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Injection Molding

The Importance of Temperature Control In Injection Molding

by Ralph January 24, 2018

written by Ralph

From the granules being fed into the barrel, to the final piece coming from the mold, injection mold temperatures are very important. Problems with quality in injection molding can occur because the flow of the heated plastic is disrupted due to the mold being over or under cooled. Under-cooled parts don’t solidify properly and stick to the mold1. Over-cooled parts may not form completely and design details could be lost due to the mold not filling correctly. Over or under cooling can also cause shrinkage or warping of the parts¹. Several areas of the molding process demonstrate the importance of temperature control in injection molding.

Barrel Temperatures

A major area that demonstrates the importance of temperature control in injection molding is the barrel of the machine. The barrel in injection molding machines the plastic travels through usually have between 3 and 5 individual heating zones⁶. The material you are using sets the barrel temperature. The temperature settings are determined by the material’s supplier. Therefore, the machine’s temperature settings should change with the material being used for the production pieces.

The heating zones of the barrel are most often set to gradually increase as the material moves from the back of the barrel toward the mold. Temperatures differences from the rear to the front of the barrel can range from 50 to 80⁰ F⁶.

If the temperature in the rear zone is too high it can cause the plastic to melt too soon and block the flow of the granules into the barrel. The cooling water from the feed throat takes away most of the rear zone heat, so too high a temperature can also waste energy⁶.

Adjusting temperature in the middle zones of the barrel is the best way to use barrel temperature. The heat in this section will be mixed by rotation before the plastic reaches the front zone and any variation in temperature will be removed⁶.

The temperature in the front zone should match the actual desired temperature for the material. Once in the front zone of the barrel the material will not be mixed again, so any plastic that is unevenly heated won’t set correctly⁶. Therefore, slowly increasing temperature from the rear zone through the middle zone, and maintaining temperature in the front zone, is the best process for obtaining quality parts⁶.

Nozzle Temperatures

The nozzle area of the injection mold is also one that demonstrates the importance of temperature control in injection molding. It is important that the nozzle temperature be lower than the mold temperature⁴. If the nozzle temperature is higher than the mold by too much it can cause the plastic to drool. If the temperature in the nozzle is too low, though, it can cause the plastic to decompose and possibly block the nozzle⁴.

Mold Temperatures

Another area that proves the importance of temperature control in injection molding is the mold itself. Maintaining optimal mold temperature reduces unit costs, ensures quality of product, and promotes uniform molding of parts³.

Mold temperature can affect product quality in various ways. Too low of a temperature can create knit lines where the plastic comes together, and can produce an incomplete part. Too high of a temperature can cause warping or blistering in the part².

The mold temperature should be lower than the temperature in the barrel. This allows the material to cool down. The temperature in the mold is usually between 150 and 350⁰ F². Cooling lines filled with water are used to lower the temperature and lines with oil are used to heat the mold and maintain a temperature above water’s boiling point when needed.

Maintaining optimum mold temperature for the material being used will improve part quality, lower cost of production, improve accuracy of parts, lower part distortion, and shorten the time it takes to cool down³.

Temperature Controller

A temperature controller installed on the injection molding machine can ensure the proper temperature is maintained during processing. Temperature controllers, or control units, preheat the mold before the melted plastic is pushed into the mold. The control units keep the mold heated to the set temperature point by circulating a coolant through the mold. The heat that has been produced by the melted plastic is absorbed from the mold by the coolant which keeps the mold at a proper temperature for precise molding⁵.

Injection molding is a process used around the globe. Producing quality, cost efficient products is important for many industries and businesses. The importance of temperature control in injection molding is a major component of producing those quality products.

