Injection Mold Cost – The Real Story

What is injection mold cost?

It is the price an injection molder will pay to purchase a mold. But that is not the full story.

If you are an injection molder then you might be interested in reading more so that you can save yourself a ton of money and avoid some serious headaches.

There is a second cost which I call residual cost. These are costs which start once a new mold is in production and occur over the life of a mold. Residual costs relate to any inefficiencies in a mold such as molding rejects or slow cycle time.

Residual costs will increase your cost per part.

The benefit of taking both costs into consideration is to get a realistic picture of your mold makers ability to improve your injection molding business.

Stage 1 – The Initial Purchase Price


This is the quoted price of a mold plus any freight costs. If a molder buys from a local injection mold manufacturer then freight costs are negligible. If a mold is bought overseas and transported by ship then costs are still relatively low.

The initial purchase price is influenced by the following factors:

  • Part size – large parts require a large mold so mold material cost is higher than with smaller parts.
  • Part design – complicated part designs will require complicated mold designs so this will make the price high. Whereas, simple part designs require simple mold designs and lower prices (although this is not always the case).
  • Part material – if the plastic material is corrosive such as PVC then stainless steels will be required and they are expensive.
  • Part quality requirement – will require quality mold steels, quality machining techniques and quality injection mold design – the purchase price will be a premium. Molders with low part quality requirement often buy cheap molds but be careful about doing this as this can cost more in the end due to slow cycle times and the cost of producing large quantities of rejects.
  • Annual quantity requirement – high volumes will require high cavitation and therefore a bigger mould. High volume requires a mold with good internal strength so high quality materials are required which increases the injection mold cost.
  • Cycle time requirement – fast cycle times will require well designed and built molds which will be a premium cost.
  • Molding machine size – mold should be big enough to support high tonnage machines. Mold should cover most of platen area to ensure quality parts are produced over the long term. Small molds in large machines will give quality problems because small molds damage the machine platens. Damaged machine platens will increase the reject rate in all molds.
  • Country of manufacture – low cost countries will be a lot cheaper than western countries.

These costs are easy to see and understand. However, what is not so easy to see and understand are the costs associated with poor mould quality –called residual costs.

Stage 2 – Residual Costs


Residual costs occur over a period of time and start from first mold trial.

A well designed and built injection mold will have a low residual cost because it will be easy and quick to setup, easy to start, have a low reject rate, have fast cycle time and the mold will consistently perform well beyond its required life expectancy.

Whereas, a poorly designed and built mold will have a high residual cost because it will have long setup times, be difficult to start, have high reject rates and a slow cycle time. And you can be sure that if a mold is delivered in this condition it will only get worse day by day.

These types of molds cannot be fixed.

These molds are usually cheap and if bought overseas there is the cost of travel – the molder must pay an airfare to meet the mold maker and sign a contract or to give final mold quality approval.

What’s more, there are other high residual costs and the effects, of which, are difficult to measure. These include the effect on employee morale (due to time pressures and unsafe work practices) and the cost of damage to molding machines (poorly made moulds will usually not be flat and this will slowly destroy tie bars, platens and toggle clamping systems).

And that’s not all, damaged molding machines will gradually damage all other moulds which will increase part reject rate day by day.

Additional Comments


Injection mold cost is really about taking into consideration long term performance not just the initial purchase price. Having this information will give the best chance of making the right decision in future mold projects.

Remember, cheap molds make expensive parts and expensive molds make cheap parts.

Which one do you prefer?

From Website
Edited by Leafly Mould Provides Injection Mold, Plastic Mold, Injection Molding, Die Casting Mold, Stamping Mold

Hot Runner Mold Benefits

There are several benefits to using a hot runner mold as opposed to a cold runner mold. When designed and built correctly, hot runners are easy to use and allow an injection molding company to save costs and increase productivity.

Eliminates Cold Runner


Not having to deal with a cold runner saves money in a number of ways:

  • no wasted plastic material
  • no need to pay someone to make regrind
  • no sprue picker robot required
  • faster cycle time for increased productivity levels

Thinner Walled Parts


A hot runner makes it easier for a molding machine to inject plastic into a mould cavity. A hot runner increases the capability of a molding machine. It reduces the plastic flow length so a molder can save material by making thinner and lighter parts.

Shorter Cycle Time


A shorter opening stroke can be used as there is no runner to eject saving cycle time.

Injection fill times are shorter because the plastic flow length is shorter which also saves cycle time.

What’s more, for high cavitation moulds runners need to be thick and cold runners will need a long cooling time before being solid enough to eject from a mold.

Hot Runner Manufacturers


There are more than 20 hot runner manufacturers making high quality hot runners around the world today. Each one can custom make a hot runner to fit a new mold design.

The high number of manufacturers means competition keeps prices under control. Good support is also available from most of them.

Mold Makers Can Make Hot Runners


Some injection mold makers are capable of making their own hot runners. The advantage is that one company can take full responsibility of the entire mold and it reduces the hot runner price.

