Overmolding is also called 2 times injection molding in China. Compared with the third-party material bonding, overmolding process makes the process faster and more cost-effective, it has been widely employed in plastic design.
Over molding are categorized into 3 types: insert molding, double shot molding, co-injection molding.
Insert molding: The most commonly used to mold soft elastomers to rigid plastics, insert molding is the most economical way to do overmolding. In the insert design, the hard segment has been separated into tools in advance, and then eject the soft materials in.
Elastomers are adhesion bond, which can be mechanical locks, chemical and other methods. In order to achieve chemical adhesion, the elastomer must be sufficiently heat to melt the surface of the hard segment to achieve chemical bonding.
Two types of injection-compression used for thin walled high aspect ratio parts. The first uses a moving side core or secondary cylinder that leaves the cavity spaced and upon injection clamps forward to compress the part stress free. This usually requires a specific capability of the press. The second method sometimes referred to as coining closes the mold under reduced clamp pressure and the cavity is filled.
In this design it is also typical to have roughly a 7 degree draft angle on the parting/vent line to avoid flashing during the injection-compression stroke depending on the material and criteria for edge definition. keep in mind other critical control parameters are melt viscosity, plastification, pellet size uniformity as the cushion is typically much lower than with standard straight injection to avoid shot to shot variance.
A book of "Mold Standards" is a detailed description of what is required to match the mold with the molding factory, their equipment, machines, clamping systems, water hook ups, hydraulics for cylinders, air hook ups and cylinders, brand and type of steels/materials that are required, Hot Runner brand, electrical hook up and wiring requirements, brand and type of components (DME, Hasco), etc. This should never come from the mold maker, he'll build you what is cheapest for him.
Mold parts that are excessively heated, like spure bushings and areas near the gates, must be cooled intensively. Rapid and even cooling is enhanced by the use of highly conductive metals, such as berylliumcopper. These metals are used to full advantage in places where it is impossible to place sufficient cooling channels. Copper transfer twice as much heat as carbon steel and four times as much heat as stainless steel. This does not mean copper mold will run 4 times faster than a stainless steel mold but they will run some thin walled parts significantly faster.
Generally, injection mold has two major components: the movable halve and the fixed halve, during injection molding process, these two halves are pressed tightly and form a sealed hollow to avoid the melt flow leakage and maintain certain holding pressure, the pressed surface are called parting surface, usually parting surface are the biggest projection outline of the part.
Flat parting surface (see figure a)
Parting surface tilt (see figure b)
Stepped parting surface (see figure c)
Curved parting surface (see figure d)
Clear plastic injection molding parts usually made in PC, POM, PMMC, AS, PET, these clear plastic kits used widely in different application, such as auto light, medical devices, cosmetic packing, food container, water tank etc.
Comparing with other colored parts, strict requirements for appearance is a must for transparent plastic parts, which makes the injection molding processing more complex. Mold design and injection molding condition are all determined factors to the final result, there are a few problems happen frequently in clear plastic molding process, we provide some solutions as below.
You can get a larger shot size out of a hydraulic injection molding machine. There are times when you are pushing the injection capacity of the injection unit that hydraulic machines are a better choice than all-electric injection molding machines. However, if the job is within the range of the injection unit and specified properly, the electric machines outperform hydraulic for repeatability and energy consumption.
The main consideration when considering an all-electric injection molding machine is energy efficiency. Electricity savings of 20%-40% are typical when compared to hydraulic machines. Also, an all-electric machine can offer unmatched repeatability due to the servo drives that are used for injection forward and clamp rather than hydraulic pumps/valves.
This technology can be very effective in eliminating or substantially reducing the stress in flatter molding. In internal gas injection, where the gas is injected into one or more gas channels. For a flattish, panel-type part such as this, this is not always the gas injection process to be recommended. The added gas channels can leave a slight witness mark on a cosmetic 'A' surface and depending on the part geometry, the gas packing pressure will probably not be equal across the whole surface area of the part, especially with thinner wall sections and wider surface areas.
Scientific Molding to me is a bit different than having a whole lot of data studies. To me, and to many of my peers, scientific molding is an disciplined elimination of multiple variables, which yields an range of conditions/settings/protocol/things that you must do. This will yields the highest volume of acceptable parts with the least amount of cost. I.E., when you do this, and you do that - the press operates thus and you get money. Going thru the methology checklist eliminates the variables in a disciplined fashion resulting in an updated group of setting, updated methods of handling material change outs, setting up a mold, scheduling jobs, etc. and reduction of scrap. Happy customers, happy plant operators, more money.