Sources

Ptonline.com – https://www.ptonline.com/articles/troubleshooting-mold-temperature-control
AccuTherm- http://accutherm.com/blog/importance-temperature-control-plastic-injection-molding/
Lanxess- https://techcenter.lanxess.com/scp/americas/en/techServscp/79183/article.jsp?docId=79173
Crescent Industries- http://info.crescentind.com/blog/bid/59146/5-factors-important-to-injection-molding
Delta systems- https://www.deltatsys.com/industries/injection-molding-temperature-controller
Paulson- https://www.paulsontraining.com/molding-machine-control-set-setting-barrel-temperatures/

January 24, 2018 0 comment

Injection Molding

Top 6 Advantages of Metal Injection Molding

by Ralph January 15, 2018

written by Ralph

Do you have a need to produce a high volume of a small, complex metal piece or component? Does the usual method of metalworking or machining seem cost prohibitive? Perhaps Metal Injection Molding is the process you are looking for. Metal Injection Molding (MIM) is a process that uses Plastic Injection Molding machinery to create metal components and pieces. The top 6 advantages of Metal Injection Molding are listed here.

Background and Process

The process of Metal Injection Molding began in the 1970s at a company called Parmatech in California. Once refined and patented, the process became popular with manufacturing during the 1980s. Improvements to the process in the 1990s awarded more recognition to the MIM process and the advantages of Metal Injection Molding have increased over the last few decades. Metal Injection Molding has become a $1.5 billion-dollar industry today, with over 500 parts producers worldwide.

The MIM molding process has several steps¹. As the image shows, the process begins with mixing the metal powder with a thermoplastic or polymer binding agent. The mixture is granulated into a feedstock material that is then liquefied and injected into the mold. The molded piece is called a “green part”, which then goes through a debinding process to remove most of the binding material from the part using a solvent, heat or a combination of both. The part is now called a “brown part” and is very fragile, but it can be carefully handled. The part is put through a sintering, or high heat and pressure, process. Sintering removes the rest of the binding ingredient, shrinks the product by 20 to 30 percent, and produces the final part¹.

Process

Advantages of Metal Injection Molding

Of the many advantages of Metal Injection Molding, the ability to design small, complex parts quickly and efficiently is one of the most important¹. Regular metalworking techniques limit the range of designs for small, intricate metal parts. Small details often need to be created with additional machining or other methods. With MIM, molds can be designed to include small details such as holes, threads, and slots all at once. A second design advantage of MIM is the fact that the final product is more like the original design, without the need for additional machining or finishing.

Another advantage is the ability to combine multiple components into one piece with MIM. Regular metal working usually requires the manufacture of separate parts that must be assembled to create the final product. Metal Injection Molding allows separate pieces to be molded into one solid piece, eliminating further machining and assembly, and lowering costs².

Size comparison

Combining multiple components also lowers production time. Some parts can be molded in as little as 10 seconds².

A third advantage of Metal Injection Molding is the creation of more complex parts at a high volume of pieces

Without the need for regular metalworking techniques, there’s the possibility of producing 10,000 to 2,000,000 or more parts per year. Parts with irregular shapes, various holes and slots, internal threads, and contours are a great fit for MIM production¹.

The range of materials available to use in MIM is also a great advantage. Metals like stainless steels, magnetic alloys, tungsten, high-speed steels, and copper alloys are possible materials. Special metals like titanium alloys, precious metals, and particle composites are also used³. Special alloys, such as super alloy Ni 625 that resists corrosive environments, and H-X that withstands high temperatures, are available for use in MIM.

The strength and density of finished products are also an important advantage of Metal Injection Molding. During the sintering process, the part is heated to temperatures near melting. This process removes any of the binding material left in the part and densifies the part, shrinking it from 20 to 30%. Finished pieces have densities between 93 and 99%⁶. MIM produced parts are usually as strong, if not stronger, than machined parts.

Powder to part

A final advantage of Metal Injection Molding is the efficiency of the process. MIM has minimal waste. Nearly all, 95-98%, of raw material is shipped as product⁵. The feedstock is recyclable and is used again, so waste is almost non-existent.

Applications

Metal Injection Molding is used in many areas of industry⁷. Industries that use small, strong and complex parts have grown the MIM business by millions of dollars over the last few decades. For instance, the medical industry uses MIM to produce surgical instruments and implantable devices. The dental industry produces orthodontics, such as seen in this photo.

The automotive industry uses MIM to produce engine parts, steering system parts, and lock parts. The IT and electronics industry makes up about 50% of MIM sales in Asia, producing items such as lightning chargers for phones and fiber optics parts⁷. The aerospace industry produces engine components and seatbelt parts. Firearms parts are produced with Metal Injection Molding and parts of Department of Defense equipment are MIM produced. Consumer products include eyeglass parts, camera equipment parts, and musical equipment pieces.