To make a hot runner requires standard tool making equipment such as a radial drill, cnc machining center, a surface grinder, a cylindrical grinder and a cnc lathe. All heater elements can be bought and a person qualified in electrical wiring can connect them to the temperature controller.

The materials required to make a hot tip hot runner are P20 for the manifold and H13 for the nozzles and insulators. The nozzle tips are usually made from a copper alloy but can also be made from H13 and thru hardened for long life.

Other Benefits:


Other benefits of hot runners:

  • hot runners available for both single cavity and multi cavity moulds
  • can be used with most plastic materials and part designs
  • are easy to maintain
  • reduce the number of moving plates in a mold
  • gives good gate vestige
  • can use with close pitch mold designs

Challenges With Hot Runners


Hot runner molds involve the use of electricity so some training will be required for die setters and process technicians so that safety procedures are followed.

A hot runner mold will have a bigger mold height compared to a cold runner mold so this may limit which molding machines can be used due to the larger physical size of the mold.

Additional Comments


The decision to use a hot runner or cold runner must be taken on a case by case basis but the fact is that a molder having a medium to high annual quantity requirement for any particular part will benefit from a hot runner mold.

The extra cost of a hot runner will be recovered through faster cycle times, better quality parts and material savings.

From Website
Edited by Leafly Mould Provides Injection Mold, Plastic Mold, Injection Molding, Die Casting Mold, Stamping Mold

3 Plate Mold Design For Plastic Injection Molding

3 plate mold designs are used in multi cavity cold runner mold tooling when a 2 plate mold design does not permit a suitable gate location.

3 Plate Mold Example.


3 plate mold with stripper plateFigure 1: two cavity 3 plate mold for 47mm alcohol cap

Figure 1 shows an assembly section of a three plate mold producing a 47mm cap.  This design allows the gate to be placed on the top of each cap.  The caps and cold runner are ejected by their own individual stripper plates during mold opening.

Right click here to download Figure 1 in PDF format.

You will need Adobe Reader (the latest version is recommended) installed on your computer in order to open and read this file. You can download Adobe Reader here (a new window will open so you can download it without leaving this page).

If you want to open the file in your browser window, just click on the link (not all browsers have this feature). However, if you want to download the file to view later, then right-click on the link and choose “Save Target As” or “Save File As.” Then select where you want to save the file on your hard drive.

Once you have saved the file, locate where you saved it, and double click to open it.

In order to print, open the downloaded file, and select the “Print” option from the e-book

3 plate mold with stripper plateFigure 2: limit screws (A) required for 1st opening limit

During the opening sequence the first split is between the cavity plate and the stripper plate (for runner) due to spring pressure (see spring in figure 3) for the distance defined by limit screws (A) in figure 2.  At this stage the runner is exposed but held firmly to the mold by the sucker pins (the sucker pins are labelled in Figure 1) .

Right click here to download Figure 2 in PDF format.

3 plate mold with stripper plateFigure 3: limit screws (B) required for 2nd opening limit

As the mold continues to open, the 2nd split is between the cavity plate and the stripper plate (for cap) for a distance defined by limit screws B in figure 3.

Right click here to download Figure 3 in PDF format.

3 plate mold with stripper plateFigure 4: limit screw C

The 3rd stage opening is between the back plate on the fixed side and the stripper plate (for runner) for a distance defined by limit screw (C) in Figure 4 which ejects the runner off the sucker pins. The runner falls to the ground.

At this stage the mould is fully opened, so the KO bar must be initiated by the machine ejector to remove the caps from the mold tool which is the 4th.

Should I Use a 3 Plate or 2 Plate Design For My Part?


When designing a cold runner mold tool a 2 plate mold design should be considered first because it is easier and cheaper to make.

One potential limitation of a 2 plate design is that the gate must come from the side of the part which has the potential to cause the following quality issues in some parts: weld lines, jetting, unfavourable shrinkage rates and wall thickness variation due to core shift in tall parts. Longer flow paths may also be required which can place higher demands on the injection molding machine and consume a lot more energy.

Having said that, the 2 plate mold is suitable for many types of plastic parts.

The advantage of a three plate mold design is that it permits the gates to be located on top or bottom of the part at any point on the surface.  Well placed gates will produce quality parts every cycle.

Figures 5 & 6 are an example of a 2 plate & a 3 plate mold design respectively for the same 47mm alcohol cap. Notice the different gate locations.

2 plate mold with stripper plateFigure 5: two cavity 2 plate mold for 47mm alcohol cap

Right click here to download Figure 5 in PDF format.

Figure 6: two cavity 3 plate mold for 47mm alcohol cap(same as figure 1)
From Website
Edited by Leafly Mould Provides Injection Mold, Plastic Mold, Injection Molding, Die Casting Mold, Stamping Mold

Heat Treating Tool Steel – How To Choose The Right Treatment For Injection Molds

Heat treating tool steel is a very complicated task. Choosing the right type of heat treatment in plastic injection mold making can also be very difficult if you don’t have the knowledge.

