Target Mould
The knowlege of plastic mould making you should know
The modern-day injection mould tool is often a complex arrangement of mechanical, electrical, pneumatic and hydraulic components expected to fulfil a range of demanding tasks. Whatever the complexity, the mould design must essentially specify a tool that will operate satisfactorily in production. To achieve this it must meet the following prime objectives:
• It must operate at the required production rate or better and last at least for the predicted design life.
• It must be well designed and produce mouldings to the required specification.
• The design must specify a tool that will operate consistently and be reliable in production. It should not be prone to frequent breakdowns and should not require frequent maintenance or servicing.
These objectives are not simple to achieve. At every cycle, the tool is clamped together under high loads and is subject to high injection pressures and high heat levels from the incoming polymer. During the cooling cycle, the moulding is cooled until it reaches ejection temperature, when the tool opens and the moulding is ejected. All these factors combine to make the mould tool a highly stressed dynamic heat exchanger.
It is important, therefore, to ensure that the mould design takes all these factors into consideration. Additionally, there are several other requirements that need to be considered, among which are the following:
• The number of impressions required
• The type of tool needed, e.g., two-plate, side core, split, multiplate, hot runner and so on
• The mould materials
• The cavity construction
• The required life of the tool
• Temperature…
An injection mold designing(the arc core-pulling mechanism)
Through the analysis of nozzle plastic parts,an injection mold with sixteen cavities was designed and the design of its gating system has been optimized using Moldflow software. A new arc core-pulling mechanism and an assistant mold opening mechanism were adopted according to the structural characteristics of this nozzle. Comparing to the traditional core-pulling mechanism, the new mechanism has greatly simplified the structure of the mold and reduced the production cost, which has been proved as a rational design by practical production.
The stamping process(auto plastic parts)
In order to investigate the influence of STAMPING process on the STRUCTURAL PERFORMANCE of auto parts, it was simulated by taking the local DENT RESISTANCE of auto parts as an example.By comparing displacements of measuring points under different conditions, it was found that the local DENT RESISTANCE was better when the STAMPING process was taken into consideration.Results show that the local DENT RESISTANCE of auto parts is greatly influenced by the STAMPING process, and the consideration of STAMPING process will increase the structural evaluation precision of auto parts.
How to reduce mould cost?
Improved Profitability through Process Improvement
As the mold industry adjusts to a global economy, and the labor cost is becoming more and more higher.
High-speed machining and hard milling as a combined process can be up to eight times faster than conventional sinker EDM. Automation reduces redundancies in labor cost and a magnet reduces setup by as much as 50 percent. The combination of the three is a recipe for significant cost reduction. These benefits alone are enough to implement hard milling automation on a magnet. But these three processes offer other benefits that make the added edge.
1. Hard Milling
Hard milling has resulted in improved part finish, tighter tolerances, and significantly improved repeatability at speeds that reduce operational costs. By its very nature, the hard milling process eliminates the redundant time spent machining an electrode only to then burn it into the steel. The reduction of graphite dust within a shop also is a nice perk.
Hard milling involves smaller cuts than conventional milling, but at speeds and feeds that are much greater. The bottom line is that hard milling can remove steel faster. A noticeable difference among hard milling, conventional milling and EDM processes is the quality of surface finish. A hard milled part (in many cases) can reduce or eliminate much of the cost associated with polishing.
According to Mark Burns, process engineer regarding hard milling versus die-sinker EDM, “Besides being faster, more accurate and improved repeatability, hard milling eliminates the setup time needed for machining electrodes and the EDM process. It eliminates the cost of electrode material and reduces the time needed to polish cavities. We have achieved confidence in hard milling to the point that very complicated contoured part lines can be machined finish leaving little, if any hand, fitting. We have minimized secondary operations (runners and venting) and hand fitting of components to virtually nothing.”
The improved tolerances achieved through hard milling also can eliminate other costly labor issues. For example, a 3-D shut off will often go together without fitting, but in the EDM process—due to wear of the electrode—the blocks often have to be fitted together (checked for size). As an electrode wears, the tolerances degrade to a point that a new electrode needs to be burned and then the machining of the electrode process starts all over again. In hard milling, if a tool dulls then replacement is easy and very little time is lost. On multiple tools there is no need for multiple electrodes and repeatability is maintained.