Engineering plastic molded parts are made of engineering plastics, through injection molding process, the engineering plastics, such as ABS, PC, POM, are molded into parts with desired shape and measurement. Parts made of engineering plastics have better mechanical and thermal properties, it can be used as a replacement of metal in many applications, for example, plastic auto parts, medical parts, electronic parts, household parts etc.
Engineering plastic molded parts required firstly part design, then you need a mold making company to fabricate an injection mold, at the end, you need an injection molder to mold it. To achieve a good result, it is important to make sure that both the mold maker and molder understand the property of the engineering plastic. Unlike other ordinary plastic parts, the parts made of engineering plastic are supposed to be applicable on many aspects besides dimension or appearance; you need to do some test to make sure there are functional.
Design For Manufacturing (DFM) report, it's a bridge between product developer and mold manufacturer. It has been implemented in many manufacturing industries and proved to a sufficient way to improve efficiency. A comprehensive DFM report for mold making project would be the first step to success. As a mold maker
, the more potential problems you foresee, the less risks you had in the manufacturing process. Here are a summary for it.
Many kinds of raw material are frequently used, such as PC, PC+ABS, ABS, PS, HIPS, Nylon, Material with glass or fiber filled suitability and price different of them are different. More importantly, the shrinkage rate is different, which is key factor to measurement and tolerance precision.
The process of compression molding may be simply described by reference like two-piece mold provides a cavity in the shape of the desired molded article. The mold is heated, and an appropriate amount of molding material is loaded into the lower half of the mold.
The two parts of the mold are brought together under pressure. The compound, softened by heat, is thereby welded into a continuous mass having the shape of the cavity. The mass then must be hardened, so that it can be removed without distortion when the mold is opened. If the plastic is a thermosetting one, the hardening is affected by further heating, under pressure, in the mold. If it is a thermoplastic, the hardening is affected by chilling, under pressure, in the mold.
Here are few topics that need to be brought up or answered.
- Ensure all necessary data are completed and authorized; usually there will be 3D drawing for 3D design and NC programming, 2d drawing must be available especially when there is precision requirement, mold factory need pay special attention to the tolerance specified. If any of the tolerance are no able to fulfilled, bring it up to customer in advance, otherwise it would be a disaster when you found it after mold is build.
- Check with customer about the resin that they are going to use for production. If it happened to be a kind of resin that is not available in local market, the mold factory needs to come a solution with customer where the resin will come from. In most occasions, customer will accept to provide material for trail if it's a very special resin. If the resin is special or you don't have much experience of it, ask opinions of the customer for the shrinkage rate.
- Discuss through with customers about the primary design by presenting parting line, ejector pins location, sliders, lifter, engraving, surface requirement etc. this would save a lot of time afterwards for official design approval. Sometimes the product design against the manufacturability, compromise needs to be made to achieve the best result.
- It's important to deeply understand the demands of the customer, it's a key factor to influence the mold project cost, let customer know what steel you are going to use and how many shorts it guarantees, make sure it fits the demands.
- Timeline need to be settled down during meeting.
Finding the right software is not easy. So the best is to do a benchmark of the software systems, cause it depends a bit of what you want get out of the simulation. It depends on if your company wants to simulate for part design, or is a mold manufacturer or a plastic part producer. Also is depends on the size of parts. Big Parts, small parts, flat parts. Big parts like bumper is hard to do in 3D, cause it takes too much time in simulation. It also depends on if you want to do simulation of assemblies with mold inserts or part inserts like core shift analysis. Not everybody needs everything.
Guiding system of injection mold works as guides to ensure precise mechanic movements. Generally the standard mold base all have guiding design, like guide pins between cavity side and core side, mold designers can just choose the proper mold base. Typical mold guiding system include, guiding between A/B plates, guiding for stripper plates, guiding for runner plates, guiding for ejector pins. All this guiding system can be customized when you order the mold base.
Plastic enclosures are plastic cases or housings manufactured by injection molding process. Usually a popular consumer product with great enclosure design catch people's eye immediately without promoting how good the function are, a very success example is Apple product, success industrial design contribute a lot to the success of Apple in worldwide.How to make a custom plastic enclosure?
First you need to make a design for your custom plastic enclosure, a complete and professional design will includes plastic parts size, structure, selection of proper plastic materials, assembly method, finish. Then you need a plastic mold maker to make a custom injection mold for it, mold price and lead-time will be determined by the quantity demanded, complexity of structure, size finish of the plastic part. If your plastic parts are in high volume demand, then a high quality and long durable mold is a must, get a warranty for how many plastic parts the mold can produce before you sign a mold manufacturing contract with your injection mold supplier. After the custom mold produced, you need to run the mold on an injection molding machine, finally, you get your custom plastic enclosure done.