The bottom line is that the heat treatment selected for an injection mold must keep the mold in good working condition for the life of the mould.

So how to choose the right treatment for your mould? I am glad you asked.

The type of heat treatment depends upon the following factors:

  • Choice of tool steel. The choice of steel largely dictates the type of heat treatment.
  • Mould price. This should take into account the type of heat treatment. If the price is too low then there is probably not going to be any heat treatment at all.
  • Part design. If part has deep undercuts or threads then mould design will need some moving components in order to release the part from the mould. Moving components require special attention so that the surfaces don’t wear out quickly or get damaged.
  • Mold design. This is heavily influenced by the part design.
  • Annual production quantities. Small quantities can use softer, less expensive materials but high volume moulds require long lasting materials and heat treatments.
  • Environmental factors. Does the molding take place in a corrosive environment?
  • Mould maintenance issues such as corrosion.

Types Of Heat Treatments For Tool Steels


  1. Surface treatment – the surface of the work piece becomes harder than the inside. Treatments include case hardening, nitriding, flame hardening, hard chromium plating, nickel plating, titanium nitride and titanium carbide.
  2. Through hardening treatment – gives uniform hardness throughout the entire work piece.

Below are 4 of the most common steels used to build injection molds and their recommended treatments:

P20 Heat Treating Tool Steel


P20 – (DIN No. 1.2312) – supplied in the thru hardened and tempered condition at a hardness of 310 HB (34HRC). It has good polishability, photo-etching properties (for surface texturing).

This steel is mainly used for the mold bolster (it is a holding steel) but can be used for core, cavity, gate inserts, sprues and sliding inserts in moulds with shot production quantities less than 500,000 per year such as in automotive and home ware products.

P20 can be hard chromium plated which is useful for mould reconditioning purposes.

P20 can also be electroless nickel plated for extra corrosion resistance. Because electroless nickel plating takes place in a bath, the plating will also cover internal water cooling channels, which makes mould maintenance easier. The plating will add 0.005mm per side or 0.01mm to plate thickness.

Sliding inserts made from P20 should be nitrided for wear resistance and guard against possible damage when using with a P20 bolster.

It can be welded which is good for repairs. It can be flame hardened or nitrided for extra resistance to wear and erosion. A nitride surface also increases the corrosion resistance.

H13 Heat Treating Tool Steel


H13 – (DIN No. 1.2344) – is a through hardening tool steel which has excellent hot tensile properties, high hot wear resistance , adequate toughness and resists tempering at high operating temperatures.

These properties makes this steel an excellent choice for cores, cavities, stripper rings, sliding parts or rotating cores in moulds designed to produce millions of parts per year at fast cycle times. Thin wall molding is an example of this type of application (containers and cutlery).

H13 can be nitrided. Nitriding is required if an H13 sliding component moves within another H13 component to prevent damage. For example, if an H13 moving centre core is fitted to an H13 core block then the normal procedure is to nitride the centre core. Without nitriding, the centre core will, in effect, weld itself to the H13 core and all movement will stop.

With great difficulty, the centre core will then have to be separated from the core and all damage (also called “pick up”) will have to be machined out. There is a good chance that the centre core will not be recoverable and a new one will have to be made.

H13 can be hard chromium plated which is useful for mould reconditioning purposes. It can be used to rebuild worn interlocking surfaces between a core and cavity. But be careful about using it around shut off edges because it is prone to chipping at corners during machining.

H13 is more expensive than P20 but the extra cost is more than offset by the outstanding performance of this steel.

Recommend through hardness 48-52 HRC. A hardness of 52 HRC will give longer mould life but it is harder to perform finish machining operations at this hardness compared with 48 HRC.

Welding is possible but proper precautions must be taken (elevated working temperature, joint preparation, choice of consumables and welding procedure).

Ramax Heat Treating Tool Steel


Ramax – (DIN No. 1.2085) – is a through hardened stainless steel that offers good corrosion resistance which prevents clogging of water cooling channels that could otherwise affect cycle time consistency and mould maintenance.

It is a holding steel and is supplied with a uniform hardness of 340HB(38HRC) (which is more than P20 ) so it is a more durable steel for mould bolsters and gives a longer life time.

Welding is possible but proper precautions must be taken (elevated working temperature, joint preparation, choice of consumables and welding procedure).

Polishable, but only recommended for parts requiring low to medium polishing demands.

Stavax Heat Treating Tool Steel


Stavax – (DIN No. 1.2083) – is a through hardened premium stainless steel with good corrosion resistance, good polishability and good wear resistance.

The combination of these properties gives a steel with outstanding production performance. The practical benefits of good corrosion resistance in a plastics mould can be summarized as follows:

  • Lower mould maintenance costs. The surface of the cavities maintain their original finish over extended running periods. Molds stored or operated in humid conditions require no special protection.
  • Lower production costs. Since water cooling channels are unaffected by corrosion (unlike P20 steel)heat transfer characteristics and therefore cooling efficiency are constant throughout the mould life, ensuring consistent cycle times.