The process of Metal Injection Molding offers many advantages for producing high volumes of small, complex metal parts or components. The advantages of Metal Injection Molding include design flexibility, a variety of materials, reduced processing and assembly costs, and a strong quickly and efficiently produced product.

Product applications of MIM products occur in many areas of industry and use, including in the medical and dental field, automotive and aerospace industries, and as consumer products. If you need to produce a high volume of a small, complex metal piece or component, then the advantages of Metal Injection Molding can work for you.

Metal Injection Molding Sources

Optimim: https://www.optimim.com/mim-process
Chinasavvy: https://www.mobile.chinasavvy.com/industrial/metal-injection-molding.html
Sandvik: https://www.materials.sandvik/en/products/metal-powder/metal-injection-moulding-mim/mim-advantages/
8 reasons: https://medium.com/amt-mim/8-reasons-metal-injection-molding-could-be-suitable-for-you-d6d8280f377
Industrialmetalcasting: http://www.industrialmetalcastings.com/casting_metal_injection_mold.html
PIM: http://www.pim-international.com/metal-injection-molding/metal-injection-moulding-introduction/

Images

Process: http://www.custompartnet.com/wu/images/metal-injection-molding/mim.png

Size comparison: http://s3files.core77.com/blog/images/2014/01/0metalinjectionmolding004.jpg

Powder to part: https://www.industr.com/en/EM-Magazine/__image/a/2298544/alias/xl/v/1/c/18/ar/flexible/fn/MIM_04.jpg

Combination process: https://upload.wikimedia.org/wikipedia/commons/thumb/8/88/OBE-Metallpulverspritzguss-Abb2.jpg/220px-OBE-Metallpulverspritzguss-Abb2.jpg

January 15, 2018 1 comment

Injection Molding

Introduction to Plastic Injection Molding

by Ralph January 5, 2018

written by Ralph

Plastic Injection Molding

The injection molding process is one of the main production processes in the processing of plastics. Injection molding has some features that provide a beneficial application of this method, especially in the manufacture of complex molded parts as mass-produced. These features are:

Direct route from the raw material to the finished part
No or only minor post-processing of the molded part is necessary
Fully automated and process
High reproducibility of production

The range of molded parts that can be produced by injection molding extends from the smallest of gear wheels or bearings to large waste containers. The weights of the molded parts are in the order of 0.001 g to 100 kg.

Machine and process flow

The task of an injection molding machine according to DIN 24450 comprises the discontinuous production of moldings of preferably macromolecular molding compositions, wherein the primary molding is done under pressure.

process flow

For this purpose, it is necessary to convert the material supplied by the raw materials manufacturer usually in granular or powder form (elastomers usually in the form of strips) so that it is converted into a flowable state. First, the material is plasticized by rotation of the screw (Figure 1). After closing the mold (step 1), which has a cavity corresponding to the molding, the plasticized material is injected by axial feed of the screw into the tool (step 2).

Figure 1: Process flow in injection molding

For thermoplastic materials, the melt is subsequently cooled in the mold (step 3). In the case of crosslinking materials (thermosets, elastomers), the tool is heated, thus initiating the crosslinking process. The last step involves opening the tool and ejecting the molding (step 5).

The outlined process steps, which sometimes overlap in time, are part of every injection molding cycle. In the production of an injection molded part, the individual production steps, which are shown again in greater detail in Figure 2, are coordinated by the control device of the machine.

Figure 2: Injection Molding

The aim in the economic production of a molded part is to reduce the cycle time required for this process in order to achieve a high output.

In addition to the above-mentioned method steps can perform other functions, such as the movement of the unit, actuation of core pulls u. a. m., However, these do not change the basic procedure.

machine design

Irrespective of the material to be processed, an injection molding machine is made up of the following assemblies (Figure 3): The machine bed is used to hold the plasticizing unit and clamping unit. The latter serves to realize the opening and closing movement of the tool during the production cycle. The course of the injection molding cycle is coordinated via a control or control unit, which is usually housed in a separate cabinet from the machine.