There are many types of injection mold and tooling in using today, such as two-plate, three-plate and stack molds. Two and three- plate molds are more commonly used for heavy wall and non-packaging products. Both cold and hot-runner systems are used for two and three plate molds. All stack molds use a hot manifold to convey the melt to the cavities. Each mold component must be machined and finished to exact dimensions with very tight tolerances and must be heat-treated to be able to withstand very high injection and clamp pressures. Injection molds are the most expensive molds used in plastics processing with very long lead times, required for their design and fabrication. Every injection mold must be tested and debugged to prove-out the ejection system, cooling and/or heating system and operating components before it is placed in production.
Amorphous resins such as ABS, Polycarbonate, and Polystyrene have much lower shrinkage values than the polyolefins. The higher shrinkage of polyolefins is due to the fact that, in their molten state, they take up more volume than in the solid state because polyolefin resins are semi-crystalline. When the resin solidifies, the chains in the crystalline regions pack tightly together resulting in a reduction in volume. In general, the polyolefins can be ranked for shrinkage:
HDPE ≥LLDPE ≥LDPE ≥PP
Once a resin has been selected, shrinkage can be controlled, to some extent, through mold design and processing conditions.
A gate is a designed small opening to allow the melted plastics into the mold cavity, a successful gate design is determined by gate type, dimensions, location, it's deeply related with the materials been used, the type of mold plates, and economic factors. Gate design is one of the most important elements to influence injection mold quality and productivity.
Single gate has always been selected as a priority unless the distance of the mold flow is too big and beyond the limits of the injection molding pressure. Multiple gates always cannot avoid the problem of weld line where the flows meet from different gates. This weld line are not allowed sometimes specially when the injection molded parts have critical appearance or strength requirement, single gate also have good performance on packing, part strength, lower scrap rates, which gating way to employ will be determined by the structure, dimension appearance requirement of the molded parts.
A good mold flow analysis has lots of benefits, although it is time consuming, the cost is much lower than the cost of trials during nights and days on a production injection molding machine. The difficulty is not to produce colored pictures but to explain to the customers the different results, some customers have enough knowledge to understand some others no.
In 90% of cases, I work before the injection mold is cut, so I am ready to take the responsibility of cycle time, warpage, sink marks and so others issues. I am specialized in gas assisted injection molding and I assist Chinese companies to produce plastic parts for the German automotive industry which generally use overflow. With short shot process, we can obtain a production costs reduction of 20% by simulation and 30% in practice.
The differences between the two styles:
- Toggles generate tonnage via tie bar stretch, Hydraulics based on ram diameter and hydraulic pressure. Toggle injection machines tend to increase tonnage as they run due to thermal expansion of the mold, tie bars, toggle links and plattens. Without a tie bar strain gauge, you never know what the true tonnage is! Hydraulics remains the same as long the pressure stays the same.
- Toggle machines open with near full close tonnage ratings. Great for deep draw parts. Hydraulic machines are limited due to the ram design as the pressure is exerted against the shaft seals and wiper. For that reason, the opening pressure is limited. Now with newer clamp designs, the hydraulics is faster and more efficient than ever. Engel uses a smaller high speed cylinder to open and close the clamp; the ram is for clamp tonnage only. That is true of their Duo and Tie Barless machine design. With a Duo the small tie bar mounted clamping cylinders are used to break open large or deep draw parts.
In a fast-paced market, it is critical for a company to get new custom products into the market quickly, in most of the cases, it could be just a market-testing product with 10,000 units' volume or even less. But the plastic parts still need to be customized by injection molding to achieve the specified tolerance, finish, function. Traditionally, a hardened steel injection mold would requires a very high investment before you get a piece of sample, and it usually take 8-12 weeks to complete, which are unacceptable for a new product developing at the earliest phrase.
We need a solution to reduce the cost of injection molding and shorten the lead-time of for companies to launch new custom plastic products. Low volume plastic injection molding is what you are looking for, which means low cost, quick turn around and on budget.
Many years ago we molded golf clubs driving heads much thicker than 25mm. One solution (also used for a number of other thick walled products) was to mold an insert to leave say a minimum 3mm wall depending on strength needed. The insert was made of all the regrind sometimes contaminated material. Molded at quite a fast cycle as distortion was not usually important for the insert. An extra mould and an extra operation but often proved economical with reduction in overall cycle time and material costs.
The marbling effect or tortoise shell effect developed in the last century was typically achieved by adding 2 or more different colors of the same basic resin and processing through a plunger style machine versus a reciprocating screw machine as is commonly found today. The reason it worked was because that type of injection molding machine did not mix the materials very well and you would have streaks of the dissimilar colors showing on the surface of the product.
