITY IN DIE CASTING
Quality in die casting is maintained through the use of process controls and feedback betweenthe process control computer and the die casting machine.
Process controllers may utilize microprocessors to access transducers mounted on the diecasting machine, to obtain velocity, position, hydraulic pressure and tie-bar strain data, etc.The microprocessor then adjusts the die casting machine operation through special va lves, thusassuring consistent castings shot after shot. The process controller also collects machineperformance data for statistical analysis in quality control.
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CONTINUOUS COMPUTERIZED PROCESS MONITORING
Step 1 -- Alarm monitoring -- A computerized remote terminal mounted near the die castingmachine continuously monitors the following: velocity, position, pressures at the accumulator,die lock-up cylinder, head and rod side of the injection cylinder, temperatures of hydraulic oil,metal (up to ten locations in the die), and strains on four tie-bars. Each of these variables ishigh/low limit checked every shot. An alarm is sounded or flashed if a casting variable goesout-of-limits.
Step 2 -- Control -- Automatic control valves and tie-bar adjusting motors are installed on thedie casting machine and connected to the computerized remote terminal unit. The computeradjusts controls to maintain satisfactory die locking force, slow shot velocity, optimum fill timeand proper intensifier timing. The computer may also be interfaced to a robot and/or aprogrammable controller.
Step 3 -- Data acquisition -- After installing computerized remote terminal units on each
machine, a data acquisition system may be formed by interconnecting these units andcommunicating all information back to a master terminal computer in the office. The mastercomputer prints out a management information report which summarizes the operation of theentire die casting shop, including which machines are running, when they stop, shots made(good and bad), which machines are out-of-limits and what to do. At the master station, themanager can analyze the process by studying shot profiles on a video monitor and statisticalreports from a high speed printer.
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