These properties makes this steel an excellent choice for cores, cavities and stripper rings in moulds designed to produce millions of parts per year at fast cycle times (containers and cutlery).

Its suitable for molding corrosive materials such as PVC and abrasive filled materials.

Its good polishability makes it suitable for optical parts such as camera and sunglass lenses.

It can be photo-etched and welded.

It is more expensive than H13 steel.

Recommended through hardnes is 45 – 54 HRC

From Website
Edited by Leafly Mould Provides Injection Mold, Plastic Mold, Injection Molding, Die Casting Mold, Stamping Mold

Plastic Parts Design and Material Selection– How To Do It Right The First Time

The most important first step in plastic parts design and material selection is to list the environmental conditions that the part will be exposed to.

For example, will it be subject to elevated temperatures? If so, for how long and how often? Plastic behaves differently at different temperatures.

This is just 2 questions of several that need to be answered before one is in a position to select the most suitable plastic material.

Plastic part failure in the field is often a result of poor research.

Delivery lead times are becoming so short  that often plastic parts design and the material selection process are not given the attention and time needed to make proper decisions.

This is where the process of Concurrent Engineering can be of great benefit to a new product project. Concurrent Engineering brings together the mold maker, molder, part designer, plastic supplier, marketer and end user so that the proposed plastic parts design can be analysed for economic and technical viability. That is, whether or not it can be made at a particular cost so that all parties involved can make a profit.

Part Shape


The next step is to decide on the shape of the part and the wall thickness. This can be done by people who have the specialized knowledge such as molders, mould makers and industrial designers.

The use of Finite Element Analysis (FEA) can also be of great benefit. FEA will identify any potential weak areas in the part design. Keep in mind however, the computer generated results are only as accurate as the information that is fed into it. So get accurate information.

Mold Design


When you are confident that the part will work in the field, an injection mold maker must check that the part can actually be made. A mould needs to be designed around the part. Where is the gate to be located? Is more than one gate required? Where are the parting line surfaces? How will the part be ejected? For complicated part shapes, computer simulation techniques must be used.

Once these mold design points are answered, make sure the plastic material selected is capable of filling the mould cavity. Some materials such as polycarbonate are very viscous so a thick wall section is required to be able to make full parts.

In addition to this, in order to have long term reliable production, there are a number of other things to consider. After all, we do want a project to work don’t we?

Draft


Draft can be the enemy for part designers. Too much draft on a cosmetic part can detract from its appearance. But the fact is, draft is required to make quality parts at fast cycle times.

Draft angle should be at least 0.5 degree per side but 3 degrees is better. The greater the draft the fewer scratches and marks will be present on the parts.

What’s more, draft is required for stacking purposes. Parts with large draft angles can be easily stacked and separated. They also reduce the combined stack height of the parts so that  transportation costs are kept as low as possible.

Uniform Wall Thickness


The easiest parts to mould have uniform wall thickness. If, for some reason, the part has to be thicker in a particular section, then consider locating the gate in this section so that sink marks can be avoided.

There are some other circumstances when uniform wall thickness does not apply. Ribs are often made thinner than the nominal wall thickness to reduce the sink mark which detracts from its appearance.

Radii


Any sharp corners on the part will not only make it more difficult to eject from the mould, it will also create stress concentrations and likely lead to part failure.

There should be at least 0.5mm radii everywhere. Bigger radii will make the part stronger and increase its lifespan. Bigger radii will also help with processing by improving material flow around corners.

Dimple


Gate brittleness ( which can cause part failure) is the result of stress set up in the gate area. In practise, these stresses are usually caused by the application of incorrect moulding conditions, such as too high or too long hold pressure. Risk of gate brittleness is substantially reduced by having a dimple opposite the gate by locally increasing the wall section by 40%.

Standard Rib Design


The main function of ribs is to improve the rigidity and strength of a molded part. They may also be used to help flow during processing and decrease part warpage.

Ribs must be carefully designed in order to minimize sink marks and stress concentrations.

Minimizing sink marks is especially important for parts that have a perfectly clean matt or glossy finish such as housings for electrical appliances. The width of the rib can be as low as 50% of the adjacent wall in order to reduce the effect of sink.

Keep in mind however, that with such a thin rib, the part will be harder to process so good mould design and molding machine capabilities are critical. The machine must be capable of applying adequate hold pressure in the rib area during processing.

Ribs have the potential to create venting issues so mold design must take this into consideration.

Alternate Rib Design


The standard rib design is very effective in creating strength in a particular area of a part. However, this type of rib can cause quality issues when venting is not taken into consideration. It can also create a high nest height which means fewer parts will fit on a standard transportation pallet which increases freight costs.

An alternative rib design is often used in the food packaging industry. To minimize warping, an angular panel is designed into a lid which acts just like a standard rib but will not cause quality issues. The lids will also maintain a low nest height.

A lid also has another built in rib which is the skirt wall. The skirt wall will also aid in minimizing warp.