Figure 3: Construction of an injection molding machine

The drive of the screw located in the plasticizing unit as well as the closing unit is carried out hydraulically or via direct electrical drives. The pumps required to provide the required hydraulic oil volume flow are housed in the machine bed and are driven electrically. The hydraulic valves required for the control of the individual movements are as far as possible in the immediate vicinity of the consumers to whom they are assigned. To operate additional functions such. As ejector, nozzle or for moving core trains, additional purely electromechanical or pneumatic drives are used.

In the following explanations only machines are to be considered whose main movement mechanisms (plasticizing, injecting, opening / closing tools) are hydraulically realized, since this type of machine is predominantly found in practical use, but all-electric machines are becoming increasingly important.

To cool the injected molten plastic, the molding material must be cooled under solidification temperature in thermoplastics before the molding can be removed from the mold. (In the case of crosslinking molding compounds, the tool is heated in order to trigger the crosslinking process). To this end, tool tempering devices (also referred to as tempering unit) are necessary. These can be an integral part of the machine or be placed as an external unit to the machine.

January 5, 2018 0 comment

Injection Molding

Six Ways To Minimize Cycle Duration In Injection Molding

by Ralph January 2, 2018

written by Ralph

Part Design

Keep the wall thickness as thin as possible according to the application. The thinner the wall thickness, the shorter the cooling time phase of the injection molding cycle. As the wall becomes thinner, the cost of the molding machine and the material cost of the parts are also reduced. In determining the wall thickness of a particular part it is ensured that the part strength is still within the quality limit and that the forming machine has the ability to make thinner parts. Clicking the link below will display a case study to reduce the wall thickness.

https://www.linkedin.com/pulse/case-study-dyson-vacuum-cleaner-bin-paul-kuklych/?lipi=urn%3Ali%3Apage%3Ad_flagship3_profile_view_base_post_details%3ByMgHE5D4StGz7JOMDibWXQ%3D%3D

Mold Design

The design of the cooling channels in the mold plays an important role in minimizing the cycle duration. Make sure there are many large channels near the molding surface. However, please be careful not to compromise the strength of the mold. If the cooling channel is made too large on the molding surface, if it is too close to the molding surface, it contributes to the deflection of the mold, causing not only cracks in the mold cavity but also part quality problems. Cracked cavities are usually a great chaos in productivity level because exchange inserts are required.

Another mold design characteristic to be considered is the ejector system. The ejector system must be robust enough to quickly damage parts from the mold. Generally, the thinner the part, the less extruded surface area, the more difficult to discharge. This is one reason why thin wall molding is difficult. For details on thin wall molding, please click the link:

https://www.improve-your-injection-molding.com/thin-wall-injection-molding.html

Molding Machine Suitability

A suitable molding machine must be able to achieve the correct filling time limit to make acceptable parts. If the filling time is too short or too long, a rejected part is generated. Accurate filling time uses specific injection pressure and injection speed.

For details of molding machine selection, please click the following link:

https://www.improve-your-injection-molding.com/plastic-injection-molding-machine.html

Process Technician’s Ability

Injection molding is a complicated process because there are many parameters in the machine controller, and when changed it affect cycle time. For example, it is possible to shorten the cycle duration by increasing the injection speed, increasing the platen speed, increasing the injection speed, reducing the mold opening stroke, shortening the holding time, and shortening the cooling time. Unless a systematic approach is taken, it is difficult to make the best combination of process parameters. The training of scientific molding principles of process engineers is a great merit.

Resin Selection

Some material suppliers claim to manufacture the same resin grade to reduce cycle time. They have a special formulation which means that parts are discharged faster than usual. If a substitute for such a resin is not available, please consider additives such as Nanosil. Clicking on this link will display information about Nanosil’s experiment which reduced cycle time by 13%.

https://www.improve-your-injection-molding.com/nucleating-agent.html

Polishing

Product designers specify polishing of a specific grade based on cosmetic purposes. Grinding grade is often high mirror polishing, causing many molding difficulties and increasing cycle time. Since there are various grades for the mirror finish, please execute only the minimum requirement according to the application.

Please let me know if you have any idea about ways to reduce cycle time.

January 2, 2018 0 comment

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