2. Automation
Automation is the process associated with the use of a robotized pallet changer that can load and unload a pallet into a machine with high accuracy and repeatability in a matter of seconds. Automation enables a single robot to operate up to three machines simultaneously. An added benefit to a robot is the ability to interrupt a job and introduce a new job in a matter of minutes—being able to continue where you left off with a push of a button is unheard of, but a reality. Automation enables a shop to run 24 hours a day, seven days a week. Automation allows a shop owner to best utilize his fixed costs (building and equipment) and make them more productive without increasing labor cost, while improving flexibility, repeatability, accuracy and part accessibility.
3. Magnetic Workholding
Magnetic workholding for milling was introduced to the U.S. in the early nineties as a means to reduce setup and offer five-face accessibility to a workpiece. Historically, magnets did not offer sufficient clamping force for machining, but today with new technology magnets can withstand some of the heaviest machining cuts. Magnetic workholding is in most cases the best way to obtain the maximum benefits of hard milling and automation. Magnetic workholding allows for complete 3-D (five-axis machining) in a single setup. There are no clamps to get in the way. In addition, magnetic fixturing offers improved tolerances, repeatability, setup time, consistency and part finish.
When a part is located on the face of a magnet, a consistent Z-axis location is achieved and a single squareness reference is established. Whereas, if a part is held within a vice the use of parallels opens the door for stacked tolerances, squareness as well as flatness issues. “The flatness of a workpiece is easily maintained and the ability to mill the complete, uninterrupted periphery is an added benefit. The need to qualify a work surface prior to the first CNC hard milling process was eliminated with the use of the magnets,” explains Burns.
Magnets also have the advantage of clamping parts without distorting them unduly. This is particularly impressive when the workpiece is delicate by geometry. An example of this is when machining a workpiece with a thin wall. A magnet does not add pressure to the walls of a workpiece, unlike a vice. The squeeze pressures exerted by a vice can alter the shape and dimension of a cavity—making it difficult to hold and repeat. Workpiece vibration is significantly lessened due to the greater contact area that a magnet uses, which further enhances part finish and machine speeds. For the same reasons, tool life is often extended when using a magnet.
Magnetic workholding works universally for small, large and odd shaped parts. Through the use of either qualified locator stops or probing, a part is quickly located for the cut.
Multiple workpieces can be set up (quite close together) when using a magnet allowing the machine to run longer unattended, because a magnet does not waste space with added external clamps. Parts can be located through the use of a side rail or by dowel pins in the face of the magnet. In addition, a part previously too large for a machine table can now be held from the underside with a magnet while overhanging all four sides. This feature increases the capacity of an existing machine.
Three-Process Combination Equals Success
Hard milling as a process is significantly faster, cleaner and more accurate than the old conventional sinker EDM method. Automation as a process significantly reduces redundant man-hours, improves repeatability and tolerances in the same 24-hour day as a manual shop. Magnetic workholding improves part finish, tolerances, repeatability and machine capacity as well as reduces setup time. These three processes on their own are steps necessary to become more competitive in a local and global economy, but collectively offer American mold builders an edge over less technologically advanced countries. To be competitive and superior in a global economy will require not only making a product for less money but also making a better product.
The Injection Molding
The injection molding
Injection molding is principally used for the production of the thermoplastic parts, although some progress has been made in developing a method for injection molding some thermosetting materials. The problem of injecting a melted plastic into a mold cavity from a reservoir of melted material has been extremely difficult to solve for thermosetting plastics which cure and harden under such conditions within a few minutes. The principle of injection molding is quite similar to that of die-casting. The process consists of feeding a plastic compound in powdered or granular form from a hopper though metering and melting stages and then injecting it into a mold. After a brief cooling period, the mold is opened and the solidified part ejected. Injection-molding machines can be arranged for manual operation, automatic single-cycle operation, and full automatic can be arranged for manual operation, automatic single-cycle operation, and full automatic operation. The advantage of injection molding are:
- a high molding speed adapted for mass production is possible.
- there is a wide choice of thermoplastic materials providing a variety of useful properties.
- it is possible to mold threads, undercuts, side holes, and large thin sections.
Fine-turning your mold cooling system
Molding is a complex business. From a technical perspective there is much to know. Molders must be versed in materials science and the workings of a molding press. They must know about hydraulics and electrical controls. And they should even be at least “shade tree” tooling experts, familiar with steels, heat treating, runners and gates, and mold cooling.