Conclusion


The most critical aspects of plastic parts design is to know where it will be used and what conditions it will be exposed to. Without this knowledge there is no chance of a successful moulding project.

At the start of a new part project, here is a list of questions to answer before selecting the plastic material:

1. What temperature range will the part be exposed to and for how long?

2. What are the mechanical loads?

3. What are the nature of loads – cyclic or constant?

4. Direction of loads – does the load act in one or more axis?

5. Environmental factors such as sunlight, water or chemicals exposure?

6. Electrical requirements?

7. Tolerance requirements? Does the part fit with other parts?

8. What are the long term effects on the chosen material? Is there any information available?

From Website
Edited by Leafly Mould Provides Injection Mold, Plastic Mold, Injection Molding, Die Casting Mold, Stamping Mold

3D Rapid Prototyping in Injection Molding

3D rapid prototyping is an additive process used to build products of different shapes and sizes from a 3D computer model for use in industries such as injection molding, medical, packaging, automotive, aviation, and electronics.

Among the materials currently available to make rapid prototyped products include plastics (Nylon, ABS), Aluminium, Tool steel, Stainless steel & Titanium.

Batch size can range from 1 to tens of thousands.

There are several different types of machines available for building a product using 3D rapid prototyping techniques. These machines use one of the following methods: Fused Deposition Modelling (FDM) which is common in household 3D printers, Stereolithography (SLA), Selective Laser Sintering (SLS), Direct Metal Laser Sintering (DMLS), Electron Beam Melting (EBM), Digital Light Processing (DLP). The method used depends upon the product application as each method has different material and size specifications.

Direct Metal Laser Sintering (DMLS)


Some of the materials currently available for this method are Stainless steel, Tool steel, Aluminium & Titanium. One of the applications of this method is the manufacture of core & cavity inserts used in plastic injection molds where water cooling channels follow the contours of the moulding surface. This is known as conformal cooling which can be difficult or impossible to manufacture using tradition manufacturing methods. Conformal cooling improves part quality and lowers cycle times allowing for more efficient production.

However, as with other rapid prototyping methods, secondary operations are required: machining of the inserts for final fitting into an injection mold as well as mirror polishing of the moulding surfaces.

Selective Laser Sintering (SLS)


Two of the materials currently available are Polyamide (with or without glass) & a TPU.

The advantage of this technique is that living hinges (0.3mm) used in packaging products are possible so fully functional parts can be made with a shorter delivery lead time compared to building an injection mould tool.  Other applications include jigs & fixture tooling.

Another advantage is that size of a product is virtually unlimited as it can consist of several sub-parts.

Surface finish can vary from very fine to rough depending upon build time allowance

Stereolithography (SLA)


There are number of plastics available for this 3D rapid prototyping method which include PP, ABS & PC.

Typical applications include master patterns for urethane castings, prosthetic legs, architectural models & injection mold inserts.

Surface finish produced is smooth & can be nickel plated or painted.

Part size is also virtually limitless.

Additional Comments on 3D Rapid Prototyping


The industry continues to evolve and as a consequence continues to find new applications. One of the biggest benefits of rapid prototyping is the reduction in the time to market of new products which has changed traditional manufacturing industries such mold making and injection moulding.

The new technology should not be seen as a threat to the injection molding industry, it is actually an aid in the complicated process of delivering new products to market which ultimately improves our standard of living.

From Website
Edited by Leafly Mould Provides Injection Mold, Plastic Mold, Injection Molding, Die Casting Mold, Stamping Mold

Mold Polishing Tips For Injection Molds

Mold polishing is primarily a manual process requiring a high level of skill and knowledge.  There are a number of finishes available to mould makers and the final finish depends upon the plastic part requirements.

Mirror polished spoon cavity

Types of Finishes in Mold Polishing


The most basic type of finish is a “stoned” finish which uses stone abrasives to get a matt finish. They range from 100 grit(roughest) to 1200 grit (finest). This is the cheapest & quickest form of polishing. Normally used to remove machining marks for the purpose of easy part ejection during molding.

Also, when a grit blasted finish is required, the surface must be stone finished first in order to get a quality grit blasted surface finish.

Then there are “paper finishes” which is essentially a fine abrasive attached to paper which is used after stoning to get  some level of gloss on the mold tool surface. The plastic part will also replicate this same level of gloss on its surface.

Finally there is the mirror polish. There are different levels of mirror polishing the highest level looks just like a glass mirror and is used for lens parts. This is the most expensive and time consuming type of finish to achieve and needs the first 2 stages (stoning and papering) to be completed before mirror polishing can begin. Mirror polishing requires the use of a buffing wheel & is often referred to as buffing.

Know The Minimum Type of Finish Required.


In order save costs and time a mould maker must know the minimum type of finish required in mold polishing.  The best way to do this is to find several sample parts of different finishes and get your customer to approve the minimum requirement. This sample can then be passed on to the mould polisher so he can replicate the required finish.