After a new injection mold is construction is finished, the mold maker need to set up the injection mold to do test or molding plastics. Setting an injection mold is more than loading and fixing the mold to injection machine, there are many other important things to do after you clamp the injection molds.
This article will give you a comprehensive explain of how to setup an injection mold, and the critical checklist you should pay attention to.
Injection molding is one of the most important processing methods to produce plastic parts. Plastic injection molding techniques have been used and developed for a long time.
Look around you, the case of your laptop, the case of intelligent cell phone, water filters, food containers, wash machines and quite a few components in your car... yes, we are living in a world that are full with plastic parts, most of the common plastic parts are made by injection molding. This article will show you the basics of plastic injection molding advantages and disadvantages.Injection Molding Basic Process
Feeding raw material from the hopper into the barrel, the plunger start to push, the plastic raw materials are pushed into a heating zone and then through the bypass shuttle, the molten plastic through the nozzle into the injection mold cavity, then water or oil run through the designed cooling system to cool down the injection mold to get a plastic article.
Some glossary of terms related with plastic parts design, mold making and plastic injection molding.
Antistatic Agent: Additive used to help eliminate or lessen static electricity from the surface of the plastic part.
Boss: Protuberance on a plastic part designed to add strength, facilitate alignment, provide fastening, etc.
Clamping Plate: A plate fitted to a plastic mold and used to fasten the mold to a platen.
Co-injection Molding: A special multilateral injection process in which a mold cavity is first partially filled with one plastic and then a second shot is injected to encapsulate the first shot.
An injection mold is a precision tool and also must be strong enough to withstand thousands of high pressure molding cycles, so the material of the injection mold must be carefully; it's normally special and expensive steel, The way of manufacturing injection mold have been changed along with modern technology developing, main steps are CNC milling, drilling, EDM, wire-cutting, CAD/CAE/CAM technology utilized in a wide range make the lead-time of mold making shorter and shorter.
Mold flow analysis is widely employed in mold making
industry, utilizing data simulation software, the injection molding process can be simulated and presented on the computer, you can improve part design or mold design base on the out put results. Moldflow, Moldex3D are very popular mold flow analysis software used by many mold makers.Advantages of mold flow analysis
Mold flow analysis will advise if the cavity is fulfilled, it can also provide other useful information such as the required injection pressure and clamping pressure.
You can know whether the filling problem exists. Many filling problems, such as short shot, bubbles and imbalances, can be predicted by a careful analysis of the filling curve. Mold flow analysis allows you to change the position of the gate, injection speed, and other processing conditions, so you would know if these problems can be improved or corrected.
Undercuts: in plastic injection molding industrial, it refers to part features that prevent straight ejection at the parting line, which cause much mold complexity and lead to higher mold construction and maintenance costs. Whenever it's possible, redesign the part to avoid undercuts. Minor part design changes can often eliminate undercuts in the mold. For example, adding through holes can give access to the underside of features that would otherwise be undercuts, simple modifications enable the mold to form a hole in the sidewall rather than with a side-action mechanism. See below figure.
Soft tool is the tool made of pre-harden steel, it is an economic solution for a small volume production. It has advantages of low cost and fast turn around, but pre-harden steel is a lower grades steel that process lower hardness and wear resistance, so the soft tool can only stand molding cycles no more than 500k shots, it's also difficult to maintain tight tolerances.
Hard tool is a high quality tooling for mass production, it's made of the best quality steel, like H13,420 etc. Hard tool requires more procedure and longer time to manufacture.
Two plate mold is the easiest injection mold structure and has many advantages. It's consist with A side and B side 2 main parts, when it is load in ejection machine to do molding, A side is fixed and held still, B side is movable.
Usually 3 plate mold is not recommended as there are some disadvantages, it's not just because of a much more complex structure but much higher scrap rate, it's also lack of stability because of complex mechanism. It's random to use for high volume production because it required longer cycle time and bigger injection molding machine as the run distance is longer comparing with 2 plate mold.
When considering the secondary mold function, ie that of a heat exchanger it is not achieving uniform temperature across the injection mould which is important. The amount of heat energy absorbed by the mould varies dependent on the flow of material through the cavity. Around feed points there will be maximum heat generated due to material flow and shear. At the end of fill the material temperature will have reduced and the surface of the injection mold will absorb less heat energy.
Physical restrictions which restrict size of cooling channels such as small inserts, deep sections, etc have to be considered in each case. Also don't forget that whatever size your cooling channels, when you come to connect them to supply and return pipes you will have a reduction in area, due to the need to fit connectors.