Of these tooling facets, it could be argued that mold cooling is one of the most important. A slight difference in cooling conditions can add or subtract seconds from the molding cycle, making the difference between a profitable molding job and a loser. Critical dimensions, surface finish, and part warpage are all affected by cooling conditions. It is ironic, then, that mold cooling is the neglected stepchild in many molding shops. We have all sorts of “gee-whiz” technology for monitoring and controlling nearly everything but mold cooling.
Like most things, there is more to know about the finer points of mold cooling and heat transfer than most of us care to learn. In fact, you could probably write a good PhD dissertation on mold cooling if you wanted to. But we’re not going to consider those complexities here. Although most molders have an idea of what mold temperature they need, they often have no idea how many gallons per minute of water they need through a cooling circuit or what size hose and fittings to use. These are some of the simple, common sense things to know on this subject; useful, well-conceived products can give you better information and control over mold temperatures. This article aims to help you gain a better understanding of mold cooling and to be helpful in your molding efforts.
Turbulent Flow
Let’s start with some engineering basics. Most of you have heard something about turbulent flow and that it is good for cooling. But just what is turbulent flow? How does it help? What flow rates are needed to achieve turbulent flow?
Turbulent flow begins when the velocity of fluid in a channel increases to a critical level. Above this critical velocity, vigorous internal mixing of the fluid occurs as it flows. This improves heat transfer by mixing warmer fluid near the wall of the cooling passage with the relatively cooler interior fluid. the precise velocity for turbulent flow depends on several variables, including the cooling passage geometry, fluid viscosity, and roughness of the pipe walls. The formula for a ratio known as Reynold’s number includes these variables. A Reynold’s number greater than 4000 denotes turbulent flow.
Table 1 shows some values for normal mold cooling situations with water as the fluid.
Table 1. Approximate flow rate needed to produce turbulent flow* in drilled passages
| Pipe Size | ID of drilled passage | Min. flow rate for turbulent flow (gal/min) |
| 1/16 NPT | 0.250 1/4- drill | 0.33 |
| 1/8 NPT | 0.339 R drill | 0.44 |
| 1/4 NPT | 0.438 7/16- drill | 0.55 |
| 3/8 NPT | 0.593 19/32- drill | 0.74 |
| 1/2 NPT | 0.719 23/32- drill | 0.90 |
* based on Reynold’s number of 4000
Having said this, I can tell you that in some cases turbulent flow doesn’t matter too much, and in other cases it matters a lot. In one example, the cycle time for a coffee mug with a 0.200-inch thick wall was very poor. The molder wanted to improve the cooling in the mold cores with the goal of achieving a substantial cycle improvement and spent a significant sum making cooling “improvements”. When the mold was sampled, the molder was surprised to learn that the cycle was about the same as before. What was going on there?
The best cooling system in the world won’t take away heat any faster than the molded part will give it up. Most unfilled resins transfer heat at a rate 1/10 to 1/25 that of steel. The outer walls of a thick part insulate the mold from the heat trapped in the center of the part. The message here is that for very thick part, the cooling system will have relatively little effect on cycle time. the other hand, let’s say you are running a very thin polyethylene lid. This part can give up its internal heat quickly because of its thin walls and typically runs on a fast cycle. These factors combine to greatly increase the demands on the cooling system, so good cooling performance requires well-placed passages in the mold as well as greater flow rates to carry away the heat. Thus, it is generally true that if the molded parts will give up their heat, it is worthwhile to use higher cooling flow rates. And it is true that the faster the flow rate, the more total heat you remove — even though the change in the temperature of the water flowing through the mold is very slight. Intuition may suggest that the water would pick up more heat at a slower flow rate, but it won’t. Although the temperature of the water increases more at a slower flow rate, total heat removed does not. Data gathered in our laboratory (Figure 1) illustrate this point
Figure1. Amount of heat removed by varying water flow rates in simulated mold with 1200-W electrical resistance heat input.