Also, knowing if the polished finish is for functional or cosmetic reasons helps in deciding the type of finish. A stoned finished is usually the minimum requirement for functional reasons (for easy ejection off the mold tool core). Mirror polished mold tool surfaces will more likely give part ejection difficulties especially for deep parts with little or no draft. This will result in longer cycle times and more part quality issues. So avoid mirror polishes if possible.

Polishing H13 Tool Steel versus 420 Stainless Tool Steel.


Different grades of tool steels will require a different approach when mirror polishing. For example: it takes more time to polish stainless steel than H13 steel. Before the mirror polish stage can be started on H13 steel a stoned finish of  600 grit is required whereas on stainless steel a stoned finish of 1000 grit is required which is 3 grades finer than 600 grit stone abrasive.  This takes more time.

In addition to this, at the start of the mirror polishing stage, stainless steel must begin with a coarser grade of diamond paste (18micron paste) compared to H13 (8micron paste). So this stage also takes more time so expect to pay a premium.

Orange Peel Effect


The orange peel finish sometimes seen on plastic parts is a result of poor polishing techniques. If this type of finish is not adequate for your parts then the mold tool surface needs to be repolished with a lot more care.

The Polishers Ability.


A person’s ability to polish is very important when it comes to the final quality. Different polishers have slightly different ways to polish which they have developed during years of practice.  The ultimate guide of a good polisher is one who can deliver the required finish on time at a reasonable price. Unfortunately, these types of polishers are becoming harder & harder to find.

From Website
Edited by Leafly Mould Provides Injection Mold, Plastic Mold, Injection Molding, Die Casting Mold, Stamping Mold

Plastic Injection Molding Process – Energy Saving Techniques

The plastic injection molding process can start saving you money immediately.

I am about to show you how to use the molding process more efficiently.

An important part of the plastic injection molding process are the process parameter settings such as hold time and screw plasticizing time. Process parameters give direct control over part quality and cycle time. Click here to read about how plastic drying also influences part quality.

But they also have another function.

Process parameters can heavily influence the energy consumption of a molding machine.

By experimenting with process parameter settings you can potentially cut thousands of dollars a year off your energy bill.

A recent case study we performed on a 260 ton Sumitomo hydraulic injection moulding machine showed that the electrical energy cost per part was reduced by 23% just by changing molding process parameters. Click here to find out about another way of reducing costs by fixing flash quality problems.

And click here to find out how to save costs by eliminating short shot quality issues.

This result was achieved during a 6 hour production run. A small investment in time for such a large, ongoing return.

We want to help you get the same result by showing you how easy it is to do.

Plastic Injection Molding Process Case Study


Figure 1 Energy Meter

Equipment used:

  • 260T Hydraulic injection molding machine with single cavity mold
  • Chiller unit
  • An energy meter (see figure 1) Also called a watt meter

Procedure


Figure 2

Disconnected moulding machine from mains power via circuit breaker and then connected the energy meter to the machines power supply.

Once barrel heaters and hydraulic oil were up to temperature production commenced and continued for one hour before the first energy consumption readings started.

A photo of the part produced is in figure 2.

In the first test, the amount of energy consumed during a 30 minute period was measured with the original plastic injection molding process parameter settings.Cycle time was 18.0 seconds. See table 1 below for a list of all parameters.

The electricity cost per part was calculated to be 2.39 cents.

For the 2nd test we chose to double the RPM speed of the plasticizing screw. At the end of the 30 minute period we could see that this reduced energy consumption by 3.5% (without effecting quality) so the cost per part reduced to 2.31 cents. Cycle time remained at 18.0 seconds.

In test 3 cycle time was reduced by increasing the mould opening and closing speeds. Although the energy consumption slightly increased during the 30 minute time interval, the production quantity actually increased from 100 parts to 120 parts so the cost per part went down to 2.06 cents.

Test 4 was to cut cooling time by 3 seconds from 8.7 to 5.7 seconds and the cost per part reduced again to 1.85 cents. A 23% reduction in cost compared to test 1.

Test 5 involved increasing the fill time from 1.2 second to 1.65 seconds and reducing the cooling time so that the cycle time remained the same as test 4 at 12.0 seconds. The result was an increase in cost per part to 1.93 cents.

All these results are in Table 1 below.