Temperature Control
In some cases you may want slower flow, and special systems are available for these situations. For example, you may have a mold that runs only if the cores are a few degrees warmer than the cavities, or vice versa. To warm up the desired zone, you merely throttle the cooling flow. A fancy name for this is heat recovery temperature control. In other words, you recover heat from the molding process to elevate the mold temperature. You may have noticed that it is very difficult to settle a mold into a steady-state condition. You’re always chasing the temperature up and down. If you are ambitious, you might hook up a mold heater to solve the problem. But there is an easier way. Heat recovery temperature control systems are available that electronically monitor cooling circuit temperature and automatically throttle flow to maintain a set temperature. The temperature sensor is normally placed in the water return from the mold but can even be placed in the mold steel. This system will not replace a mold heater in situations that require adding heat from outside the mold — when the mold must be hot before you can start molding, for example. But it can make life easier when different zones require slightly different temperatures or when you want to run a mold warmer than tower or chiller water allows at full flow. These systems allow you to throttle the flow with precise temperature control. With their modest initial cost and operating energy savings, heat recovery systems can be an attractive alternative to traditional mold heating systems. The accompanying box illustrates an example of this.
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Table 2 Cooling water conditions for selected cooling circuits
*NA = Not Applicable |
Flow Rates
With the preceding basics in mind, let’s look at some cooling conditions in actual molding situations and some data taken from lab experiments. Once you decide you need a certain flow rate, you need to know what it takes to get there. Table 2 shows cooling data taken from selected operating molds and from our lab.Higher flow rates can be achieved by increasing pressure or reducing flow resistance. If you are installing a new plant circulating system, it’s a good idea to pay careful attention to the pressure issue. This means using a big enough pump and large enough distribution lines throughout the plant. But when you are stuck with the water delivery system you already have, you must work on reducing resistance. Here are some suggestions.
Design mold cooling passages as large as practical to reduce resistance to flow. Next, look at the size of pipe or quick-connect fittings going to the mold. Note in Table 2 the change to 2.3 gal/min from 1.7 gal/min brought about just by changing from 200 series to 300 series quick-connect fittings and changing to a slightly larger drilled passage. The same effect generally follows increasing hose sizes. For example, our lab has an available water pressure of 85 psi, but it is impossible for more than about 2.5 gal/min to flow through 0.25-inch hose. In many plant situations, water pressure is much lower than 85 psi.
Water manifolds can also make a big difference. It does no good at all to have 12 0.5-inch NPT(National Pipe Taper) fittings coming off a manifold with only a 0.75-inch NPT inlet to supply all those fittings. A well-designed manifold should have a supply area roughly equal to the discharge area, or as large as practical. For example, 16 0.5-inch NPT fittings require about a 2-inch NPT supply for best performance. Also, the main supply and return fittings and hoses to the manifolds should not be smaller than the manifold inlet. Attention to these details can improve the pressure available at the mold.
If you are interested enough in all of this that you would like to learn more about your cooling conditions, you need to know what equipment is available to monitor and control flow rates, pressure, and temperature in your mold cooling circuits. A number of companies offer products to distribute cooling water and to monitor or control mold cooling variables. They, and others, can help meet your equipment needs and offer technical assistance if you have questions.
Attend Moscow Exhibition(International Trade Fair Plastics and Rubber)
Every year, our company attends the Moscow Exhibition( International Trade Fair Plastics and Rubber). Look at the Photo, Our manager here. Next time, we will inform you the time and position . Welcome to visit.
Target Mould, 24 years of expertise in plastic mould. Your no hassle mold source.
Target Mould
Established in 1983. 23 years of expertise in mould,every year, Target Mould has had great development in management, quality and turnover. Based on the precision tooling, high technology and top mentality mould design. we has established the main market in Spain , Italy , France , Portugal , Iran and Australia… Target Mould use Pro-E, Solidworks, U.G., and Auto-CAD for moulds and plastic parts design, with very strong mould design and drawing reading ability. This ensures the good technical communications with clients, which can avoid any mistake occur. Target Mould creates a special and professional management system, which is specially suitable for mould design and parts quality controlling, moulds tooling and processing controlling, mould operation quality controlling… Our whole working team absolutely trusts that good quality and services are based on good management. Target Mould tooling range: The biggest mould we can make currently is 60 TONS. Our major: washing machine mould, bumper mould, automotive inner trim parts, refrigerator mould, air conditioner mould, water dispenser high standard moulds. Also, Target Mould is professional in other high standard moulds design and manufacture, such as industry dust bin, various bin moulds, crate, chair, thin wall injection moulds, PET perform moulds, stamping mould,Target Mould produces annually 800to 1000sets of medium to large sizes of moulds, with a turnover of more than 8M USD in the year 2006. Target Mould sincerely express keen interest to invite your down visit and receive any further inquiries related to plastic mould or plastic parts cooperation.
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