RESULTS
TEST NO. 1 2 3 4 5
PROCESS CHANGE INITIAL SETUP INCREASED SCREW RPM SAME AS 2 & REDUCED MOULD OPENING & CLOSING TIMES SAME AS 3 & CUT COOLING TIME SAME AS 4 & INCREASED INJECTION TIME
CYCLE TIME seconds 18.0 18.0 15.0 12.0 12.0
INJECTION TIME seconds 1.2 1.2 1.2 1.2 1.65
HOLD TIME seconds 2 stages 0.8 0.2 2 stages 0.8 0.2 2 stages 0.8 0.2 2 stages 0.8 0.2 2 stages 0.8 0.2
HOLD PRESSURE bar 2 stages 504 420 2 stages 504 420 2 stages 504 420 2 stages 504 420 2 stages 504 420
COOLING TIME seconds 8.7 8.7 8.7 5.7 5.25
PLASTICIZING SPEED rpm 125 250 250 250 250
PLASTICIZING TIME seconds 5.0 2.55 2.55 2.55 2.55
BACK PRESSURE bar 4 stages 224 224 224 56 4 stages 224 224 224 56 4 stages 224 224 224 56 4 stages 224 224 224 56 4 stages 224 224 224 56
INJECTION PRESSURE bar Set to maximum Set to maximum Set to maximum Set to maximum Set to maximum
MOLD OPEN TIME seconds 1.5 1.5 1.1 1.1 1.1
MOLD OPEN STROKE mm 450 450 250 250 250
MOLD CLOSE TIME seconds 1.3 1.3 1.1 1.1 1.1
EJECTION STROKE mm 70 70 70 70 70
EJECTION TIME seconds 1.0 1.0 1.0 1.0 1.0
BARREL TEMPERATURES ⁰C 235-230-210-205 235-230-210-205 235-230-210-205 235-230-210-205 235-230-210-205
MOLD HOT TIP ⁰C 230 230 230 230 230
ENERGY CONSUMPTION PER 30 MINS kwhr 13.3 12.85 13.75 15.45 16.1
ENERGY CONSUMPTION PER 1 HOUR kwhr 26.6 25.7 27.5 30.9 32.2
TARIFF $ PER kwhr 0.18 0.18 0.18 0.18 0.18
PARTS MADE PER HOUR 200.0 200.0 240.0 300.0 300.0
MATERIAL CONSUMPTION PER HOUR kg/hr 15.2 15.2 18.2 22.8 22.8
ENERGY CONSUMPTION PER Kg kwhr/Kg 1.75 1.69 1.51 1.36 1.41
COST PER HOUR $/hr 4.79 4.63 4.95 5.56 5.80
COST PER PART $/part 0.02394 0.02313 0.02063 0.01854 0.01932
COST PER PART cents/part 2.39 2.31 2.06 1.85 1.93
COST REDUCTION PER PART cents 0.0 0.081 0.332 0.540 0.462
% COST REDUCTION PER PART ZERO 3% 14% 23% 19%

Results


The results for this experiment show that for this particular machine producing this part, energy consumption was reduced by up to 23% from the original settings. This translates directly into a 23% saving in electricity costs per part. And this was done just by changing some of the parameters in the plastic injection molding process.

If your annual electricity cost for this machine and part was $10,000 then that translates into a saving of $2,300 per year.

Imagine if all of your machines could have at least a 10% reduction in cost then this would mean tens of thousands of dollars in savings per year. That’s capital that can be used to grow your business.

More importantly, the results show that the machine uses energy more efficiently at faster cycle times. This is one benefit of fast cycling thin wall injection molding.

Click here to learn more about the benefits of thin wall injection molding.

In test 1 the kwhr per kg of polypropylene was 1.75 at a cycle of 18.0 seconds. In test 4 the kwhr per kg reduced to 1.36 at a cycle time of 12.0. So there is a double benefit of having the fastest cycle time possible: the most obvious is the increased production output but the hidden benefit is the reduced electricity cost. It is cheaper to make parts at faster cycle times with hydraulic machines. 

Conclusion


The fact is, it easy for an injection molder to reduce electricity costs on existing hydraulic machines just by adjusting parameters in the plastic injection molding process.

The ability to reduce costs without having to invest in expensive new technology machines is totally in your control.

From Website
Edited by Leafly Mould Provides Injection Mold, Plastic Mold, Injection Molding, Die Casting Mold, Stamping Mold

Plastic Raw Material Technology For Increased Productivity

When it comes to trends in the injection molding industry, plastic raw material technology plays a critical role.  Improved part quality at shorter lead times and lower unit costs are 3 of the most important current trends. Material technology contributes to all three.

Polypropylene


One of the most commonly used plastic raw materials is polypropylene resin. Polypropylene has a wide variety of applications and packaging is one of the largest.  A number of major plastic manufactures have developed materials for thin wall applications that claim to reduce cycle time and machine energy consumption while increasing part quality.

For example, one manufacturer claims that their high flow polymers (up to 110 MFI) allow a broader processing window, lower machine energy consumption and give a shorter cycle time. The shorter cycle time and lower energy consumption is because lower barrel temperatures can be used.

Similarly, a plastic injection molding company claim they have achieved nearly 8% energy saving by switching to a different random PP copolymer for their houseware products.  The melt temperature was reduced by 35 degrees celsius while cycle times were cut by 15.5% due to improved flow. That resulted in a 7.7% reduction in energy use. Click here to get help with finding a suitable material for your next project.

Polycarbonate


A polycarbonate is another resin that has been developed for easier processing purposes.  Bayer Material Science have developed a grade that provides ease of colouring as well as high flow characteristics for production of complex part designs.

Other polycarbonate grades have been developed for easier demoulding. These grades are useful when parts are difficult to eject from a mold core. They are available in the basic grade, medical grade and the easy flowing grades.

Polyamides


In regards to polyamides,  one manufacturer claims that their material not only provides a higher flow –which should give easier processing- but also minimizes machine corrosion which can be a problem with flame retardant polyamides.

Polymer Additives


Another important field is that of polymer additives.  They have the potential to increase part quality and productivity. Commonly used additives are slip agents for easier demoulding, process stabilizers for melt and colour stability and nucleating agents for faster cycle times.

Nucleating agent additives effectively reduce the time required for a plastic part to cool from a melt to a solid inside a mould tool. This means the cooling time component of a cycle can be reduced.  Nucleating agents can be added to polypropylene, polyethylene, nylons, PBT and PVC plastic raw materials. Click here to read about a case study that improved productivity by 13%.

Additional Comments


Although there are a number of ways to make processing techniques easier and to improve part quality or reduce energy consumption, few techniques are more immediate than the appropriate change in plastic raw material or the addition of an additive resin.

In any case, they should not be a substitute for poor research and planning at the beginning of a new molding project.  Proper part and mold design, material and machine selection will avoid any need for change in materials or additives at a later time. This will only eat into your profit margins.

From Website
Edited by Leafly Mould Provides Injection Mold, Plastic Mold, Injection Molding, Die Casting Mold, Stamping Mold

Correct Plastic Injection Mold Design for Interlocking

In plastic injection mold design, interlocking refers to the way the fixed half and moving half of a mold are locked together.

Interlocking makes use of angled surfaces on both halves of the mold which engage when the mold is closed.

The purpose of interlocking is to prevent any small sideways movement of the moving side relative to the fixed side so that part wall section and weight remains even for every cycle.

The fact is, when one side moves relative to the other side, part quality problems will get worse everyday.

Interlocking is one of the most overlooked areas of plastic injection mold design. Plastic parts design is another overlooked area. Click here to learn about plastic parts design.

Interlocking must rigidly lock the fixed and moving sides of a mold together every cycle. Correct interlock design will ensure quality parts are produced for the expected life of the mold.

Correct interlock design also depends on using the right tool steels and heat treatments. Click here to learn more about heat treating tool steel.

Guide Pins And Plastic Injection Mold Design


In general, guide pins (sometimes called leader pins) do not accurately align the fixed and moving sides together so if they are used in place of proper interlocks expect some part quality problems such as wall thickness variation. There is a small amount of clearance between a leader pin and bush so this will allow movement between the fixed and moving sides of the mold.

Guide pins are used during assembly and disassembly of the mold so that the mold maker does not damage the core or cavity during mold maintenance.

Once the mold is in the molding machine the guide pins could, in theory be removed as they serve no purpose after installation – in fact some food packaging injection molders remove them so they don’t contaminate the parts with grease during ejection.

Guide pins have clearance on them that’s why they slide into the bush easily. Proper interlocking design will not allow sideways movement between the 2 halves of the mold.

Interlocking Case Study


Figures 1 and 2 show two different interlocking design for a standard square food container part.

food container mold
food container mold

Both designs have a stripper plate which is used to eject the container off the core. The only difference between the 2 designs is the interlocking design on the stripper plate. Click here to learn more about stripper plates.

Which one would you use?

Which design is more likely to make poor quality parts and which one will give long term quality results?

In theory, both plastic injection mold designs should work. The problem is however, for both designs to work everything must be perfect. That is, all mould plates must be flat and free of damage. The machine platens must also be flat and free of damage. The machine tie bar stretch must be equal in all 4 tie bars – and this is usually not the case especially when machines have not been maintained properly.

Uneven tie bar stretch or any damage on the mould or platens will put the mould on a slight angle when clamp tonnage is applied creating sideways forces when the cavity is filled with plastic. If the interlock design does not allow for this, then the stripper plate will be forced open on one side creating a GAP and the parts will flash.

See figure 3 where interlock A forces interlock B to open allowing flash to occur.

food container mold
food container mold

However, figure 4 shows a design which will not allow flash even if the there is some sideways force because the gap is created on the other side at interlock C where there is no molding. In this tool design, any sideways force will act towards the centre of the mold so there is no way the stripper plate can be forced open. The force on interlock C is transferred to interlock D holding it closed on that side of the interlock.

This is a plastic injection mold design that will last for millions of cycles provided it is made correctly and properly maintained.

Additional Comments


The sideways movement I am writing about is so small that one cannot see it with the naked eye. It is a vibration. Placing a dial indicator on the mold might show the vibration. In any case, with time, the hard mark wear pattern on the shutoff faces of the core and cavity will show evidence of this movement.

The fact is, both of these designs are easy to make with standard toolmaking equipment but they give a profoundly different result for the molder. So it is critical that correct plastic injection mold design is used so that quality parts can be manufactured for the life of a mold.

From Website
Edited by Leafly Mould Provides Injection Mold, Plastic Mold, Injection Molding, Die Casting Mold, Stamping Mold